Inter-CU cell change procedure

Abstract

Example embodiments of the present disclosure are directed to inter-centralized unit (CU) cell change procedure. In a method, an apparatus transmits, to one of the prepared candidate nodes that becomes a new serving node after an inter-(CU) layer 1 or layer 2 triggered mobility (LTM) cell change, a first message including a list of prepared target inter-CU cells. The apparatus is a serving node before the inter-CU LTM cell change.

Description

INTER-CU CELL CHANGE PROCEDUREFIELD

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for inter-centralized unit (CU) cell change procedure.

[0002] BACKGROUND

[0003] With the continuous development of mobile networks, managing and optimizing user mobility between different network nodes has become crucial. Modern mobile communication systems require seamless connectivity between various centralized units to ensure efficient and reliable handovers. The increasing complexity of networks adds to the challenge of achieving smooth transitions between different CUs, making advancements in mobility management techniques essential for enhancing network performance and user experience.

[0004] SUMMARY

[0005] In a first aspect of the present disclosure, there is provided an apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: transmit, to one of the prepared candidate nodes that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change, a first message including a list of prepared target inter-CU cells, wherein the apparatus is a serving node before the inter-CU LTM cell change.

[0006] In a second aspect of the present disclosure, there is provided an apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: receive, from a serving node, a first message including a list of prepared target cells ifor an inter-centralized unit (CU) cell change, wherein the apparatus is a prepared candidate node that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

[0007] In a third aspect of the present disclosure, there is provided an apparatus. The third apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: transmit, to a plurality of prepared candidate nodes, a first message indicative of a preparation of identifiers of a prepared candidate node, wherein the apparatus is a serving node before an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change; receive, from the plurality of prepared candidate nodes, a plurality of second messages, each second message including a pair of identifiers of a respective prepared candidate node, the pair of identifiers comprising a first identifier with the respective prepared candidate node meant to be used when the candidate node becomes a new serving node and a second identifier with the respective prepared candidate node meant to be used when the candidate node remains a candidate node; and transmit, to the plurality of prepared candidate nodes, a third message including a list of prepared target cells for the inter-CU cell change and a configuration of a plurality of pairs of identifiers of the plurality of prepared candidate nodes.

[0008] In a fourth aspect of the present disclosure, there is provided an apparatus. The fourth apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: receive, from a serving node, a first message indicative of a preparation of identifiers of the apparatus, wherein the apparatus is a prepared candidate node for an intercentralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change; transmit, to the serving node, a second message including a pair of identifiers of the apparatus, the pair of identifiers comprising a first identifier with the apparatus meant to be used when the candidate node becomes new serving node and a second identifier is meant to be used when the candidate node remains a candidate node; and receive, from the serving node, a third message including a list of prepared target cells for the inter-CU LTM cell change and a configuration of a plurality of pairs of identifiers of a plurality of prepared candidate nodes, the plurality of prepared candidate nodes comprising the apparatus.

[0009] In a fifth aspect of the present disclosure, there is provided an apparatus. The fifth apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: transmit, to a candidate node, after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the candidate node is a new serving node after the inter-CU LTM cell change.

[0010] In a sixth aspect of the present disclosure, there is provided an apparatus. The sixth apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: receive, from a serving node after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a new serving node after the inter-CU LTM cell change; and store the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0011] In a seventh aspect of the present disclosure, there is provided an apparatus. The seventh apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: transmit, to a plurality of prepared candidate nodes, during a preparation of inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the plurality of prepared candidate nodes comprising node which is a new serving node after the inter-CU LTM cell change.

[0012] In an eighth aspect of the present disclosure, there is provided an apparatus. The eighth apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: receive, from a serving node, during a preparation of inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and executionof the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a prepared candidate node for the inter-CU LTM cell change; and store the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0013] In a ninth aspect of the present disclosure, there is provided a method. The method comprises: transmitting, to one of the prepared candidate nodes that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change, a first message including a list of prepared target inter- CU cells, wherein the apparatus is a serving node before the inter-CU LTM cell change.

[0014] In a tenth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a serving node, a first message including a list of prepared target cells for an inter-centralized unit (CU) cell change, wherein the apparatus is a prepared candidate node that becomes a new serving node after an intercentralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

[0015] In an eleventh aspect of the present disclosure, there is provided a method. The method comprises: transmitting, to a plurality of prepared candidate nodes, a first message indicative of a preparation of identifiers of a prepared candidate node, wherein the apparatus is a serving node before an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change; receiving, from the plurality of prepared candidate nodes, a plurality of second messages, each second message including a pair of identifiers of a respective prepared candidate node, the pair of identifiers comprising a first identifier with the respective prepared candidate node meant to be used when the candidate node becomes a new serving node and a second identifier with the respective prepared candidate node meant to be used when the candidate node remains a candidate node; and transmitting, to the plurality of prepared candidate nodes, a third message including a list of prepared target cells for the inter-CU cell change and a configuration of a plurality of pairs of identifiers of the plurality of prepared candidate nodes.

[0016] In a twelfth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a serving node, a first message indicative of a preparation of identifiers of the apparatus, wherein the apparatus is a prepared candidate node for an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility(LTM) cell change; transmitting, to the serving node, a second message including a pair of identifiers of the apparatus, the pair of identifiers comprising a first identifier with the apparatus meant to be used when the candidate node becomes new serving node and a second identifier is meant to be used when the candidate node remains a candidate node; and receiving, from the serving node, a third message including a list of prepared target cells for the inter-CU LTM cell change and a configuration of a plurality of pairs of identifiers of a plurality of prepared candidate nodes, the plurality of prepared candidate nodes comprising the apparatus.

[0017] In a thirteenth aspect of the present disclosure, there is provided a method. The method comprises: transmitting, to a candidate node, after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the candidate node is a new serving node after the inter-CU LTM cell change.

[0018] In a fourteenth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a serving node after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a new serving node after the inter-CU LTM cell change ; and storing the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0019] In a fifteenth aspect of the present disclosure, there is provided a method. The method comprises: transmitting, to a plurality of prepared candidate nodes, during a preparation of inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the plurality of prepared candidate nodes comprising node which is a new serving node after the inter-CU LTM cell change.

[0020] In a sixteenth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a serving node, during a preparation of inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter- CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a prepared candidate node for the inter-CU LTM cell change; and storing the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0021] In a seventeenth aspect of the present disclosure, there is provided an apparatus. The first apparatus comprises means for transmitting, to one of the prepared candidate nodes that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change, a first message including a list of prepared target inter-CU cells, wherein the apparatus is a serving node before the inter-CU LTM cell change.

[0022] In an eighteenth aspect of the present disclosure, there is provided an apparatus. The second apparatus comprises means for receiving, from a serving node, a first message including a list of prepared target cells for an inter-centralized unit (CU) cell change, wherein the apparatus is a prepared candidate node that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

[0023] In a nineteenth aspect of the present disclosure, there is provided an apparatus. The third apparatus comprises means for transmitting, to a plurality of prepared candidate nodes, a first message indicative of a preparation of identifiers of a prepared candidate node, wherein the apparatus is a serving node before an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change; means for receiving, from the plurality of prepared candidate nodes, a plurality of second messages, each second message including a pair of identifiers of a respective prepared candidate node, the pair of identifiers comprising a first identifier with the respective prepared candidate node meant to be used when the candidate node becomes a new serving node and a second identifier with the respective prepared candidate node meant to be used when the candidate node remains a candidate node; and means for transmitting, to the plurality of prepared candidate nodes, a third message including a list of prepared target cells for the inter-CU cell change and a configuration of a plurality of pairs of identifiers of the plurality of prepared candidate nodes.

[0024] In a twentieth aspect of the present disclosure, there is provided an apparatus. The fourth apparatus comprises means for receiving, from a serving node, a first message indicative of a preparation of identifiers of the apparatus, wherein the apparatus is a prepared candidate node for an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change; means for transmitting, to the serving node, a second message including a pair of identifiers of the apparatus, the pair of identifiers comprising a first identifier with the apparatus meant to be used when the candidate node becomes new serving node and a second identifier is meant to be used when the candidate node remains a candidate node; and means for receiving, from the serving node, a third message including a list of prepared target cells for the inter-CU LTM cell change and a configuration of a plurality of pairs of identifiers of a plurality of prepared candidate nodes, the plurality of prepared candidate nodes comprising the apparatus.

[0025] In a twenty-first aspect of the present disclosure, there is provided an apparatus. The fifth apparatus comprises means for transmitting, to a candidate node, after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the candidate node is a new serving node after the inter-CU LTM cell change.

[0026] In a twenty-second aspect of the present disclosure, there is provided an apparatus. The sixth apparatus comprises means for receiving, from a serving node after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a new serving node after the inter-CU LTM cell change ; and means for storing the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0027] In a twenty-third aspect of the present disclosure, there is provided an apparatus. The seventh apparatus comprises means for transmitting, to a plurality of prepared candidate nodes, during a preparation of inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and executionof the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the plurality of prepared candidate nodes comprising node which is a new serving node after the inter-CU LTM cell change.

[0028] In a twenty-fourth aspect of the present disclosure, there is provided an apparatus. The eighth apparatus comprises means for receiving, from a serving node, during a preparation of inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a prepared candidate node for the inter-CU LTM cell change; and means for storing the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0029] In a twenty-fifth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the ninth aspect.

[0030] In a twenty-sixth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the tenth aspect.

[0031] In a twenty-seventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the eleventh aspect.

[0032] In a twenty-eighth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the twelfth aspect.

[0033] In a twenty -ninth aspect of the present disclosure, there is provided a computerreadable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the thirteenth aspect.

[0034] In a thirtieth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourteenth aspect.

[0035] In a thirty-first aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fifteenth aspect.

[0036] In a thirty-second aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the sixteenth aspect.

[0037] It is to be understood that the Summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0040] FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0041] FIG. 2 illustrates a signaling flow for Layer 1 / Layer 2 triggered Mobility (LTM) procedure based on a standard;

[0042] FIG. 3A illustrates a signaling flow showing a problem in LTM inter-CU subsequent cell change scenario;

[0043] FIG. 3B illustrates another signaling flow showing a problem in LTM inter- CU subsequent cell change scenario;

[0044] FIG. 4A to FIG. 4D illustrate example signaling flows for inter-CU cell change procedure in accordance with some example embodiments of the present disclosure, respectively;

[0045] FIG. 5 illustrates an example signaling flow for inter-CU cell change procedure in accordance with some example embodiments of the present disclosure;

[0046] FIG. 6A and FIG. 6B illustrate another example signaling flow for inter-CU cell change procedure in accordance with some example embodiments of the present disclosure;

[0047] FIG. 7 illustrates another example signaling flow for inter-CU cell change procedure in accordance with some example embodiments of the present disclosure;

[0048] FIG. 8 illustrates another example signaling flow for inter-CU cell change procedure in accordance with some example embodiments of the present disclosure

[0049] FIG. 9 illustrates a flowchart of a method implemented at an apparatus in accordance with some example embodiments of the present disclosure;

[0050] FIG. 10 illustrates another flowchart of a method implemented at an apparatus in accordance with some example embodiments of the present disclosure;

[0051] FIG. 11 illustrates another flowchart of a method implemented at an apparatus in accordance with some example embodiments of the present disclosure;

[0052] FIG. 12 illustrates another flowchart of a method implemented at an apparatus in accordance with some example embodiments of the present disclosure;

[0053] FIG. 13 illustrates another flowchart of a method implemented at an apparatus in accordance with some example embodiments of the present disclosure;

[0054] FIG. 14 illustrates another flowchart of a method implemented at an apparatus in accordance with some example embodiments of the present disclosure;

[0055] FIG. 15 illustrates another flowchart of a method implemented at an apparatus in accordance with some example embodiments of the present disclosure;

[0056] FIG. 16 illustrates another flowchart of a method implemented at an apparatus in accordance with some example embodiments of the present disclosure;

[0057] FIG. 17 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0058] FIG. 18 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0059] Throughout the drawings, the same or similar reference numerals represent the same or similar element.

