First or second or third node and method performed by same

Abstract

The present disclosure provides a method executed by a first node in a communication system, the method comprising: receiving a first message from a second node, the first message comprising information related to a first physical random access channel (PRACH) resource, the information related to the first PRACH resource comprising a first cell identifier or a first node identifier corresponding to the PRACH resource; and sending a second message to a third node, the second message comprising information related to a second PRACH resource, and the PRACH resource being used for obtaining a timing advance (TA) value in advance; wherein the third node is a node where a cell indicated by the first cell identifier is located or a node indicated by the first node identifier.

Description

Technical Field

[0001] The present disclosure relates to the field of communications, and more particularly, to a first or second or third node and a method executed thereby. Background Art

[0002] In order to meet the increased demand for wireless data communication services since the deployment of 4G communication systems, efforts have been made to develop improved 5G or quasi-5G communication systems. Therefore, 5G or quasi-5G communication systems are also referred to as "super 4G networks" or "post-LTE systems."

[0003] Wireless communication is one of the most successful innovations in modern history. The number of subscribers to wireless communication services recently exceeded 5 billion and continues to grow rapidly. The demand for wireless data services is growing rapidly due to the increasing popularity of smartphones and other mobile data devices (e.g., tablets, laptops, netbooks, e-book readers, and machine-type devices) among consumers and enterprises. In order to meet the high growth of mobile data services and support new applications and deployments, it is critical to improve the efficiency and coverage of the wireless interface. Summary of the invention

[0004] According to one aspect of the present disclosure, a method performed by a first node in a communication system is provided, the method comprising: receiving a first message from a second node, wherein the first message includes information related to a first physical random access channel (PRACH) resource, and the information related to the first PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource; and sending a second message to a third node, wherein the second message includes information related to a second PRACH resource, and the PRACH resource is used to obtain a timing advance (TA) value in advance; wherein the third node is a node where the cell indicated by the first cell identifier is located or a node indicated by the first node identifier.

[0005] According to the method provided by the present disclosure and executed by the first node in the communication system, the information related to the first or second PRACH resource also includes at least one of the following: a second cell identifier, used to indicate the cell to which the PRACH resource is allocated; a second node identifier, used to indicate the node where the cell to which the PRACH resource is allocated is located; a first group identifier, used to indicate the group to which the cell to which the PRACH resource is allocated belongs, wherein for cells in the same group, the TA values ​​of the user equipment UE are the same; first PRACH resource information, wherein the first PRACH resource information includes at least one of the following: time domain and frequency domain information of the PRACH resource, a PRACH configuration index, frequency domain parameters of the PRACH opportunity, and the total number of random access codes.

[0006] According to the method provided by the present disclosure and executed by the first node in the communication system, the method further includes: receiving a third message from the second node, wherein the third message includes first TA information, which is used to indicate the TA information detected on the PRACH resource included in the information related to the first PRACH resource; wherein the third message also includes at least one of the following: a third cell identifier, which is used to indicate the cell corresponding to the first TA information; a third node identifier, which is used to indicate the node where the cell corresponding to the first TA information is located or the node corresponding to the first TA information; wherein the first TA information includes at least one of the following: a fourth cell identifier, which is used to indicate the cell where the TA value is detected; second PRACH resource information, which is used to indicate the PRACH resource information where the TA value is detected; a first TA value, and the first TA value is the TA value detected on the second PRACH resource.

[0007] According to the method provided by the present disclosure and executed by the first node in the communication system, the method further includes: sending a fourth message to the third node, wherein the third node is determined based on the third cell identifier or the third node identifier, and the fourth message includes TA information corresponding to the cell of the third node or the third node.

[0008] According to the method provided by the present disclosure and executed by the first node in the communication system, the fourth message includes at least one of the following: a fourth cell identifier, used to indicate the cell in which the TA value is detected; second PRACH resource information, used to indicate PRACH resource information in which the TA value is detected; a first TA value, wherein the first TA value is a TA value detected on the second PRACH resource.

[0009] According to the method performed by the first node in the communication system provided by the present disclosure, if the information related to the second PRACH resource does not include the first cell identifier corresponding to the second PRACH resource, the second PRACH resource is allocated to the node indicated by the first node identifier.

[0010] According to the method performed by the first node in the communication system provided by the present disclosure, the first message includes a first PRACH resource information list.

[0011] According to the method provided by the present disclosure and executed by the first node in the communication system, the method further includes: receiving a fifth message from the third node, wherein the fifth message includes information sent to the target cell, wherein the information sent to the target cell includes at least one of the following: a fifth cell identifier, used to indicate the candidate cell of the UE; a fourth node identifier, used to indicate the node where the candidate cell of the UE is located; a second group identifier, used to indicate the group to which the candidate cell of the UE belongs; a second TA value, wherein the second TA value is the TA value of the UE in the candidate cell; a time alignment timer TAT value, used to indicate the TAT running time length corresponding to the TA value of the candidate cell; and a time alignment timer TAT length, used to indicate the length of the TAT timer.

[0012] According to one aspect of the present disclosure, a method performed by a first node in a communication system is provided, the method comprising: receiving a sixth message from a second node, or receiving a seventh message from a fourth node, wherein the sixth message or the seventh message includes information related to a third physical random access channel (PRACH) resource; and sending an eighth message to a third node based on the sixth message or the seventh message, wherein the eighth message includes information related to a fourth PRACH resource, and the information related to the fourth PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource, wherein the PRACH resource is used to obtain a timing advance (TA) value in advance; wherein the third node is a node where the cell indicated by the first cell identifier is located or a node indicated by the first node identifier.

[0013] According to the method performed by the first node in the communication system provided by the present disclosure, the information related to the third or fourth PRACH resource includes at least one of the following: a sixth cell identifier, used to indicate the cell to which the PRACH resource is allocated; a fifth node identifier, used to indicate the node where the cell to which the PRACH resource is allocated is located; a third group identifier, used to indicate the group to which the cell to which the PRACH resource is allocated belongs, wherein for cells in the same group, the timing advance TA values ​​of the user equipment UE are the same; third PRACH resource information; wherein the third PRACH resource information includes at least one of the following: time domain and frequency domain information of the PRACH resource, a PRACH configuration index, frequency domain parameters of the PRACH opportunity, and the total number of random access codes.

[0014] According to the method provided by the present disclosure and executed by the first node in the communication system, the method further includes: receiving a ninth message from the second node, wherein the ninth message includes at least one of the following: a seventh cell identifier, used to indicate the cell in which the TA value is detected; fourth PRACH resource information, used to indicate PRACH resource information in which the TA value is detected; a third TA value, the third TA value being the TA value detected on the fourth PRACH resource.

[0015] According to the method provided by the present disclosure and executed by the first node in the communication system, the method further includes: sending a fourth message to the third node, wherein the third node is determined based on the fourth cell identifier and / or the fourth PRACH resource information, and the fourth message includes TA information corresponding to the third node.

[0016] According to the method provided by the present disclosure, the first node is executed by a first node in a communication system, wherein the first node includes a centralized unit of a base station, the second node includes a distributed unit of a base station where a candidate cell is located, the third node includes a distributed unit of a base station where a source cell is located, and the fourth node includes an operation management and maintenance OAM node.

[0017] According to one aspect of the present disclosure, a method performed by a second node in a communication system is provided, the method comprising: sending a first message to a first node, wherein the first message includes information related to a first physical random access channel (PRACH) resource, and the information related to the first PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource; performing detection on the PRACH resource to determine a first TA value; and sending a third message to the first node, the third message including first TA information, and the first TA information including the first TA value.

[0018] According to the method provided by the present disclosure and executed by the second node in the communication system, the information related to the first PRACH resource includes at least one of the following: a second cell identifier, used to indicate the cell to which the PRACH resource is allocated; a second node identifier, used to indicate the node where the cell to which the PRACH resource is allocated is located; a first group identifier, used to indicate the group to which the cell to which the PRACH resource is allocated belongs, wherein for cells in the same group, the timing advance TA value of the UE is the same; first PRACH resource information; wherein the first PRACH resource information includes at least one of the following: time domain and frequency domain information of the PRACH resource, a PRACH configuration index, frequency domain parameters of the PRACH opportunity, and the total number of random access codes.

[0019] According to the method provided by the present disclosure and executed by the second node in the communication system, the third message also includes at least one of the following: a third cell identifier, used to indicate the cell corresponding to the first TA information; a third node identifier, used to indicate the node where the cell corresponding to the first TA information is located or the node corresponding to the TA information; wherein the first TA information included in the third message also includes at least one of the following: a fourth cell identifier, used to indicate the cell where the TA value is detected; second PRACH resource information, used to indicate the PRACH resource information where the TA value is detected.

[0020] According to the method provided by the present disclosure and performed by the second node in the communication system, the first node includes a centralized unit of the base station, the second node includes a distributed unit of the base station where the candidate cell is located, the third node includes a distributed unit of the base station where the source cell is located, and the fourth node includes an operation management and maintenance OAM node.

[0021] According to one aspect of the present disclosure, a method performed by a third node in a communication system is provided, the method comprising: receiving a second message sent by a first node; or receiving a tenth message sent by a fourth node, wherein the second message and the tenth message include information related to the second physical random access channel (PRACH) resource, and the information related to the second PRACH resource includes a PRACH resource used to obtain a timing advance (TA) value in advance; a cell in the third node allocates the PRACH resource to a user equipment (UE) for performing a random access process for obtaining a timing advance (TA) value in advance; wherein the second message is sent by the first node in response to a received first message, and the first message includes information related to the first PRACH resource, and the information related to the first PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource.

[0022] According to the method provided by the present disclosure and executed by the third node in the communication system, the method further includes: receiving a fourth message sent by the first node, wherein the fourth message includes the cell of the third node or TA information corresponding to the third node, wherein the fourth message includes at least one of the following: a fourth cell identifier, used to indicate the cell in which the TA value is detected; second PRACH resource information, used to indicate PRACH resource information in which the TA value is detected; a first TA value, wherein the first TA value is the TA value detected on the second PRACH resource.

[0023] According to the method provided by the present disclosure and performed by the third node in the communication system, the first node includes a centralized unit of the base station, the second node includes a distributed unit of the base station where the candidate cell is located, the third node includes a distributed unit of the base station where the source cell is located, and the fourth node includes an operation management and maintenance OAM node.

[0024] According to another aspect of the present disclosure, a first node is provided, comprising: a transceiver configured to send and receive signals to and from the outside; and a controller configured to control the transceiver to execute the method executed by the first node.

[0025] According to another aspect of the present disclosure, a second node is provided, wherein the first node includes: a transceiver configured to send and receive signals to and from the outside; and a controller configured to control the transceiver to execute the method executed by the second node.

[0026] According to another aspect of the present disclosure, a third node is provided, wherein the first node includes: a transceiver configured to send and receive signals to and from the outside; and a controller configured to control the transceiver to execute the method executed by the third node.

[0027] According to another aspect of the present disclosure, a non-transitory computer-readable recording medium is provided, on which a program for executing any of the above methods when executed by a computer is stored. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is an exemplary system architecture for System Architecture Evolution (SAE).

[0029] Figure 2 is an exemplary system architecture according to various embodiments of the present disclosure.

[0030] Figure 3a is a diagram of a process in which a user equipment (UE) obtains a target cell TA in a normal random access process when a handover occurs according to various embodiments of the present disclosure;

[0031] Figure 3b is a diagram of a process for implementing uplink synchronization between a UE and a source cell according to various embodiments of the present disclosure;

[0032] Figure 3c is a diagram of a process in which a UE obtains a TA value of a target cell during a random access process of early TA acquisition of timing advance according to various embodiments of the present disclosure;

[0033] Figure 4 It is an interactive diagram of a PRACH resource allocation method according to various embodiments of the present disclosure.

[0034] Figure 5 is an interaction diagram of another PRACH resource allocation method according to various embodiments of the present disclosure.

[0035] Figure 6 is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0036] Figure 7 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0037] Figure 8 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0038] Fig. 9 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0039] Fig.10 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0040] Fig.11 is a block diagram of a first node according to various embodiments of the present disclosure.

[0041] Fig.12 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0042] Fig.13 It is an interaction diagram of a method for providing candidate cell grouping identifiers according to the present disclosure. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0044] Before carrying out the description of the following specific embodiments, it may be advantageous to elaborate on the definitions of certain words and phrases used throughout this patent document.The term "coupling" and its derivatives refer to any direct or indirect communication between two or more elements, regardless of whether these elements are in physical contact with each other.The terms "send", "receive" and "communication" and their derivatives cover direct and indirect communication.The terms "include" and "comprise" and their derivatives mean including but not limited to.The term "or" is inclusive, meaning and / or.The phrase "associated with..." and its derivatives mean including, included in, connected to, interconnected with, included in, connected to or connected with, coupled to or coupled with, can communicate with, collaborate with, interweave, juxtapose, approach, bind to or bind with, have, have... attributes, have... relationships or have relationships with, etc.The term "controller" means any device, system or part thereof that controls at least one operation.Such a controller can be implemented in hardware, or implemented in a combination of hardware and software and / or firmware.The functions associated with any particular controller can be centralized or distributed locally or remotely. The phrase "at least one of" when used with a list of items means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, "at least one of A, B, and C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. For example, "at least one of A, B, or C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.

[0045] In addition, the various functions described below can be implemented or supported by one or more computer programs, each of which is formed by a computer-readable program code and embodied in a computer-readable medium. The terms "application" and "program" refer to one or more computer programs, software components, instruction sets, processes, functions, objects, classes, instances, related data or parts thereof suitable for implementation in a suitable computer-readable program code. The phrase "computer-readable program code" includes any type of computer code, including source code, object code and executable code. The phrase "computer-readable medium" includes any type of medium that can be accessed by a computer, such as a read-only memory (ROM), a random access memory (RAM), a hard drive, a compact disc (CD), a digital video disc (DVD) or any other type of memory. "Non-transitory" computer-readable media excludes wired, wireless, optical or other communication links that transmit temporary electrical signals or other signals. Non-transitory computer-readable media include media that can permanently store data and media that can store and rewrite data later, such as rewritable optical discs or erasable memory devices.

[0046] The terms used to describe the embodiments of the present application are not intended to limit and / or define the scope of the present application. For example, unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be the common meanings understood by people with ordinary skills in the field to which the present application belongs.

[0047] It should be understood that the words "first", "second" and the like used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Unless the context clearly indicates otherwise, the singular forms "a", "an" or "the" and the like do not indicate quantity limitation, but indicate the presence of at least one.

[0048] As used herein, any reference to "one example" or "example", "one embodiment" or "embodiment" means that a particular element, feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment. The phrases "in one embodiment" or "in an example" appearing in different places in the specification do not necessarily all refer to the same embodiment.

[0049] As used herein, "a portion" of something means "at least some" of that thing, and thus may mean less than all of that thing or all of that thing. Thus, "a portion" of a thing includes the entire thing as a special case, i.e., the entire thing is an example of a portion of a thing.

[0050] It will be further understood that the terms "include" or "comprises" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connected" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right", etc. are only used to indicate relative position relationships. When the absolute position of the object being described changes, the relative position relationship may also change accordingly.

[0051] The various embodiments discussed below for describing the principles of the present disclosure in this patent document are intended to be illustrative only and should not be interpreted in any way as limiting the scope of the present disclosure. Those skilled in the art will appreciate that the principles of the present disclosure can be implemented in any appropriately arranged wireless communication system. For example, although the following detailed description of the embodiments of the present disclosure will be directed to LTE and 5G communication systems, those skilled in the art will appreciate that the main points of the present disclosure can also be applied to other communication systems with similar technical backgrounds and channel formats with slight modifications without substantially departing from the scope of the present disclosure. The technical solutions of the embodiments of the present application can be applied to various communication systems, for example, the communication system may include a global system for mobile communications (GSM) system, a code division multiple access (CDMA) system, a wideband code division multiple access (WCDMA) system, a general packet radio service (GPRS), a long term evolution (LTE) system, a LTE frequency division duplex (FDD) system, a LTE time division duplex (TDD), a universal mobile telecommunication system (UMTS), a world-wide interoperability for microwave access (WiMAX) communication system, a fifth generation (5G) system or a new radio (NR), etc. In addition, the technical solutions of the embodiments of the present application can be applied to future-oriented communication technologies. In addition, the technical solutions of the embodiments of the present application can be applied to future-oriented communication technologies.

[0052] The following description with reference to the accompanying drawings is provided to facilitate a comprehensive understanding of the various embodiments of the present disclosure as defined by the claims and their equivalents. This description includes various specific details to facilitate understanding but should be considered as exemplary only. Therefore, one of ordinary skill in the art will recognize that various changes and modifications can be made to the various embodiments described herein without departing from the scope and spirit of the present disclosure. In addition, for the sake of clarity and conciseness, descriptions of well-known functions and structures may be omitted.

[0053] The terms and expressions used in the following specification and claims are not limited to their dictionary meanings, but are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Therefore, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purposes only and not for the purpose of limiting the present disclosure as defined in the appended claims and their equivalents.

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

[0055] The term "include" or "may include" refers to the presence of the corresponding disclosed functions, operations or components that can be used in various embodiments of the present disclosure, rather than limiting the presence of one or more additional functions, operations or features. In addition, the term "include" or "have" may be interpreted as indicating certain characteristics, numbers, steps, operations, constituent elements, components or combinations thereof, but should not be interpreted as excluding the possibility of the presence 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 present disclosure includes any of the listed terms and 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 (including technical terms or scientific terms) used in the present disclosure have the same meanings as understood by those skilled in the art described in the present disclosure. Common terms as defined in dictionaries are interpreted as having meanings consistent with the context in the relevant technical field, and should not be interpreted ideally or overly formally unless clearly defined in the present disclosure.

[0058] The following discussion Figures 1 to 13 The various embodiments used to describe the principles of the present disclosure in this patent document are for illustration only and should not be interpreted in any way as limiting the scope of the present disclosure. Those skilled in the art will appreciate that the principles of the present disclosure can be implemented in any appropriately arranged system or device.

[0059] Figure 1 It is an exemplary system architecture 100 of System Architecture Evolution (SAE). User Equipment (UE) 101 is a terminal device used to receive data. Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 102 is a radio access network, which includes a macro base station (eNodeB / NodeB) that provides a wireless network interface for the UE to access. The Mobility Management Entity (MME) 103 is responsible for managing the mobility context, session context and security information of the UE. The Serving Gateway (SGW) 104 mainly provides user plane functions, and the MME 103 and SGW 104 may be in the same physical entity. The Packet Data Network Gateway (PGW) 105 is responsible for functions such as billing and lawful interception, and may also be in the same physical entity as the SGW 104. The Policy and Charging Rules Function Entity (PCRF) 106 provides Quality of Service (QoS) policies and charging criteria. The General Packet Radio Service Support Node (SGSN) 108 is a network node device that provides routing for data transmission in the Universal Mobile Telecommunications System (UMTS). The Home Subscriber Server (HSS) 109 is the home subsystem of the UE and is responsible for protecting user information including the current location of the user equipment, the address of the service node, user security information, and the packet data context of the user equipment.

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

[0061] User equipment (UE) 201 is a terminal device used to receive data. The next generation radio access network (NG-RAN) 202 is a radio access network, which includes a base station (gNB or eNB connected to the 5G core network 5GC, the eNB connected to the 5GC is also called ng-gNB) that provides the UE with an access wireless network interface. The access control and mobility management function entity (AMF) 203 is responsible for managing the mobility context and security information of the UE. The user plane function entity (UPF) 204 mainly provides user plane functions. The session management function entity SMF 205 is responsible for session management. The data network (DN) 206 includes services such as operators, Internet access, and third-party services.

[0062] Exemplary embodiments of the present disclosure are further described below in conjunction with the accompanying drawings.

[0063] The text and drawings are provided as examples only to help understand the present disclosure. They should not be interpreted as limiting the scope of the present disclosure in any way. Although certain embodiments and examples have been provided, it will be apparent to those skilled in the art based on what is disclosed herein that the embodiments and examples shown may be changed without departing from the scope of the present disclosure.

[0064] Detailed descriptions of steps not related to the present disclosure are omitted in this application. In the following embodiments, the 5G system is taken as an example, the access network centralized unit is taken as an example of CU (Central Unit), and the distributed unit is taken as an example of DU (Distributed Unit). However,

[0065] It can be understood that the present disclosure is not limited to the 5G system, and the method of the present disclosure can also be applied to corresponding entities of other systems.

[0066] In the present application, a node may be a complete base station (e.g., gNB, or eNB, or en-gNB, or ng-eNB), or a base station including a centralized unit and a distributed unit. The gNB may be a single base station, or a master base station / master node (MN) or an auxiliary base station / auxiliary node (SN) under dual connectivity (DC, Dual Connectivity). A group of cells serving UEs in MN is called a master cell group (MCG, Master Cell Group), and a group of cells serving UEs in SN is called a secondary (second) cell group (SCG, Secondary Cell Group). The primary cell in MCG is called PCell (Primary Cell), and the primary cell in SCG is called PSCell (Primary SCG Cell). When MCG or SCG adopts carrier aggregation CA (Carrier Aggregation), cells other than PCell and PSCell are called SCell (Secondary Cell).

[0067] In the centralized unit (CU) / distributed unit (DU) separation structure, when switching, the source cell and the target cell can be located in the same gNB-DU or in different gNB-DUs.

