WO2025172761A1

WO2025172761A1 - Ltm configuration after pscell change

Info

Publication number: WO2025172761A1
Application number: PCT/IB2024/063049
Authority: WO
Inventors: Halit Murat Gürsu; Srinivasan Selvaganapathy; Endrit DOSTI; Panagiotis SPAPIS; Riikka Karoliina DIMNIK; Ayaz AHMED; Andres ARJONA
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2024-02-15
Filing date: 2024-12-20
Publication date: 2025-08-21
Anticipated expiration: 2026-08-15

Abstract

A user equipment is caused at least to perform: being in DC with a MN and a SN being associated with a SCG; in relation to a change from a source to a target PSCell, the source PSCell being a primary cell of the SCG, performing at least one of: (i) removing at least part of a LTM configuration, the at least part of the LTM configuration being related to the SCG; (ii) updating at least part of a LTM configuration based on an SCG configuration for the target PSCell, the at least part of the LTM configuration being related to the SCG.

Description

LTM CONFIGURATION AFTER PSCELL CHANGE

FIELD OF DISCLOSURE

The following disclosure relates to the field of communication technology, in particular communication networks, in particular wireless communication networks. The disclosure may for example relate to an apparatus and one or more network nodes that can be used for low-layer triggered mobility (LTM) and dual connectivity in a communication network, in particular for having an up-to-date LTM configuration after PSCell change.

BACKGROUND

Modem communication technologies such as 5G systems provide support for Dual Connectivity, e.g., Multi Radio Dual Connectivity (MR-DC). Dual Connectivity allows that a UE may be configured to utilise resources provided by two different nodes that are connected. One node acts as the master node, MN, and the other as the secondary node, SN. The MN and SN are connected via a network interface and at least the MN is connected to the core network.

Recently, Low-layer (L1/L2) Triggered Mobility (LTM) has been introduced. LTM is a cell switch procedure that the network triggers, for example via MAC CE and for example based on layer 1 (LI) measurements. LTM provides further mobility in addition to the widely known and used layer 3 (L3) mobility.

A user equipment may be simultaneously configured to support both LTM and L3 mobility. However, in the context of dual connectivity, situations may occur in which the UE uses an outdated configuration. For instance, this may happen in the context of L3 mobility concerning the PSCell of a secondary cell group (SCG) associated with the SN. The use of outdated configurations is disadvantageous as it may lead to radio link failure (RLF). It is desirable to, at least partly, alleviate or even overcome this problem.

SUMMARY OF SOME EXAMPLE EMBODIMENTS

Example aspects and embodiments may, at least partly, alleviate or even overcome the problem.

According to a first example aspect, the following is disclosed: A method, performed by a user equipment, the method comprising: being in dual connectivity with a master node, MN, and a secondary node, SN, the SN being associated with a secondary cell group, SCG; in relation to a change from a source PSCell to a target PSCell, the source PSCell being a primary cell of the SCG, performing at least one of:

(i) removing at least part of a low-layer triggered mobility, LTM, configuration, the at least part of the LTM configuration being related to the SCG;

(ii) updating at least part of a LTM configuration based on an SCG configuration for the target PSCell, the at least part of the LTM configuration being related to the SCG.

A method, performed by a network node, the method comprising: functioning as a master node, MN, for a user equipment that is in dual connectivity with the MN and a secondary node, SN, the SN being associated with a secondary cell group, SCG; and transmitting information for configuring the user equipment to, in relation to a change of a source PSCell, the source PSCell being a primary cell of the SCG:

(i) remove at least part of a low-layer triggered mobility, LTM, configuration, the at least part of the LTM configuration being related to the SCG;

(ii) update at least part of a LTM configuration, the at least part of the LTM configuration being related to the SCG.

According to a second example aspect, the following is disclosed:

A method, performed by a user equipment, the method comprising: being in dual connectivity with a master node, MN, and a secondary node, SN, the SN being associated with a secondary cell group, SCG; receiving information relating to a low-layer triggered mobility, LTM, configuration for the user equipment; storing the information relating to the LTM configuration for the user equipment; performing a change from a source PSCell to a target PSCell, comprising indicating to the SN that the change is completed; and in response to indicating to the SN that the change is completed, receiving information, wherein at least one of option (i) or option (ii) applies: option (i): the information comprise at least part of an updated LTM configuration that is based on an SCG configuration for the target PSCell, and the instructions, when executed by the at least one processor, cause the user equipment to store the at least part of the updated LTM configuration; option (ii): the information relate to an indication to remove at least part of the LTM configuration for the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to remove the stored information relating to the LTM configuration for the user equipment.

A method, performed by a network node, the method comprising: functioning as a master node, MN, for a user equipment that is in dual connectivity with the MN and a secondary node, SN, the SN being associated with a secondary cell group, SCG; transmitting, to the user equipment, information relating to a low-layer triggered mobility, LTM, configuration for the user equipment; transmitting, to the SN, information relating to the LTM configuration for the user equipment; receiving, from the SN, information relating to a change of the user equipment from a source PSCell to a target PSCell; and performing at least one of option (i) or option (ii): option (i): updating at least part of the LTM configuration based on an SCG configuration for the target PSCell, the SCG configuration for the target PSCell being comprised in the received information relating to the change of the user equipment from the source PSCell to the target PSCell; and transmitting, to the user equipment, information comprising at least part of the updated LTM configuration; option (ii): transmitting, to the user equipment, information relating to an indication to remove at least part of the LTM configuration for the user equipment.

A method, performed by a network node, the method comprising: functioning as a secondary node, SN, for a user equipment that is in dual connectivity with a master node, MN, and the SN, the SN being associated with a secondary cell group, SCG; receiving, from the MN, information relating to a low-layer triggered mobility, LTM, configuration for the user equipment; providing information to the user equipment for performing a change from a source PSCell to a target PSCell; transmitting, to the MN, information relating to the change of the user equipment from the source PSCell to the target PSCell, wherein at least one of option (i) or option (ii) applies: option (i): the information enable the MN to update at least part of the LTM configuration based on an SCG configuration for the target PSCell comprised in the provided information relating to the change of the user equipment from the source PSCell to the target PSCell; option (ii): the information enable the MN to transmit, to the user equipment, information relating to an indication to remove at least part of the LTM configuration for the user equipment.

According to a third example aspect, the following is disclosed:

A method, performed by a user equipment, the method comprising: being in dual connectivity with a master node, MN, and a secondary node, SN, the SN being associated with a secondary cell group, SCG; receiving information relating to a low-layer triggered mobility, LTM, configuration for the user equipment; storing the information relating to the LTM configuration for the user equipment; receiving information instructing a change from a source PSCell to a target PSCell; wherein at least one of option (i) or option (ii) applies: option (i): the information instructing the change from the source PSCell to the target PSCell comprise at least part of an updated LTM configuration that is based on an SCG configuration for the target PSCell; and the method further comprises: storing the at least part of the updated LTM configuration; option (ii): the information instructing the change from the source PSCell to the target PSCell relate to an indication to remove at least part of the LTM configuration for the user equipment; and the method further comprises: removing the stored information relating to the LTM configuration for the user equipment; wherein the method further comprises: performing the change from the source PSCell to the target PSCell.

A method, performed by a network node, the method comprising: functioning as a master node, MN, for a user equipment that is in dual connectivity with the MN and a secondary node, SN, the SN being associated with a secondary cell group, SCG; transmitting, to the user equipment, information relating to a low-layer triggered mobility, LTM, configuration for the user equipment; transmitting, to the SN, information relating to the LTM configuration for the user equipment; receiving, from the SN, information relating to an upcoming change of the user equipment from a source PSCell to a target PSCell; and performing at least one of option (i) or option (ii): option (i):

(i) updating at least part of the LTM configuration based on an SCG configuration for the target PSCell, the SCG configuration for the target PSCell being comprised in the received information relating to the upcoming change of the user equipment from the source PSCell to the target PSCell; and

(ii) transmitting, to the user equipment, information instructing the change from the source PSCell to the target PSCell, the information comprising at least part of the updated LTM configuration; option (ii):

(iii) transmitting, to the user equipment, information relating to an indication to remove at least part of the LTM configuration for the user equipment.

A method, performed by a network node, the method comprising: functioning as a secondary node, SN, for a user equipment that is in dual connectivity with a master node, MN, and the SN, the SN being associated with a secondary cell group, SCG; receiving, from the MN, information relating to a LTM configuration for the user equipment; and providing, to the MN, information relating to an upcoming change of the user equipment from a source PSCell to a target PSCell, wherein at least one of option (i) or option (ii) applies: option (i): the information enable the MN to update at least part of the LTM configuration based on an SCG configuration for the target PSCell, the SCG configuration for the target PSCell being comprised in the provided information relating to the upcoming change of the user equipment from the source PSCell to the target PSCell; option (ii): the information enable the MN to transmit, to the user equipment, information relating to an indication to remove at least part of the LTM configuration for the user equipment. Any disclosure herein relating to any example aspect is to be understood to be equally disclosed with respect to any subject-matter according to the respective example aspect, e.g. relating to an apparatus, a method, a computer program, and a computer-readable medium. For example, any passage describing at least one processor; and at least one memory including instructions; the at least one memory and the instructions configured to, with the at least one processor, cause a user equipment or network node at least to perform a step is to be understood as disclosing the step as a method step itself. The same holds the other way around, i.e., any passage describing a method or method step is to be understood as disclosing that at least one processor; and at least one memory including instructions; the at least one memory and the instructions configured to, with the at least one processor, cause a user equipment or network node at least to perform the method or method step. The disclosure of a method or a method step shall also be considered as a disclosure of means for performing and/or causing to perform the respective method or method step. Likewise, the disclosure of means for performing and/or causing to perform a method or method step shall also be considered as a disclosure of the method or method step itself.

Specifically, an apparatus (e.g., a user equipment or network node) is disclosed, configured to carry out, perform and/or control or comprising respective means for performing and/or controlling the method according to any of the above-mentioned example aspects. According to a further example aspect, an apparatus (e.g., a user equipment or network node) is disclosed comprising at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform the method according to any aspect.

The user equipment and/or network node according to any aspect may comprise means for performing the specified method or steps.

The disclosed apparatus according to any aspect may comprise only (i.e., consist of) the disclosed components, for instance means, processor, memory, or may further comprise one or more additional components.

The means may be implemented in hardware and/or software. They may comprise for instance at least one processor for executing processor instructions for performing the required functions, at least one memory storing the instructions, or both. Alternatively, they could comprise for instance circuitry that is designed or configured to implement the required functions, for instance implemented in a chipset or a chip, like an integrated circuit. In general, the means may comprise for instance one or more processing means or processors.

