Method and apparatus in a wireless communication system

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. Various embodiments of the disclosure provide a method performed by user equipment (UE) in a communication system, which includes: transmitting a preamble to a second node where a candidate cell is located; And receiving timing advance TA information of the candidate cell from the first node, wherein the TA information is used for executing conditional layer 1 or layer 2 triggering mobility LTM.

Description

METHOD AND APPARATUS IN A WIRELESS COMMUNICATION SYSTEM

[0001] The disclosure relates to the field of communication, and more specifically, to a method performed by a user equipment, a method performed by a first node, a method performed by a second node, a user equipment, a first node, and a second node.

[0002] Considering the development of wireless communication from generation to generation, the technologies have been developed mainly for services targeting humans, such as voice calls, multimedia services, and data services. Following the commercialization of 5G (5th generation) communication systems, it is expected that the number of connected devices will exponentially grow. Increasingly, these will be connected to communication networks. Examples of connected things may include vehicles, robots, drones, home appliances, displays, smart sensors connected to various infrastructures, construction machines, and factory equipment. Mobile devices are expected to evolve in various form-factors, such as augmented reality glasses, virtual reality headsets, and hologram devices. In order to provide various services by connecting hundreds of billions of devices and things in the 6G (6th generation) era, there have been ongoing efforts to develop improved 6G communication systems. For these reasons, 6G communication systems are referred to as beyond-5G systems.

[0003] 6G communication systems, which are expected to be commercialized around 2030, will have a peak data rate of tera (1,000 giga)-level bit per second (bps) and a radio latency less than 100μsec, and thus will be 50 times as fast as 5G communication systems and have the 1 / 10 radio latency thereof.

[0004] In order to accomplish such a high data rate and an ultra-low latency, it has been considered to implement 6G communication systems in a terahertz (THz) band (for example, 95 gigahertz (GHz) to 3THz bands). It is expected that, due to severer path loss and atmospheric absorption in the terahertz bands than those in mmWave bands introduced in 5G, technologies capable of securing the signal transmission distance (that is, coverage) will become more crucial. It is necessary to develop, as major technologies for securing the coverage, Radio Frequency (RF) elements, antennas, novel waveforms having a better coverage than Orthogonal Frequency Division Multiplexing (OFDM), beamforming and massive Multiple-input Multiple-Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antennas, and multiantenna transmission technologies such as large-scale antennas. In addition, there has been ongoing discussion on new technologies for improving the coverage of terahertz-band signals, such as metamaterial-based lenses and antennas, Orbital Angular Momentum (OAM), and Reconfigurable Intelligent Surface (RIS).

[0005] Moreover, in order to improve the spectral efficiency and the overall network performances, the following technologies have been developed for 6G communication systems: a full-duplex technology for enabling an uplink transmission and a downlink transmission to simultaneously use the same frequency resource at the same time; a network technology for utilizing satellites, High-Altitude Platform Stations (HAPS), and the like in an integrated manner; an improved network structure for supporting mobile base stations and the like and enabling network operation optimization and automation and the like; a dynamic spectrum sharing technology via collision avoidance based on a prediction of spectrum usage; an use of Artificial Intelligence (AI) in wireless communication for improvement of overall network operation by utilizing AI from a designing phase for developing 6G and internalizing end-to-end AI support functions; and a next-generation distributed computing technology for overcoming the limit of UE computing ability through reachable super-high-performance communication and computing resources (such as Mobile Edge Computing (MEC), clouds, and the like) over the network. In addition, through designing new protocols to be used in 6G communication systems, developing mechanisms for implementing a hardware-based security environment and safe use of data, and developing technologies for maintaining privacy, attempts to strengthen the connectivity between devices, optimize the network, promote softwarization of network entities, and increase the openness of wireless communications are continuing.

[0006] It is expected that research and development of 6G communication systems in hyper-connectivity, including person to machine (P2M) as well as machine to machine (M2M), will allow the next hyper-connected experience. Particularly, it is expected that services such as truly immersive eXtended Reality (XR), high-fidelity mobile hologram, and digital replica could be provided through 6G communication systems. In addition, services such as remote surgery for security and reliability enhancement, industrial automation, and emergency response will be provided through the 6G communication system such that the technologies could be applied in various fields such as industry, medical care, automobiles, and home appliances.

[0007] 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".

[0008] 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.

[0009] According to an aspect of the disclosure, there is provided a method performed by user equipment (UE) in a communication system, the method comprising: transmitting a preamble to a second node where a candidate cell is located; and receiving timing advance (TA) information of the candidate cell from a first node, wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM).

[0010] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the transmitting the preamble to the second node comprises: selecting, by the UE, a first random access (RA) resource for performing an uplink synchronization process in advance from among RA resources for performing the uplink synchronization process allocated to the first node by the candidate cell, to transmit a first preamble, wherein the first preamble is selected by UE; wherein the RA resources for performing the uplink synchronization process in advance allocated to the first node by the candidate cell are transmitted to the UE by the candidate cell through a third node and the first node.

[0011] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the receiving the TA comprises: monitoring, by the UE, a physical downlink control channel (PDCCH) using a first radio network temporary identification (RNTI), wherein the PDCCH includes resources for transmitting a media access control protocol data unit (MAC PDU) including the TA information of the candidate cell, wherein the TA information includes one or more TA information for one or more UEs.

[0012] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the first RNTI is an RNTI allocated by the first node and related to the MAC PDU including the TA information of the candidate cell.

[0013] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the transmitting the preamble to the second node comprises: transmitting, by the UE, a second preamble on a second RA resource allocated to the UE by the candidate cell for performing the uplink synchronization process in advance, wherein the second preamble is a preamble allocated to the UE by the candidate cell.

[0014] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, the method further comprises: transmitting, by the UE, a first message to the first node, wherein the first message includes a candidate cell selected by the UE and / or a measurement result of the candidate cell; and receiving, by the UE, a second message transmitted by the first node, wherein the second message instructs the UE to perform an uplink synchronization process with the candidate cell in advance; wherein the second message includes at least one of: a candidate cell identification, a fourth RA resource for performing the uplink synchronization process in advance, and a fourth preamble; wherein the fourth RA resource and the fourth preamble are selected by the first node based on the RA resources allocated to the first node by the candidate cell for performing the uplink synchronization process in advance; wherein the RA resources allocated to the first node by the candidate cell for performing the uplink synchronization process in advance are transmitted to the first node by the candidate cell through a third node.

[0015] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the monitoring the PDCCH transmitted by the first node comprises: monitoring, by the UE, the PDCCH using a cell radio network temporary identification (C-RNTI) allocated to the UE by the first node, wherein the PDCCH includes resources for transmitting a MAC PDU including the TA information of the candidate cell, wherein the MAC PDU includes one or more media access control control element (MAC CE), and the TA information is included in the MAC CE.

[0016] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the MAC CE including the TA information is identified by a logical channel identification.

[0017] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the TA information comprises at least one of: candidate configuration identification; a TA value, wherein the TA value is determined by the candidate cell through the detected preamble; a value of a random access radio network temporary identification (RA-RNTI), wherein the value of the RA-RNTI is determine by the candidate cell according to resources where the preamble is detected; information of RA resources where the preamble is detected.

[0018] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the method further comprises: starting or restarting a timer when the UE receives a TA value of the candidate cell, wherein the TA value is valid before the timer expires.

[0019] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein that the TA information is used for performing the conditional LTM comprises: transmitting, by the UE, a scheduling request to the second node on a first resource or uplink data to the second node on a second resource, if a TA value of the target cell is valid; wherein the first resource is a resource allocated to the UE by the target cell for transmitting the scheduling request, and the second resource is a resource allocated to the UE by the target cell for transmitting the uplink data; considering, by the UE, that the conditional LTM is successfully performed, if the scheduling request or the uplink data is successfully received by the second node.

[0020] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein that the TA information is used for performing the conditional LTM comprises: transmitting, by the UE, a conditional LTM indication to the first node, if a TA value of the target cell is valid, wherein the conditional LTM indication is used to indicate that the UE will perform the conditional LTM; receiving resource scheduling information transmitted by the target cell; and performing uplink transmission on the resource; wherein the resource scheduling information is transmitted through the PDCCH.

[0021] According to the method performed by the user equipment (UE) in a communication system provided by the disclosure, wherein the method further comprises: evaluating, by the UE, an LTM execution condition of the candidate cell according to a measurement result of Layer 1, selecting one candidate cell as a target cell and t performing conditional L1 / L2 Triggered Mobility (LTM), when there are candidate cells meeting the LTM execution condition.

[0022] According to an aspect of the disclosure, there is provided a method performed by a first node in a communication system, the method comprising: receiving timing advance (TA) information of a candidate cell from a third node, wherein the TA information of the candidate cell is transmitted to the third node by a second node after receiving a preamble transmitted by a user equipment (UE); and transmitting the TA information of the candidate cell to the UE, wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM).

[0023] According to the method performed by the first node in a communication system provided by the disclosure, wherein the method further comprises: transmitting, to the UE, a physical downlink control channel (PDCCH), wherein the PDCCH includes resources for transmitting a media access control protocol data unit (MAC PDU) including the TA information of the candidate cell.

[0024] According to the method performed by the first node in a communication system provided by the disclosure, wherein the MAC PDU includes one or more media access control control element (MAC CE), and the TA information is included in the MAC CE.

[0025] According to the method performed by the first node in a communication system provided by the disclosure, wherein the PDCCH is scrambled by a first radio network temporary identification (RNTI) or by a cell radio network temporary identification (C-RNTI) of the UE, wherein the first RNTI is allocated by a first node to the UE in the first node for receiving the MAC PDU including the TA information.

[0026] According to an aspect of the disclosure, there is provided a method performed by a second node in a communication system, the method comprising: receiving a preamble transmitted by user equipment (UE); and transmitting timing advance (TA) information of a candidate cell to a third node, wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM).

[0027] According to another aspect of the disclosure, there is provided a user equipment (UE) comprising: a transceiver configured to transmit and receive signals with the outside; and a controller configured to control the transceiver to perform the above method performed by the user equipment (UE).

[0028] According to another aspect of the disclosure, there is provided a first node comprising: a transceiver configured to transmit and receive signals with the outside; and a controller configured to control the transceiver to perform the above method performed by the first node.

[0029] According to another aspect of the disclosure, there is provided a second node comprising: a transceiver configured to transmit and receive signals with the outside; and a controller configured to control the transceiver to perform the above method performed by the second node.

[0030] According to another aspect of the disclosure, there is provided a non-transitory computer-readable recording medium having stored thereon a program which, when being executed by a computer, performs any of the above methods.

[0031] Aspects of the disclosure are to address at least the above-mentioned problems and / or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the disclosure is to provide efficient communication methods in a wireless communication system.

[0032] Fig. 1 is an exemplary system architecture of System Architecture Evolution (SAE).

[0033] Fig. 2 is an exemplary system architecture according to various embodiments of the disclosure.

[0034] Fig. 3 is a schematic diagram of interaction among a user equipment, a first node, a second node and a third node according to various embodiments of the disclosure.

[0035] Fig. 4A is another schematic diagram of interaction among a user equipment, a first node, a second node and a third node according to various embodiments of the disclosure.

[0036] Fig. 4B is an example of a MAC PDU structure according to various embodiments of the disclosure.

[0037] Fig. 4C is an example of a Timing Advance Command for Early TA acquisition MAC CE according to various embodiments of the disclosure.

[0038] Fig. 5A is a further schematic diagram of interaction among a user equipment, a first node, a second node and a third node according to various embodiments of the disclosure.

[0039] Fig. 5B is an example of a MAC PDU for Early Timing Advanced Command in advance according to various embodiments of the disclosure.

[0040] Fig. 5C is an example of a TA command according to various embodiments of the disclosure.

[0041] Fig. 6 is another schematic diagram of interaction among a user equipment, a first node, a second node and a third node according to various embodiments of the disclosure.

[0042] Fig. 7 is an interactive schematic diagram of an execution method of conditional LTM according to various embodiments of the disclosure.

[0043] Fig. 8 is an interactive schematic diagram of another execution method of conditional LTM according to various embodiments of the disclosure.

[0044] Fig. 9 is an interactive schematic diagram of a further execution method of conditional LTM according to various embodiments of the disclosure.

[0045] Fig. 10 is a block diagram illustrating the structure of user equipment according to an embodiment of the disclosure.

[0046] Fig. 11 is a block diagram illustrating the structure of a first node according to an embodiment of the disclosure.

[0047] Fig. 12 is a block diagram illustrating the structure of a second node according to an embodiment of the disclosure.

[0048] Fig. 13 is a block diagram illustrating the structure of a third node according to an embodiment of the disclosure.

[0049] Fig. 14 is a block diagram illustrating the structure of a user equipment according to an embodiment of the disclosure.

[0050] Fig. 15 is a block diagram illustrating the structure of a base station according to an embodiment of the disclosure.

[0051] Aspects of the disclosure are to address at least the above-mentioned problems and / or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the disclosure is to provide a terminal and a communication method thereof in a wireless communication system.

[0052] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the disclosure as defined by the claims and their equivalents. The description includes various specific details to assist in that understanding but should be regarded as exemplary only. Accordingly, the ordinary skilled in the art will recognize that various changes and modifications to the various embodiments described herein can be made without departing from the scope and spirit of the disclosure. In addition, descriptions of well-known functions and structures may be omitted for clarity and conciseness. In the disclosure, elements expressed in the singular form may also be understood to be expressed in the plural form. Similar words such as singular forms "a", "an" or "the" do not express a limitation of quantity, but express the existence of at least one of the referenced item, unless the context clearly dictates otherwise. For example, reference to "a component surface" includes reference to one or more of such surfaces.

[0053] The terms and wordings 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 disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the disclosure is provided for illustration purpose only, but not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents.

