XN UE assocation management

Abstract

Exemplary embodiments of the present disclosure relate to an enhancement on Xn UE association management In an aspect, a first network device transmits, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device. The first network device receives, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

Description

XN UE ASSCOICATION MANAGEMENTFIELD

[0001] Various example embodiments relate to the field of communication and in particular, to a terminal device, a network device, methods, apparatuses and a computer readable storage medium for an enhancement on Xn UE association management.BACKGROUND

[0002] A communication network can be seen as a facility that enables communications between two or more communication devices, or provides communication devices access to a data network. A mobile or wireless communication network is one example of a communication network.

[0003] Such communication networks operate in accordance with standards, such as those promulgated by 3GPP (Third Generation Partnership Project) or ETSI (European Telecommunications Standards Institute). Examples of such standards include the so-called 5G (5th Generation) standard or other standards promulgated by 3GPP.SUMMARY

[0004] In general, exemplary embodiments of the present disclosure provide a solution for providing an enhancement on Xn UE association management.

[0005] In a first aspect, there is provided a first network device. The first network device may include at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the first network device at least to: transmit, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device; and receive, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0006] In a second aspect, there is provided a second network device. The second network device may include at least one processor and at least one memory storing instructions that,when executed by the at least one processor, cause the second network device at least to: receive, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device; and transmit, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0007] In a third aspect, there is provided a method. The method may include: transmitting, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device; and receiving, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0008] In a fourth aspect, there is provided a method. The method may include: receiving, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device; and transmitting, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0009] In a fifth aspect, there is provided an apparatus. The apparatus may include: means for transmitting, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device; and means for receiving, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0010] In a sixth aspect, there is provided an apparatus. The apparatus may include: means for receiving, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device; and means for transmitting, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the secondnetwork device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0011] In a seventh aspect, there is provided a non-transitory computer readable medium including program instructions for causing an apparatus to perform at least the method according to any of fourth or sixth aspects.

[0012] In an eighth aspect, there is provided a computer program including instructions, which, when executed by an apparatus, cause the apparatus at least to: transmit, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device; and receive, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0013] In a ninth aspect, there is provided a computer program including instructions, which, when executed by an apparatus, cause the apparatus at least to: receive, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device; and transmit, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0014] In an eleventh aspect, there is provided a first network device. The first network device may include: transmitting circuitry configured to transmit, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device; and receiving circuitry configured to receive, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0015] In a twelfth aspect, there is provided a second network device. The network device may include: receiving circuitry configured to receive, from a first network device, a first message comprising an indication of the second network device which is a target candidatenetwork device, and at least one other target candidate network device; and transmitting circuitry configured to transmit, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0016] 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.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Some exemplary embodiments will now be described with reference to the accompanying drawings, in which:

[0018] Fig. 1 A illustrates a communication environment in which some embodiments of the present disclosure can be implemented;

[0019] Fig. IB illustrates a signaling procedure for LTM in Rel. 18;

[0020] Fig. 1C illustrates a conditional handover for intra-NR;

[0021] Fig. ID illustrates a simple LTM inter-CU subsequent cell change scenario capturing the problem;

[0022] Fig. 2 illustrates an exemplary signaling chart illustrating communication process in accordance with some embodiments of the present disclosure;

[0023] Fig. 3 illustrates an example of a signaling process of enhancement on Xn UE association management according to some embodiments of the present disclosure;

[0024] Fig. 4 illustrates an example of a signaling process of enhancement on Xn UE association management according to some embodiments of the present disclosure;

[0025] Fig. 5 illustrates a flowchart of a method implemented at a first network device in accordance with some embodiments of the present disclosure;

[0026] Fig. 6 illustrates a flowchart of a method implemented at a second network device in accordance with some embodiments of the present disclosure;

[0027] Fig. 7 illustrates a simplified block diagram of an apparatus that is suitable forimplementing embodiments of the present disclosure; and

[0028] Fig. 8 illustrates a block diagram of an example computer readable medium in accordance with some embodiments of the present disclosure.

[0029] Throughout the drawings, the same or similar reference numerals represent the same or similar elements.DETAILED DESCRIPTION

[0030] Principles 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. The disclosure described herein can be implemented in various manners other than the ones described below.

[0031] 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.

[0032] 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.

[0033] It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. 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.

[0034] 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 singularforms “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. 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.

[0035] 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 (including digital 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.

[0036] 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.

[0037] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as 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-IoT) 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 future fifth generation (5G) 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.

[0038] 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 services therefrom. 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), a NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, a low power node such as a femto, a pi co, and so forth, depending on the applied terminology and technology.

[0039] 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 industrialwireless networks, and the like. In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0040] As part of Rel. 19 Mobility work item (RP -234036) the following objective is captured:- 4.1 Objective of SI or Core part WI or Testing part WI- Specify support for subsequent LTM mobility procedures aiming to avoid RRC configuration between cell switches as per Rel-18 LTM- Note: Rel. 18 intra-CU LTM procedure is considered as baseline for adding inter-CU support

[0041] Reference is first made to Fig. 1 A, which illustrates an example communication system 100 in which embodiments of the present disclosure may be implemented. The system 100 includes a first network device 110, a second network device 120, a third network device 130, and a terminal device 140. The terminal device 140 is capable of connecting and communicating in an UL or DL with the network devices 110, 120 and 130 as long as the terminal device 140 is located within the corresponding cells of the network devices 110, 120 and 130. In communication systems, an UL refers to a link in a direction from a terminal device 140 to the network devices 110, 120 and 130, and a DL refers to a link in a direction from the network devices 110, 120 and 130 to the terminal device 140. The network devices 110, 120 and 130 may transmit scheduling information scheduling an uplink transmission to the terminal device 140, and the terminal device 140 may transmit a plurality of repetitions of the uplink transmission to the network devices 110, 120 and 130.