As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in e.g. analog and/or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable):

(i) a combination of analog and/or digital hardware circuit(s) with software/firmware and

(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

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

A network node may be a network entity of a communications network, for instance a gNB, a RAN node, a base station, or part thereof. It may be logically and/or physically distributed.

A user equipment (UE) may be an apparatus that allows a user access to network services. For example, a user equipment may be a cell phone, smartphone, tablet, laptop, TV or loT-device. The interface between the UE and the network may be a radio interface.

Further, a computer program product is disclosed, the computer program product when executed by a processor of an apparatus (e.g., a user equipment or network node) causing said apparatus to perform a method according to any example aspect.

Moreover, a computer program is disclosed, the computer program when executed by a processor causing one or more apparatuses, for instance a user equipment or network node, to perform and/or control the actions of the method according to any example aspect. Additionally, a computer readable storage medium (e.g. tangible and/or non-transitory) is disclosed, the computer readable storage medium comprising at least one of the disclosed computer program products or computer programs.

Furthermore, a system is disclosed. The system may comprise at least one of the following: one or more user equipment and one or more network nodes, e.g., a network node functioning as a MN for the UE and a network node functioning as a SN for the UE.

In the following, example features and example embodiments of all aspects will be described in further detail.

Dual Connectivity allows that a multiple Rx/Tx capable UE may be configured to utilise resources provided by two different nodes that are connected. One node acts as the master node, MN, and the other as the secondary node, SN. The MN and SN may be connected via a network interface and at least the MN may be connected to the core network. An example of dual connectivity is MultiRadio Dual Connectivity (MR-DC), where there is Dual Connectivity between E-UTRA and NR nodes, or between two NR nodes.

Thus, a UE may be in dual connectivity with a MN and a SN. Accordingly, there is a network node functioning as the MN for the UE that is in dual connectivity and there is a network node functioning as the SN for the UE.

A network node may be split into a Distributed Unit and a Control Unit (CU). A CU may be understood as a logical node that includes functions (e.g., gNB functions) like transfer of user data, mobility control, Radio access network sharing, Positioning, Session Management etc., except those functions allocated exclusively to the DU. A DU may be understood as a logical node including a subset of functions (e.g., gNB functions). Its operation may be controlled by the CU. A gNB may consist of a gNB-CU-CP, multiple gNB-CU-UPs and multiple gNB-DUs, which may provide multiple cells.

A master node may be a radio access node. In particular, it may be the radio access node that provides a control plane connection to the core network. For example, it may be a Master eNB (e.g., in EN- DC), a Master ng-eNB (e.g., in NGEN-DC) or a Master gNB (e.g., in NR-DC and NE-DC). The MN may be associated with a group of one or more serving cells. The group of one or more serving cells may comprise of a special cell, SpCell, (here: the PCell) and optionally one or more SCells. The group is called the master cell group, MCG.

The term SpCell may be used to refer to the primary cell of a master or secondary cell group.

The SpCell of the MCG is the Primary Cell, PCell. It may be that MCG cell in which the UE performs the initial connection establishment procedure or initiates the connection re-establishment procedure.

The secondary node may also be radio access node . It may or may not have a control plane connection to the core network. It may provide additional resources to the UE. For example, it may be an en- gNB (e.g., in EN-DC), a Secondary ng-eNB (e.g., in NE-DC) or a Secondary gNB (e.g., in NR-DC or NGEN-DC)

The SN may be associated with a group of one or more serving cells. This group of one or more serving cells may comprise of a special cell, SpCell, (here: the PSCell) and optionally one or more SCells. The group is called the secondary cell group, SCG.

The SpCell of the SCG is the Primary SCG Cell, PSCell. For example, it may be the SCG cell in which the UE performs random access, for instance when performing a Reconfiguration with Sync procedure.

The UE may change the PSCell, i.e., it may perform a change of a PSCell, e.g., from a source PSCell to a target PSCell. The UE may do so using mobility, e.g., L3 mobility, for example a handover or Conditional Handover (CHO) and/or Conditional PSCell Addition or Change (CPAC). The change may involve a reconfiguration and/or synchronization. The change may be triggered by the SN.

In various embodiments, the change from the source PSCell to the target PSCell comprises: receiving (e.g., from the MN or the SN) information instructing the change from the source PSCell to the target PSCell; and in response to receiving the information instructing the change, performing the change from the source PSCell to the target PSCell.

The information instructing the change from the source PSCell to the target PSCell may be a RRCReconfiguration message originating at the SN. Performing the change from the source PSCell to the target PSCell may comprise transmitting a RRCReconfigurationComplete message. For example, the SN may transmit a RRCReconfiguration message that the UE receives. The SN may transmit the RRCReconfiguration message directly to the UE, e.g., wirelessly, or it may send it to the MN where it is forwarded to the UE. The UE may, e.g., in response to the RRCReconfiguration message, perform a Random Access (RA) to a target PSCell. This may involve transmitting a preamble to the target PSCell, receiving a RA response (RAR), and/or transmitting a RRCReconfiguration complete message to the target PSCell/SN.

The change may be an intra-SN PSCell change.

The SN may trigger the change in response to or based on information relating to measurements of the UE. For example, the information may be or relate to a PSCell link quality indicator. For instance, it may indicate a PSCell link quality and/or indicate that a PSCell link quality is above or below a threshold and/or is expected to increase above or decrease below a threshold.

Additionally, UE may be configured with an LTM configuration. The UE may be configured with an LTM configuration before the PSCell change, during the PSCell change or at least when the PSCell change is completed. Thus, for example, while the UE has stored LTM candidate configurations the UE can also execute one or more or any L3 handover command that is, e.g., sent by the network to the UE.

LTM may be understood to be a procedure in which a network node, e.g., gNB, receives measurement report(s) (e.g., LI measurements reports) from a UE, and on their basis the network node changes UE serving cell by a cell switch command that is, e.g., signalled via a MAC CE. The cell switch command may indicate that an LTM candidate configuration that the gNB previously prepared and provided to the UE, e.g., through RRC signalling, is to be used. Then the UE may switch to the target configuration according to the cell switch command. The LTM procedure can be used to reduce the mobility latency.

The LTM configuration may relate to master cell group, MCG, LTM. For example, the LTM configuration may be associated at least with the MCG. The LTM configuration may enable the UE to perform a LTM cell change on an MCG cell, e.g., the PCell.

The UE may receive information relating to the LTM configuration for the UE. In particular, the UE may receive a message relating to the LTM configuration for the UE. Further, the UE may store the information. This way, the UE may be configured for LTM. Specifically, it may be information that the UE will have to use as at least part of an LTM configuration. The UE may receive the information from the MN and, thus, the MN may transmit it to the UE. Additionally or alternatively, the UE may be at leastly partly pre-configured with an LTM configuration.

The LTM configuration may comprise or consist of at least one of a LTM reference configuration and a LTM delta configuration. A reference configuration may be a configuration that is incomplete. For example, it may be common to a group of configured non-complete candidate configurations. A candidate configuration may be a configuration that is part of a message, e.g., an RRCReconfiguration message, associated with a candidate cell, e.g., for LTM or subsequent CPAC. A candidate configuration can be a complete candidate configuration or a delta configuration relatively to a reference configuration. A delta configuration may be combined with, e.g., applied on top of, a reference configuration to obtain a complete candidate configuration.

The LTM configuration may be a reference configuration or a target configuration to be used by a UE in a cell change, e.g., a PCell change. Additionally or alternatively, the LTM configuration may be a reference configuration or a target configuration to be used by a UE in a PSCell change.

The UE may perform a LTM change from a primary cell, PCell, of a master cell group, MCG to another PCell. This may trigger, e.g., after completion, that the UE has to replace or update the current UE configuration with another, e.g., newly determined, complete candidate configuration. The complete candidate configuration that is used for replacing the current UE configuration may be based on a stored candidate or reference configuration. It may be beneficial to ensure that the stored candidate or reference configuration is up-to-date.

According to the first example aspect, the UE may in relation to a change from a source PSCell to a target PSCell, the source PSCell being a primary cell of the SCG, perform at least one of:

(i) removing at least part of a LTM configuration, the at least part of the LTM configuration being related to the SCG;

The updated or removed at least part of the LTM configuration may be or comprise of at least a reference LTM configuration or candidate LTM configuration. The UE may remove or update the at least part of the LTM configuration in response to the change from the source PSCell to the target PSCell. For instance, it may determine locally and/or without further information from the MN or the SN whether to remove or update at least part of the LTM configuration. This way, the UE may be able to avoid using an outdated LTM configuration. It is important to note that the UE may perform actions that are not directly in response to a message from MN or SN. Thus, in various embodiments, the UE may be deciding autonomously whether to remove or update the at least part of the LTM configuration.

In various embodiments, the UE may perform a LTM change from a primary cell, PCell, of a master cell group, MCG, to another PCell and use the updated at least part of the LTM configuration for a connection to the target PSCell after performing the LTM change to the another PCell. The MCG may be associated with the MN.

The UE may be pre -configured to remove the at least part of the LTM configuration or to update the at least part of the LTM configuration (e.g., reference LTM configuration or candidate LTM configuration) in relation to a change of the source PSCell. For example, it may be defined, e.g., in a standard specification, that the UE must remove or update at least part of the LTM configuration in relation to a PSCell change, e.g., at least when potential further conditions are met.

Additionally or alternatively, the UE may receive information for configuring the UE to remove the at least part of the LTM configuration or to update the at least part of the LTM configuration in relation to a change of the source PSCell. For instance, if the UE has received the information for configuring the UE to remove the at least part of the LTM configuration or to update the at least part of the LTM configuration in relation to a change of the source PSCell, the UE will remove or update the at least part of the LTM configuration in relation to a change of the source PSCell. If the UE has not received the information, it will for example not or only under certain other conditions remove or update the at least part of the LTM configuration in relation to a change of the source PSCell.

The UE may receive the information, e.g., from the MN that transmits the information. Moreover, the information for configuring the UE to remove the at least part of the LTM configuration or to update the at least part of the LTM configuration in relation to a change of the source PSCell, may be comprised in a same message that comprises the information relating to the LTM configuration for the user equipment. For example, the UE may receive the information as part of LTM configuration. For instance, the information may be comprised in a Itm Config information element (IE) or be transported in the same message as a ItmConfig IE. The received information for configuring the UE to remove or to update the at least part of the LTM configuration in relation to a change of the source PSCell, may originate from the MN. For example, it may be directly received from the MN. Alternatively, it may originate from the SN. The information may, for example, be a flag.

In various embodiments, the MN may transmit information for configuring the UE to, in relation to a change of a source PSCell, the source PSCell being a primary cell of the SCG:

(i) remove at least part of a LTM configuration, the at least part of the LTM configuration being related to the SCG;

(ii) update at least part of a LTM configuration (e.g., reference LTM configuration or candidate LTM configuration), the at least part of the LTM configuration being related to the SCG.

