CHO CPAC interruption reduction for successful cell changes

Abstract

A terminal device, i.e. user equipment (UE) 110, evaluates 226 a conditional handover (CHO) execution condition and a conditional primary secondary cell addition or change (CPAC) execution condition and determines an interruption 228 of a connection with a source master node 120A or a connection with a source secondary node. The terminal device 110 executes an access procedure 234 towards a target master node 120C and an access procedure 236 towards a target secondary node 120D based on a CHO and CPAC configuration when both the CHO execution condition and the CPAC execution condition are fulfilled 232, and sends 240 to the target master node 120C a successful cell change report containing cause information of the interruption indicating which one of the CHO execution condition and the CPAC execution condition was fulfilled later. A core network device 132 receives 242 from the source master node 120A or the target master node 120C an interruption report containing the cause information of the interruption experienced at the terminal device 110 before handover of the terminal device 110 and determines optimization information for at least one of the CHO execution condition or the CPAC execution condition based on the received interruption report.

Description

TECHNICAL FIELD

[0001] Various example embodiments described herein generally relate to communication 5 technologies, and more particularly, to devices, methods, apparatuses and computer readable mediums for reducing interruption experienced at a user equipment (UE) in a conditional handover (CHO) with candidate secondary cell group(s) (SCG(s)) procedure. BACKGROUND 10

[0002] Certain abbreviations that may be found in the description and / or in the figures are herewith defined as follows: AMF CHO CPA Access and mobility Management Function Conditional Handover Conditional PSCell Addition 15 CPAC Conditional PSCell Addition or Change cpc JL Conditional PSCell Change MCG Master Cell Group MN Master Node MR-DC Multi-Radio Dual Connectivity 20 MRO Mobility Robustness Optimization 0AM Operations Administration and Maintenance PCell Primary Cell PSCell Primary Secondary Cell RLF Radio Link Failure 25 RRC Radio Resource Control Cil 1 Secondary Cell SCG Secondary Cell Group SHR Successful Handover Report SN Secondary Node 30 SPCR Successful PSCell Change Report SPR Successful PSCell Report

[0003] Massive deployment of dense small cells for 5G network will enhance coverage and capacity, but on the other hand it would increase handover probability, potentially causing radio 35 link failure (RLF). Therefore, mobility robustness optimization (MRO) solutions for mobility frameworks including conditional handover (CHO) with candidate secondary cell groups (SCG(s)) is under investigation in order to ensure reliable and stable communication during movements of mobile users. SUMMARY

[0004] A brief summary of example embodiments is provided below to provide basic understanding of some aspects of various embodiments. It should be noted that this summary is not intended to identify key features of essential elements or define scopes of the embodiments, and its sole purpose is to introduce some concepts in a simplified form as a preamble for a more detailed description provided below.

[0005] In a first aspect, an example embodiment of an apparatus for a terminal device is provided. The apparatus may comprise at least one processor and at least one memory. The at least one memory may store instructions that, when executed by the at least one processor, cause the apparatus at least to evaluate a conditional handover (CHO) execution condition and a conditional primary secondary cell addition or change (CPAC) execution condition, to determine an interruption of a connection with a source master node or a connection with a source secondary node, to execute an access procedure towards a target master node and an access procedure towards a target secondary node based on a CHO and CPAC configuration in response to both the CHO execution condition and the CPAC execution condition being fulfilled, and to send a successful cell change report to the target master node. The successful cell change report may contain cause information of the interruption experienced at the apparatus, and the cause information may indicate which one of the CHO execution condition and the CPAC execution condition was fulfilled later.

[0006] In a second aspect, an example embodiment of an apparatus for a radio access network device is provided. The apparatus may comprise at least one processor and at least one memory. The at least one memory may store instructions that, when executed by the at least one processor, cause the apparatus at least to execute an access procedure with a terminal device to accept handover of the terminal device from a source master node, and to receive a successful cell change report from the terminal device. The successful cell change report may contain cause information of an interruption experienced at the terminal device before the access procedure. The cause information may indicate which one of a conditional handover (CHO) execution condition and a conditional primary secondary cell addition or change (CPAC) execution condition is fulfilled later.

[0007] In a third aspect, an example embodiment of an apparatus for a radio access network device is provided. The apparatus may comprise at least one processor and at least one memory. The at least one memory may store instructions that, when executed by the at least one processor, cause the apparatus at least to send a conditional handover (CHO) with candidate secondary cell group(s) (SCG(s)) configuration comprising CHO and conditional primary secondary cell addition or change (CPAC) configurations to a terminal device, and to receive from a target master node a successful cell change report containing cause information of an interruption experienced at the terminal device before execution of the CHO and CPAC configuration. The cause information may indicate which one of a CHO execution condition and a CPAC execution relating to the CHO and CPAC configuration is fulfilled later.

[0008] In a fourth aspect, an example embodiment of an apparatus for a core network device is provided. The apparatus may comprise at least one processor and at least one memory. The at least one memory may store instructions that, when executed by the at least one processor, cause the apparatus at least to receive from a source master node or a target master node an interruption report containing cause information of an interruption experienced at a terminal device before handover of the terminal device from the source master node to the target master node based on a conditional handover (CHO) and conditional primary secondary cell addition or change (CPAC) configuration, and to determine optimization information for at least one of the CHO execution condition or the CPAC execution condition based on the received interruption report. The cause information contained in the interruption report may indicate which one of a CHO execution condition and a CPAC execution condition associated with the CHO and CPAC configuration is fulfilled later.

[0009] In a fifth aspect, an example embodiment of a method is provided. The method may comprise: evaluating a conditional handover, CHO, execution condition and a conditional primary secondary cell addition or change, CPAC, execution condition; determining an interruption of a connection with a source master node or a connection with a source secondary node; executing an access procedure towards a target master node and an access procedure towards a target secondary node based on a CHO and CPAC configuration, in response to both the CHO execution condition and the CPAC execution condition being fulfilled; and sending, to the target master node, a successful cell change report containing cause information of the interruption, wherein the cause information indicates which one of the CHO execution condition and the CPAC execution condition was fulfilled later.

[0010] In an embodiment, the method further comprises: receiving, from the source master node, a CHO with candidate secondary cell group configuration comprising CHO and CPAC configurations and associated CHO and CPAC execution conditions.

[0011] In an embodiment, the method further comprises: starting a condition fulfillment interval timer in response to one of the CHO execution condition and the CPAC execution condition being fulfilled and the other being not fulfilled; and stopping the condition fulfillment interval timer in response to both the CHO execution condition and the CPAC execution condition being fulfilled, wherein the cause information indicates a time measured by the condition fulfillment interval timer.

[0012] In an embodiment, the successful cell change report comprises a successful handover report in case the CPAC execution condition is fulfilled earlier than the CHO execution condition, the successful cell change report comprises a successful primary secondary cell report in case the CHO execution condition is fulfilled earlier than the CPAC execution condition, or the successful cell change report comprises a new report different from the successful handover report and the successful primary secondary cell report, regardless of which of the CHO execution condition and the CPAC execution condition is fulfilled earlier.

[0013] In an embodiment, the successful cell change report is triggered in response to the following triggering condition being satisfied: a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled exceeds a threshold.

[0014] In an embodiment, the method further comprises: receiving, from the source master node, a successful cell change report configuration specifying at least one of: one or more triggering conditions for the successful cell change report; or content of the successful cell change report.

[0015] In an embodiment, the successful cell change report further contains an identifier of the CHO and CPAC configuration and a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled.

[0016] In an embodiment, the successful cell change report further contains one or more of the following: type of the interruption, including interruption of the connection with the source master node or interruption of the connection with the source secondary node; an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled; an identifier of at least one CHO and CPAC configuration stored but not executed; or information of a condition fulfillment interval timer associated with the at least one CHO and CPAC configuration not executed.

[0017] In an embodiment, the method further comprises: creating the successful cell change report in response to successfully executing the access procedure towards the target master node and the access procedure towards the target secondary node, in case the successful cell change report comprises the successful handover report or the successful primary secondary cell report and at least one triggering condition for the successful handover report or the successful primary secondary cell report is satisfied, or creating the successful cell change report in response to one of the CHO execution condition and the CPAC execution condition being fulfilled and the other being not fulfilled, in response to the CHO execution condition and the CPAC execution condition being fulfilled, or in response to successfully executing the access procedure towards the target master node and the access procedure towards the target secondary node, in case the successful cell change report comprises the new report and a triggering condition for the new report is satisfied.

[0018] According to an aspect, there is provided an apparatus for a terminal device, comprising means for performing the method of any of the above-described methods of the fifth aspect.

[0019] According to an aspect, there is provided a computer readable medium comprising instructions that, when executed by an apparatus for a terminal device, cause the apparatus to perform the method of any of the above-described methods of the fifth aspect.

[0020] According to a sixth aspect, there is provided a method comprising: executing an access procedure with a terminal device to accept handover of the terminal device from a source master node; receiving, from the terminal device, a successful cell change report containing cause information of an interruption experienced at the terminal device before the access procedure, wherein the cause information indicates which one of a conditional handover, CHO, execution condition and a conditional primary secondary cell addition or change, CPAC, execution condition is fulfilled later.

[0021] In an embodiment, the method further comprises: sending, to the source master node, a successful cell change report configuration specifying at least one of: one or more triggering conditions for the successful cell change report; or content of the successful cell change report.

[0022] In an embodiment, the successful cell change report further contains an identifier of a CHO and CPAC configuration associated with the executed access procedure and a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled.

[0023] In an embodiment, the successful cell change report further contains one or more of the following: type of the interruption, including interruption with a connection between the terminal device and the source master node or interruption with a connection between the terminal device and a source secondary node; an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled; an identifier of at least one CHO and CPAC configuration not executed at the terminal device; or information of a condition fulfillment interval timer associated with the at least one CHO and CPAC configuration not executed.

[0024] In an embodiment, the successful cell change report comprises a successful handover report in case the CPAC execution condition is fulfilled earlier than the CHO execution condition, the successful cell change report comprises a successful primary secondary cell report in case the CHO execution condition is fulfilled earlier than the CPAC execution condition, or the successful cell change report comprises a new report different from the successful handover report and the successful primary secondary cell report, regardless of which of the CHO execution condition and the CPAC execution condition is fulfilled earlier.