[0054] It should be understood that the singular forms "a," "an," and "the" include plural referents, unless clearly indicated otherwise in the context. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0055] 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 disclosure, and does not limit the existence of one or more additional functions, operations, or components. The terms "include" and / or "have" may be construed to represent certain characteristics, numbers, steps, operations, constituent elements, components or combinations thereof, but may not be construed to exclude the possibility of existence of one or more other characteristics, numbers, steps, operations, constituent elements, components or combinations thereof.

[0056] The term "or" used in various embodiments of the disclosure includes any of the listed terms or all combinations thereof. For example, "A or B" may include A, may include B, or may include both A and B.

[0057] Unless defined differently, all terms used in the disclosure, including technical or scientific terms, have the same meanings as those understood by the skilled in the art as described in the disclosure. Common terms as defined in a dictionary are to be interpreted to have meanings consistent with the context in the relevant technical field o, and are not to be interpreted ideally or excessively, unless clearly defined as such in the disclosure.

[0058] Figs. 1 to 15 discussed below and various embodiments for describing the principle of the 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 principle of the disclosure may be implemented in any suitably arranged system or device.

[0059] 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 user equipment, an address of a serving node, user security information, and packet data context of the user equipment, etc.

[0060] Fig. 2 is an exemplary system architecture 200 according to various embodiments of the disclosure. Other embodiments of the system architecture 200 can be used without departing from the scope of the disclosure.

[0061] 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.

[0062] The text and drawings are provided as examples only to help understand the disclosure. They should not be construed as limiting the scope of the disclosure in any way. Although certain embodiments and examples have been provided, based on the contents disclosed herein, it is obvious to those skilled in the art that changes can be made to the illustrated embodiments and examples without departing from the scope of the disclosure.

[0063] Detailed descriptions of steps unrelated to the present invention are omitted in this disclosure. In the following embodiments, the 5G system is taken as an example, the centralized unit of the access network is taken CU as an example, and the distributed unit is taken DU as an example to describe. The method is also used for corresponding entities in other systems.

[0064] LTM (L1 / L2-triggered mobility) handover mode, is called Layer 1 / Layer 2 handover (L1 / L2 handover), or called LTM Cell Switch, or called LTM Cell handover, or called L1 / L2 mobility. The base station or gNB-DU transmits an LTM Cell Switch Command to the UE through the MAC CE (MAC Control Eelement) of the MAC layer (L2, Layer 2) to instruct the UE to change the serving cell.

[0065] Conditional LTM cell handover can also be called conditional LTM handover, or conditional LTM cell switch or conditional LTM.

[0066] In this disclosure, the LTM candidate cell may be called a candidate cell or a target candidate cell. The target cell may be called a target candidate cell, or an LTM target candidate cell, or an LTM target cell.

[0067] In this disclosure, the content is applicable to perform MCG LTM by the master base station / master node in the DC (Dual Connectivity) system (or to change PCell by MN through LTM), and is also applicable to perform SCG LTM by the secondary base station / secondary node (or to change PSCell by SN through LTM). Therefore, the LTM candidate cell mentioned in this disclosure can be the LTM candidate cell of PCell and the candidate cell of PSCell of LTM.

[0068] In LTM, the network selects the target cell for the user equipment (UE) according to the measurement result reported by the UE, and instructs the UE to perform the cell switch by transmitting a cell switch command. The delay of signaling transmission between the network and the UE may cause handover failure due to the change of radio link state.

[0069] Various embodiments of the disclosure provide a method performed by user equipment (UE) in a communication system, which includes: transmitting a preamble to a second node where a candidate cell is located (which can be a target gNB-DU / candidate gNB-DU, for example); and receiving timing advance (TA) information of the candidate cell from a first node (which can be the source gNB-DU, for example), wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM).

[0070] In the method performed by the user equipment (UE) in the communication system provided by various embodiments of the disclosure, the execution condition is configured for conditional LTM handover through the network, and when the execution condition is met, the UE actively performs the LTM for cell handover without waiting for the source node to send a handover command. Thus, that signal interaction between the UE and the network can be reduced, and the situation that the handover of the UE fails due to the change of the state of the radio link during the signaling interaction between the UE and the network can also be avoided, thereby improve the robustness of the handover. Moreover, before performing the conditional LTM, the UE performs uplink synchronization with the candidate cell (including the target cell) in advance to obtain (or acquire) the TA value of the candidate cell (including the target cell) in advance, which can also be called the process of acquiring (or obtaining) the TA in advance (Early TA Acquisition), or the process of acquiring the TA of the candidate cell in advance, or the process of UE performing the uplink in the candidate cell in advance. Through the process of performing uplink synchronization between UE and candidate cell in advance, it is avoided that UE needs to perform uplink synchronization with target cell during performing handover, thus reducing handover delay.

[0071] In this disclosure, the TA value of the UE in the candidate cell can also be called the Early TA value of the UE in the candidate cell, the Early TA value or the TA value of the candidate cell. TA information is information containing the TA value. The TA information of the UE in the candidate cell can also be called Early TA information of the UE in the candidate cell, Early TA information or TA information of the candidate cell.

[0072] Various embodiments of the disclosure relate to the configuration method and execution process of conditional LTM, the method for UE to obtain the TA value of the target cell (candidate cell) in advance, and the execution method of conditional LTM. The following will be described in detail with reference to figs. 3 to 9.

[0073] Embodiment 1: Configuration method and execution process of conditional LTM

[0074] Please refer to Fig. 3. Fig. 3 is a schematic diagram of interaction among a user equipment, a first node, a second node and a third node according to various embodiments of the disclosure. The method illustrated in Fig. 3 may include one or more of steps S300a to S318:

[0075] Step 300a: The UE transmits a message to the source gNB-DU (which can also be called the first node), wherein the message contains a L3 measurement result. Alternatively, the message may be a Measurement Report, or other messages. The measurement result includes measurement results of neighbor cells.

[0076] Step 300b: The source gNB-DU transmits a message to gNB-CU (also called the third node) and transmits the received measurement report to gNB-CU. Optionally, the message may be an uplink RRC message transfer（UL RRC MESSAGE TRANSFER message, or other messages.

[0077] In step 301, gNB-CU decides to trigger the conditional LTM Configuration. gNB-CU selects an LTM candidate cell for UE.

[0078] Step 302a: gNB-CU transmits a message to the candidate gNB-DU (also called the second node) to request the configuration of the LTM candidate cell. Optionally, the message may be a UE CONTEXT SETUP REQUEST message, or other messages.

[0079] The message contains at least one of the following information:

[0080] (1) The identification information of UE in gNB-CU is the identification allocated to UE by gNB-CU, which can be gNB-CU UE F1AP ID or other identification.

[0081] (2) Conditional LTM indication, which indicates that the request is a conditional LTM candidate cell request. The candidate gNB-DU provides the execution condition of the conditional LTM.

[0082] (3) Candidate cell identification, which is the requested LTM candidate cell identification. The cell identification can be CGI or other identifications.

[0083] (4) LTM configuration identification. The LTM configuration identification corresponds (or is associated) with the candidate cell identification, that is, each LTM candidate cell has a corresponding LTM configuration identification.

[0084] (5) LTM configuration ID mapping list, which contains cell identifications of all LTM candidate cells and LTM configuration identifications.

[0085] (6) CSI resource configuration.

[0086] Step 302b: The candidate gNB-DU transmits a message to gNB-CU. If receiving the requested LTM configuration, the candidate gNB-DU sends the message for feedback and provides RRC configuration information of the candidate cells that accept the request.

[0087] Optionally, the message may be a UE CONTEXT SETUP RESPONSE, or other messages.

[0088] The message contains at least one of the following information:

[0089] (1) The identification information of UE in gNB-CU, which is the identification allocated to UE by gNB-CU. It can be gNB-CU UE F1AP ID or other identification, that is, the identification allocated to UE by gNB-CU in step 302a.

[0090] (2) The identification information of the UE in gNB-DU, which is the identification allocated to the UE by the candidate gNB-DU. It can be gNB-DU UE F1AP ID or other identification.

[0091] (3) a cell identification indicating the requested candidate cell ID, which is the candidate cell identification requested in step 302a. The cell identification may be CGI (Cell Global ID) or other identifications.

[0092] (4) LTM configuration information indicating the configuration information of the cell indicated by the cell identification. It contains at least one of the following information:

[0093] - SSB (synchronization signal block) configuration information indicating the time and frequency information of SSB of the cell indicated by the cell identification. The frequency information is ARFCN. SSB is also called Synchronization Signal / Physical Broadcast Channel Block (SS / PBCH Block).

[0094] - a physical cell identification (physical cell ID，PCI), indicating the physical cell identification of the cell indicated by the cell identification.

[0095] (5) TCI (transmission configuration indicator) status configuration list.

[0096] (6) RACH (Random Access Channel) configuration information list, which contains one or more RACH configuration information, wherein the RACH configuration information contains at least one of the following information:

[0097] - The first RACH configuration (which can also be called the first resource configuration, or other names, but the present invention is not limited to this) includes the Random Access (RA) resource configured (or allocated) by the candidate cell for performing the uplink synchronization process in advance, that is, the RA resource for obtaining the TA value of the candidate cell in advance. Herein, the RA resource can also be called RACH resource. The first RACH configuration is RA resource allocated by the candidate cell to other gNB-DU for the UE in the other gNB-DU to acquire the TA value of the candidate cell in advance.

[0098] - gNB-DU ID, which is the identification of gNB-DU, that is, the identification of gNB-DU using the RA resource of the first RACH configuration.

[0099] (7) CSI reporting configuration.

[0100] (8) The second RACH configuration (also called the second resource configuration, or other names, but the present invention is not limited to this) includes the dedicated RA resource configured (or allocated) by the candidate cell to the UE for performing the uplink synchronization process in advance, that is, the dedicated RA resource for obtaining the TA value of the candidate cell in advance. Herein, the RA resource can also be called RACH resource.

[0101] (9) The third RACH configuration (also referred to as the third resource configuration, or other names, the present invention is not limited to this), that is, the RA resource configured (or allocated) by the candidate cell for performing RACH-based LTM. It is the RA resource used for random access if the candidate cell is selected as the target cell. Herein, the RA resource can also be called RACH resource.

[0102] (10) a dedicated uplink resource, that is, the dedicated uplink resource configured (or allocated) by the candidate cell for the UE, that is, Configured Grant. It is used for uplink transmission in the target cell when UE performs LTM.

[0103] (11) an LTM execution condition (also called a second LTM execution condition, or other names, the present invention is not limited to this), that is, the LTM execution condition provided by candidate cell (also called a conditional LTM execution condition). Herein the LTM execution condition is related to Layer 1 (L1) measurement. When the UE selects the candidate cell as the target cell to access, the UE monitors the candidate cell, and according to the L1 measurement result, when one or more cells meet the LTM execution condition, it selects one of them as the new target cell and performs the LTM, that is, triggers the cell switch and accesses to the new target cell.

[0104] (12) C-RNTI (cell radio network temporary identification). The value of the C-RNTI allocated by the candidate cell for the UE is taken as the identification of the UE in the candidate cell.

[0105] (13) RNTI (Radio Network Temporary Identification), that is, the RNTI value configured (or allocated) by candidate cell. It is the RNTI used for the UE to receive the TA information obtained in advance in the target cell after the candidate cell is used as the target cell (serving cell). Optionally, the RNTI may be a dedicated RA-RNTI (Random Access RNTI) (also called the second RA-RNTI, or other names, and the present invention is not limited to this), or other RNTI.

[0106] (14) Physical Uplink Control Channel (PUCCH) resource information, which is the PUCCH resource information allocated (or configured) by the candidate cell for the UE.

[0107] The first RACH configuration and the third RACH configuration at least include one of the following information:

[0108] - Uplink frequency information, including a carrier bandwidth, a subcarrier spacing, and a carrier offset value (offsetToCarrier). Herein, the carrier offset value indicates the starting point of the PRB of the actual effective use of the carrier.

[0109] - RACH parameters, which are used to (perform) random access process in the candidate cell. For example, a general RACH configuration (Rach Config Generic) can be used.

[0110] - BWP (Bandwidth Part) information, indicating the frequency domain position (indicating the starting point of BWP) and bandwidth of BWP.

[0111] - a number of SSBs, indicating the number of SSBs on the RACH occasion. The RACH occasion may also be referred to as a RACH opportunity.

[0112] - a PRACH root sequence index.

[0113] - a PRACH subcarrier spacing, indicating the subcarrier spacing of PRACH used for LTM (which can be expressed by ltm prach Subcarrier Spacing).

[0114] - a Timing Advance Offset value, which is used for the timing advance offset value of all uplink transmissions on the candidate cell.

[0115] The second RACH configuration includes at least one of the following information:

[0116] - RACH common configuration information. The information contained in the RACH common configuration information is the same as that contained in the first RACH configuration, which is not repeated here.

[0117] - a Random Access preamble index, which indicates the index of preamble used for performing the uplink synchronization.

[0118] - a SS / PBCH index, indicating SS / PBCH used to determine the RACH occasion of PRACH transmission.

[0119] - a PRACH Mask Index, which indicates the RACH occasion for PRACH transmission related to SS / PBCH. Herein, the SS / PBCH is the SS / PBCH indicated by the SS / PBCH index.

[0120] If the candidate cell belongs to the source gNB-DU, the configuration of the candidate cell is completed through steps 303a-303b.

[0121] 303a, gNB-CU transmits a message to the source gNB-DU.

[0122] Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages.

[0123] For the information contained in the message, please refer to step 302a, which will not be repeated here.

[0124] 303b, the source gNB-DU transmits a message to gNB-CU.

[0125] Optionally, the message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages.

[0126] For the information contained in the message, please refer to step 302b, which is not repeated here.