[0068] There is one or more cells under one gNB-DU, and one or more UEs in each cell. Therefore, the UEs in the cell are also the UEs in the gNB-DU.

[0069] A gNB-CU is connected to one or more gNB-DUs, so the cells in the gNB-DU are also the cells in the gNB-CU. The UEs in the gNB-DU are also the UEs in the gNB-CU.

[0070] In this application, the message names are only examples, and other names can be used to name the messages. The sequence number of the message does not represent the order in which the messages are executed, but only represents the name of the message.

[0071] For the convenience of description, in the present disclosure, the cell indicates a SpCell (including a PCell and a PSCell). For example, in the present disclosure, a candidate cell, a target cell and a source cell indicate a candidate SpCell, a target SpCell and a source SpCell, respectively.

[0072] The contents described in this disclosure are applicable to the scenario where the MN uses LTM (L1 / L2-Triggered Mobility) to adjust the PCell, and are also applicable to the scenario where the SN adjusts the PSCell by LTM. However, it is understandable that this disclosure is not limited to the LTM switching mechanism, and the disclosure can also be applied to other switching mechanisms. The LTM switching mechanism is used as an example for explanation below.

[0073] When carrier aggregation is supported, the candidate cell described in the present disclosure may be a candidate cell of a PCell (candidate PCell cell), a candidate cell of a PSCell (candidate PSCell cell), or a candidate cell of a SCell (candidate SCell cell).

[0074] Under the LTM switching mechanism, in order to save switching delay, the UE needs to obtain the uplink timing advance information in the candidate cell (or target cell) in advance, that is, the early acquisition (Early TA (Time Advance) Acquisition) of the uplink timing advance of the candidate cell (or target cell). The early acquisition of the uplink timing advance of the UE in the candidate cell is also achieved through a random access process, which is called the random access process of Early TA acquisition to distinguish it from the ordinary random access process (existing random access process). The purpose of the random access process is for the UE to obtain the uplink TA value in the cell (that is, the uplink TA value used by the UE in the cell), so as to achieve uplink synchronization between the UE and the cell. The network determines the TA value by detecting the uplink synchronization code (preamble code) sent by the UE in the cell. The process of the network determining the TA value by detecting the Preamble code can also be referred to as detecting the TA value.

[0075] See also Figure 3a , Figure 3aIt is a diagram of a process in which a user equipment (UE) obtains the TA of a target cell during a normal random access process when a handover occurs according to various embodiments of the present disclosure. As shown in FIG3 , Cell1 is the source cell of the UE (also referred to as the current serving cell of the UE), and Cell2 is the target cell of the UE. When the UE receives a handover command, the target cell Cell2 determines the TA value of the UE in the target cell Cell2 by detecting an uplink synchronization code (Preamble code) on a PRACH (Physical Random Access Channel) resource, and the TA value is directly sent to the UE via a random access response RAR (Random Access Response) message.

[0076] See also Figure 3b , Figure 3b FIG. 1 is a diagram of a process for implementing uplink synchronization between a UE and a source cell according to various embodiments of the present disclosure. Figure 3b As shown, when the UE loses synchronization in the uplink of the source cell Cell1, the source cell can trigger the UE to perform a normal random access process in the source cell Cell1 through a PDCCH (Physical Downlink Control Channel) command (PDCCH order), that is, send a Preamble code on the PRACH resource of the source cell, and the UE obtains the TA value in the source cell through the RAR response, thereby achieving uplink synchronization between the UE and the source cell.

[0077] See also Figure 3c , Figure 3c 1 is a diagram of a process in which a UE obtains a TA value of a target cell during a random access process of an early acquisition of timing advance (EarlyTA acquisition) according to various embodiments of the present disclosure. Figure 3cAs shown, Cell1 is the source cell of the UE (also referred to as the current serving cell of the UE), and Cell2 is the candidate cell (or target cell). The source cell Cell1 sends a PDCCH order to the UE, instructing the UE to send a Preamble code on the PRACH resource of the candidate cell (or target cell) Cell2. Cell2 determines the TA value of the UE in Cell2 by detecting the Preamble code on the PRACH resource. Since the UE is still connected to the source cell, in order to ensure that the service transmission of the UE in the source cell is not affected, after successfully sending the Preamble code to the candidate cell, the UE will not obtain the TA value of the candidate cell by receiving the random access response message sent by the candidate cell, but will send the determined TA value (or the detected TA value) to the source cell of the UE through the candidate cell. When the source cell selects the candidate cell Cell2 as the target cell of the UE, the source cell includes the TA value in the LTM switching command (or cell exchange command) sent to the UE, and the UE obtains the TA value of the target cell through the cell exchange command. Therefore, through the random access process obtained by Early TA, when the UE switches to the target cell, it is no longer necessary to obtain the uplink timing advance (TA) with the target cell through the ordinary random access process. The target cell can directly schedule the UE for uplink data transmission, thereby reducing the switching delay and service interruption caused by the switching.

[0078] The random access process in Early TA is different from the normal random access process in the following ways:

[0079] -The PDCCH order received by the UE in the source cell instructs the UE to send the Preamble code on the PRACH resources of the candidate cell or the cell indicated in the PDCCH order;

[0080] -The candidate cell determines the TA value by detecting the Preamble code on the PRACH resource. It is not sent directly to the UE but to the source cell (if the source cell and the candidate cell are in different gNB-DUs, it needs to be forwarded through the gNB-CU).

[0081] Therefore, under the LTM switching mechanism, if the random access process of Early TA acquisition is supported:

[0082] -The candidate cell needs to divide the PRACH resources into the random access process for the normal random access process and the random access process for the Early TA acquisition. Thus, after the candidate cell detects the Preamble code on the corresponding PRACH resource, it can confirm whether the random access process is a normal random access process or a random access process for the Early TA acquisition. Among them, the PRACH resources allocated for the random access process for the Early TA acquisition can be called the PRACH resources for the Early TA acquisition (PRACH resources for short).

[0083] -Since the PDCCH order is sent to the UE by the source cell, when the candidate cell detects the Preamble code in the PRACH resource used for Early TA acquisition and determines the TA value, it is necessary to send the determined TA value to the corresponding UE. Therefore, a dedicated PRACH resource and Preamble code for Early TA acquisition are allocated to the UE on the candidate cell. Then, through the correspondence between the PRACH resource and the Preamble code and the UE, the UE corresponding to the TA value can be determined, and the TA value can be sent to the source cell of the UE.

[0084] Under the LTM switching mechanism, the UE will configure multiple candidate cells, and during cell switching or cell switching, the UE and the network will maintain the configuration of the candidate cells for the next cell switching or cell switching. If each candidate cell allocates dedicated PRACH resources to the UE for the random access process of Early TA acquisition, the UE and the network will maintain the dedicated PRACH resource information. The UE will only use the dedicated PRACH resources allocated to the UE by the candidate cell during the random access process of Early TA acquisition to the candidate cell. Moreover, as the number of UEs increases, each candidate cell needs to allocate more dedicated PRACH resources for the random access process of Early TA acquisition, resulting in low PRACH resource utilization.

[0085] The present disclosure proposes a method executed by a first node in a communication system, the method comprising: receiving a first message from a second node, wherein the first message comprises information related to a first physical random access channel (PRACH) resource, and the information related to the first PRACH resource comprises a first cell identifier or a first node identifier corresponding to the PRACH resource; and sending a second message to a third node, wherein the second message comprises information related to a second PRACH resource, and the PRACH resource is used to obtain a timing advance (TA) value in advance; wherein the third node is a node where a cell indicated by the first cell identifier is located or a node indicated by the first node identifier.

[0086] Through the above method, the PRACH resources used for Early TA acquisition can be shared by multiple UEs in a cell or a node, thereby improving the utilization rate of the PRACH resources used for Early TA acquisition in the candidate cell.

[0087] In addition, the present disclosure proposes a method executed by a first node in a communication system, the method comprising: receiving a sixth message from a second node, or receiving a seventh message from a fourth node, wherein the sixth message or the seventh message includes information related to a third physical random access channel (PRACH) resource; and sending an eighth message to a third node based on the sixth message or the seventh message, wherein the eighth message includes information related to a fourth PRACH resource, and the information related to the fourth PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource, wherein the PRACH resource is used to obtain a timing advance (TA) value in advance; wherein the third node is a node where the cell indicated by the first cell identifier is located or a node indicated by the first node identifier.

[0088] Through the above method, in addition to enabling the PRACH resources used for Early TA acquisition to be shared by multiple UEs in a cell or a node, thereby improving the utilization rate of the PRACH resources used for Early TA acquisition in the candidate cell, the first node can also re-allocate the received PRACH resources, making the allocation of PRACH resources more flexible and further improving the utilization rate of PRACH resources.

[0089] In addition, the present disclosure proposes a method executed by a third node in a communication system, the method comprising: receiving a second message sent by a first node; or receiving a tenth message sent by a fourth node, wherein the second message and the tenth message include information related to the second physical random access channel PRACH resource, and the PRACH resource corresponding to the information related to the second PRACH resource is used to obtain a timing advance TA value in advance; the cell in the third node allocates the PRACH resource to a user equipment UE for performing a random access process for obtaining a timing advance TA value in advance; wherein the second message is sent by the first node in response to a received first message, the first message includes information related to the first PRACH resource, and the information related to the first PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource.

[0090] Through the above method, in addition to enabling the PRACH resources used for Early TA acquisition to be shared by multiple UEs, thereby improving the utilization rate of the PRACH resources used for Early TA acquisition in the candidate cell, the third node can also allocate the acquired PRACH resources again, dynamically allocate them to the cells therein (for example, according to factors such as the number of user equipment in the cell), so that the allocation of PRACH resources is more utilized and the resource utilization rate is further improved. In addition, the third node (for example, the source node) can also obtain PRACH resource allocation information from the fourth node, making the implementation of the present disclosure more flexible and applicable to a more flexible network environment. And the third node triggers the user equipment and a cell in the group to perform the random access process for Early TA acquisition based on the group identifier of the candidate cell, and obtains the TA value of all cells in the group of the UE. Thereby reducing the triggering of the UE to perform uplink synchronization processing, and reducing the information transmission overhead between nodes.

[0091] In addition, the present disclosure also provides a method for acquiring uplink synchronization information. As an embodiment, the present disclosure also provides a method executed by a second node in a communication system, the method comprising: sending a first message to a first node, wherein the first message includes information related to a first physical random access channel PRACH resource, and the information related to the first PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource; performing detection on the PRACH resource to determine a first TA value; sending a third message to the first node, the third message including first TA information, and the first TA information including the first TA value.

[0092] Through the above method, while improving resource utilization, the TA value of the UE in the candidate cell can be obtained in advance and accurately. At the same time, when the cell of the second node is used as the target cell of the user terminal, the received information related to the uplink synchronization between the user terminal and the candidate cell can further reduce the triggering of the UE to perform uplink synchronization processing, and reduce the information transmission overhead between nodes.

[0093] Various embodiments of the present disclosure provide a method for allocating PRACH resources, thereby achieving an improvement in PRACH resource utilization. The basic idea of ​​the PRACH resource allocation method is to convert the dedicated Early TA acquisition PRACH resources allocated to the UE into PRACH resources for Early TA acquisition allocated to the cell (cell-level resource allocation method) or allocated to the node (node-level resource allocation method). For example, Cell 2 (Cell2) divides part of the wireless resources of this cell for PRACH resources acquired by Early TA, then Cell2 can allocate the PRACH resources to Cell1 or to gNB-DU1. The cell in Cell1 or gNB-DU1 allocates the obtained PRACH resources to the UE it serves, triggering the UE to use the allocated PRACH resources to perform the Early TA random access process in Cell2, thereby obtaining the TA value of the UE on Cell2. Among them, Cell2 is a cell that allocates PRACH resources (or a cell that provides PRACH resources), Cell1 or the cell in gNB-DU1 is a cell that uses PRACH resources (or a cell that is allocated PRACH resources, or a cell corresponding to PRACH resources), and gNB-DU1 is a node that uses PRACH resources (or a node that is allocated PRACH resources, or a node corresponding to PRACH resources). The above description is applicable to all embodiments in the present disclosure.

[0094] The following describes in detail the PRACH resource allocation method provided by each embodiment of the present disclosure.

[0095] See also Figure 4 , Figure 4 It is an interactive diagram of a PRACH resource allocation method according to various embodiments of the present disclosure.

[0096] In this embodiment, when the network is ready to trigger LTM, when performing candidate cell configuration (candidate cell preparation), the candidate cell allocates the PRACH resources used for Early TA acquisition to the source cell, and the source cell dynamically allocates the PRACH resources to the UE in the source cell for performing the random access process of Early TA acquisition, thereby obtaining the TA value of the UE in the candidate cell. In this method, the candidate cell allocates PRACH resources to the source cell using a cell-level resource allocation method. When the source cell triggers the UE in the cell to perform the random access process of Early TA acquisition, the source cell dynamically allocates the PRACH resources to the UE in the cell, thereby realizing the sharing of PRACH resources by different UEs in the source cell and improving the utilization rate of PRACH resources. Among them, the source cell is the current serving cell of the UE (which can be a PCell or a PSCell).

[0097] In this embodiment, the basic idea of ​​the method for allocating PRACH resources to the source cell where the UE is located is: in the LTM candidate cell preparation stage, in addition to establishing a communication context for the UE of the source cell and allocating resources of the candidate cell, the candidate cell also allocates PRACH resources for Early TA acquisition to the source cell, and the PRACH resources are used to be allocated by the source cell to the UE in the source cell, so that the UE performs the random access process of Early TA acquisition in the candidate cell. In this embodiment, the PRACH resource information for Early TA acquisition allocated by the candidate cell to the source cell is provided to the source cell through UE-associated signaling. Therefore, in the LTM candidate cell preparation stage for the UE in the source cell, for different UEs, the source cell may obtain the PRACH resources allocated to the source cell multiple times through UE-associated signaling. These PRACH resources may be the same or different, and the source cell only uses the most recently obtained PRACH resources allocated by the candidate cell. That is, if the candidate cell needs to update the PRACH resources allocated to the source cell, it will send the updated PRACH resource information to the source cell in the UE-associated signaling sent to the source cell.

[0098] The specific process of the PRACH resource allocation method provided in this embodiment is as follows: Figure 4 As shown. Figure 4 As shown, the PRACH resource allocation method provided in this embodiment may include one or more steps from step S301 to step S319. The detailed description of each step is as follows.

[0099] Step 301: The UE sends a measurement report to the gNB-CU via the source gNB-DU (gNB-DU1). The current source cell of the UE is Cell1, which belongs to gNB-DU1.

[0100] In step 302, the gNB-CU decides to trigger the handover configuration based on the measurement report and performs candidate cell configuration (in the LTM system, it is the LTM configuration, i.e., the LTM candidate cell configuration). The gNB-CU selects candidate cells (in the LTM system, it is the LTM candidate cells) for the UE based on the measurement results, assuming that they are Cell 2 (Cell2) and Cell 3 (Cell3). Cell 2 (Cell2) and Cell 3 (Cell3) are located in two candidate gNB-DUs, i.e., gNB-DU2 and gNB-DU3.

[0101] In step 303, the gNB-CU sends messages to the candidate gNB-DUs (i.e., gNB-DU2 and gNB-DU3) respectively, indicating that the cells in gNB-DU2 and gNB-DU3 are used as LTM candidate cells of the UE (e.g., cell 2 and cell 3), and requests gNB-DU2 and gNB-DU3 to provide the UE with configuration information of Cell2 and Cell3, and / or allocate PRACH resources for Early TA acquisition to the source cell and / or other cells. The message may be a UE CONTEXT SETUPREQUEST message, or other messages. The message may include at least one of the following information:

[0102] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0103] -Candidate cell identifier, the identifier of the candidate cell of the UE. If it is an LTM system, it is the identifier of the LTM candidate cell. The identifier can be CGI (Cell Global Identifier, Cell Global ID), or PCI, or other identifiers. If the candidate cell needs to allocate PRACH resources to the source cell and / or other cells for Early TA acquisition and / or for ordinary random access procedures, the candidate cell is the cell that allocates PRACH resources.

[0104] If carrier aggregation is supported, the candidate cell identifiers will be provided in a list, including candidate PCell and / or candidate PSCell), and candidate SCell (Secondary Cell) cell identifiers. The candidate SCell cell identifier can be CGI (Cell Global ID), or PCI, or other identifiers. If the candidate SCell cell needs to allocate PRACH resources to the source gNB-DU and / or other gNB-DU for Early TA acquisition and / or for normal random access procedures, then the candidate SCell cell is the cell that allocates PRACH resources.

[0105] -LTM handover indication, indicating that this process is to configure candidate cells for LTM handover of UE.

[0106] -PRACH resource request indication, instructing the candidate cell to allocate PRACH resources for Early TA acquisition and / or for normal random access process.

[0107] -Cell identifier, the cell identifier for requesting allocation of PRACH resources, that is, the identifier of the cell to which PRACH resources are allocated. The cell may be the source cell or other cell where the UE is located. The candidate cell (the cell indicated by the candidate cell identifier) ​​will allocate PRACH resources to the cell indicated by the cell identifier for acquiring EarlyTA on the candidate cell and / or for a normal random access process. Therefore, the cell indicated by the cell identifier is the cell to which PRACH resources are allocated (or the cell using PRACH resources). The cell identifier may be a CGI (Cell Global ID), a PCI, or another identifier. If PRACH resources need to be requested for the source cell and / or one or more other cells, multiple cell identifiers will be provided in the form of a list.

[0108] For the cell-level PRACH resource allocation method, after receiving the message, the candidate gNB-DU uses the cell indicated by the candidate cell identifier as the LTM candidate cell of the UE, indicating that in addition to providing cell configuration information to the UE, the candidate cell also needs to allocate PRACH resources to the cell indicated by the cell identifier for Early TA acquisition.

[0109] In step 304, the candidate gNB-DU (gNB-DU2 and gNB-DU3) sends a message to the gNB-CU, which is used by the candidate gNB-DU to provide candidate cell configuration information and PRACH resource-related information. The PRACH resource-related information includes at least one of the following information: the cell identifier of the allocated PRACH resource, the node where the cell where the PRACH resource is allocated is located, the allocated PRACH resource information, and the cell identifier of the allocated PRACH resource. The message can be a UECONTEXT SETUP RESPONSE message, or other messages. The message can include at least one of the following information:

[0110] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0111] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0112] - The requested candidate cell identifier is the candidate cell identifier in step 303. The identifier may be a CGI (Cell Global ID), or a PCI, or other identifiers. The cell indicated by the requested candidate cell identifier is the cell to which the PRACH resources are allocated.

[0113] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the requested candidate cell is located.

[0114] - Group ID, indicating the ID of the group to which the requested candidate cell belongs.

[0115] The cells within the same gNB-DU are grouped, that is, the cells are grouped independently within each gNB-DU.

[0116] -PRACH resource information (list), indicating the PRACH resources (PRACH resources) information allocated by the requested candidate cell for Early TA acquisition and / or for normal random access process. If PRACH resources are allocated to the source cell and / or one or more other cells, the PRACH resource information allocated to each cell will be provided in the form of a list:

[0117] ●Cell ID: the ID of the cell to which the PRACH resources are allocated. The ID may be a CGI (Cell Global ID), a PCI, or other IDs.

[0118] ●PRACH resource information, which includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. The parameters or information are used to determine the random access resources (PRACH resources). The PRACH resource information may include at least one of the following information:

[0119] ◆PRACH configuration index (prach-ConfigurationIndex), indicating the time domain information of the PRACH opportunity (or PRACH opportunity, PRACH Occasion). The PRACH Occasion is a resource (including a time domain resource and a frequency domain resource) that can be used to send the Preamble. Each index corresponds to a set of information, including:

[0120] ● System frame (SFN) with PRACH Occasion;

[0121] ●The number of PRACH Occasions contained in the subframe;

[0122] ●The starting symbol of PRACH Occasion transmission in a subframe;

[0123] ●The number of PRACH slots contained in a subframe;

[0124] ●The number of PRACH Occasions in a PRACH slot;

[0125] ●The length of a PRACH (in symbols);

[0126] The FDM (Frequency Division Multiplexing) information of message 1 (msg1-FDM) indicates the frequency domain information of the PRACH Occasion. Its value indicates the number of frequency domain PRACH Occasions in a time domain PRACH Occasion.

[0127] ◆The frequency starting point of message 1 (msg1-FrequencyStart), its value indicates the frequency starting position of the frequency domain PRACH Occasion;

[0128] ◆Total number of random access codes (totalNumberOfRA-Preambles), its value indicates the total number of preambles.

[0129] ●BWP (Bandwidth Part) information, indicating the frequency domain position of BWP (indicating the starting point of BWP) and bandwidth.

[0130] ● Uplink frequency information (FrequencyInfoUL), including carrier bandwidth, subcarrier spacing, and carrier offset value (offsetToCarrier). The carrier offset value indicates the starting point of the PRB actually used by the carrier.

[0131] The BWP information and uplink frequency information indicate the frequency information where the PRACH resource is located.

[0132] ●PRACH resource usage indication information, used to indicate whether the PRACH resource provided in the PRACH resource information is used for Early TA acquisition, or for a normal random access procedure, or can be used for both Early TA acquisition and a normal random access procedure. If the PRACH resource can only be used for a normal random access, the gNB-DU receiving the resource shall not allocate the PRACH resource for the UE to perform a random access procedure for Early TA acquisition.