[0060] DETAILED DESCRIPTION

[0061] Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

[0062] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

[0063] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0064] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like may be used herein to describe various elements, these elementsshould not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0065] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0066] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0067] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0068] As used in this application, the term “circuitry” may refer to one or more or all of the following:(a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and(b) combinations of hardware circuits and software, such as (as applicable):(i) a combination of analog and / or digital hardware circuit(s) with software / firmware and(ii) any portions of hardware processor(s) with software (includingdigital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0069] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0070] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB- loT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G), 5.5G, the sixth generation (6G) communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0071] As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives servicestherefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non -terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0072] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0073] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0074] As used herein, “inter-centralized unit” may refer to the interactions and handovers occurring between different centralized units within a mobile communication network. Centralized units (CUs) are network nodes responsible for handling higher-layer functions such as radio resource control and mobility management. The term “inter-centralized unit” specifically pertains to the processes, procedures, and mechanisms involved when a user equipment (UE) transitions from one CU to another, ensuring continuous and seamless connectivity during the handover.

[0075] FIG. 1 illustrates a schematic diagram of an example communication environment 100 in which example embodiments of the present disclosure can be implemented. In the communication environment 100, a plurality of communication devices, including a terminal device 110 and a network device 120-1, a network device 120-2, . . ., a network device 120-N, can communicate with each other. The network device 120-1, network device 120-2, . . ., and network device 120-N can be collectively referred to as “network device(s) 120” or individually referred to as a “network device 120”. The number N can be any suitable integer number.

[0076] In the example of FIG. 1, the terminal device 110 may be a UE and the network device 120 may be a base station serving the UE. The serving area of the network device 120 may be called a cell 122. For example, the serving area of the network device 120-1 is a cell 122-1, the serving area of the network device 120-2 is a cell 122- 2, and the serving area of the network device 120-N is a cell 122-N. The cell 122-1, cell 122-2, ... and cell 122-N can be collectively referred to as “cell(s) 122” orindividually referred to as a “cell 122”.

[0077] As shown, the terminal device 120 is served by the cell 122-1 of the network device 120-1 at present. In such cases, the cell 122-1 may be referred to as a serving cell or a first cell, and the network device 120-1 may be referred to as a serving network device or a first network device. In the scenario of handover, the cell 122-2 or cell 122- N may be referred to as a candidate cell or a second cell for handover, and the network device 120-2 or network device 120-N may be referred to as a candidate network device or a second network device.

[0078] In some example embodiments, the terminal device 110 may move to another cell. For example, if the terminal device 110 moves to the cell 122-2 of the network device 120-2, a handover or cell switch may happen. After the handover, the cell 122- 2 becomes the serving cell, and the cell 122-1 may become a candidate cell. It is to be understood that any cell may become the serving cell or candidate cell under different situations.

[0079] In the communication environment 100, the network device 120 and the terminal devices 110 may communicate data and control information to each other. The terminal devices 110 may also communicate with each other.

[0080] It is to be understood that the number of devices and their connections shown in FIG. 1 are only for the purpose of illustration without suggesting any limitation. The communication environment 100 may include any suitable number of devices configured to implementing example embodiments of the present disclosure. Although not shown, it would be appreciated that one or more additional devices may be located in the cell, and one or more additional cells may be deployed in the communication environment 100. It is noted that although illustrated as a network device, the network device 120 may be another device than a network device. Although illustrated as a terminal device, the terminal device 110 may be other device than a terminal device.

[0081] In the following, for the purpose of illustration, some example embodiments are described with the terminal device 110 operating as a UE and the network device 120 operating as a base station. However, in some example embodiments, operations described in connection with a terminal device may be implemented at a network device or other device, and operations described in connection with a network device may beimplemented at a terminal device or other device.

[0082] In some example embodiments, if the terminal device 110 is a terminal device and the network device 120 is a network device, a link from the network device 120 to the terminal device 110 is referred to as a downlink (DL), while a link from the terminal device 110 to the network device 120 is referred to as an uplink (UL). In DL, the network device 120 is a transmitting (TX) device (or a transmitter) and the terminal device 110 is a receiving (RX) device (or a receiver). In UL, the terminal device 110 is a TX device (or a transmitter) and the network device 120 is a RX device (or a receiver).

[0083] The communications in the communication environment 100 may conform to any suitable standards including, but not limited to, Global System for Mobile Communications (GSM), Long Term Evolution (LTE), LTE -Evolution, LTE- Advanced (LTE-A), New Radio (NR), Wideband Code Division Multiple Access (WCDMA), Code Division Multiple Access (CDMA), GSM EDGE Radio Access Network (GERAN), Machine Type Communication (MTC) and the like. The embodiments of the present disclosure may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G- Advanced networks, or the sixth generation (6G) networks.

[0084] In some solutions, objectives of LTM procedure are provided. One of the key objectives is to specify support for subsequent LTM mobility procedures aiming to avoid RRC configuration between cell switches as per Rel-18 LTM.

[0085] LTM is a cell switch procedure, where UE’s serving cell (PCell or PSCell) is switched by the network by sending an LTM cell switch command. An LTM switch command is currently assumed delivered by MAC signaling using a MAC CE. Hence, not using RRC signaling as a L3 based handover which is one of the current methods for changing between cells. LTM cell switch decision is based on measurements (for example LI measurements) that are performed and reported (for example LI measurement report) by the UE. Measurements and reporting are based on LTM candidate cell configuration provided by the network for one or more LTM candidatecells. An LTM candidate cell may be neighboring cells or a UE’s current serving cells (e.g. SCells).

[0086] In a predefined standard, LTM measurements on a neighboring candidate cell are performed using SSBs transmitted by the candidate cell for which the SSB configuration is provided to the UE.

[0087] Before the cell switch, network may optionally activate one or more TCI state(s) for one or more candidate cells. Once a candidate cell TCI state is activated the UE may start tracking the time / frequency synchronization using the reference signals associated with the activated TCI state(s). The UE may also perform early UL synchronization before the cell switch if this is requested by the network.

[0088] FIG. 2 illustrates a signaling flow 200 for Layer 1 / Layer 2 triggered Mobility (LTM) procedure based on a standard. As shown in FIG. 2, the procedure for LTM is as follows: In the first part of LTM preparation, the UE 210 transmits (2005) a MeasurementReport message to the gNB 220, then the gNB 220 decides to configure LTM and initiates LTM preparation. After LTM candidate preparation, the gNB 210 transmits (2010) an RRCReconfiguration message to the UE including the LTM candidate configurations. In addition, the UE 210 stores the LTM candidate configurations and transmits (2015) an RRCReconfigurationComplete message to the gNB 220.

[0089] The LTM preparation is followed by early sync. At block 2020A, the UE 210 performs DL synchronization with the candidate cell(s) before receiving the cell switch command. At block 2020B, the UE 210 performs early TA acquisition with the candidate cell(s) as requested by the network before receiving the cell switch command as specified in a predefined standard. This is done via CFRA triggered by a PDCCH order from the source cell, following which the UE 210 sends preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the UE 210 doesn’t receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command. The UE 210 doesn’t maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity.

[0090] After the LTM preparation, in the part of LTM execution, the UE 210 performs LI measurements on the configured candidate cell(s) and transmits (2025) LI measurement reports to the gNB 220. LI measurement should be performed as long as RRC reconfiguration (at 2010) is applicable. After receiving the measurement reports, the gNB 220 decides to execute cell switch to a target cell and transmits (2030) a MAC CE triggering cell switch by including the candidate configuration index of the target cell. The UE 210 switches to the target cell and applies the configuration indicated by candidate configuration index. At block 2035, the UE 210 performs the random access procedure towards the target cell, if UE 210 does not have valid TA of the target cell as specified in a predefined standard.

[0091] The LTM completion is followed by the LTM execution, at block 2040, the UE 210 completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to target cell. If the UE 210 has performed a RA procedure at block 2035, the UE 210 considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For RACH-less LTM, the UE 210 considers that LTM cell switch execution is successfully completed when the UE 210 determines that the network has successfully received its first UL data.

[0092] The steps in early sync to LTM completion, that is, from 2020A or 2020B to 2040, can be performed multiple times for subsequent LTM using the LTM candidate configuration(s) provided in 2010. The procedure over the air interface described above is applicable to both intra-gNB-DU LTM and inter-gNB-DU LTM. The overall LTM procedures over Fl -Control Plane (Fl-C) interface are captured in a standard.

[0093] FIG. 3A illustrates a signaling flow 300 showing a problem in LTM inter-CU subsequent cell change scenario. As shown in FIG. 3A, in inter-CU subsequent cell change, the source node prepares the candidate target nodes. However, after inter-CU cell change is executed, one of the prepared candidate target nodes become the new serving node and the source node might become a candidate target node.

[0094] As the source node triggers the initial preparation of all the candidate target nodes, the UE associated Xn logical connection is setup between the source node and the candidate target nodes during HO preparation, i.e. when source node includes its XnAP Id for a given UE in the HO Request message and the candidate target noderesponds with HO Request Ack by including its XnAP Id for that UE, thus creating a UE associated Xn logical connection. The target node stores the source and target XnAP ID pair in UE context created at the target.

[0095] A UE associated Xn logical connection setup is needed to transfer a UE specific control plane messages from one node to the other node. When a node wants to transfer a UE specific control plane message, it retrieves the XnAP Id of the destination node from the UE context.

[0096] However, as shown in block 310, the problem is that after LTM inter-CU subsequent cell change HO execution, one of the candidate target nodes becomes the new serving node, and it shall not have the UE associated Xn logical connection with other prepared candidate target nodes to exchange UE specific control plane messages.

[0097] In some scenarios, as shown in FIG. 3B, which illustrates another signaling flow 300' showing a problem in LTM inter-CU subsequent cell change scenario, in inter-CU subsequent cell change, the source node prepares the candidate target nodes. However, after an inter-CU cell change is executed, one of the prepared candidate target nodes become the new serving node and the source node might become a candidate target node.