[0127] Step 304: gNB-CU transmits a message to the source gNB-DU.

[0128] Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages.

[0129] The message contains at least one of the following information:

[0130] (1) candidate cell information. The candidate cell information includes one or more candidate cell information, and the candidate cell information includes at least one of the following information:

[0131] - LTM Cell ID, indicating the identification of the LTM candidate cell, which can be CGI (Cell Global ID) or other identifications.

[0132] - LTM Configuration ID, corresponding to LTM Candidate ID which indicates LTM candidate configuration and is related to LTM candidate cell.

[0133] - gNB ID, which indicates the identification of the gNB to which the cell indicated by the LTM cell ID belongs.

[0134] - TCI status configuration list.

[0135] - The first RACH configuration (which can also be called the first resource configuration, or other names, but the present invention is not limited to this), which contains the RA resource configured by the candidate cell for performing the uplink synchronization process in advance.

[0136] - The second RACH configuration (which can also be called the second resource configuration, or other names, but the present invention is not limited to this), which contains the dedicated RA resource allocated to the UE by the candidate cell for performing the uplink synchronization process in advance.

[0137] - The third RACH configuration (also called the third resource configuration, or other names, but the present invention is not limited to this), which contains the RA resource configured by the candidate cell for performing RACH-based LTM, that is, the RA resource used for the random access when the candidate cell is selected as the target cell.

[0138] - CSI reporting configuration (also called second CSI reporting configuration, or other names, the present invention is not limited to this).

[0139] - a dedicated uplink resource, which is configured (or allocated) by the candidate cell for the UE, that is, Configured Grant. It is used for uplink transmission in the target cell when UE performs LTM.

[0140] - an LTM execution condition (also called second LTM execution condition, or other names, the invention is not limited to this), that is, the LTM execution condition provided by the candidate cell.

[0141] - C-RNTI. The value of the C-RNTI allocated by the candidate cell for the UE is taken as the identification of the UE in the candidate cell.

[0142] (2) LTM configuration ID mapping list. It contains cell identifications of all LTM candidate cells and LTM configuration identifications.

[0143] Step 305: The source gNB-DU transmits a message to gNB-CU.

[0144] The message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages.

[0145] The message contains at least one of the following information:

[0146] (1) CSI report configuration, which is provided by the source cell.

[0147] (2) an LTM execution condition (also called a first LTM execution condition, or other names, the present invention is not limited to this), that is, the LTM execution condition provided by source cell. Herein the LTM execution condition is related to Layer 1 (L1) measurement. The UE monitors the candidate cell, and according to the L1 measurement result, when one or more cells meet the LTM execution condition, it selects one of them as the target cell and performs the conditional LTM, that is, triggers the cell switch and accesses to the target cell.

[0148] (3) RNTI, which is the RNTI value allocated (or configured) by the source cell. It is the RNTI used for the UE to receive the TA information obtained in advance on the source cell. Optionally, the RNTI may be a dedicated RA-RNTI (Random Access RNTI) (also called the first RA-RNTI, or other names, and the present invention is not limited to this), or other RNTI.

[0149] Step 306-307: If there is a candidate cell update, all the finally determined candidate cell information is transmitted to each candidate cell through step 306-307.

[0150] Step 306: gNB-CU transmits a message to the candidate gNB-DU. Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages. See step 304 for details.

[0151] Step 307: The candidate gNB-DU transmits a message to gNB-CU as feedback. Optionally, the message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages.

[0152] Step 308: gNB-CU transmits a message to the source gNB-DU. The message includes an RRC reconfiguration message sent to the UE.

[0153] Optionally, the message may be a downlink RRC message transfer （DL RRC MESSAGE TRANSFER）message, or other messages.

[0154] The message contains at least one of the following information:

[0155] (1) an RRC reconfiguration message, which is an RRCReconfiguration message sent to UE.

[0156] Step 309: The source gNB-DU transmits a message to the UE. The source gNB-DU forwards the RRC reconfiguration message received from step 308 to the UE.

[0157] Optionally, the message is an RRCReconfiguration message, or other messages.

[0158] The message contains at least one of the following information:

[0159] (1) LTM candidate configuration related information of one or more LTM candidate cells. The LTM candidate configuration related information includes at least one of the following information:

[0160] - LTM candidate identification (LTM Candidate Id), which corresponds to the LTM configuration identification and is associated with (or corresponds to) the LTM candidate cell.

[0161] - LTM candidate physical cell identification (LTM candidate PCI), indicating the physical cell identification of the candidate cell corresponding to (or associated with) the LTM candidate identification.

[0162] - SSB configuration information of LTM, indicating the time and frequency information of SSB of the candidate cell corresponding to (or associated with) the LTM candidate identification. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0163] - LTM candidate configuration information, including Cell Group configuration information, Radio Bearer (RB) configuration information, etc.

[0164] - The first LTM RACH resource configuration (also called the first resource configuration, or other names, and the present invention is not limited to this) (also called LTM early uplink synchronization configuration, ltm Early UL Sync Config) which contains the RA (Random Access) resource configured by the candidate cell for performing uplink synchronization in advance. That is, the RACH configuration received by gNB-CU in steps 302b and / or 303b. Herein, the RA resource can also be called RACH resource.

[0165] - an LTM execution condition, which are provided by the candidate cell.

[0166] - The second LTM RACH resource configuration (also called dedicated LTM Early uplink synchronization configuration, dedicated ltm Early UL Sync Config) (also called second resource configuration, or other names, the invention is not limited to this) which includes the dedicated RA resource configured by the candidate cell for the UE to perform the uplink synchronization process in advance. That is, it is the second RACH configuration received by gNB-CU in steps 302b and / or 303b. Herein, the RA resource can also be called RACH resource.

[0167] - a dedicated uplink resource, which is configured (or allocated) by the candidate cell for the UE, that is, Configured Grant. It is used for uplink transmission in the target cell when UE performs LTM.

[0168] - The third RACH resource configuration (which can also be called the third resource configuration, or other names, but the present invention is not limited to this) which contains the RA resource configured by the candidate cell for performing RACH-based LTM. It is the RA resource used for random access when the candidate cell is selected as the target cell. That is, it is the third RACH configuration received by gNB-CU in steps 302b and / or 303b. Herein, the RA resource can also be called RACH resource.

[0169] - RNTI, which is RNTI value configured (allocated) by the candidate cell. It is RNTI used for the UE to receive the TA information obtained in advance in the target cell after the candidate cell is used as the target cell (serving cell). Optionally, the RNTI may be a dedicated RA-RNTI (Random Access RNTI) (also called the second RA-RNTI, or other names, and the present invention is not limited to this), or other RNTI.

[0170] - PUCCH resource information, which is allocated (or configured) by the candidate cell for the UE.

[0171] (2) an LTM execution condition (also called first LTM execution condition, or other names, the present invention is not limited to this), which is the LTM execution condition provided by the source cell. Herein the LTM execution condition is related to Layer 1 (L1) measurement. The UE monitors the candidate cell, and according to the L1 measurement result, when one or more cells meet the LTM execution condition, it selects one of them as the target cell and performs the conditional LTM, that is, triggers cell switch and accesses to the target cell.

[0172] (3) RNTI, which is the RNTI value configured (allocated) by the source cell. It is the RNTI used for the UE to receive the TA information obtained in advance on the source cell. Optionally, the RNTI may be a dedicated RA-RNTI (Random Access RNTI) (also called the first RA-RNTI, or other names, and the present invention is not limited to this), or other RNTI.

[0173] (4) C-RNTI, which is the C-RNTI allocated by the source cell for the UE, as the identification of the UE in the source cell.

[0174] In step 310, the UE transmits an RRCReconfigurationComplete message to the source gNB-DU.

[0175] Step 311: The source gNB-DU transmits an uplink RRC message transfer （UL RRC MESSAGE TRANSFER）message to the source gNB-CU. The source gNB-DU forwards the RRC reconfiguration complete message received in step 310 to the source gNB-CU.

[0176] In step 312, the UE evaluates (or monitors) the LTM execution condition according to the information received in step 309, that is, evaluates whether the candidate cell meets the LTM execution condition.

[0177] According to the L1 measurement result, when one or more cells meet the LTM execution condition, the UE selects one of them as the target cell to trigger cell switch.

[0178] In step 313, the UE performs the process of Early TA Acquisition.

[0179] If the conditional LTM handover of RACH-less is supported, if the UE does not have a valid TA value in the candidate cell, the UE will perform the process of the process of Early TA Acquisition to obtain the TA value of the candidate cell in advance, that is, the Early TA value. Among them, there are two ways to acquire the TA value in advance:

[0180] - UE obtains the TA value of the candidate cell in advance by UE-based TA measurement.

[0181] - UE can obtain the TA value of the candidate cell in advance by a random access process. Among them, there are three ways to obtain the TA value of the candidate cell in advance by the random access process, see the description in Embodiments 2, 3 and 4 for details.

[0182] When evaluating (or monitoring) the LTM execution condition, when one or more cells meet the LTM execution condition, the UE selects one of them as the target cell, performs the conditional LTM, and performs cell switch.

[0183] Step 314: The conditional LTM is performed. The UE performs the condition LTM, and accesses the target cell, that is, the target cell (target gNB-DU) detects the UE access. There are three methods for conditional LTM execution. See Embodiments 5, 6 and 7 for details. Among them:

[0184] - If the UE has a valid TA value in the target cell, it will perform RACH-Less conditional LTM handover to realize cell switch. In the RACH-less conditional LTM handover, when the first uplink transmission is correctly received, the UE and the network consider that the conditional LTM handover is successful (or the conditional LTM handover is successful), that is, the UE accesses the target cell.

[0185] - If the UE does not have a valid TA value in the target cell, it will perform a RACH-based conditional LTM handover to realize cell switch. If the network configures the dedicated RACH resource for the UE, then the CFRA (Content Free Random Access) process will be performed, otherwise the CBRA (Contention Based Random Access) process will be performed. If the random access process is successfully completed, the UE and the network consider that the conditional LTM handover is successfully performed, that is, the UE accesses the target cell.

[0186] Step 315: The target gNB-DU transmits a message to gNB-CU.

[0187] When the target gNB-DU detects that the UE has accessed to the target cell, it considers that the conditional LTM handover has been successfully performed, and will send a message to gNB-CU to indicate that the UE has successfully accessed to the target cell.

[0188] Alternatively, the message may be an ACCESS SUCCESS message, or other messages.

[0189] The message contains at least one of the following information:

[0190] (1) a cell identification, which indicates the identification of the target cell, and can be CGI or other cell identifications.

[0191] If the source gNB-DU contains LTM candidate cells, step 316 will be performed, otherwise steps 317 and 318 will be performed.

[0192] Step 316: gNB-CU transmits a message to the source gNB-DU, indicating that the UE has accessed to the target cell, and the source cell stops transmitting data to the UE and reserves the candidate cell resource configured for the UE.

[0193] Optionally, the message may be an LTM CELL SWITCH SUCCESS message, or other messages.

[0194] The message contains at least one of the following information:

[0195] (1) a cell identification, which indicates the identification of the target cell accessed by the UE, and can be CGI or other cell identifications.

[0196] Step 317: gNB-CU transmits a message to the source gNB-DU, indicating that the UE has accessed to the target cell, and the source cell stops transmitting data to the UE and releases the configured cell resource. Optionally, the message may be a UE CONTEXT RELEASE COMMAND message, or other messages.

[0197] The message contains at least one of the following information:

[0198] (1) a cell identification, which indicates the identification of the target cell accessed by the UE, and can be CGI or other cell identifications.

[0199] In step 318, the source gNB-DU transmits a message to gNB-CU as a response. Optionally, the message may be a UE CONTEXT RELEASE COMPLETE message, or other messages.

[0200] Through the above process, the network configures the execution conditions for conditional LTM handover, and when the execution condition is met, the UE actively performs LTM for cell handover without waiting for the network to transmit a handover command. Thus, that signal interaction between the UE and the network can be reduced, and the situation that the handover of the UE fails due to the change of the state of the radio link during the signaling interaction between the UE and the network can also be avoided, thereby improve the robustness of the handover.

[0201] Embodiment 2: A method for acquiring TA value of the candidate cell in advance

[0202] Please refer to Fig. 4A. Fig. 4A is another schematic diagram of interaction among a user equipment, a first node, a second node and a third node according to various embodiments of the disclosure. The method illustrated in Fig. 4A may include one or more of steps S400a to S417:

[0203] In the second embodiment, if the candidate cell allocates the dedicated RACH resource for the UE, it is used for the UE to obtain the TA value in the candidate cell in advance. The process is illustrated in Fig. 4A, and is described in detail as follows.

[0204] Steps 400a-411 are the candidate cell configuration process. The specific process is the same as steps 300a-311.

[0205] In steps 400a-411, the candidate cell configuration is completed, and the candidate cell allocates a RACH resource for the UE to obtain the TA value in advance. The network transmits the candidate cell information and the allocated RACH resource information to the UE, that is, step 409 contains the dedicated LTM RACH resource configuration information allocated to the UE, and the dedicated LTM RACH resource is used to obtain the TA value of the candidate cell in advance.

[0206] When the UE decides to trigger the uplink synchronization process with the candidate cell in advance (that is, the process of obtaining the TA value of the candidate cell in advance), it will select the candidate cell and send a dedicated preamble, or uplink synchronization code, random access preamble or random access preamble, on the RACH resource allocated by the candidate cell for performing the uplink synchronization process in advance.

[0207] Steps 400a- 402a are the same as steps 300a-302a. Please refer to Embodiment 1 for details, and they will not be repeated here.

[0208] Step 402b: The candidate gNB-DU transmits a message to gNB-CU. If receiving the requested LTM configuration, the candidate gNB-DU transmits the message for feedback, and provides RRC configuration information of the candidate cells that accept the request.