[0133] - DU to CU RRC Information, including candidate cell configuration information and / or PRACH resource information. The specific content of the PRACH resource information is the same as above and will not be repeated here.

[0134] If carrier aggregation is supported, the requested candidate cell (including candidate PCell and / or candidate PSCell and / or candidate SCell) configuration information will be provided in the form of a list, including at least one of the following information, and the specific information is described as above:

[0135] -The requested candidate cell identifier may be the cell identifier of a candidate PCell, a candidate PSCell or a candidate SCell.

[0136] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the requested candidate cell is located.

[0137] -Group ID, indicating the ID of the group to which the requested candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0138] -PRACH resource information (list), indicating the PRACH resource (PRACH resource) information allocated by the requested candidate cell for Early TA acquisition and / or for a normal random access procedure.

[0139] The group identifier (Group ID) is used to indicate the group to which the cell belongs, or is called a synchronization group or a TA (Timing Advance) group, wherein the group identifier is used to identify the group to which the cell belongs, and the UE has the same uplink synchronization relationship with the cells in the same group, that is, if the UE achieves uplink synchronization with one of the cells in the same group, it means that the UE and the uplink of all the cells in the group are synchronized. Each group corresponds to a TA value (or TA amount) and a time alignment timer TAT (TimeAlignmentTimer). That is to say, for each cell in the same group, the UE uses the same TA value for uplink transmission (that is, the TA value of the cells in the same group of the UE is the same, or for the UE, the cells in the same group have the same TA, or the TA value of the cells in the same group of the UE is the same), and uses the TAT to determine whether the TA value of the group is valid. If the TAT does not time out, it means that the TA value is valid, and the UE and all the cells in the group maintain uplink synchronization. Otherwise, it means that the TA value is invalid, and the UE and all the cells in the group no longer maintain uplink synchronization.

[0140] Therefore, when the UE performs the random access process of Early TA acquisition in a cell in the group, achieves uplink synchronization, and obtains the TA value of the UE in the cell, then the TA value of the UE in other cells in the group is obtained. Therefore, the Early TA acquisition process can be reduced. Moreover, when the TAT of the group has not timed out, the TA value of the group is valid, and there is no need to trigger the Early TA acquisition process. Therefore, by introducing the grouping mechanism and maintaining the TA value and TAT timer of the group, unnecessary Early TA acquisition processes can be avoided, thereby reducing the processing of UE and nodes (gNB-DU, gNB-CU), as well as message interactions between nodes.

[0141] Optionally, the group identifier may also use other identifiers, such as "using the same TA identifier" or other identifiers, but the present disclosure is not limited thereto. The other identifier has the same function as the group identifier, that is, if the other identifiers of two cells have the same value, then it is considered that the TA of the UE in the two cells is the same, or it can be said that the UE can use the same TA in the two cells, or it can be said that the TA of the two cells is the same. For the convenience of description, the present disclosure uniformly uses the group identifier for description.

[0142] Optionally, the gNB-CU may send the group identifier (Group ID) of the candidate cell received from the candidate gNB-DU and the gNB-DU identifier (gNB-DU ID) to which the candidate cell belongs (or is located) to the source cell.

[0143] When the source cell obtains the group identifier of the candidate cells belonging to the same gNB-DU, if the TA value of a cell in the group of the UE is obtained, the TA values ​​of other cells in the group of the UE are also obtained, thereby avoiding unnecessary Early TA acquisition process.

[0144] Optionally, the gNB-CU may also uniformly allocate (or set) group IDs for all candidate cells according to the group IDs (Group IDs) of the candidate cells received from all candidate gNB-DUs. For example, if the gNB-CU receives group IDs of candidate cells Cell1 and Cell2 from candidate gNB-DU1 as 1 and 2 respectively, the group IDs of candidate cells Cell3 and Cell4 from candidate gNB-DU2 as 1 and 1 respectively, and the group IDs of candidate cells Cell5, Cell6 and Cell7 from gNB-DU3 as 1, 2 and 2 respectively. Optionally, the principle of uniform allocation of candidate cell group IDs by the gNB-CU may be based on the following principle, but is not limited thereto: the group IDs of cells between different gNB-DUs cannot be the same, and whether the group IDs of cells within the same gNB-DU are the same is determined based on whether the group IDs provided by the gNB-DU are the same. Based on the above principle, the values ​​of the candidate cell group IDs uniformly allocated by the gNB-CU to Cell1-Cell7 are 1, 2, 3, 3, 4, 5, 5 in order.

[0145] The gNB-CU provides the uniformly allocated candidate cell group identifier to the source cell. When the source cell obtains the group identifier of the candidate cell, if the TA value of the UE in a candidate cell is obtained, the TA value of the UE in other candidate cells with the same group identifier as the candidate cell is also obtained, thereby avoiding unnecessary Early TA acquisition process.

[0146] Through steps 303 and 304, the gNB-CU obtains the candidate cell configuration information provided by each candidate cell, and the PRACH resource information allocated by each cell to the source cell and / or other cells. The gNB-CU saves the PRACH resource information allocated by each cell to the source cell and / or other cells, and sends the PRACH resource information allocated by each candidate cell to the source cell to the source cell through step 305.

[0147] In step 305, the gNB-CU sends a message to the source gNB-DU, sending the candidate cell configuration information and PRACH resource-related information to the source gNB-DU (source cell). If carrier aggregation is supported, the candidate cell configuration information includes the configuration information of the candidate PCell and / or candidate PSCell and / or candidate SCell. The PRACH resource-related information includes at least one of the following information: the cell identifier of the allocated PRACH resources, the node where the cell where the PRACH resources are allocated is located, the allocated PRACH resource information, and the cell identifier of the allocated PRACH resources. The message may be a downlink RRC message transmission message (DL RRCMESSAGE TRANSFER), or a UE context modification request message (UE CONTEXT MODIFICATION REQUEST), or other messages. The message may include at least one of the following information:

[0148] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0149] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the source gNB-DU to the UE.

[0150] -LTM switching indication, indicating that the gNB-DU can use the LTM switching mechanism to adjust the UE's cell.

[0151] -Candidate cell information, providing information of each candidate cell in the form of a list, which may include at least one of the following information:

[0152] ●Candidate cell identifier, indicating the identifier of the candidate cell of the UE, the candidate cell identifier can be a global cell identifier (Cell Global ID, CGI), or a physical cell identifier (Physical Cell ID, PCI), or other cell identifiers. The cell indicated by the candidate cell identifier is the cell to which PRACH resources are allocated. If carrier aggregation is supported, the candidate cell identifier can be the cell identifier of the candidate PCell, candidate PSCell, or candidate SCell.

[0153] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0154] ● Group ID, indicating the ID of the group to which the candidate cell belongs. Grouping is performed for cells within the same gNB-DU, that is, cells are grouped independently within each gNB-DU. Optionally, the group ID can also be uniformly allocated by the gNB-CU. For the UE, cells in the same group have the same TA. That is, cells with the same group ID have the same TA.

[0155] ●PRACH resource information, the PRACH resource information for Early TA acquired by the candidate cell allocated to the source cell. The PRACH resource information at least includes time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0156] -The RRC reconfiguration message sent to the UE is provided in the form of an RRC container, which may include the configuration information of the LTM handover, the candidate cell configuration information and / or the PRACH resource information. Specifically, the RRC reconfiguration message may include at least one of the following information:

[0157] ●Candidate cell identifier, the identifier of the LTM candidate cell of the UE, which may be a global cell identifier (CellGlobal ID, CGI), or a physical cell identifier (Physical Cell ID, PCI), or other identifiers used to identify the candidate cell. If carrier aggregation is supported, the candidate cell identifier may be the cell identifier of the candidate PCell, candidate PSCell, or candidate SCell.

[0158] ●Group ID, indicating the ID of the group to which the candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0159] ●Candidate cell configuration information, including at least one of the following information: master cell group configuration information (Master CellGroupConfig), second cell group configuration information (Secondary CellGroupConfig), and radio bearer configuration information (RadioBearerConfig).

[0160] ●PRACH resource information: The PRACH resource information includes at least one of the following information: time domain related parameters or information, frequency domain related parameters or information, and Preamble code information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0161] -Candidate cell indication, indicating whether the source cell is used as the LTM candidate cell of the UE for subsequent LTM handover.

[0162] In step 306, the source gNB-DU forwards the “RRC reconfiguration message sent to the UE” received in step 305 to the UE. The message may be an RRC reconfiguration message (RRCReconfiguration) or other messages.

[0163] Step 307: The UE sends a message to the source gNB-DU, indicating that the UE has received the configuration information for the LTM switch. The message may be an RRC reconfiguration complete message (RRCReconfigurationComplete) or other messages.

[0164] In step 308, the source gNB-DU sends a message to the gNB-CU to instruct the UE and / or the source gNB-DU to complete the configuration of the LTM candidate cell. The message may be an uplink RRC message transfer message (UL RRC MESSAGE TRANSFER) or a UE CONTEXT MODIFICATION RESPONSE message (UE CONTEXT MODIFICATION RESPONSE), or other messages.

[0165] In step 309a, the UE sends a layer 1 (L1) measurement report to the source gNB-DU. The source cell selects one or more cells from the candidate cells based on the L1 measurement report, and determines whether the UE is uplink synchronized with the one or more cells, that is, whether the UE has the TA value of the one or more candidate cells. If not, the source cell triggers the UE to perform the Early TA acquisition random access process on the corresponding candidate cell, thereby obtaining the TA value of the UE on the candidate cell.

[0166] In step 309b, the source gNB-DU sends a message to the UE, instructing the UE to perform the random access process for Early TA acquisition, that is, to send a random access code (Random Access Preamble, referred to as Preamble code) on the PRACH resources of the candidate cell. If carrier aggregation is supported, the source gNB-DU can also instruct the UE to perform the random access process for Early TA acquisition on the candidate SCell through the message. This avoids the UE switching to the target PCell or target PSCell and then performing a random access process to obtain the TA value of the SCell. The message may be a physical layer downlink control channel (PDCCH) command (PDCCHorder). The message may include at least one of the following information:

[0167] - Candidate cell identifier, the candidate cell identifier of the random access procedure acquired by the UE during Early TA, the candidate cell identifier may be the PCI, or other forms of cell identifiers. If carrier aggregation is supported, the candidate cell identifier may be the cell identifier of the candidate PCell, candidate PSCell, or candidate SCell.

[0168] -PRACH resource scheduling information, indicating the PRACH resources of the candidate cell allocated to the UE by the source cell, or the PRACH resources scheduled by the source cell for the UE to use in the candidate cell. The UE sends a preamble code on the PRACH resource. It may include at least one of the following information:

[0169] ●SSB Index: indicates the SSB used when sending the Preamble code, that is, the best uplink beam selected for the UE.

[0170] PRACH Occasion information may include at least one of the following information:

[0171] ◆PRACH Mask Index: used to indicate the location of PRACH frequency domain resources.

[0172] ◆PRACH time domain information.

[0173] ●Random access code index (ra-PreambleIndex), indicating the random access code used for the random access process.

[0174] Step 310: The UE sends a random access code (Random Access Preamble) to the candidate cell. The UE sends the random access code on the PRACH resource of the candidate cell obtained in step 309b.

[0175] When the candidate cell detects a random access code on the PRACH resources and determines the TA value, if the candidate cell uses a cell-level PRACH resource allocation method to allocate PRACH resources for Early TA acquisition to the source cell and / or other cells, the candidate cell can determine the cell using the PRACH resources and the gNB-DU (gNB-DU ID) where the cell using the PRACH resources is located based on the PRACH resources detected with the access code, and send the determined TA value and the PRACH resource information corresponding to the TA value (that is, the PRACH resource information where the TA value is detected) to the cell using the PRACH resources (for example, forwarded by the gNB-CU).

[0176] In step 311, the candidate gNB-DU sends a first Early TA information transmission message to the gNB-CU, and sends the Early TA information (including the TA value and the PRACH resource information corresponding to the TA value) determined in step 310 to the gNB-CU. The first Early TA information transmission message may be a new message or a UE CONTEXT MODIFICATION REQUIRED message. The message may include at least one of the following information:

[0177] -First cell identifier, indicating the cell corresponding to the Early TA information (also called TA information), that is, the Preamble code is detected on the PRACH resources allocated to the first cell, and the TA value is determined. That is, the cell identifier using the PRACH resources. If the Early TA information is determined on the PRACH resources allocated to the source cell, then the first cell identifier is the source cell identifier. The cell identifier can be CGI, or PCI, or other cell identifiers.

[0178] -gNB-DU identifier (gNB-DU ID), indicating the ID of the gNB-DU where the cell indicated by the first cell identifier is located.

[0179] -TA information, including the TA value detected on the PRACH resource. Since multiple candidate cells of the UE may belong to the candidate gNB-DU, if one or more candidate cells detect the Preamble code on the PRACH resource of the Early TA allocated to the source cell and determine the TA value, the information may include the Early TA information (also called TA information) determined on the PRACH resource of one or more cells in the candidate gNB-DU, and the PRACH resource is the PRACH resource allocated to the source cell. The TA information includes at least one of the following information:

[0180] ● A second cell identifier, indicating a cell to which PRACH resources are allocated, that is, indicating a cell to which PRACH resources of a TA value are detected. The cell identifier may be a CGI, or a PCI, or other cell identifiers.

[0181] ●PRACH resource scheduling information, PRACH resource information of which the Preamble code is detected, that is, PRACH resource information of which the TA value is detected. The content of the PRACH resource scheduling information is shown in "PRACH resource scheduling information" in step 309b. No further details will be given here.

[0182] ●TA value, the TA value determined on the PRACH resource, that is, the TA value detected on the PRACH resource.

[0183] Assuming that cell A is a cell of gNB-DU, cell A may allocate PRACH resources for Early TA to multiple cells (source cell or other cells). If cell A detects the Preamble code on multiple PRACH resources (PRACH resources allocated to different cells) and determines the TA value, the message will contain Early TA information of multiple cells (cells using PRACH resources), which are distinguished by the first cell identifier, that is, the identifier of the cell using PRACH resources.

[0184] In step 312, the gNB-CU sends a second Early TA information transmission message to the source gNB-DU. The gNB-CU sends TA information to the corresponding node (gNB-DU) according to the first cell identifier and / or gNB-DU identifier in the message of step 311. If the first cell identifier indicates the source cell or the gNB-DU identifier indicates the source gNB-DU, the gNB-CU sends the corresponding TA information to the source gNB-DU. The second Early TA information transmission message may be a new message or a UE CONTEXT MODIFICATION REQUEST message. The message may include at least one of the following information:

[0185] - A third cell identifier, indicating the cell identifier corresponding to the TA information. The cell identifier may be a CGI, a PCI, or other cell identifiers. If the TA information is provided to the source cell, the third cell identifier is the source cell identifier.

[0186] -TA information, which may include at least one of the following information:

[0187] ● A fourth cell identifier, used to indicate the cell on which the TA value is determined based on the PRACH resources allocated by the cell, that is, to indicate the cell on which the PRACH resources of the TA value are detected. If the first cell identifier is the source cell, the fourth cell identifier indicates the cell on which the PRACH resources are allocated to the source cell. The cell identifier may be a CGI, a PCI, or another cell identifier.

[0188] ●PRACH resource scheduling information, PRACH resource information of which the Preamble code is detected, that is, PRACH resource information of which the TA value is detected. The content of the PRACH resource scheduling information is shown in "PRACH resource scheduling information" of step 309b. No further details will be given here.

[0189] ●TA value, the TA value determined on the PRACH resource, that is, the TA value detected on the PRACH resource.

[0190] Since the source gNB-DU may trigger the UE to perform a random access procedure for Early TA acquisition of a candidate cell and / or one or more candidate SCell cells when carrier aggregation is supported, the gNB-CU may obtain multiple TA information from the same gNB-DU, and each TA information contains the TA value detected by different cells in the PRACH resources.

[0191] Since the gNB-CU may also receive TA information sent to the cell indicated by the third cell identifier (for example, the source cell) from other candidate gNB-DUs, the message may contain multiple TA information, and the multiple TA information come from different gNB-DUs (or different cells of different gNB-DUs).

[0192] The third cell will determine the UE corresponding to the received TA value based on the fourth cell identifier and PRACH resource information. In step 313, when the cell indicated by the fourth cell identifier is selected as the target cell of the UE to perform cell switching or cell exchange, the cell switching command or cell exchange command sent by the source cell to the UE includes the fourth cell identifier and the TA value. If carrier aggregation is supported, in step 313, when the cell indicated by the fourth cell identifier is selected as the target SCell cell of the UE, the cell switching command or cell exchange command sent by the source cell to the UE may also include the fourth cell identifier and the TA value.

[0193] Step 313: The source gNB-DU sends a handover command to the UE. In the LTM system, this is the LTM command (LTMCommand), instructing the UE to perform a cell switch (Cell Switch) and switch to the target cell. The handover command contains at least one of the following information:

[0194] -Cell ID, indicating the cell ID of the target cell for the UE to perform Cell switch, which can be PCI, CGI, or other cell IDs.

[0195] -TA value, which is the TA value used by the UE in the target cell. The TA value is the TA value obtained in step 312.

[0196] -PRACH resource information, indicating the PRACH resource information used by the UE for random access in the target cell.

[0197] If the TA value is not included in the LTM handover command, it indicates that the UE needs to obtain the uplink TA value of the target cell through a random access (RA) process. If the LTM handover command contains PRACH resource information, it indicates that the UE uses the resources to perform a non-contention-free random access process (CFRA) to obtain the TA value in the target cell; if the PRACH resource information is not included, the UE performs a contention-based random access process (CBRA) to obtain the uplink TA value of the target cell.

[0198] If carrier aggregation is supported and the source gNB-DU obtains the TA value of the UE on the target SCell, the handover command may also include at least one of the following information:

[0199] -SCell cell identifier, indicating the cell identifier of the target SCell of the UE, in which case the cell identifier corresponds to the cell identifier of the target PCell or the target PSCell. The SCell cell identifier may be a PCI, a CGI, or other cell identifiers.

[0200] - Group ID, indicating the ID of the group to which the target SCell belongs.

[0201] -TA value, the TA value used by the UE in the target SCell cell, where the TA value is the TA value obtained in step 312.

[0202] If the UE has multiple target SCells and they do not belong to the same group, then multiple SCell cell identifiers and corresponding group identifiers will be included.

[0203] Step 314: The source gNB-DU sends an LTM Cell change notification message or other message to the gNB-CU to indicate to the gNB-CU that the source cell instructs the UE to switch to the target cell through the LTM handover command. The message may include at least one of the following information:

[0204] - A fifth cell identifier, indicating the cell identifier of the target cell to which the UE switches, which may be a CGI, a PCI, or other cell identifiers.

[0205] -gNB-DU identity (gNB-DU ID), the identity of the gNB-DU of the target cell.

[0206] - Information sent to the target cell, including uplink synchronization information between the UE and the candidate cell, and providing candidate cell related information to the target cell in the form of a list. The candidate cell may be a candidate PCell, a candidate PSCell, or a candidate SCell. The information sent to the target cell includes at least one of the following information:

[0207] ●A sixth cell identifier, which is a cell identifier of a candidate cell. The cell identifier may be a CGI, a PCI, or other cell identifiers.

[0208] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0209] ●Group ID, which indicates the group to which the candidate cell belongs. Cells in the same gNB-DU are grouped, that is, cells are grouped independently in each gNB-DU.

[0210] ●TA (Timing Advance) value, the uplink timing advance of the UE in the cell indicated by the sixth cell identifier.

[0211] ●Timer TAT (timeAlignmentTimer) value, indicating the length of time the timer TAT runs after it is started. The unit is milliseconds (ms).

[0212] ●Timer TAT length: If the running time of the timer reaches the TAT length after it is started, it means that the TAT has timed out and the corresponding TA value is invalid. The unit is milliseconds (ms).

[0213] The TA value and the timer TAT value are optional items, and the two appear together. If the UE has an uplink TA value in the cell indicated by the sixth cell identifier and it is valid, the LTM cell change indication message includes the TA value and TAT value of the UE in the cell, wherein the TAT value indicates the length of time the timer runs after it is started. If the UE does not have an uplink TA value in the cell indicated by the sixth cell identifier and it is valid, the LTM cell change indication message does not include the TA value and TAT value of the UE in the cell.

[0214] Among them, after the UE accesses the target cell and completes the cell switch (Cell Switch), the gNB-CU forwards the information sent to the target cell to the target cell (target gNB-DU). The target cell can obtain the uplink synchronization related information between the UE and the candidate cell, such as the TA value, the timer TAT value and the timer TAT length, based on the "information sent to the target cell" sent by the source cell, so as to determine the uplink synchronization status between the UE and each candidate cell. If the information sent to the target cell contains the TA value, it means that the UE has achieved uplink synchronization with the candidate cell indicated by the sixth cell identifier, and the effective duration of the TA value (that is, when the TA value expires) is determined by the TAT value and the TAT length. If the TA value is not included, it means that the UE and the candidate cell indicated by the sixth cell identifier have not achieved uplink synchronization. At the same time, according to the grouping identifier, it can be determined whether the UE has the same timing relationship with multiple cells (that is, whether uplink synchronization is achieved). Therefore, when the target cell is preparing for LTM handover for the UE and needs to obtain the TA value of the candidate cell in advance, the uplink synchronization status of the UE and each candidate cell can be determined according to the information in the "information sent to the target cell", so as to decide whether it is necessary to trigger the process of obtaining the TA value in advance for the corresponding candidate cell. In this way, it can avoid the target cell triggering the UE to perform an unnecessary Early TA acquisition process.