[0042] It is to be understood that the particular number of various communication devices, the particular number of various communication links, the particular number of other elements, and the particular shape of the cells as shown in Fig. 1A is for illustration purpose only without suggesting any limitations. The communication system 100 may include any suitable number of communication devices, any suitable number of communication links, and any suitable number of other elements and any suitable shape of the cells adapted for implementing embodiments of the present disclosure. In addition, it should be appreciated that there may be various wireless as well as wireline communications (if needed) among all of the communication devices.

[0043] Communications in the communication system 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), thefourth generation (4G) and the fifth generation (5G) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 1002.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0044] Embodiments of the present disclosure proposes enhancement necessary to setup UE associated Xn logical connection for the transfer of UE specific control plane messages after each layerl (Ll) / layer 2 (L2) triggered mobility (LTM) inter-centralized unit (inter-CU) subsequent cell change handover (HO) execution.

[0045] 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.

[0046] 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.

[0047] 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 medium access control (MAC) signaling using a MAC control element (CE). Hence, not using RRC signaling as a L3 based handover is one of the current methods for changing between cells. An 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 an LTM candidate cell configuration provided by the network for one or more LTM candidate cells. An LTM candidate cell may be neighbouring cells or a UE’s current serving cells (e.g. SCells).

[0048] In Release-18, LTM measurements on a neighbouring candidate cell are performed using synchronization signal / PBCH blocks (SSB) transmitted by the candidate cell for which the SSB configuration is provided to the UE.

[0049] Before the cell switch, the network may optionally activate one or more transmission configuration indication (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.

[0050] Fig. IB illustrates a signaling procedure for LTM in Rel. 18, and it should be noted that Rel. 18 only covers intra-CU LTM handovers. The procedure for LTM is as follows:

[0051] At step 1, the UE sends a MeasurementReport message to the gNB, and the gNB decides to configure LTM and initiates LTM preparation. At step 2, the gNB transmits an RRCReconfiguration message to the UE including the LTM candidate configurations. At step 3, the UE stores the LTM candidate configurations and transmits an RRCReconfigurationComplete message to the gNB. At step 4a, the UE performs DL synchronization with the candidate cell(s) before receiving the cell switch command. At step 4b, the UE performs early TA acquisition with the candidate cell(s) as requested by the network before receiving the cell switch command as specified in clause 9.2.6 [38.300], This is done via CFRA triggered by a PDCCH order from the source cell, following which the UE 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 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 doesn’t maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity.

[0052] At step 5, the UE performs LI measurements on the configured candidate cell(s) and transmits LI measurement reports to the gNB. LI measurement should be performed as long as RRC reconfiguration (step 2) is applicable. At step 6, the gNB decides to execute cell switch to a target cell and transmits a MAC CE triggering cell switch by including the candidate configuration index of the target cell. The UE switches to the target cell and applies the configuration indicated by candidate configuration index. At step 7, the UE performs the random access procedure towards the target cell, if the UE does not have valid TA of the target cell as specified in clause 6.1.3.75 of TS 38.321. At step 8, the UE completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to the target cell. If the UE has performed a RA procedure in step 7, the UE considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For RACH-less LTM, the UE considers that LTM cell switch execution is successfully completedwhen the UE determines that the network has successfully received its first UL data.

[0053] The steps 4 to 8 may be performed multiple times for subsequent LTM using the LTM candidate configuration(s) provided in step 2. 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 -C interface are captured in TS 38.401.

[0054] In conditional handover (CHO) Rel. 16, the UE is configured with a CHO command containing the target cell configuration and a condition to execute the handover for one or multiple target cells. The condition is based on radio measurements. In CHO command, the target cell may have reserved CFRA resources for the UE. When the UE evaluates the CHO condition and the condition holds for a specific target cell, the UE applies the CHO command and may use the reserved CFRA resources to initiate the random access to the target cell, the UE may be configured with multiple conditions for multiple target cells.

[0055] Fig. 1C illustrates a conditional handover for intra-NR. CHO is designed so that the UE can do the handover without the need of the serving cell triggering the HO execution after the measurement report.

[0056] Although CHO is useful in enhancing the mobility robustness, it has the following additional challenges and complexity compared to the baseline handover of NR Rel. 15:

[0057] 1) In CHO, multiple target cells may be prepared where each target cell has to reserve radio resources for some time which can be up to 15 seconds in some cases.

[0058] 2) CHO is an optional feature which may not be implemented by all UEs. For these UEs, it would beneficial to have a method that can be applied by the network to improve the mobility robustness of NR Rel. 15 handover mechanism in CU-DU without impacting the UEs.