[0025] In an embodiment, the method further comprises: sending, to a core network device, an interruption report containing the cause information of the interruption experienced at the terminal device; and receiving, from the core network device, optimization information for optimizing at least one of the CHO execution condition and the CPAC execution condition.

[0026] In an embodiment, the interruption report contains one or more of the following: a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled; an identifier of a CHO and CPAC configuration executed at the terminal device, an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled; the CHO execution condition and information of a target primary cell related to the CHO execution condition; the CPAC execution condition and information of a target primary secondary cell related to the CPAC execution condition; an identifier of a target master node for the terminal device; an identifier of the source master node.

[0027] In an embodiment, the interruption report comprises the successful cell change report.

[0028] In an embodiment, the method further comprises: sending, to the source master node, the optimization information for optimizing the CHO execution condition.

[0029] In an embodiment, the method further comprises: sending, to the source master node, the successful cell change report; and receiving, from the source master node or from a core network device, optimization information for optimizing the CPAC execution condition.

[0030] In an embodiment, the core network device is an operations administration and maintenance entity or an access and mobility management function entity.

[0031] In an embodiment, the method further comprises: determining optimization for the CPAC execution condition in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later; or sending, to the source master node, the successful cell change report in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later.

[0032] In an embodiment, the method further comprises: in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later: determining optimization for the CPAC execution condition; in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later: determining optimization for the CHO execution condition; and sending, to the source master node, the determined optimization for the CHO execution condition.

[0033] According to an aspect, there is provided an apparatus for a radio access network device, comprising means for performing any of the above-described methods of the sixth aspect.

[0034] According to an aspect, there is provided a computer readable medium comprising instructions that, when executed by an apparatus for a radio access network device, cause the apparatus to perform any of the above-described methods of the sixth aspect.

[0035] According to a seventh aspect, there is provided a method comprising: sending, to a terminal device, a conditional handover, CHO, with candidate secondary cell group configuration comprising CHO and conditional primary secondary cell addition or change, CPAC, configurations; and receiving, from a target master node of the terminal device, a successful cell change report containing cause information of an interruption experienced at the terminal device before execution of the CHO and CPAC configuration, wherein the cause information indicates which one of a CHO execution condition and a CPAC execution relating to the CHO and CPAC configuration is fulfilled later.

[0036] In an embodiment, the method further comprises: sending, to a core network device, an interruption report containing the cause information of the interruption experienced at the terminal device; and receiving, from the core network device, optimization information for optimizing at least one of the CHO execution condition and the CPAC execution condition.

[0037] In an embodiment, the method further comprises: sending, to the target master node, the optimization information for optimizing the CPAC execution condition.

[0038] In an embodiment, the core network device is an operations administration and maintenance entity or an access and mobility management function entity.

[0039] In an embodiment, the method further comprises: determining optimization for the CHO execution condition associated with the CHO and CPAC configuration executed at the terminal device, in case the cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later than the CPAC execution condition.

[0040] In an embodiment, the method further comprises: in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later than the CPAC execution condition: determining optimization for the CHO execution condition; in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later than the CHO execution condition: determining optimization for the CPAC execution condition; and sending, to the target master node, the determined optimization for the CPAC execution condition.

[0041] In an embodiment, the method further comprises: sending, to the terminal device, a successful cell change report configuration specifying at least one of: one or more triggering conditions for the successful cell change report; or content of the successful cell change report, wherein the successful cell change report configuration is determined at a source master node of the terminal device or at least partly received from the target master node.

[0042] According to an eighth aspect, there is provided a method comprising: receiving, from a source master node or a target master node, an interruption report containing cause information of an interruption experienced at a terminal device before handover of the terminal device from the source master node to the target master node based on a conditional handover, CHO, and conditional primary secondary cell addition or change, CPAC, configuration, wherein the cause information indicates which one of a CHO execution condition and a CPAC execution condition associated with the CHO and CPAC configuration is fulfilled later; and determining optimization information for at least one of the CHO execution condition or the CPAC execution condition, based on the received interruption report.

[0043] In an embodiment, the method further comprises: sending the optimization information for the CHO execution condition to the source master node; sending the optimization information for the CPAC execution condition to the target master node; or sending the optimization information to one of the source master node and the target master node from which the interruption report is received, regardless of whether the optimization information contains the optimization information for the CHO execution condition, the optimization information for the CPAC execution condition, or both.

[0044] In an embodiment, the method is implemented at an operations administration and maintenance entity or an access and mobility management function entity.

[0045] Example embodiments of methods, apparatuses and computer readable mediums are also provided. The example embodiments of methods, apparatuses and computer readable mediums each generally correspond to the example embodiments of the terminal device, the radio access network (RAN) devices and the core network device described above, and a repetitive description thereof is omitted here for convenience.

[0046] Other features and advantages of the example embodiments of the present disclosure will also be apparent from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of example embodiments of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Some example embodiments will now be described, by way of non-limiting examples, with reference to the accompanying drawings.

[0048] Fig 1 is a schematic diagram illustrating an example communication network in which example embodiments of the present disclosure can be implemented.

[0049] Fig 2 is a schematic flow diagram illustrating a process according to an example embodiment of the present disclosure.

[0050] Fig. 3 is a schematic flow diagram illustrating a process according to an example embodiment of the present disclosure.

[0051] Fig. 4 is a schematic flow diagram illustrating a process according to an example embodiment of the present disclosure.

[0052] Fig 5 is a schematic flow diagram illustrating a process according to an example embodiment of the present disclosure.

[0053] Fig. 6 is a schematic flow diagram illustrating a process according to an example embodiment of the present disclosure.

[0054] Fig. 7 is a schematic block diagram illustrating an apparatus according to an example embodiment of the present disclosure.

[0055] Fig 8 is a schematic block diagram illustrating an apparatus according to an example embodiment of the present disclosure.

[0056] Fig 9 is a schematic block diagram illustrating an apparatus according to an example embodiment of the present disclosure.

[0057] Fig 10 is a schematic block diagram illustrating an apparatus according to an example embodiment of the present disclosure.

[0058] Fig 11 is a schematic block diagram illustrating devices in a communication system according to an example embodiment of the present disclosure.

[0059] Throughout the drawings, same or similar reference numbers indicate same or similar elements. A repetitive description on the same elements would be omitted. DETAILED DESCRIPTION

[0060] Herein below, some example embodiments are described in detail with reference to the accompanying drawings. The following description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known circuits, techniques and components are shown in block diagram form to avoid obscuring the described concepts and features.

[0061] Fig 1 illustrates a schematic diagram of an example communication network 100 in which example embodiments of the present disclosure can be implemented. The communication network 100 may be a wireless, mobile or cellular communication network. Referring to Fig. 1, the communication network 100 may comprise two domains: radio access network (RAN) 120 and core network (CN) 130. The RAN 120 may include a plurality of base stations (BSs), shown as BS 120A and BS 120B, to provide network access for a plurality of user equipment (UEs) 110 (only one is shown). Each base station 120A, 120B may provide communication coverage for a particular geographic area, which is also known as cell. It would be appreciated that the term “cell” may refer to a coverage area of a base station or a subsystem of the base station for serving the coverage area, depending on the context in which the term is used.

[0062] The core network 130 may include numerous network functions (NFs) (not shown) to provide various functionalities. For instance, it can provide access controls to ensure that the UEs 110 are authenticated for the services they are using, route telephone calls over the public switched telephone network, connect the UEs 110 to a data network e.g. the internet, and enable operators to charge for calls and data use. The core network 130 can also control the network by making handover happen as a UE moves from a cell coverage provided by a base station to another cell coverage provided by the same or a different base station. In an example embodiment, the core network 130 may be deployed on cloud, e.g. a public cloud, a private cloud or a hybrid cloud.

[0063] The UE 110 may be configured to operate in a Dual Connectivity (DC) mode. In the DC mode, the UE 110 is connected to two base stations, e.g. the first base station 120A and the second base station 120B as shown in Fig. 1. It is assumed that the first base station 120A acts as a master node (MN) for the UE 110 and the second base station 120B acts as a secondary node (SN) for the UE 110. The MN 120A has a radio resource control (RRC) connection with the UE 110 and provides both control plane (CP) and user plane (UP) connections to the core network 130. The SN 120B provides additional resources to the UE 110, but it does not provide for the UE 110 a CP connection to the core network 130. The UE 110 can simultaneously receive and transmit data on a plurality of component carriers from serving cells of the MN 120 A and the SN 120B. The serving cells of the MN 120Amay be referred to as a master cell group (MCG), which includes a primary cell (PCell) 121 and optionally one or more secondary cells (SCells) 122. The PCell 121 is used to initiate an initial access of the UE 110 to the network 100, and it serves as a main point of connection for the UE 110. The UE 110 aggregates the PCell 121 and the one or more SCells 122 by carrier aggregation (CA). The CA may be used without the DC, as known in the art. The serving cells of the SN 120B may be referred to as a secondary cell group (SCG), which includes a primary secondary cell (PSCell) 123 and optionally one or more secondary cells (SCells) 124. Similarly, the PSCell 123 is used to initiate an initial access under SCG, and it is aggregated with the one or more SCells 124 by carrier aggregation. The dual connectivity and carrier aggregation technologies enable the UE 110 to combine resources of multiple cells or carriers, thereby achieving higher data rate. In case of multi-radio dual-connectivity (MR-DC), one of the MN 120A and the SN 120B may be a 5G New Radio (NR) base station, and the other may be either an E-UTRA base station or a NR base station.

[0064] When the UE 110 moves from one cell to another, a handover procedure may be executed to ensure reliable and stable communication between the UE 110 and the network. In a conditional handover (CHO) procedure, the UE 110 may evaluate certain execution conditions and decide to perform handover when the execution conditions are met. The UE 110 may be provided with a CHO with SN or CHO with candidate SCG configuration, which may include a CHO configuration (also referred to as MCG configuration) for PCell change, a conditional PSCell addition or change (CPAC) configuration (also referred to as SCG configuration) for PSCell addition or change, and associated execution conditions. Upon receiving the configuration, the UE 110 may start evaluating the execution conditions for the candidate PCell and PSCell. In Release 17, CHO in MR-DC is limited to a scenario where the target MN can prepare a single target PSCell (under the control of an SN), and the execution conditions for the candidate PCell, PSCell are not tied to each other. The UE 110 can execute the PCell change or the PSCell addition or change independently when the associated execution condition is satisfied.