In the context of the first example aspect, at least two approaches may be distinguished with regard to how a UE may update or remove at least part of an LTM configuration.

First, the UE may be configured to update the at least part of the LTM configuration by at least keeping the LTM configuration aligned with the UE’s currently used SCG configuration. For example, the UE may update at least part of the LTM configuration after a change from a source PSCell to a target PSCell with the configuration that it is currently using for the target PSCell. As outlined above, a UE may be pre-configured to do so or receive corresponding information configuring the UE to do so, e.g., from the SN or from the MN.

Second, the UE may be configured to update the at least part of the LTM configuration using information it has received, e.g., from the SN or from the MN.

For example, the change from the source PSCell to the target PSCell may comprise: receiving information instructing the change from the source PSCell to the target PSCell, the information comprising the SCG configuration for the target PSCell that is used in updating the at least part of the LTM configuration; and in response to receiving the information instructing the change, performing the change from the source PSCell to the target PSCell.

The UE may use the information comprising the SCG configuration for the target PSCell in updating the at least part of the LTM configuration. In various embodiments, the LTM configuration may comprise separate configurations for SCG and MCG, e.g., separate reference configurations for SCG and MCG.

In such a scenario, the UE may update the at least part of the LTM configuration by at least updating the separate reference configuration for SCG. The updating of the at least part of the LTM configuration may comprise combining the separate reference configuration for SCG (and/or MCG) with a (e.g., respective) LTM delta configuration. In various embodiments, the information for configuring the user equipment to update the at least part of the LTM configuration in relation to a change of the source PSCell, may configure the UE to update the at least part of the LTM configuration by at least updating the separate reference configuration for SCG based on the SCG configuration for a target PSCell.

The separate reference configuration for SCG may be provided to the UE by the SN or, alternatively, by the MN.

Whether to remove or to update and how to update the at least part of the LTM configuration may be pre-configured. Alternatively, the UE may receive information configuring the UE to remove the at least part of the LTM configuration or to update the at least part of the LTM configuration and/or how to update the at least part of the LTM configuration. In various embodiments, a UE may be configured to be able to do both, removing or updating the at least part of the LTM configuration, for example depending on received information. In alternative embodiments, a UE is only configured to remove the at least part of the LTM configuration and does not provide any updating functionality. In other embodiments, a UE is only configured to update the at least part of the LTM configuration (e.g., according to a single approach) and does not provide any removing functionality.

The examples described above relate to an active UE that removes or updates at least part of an LTM configuration by itself. In these examples, the UE may remove or update at least part of an LTM configuration in relation or in response to a PSCell change. In other words, the PSCell change may be the trigger for the UE to remove or update at least part of the LTM configuration. This may be in contrast to methods where a message, e.g., from the network, triggers the updating or removing.

In the following, examples will be described relating to the second and third example aspect. In these examples, the network nodes may play a more active role in attempting to avoid that the UE has an outdated configuration. However, it is to be understood that all disclosure made with respect to the first embodiment, for example regarding characteristics of the LTM configuration, also apply to the embodiments according to the second and third example aspect. One (or in some embodiments even the only) difference may be that, in embodiments according to the second and third aspect, the updating or removing at the UE may happen, e.g., based on or in response to information received from the MN or SN.

According to the second example aspect, as described above, the MN transmits, to the UE, information relating to a LTM configuration for the UE. The UE receives the information relating to the LTM configuration for the UE and stores the information relating to the LTM configuration for the UE.

Additionally, the MN transmits, to the SN, information relating to the LTM configuration for the UE, for example, comprised in a SN modification request message.

The transmitting to the SN may happen in the context of transmitting, to the UE, information relating to the LTM configuration for the UE. The SN receives, from the MN, the information relating to a LTM configuration for the UE. For example, when the UE is configured with a LTM configuration, the SN may be informed about this LTM configuration. The order of these operations (as should generally understood for steps described herein) may be different, i.e., the MN may first transmit the information to the SN and only then to the UE, or even transmit both simultaneously.

In various embodiments, the information, relating to the LTM configuration for the UE and transmitted from the MN to the SN, trigger that the SN will indicate, to the MN, the change of the UE from the source PSCell to the target PSCell once the change occurs. The information may comprise or consist of an indication that the UE has a LTM configuration and/or has a particular type of LTM configuration, e.g., an LTM configuration relating to the source PSCell. Additionally or alternatively, the information may comprise or consist of the entire LTM configuration for the UE itself.

The information relating to the LTM configuration for the UE and transmitted from the MN to the SN may be transmitted over a Xn interface and/or be comprised in a SN modification request message. Alternatively, the information relating to the LTM configuration for the UE and transmitted from the MN to the SN may be comprised in a message sent over an Xn interface that is not a SN modification request message. Instead, it may for example be transmitted in a new message, e.g., a SN inform message. This new message may not need to be acknowledged. The SN provides information to the UE for performing a change from a source PSCell (which may be a PSCell of the SCG and/or associated with the SCG) to a target PSCell. By way of example, the SN may do so in response to information received from the UE about a UE measurement, for instance, an L3 measurement report. The L3 measurement report may be A3 event based. The information sent from the SN to the UE may be or comprise an RRCReconfiguration message. The information may instruct the UE to perform a PSCell change, e.g., a change from a source PSCell to a target PSCell. The UE may react to the information as described before, e.g., it may perform a RA procedure to the target PSCell. The RA procedure may comprise the UE transmitting a RA preamble to the target PSCell/SN, the UE receiving a RAR, and/or the UE transmitting a RRCReconfigurationComplete message to the PSCell/SN.

The above-described steps apply accordingly to the UE. The UE performs a change from a source PSCell (which may be a PSCell of the SCG) to a target PSCell, comprising indicating to the SN that the change is completed. The UE may do so in response to receiving information for performing a change from a source PSCell to a target PSCell. Specifically, from UE perspective, the change from the source PSCell to the target PSCell may comprise: receiving information (e.g., a RRC Reconfiguration message) instructing a change from the source PSCell to the target PSCell; and in response to receiving the information instructing the change, performing the change from the source PSCell to the target PSCell.

The UE may indicate to the SN that the change is completed by transmitting, e.g., to the SN, a RRC Reconfiguration Complete message. Additionally or alternatively, the UE may indicate to the MN that the change is completed.

Furthermore, the SN transmits, to the MN, information relating to the change of the UE from the source PSCell to the target PSCell. The MN receives the information, i.e., the MN receives, from the SN, information relating to a change of the UE from a source PSCell to a target PSCell

In various embodiments, the information relating to the change of the UE from the source PSCell to the target PSCell is comprised in a SN modification required message and/or sent over an Xn interface. Alternatively, the information relating to the change of the UE from the source PSCell to the target PSCell is comprised in a message sent over an Xn interface that is not a SN modification required message. Instead, it may for example be transmitted in a new message, e.g., a SN inform message. This new message may not need to be acknowledged. In various embodiments, the information relating to the change of the UE from the source PSCell to the target PSCell indicates to the MN that an update or removal of the LTM configuration is required. The indication to the MN that an update or removal of the LTM configuration is required may be or comprise a flag.

The information relating to the change of the UE from the source PSCell to the target PSCell may indicate, e.g., to the MN, a PSCell change of the UE. Again, the indication may be or comprise a flag. Additionally or alternatively, the indication can be done by setting a cause value accordingly, e.g., to a predetermined value. The cause value may, for instance, be the cause value of the SN modification required message.

At least one of option (i) or option (ii) applies to the information relating to the change of the UE from the source PSCell to the target PSCell that the SN transmits and the MN receives.

According to option (i), the information enable the MN to update at least part of the LTM configuration based on an SCG configuration for the target PSCell comprised in the provided information relating to the change of the UE from the source PSCell to the target PSCell. For example, the SN may transmit, to the MN, at least part of the SCG configuration for the target PSCell.

Accordingly, the MN may update at least part of the LTM configuration based on the SCG configuration for the target PSCell, the SCG configuration for the target PSCell being comprised in the received information relating to the change of the UE from the source PSCell to the target PSCell. For instance, the MN may replace at least some parts of the LTM configuration by SCG configuration for the target PSCell. It is important to note that, in contrast to the embodiments according to the first example aspect, in this embodiment the MN updates the LTM configuration, not the UE.

The MN may transmit, to the UE, information comprising at least part of the updated LTM configuration. For example, the MN may transmit the at least part of the updated LTM configuration.

The LTM configuration may comprise at least one of LTM reference configuration and LTM delta configuration. In various embodiments, the updated LTM configuration comprises an updated LTM reference configuration, and the at least part of the updated LTM configuration that is comprised in the information transmitted to the UE is the updated LTM reference configuration. As described before, the LTM configuration may relate to a master cell group, MCG, LTM, and/or is a reference configuration or a target configuration to be used by the UE in a cell change.

Still according to option (i), in response to indicating to the SN that the change is completed, the UE may receive information, the information comprising at least part of an updated LTM configuration that is based on an SCG configuration for the target PSCell. The UE may store the at least part of the updated LTM configuration. In particular, the UE may replace at least part of the LTM configuration based on the at least part of the updated LTM configuration. For example, the UE may replace at least part of a previous LTM reference configuration with at least part of the updated LTM reference configuration.

Finally, the UE may perform a LTM change from a primary cell, PCell, of a master cell group, MCG, associated with the MN, to another PCell. It may use the information relating to the updated LTM configuration for a connection to the target PSCell after performing the LTM change to the another PCell.

According to option (ii), the information relating to the change of the UE from the source PSCell to the target PSCell that the SN transmits and the MN receives enable the MN to transmit, to the UE, information relating to an indication to remove at least part of the LTM configuration for the UE. Accordingly, the MN may transmit, to the UE, information relating to an indication to remove at least part of the LTM configuration for the UE.

Additionally (and optionally), the MN may remove at least part of the LTM configuration, e.g., at the MN. In particular, the MN may remove the LTM configuration for the UE based on the information relating to the change of the UE from the source PSCell to the target PSCell.

The information relating to the indication to remove transmitted to the UE may be an instruction for the UE. It may be embodied, e.g., as a flag. In various embodiments, the UE may remove the stored information relating to the LTM configuration for the UE. The UE may do so, for instance, in response to or based on the received information.

It can be seen that both option (i) and option (ii) may be able to prevent the UE from using an outdated LTM configuration. Embodiments according to the third example aspect are similar to those according to the second example aspect. Therefore, all disclosure made with respect to the second example aspect is not repeated but is to be understood as disclosed also for the third example aspect and vice versa.