[0059] 3) Each CHO configuration for a prepared target cell requires additional radio signalling, i.e., RRC Reconfiguration if the preparation is performed at different time instants which is the most likely scenario.

[0060] 4) CHO configurations may need to be updated with changing conditions of the prepared target cells (which may no longer be relevant to be prepared due to a degradation in radio link). Such re-configurations need further radio and network signalling.

[0061] 5) The UE may be configured with multiple CHO conditions that it has to continuously evaluate, i.e., increased complexity for the UE.

[0062] Moreover, as the source node triggers the initial preparation of all the candidate targetnodes, 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 node responds 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 node.

[0063] During LTM inter-CU subsequent cell change HO execution, one of the candidate target nodes becomes the new serving node, and the new serving node may not have the UE associated Xn logical connection with every other prepared candidate target node to exchange UE specific control plane messages. Fig. ID illustrates a simple LTM inter-CU subsequent cell change scenario capturing the problem, which is the core problem that the present disclosure aims to address by proposing a solution that shall resolve this problem and enable LTM inter-CU subsequent cell change functionality to work.

[0064] At steps 1 to 4: UE registered, PDU Session setup, L3 measurement received for LTM candidate preparation, and the target LTM candidates are selected. At steps 5 to 6: gNBl (the source / serving gNB) sends a handover request message to the target gNB and other target gNBs. At steps 7 to 10: the target gNBs perform the admission control procedures. At steps 11 to 14: the target gNBs allocate XnAP IDs for the UE for the source gNB. For example, the target gNB will allocate XnAP ID for the source gNB considering the XN interface between the source gNB and the target GNB, and the other target gNBs will allocate XnAP ID for the source gNB considering the XN interface between the source gNB and the other target gNBs. This establishes the Xn UE associated logical connection between the source gNB and the target gNBs. At steps 15 to 17: the source gNB sends the prepared configurations to the UE through RRC Reconfiguration procedure. At steps 18 to 22: the source gNB on receiving LI measurement report from the UE, takes a decision for LTM HO and sends a cell switch command to the UE to perform LTM handover. The UE performs LTM handover to the target gNB on sending a RRC reconfiguration complete message. Steps 23 to 24: the target gNB (the new serving gNB) sends a handover success message to the source gNB.

[0065] At steps 25 to 26: the new serving node (the target gNB) does not have Xn UE associated logical connection with the other target gNBs and cannot share the UE specific control information to the other target gNBs.

[0066] At steps 27 to 36: LTM handover completion steps. The UPF transmits the user data to the new serving node (the target gNB) via the pervious serving node (the source gNB). Thenew serving node transmits a path switch message to the AMF. The AMF and UPF performs the path switch. After the path switch is completed, the UE is communicated with the UPF through the new serving node to transmit the user data.

[0067] In view of the above, some embodiments of this disclosure propose a solution for providing enhancement on Xn UE association management. In this solution, a first network device transmits a first message to a second network device which is a target candidate network device, and the first message includes an indication of the second network device and at least one other target candidate network device. The second network device transmits second message to the first network device, and the second message includes (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0068] With the embodiments, allocating the XnAP IDs at target gNBs during preparation phase for all Xn connections of the UE avoids delays and processing time for the establishment of the Xn logical connection in the RAN when the UE actually changes the cell. The UE cell change is faster since the negotiation and preparation of the logical Xn connections between new serving cell and all candidate target cells have been prepared previously and thereby reduces the overall cell change duration for the UE. This may possibly be considered as part of base line signalling enhancement for inter CU subsequent mobility.

[0069] Hereinafter, the example method for performing enhancement on Xn UE association management will be described with reference to Fig. 2 to Fig. 6. Reference is first made to Fig. 2, which illustrates an exemplary signaling chart illustrating communication process in accordance with some embodiments of the present disclosure.

[0070] As shown in Fig. 2, a first network device 110 (also referred to as a source / serving node) transmits 210 a first message 212 to a second network device 120 which is a target candidate network device, and the first message 212 includes an indication of the second network device and at least one other target candidate network device. Accordingly, the second network device 120 receives 214 the first message 212 from the first network device 110, and the second network device 120 transmits 216 a second message 218 to the first network device 110. The second message 218 includes (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device. Accordingly, the first network device 110 receives 220 the second message 218 from the secondnetwork device 120.

[0071] In some embodiments, the first message 212 may be a handover request message. In an example, after the target candidate network devices are determined by the first network device 110 as the source / severing node, the first message 212, i.e., the handover request message, may be transmitted from the first network device 110 to the second network device 120, and the first message 212 may include an indication of the determined target candidate network devices.

[0072] In some embodiments, the first network device 110 may allocate an XnAP ID for the second network device considering the Xn interface between the first network device and the second network device. The XnAP ID of the first network device for the second network device may also be included in the first message 212, and then transmitted from the first network device 110 to the second network device 120. For example, the first message 212 may include the determined target candidate network devices and the XnAP ID of the first network device for the second network device.

[0073] In some embodiments, the first network device 110 may further transmit a third message to the at least one other target candidate network device. The third message may include the indication of the second network device and the at least one other target candidate network device.

[0074] In some embodiments, the third message may be a handover request message. In an example, after the target candidate network devices are determined by the first network device 110 as the source / severing node, the third message, i.e., the handover request message, may be transmitted from the first network device 110 to the at least one other target candidate network device, and the third message may include an indication of the determined target candidate network devices.