[0098] As the source node triggers the initial preparation of all the candidate target nodes and stores the prepared candidate node configuration; to avoid new serving node after inter-CU cell change triggering fresh preparation of candidate target nodes, the source node must transfer the admitted PDU session resource list of all the inter-CU candidate target cells to all the prepared candidate target nodes, to enable data forwarding.

[0099] Otherwise, the new serving node after LTM inter-CU cell change shall not have the TNL information of the admitted PDU sessions to initiate data forwarding. The problem is similar to the signaling flow 300 in FIG. 3A. As shown in block 340 in FIG. 3B, the problem is that when target node becomes the new serving node at this step after inter-CU cell change execution, it does not have the admitted PDU session resource configuration of the other candidate nodes. So, the new serving node cannot initiate data forwarding after next inter-CU cell change.

[0100] In accordance with some example embodiments of the present disclosure, thereis provided a solution for inter-CU cell change procedure. In the present disclosure, enhancements which is necessary to setup UE associated Xn logical connection for the transfer of UE specific control plane messages after each LTM inter-CU subsequent cell change HO execution are proposed. LTM inter-CU subsequent cell change enables cell change to be executed based on pre-configured subsequent cell change configuration of inter-CU candidate cells without having to reconfigure the UE.

[0101] In order to solve at least part of the above problems or other potential problems, a solution on inter-CU cell change procedure is proposed. According to example embodiments, an apparatus such as a serving node transmits, to one of the prepared candidate nodes that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change, a first message including a list of prepared target inter-CU cells, wherein the apparatus is a serving node before the inter-CU LTM cell change.

[0102] According to example embodiments, an apparatus such as a serving node transmits, to a plurality of prepared candidate nodes, a first message indicative of a preparation of identifiers of a prepared candidate node, wherein the apparatus is a serving node before an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change. The apparatus receives, from the plurality of prepared candidate nodes, a plurality of second messages, each second message including a pair of identifiers of a respective prepared candidate node, the pair of identifiers comprising a first identifier with the respective prepared candidate node meant to be used when the candidate node becomes a new serving node and a second identifier with the respective prepared candidate node meant to be used when the candidate node remains a candidate node. The apparatus transmits, to the plurality of prepared candidate nodes, a third message including a list of prepared target cells for the inter-CU cell change and a configuration of a plurality of pairs of identifiers of the plurality of prepared candidate nodes.

[0103] According to example embodiments, an apparatus such as a serving node transmits, to a candidate node, after inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and thecandidate node is a new serving node after the inter-CU LTM cell change. According to example embodiments, an apparatus such as a serving node transmits, to a plurality of prepared candidate nodes, during a preparation of inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the plurality of prepared candidate nodes comprising node which is a new serving node after the inter-CU LTM cell change.

[0104] In this manner, various information regarding the candidate cells may be provided to a target node or candidate node. Such information may be used in the following or subsequent inter-CU cell change procedure. The inter-CU cell change procedure may thus be enhanced.

[0105] Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It is noted the order acts shown in FIG. 4A-8 is only an example not limitation. Acts can be performed in any suitable manner. Example embodiments described with reference to FIG. 4A to FIG. 8 can be implemented separately or combined in any manner. For example, one or more example embodiments shown in FIG. 4A can be combined with one or more example embodiments shown in one or more other drawings.

[0106] FIG. 4A illustrates a signaling flow 400 for inter-CU cell change procedure according to some example embodiments of the present disclosure. The signaling flow 400 involves a serving node 410 and a candidate node 420. By way of example, the serving node 410 may be the network device 120-1 in FIG. 1, and the candidate node 420 may be another network device such as the network device 120-2 or the network device 120-N in FIG. 1. In the following description, it is assumed that the serving node 410 is a source apparatus (also referred to as a source node), and the candidate node 420 is a target apparatus (also referred to as a target node or a prepared candidate node). It is to be understood that although there is a single candidate node 420 shown in the signaling flow 400, in some embodiments, there may be a plurality of second apparatuses such as a plurality of target nodes or candidate nodes in the signaling flow 400.

[0107] In operation, the serving node 410 transmits (4005), to one of the prepared candidate nodes such as the candidate node 420 that becomes a new serving node after an inter-CU LTM cell change, a first message including a list of prepared target inter- CU cells. The serving node 410 is a serving node before the inter-CU LTM cell change.

[0108] In some example embodiments, the serving node 410 may receive, from the candidate node 420 upon becoming the new serving node, a second message including a first identifier of the candidate node 420. The serving node 410 may transmit, to the new serving node, a third message including a second identifier of the serving node 410. The serving node 410 may become a prepared candidate node after the inter-CU LTM cell change.

[0109] In some example embodiments, the second message further includes a serving cell configuration of the candidate node 420.

[0110] In some example embodiments, at least one of the transmission of the first message or the reception of the second message is upon an execution of the inter-CU cell change, or during a preparation of the inter-CU LTM cell change.[OHl] In some example embodiments, in response to receiving the second message, the serving node 410 may update a configuration of packet data unit session resources.

[0112] In some example embodiments, the serving node 410 may store the prepared inter-CU target cell list of all the prepared inter-CU candidate nodes

[0113] In some example embodiments, at least one of the first message, the second message or the third message is via an Xn interface message. For example, the Xn interface message may include a transparent container.

[0114] In some example embodiments, at least one of the first identifier and the second identifier comprises an Xn application protocol (XnAP) identifier.

[0115] In some example embodiments, the candidate node 420 may store the list of prepared target cells in the first message. The candidate node 420 may initiate an Xn logical connection setup towards the plurality of prepared candidate nodes based on the list of prepared target cells after an execution of the inter-CU cell change.

[0116] In an option, the serving node upon inter-CU cell change HO execution,transfers the prepared candidate cell list to all the prepared candidate target nodes. In another option, the source node after the initial preparation of LTM Inter-CU subsequent cell change, transfers the prepared target cell list to all the prepared candidate target nodes during preparation phase. These options may be used to initiate Xn logical connection setup towards prepared candidate target nodes after subsequent inter-CU cell change HO execution.

[0117] The new serving node initiates a message (e.g. HO Update message) over the Xn interface towards the prepared candidate target nodes, intended to create Xn UE associated logical connection. In it, the new serving node includes its XnAP Id.

[0118] The new serving node may use this Xn message to also transfer current serving cell configuration to the candidate target nodes, to allow the candidate target cells to update the prepared configuration related to admitted PDU session resources. This shall enable optimal preparation of resources at candidate target nodes.

[0119] In one alternative, HO Update message may be after the execution of inter-CU LTM cell change. In another alternative, HO Update message may be before the execution of inter-CU LTM cell change (e.g. during preparation phase).

[0120] The candidate target node in response to HO Update, allocates its XnAP Id and responds to the HO Update message with a message (e.g. HO Update Ack) by including the allocated XnAP Id.

[0121] The candidate target node stores the allocated XnAP Id mapped to the new serving node’s XnAP Id received in HO Update message in the UE context for subsequent transfer of UE specific control plane messages.

[0122] The above steps would result in the setup of Xn UE associated logical connection. The ‘HO Update’ and ‘HO Update Ack’ message pair shall be new Xn interface class 1 messages that 3 GPP needs to specify, including the message content (i.e. IES and its definition). Xn based mobility is prioritized. When the scope is expanded to N2 based mobility, then the essence of solution embodiments 1 and 2 shall be applicable also to N2 based HO involving inter-CU subsequent cell change.

[0123] Further details of the signaling flow 400 may be illustrated with respect to FIG. 5. With the signaling flow 440, the candidate node 420 such as a new serving node may be informed about various information which may be used for the subsequent inter-CUcell change procedure. The UE associated Xn logical connection with other prepared candidate target nodes may be established to exchange UE specific control plane messages. The inter-CU cell change procedure may be enhanced.

[0124] FIG. 4B illustrates a signaling flow 430 for inter-CU cell change procedure according to some example embodiments of the present disclosure. The signaling flow 400 involves a serving node 410 (also referred to as a source node) and a plurality of prepared candidate nodes 440-1, 440-2, ... 440-N (N being a positive integer). As used herein, the prepared candidate nodes 440-1, 440-2, ... 440-N may be referred to as a plurality of prepared candidate nodes 440, or individually referred to as a prepared candidate node 440. By way of example, the serving node 410 may be the network device 120-1 in FIG. 1, and the prepared candidate nodes 440 may be another network device such as the network device 120-2 or the network device 120-N in FIG. 1. In the following description, it is assumed that the serving node 410 is a source apparatus (also referred to as a source node), and the candidate node 440 is a target apparatus (also referred to as a target node or a prepared candidate node).

[0125] In operation, the serving node 410 transmits (4305), to the plurality of prepared candidate nodes 440, a first message indicative of a preparation of identifiers of a prepared candidate node. The serving node 410 is a serving node before an intercentralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

[0126] The serving node 410 receives (4310), from the plurality of prepared candidate nodes 440, a plurality of second messages, each second message including a pair of identifiers of a respective prepared candidate node, the pair of identifiers comprising a first identifier with the respective prepared candidate node meant to be used when the candidate node becomes a new serving node and a second identifier with the respective prepared candidate node meant to be used when the candidate node remains a candidate node.

[0127] The serving node 410 transmits (4315), to the plurality of prepared candidate nodes 440, a third message including a list of prepared target cells for the inter-CU cell change and a configuration of a plurality of pairs of identifiers of the plurality of prepared candidate nodes.

[0128] In some example embodiments, the transmission of the first message is duringa preparation of the inter-CU cell change.

[0129] In some example embodiments, the transmission of the third message is during a preparation of the inter-CU cell change and before an evaluation and execution of the inter-CU cell change.

[0130] In some example embodiments, at least one of the first message, the plurality of second messages or the third message is via an Xn interface message. For example, the Xn interface message may include a transparent container.

[0131] In some example embodiments, each identifier of the plurality of pairs of identifiers comprises an Xn application protocol (XnAP) identifier.

[0132] In some example embodiments, the plurality of prepared candidate nodes comprises a target node. The target node is a new serving node after the inter-CU LTM cell change. The serving node 410 may receive, from the target node, a notification of a change of serving node.

[0133] In some example embodiments, the prepared candidate node 440 may store the configuration of the plurality of pairs of identifiers of the plurality of prepared candidate nodes associated with cell identifiers of the list of prepared target cells.

[0134] In some example embodiments, in response to the prepared candidate node 440 becoming a new serving node after the inter-CU LTM cell change, the prepared candidate node 440 may retrieve a target identifier associated with the new serving cell and a further identifier of a candidate target cell. The prepared candidate node 440 may transmit a control plane message to the candidate target cell via a logical connection based on the target identifier and the further identifier.

[0135] In some example embodiments, in response to the apparatus becoming a new serving cell after the inter-CU cell change, the prepared candidate node 440 may transmit to a plurality of prepared candidate nodes, a notification of a change of serving node.