[0065] Release 18 has extended the CHO in MR-DC to a scenario where the target MN can prepare multiple candidate PSCells for the same candidate PCell. It improves usefulness of the CHO in MR-DC feature where a UE may need to access a different candidate PSCell when the CHO needs to be executed. In case there are multiple candidate PSCells associated with one candidate PCell, the CHO with candidate SCG(s) configuration provided from the network to the UE 110 may include multiple CHO and CPAC configurations for the same candidate PCell and different candidate PSCells, i.e. each one contains one CHO / MCG configuration for the same candidate PCell and one CPAC / SCG configuration for a different candidate PSCell, and associated execution conditions. The CHO and CPAC execution conditions associated with one CHO and CPAC configuration are tied to each other and will be evaluated in parallel at the UE 110. If one of the CHO and CPAC execution conditions is met but the other is not met, the UE 110 will continue to evaluate both CHO and CPAC execution conditions. In other words, the UE 110 will not perform PCell change and PSCell addition or change until both CHO and CPAC execution conditions are met.

[0066] In Release 17, it is possible to optimize the CHO and CPAC execution conditions by looking at a successful handover report (SHR) indicating a successful PCell change or a successful PSCell Report (SPR) (also known as successful PSCell change report, SPCR) indicating a successful PSCell addition or change, as the CHO and CPAC execution conditions are not tied to each other and execution thereof is independent. If the CHO execution is delayed with an interruption experienced at the UE (e.g., the T310 timer runs and does not stop) due to a wrong or improper CHO execution condition configuration, the UE may indicate via the SHR that the CHO execution is delayed, and the network would know something goes wrong with the CHO execution condition. Similarly, if the CPAC execution is delayed with an interruption experienced at the UE, the UE may indicate via the SPR / SPCR that the CPAC execution is delayed, and the network would know the CPAC execution condition is wrong or improper. Then the network can optimize the CHO or CPAC execution conditions to minimize the interruption.

[0067] When the UE is configured with the Release 18 CHO with candidate SCG(s) configuration comprising one CHO and CPAC configuration containing both MCG and SCG configurations, however, even if the SHR and SPR are applicable for the Release 18 CHO with candidate SCG(s) configuration, the network cannot determine, by monitoring the SHR and SPR, which of the CHO and CPAC execution conditions is sub-optimal, wrong or improper because the UE performs the CHO and CPAC only when both CHO and CPAC execution conditions are met. If one of the CHO and CPAC execution conditions is not configured properly, the entire CHO and CPAC execution would be delayed as the CHO and CPAC configuration cannot be executed partially. The delayed execution due to the unsatisfied execution condition may render the UE susceptible to interference from the target PCell or the target PSCell, resulting in an interruption at the UE side. Currently, there is no mechanism to identify the cause of interruption after a successful CHO and CPAC execution, i.e., whether the interruption before the successful CHO and CPAC execution is caused by the CHO execution condition or the CPAC execution condition. Therefore, it is not possible for the network to fix the problems when both CHO and CPAC execution conditions are configured as it does not know which of the execution conditions causes the problems.

[0068] Example embodiments of the present disclosure provide mobility robustness optimization (MRO) solutions for Release 18 CHO with candidate SCG(s) mobility. The MRO solutions can identify which of the execution conditions of the CHO with candidate SCG(s) configuration causes the robustness issues, i.e., interruption before the successful execution of the CHO and CPAC. In some example embodiment, the UE may log in a successful cell change report which execution condition is fulfilled later and leads to the interruption, and optionally a time duration between a time when one of the CHO and CPAC execution conditions is fulfilled and a time when the other is fulfilled. The successful cell change report may re-use the legacy successful handover report or successful PSCell change report depending on the scenario, which may be enhanced / extended to indicate the interruption cause and relevant information. In another example embodiment, the successful cell change report may comprise a new report rather than the SHR and SPR. Then the network can identify the interruption cause and optimize the execution condition related to the interruption cause. Some example embodiments also propose new triggering conditions for the successful cell change report in the context of CHO and CPAC and define the UE behavior when the successful cell change report is configured.

[0069] Fig. 2 illustrate a process 200 according to an example embodiment of the present disclosure. The process 200 may be implemented at a UE 110, a plurality of base stations 120A, 120C, 120D, and a core network device 132. The UE 110 may operate in the dual connectivity (DC) mode, connecting to the base station 120A acting as a master node (MN) and optionally to a base station 120B (not shown) acting as a secondary node (SN). The base stations 120C, 120D may act as a target master node (T-MN) and a target secondary node (T-SN) for the UE 110, respectively, in a handover procedure. The core network device 132 may be an operations administration and maintenance (0AM) entity, an access and mobility management function (AMF) entity, or other network functions that can be configured to perform the process 200.

[0070] As shown in Fig. 2, the source MN (S-MN) 120Amay initiate a conditional handover preparation procedure by sending at 210 a handover (HO) request message to one or more potential / candidate target master nodes (T-MNs) including the T-MN 120C. In an example embodiment, the handover request may indicate the maximum number of conditional reconfigurations that the candidate MNs can prepare for the UE 110.

[0071] Upon receiving the handover request, the T-MN 120C may decide to prepare a CHO with candidate SCG(s) configuration for the UE 110 and send at 212 a SN addition request to one or more potential / candidate target secondary nodes (T-SNs) including the T-SN 120D. The SN addition request may include CHO related information e.g. the source MN ID and the UE ID in the source MN to indicate that the SN addition preparation procedure is triggered in relation to a CHO and to enable the candidate SN to identify requests related to the same UE. The T-MN 120C may indicate one or more candidate PSCells recommended by the T-MN 120C via the latest measurement results for the T-SN 120D to choose and configure candidate SCG cell(s), and the maximum number of candidate PSCells that the T-SN 120D can prepare for the UE 110, in the SN addition request.

[0072] At 214, the T-SN 120D may respond to the T-MN 120C with a SN addition request acknowledge message. The SN addition request acknowledge message may include a list of PSCell(s) to prepare (considering the maximum number indicated by the T-MN 120C) and other SCG SCells for each prepared PSCell.

[0073] At 216, the T-MN 120C may determine the CHO with candidate SCG(s) configuration for the UE 110. The CHO with candidate SCG(s) configuration may include one or more pairs of MCG configuration and SCG configuration. The MCG configuration is determined at the T-MN 120C, and each MCG configuration may indicate a candidate PCell and optionally one or more MCG SCells prepared at the T-MN 120C. The SCG configuration is received from the T-SN 120D (and other potential T-SNs) at 214, and each SCG configuration may indicate a candidate PSCell and optionally one or more SCG SCells prepared at the T-SN 120D (or the other potential T-SNs). It would be appreciated that the T-MN 120C may prepare multiple candidate PCells for the UE 110, and for each PCell, multiple PSCells may be prepared at the T-SN 120D (and / or other potential T-SNs). Throughout the present disclosure, the MCG configuration is also referred to as conditional handover (CHO) configuration, the SCG configuration is also referred to as conditional PSCell addition or change (CPAC) configuration, and a pair of MCG configuration and SCG configuration associated with each other may be collectively referred to as CHO and / with CPAC configuration or independently as CHO and CPAC configurations.

[0074] The T-MN 120C may determine at 216 one or more CPAC execution conditions (or CPAC conditions for short) for each CPAC configuration, or exactly the PSCell in the CPAC configuration. In an example embodiment, one of the one or more CPAC execution conditions may include an event A4 threshold for the PSCell.

[0075] Optionally, the T-MN 120C may also determine at 216 a successful cell change report configuration for the UE 110. The successful cell change report configuration may specify one or more triggering conditions for a successful cell change report and / or content of the successful cell change report. The successful cell change report is defined as a report sent from the UE 110 to the T-MN 120C after successful handover of the UE 110 from the S-MN 120 A to the T-MN 120C, which may log risk or near failure information related to the conditional handover procedure. Details of the successful cell change report configuration and the successful cell change report will be described below.

[0076] With continuous reference to Fig. 2, the T-MN 120C may send a handover request acknowledge message to the S-MN 120A at 218. The handover request acknowledge message may contain the CHO with candidate SCG(s) configuration, the CPAC execution condition(s), and optionally the successful cell change report configuration. It would be appreciated that the S-MN 120A may receive the handover request acknowledge message from a plurality of potential T-MNs.

[0077] In response to the handover request acknowledge message, the S-MN 120A may determine at 220 one or more CHO execution conditions (or CHO conditions for short) for each CHO configuration, or exactly the PCell in the CHO configuration received in the handover request acknowledge message. In an example embodiment, one of the one or more CHO execution conditions may include an event A4 threshold for the PCell. It would be appreciated that the CHO execution condition and the corresponding CPAC execution condition are determined in a way that they will be in line with each other, i.e. one of the CHO and CPAC conditions would not necessarily block the other.

[0078] In an example embodiment, the T-MN 120C may not determine the successful cell change report configuration for the UE 110 at 216, and the handover request acknowledge message received at the S-MN 120A may not contain the successful cell change report configuration. The S-MN 120A may determine the successful cell change report configuration for the UE 110 at 220. In another example embodiment, the successful cell change report configuration may be partly determined at the T-MN 120C, and the S-MN 120A may determine a remaining part of the successful cell change report configuration. As discussed above, the successful cell change report configuration may specify one or more triggering conditions for the successful cell change report and / or content of the successful cell change report. Details of the successful cell change report configuration and the successful cell change report will be described below.

[0079] At 222, the S-MN 120 A may send an RRC reconfiguration message containing the CHO with candidate SCG(s) configuration to the UE 110. The CHO with candidate SCG(s) configuration may include a list of CHO and CPAC configurations and associated execution conditions, each CHO and CPAC configuration including a CHO / MCG configuration and a corresponding CPAC / SCG configuration. As discussed above, multiple candidate PCells may be prepared for the UE 110, and for each PCell, multiple candidate PSCells may be prepared. The CHO execution condition and the CPAC execution condition associated with each CHO and CPAC configuration are tied to each other. It means that only when both the CHO and CPAC execution conditions are satisfied, the UE 110 would trigger execution of CHO and CPAC based on the corresponding CHO and CPAC configuration, which will be described in detail below.

[0080] Here it is assumed that the UE 110 is not provided with a CHO-only configuration or a Release 17 CHO with candidate SCG configuration. If the UE 110 is configured with the CHO-only configuration or the Release 17 CHO with candidate SCG configuration and the CHO execution condition used for one of the CHO and CPAC configurations is also used for the CHO-only configuration or the Release 17 CHO with candidate SCG configuration, when the CHO execution condition is fulfilled and the corresponding CPAC execution condition is not fulfilled, the UE 110 will trigger the PCell change based on the CHO-only configuration or the Release 17 CHO with candidate SCG configuration, not waiting for the CPAC execution condition being fulfilled.