However, one difference between embodiments according to the third example aspect and embodiments according to the second example aspect may relate to the question when the SN transmits, to the MN, information relating to the change of the UE from the source PSCell to the target PSCell. For instance, in embodiments according to the second example aspect the SN may transmit, to the MN, information relating to the change of the UE from the source PSCell to the target PSCell after or in response to a completed change of the UE from the source PSCell to the target PSCell. In embodiments according to the third example aspect, the SN may transmit, to the MN, information relating to an upcoming change of the UE from the source PSCell to the target PSCell, e.g., to change of the UE from the source PSCell to the target PSCell that has not yet been started, instructed to the UE or at least completed. As a result, MN may transmit information relating to an updated configuration to the UE, e.g., in a RRCReconfiguration message that instructs the UE to perform a PSCell change.

As before, in embodiments according to the third example aspect, there is a UE being in dual connectivity with a MN and a SN, the SN being associated with a secondary cell group, SCG.

The MN transmits, to the UE, information relating to a LTM configuration for the UE.

The UE receives the information relating to the LTM configuration for the UE. Further, the UE stores the information relating to the LTM configuration for the UE.

The MN transmits, to the SN, information relating to the LTM configuration for the UE.

The SN receives, from the MN, the information relating to the LTM configuration for the UE.

In various embodiments, the information, relating to the LTM configuration for the UE and transmitted from the MN to the SN, trigger that the SN will provide, to the MN, the information relating to the upcoming change of the UE from the source PSCell to the target PSCell once the SN prepares the change. Preparing the change may, for instance, comprise determining that a link quality indicator is below a threshold. The SN provides, to the MN, information relating to the upcoming change of the UE from the source PSCell to the target PSCell, e.g., after it has started preparing the change or while it is preparing the change.

In various embodiments, the information relating to the upcoming change of the UE from the source PSCell to the target PSCell may indicate to the MN, using a designated value or field in a SN modification required message (e.g., a new cause value), that the update or removal of the LTM configuration may be required due to a PSCell change of the UE.

Moreover, at least one of option (i) or option (ii) applies.

According to option (i), the information enable the MN to update at least part of the LTM configuration based on an SCG configuration for the target PSCell, the SCG configuration for the target PSCell being comprised in the provided information relating to the upcoming change of the UE from the source PSCell to the target PSCell.

The MN receives, from the SN, the information relating to the upcoming change of the UE from the source PSCell to the target PSCell. Furthermore, the MN updates at least part of the LTM configuration based on an SCG configuration for the target PSCell, the SCG configuration for the target PSCell being comprised in the received information relating to the upcoming change of the UE from the source PSCell to the target PSCell.

The MN transmits, to the UE, information instructing the change from the source PSCell to the target PSCell, the information comprising at least part of the updated LTM configuration.

The UE receives the information instructing the change from the source PSCell to the target PSCell. The information instructing the change from the source PSCell to the target PSCell comprise at least part of an updated LTM configuration that is based on an SCG configuration for the target PSCell. The UE stores the at least part of the updated LTM configuration and performs the change from the source PSCell to the target PSCell.

According to option (ii), the information relating to the upcoming change of the UE from the source PSCell to the target PSCell, the information being transmitted from the SN to the MN, enable the MN to transmit, to the UE, information relating to an indication to remove at least part of the LTM configuration for the UE. The MN transmits, to the UE, information instructing the change from the source PSCell to the target PSCell, the information relating to an indication to remove at least part of the LTM configuration for the UE.

Moreover, in various embodiments, the MN may remove the LTM configuration for the UE based on the SCG configuration for the target PSCell comprised in the information relating to the change of the UE from the source PSCell to the target PSCell or based on the designated value or field in a SN modification required message. Specifically, MN may remove the LTM configuration for the UE by transmitting one or more instructions to the UE to remove the LTM configuration.

The UE receives the information instructing the change from the source PSCell to the target PSCell relating to an indication to remove at least part of the LTM configuration for the UE.

The UE removes the stored information relating to the LTM configuration for the UE.

It is to be understood that the presentation in this section is merely by way of examples and nonlimiting. Each step described above may happen after or in response to another, e.g., the preceding step. However, a different order of steps is also possible.

The term “information relating to X” is to be understood as at least comprising the cases that “information comprises X (partly or fully)” or “information is X”.

Other features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits, for which reference should be made to the appended claims. It should be further understood that the drawings are not drawn to scale and that they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are:

Fig. 1 a block diagram showing an example of a control plane architecture for dual connectivity; Fig. 2 a message sequence chart showing an example of a message sequence in which the

UE experiences SCG RLF due to an outdated configuration;

Fig. 3 a flowchart showing an example embodiment of a method according to the first example aspect that may be performed by a UE;

Fig. 4 a flowchart showing an example embodiment of a method according to the first example aspect that may be performed by a network node functioning as a MN;

Fig. 5 a message sequence chart showing an example of a message sequence according to the first example aspect;

Fig. 6 a flowchart showing an example embodiment of a method according to the second example aspect that may be performed by a UE;

Fig. 7 a flowchart showing an example embodiment of a method according to the second example aspect that may be performed by a MN;

Fig. 8 a flowchart showing an example embodiment of a method according to the second example aspect that may be performed by a SN;

Fig. 9 a message sequence chart showing an example of a message sequence according to the second example aspect;

Fig. 10 a flowchart showing an example embodiment of a method according to the third example aspect that may be performed by a UE;

Fig. 11 a flowchart showing an example embodiment of a method according to the third example aspect that may be performed by a MN;

Fig. 12 a flowchart showing an example embodiment of a method according to the third example aspect that may be performed by a SN;

Fig. 13 a message sequence chart showing an example of a message sequence according to the third example aspect;

Fig. 14 a schematic block diagram of an example of a UE or network node according to any example aspect.

DETAILED DESCRIPTION OF SOME EXAMPLES

The following description serves to deepen the understanding and shall be understood to complement and be read together with the description as provided in the above summary section of this specification. Some aspects may have a different terminology than e.g. provided in the description above. The skilled person will nevertheless understand that those terms refer to the same subject-matter, e.g. by being more specific. Fig. 1 is a block diagram showing an example of a control plane architecture 100 for dual connectivity. The control plane architecture is shown for a system comprising a UE 1, a master node (MN) 2 and a secondary node (SN) 3. The UE 1 may be a multiple Rx/Tx capable UE 1. It may be configured to utilise resources provided by two different nodes. One node acts as the MN 2 and the other as the SN 3. The UE 1 may be connected to the MN 2 via an interface 101, e.g., a radio interface, for example, a Uu interface. Furthermore, the UE 1 may be connected to the SN 3 via an interface 104, e.g., a radio interface, for example, a Uu interface. The MN 2 and SN 3 are connected via a network interface 103, e.g., a Xn interface. At least the MN 2 is connected to the core network via interface 102.

The MN 2 and the SN 3 involved in dual connectivity for a certain UE 1 may control their radio resources and may be (e.g., primarily) responsible for allocating radio resources of their cells.

One example of dual connectivity may be MR-DC. In MR-DC (or similar technologies), the UE 1 may have a single RRC state, based on the MN RRC and a single control -plane (C-plane) connection towards the Core Network. Each radio node (e.g., MN 2 and SN 3) may have its own RRC entity. Each RRC entity may be able to generate messages, e.g., RRC PDUs, to be sent to the UE 1.

Messages generated by the SN 3 can be transported via the MN 2 to the UE 1. The MN 2 may always send the initial SN RRC configuration via MCG SRB (SRB1), but subsequent reconfigurations may be transported via MN 2 or SN 3. When transporting messages from the SN 3, in various embodiment, the MN 2 does not modify the UE configuration provided by the SN 3.

Signalling Radio Bearers (SRBs) may be defined as Radio Bearers (RBs) that are used for the transmission of messages (e.g., RRC and NAS messages, for example, only).

SRB1 may allow messages (e.g., RRC PDUs) to be sent directly between the UE 1 and the MN 2.

In various embodiments, the UE 1 can be configured to establish a SRB with the SN 3 (SRB3) to enable messages (e.g., RRC PDUs) for the SN 3 to be sent directly between the UE 1 and the SN 3. This may be the case, for example, when the SN 3 is a gNB. The SRB3 may be a direct SRB between the SN 3 and the UE 1. In various embodiments, messages (e.g., RRC PDUs) for the SN 3 can only be transported directly to the UE 1 for SN RRC reconfiguration not requiring any coordination with the MN 2. In various embodiments, measurement reporting for mobility within the SN 3 may be done directly from the UE 1 to the SN 3. This may be the case, for instance, if SRB3 is configured. The decision to establish SRB3 may be taken by the SN 3, which may provide the SRB3 configuration using an SN RRC message. SRB3 establishment and release can be done at Secondary Node Addition and Secondary Node Change. SRB3 reconfiguration can be done at Secondary Node Modification procedure.

SRB3 may be used to send SN RRC Reconfiguration, SN RRC Reconfiguration Complete, SN Measurement Report, SN Failure Information (i.e., in case of failure for an SCG RLC bearer), SN UE Assistance Information message and SN lABOtherlnformation, e.g., only in procedures where the MN 2 is not involved. SN RRC Reconfiguration Complete messages may be mapped to the same SRB as the message initiating the procedure. SN Measurement Report messages may be mapped to SRB3, if configured, regardless of whether the configuration is received directly from the SN 3 or via the MN 2. It may be that no MN RRC messages are mapped to SRB3.

Split SRB may be supported as well. It may allow duplication of messages (e.g., RRC PDUs) generated by the MN 2, via the direct path and via the SN 3 (split SRB 1 ) . Additionally or alternatively, duplication of messages (e.g., RRC PDUs) generated by the SN 3 via the MN 2 and SN 3 paths may be allowed as well.

Fig. 2 is a message sequence chart showing an example of a message sequence in which the UE 1 experiences SCG RLF due to an outdated configuration.

As a background to Fig. 2, it has to be noted that recently, a LTM procedure has been proposed. LTM may be a procedure in which a network node receives low layer (e.g., LI) measurement report(s) from a UE 1, and on their basis the network node changes UE 1 serving cell, e.g., by a cell switch command. The cell switch command may be signalled via a MAC CE. The cell switch command may indicate an LTM candidate configuration that the network node previously prepared and provided to the UE 1, e.g., through RRC signalling. Then the UE 1 may switch to the target configuration according to the cell switch command.

According to 3GPP TS 38.300 V18.0.0 (2023-12), in dual connectivity scenarios, LTM for simultaneous PCell and PSCell change is not supported. Up to now, LTM for MCG with SCG has not been supported and MCG LTM and SCG LTM is done independently. Hence, so far, the reference and candidate configuration for LTM could contain either the MCG LTM configuration or the SCG LTM configuration (not both).