[0075] In some embodiments, the first network device 110 may further allocate at least one XnAP ID for the at least one other target candidate network device considering the at least one Xn interface between the first network device 110 and the at least one other target candidate network device. The at least one XnAP ID of the first network device for the at least one other target candidate network device may also be included in the third message, and then transmitted from the first network device 110 to the at least one other target candidate network device. For example, the third message may include the indication of the determined target candidate network devices and the at least one XnAP ID of the first network device for the at least oneother target candidate network device.

[0076] In some embodiments, the first message may include at least one of (i) a set of target cells of the first network device, or (ii) a set of target candidate cells of the at least one other target candidate network device. For example, the first message may include an indication of cell 1, cell 2 of the second network device, and cell 1, cell 2 of a third network device of the at least one other target candidate network device.

[0077] In addition or alternatively, the second message may include at least one of (i) a set of target cells of the first network device, or (ii) a set of target candidate cells of the at least one other target candidate network device. For example, the second message may include an indication of cell 1, cell 2 of the second network device, and cell 1, cell 2 of a third network device of the at least one other target candidate network device.

[0078] It should be appreciated that the terms “first” and “second” are not intended to limit the sequence of the first message and the third message. The first message and the third message may be transmitted by the first network device 110 simultaneously, or the first message may be transmitted by the first network device 110 after or before the third message.

[0079] After the determined target candidate network devices receive the respective handover request messages, the determined target candidate network devices each perform an admission control procedure.

[0080] Subsequently, in some embodiment, the second network device 120 may allocate the XnAP IDs for the first network device 110 and the at least one other target candidate network device in a case where the handover preparation is completed at the second network device 120, and then the second network device 120 may transmit, to the first network device 110, the second message including the XnAP IDs for the first network device 110 and the at least one other target candidate network device.

[0081] Specifically, the second network device 120 may allocate the first XnAP ID for the first network device considering the Xn interface between the first network device and the second network device, and the second network device 120 may allocate the at least one XnAP ID for the at least one other target candidate network device considering the Xn interface between the second network device 120 and the at least one other target candidate network device.

[0082] In some embodiments, the first XnAP ID of the second network device for the first network device and the at least one XnAP ID of the second network device for the at least oneother target candidate network device are included in the second message. The second message may be, for example, a handover request acknowledge message. The second message may further include the XnAP ID of the first network device for the second network device.

[0083] Similarly, in some embodiment, the at least one other target candidate network device may allocate the XnAP IDs for the first network device 110 and the second network device 120 in a case where the handover preparation is completed at the at least one other target candidate network device, and then the at least one other target candidate network device may transmit, to the first network device 110, the fifth message including the XnAP IDs for the first network device 110 and the second network device 120. The case where the handover preparation failed at the at least one other target candidate network device may be descried later.

[0084] Specifically, the at least one other target candidate network device may allocate the at least one XnAP ID for the first network device considering the Xn interface between the first network device 110 and the at least one other target candidate network device, and the at least one other target candidate network device may allocate the at least one XnAP ID for the second network device considering the Xn interface between the second network device 120 and the at least one other target candidate network device.

[0085] In some embodiments, the at least one XnAP ID of the at least one other target candidate network device for the first network device and the at least one XnAP ID of the at least one other target candidate network device for the second network device may be included in the fifth message. The fifth message may be, for example, a handover request acknowledge message. The fifth message may further include the at least one XnAP ID of the first network device for the at least one other target candidate network device.

[0086] After receiving the fifth message including the at least one XnAP ID of the at least one other target candidate network device for the second network device, the first network device 110 may share, with the second network device 120, the at least one XnAP ID of the at least one target candidate network device for the second network device.

[0087] Specifically, the first network device 110 may transmit a fourth message to the second network device 120, and the at least one XnAP ID of the at least one other target candidate network device for the second network device may be included in the fourth message. For example, the fourth message may be a handover update message. The fourth message may further include the XnAP ID of the first network device for the second network device and thefirst XnAP ID of the second network device for the first network device.

[0088] Based on receiving the at least one XnAP ID of the at least one other target candidate network device for the second network device, the second network device 120 may create Xn mapping for the second network device and the at least one other target candidate network device. For example, the second network device 120 may create mapping <XnAP ID of the second network device for the at least one other target candidate network device, XnAP ID of the at least one other target candidate network device for the second network device> considering the Xn interface between the second network device 120 and the at least one other target candidate network device.

[0089] In some further embodiments, after receiving the second message including the at least one XnAP ID of the second network device for the at least one other target candidate network device, the first network device 110 may share, with the at least one other target candidate network device, the at least one XnAP ID of the second network device for the at least one target candidate network device.

[0090] Specifically, the first network device 110 may transmit a sixth message to the at least one other target candidate network device, and the at least one XnAP ID of the second network device for the at least one other target candidate network device may be included in the sixth message. For example, the sixth message may be a handover update message. The sixth message may further include the at least one XnAP ID of the first network device for the at least one other target candidate network device and the at least one XnAP ID of the at least one other target candidate network device for the first network device.