[0136] In some example embodiments, the source node during initial inter-CU subsequent cell change preparation, indicates the candidate target node to prepare additional pair of XnAP Ids to be used by the candidate target node, after inter-CU subsequent cell change. The source node may do this by including a‘Prepare XnAP Ids FLAG’ in HO Request message.

[0137] When the ‘Prepare XnAP Ids FLAG’ is enabled in HO Request message, the candidate target node prepares additional pair of XnAP Ids e.g. ‘XnAP_Id_when_serving’, ‘XnAP_Id_when_target’; the ‘XnAP_Id_when_serving’ is meant to be used when the prepared candidate target node becomes the new serving node and ‘XnAP Id when target’ is meant to be used when the prepared candidate target node remains a prepared candidate target.

[0138] After the preparation of candidate target nodes with LTM inter-CU subsequent cell change configuration, the source node before inter-CU cell-change HO evaluation and execution, transfers over Xn interface, the ‘XnAP Id pair’ of all the prepared target cells to all the prepared candidate target nodes.

[0139] The transfer of the above information might be via a new or an existing Xn interface message. The above information might be transferred in a transparent container.

[0140] Each prepared candidate target node stores the received information for use after inter-CU subsequent cell change; to enable the exchange of UE specific control plane messages.

[0141] In this approach, when a candidate target node becomes a new serving node, it can use the stored XnAP Ids of the prepared candidate target nodes to enable the setup and tear-down of Xn UE associated logical connection dynamically with each inter-CU subsequent cell change, without the need for sending dedicated Xn interface message after LTM inter-CU cell change (as in the case of embodiments with respect to FIG. 4A). In embodiments with respect to FIG. 4A, the setup of Xn UE associated logical connection is via a pair of new Xn messages that shall be used after LTM inter-CU subsequent cell change HO execution.

[0142] The advantage of this solution approach might be: a pair of light weight new Xn messages may serve two key functions, a) Xn UE associated logical connection setup after inter-CU cell subsequent cell change execution, thus avoiding preparation of additional XnAP Ids in advance (which is the case in embodiment 2), and b) the new message pair may be used to update the prepared candidate target cell configuration consistent with last serving cell latest configuration[because the serving cellconfiguration may change from the time of initial inter-CU subsequent cell change preparation],

[0143] Whereas in embodiments with respect to FIG. 4B, the source during initial inter-CU subsequent cell change preparation, is requesting the candidate target nodes to prepare additional pair of XnAP Ids to be used for dynamic Xn logical connection setup and tear-down after inter-CU subsequent cell change HO execution. In this solution alternative, due to the preparation of XnAP Ids in advance, the need for a pair of new Xn interface message to setup Xn UE associated logical connection after inter- CU subsequent cell change HO execution may be avoided. However, this may increase the Xn signaling during initial Inter-CU subsequent cell change preparation. But this may still require an indication over Xn after each inter-CU cell change execution to enable remapping of XnAP Id pairs at each prepared candidate target node.

[0144] Furthermore, as the XnAP Ids are prepared in advance, LTM recovery procedure execution time may be faster.

[0145] Further details of the signaling flow 430 may be illustrated with respect to FIG. 6 A and FIG. 6B. With the signaling flow 430, the prepared candidate node 440 such as a new serving node may be informed about various information which may be used for the subsequent inter-CU cell change procedure. The UE associated Xn logical connection with other prepared candidate target nodes may be established to exchange UE specific control plane messages. The inter-CU cell change procedure may be enhanced.

[0146] In some example embodiments, during the initial preparation, source node indicates that the preparation is for LTM inter-CU subsequent cell change, and each target node assigns ‘LTM-XnAP-Id’ which is independent of source and target node Ids. This Id will be referred by all candidate CUs during subsequent interactions. The source-XnAP-Id for LTM context identification can have fixed value generated from initial source-node. The LTM UE context Id is always referred by ‘Initial-source-gNB- Id + source-UE-Id’ + Target-gNB-Id + LTM-XnAP-Id’ combination.

[0147] FIG. 4C illustrates a signaling flow 450 for inter-CU cell change procedure according to some example embodiments of the present disclosure. The signaling flow 450 involves a serving node 410 and a candidate node 420. By way of example,the serving node 410 may be the network device 120-1 in FIG. 1, and the candidate node 420 may be another network device such as the network device 120-2 or the network device 120-N in FIG. 1. In the following description, it is assumed that the serving node 410 is a source apparatus (also referred to as a source node), and the candidate node 420 is a target apparatus (also referred to as a target node or a prepared candidate node). It is to be understood that although there is a single candidate node 420 shown in the signaling flow 450, in some embodiments, there may be a plurality of second apparatuses such as a plurality of target nodes or candidate nodes in the signaling flow 450.

[0148] In operation, the serving node 410 transmits (4505), to the candidate node 420, after inter-CU LTM cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources. The serving node 410 is a serving node before the inter-CU LTM cell change. The candidate node 420 is a new serving node after the inter-CU LTM cell change. The candidate node 420 receives the list of prepared inter-CU candidate target cells and associated configuration of packet data unit session resources. The candidate node 420 stores the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0149] In some example embodiments, the configuration of packet data unit session resources comprises transport network layer information associated with the packet data unit session resources. Upon a next inter-CU cell change, the candidate node 420 (the new serving node) may initiate data forwarding based on the transport network layer information. Further details of the signaling flow 450 may be illustrated with respect to FIG. 7. With the signaling flow 450, the candidate node 420 such as a new serving node may be informed about the configuration of admitted PDU session resources. Data forwarding may be enabled based on the configuration of admitted PDU session resources.

[0150] FIG. 4D illustrates a signaling flow 470 for inter-CU cell change procedure according to some example embodiments of the present disclosure. The signaling flow 470 involves a serving node 410 and a plurality of prepared candidate nodes 440- 1, 440-2, ... 440-N (N being a positive integer). As used herein, the prepared candidate nodes 440-1, 440-2, ... 440-N may be referred to as a plurality of preparedcandidate nodes 440, or individually referred to as a prepared candidate node 440. By way of example, the serving node 410 may be the network device 120-1 in FIG. 1, and the prepared candidate nodes 440 may be another network device such as the network device 120-2 or the network device 120-N in FIG. 1. In the following description, it is assumed that the serving node 410 is a source apparatus (also referred to as a source node), and the candidate node 440 is a target apparatus (also referred to as a target node or a prepared candidate node).

[0151] In operation, the serving node 410 transmits (4705), to the plurality of prepared candidate nodes 440, during a preparation of inter-CU LTM cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit (PDU) session resources such as admitted PDU session resources. The serving node 410 is a serving node before the inter-CU LTM cell change, and the plurality of prepared candidate nodes 440 comprising a node which is a new serving node after the inter-CU LTM cell change. The plurality of prepared candidate nodes 440 receive and store the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0152] In some example embodiments, in response to a change of the configuration of the packet data unit session resources, the serving node 410 may transmit the configuration of the packet data unit session resources to the plurality of prepared candidate nodes.

[0153] In some example embodiments, the list of prepared inter-CU candidate target cells and the associated configuration of the packet data unit session resources is transmitted via at least one of an Xn interface message. For example, the Xn interface message may include a transparent container.

[0154] In some example embodiments, the configuration of packet data unit session resources comprises transport network layer information associated with the packet data unit session resources. If a prepared candidate node 440 becomes a new serving node after the inter-CU LTM cell change, the prepared candidate node 440 may initiate data forwarding based on the transport network layer information. Further details of the signaling flow 470 may be illustrated with respect to FIG. 8. With the signaling flow 470, the prepared candidate node 440 such as a new serving node or furthercandidate node may be informed about the configuration of admitted PDU session resources. Data forwarding may be enabled based on the configuration of admitted PDU session resources.

[0155] It is to be understood that after an inter-CU cell change procedure, the serving node 410 may become a candidate node or target node, and the candidate node 420 or prepared candidate node 440 may become a new serving node or a source node. That is, the role of the serving node 410 and the role of the candidate node 420 or prepared candidate node 440 may change. Actions or operations described with respect to the serving node 410 may be performed by the candidate node 420 or prepared candidate node 440 after the inter-CU cell change procedure, and actions or operations described with respect to the candidate node 420 or prepared candidate node 440 may be performed by the serving node 410 after the inter-CU cell change procedure. The roles or actions of the serving node 410 and the candidate node 420 or the prepared candidate node 440 may vary over the time. Embodiments of the present disclosure is not limited here.

[0156] As mentioned, in some example embodiments, the serving node may inform the candidate node (or target candidate node) about the prepared target candidate cell list. Embodiments regarding informing the candidate node about the prepared target candidate cell list will be described with respect to FIG. 5, which illustrates an example signaling flow 500 for inter-CU cell change procedure in accordance with some example embodiments of the present disclosure. The signaling flow 500 involves a UE 510, a source gNB 520, a target gNB 530, other potential target gNB(s) 540, an AMF 542 and a UPF(s) 544. By way of example, the UE 510 may be an example of the terminal device 110 in FIG. 1, the source gNB 520 may be an example of the network device 120-1 in FIG. 1 or the serving node 410 in FIG. 4A, the target gNB 530 may be an example of the network device 120-2 in FIG. 1 or the candidate node 420 in FIG. 4 A, and the other potential target gNB may be the network device 120-N.

[0157] As shown in FIG. 5, actions before and after block 550 are the same as steps shown in FIG. 3A and FIG. 3B, which will not be described here. At block 560, the inter-CU subsequent cell change HO is executed, and at block 570, the target gNB 530 becomes new serving node. At block 550, the source gNB 520 transmits (5010) prepared target cell list included in LTM cell change info transfer message to thetarget gNB 530. In other words, the source gNB 520 upon receiving HO Success from the candidate target node, transfers the prepared candidate target cell list to the new serving node. Alternatively, after the initial inter-CU subsequent cell change preparation, source gNB 520 transfers the prepared target cell list to all the candidate target gNB 530 during preparation, which may be used to initiate Xn logical connection setup towards prepared candidate target nodes after subsequent inter-CU cell change HO execution.

[0158] After receiving the prepared candidate cell list, the target gNB 530 stores (5015) the prepared candidate cell list. In this case, the prepared candidate cell list may be used by new serving node to setup UE 510 associated Xn logical connection, towards prepared candidate target nodes, which is shown in the following steps 5020 to 5045.

[0159] After storing the prepared candidate cell list, the target gNB 530 transmits (5020) HO update message to the other potential target gNB(s) 540. In this case, the target gNB 530, which is the new serving node, initiates HO Update message by including its XnAP Id for the given UE to setup Xn UE associated logical connection. The serving node XnAP Id is required to create candidate node XnAP Id or target node XnAP Id. In some example embodiments, the new serving node may optionally include the serving cell configuration in HO Update message, to allow the other potential target gNB(s) 540 to update the prepared configuration related to PDU session resources, in order to avoid over-booking of resources.

[0160] In addition, the other potential target gNB(s) 540 transmits (5025) the HO update acknowledgement to the target gNB 530, with the XnAP Id it has allocated. In this case, the other potential target gNB(s) 540 stores the XnAP Id pair in HO Update and HO Update acknowledgement in the UE 510 context. It is noted that the foregoing HO update message and HO update acknowledgement shall be new class 1 Xn interface messages.

