WO2024068131A1

WO2024068131A1 - Delayed access to primary cell of secondary cell group

Info

Publication number: WO2024068131A1
Application number: PCT/EP2023/072723
Authority: WO
Inventors: Halit Murat Gürsu; Ahmad AWADA; Panagiotis SPAPIS; Shehzad Ali ASHRAF; Umur KARABULUT; Jedrzej STANCZAK
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2022-09-30
Filing date: 2023-08-17
Publication date: 2024-04-04
Anticipated expiration: 2025-03-30
Also published as: CN119790707A

Abstract

Disclosed is a method comprising receiving one or more configurations for a conditional handover, wherein a configuration comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; accessing the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delaying accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

Description

DELAYED ACCESS TO PRIMARY CELL OF SECONDARY CELL GROUP

FIELD

The following example embodiments relate to wireless communication.

BACKGROUND

In a handover procedure, a cellular transmission may be transferred from one cell to another. However, if the handover is not timed appropriately, it may lead to a negative impact on the quality of the cellular transmission. Therefore, it is desirable to provide an improved handover procedure.

BRIEF DESCRIPTION

The scope of protection sought for various example embodiments is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments.

According to an aspect, there is provided an apparatus comprising at least one processor, and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus at least to: receive one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; access the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided an apparatus comprising: means for receiving one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; means for accessing the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and means for delaying accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided a method comprising: receiving one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; accessing the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delaying accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receive one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; access the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided a computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receive one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; access the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receive one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; access the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided an apparatus comprising at least one processor, and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus at least to: determine one or more configurations for a conditional handover of a user device, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; transmit the one or more configurations, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided an apparatus comprising: means for determining one or more configurations for a conditional handover of a user device, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; and means for transmitting the one or more configurations, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided a method comprising: determining one or more configurations for a conditional handover of a user device, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; and transmitting the one or more configurations, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: determine one or more configurations for a conditional handover of a user device, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; transmit the one or more configurations, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided a computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: determine one or more configurations for a conditional handover of a user device, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; transmit the one or more configurations, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: determine one or more configurations for a conditional handover of a user device, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; transmit the one or more configurations, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled. LIST OF DRAWINGS

In the following, various example embodiments will be described in greater detail with reference to the accompanying drawings, in which

FIG. 1 illustrates an example of a cellular communication network;

FIG. 2 illustrates an example of a wireless communication system;

FIG. 3 illustrates a signaling diagram;

FIG. 4 illustrates a signaling diagram;

FIG. 5 illustrates a signaling diagram;

FIG. 6 illustrates a signaling diagram;

FIG. 7 illustrates a signaling diagram;

FIG. 8 illustrates a signaling diagram;

FIG. 9 illustrates a signaling diagram;

FIG. 10 illustrates a flow chart;

FIG. 11 illustrates a flow chart;

FIG. 12 illustrates an example of an apparatus; and

FIG. 13 illustrates an example of an apparatus.

DETAILED DESCRIPTION

The following embodiments are exemplifying. Although the specification may refer to “an”, “one”, or “some” embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

In the following, different example embodiments will be described using, as an example of an access architecture to which the example embodiments may be applied, a radio access architecture based on longterm evolution advanced (LTE Advanced, LTE-A), new radio (NR, 5G), beyond 5G, or sixth generation (6G) without restricting the example embodiments to such an architecture, however. It is obvious for a person skilled in the art that the example embodiments may also be applied to other kinds of communications networks having suitable means by adjusting parameters and procedures appropriately. Some examples of other options for suitable systems may be the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E-UTRAN), long term evolution (LTE, substantially the same as E-UTRA), wireless local area network (WLAN or Wi-Fi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad-hoc networks (MANETs) and Internet Protocol multimedia subsystems (IMS) or any combination thereof.

FIG. 1 depicts examples of simplified system architectures showing some elements and functional entities, all being logical units, whose implementation may differ from what is shown. The connections shown in FIG. 1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the system may also comprise other functions and structures than those shown in FIG. 1.

The example embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties.

The example of FIG. 1 shows a part of an exemplifying radio access network.

FIG. 1 shows user devices 100 and 102 configured to be in a wireless connection on one or more communication channels in a radio cell with an access node (AN) 104, such as an evolved Node B (abbreviated as eNB or eNodeB) or a next generation Node B (abbreviated as gNB or gNodeB), providing the radio cell. The physical link from a user device to an access node may be called uplink (UL) or reverse link, and the physical link from the access node to the user device may be called downlink (DL) or forward link. A user device may also communicate directly with another user device via sidelink (SL) communication. It should be appreciated that access nodes or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage.

A communication system may comprise more than one access node, in which case the access nodes may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used for signaling purposes and also for routing data from one access node to another. The access node may be a computing device configured to control the radio resources of communication system it is coupled to. The access node may also be referred to as a base station, a base transceiver station (BTS), an access point or any other type of interfacing device including a relay station capable of operating in a wireless environment. The access node may include or be coupled to transceivers. From the transceivers of the access node, a connection may be provided to an antenna unit that establishes bi-directional radio links to user devices. The antenna unit may comprise a plurality of antennas or antenna elements. The access node may further be connected to a core network 110 (CN or next generation core NGC). Depending on the deployed technology, the counterpart that the access node may be connected to on the CN side may be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW) for providing connectivity of user devices to external packet data networks, user plane function (UPF), mobility management entity (MME), or an access and mobility management function (AMF), etc.