[0215] Step 315: The UE accesses the target cell and completes the cell switch, that is, completes the LTM switch.

[0216] -If the LTM switching command in step 313 contains the TA value information of the target cell, then the downlink control channel is detected in the target cell. When the UE receives the uplink authorization and / or downlink scheduling information sent to itself, the TA value is used to send an RRC reconfiguration completion message in the uplink authorization resource.

[0217] - If the LTM handover command in step 313 does not include the TA value information of the target cell, then the UE will perform a random access process in the target cell to obtain the TA value of the target cell.

[0218] ●If the LTM handover command includes PRACH resource information, the UE performs a non-contention based random access procedure (CFRA), and message 3 (MSG3) or message A (MSGA) in the CFRA procedure includes an RRC reconfiguration complete message sent to the target cell.

[0219] ●If the LTM handover command does not include PRACH resource information, the UE performs a contention-based random access procedure (CBRA).

[0220] In step 316, the target gNB-DU sends a message to the gNB-CU to indicate the target cell that the UE successfully accesses. The message may be an access success message (Access Success) or other messages. The message at least includes the target cell identifier. The target cell identifier may be a CGI, a PCI, or other cell identifiers.

[0221] When the UE accesses the target cell (assuming it is Cell2), the source cell may become the candidate cell of the UE, and the target cell (Cell2) becomes the new source cell of the UE. Cell2 schedules uplink and downlink resources to achieve the transmission of UE service data. Then Cell2, as the source cell, will select a new target cell for the UE and instruct the UE to obtain the TA value of the candidate cell or the new target cell in advance (i.e., perform Early TA acquisition). Therefore, Cell2 needs to obtain the PRACH resource information of the candidate cell allocated to Cell2. There are three ways for Cell2 to obtain the PRACH resource information allocated to Cell2 by the candidate cell:

[0222] Method 1: If in step 304, the PRACH resource information includes not only the PRACH resource information allocated by the candidate cell to the source cell, but also the PRACH resource information allocated by the candidate cell to other cells (including Cell2), then the gNB-CU obtains and stores the PRACH resource information allocated by each cell to the source cell and other cells, and the PRACH resource information includes the PRACH resource information allocated by the candidate cell to Cell2. Therefore, when the gNB-CU knows that the UE has successfully accessed the target cell through step 316, it sends the PRACH resource information allocated by the candidate cell to Cell2 to Cell2, that is, executes step 319.

[0223] Method 2: Cell2 obtains the PRACH resource information for Early TA acquisition allocated by the candidate cell to Cell2 through steps 317-319. Steps 317-319 may also be performed after step 314, that is, when the gNB-CU knows that the source cell triggers the UE to perform LTM switching, it prepares PRACH resource information for Early TA acquisition for the target cell (new source cell).

[0224] Method 3: If in step 304, the PRACH resource information includes not only the PRACH resource information allocated by the candidate cell to the source cell, but also the PRACH resource information allocated by the candidate cell to other cells (including Cell2), then the gNB-CU obtains and stores the PRACH resource information allocated by each candidate cell to the source cell and other cells. Therefore, when the gNB-CU knows through step 314 that the UE will switch to the target cell, it sends the PRACH resource information allocated by the candidate cell to Cell2 to Cell2, that is, directly executes step 314a.

[0225] In step 314a, gNB-CU sends a message to gNB-DU2, where the message contains PRACH resource information allocated to the target cell by other candidate cells. The PRACH resources can be used to obtain Early TA.

[0226] The message may be an LTM cell change indication message (LTM Cell change notification) sent by the CU to the DU, or other messages. The message is used by the gNB-CU to indicate to the target cell that the UE will switch to the target cell. The message may include at least one of the following information:

[0227] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0228] -The F1 application protocol identifier assigned to the UE by the gNB-DU, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned to the UE by the gNB-DU2.

[0229] -Target cell identifier, indicating the target cell identifier to which the UE will switch, which can be CGI, PCI, or other cell identifiers.

[0230] -Candidate cell information, providing information of each candidate cell in the form of a list, which may include at least one of the following information:

[0231] ●Candidate cell identifier, the identifier of the candidate cell of the UE. The candidate cell identifier may be a Cell Global ID (CGI), or a Physical Cell ID (PCI), or other cell identifiers. The cell indicated by the candidate cell identifier is the cell to which PRACH resources are allocated.

[0232] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0233] ●Group ID, indicating the ID of the group to which the candidate cell belongs.

[0234] ●PRACH resource information, the candidate cell is the PRACH resource information for Early TA acquisition allocated by the current source cell. The PRACH resource information at least includes time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0235] -Information sent to the target cell, the information is sent by the source cell to the gNB-CU in step 314, and the gNB-CU forwards it to the target cell. The relevant description and function of the information can be found in the content of "Information sent to the target cell" in step 319, which will not be repeated here.

[0236] Through step 314a, Cell2 obtains the PRACH resource information allocated by the candidate cell for Cell2 for Early TA acquisition. Cell2 can obtain the TA value of the UE in the candidate cell in advance by allocating the PRACH resource to the UE it serves.

[0237] Steps 317-319 are described as follows.

[0238] In step 317, the gNB-CU sends messages to the candidate gNB-DUs (gNB-DU1 and gNB-DU3) respectively, instructing Cell1 and Cell3 to allocate PRACH resources to Cell2 for Early TA acquisition. The message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages. The message may include at least one of the following information:

[0239] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0240] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0241] -Candidate cell identifier, indicating the identifier of the candidate cell of the UE, the candidate cell identifier may be a CGI (Cell Global ID), or a PCI, or other identifiers. The cell indicated by the candidate cell identifier is the cell to which the PRACH resources are allocated.

[0242] -PRACH resource request indication, instructing the candidate cell to allocate PRACH resources for Early TA acquisition.

[0243] -Cell ID, the cell ID of the requested PRACH resource, that is, the ID of the cell to which the PRACH resource is allocated (the cell ID using the PRACH resource), that is, the ID of the current source cell of the UE. The cell ID may be a CGI (Cell Global ID), or a PCI, or other IDs.

[0244] After receiving the message, the candidate gNB-DU uses the cell indicated by the candidate cell identifier as the LTM candidate cell of the UE, and needs to allocate PRACH resources to the cell indicated by the cell identifier for Early TA acquisition.

[0245] In step 318, the candidate gNB-DU (gNB-DU1 and gNB-DU3) sends a message to the gNB-CU for the candidate gNB-DU to provide candidate cell configuration information. The message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages. The message may include at least one of the following information:

[0246] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0247] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0248] - The requested candidate cell identifier is the candidate cell identifier in step 317, which may be a CGI (Cell Global ID), or a PCI, or other identifiers. The cell indicated by the requested candidate cell identifier is the cell to which the PRACH resources are allocated.

[0249] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the requested candidate cell is located.

[0250] -Group ID, indicating the ID of the group to which the requested candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0251] -PRACH resource information, indicating the acquisition of PRACH resource information for Early TA allocated by the requested candidate cell to the source cell. The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0252] In step 319, the gNB-CU sends a message to gNB-DU2 (target cell Cell2 / new source cell Cell2), where the message includes the PRACH resource information allocated to Cell2 and the "information sent to the target cell" received by the gNB-CU in step 314. The message may be a downlink RRC message transfer message (DL RRC MESSAGE TRANSFER), or a UE CONTEXT MODIFICATION REQUEST message, or other messages. The message includes at least one of the following information:

[0253] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0254] -The F1 application protocol identifier assigned to the UE by the gNB-DU, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned to the UE by the gNB-DU2.

[0255] -Candidate cell information, providing information of each candidate cell in the form of a list, which may include at least one of the following information:

[0256] ●Candidate cell identifier, the identifier of the candidate cell of the UE. The candidate cell identifier may be a Cell Global ID (CGI), or a Physical Cell ID (PCI), or other cell identifiers. The cell indicated by the candidate cell identifier is the cell to which PRACH resources are allocated.

[0257] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0258] ●Group ID, indicating the ID of the group to which the candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0259] ●PRACH resource information, the candidate cell is the PRACH resource information for Early TA allocated by the current source cell. The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0260] -Information sent to the target cell, the information is sent by the source cell to the gNB-CU through step 314, and the gNB-CU forwards it to the target cell. See step 314 for specific information. The target cell can obtain information related to the uplink synchronization between the UE and the candidate cell, such as the TA value, the timer TAT value, and the timer TAT length, based on the "information sent to the target cell" sent by the source cell, so as to determine the uplink synchronization status between the UE and each candidate cell. If the information sent to the target cell contains the TA value, it means that the UE has achieved uplink synchronization with the cell indicated by the candidate cell identifier, and the effective duration of the TA value (i.e., when the TA value expires) is determined by the TAT value and the TAT length. If the TA value is not included, it means that the UE and the cell indicated by the candidate cell identifier have not achieved uplink synchronization. At the same time, according to the grouping identifier, it can be determined whether the UE has the same timing relationship with multiple cells (i.e., whether uplink synchronization is achieved). Therefore, when the target cell is preparing for LTM handover for the UE and needs to obtain the TA value of the candidate cell in advance, the uplink synchronization status of the UE and each candidate cell can be determined according to the information in the "information sent to the target cell", so as to decide whether it is necessary to trigger the process of obtaining the TA value in advance for the corresponding candidate cell. In this way, it can avoid the target cell triggering the UE to perform an unnecessary Early TA acquisition process.

[0261] Through steps 317-319, after Cell2 obtains the PRACH resource information allocated by the candidate cell for Early TA acquisition for Cell2, Cell2 can obtain the TA value of the UE in the candidate cell in advance by allocating the PRACH resource to the UE it serves.

[0262] Please refer to Figure 5 , Figure 5 is an interaction diagram of another PRACH resource allocation method according to various embodiments of the present disclosure.

[0263] exist Figure 5In the illustrated embodiment, when the network is ready to trigger LTM, when performing candidate cell configuration (candidate cell preparation), the candidate cell allocates the PRACH resources used for Early TA acquisition to the source gNB-DU, and dynamically allocates the PRACH resources to the source cell through the source gNB-DU, and the source cell allocates the PRACH resources to the UE for performing the random access process of Early TA acquisition, thereby obtaining the TA value of the UE in the candidate cell. In this method, the candidate cell allocates PRACH resources to the source gNB-DU (the gNB-DU where the source cell is located) using a node-level resource allocation method, and the source gNB-DU dynamically selects and allocates the PRACH resources from the obtained PRACH resources to the source cell (for example, according to factors such as the number of user equipment in the cell), and the source cell is allocated to the UE for Early TA acquisition. Thereby, the UE in the gNB-DU shares the PRACH resources, and the utilization rate of the PRACH resources is improved. Among them, the source cell is the current serving cell of the UE (which can be a PCell or a PSCell).

[0264] In this embodiment, the basic idea of ​​the method for allocating PRACH resources to the source gNB-DU where the source cell of the UE is located is: in the LTM candidate cell preparation stage, in addition to establishing a communication context for the UE of the source cell and allocating resources of the candidate cell, the candidate cell also allocates PRACH resources for Early TA acquisition to the source gNB-DU where the source cell is located, and the PRACH resources are used by the source gNB-DU to dynamically allocate to the cell (including the source cell) therein, and the cell (including the source cell) is then allocated to the UE in the cell for the UE to perform the random access process of Early TA acquisition in the candidate cell. In this embodiment, the PRACH resource information for Early TA acquisition allocated by the candidate cell to the source gNB-DU is provided to the source gNB-DU through UE-associated signaling. Therefore, in the LTM candidate cell preparation stage for the UE in the source cell, the source gNB-DU may obtain the PRACH resources allocated to the source gNB-DU multiple times for different UEs through UE-associated signaling. These PRACH resources may be the same or different, and the source gNB-DU only uses the most recently acquired PRACH resources allocated by the candidate cell. That is, if the candidate cell needs to update the PRACH resources allocated to the source gNB-DU, it will send the updated PRACH resource information to the source gNB-DU in the UE-associated signaling sent to the cell (including the source cell) of the source gNB-DU.

[0265] The specific process of the PRACH resource allocation method provided in this embodiment is as follows: Figure 5 As shown. Figure 5As shown, the PRACH resource allocation method provided in this embodiment may include one or more steps from step S401 to step S419. The detailed description of each step is as follows.

[0266] Step 401: The UE sends a measurement report to the gNB-CU via the source gNB-DU (gNB-DU1). The current source cell of the UE is Cell1, which belongs to gNB-DU1.

[0267] In step 402, the gNB-CU decides to trigger the handover configuration based on the measurement report. In the LTM system, it is the LTM configuration. The gNB-CU selects the LTM candidate cells for the UE based on the measurement results, assuming they are Cell 2 and Cell 3. Cell 2 and Cell 3 are located in two candidate gNB-DUs, namely gNB-DU2 and gNB-DU3.

[0268] In step 403, the gNB-CU sends messages to the candidate gNB-DUs (gNB-DU2 and gNB-DU3) respectively, indicating that the cells in gNB-DU2 and gNB-DU3 are used as LTM candidate cells for the UE, for example, cell 2 and cell 3. Request gNB-DU2 and gNB-DU3 to provide the UE with configuration information of Cell2 and Cell3, and / or allocate PRACH resources for Early TA acquisition to the source gNB-DU and / or other gNB-DUs. The message may be a UE CONTEXT SETUPREQUEST message, or other messages. The message may include at least one of the following information:

[0269] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0270] -Candidate cell identifier, the identifier of the candidate cell of the UE. If it is an LTM system, it is the identifier of the LTM candidate cell. The identifier can be CGI (Cell Global ID), or PCI, or other identifiers. If the candidate cell needs to allocate PRACH resources to the source gNB-DU and / or other gNB-DU for Early TA acquisition and / or for normal random access process,

[0271] Then the candidate cell is the cell to which the PRACH resources are allocated.

[0272] If carrier aggregation is supported, the candidate cell identifiers will be provided in a list, including candidate PCell and / or candidate PSCell), and candidate SCell (Secondary Cell) cell identifiers. The candidate SCell cell identifier can be CGI (Cell Global ID), or PCI, or other identifiers. If the candidate SCell cell needs to allocate PRACH resources to the source gNB-DU and / or other gNB-DU for Early TA acquisition and / or for normal random access procedures, then the candidate SCell cell is the cell that allocates PRACH resources.

[0273] -LTM handover indication, indicating that this process is to configure candidate cells for LTM handover of UE.

[0274] -PRACH resource request indication, indicating whether the candidate cell needs to allocate PRACH resources and the allocation method.

[0275] ● Resource allocation request indication, indicating whether the candidate cell needs to perform PRACH resource allocation, and the PRACH resource is used for Early TA acquisition and / or for ordinary random access process. If the resource allocation request indication exists, it means that the candidate cell needs to perform PRACH resource allocation. If the resource allocation request indication does not exist, it means that PRACH resource allocation is not required.

[0276] ● Allocation mode indication information. Indicates whether PRACH resource allocation adopts cell-level or node-level. When the indication exists, if the allocation mode is set to Cell-level, the candidate cell adopts the cell-level PRACH resource allocation mode; if the allocation mode is set to Node-level, the candidate cell adopts the node-level PRACH resource allocation mode.

[0277] -Candidate cell identifier, indicating the identifier of the candidate cell located in other candidate gNB-DUs. If it is an LTM system, it is the identifier of the LTM candidate cell located in other candidate gNB-DUs. The identifier can be CGI (Cell Global ID), PCI, or other identifiers.

[0278] -gNB-DU identifier (gNB-DU ID), the identifier of the gNB-DU requesting the allocation of PRACH resources, that is, the identifier of the gNB-DU to which PRACH resources are allocated. The gNB-DU may be the source gNB-DU where the UE is located (that is, the gNB-DU to which the source cell where the UE is located belongs) or other gNB-DU. The candidate cell (the cell indicated by the candidate cell identifier) ​​will allocate PRACH resources to the gNB-DU indicated by the gNB-DU identifier for the acquisition of Early TA on the candidate cell and / or for the normal random access process. Therefore, the gNB-DU indicated by the gNB-DU identifier is the gNB-DU to which PRACH resources are allocated (or the gNB-DU using PRACH resources). The gNB-DU identifier is the identifier of the gNB-DU where the cell indicated by the candidate cell identifier is located.

[0279] If PRACH resources need to be requested for the source gNB-DU and / or one or more other gNB-DUs, multiple gNB-DU identifiers and / or one or more candidate cell identifiers located at the gNB-DUs shall be provided in the form of a list.

[0280] For the node-level PRACH resource allocation method, after receiving the message, the candidate gNB-DU uses the cell indicated by the candidate cell identifier as the LTM candidate cell of the UE, indicating that in addition to providing cell configuration information for the UE, the candidate cell also needs to allocate PRACH resources to the gNB-DU indicated by the gNB-DU identifier for Early TA acquisition.

[0281] In step 404, the candidate gNB-DU (gNB-DU2 and gNB-DU3) sends a message to the gNB-CU, which is used by the candidate gNB-DU to provide candidate cell configuration information. And information related to PRACH resources. The information related to the PRACH resources includes at least one of the following information: the cell identifier of the allocated PRACH resources, the node where the cell where the PRACH resources are allocated is located, the allocated PRACH resource information, and the node identifier of the allocated PRACH resources. The message can be a UE context establishment response message UECONTEXT SETUP RESPONSE, or other messages. The message may include at least one of the following information:

[0282] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0283] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0284] - The requested candidate cell identifier is the candidate cell identifier in step 403. The identifier may be a CGI (Cell Global ID), or a PCI, or other identifiers. The cell indicated by the requested candidate cell identifier is the cell to which the PRACH resources are allocated.

[0285] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the requested candidate cell is located.

[0286] -Group ID, indicating the ID of the group to which the requested candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0287] -PRACH resource information (list), indicating the PRACH resources (PRACH resources) information allocated by the requested candidate cell for Early TA acquisition and / or for normal random access process. If PRACH resources are allocated for the source gNB-DU and / or one or more other gNB-DUs (other candidate gNB-DUs), the PRACH resource information allocated to each gNB-DU will be provided in the form of a list:

[0288] ●Candidate cell identifier, the identifier of the candidate cell. The candidate cell identifier indicates the identifier of the candidate cell located in other candidate gNB-DUs. If it is an LTM system, it is the identifier of the LTM candidate cell located in other candidate gNB-DUs. The identifier can be CGI (Cell Global ID), or PCI, or other identifiers.

[0289] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU to which the PRACH resources are allocated. The gNB-DU identifier is the identifier of the gNB-DU where the cell indicated by the candidate cell identifier is located.

[0290] ●PRACH resource information, the PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. The parameters or information are used to determine the random access resources (PRACH resources). For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0291] ●BWP information, indicating the frequency domain position of BWP (indicating the starting point of BWP) and bandwidth.

[0292] ● Uplink frequency information, including carrier bandwidth, subcarrier spacing, and carrier offset value (offsetToCarrier). The carrier offset value indicates the starting point of the PRB actually used by the carrier.

[0293] ●PRACH resource usage indication information, used to indicate whether the PRACH resource provided in the PRACH resource information is used for Early TA acquisition, or for a normal random access procedure, or can be used for both Early TA acquisition and a normal random access procedure. If the PRACH resource can only be used for a normal random access, the gNB-DU receiving the resource shall not allocate the PRACH resource for the UE to perform a random access procedure for Early TA acquisition.

[0294] - DU to CU RRC Information, including candidate cell configuration information and / or PRACH resource information. See step 304 for related description, which will not be repeated here.

[0295] If carrier aggregation is supported, the requested candidate cell (including candidate PCell and / or candidate PSCell and / or candidate SCell) configuration information will be provided in the form of a list, including at least one of the following information, and the specific information is described as above:

[0296] -The requested candidate cell identifier may be the cell identifier of a candidate PCell, a candidate PSCell or a candidate SCell.

[0297] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the requested candidate cell is located.

[0298] -Group ID, indicating the ID of the group to which the requested candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0299] -PRACH resource information (list), indicating the PRACH resource (PRACH resource) information allocated by the requested candidate cell for Early TA acquisition and / or for a normal random access procedure.

[0300] Through steps 403 and 404, the gNB-CU obtains the candidate cell configuration information provided by each candidate cell (if carrier aggregation is supported, the candidate cells include candidate PCell and / or candidate PSCell and / or candidate SCell) and the PRACH resource information allocated by each candidate cell to the source gNB-DU and / or other gNB-DUs. The gNB-CU saves the PRACH resource information allocated by each candidate cell to the source gNB-DU and / or other gNB-DUs, and sends the PRACH resource information allocated by each candidate cell to the source gNB-DU (source cell) through step 405.

[0301] In step 405, the gNB-CU sends a message to the source gNB-DU to send the LTM candidate cell configuration information and PRACH resource-related information to the source gNB-DU (source cell). If carrier aggregation is supported, the LTM candidate cell configuration information includes the configuration information of the candidate PCell and / or candidate PSCell and / or candidate SCell. The PRACH resource-related information includes at least one of the following information: the cell identifier of the allocated PRACH resources, the node where the cell where the PRACH resources are allocated is located, the allocated PRACH resource information, and the node identifier of the allocated PRACH resources. The message may be a downlink RRC message transfer message (DLRRC MESSAGE TRANSFER), or a UE context modification request message (UE CONTEXT MODIFICATIONREQUEST), or other messages. The message may include at least one of the following information:

[0302] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0303] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the source gNB-DU to the UE.