[0081] In an example embodiment, the S-MN 120Amay also send the successful cell change report configuration to the UE 110 at 222. The successful cell change report configuration may be determined at the S-MN 120Aor at least partly received from the T-MN 1200. As discussed above, the successful cell change report configuration may specify one or more triggering conditions for the successful cell change report and / or content of the successful cell change report. In another example embodiment, the triggering conditions and content of the successful cell change report may be pre-defmed / pre-configured at the UE 110, neither the T-MN 120C nor the S-MN 120A needs to determine the successful cell change report configuration for the UE 110.

[0082] In an example embodiment, the successful cell change report may be configured to reuse a legacy successful handover report (SHR) or a legacy successful PSCell report (SPR) (also known as successful PSCell change report, SPCR). Based on the configuration, the UE 110 will send the SHR to the T-MN 120C after successful handover from the S-MN 120A to the T-MN 120C if the CPAC execution condition is met first and the CHO execution condition is met later, or send the SPR to the T-MN 120C if the CHO execution condition is met first and the CPAC execution condition is met later. Therefore, the type of the report may directly indicate which execution condition was met first and which execution condition was met last. In another example embodiment, the SHR and SPR may be enhanced / extended to include additional information related to the conditional handover procedure, which will be described in detail later. In another example embodiment, the successful cell change report may be configured as a new report rather than the SHR or SPR. Based on the configuration, the UE 110 will send the new report to the T-MN 120C after successful handover from the S-MN 120A to the T-MN 120C, regardless of which one of the CHO execution condition and the CPAC execution condition is met later.

[0083] If the successful cell change report is configured to re-use the SHR or SPR, the successful cell change report may be triggered when at least one of the below four conditions is satisfied: - T310 timer of the UE exceeds a first threshold; - T312 timer of the UE exceeds a second threshold; - T304 timer of the UE exceeds a third threshold; - Time duration between a time when one of the CHO and CPAC execution conditions is met and a time when the other of the CHO and CPAC execution conditions is met exceeds a fourth threshold. The timers T310, T312 and T304 are defined in 3GPP specifications. The first to third thresholds may be percentage values e.g. 40%, 60%, 80%, which indicate a ratio of the threshold timer value (e.g., in unit of ms) over the T310, T312, T304 timer expiry value (e.g., in unit of ms). The fourth threshold may be a time duration value in unit of ms. If the successful cell change report is configured as the new report rather than the SHR or SPR, the last (fourth) triggering condition may be used to trigger the new report. At least one of the triggering conditions and the related thresholds may be configured in the successful cell change report configuration. In an example embodiment, the fourth triggering condition and the fourth threshold may be configured in the successful cell change report configuration, while the first, second and third triggering conditions and the related thresholds may be configured in a legacy way where they are configured for the SHR and SPR.

[0084] At 224, the UE 110 may respond to the S-MN 120A with an RRC reconfiguration complete message.

[0085] After receiving the CHO with candidate SCG(s) configuration, the UE 110 may start evaluating the CHO execution condition for the candidate PCell(s) and the CPAC execution condition for the candidate PSCell(s). When the UE 110 determines at 226 based on measurement results that one of the CHO and CPAC execution conditions is fulfilled and the other of the CHO and CPAC execution conditions is not fulfilled, the UE 110 may start a condition fulfillment interval timer Tbetween-conditions. The condition fulfillment interval timer Tbetween-conditions is associated with every single CHO and CPAC configuration. For example, if the T-MN 120C prepares two PSCells PSCell#l, PSCell#2 for the same candidate PCell PCell#l, two CHO and CPAC configurations are provided to the UE 110, corresponding to two timer Tbetween-conditions_1, Tbetween-conditions_2, respectively. If the CHO execution condition for PCell#l is fulfilled but the CPAC execution conditions for PSCell#l, PSCell#2 are not fulfilled, the UE 110 will start both timers Tbetween-conditions_l and Tbetween-conditions_2. If the CPAC execution condition for PSCell#l is fulfilled but the CPAC execution condition for PSCell#2 and the CHO execution condition for PCell#l are not fulfilled, the UE 110 will start the timer Tbetween-conditions^l. If the CPAC execution condition for PSCell#2 is fulfilled but the CPAC execution condition for PSCell#l and the CHO execution condition for PCell# 1 are not fulfilled, the UE 110 will start the timer Tbetween-conditions_2.

[0086] As mentioned above, the UE 110 would not perform the CHO and CPAC when any one of the CHO execution condition and the CPAC execution condition is not fulfilled. The CHO and CPAC is delayed due to the unfulfilled condition. At 228, the UE 110 may detect an interruption with the connection to the S-MN 120A or the connection to the S-SN 120B (not shown in Fig. 2). In response to the interruption, the UE 110 may start a T310 timer for the S-MN link or the S-SN link. The interruption may be caused by link quality deterioration or interference of the T-MN 120C and the T-SN 120D, as the UE 110 moves away from the S-MN 120A and the S-SN 120B. In an example embodiment, the UE 110 may experience the interruption first, and then one of the CHO and CPAC execution conditions is met. In other words, when the interruption happens, neither the CHO execution condition nor the CPAC execution condition is fulfilled. Four scenarios of the interruption are list below: - Case 1: interruption with MCG due to delayed CHO+CPAC execution: • Case 1A: When the CHO execution condition is met but the CPAC execution condition is not met, the UE 110 experiences interruption with the S-MN 120A due to interference of the T-MN 120C; • Case IB: When the CPAC execution condition is met but the CHO execution condition is not met, the UE 110 experiences interruption with the S-MN 120A due to low link quality with the S-MN 120A (e.g. S-MN coverage hole); - Case 2: interruption with SCG due to delayed CHO+CPAC execution: • Case 2A: When the CPAC execution condition is met but the CHO execution condition is not met, the UE 110 experiences interruption with the S-SN 120B due to interference of the T-SN 120D; • Case 2B: When the CHO execution condition is met but the CPAC execution condition is not met, the UE 110 experiences interruption with the S-SN 120B due to low link quality with the S-SN 120B (e.g. S-SN coverage hole).

[0087] If the successful cell change report configured for the UE 110 is a new report rather than the SHR and SPR and the triggering condition for the new report is satisfied, i.e. the timer Tbetween-conditions has a value exceeding the fourth threshold, the UE 110 may create the successful cell change report (i.e. the new report) at 230. For example, the UE 110 may log in the successful cell change report an identifier of the CHO and CPAC configuration which has the one execution condition fulfilled. The UE 110 may also log in the report which execution condition is met and which execution condition is not met. Alternatively, the UE 110 may log in the report only the execution condition that is not met, i.e. the problematic condition causing the interruption, or only the execution condition that is met. It would be appreciated that the condition which is not met can be determined from the indication of the condition which is met, or vice versa. In an example embodiment, the UE 110 may also log the interruption type in the successful cell change report, e.g. interruption with MCG (i.e., interruption with the connection between UE and S-MN) or interruption with SCG (i.e., interruption with the connection between UE and S-SN). The UE 110 may also log in the successful cell change report whether the interruption happens before any one of the CHO and CPAC execution conditions is fulfilled.

[0088] At 232, the UE 110 may detect that both the CHO and CPAC execution conditions are fulfilled. Upon this condition, the UE 110 may stop the timer Tbetween-conditions and log the timer value in the successful cell change report. In an example embodiment, a plurality of execution conditions may be configured for each of the CHO configuration and the CPAC configuration. The UE 110 may start the timer Tbetween-conditions when one or more of the execution conditions for one of the CHO and CPAC configurations is fulfilled, and stop the timer Tbetween-conditions when one or more of the execution conditions for the other of the CHO and CPAC configurations is fulfilled. The Tbetween-conditions timer value indicates a time duration between a time when one of the CHO and CPAC execution conditions is met and a time when the other of the CHO and CPAC execution conditions is met and, to some extent, reflects inconsistency between the CHO and CPAC execution conditions that leads to the interruption. Therefore, the UE 110 may log the Tbetween-conditions timer value in the successful cell change report for subsequent optimization of the problematic condition which caused the interruption. The UE 110 may also log the identifier of the CHO and CPAC configuration of which both the CHO and CPAC execution conditions are fulfilled.

[0089] Since the UE 110 may be provided with a plurality of CHO and CPAC configurations, it could happen that one or more timers Tbetween-conditions may be started when one condition is fulfilled but not stopped because the stop condition (i.e. both CHO and CPAC execution conditions are fulfilled) is never satisfied. This may be due to various reasons such as the UE 110 executes another CHO and CPAC configuration of which both CHO and CPAC execution conditions are met, or the UE 110 experiences failure like radio link failure (RLF), SCG failure, etc. In an example embodiment, the UE 110 may log the identifier of the CHO and CPAC configuration(s) not executed at the UE 110 and information of the timer Tbetween-conditions associated with the CHO and CPAC configuration(s) not executed in the successful cell change report. For example, the UE 110 may log the current value of the timer Tbetween-conditions associated with the CHO and CPAC configuration(s) not executed. The UE 110 may reset the timer(s) Tbetween-conditions after logging the timer value.

[0090] In an example embodiment, the UE 110 may create the successful cell change report (i.e., the new report) at 232 when both the CHO and CPAC execution conditions are fulfilled, instead of at 230 when only one of the CHO and CPAC execution conditions is fulfilled.

[0091] When both the CHO and CPAC execution conditions are fulfilled, the UE 110 may perform the CHO and CPAC based on the CHO and CPAC configuration associated with the fulfilled conditions. Concretely, the UE 110 may detach from the S-MN 120A and execute an access procedure towards the T-MN 120C based on the CHO configuration at 234 and an access procedure towards the T-SN 120D based on the CPAC configuration at 236.