[0161] In this way, at 5030, the Xn UE associated logical connection between the target gNB 530 and the other potential target gNB(s) 540 may be set up. The Xn UE associated logical connection is setup for the transfer of UE specific control plane messages.

[0162] Similar to step 5020 to step 5030, after the Xn UE associated logicalconnection between the target gNB 530 and the other potential target gNB(s) 540 being set up, the target gNB 5030 transmits (5035) HO update message to the source gNB 520. The source gNB 520 then transmits (5040) the HO update acknowledgement to the target gNB 5030. In this way, at 5045, the Xn UE associated logical connection between the source gNB 520 and the target gNB 530 540 may be set up.

[0163] It is noted that when the scope is expanded from Xn based mobility to N2 based mobility, the essence of the above example embodiments shall be applicable also to N2 based HO involving inter-CU subsequent cell change.

[0164] In some example embodiments, the serving node upon inter-CU cell change HO execution, may transmit the prepared candidate cell list to all the prepared candidate target nodes. In some other example embodiments, after the initial preparation of LTM Inter-CU subsequent cell change, the source node may transmit the prepared target cell list to all the prepared candidate target nodes during preparation phase. The above example embodiments may be used to initiate Xn logical connection setup towards prepared candidate target nodes after subsequent inter-CU cell change HO execution.

[0165] In some example embodiments, the new serving node may initiate a message, such as HO Update message, over the Xn interface towards the prepared candidate target nodes, intended to create Xn UE associated logical connection. In this case, the new serving node includes its XnAP Id. In some example embodiments, the new serving node may use this Xn message to also transmit current serving cell configuration to the candidate target nodes, to allow the candidate target cells to update the prepared configuration related to admitted PDU session resources. In some other example embodiments, HO update message may be after the execution of inter-CU LTM cell change. Alternatively, HO update message may be before the execution of inter-CU LTM cell change, for example, may be during preparation phase.

[0166] In some example embodiments, in response to HO update message, the candidate target node may allocate its XnAP Id and responds to the HO update message with a message, for example, HO Update Ack, by including the allocated XnAP Id. In some example embodiments, the candidate target node may store the allocated XnAP Id mapped to the new serving node’s XnAP Id received in HO update message in the UE context for subsequent transfer of UE specific control plane messages.

[0167] As mentioned, in some example embodiments, the serving node may transmit a message indicative of a preparation of identifiers to prepared candidate nodes. Such embodiments will be further described with respect to FIG. 6A and FIG. 6B, which illustrates signaling flow 600 and signaling flow 690 for inter-CU cell change procedure in accordance with some example embodiments of the present disclosure. The signaling flow 600 and the signaling flow 690 involves a UE 610, a source gNB 620, a target gNB 630, other potential target gNB(s) 640, an AMF 642 and a UPF(s) 644. By way of example, the UE 610 may be an example of the terminal device 110 in FIG. 1, the source gNB 630 may be an example of the network device 120-1 in FIG. 1 or the serving node 410 in FIG. 4B, the target gNB may be an example of the network device 120-2 in FIG. 1 or the prepared candidate node 440 in FIG. 4B, and the other potential target gNB may be the network device 120-N. It is noted that the order of acts / steps shown in FIG. 6A and FIG. 6B is only an example not limitation. With the procedure shown in FIG. 6A and FIG. 6B, there would be essential enhancements to support setup UE associated Xn Logical connection in LTM inter-CU subsequent cell change feature. In addition, the proposed enhancements are expected to be integral to Inter-CU LTM subsequent cell change baseline signaling, and the procedure can avoid the need for re-preparation of candidate target nodes by the new serving node after inter-CU subsequent cell change.

[0168] As shown in FIG. 6 A, at block 650, the source gNB 620 triggers the preparation of candidate target cells for LTM inter-CU subsequent cell change with a new indication “Prepare XnAP Ids FLAG”. In addition, at block 660, the target gNB 630 and the other potential target gNB(s) 640 responds to the indication “Prepare XnAP Ids FLAG” by including prepared pair of XnAP Ids. For example, the prepared pair of XnAP Ids may be “XnAP ID when serving” and “Xn AP ID when targef ’ .

[0169] The source gNB 620 transmits (6005) LTM cell change info transfer message to the target gNB 630. In other words, the source gNB 620 transmits (6005) prepared candidate target cell list with associated XnAP Id pair to the target gNB 630 via Xn interface message. After receiving the message, the target gNB 630 stores (6010) the received XnAP Id configuration associated with the prepared target cell Id.

[0170] The source gNB 620 transmits (6015) LTM cell change info transfermessage to the other potential target gNB(s) 640. In other words, the source gNB 620 transmits (6015) prepared candidate target cell list with associated XnAP Id pair to the other potential target gNB(s) 640 via Xn interface message. After receiving the message, the other potential target gNB(s) 640 stores (6020) the received XnAP Id configuration associated with the prepared target cell Id.

[0171] At block 680, the LTM inter-CU subsequent cell change HO is executed, then the target gNB 630 becomes the new serving node at 6030. In addition, the target gNB 630, i.e., the new serving node, shall retrieve (6035) the XnAP Id associated with the current serving cell and the XnAP Id of the candidate target cell to which it may want to send a control plane message. If the new serving node such as the target gNB 630 wants to send UE specific control plane messages to the candidate target nodes, then it may use the stored XnAP Ids, thus creating the Xn UE associated logical connection at 6040 and 6045.

[0172] The new serving node such as the target gNB 630 may initiate (6042) an “LTM serving node change notification” via a new or class 2 existing Xn message to the other potential target gNB(s) 640 and the source gNB 620, to notify each of the prepared candidate nodes that the serving node has changed.

[0173] In some example embodiments, during initial inter-CU subsequent cell change preparation, the source node may indicate the candidate target node to prepare additional pair of XnAP Ids to be used by the candidate target node, after inter-CU subsequent cell change. In some examples, the source node may include an indication “Prepare XnAP Ids FLAG” in HO Request message.

[0174] In some example embodiments, when the indication “Prepare XnAP Ids FLAG” is enabled in HO request message, the candidate target node may prepare additional pair of XnAP Ids. For example, “XnAP Id when serving”, which may be used when the prepared candidate target node becomes the new serving node, and “XnAP Id when target”, which may be used when the prepared candidate target node remains a prepared candidate target.

[0175] In some example embodiments, after the preparation of candidate target nodes with LTM inter-CU subsequent cell change configuration, the source node may transfer the “XnAP Id pair” of all the prepared target cells over Xn interface to all the preparedcandidate target nodes before inter-CU cell-change HO evaluation and execution. In some examples, the transfer of the above information may be via a new or an existing Xn interface message. In some other examples, the above information may be transferred in a transparent container.

[0176] In some example embodiments, each prepared candidate target node may store the received information for use after inter-CU subsequent cell change, in order to enable the exchange of UE specific control plane messages. When a candidate target node becomes a new serving node, it may use the stored XnAP Ids of the prepared candidate target nodes to enable the setup and tear-down of Xn UE associated logical connection dynamically with each inter-CU subsequent cell change, without the need for sending dedicated Xn interface message after LTM inter-CU cell change, as the case shown in FIG. 7.

[0177] In some example embodiments, the setup of Xn UE associated logical connection may be via a pair of new Xn messages that shall be used after LTM inter- CU subsequent cell change HO execution. The advantage of this example embodiment is that, a pair of light weight new Xn messages may serve two key functions, the first one is Xn UE associated logical connection setup after inter-CU cell subsequent cell change execution, thus avoiding preparation of additional XnAP Ids in advance, as shown in FIG. 6A. The second one is that the new message pair may be used to update the prepared candidate target cell configuration consistent with last serving cell latest configuration, since the serving cell configuration may change from the time of initial inter-CU subsequent cell change preparation.

[0178] In some other example embodiments, during initial inter-CU subsequent cell change preparation, the source node is requesting the candidate target nodes to prepare additional pair of XnAP Ids. The additional pair of XnAP Ids are used for dynamic Xn logical connection setup and tear-down after inter-CU subsequent cell change HO execution. Alternatively, due to the preparation of XnAP Ids in advance, the need for a pair of new Xn interface message to setup Xn UE associated logical connection after inter-CU subsequent cell change HO execution may be avoided. However, this may increase the Xn signaling during initial Inter-CU subsequent cell change preparation. But this may still require an indication over Xn after each inter-CU cell change execution to enable remapping of XnAP Id pairs at each prepared candidate target node.Furthermore, as the XnAP Ids are prepared in advance, LTM recovery procedure execution time may be faster.

[0179] Alternatively, during the initial preparation, source node may indicate that the preparation is for LTM inter-CU subsequent cell change, and each target node assigns “LTM-XnAP-Id” which is independent of source and target node Ids. This Id will be referred by all candidate CUs during subsequent interactions, and the source-XnAP-Id for LTM context identification may have fixed value generated from initial sourcenode. The LTM UE context Id is always referred by a combination of “Initial-source- gNB-Id”, “source-UE-Id”, “Target-gNB-Id”, and “LTM-XnAP-Id”.

[0180] In some example embodiments, the signaling flow 690 may be performed after the handover completion. As shown in the signaling flow 690, the target gNB 630 becomes the new serving node. The UE 610 may transmit LI measurement report to the target gNB 630. The target gNB 630 may trigger LTM. The target gNB may transmit LTM cell swith command to UE 610. LTM handover completion may be performed. The UE 610 may transmit RRC reconfiguration completion to other potential target gNB(s) 640 which may become a new serving node. The other potential target gNB(s) 640 may transmit (6910) an HO success to the target gNB 630. The other potential target gNB(s) 640 may become (6930) a new serving node. Then, a handover completion may be performed in a similar way as described with respect to FIG. 6A. That is, the new serving node (that is, the other potential target gNB(s) 640) may retrieve stored XnAP IDs to trigger the Xn UE associated logical connection setup. The new serving node (that is, the other potential target gNB(s) 640) may transmit LTM serving node change notification to other candidate nodes, such as the source gNB 620 and the target gNB 630. In this way, it provides enhancements to support setup UE associated Xn Logical connection in LTM inter-CU subsequent cell change feature. Enhancements are expected to be integral to Inter-CU LTM subsequent cell change baseline signaling. In addition, it avoids the need for re-preparation of candidate target nodes by the new serving node after inter-CU subsequent cell change.

[0181] As mentioned above, in some example embodiments, the serving node may transmit the configuration of PDU session resources to the new serving node or to the prepared candidate nodes. Details of such embodiments are now described with respect to FIG. 7 and FIG. 8.