[0304] -LTM switching indication, indicating that the gNB-DU can use the LTM switching mechanism to adjust the UE's cell.

[0305] -Candidate cell information, which provides information about each LTM candidate cell in the form of a list and may include at least one of the following information:

[0306] ●Candidate cell identifier, the identifier of the candidate cell of the UE, the candidate cell identifier can be a global cell identifier (Cell Global ID, CGI), or a physical cell identifier (Physical Cell ID, PCI), or other cell identifiers. The cell indicated by the candidate cell identifier is the cell to which PRACH resources are allocated. If carrier aggregation is supported, the candidate cell identifier can be the cell identifier of the candidate PCell, candidate PSCell, or candidate SCell.

[0307] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0308] ●Group ID, which indicates the group to which the candidate cell belongs. Cells in the same gNB-DU are grouped, that is, cells are grouped independently in each gNB-DU.

[0309] ●PRACH resource information, the candidate cell allocated to the source gNB-DU for Early TA acquisition PRACH resource information. The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0310] - The RRC reconfiguration message sent to the UE is provided in the form of an RRC container, and includes the configuration information of the LTM switching, including the candidate cell configuration information and / or the PRACH resource information. The specific information of the RRC reconfiguration message is shown in step 305, which will not be repeated here.

[0311] -Candidate cell indication, indicating whether the source cell is used as the LTM candidate cell of the UE for subsequent LTM handover.

[0312] The source gNB-DU can proactively allocate the obtained PRACH resources to the cell in the source gNB-DU, or the source gNB-DU can allocate the PRACH resources of the candidate cell to the cell after receiving the resource request of the cell of the source gNB-DU, so that the cell of the source gNB-DU triggers the UE to perform the Early TA random access process in the candidate cell.

[0313] Steps 406-410 are the same as steps 306-310 and are not described here. The difference may be that before executing step 409a, the source gNB-DU may actively allocate the PRACH resources of the candidate cell to the source cell, or the source gNB-DU allocates the PRACH resources of the candidate cell to the source cell after receiving the resource request from the source cell, which is used to trigger the UE in the source cell to perform the Early TA random access process in the candidate cell.

[0314] When the candidate cell detects a random access code on the PRACH resource and determines the TA value, if the candidate cell adopts a node-level PRACH resource allocation method, the source gNB-DU or other gNB-DU is allocated PRACH resources for EarlyTA acquisition. The candidate cell can determine the gNB-DU using the PRACH resources based on the PRACH resources detected with the access code, and send the determined TA value and the PRACH resource information corresponding to the TA value to the gNB-DU using the PRACH resources.

[0315] In step 411, the candidate gNB-DU sends a third Early TA information transmission message to the gNB-CU, and sends the Early TA information (including the TA value and the PRACH resource information corresponding to the TA value) determined in step 410 to the gNB-CU. The third Early TA information transmission message may be a new message or a UE CONTEXT MODIFICATION REQUIRED message. The message may include at least one of the following information:

[0316] -First gNB-DU identifier (gNB-DU ID), indicating the gNB-DU identifier corresponding to the Early TA information (also called TA information). That is, the Preamble code is detected on the PRACH resources allocated to the first gNB-DU and the TA value is determined. That is, the gNB-DU identifier using the PRACH resources.

[0317] -TA information, including the TA value detected on the PRACH resources of the cell of the candidate gNB-DU. Since one or more cells in the candidate gNB-DU may allocate PRACH resources to the first gNB-DU, if the cell detects the Preamble code on the PRACH resources allocated to the first gNB-DU and determines the TA value, the information may include Early TA information (also called TA information) determined on the PRACH resources of one or more cells in the candidate gNB-DU. The TA information includes at least one of the following information:

[0318] ● A second cell identifier, indicating a cell to which PRACH resources are allocated, that is, indicating a cell to which PRACH resources of a TA value are detected. The cell identifier may be a CGI, or a PCI, or other cell identifiers.

[0319] ●PRACH resource scheduling information, PRACH resource information of which the Preamble code is detected, that is, PRACH resource information of which the TA value is detected. The content of the PRACH resource scheduling information is shown in the "PRACH resource scheduling information" of step 309b. No further details will be given here.

[0320] ●TA value, the TA value determined on the PRACH resource, that is, the TA value detected on the PRACH resource.

[0321] Assuming that cell A is a cell of gNB-DU, cell A may allocate PRACH resources for Early TA to multiple gNB-DUs (source gNB-DU or other gNB-DUs). If cell A detects the Preamble code on multiple PRACH resources (PRACH resources allocated to different gNB-DUs) and determines the TA value, the message will contain Early TA information of multiple gNB-DUs (gNB-DUs using PRACH resources), which are distinguished by the first gNB-DU identifier, that is, the gNB-DU identifier using PRACH resources.

[0322] In step 412, the gNB-CU sends a fourth Early TA information transmission message to the source gNB-DU. The gNB-CU sends TA information to the corresponding node (gNB-DU) according to the first gNB-DU identifier in the message of step 411. If the first gNB-DU identifier indicates the source gNB-DU, the gNB-CU sends the corresponding TA information to the source gNB-DU. The fourth Early TA information transmission message may be a new message or a UE CONTEXT MODIFICATION REQUEST message. The message may include at least one of the following information:

[0323] -TA information, including at least one of the following information:

[0324] ● A second cell identifier is used to indicate the cell on which the TA value is determined by the PRACH resources allocated by the cell, that is, to indicate the cell on which the PRACH resources of the TA value are detected. The cell identifier may be a CGI, or a PCI, or other cell identifiers.

[0325] ●PRACH resource scheduling information, PRACH resource information of which the Preamble code is detected, that is, PRACH resource information of which the TA value is detected. The content of the PRACH resource scheduling information is shown in the PRACH resource scheduling information of step 309b, which will not be described here.

[0326] ●TA value, the TA value determined on the PRACH resource, that is, the TA value detected on the PRACH resource.

[0327] Since the source gNB-DU may trigger the UE to perform a random access procedure for Early TA acquisition of a candidate cell and / or one or more candidate SCell cells when carrier aggregation is supported, the gNB-CU may obtain multiple TA information from the same gNB-DU, and each TA information contains the TA value detected by different cells in the PRACH resources.

[0328] Since the gNB-CU may also receive TA information sent to the source gNB-DU from other candidate gNB-DUs, the message may contain one or more TA information, and the multiple TA information come from different gNB-DUs (or different cells of different gNB-DUs).

[0329] The source gNB-DU determines the cell in the source gNB-DU that uses the PRACH resource of the second cell according to the second cell identifier and the PRACH resource information, that is, determines to which cell the source gNB-DU allocates the PRACH resource of the second cell, thereby determining the TA value to be sent to the cell that uses the PRACH resource of the second cell, and further determines the UE corresponding to the TA value by the cell that uses the PRACH resource. If it is determined that the PRACH resource is used by the source cell, the source cell determines the UE that uses the PRACH resource. In step 413, when the source cell selects the cell indicated by the second cell identifier as the target cell of the UE, the cell switching command or cell exchange command sent by the source cell to the UE includes the second cell identifier and the TA value. If carrier aggregation is supported, in step 413, when the cell indicated by the second cell identifier is selected as the target SCell cell of the UE, the cell switching command or cell exchange command sent by the source cell to the UE may also include the second cell identifier and the TA value.

[0330] Step 413: The source gNB-DU sends an LTM handover command to the UE, instructing the UE to perform a cell switch and switch to the target cell. The LTM handover command includes at least one of the following information:

[0331] -Cell ID, indicating the cell ID of the target cell for the UE to perform Cell switch, which can be PCI, CGI, or other cell IDs.

[0332] -TA value, which is the TA value used by the UE in the target cell. The TA value is the TA value obtained in step 412.

[0333] -PRACH resource information, PRACH resource information used by the UE for random access in the target cell.

[0334] If the TA value is not included in the LTM handover command, it indicates that the UE needs to obtain the uplink TA value of the target cell through a random access (RA) process. If the LTM handover command contains PRACH resource information, it indicates that the UE uses the resources to perform a non-contention-free random access process (CFRA) to obtain the TA value in the target cell; if the PRACH resource information is not included, the UE performs a contention-based random access process (CBRA) to obtain the uplink TA value of the target cell.

[0335] If carrier aggregation is supported and the source gNB-DU obtains the TA value of the UE on the target SCell, the handover command may also include at least one of the following information:

[0336] -SCell cell identifier, indicating the cell identifier of the target SCell of the UE. At this time, the cell identifier corresponds to the cell identifier of the target PCell or the target PSCell. The SCell cell identifier can be PCI, CGI, or other cell identifiers.

[0337] - Group ID, indicating the ID of the group to which the target SCell belongs.

[0338] -TA value, the TA value used by the UE in the target SCell cell, wherein the TA value is the TA value obtained in step 412.

[0339] If the UE has multiple target SCells and they do not belong to the same group, then multiple SCell cell identifiers and group identifiers will be included.

[0340] Steps 414-415 are the same as steps 314-315 and are not described again here.

[0341] In step 416, the target gNB-DU sends a message to the gNB-CU to indicate the target cell that the UE successfully accesses. The message may be an access success message (Access Success) or other messages. The message at least includes the target cell identifier. The target cell identifier may be a CGI, a PCI, or other cell identifiers.

[0342] When the UE accesses the target cell (assuming it is Cell2), the source cell may become the candidate cell of the UE, and the target cell (Cell2) becomes the new source cell of the UE, and gNB-DU2 becomes the new source gNB-DU of the UE. Cell2 schedules uplink and downlink resources to transmit UE service data. Then Cell2, as the source cell, will select a new target cell for the UE and instruct the UE to obtain the TA value of the candidate cell or the new target cell in advance (i.e., perform Early TA acquisition). Therefore, Cell2 needs to obtain the PRACH resource information of the candidate cell allocated to Cell2 from gNB-DU2 (i.e., the PRACH resources used for Early TA acquisition). There are two ways for gNB-DU2 to obtain the PRACH resource information allocated by the candidate cell:

[0343] Method 1: If in step 404, the PRACH resource information includes not only the PRACH resource information allocated by the candidate cell to the source gNB-DU, but also the PRACH resource information allocated by the candidate cell to other gNB-DUs (including gNB-DU2), then the gNB-CU obtains and stores the PRACH resource information allocated by each cell to the source gNB-DU and other gNB-DUs, and the PRACH resource information includes the PRACH resource information allocated by the candidate cell to gNB-DU2. Therefore, when the gNB-CU knows through step 416 that the UE has successfully accessed the target cell, it sends the PRACH resource information allocated by the candidate cell to gNB-DU2 to gNB-DU2, that is, executes step 419.

[0344] Method 2: Steps 417-419 can be used to enable gNB-DU2 to obtain the PRACH resource information for Early TA acquisition allocated by the candidate cell to gNB-DU2. Steps 417-419 can also be triggered after step 414, that is, when the gNB-CU knows that the source cell triggers the UE to perform LTM handover, the PRACH resource information for Early TA acquisition is prepared for the gNB-DU where the target cell is located.

[0345] Method 3: If in step 404, the message sent by the candidate gNB-DU to the gNB-CU contains PRACH resource information, the PRACH resource information includes not only the PRACH resource information allocated by the candidate cell to the source gNB-DU, but also the PRACH resource information allocated by the candidate cell to other gNB-DUs (including gNB-DU2). The gNB-CU receives and stores the PRACH resource information. When the gNB-CU knows through step 414 that the UE will switch to the target cell (belonging to gNB-DU2), it sends the PRACH resource information allocated by the candidate cell to gNB-DU2 to gNB-DU2, that is, directly executes step 414a.

[0346] In step 414a, the gNB-CU sends a message to gNB-DU2, where the message contains the PRACH resource information allocated to the target gNB-DU by other candidate cells. The PRACH resources can be used to obtain Early TA.

[0347] The message may be an LTM Cell change notification message sent by the CU to the DU, or other messages. The message is used by the gNB-CU to indicate to the target cell (target gNB-DU) that the UE will be handed over to the target cell. The message may include at least one of the following information:

[0348] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0349] -The F1 application protocol identifier assigned to the UE by the gNB-DU, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned to the UE by the candidate gNB-DU (gNB-DU2).

[0350] -Target cell identifier, indicating the target cell identifier to which the UE will switch, which can be CGI, PCI, or other cell identifiers.

[0351] -Candidate cell information, providing information of each candidate cell in the form of a list, which may include at least one of the following information:

[0352] ●Candidate cell identifier, the identifier of the LTM candidate cell of the UE. The candidate cell identifier may be a Cell Global ID (CGI), or a Physical Cell ID (PCI), or other cell identifiers. The cell indicated by the candidate cell identifier is the cell to which PRACH resources are allocated.

[0353] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0354] ●Group ID, indicating the ID of the group to which the candidate cell belongs.

[0355] ●PRACH resource information, the PRACH resource information for Early TA acquisition allocated by the candidate cell to the new source gNB-DU (that is, allocated to candidate gNB-DU2). The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0356] - Information sent to the target cell, which the source cell sends to the gNB in ​​step 414 -

[0357] CU, gNB-CU forwards to the target cell. The relevant description and function of the information can be found in the content of "Information sent to the target cell" in step 419, which will not be repeated here.

[0358] Through step 414a, gNB-DU2 obtains the PRACH resource information for Early TA acquisition allocated by the candidate cell to gNB-DU2, and allocates it to the cell in gNB-DU2, so that the cell in gNB-DU2 triggers the Early TA acquisition process and obtains the TA value of the UE in the candidate cell in advance. Optionally, gNB-DU2 can actively allocate the PRACH resources of the candidate cell to the cell in gNB-DU2, or gNB-DU2 allocates the PRACH resources of the candidate cell to the cell after receiving the resource request of the cell in gNB-DU2.

[0359] Steps 417-419 are described as follows.

[0360] In step 417, the gNB-CU sends messages to the candidate gNB-DUs (gNB-DU1 and gNB-DU3) respectively, instructing Cell1 and Cell3 to allocate PRACH resources for Early TA acquisition to gNB-DU2 where Cell2 is located. The message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages. The message may include at least one of the following information:

[0361] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0362] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0363] -Candidate cell identifier, indicating the identifier of the candidate cell of the UE, which may be a CGI (Cell Global ID), or a PCI, or other identifiers. The cell indicated by the candidate cell identifier is the cell to which the PRACH resources are allocated.

[0364] -PRACH resource request indication, instructing the candidate cell to allocate PRACH resources for Early TA acquisition.

[0365] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU requesting the allocation of PRACH resources, that is, the identifier of the gNB-DU using PRACH resources, that is, the identifier of the gNB-DU to which PRACH resources are allocated. The gNB-DU may be the source gNB-DU where the UE is located (that is, the gNB-DU to which the source cell where the UE is located belongs) or other gNB-DU. The cell indicated by the candidate cell identifier will allocate PRACH resources to the gNB-DU indicated by the gNB-DU identifier for Early TA acquisition on the candidate cell. Therefore, the gNB-DU indicated by the gNB-DU identifier is the gNB-DU to which PRACH resources are allocated (or the gNB-DU using PRACH resources). If PRACH resources need to be requested for the source gNB-DU and / or one or more other gNB-DUs, multiple gNB-DU identifiers will be provided in the form of a list.

[0366] For the node-level PRACH resource allocation method, after receiving the message, the candidate gNB-DU uses the cell indicated by the candidate cell identifier as the LTM candidate cell of the UE, indicating that in addition to providing cell configuration information for the UE, the candidate cell also needs to allocate PRACH resources to the gNB-DU indicated by the gNB-DU identifier for Early TA acquisition.

[0367] In step 418, the candidate gNB-DU (gNB-DU1 and gNB-DU3) sends a message to the gNB-CU for the candidate gNB-DU to provide candidate cell configuration information. The message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages. The message may include at least one of the following information:

[0368] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0369] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0370] - The requested candidate cell identifier is the LTM candidate cell identifier in step 417, which may be a CGI (Cell Global ID), or a PCI, or other identifiers. The cell indicated by the requested candidate cell identifier is the cell to which PRACH resources are allocated.

[0371] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the requested candidate cell is located.

[0372] - Group ID, indicating the ID of the group to which the requested candidate cell belongs.

[0373] The cells within the same gNB-DU are grouped, that is, the cells are grouped independently within each gNB-DU.

[0374] -PRACH resource information, indicating the PRACH resource information for Early TA allocated by the requested candidate cell to the new source gNB-DU. The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0375] In step 419, the gNB-CU sends a message to gNB-DU2 to send the LTM candidate cell configuration information to gNB-DU2 (target cell Cell2 / new source cell Cell2). The message may be a downlink RRC message transmission message (DL RRC MESSAGETRANSFER), or a UE CONTEXT MODIFICATION REQUEST message, or a UE successful access indication message, or other messages. The message may include at least one of the following information:

[0376] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0377] -The F1 application protocol identifier assigned to the UE by the gNB-DU, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned to the UE by the gNB-DU2.

[0378] -Candidate cell information, providing information of each candidate cell in the form of a list, which may include at least one of the following information:

[0379] ●Candidate cell identifier, the identifier of the LTM candidate cell of the UE. The candidate cell identifier may be a Cell Global ID (CGI), or a Physical Cell ID (PCI), or other cell identifiers. The cell indicated by the candidate cell identifier is the cell to which PRACH resources are allocated.

[0380] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0381] ●Group ID, which indicates the group to which the candidate cell belongs. Cells in the same gNB-DU are grouped, that is, cells are grouped independently in each gNB-DU.

[0382] ●PRACH resource information, the PRACH resource information for Early TA acquired by the candidate cell allocated to the new source gNB-DU (that is, allocated to candidate gNB-DU2). The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0383] -Information sent to the target cell, the source cell sends the information to the gNB-CU through step 414, and the gNB-CU forwards it to the target cell. See step 414 for specific information. The target cell can obtain the uplink synchronization related information between the UE and the candidate cell, such as the TA value, the timer TAT value and the timer TAT length, based on the "information sent to the target cell" sent by the source cell, so as to determine the uplink synchronization status between the UE and each candidate cell. If the information sent to the target cell contains the TA value, it means that the UE has achieved uplink synchronization with the cell indicated by the candidate cell identifier, and the effective duration of the TA value (that is, when the TA value expires) is determined by the TAT value and the TAT length. If the TA value is not included, it means that the UE and the cell indicated by the candidate cell identifier are not uplink synchronized. At the same time, according to the grouping identifier, it can be determined whether the UE has the same timing relationship with multiple cells (that is, whether uplink synchronization is completed). Therefore, when the target cell is preparing for LTM handover for the UE and needs to obtain the TA value of the candidate cell in advance, the uplink synchronization status of the UE and each candidate cell can be determined according to the information in the "information sent to the target cell", so as to decide whether it is necessary to trigger the process of obtaining the TA value in advance for the corresponding candidate cell. In this way, unnecessary Early TA acquisition process of the UE on the target side can be avoided.

[0384] After gNB-DU2 obtains the PRACH resource information for Early TA acquired by the candidate cell allocated to gNB-DU2 through steps 417-419, gNB-DU2 actively allocates the PRACH resources of the candidate cell to the cell in gNB-DU2, or gNB-DU2 allocates the PRACH resources of the candidate cell to the cell after receiving the resource request of the cell in gNB-DU2, so as to trigger the UE in the cell to perform the random access process of Early TA in the candidate cell.

[0385] See also Figure 6 , Figure 6 is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0386] In this embodiment, when the network prepares to trigger LTM, when performing candidate cell configuration (candidate cell preparation), the candidate cell (cell A) allocates PRACH resources for Early TA acquisition, and sends the PRACH resource information to the gNB-CU. The gNB-CU decides how to allocate the received PRACH resources of cell A to other cells (i.e., cells using the PRACH resources) or other gNB-DUs (i.e., nodes using PRACH resources).

[0387] - If the gNB-CU allocates the received PRACH resources of cell A to other cells, that is, adopts the cell-level resource allocation method, then other cells receive the received PRACH resources from gNB-

[0388] The CU obtains PRACH resources and dynamically allocates them to the UE it serves, so that the UE performs Early TA acquisition, thereby obtaining the TA value of the UE in the cell A.

[0389] -If the gNB-CU allocates the received PRACH resources of the cell A to other gNB-DUs, that is, adopts the node-level resource allocation method, then the other gNB-DUs dynamically allocate the PRACH resources allocated to them to the cells in the other gNB-DUs, so that the cells in the other gNB-DUs are dynamically allocated to the UEs they serve, so that the UEs can perform the Early TA acquisition process and obtain the TA value of the UE in the cell A.

[0390] The PRACH resources used for Early TA acquisition in cell A are allocated to other cells or other gNB-DUs through the gNB-CU (other gNB-DUs are allocated to cells in the other gNB-DUs). Different UEs in other cells or different UEs in cells in other gNB-DUs share the PRACH resources, thereby improving the utilization of PRACH resources.