[0091] Based on receiving the at least one XnAP ID of the second network device for the at least one other target candidate network device, the at least one other target candidate network device may create Xn mapping for the at least one other target candidate network device and the second network device. For example, the at least one other target candidate network device may create mapping <XnAP ID of the second network device for the at least one other target candidate network device, XnAP ID of the at least one other target candidate network device for the second network device> considering the Xn interface between the at least one other target candidate network device and the second network device.

[0092] Subsequently, LTM handover execution are performed. Based on receiving a RRC reconfiguration complete message from the UE, the second network device 120 is the new source / serving node. The new source / serving node, i.e., the second network device 120, maytransmit update configuration to the at least one other target candidate network device by using the previously shared XnAP IDs (i.e., the XnAP ID of the second network device for the at least one other target candidate network device, XnAP ID of the at least one other target candidate network device for the second network device).

[0093] Back to the case where the handover preparation fails at the at least one other target candidate network device, the at least one other target candidate network device may report a handover preparation failure to the first network device 110 based on the handover preparation failed at the at least one other target candidate network device.

[0094] Specifically, the at least one other target candidate network device may transmit a seventh message to the first network device 110, and the handover preparation failure of the at least one other target candidate network device may be included in the seventh message. The seventh message may be, for example, a handover preparation failure message.

[0095] After receiving the seventh message including the handover preparation failure of the at least one other target candidate network device, the first network device 110 may inform the second network device 120 to release its XnAP ID allocated for the at least one other target candidate network device.

[0096] Specifically, based on receiving the seventh message including the handover preparation failure of the at least one other target candidate network device, the first network device 110 may transmit a fourth message to the second network device 120, and a network device release list may be included in the fourth message.

[0097] In another example, the network device release list may be included in the handover request acknowledge message.

[0098] In some embodiments, after receiving the network device release list, the second network device 120 may know which XnAP ID allocated by the second network device should be released.

[0099] For example, the network device release list may include the at least one other target candidate network device. The second network device 120 may obtain the network device release list, and the second network device 120 may then release the XnAP ID of the second network device for the at least one other target candidate network device.

[0100] In another example, there may be a plurality of other target candidate network devices. The network device release list may include one or more among the plurality of target candidate network devices whose handover preparation fails. The first network device 110 informs thesecond network device 120 and the target candidate network devices among the plurality of other target candidate network device whose handover preparation is successful to release their XnAP IDs allocated for these target candidate network device whose handover preparation fails.

[0101] Fig. 3 illustrates an example of a signaling process 300 of enhancement on Xn UE association management according to some embodiments of the present disclosure. The signaling process 300 may be a more specific example of the process 300 of Fig. 2, and in this example, XnAP IDs are allocated per Xn interface of target LTM candidates during preparation phase. The gNB-1 may be, for example, the first network device 110. One of the gNB-2 and the gNB-3 may be, for example, the second network device 120, and the other of the gNB-2 and the gNB-3 may be, for example, the at least one other target candidate network device.

[0102] In this example, single handover request message (consolidating all targets cells of the gNB and all other candidate cells for corresponding gNBs) is used. The target gNB allocates XnAP IDs for the UE considering the source gNB and the other target gNB. The target node consolidates the configurations for all target candidates for a GNB in a single Handover Request Acknowledge message.

[0103] At steps 1 to 5, UE is registered, PDU session is setup, L3 measurement is received for LTM candidate preparation, and target LTM candidates are selected. The gNB-1 now serves as the source / serving node.

[0104] At steps 6 and 7, the gNB-1 consolidates the selected target candidates for the gNB and also for other target candidates gNBs. The selected target candidates for the gNB and also for other target candidates gNBs are included in handover request messages and send to the target gNBs (for example, send to gNB-2 and gNB-3). For example, the selected target candidates for gNB-2 are cell 1 and cell 2 of gNB-2, and the selected target candidates for the gNB-3 are cell 1 and cell 2 of gNB-3. In other words, the current serving node sends handover request message to all candidate gNBs. The current serving node consolidates all target candidate cells per gNB. The target gNB candidate (includes all target cells of gNB) and list of other target gNB (includes all target cells of gNBs) candidates are included.

[0105] It should be noted that the cells in the handover request message maybe optionally present. In other alternatives, only the candidate gNB IDs maybe present, for example, only gNB-2 ID and gNB-3 ID. Addition of cells may be used as an additional information to let the gNB to decide to provide XnAP ID for a candidate gNB or not. Similar behaviour may also be done by having candidate gNB ID.

[0106] At steps 8 and 9: the target gNBs perform the admission control procedures.

[0107] At steps 10 and 11 : the target gNBs allocate XnAP IDs for the UE for the source GNB and as well as for other target gNBs. For example, target gNB-2 will allocate XnAP ID for GNB-1 (serving / source gNB) considering the Xn interface between gNB-1 and gNB-2, and allocate another XnAP ID for gNB-3 (other candidate target gNB) considering the Xn interface between gNB2 and gNB3. The allocated XnAP IDs of gNB-2 for gNB-1 and gNB-3 are included in the handover request acknowledge message and sent to the gNB-1. The allocated XnAP IDs of gNB-3 for gNB-1 and gNB-2 are included in the handover request acknowledge message and sent to the gNB-1. In other words, the target gNB allocates one XnAP ID for the source node, and the target gNB also allocates XnAP IDs per gNB for other target candidates. All the XnAP IDs are included in Handover Request Acknowledge message.