[0092] In an example embodiment, the UE 110 may create the successful cell change report (either the SHR, the SPR or the new report) at 238 after successful execution of the CHO and CPAC based on the CHO and CPAC configuration, i.e., after successful access to the T-MN 120C and the T-SN 120D, instead of at 230 when only one of the CHO and CPAC execution conditions is fulfilled or at 232 when both the CHO and CPAC execution conditions are fulfilled but the CHO and CPAC have not been performed. Before creating the successful cell change report, the UE 110 may determine that one or more triggering conditions for the successful cell change report are satisfied. In an example embodiment, in case the CHO execution condition is fulfilled first and the CPAC execution condition is fulfilled later, the created successful cell change report may be the SPR because the CPAC execution condition is the cause of the interruption. In case the CPAC execution condition is fulfilled first and the CHO execution condition is fulfilled later, the created successful cell change report may be the SHR because the CHO execution condition is the cause of the interruption. In this way, the successful cell change report can implicitly indicate the cause of the interruption experienced at the UE 110. In another example embodiment, the successful cell change report can explicitly indicate the cause of the interruption. For example, the successful cell change report may indicate the first fulfilled condition, the last fulfilled condition, or both. Additional information that the UE 110 can log in the successful cell change report has been discussed above and a repetitive description is omitted here.

[0093] Then at 240, the UE 110 may send the successful cell change report to the T-MN 120C. In an example embodiment, the UE 110 may indicate availability of the successful cell change report to the T-MN 120C in an RRC complete message, e.g. RRCReconfigurationComplete, RRCReestablishmentComplete, RRCSetupComplete, or RRCResumeComplete messages, and then the T-MN 120C may fetch the successful cell change report by a UE information request procedure. In another example embodiment, the T-MN 120C may blindly fetch the successful cell change report from the UE 110 after the UE 110 is successfully handed over to the T-MN 120C, or the UE 110 may directly send the successful cell change report to the T-MN 120C after the successful handover of the UE 110.

[0094] The successful cell change report may include cause information of the interruption experienced at the UE 110. As discussed above, the interruption may be caused by one of the CHO and CPAC execution conditions fulfilled later. The successful cell change report may then indicate the interruption cause implicitly. For instance, the successful cell change report reusing the SHR implies that the CHO execution condition was fulfilled later and hence potentially caused the interruption, and the successful cell change report reusing the SPR implies that the CPAC execution condition was fulfilled later and hence potentially caused the interruption. In another example embodiment, the successful cell change report may explicitly indicate the interruption cause. For instance, the successful cell change report, either the SHR, the SPR or the new report, may comprise an information element that explicitly indicates the first fulfilled execution condition, the last fulfilled execution condition or both.

[0095] As discussed above, the successful cell change report may further contain the identifier of the CHO and CPAC configuration executed at the UE 110 and the time duration between the CHO and CPAC execution conditions being fulfilled. In an example embodiment, the successful cell change report may further contain one or more of the following: - type of the interruption, including interruption with MCG (i.e., interruption with the connection between UE and S-MN) or interruption with SCG (i.e., interruption with the connection between UE and S-SN); - an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled; - an identifier of at least one CHO and CPAC configuration stored but not executed at the UE 110, or - information of the condition fulfillment interval timer Tbetween-conditions associated with the at least one CHO and CPAC configuration not executed. It would be appreciated that the successful cell change report may also include additional information that can help the network to optimize the CHO and CPAC procedure.

[0096] In response to the received successful cell change report, the T-MN 120C may generate and send at 242 an interruption report containing the interruption cause information to the core network device 132. As discussed above, the interruption cause information may indicate which one of the CHO execution and the CPAC execution was fulfilled later and hence caused the interruption experienced at the UE 110. In an example embodiment, the interruption report may further contain the time duration between the CHO and CPAC execution conditions being fulfilled and the identifier of the CHO and CPAC configuration executed at the UE 110. Optionally, the interruption report may further contain additional information that may be used to optimize the problematic execution condition which caused the interruption, e.g. one or more of the following: - type of the interruption, including interruption with MCG (i.e., interruption with the connection between UE and S-MN) or interruption with SCG (i.e., interruption with the connection between UE and S-SN); - indication of whether the interruption happens before neither the CHO execution condition nor the CPAC execution condition is fulfilled; - the CHO execution condition and information of the candidate PCell related to the CHO execution condition, such as physical cell identifier (PCI) and frequency of the PCell; - the CPAC execution condition and information of the candidate PSCell related to the CPAC execution condition, such as physical cell identifier (PCI) and frequency of the PSCell; - the identifier of one or more CHO and CPAC configurations stored but not executed at the UE 110; - information of the condition fulfillment interval timer Tbetween-conditions associated with the one or more CHO and CPAC configurations not executed; - the identifier of the T-MN 120C which configured the CPAC execution condition; or - the identifier of the S-MN 120A which configured the CHO execution condition. In an example embodiment, the interruption report may include the successful cell change report received from the UE 110. In another embodiment, the T-MN 120C may form a more holistic picture of the cause of the interruption. For example, the T-MN 120C may combine the SHR / SPR received from the UE 110 with SHR(s) and / or SPR(s) received from other UEs and determine whether or not there is correlation between the contents of the received reports. For example, an execution condition to a certain cell may be sub-optimal. The T-MN 120C may then formulate the interruption report to indicate any such more refined information on the source of the interruption.

[0097] The core network device 132 may collect the interruption reports from a plurality of base stations and analyze statistics of the interruptions to optimize the problematic execution conditions that caused the interruptions. For instance, the core network device 132 may decrease the event A4 threshold specified in the last fulfilled execution condition so that the execution condition can be fulfilled earlier, thereby reducing or eliminating the interruption. The core network device 132 may decrease the event A4 threshold by a predefined amount, or an amount depending on the time duration between the two execution conditions being fulfilled. The longer the time duration is, the larger the decreased amount is. As an option, the core network device 132 may also increase the event A4 threshold in the first fulfilled execution condition to delay its fulfillment, as long as the fulfillment is still prior to the interruption. If the interruption happens before any one of the CHO and CPAC execution conditions is fulfilled, the core network 132 may decrease the event A4 threshold in the first fulfilled execution condition by a first amount and decrease the event A4 threshold in the second fulfilled execution condition by a second amount, where the second amount may be larger than the first amount, so that the first fulfilled execution condition can be fulfilled before the interruption and the second fulfilled execution condition can be fulfilled closer to the first fulfilled execution. As discussed above, additional information may also be considered in optimizing the execution conditions. In an example embodiment, the core network device 132 may execute a machine learning algorithm to optimize the execution conditions. The machine learning algorithm may receive information elements in the interruption report as input, and provide optimization parameters as output. In an example embodiment, the core network device 132 may provide optimized parameters for the execution conditions in case the core network device 132 has knowledge of the execution conditions, or provide delta amounts for optimizing parameters in the execution conditions in case the core network device 132 does not have knowledge of the execution conditions.

[0098] In an example embodiment, the core network device 132 may send at 244 the optimization information to the T-MN 120C. The optimization information may contain optimization information for the CHO execution condition, optimization information for the CPAC execution condition, or both. The T-MN 120C may forward at 246 the optimization information for the CHO execution condition, if any, to the S-MN 120A. In another example embodiment, if the interruption report contains information of the S-MN 120A where the CHO execution condition is determined, the core network device 132 may send the optimization information for the CHO execution condition directly to the S-MN 120A at 248, and send only the optimization information for the CPAC execution condition to the T-MN 120C at 244. Then the S-MN 120A and the T-MN 120C may use the optimized CHO and CPAC execution conditions for the CHO with candidate SCG(s) procedure. In an example embodiment, if the core network device 132 decides no optimization is necessary, the core network device 132 may inform the T-MN 120C and optionally the S-MN 120Athat no optimization is needed. Then the S-MN 120A and the T-MN 120C do not need to update the CHO and CPAC execution conditions for the CHO with candidate SCG(s) procedure.

[0099] In the process 200, the successful cell change report is transmitted to the T-MN 120C, and the T-MN 120C directly contacts the core network device 132 for optimization of the CHO and CPAC execution conditions. In another example embodiment, the successful cell change report may be transmitted to the S-MN 120A via the T-MN 120C, and the S-MN 120A may contact the core network device 132 for the execution condition optimization. It is very likely especially when the successful cell change report is configured by the S-MN 120A. Fig. 3 illustrates such a process 300 according to an example embodiment of the present disclosure. The process 300 includes the same steps 210-240 as in the process 200, and a repetitive description of the steps 210-240 is omitted here. Below a description will be given to only different steps in the process 300.

[00100] Referring to Fig. 3, when the T-MN 120C receives the successful cell change report from the UE 110 at 240, the T-MN 120C may forward at 310 the successful cell change report to the S-MN 120A. Similar to the step 242, the S-MN 120A may send at 312 an interruption report containing the interruption cause information to the core network device 132. The core network device 132 may collect the interruption reports from a plurality of base stations and analyze statistics of the interruptions to optimize the problematic execution conditions that caused the interruptions. Then at 314, the core network device 132 may send the optimization information to the S-MN 120A. The optimization information may contain optimization information for the CHO execution condition, optimization information for the CPAC execution condition, or both. The S-MN 120A may forward at 316 the optimization information for the CPAC execution condition, if any, to the T-MN 120C. In another example embodiment, if the interruption report contains information of the T-MN 120C where the CPAC execution condition is determined, the core network device 132 may send the optimization information for the CPAC execution condition directly to the T-MN 120C at 318, and send only the optimization information for the CHO execution condition to the S-MN 120A at 314. Then the S-MN 120A and the T-MN 120C may use the optimized CHO and CPAC execution conditions for the CHO with candidate SCG(s) procedure. In an example embodiment, if the core network device 132 decides no optimization is necessary, the core network device 132 may inform the S-MN 120A and optionally the T-MN 120C that no optimization is needed. Then the S-MN 120A and the T-MN 120C do not need to update the CHO and CPAC execution conditions for the CHO with candidate SCG(s) procedure.

[00101] In the process 200 and the process 300, the execution condition optimization is performed in a centralized manner, i.e. the core network device 132 acts as the entity who collects the interruption reports to derive the statistics and optimize the condition parameters. In another example embodiment, the execution condition optimization may be performed in a distributed manner, i.e. at the base stations. In this case, the signaling from / to the 0AM is not needed, and the work load is distributed to a plurality of network nodes. Fig. 4 illustrates such a process 400 according to an example embodiment of the present disclosure. The process 400 includes the same steps 210-240 as in the process 200, and a repetitive description of the steps 210-240 is omitted here. Below a description will be given to only different steps in the process 400.