[0391] In this embodiment, the method of allocating PRACH resources to the source cell is as follows: in the LTM candidate cell preparation phase of the UE, the candidate cell not only establishes a communication context for the UE and allocates resources for the service bearer of the UE, but also allocates PRACH resource information for Early TA acquisition for the random access process of Early TA acquisition. In this embodiment, the PRACH resource information allocated by the candidate cell for Early TA acquisition is sent to the gNB-CU through UE-associated signaling. The gNB-CU then allocates the obtained PRACH resources for Early TA acquisition to other cells (including the source cell) or other gNB-DUs (including the source gNB-DU). If the node-level resource allocation method is adopted, the gNB-DU dynamically allocates the received PRACH resources to the cell of the gNB-DU. After the source cell obtains the PRACH resources, it will be allocated to the UE in the source cell for the UE to trigger the Early TA acquisition process on the candidate cell.

[0392] The specific process of the PRACH resource allocation method provided in this embodiment is as follows: Figure 6 As shown. Figure 6As shown, the PRACH resource allocation method provided in this embodiment may include one or more steps from step S501 to step S517. The detailed description of each step is as follows

[0393] Steps 501 and 502 are the same as steps 301-302 and will not be described again here.

[0394] In step 503, the gNB-CU sends messages to the candidate gNB-DUs (gNB-DU2 and gNB-DU3) respectively, indicating that the cells in gNB-DU2 and gNB-DU3 are used as candidate cells for the UE, for example, cell 2 and cell 3. gNB-DU2 and gNB-DU3 are requested to provide the UE with configuration information of Cell2 and Cell3. The message may be a UE CONTEXTSETUP REQUEST message, or other messages. The message may include at least one of the following information:

[0395] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0396] -Candidate cell identifier, the identifier of the candidate cell of the UE. If it is an LTM system, it is the identifier of the LTM candidate cell. The identifier can be CGI (Cell Global ID), or PCI, or other identifiers. If the candidate cell needs to allocate PRACH resources to the source cell and / or other cells for Early TA acquisition and / or for ordinary random access procedures, the candidate cell is the cell that allocates PRACH resources.

[0397] If carrier aggregation is supported, the candidate cell identifiers will be provided in a list, including candidate PCell and / or candidate PSCell), and candidate SCell (Secondary Cell) cell identifiers. The candidate SCell cell identifier can be CGI (Cell Global ID), or PCI, or other identifiers. If the candidate SCell cell needs to allocate PRACH resources to the source gNB-DU and / or other gNB-DU for Early TA acquisition and / or for normal random access procedures, then the candidate SCell cell is the cell that allocates PRACH resources.

[0398] -LTM handover indication, indicating that this process is to configure candidate cells for LTM handover of UE.

[0399] -PRACH resource request indication, instructing the candidate cell to allocate PRACH resources for Early TA acquisition and / or for normal random access process.

[0400] After receiving the message, the candidate gNB-DU takes the cell indicated by the candidate cell identifier as the candidate cell of the UE, indicating that in addition to providing cell configuration information for the UE, the candidate cell also needs to allocate PRACH resources for Early TA acquisition.

[0401] In step 504, the candidate gNB-DU (gNB-DU2 and gNB-DU3) sends a message to the gNB-CU, which is used by the candidate gNB-DU to provide candidate cell configuration information and PRACH resource-related information. The PRACH resource-related information includes at least one of the following information: the cell identifier of the allocated PRACH resource, the node where the cell allocated PRACH resource is located, and the allocated PRACH resource information. The message can be a UE CONTEXT SETUP RESPONSE message, or other messages. The message can include at least one of the following information:

[0402] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0403] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0404] - The requested candidate cell identifier is the identifier of the candidate cell of the UE in step 503. The identifier may be a CGI (Cell Global ID), or a PCI, or other identifiers. The cell indicated by the requested candidate cell identifier is the cell to which the PRACH resources are allocated.

[0405] -gNB-DU ID, indicating the ID of the gNB-DU where the candidate cell of the request is located, that is, the ID of the candidate gNB-DU. The cells in the same gNB-DU are grouped, that is, the cells are grouped independently in each gNB-DU.

[0406] -Group ID, indicating the ID of the group to which the requested candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0407] -PRACH resource information, indicating the PRACH resource information allocated by the requested candidate cell for Early TA acquisition and / or for normal random access process. The PRACH resource is sent to the gNB-CU and allocated by the gNB-CU to other cells or other nodes. The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0408] -BWP information, indicating the frequency domain position of the BWP (indicating the starting point of the BWP) and the bandwidth.

[0409] - Uplink frequency information, including carrier bandwidth, subcarrier spacing, and carrier offset value (offsetToCarrier). The carrier offset value indicates the starting point of the PRB actually used by the carrier.

[0410] - DU to CU RRC Information, including candidate cell configuration information and / or PRACH resource information. See step 304 for related description, which will not be repeated here.

[0411] If carrier aggregation is supported, the requested candidate cell (including candidate PCell and / or candidate PSCell and / or candidate SCell) configuration information will be provided in the form of a list, including at least one of the following information, and the specific information is described as above:

[0412] -The requested candidate cell identifier may be the cell identifier of a candidate PCell, a candidate PSCell or a candidate SCell.

[0413] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the requested candidate cell is located.

[0414] -Group ID, indicating the ID of the group to which the requested candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0415] -PRACH resource information (list), indicating the PRACH resource (PRACH resource) information allocated by the requested candidate cell for Early TA acquisition and / or for a normal random access procedure.

[0416] The role of the group identifier (Group ID) is described in step 304 and will not be repeated here. The information of the PRACH resources allocated to the requested candidate cell is provided through UE-related signaling, such as through a UE context establishment response message sent to the gNB-CU. The PRACH resources allocated to the requested candidate cell are not dedicated to the UE, but are allocated by the gNB-CU to the corresponding cell or gNB-DU.

[0417] In step 505a, the gNB-CU obtains the PRACH resources allocated by each candidate cell for Early TA acquisition through step 504. The gNB-CU will decide how to allocate the received PRACH resources of each cell. The allocation can be performed using a cell-level resource allocation method or a node-level resource allocation method. The gNB-CU needs to ensure that different PRACH resources (PRACH resources here refer to the PRACH resources allocated by the same candidate cell) are allocated to different cells or different gNB-DUs to avoid conflicts in the use of PRACH resources. If the gNB-CU uses a node-level resource allocation method to allocate the PRACH resources of the candidate cell to different gNB-DUs, then each gNB-DU will reallocate the received PRACH resources to the cells within the gNB-DU.

[0418] The gNB-CU sends the PRACH resources for Early TA acquisition allocated to the source cell or source gNB-DU to the source gNB-DU through step 505.

[0419] In step 505, the gNB-CU sends a message to the source gNB-DU, sending the candidate cell configuration information and PRACH resource-related information to the source gNB-DU (or source cell). If carrier aggregation is supported, the candidate cell configuration information includes the configuration information of the candidate PCell and / or candidate PSCell and / or candidate SCell. The PRACH resource-related information includes at least one of the following information: the cell identifier of the allocated PRACH resources, the node where the cell where the PRACH resources are allocated is located, the allocated PRACH resource information, the node identifier of the allocated PRACH resources, and the cell identifier of the allocated PRACH resources. The message may be a downlink RRC message transfer message (DL RRC MESSAGE TRANSFER), or a UE context modification request message (UE CONTEXT MODIFICATION REQUEST), or other messages. The message may include at least one of the following information:

[0420] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0421] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the source gNB-DU to the UE.

[0422] -LTM switching indication, indicating that the gNB-DU can use the LTM switching mechanism to adjust the UE's cell. -Candidate cell information, providing information about each candidate cell in the form of a list, including information about the group to which the candidate cell belongs, and information about the PRACH resources that the candidate cell allocates to the source cell for Early TA acquisition. The candidate cell information may include at least one of the following information:

[0423] ●Candidate cell identifier, indicating the candidate cell identifier of the UE, which may be a global cell identifier (Cell Global ID, CGI), a physical cell identifier (Physical Cell ID, PCI), or other cell identifiers. The cell indicated by the candidate cell identifier is the cell to which PRACH resources are allocated. If carrier aggregation is supported, the candidate cell identifier may be the cell identifier of a candidate PCell, a candidate PSCell, or a candidate SCell.

[0424] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0425] ●Group ID to which the candidate cell belongs, indicating the ID of the group to which the candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0426] ●First PRACH resource information, PRACH resource information of the candidate cell. The PRACH resource is the PRACH resource allocated by the gNB-CU to the source cell or source gNB-DU, which is used for Early TA acquisition. If it is a PRACH resource allocated to the source gNB-DU, the source gNB-DU dynamically allocates the obtained PRACH resource to the cell in the source gNB-DU (including the source cell). The source gNB-DU can actively allocate the PRACH resources of the candidate cell to the cell in the gNB-DU, or allocate the PRACH resources of the candidate cell to the cell after receiving the resource request from the cell in the source gNB-DU. The first PRACH resource information may include at least one of the following information:

[0427] -Second PRACH resource information, PRACH resources of the candidate cell allocated by the gNB-CU.

[0428] -Cell ID, indicating the cell ID to which the second PRACH resource is allocated. The cell is a cell in the source gNB-DU. The cell ID is optional. If the message sent by the gNB-CU to the source gNB-DU does not include the cell ID, it means that the second PRACH resource is a resource allocated to the source gNB-DU.

[0429] The second PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0430] - The RRC reconfiguration message sent to the UE is provided in the form of an RRC container (RRC-Container), and includes the configuration information of the LTM switching. For specific information, see the "RRC reconfiguration message sent to the UE" in step 305, which will not be repeated here.

[0431] -Candidate cell indication, indicating whether the source cell is used as a candidate cell for the UE for subsequent LTM handover.

[0432] If the gNB-CU adopts the cell-level resource allocation method, steps 506-510 are the same as steps 306-310 and are not repeated here.

[0433] If the gNB-CU adopts a node-level resource allocation method, steps 506-510 are the same as steps 406-410 and are not repeated here.

[0434] In step 511, the candidate gNB-DU sends a first Early TA information transmission message to the gNB-CU, and sends the Early TA information (including the TA value and the PRACH resource information corresponding to the TA value) determined in step 510 to the gNB-CU. The first Early TA information transmission message may be a new message or a UE CONTEXT MODIFICATION REQUIRED message. The message may include at least one of the following information:

[0435] -TA information, including the TA value detected on the PRACH resource. The TA information includes at least one of the following information:

[0436] ●Cell ID, the cell ID of the cell in the candidate gNB-DU. Since there are multiple cells in the candidate gNB-DU, if the TA value is detected on the PRACH resources of one or more cells of the candidate gNB-DU, it is necessary to provide the cell ID where the PRACH resource for determining the TA value is located to indicate the cell where the TA value is detected. The cell ID can be CGI, PCI, or other cell IDs.

[0437] ●PRACH resource scheduling information, PRACH resource information of which the Preamble code is detected, that is, PRACH resource information of which the TA value is detected. The content of the PRACH resource scheduling information is shown in the PRACH resource scheduling information of step 309b, which will not be described here.

[0438] ●TA value, the TA value determined on the PRACH resource, that is, the TA value detected on the PRACH resource. The TA value determined by the candidate cell in step 510.

[0439] There are multiple candidate cells under the candidate gNB-DU, and each candidate cell may be allocated multiple PRACH resources for Eerly TA acquisition. If multiple candidate cells detect the Preamble code (or signal) on the corresponding PRACH resource and determine the corresponding TA value, the candidate gNB-DU may send multiple TA information (Early TA information) to the gNB-CU. Therefore, the message may contain the TA value on one or more PRACH resources of one or more candidate cells, which are distinguished by the cell identity and PRACH resource scheduling information.

[0440] In step 512a, the gNB-CU determines the identifier of the cell using the PRACH resources and / or the gNB-DU identifier according to the PRACH resources in step 510 and the allocation of the PRACH resources in step 504. If in step 504, the gNB-CU adopts a node-level resource allocation method, that is, the gNB-CU allocates the PRACH resources to each gNB-DU, then the gNB-CU will determine the gNB-DU using the PRACH resources, that is, determine the gNB-DU corresponding to the TA information, and send the relevant TA information to the gNB-DU through step 512. If in step 504, the gNB-CU adopts a cell-level resource allocation method, that is, the gNB-CU allocates the PRACH resources to each cell, then the gNB-CU will determine the cell using the PRACH resources (that is, the cell corresponding to the TA information) and the gNB-DU where the cell is located according to the PRACH resources in step 510, and send the relevant TA information and the cell identifier corresponding to the TA information to the gNB-DU through step 512.

[0441] Step 512: The gNB-CU sends a second Early TA information transmission message to the source gNB-DU. The first Early TA information transmission message may be a new message or a UE CONTEXT MODIFICATION REQUEST message. The message may include at least one of the following information:

[0442] - A first cell identifier, indicating the cell identifier corresponding to the TA information, that is, the cell identifier determined in step 512a. The cell identifier may be a CGI, a PCI, or other cell identifiers. If the TA information is provided to the source cell, the first cell identifier is the source cell identifier.

[0443] -TA information, which may include at least one of the following information:

[0444] ●The second cell identifier is used to indicate the cell on which the TA value is determined based on the PRACH resources allocated by the cell, that is, to indicate the cell on which the PRACH resources of the TA value are detected. If the first cell identifier is the source cell, then the second cell identifier indicates the cell on which the PRACH resources are allocated to the source cell. The cell identifier may be a CGI, or a PCI, or other cell identifiers.

[0445] ●PRACH resource scheduling information, PRACH resource information of the detected Preamble code, that is, PRACH resource information of the detected TA value. The content of the PRACH resource scheduling information is shown in the "PRACH resource scheduling information" in step 309b, which will not be repeated here.

[0446] ●TA value, the TA value determined on the PRACH resource, that is, the TA value detected on the PRACH resource.

[0447] Since the source gNB-DU may trigger the UE to perform a random access procedure for Early TA acquisition of a candidate cell and / or one or more candidate SCell cells when carrier aggregation is supported, the gNB-CU may obtain multiple TA information from the same gNB-DU, and each TA information contains the TA value detected by different cells in the PRACH resources.

[0448] Since the gNB-CU may also receive TA information sent to the cell indicated by the cell identifier (e.g., the source cell) from other candidate gNB-DUs, the message may contain multiple TA information, and the multiple TA information come from different gNB-DUs (or different cells of different gNB-DUs).

[0449] If the message does not contain the first cell identifier, the source gNB-DU determines the cell that uses the PRACH resources of the second cell based on the received second cell identifier and the PRACH resource information. Assuming that the cell is the source cell of the UE, the source gNB-DU sends the received TA information to the source cell. If the message contains the first cell identifier, assuming that the first cell identifier is the source cell identifier, the source gNB-DU sends the received TA information to the source cell.

[0450] The source cell determines the UE that uses the PRACH resource for random access in the second cell through the second cell identifier and the PRACH resource in the TA information, thereby determining the TA value of the UE in the second cell. In step 513, when the cell indicated by the second cell identifier is selected as the target cell of the UE to perform cell switching or cell exchange (Cell switch), the cell switching command or cell exchange command sent by the source cell to the UE includes the second cell identifier and the TA value. If carrier aggregation is supported, in step 513, when the cell indicated by the second cell identifier is selected as the target SCell cell of the UE, the cell switching command or cell exchange command sent by the source cell to the UE may also include the second cell identifier and the TA value.

[0451] Step 513: The source gNB-DU sends a handover command to the UE. In the LTM system, this is the LTM handover command (LTMCommand), which instructs the UE to perform a cell switch (Cell Switch) and switch to the target cell. The LTM handover command may include at least one of the following information:

[0452] -Cell ID, indicating the cell ID of the target cell for the UE to perform Cell switch, which can be PCI, CGI, or other cell IDs.

[0453] -TA value, which is the TA value of the UE in the target cell, that is, the TA value used by the UE when performing uplink transmission in the target cell. The TA value is the TA value obtained in step 512.

[0454] -PRACH resource information, PRACH resource information used by the UE for random access in the target cell.

[0455] If the TA value is not included in the LTM handover command, it indicates that the UE needs to obtain the uplink TA value of the target cell through a random access (RA) process. If the LTM handover command contains PRACH resource information, it indicates that the UE uses the resources to perform a non-contention-free random access process (CFRA) to obtain the TA value in the target cell; if the PRACH resource information is not included, the UE performs a contention-based random access process (CBRA) to obtain the uplink TA value of the target cell.

[0456] If carrier aggregation is supported and the source gNB-DU obtains the TA value of the UE on the target SCell, the handover command may also include at least one of the following information:

[0457] -SCell cell identifier, indicating the cell identifier of the target SCell of the UE, in which case the cell identifier corresponds to the cell identifier of the target PCell or the target PSCell. The SCell cell identifier may be a PCI, a CGI, or other cell identifiers.

[0458] - Group ID, indicating the ID of the group to which the target SCell belongs.

[0459] -TA value, the TA value used by the UE in the target SCell cell, wherein the TA value is the TA value obtained in step 512.

[0460] If the UE has multiple target SCells and they do not belong to the same group, then multiple SCell cell identifiers and group identifiers will be included.

[0461] In step 514, the source gNB-DU sends an LTM cell change indication message (LTM Cell change notification) to the gNB-CU, indicating to the gNB-CU that the source cell instructs the UE to switch to the target cell through the LTM handover command. The specific content is the same as step 314 and will not be repeated here.

[0462] Step 515: The UE accesses the target cell and completes the Cell Switch. The specific content is the same as step 315 and will not be repeated here.

[0463] In step 516, the target gNB-DU sends a message to the gNB-CU to indicate the target cell that the UE successfully accesses. The message may be an access success message (Access Success) or other messages. The message at least includes the target cell identifier. The target cell identifier may be a CGI, a PCI, or other cell identifiers.

[0464] When the UE accesses the target cell (assuming it is Cell2), the target cell (Cell2) becomes the new source cell of the UE. Then Cell2, as the source cell, will select a new target cell for the UE and instruct the UE to obtain the TA value of the candidate cell or the new target cell in advance (i.e., perform Early TA acquisition). Therefore, Cell2 needs to obtain the PRACH resource information of the candidate cell allocated to Cell2. In step 517a, the gNB-CU determines the PRACH resources allocated to the candidate cell of Cell2, and through step 517, the gNB-CU will allocate PRACH resources to the UE's new source cell Cell2 or the gNB-DU2 where Cell2 is located. Step 517a is the same as step 505a and will not be repeated here.

[0465] In step 517, the gNB-CU sends a message to gNB-DU2 to send the candidate cell configuration information to gNB-DU2 (target cell Cell2 / new source cell Cell2). The message may be a downlink RRC message transmission message (DL RRC MESSAGETRANSFER), or a UE CONTEXT MODIFICATION REQUEST message, or other messages. The message may include at least one of the following information:

[0466] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0467] -The F1 application protocol identifier assigned to the UE by the gNB-DU, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned to the UE by the gNB-DU2.

[0468] -Candidate cell information, providing information of each candidate cell in the form of a list, which may include at least one of the following information:

[0469] ●Candidate cell identifier, indicating the candidate cell identifier of the UE, the candidate cell identifier may be a Cell Global ID (CGI), or a Physical Cell ID (PCI), or other cell identifiers. The cell indicated by the candidate cell identifier is the cell to which PRACH resources are allocated.

[0470] ●gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU where the candidate cell is located.

[0471] ●Group ID, indicating the ID of the group to which the candidate cell belongs. Cells within the same gNB-DU are grouped, that is, cells are grouped independently within each gNB-DU.

[0472] ●First PRACH resource information, PRACH resource information of the candidate cell. The PRACH resource is the PRACH resource allocated by the gNB-CU to the current source cell or the current source gNB-DU, which is used for Early TA acquisition. For a specific description, see "First PRACH Resource Information" in step 505, which will not be repeated here.

[0473] -Information sent to the target cell, the information is sent by the source cell to the gNB-CU in step 514, and the gNB-CU forwards it to the target cell. For detailed description, see 319, which will not be repeated here.

[0474] The gNB-CU determines and provides PRACH resources allocated to the candidate cell of Cell2, optionally after knowing that the UE will switch to the target cell, or after the UE accesses the target cell. That is, steps 517a-517 can be performed after step 514 or after step 516.

[0475] See also Figure 7 , Figure 7 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0476] The difference between this embodiment and the previous embodiment is that this embodiment uses a non-UE associated message to send the PRACH resource information to the gNB-CU. When the interface between the gNB-DU and the gNB-CU is established, or in other cases, the gNB-DU sends a non-UE associated message to the gNB-DU, which includes the PRACH resource allocation information of each cell in the gNB-DU.

[0477] When the gNB-CU receives the PRACH resources sent by the candidate cell, the gNB-CU decides how to allocate the received PRACH resources to other cells or other gNB-DUs, and sends the allocated resource information to the other cells or other gNB-DUs. The basic idea is the same as the previous embodiment and will not be repeated here.

[0478] In this embodiment, the method for allocating PRACH resources to the source cell of the UE is as follows: the candidate cell allocates PRACH resources for EarlyTA acquisition and sends the PRACH resource information to the gNB-CU through non-UE-associated signaling. The gNB-CU then sends the obtained RACH for Early TA acquisition to the source cell or other gNB-DU source gNB-DU.

[0479] - If the gNB-CU allocates the received PRACH resources of the candidate cell to other cells, that is, adopts the cell-level resource allocation method, then other cells receive the PRACH resources from the gNB-

[0480] After the CU obtains the PRACH resources, it dynamically allocates them to the UE it serves, so that the UE can perform the Early TA acquisition process and obtain the TA value of the UE in the cell A.