[0182] FIG. 7 illustrates a signaling flow 700 for an inter-CU cell change procedure according to some example embodiments of the present disclosure. The signaling flow 700 involves a UE 701, a source gNB 702, a target gNB 703, other potential target gNB(s) 704, an AMF 705 and a UPF(s) 706. By way of example, the UE 701 may be an example of the terminal device 110 in FIG. 1, the source gNB 702 may be an example of the network device 120-1 in FIG. 1 or the serving node 410 in FIG. 4C and FIG. 4D, the target gNB may be an example of the network device 120-2 in FIG. 1 or the candidate node 420 in FIG. 4C or the prepared candidate node 440 in FIG. 4D, and the other potential target gNB may be the network device 120-N.

[0183] In operation, a handover preparation 710 may be performed. In the handover preparation 710, the source gNB 702 may be an initial serving node for the UE 701. That is, the UE 701 and the source gNB 702 may communicate (712) user data with each other. The source gNB 702 may also communicate (714) the user data with other device such as the UPD(s) 706. The UE 701 may perform L3 measurements and transmit (716) the L3 measurement reports to the source gNB 702.

[0184] In response to receiving the L3 measurement reports, the source gNB 702 may make (718) an LTM decision. The source gNB 701 may transmit (720) a handover request to the target gNB 703, and transmit (722) a handover request to the other potential target gNB(s) 704. The handover request may include a configuration of a source cell such as a source cell corresponding to the source gNB 702. That is, the source gNB 702 (that is, the source node) triggers the preparation of candidate target cells for LTM inter-CU subsequent cell change.

[0185] In response to receiving the handover request, the target gNB 703 may perform (724) an admission control. The target gNB 703 may also perform (726) a bearer context setup at gNB-CU-UP and UE context setup at gNB -DU. Likewise, the other potential target gNB(s) 704 may perform (728) an admission control and perform (730) bearer context setup at gNB-CU-UP and UE context setup at gNB-DU.

[0186] The target gNB 703 may transmit (732) a handover request acknowledgement (ACK) to the source gNB 702. The handover request ACK may include admitted PDU session resources list. Likewise, the other potential target gNB(s) 704 may transmit (734) a handover request ACK including the admitted PDU session resources list to the source gNB 702. That is, the (potential) target gNB(s) such as candidatetarget nodes may respond with admitted PDU session resources list.

[0187] The source gNB 702 may transmit an RRC reconfiguration to the UE 701. The RRC reconfiguration may include LTM Inter- CU_SubSeqCellChange_candidate_Conf_list. The RRC reconfiguration may include re-prepared source cell reconfiguration. That is, the source gNB 702 such as source node may reconfigure the UE 701 with LTM inter-CU subsequent cell change candidate target cells configuration. The UE 701 may transmit (738) an RRC reconfiguration complete message to the source gNB 702. In this way, the handover preparation 710 may be completed.

[0188] A handover evaluation and execution 740 may be performed after the handover preparation 710. In some example embodiments, the UE 701 may transmit (742) a LI measurement report to the source gNB 702. That is, UE 701 reports LI measurements. The source gNB 702 may trigger (744) an LTM based on the LI measurement report. The source gNB 702 may transmit (746) an LTM cell switch command to the UE 701. In other words, the source node triggers LTM cell switch command. The UE 701 may store (748) the candidate configuration of prepared targets after cell change.

[0189] In some example embodiments, the source gNB 702 may transmit (750) a message such as LTM Cell Change lnfo Transfer to the target gNB 703. The message may include the information regarding the set of candidate cells aforementioned. For example, the source gNB 702 (that is, the source node) transfers prepared candidate target cell list with a configuration of PDU session resources for the set of candidate cells such as associated admitted PDU session list to the new serving node (that is, the target gNB 703) via Xn interface message. That is, after the execution of inter-CU LTM cell change, the source node (that is, the current serving node) may transfer, over Xn interface, a configuration of the admitted PDU session resources of all the inter-CU candidate target cells to the new serving node.

[0190] As an example, the transfer of the above information might be via a new or an existing Xn interface message. As another example, the above information might be transferred in a transparent container.

[0191] In some example embodiments, the source node may also optionally transferserving cell configuration to allow the new serving node to synchronize with the last serving cell configuration. For example, the source node, in addition to the admitted PDU session resources of all the inter-CU candidate target cells, may transfer the latest last serving cell configuration via the Xn message, which may allow the new serving node to update its prepared LTM inter-CU subsequent cell change configuration.

[0192] The target gNB 703 (that is, the new serving node) may extract, process and store (752) the other prepared candidate cells information. For example, the target gNB 703 such as the new serving node may store the received candidate target cell list and the associated admitted PDU session resources list. The stored PDU session resource info may contain the TNL information which shall be used by the new serving node to initiate data forwarding upon next inter-CU LTM cell change. The target gNB 703 may synchronize (754) the configurations of the last serving cell. The new serving node may store the received other prepared candidate target cells configuration related to admitted PDU session resources (e.g. to be added). The stored configuration may be used during the next inter-CU cell change to initiate (or support) data forwarding.

[0193] After that, an LTM handover completion (756) may be performed by the UE 701, the source gNB 702 and the target gNB 703. In this way, the handover evaluation and execution (740) may be completed. The UE 701 may transmit (758) an RRC reconfiguration complete message to the target gNB 703 after the handover evaluation and execution (740).

[0194] It is to be noted that although in FIG. 7, the transmission of the LTM Cell Change lnfo Transfer is before the storing (752) of the other prepared candidate cells information, in some other embodiments, the transmission of the LTM Cell Change lnfo Transfer may be after the transmitting (758) of the RRC reconfiguration complete message.

[0195] In embodiments described with respect to FIG. 7, the transfer of admitted PDU session resources of all the inter-CU candidate target cells is done at the time of inter- CU LTM subsequent cell change HO execution. Thus, the source / serving node may transfer the information over Xn only to the new serving node and not to all the prepared candidate target nodes. Resulting in reduced Xn signaling. However, in the case of LTM recovery, the serving node may have to transfer the above information tothe candidate target node of the selected inter-CU LTM cell for recovery.

[0196] The UE 701 and the target gNB 703 may perform an RRC reconfiguration procedure (760). For example, data radio bearer (DRB) setup or release and / or quality of service (QoS) flow to DRB mapping may be performed.

[0197] The target gNB 703 may transmit (762) a handover success message to the source gNB 702. The source gNB 702 may transmit a secondary node (SN) status transfer to the target gNB 703. The target gNB 703 (that is, the target node) becomes (766) the new serving node. The user data may be transmitted (768) from the UPF(s) to the source gNB 702 and then be forwarded to the target gNB 703. The target gNB 703 may transmit (770) a path switch message to the AMF 705. A path switch in UPF (772) may be performed by the AMF 705 and the UPF(s) 706.

[0198] An end marker may be transmitted (774) from the UPF(s) 706 to the source gNB 702 and then be forwarded to the target gNB 703. The UPF(s) 706 may then transmit (776) user data to the target gNB 703. In response to receiving the user data from the UPF(s) 706, the target gNB 703 may transmit (778) a path switch ACK to the AMF 705. In this way, user data may be transmitted (782) between the UE 701 and the target gNB 703, and transmitted (780) between the target gNB 703 and the UPF(s) 706. The target gNB 703 may transmit (784) a UE context release message to the source gNB 702.

[0199] An example procedure of inter-CU cell change procedure has been described with respect to FIG. 7. FIG. 8 illustrates a signaling flow 800 of another example of inter-CU cell change procedure. Similar to the signaling flow 700, the signaling flow 800 involves the UE 701, the source gNB 702, the target gNB 703, the other potential target gNB(s) 704, the AMF 705 and the UPF(s) 706. It is to be understood that several signaling or operations involved in the signaling flow 800 are same or similar with those of the signaling flow 700. Details of some same or similar signaling or operations will not be repeated here.

[0200] As shown, a handover preparation (810) may be performed. The difference between the handover preparation (810) and the handover preparation (710) in FIG. 7 is that in the handover preparation (810), after receiving the RRC refiguration complete message transmitted (738) by the UE 701, the source gNB 702 may transmit (812) amessage such as LTM Cell Change lnfor Transfer to the target gNB 703. The message may include the information regarding the set of candidate cells aforementioned. For example, the message may include the prepared target cell list together with a configuration of associated admitted PDU session resources list. The target gNB 703 may extract, process and store (814) other prepared candidate cells information received from the source gNB. For example, the target gNB 703 such as the new serving node may store the received candidate target cell list and the associated admitted PDU session resources list.

[0201] Likewise, the source gNB 702 may transmit (816) a message such as LTM Cell Change lnfor Transfer to the other potential target gNB(s) 704. The message may include the prepared target cell list together with associated admitted PDU session resources list. The other potential target gNB(s) 704 may extract, process and store (818) other prepared candidate cells information received from the source gNB. That is, the other potential target gNB(s) 704 may store the received candidate target cell list and the associated admitted PDU session resources list.

[0202] That is, after the preparation of candidate target nodes with LTM inter-CU subsequent cell change configuration and before inter-CU cell-change HO evaluation and execution, the source gNB 702 (that is, the source node), transfers over Xn interface, the admitted PDU session resources of all the inter-CU candidate target cells to all the prepared candidate target nodes. As an example, the transfer of the above information might be via a new or an existing Xn interface message. As another example, the above information might be transferred in a transparent container.

[0203] In this way, the source node transfers prepared candidate target cell list with associated admitted PDU session list to all the prepared candidate target nodes via Xn interface message. The stored PDU session resource info may contain the TNL information which shall be used after inter-CU cell change by the candidate target node that becomes new serving node to initiate data forwarding upon next inter-CU LTM cell change. After inter-CU subsequent cell change, when one of the prepared candidate target nodes become the new serving node, it may have the TNL information of the admitted PDU sessions, to initiate data forwarding.

[0204] After the handover preparation (810), a handover evaluation and execution (820) may be performed. In the handover evaluation and execution (820), the UE 701may transmit (742) a LI measurement report to the source gNB 702. That is, UE 701 reports LI measurements. The source gNB 702 may trigger (744) an LTM based on the LI measurement report. The source gNB 702 may transmit (746) an LTM cell switch command to the UE 701. In other words, the source node triggers LTM cell switch command. The UE 701 may store (748) the candidate configuration of prepared targets after cell change. After that, an LTM handover completion (756) may be performed by the UE 701, the source gNB 702 and the target gNB 703. The handover evaluation and execution (820) may thus be completed.

[0205] After the handover evaluation and execution (820), the target gNB 703 may transmit (762) a handover success message to the source gNB 702. The source gNB 702 may transmit a secondary node (SN) status transfer to the target gNB 703. The target gNB 703 (that is, the target node) becomes (766) the new serving node. The user data may be transmitted (768) from the UPF(s) to the source gNB 702 and then be forwarded to the target gNB 703. The target gNB 703 may transmit (770) a path switch message to the AMF 705. A path switch in UPF (772) may be performed by the AMF 705 and the UPF(s) 706.

[0206] An end marker may be transmitted (774) from the UPF(s) 706 to the source gNB 702 and then be forwarded to the target gNB 703. The UPF(s) 706 may then transmit (776) user data to the target gNB 703. In response to receiving the user data from the UPF(s) 706, the target gNB 703 may transmit (778) a path switch ACK to the AMF 705. In this way, user data may be transmitted (782) between the UE 701 and the target gNB 703, and transmitted (780) between the target gNB 703 and the UPF(s) 706. The target gNB 703 may transmit (784) a UE context release message to the source gNB 702.