Moreover, it has been agreed in RAN2#123bis that UE 1 only releases SCG configuration at MCG LTM execution if configured by the network. Additionally, it has been agreed in RAN2#121 that a candidate delta configuration is applied on top of the reference configuration to form a complete candidate configuration and that the complete candidate configuration is applied and replacing the current UE configuration.

The above constraints may apply to SCG configuration as well. This means the source SCG configuration may have to be part of either reference configuration or candidate delta configuration, e.g., when MCG LTM with SCG shall be supported. A source configuration may be understood to be an active cell group configuration that a UE uses. A source SCG configuration may be understood be the active cell group configuration that a UE uses for the secondary cell group.

Furthermore, it has to be noted that L3 mobility may be configured in addition to LTM. For the coexistence of LTM and the L3 mobility (e.g., legacy CHO/CPAC), there are two aspects that can be considered:

1) LTM and the CHO/CPAC can be configured simultaneously;

2) Sharing candidate configurations between CHO/CPAC and LTM a. To allow LTM candidate configuration used for CHO/CPAC procedure, b. To allow CHO/CPAC candidate configuration used for LTM procedure.

Against this background, in RAN2# 123bis, RAN2 assumed that L3 handover may happen while LTM is configured / evaluated / used. For the robustness, CHO/CPAC has been introduced in Rel-16, which may be like any other L3 mobility. To align with the legacy L3 handover, while configured with LTM candidate cells, the UE 1 can also be configured with CHO/CPAC configurations to support that LTM and CHO/CPAC can be configured simultaneously. And according to RAN2, the race conditions for the coexistence of LTM and CHO/CPAC could be avoid by the network configuration.

Standardization contribution R2 -2313167 by Xiaomi, titled “RRC open issues for LTM” and submitted to 3GPP TSG-RAN WG2 Meeting #124 suggests that, upon CHO/CPAC execution, the UE 1 does not autonomously release the LTM configuration and the RRCReconfiguration message to be applied for CHO/CPAC execution can reconfigure (setup, release) the LTM configuration.

However, these assumptions do not solve the problem of a potentially outdated reference configuration problem, as outlined in the following with respect to an example in Fig. 2.

Fig. 2 shows an example message sequence involving a UE 1, a source MN-DU 2a and source MN- CU 2b (forming part of a MN 2), and a source SN 3. As shown in step 201, UE 1 is configured with dual connectivity. The scenario depicts an example of SRB3 or split SRB 1 configuration. However, a similar problem may apply to different configurations, e.g., UE 1 configured with SRB1 only.

In step 202, UE 1 is configured with MCG LTM.

As shown in 203, the MCG LTM configuration may comprise at least one of a LTM reference configuration and a LTM candidate delta configuration which may have a source PSCell 1 configuration. PSCell 1 may be associated with the SCG of the source SN 3. The UE 1 may be connected to PSCell 1, also called source PSCell herein.

In step 204, UE 1 may report decreasing PSCell link quality to source SN 3. To that end, the UE 1 may use, e.g., a measurement report, for instance, an L3 measurement report which may be A3 event based.

In steps 205 and 206, the source SN 3 may configure an PSCell change. The PSCell change may be an intra-SN cell change. It may concern a change of the UE 1 from the source PSCell (PSCell 1) to a target PSCell (PSCell 2). Specifically, in step 205, the source SN 3 may prepare the target PSCell for the UE 1. In step 206, the source SN 3 may transmit a message (e.g., a RRCReconfiguration message) to the UE 1. The message may instruct the UE 1 to connect to the target PSCell.

Steps 207 to 209 depict an example RA procedure. By way of example, the RA procedure comprises that the UE 1 transmits a preamble to the target PSCell/source SN 3 (207), the target PSCell/source SN 3 transmits a RAR to the UE 1 (208), and the UE 1 transmits a RRCReconfiguration complete message to the target PSCell/source SN 3 (209).

After these steps, the following problem may occur. After UE 1 applies the PSCell change, the SCG part of the full configuration is invalid (the old PSCell configuration). As shown in 210, the LTM reference configuration or LTM candidate delta configuration still has PSCell 1 configuration.

SN 3 is not aware of the LTM reference configuration and the LTM candidate cell configuration. MN 2 is not aware of the PSCell change. This means applying LTM PCell change may cause wrong PSCell configuration as the reference configuration is not updated.

MN 2 may be similarly unaware in case SRB1 is used (e.g., only SRB1). The UE measurement of SCG (cf. step 204) may still reach the SN 3, e.g., via the MN 2 and/or via RRC TRANSFER message in the RRC Container IE in the UE Report IE. The trigger for PSCell change (cf. step 206) may be encapsulated as RRC message in RRC Container and sent back to MN 2 via RRC TRANSFER message where it may be forwarded to the UE 1. MN 2 may be not allowed or not configured to read the message to that MN 2 will not be aware of PSCell change.

Subsequently, a LTM cell change may occur. In step 211, the UE 1 may report an LI measurement to the MN 2, in particular to the MN-DU 2a. In step 212, the MN-DU 2a may instruct the UE 1 to perform a cell change, for instance, a PCell change.

After the PCell change, UE 1 may be forced (e.g., pre -configured) to redetermine the complete configuration. In step 213, the UE 1 may form this complete configuration. As UE 1 still has PSCell 1 configuration, it will use PSCell 1 configuration. For this reason it will lose the current PSCell connection to PSCell 2, thus experiencing SCG RLF.

One or more embodiments may allow to update the LTM configurations to enable co-existence of PSCell change at the same time of LTM configuration.

Fig. 3 is a flowchart showing an example embodiment of a method 300 according to the first example aspect. The example method may be performed or carried out by a UE 1, and comprises:

Step 301 : being in dual connectivity with a master node, MN 2, and a secondary node, SN 3, the SN 3 being associated with a secondary cell group, SCG.

Step 302: in relation to a change from a source PSCell to a target PSCell, the source PSCell being a primary cell of the SCG, performing at least one of:

Fig. 4 is a flowchart showing an example embodiment of a method 400 according to the first example aspect. The example method may be performed or carried out by a network node functioning as a MN 2, and comprises: Step 401 : functioning as a MN 2 for a UE 1 that is in dual connectivity with the MN 2 and a SN 3, the SN 3 being associated with a secondary cell group, SCG.

Step 402: transmitting information for configuring the UE 1 to, in relation to a change of a source PSCell, the source PSCell being a primary cell of the SCG:

(ii) update at least part of a LTM configuration , the at least part of the LTM configuration being related to the SCG.

Fig. 5 shows a message sequence chart showing an example of a message sequence 500 according to the first example aspect.

Like Fig. 2, Fig. 5 shows an example of a message sequence involving a UE 1, a source MN-DU 2a and source MN-CU 2b (both forming part of a MN 2), and a source SN 3.

Step 501 represents that UE 1 is in dual connectivity with the MN 2 (here represented by way of example by source MN-DU 2a and source MN-CU 2b) and the SN 3, the SN 3 being associated with a secondary cell group, SCG. By way of example, the dual connectivity may comprise a SRB3 and/or split SRB1. Thus, messages shown in the following may be sent using SRB3 and/or split SRB 1 bearer.

In step 502, the UE 1 is configured with MCG LTM. This is an example of the UE 1 receiving a message relating to the LTM configuration for the UE 1, the LTM configuration relating to MCG LTM. The LTM configuration relating to MCG LTM may additionally relate to SCG, e.g., an SCG configuration. Thus, it may also effect PSCell connection. The LTM configuration may be received and stored by the UE 1 or, alternatively, pre -configured and, thus, stored on the UE 1.

By way of example, step 502 further comprises so-called “Option la” or “Option lb”. In various embodiments, UE 1 and/or network supports only one of these options. In other embodiments, UE 1 and/or network may support both options so that it may be decided on a case-by-case basis which option is used.

According to Option la, UE 1 is indicated to update a reference configuration with the new SCG configuration, e.g., if or when a PSCell change occurs. The new SCG configuration may refer to the SCG configuration that is received later on, e.g., for or after or during a PSCell change. It may relate to the target PSCell. This is an example for UE 1 receiving information for configuring the UE 1 to update the at least part of the LTM configuration in relation to a change of the source PSCell, the information configuring the UE 1 to update the at least part of the LTM configuration by at least updating the separate reference configuration for SCG based on the SCG configuration for a target PSCell.

According to Option lb, UE 1 is indicated a separate reference configuration for SCG and the separate reference configuration is the source SCG configuration. Network may also indicate to UE 1 that the SCG reference configuration is to be updated by the UE 1 using the reconfiguration of the PSCell. For example, the reference configuration may be maintained in a separate container and updated to align with the source SCG configuration. This is an example for UE 1 receiving information for configuring the UE 1 to update at least part of the LTM configuration in relation to a change of the source PSCell, the information configuring the UE 1 to update the at least part of the LTM configuration by at least keeping the LTM configuration aligned with the UE 1’s currently used SCG configuration.

In the present example, Options la and lb are part of step 502, i.e., part of the process in which the UE 1 is configured with MCG LTM. However, in other embodiments Options la and lb may be independent of step 502 and/or happen before or after step 502.

Options la and lb are examples for the UE 1 receiving information for configuring the UE 1 to update the at least part of the LTM configuration in relation to a change of the source PSCell. In other embodiments, options la and/or lb may be at least partly pre -configured.

Step 503 shows that UE 1 transmits a measurement report to the source SN 3. By way of example, the measurement report is an A3 event based L3 measurement report.

Step 504 shows that the source SN 3 prepares a target PSCell for the UE 1. For example, the measurement report may have enabled the source SN 3 to determine that a PSCell change should be done.

In step 505, the source SN 3 transmits a RRCReconfiguration message to the UE 1, indicating a PSCell change. This is an example for the UE 1 receiving information instructing the change from the source PSCell to the target PSCell. The information may be sent (e.g., from SN 3) over MN 2 or it maybe sent by MN 2. In response to receiving the information instructing the change, the UE 1 may perform the change from the source PSCell to the target PSCell. For example, UE 1 may send a preamble to the target PSCell/source SN 3 in step 506. Further, it may receive a RAR in step 507 and transmit a RRCReconfiguration complete in step 508. However, this RA procedure is merely an example and other RA procedures may be used.

In step 509, the UE 1 updates the reference configuration. Step 509 is an example for the UE 1, in relation to a change from a source PSCell to a target PSCell, the source PSCell being a primary cell of the SCG, updating at least part of a LTM configuration based on an SCG configuration for the target PSCell, the at least part of the LTM configuration being related to the SCG.

In an Option la scenario, the UE 1 may have received the target PSCell configuration, e.g., in the RRCReconfiguration message in step 505. The UE 1 can use the new SCG configuration for updating the reference configuration.