[0108] At steps 12 and 17 : the serving gNB-1 sends the prepared configurations to UE through RRC Reconfiguration procedure.

[0109] At steps 13 to 16: the serving gNBl shares the XnAP IDs allocated by other candidates. All target candidates will create / update the XnAP ID mappings for all target candidates. For example, gNB-2 will create mapping <GNB2_UE_XNAP_ID_FOR_GNB3, GNB3_UE_XNAP_ID_FOR_GNB2> for XN interface between the gNB-2 and the gNB-3. Handover Update message may be used to update the IDs. In other words, the serving gNB shares the other target XnAP IDs with the target gNBs and all target gNBs creates / updates the XnAP ID mapping for the UE for all Xn interfaces for the prepared candidates.

[0110] At steps 18 to 29: LTM Handover execution are performed.

[0111] At step 30: the new serving node (for example, gNB-2) may update configurations at other candidate gNBs by using the previously shared XnAP IDs.

[0112] Fig. 4 illustrates an example of a signaling process 400 of enhancement on Xn UE association management according to some embodiments of the present disclosure. The signaling process 400 may be a more specific example of the process 400 of Fig. 2, and this example relates to handling of XnAP IDs for failure case. The gNB-1 may be, for example, the first network device 110. One of the gNB-2 and the gNB-3 may be, for example, the second network device 120, and the other of the gNB-2 and the gNB-3 may be, for example, the at least one other target candidate network device.

[0113] In this example, if the preparation of LTM at the target nodes are not successful, the initial serving node will inform the candidates to remove the ID allocated for the target node.Whenever LTM configuration releases specific candidate node, all other candidate nodes will be informed to release the XN-AP-ID binding.

[0114] At steps 1 to 5, UE is registered, PDU session is setup, L3 measurement is received for LTM candidate preparation, and target LTM candidates are selected. The gNB-1 now serves as the source / serving node.

[0115] At steps 6 and 7, the gNB-1 consolidates the selected target candidates for the gNB and also for other target candidates gNBs. The selected target candidates for the gNB and also for other target candidates gNBs are included in handover request messages and send to the target gNBs (for example, send to gNB-2 and gNB-3). For example, the selected target candidates for gNB-2 are cell 1 and cell 2 of gNB-2, and the selected target candidates for the gNB-3 are cell 1 and cell 2 of gNB-3.

[0116] At steps 8 and 9: the target gNBs perform the admission control procedures.

[0117] At step 10: the target gNBs allocate XnAP IDs for the UE for the source GNB and as well as for other target gNBs. For example, target gNB-2 will allocate XnAP ID for GNB-1 (serving / source gNB) considering the Xn interface between gNB-1 and gNB-2, and allocate another XnAP ID for gNB-3 (other candidate target gNB) considering the Xn interface between gNB2 and gNB3. The allocated XnAP IDs of gNB-2 for gNB-1 and gNB-3 are included in the handover request acknowledge message and sent to the gNB-1.

[0118] At steps 12 and 15: the serving gNB-1 sends the prepared configurations to the UE through RRC Reconfiguration procedure.

[0119] At steps 13 and 14: as the handover preparation is failed at the gNB-3, the gNB-1 shall send the handover update message to target gNB-2 for releasing the XnAP IDs the gNB-2 has allocated for gNB-3. The gNB-2 releases the XnAP IDs that’s allocated for gNB-3, to establish Xn UE associated logical connection with gNB-3.

[0120] At steps 16 to 29: LTM Handover execution is performed.

[0121] Fig. 5 illustrates a flowchart of a method 500 implemented at a first network device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 500 will be described from the perspective of the first network device 110 with reference to Fig. 1.

[0122] At block 510, the first network device 110 transmits, to a second network device which is a target candidate network device, a first message comprising an indication of the secondnetwork device and at least one other target candidate network device. At block 520, the first network device 110 receives, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0123] In some embodiments, the first network device 110 transmits, to the at least one other target candidate network device, a third message comprising the indication of the second network device and the at least one other target candidate network device.

[0124] In some embodiments, the first network device 110 transmits, to the second network device, a fourth message.

[0125] In some embodiments, based on receiving, from the at least one other target candidate network device, a fifth message comprising at least one XnAP ID of the at least one other target candidate network device for the second network device, the first network device 110 transmits, to the second network device, the fourth message comprising the at least one XnAP ID of the at least one other target candidate network device for the second network device.

[0126] In some embodiments, the first network device 110 transmits, to the at least one other target candidate network device, a sixth message comprising the at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0127] In some embodiments, based on receiving, from the at least one other target candidate network device, a seventh message comprising handover preparation failure of the at least one other target candidate network device, the first network device 110 transmits, to the second network device, the fourth message comprising a network device release list.

[0128] In some embodiments, the network device release list comprises the at least one other target candidate network device.

[0129] In some embodiments, the first message comprises at least one of (i) a set of target candidate cells of the first network device, or (ii) a set of target candidate cells of the at least one other target candidate network device.

[0130] In some embodiments, the first message is a handover request message; the second message is a handover request acknowledge message; the third message is a handover request message; the fourth message is a handover update message; the fifth message is a handover request acknowledge message; the sixth message is a handover update message; or the seventh message is a handover preparation failure message.