[0207] In the signaling flow 800, the transfer of admitted PDU session resources of all the inter-CU candidate target cells is done during inter-CU LTM subsequent cell change preparation phase. Thus, the source / serving node must transfer the information over Xn to all the prepared candidate nodes. Such transmission may result in increased Xn signaling, but with a potential advantage of marginally faster inter-CU subsequent cell change execution time, compared to embodiments of the signaling flow 700.

[0208] Alternatively, in some embodiments, the signaling of all the preparedcandidates may be provided to new serving-node only for the first time. For further serving node changes this information need not be exchanged. Each node keeps track of the information change done across other nodes to avoid this repeated for every node change.

[0209] It is to be understood that although the signaling flows 700 and 800 are described with the inter-CU cell change being an Xn based mobility, some embodiments described with respect to the signaling flows 700 and 800 may also be applicable for N2 based mobility or any other suitable mobility, such as N2 based HO involving inter-CU subsequent cell change. Scope of embodiments of the present disclosure is not limited here.

[0210] These embodiments described with respect to the signaling flows 700 and 800 may achieve enhancements to support data forwarding in LTM inter-CU subsequent cell change feature. Such enhancements may be integral to inter-CU LTM subsequent cell change baseline signaling. The need for re-preparation of candidate target nodes may be avoided by the new serving node after inter-CU subsequent cell change.

[0211] It would be appreciated that some example specifications, signaling flows and embodiments are provided above, and the detailed description may be varied. It is to be understood that these signaling flows 200, 300, 300', 400, 430, 450, 470, 500, 600, 690, 700, and / or 800 may be used separately, or in any suitable combinations. In this way, the inter-CU cell change procedure such as LTM inter-CU subsequent cell change procedure can be enhanced.

[0212] FIG. 9 shows a flowchart of an example method 900 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 900 will be described from the perspective of the network device 120 in FIG. 1.

[0213] At block 910, the network device 120 transmits, to one of the prepared candidate nodes that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change, a first message including a list of prepared target inter-CU cells. The network device 120 is a serving node before the inter-CU LTM cell change.

[0214] In some example embodiments, the method 900 further comprising: receiving,from the prepared candidate node upon becoming the new serving node, a second message including a first identifier of the prepared candidate node; and transmitting, to the new serving node, a third message including a second identifier of the apparatus, wherein the apparatus becomes a prepared candidate node after the inter-CU LTM cell change.

[0215] In some example embodiments, the second message further includes a serving cell configuration of the target node.

[0216] In some example embodiments, at least one of the transmission of the first message or the reception of the second message is upon an execution of the inter-CU cell change, or during a preparation of the inter-CU LTM cell change.

[0217] In some example embodiments, the method 900 further comprising: in response to receiving the second message, updating a configuration of packet data unit session resources.

[0218] In some example embodiments, the method 900 further comprising: storing the prepared inter-CU target cell list of all the prepared inter-CU candidate nodes.

[0219] In some example embodiments, at least one of the first message, the second message or the third message is via an Xn interface message.

[0220] In some example embodiments, at least one of the first identifier and the second identifier comprises an Xn application protocol (XnAP) identifier.

[0221] FIG. 10 shows a flowchart of an example method 1000 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1000 will be described from the perspective of the network device 120 in FIG. 1.

[0222] At block 1010, the network device 120 receives, from a serving node, a first message including a list of prepared target cells for an inter-centralized unit (CU) cell change. The network device 120 is a prepared candidate node that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

[0223] In some example embodiments, the network device 120 may transmit, to a plurality of prepared candidate nodes, a second message including a first identifier ofthe apparatus, the plurality of prepared candidate nodes comprising the serving node before the inter-CU LTM cell change; and receive, from the plurality of prepared candidate nodes, a plurality of third messages including respective identifiers of the plurality of prepared candidate node.

[0224] In some example embodiments, the second message further comprises a serving cell configuration of the apparatus.

[0225] In some example embodiments, the method 1000 further comprising: storing the list of prepared target cells in the first message; and initiating an Xn logical connection setup towards the plurality of prepared candidate nodes based on the list of prepared target cells after an execution of the inter-CU cell change.

[0226] FIG. 11 shows a flowchart of an example method 1100 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1100 will be described from the perspective of the network device 120 in FIG. 1.

[0227] At block 1110, the network device 120 transmits, to a plurality of prepared candidate nodes, a first message indicative of a preparation of identifiers of a prepared candidate node. The network device 120 is a serving node before an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

[0228] At block 1120, the network device 120 receives, from the plurality of prepared candidate nodes, a plurality of second messages, each second message including a pair of identifiers of a respective prepared candidate node, the pair of identifiers comprising a first identifier with the respective prepared candidate node meant to be used when the candidate node becomes a new serving node and a second identifier with the respective prepared candidate node meant to be used when the candidate node remains a candidate node.

[0229] At block 1130, the network device 120 transmits, to the plurality of prepared candidate nodes, a third message including a list of prepared target cells for the inter- CU cell change and a configuration of a plurality of pairs of identifiers of the plurality of prepared candidate nodes.

[0230] In some example embodiments, the transmission of the first message is during a preparation of the inter-CU cell change.

[0231] In some example embodiments, the transmission of the third message is during a preparation of the inter-CU cell change and before an evaluation and execution of the inter-CU cell change.

[0232] In some example embodiments, each identifier of the plurality of pairs of identifiers comprises an Xn application protocol (XnAP) identifier.

[0233] In some example embodiments, the plurality of prepared candidate nodes comprises a target node, wherein the target node is a new serving node after the inter- CU LTM cell change, and the network device 120 may receive, from the target node, a notification of a change of serving node.

[0234] In some example embodiments, at least one of the first message, the plurality of second messages or the third message is via an Xn interface message.

[0235] FIG. 12 shows a flowchart of an example method 1200 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1200 will be described from the perspective of the network device 120 in FIG. 1.

[0236] At block 1210, the network device 120 receives, from a serving node, a first message indicative of a preparation of identifiers of the apparatus. The network device 120 is a prepared candidate node for an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

[0237] At block 1220, the network device 120 transmits, to the serving node, a second message including a pair of identifiers of the apparatus, the pair of identifiers comprising a first identifier with the apparatus meant to be used when the candidate node becomes new serving node and a second identifier is meant to be used when the candidate node remains a candidate node.

[0238] At block 1230, the network device 120 receives, from the serving node, a third message including a list of prepared target cells for the inter-CU LTM cell change and a configuration of a plurality of pairs of identifiers of a plurality of prepared candidate nodes, the plurality of prepared candidate nodes comprising the apparatus.

[0239] In some example embodiments, the method 1200 further comprises: storing the configuration of the plurality of pairs of identifiers of the plurality of preparedcandidate nodes associated with cell identifiers of the list of prepared target cells.

[0240] In some example embodiments, the method 1200 further comprises: in response to the apparatus becoming a new serving node after the inter-CU LTM cell change, retrieving a target identifier associated with the new serving cell and a further identifier of a candidate target cell; and transmitting a control plane message to the candidate target cell via a logical connection based on the target identifier and the further identifier.

[0241] In some example embodiments, the method 1200 further comprises: in response to the apparatus becoming a new serving cell after the inter-CU cell change, transmitting to a plurality of prepared candidate nodes, a notification of a change of serving node.

[0242] FIG. 13 shows a flowchart of an example method 1300 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1300 will be described from the perspective of the network device 120 in FIG. 1.

[0243] At block 1310, the network device 120 transmits, to a candidate node, after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources. The network device 120 is a serving node before the inter-CU LTM cell change, and the candidate node is a new serving node after the inter-CU LTM cell change.

[0244] FIG. 14 shows a flowchart of an example method 1400 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1400 will be described from the perspective of the network device 120 in FIG. 1.

[0245] At block 1410, the network device 120 receives, from a serving node after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources. The network device 120 is a new serving node after the inter-CU LTM cell change.

[0246] At block 1420, the network device 120 stores the list of prepared inter-CUcandidate target cells and the associated configuration of packet data unit session resources.

[0247] In some example embodiments, the configuration of packet data unit session resources comprises transport network layer information associated with the packet data unit session resources, and the network device 120 may upon a next inter-CU cell change, initiate data forwarding based on the transport network layer information.

[0248] FIG. 15 shows a flowchart of an example method 1500 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1500 will be described from the perspective of the network device 120 in FIG. 1.

[0249] At block 1510, the network device 120 transmits, to a plurality of prepared candidate nodes, during a preparation of inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources. The network device 120 is a serving node before the inter-CU LTM cell change, and the plurality of prepared candidate nodes comprising node which is a new serving node after the inter-CU LTM cell change .

[0250] In some example embodiments, the method 1500 further comprises: in response to a change of the configuration of the packet data unit session resources, transmitting the configuration of the packet data unit session resources to the plurality of prepared candidate nodes.

[0251] In some example embodiments, the list of prepared inter-CU candidate target cells and the associated configuration of the packet data unit session resources is transmitted via at least one of an Xn interface message.

[0252] FIG. 16 shows a flowchart of an example method 1600 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1600 will be described from the perspective of the network device 120 in FIG. 1.

[0253] At block 1610, the network device 120 receives, from a serving node, during a preparation of inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM)cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources. The network device 120 is a prepared candidate node for the inter-CU LTM cell change.

[0254] At block 1620, the network device 120 stores the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0255] In some example embodiments, the configuration of packet data unit session resources comprises transport network layer information associated with the packet data unit session resources. In response to the apparatus becoming a new serving node after the inter-CU LTM cell change, the network device 120 may initiate data forwarding based on the transport network layer information.

[0256] In some example embodiments, an apparatus capable of performing any of the method 900 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 900. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the network device 120 in FIG. 1.

[0257] In some example embodiments, the apparatus comprises means for transmitting, to one of the prepared candidate nodes that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change, a first message including a list of prepared target inter-CU cells, wherein the apparatus is a serving node before the inter-CU LTM cell change.

[0258] In some example embodiments, an apparatus capable of performing any of the method 1000 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the network device 120 in FIG. 1.

[0259] In some example embodiments, the apparatus comprises means for receiving, from a serving node, a first message including a list of prepared target cells for an inter-centralized unit (CU) cell change, wherein the apparatus is a prepared candidate node that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

[0260] In some example embodiments, an apparatus capable of performing any of the method 1100 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 1100. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the network device 120 in FIG. 1.

[0261] In some example embodiments, the apparatus comprises means for transmitting, to a plurality of prepared candidate nodes, a first message indicative of a preparation of identifiers of a prepared candidate node, wherein the apparatus is a serving node before an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change; means for receiving, from the plurality of prepared candidate nodes, a plurality of second messages, each second message including a pair of identifiers of a respective prepared candidate node, the pair of identifiers comprising a first identifier with the respective prepared candidate node meant to be used when the candidate node becomes a new serving node and a second identifier with the respective prepared candidate node meant to be used when the candidate node remains a candidate node; and means for transmitting, to the plurality of prepared candidate nodes, a third message including a list of prepared target cells for the inter-CU cell change and a configuration of a plurality of pairs of identifiers of the plurality of prepared candidate nodes.