[0209] Optionally, the message may be a UE CONTEXT SETUP RESPONSE, or other messages.

[0210] The message contains at least one of the following information:

[0211] (1) The identification information of UE in gNB-CU, which is the identification allocated to UE by gNB-CU and can be gNB-CU UE F1AP ID or other identification. That is, the identification allocated to UE by gNB-CU in step 402a.

[0212] (2) The identification information of the UE in gNB-DU, which is the identification allocated to the UE by the candidate gNB-DU and can be gNB-DU UE F1AP ID or other identification.

[0213] (3) a cell identification indicating the requested candidate cell identification, which is the candidate cell identification requested in step 402a. The cell identification may be CGI (Cell Global ID) or other identifications.

[0214] (4) LTM configuration information indicating the configuration information of the cell indicated by the cell identification. It contains at least one of the following information:

[0215] - SSB configuration information indicating time and frequency information of SSB of the cell indicated by the cell identification. The frequency information is ARFCN.

[0216] - Physical cell ID (PCI), indicating the physical cell identification of the cell indicated by the cell identification.

[0217] (5) TCI status configuration list.

[0218] (6) CSI reporting configuration.

[0219] (7) The first RACH configuration, which includes the RA resources configured (or allocated) by the candidate cell for performing the uplink synchronization process in advance.

[0220] (8) The second RACH configuration, which includes the dedicated RA resource configured (or allocated) to the UE by the candidate cell for performing the uplink synchronization process in advance.

[0221] (9) The third RACH configuration, which includes the RA resource configured (or allocated) by the candidate cell for performing RACH-based LTM. It is the RA resource used for performing random access if the candidate cell is selected as the target cell.

[0222] (10) a dedicated uplink resource, that is, the dedicated uplink resource configured (or allocated) by the candidate cell for the UE, that is, Configured Grant. It is used for uplink transmission in the target cell when UE performs LTM.

[0223] (11) an LTM execution condition, which are provided by the candidate cell. Herein the LTM execution condition is related to Layer 1 (L1) measurement. When the UE selects the candidate cell as the target cell to access, the UE monitors other candidate cells, and according to the L1 measurement result, when one or more cells meet the LTM execution condition, it selects one of them as the new target cell and performs the LTM, that is, triggers the cell switch and accesses to the new target cell.

[0224] (12) C-RNTI. The value of the C-RNTI allocated by the candidate cell for the UE is taken as the identification of the UE in the candidate cell.

[0225] (13) PUCCH resource information, which is the PUCCH resource information allocated (or configured) by the candidate cell for the UE.

[0226] If the candidate cell belongs to the source gNB-DU, the configuration of the candidate cell is completed through steps 403a-403b.

[0227] Steps 403a-403b are the same as steps 303a-303b. Please refer to Embodiment 1 for detailed description, and they will not be repeated here.

[0228] In steps 404-405, gNB-CU provides all candidate cell information to the source cell (source gNB-DU), and the source cell provides CSI report configuration and LTM execution condition to gNB-CU. Steps 404-405 are the same as steps 304-305. Please refer to Embodiment 1 for detailed description, and they will not be repeated here.

[0229] Steps 406-408 are the same as steps 306-308. Please refer to Embodiment 1 for details, and they will not be repeated here.

[0230] Step 409: The source gNB-DU transmits a message to the UE.

[0231] Optionally, the message is an RRCReconfiguration message, or other messages.

[0232] The message contains at least one of the following information:

[0233] (1) LTM candidate configuration related information of one or more LTM candidate cells. The LTM candidate configuration related information includes at least one of the following information:

[0234] - LTM candidate identification (LTM Candidate Id), which corresponds to the LTM configuration identification and is associated with (or corresponds to) the LTM candidate cell.

[0235] - LTM candidate physical cell identification (LTM candidate PCI), indicating the physical cell identification of the candidate cell corresponding to (or associated with) the LTM candidate identification.

[0236] - SSB configuration information of LTM, indicating the time and frequency information of SSB of the candidate cell corresponding to (or associated with) the LTM candidate identification. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0237] - LTM candidate configuration information, including Cell Group configuration information, Radio Bearer (RB) configuration information, etc.

[0238] - an LTM execution condition, which is provided by candidate cells.

[0239] - a first LTM RACH resource configuration (ltm Early UL Sync Config) which contains the RA resource configured (or allocated) by the candidate cell for performing the uplink synchronization process in advance. That is, it is the first RACH configuration received by gNB-CU in steps 402b and / or 403b.

[0240] - a second LTM RACH resource configuration (which can also be called second resource configuration, or other names, and the present invention is not limited to this) (dedicate ltm Early UL Sync Config), which is the dedicated RA resource configured (or allocated) by the candidate cell for the UE to perform the uplink synchronization process in advance. That is, it is the second RACH configuration received by gNB-CU in steps 402b and / or 403b.

[0241] - a dedicated uplink resource, which are configured (or allocated) by the candidate cell for the UE, that is, Configured Grant. It is used for uplink transmission in the target cell when UE performs LTM.

[0242] - a third RACH resource configuration (also called the third resource configuration, or other names, but the present invention is not limited to this), that is, the RA resource configured (or allocated) by the candidate cell for performing RACH-based LTM. It is the RA resource used for random access when the candidate cell is selected as the target cell. That is, it is the third RACH configuration received by gNB-CU in steps 402b and / or 403b.

[0243] - C-RNTI. The value of the C-RNTI allocated by the candidate cell for the UE is taken as the identification of the UE in the candidate cell.

[0244] - PUCCH resource information, which is allocated (or configured) by the candidate cell for the UE.

[0245] (2) LTM execution condition (also called first LTM execution condition, or other names, the present invention is not limited to this), that is, the execution condition provided by the source cell. Herein the LTM execution condition is related to Layer 1 (L1) measurement. The UE monitors the candidate cell, and according to the L1 measurement result, when one or more cells meet the LTM execution condition, it selects one of them as the target cell, performs the conditional LTM, that is, triggers cell switch and accesses to the target cell.

[0246] Steps 410-411 are the same as steps 310-311. Please refer to Embodiment 1 for details, and they will not be repeated here.

[0247] In step 412, the UE transmits a preamble (also called the second preamble) to the candidate gNB-DU (candidate cell). The UE uses the dedicated RACH resource (also called the second RA resource) allocated to the UE by the candidate cell to send a preamble to the candidate cell. The candidate cell is selected by the UE, and optionally, the selection of the candidate cell can be based on the measurement result or other information.

[0248] Step 413: The candidate gNB-DU transmits a message to gNB-CU. The candidate cell detects the preamble on the RACH resource used for performing the uplink synchronization in advance, and determines the TA value. The candidate gNB-DU can determine the UE corresponding to the TA value according to the received preamble and RACH resource. The candidate gNB-DU transmits the TA value to gNB-CU, and the gNB-CU transmits the TA value to the UE through the source gNB-DU.

[0249] Alternatively, the message may be a DU-CU TA INFORMATION TRANSFER message, or other messages. The message may contain one or more TA information. The TA information is the TA information of the candidate cell and contains the TA value of the candidate cell.

[0250] The TA information includes at least one of the following information:

[0251] (1) a candidate cell identification, which the identification of candidate cell which detects the preamble. The candidate cell identification can be CGI or other identification.

[0252] (2) a preamble index, that is, random access preamble index. It is the index of the preamble detected by the candidate cell on the allocated RACH resources for performing the uplink synchronization process in advance.

[0253] (3) a value of Timing Advance (TA), which can also be called TA value. The value of timing advance is the TA value determined by the candidate cell according to the detected preamble.

[0254] (4) RA-RNTI (also called the third RA-RNTI, or other names, the present invention is not limited to this). The value of RA-RNTI is determined by detecting the resource-related information of the preamble based on formula (1).

[0255] (5) a gNB-DU identification (which can also be called the first node identification information, or other names, and the present invention is not limited to this), which is the gNB-DU where the UE to which the TA value belongs is located.

[0256] (6) a UE identification, which may be the identification of UE in candidate gNB-DU (gNB-DU UE F1AP ID), or the identification of UE in gNB-CU (gNB-CU UE F1AP ID), or C-RNTI, or other identifications. Herein,

[0257] - If it is the identification of the UE in gNB-CU, it is the identification allocated to the UE by gNB-CU during the candidate cell configuration in step 400. See step 302a.

[0258] - If it is the identification of the UE in gNB-DU, it is the identification allocated to the UE by the candidate gNB-DU during the candidate cell configuration in step 400. See step 302b.

[0259] If it is a C-RNTI identification, it can be the value of the C-RNTI allocated by the candidate cell for the UE.

[0260] gNB-CU can determine the identification of the UE in the source gNB-DU according to the UE identification. In the process of candidate cell configuration in steps 402a-402b, gNB-CU can obtain the UE identification, so it can be associated with the identification allocated to the UE by the source gNB-DU (source cell). The identification allocated to the UE by the source gNB-DU (source cell) may be the gNB-DU UE F1AP ID of the UE in the source gNB-DU or the C-RNTI of the UE in the source cell.

[0261] Step 414: gNB-CU transmits a message to the source gNB-DU. gNB-CU transmits the TA information belonging to the source gNB-DU among the TA information obtained in step 413 to the source gNB-DU.

[0262] Alternatively, the message may be a CU-DU TA INFORMATION TRANSFER message, or other messages. The message may contain one or more TA information. The TA information may be of the same UE or of different UEs.

[0263] The TA information includes at least one of the following information:

[0264] (1) a candidate cell identification, which is the identification of the candidate cell which detects the preamble. The candidate cell identification can be CGI or other identification.

[0265] (2) a value of Timing Advance (TA), which can also be called TA value. The TA value is the TA value determined by the candidate cell according to the detected preamble.

[0266] (3) a preamble index, that is, random access preamble index. It is the index of the preamble detected on the candidate cell.

[0267] (4) RA-RNTI (also called the third RA-RNTI, or other names, the present invention is not limited to this). The value of RA-RNTI is determined by detecting the resource-related information of the preamble, based on formula (1).

[0268] (5) a gNB-DU identification (which can also be called the first node identification information, or other names, and the present invention is not limited to this), which is the gNB-DU where the UE to which the TA value belongs is located.

[0269] (6) a UE identification, which is the identification (gNB-DU UE F1AP ID) of the UE in the source gNB-DU (serving gNB-DU), or the C-RNTI in the source cell (serving cell), or other identifications.

[0270] Step 415: The source gNB-DU transmits a message to the UE, and transmits the TA value of the UE in the candidate cell (included in the TA information) to the UE. The source gNB-DU transmits the TA information belonging to the same UE received in step 414 to the UE. The TA information is the TA information provided by the candidate cell, that is, the Early TA information of the UE in the candidate cell.

[0271] The message may contain TA information of one or more candidate cells.

[0272] The TA information includes at least one of the following information:

[0273] (1) an LTM configuration identification, that is, the LTM configuration identification associated (or corresponding) to the candidate cell. It indicates the LTM configuration identification corresponding to the candidate cell where the preamble is detected. The value range of the LTM configuration identification is 0-7. The LTM configuration identification corresponds to an LTM candidate identification (LTM Candidate Id).

[0274] (2) a value of Timing Advance (TA), which can also be called TA value. The TA value is the TA value determined by the candidate cell according to the detected preamble.

[0275] (3) a Random Access preamble Index, that is, a preamble index or preamble Identification. It is the index or identification of the preamble detected on the candidate cell.

[0276] (4) RA-RNTI (also called the third RA-RNTI, or other names, the present invention is not limited to this). The value of RA-RNTI is determined by detecting the resource-related information of the preamble, based on formula (1).

[0277] Optionally, the TA information transmission can adopt a MAC control unit (MAC CE), which is included in a MAC PDU and sent to the UE through PDSCH. Or the TA information is transmitted to the UE through other messages or modes. The MAC CE for transmitting TA information can be called a timing advance command for early TA acquisition MAC CE, or Early TA command MAC CE (Early Timing Advance Command MAC CE), or candidate TA information MAC CE, or a Random Access Response for Early TA acquisition MAC CE (RAR for Early TA Acquisition MAC CE).

[0278] A MAC PDU is a bit string whose length is byte-aligned (that is, a multiple of 8 bits). MAC CE is a bit string whose length is byte-aligned (that is, a multiple of 8 bits). A MAC sub-head is a bit string whose length byte-aligned (that is, a multiple of 8 bits).

[0279] A MAC PDU is composed of one or more MAC sub-PDUs, wherein the MAC sub-PDUs contain a MAC sub-header (sub-head for short) and a MAC CE, or contain a sub-header and a MAC SDU (the MAC SDU contains RLC layer data). Among them, the lengths of MAC PDU, MAC CE and MAC sub-head are all byte-aligned (that is, multiples of 8 bits) bit strings. An example of a MAC PDU structure is given in Fig. 4B. MAC PDU will be sent to UE through PDSCH. Optionally, the Timing Advance Command for Early TA acquisition MAC CE for obtaining the TA value in advance may be included in a MAC sub-PDU of a MAC PDU and transmitted to the UE. The network will assign a Logical Channel ID (LCID), which can be used to identify (or indicate) that the MAC CE is a Timing Advance Command for Early TA acquisition MAC CE for obtaining the TA value in advance by setting the value of the logical channel. The logical channel identification will be included in the MAC sub-header.

[0280] Wherein the sub-header contains at least one of the following information:

[0281] - reserved (R): reserved bit;

[0282] - a logical channel identification, which is the logical channel identification of Timing Advance Command for Early TA acquisition MAC CE for obtaining the TA value in advance. The MAC CE is identified by setting the value of the logical channel identification.