[0131] Fig. 6 illustrates a flowchart of a method implemented at a second network device according to some other embodiments of the present disclosure. For the purpose of discussion, the method 600 will be described from the perspective of the second network device 120 with reference to Fig. 1.

[0132] At block 610, the second network device 120 receives, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device. At block 620, the second network device 120 transmits, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0133] In some embodiments, the second network device 120 receives, from the first network device, a fourth message.

[0134] In some embodiments, the second network device 120 receives, from the first network device, the fourth message comprising at least one XnAP ID of the at least one other target candidate network device for the second network device.

[0135] In some embodiments, the second network device 120 creates Xn mapping for the second network device and the at least one other target candidate network device based on (i) the at least one XnAP ID of the second network device for the at least one other target candidate network device and (ii) the at least one XnAP ID of the at least one other target candidate network device for the second network device.

[0136] In some embodiments, the second network device 120 receives, from the first network device, the fourth message comprising a network device release list.

[0137] In some embodiments, the network device release list comprises the at least one other target candidate network device.

[0138] In some embodiments, the second network device 120 releases the at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0139] In some embodiments, the first message comprises at least one of (i) a set of target candidate cells of the first network device, or (ii) a set of target candidate cells of the at least one other target candidate network device.

[0140] In some embodiments, the first message is a handover request message; the second message is a handover request acknowledge message; the fourth message is a handover update message.

[0141] In some embodiments, an apparatus (for example, the first network device 110) capable of performing the method 500 may comprise means for performing the respective steps of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0142] In some embodiments, the apparatus comprises means for transmitting, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device. The apparatus further comprises means for receiving, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0143] In some embodiments, the apparatus comprises means for transmitting, to the at least one other target candidate network device, a third message comprising the indication of the second network device and the at least one other target candidate network device.

[0144] In some embodiments, the apparatus comprises means for transmitting, to the second network device, a fourth message.

[0145] In some embodiments, the apparatus comprises means for based on receiving, from the at least one other target candidate network device, a fifth message comprising at least one XnAP ID of the at least one other target candidate network device for the second network device, transmitting, to the second network device, the fourth message comprising the at least one XnAP ID of the at least one other target candidate network device for the second network device.

[0146] In some embodiments, the apparatus comprises means for transmitting, to the at least one other target candidate network device, a sixth message comprising the at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0147] In some embodiments, the apparatus comprises means for based on receiving, from the at least one other target candidate network device, a seventh message comprising handover preparation failure of the at least one other target candidate network device, transmitting, to the second network device, the fourth message comprising a network device release list.

[0148] In some embodiments, the network device release list comprises the at least one other target candidate network device.

[0149] In some embodiments, the first message comprises at least one of (i) a set of target candidate cells of the first network device, or (ii) a set of target candidate cells of the at least one other target candidate network device.

[0150] In some embodiments, the first message is a handover request message; the second message is a handover request acknowledge message; the third message is a handover request message; the fourth message is a handover update message; the fifth message is a handover request acknowledge message; the sixth message is a handover update message; or the seventh message is a handover preparation failure message.

[0151] In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 500. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

[0152] In some embodiments, an apparatus (for example, the second network device 120) capable of performing the method 600 may comprise means for performing the respective steps of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0153] In some embodiments, the apparatus comprises means for receiving, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device. The apparatus further comprises means for transmitting, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0154] In some embodiments, the apparatus comprises means for receiving, from the first network device, a fourth message.

[0155] In some embodiments, the apparatus comprises means for receiving, from the first network device, the fourth message comprising at least one XnAP ID of the at least one other target candidate network device for the second network device.

[0156] In some embodiments, the apparatus comprises means for creating Xn mapping for the second network device and the at least one other target candidate network device based on (i) the at least one XnAP ID of the second network device for the at least one other target candidate network device and (ii) the at least one XnAP ID of the at least one other target candidate network device for the second network device.

[0157] In some embodiments, the apparatus comprises means for receiving, from the first network device, the fourth message comprising a network device release list.

[0158] In some embodiments, the network device release list comprises the at least one other target candidate network device.

[0159] In some embodiments, the apparatus comprises means for releasing the at least one XnAP ID of the second network device for the at least one other target candidate network device.

[0160] In some embodiments, the first message comprises at least one of (i) a set of target candidate cells of the first network device, or (ii) a set of target candidate cells of the at least one other target candidate network device.

[0161] In some embodiments, the first message is a handover request message; the second message is a handover request acknowledge message; the fourth message is a handover update message.

[0162] In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 600. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

[0163] Fig. 7 is a simplified block diagram of a device 700 that is suitable for implementing embodiments of the present disclosure. The device 700 may be provided to implement the communication device, for example the first network device 110, and the second network device 120 as shown in Fig. 1. As shown, the device 700 includes one or more processors 710, one or more memories 720 coupled to the processor 710, and one or more communication modules 740 coupled to the processor 710.

[0164] The communication module 740 is for bidirectional communications. The communication module 740 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network devices.

[0165] The processor 710 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 700 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.

[0166] The memory 720 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a read only memory (ROM) 724, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 722 and other volatile memories that may not last in the power-down duration.