The user device illustrates one type of an apparatus to which resources on the air interface may be allocated and assigned, and thus any feature described herein with a user device may be implemented with a corresponding apparatus, such as a relay node.

An example of such a relay node may be a layer 3 relay (self-backhauling relay) towards the access node. The self-backhauling relay node may also be called an integrated access and backhaul (1AB) node. The 1AB node may comprise two logical parts: a mobile termination (MT) part, which takes care of the backhaul link(s) (i.e., link(s) between 1AB node and a donor node, also known as a parent node) and a distributed unit (DU) part, which takes care of the access link(s), i.e., child link(s) between the 1AB node and user device(s), and/or between the 1AB node and other 1AB nodes (multi-hop scenario).

Another example of such a relay node may be a layer 1 relay called a repeater. The repeater may amplify a signal received from an access node and forward it to a user device, and/or amplify a signal received from the user device and forward it to the access node.

The user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal, terminal device, or user equipment (UE) just to mention but a few names or apparatuses. The user device may refer to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (mobile phone), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and/or touch screen computer, tablet, game console, notebook, multimedia device, reduced capability (RedCap) device, wireless sensor device, or any device integrated in a vehicle. It should be appreciated that a user device may also be a nearly exclusive uplink-only device, of which an example may be a camera or video camera loading images or video clips to a network. A user device may also be a device having capability to operate in Internet of Things (loT) network which is a scenario in which objects may be provided with the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. The user device may also utilize cloud. In some applications, a user device may comprise a small portable or wearable device with radio parts (such as a watch, earphones or eyeglasses) and the computation may be carried out in the cloud or in another user device. The user device (or in some example embodiments a layer 3 relay node) may be configured to perform one or more of user equipment functionalities.

Various techniques described herein may also be applied to a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question may have inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals.

Additionally, although the apparatuses have been depicted as single entities, different units, processors and/or memory units (not all shown in FIG. 1) may be implemented.

5G enables using multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. 5G mobile communications may supporta wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications (such as (massive) machine-type communications (mMTC), including vehicular safety, different sensors and real-time control. 5G may have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integrable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage may be provided by the LTE, and 5G radio interface access may come from small cells by aggregation to the LTE. In other words, 5G may support both inter- RAT operability (such as LTE-5G) and inter-Rl operability (inter-radio interface operability, such as below 6GHz - cmWave - mmWave). One of the concepts considered to be used in 5G networks may be network slicing, in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the substantially same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

The current architecture in LTE networks may be fully distributed in the radio and fully centralized in the core network. The low latency applications and services in 5G may need to bring the content close to the radio which leads to local break out and multiaccess edge computing (MEC). 5G may enable analytics and knowledge generation to occur at the source of the data. This approach may need leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC may provide a distributed computing environment for application and service hosting. It may also have the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing may cover a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer-to-peer ad hoc networking and processing also classifiable as local cloud/fog computing and grid/mesh computing, dew computing, mobile edge computing, cloudlet, distributed data storage and retrieval, autonomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications).

The communication system may also be able to communicate with one or more other networks 113, such as a public switched telephone network or the Internet, or utilize services provided by them. The communication network may also be able to support the usage of cloud services, for example at least part of core network operations may be carried out as a cloud service (this is depicted in FIG. 1 by “cloud” 114). The communication system may also comprise a central control entity, or the like, providing facilities for networks of different operators to cooperate for example in spectrum sharing. An access node may also be split into: a radio unit (RU) comprising a radio transceiver (TRX), i.e., a transmitter (Tx) and a receiver (Rx); one or more distributed units (DUs) 105 that may be used for the so-called Layer 1 (LI) processing and real-time Layer 2 (L2) processing; and a central unit (CU) 108 (also known as a centralized unit) that may be used for non-real-time L2 and Layer 3 (L3) processing. The CU 108 may be connected to the one or more DUs 105 for example via an Fl interface. Such a split may enable the centralization of CUs relative to the cell sites and DUs, whereas DUs may be more distributed and may even remain at cell sites. The CU and DU together may also be referred to as baseband or a baseband unit (BBU). The CU and DU may also be comprised in a radio access point (RAP).

The CU 108 may be defined as a logical node hosting higher layer protocols, such as radio resource control (RRC), service data adaptation protocol (SDAP) and/or packet data convergence protocol (PDCP), of the access node. The DU 105 may be defined as a logical node hosting radio link control (RLC), medium access control (MAC) and/or physical (PHY) layers of the access node. The operation of the DU may be at least partly controlled by the CU. The CU may comprise a control plane (CU-CP), which may be defined as a logical node hosting the RRC and the control plane part of the PDCP protocol of the CU for the access node. The CU may further comprise a user plane (CU-UP), which may be defined as a logical node hosting the user plane part of the PDCP protocol and the SDAP protocol of the CU for the access node.