[0481] -If the gNB-CU allocates the PRACH resources to other gNB-DUs, that is, the node-level resource allocation method is adopted, then the other gNB-DU dynamically allocates the PRACH resources allocated to it to the cells in the other gNB-DUs (for example, according to factors such as the number of user equipments in the cell), so that the cells in the other gNB-DUs are dynamically allocated to the UEs they serve, so that the UEs can perform the Early TA acquisition process and obtain the TA value of the UE in the cell A.

[0482] The PRACH resources obtained by the candidate cell for Early TA are allocated to other cells or other gNB-DUs through the gNB-CU (other gNB-DUs are allocated to cells in the other gNB-DUs). Different UEs in other cells or cells in other gNB-DUs share the PRACH resources, thereby improving the utilization rate of PRACH resources.

[0483] The specific process of the PRACH resource allocation method provided in this embodiment is as follows: Figure 7 As shown. Figure 7 As shown, the PRACH resource allocation method provided in this embodiment may include one or more steps from step S601a to step S609. The detailed description of each step is as follows.

[0484] In step 601a, gNB-DU1 or gNB-DU2 sends a resource configuration information message to the gNB-CU, providing the gNB-CU with the PRACH resources allocated by the cell in gNB-DU1 or gNB-DU2. The message may be an F1 SETUPREQUEST message or a gNB-DU CONFIGURATION UPDATE message, or other messages. The message may include at least one of the following information:

[0485] -Cell ID, indicating the ID of the cell to which the PRACH resources are allocated. The cell is a cell in gNB-DU1 or gNB-DU2.

[0486] -PRACH resource information, the PRACH resource information allocated by the cell for Early TA. The PRACH resource is sent to the gNB-CU and allocated by the gNB-CU to other cells or other nodes. The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0487] Since there are multiple cells in gNB-DU1 or gNB-DU2, the resource configuration information message will include one or more groups of the above information, which will be distinguished by the cell identifier.

[0488] When the gNB-CU receives the PRACH resource information of each cell, the gNB-CU will decide how to allocate the PRACH resources. The allocation can be done using a cell-level resource allocation method or a node-level resource allocation method.

[0489] In step 601b, the gNB-CU sends a resource configuration information feedback message to gNB-DU1 or gNB-DU2, indicating that the resource configuration information has been received. The message may be an F1 SETUP RESPONSE message or a gNB-DU CONFIGURATION UPDATE ACKNOWLEDGE message, or other messages.

[0490] Step 602, handover configuration process, this step is the process of performing handover configuration according to the UE measurement result. The handover configuration process of this step is the same as steps 501-508, and will not be repeated here.

[0491] Steps 603-609 are the same as steps 509a-514 and will not be repeated here.

[0492] See also Figure 8 , Figure 8 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0493] In this embodiment, PRACH resources are allocated through OAM. In the OAM mode, OAM determines which resources of the cell that allocates PRACH resources are used for the PRACH resources acquired by Early TA, so the cell that allocates PRACH resources does not need to decide which resources are used for the PRACH resources acquired by Early TA. The PRACH resources will be allocated to other cells or other gNB-DUs, and the PRACH resources allocated to other cells or other gNB-DUs are different, thereby avoiding conflicts in the use of PRACH resources between cells, thereby affecting the determination of the TA value. Therefore, OAM will also determine the PRACH resources allocated to other cells or other gNB-DUs, and send the PRACH resource allocation information to the cell that allocates PRACH resources (that is, the cell that provides PRACH resources) and other cells or other gNB-DUs (that is, the cell that uses PRACH resources or the gNB-DU that uses PRACH resources).

[0494] At the same time, other cells also need to allocate resources to the cell that allocates PRACH resources, so that the UE in the cell that allocates PRACH resources can perform the Early TA acquisition process. Therefore, OAM also needs to decide the allocation of PRACH resources on other cells and the resource allocation method to be adopted, and send the PRACH resource information allocated by other cells to the PRACH resource cell.

[0495] In this embodiment, the allocation method of PRACH resources used for Early TA acquisition in the cell is changed from the allocation method of UE's dedicated PRACH resources to the allocation method of cell-level PRACH resources (called Cell-level PRACH resources) or node-level PRACH resources (called Node-level PRACH resources). Taking Cell1 (belonging to gNB-DU1) and Cell2 as examples, Cell2 is the cell that allocates PRACH resources, Cell1 is the cell that uses PRACH resources, and gNB-DU1 is the node that uses PRACH resources. OAM can allocate Cell2's PRACH resources to Cell1 according to the Cell-level PRACH resource allocation method; OAM can also allocate Cell2's PRACH resources to gNB-DU1 according to the Node-level PRACH resource allocation method, and gNB-DU1 allocates the PRACH resources to the cell in gNB-DU1 for use. The cell in Cell1 or gNB-DU1 allocates the obtained PRACH resources to the UE it serves, so that the UE can trigger the Early TA random access process on Cell1 and obtain the TA value of the UE on Cell2.

[0496] Since a Cell-level or Node-level PRACH resource allocation method is adopted, the PRACH resources are shared by different UEs in a cell using the PRACH resources, thereby improving the utilization rate of the PRACH resources.

[0497] The specific process of the PRACH resource allocation method provided in this embodiment is as follows: Figure 8 As shown. Figure 8 As shown, the PRACH resource allocation method provided in this embodiment may include one or more steps from step S701 to step S709. The detailed description of each step is as follows.

[0498] In step 701, OAM sends a resource configuration information message or other message to gNB-DU1 and gNB-DU2. This message is used by OAM to send PRACH resource allocation information of cells in gNB-DU to gNB-DU, as well as PRACH resource information allocated by other cells to cells in the gNB-DU or allocated to the gNB-DU. Since there are two PRACH resource allocation methods, namely, cell-level PRACH resource allocation method and node-level PRACH resource allocation method, the information contained in this message will be different from the PRACH resource allocation method.

[0499] If a cell-level PRACH resource allocation method is used, the message may include at least one of the following information. Since there are multiple cells in gNB-DU1 or gNB-DU2, the resource configuration information message may include one or more groups of the following information, which are distinguished by the third cell identifier.

[0500] -The third cell identifier is used to indicate the identifier of the cell to which PRACH resources are allocated, that is, the cell identifier that provides PRACH resources. In the figure, it indicates the cell identifier in gNB-DU1 or gNB-DU2. Since a gNB-CU manages one or more gNB-DUs, the cells in the gNB-DU are also the cells in the gNB-CU.

[0501] -PRACH resource allocation information may include the allocation of PRACH resources of the cell indicated by the third cell identifier to other cells. For example, it may include at least one of the following information:

[0502] ■ A fourth cell identifier, an identifier of a cell using PRACH resources, that is, an identifier of a cell using PRACH resources allocated by the third cell. The cell identifier may be a CGI, or a PCI, or other cell identifiers.

[0503] ■The fourth gNB-DU identifier indicates the identifier (gNB-DU ID) of the gNB-DU where the fourth cell is located.

[0504] ■ Fourth PRACH resource information, PRACH resource information allocated by the third cell to the fourth cell, used for UE in the fourth cell to obtain PRACH resources of the third cell TA value in advance. The fourth PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0505] -The received PRACH resource information may include PRACH resources for Early TA acquisition allocated by other cells to the cell indicated by the third cell identifier. For example, it may include at least one of the following information:

[0506] ■ A fifth cell identifier, an identifier of a cell to which PRACH resources are allocated, that is, an identifier of a cell to which PRACH resources are allocated for the third cell. The cell identifier may be a CGI, a PCI, or other cell identifiers.

[0507] ■Fifth gNB-DU identifier, identifier of the gNB-DU where the fifth cell is located (gNB-DU ID).

[0508] ■Fifth PRACH resource information, PRACH resource information allocated by the fifth cell to the third cell, used by the UE in the third cell to obtain the PRACH resource of the fifth cell TA value in advance. The fifth PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0509] If the node-level PRACH resource allocation method is adopted, the message includes at least one of the following information:

[0510] - Allocated resource information:

[0511] ■The third cell identifier indicates the identifier of the cell to which the PRACH resources are allocated, that is, the cell identifier that provides the PRACH resources. In this embodiment, it indicates the cell identifier in gNB-DU1 or gNB-DU2. The cell identifier may be CGI, PCI, or other cell identifiers.

[0512] ■PRACH resource allocation information, including the allocation of the PRACH resources of the third cell to other cells. It includes at least one of the following information:

[0513] ◆The fourth gNB-DU identifier indicates the identifier of the gNB-DU using the PRACH resources, that is, the identifier of the gNB-DU using the PRACH resources allocated by the third cell (gNB-DU ID).

[0514] ◆Fourth PRACH resource information, PRACH resource information allocated by the third cell to the fourth gNB-DU, used for the UE in the fourth gNB-DU to obtain the PRACH resource of the third cell TA value in advance. The fourth PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0515] Among them, since there are multiple cells in gNB-DU1 or gNB-DU2, the resource configuration information message may include one or more allocated resource information, which are distinguished by a third cell identifier.

[0516] -The received PRACH resource information may include PRACH resources allocated by other cells to gNB-DU (including gNB-DU1 and gNB-DU2) for Early TA acquisition. Taking gNB-DU1 in this embodiment as an example, it is the PRACH resources allocated by other cells (cells not in gNB-DU1) to gNB-DU1. For example, it may include at least one of the following information:

[0517] ■Fifth cell identifier, the identifier of the cell to which PRACH resources are allocated, that is, the identifier of the cell to which PRACH resources are allocated for the gNB-DU (in this embodiment, gNB-DU1 or gNB-DU2). The cell identifier may be CGI, PCI, or other cell identifiers.

[0518] ■Fifth gNB-DU identifier, identifier of the gNB-DU where the fifth cell is located (gNB-DU ID).

[0519] ■Fifth PRACH resource information, the PRACH resource information of the fifth cell allocated to the gNB-DU (in this embodiment, gNB-DU1 or gNB-DU2), which is allocated by the gNB-DU to the cell therein, and is used for the UE in the cell (i.e., the UE in the gNB-DU) to obtain the PRACH resource of the fifth cell TA value in advance. The fifth PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0520] Among them, since there are multiple cells in other gNB-DU that will allocate resources to gNB-DU1 or gNB-DU2, the resource configuration information message may include one or more received PRACH resource information, which are distinguished by the fifth cell identifier.

[0521] Step 702, switching configuration process. In the LTM system, it is LTM configuration, and this step is the LTM candidate cell configuration process of the UE, which is the same as the candidate cell configuration process of the UE in steps 301-308, and will not be repeated here. Since the transmission of the allocation information of the PRACH resources for Early TA acquisition has been completed in step 701 in this embodiment, the message corresponding to steps 303-305 in the LTM configuration will not need to include PRACH resource information.

[0522] If a cell-level PRACH resource allocation method is used, steps 703-709 are the same as steps 309a-314 and are not described in detail here.

[0523] If the node-level PRACH resource allocation method is adopted, steps 703-709 are the same as steps 409a-414 and are not described again here.

[0524] See also Fig. 9 , Fig. 9 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0525] In this embodiment, PRACH resources are allocated through OAM. In the OAM mode, OAM determines the PRACH resources (PRACH resources for short) used for Early TA acquisition for the cell that allocates PRACH resources, so the cell that allocates PRACH resources does not need to decide the PRACH resources for Early TA acquisition by itself. The difference between this embodiment six and the previous embodiment is that OAM determines the PRACH resources used for Early TA for each cell that allocates PRACH resources, sends the PRACH resource information to the gNB-CU, and the gNB-CU decides how to allocate the received PRACH resources to other Cells or other gNB-DUs. For example, OAM sends the PRACH resource information on Cell1, Cell2, and Cell3 to the gNB-CU.

[0526] If allocation method 1 (cell-level resource allocation method) is used, gNB-CU allocates PRACH resources on Cell1 to Cell2 and Cell3, allocates resources on Cell2 to Cell1 and Cell3, and allocates resources on Cell3 to Cell1 and Cell2. Cell1, Cell2, and Cell3 are in gNB-DU1, gNB-DU2, and gNB-DU3, respectively.

[0527] If allocation method 2 (node-level resource allocation method) is used, gNB-CU allocates PRACH resources on Cell1 to gNB-DU2 and gNB-DU3, allocates PRACH resources on Cell2 to gNB-DU1 and gNB-DU3, and allocates PRACH resources on Cell3 to gNB-DU1 and gNB-DU2.

[0528] By allocating PRACH resources to gNB-CU, conflicts caused by the same PRACH resources in the same cell being used by UEs in different cells can be avoided. At the same time, PRACH resources can be shared among UEs in the cell or UEs in gNB-DU, thereby improving resource utilization.

[0529] The specific process of the PRACH resource allocation method provided in this embodiment is as follows: Fig. 9 As shown. Fig. 9 As shown, the PRACH resource allocation method provided in this embodiment may include one or more steps from step S801a to step S809. The detailed description of each step is as follows.

[0530] Step 801a: OAM sends a first resource configuration information message or other message to the gNB-CU. This message is used by OAM to provide the gNB-CU with PRACH resource information for Early TA acquisition of each cell in the gNB-CU. The message may include PRACH resource information allocated by one or more cells, wherein the allocated PRACH resource information includes at least one of the following information:

[0531] - A first cell identifier, which is used to indicate the identifier of the cell to which the PRACH resources are allocated, that is, the identifier of the cell providing the PRACH resources. The cell identifier may be a CGI, or a PCI, or

[0532] It is another cell ID.

[0533] -PRACH resource information, PRACH resource information allocated by the first cell for Early TA acquisition. The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0534] The gNB-CU decides how to allocate the PRACH resources to other Cells or other gNB-DUs.

[0535] In step 801b, the gNB-CU sends a second resource configuration information message or other message to gNB-DU1, gNB-DU2, and gNB-DU3. The message is used by the gNB-CU to provide the gNB-DU (including gNB-DU1, gNB-DU2, and gNB-DU3) with the PRACH resource allocation information of the cells in the gNB-DU, as well as the PRACH resources allocated by other cells to the cells or the gNB-DU.

[0536] The gNB-CU may adopt a cell-level PRACH resource allocation method or a node-level PRACH resource allocation method. Under different resource allocation methods, the information contained in the second resource configuration information message is shown in step 701 and will not be repeated here.

[0537] Steps 802-809 are the same as steps 702-709 and are not described again here.

[0538] See also Fig.10, Fig.10 It is an interaction diagram of yet another PRACH resource allocation method according to various embodiments of the present disclosure.

[0539] In this example, the gNB-CU receives the PRACH resources of each cell sent by OMA, and the gNB-CU decides how to allocate the received PRACH resources to other cells or other gNB-DUs.

[0540] This embodiment and Figure 6 The difference of the embodiment shown is that Figure 6 In the embodiment shown, the PRACH resources of each cell obtained by the gNB-CU are determined by each cell itself and sent to the gNB-CU. In this embodiment, the PRACH resources of each cell are determined by OAM and sent to the gNB-CU. Basic idea and the way gNB-CU allocates PRACH and Figure 6 The embodiments shown are the same and will not be described again here.

[0541] The specific process of the PRACH resource allocation method provided in this embodiment is as follows: Fig.10 As shown. Fig.10 As shown, the PRACH resource allocation method provided in this embodiment may include one or more steps from step S901 to step S909. The detailed description of each step is as follows.

[0542] Step 901: OAM sends a resource configuration information message to the gNB-CU, providing the gNB-CU with the PRACH resources allocated to each cell. The message includes at least one of the following information:

[0543] -Cell ID, indicating the ID of the cell to which the PRACH resources are allocated. The cell is a cell in the gNB-CU.

[0544] -PRACH resource information, the PRACH resource information allocated by the cell for Early TA. The PRACH resource is sent to the gNB-CU and allocated by the gNB-CU to other cells or other nodes. The PRACH resource information includes at least time domain related parameters or information, frequency domain related parameters or information, and Preamble code and other information. For specific information and description, see "PRACH resource information" in step 304, which will not be repeated here.

[0545] Since there are multiple cells in the gNB-CU, the resource configuration information message will include one or more groups of the above information, which will be distinguished by the cell identifier.

[0546] When the gNB-CU receives the PRACH resource information of each cell, the gNB-CU will decide how to allocate the PRACH resources. The allocation can be done using a cell-level resource allocation method or a node-level resource allocation method.

[0547] Step 902, handover configuration process, this step is the process of performing handover configuration according to the UE measurement result. The handover configuration process of this step is the same as steps 501-508, and will not be repeated here.

[0548] Steps 903-909 are the same as steps 509a-514 and will not be repeated here.

[0549] Please refer to Fig.12 , Fig.12 is an interaction diagram of another PRACH resource allocation method according to various embodiments of the present disclosure.

[0550] Fig.12 The design concept and Figure 5 The embodiments shown are the same, and the main difference lies in the timing of configuring PRACH resources for other candidate gNB-DUs on the candidate cell. There are two schemes for the timing of configuring PRACH resources for other candidate gNB-DUs on the candidate cell. Among them, scheme 1 allocates PRACH resources to other candidate gNB-DUs while configuring each candidate cell, and scheme 2 allocates PRACH resources to other candidate gNB-DUs after completing the configuration of all candidate cells.

[0551] exist Figure 5 The illustrated embodiment adopts scheme 1 to allocate PRACH resources for candidate gNB-DUs. The configuration of the candidate cell (e.g., Cell3, belonging to gNB-DU3) is completed through steps 403-404, and the candidate cell (Cell3) allocates PRACH resources to other candidate gNB-DUs (e.g., gNB-DU2). In step 403, when the gNB-CU sends a request to the candidate gNB-DU3 to provide the candidate cell (Cell3, belonging to gNB-DU3) configuration for the UE, it may also provide the identifier of the gNB-DU requesting the candidate cell (Cell3) to allocate PRACH resources, which may include other candidate gNB-DU identifiers, such as gNB-DU2, in addition to the source gNB-DU identifier. In step 404, the candidate gNB-DU3 provides the gNB-CU with the UE candidate cell configuration information and the PRACH resource information allocated to the candidate cell, including the resource information allocated to each gNB-DU requesting PRACH resources, including the PRACH resources allocated to the source gNB-DU, and may also include the PRACH resources allocated to other candidate gNB-DUs.

[0552] Fig.12 The embodiment shown adopts scheme 2 to allocate PRACH resources to the candidate gNB-DU. The specific process of the PRACH resource allocation method provided in this embodiment is as follows Fig.12 As shown. Fig.12 As shown, the PRACH resource allocation method provided in this embodiment may include one or more steps from step S1101 to step S1117. Steps 1103-1104 are used to configure the candidate cell (e.g., Cell3) and the candidate cell (Cell3) configures PRACH resources for the source gNB-DU, and steps 1105a-1105b are used to configure PRACH resources for other candidate gNB-DUs by the candidate cell (e.g., Cell3). The detailed description of each step is as follows.

[0553] Steps 1101-1102 are the same as steps 401-402 and are not described again here.

[0554] The difference between step 1103 and step 403 is the content of the gNB-DU identification information. Step 1103 only contains the source gNB-DU identification of the UE, as shown below. The other information content in step 1103 is the same as that in step 403, and the same content is not repeated here.

[0555] -gNB-DU identifier (gNB-DU ID), the identifier of the gNB-DU requesting the allocation of PRACH resources, that is, the identifier of the gNB-DU to which the PRACH resources are allocated. The gNB-DU is the source gNB-DU where the UE is located.

[0556] The difference between step 1104 and step 404 is the PRACH resource information. Step 1104 only contains the PRACH resource information of the source gNB-DU where the candidate cell is allocated to the UE, as shown below. The other information in step 1104 is the same as step 404 and will not be repeated here.

[0557] -PRACH resource information, indicating the PRACH resource (PRACH resource) information allocated by the requested candidate cell for Early TA acquisition and / or for normal random access process. The gNB-DU identifier only includes the source gNB-DU identifier and does not include other gNB-DU identifiers.

[0558] -gNB-DU identifier (gNB-DU ID), indicating the identifier of the gNB-DU to which the PRACH resources are allocated. The identifier of the gNB-DU is the source gNB-DU identifier where the UE is located.

[0559] Other information included in the PRACH resource information is the same as that in step 404 and will not be described again here.

[0560] In step 1105a, gNB-CU sends a message to gNB-DU2 and gNB-DU3, requesting candidate cell Cell2 (belonging to gNB-DU2) to allocate PRACH resources to other candidate gNB-DUs (e.g., gNB-DU3), and requesting candidate cell Cell3 (belonging to gNB-DU3) to allocate PRACH resources to other candidate gNB-DUs (e.g., gNB-DU2). The specific content of the message is the same as step 403 and is not repeated here. The message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages.

[0561] In step 1105b, gNB-DU2 and gNB-DU3 send a message to gNB-CU, respectively sending the PRACH resource information of the candidate cell (Cell2) of gNB-DU2 and the candidate cell (Cell3) of gNB-DU3 allocated to other candidate gNB-DUs to gNB-CU. The specific content of the message is the same as step 404 and is not repeated here. The message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages.

[0562] Steps 1105-1114 are the same as steps 405-414 and are not repeated here.

[0563] There are two methods for the target gNB-DU (e.g., gNB-DU2) to obtain the PRACH resource information of the candidate cell:

[0564] Method 1: Through steps 1104-1105b, the gNB-CU obtains and stores the PRACH resource information allocated by each cell to the source gNB-DU and other gNB-DUs. The PRACH resource information includes the PRACH resource information allocated by the candidate cell to gNB-DU2. Therefore, when the gNB-CU knows through step 1116 that the UE has successfully accessed the target cell, it sends the PRACH resource information allocated by the candidate cell to gNB-DU2 to gNB-DU2, that is, executes step 1117.