[0167] A computer program 730 includes computer executable instructions that are executed by the associated processor 710. The program 730 may be stored in the ROM 724. The processor 710 may perform any suitable actions and processing by loading the program 730 into the RAM 722.

[0168] The embodiments of the present disclosure may be implemented by means of the program so that the device 700 may perform any process of the disclosure as discussed with reference to Figs. 2 to 6. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0169] In some embodiments, the program 730 may be tangibly contained in a computer readable medium which may be included in the device 700 (such as in the memory 720) or other storage devices that are accessible by the device 700. The device 700 may load the program 730 from the computer readable medium to the RAM 722 for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like.

[0170] Fig. 8 illustrates an example of the computer readable medium 800 in form of CD or DVD in accordance with some embodiments of the present disclosure. The computer readable medium has the program 730 stored thereon. It is noted that although the computer-readable medium 800 is depicted in form of CD or DVD, the computer-readable medium 800 may be in any other form suitable for carry or hold the program 730.

[0171] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While 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.

[0172] The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the methods 500 or 600 as described above with reference to Fig. 5 to Fig. 6. 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.

[0173] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes 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 codes, 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.

[0174] In the context of the present disclosure, the computer program codes or related data 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.

[0175] 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 readonly 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. 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).

[0176] Further, while 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, while 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. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that may be described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

[0177] 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 may be disclosed as example forms of implementing the claims.

Claims

WHAT IS CLAIMED IS:

1. A first network device, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first network device at least to: transmit, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device; and receive, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

2. The first network device of claim 1, wherein the first network device is further caused to: transmit, to the at least one other target candidate network device, a third message comprising the indication of the second network device and the at least one other target candidate network device.

3. The first network device of claim 1 or 2, wherein the first network device is further caused to: transmit, to the second network device, a fourth message.

4. The first network device of claim 3, wherein the first network device is caused to transmit the fourth message by: based on receiving, from the at least one other target candidate network device, a fifth message comprising at least one XnAP ID of the at least one other target candidate network device for the second network device, transmitting, to the second network device, the fourth message comprising the at least one XnAP ID of the at least one other target candidate network device for the second network device.

5. The first network device of claim 4, wherein the first network device is further caused to:transmit, to the at least one other target candidate network device, a sixth message comprising the at least one XnAP ID of the second network device for the at least one other target candidate network device.

6. The first network device of any of claims 3-5, wherein the first network device is caused to transmit the fourth message by: based on receiving, from the at least one other target candidate network device, a seventh message comprising handover preparation failure of the at least one other target candidate network device, transmitting, to the second network device, the fourth message comprising a network device release list.

7. The first network device of claim 6, wherein the network device release list comprises the at least one other target candidate network device.

8. The first network device of any of claims 1-7, wherein the first message comprises at least one of (i) a set of target candidate cells of the first network device, or (ii) a set of target candidate cells of the at least one other target candidate network device.

9. The first network device of any of claims 1-8, wherein at least one of the following: the first message is a handover request message; the second message is a handover request acknowledge message; the third message is a handover request message; the fourth message is a handover update message; the fifth message is a handover request acknowledge message; the sixth message is a handover update message; or the seventh message is a handover preparation failure message.

10. A second network device, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second network device at least to:receive, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device; and transmit, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

11. The second network device of claim 10, wherein the second network device is further caused to: receive, from the first network device, a fourth message.

12. The second network device of claim 11, wherein the second network device is caused to receive the fourth message by: receiving, from the first network device, the fourth message comprising at least one XnAP ID of the at least one other target candidate network device for the second network device.

13. The second network device of claim 12, wherein the second network device is further caused to: create Xn mapping for the second network device and the at least one other target candidate network device based on (i) the at least one XnAP ID of the second network device for the at least one other target candidate network device and (ii) the at least one XnAP ID of the at least one other target candidate network device for the second network device.

14. The second network device of any of claims 11-13, wherein the second network device is caused to receive the fourth message by: receiving, from the first network device, the fourth message comprising a network device release list.

15. The second network device of claim 14, wherein the network device release list comprises the at least one other target candidate network device.

16. The second network device of claim 15, wherein the second network device is further caused to: release the at least one XnAP ID of the second network device for the at least one other target candidate network device.

17. The second network device of any of claims 10-16, wherein the first message comprises at least one of (i) a set of target candidate cells of the first network device, or (ii) a set of target candidate cells of the at least one other target candidate network device.

18. The second network device of any of claims 10-17, wherein at least one of the following: the first message is a handover request message; the second message is a handover request acknowledge message; or the fourth message is a handover update message.

19. A method comprising: transmitting, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device; and receiving, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

20. A method comprising: receiving, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device; and transmitting, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

21. An apparatus comprising:means for transmitting, to a second network device which is a target candidate network device, a first message comprising an indication of the second network device and at least one other target candidate network device; and means for receiving, from the second network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

22. An apparatus comprising: means for receiving, from a first network device, a first message comprising an indication of the second network device which is a target candidate network device, and at least one other target candidate network device; and means for transmitting, to the first network device, a second message comprising (i) a first Xn application protocol (XnAP) identification (ID) of the second network device for the first network device and (ii) at least one XnAP ID of the second network device for the at least one other target candidate network device.

23. A computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least one of the methods of claims 19 and 20.

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