Cloud computing platforms may also be used to run the CU 108 and/or DU 105. The CU may run in a cloud computing platform, which may be referred to as a virtualized CU (vCU). In addition to the vCU, there may also be a virtualized DU (vDU) running in a cloud computing platform. Furthermore, there may also be a combination, where the DU may use so-called bare metal solutions, for example application-specific integrated circuit (ASIC) or customer-specific standard product (CSSP) system-on-a-chip (SoC) solutions. It should also be understood that the distribution of functions between the above- mentioned access node units, or different core network operations and access node operations, may differ.

Edge cloud may be brought into radio access network (RAN) by utilizing network function virtualization (NFV) and software defined networking (SDN). Using edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head (RRH) or a radio unit (RU), or an access node comprising radio parts. It is also possible that node operations may be distributed among a plurality of servers, nodes or hosts. Application of cloudRAN architecture enables RAN real-time functions being carried out at the RAN side (e.g., in a DU 105) and non-real-time functions being carried out in a centralized manner (e.g., in a CU 108).

It should also be understood that the distribution of functions between core network operations and access node operations may differ from that of the LTE or even be non-existent. Some other technology advancements that may be used include big data and all-IP, which may change the way networks are being constructed and managed. 5G (or new radio, NR) networks may be designed to support multiple hierarchies, where MEC servers may be placed between the core and the access node. It should be appreciated that MEC may be applied in 4G networks as well.

5G may also utilize non-terrestrial communication, for example satellite communication, to enhance or complement the coverage of 5G service, for example by providing backhauling. Possible use cases may be providing service continuity for machine-to-machine (M2M) or Internet of Things (loT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway/maritime/aeronautical communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano) satellites are deployed). A given satellite 106 in the mega- constellation may cover several satellite- enabled network entities that create on-ground cells. The on-ground cells may be created through an on-ground relay node or by an access node 104 located on-ground or in a satellite.

6G networks are expected to adopt flexible decentralized and/or distributed computing systems and architecture and ubiquitous computing, with local spectrum licensing, spectrum sharing, infrastructure sharing, and intelligent automated management underpinned by mobile edge computing, artificial intelligence, short-packet communication and blockchain technologies. Key features of 6G may include intelligent connected management and control functions, programmability, integrated sensing and communication, reduction of energy footprint, trustworthy infrastructure, scalability and affordability. In addition to these, 6G is also targeting new use cases covering the integration of localization and sensing capabilities into system definition to unifying user experience across physical and digital worlds.

It is obvious for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of access nodes, the user device may have access to a plurality of radio cells and the system may also comprise other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the access nodes may be a Home eNodeB or a Home gNodeB.

Additionally, in a geographical area of a radio communication system, a plurality of different kinds of radio cells as well as a plurality of radio cells may be provided. Radio cells may be macro cells (or umbrella cells) which may be large cells having a diameter of up to tens of kilometers, or smaller cells such as micro-, femto- or picocells. The access node(s) of FIG. 1 may provide any kind of these cells. A cellular radio system may be implemented as a multilayer network including several kinds of radio cells. In multilayer networks, one access node may provide one kind of a radio cell or radio cells, and thus a plurality of access nodes may be needed to provide such a network structure.

For fulfilling the need for improving the deployment and performance of communication systems, the concept of “plug-and-play” access nodes may be introduced. A network which may be able to use “plug-and-play” access nodes, may include, in addition to Home eNodeBs or Home gNodeBs, a Home Node B gateway, or HNB-GW (not shown in FIG. 1). An HNB-GW, which may be installed within an operator’s network, may aggregate traffic from a large number of Home eNodeBs or Home gNodeBs back to a core network.

FIG. 2 illustrates an example of a wireless communication system 200, to which some example embodiments may be applied. At least portions of the wireless communication system 200 may be configured for implementing dual connectivity (DC). Dual connectivity enables a UE 203 to be simultaneously connected to two cell groups: a master cell group (MCG) 210 and a secondary cell group (SCG) 220. Dual connectivity may be combined with carrier aggregation, and there may be multiple cells (for example one per aggregated carrier) in a given cell group. The two cell groups may be associated with different RAN nodes 201, 202 (i.e., access nodes). The two cell groups may be based on different radio access technologies (e.g., LTE and 5G), or they may be based on the same radio access technology. Herein the term “cell” refers to a radio cell.

The MCG 210 is a group of serving cells associated with the master node (MN) 201 (i.e., a RAN node providing the control plane connection to the core network). The MCG 210 comprises a primary cell (PCell) 211, i.e., the primary serving cell of the MCG 210, and optionally one or more secondary cells (SCells) 212. The PCell 211 is a cell operating on a primary frequency that may be used for initial access under the MCG 210. An SCell is a cell, operating on a secondary frequency, which may be configured once an RRC connection is established, and which may be used to provide additional radio resources. A given serving cell may be associated with physical resources that may be coming from one or more actual transmission and reception points (TRPs), and the UE 203 may also be configured to utilize one or more TRPs. In such a case, the UE 203 may use resources from more than one cell per aggregated carrier or frequency.