[0283] Fig. 4C is an example of a Timing Advance Command for Early TA acquisition MAC CE according to various embodiments of the disclosure. The MAC CE contains TA information, which is Early TA information. The Timing Advance Command for Early TA acquisition MAC CE contains at least one of the following information:

[0284] - reserved (R): Reserved bit.

[0285] - LTM configuration identification, that is, the LTM configuration identification associated (or corresponded) to the candidate cell. It corresponds to the LTM candidate identification and the candidate cell.

[0286] - a Timing Advance command, that is, the TA value of the candidate cell.

[0287] - a random access preamble index indicating that the TA value is determined by detecting the random access preamble.

[0288] - RA-RNTI. The value of RA-RNTI is determined by detecting the resource-related information of the random access preamble, based on formula (1).

[0289] The UE receives (or monitors) a Physical Downlink Control Channel (PDCCH). If the received PDCCH is scrambled by using the C-RNTI allocated to the UE by the source cell, the UE obtains radio resource information (or scheduling resource information or dynamic scheduling information) from the PDCCH, and receives PDCCH for transmitting MAC PDU from the resource. The UE determines the Timing Advance Command for Early TA acquisition MAC CE for obtaining the TA value in advance according to the logical channel identification, so as to obtain the TA value of the candidate cell. The C-RNTI is the C-RNTI allocated to the UE by the source cell (serving cell) as the identification of the UE in the source cell. When the UE selects a candidate cell as the target cell (that is, the serving cell of the UE) and accesses to the target cell, then the C-RNTI is the C-RNTI allocated to the UE by the candidate cell. The C-RNTI allocated to the UE by the source cell is obtained by the UE when RRC connection establishment is realized with the network through the source cell.

[0290] In step 416, the timer T is started or restarted. After receiving the TA information of the candidate cell in step 415, the UE can determine whether it is the TA value sent to itself according to the RA-RNTI and the random access preamble index. Each candidate cell corresponds to a timer. If it is determined that it is the TA value of the candidate cell sent to the UE, the UE starts or restarts the timer T corresponding to the candidate cell. Before the timer corresponding to the candidate cell expires, the TA value of the candidate cell is considered valid; otherwise, if the timer expires, the TA value of the candidate cell is considered invalid.

[0291] The UE evaluates (or monitors) the execution condition of the candidate cell according to the L1 measurement result. If one or more candidate cells meet the execution conditions. The UE selects one of them as the target cell, performs conditional LTM, performs cell switch, accesses the target cell, and performs step 417. There are three ways to perform conditional LTM, see Embodiments 5, 6 and 7 respectively.

[0292] In the above method, the network configures the execution condition for conditional LTM handover, and when the execution condition is met, the UE actively performs LTM for cell handover without waiting for the network to send a handover command. Thus, that signal interaction between the UE and the network can be reduced, and the situation that the handover of the UE fails due to the change of the state of the radio link during the signaling interaction between the UE and the network can also be avoided, thereby improve the robustness of the handover. Moreover, before performing the conditional LTM, the UE performs uplink synchronization with the candidate cell (including the target cell) in advance to obtain (or acquire) the TA value of the candidate cell (including the target cell) in advance (it can also be called obtaining the TA value in advance). This process can also be called the process of obtaining (or acquiring) the TA in advance (Early TA Acquisition), or the process of obtaining the TA of the candidate cell in advance, or the process of the UE performing uplink in the candidate cell in advance. Through the process of uplink synchronization between UE and candidate cell in advance, it is avoided that UE needs to perform uplink synchronization with target cell during handover execution, thus reducing handover delay. Therefore, while improving the robustness of LTM switching, the invention reduces the handover delay, improves the handover performance and reduces the signaling overhead.

[0293] Embodiment 3: Another method of obtaining the TA value of the candidate cell in advance

[0294] Please refer to Fig. 5A. Fig. 5A is a further schematic diagram of interaction among a user equipment, a first node, a second node and a third node according to various embodiments of the disclosure. The method illustrated in Fig. 5A may include one or more of steps S500a to S517.

[0295] In the third embodiment, the candidate cell allocates the RACH resource for each gNB-DU, which is used for the UE in each gNB-DU to perform uplink synchronization with the candidate cell in advance, that is, the TA value is obtained in the candidate cell in advance. The process is illustrated in Fig. 5A, and is described in detail as follows.

[0296] Steps 500a-511, that is candidate cell configuration process. The specific process is basically the same as steps 300a-311.

[0297] In steps 500a-511, the candidate cell configuration is completed, and the candidate cell allocates a RACH resource for obtaining the TA value in advance to the gNB-DU where the UE is located, wherein the RACH resource is shared by the UEs served by the source gNB-DU. The network transmits the candidate cell information and the allocated RACH resource information to the UE, that is, step 509 contains the LTM RACH resource configuration information, and the LTM RACH resource is used to obtain the TA value in advance.

[0298] When the UE decides to trigger the uplink synchronization process with the candidate cell (that is, the process of obtaining the TA value of the candidate cell in advance), it will select the candidate cell and the preamble, select the RACH resource allocated by the candidate cell for performing the uplink synchronization process in advance, and send the selected preamble on the selected RACH resource. The UE calculates the RA-RNTI value related to the candidate cell according to the RACH resource information of the selected candidate cell.

[0299] Steps 500a- 502a are the same as steps 300a-302a. Please refer to Embodiment 1 for details, and they will not be repeated here.

[0300] Step 502b: The candidate gNB-DU transmits a message to gNB-CU. If receiving the requested LTM configuration, the candidate gNB-DU sends the message for feedback, and provides RRC configuration information of the candidate cell that accepts the request.

[0301] Optionally, the message may be a UE CONTEXT SETUP RESPONSE, or other messages.

[0302] The message contains at least one of the following information:

[0303] (1) The identification information of UE in gNB-CU, which is the identification allocated to UE by gNB-CU and can be gNB-CU UE F1AP ID or other identification, that is, the identification allocated to UE by gNB-CU in step 502a.

[0304] (2) The identification information of the UE in gNB-DU, which is the identification allocated to the UE by the candidate gNB-DU and can may be gNB-DU UE F1AP ID or other identification.

[0305] (3) a cell identification indicating the requested candidate cell identification, which is the candidate cell identification requested in step 502a. The cell identification may be CGI (Cell Global ID) or other identifications.

[0306] (4) LTM configuration information indicating the configuration information of the cell indicated by the cell identification. It contains at least one of the following information:

[0307] - SSB configuration information indicating time and frequency information of SSB of the cell indicated by the cell identification. The frequency information is ARFCN.

[0308] - Physical cell ID (PCI), indicating the physical cell identification of the cell indicated by the cell identification.

[0309] (5) TCI status configuration list.

[0310] (6) RACH configuration information list, including one or more RACH configuration information, wherein the RACH configuration information includes at least one of the following information:

[0311] - a first RACH configuration, which contains the RA resources configured (or allocated) by the candidate cell for performing the uplink synchronization process in advance.

[0312] - a gNB-DU ID, the identification of the candidate gNB-DU, that is, the identification of the gNB-DU using the RA resource configured by the first RACH.

[0313] (7) CSI reporting configuration.

[0314] (8) a second RACH configuration, which includes the dedicated RA resource configured (or allocated) to the UE by the candidate cell for performing the uplink synchronization process in advance.

[0315] (9) a third RACH configuration, which includes the RA resource configured (or allocated) by the candidate cell for performing RACH-based LTM. It is the RA resources used for random access if the candidate cell is selected as the target cell.

[0316] (10) a dedicated uplink resource, that is, the dedicated uplink resources configured (or allocated) by the candidate cell for the UE, that is, Configured Grant. It is used for uplink transmission in the target cell when UE performs LTM.

[0317] (11) an LTM execution condition, which is provided by candidate cell. Herein the LTM execution condition is related to Layer 1 (L1) measurement. When the UE selects the candidate cell as the target cell to access, the UE monitors the candidate cell, and according to the L1 measurement result, when one or more cells meet the LTM execution condition, it selects one of them as the new target cell, performs the LTM, that is, triggers cell switch and accesses to the new target cell.

[0318] (12) C-RNTI. The value of the C-RNTI allocated by the candidate cell for the UE is taken as the identification of the UE in the candidate cell.

[0319] (13) RNTI, which is the RNTI value allocated (or configured) by the candidate cell. It is the RNTI used for the UE to receive the TA information obtained in advance in the target cell after the candidate cell is used as the target cell (serving cell). Optionally, the RNTI may be a dedicated RA-RNTI (Random Access RNTI), or other RNTI.

[0320] (14) PUCCH resource information, which is the PUCCH resource information allocated (or configured) by the candidate cell for the UE.

[0321] If the candidate cell belongs to the source gNB-DU, the configuration of the candidate cell is completed through steps 503a-503b.

[0322] Steps 503a-503b are the same as steps 303a-303b. Please refer to Embodiment 1 for detailed description, and they will not be repeated here.

[0323] In steps 504-505, gNB-CU provides all candidate cell information to the source cell (source gNB-DU), and the source cell provides CSI report configuration and LTM execution condition to gNB-CU. Steps 504-505 are the same as steps 304-305. Please refer to Embodiment 1 for the detailed description, which will not be repeated here.

[0324] Steps 506-508 are the same as steps 306-308. Please refer to Embodiment 1 for details, and they will not be repeated here.

[0325] Step 509: The source gNB-DU transmits a message to the UE.

[0326] Optionally, the message is an RRCReconfiguration message, or other messages.

[0327] The message contains at least one of the following information:

[0328] (1) LTM candidate configuration related information of one or more LTM candidate cells. The LTM candidate configuration related information includes at least one of the following information:

[0329] - LTM candidate identification (LTM Candidate Id), which corresponds to the LTM configuration identification and is associated with (or corresponds to) the LTM candidate cell.

[0330] - LTM candidate physical cell identification (LTM candidate PCI), indicating the physical cell identification of the candidate cell corresponding to (or associated with) the LTM candidate identification.

[0331] - SSB configuration information of LTM, indicating the time and frequency information of SSB of the candidate cell corresponding to (or associated with) the LTM candidate identification. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0332] - LTM candidate configuration information, including Cell Group configuration information, Radio Bearer (RB) configuration information, etc.

[0333] - a first LTM RACH resource configuration (ltm-EarlyUL-SyncConfig) (which can also be called the first resource configuration, or other names, and the present invention is not limited to this) contains the RA resource configured (or allocated) by the candidate cell for performing the uplink synchronization process in advance. That is, the first RACH configuration received by gNB-CU in steps 502b and / or 503b.

[0334] - an LTM execution condition (also called second LTM execution condition, or other names, the invention is not limited to this), that is, the LTM execution condition provided by the candidate cell.

[0335] - a dedicated uplink resource, which are configured (or allocated) by the candidate cell for the UE, that is, Configured Grant. It is used for uplink transmission in the target cell when UE performs LTM.

[0336] - a third RACH resource configuration (which can also be called the third resource configuration, or other names, but the present invention is not limited to this), which includes the RA resource configured (or allocated) by the candidate cell for performing RACH-based LTM. It is the RA resource used for random access when the candidate cell is selected as the target cell. That is, the third RACH configuration received by gNB-CU in steps 502b and / or 503b.

[0337] - RNTI, which is RNTI value configured (allocated) by the candidate cell. It is RNTI used for the UE to receive the TA information obtained in advance in the target cell after the candidate cell is used as the target cell (serving cell). Optionally, the RNTI may be a dedicated RA-RNTI (Random Access RNTI) (also called the second RA-RNTI, or other names, and the present invention is not limited to this), or other RNTI.

[0338] - PUCCH resource information, which is allocated (or configured) by the candidate cell for the UE.

[0339] (2) an LTM execution condition (also called first LTM execution condition, or other names, the present invention is not limited to this), which is the LTM execution condition provided by the source cell. Herein the LTM execution condition is related to Layer 1 (L1) measurement. The UE monitors the candidate cell, and according to the L1 measurement result, when one or more cells meet the LTM execution condition, it selects one of them as the target cell and performs the conditional LTM, that is, triggers cell switch and accesses to the target cell.

[0340] (3) RNTI, which is the RNTI value allocated (or configured) by the source cell. It is the RA-RNTI used for the UE to receive the TA information obtained in advance in the source cell. Optionally, the RNTI may be a dedicated RA-RNTI (Random Access RNTI) (It can also be called the first RA-RNTI, or other names, and the present invention is not limited to this), or other RNTI.

[0341] Steps 510-511 are the same as steps 310-311. Please refer to Embodiment 1 for details, and they will not be repeated here.

[0342] Step 512a: Select a candidate cell. When the UE decides to trigger the uplink synchronization process with the candidate cell, it will select the candidate cell, as well as the RACH resource (also called the first RA resource) and the preamble (also called the first preamble).

[0343] In step 512, the UE transmits a preamble to the candidate cell.

[0344] Step 513: The candidate gNB-DU transmits a message to gNB-CU. The candidate cell detects preamble on the RACH resource used for performing the uplink synchronization in advance, and determines the TA value. Since in step 502b, the candidate cell of the candidate gNB-DU transmits its RACH resource information to other gNB-DUs, for the UE in other gNB-DUs to obtain the TA value of the candidate cell in advance. Optionally, the RACH resources provided to other gNB-DUs are different. Therefore, according to the detected preamble and RACH resource, the candidate gNB-DU can determine the serving gNB-DU of the UE to which the TA value belongs (that is, the gNB-DU to which the UE's serving cell belongs). The candidate gNB-DU transmits the TA value to gNB-CU and forwards it to the corresponding gNB-DU through gNB-CU.

[0345] Alternatively, the message may be a DU-CU TA INFORMATION TRANSFER message, or other messages. The message may contain one or more TA information.

[0346] The TA information includes at least one of the following information:

[0347] (1) a candidate cell identification, which is the identification of the candidate cell where the preamble is detected. The candidate cell identification can be CGI or other identification.