[00102] Referring to Fig. 4, the T-MN 120C receives the successful cell change report containing the interruption cause information from the UE 110 at 240. If the successful cell change report indicates that the CPAC execution condition was fulfilled later than the CHO execution condition or later than the starting time of the interruption experienced at the UE 110, the T-MN 120C may determine optimization for the CPAC execution condition based on the successful cell change report at 410. If the successful cell change report indicates that the CHO execution condition was fulfilled later than the CHO execution condition or later than the starting time of the interruption experienced at the UE 110, the T-MN 120C may forward at 412 the successful cell change report to the S-MN 120A. The S-MN 120A may determine optimization for the CHO execution condition based on the successful cell change report at 414. If the successful cell change report indicates that the CHO execution condition was fulfilled earlier than the CHO execution condition and earlier than the starting time of the interruption experienced at the UE 110, the T-MN 120C may inform the S-MN 120A that no optimization is needed for the CHO execution condition. The operation of determining the execution condition optimization may be similar to that performed at the core network device 132 in the process 200, and a repetitive description thereof is omitted here for convenience.

[00103] Fig 5 illustrate a process 500 according to an example embodiment of the present disclosure. Unlike the process 400 where the CHO and CPAC execution condition optimizations are performed at the S-MN 120A and T-MN 120C respectively, in the process 500 both the CHO and CPAC execution condition optimizations are performed at the T-MN 120C.

[00104] Referring to Fig. 5, the T-MN 120C receives the successful cell change report containing the interruption cause information from the UE 110 at 240. Based on the received successful cell change report, the T-MN 120C may determine at 510 optimization for one or both of the CHO and CPAC execution conditions. For instance, if the successful cell change report indicates that the CPAC execution condition was fulfilled later than the CHO execution condition or later than the starting time of the interruption experienced at the UE 110, the T-MN 120C may determine optimization for the CPAC execution condition. If the successful cell change report indicates that the CHO execution condition was fulfilled later than the CHO execution condition or later than the starting time of the interruption experienced at the UE 110, the T-MN 120C may determine optimization for the CHO execution condition. Then the T-MN 120C may send the determined optimization information of the CHO execution condition to the S-MN 120A at 512. If the T-MN 120C determines at 510 that no optimization is needed for the CHO execution condition, the T-MN 120C may inform the S-MN 120A that no optimization is needed for the CHO execution condition at 512. The operation of determining the execution condition optimization may be similar to that performed at the core network device 132 in the process 200, and a repetitive description thereof is omitted here for convenience.

[00105] Fig 6 illustrate a process 600 according to an example embodiment of the present disclosure. Unlike the process 500 where the CHO and CPAC execution condition optimizations are performed at the T-MN 120C, in the process 600 the CHO and CPAC execution condition optimizations are performed at the S-MN 120A.

[00106] Referring to Fig. 6, after receiving the successful cell change report from the UE 110 at 240, the T-MN 120C may forward the successful cell change report to the S-MN 120A at 610. Based on the received successful cell change report, the S-MN 120A may determine at 612 optimization for one or both of the CHO and CPAC execution conditions. For instance, if the successful cell change report indicates that the CPAC execution condition was fulfilled later than the CHO execution condition or later than the starting time of the interruption experienced at the UE 110, the S-MN 120A may determine optimization for the CPAC execution condition. If the successful cell change report indicates that the CHO execution condition was fulfilled later than the CHO execution condition or later than the starting time of the interruption experienced at the UE 110, the S-MN 120A may determine optimization for the CHO execution condition. Then the S-MN 120A may send the determined optimization information of the CPAC execution condition to the T-MN 120C at 614. If the S-MN 120A determines at 612 that no optimization is needed for the CPAC execution condition, the S-MN 120A may inform the T-MN 120C that no optimization is needed at 614. The operation of determining the execution condition optimization may be similar to that performed at the core network device 132 in the process 200, and a repetitive description thereof is omitted here for convenience.

[00107] Fig. 7 is a schematic block diagram illustrating an apparatus 700 according to an example embodiment of the present disclosure. The apparatus 700 may be implemented to comprise or to form at least a part of a terminal device such as the UE 110 discussed above to perform at least a part of operations related to the UE 110. In particular, the apparatus 700 may be implemented to perform operations in the processes 200-600 relating to the UE 110. Since the processes 200-600 have been described in detail with reference to Figs. 2-6, the blocks of the apparatus 700 will be described briefly here and details thereof may refer to the above description.

[00108] Referring to Fig. 7, the apparatus 700 may comprise a first means 710 for evaluating a CHO execution condition and a CPAC execution condition, a second means 712 for determining an interruption of a connection with a source master node or a connection with a source secondary node, a third means 714 for executing an access procedure towards a target master node and an access procedure towards a target secondary node based on a CHO and CPAC configuration in response to both the CHO execution condition and the CPAC execution condition being fulfilled, and a fourth means 716 for sending a successful cell change report containing cause information of the interruption to the target master node. The cause information may indicate which one of the CHO execution condition and the CPAC execution condition was fulfilled later.

[00109] In an example embodiment, the apparatus 700 may further comprise a fifth means 718 for receiving a CHO with SCG(s) configuration from the source master node. The CHO with SCG(s) configuration may comprise CHO and CPAC configurations and associated CHO and CPAC execution conditions.

[00110] In an example embodiment, the apparatus 700 may further comprise a sixth means 720 for starting a condition fulfillment interval timer in response to one of the CHO execution condition and the CPAC execution condition being fulfilled and the other being not fulfilled, and a seventh means 722 for stopping the condition fulfillment interval timer in response to both the CHO execution condition and the CPAC execution condition being fulfilled. The cause information contained in the successful cell change report may indicate a time measured by the condition fulfillment interval timer.

[00111] In an example embodiment, the successful cell change report may comprise a successful handover report in case the CPAC execution condition is fulfilled earlier than the CHO execution condition, or a successful primary secondary cell report in case the CHO execution condition is fulfilled earlier than the CPAC execution condition. In an example embodiment, the successful cell change report may comprise a new report different from the successful handover report and the successful primary secondary cell report, regardless of which of the CHO execution condition and the CPAC execution condition is fulfilled earlier.

[00112] In an example embodiment, the successful cell change report may be triggered when a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled exceeds a threshold.

[00113] In an example embodiment, the apparatus 700 may further comprise an eighth means 724 for receiving a successful cell change report configuration from the source master node. The successful cell change report configuration may specify at least one of the following: one or more triggering conditions for the successful cell change report, or content of the successful cell change report.

[00114] In an example embodiment, the successful cell change report may further contain an identifier of the CHO and CPAC configuration and a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled.

[00115] In an example embodiment, the successful cell change report may further contain one or more of the following: - type of the interruption, including interruption of the connection with the source master node or interruption of the connection with the source secondary node; - an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled; - an identifier of at least one CHO and CPAC configuration stored but not executed; or - information of a condition fulfillment interval timer associated with the at least one CHO and CPAC configuration not executed.

[00116] In an example embodiment, the apparatus 700 may further comprise a ninth means 726 for creating the successful cell change report in response to successfully executing the access procedure towards the target master node and the access procedure towards the target secondary node, in case the successful cell change report comprises the successful handover report or the successful primary secondary cell report and at least one triggering condition for the successful handover report or the successful primary secondary cell report is satisfied.

[00117] In an example embodiment, the apparatus 700 may further comprise a tenth means 728 for creating the successful cell change report in response to one of the CHO execution condition and the CPAC execution condition being fulfilled and the other being not fulfilled, in response to the CHO execution condition and the CPAC execution condition being fulfilled, or in response to successfully executing the access procedure towards the target master node and the access procedure towards the target secondary node, in case the successful cell change report comprises the new report and a triggering condition for the new report is satisfied.

[00118] Fig 8 is a schematic block diagram illustrating an apparatus 800 according to an example embodiment of the present disclosure. The apparatus 800 may be implemented to comprise or to form at least a part of a radio access network (RAN) device such as the base station 120C discussed above to perform at least a part of operations related to the base station 120C. In particular, the apparatus 800 may be implemented to perform operations in the processes 200-600 relating to the base station 120C. Since the processes 200-600 have been described in detail with reference to Figs. 2-6, the blocks of the apparatus 800 will be described briefly here and details thereof may refer to the above description.

[00119] Referring to Fig. 8, the apparatus 800 may comprise a first means 810 for executing an access procedure with a terminal device to accept handover of the terminal device from a source master node, and a second means 812 for receiving from the terminal device a successful cell change report containing cause information of an interruption experienced at the terminal device before the access procedure. The cause information may indicate which one of a CHO execution condition and a CPAC execution condition is fulfilled later.

[00120] In an example embodiment, the apparatus 800 may further comprise a third means 814 for sending a successful cell change report configuration to the source master node. The successful cell change report configuration may specify at least one of the following: one or more triggering conditions for the successful cell change report, or content of the successful cell change report.

[00121] In an example embodiment, the successful cell change report may further contain an identifier of a CHO and CPAC configuration associated with the executed access procedure and a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled.

[00122] In an example embodiment, the successful cell change report may further contain one or more of the following: - type of the interruption, including interruption with a connection between the terminal device and the source master node or interruption with a connection between the terminal device and a source secondary node; - an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled; - an identifier of at least one CHO and CPAC configuration not executed at the terminal device; or - information of a condition fulfillment interval timer associated with the at least one CHO and CPAC configuration not executed.

[00123] In an example embodiment, the successful cell change report may comprise a successful handover report in case the CPAC execution condition is fulfilled earlier than the CHO execution condition, or a successful primary secondary cell report in case the CHO execution condition is fulfilled earlier than the CPAC execution condition. In another example embodiment, the successful cell change report may comprise a new report different from the successful handover report and the successful primary secondary cell report, regardless of which of the CHO execution condition and the CPAC execution condition is fulfilled earlier.

[00124] In an example embodiment, the apparatus 800 may further comprise a fourth means 816 for sending to a core network device an interruption report containing the cause information of the interruption experienced at the terminal device, and a fifth means 818 for receiving from the core network device optimization information for optimizing at least one of the CHO execution condition and the CPAC execution condition.

[00125] In an example embodiment, the interruption report may contain one or more of the following: - a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled; - an identifier of a CHO and CPAC configuration executed at the terminal device; - an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled; - the CHO execution condition and information of a target primary cell related to the CHO execution condition; - the CPAC execution condition and information of a target primary secondary cell related to the CPAC execution condition; - an identifier of a target master node for the terminal device; - an identifier of the source master node.

[00126] In an example embodiment, the interruption report may comprise the successful cell change report.