[0262] In some example embodiments, an apparatus capable of performing any of the method 1200 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 1200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the network device 120 in FIG. 1.

[0263] In some example embodiments, the apparatus comprises means for receiving, from a serving node, a first message indicative of a preparation of identifiers of the apparatus, wherein the apparatus is a prepared candidate node for an inter-centralizedunit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change; means for transmitting, to the serving node, a second message including a pair of identifiers of the apparatus, the pair of identifiers comprising a first identifier with the apparatus meant to be used when the candidate node becomes new serving node and a second identifier is meant to be used when the candidate node remains a candidate node; and means for receiving, from the serving node, a third message including a list of prepared target cells for the inter-CU LTM cell change and a configuration of a plurality of pairs of identifiers of a plurality of prepared candidate nodes, the plurality of prepared candidate nodes comprising the apparatus.

[0264] In some example embodiments, an apparatus capable of performing any of the method 1300 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 1300. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the network device 120 in FIG. 1.

[0265] In some example embodiments, the apparatus comprises means for transmitting, to a candidate node, after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the candidate node is a new serving node after the inter-CU LTM cell change.

[0266] In some example embodiments, an apparatus capable of performing any of the method 1400 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 1400. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the network device 120 in FIG. 1.

[0267] In some example embodiments, the apparatus comprises means for receiving, from a serving node after inter- centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a new serving node after the inter-CU LTM cell change ; and means forstoring the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0268] In some example embodiments, the configuration of packet data unit session resources comprises transport network layer information associated with the packet data unit session resources, and the apparatus further comprises: means for upon a next inter-CU cell change, initiating data forwarding based on the transport network layer information.

[0269] In some example embodiments, an apparatus capable of performing any of the method 1500 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 1500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the network device 120 in FIG. 1.

[0270] In some example embodiments, the apparatus comprises means for transmitting, to a plurality of prepared candidate nodes, during a preparation of intercentralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter- CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the plurality of prepared candidate nodes comprising node which is a new serving node after the inter-CU LTM cell change .

[0271] In some example embodiments, the list of prepared inter-CU candidate target cells and the associated configuration of the packet data unit session resources is transmitted via at least one of an Xn interface message.

[0272] In some example embodiments, an apparatus capable of performing any of the method 1600 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 1600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the network device 120 in FIG. 1.

[0273] In some example embodiments, the apparatus comprises means for receiving,from a serving node, during a preparation of inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a prepared candidate node for the inter-CU LTM cell change; and means for storing the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

[0274] In some example embodiments, the configuration of packet data unit session resources comprises transport network layer information associated with the packet data unit session resources, and the apparatus further comprises: means for in response to the apparatus becoming a new serving node after the inter-CU LTM cell change, initiating data forwarding based on the transport network layer information.

[0275] FIG. 17 is a simplified block diagram of a device 1700 that is suitable for implementing example embodiments of the present disclosure. The device 1700 may be provided to implement a communication device, for example, the terminal device 110 or the network device 120 as shown in FIG. 1. As shown, the device 1700 includes one or more processors 1710, one or more memories 1720 coupled to the processor 1710, and one or more communication modules 1740 coupled to the processor 1710.

[0276] The communication module 1740 is for bidirectional communications. The communication module 1740 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 1740 may include at least one antenna.

[0277] The processor 1710 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1700 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

[0278] The memory 1720 may include one or more non-volatile memories and one ormore volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 1724, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a randomaccess memory (RAM) 1722 and other volatile memories that will not last in the powerdown duration.

[0279] A computer program 1730 includes computer executable instructions that are executed by the associated processor 1710. The instructions of the program 1730 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 1730 may be stored in the memory, e.g., the ROM 1724. The processor 1710 may perform any suitable actions and processing by loading the program 1730 into the RAM 1722.

[0280] The example embodiments of the present disclosure may be implemented by means of the program 1730 so that the device 1700 may perform any process of the disclosure as discussed with reference to FIG. 4A to FIG. 16. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0281] In some example embodiments, the program 1730 may be tangibly contained in a computer readable medium which may be included in the device 1700 (such as in the memory 1720) or other storage devices that are accessible by the device 1700. The device 1700 may load the program 1730 from the computer readable medium to the RAM 1722 for execution. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non- transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0282] FIG. 18 shows an example of the computer readable medium 1800 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 1800 has the program 1730 stored thereon.

[0283] Generally, various embodiments of the present disclosure may be implementedin hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0284] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

[0285] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may be provided to a processor or controller of a general-purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[0286] In the context of the present disclosure, the computer program code or relateddata may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0287] The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0288] Further, although operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, although several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable subcombination.

[0289] Although the present disclosure has been described in languages specific to structural features and / or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: transmit, to one of prepared candidate nodes that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change, a first message including a list of prepared target inter-CU cells, wherein the apparatus is a serving node before the inter-CU LTM cell change.

2. The apparatus of claim 1, wherein the apparatus is further caused to: receive, from the prepared candidate node upon becoming the new serving node, a second message including a first identifier of the prepared candidate node; and transmit, to the new serving node, a third message including a second identifier of the apparatus, wherein the apparatus becomes a prepared candidate node after the inter-CU LTM cell change.

3. The apparatus of claim 2, wherein the second message further includes a serving cell configuration of the prepared candidate node.

4. The apparatus of claim 2 or 3, wherein at least one of the transmission of the first message or the reception of the second message is upon an execution of the inter-CU cell change, or during a preparation of the inter-CU LTM cell change.

5. The apparatus of any of claims 2-4, wherein the apparatus is further caused to: in response to receiving the second message, update a configuration of packet data unit session resources.

6. The apparatus of any of claims 1-5, wherein the first identifier and the second identifier comprise Xn application protocol (XnAP) identifiers.

587. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: receive, from a serving node, a first message including a list of prepared target cells for an inter-centralized unit (CU) cell change, wherein the apparatus is a prepared candidate node that becomes a new serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change.

8. The apparatus of claim 7, wherein the apparatus is further caused to: transmit, to a plurality of prepared candidate nodes, a second message including a first identifier of the apparatus, wherein the plurality of prepared candidate nodes comprising the serving node before the inter-CU LTM cell change; and receive, from the plurality of prepared candidate nodes, a plurality of third messages including respective identifiers of the plurality of prepared candidate node.

9. The apparatus of claim 8, wherein the second message further comprises a serving cell configuration of the apparatus.

10. The apparatus of claim 8 or 9, wherein the apparatus is further caused to: store the list of prepared target cells in the first message; and initiate an Xn logical connection setup towards the plurality of prepared candidate nodes based on the list of prepared target cells after an execution of the inter-CU cell change.

11. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: transmit, to a plurality of prepared candidate nodes, a first message indicative of a preparation of identifiers of a prepared candidate node, wherein the apparatus is a serving node before an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change;receive, from the plurality of prepared candidate nodes, a plurality of second messages, each second message including a pair of identifiers of a respective prepared candidate node, the pair of identifiers comprising a first identifier with the respective prepared candidate node meant to be used when the candidate node becomes a new serving node and a second identifier with the respective prepared candidate node meant to be used when the candidate node remains a candidate node; and transmit, to the plurality of prepared candidate nodes, a third message including a list of prepared target cells for the inter-CU cell change and a configuration of a plurality of pairs of identifiers of the plurality of prepared candidate nodes.

12. The apparatus of claim 11, wherein the transmission of the first message is during a preparation of the inter-CU cell change, and wherein the transmission of the third message is during the preparation of the inter- CU cell change and before an evaluation and execution of the inter-CU cell change.

13. The apparatus of any of claims 11-12, wherein each identifier of the plurality of pairs of identifiers comprises an Xn application protocol (XnAP) identifier.

14. The apparatus of any of claims 11-13, wherein the plurality of prepared candidate nodes comprises a target node, wherein the target node is a new serving node after the inter- CU LTM cell change, and the apparatus is further caused to: receive, from the target node, a notification of a change of serving node.

15. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: receive, from a serving node, a first message indicative of a preparation of identifiers of the apparatus, wherein the apparatus is a prepared candidate node for an intercentralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change; transmit, to the serving node, a second message including a pair of identifiers of the apparatus, the pair of identifiers comprising a first identifier with the apparatus meant to beused when the candidate node becomes a new serving node and a second identifier is meant to be used when the candidate node remains a candidate node; and receive, from the serving node, a third message including a list of prepared target cells for the inter-CU LTM cell change and a configuration of a plurality of pairs of identifiers of a plurality of prepared candidate nodes, the plurality of prepared candidate nodes comprising the apparatus.

16. The apparatus of claim 15, wherein the apparatus is further caused to: store the configuration of the plurality of pairs of identifiers of the plurality of prepared candidate nodes associated with cell identifiers of the list of prepared target cells.

17. The apparatus of claim 15 or 16, wherein the apparatus is further caused to: in response to the apparatus becoming a new serving node after the inter-CU LTM cell change, retrieve a target identifier associated with the new serving cell and a further identifier of a candidate target cell; and transmit a control plane message to the candidate target cell via a logical connection based on the target identifier and the further identifier.

18. The apparatus of any of claims 15-17, wherein the apparatus is further caused to: in response to the apparatus becoming a new serving cell after the inter-CU cell change, transmit, to a plurality of prepared candidate nodes, a notification of a change of serving node.

19. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: transmit, to a candidate node, after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the candidate node is a new serving node after the inter-CU LTM cell change.

20. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: receive, from a serving node after an inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change execution, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a new serving node after the inter-CU LTM cell change; and store the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

21. The apparatus of claim 20, wherein the configuration of packet data unit session resources comprises transport network layer information associated with the packet data unit session resources, and the apparatus is further caused to: upon a next inter-CU cell change, initiate data forwarding based on the transport network layer information.

22. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to: transmit, to a plurality of prepared candidate nodes, during a preparation of intercentralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a serving node before the inter-CU LTM cell change, and the plurality of prepared candidate nodes comprising node which is a new serving node after the inter-CU LTM cell change.

23. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to:62receive, from a serving node, during a preparation of inter-centralized unit (CU) layer 1 or layer 2 triggered mobility (LTM) cell change or before an evaluation and execution of the inter-CU LTM cell change, a list of prepared inter-CU candidate target cells and an associated configuration of packet data unit session resources, wherein the apparatus is a prepared candidate node for the inter-CU LTM cell change; and store the list of prepared inter-CU candidate target cells and the associated configuration of packet data unit session resources.

24. The apparatus of claim 23, wherein the configuration of packet data unit session resources comprises transport network layer information associated with the packet data unit session resources, and the apparatus is further caused to: in response to the apparatus becoming a new serving node after the inter-CU LTM cell change, initiate data forwarding based on the transport network layer information.

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