[0348] (2) a preamble index, that is, random access preamble index. It is the index of the preamble detected by the candidate cell on the allocated RACH resources for performing the uplink synchronization process in advance.

[0349] (3) a value of Timing Advance (TA), which can also be called TA value. The value of timing advance is the TA value determined by the candidate cell according to the detected preamble.

[0350] (4) RA-RNTI (also called the third RA-RNTI, or other names, the present invention is not limited to this). The value of RA-RNTI is determined by detecting the resource-related information of the preamble based on formula (1).

[0351] (5) a gNB-DU identification (which can also be called the first node identification information, or other names, and the present invention is not limited to this), which is the gNB-DU where the UE to which the TA value belongs is located.

[0352] If the candidate gNB-DU determines that the serving gNB-DU of the UE is the source gNB-DU, then the gNB-DU is the identification of the source gNB-DU.

[0353] According to the gNB-DU identification, the gNB-CU can determine which gNB-DU to send the received TA information to.

[0354] Step 514: gNB-CU transmits a message to the source gNB-DU.

[0355] If the gNB-DU identification in step 513 is the source gNB-DU identification, gNB-CU transmits the corresponding TA information to the source gNB-DU.

[0356] Alternatively, the message may be a CU-DU TA INFORMATION TRANSFER message, or other messages. The message may contain one or more TA information. The TA information may belong to the same UE or different UEs.

[0357] The TA information includes at least one of the following information:

[0358] (1) a candidate cell identification, which the identification of candidate cell which detects the preamble. The candidate cell identification can be CGI or other identification.

[0359] (2) a value of Timing Advance (TA), which can also be called TA value. The value of timing advance is the TA value determined by the candidate cell according to the detected preamble.

[0360] (3) a preamble index, that is, random access preamble index. It is the index of the preamble detected on the candidate cell.

[0361] (4) RA-RNTI (also called the third RA-RNTI, or other names, the present invention is not limited to this). The value of RA-RNTI is determined by detecting the resource-related information of the preamble based on formula (1).

[0362] Step 515: The source gNB-DU transmits a message to the UE. The source gNB-DU transmits the TA information received in step 514 to the UE. The TA information is the TA information provided by the candidate cell, that is, the Early TA information determined on the candidate cell. Since the UE has selected the RACH resource to perform uplink synchronization with the candidate cell in advance, the source gNB-DU cannot determine which UE the TA information obtained in step 514 belongs to, so it transmits the received TA information of the candidate cell to all UEs in the cell, and transmits it to the UE in the form of public information, for example, broadcast or multicast.

[0363] Optionally, the message may be a MAC PDU, sent to the UE through PDSCH, or sent to the UE through other messages or modes. TA information of the candidate cell may be included in a MAC PDU. The MAC PDU may be called a MAC PDU for Early Timing Advanced Command, or called MAC PDU for Ealry TA acquisition, or MAC PDU for TA information of candidate cell.

[0364] The MAC PDU is transmitted to the UE through PDSCH. The resources used to send the PDSCH are included in the PDCCH transmitted by the source cell to the UE. The PDCCH is scrambled by RNTI allocated by the source cell, or by RA-RNTI received from step 514, thus indicating that the resource in the PDCCH received by the UE is to transmit the MAC PDU for Early Timing Advanced Command. Among them:

[0365] - If the RNTI value allocated by the source cell is included in step 509, the UE monitors the PDCCH, and if the received PDCCH is scrambled using the RNTI, the UE obtains the scheduling resource (or radio resource) information from the PDCCH and receives the PDSCH from the resource. The MAC PDU for Early Timing Advanced Command (MAC PDU for TA information of candidate cell) is transmitted on the PDSCH. Herein the RNTI allocated by the source cell is used for the MAC PDU for TA information of candidate cell, or is related to (or corresponds to) the MAC PDU for TA information of candidate cell. When the candidate cell is the target cell (serving cell), the RNTI allocated by the candidate cell is used for the MAC PDU for TA information of candidate cell, or it is related to (or corresponds to) MAC PDU for TA information of candidate cell.

[0366] - If the RNTI value allocated by the source cell is not included in step 509, the UE calculates the RA-RNTI by the related information of resource where preamble is transmitted. Alternatively, the obtained RA-RNTI value can be calculated according to Formula (1). If the PDCCH received by the UE uses the calculated RA-RNTI for scrambling, the UE receives PDSCH on the scheduling resource obtained from the PDCCH. The MAC PDU for Early Timing Advanced Command (MAC PDU for TA information of candidate cell) is transmitted on the PDSCH.

[0367] RA-RNTI = 1 + s_id + 14 Х t_id + 14 Х 80 Х f_id + 14 Х 80 Х 8 Х ul_carrier_id formula (1)

[0368] Among them,

[0369] - s _ id: indicating an index of the PRACH occasion, or the first OFDM symbol of the PRACH occasion;

[0370] - t _ id: indicating an index of the first slot of the PRACH occasion in a system frame;

[0371] - f _ id: indicating an index of the PRACH occasion in the frequency domain;

[0372] - ul_carrier_id: indicating an uplink carrier identification used to transmit the random access preamble (preamble).

[0373] The MAC PDU for Early Timing Advanced Command may contain TA information of one or more candidate cells.

[0374] The TA information includes at least one of the following information:

[0375] (1) a candidate cell identification, which the identification of candidate cell which detects the preamble. The candidate cell identification can be CGI or other identification.

[0376] (2) a value of Timing Advance (TA), which can also be called TA value. The value of timing advance is the TA value determined by the candidate cell according to the detected preamble.

[0377] (3) a Random Access preamble Index, that is, a preamble Index or preamble identification. It is the index or identification of the preamble detected on the candidate cell.

[0378] (4) RA-RNTI. The value of RA-RNTI is determined by detecting information such as the resource of the Random access preamble, etc., based on formula (1).

[0379] (5) RACH resource information. The candidate cell detects the preamble to determine the RACH resource information of the TA value.

[0380] The UE can determine whether the TA value contained in the TA information is a TA value sent to itself according to the RA-RNTI and the random access preamble index contained in the TA information.

[0381] Based on formula (1), the UE calculates the RA-RNTI according to the resource-related information of the preamble transmitted to the candidate cell. If the RA-RNTI value contained in the TA information is equal to the RA-RNTI value calculated by the UE, and the random access preamble index contained in the TA information is the same as the random access preamble index transmitted by the UE, then the TA value contained in the TA information is the TA value sent to the UE. The TA value is the TA value of the candidate cell (that is, the candidate cell corresponding to the candidate cell identification).

[0382] Fig. 5B is an example of a MAC PDU for Early Timing Advanced Command (containing one or more TA information) according to various embodiments of the disclosure. Herein the MAC PDU comprises one or more MAC sub-PDUs and / or one padding. Each MAC sub-PDU contains a MAC sub-header (or MAC sub header) and a TA command.

[0383] Wherein the sub-header contains at least one of the following information:

[0384] - E: Extension field. It used to indicate whether the MAC sub-PDU containing this MAC sub-header (or sub header) is the last MAC sub-PDU in the MAC PDU. The E field is set to 1, indicating that there is at least another MAC sub-PDU behind it. The E field is set to 0, indicating that the MAC sub-PDU containing this MAC sub-header is the last MAC sub-PDU in the MAC PDU.

[0385] - Reserved (R): Reserved bit.

[0386] - Random access preamble index: the index or identification of the preamble detected on the candidate cell.

[0387] The TA command contains TA information, which contains at least one of the following information:

[0388] - Reserved (r): Reserved bit.

[0389] - a candidate cell identification, which can be PCI, or CGI (Cell Global ID), or other identification.

[0390] - a Timing advance command, that is, the TA value of the candidate cell.

[0391] - RA-RNTI. The value of RA-RNTI is determined by detecting the resource-related information of the preamble based on formula (1).

[0392] Fig. 5C is an example of a TA command. Herein the candidate cell identification uses PCI.

[0393] In step 516, UE starts or restarts the timer T. Each candidate cell corresponds to a timer. After receiving the TA information of the candidate cell in step 515, the UE starts or restarts the timer T corresponding to the candidate cell. Before the timer corresponding to the candidate cell expires, the TA value of the candidate cell is considered valid; otherwise, if the timer expires, the TA value of the candidate cell is considered invalid.

[0394] The UE evaluates (or monitors) the execution condition of the candidate cell according to the L1 measurement result. If one or more candidate cells meet the execution conditions. The UE selects one of them as the target cell, performs conditional LTM, performs cell switch, accesses the target cell, and performs step 517. There are three ways to perform conditional LTM, see Embodiments 5, 6 and 7 respectively.

[0395] In the above method, the network configures the execution condition for conditional LTM handover, and when the execution condition is met, the UE actively performs LTM for cell handover without waiting for the network to send a handover command. Thus, that signal interaction between the UE and the network can be reduced, and the situation that the handover of the UE fails due to the change of the state of the radio link during the signaling interaction between the UE and the network can also be avoided, thereby improve the robustness of the handover. Moreover, before performing the conditional LTM, the UE performs uplink synchronization with the candidate cell (including the target cell) in advance to obtain (or acquire) the TA value of the candidate cell (including the target cell) in advance (it can also be called obtaining the TA value in advance). This process can also be called the process of obtaining (or acquiring) the TA in advance (Early TA Acquisition), or the process of obtaining the TA of the candidate cell in advance, or the process of the UE performing uplink in the candidate cell in advance. Through the process of uplink synchronization between UE and candidate cell in advance, it is avoided that UE needs to perform uplink synchronization with target cell during handover execution, thus reducing handover delay. Therefore, while improving the robustness of LTM switching, the invention reduces the handover delay, improves the handover performance and reduces the signaling overhead.

[0396] Embodiment 4: Another method of obtaining the TA value of the candidate cell in advance

[0397] Please refer to Fig. 6. Fig. 6 is another schematic diagram of interaction among a user equipment, a first node, a second node and a third node according to various embodiments of the disclosure. The method illustrated in Fig. 6 may include one or more of steps S600 to S609.

[0398] Step 600, that is candidate cell configuration process. The specific process is the same as steps 500a-511, and will not be described here.

[0399] In step 601, the UE transmits a message to the source gNB-DU (which can also be called the first message or other names, but the present invention is not limited to this). Optionally, the message may include the L1 measurement result, through which the source cell can determine the candidate cell selected by the UE for performing the uplink synchronization in advance. The message may also contain a candidate cell identification, which is used to directly indicate the candidate cell selected by the UE for performing the uplink synchronization in advance. The candidate cell identification may be an LTM configuration identification corresponding to the candidate cell, or an LTM candidate identification, or CGI, or PCI, or other cell identifications. The message may be transmitted through PUCCH or at PUSCH through MAC CE.

[0400] Step 602: The source gNB-DU decides to trigger the UE and the candidate cell to perform uplink synchronization in advance. Herein the source gNB-DU selects a candidate cell for UE to perform uplink synchronization in advance. Optionally, the selection of the candidate cell may be determined based on the L1 measurement result obtained in step 601 or the candidate cell identification.

[0401] In step 603, the source gNB-DU transmits physical layer signaling (also called second message, or other names, the present invention is not limited to this) to the UE, instructing the UE to send a preamble to the candidate cell, or instructing the UE to perform uplink synchronization with the candidate cell in advance. Optionally, the physical layer signaling may be a PDCCH order or other signaling.

[0402] The signaling includes at least one of the following information:

[0403] (1) an LTM candidate identification, corresponding to the LTM configuration identification and associated with (or corresponding to) the LTM candidate cell;

[0404] (2) RACH configuration information, which includes the resource information of the preamble transmitted by the UE to the candidate cell, that is, the information related to the RA resource (or RACH resource, which can also be called the fourth RA resource). The RACH configuration information includes at least one of the following information:

[0405] - SS / PBCH index, indicating SS / PBCH used to determine the RACH occasion of PRACH transmission.

[0406] - PRACH Mask Index, which indicates the RACH occasion for PRACH transmission related to SS / PBCH. The SS / PBCH is the SS / PBCH indicated by the SS / PBCH index.

[0407] (3) a preamble index, which indicates the index of the preamble transmitted by the UE on the resource included in the RACH configuration information.

[0408] In step 604, the UE transmits a preamble (also called the fourth preamble) to the candidate gNB-DU (candidate cell). According to the RACH configuration information received in step 603 and the first RACH configuration information allocated by the candidate cell obtained in step 600, the UE determines the resource for transmitting the preamble. The transmitted preamble is the preamble received in step 603.

[0409] Step 605 is the same as step 513. The candidate gNB-DU transmits a message to gNB-CU. The candidate cell detects preamble on the RACH resource used for performing the uplink synchronization in advance, and determines the TA value. Since in step 502b, the candidate cell of the candidate gNB-DU transmits its RACH resource information to other gNB-DUs, for the UE in other gNB-DUs to obtain the TA value of the candidate cell in advance. Optionally, the RACH resources provided to other gNB-DUs are different. Therefore, according to the detected preamble and RACH resource, the candidate gNB-DU can determine the serving gNB-DU of the UE to which the TA value belongs (that is, the gNB-DU to which the UE's serving cell belongs). The candidate gNB-DU transmits the TA value to gNB-CU and forwards it to the corresponding gNB-DU through gNB-CU.

[0410] Alternatively, the message may be a DU-CU TA INFORMATION TRANSFER message, or other messages. The message may contain one or more TA information.

[0411] The TA information includes at least one of the following information:

[0412] (1) a candidate cell identification, which the identification of candidate cell which detects the preamble. The candidate cell identification can be CGI or other identification.

[0413] (2) a value of Timing Advance (TA), which can also be called TA value. The value of timing advance is the TA value determined by the candidate cell according to the detected preamble.