In an Option lb scenario, the UE 1 may use the reconfiguration of the PSCell. For example, the reference configuration may be maintained in a separate container and it may be updated to align with the source SCG configuration. This is an example of the UE 1 updating the at least part of the LTM configuration by at least keeping the LTM configuration aligned with the UE 1’s currently used SCG configuration.

Accordingly, the agreement from RAN2#121 that the candidate delta configuration is applied on top of the reference configuration to form a complete candidate configuration may need to be updated. For example, it may be updated to define that:

Candidate delta configuration is applied on top of the MCG reference configuration and SCG reference configuration to form a complete candidate configuration; and/or SCG reference configuration is explicitly signalled to the UE 1 or the SCG reference configuration is indicated with a flag to the UE 1 that it is the source SCG configuration.

In step 510 the UE 1 may transmit a LI measurement to the source MN-DU 2a. In step 511, the source MN-DU 2b may indicate a cell change to the UE 1. The UE 1 may perform this cell change. This is an example for performing a LTM change from a primary cell, PCell, of a master cell group, MCG to another PCell.

After the PCell change, the UE 1 may use the updated configuration for a connection to the target PSCell. Overall, an example of a process involving option la may be summarized as follows. At the time of LTM configuration, UE 1 is indicated (e.g., by the MN 2) to update the SCG part of the reference LTM configuration or the candidate LTM configuration with the source SCG configuration if PSCell change occurs. Once PSCell change occurs, UE 1 updates the SCG part of the reference configuration or the candidate LTM configuration.

An example of a process involving option lb may be summarized as follows. At the time of LTM configuration, UE 1 is indicated a separate reference configuration for the SCG configuration and MCG configuration. Network may indicate to UE 1 that the SCG reference configuration is the source SCG configuration. Network may also indicate to UE 1 that the SCG reference configuration is to be updated by the UE 1 using the reconfiguration of the PSCell, e.g., reference configuration may be maintained in a separate container and may be updated to align with the source SCG configuration.

It has to be understood that the order of steps in the message sequence 500 may vary. For example, step 509 may happen before step 506, 507, or 508. Similarly, option la (and/or lb) may be indicated before or after step 502, e.g., after step 503 or after step 504. Moreover, messages may be relayed by a third node when transmitted between two nodes.

By way of example, it has been shown above that the SCG reference configuration may be provided to the UE 1 by the MN 2. However, in an alternative, the SCG reference configuration may be provided by the SN 3. The SN configuration can be relayed over MN 2 to the UE 1 or directly indicated to the UE 1 by SN 3.

The embodiment as explained with respect to Fig. 5 relates to the embodiments explained with respect to Figs. 3 and 4 as follows. Step 501 is an example of steps 301 and 401. Step 502 is an example of step 402. Steps 506 to 508 are an example of a change from a source PSCell to a target PSCell, as mentioned in steps 302 and 402. Step 509 is an example of step 302.

Fig. 6 is a flowchart showing an example embodiment of a method 600 according to the second example aspect. The method 600 may be performed, carried out or controlled by UE 1. It comprises the following steps:

Step 601 comprises being in dual connectivity with a MN 2 and a SN 3, the SN 3 being associated with a secondary cell group, SCG. Step 602 comprises receiving, e.g., from the MN 2, information relating to a LTM configuration for the UE 1.

Step 603 comprises storing the information relating to the LTM configuration for the UE 1.

Step 604 comprises performing a change from a source PSCell to a target PSCell, comprising indicating to the SN 3 that the change is completed.

Step 605 comprises, in response to indicating to the SN 3 that the change is completed, receiving information, wherein at least one of option (i) or option (ii) applies: option (i): the information comprise at least part of an updated LTM configuration that is based on an SCG configuration for the target PSCell, and the instructions, when executed by the at least one processor, cause the UE 1 to store the at least part of the updated LTM configuration; option (ii): the information relate to an indication to remove at least part of the LTM configuration for the UE 1, and the instructions, when executed by the at least one processor, cause the UE 1 to remove the stored information relating to the LTM configuration for the UE 1.

Fig. 7 is a flowchart showing an example embodiment of a method 700 according to the second example aspect. The method 700 may be performed, carried out or controlled by a network node. It comprises the following steps:

Step 701 comprises functioning as a MN 2 for a UE 1 that is in dual connectivity with the MN 2 and a SN 3, the SN 3 being associated with a secondary cell group, SCG.

Step 702 comprises transmitting, to the UE 1, information relating to a LTM configuration for the UE 1.

Step 703 comprises transmitting, to the SN 3, information relating to the LTM configuration for the UE 1.

Step 704 comprises receiving, from the SN 3, information relating to a change of the UE 1 from a source PSCell to a target PSCell.

Step 705 comprises performing at least one of option (i) or option (ii): option (i): updating at least part of the LTM configuration based on an SCG configuration for the target PSCell, the SCG configuration for the target PSCell being comprised in the received information relating to the change of the UE 1 from the source PSCell to the target PSCell; and transmitting, to the UE 1, information comprising at least part of the updated LTM configuration; option (ii): transmitting, to the UE 1, information relating to an indication to remove at least part of the LTM configuration for the UE 1.

Fig. 8 is a flowchart showing an example embodiment of a method 800 according to the second example aspect. The method 800 may be performed, carried out or controlled by a network node. It comprises the following steps:

Step 801 comprises functioning as a SN 3 for a UE 1 that is in dual connectivity with a MN 2 and the SN 3, the SN 3 being associated with a secondary cell group, SCG.

Step 802 comprises receiving, from the MN 2, information relating to a LTM configuration for the UE 1.

Step 803 comprises providing information to the UE 1 for performing a change from a source PSCell to a target PSCell.

Step 804 comprises transmitting, to the MN 2, information relating to the change of the UE 1 from the source PSCell to the target PSCell, wherein at least one of option (i) or option (ii) applies: option (i): the information enable the MN 2 to update at least part of the LTM configuration based on an SCG configuration for the target PSCell comprised in the provided information relating to the change of the UE 1 from the source PSCell to the target PSCell; option (ii): the information enable the MN 2 to transmit, to the UE 1, information relating to an indication to remove at least part of the LTM configuration for the UE 1.

Fig. 9 is a message sequence chart showing an example of a message sequence 900 according to the second example aspect. Like Fig. 5, Fig. 9 shows an example of a message sequence involving a UE 1, a source MN-DU 2a and source MN-CU 2b (both forming part of a MN 2), and a source SN 3.

Step 901 represents that UE 1 is in dual connectivity with the MN 2 (here represented by way of example by source MN-DU 2a and source MN-CU 2b) and the SN 3, the SN 3 being associated with a secondary cell group, SCG. By way of example, the dual connectivity may comprise a SRB3 and/or split SRB1. Thus, messages shown in the following may be sent using SRB3 and/or split SRB 1 bearer.

In step 902, the UE 1 is configured with MCG LTM. This is an example of the UE 1 receiving a message relating to the LTM configuration for the UE 1, the LTM configuration relating to MCG LTM.

In step 903, the source MN-CU 2b transmits a SN modification request message to the source SN 3. The message may be transmitted over an Xn interface. The message informs the SN 3 of the configured LTM. This is an example for transmitting, to the SN 3, information relating to the LTM configuration for the UE 1.

In an alternative embodiment, the information relating to the LTM configuration for the UE 1 and transmitted from the MN 2 to the SN 3 is comprised in a message sent over an Xn interface that is not a SN modification request message

In various embodiments, the information, relating to the LTM configuration for the UE 1 and transmitted from the MN 2 to the SN 3 (e.g., the SN modification request message informing about the configured LTM), trigger that the SN 3 will indicate, to the MN 2, the change of the UE 1 from the source PSCell to the target PSCell once the change occurs.

In step 904 the source SN 3 transmits an SN modification request ack to the source MN-CU 2b.

Step 905 shows that UE 1 transmits a measurement report to the source SN 3. By way of example, the measurement report is an A3 event based L3 measurement report.

Step 906 shows that the source SN 3 prepares a target PSCell for the UE 1. For example, the measurement report may have enabled the source SN 3 to determine that a PSCell change should be done, e.g., because source PSCell link quality has decreased below a threshold. In step 907, the source SN 3 transmits a RRCReconfiguration message to the UE 1, indicating a PSCell change. This is an example for the UE 1 receiving information instructing the change from the source PSCell to the target PSCell. The information may be sent (e.g., from SN 3) over MN 2 or it maybe sent by MN 2.

In response to receiving the information instructing the change, the UE 1 may perform the change from the source PSCell to the target PSCell. For example, UE 1 may send a preamble to the target PSCell/source SN 3 in step 908. Further, it may receive a RAR in step 909 and transmit a RRCReconfiguration complete in step 910. However, this RA procedure is merely an example and other RA procedures may be used.

In step 911, source SN 3 prepares to indicate PSCell change and to update or remove LTM configuration.

Step 912 shows that source SN 3 transmit a SN modification required message to the source MN- CU 2b. The message indicates, to the MN 2, that a PSCell has been changed. It further comprises or relates to the new source SCG configuration. Step 912 is an example of step 804.

In step 913 source MN-CU 913 sends a SN modification confirm message to the source SN 3.

Before or after performing step 913, the MN-CU 2b starts performing at least one of option (i) or option (ii).

According to option (i), the MN-CU 2b updates at least part of the LTM configuration based on the new SCG configuration for the target PSCell that it received in step 912.

In step 914, the MN-CU 2b transmits to the UE 1 a RRCReconfiguration message comprising the reference configuration update. This is an example for transmitting, to the UE 1, information comprising at least part of an updated LTM configuration.

The UE 1 may store this reference configuration update. This may comprise replacing at least parts of a previous configuration with new information based on the reference configuration update. Note that in this example, the MN 2 has updated the configuration and informed the UE 1 accordingly. This contrasts with the embodiment described with respect to Fig. 5 in which the UE 1 updated the configuration. In step 915, the UE 1 transmits a RRCReconfiguration complete message to the source MN-CU 2b.

Steps 916 and 917 are similar to steps 510 and 511. After the PCell change, the UE 1 may use the updated configuration for a connection to the target PSCell.

According to option (ii), it is not necessary that the MN-CU 2b updates at least part of the LTM configuration based on the new SCG configuration for the target PSCell (thus, source SN 3 can, but does not have to send it to source MN-CU in step 912) and/or transmits to the UE 1 a RRCReconfiguration message comprising the reference configuration update. Instead, MN-CU 2b transmits, to the UE 1, information relating to an indication to remove at least part of the LTM configuration for the UE 1. Thus, instead of storing this reference configuration update, UE 1 may remove the (previously) stored information relating to the (e.g., outdated) LTM configuration for the UE 1.