The SCG 220 is a group of serving cells associated with the secondary node (SN) 202 (i.e., a RAN node providing additional resources to the UE). The SCG 220 comprises a PSCell 221, i.e., the primary serving cell of the SCG 220, and optionally one or more SCells 222. The PSCell 221 is a cell that may be used for initial access under the SCG 220.

To provide a continuous service for the user of a moving UE, the UE may carry out a handover procedure, which may also be referred to as handoff, to change from one cell to another. For example, when a UE with an ongoing call or data session is moving away from an area covered by a source cell and entering an area covered by a neighbor cell, the session may be handed over from the source cell to the neighbor cell in order to avoid terminating or interrupting the session, when the UE moves outside the range of the source cell.

Some example embodiments relate to enhancements of conditional handover (CHO) with SCG configuration.

The CHO procedure has been introduced in NR Release 16 to improve the mobility robustness. A conditional handover may be defined as a handover that is executed by the UE, when one or more handover execution conditions are met. In other words, the UE receives a handover command with a CHO configuration indicating one or more handover execution conditions, but the UE does not execute the handover command until the one or more execution conditions are met. The UE may start evaluating the execution condition(s) upon receiving the CHO configuration from the source gNB, and stop evaluating the execution conditions] once a handover is executed. An advantage of CHO is that it improves the mobility robustness compared to legacy handover by reducing the number of radio link failures and handover failures. This is achieved by de-coupling the handover execution phase from the preparation phase, thus enabling the UE to receive the handover command early when the radio link of the source cell is still sufficient, and to execute the handover later when the radio link of the target cell is strong enough.

In case of CHO, the network may prepare multiple target cells, where a given conditional handover reconfiguration is associated with at least one CHO execution condition that is evaluated by the UE. The CHO execution condition refers to a measurement ID associating a measurement object with a reporting configuration and is configured by the source gNB. The reporting configuration defines the measurement event (e.g., A3 or A5], which triggers the CHO execution. One or more reference signal types may be supported and one or more trigger quantities may be configured for the evaluation of the CHO execution condition of a given candidate cell. The one or more trigger quantities may comprise, for example, reference signal received power (RSRP), reference signal received quality (RSRQ), and/or signal-to-interference-plus-noise ratio [S1NR]. Whenever the CHO execution condition is met, the corresponding target configuration is selected and a handover is executed towards the selected target cell.

CHO event A3 means that a trigger quantity of a CHO candidate cell indicated in the CHO configuration exceeds the trigger quantity of the serving cell by an offset for a certain time-to-trigger (TTT) period.

CHO event A5 means that the trigger quantity of the serving cell becomes lower than a first threshold, and the trigger quantity of a CHO candidate cell indicated in the CHO configuration exceeds a second threshold for a certain TTT period.

In CHO, the source gNB may start early data forwarding of user plane data to the prepared target cells after sending RRC reconfiguration or receiving RRC reconfiguration complete. As the communication with the UE continues after sending the RRC reconfiguration, the source gNB sends an early SN status transfer message to the target gNB indicating the data packets that have been received by the UE and which shall be deleted from the buffer maintained for a given prepared target PCelL

In NR Release 17, signaling enhancements to support CHO with SCG have been specified, where the target MN receiving the handover request from the source MN may add and prepare a target SN, i.e., handover to DC connection. In this case, the CHO configuration provided by the target MN back to the source MN may comprise an MCG configuration to be applied with respect to the target PCell, and an SCG configuration to be applied with respect to the target PSCell, i.e., the primary serving cell of the SCG. The CHO execution condition(s) may be evaluated by the UE based on the measurements of the target PCell, i.e., the measurement of the target PSCell are not considered in the evaluation. The UE may perform random access to the target PCell and target PSCell, when the CHO execution condition(s) is met.

The MCG configuration is a cell group configuration in RRCReconfiguration, wherein the MCG configuration comprises an SpCell configuration and/or SCell configuration of the MCG. The SCG configuration is a cell group configuration in RRCReconfiguration, wherein the SCG configuration comprises an SpCell configuration and/or SCell configuration of the SCG. The SpCell (special cell) refers to either the primary cell of the MCG, or the primary cell of the SCG. As an example, an MCG configuration or SCG configuration may include the following: cellGroupId CellGroupId, rlc-BearerToAddModList SEQUENCE

( S I ZE ( 1 . . maxLC- ID) ) OF RLC-BearerConf ig

OPTIONAL, — Need N rlc-BearerToReleaseList SEQUENCE

( S I ZE ( 1 . . maxLC- ID) ) OF LogicalChannel Identity

OPTIONAL, — Need N mac-CellGroupConf ig MAC-

CellGroupConf ig

OPTIONAL, — Need M physicalCellGroupConf ig

PhysicalCellGroupConf ig

OPTIONAL, — Need M spCellConfig SpCellConfig

OPTIONAL, — Need M sCellToAddModList SEQUENCE ( S I ZE

( 1 . .maxNrof SCells ) ) OF SCellConfig

OPTIONAL, — Need N sCellToReleaseList SEQUENCE ( S I ZE

( 1 . . maxNrof SCells ) ) OF SCell lndex

OPTIONAL, — Need N

Given that there is time between the CHO preparation and execution, the radio signal quality of the target PSCell may not be sufficient at the time of the CHO execution, which may result in SCG failure and interruption on the SCG radio bearers which may be up to 500 ms or more (depending on the T304 value supervising the random access to the target PSCell). This issue is to be addressed in NR Release 18 by: 1) providing a PSCell access condition (separate from the CHO execution condition) to decide whether to access the target PSCell/SN, and 2) allowing the target MN to prepare more than one candidate target PSCells/SNs. For example, this PSCell access condition (e.g., conditional PSCell addition change, CPAC, condition) may be evaluated using target PSCell measurements.