[00127] In an example embodiment, the apparatus 800 may further comprise a sixth means 820 for sending the optimization information for optimizing the CHO execution condition to the source master node.

[00128] In an example embodiment, the apparatus 800 may further comprise a seventh means 822 for sending the successful cell change report to the source master node, and an eighth means 824 for receiving optimization information for optimizing the CPAC execution condition from the source master node or from a core network device.

[00129] In an example embodiment, the core network device may be an operations administration and maintenance entity or an access and mobility management function entity.

[00130] In an example embodiment, the apparatus 800 may further comprise a ninth means 826 for determining optimization for the CPAC execution condition in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later, and a tenth means 828 for sending the successful cell change report to the source master node in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later.

[00131] In an example embodiment, the apparatus 800 may further comprise an eleventh means 830 for determining optimization for the CPAC execution condition in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later.

[00132] In an example embodiment, the apparatus 800 may further comprise a twelfth means 832 for determining optimization for the CHO execution condition in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later, and a thirteenth means 834 for sending the determined optimization for the CHO execution condition to the source master node.

[00133] Fig 9 is a schematic block diagram illustrating an apparatus 900 according to an example embodiment of the present disclosure. The apparatus 900 may be implemented to comprise or to form at least a part of a radio access network (RAN) device such as the base station 120A discussed above to perform at least a part of operations related to the base station 120A. In particular, the apparatus 900 may be implemented to perform operations in the processes 200-600 relating to the base station 120A. Since the processes 200-600 have been described in detail with reference to Figs. 2-6, the blocks of the apparatus 900 will be described briefly here and details thereof may refer to the above description.

[00134] Referring to Fig. 9, the apparatus 900 may comprise a first means 910 for sending a CHO with candidate SCG(s) configuration comprising CHO and CPAC configurations to a terminal device, and a second means 912 for receiving a successful cell change report from a target master node of the terminal device. The successful cell change report may contain cause information of an interruption experienced at the terminal device before execution of the CHO and CPAC configuration. The cause information may indicate which one of a CHO execution condition and a CPAC execution relating to the CHO and CPAC configuration is fulfilled later.

[00135] In an example embodiment, the apparatus 900 may further comprise a third means 914 for sending an interruption report containing the cause information of the interruption experienced at the terminal device to a core network device, and a fourth means 916 for receiving optimization information for optimizing at least one of the CHO execution condition and the CPAC execution condition from the core network device.

[00136] In an example embodiment, the apparatus 900 may further comprise a fifth means 918 for sending the optimization information for optimizing the CPAC execution condition to the target master node.

[00137] In an example embodiment, the core network device is an operations administration and maintenance entity or an access and mobility management function entity.

[00138] In an example embodiment, the apparatus 900 may further comprise a sixth means 920 for determining optimization for the CHO execution condition associated with the CHO and CPAC configuration executed at the terminal device, in case the cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later than the CPAC execution condition.

[00139] In an example embodiment, the apparatus 900 may further comprise a seventh means 922 for determining optimization for the CHO execution condition in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later than the CPAC execution condition.

[00140] In an example embodiment, the apparatus 900 may further comprise an eighth means 924 for determining optimization for the CPAC execution condition in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later than the CHO execution condition, and a ninth means 926 for sending the determined optimization for the CPAC execution condition to the target master node.

[00141] In an example embodiment, the apparatus 900 may further comprise a tenth means 928 for sending a successful cell change report configuration to the terminal device. The successful cell change report configuration may specify at least one of the following: one or more triggering conditions for the successful cell change report, or content of the successful cell change report. The successful cell change report configuration may be determined at a source master node of the terminal device or at least partly received from the target master node.

[00142] Fig 10 is a schematic block diagram illustrating an apparatus 1000 according to an example embodiment of the present disclosure. The apparatus 1000 may be implemented to comprise or to form at least a part of a core network device such as the core network device 132 discussed above to perform at least a part of operations related to the core network device 132. In particular, the apparatus 1000 may be implemented to perform operations in the processes 200-600 relating to the core network device 132. Since the processes 200-600 have been described in detail with reference to Figs. 2-6, the blocks of the apparatus 1000 will be described briefly here and details thereof may refer to the above description.

[00143] Referring to Fig. 10, the apparatus 1000 may comprise a first means 1010 for receiving from a source master node or a target master node an interruption report containing cause information of an interruption experienced at a terminal device before handover of the terminal device from the source master node to the target master node based on a CHO and CPAC configuration, and a second means 1012 for determining optimization information for at least one of the CHO execution condition or the CPAC execution condition based on the received interruption report. The cause information contained in the interruption report may indicate which one of a CHO execution condition and a CPAC execution condition associated with the CHO and CPAC configuration is fulfilled later.

[00144] In an example embodiment, the apparatus 1000 may comprise a third means 1014 for sending the optimization information for the CHO execution condition to the source master node and a fourth means 1016 for sending the optimization information for the CPAC execution condition to the target master node.

[00145] In an example embodiment, the apparatus 1000 may comprise a fifth means 1018 for sending the optimization information to one of the source master node and the target master node from which the interruption report is received, regardless of whether the optimization information contains the optimization information for the CHO execution condition, the optimization information for the CPAC execution condition, or both.

[00146] Fig 11 is a schematic block diagram illustrating devices in a communication system 1100 according to an example embodiment of the present disclosure. As shown in Fig. 11, the communication system 1100 may include a terminal device 1110, a radio access network (RAN) device 1120, and a core network device 1130. It would be appreciated that the communication system 1100 may include a plurality of RAN devices 1120. For example, the plurality of RAN devices 1120 may be implemented as the base stations 120A, 120B, 120C and 120D discussed above. The terminal device 1110 may be implemented as the UE 110 discussed above, and the core network device 1130 may be implemented as the core network device 132 discussed above.

[00147] Referring to Fig. 11, the terminal device 1110 may comprise one or more processors 1111, one or more memories 1112 and one or more transceivers 1113 interconnected through one or more buses 1114. The one or more buses 1114 may be address, data, or control buses, and may include any interconnection mechanism such as series of lines on a motherboard or integrated circuit, fiber, optics or other optical communication equipment, and the like. Each of the one or more transceivers 1113 may comprise a receiver and a transmitter, which are connected to one or more antennas 1116. The terminal device 1110 may wirelessly communicate with the radio access network device 1120 through the one or more antennas 1116. The one or more memories 1112 may include instructions 1115 which, when executed by the one or more processors 1111, may cause the terminal device 1110 to perform operations relating to the UE 110 as described above.

[00148] The RAN device 1120 may comprise one or more processors 1121, one or more memories 1122, one or more transceivers 1123 and one or more network interfaces 1127 interconnected through one or more buses 1124. The one or more buses 1124 may be address, data, or control buses, and may include any interconnection mechanism such as a series of lines on a motherboard or integrated circuit, fiber, optics or other optical communication equipment, and the like. Each of the one or more transceivers 1123 may comprise a receiver and a transmitter, which are connected to one or more antennas 1126. The RAN device 1120 may operate as a base station for the terminal device 1110 and wirelessly communicate with terminal device 1110 through the one or more antennas 1126. The one or more network interfaces 1127 may provide wired or wireless communication links through which the RAN device 1120 may communicate with other network devices, entities, elements or functions. For example, the RAN device 1120 may communicate with the core network device 1130 via backhaul connections 1128. The one or more memories 1122 may include instructions 1125 which, when executed by the one or more processors 1121, may cause the RAN device 1120 to perform operations relating to any one of the base stations 120A, 120B, 120C and 120D as described above.

[00149] The core network device 1130 may comprise one or more processors 1131, one or more memories 1132, and one or more network interfaces 1137 interconnected through one or more buses 1134. The one or more buses 1134 may be address, data, or control buses, and may include any interconnection mechanism such as a series of lines on a motherboard or integrated circuit, fiber, optics or other optical communication equipment, and the like. The core network device 1130 may operate as a core network function node and wired or wirelessly communicate with the radio access network device 1120 through one or more links. The one or more network interfaces 1137 may provide wired or wireless communication links through which the core network device 1130 may communicate with other network devices, entities, elements or functions. The one or more memories 1132 may include instructions 1135 which, when executed by the one or more processors 1131, may cause the core network device 1130 to perform operations and procedures relating to the core network device 132 as described above.

[00150] The one or more processors 1111, 1121 and 1131 discussed above may be of any appropriate type that is suitable for the local technical network, and may include one or more of general purpose processors, special purpose processor, microprocessors, a digital signal processor (DSP), one or more processors in a processor based multi-core processor architecture, as well as dedicated processors such as those developed based on Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuit (ASIC). The one or more processors 1111, 1121 and 1131 may be configured to control other elements of the terminal / RAN / core network devices and operate in cooperation with them to implement the procedures discussed above.

[00151] The one or more memories 1112, 1122 and 1132 may include at least one storage medium in various forms, such as a transitory memory and / or a non-transitory memory. The transitory memory may include, but not limited to, for example, a random access memory (RAM) or a cache. The non-transitory memory may include, but not limited to, for example, a read only memory (ROM), a hard disk, a flash memory, 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). Further, the one or more memories 1112, 1122 and 1132 may include but not limited to an electric, a magnetic, an optical, an electromagnetic, an infrared, or a semiconductor system, apparatus, or device or any combination of the above.

[00152] It would be understood that blocks in the drawings may be implemented in various manners, including software, hardware, firmware, or any combination thereof. In some embodiments, one or more blocks may be implemented using software and / or firmware, for example, machine-executable instructions stored in the storage medium. In addition to or instead of machine-executable instructions, parts or all of the blocks in the drawings may be implemented, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application-Specific Standard Products (ASSPs), System-on-Chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), etc.

[00153] Some exemplary embodiments further provide program instruction or instructions which, when executed by one or more processors, may cause a device or apparatus to perform the procedures described above. The program instruction for carrying out procedures of the exemplary embodiments may be written in any combination of one or more programming languages. The program instruction may be provided to one or more processors or controllers of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program instruction, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program instruction may execute entirely on a machine, partly on the machine, as a standalone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[00154] Some exemplary embodiments further provide a computer program product or a computer readable medium having the program instruction or instructions stored therein. The computer readable medium may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but is 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 machine 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.

[00155] 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.

[00156] 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 are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

[00157] Although the subject matter has been described in a language that is specific to structural features and / or method actions, it is to be understood the subject matter defined in the appended claims is not limited to the specific features or actions described above. On the contrary, the above-described specific features and actions are disclosed as an example of implementing the claims.