In various embodiments, step 903 and/or 912 can use a different Xn message then the SN modification required message. The reason is that this message is used to inform SN 3 only and does not need an acknowledgement. This can be a new message called SN inform message.

In a nutshell, the embodiment of Fig. 9 may involve, by way of example, the following. After MCG LTM is configured, SN 3 may be informed of the LTM configuration. SN 3 may use this information as a trigger to indicate the PSCell change to MN 2 once it happens. The indication can be in the form of a flag. MN 2 updates the reference configuration once it is informed about the PSCell change and the new source SCG configuration.

The embodiment as explained with respect to Fig. 9 relates to the embodiments explained with respect to Figs. 6 to 8 as follows. Step 901 is an example of steps 601, 701, and 801. Step 902 is an example of steps 602-603, 702. Step 903 is an example of steps 703, 802. Step 907 is an example of step 803. Step 912 is an example of steps 704, 804. Step 914 is an example of steps 605, 705.

Fig. 10 is a flowchart showing an example embodiment of a method 1000 according to the third example aspect. The example method may be performed or carried out by a UE 1. By way of example, it comprises:

Step 1001: being in dual connectivity with a MN 2 and a SN 3, the SN 3 being associated with a secondary cell group, SCG. Step 1002: receiving information relating to a LTM configuration for the UE 1.

Step 1003: storing the information relating to the LTM configuration for the UE 1.

Step 1004: performing a change from a source PSCell to a target PSCell, comprising indicating to the SN 3 that the change is completed.

Step 1005: in response to indicating to the SN 3 that the change is completed, receiving information, wherein at least one of option (i) or option (ii) applies: option (i): the information comprise at least part of an updated LTM configuration that is based on an SCG configuration for the target PSCell, and the instructions, when executed by the at least one processor, cause the UE 1 to store the at least part of the updated LTM configuration; option (ii): the information relate to an indication to remove at least part of the LTM configuration for the UE 1, and the instructions, when executed by the at least one processor, cause the UE 1 to remove the stored information relating to the LTM configuration for the UE 1.

Fig. 11 is a flowchart showing an example embodiment of a method 1100 according to the third example aspect. The example method may be performed or carried out by a network node. By way of example, it comprises:

Step 1101: functioning as a MN 2 for a UE 1 that is in dual connectivity with the MN 2 and a SN 3, the SN 3 being associated with a secondary cell group, SCG.

Step 1102: transmitting, to the UE 1, information relating to a LTM configuration for the UE 1.

Step 1103: transmitting, to the SN 3, information relating to the LTM configuration for the UE 1.

Step 1104: receiving, from the SN 3, information relating to a change of the UE 1 from a source PSCell to a target PSCell;

Step 1105: performing at least one of option (i) or option (ii): option (i): updating at least part of the LTM configuration based on an SCG configuration for the target PSCell, the SCG configuration for the target PSCell being comprised in the received information relating to the change of the UE 1 from the source PSCell to the target PSCell; and transmitting, to the UE 1, information comprising at least part of the updated LTM configuration; option (ii): transmitting, to the UE 1, information relating to an indication to remove at least part of the LTM configuration for the UE 1.

Fig. 12 is a flowchart showing an example embodiment of a method 1200 according to the third example aspect. The example method may be performed or carried out by a network node. By way of example, it comprises:

Step 1201: functioning as a SN 3 for a UE 1 that is in dual connectivity with a MN 2 and the SN 3, the SN 3 being associated with a secondary cell group, SCG.

Step 1202: receiving, from the MN 2, information relating to a LTM configuration for the UE 1.

Step 1203: providing information to the UE 1 for performing a change from a source PSCell to a target PSCell.

Step 1204: transmitting, to the MN 2, information relating to the change of the UE 1 from the source PSCell to the target PSCell, wherein at least one of option (i) or option (ii) applies: option (i): the information enable the MN 2 to update at least part of the LTM configuration based on an SCG configuration for the target PSCell comprised in the provided information relating to the change of the UE 1 from the source PSCell to the target PSCell; option (ii): the information enable the MN 2 to transmit, to the UE 1, information relating to an indication to remove at least part of the LTM configuration for the UE 1.

Fig. 13 shows a message sequence chart showing an example of a message sequence 1300 according to the third example aspect.

Like Fig. 9, Fig. 13 shows an example of a message sequence involving a UE 1, a source MN-DU 2a and source MN-CU 2b (both forming part of a MN 2), and a source SN 3.

As can be seen, many steps in Fig. 13 are like steps in Fig. 9. Therefore, the description of steps in Fig. 9 applies, mutatis mutandis, to the corresponding steps in Fig. 13. In particular, steps 901, 902, 903, 904, 905, 906, 908, 909, 911, 912, 913, 916, and 917 correspond to steps 1301, 1302, 1303, 1304, 1305, 1306, 1310, 1311, 1307, 1308, 1313, 1314, 1315, respectively. A difference between the message sequence 900 and the message sequence 1300 relates to the order of steps. In message sequence 900, source SN 3 transmits an RRC Reconfiguration message (step 907) and interacts with the UE 1 for a RA procedure (steps 908-910) before indicating the PSCell change to the MN 2 (steps 911, 912). In contrast, in message sequence 1300, source SN 3 indicates an upcoming PSCell change to the MN 2 (steps 1307, 1308). Step 1308 is an example of the SN 3 providing, to the MN 2, information relating to an upcoming change of the UE 1 from a source PSCell to a target PSCell. The RRCReconfiguration in step 1309 may comprise the reference configuration update. The UE 1 may store (and, thus, e.g., apply) the reference configuration update.

An indication to the MN 2 (e.g., in step 1308) that a reconfiguration (e.g., update or removal) is required and/or related to a PSCell change may inform the MN 2 accordingly. It may allow the MN 2 to transmit information instructing the UE 1 to perform the PSCell change together with a reference config update (step 1309).

The information relating to the upcoming change of the UE 1 from the source PSCell to the target PSCell may indicate to the MN 2, using a designated value or field in the SN modification required message (e.g., a new cause value), that the update or removal of the LTM configuration is required. Additionally, it may indicate to the MN 2 that the update or removal is required due to a PSCell change of the UE 1. The indication in step 1308 can be done to the MN 2 through a modification in the cause value of the SN modification required message.

The procedure described above may be used, for example, in case SRB1 is used. In various embodiments, SRB3 is not used for dual connectivity.

Other embodiments need not include an indication to the MN 2 that a reconfiguration is required and/or related to a PSCell change. For example, after MCG LTM is configured, SN 3 may be informed of the LTM configuration. SN 3 may use this information as a trigger to send the PSCell change configuration over MN 2 as needed (e.g., similar to SRB 1 behavior). This indication to MN 2 may also indicate that this message is for PSCell change configuration and as such the reference configuration needs or may need to be updated. MN 2 may piggy back the updated reference configuration to the PSCell change configuration and may indicate this to the UE 1. In the following, further embodiments that may be used in addition or in alternative to those described before to alleviate or even overcome the problem of the use of outdated configurations are described.

For example, the network (e.g., a network node) may configure the UE 1 to stop LI measurement reporting once/after/when/in response to that PSCell is changed. MN-CU and/or MN-DU may be informed about the PSCell change. Such UE behavior may be pre-configured. For example, this can be captured via specification indicating the UE behavior to stop measurements. Alternatively, such UE behavior may be configured by a network node. Stopping LI measurements (e.g., until further notice from the network) may imply that there is no LTM (e.g., for a particular cell/cell group and/or until the further notice). Therefore, even if UE 1 has an outdated configuration stored, it may not need to apply it due to LTM cell change since there is no LTM cell change (e.g., for a particular cell/cell group or until the further notice).

As another example, network (e.g., a network node) may configure the UE 1 with two LTM delta configurations. One delta configuration may be with single connectivity and the other one may be (at least) with source SCG (configuration). For or at the time of LTM PCell change, UE 1 may execute single connectivity (e.g., it may apply the single connectivity LTM delta configuration) if source SCG has changed after UE 1 is configured with LTM configuration. If PSCell is not changed at the time of LTM PCell change, UE 1 may execute the dual connectivity configuration. UE 1 may also inform the network (e.g., a network node) of the selection (e.g., the applied configuration).

In a further example, UE 1 may be configured to release some or all LTM configurations once/after/ when/in response to that PSCell is changed. Source MN-CU and/or MN-DU are informed about PSCell change.

Moreover, in an example, SN 3 may be informed that MCG LTM is configured. SN 3 can release LTM configurations (e.g., instruct the UE 1 to release LTM configurations) with PSCell change configuration (e.g., in the same message or in another message), for instance in SRB3.

Furthermore, it is possible for inter-SN PSCell change (e.g., not only PSCell changes but also the associated SN), that the MN 2 can update the reference configuration (and, e.g., transmits it or information relating to it to the UE 1) once/after/when/in response to that it receives the target SCG configuration, e.g., from the target SN. Finally, for inter-SN CPC, the MN 2 can update the configuration (and, e.g., transmits it or information relating to it to the UE 1) once/after/when/in response to that it receives an indication from the UE 1, the source SN 3 or the target SN that the UE 1 has applied a new SCG configuration.

Fig. 14 shows a schematic block diagram of an example of an apparatus 1400, e.g., a UE or a network node, according to any example aspect.

Apparatus or network entity 1400 comprises a processor 1401, program memory 1402, working or main memory 1403, data memory, communication interface(s) 1404, and an optional user interface 1405.

Apparatus 1400 may for instance be configured to perform and/or control or comprise respective means (at least one of 1401 to 1405) for performing and/or controlling the method according to the any example aspect. Apparatus 1400 may as well constitute a UE 1 or network node comprising at least one processor (1401) and at least one memory (1402) storing instructions that, when executed by the at least one processor, cause a UE 1 or network network node, e.g. apparatus 1400, at least to perform and/or control the method according to any or all example aspects.

Processor 1401 may for instance control at least one of the memories 1402 to 1403, the communication interface(s) 1404, and/or the optional user interface 1405.

Processor 1401 may for instance execute program code stored in program memory 1402, which may for instance represent a readable storage medium comprising program code that, when executed by processor 1401, causes the processor 1401 to perform the method according to any example aspect.

Processor 1401 (and also any other processor mentioned in this specification) may be a processor of any suitable type. Processor 1401 may comprise but is not limited to one or more microprocessor(s), one or more processor(s) with accompanying one or more digital signal processor(s), one or more processor(s) without accompanying digital signal processor(s), one or more special-purpose computer chips, one or more field-programmable gate array(s) (FPGA(s)), one or more controller(s), one or more application-specific integrated circuit(s) (ASIC(s)), or one or more computer(s)/server(s). The relevant structure/hardware has been programmed in such a way to carry out the described function. Processor 1401 may for instance be an application processor that runs an operating system. Program memory 1402 may also be included into processor 1401. This memory may for instance be fixedly connected to processor 1401, or be at least partially removable from processor 1401, for instance in the form of a memory card or stick. Program memory 1402 may for instance be nonvolatile memory. It may for instance be a FLASH memory (or a part thereof), any of a ROM, PROM, EPROM and EEPROM memory (or a part thereof) or a hard disc (or a part thereof), to name but a few examples. Program memory 1402 may comprise an operating system for processor 1401. Program memory 1402 may comprise a firmware for apparatus or network entity 1400.