For example, the PSCell access condition may refer to an A3 or A5 event related to the PSCell, whereas the CHO execution condition may refer to an A3 or A5 event related to the PCelL

To overcome the aforementioned issues, the UE should start the evaluation of the access condition(s) for prepared target PSCells already at the time when it receives the CHO configuration. As such, the UE may simultaneously perform measurements for the prepared target PCell and target PSCell, and consider their radio link strength/quality when deciding on CHO execution.

In case the PSCell access condition for a prepared target PSCell is met while evaluating the CHO execution condition, the UE waits and does not perform random access to the target PSCell until the CHO execution condition of the corresponding target PCell is met.

When the CHO execution condition is met, it may still be useful to check if the leaving condition of the target PSCell (whose PSCell access condition has been met before) is not met to ensure that the radio signal of the target PSCell is still sufficient. If the leaving condition is not met, the UE executes CHO and performs random access to the target PCell and selected target PSCell.

Otherwise, if the leaving condition is met (or if none of the prepared target PSCells have met the PSCell access conditions while evaluating the CHO condition), the UE may execute the MCG configuration and perform random access to the target MN, but not to any of the target PSCells. Herein, the UE may inform the MN that none of the prepared target PSCells have met the PSCell access condition. Using this information, the MN may reconfigure the UE by, for example, remapping the SN radio bearers to the MN. It should be noted that delaying the PCell access until one of the PSCell access conditions is met may not be useful as it may lead to radio link failure (RLF).

In case the PSCell access condition is not met at the time when the CHO execution condition is met, the UE may execute the CHO configuration (comprising MCG and SCG configuration), but perform random access only to the target PCell, i.e., the UE may skip the random access to the target PSCell. The UE may indicate to the target MN that the PSCell condition is not met.

Once the UE completes the random access to the target PCell, the UE may release all other CHO configurations (which may also include the SCG configurations of the prepared target PSCells).

Upon receiving an indication from the UE that the PSCell access condition is not met, the target MN may reconfigure the UE, which may increase the signaling overhead and delay. For instance, for configuring a new SCG, the target MN may need to contact the SN over the Xn interface (2 Xn signaling) and reconfigure the UE using RRC reconfiguration. This delays the PSCell access for the UE, which may result in service interruption or throughput loss.

Some example embodiments may address the above issue by making use of the SCG configuration inside the CHO configuration (comprising the MCG configuration and the SCG configuration) after the CHO execution condition is met and random access is performed to the target PCell (but not yet to the target PSCell).

In an example embodiment, if the PSCell access condition is not fulfilled at the time when the CHO execution condition is fulfilled, the UE applies the CHO configuration (the MCG and SCG configurations) and performs random access to the target PCell, but delays random access to the target PSCell. The UE continues to evaluate the PSCell access condition for a time period that may be pre-configured by the network.

In a first option, if the PSCell access condition is fulfilled within this time period, the UE may perform the random access to the target PSCell. Otherwise, if the PSCell access condition is not fulfilled within this time period, the UE may inform the target MN that the second PSCell access condition was not fulfilled within the configured time period. Having received the indication from the UE, the network may reconfigure the UE. In other words, in the first option, the UE may apply the SCG configuration when the CHO execution condition is fulfilled, but the UE delays the access to the PSCell.

Alternatively, in a second option, if the PSCell access condition is fulfilled within the configured time period, the UE may apply either 1) the SCG configuration, as the MCG configuration may be the same in multiple CHO configurations or, 2) both the MCG configuration and the SCG configuration, and transmits the indication to the network. In other words, in the second option, the UE may not yet apply any SCG configuration when the CHO execution condition is fulfilled, and the UE waits to access the PSCell and apply the SCG configuration at the same time. Applying the MCG configuration means changing the UE parameters to follow the parameters provided by the MCG configuration. Applying the SCG configuration means changing the UE parameters to follow the parameters provided by the SCG configuration.

In case the timer is not configured, the network may signal the UE to release the maintained configurations.

In another example embodiment, after the target MN receives the indication that the PSCell condition was not fulfilled at the time when the CHO condition is fulfilled, the target MN may not release any of the SCG configurations. The target MN may configure the UE to report measurements related to the candidate PSCells. In case the measurement condition to add any of the PSCells is fulfilled, the network may trigger PSCell addition using the stored SCG configurations.

Some example embodiments are described below using principles and terminology of 5G technology without limiting the example embodiments to 5G communication systems, however.

FIG. 3 illustrates a signaling diagram according to an example embodiment.