Claims

1. An apparatus for a terminal device, comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:evaluating a conditional handover, CHO, execution condition and a conditional primary secondary cell addition or change, CPAC, execution condition;determining an interruption of a connection with a source master node or a connection with a source secondary node;executing an access procedure towards a target master node and an access procedure towards a target secondary node based on a CHO and CPAC configuration, in response to both the CHO execution condition and the CPAC execution condition being fulfilled; andsending, to the target master node, a successful cell change report containing cause information of the interruption experienced at the apparatus, wherein the cause information indicates which one of the CHO execution condition and the CPAC execution condition was fulfilled later.

2. The apparatus of claim 1, wherein the apparatus is configured to perform:receiving, from the source master node, a CHO with candidate secondary cell group configuration comprising CHO and CPAC configurations and associated CHO and CPAC execution conditions.

3. The apparatus of claim 1 or 2, wherein the apparatus is configured to perform:starting a condition fulfillment interval timer in response to one of the CHO execution condition and the CPAC execution condition being fulfilled and the other being not fulfilled; andstopping the condition fulfillment interval timer in response to both the CHO execution condition and the CPAC execution condition being fulfilled, wherein the cause information indicates a time measured by the condition fulfillment interval timer.

4. The apparatus of any of claims 1-3, wherein the successful cell change report comprises a successful handover report in case the CPAC execution condition is fulfilled earlier than the CHO execution condition,the successful cell change report comprises a successful primary secondary cell report in case the CHO execution condition is fulfilled earlier than the CPAC execution condition, orthe successful cell change report comprises a new report different from the successful handover report and the successful primary secondary cell report, regardless of which of the CHO execution condition and the CPAC execution condition is fulfilled earlier.

5. The apparatus of any of claims 1-4, wherein the successful cell change report is triggered in response to the following triggering condition being satisfied:a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled exceeds a threshold.

6. The apparatus of any of claims 1-5, wherein the apparatus is configured to perform:receiving, from the source master node, a successful cell change report configuration specifying at least one of:one or more triggering conditions for the successful cell change report; or content of the successful cell change report.

7. The apparatus of any of claims 1-6, wherein the successful cell change report further contains an identifier of the CHO and CPAC configuration and a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled.

8. The apparatus of any of claims 1-7, wherein the successful cell change report further contains one or more of the following:type of the interruption experienced at the apparatus, including interruption with the connection between the apparatus and the source master node or interruption with the connection between the apparatus and the source secondary node;an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled;an identifier of at least one CHO and CPAC configuration stored but not executed at the apparatus; orinformation of a condition fulfillment interval timer associated with the at least one CHO and CPAC configuration not executed.

9. The apparatus of any of claims 1-8, wherein the apparatus is configured to perform:creating the successful cell change report in response to successfully executing the access procedure towards the target master node and the access procedure towards the target secondary node, in case the successful cell change report comprises the successful handover report or the successful primary secondary cell report and at least one triggering condition for the successful handover report or the successful primary secondary cell report is satisfied, orcreating the successful cell change report in response to one of the CHO execution condition and the CPAC execution condition being fulfilled and the other being not fulfilled, in response to the CHO execution condition and the CPAC execution condition being fulfilled, or in response to successfully executing the access procedure towards the target master node and the access procedure towards the target secondary node, in case the successful cell change report comprises the new report and a triggering condition for the new report is satisfied.

10. An apparatus for a radio access network device, comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:executing an access procedure with a terminal device to accept handover of the terminal device from a source master node;receiving, from the terminal device, a successful cell change report containing cause information of an interruption experienced at the terminal device before the access procedure, wherein the cause information indicates which one of a conditional handover, CHO, execution condition and a conditional primary secondary cell addition or change,CPAC, execution condition is fulfilled later.

11. The apparatus of claim 10, wherein the apparatus is configured to perform:sending, to the source master node, a successful cell change report configuration specifying at least one of:one or more triggering conditions for the successful cell change report; or content of the successful cell change report.

12. The apparatus of claim 10 or 11, wherein the successful cell change report further contains an identifier of a CHO and CPAC configuration associated with the executed access procedure and a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled.

13. The apparatus of any of claims 10-12, wherein the successful cell change report further contains one or more of the following:type of the interruption, including interruption with a connection between the terminal device and the source master node or interruption with a connection between the terminal device and a source secondary node;an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled;an identifier of at least one CHO and CPAC configuration not executed at the terminal device; orinformation of a condition fulfillment interval timer associated with the at least one CHO and CPAC configuration not executed.

14. The apparatus of any of claims 10-13, wherein the successful cell change report comprises a successful handover report in case the CPAC execution condition is fulfilled earlier than the CHO execution condition,the successful cell change report comprises a successful primary secondary cell report in case the CHO execution condition is fulfilled earlier than the CPAC execution condition, orthe successful cell change report comprises a new report different from the successful handover report and the successful primary secondary cell report, regardless of which of the CHO execution condition and the CPAC execution condition is fulfilled earlier.

15. The apparatus of any of claims 10-14, wherein the apparatus is configured to perform:sending, to a core network device, an interruption report containing the cause information of the interruption experienced at the terminal device; andreceiving, from the core network device, optimization information for optimizing at least one of the CHO execution condition and the CPAC execution condition.

16. The apparatus of claim 15, wherein the interruption report contains one or more of the following:a time duration between a time when one of the CHO execution condition and the CPAC execution condition is fulfilled and a time when the other is fulfilled;an identifier of a CHO and CPAC configuration executed at the terminal device;an indication of whether the interruption happens before any one of the CHO execution condition and the CPAC execution condition is fulfilled;the CHO execution condition and information of a target primary cell related to the CHO execution condition;the CPAC execution condition and information of a target primary secondary cell related to the CPAC execution condition;an identifier of the radio access network device which serves as a target master node for the terminal device;an identifier of the source master node.

17. The apparatus of claim 15, wherein the interruption report comprises the successful cell change report.

18. The apparatus of claim 15, wherein the apparatus is configured to perform:sending, to the source master node, the optimization information for optimizing the CHOexecution condition.

19. The apparatus of any of claims 10-14, wherein the apparatus is configured to perform: sending, to the source master node, the successful cell change report; andreceiving, from the source master node or from a core network device, optimization information for optimizing the CPAC execution condition.

20. The apparatus of any of claims 15-19, wherein the core network device is an operations administration and maintenance entity or an access and mobility management function entity.

21. The apparatus of any of claims 10-14, wherein the apparatus is configured to perform:determining optimization for the CPAC execution condition in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later; orsending, to the source master node, the successful cell change report in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later.

22. The apparatus of any of claims 10-14, wherein the apparatus is configured to perform:in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later:determining optimization for the CPAC execution condition;in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later:determining optimization for the CHO execution condition; andsending, to the source master node, the determined optimization for the CHO execution condition.

23. An apparatus for a radio access network device, comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:sending, to a terminal device, a conditional handover, CHO, with candidate secondary cell group configuration comprising CHO and conditional primary secondary cell addition or change, CPAC, configurations; andreceiving, from a target master node, a successful cell change report containing cause information of an interruption experienced at the terminal device before execution of the CHO and CPAC configuration, wherein the cause information indicates which one of a CHO execution condition and a CPAC execution relating to the CHO and CPAC configuration is fulfilled later.

24. The apparatus of claim 23, wherein the apparatus is configured to perform:sending, to a core network device, an interruption report containing the cause information of the interruption experienced at the terminal device; andreceiving, from the core network device, optimization information for optimizing at least one of the CHO execution condition and the CPAC execution condition.

25. The apparatus of claim 24, wherein the apparatus is configured to perform:sending, to the target master node, the optimization information for optimizing the CPAC execution condition.

26. The apparatus of claim 24, wherein the core network device is an operations administration and maintenance entity or an access and mobility management function entity.

27. The apparatus of claim 23, wherein the apparatus is configured to perform:determining optimization for the CHO execution condition associated with the CHO and CPAC configuration executed at the terminal device, in case the cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later thanthe CPAC execution condition.

28. The apparatus of claim 23, wherein the apparatus is configured to perform:in case the interruption cause information contained in the successful cell change report indicates that the CHO execution condition is fulfilled later than the CPAC execution condition:determining optimization for the CHO execution condition;in case the interruption cause information contained in the successful cell change report indicates that the CPAC execution condition is fulfilled later than the CHO execution condition:determining optimization for the CPAC execution condition; andsending, to the target master node, the determined optimization for the CPAC execution condition.

29. The apparatus of any of claims 23-28, wherein the apparatus is configured to perform: sending, to the terminal device, a successful cell change report configuration specifying at least one of:one or more triggering conditions for the successful cell change report; orcontent of the successful cell change report.wherein the successful cell change report configuration is determined at the apparatus or at least partly received from the target master node.

30. An apparatus for a core network device, comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:receiving, from a source master node or a target master node, an interruption report containing cause information of an interruption experienced at a terminal device before handover of the terminal device from the source master node to the target master node based on a conditional handover, CHO, and conditional primary secondary cell addition or change, CPAC, configuration, wherein the cause information indicates which one of a CHO execution condition and a CPAC execution condition associated with the CHO and CPACconfiguration is fulfilled later; anddetermining optimization information for at least one of the CHO execution condition or the CPAC execution condition, based on the received interruption report.

31. The apparatus of claim 30, wherein the apparatus is configured to perform at least one of the following:sending the optimization information for the CHO execution condition to the source master node;sending the optimization information for the CPAC execution condition to the target master node; orsending the optimization information to one of the source master node and the target master node from which the interruption report is received, regardless of whether the optimization information contains the optimization information for the CHO execution condition, the optimization information for the CPAC execution condition, or both.

32. The apparatus of claim 30 or 31, wherein the core network device is an operations administration and maintenance entity or an access and mobility management function entity.

33. A method, comprising:evaluating a conditional handover, CHO, execution condition and a conditional primary secondary cell addition or change, CPAC, execution condition;determining an interruption of a connection with a source master node or a connection with a source secondary node;executing an access procedure towards a target master node and an access procedure towards a target secondary node based on a CHO and CPAC configuration, in response to both the CHO execution condition and the CPAC execution condition being fulfilled; andsending, to the target master node, a successful cell change report containing cause information of the interruption, wherein the cause information indicates which one of the CHO execution condition and the CPAC execution condition was fulfilled later.

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