[0414] (3) a preamble index, that is, random access preamble index. It is the index of the preamble detected on the candidate cell.

[0415] (4) RA-RNTI. The value of RA-RNTI is determined by detecting the resource-related information of the preamble based on formula (1).

[0416] (5) a gNB-DU identification, which is the gNB-DU where the UE to which the TA value belongs is located.

[0417] If the candidate gNB-DU determines that the serving gNB-DU of the UE is the source gNB-DU, then the gNB-DU is the identification of the source gNB-DU.

[0418] According to the gNB-DU identification, the gNB-CU can determine which gNB-DU to send the received TA information to.

[0419] Step 606 is the same as step 514, and gNB-CU transmits a message to the source gNB-DU.

[0420] If the gNB-DU identification in step 605 is the source gNB-DU identification, gNB-CU transmits the corresponding TA information to the source gNB-DU.

[0421] Alternatively, the message may be a CU-DU TA INFORMATION TRANSFER message, or other messages. The message may contain one or more TA information. The TA information may belong to the same UE or different UEs.

[0422] The TA information includes at least one of the following information:

[0423] (1) a candidate cell identification, which the identification of candidate cell which detects the preamble. The candidate cell identification can be CGI or other identification.

[0424] (2) a value of Timing Advance (TA).

[0425] (3) a preamble index, that is, random access preamble index. It is the index of the preamble detected on the candidate cell.

[0426] (4) RA-RNTI. The value of RA-RNTI is determined by detecting the resource-related information of the preamble based on formula (1).

[0427] Step 607: The source gNB-DU transmits a message to the UE, and transmits the TA value of the UE in the candidate cell received in step 606 to the UE.

[0428] The message may contain TA information of one or more candidate cells.

[0429] Please refer to step 415 for details of the content of the TA information and the content and mode of the message, which will not be repeated here.

[0430] Steps 608-609 are the same as steps 416-417. Please refer to steps 416-417 for details, and they will not be repeated here.

[0431] The UE evaluates (or monitors) the execution conditions of the candidate cell according to the L1 measurement result. If one or more candidate cells meet the execution condition, the UE selects one of them as the target cell, performs conditional LTM, and performs cell switch. In conditional LTM, the target cell is selected by the UE from the candidate cells that meet the execution conditions.

[0432] (1) If the UE has a valid TA value in the target cell, the RACH-less conditional LTM will be performed.

[0433] (2) If the UE does not have a valid TA value in the target cell, the RACH-based conditional LTM will be performed. If the network configures dedicated RACH resources for the UE, the CFRA process will be performed, otherwise the CBRA process will be performed.

[0434] In the above method, the network configures the execution condition for conditional LTM handover, and when the execution condition is met, the UE actively performs LTM for cell handover without waiting for the network to send a handover command. Thus, that signal interaction between the UE and the network can be reduced, and the situation that the handover of the UE fails due to the change of the state of the radio link during the signaling interaction between the UE and the network can also be avoided, thereby improve the robustness of the handover. Moreover, before performing the conditional LTM, the UE performs uplink synchronization with the candidate cell (including the target cell) in advance to obtain (or acquire) the TA value of the candidate cell (including the target cell) in advance (it can also be called obtaining the TA value in advance). This process can also be called the process of obtaining (or acquiring) the TA in advance (Early TA Acquisition), or the process of obtaining the TA of the candidate cell in advance, or the process of the UE performing uplink in the candidate cell in advance. Through the process of uplink synchronization between UE and candidate cell in advance, it is avoided that UE needs to perform uplink synchronization with target cell during handover execution, thus reducing handover delay. Therefore, while improving the robustness of LTM switching, the invention reduces the handover delay, improves the handover performance and reduces the signaling overhead.

[0435] Embodiments 5, 6 and 7 respectively provide three methods of conditional LTM execution to realize that the target cell detects UE access. See Embodiments 5, 6 and 7 for details.

[0436] Embodiment 5: A Method of Conditional LTM Execution

[0437] Please refer to Fig. 7. Fig. 7 is an interactive schematic diagram of an execution method of conditional LTM according to various embodiments of the disclosure. The method illustrated in Fig. 7 may include one or more of steps S701 to S703:

[0438] Step 701: The UE transmits uplink data to a target gNB-DU (target cell).

[0439] If the UE has a valid TA value in the target cell, the RACH-less conditional LTM will be performed. If the network configures the dedicated uplink resource for the UE in the target cell, that is, configures a Configured Grant for the UE, then the UE uses the TA value to send uplink data to the target gNB-DU (target cell) on the configured grant. Then the uplink data may be an RRCReconfigurationComplete message or other uplink data. Among them, the uplink transmission beam used by the UE when transmitting uplink data is determined by measurement.

[0440] Step 702: The target gNB-DU (target cell) transmits a message to the UE. The target cell determines the downlink transmission beam according to the uplink transmission beam of the UE, and uses the downlink transmission beam to send messages to the UE. The message is transmitted through the PDCCH, which contains dynamic scheduling information and / or ACK feedback to the uplink data. At the same time, the target cell thinks that the UE has accessed the target cell through the conditional LTM, and transmits a message to gNB-CU, that is, step 703.

[0441] After receiving the message transmitted by the target cell, the UE considers that the conditional LTM has been successfully performed, that is, the UE has successfully accessed to the target cell.

[0442] Step 703: The target gNB-DU transmits a message to gNB-CU. When the target gNB-DU thinks that the conditional LTM is successfully performed, the message is used to indicate to gNB-CU that the UE has successfully accessed to the target cell.

[0443] Alternatively, the message may be an ACCESS SUCCESS message, or other messages. The message contains at least one of the following information:

[0444] (1) a cell identification, which indicates the identification of the target cell, and can be CGI or other cell identifications.

[0445] If a candidate cell meets the execution conditions, and the TA value of the target cell selected by the UE is valid, the UE can directly send uplink data (or messages) to the target cell and execute the condition LTM. When the target cell receives the uplink data (or message) of the UE and determines that the UE has switched to the target cell, it can send resource scheduling information to the UE for data transmission, which reduces data transmission interruption time while reducing the handover delay of UE.

[0446] Embodiment 6: A Method of Conditional LTM Execution

[0447] Please refer to Fig. 8. Fig. 8 is an interactive schematic diagram of another execution method of conditional LTM according to various embodiments of the disclosure. The method illustrated in Fig. 8 may include one or more of steps S801 to S804:

[0448] Step 801: UE transmits a message to a target gNB-DU (target cell).

[0449] If the UE has a valid TA value in the target cell, the RACH-less conditional LTM will be performed. If the network does not configure the dedicated uplink resource for the UE in the target cell, but configures the PUCCH resources for the UE, then the UE uses the TA value to send a Scheduling Request (SR) on the PUCCH resources to the target gNB-DU (target cell), requesting the target cell to provide the uplink resource for the UE for uplink transmission. The uplink transmission beam used by the UE when transmitting the message for uplink transmission is determined through measurement.

[0450] Step 802: The target gNB-DU (target cell) transmits a message to the UE.

[0451] The target cell determines the downlink transmission beam according to the uplink transmission beam of the UE, and uses the downlink transmission beam to send messages to the UE. The message is transmitted through the PDCCH and contains dynamic scheduling information. When the UE receives the message, it means that the uplink transmission in step 801 is successful, and optionally, it can be considered that the conditional LTM is successfully performed.

[0452] In step 803, the UE transmits a message to the target gNB-DU (target cell).

[0453] The UE transmits a message to the target cell using the resource provided in the dynamic scheduling information received in step 802. Optionally, the message may be an RRCReconfigurationComplete message, or other messages.

[0454] Step 804: The target gNB-DU transmits a message to gNB-CU. When the target gNB-DU thinks that the conditional LTM is successfully performed, the message is used to indicate to gNB-CU that the UE has successfully accessed to the target cell.

[0455] Alternatively, the message may be an ACCESS SUCCESS message, or other messages. The message contains at least one of the following information:

[0456] (1) a cell identification, which indicates the identification of the target cell, and can be CGI or other cell identifications.

[0457] Optionally, steps 802 and 804 are not strictly ordered.

[0458] If a candidate cell meets the execution conditions and the TA value of the target cell selected by the UE is valid, the UE can directly send a message to the target cell and execute the conditional LTM. When the target cell receives the message transmitted by the UE and determines that the UE has switched to the target cell, it can send resource scheduling information to the UE for data transmission, which reduces data transmission interruption time while reducing the handover delay of UE.

[0459] Embodiment 7: A Method of Conditional LTM Execution

[0460] Please refer to Fig. 9. Fig. 9 is an interactive schematic diagram of a further execution method of conditional LTM according to various embodiments of the disclosure. The method illustrated in Fig. 9 may include one or more of steps S901 to S907:

[0461] In Embodiment 7, the UE transmits the selected target cell information to the target cell (target gNB-DU) through the source cell (source gNB-DU). The specific process is illustrated in Figure 9. Among them:

[0462] Step 901: UE transmits a message to a source gNB-DU (source cell), indicating that the UE has selected the target cell to be ready to execute LTM and the selected target cell information.

[0463] Optionally, the target cell information can be transmitted through MAC CE. The MAC CE may be called LTM CELL SWITCH MAC CE. The MAC CE contains at least one of the following information:

[0464] (1) a target cell identification, which may be an LTM configuration identification corresponding to the target cell, an LTM candidate identification corresponding to the target cell, or other identifications.

[0465] (2) TCI status identification, which is determined by the UE according to the measurement result.

[0466] Step 902: The source gNB-DU transmits a message to gNB-CU, indicating to gNB-CU that the UE has selected the target cell, the conditional LTM will be performed.

[0467] Optionally, the message may be a DU-CU CELL SWITCH NOTIFICATION message, or other messages. The message contains at least one of the following information:

[0468] (1) a target cell identification, which indicates the identification of the target cell selected by the UE. The cell identification may be CGI, or other identifications.

[0469] (2) TCI status identification, which is determined by the UE according to the measurement result.

[0470] Step 903: gNB-CU transmits a message to the target gNB-DU, indicating to the target gNB-DU that the UE has selected the target cell, the conditional LTM will be performed.

[0471] Optionally, the message may be a CU-DU CELL SWITCH NOTIFICATION message, or other messages. The message contains at least one of the following information:

[0472] (1) a target cell identification, which indicates the identification of the target cell selected by the UE. The cell identification may be CGI, or the LTM configuration identification corresponding to the target cell, or other identifications.

[0473] (2) TCI status identification, which is determined by the UE according to the measurement result.

[0474] If the UE does not have a valid TA value in the target cell, the UE performs RACH-based conditional LTM.

[0475] If the UE has a valid TA value in the target cell, the RACH-less conditional LTM will be performed.

[0476] - If the network configures the dedicated uplink resource for the UE in the target cell, that is, Configured Grant for the UE, then the UE uses the TA value to send uplink data to the target gNB-DU (target cell) on the Configured Grant. That is, step 905 is directly executed.

[0477] - If the network does not configure the dedicated uplink resource for the UE in the target cell, the UE monitors the PDCCH in the target cell. That is, steps 904 and 905 are performed.

[0478] Step 904: The target gNB-DU (target cell) transmits a message to the UE.

[0479] The target cell determines the downlink transmission beam according to the TCI status identification received in step 903, and uses the downlink transmission beam to send a message to the UE. The message is transmitted through the PDCCH, which contains dynamic scheduling information (or resource scheduling information) and provides dynamic resource information. The UE receives (monitors) the dynamic scheduling information received by the PDCCH in the target cell, and performs uplink transmission on the resources contained in the scheduling information.

[0480] In step 905, the UE transmits a message to the target gNB-DU (target cell). The UE uses a Configured Grant or a dynamically scheduled resource to send the message, that is, performs uplink transmission.

[0481] Optionally, the message may be an RRCReconfigurationComplete message, or other messages.

[0482] Step 906: The target gNB-DU (target cell) transmits a message to the UE. The message is transmitted through the PDCCH, which contains dynamic scheduling information (or resource scheduling information) and provides the dynamic resource for the UE to transmit data. When the UE receives the message, it thinks that the conditional LTM has been successfully performed, that is, the UE has successfully accessed the target cell.

[0483] Step 907: The target gNB-DU transmits a message to gNB-CU. When the target gNB-DU thinks that the conditional LTM is successfully performed, the message is used to indicate to gNB-CU that the UE has successfully accessed to the target cell.

[0484] Alternatively, the message may be an ACCESS SUCCESS message, or other messages. The message contains at least one of the following information:

[0485] (1) a cell identification, which indicates the identification of the target cell, and can be CGI or other cell identifications.

[0486] Optionally, steps 906 and 907 are not strictly ordered.

[0487] If a candidate cell meets the execution conditions and the TA value of the target cell selected by the UE is valid, the UE performs the condition LTM and receives the scheduling information (resource information) transmitted by the target cell. When the target cell receives the uplink transmission transmitted by the UE on the resource and determines that the UE has hardcovered to the target cell, it can continue to send resource scheduling information to the UE for data transmission, which reduces data transmission interruption time while reducing the handover delay of UE.

[0488] In addition, it can be understood that the contents contained in each message in the above-mentioned embodiment are only examples of this disclosure, and the contents contained in various similar or identical messages can be replaced with each other, or named with different names, or some items can be added or deleted according to the situation, and for the sake of brevity, the meanings of similar content items can be mutually explained according to the context without being repeated, and the modified and explained embodiments still belong to the scope of protection of the present invention.

[0489] Fig. 10 is a block diagram illustrating the structure of a user equipment 1000 according to an embodiment of the disclosure.

[0490] Referring to Fig. 10, a user equipment 1000 includes a transceiver 1001 and a controller 1002. The transceiver 1001 is configured to transmit and receive signals to and from the outside. The controller 1002 is configured to perform the above-described method performed by the user equipment. The user equipment 1000 may be implemented in the form of hardware, software, or a combination of hardware and software, so that it can perform the method performed by the user equipment described in the disclosure.