Initially, a UE may be configured with a measurement configuration and report the measurements of neighbor PCells and possibly PSCells. The source MN may determine that CHO preparation for the UE is necessary.

Referring to FIG. 3, in block 301, the source MN transmits a handover request for CHO to a target MN. In other words, the source MN indicates a CHO request with measurements for the target PSCells to the target MN.

In block 302, the target MN prepares the target PSCells (e.g., PSCell-1 and PSCell-2) by transmitting an SN addition request to a target SN.

In block 303, the target SN transmits, to the target MN, an acknowledgement (ACK) to the SN addition request.

In block 304, each SCG configuration for a target PSCell may be configured in a separate CHO configuration at the target MN. For example, the target MN may determine a first CHO configuration for PCell-1 and PSCell-1, and a second CHO configuration for PCell-1 and PSCell-2. Herein a PCell refers to a primary cell of a master cell group, and PSCell refers to a primary cell of a secondary cell group.

In other words, the target MN may determine one or more configurations for a conditional handover of the UE, wherein a given configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group.

In block 305, the target MN transmits, to the source MN, an ACK to the handover request. The target MN also transmits the one or more CHO configurations to the source MN, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 306, the source MN performs RRC reconfiguration to configure the UE with the one or more CHO configurations and related conditions, i.e., the at least one CHO execution condition and the at least one PSCell access condition. In other words, the UE receives the one or more CHO configurations and the related conditions. The UE may be configured to maintain only the selected SCG configuration. The selected SCG configuration refers to the SCG configuration, for which the CHO execution condition is fulfilled. Herein the maintaining may mean that the UE stores the selected SCG configuration in its memory, and the UE may discard the other SCG configuration^]. Furthermore, the UE is configured with a maintenance timer to not apply the SCG configuration and delay PSCell access after the CHO execution. The access may mean random access towards the PSCell. The CHO configurations may be transmitted with a handover command for conditional handover.

In block 307, the UE transmits an RRC reconfiguration complete message to the source MN to confirm the successful completion of the RRC reconfiguration.

In block 308, the UE determines that the at least one CHO execution condition for a target PCell is fulfilled, and the UE executes PCell change towards the target PCell.

In block 309, the UE maintains, or stores, the selected SCG configuration (e.g., for PSCell-1] and starts the maintenance timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period. In other words, the UE may maintain just a single SCG configuration from one of the CHO configurations.

In block 310, the UE performs a random-access procedure to the target MN to access the target PCelL In other words, the UE accesses the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled. However, the UE delays accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 311, the target MN starts the maintenance timer at the target MN during the random-access procedure, for example upon receiving the random-access preamble from the UE.

In block 312, the target MN initiates an RRC reconfiguration procedure to the UE after the random-access procedure is completed.

In block 313, the UE keeps evaluating the at least one PSCell access condition.

In block 314, based on the evaluation, the UE determines that the at least one PSCell access condition is fulfilled (e.g., for PSCell-1), while the timer is configured and it is running. In other words, the UE monitors the at least one PSCell access condition and detects that the at least one access condition is fulfilled before the maintenance timer expires.

In block 315, the UE applies the SCG configuration (e.g., for PSCell-1) and performs a random-access procedure to access the PSCell. In other words, the UE accesses the target primary cell of the secondary cell group based on the stored secondary cell group configuration upon detecting that the at least one access condition is fulfilled before the maintenance timer expires.

In block 316, the UE transmits the SN RRC reconfiguration to the target MN.

In block 317, the target MN stops the maintenance timer upon receiving the SN RRC reconfiguration.

In block 318, the target MN transmits an SN modification confirmation (RRC reconfiguration complete) message to the target SN.

FIG. 4 illustrates a signaling diagram according to an example embodiment.

Referring to FIG. 4, in block 401, the source MN transmits a handover request for CHO to a target MN. In other words, the source MN indicates a CHO request with measurements for the target PSCells to the target MN. In block 402, the target MN prepares the target PSCells (e.g., PSCell-1 and PSCell-2) by transmitting an SN addition request to a target SN.

In block 403, the target SN transmits, to the target MN, an acknowledgement (ACK) to the SN addition request.

In block 404, each SCG configuration for a target PSCell may be configured in a separate CHO configuration at the target MN. For example, the target MN may determine a first CHO configuration for PCell-1 and PSCell-1, and a second CHO configuration for PCell-1 and PSCell-2. The source MN indicates to the target MN the timer to be configured to the UE. Herein a PCell refers to a primary cell of a master cell group, and PSCell refers to a primary cell of a secondary cell group.

In block 405, the target MN transmits, to the source MN, an ACK to the handover request. The target MN also transmits the one or more CHO configurations to the source MN, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 406, the source MN performs RRC reconfiguration to configure the UE with the one or more CHO configurations and related conditions, i.e., the at least one CHO execution condition and the at least one PSCell access condition. In other words, the UE receives the one or more CHO configurations and the related conditions. The UE may be configured to maintain only the selected SCG configuration. Furthermore, the UE is configured with a maintenance timer to delay PSCell access after the CHO execution. The access may mean random access towards the PSCell. The CHO configurations may be transmitted with a handover command for conditional handover.