Communication interface(s) 1404 enable the apparatus 1400 to communicate with other entities, e.g., one or more UE or one or more network nodes. The communication interface(s) 1404 may for instance comprise a wireless interface, e.g., a cellular radio communication interface and/or a WLAN interface) and/or wire-bound interface, e.g., an IP -based interface, for instance to communicate with entities via the Internet. Communication interface(s) may enable apparatus 1400 to communicate with other entities, for instance one or more entities as comprised in a mobile communication network.

User interface 1405 is optional and may comprise a display for displaying information to a user and/or an input device (e.g. a keyboard, keypad, touchpad, mouse, etc.) for receiving information from a user.

Some or all of the components of the apparatus 1400 may for instance be connected via a bus. Some or all of the components of the apparatus or network entity 1400 may for instance be combined into one or more modules.

An apparatus 1400 may further comprise at least one of the following: a receiver, e.g., for receiving information, e.g., from a network node or a UE; a transmitter, e.g., for transmitting information, e.g., to a network node or UE; an updater, e.g., for updating at least part of a configuration; a remover e.g., for removing at least part of a configuration; a Storer, e.g., for storing information; a transceiver, e.g., for being in dual connectivity and/or for performing a PSCell change and/or performing a PCell change; a provider, e.g., for providing master node or secondary node functionality.

In the present specification, any presented connection in the described embodiments is to be understood in a way that the involved components are operationally coupled. Thus, the connections can be direct or indirect with any number or combination of intervening elements, and there may be merely a functional relationship between the components.

Moreover, any of the methods, processes and actions described or illustrated herein may be implemented using executable instructions in a general-purpose or special-purpose processor and stored on a computer-readable storage medium (e.g., disk, memory, or the like) to be executed by such a processor. References to a ‘computer-readable storage medium’ should be understood to encompass specialized circuits such as FPGAs, ASICs, signal processing devices, and other devices.

The expression “A and/or B” is considered to comprise any one of the following three scenarios: (i) A, (ii) B, (iii) A and B. Furthermore, the article “a” is not to be understood as “one”, i.e., use of the expression “an element” does not preclude that also further elements are present. The term “comprising” is to be understood in an open sense, i.e., in a way that an object that “comprises an element A” may also comprise further elements in addition to element A. Further, the term “comprising” may be understood to also disclose “consisting of’, i.e., consisting of only the specified elements.

The expression “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” 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.

It will be understood that all presented embodiments are only examples, and that any feature presented for a particular example embodiment may be used with any aspect on its own or in combination with any feature presented for the same or another particular example embodiment and/or in combination with any other feature not mentioned. In particular, the example embodiments presented in this specification shall also be understood to be disclosed in all possible combinations with each other, as far as it is technically reasonable and the example embodiments are not alternatives with respect to each other. It will further be understood that any feature presented for an example embodiment in a particular category (method/apparatus/computer program/system) may also be used in a corresponding manner in an example embodiment of any other category. It should also be understood that presence of a feature in the presented example embodiments shall not necessarily mean that this feature forms an essential feature and cannot be omitted or substituted. The statement of a feature comprises at least one of the subsequently enumerated features is not mandatory in the way that the feature comprises all subsequently enumerated features, or at least one feature of the plurality of the subsequently enumerated features. Also, a selection of the enumerated features in any combination or a selection of only one of the enumerated features is possible. The specific combination of all subsequently enumerated features may as well be considered. Also, a plurality of only one of the enumerated features may be possible.

The sequence of all method steps presented above is not mandatory, also alternative sequences may be possible. Nevertheless, the specific sequence of method steps exemplarily shown in the drawings shall be considered as one possible sequence of method steps for the respective embodiment described by the respective drawing.

The subject-matter has been described above by means of example embodiments. It should be noted that there are alternative ways and variations which are obvious to a skilled person in the art and can be implemented without deviating from the scope of the appended claims.

List of abbreviations:

3 GPP Third Generation Partnership Project

5G 5-th Generation

CHO Conditional Handover

CPAC Conditional PSCell Addition or Change

CU Central Unit

DU Distributed Unit gNB next generation NodeB

IE Information Element

LI Layer 1

L2 Layer 2

L3 Layer 3

LTM Low-layer triggered mobility; L 1/L2 triggered mobility

MAC Medium Access Control

MCG Master Cell Group

MN Master Node

PCell Primary Cell

PSCell Primary SCG Cell

RAN Radio Access Network

RLE Radio Link Failure RRC Radio Resource Control

Rx Receiver

SCG Secondary Cell Group

SN Secondary Node SRB Signalling Radio Bearer

Tx Transmitter

UE User Equipment

Claims

C l a i m s

1. A user equipment comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment at least to perform: being in dual connectivity with a master node, MN, and a secondary node, SN, the SN being associated with a secondary cell group, SCG; in relation to a change from a source PSCell to a target PSCell, the source PSCell being a primary cell of the SCG, performing at least one of:

2. The user equipment according to claim 1, wherein the instructions, when executed by the at least one processor, cause the user equipment at least to perform: receiving information relating to the LTM configuration for the user equipment; and storing the information relating to the LTM configuration.

3. The user equipment according to claim 1 or 2, wherein the instructions, when executed by the at least one processor, cause the user equipment at least to perform: receiving information for configuring the user equipment to remove the at least part of the LTM configuration or to update the at least part of the LTM configuration in relation to a change of the source PSCell.

4. The user equipment according to claim 3, as far as dependent on claim 2, wherein the information for configuring the user equipment to remove or to update the at least part of the LTM configuration in relation to a change of the source PSCell, is comprised in a same message that comprises information relating to the LTM configuration for the user equipment.

5. The user equipment according to claim 3 or 4, wherein the received information for configuring the user equipment to remove or to update the at least part of the LTM configuration in relation to a change of the source PSCell, originates from the MN.

6. The user equipment according to claim 1 or 2, wherein the user equipment is pre -configured to remove the at least part of the LTM configuration or to update the at least part of the LTM configuration in relation to a change of the source PSCell.

7. The user equipment according to any one of the preceding claims, wherein the instructions, when executed by the at least one processor, cause the user equipment at least to perform: performing a LTM change from a primary cell, PCell, of a master cell group, MCG to another PCell; and using the updated at least part of the LTM configuration for a connection to the target PSCell after performing the LTM change to the another PCell.

8. The user equipment according to any one of the preceding claims, wherein the change from the source PSCell to the target PSCell comprises: receiving information instructing the change from the source PSCell to the target PSCell, the information comprising the SCG configuration for the target PSCell that is used in updating the at least part of the LTM configuration; and in response to receiving the information instructing the change, performing the change from the source PSCell to the target PSCell.

9. The user equipment according to claim 8, wherein the information instructing the change from the source PSCell to the target PSCell is a RRCReconfiguration message originating at the SN, and wherein performing the change from the source PSCell to the target PSCell comprises transmitting a RRCReconfigurationComplete message.

10. The user equipment according to any one of the preceding claims, wherein the LTM configuration comprises separate reference configurations for SCG and MCG.

11. The user equipment according to claim 10, wherein the user equipment is configured to update the at least part of the LTM configuration by at least updating the separate reference configuration for SCG.

12. The user equipment according to claim 10 or 11, wherein updating the at least part of the LTM configuration further comprises combining the separate reference configuration for SCG with a LTM delta configuration.

13. The user equipment according to any one of claims 10 to 12, wherein the separate reference configuration for SCG is provided to the user equipment by the SN.

14. The user equipment according to any one of the preceding claims, wherein the user equipment is configured to update the at least part of the LTM configuration by at least keeping the LTM configuration aligned with the user equipment’s currently used SCG configuration.

15. A network node comprising : at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network node at least to perform: functioning as a master node, MN, for a user equipment that is in dual connectivity with the MN and a secondary node, SN, the SN being associated with a secondary cell group, SCG; and transmitting information for configuring the user equipment to, in relation to a change of a source PSCell, the source PSCell being a primary cell of the SCG:

16. The network node according to claim 15, wherein the instructions, when executed by the at least one processor, cause the network node at least to perform: transmitting, to the user equipment, information relating to the LTM configuration for the user equipment.

17. The network node according to claim 16, wherein the information for configuring the user equipment to remove or to update at least part of the LTM configuration in relation to a change of the source PSCell, is comprised in a same message that comprises information relating to the LTM configuration for the user equipment.

18. The network node according to any one of claims 15 to 17, wherein the LTM configuration comprises separate reference configurations for SCG and master cell group, MCG.

19. The network node according to claim 18, wherein the information for configuring the user equipment to update the at least part of the LTM configuration in relation to a change of the source PSCell, configures the UE to update the at least part of the LTM configuration by at least updating the separate reference configuration for SCG based on the SCG configuration for a target PSCell.

20. The network node according to any one of claims 15 to 19, wherein the information for configuring the user equipment to update at least part of the LTM configuration in relation to a change of the source PSCell, configures the user equipment to update the at least part of the LTM configuration by at least keeping the LTM configuration aligned with the user equipment’s currently used SCG configuration.

21. The subject-matter according any one of the preceding claims, wherein the LTM configuration comprises at least one of a LTM reference configuration and a LTM delta configuration.

22. The subject-matter according any one of the preceding claims, wherein the LTM configuration relates to master cell group, MCG, LTM.

23. The subject-matter according to any one of the preceding claims, wherein the LTM configuration is a reference configuration or a target configuration to be used by the user equipment in a cell change.

24. A method, performed by a user equipment, the method comprising: being in dual connectivity with a master node, MN, and a secondary node, SN, the SN being associated with a secondary cell group, SCG; in relation to a change from a source PSCell to a target PSCell, the source PSCell being a primary cell of the SCG, performing at least one of:

25. A method, performed by a network node, the method comprising: functioning as a master node, MN, for a user equipment that is in dual connectivity with the MN and a secondary node, SN, the SN being associated with a secondary cell group, SCG; and transmitting information for configuring the user equipment to, in relation to a change of a source PSCell, the source PSCell being a primary cell of the SCG:

26. A computer program comprising instructions, which, when executed by an apparatus, cause the apparatus to perform the method of any one of claims 24 or 25.

27. A computer-readable storage medium having stored thereon the computer program of claim 26.