[0491] Fig. 11 is a block diagram illustrating the structure of a first node 1100 according to an embodiment of the disclosure.

[0492] Referring to Fig. 11, a first node 1100 includes a transceiver 1101 and a controller 1102. The transceiver 1101 is configured to transmit and receive signals to and from the outside. The controller 1102 is configured to perform a method performed by a first node. The first node 1100 may be implemented in the form of hardware, software, or a combination of hardware and software, so that it can perform the method described in the disclosure and performed by the first node.

[0493] Fig. 12 is a block diagram illustrating the structure of a second node 1200 according to an embodiment of the disclosure.

[0494] Referring to Fig. 12, the second node 1200 includes a transceiver 1201 and a controller 1202. The transceiver 1201 is configured to transmit and receive signals to and from the outside. The controller 1202 is configured to perform a method performed by the second node. The second node 1200 may be implemented in the form of hardware, software, or a combination of hardware and software, so that it can perform the method performed by the second node described in the disclosure.

[0495] Fig. 13 is a block diagram illustrating the structure of a third node 1300 according to an embodiment of the disclosure.

[0496] Referring to Fig. 13, the third node 1300 includes a transceiver 1301 and a controller 1302. The transceiver 1301 is configured to transmit and receive signals to and from the outside. The controller 1302 is configured to perform a method performed by a third node. The third node 1300 may be implemented in the form of hardware, software, or a combination of hardware and software, so that it can perform the method performed by the third node described in the disclosure.

[0497] Fig. 14 is a block diagram illustrating the structure of a user equipment according to an embodiment of the disclosure.

[0498] As shown in FIG. 14, the UE according to an embodiment may include a transceiver 1410, a memory 1420, and a processor 1430. The transceiver 1410, the memory 1420, and the processor 1430 of the UE may operate according to a communication method of the UE described above. However, the components of the UE are not limited thereto. For example, the UE may include more or fewer components than those described above. In addition, the processor 1430, the transceiver 1410, and the memory 1420 may be implemented as a single chip. Also, the processor 1430 may include at least one processor. Furthermore, the UE of FIG. 14 corresponds to a UE according to embodiments of the disclosure.

[0499] The transceiver 1410 collectively refers to a UE receiver and a UE transmitter, and may transmit / receive a signal to / from a base station or a network entity. The signal transmitted or received to or from the base station or a network entity may include control information and data. The transceiver 1410 may include a RF transmitter for up-converting and amplifying a frequency of a transmitted signal, and a RF receiver for amplifying low-noise and down-converting a frequency of a received signal. However, this is only an example of the transceiver 1410 and components of the transceiver 1410 are not limited to the RF transmitter and the RF receiver.

[0500] Also, the transceiver 1410 may receive and output, to the processor 1430, a signal through a wireless channel, and transmit a signal output from the processor 1430 through the wireless channel.

[0501] The memory 1420 may store a program and data required for operations of the UE. Also, the memory 1420 may store control information or data included in a signal obtained by the UE. The memory 1420 may be a storage medium, such as read-only memory (ROM), random access memory (RAM), a hard disk, a CD-ROM, and a DVD, or a combination of storage media.

[0502] The processor 1430 may control a series of processes such that the UE operates as described above. For example, the transceiver 1410 may receive a data signal including a control signal transmitted by the base station or the network entity, and the processor 1430 may determine a result of receiving the control signal and the data signal transmitted by the base station or the network entity.

[0503] Fig. 15 is a block diagram illustrating the structure of a base station according to an embodiment of the disclosure.

[0504] As shown in FIG. 15, the base station according to an embodiment may include a transceiver 1510, a memory 1520, and a processor 1530. The transceiver 1510, the memory 1520, and the processor 1530 of the base station may operate according to a communication method of the base station described above. However, the components of the base station are not limited thereto. For example, the base station may include more or fewer components than those described above. In addition, the processor 1530, the transceiver 1510, and the memory 1520 may be implemented as a single chip. Also, the processor 1530 may include at least one processor. Furthermore, the base station of FIG. 15 corresponds to a base station according to embodiments of the disclosure.

[0505] The transceiver 1510 collectively refers to a base station receiver and a base station transmitter, and may transmit / receive a signal to / from a terminal (UE) or a network entity. The signal transmitted or received to or from the terminal or a network entity may include control information and data. The transceiver 1510 may include a RF transmitter for up-converting and amplifying a frequency of a transmitted signal, and a RF receiver for amplifying low-noise and down-converting a frequency of a received signal. However, this is only an example of the transceiver 1510 and components of the transceiver 1510 are not limited to the RF transmitter and the RF receiver.

[0506] Also, the transceiver 1510 may receive and output, to the processor 1530, a signal through a wireless channel, and transmit a signal output from the processor 1530 through the wireless channel.

[0507] The memory 1520 may store a program and data required for operations of the base station. Also, the memory 1520 may store control information or data included in a signal obtained by the base station. The memory 1520 may be a storage medium, such as read-only memory (ROM), random access memory (RAM), a hard disk, a CD-ROM, and a DVD, or a combination of storage media.

[0508] The processor 1530 may control a series of processes such that the base station operates as described above. For example, the transceiver 1510 may receive a data signal including a control signal transmitted by the terminal, and the processor 1530 may determine a result of receiving the control signal and the data signal transmitted by the terminal.

[0509] At least one embodiment of the disclosure also provides a non-transitory computer-readable recording medium, on which a program for executing the above method when a computer runs has been stored.

[0510] Various embodiments of the disclosure can be realized as computer-readable codes embodied on a computer-readable recording medium from a specific perspective. A computer-readable recording medium is any data storage device that can store data readable by a computer system. Examples of computer-readable recording media may include read-only memory (ROM), random access memory (RAM), compact disk read-only memory (CD-ROM), magnetic tape, floppy disk, optical data storage device, carrier wave (for example, data transmission via the Internet), and the like. Computer-readable recording media can be distributed through computer systems connected via a network, and thus computer-readable codes can be stored and executed in a distributed manner. Moreover, functional programs, codes and code segments for implementing various embodiments of the disclosure can be easily interpreted by those skilled in the art to which the embodiments of the disclosure are applied.

[0511] It will be understood that the embodiments of the disclosure can be implemented in the form of hardware, software, or a combination of hardware and software. The software can be stored as program instructions or computer-readable code executable on a controller on a non-transient computer-readable medium. Examples of non-transient computer-readable recording media include magnetic storage media (e.g., ROM, floppy disk, hard disk, etc.) and optical recording media (e.g., CD-ROM, digital video disk (DVD), etc.). Non-transient computer-readable recording media can also be distributed on network-coupled computer systems, so that computer-readable codes are stored and executed in a distributed manner. The medium can be read by a computer, stored in a memory, and executed by a controller. Various embodiments may be implemented by a computer or a portable terminal including a controller and a memory, and the memory may be an example of a non-transitory computer-readable recording medium suitable for storing program (s) having instructions for implementing embodiments of the disclosure. The disclosure can be realized by a program having codes for concretely implementing the apparatus and method described in the claims, which is stored in a machine (or computer) readable storage medium. The program may be electronically carried on any medium, such as a communication signal transmitted via a wired or wireless connection, and this disclosure suitably includes its equivalents.

[0512] What has been described above is only the specific implementation of this disclosure, but the protection scope of this disclosure is not limited to this. Any person familiar with this technical field can make various changes or substitutions within the technical scope disclosed in this disclosure, and these changes or substitutions should be included in the protection scope of this disclosure. Therefore, the scope of protection of this disclosure should be based on the scope of protection of the claims.

Claims

1.A method performed by user equipment (UE) in a wireless communication system, the method comprising:transmitting a preamble to a second node where a candidate cell is located; andreceiving timing advance (TA) information of the candidate cell from a first node, wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM).2.The method of claim 1, wherein the transmitting the preamble to the second node comprises:selecting, by the UE, a first random access (RA) resource for performing an uplink synchronization process in advance from among RA resources for performing the uplink synchronization process allocated to the first node by the candidate cell, to transmit a first preamble, wherein the first preamble is selected by UE;wherein the RA resources for performing the uplink synchronization process in advance allocated to the first node by the candidate cell are transmitted to the UE by the candidate cell through a third node and the first node.3.The method of claim 1, wherein the receiving the TA comprises:monitoring, by the UE, a physical downlink control channel (PDCCH) using a first radio network temporary identification (RNTI), wherein the PDCCH includes resources for transmitting a media access control protocol data unit (MAC PDU) including the TA information of the candidate cell, wherein the TA information includes one or more TA information for one or more UEs,wherein the first RNTI is an RNTI allocated by the first node and related to the MAC PDU including the TA information of the candidate cell.4.The method of claim 1, wherein the transmitting the preamble to the second node comprises:transmitting, by the UE, a second preamble on a second RA resource allocated to the UE by the candidate cell for performing the uplink synchronization process in advance, wherein the second preamble is a preamble allocated to the UE by the candidate cell.5.The method of claim 1, further comprising:transmitting, by the UE, a first message to the first node, wherein the first message includes a candidate cell selected by the UE and / or a measurement result of the candidate cell; andreceiving, by the UE, a second message transmitted by the first node, wherein the second message instructs the UE to perform an uplink synchronization process with the candidate cell in advance;wherein the second message includes at least one of: a candidate cell identification, a fourth RA resource for performing the uplink synchronization process in advance, and a fourth preamble;wherein the fourth RA resource and the fourth preamble are selected by the first node based on the RA resources allocated to the first node by the candidate cell for performing the uplink synchronization process in advance;wherein the RA resources allocated to the first node by the candidate cell for performing the uplink synchronization process in advance are transmitted to the first node by the candidate cell through a third node.6.The method of claim 1, wherein the monitoring the PDCCH transmitted by the first node comprises:monitoring, by the UE, the PDCCH using a cell radio network temporary identification (C-RNTI) allocated to the UE by the first node, wherein the PDCCH includes resources for transmitting a MAC PDU including the TA information of the candidate cell, wherein the MAC PDU includes one or more media access control control element (MAC CE), and the TA information is included in the MAC CE; andstarting or restarting a timer when the UE receives a TA value of the candidate cell;wherein the TA value is valid before the timer expires, andwherein the MAC CE including the TA information is identified by a logical channel identification.7.The method of claim 1, wherein the TA information comprises at least one of:candidate configuration identification;a TA value, wherein the TA value is determined by the candidate cell through the detected preamble;a value of a random access radio network temporary identification (RA-RNTI), wherein the value of the RA-RNTI is determine by the candidate cell according to resources where the preamble is detected;information of RA resources where the preamble is detected.8.The method of claim 1, wherein that the TA information is used for performing the conditional LTM comprises:transmitting, by the UE, a scheduling request to the second node on a first resource or uplink data to the second node on a second resource, if a TA value of the target cell is valid; wherein the first resource is a resource allocated to the UE by the target cell for transmitting the scheduling request, and the second resource is a resource allocated to the UE by the target cell for transmitting the uplink data;considering, by the UE, that the conditional LTM is successfully performed, if the scheduling request or the uplink data is successfully received by the second node.9.The method of claim 1, wherein that the TA information is used for performing the conditional LTM comprises:transmitting, by the UE, a conditional LTM indication to the first node, if a TA value of the target cell is valid, wherein the conditional LTM indication is used to indicate that the UE will perform the conditional LTM;receiving resource scheduling information transmitted by the target cell; andperforming uplink transmission on the resource;wherein the resource scheduling information is transmitted through the PDCCH.10.The method of claim 1, further comprising:evaluating, by the UE, an LTM execution condition of the candidate cell according to a measurement result of Layer 1,selecting one candidate cell as a target cell and performing conditional L1 / L2 Triggered Mobility (LTM), when there are candidate cells meeting the LTM execution condition.11.A method performed by a first node in a wireless communication system, the method comprising:receiving timing advance (TA) information of a candidate cell from a third node, wherein the TA information of the candidate cell is transmitted to the third node by a second node after receiving a preamble transmitted by a user equipment (UE);transmitting the TA information of the candidate cell to the UE, wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM); andtransmitting, to the UE, a physical downlink control channel (PDCCH), wherein the PDCCH includes resources for transmitting a media access control protocol data unit (MAC PDU) including the TA information of the candidate cell.12.The method of claim 11, wherein the MAC PDU includes one or more media access control control element (MAC CE), and the TA information is included in the MAC CE,wherein the PDCCH is scrambled by a first radio network temporary identification (RNTI) or by a cell radio network temporary identification (C-RNTI) of the UE, andwherein the first RNTI is allocated by a first node to the UE in the first node for receiving the MAC PDU including the TA information.13.A method performed by a second node in a wireless communication system, the method comprising:receiving a preamble transmitted by user equipment (UE); andtransmitting timing advance (TA) information of a candidate cell to a third node, wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM).14.A user equipment in a wireless communication system, comprising:a transceiver; anda controller coupled with the transceiver and configured:transmit a preamble to a second node where a candidate cell is located; andreceive timing advance (TA) information of the candidate cell from a first node, wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM).15.A first node in a wireless communication system, comprising:a transceiver; anda controller coupled with the transceiver and configured:receive timing advance (TA) information of a candidate cell from a third node, wherein the TA information of the candidate cell is transmitted to the third node by a second node after receiving a preamble transmitted by a user equipment (UE);transmit the TA information of the candidate cell to the UE, wherein the TA information is used for performing conditional L1 / L2 Triggered Mobility (LTM); andtransmitting, to the UE, a physical downlink control channel (PDCCH), wherein the PDCCH includes resources for transmitting a media access control protocol data unit (MAC PDU) including the TA information of the candidate cell.

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