In block 407, the UE transmits an RRC reconfiguration complete message to the source MN to confirm the successful completion of the RRC reconfiguration. In block 408, the UE determines that the at least one CHO execution condition for a target PCell is fulfilled, and the UE executes PCell change towards the target PCelL

In block 409, the UE maintains, or stores, the selected SCG configuration (e.g., for PSCell 1) and starts the maintenance timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period. In other words, the UE may maintain just a single SCG configuration from one of the CHO configurations.

In block 410, the UE performs a random-access procedure to the target MN to access the target PCell. In other words, the UE accesses the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled. However, the UE delays accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 411, the target MN may start a timer upon detecting that the UE is connected to the target primary cell associated with the target MN, wherein the timer is configured to expire after a time period. The target MN may start the timer during the random-access procedure, for example upon receiving the random-access preamble from the UE. This timer may correspond to the maintenance timer of the UE.

In block 412, the target MN initiates an RRC reconfiguration procedure to the UE after the random-access procedure is completed.

In block 413, the UE keeps evaluating the at least one PSCell access condition.

In block 414, the UE detects that the maintenance timer expires, and the UE determines that the at least one access condition is not fulfilled within the configured time period. In other words, the UE monitors the at least one PSCell access condition and the at least one access condition is not fulfilled before the timer expires.

In block 415, the UE may optionally transmit an indication to the target MN associated with the target PSCell to indicate that the at least one access condition was not fulfilled within the configured time period.

In block 416, based on the indication or the expiry of the timer that the target MN started, the target MN releases, i.e., deletes, the maintained (stored) SCG configuration (e.g., for PSCell-1).

In block 417, the target MN transmits an RRC reconfiguration message to the UE to re-map the SCG radio bearers to the MCG. In block 418, the UE transmits an RRC reconfiguration complete message to the target MN to confirm the successful completion of the RRC reconfiguration (i.e., the re-mapping).

FIG. 5 illustrates a signaling diagram according to an example embodiment.

Initially, a UE maybe configured with a measurement configuration and report the measurements of neighbor PCells and possibly PSCells. The source MN may determine that CHO preparation for the UE is necessary.

Referring to FIG. 5, in block 501, the source MN transmits a handover request for CHO to a target MN. In other words, the source MN indicates a CHO request with measurements for the target PSCells to the target MN.

In block 502, the target MN prepares the target PSCells (e.g., PSCell-1 and PSCell-2) by transmitting an SN addition request to a target SN.

In block 503, the target SN transmits, to the target MN, an acknowledgement (ACK) to the SN addition request.

In block 504, each SCG configuration for a target PSCell may be configured in a separate CHO configuration at the target MN. For example, the target MN may determine a first CHO configuration for PCell-1 and PSCell-1, and a second CHO configuration for PCell-1 and PSCell-2. Herein a PCell refers to a primary cell of a master cell group, and PSCell refers to a primary cell of a secondary cell group.

In block 505, the target MN transmits, to the source MN, an ACK to the handover request. The target MN also transmits the one or more CHO configurations to the source MN, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 506, the source MN performs RRC reconfiguration to configure the UE with the one or more CHO configurations and related conditions, i.e., the at least one CHO execution condition and the at least one PSCell access condition. In other words, the UE receives the one or more CHO configurations and the related conditions. The CHO configurations may be transmitted with a handover command for conditional handover. The UE is configured to maintain at least all the SCG configurations in the CHO configurations after executing the PCell change. The UE may also be configured to maintain all the MCG configurations after executing the PCell change. The UE may be configured to maintain these configurations with respect to a maintenance timer, i.e., to delete the maintained configurations when the timer expires.

In block 507, the UE transmits an RRC reconfiguration complete message to the source MN to confirm the successful completion of the RRC reconfiguration.

In block 508, the UE determines that the at least one CHO execution condition for a target PCell is fulfilled, and the UE executes PCell change towards the target PCell.

In block 509, the UE maintains, or stores, at least the SCG configurations and starts the maintenance timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period. The UE may also maintain (store) the MCG configurations.

In block 510, the UE performs a random-access procedure to the target MN to access the target PCell. In other words, the UE accesses the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled. However, the UE delays accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 511, the target MN initiates an RRC reconfiguration procedure to the UE after the random-access procedure is completed.

In block 512, the UE keeps evaluating the PSCell access conditions of the maintained SCG configurations.

In block 513, based on the evaluation, the UE determines that the at least one PSCell access condition is fulfilled for one of the target PSCells (e.g., for PSCell- 1), while the timer is configured and it is running. In other words, the UE monitors the PSCell access conditions and at least one access condition is fulfilled before the maintenance timer expires.

In block 514, based on detecting that the at least one access condition is fulfilled within the configured time period, the UE applies at least the stored SCG (e.g., PSCell-1) configuration associated with the at least one access condition that was fulfilled. The UE may also apply the stored MCG configuration (if it was stored in block 509).

In block 515, the UE performs a random-access procedure to access the target PSCell, for which the at least one access condition was fulfilled.

In block 516, the UE transmits the SN RRC reconfiguration to the target MN.