[0565] Method 2: Through steps 1104-1105b, the gNB-CU obtains and stores the PRACH resource information allocated by each cell to the source gNB-DU and other gNB-DUs. The PRACH resource information includes the PRACH resource information allocated by the candidate cell to gNB-DU2. Therefore, when the gNB-CU knows through step 1114 that the UE will switch to the target cell (the target cell belongs to gNB-DU2), the PRACH resource information allocated by the candidate cell to gNB-DU2 is sent to gNB-DU2, that is, step 1114a is directly executed.

[0566] Step 1114a is the same as step 414a and will not be repeated here.

[0567] Steps 1115-1116 are the same as steps 415-416 and will not be repeated here.

[0568] Step 1117 is the same as step 419 and will not be described again here. The information sent by the gNB-CU to the gNB-DU2 in step 1117 is obtained through steps 1103-1105b and / or steps 1111 and / or 1114, or is formed based on the obtained information.

[0569] The present disclosure provides a method for setting a candidate cell grouping identifier (setting method one).

[0570] The gNB-CU can obtain the cell grouping identifier of the candidate cells in each gNB-DU through OAM or other methods, or obtain the synchronization relationship between cells within the gNB-DU. If different cells have the same synchronization relationship, different cells can use the same TA. In the same gNB-DU, the same cell grouping identifier can be set for cells with the same TA. When the gNB-CU determines to trigger LTM switching, it sets (or allocates) the grouping identifier of the candidate cells in each gNB-DU, and sends the set candidate cell grouping identifier and the gNB-DU identifier to which the candidate cell belongs to the source gNB-DU and the candidate gNB-DU respectively through steps 1204a and 1203. See the specific process for details. Fig.13 , the specific description is as follows. As mentioned above, the group identifier may also use other identifiers, such as "using the same TA identifier", or other identifiers, and the present invention is not limited thereto. For the convenience of description, the present disclosure uniformly uses group identifiers for illustration.

[0571] Step 1201 is the same as step 401 and will not be described again here.

[0572] Step 1202, gNB-CU decides to trigger the handover configuration according to the measurement report and performs candidate cell configuration. gNB-CU selects candidate cells for UE according to the measurement results (in the LTM system, it is the LTM candidate cell). For example, gNB-CU selects 7 candidate cells Cell1-Cell7, Cell1-Cell2 belongs to gNB-DU1, Cell3-Cell4 belongs to gNB-DU2, and Cell5-Cell7 belongs to gNB-DU3. If Cell1 and Cell2 in gNB-DU1 cannot use the same TA, the group identifiers of Cell1 and Cell2 are set to 1 and 2 respectively, Cell3 and Cell4 in gNB-DU2 can use the same TA, then the group identifiers of Cell3 and Cell4 are set to 1 and 1 respectively, Cell6 and Cell7 in gNB-DU3 can use the same TA, but Cell5 and Cell6, Cell7 cannot use the same TA, then the group identifiers of Cell5-Cell7 are set to 1, 2 and 2 respectively. The gNB-CU sends the group identifiers of all candidate cells and the gNB-DU identifiers where the candidate cells are located to the source gNB-DU and the candidate gNB-DU.

[0573] Step 1203: The gNB-CU sends a message to each candidate gNB-DU. The message may be a UE CONTEXT SETUP REQUEST message or other message. The message may include at least one of the following information:

[0574] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0575] -Candidate cell identifier, the identifier of the requested candidate cell. The identifier may be CGI, PCI, or other identifiers.

[0576] - Group ID: the group ID of the candidate cells in the request.

[0577] -LTM handover indication, indicating that this process is to configure candidate cells for LTM handover of UE.

[0578] -PRACH resource request indication, indicating that the candidate cell allocates PRACH resources for Early TA acquisition and / or for ordinary random access process. If the resource allocation request indication exists, it means that the candidate cell needs to perform PRACH resource allocation. If the resource allocation request indication does not exist, it means that PRACH resource allocation is not required.

[0579] -Candidate cell list, including information of one or more candidate cells. It includes information of all candidate cells. The information includes at least one of the following information:

[0580] ●Cell identifier, which can be CGI, PCI, or other identifiers.

[0581] ●Group ID.

[0582] ●gNB-DU identifier (gNB-DU ID), the identifier of the gNB-DU to which the candidate cell belongs.

[0583] In step 1204, the candidate gNB-DU sends a message to the gNB-CU to provide the requested candidate cell configuration information and PRACH resource related information. The message may be a UE CONTEXT SETUP RESPONSE message, or other message. The message may include the content shown in step 404.

[0584] In step 1204a, the gNB-CU sends a message to the source gNB-DU (gNB-DU1) to provide candidate cell information. If a cell in the source gNB-DU is selected as a candidate cell, the source gNB-DU is requested to provide the requested candidate cell information through the message. The message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages. The message may include at least one of the following information:

[0585] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0586] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the source gNB-DU to the UE.

[0587] -LTM switching indication, indicating that the gNB-DU can use the LTM switching mechanism to adjust the UE's cell.

[0588] -Candidate cell identifier, the identifier of the requested candidate cell. The identifier can be CGI, PCI, or other identifiers. The candidate cell identifier is optional. If the candidate cell selected by the gNB-CU includes the cell in the source gNB-DU, the message contains the candidate cell identifier and the group identifier of the candidate cell.

[0589] - Group ID: the group ID of the candidate cells in the request.

[0590] -Candidate cell list, including information of one or more candidate cells. It includes information of all candidate cells. The information includes at least one of the following information:

[0591] ●Cell identifier, which can be CGI, PCI, or other identifiers.

[0592] ●Group ID.

[0593] ●gNB-DU identifier (gNB-DU ID), the identifier of the gNB-DU to which the candidate cell belongs.

[0594] ●PRACH resource information, the PRACH resource information for Early TA acquired by the candidate cell allocated to the source cell. For specific information and description, see "PRACH resource information" in step 404, which will not be repeated here. The PRACH resource information is optional. If the cell corresponding to the cell identifier is the cell of the source gNB-DU, the PRACH resource information is not included.

[0595] In step 1204b, the source gNB-DU sends a message to the gNB-CU. The message includes candidate cell configuration information for providing the request and information related to PRACH resources. The message may be a UE CONTEXT MODIFICATION RESPONSE message, or other message. The message may include at least one of the following information:

[0596] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0597] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0598] - The requested candidate cell identifier is the candidate cell identifier in step 1204a. The identifier may be a CGI, a PCI, or other identifiers.

[0599] -PRACH resource information (list), see step 304 for a detailed description.

[0600] -DU to CU RRC Information, including candidate cell configuration information and / or PRACH resource information.

[0601] Steps 1204c-1204d, if the requested candidate cell has changed, the updated candidate cell information is sent to the candidate cell through the steps, for example, including the candidate cell information in the source gNB-DU.

[0602] Step 1204c: The gNB-CU sends a message to the candidate gNB-DU (gNB-DU2 / DU3). The message may be a UE CONTEXT MODIFICATION REQUEST message or other message. The message may include at least one of the following information:

[0603] -The F1 application protocol identifier of the UE allocated by the gNB-CU, i.e., the gNB-CU UE F1AP ID.

[0604] -F1 application protocol identifier assigned by the gNB-DU to the UE, i.e., gNB-DU UE F1AP ID, is the F1 application protocol identifier assigned by the candidate gNB-DU to the UE.

[0605] -LTM switching indication, indicating that the gNB-DU can use the LTM switching mechanism to adjust the UE's cell.

[0606] -Candidate cell list, including information of one or more candidate cells. It includes information of all candidate cells. The information includes at least one of the following information:

[0607] ●Cell identifier, which can be CGI, PCI, or other identifiers.

[0608] ●Group ID.

[0609] ●gNB-DU identifier (gNB-DU ID), the identifier of the gNB-DU to which the candidate cell belongs.

[0610] ●PRACH resource information, the PRACH resource information for Early TA acquired by the candidate cell allocated to the source cell. For specific information and description, see "PRACH resource information" in step 404, which will not be repeated here. The PRACH resource information is optional. If the cell corresponding to the cell identifier is the cell of the source gNB-DU, the PRACH resource information is not included.

[0611] In step 1204d, the candidate gNB-DU sends a message to the gNB-CU to feedback that the information in step 1204c has been received. The message may be a UE CONTEXT SETUP RESPONSE message or other message.

[0612] In step 1205, the gNB-CU sends a message to the source gNB-DU, and the source gNB-DU forwards it to the UE. The message may be a DL RRC MESSAGE TRANSFER message, or other message. The message includes an RRC reconfiguration message sent to the UE, which is provided in the form of an RRC container. The specific content of the RRC reconfiguration message sent to the UE is shown in step 405 and will not be repeated here.

[0613] Step 1206: The source gNB-DU sends a message to the UE, forwarding the message received from the gNB-CU to the UE. The message may be an RRC reconfiguration message (RRCReconfiguration) or other messages.

[0614] Step 1207: The UE sends a message to the source gNB-DU as feedback. The message may be an RRC reconfiguration complete message (RRCReconfigurationComplete) or other messages.

[0615] In step 1208, the source gNB-DU sends a message to the gNB-CU to forward the message received from the UE to the gNB-CU. The message may be an uplink RRC message transfer message (UL RRC MESSAGE TRANSFER) or other messages.

[0616] When the candidate cell becomes the target cell, it will become the new source cell. Therefore, the source cell (or new source cell) can select one of the cells belonging to the same gNB-DU and with the same grouping identifier through the grouping identifier of the candidate cell and the gNB-DU identifier to which the candidate cell belongs, triggering the UE to perform the Early TA acquisition process, thereby avoiding triggering unnecessary Early TA acquisition processes.

[0617] The present disclosure provides another method for setting a candidate cell grouping identifier (setting method 2).

[0618] The gNB-CU can obtain the cell grouping identifier of the candidate cells in each gNB-DU through OAM or other methods, or obtain the synchronization relationship between cells in the gNB-DU. If different cells have the same synchronization relationship, different cells can use the same TA. The gNB-CU uniformly sets the candidate cell grouping identifier based on the synchronization relationship between the cells or the grouping identifier. Therefore, when the gNB-CU determines to trigger LTM switching, the candidate cell grouping identifier is uniformly set for the selected candidate cells, and is sent to the candidate gNB-DU through step 1203 and to the source gNB-DU through 1204a. See the process. Fig.12, the specific description is as follows. The difference between setting method 2 and setting method 1 lies in steps 1202, 1203, and 1204a, and the other steps are the same as setting method 1. Only the steps that are different from setting method 1 are described here, and the other steps refer to the description in setting method 1. Among them, the difference between steps 1203 and 1204a of method 2 and steps 1203 and 1204a of method 1 is that the "candidate cell list" does not need to include the gNB-DU ID to which the candidate cell belongs. The description of step 1202 in method 2 is as follows.

[0619] In step 1202, the gNB-CU decides to trigger the handover configuration according to the measurement report and performs candidate cell configuration. The gNB-CU selects candidate cells for the UE according to the measurement results (in the LTM system, LTM candidate cells). For example, the gNB-CU selects 7 candidate cells Cell1-Cell7, Cell1-Cell2 belongs to gNB-DU1, Cell3-Cell4 belongs to gNB-DU2, and Cell5-Cell7 belongs to gNB-DU3. If Cell1 and Cell2 in gNB-DU1 cannot use the same TA; Cell3 and Cell4 in gNB-DU2 can use the same TA; Cell6 and Cell7 in gNB-DU3 can use the same TA, but Cell5 and Cell6, Cell7 cannot use the same TA. Optionally, the principle of gNB-CU uniformly setting the candidate cell grouping identifier can be based on the following principle, but not limited to this: the grouping identifiers of cells between different gNB-DUs cannot be the same, and whether the grouping identifiers of cells in the same gNB-DU are the same is determined based on whether the same TA can be used between cells. Based on the above principles, the gNB-CU uniformly sets the candidate cell grouping identifiers for Cell1-Cell7 in the following order: 1, 2, 3, 3, 4, 5, 5.

[0620] When the candidate cell becomes the target cell, it will become the new source cell. Therefore, the source cell (or new source cell) can select one of the cells with the same grouping identifier through the grouping identifier of the candidate cell, triggering the UE to perform the Early TA acquisition process, thereby avoiding triggering unnecessary Early TA acquisition process.

[0621] Fig.11 is a block diagram showing the structure of a first node 400 according to an embodiment of the present disclosure.

[0622] refer to Fig.11, the first node 1000 includes a transceiver 1001 and a controller 1002. The transceiver 1001 is configured to send signals to the outside and receive signals from the outside. The controller 1002 is configured to execute the method performed by the first node. The first node 1000 can be implemented in the form of hardware, software, or a combination of hardware and software so that it can execute the method performed by the first node described in the present disclosure.

[0623] Those skilled in the art will appreciate that the above illustrative embodiments are described herein and are not intended to be limiting. It should be understood that any two or more of the embodiments disclosed herein may be combined in any combination. In addition, other embodiments may be utilized and other changes may be made without departing from the spirit and scope of the subject matter presented herein. It will be readily understood that the various aspects of the invention of the present disclosure as generally described herein and shown in the accompanying drawings may be arranged, replaced, combined, separated and designed in a variety of different configurations, all of which are contemplated herein.

[0624] Those skilled in the art will appreciate that the various illustrative logic boxes, modules, circuits, and steps described in the present application can be implemented as hardware, software, or a combination of the two. To clearly illustrate this interchangeability of hardware and software, various illustrative components, boxes, modules, circuits, and steps are described generally in the form of their function sets above. Whether such function sets are implemented as hardware or software depends on specific applications and the design constraints imposed on the overall system. Technicians can implement the described function sets in different ways for each specific application, but such design decisions should not be interpreted as causing a departure from the scope of the present application.

[0625] The various illustrative logic blocks, modules, and circuits described in this application may be implemented or executed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in an alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors cooperating with a DSP core, or any other such configuration.

[0626] The method or algorithm described in the present application can be directly embodied in hardware, in a software module executed by a processor, or in a combination of the two. The software module can reside in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, or any other form of storage medium known in the art. An exemplary storage medium is coupled to a processor so that the processor can read and write information from / to the storage medium. In an alternative, a storage medium can be integrated into a processor. The processor and the storage medium can reside in an ASIC. The ASIC can reside in a user terminal. In an alternative, the processor and the storage medium can reside in a user terminal as discrete components.

[0627] In one or more exemplary designs, the functions may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted as one or more instructions or codes on a computer-readable medium. Computer-readable media include both computer storage media and communication media, the latter including any media that facilitates the transfer of a computer program from one place to another. Storage media may be any available media that can be accessed by a general or special purpose computer.

[0628] The above description is merely an exemplary embodiment of the present application and is not intended to limit the protection scope of the present application. The protection scope of the present application is determined by the appended claims.

Claims

1. A method performed by a first node in a communication system, the method comprising: receiving a first message from the second node, wherein the first message includes information related to a first physical random access channel (PRACH) resource, and the information related to the first PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource; and Sending a second message to the third node, wherein the second message includes information related to a second PRACH resource, where the PRACH resource is used to obtain a timing advance TA value in advance; The third node is a node where the cell indicated by the first cell identifier is located or a node indicated by the first node identifier.

2. The method according to claim 1, wherein: The information related to the first or second PRACH resource further includes at least one of the following: A second cell identifier, used to indicate a cell to which the PRACH resource is allocated; A second node identifier, used to indicate a node where a cell to which the PRACH resource is allocated is located; a first group identifier, used to indicate the group to which the cell to which the PRACH resource is allocated belongs, wherein for cells in the same group, the TA values ​​of the user equipments UE are the same; First PRACH resource information, wherein the first PRACH resource information includes at least one of the following: time domain and frequency domain information of PRACH resources, a PRACH configuration index, a frequency domain parameter of a PRACH opportunity, and a total number of random access codes.

3. The method according to claim 1, further comprising: receiving a third message from the second node, wherein the third message includes first TA information, which is used to indicate TA information detected on the PRACH resource included in the information related to the first PRACH resource; The third message further includes at least one of the following: A third cell identifier, used to indicate a cell corresponding to the first TA information; A third node identifier, used to indicate a node where the cell corresponding to the first TA information is located or a node corresponding to the first TA information; The first TA information includes at least one of the following: A fourth cell identifier, used to indicate a cell in which a TA value is detected; Second PRACH resource information, used to indicate PRACH resource information in which a TA value is detected; A first TA value is a TA value detected on the second PRACH resource.

4. The method according to claim 3, further comprising: sending a fourth message to the third node, wherein the third node is determined based on the third cell identifier or the third node identifier, and the fourth message includes TA information corresponding to the cell of the third node or the third node; The fourth message includes at least one of the following: A fourth cell identifier, used to indicate a cell in which a TA value is detected; Second PRACH resource information, used to indicate PRACH resource information in which a TA value is detected; A first TA value is a TA value detected on the second PRACH resource.

5. The method according to claim 1, wherein: If the information related to the second PRACH resource does not include the first cell identifier corresponding to the second PRACH resource, the second PRACH resource is allocated to the node indicated by the first node identifier.

6. The method according to claim 1, wherein: The first message includes a first PRACH resource information list.

7. The method according to claim 4, further comprising: receiving a fifth message from the third node, wherein the fifth message includes information sent to the target cell, The information sent to the target cell includes at least one of the following: a fifth cell identifier, used to indicate a candidate cell for the UE; a fourth node identifier, used to indicate a node where a candidate cell of the UE is located; A second group identifier, used to indicate the group to which the candidate cell of the UE belongs; a second TA value, where the second TA value is a TA value of the UE in the candidate cell; A time alignment timer TAT value, used to indicate the TAT running time length corresponding to the TA value of the candidate cell; The time alignment timer TAT length is used to indicate the length of the TAT timer.

8. A method performed by a first node in a communication system, the method comprising: receiving a sixth message from the second node, or receiving a seventh message from the fourth node, wherein the sixth message or the seventh message includes information related to a third physical random access channel PRACH resource; and Sending an eighth message to the third node based on the sixth message or the seventh message, wherein the eighth message includes information related to the fourth PRACH resource, and the information related to the fourth PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource, wherein the PRACH resource is used to obtain a timing advance TA value in advance; The third node is the node where the first cell identifier is located or the node indicated by the first node identifier.

9. The method according to claim 8, wherein: The information related to the third or fourth PRACH resource includes at least one of the following: a sixth cell identifier, used to indicate a cell to which the PRACH resources are allocated; a fifth node identifier, used to indicate a node where a cell to which the PRACH resource is allocated is located; a third group identifier, used to indicate the group to which the cell to which the PRACH resource is allocated belongs, wherein, for cells in the same group, the timing advance TA values ​​of the user equipment UE are the same; The third PRACH resource information includes at least one of the following: time domain and frequency domain information of PRACH resources, a PRACH configuration index, a frequency domain parameter of a PRACH opportunity, and a total number of random access codes.

10. The method according to claim 8, further comprising: receiving a ninth message from the second node, The ninth message includes at least one of the following: A seventh cell identifier, used to indicate a cell in which a TA value is detected; Fourth PRACH resource information, used to indicate PRACH resource information in which a TA value is detected; A third TA value is a TA value detected on the fourth PRACH resource.

11. The method according to claim 10, further comprising: A fourth message is sent to the third node, wherein the third node is determined based on the fourth cell identifier and / or the fourth PRACH resource information, and the fourth message includes TA information corresponding to the third node.

12. A method performed by a second node in a communication system, the method comprising: Sending a first message to a first node, wherein the first message includes information related to a first physical random access channel PRACH resource, and the information related to the first PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource; Perform detection on the PRACH resource to determine a first TA value; A third message is sent to the first node, where the third message includes first TA information, and the first TA information includes the first TA value.

13. The method according to claim 12, wherein: The third message further includes at least one of the following: A third cell identifier, used to indicate a cell corresponding to the first TA information; A third node identifier, used to indicate a node where the cell corresponding to the first TA information is located or a node corresponding to the TA information; The first TA information included in the third message further includes at least one of the following: A fourth cell identifier, used to indicate a cell in which a TA value is detected; The second PRACH resource information is used to indicate the PRACH resource information of the detected TA value.

14. A method performed by a third node in a communication system, the method comprising: receiving a second message sent by the first node; or receiving a tenth message sent by the fourth node, wherein the second message and the tenth message include information related to the second physical random access channel PRACH resource, and the information related to the second PRACH resource includes a PRACH resource used to obtain a timing advance TA value in advance; The cell in the third node allocates the PRACH resource to the user equipment UE for performing a random access process for obtaining a timing advance TA value in advance; The second message is sent by the first node in response to a received first message, the first message includes information related to the first PRACH resource, and the information related to the first PRACH resource includes a first cell identifier or a first node identifier corresponding to the PRACH resource.

15. The method according to claim 14, further comprising: receiving a fourth message sent by the first node, wherein the fourth message includes a cell of the third node or TA information corresponding to the third node, wherein the fourth message includes at least one of the following: A fourth cell identifier, used to indicate a cell in which a TA value is detected; Second PRACH resource information, used to indicate PRACH resource information in which a TA value is detected; A first TA value is a TA value detected on the second PRACH resource.

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