In block 517, the target MN stops the timer upon receiving the SN RRC reconfiguration. The target MN may release at least the SCG configuration(s) (e.g., for PSCell-2) that were not applied by the UE. The target MN may also release the MCG configuration(s) that were not applied by the UE.

In block 518, the target MN transmits an SN modification confirmation (RRC reconfiguration complete) message to the target SN.

FIG. 6 illustrates a signaling diagram according to an example embodiment.

Referring to FIG. 6, in block 601, the source MN transmits a handover request for CHO to a target MN. In other words, the source MN indicates a CHO request with measurements for the target PSCells to the target MN.

In block 602, the target MN prepares the target PSCells (e.g., PSCell-1 and PSCell-2) by transmitting an SN addition request to a target SN.

In block 603, the target SN transmits, to the target MN, an acknowledgement (ACK) to the SN addition request.

In block 604, each SCG configuration for a target PSCell may be configured in a separate CHO configuration at the target MN. For example, the target MN may determine a first CHO configuration for PCell-1 and PSCell-1, and a second CHO configuration for PCell-1 and PSCell-2. Herein a PCell refers to a primary cell of a master cell group, and PSCell refers to a primary cell of a secondary cell group.

In block 605, the target MN transmits, to the source MN, an ACK to the handover request. The target MN also transmits the one or more CHO configurations to the source MN, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 606, the source MN performs RRC reconfiguration to configure the UE with the one or more CHO configurations and related conditions, i.e., the at least one CHO execution condition and the at least one PSCell access condition. In other words, the UE receives the one or more CHO configurations and the related conditions. The CHO configurations may be transmitted with a handover command for conditional handover. The UE is configured to maintain at least all the SCG configurations in the CHO configurations after executing the PCell change. The UE may also be configured to maintain all the MCG configurations after executing the PCell change. The UE may be configured to maintain these configurations with respect to a maintenance timer, i.e., to delete the maintained configurations when the timer expires.

In block 607, the UE transmits an RRC reconfiguration complete message to the source MN to confirm the successful completion of the RRC reconfiguration.

In block 608, the UE determines that the at least one CHO execution condition for a target PCell is fulfilled, and the UE executes PCell change towards the target PCell.

In block 609, the UE maintains, or stores, at least the SCG configurations and starts the maintenance timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period. The UE may also maintain (store) the MCG configurations.

In block 610, the UE performs a random-access procedure to the target MN to access the target PCell. In other words, the UE accesses the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled. However, the UE delays accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 611, the target MN initiates an RRC reconfiguration procedure to the UE after the random-access procedure is completed.

In block 612, the UE keeps evaluating the PSCell access conditions of the maintained SCG configurations.

In block 613, the UE detects that the maintenance timer expires, and the UE determines that none of the access conditions is fulfilled within the configured time period. In other words, the UE monitors the PSCell access conditions and the access conditions are not fulfilled before the timer expires. Upon determining that the access conditions are not fulfilled within the configured time period, the UE deletes, i.e., releases, all the maintained SCG configurations (e.g., for PSCell- 1 and PSCell-2). The UE may also delete the maintained MCG configurations, if they were maintained in block 609.

In block 614, the UE transmits an indication to the target MN to indicate that the at least one access condition was not fulfilled within the configured time period.

In block 615, based on the indication, the target MN releases at least the maintained SCG configurations (e.g., for PSCell-1 and PSCell-2). The target MN may also release the maintained MCG configurations other than the executed MCG configuration (i.e., the executed MCG configuration is not released), if the MCG configurations were maintained.

FIG. 7 illustrates a signaling diagram according to an example embodiment. In this example embodiment, no maintenance timer is configured, and the network may determine to release or keep the maintained configurations at the UE side using dedicated signaling.

Referring to FIG. 7, in block 701, the source MN transmits a handover request for CHO to a target MN. In other words, the source MN indicates a CHO request with measurements for the target PSCells to the target MN.

In block 702, the target MN prepares the target PSCells (e.g., PSCell-1 and PSCell-2) by transmitting an SN addition request to a target SN.

In block 703, the target SN transmits, to the target MN, an acknowledgement (ACK) to the SN addition request.

In block 704, each SCG configuration for a target PSCell may be configured in a separate CHO configuration at the target MN. For example, the target MN may determine a first CHO configuration for PCell-1 and PSCell-1, and a second CHO configuration for PCell-1 and PSCell-2. Herein a PCell refers to a primary cell of a master cell group, and PSCell refers to a primary cell of a secondary cell group.

In block 705, the target MN transmits, to the source MN, an ACK to the handover request. The target MN also transmits the one or more CHO configurations to the source MN, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 706, the source MN performs RRC reconfiguration to configure the UE with the one or more CHO configurations and related conditions, i.e., the at least one CHO execution condition and the at least one PSCell access condition. In other words, the UE receives the one or more CHO configurations and the related conditions. The CHO configurations may be transmitted with a handover command for conditional handover. The UE is configured to maintain at least all the SCG configurations in the CHO configurations after executing the PCell change. The UE may also be configured to maintain all the MCG configurations after executing the PCell change.

In block 707, the UE transmits an RRC reconfiguration complete message to the source MN to confirm the successful completion of the RRC reconfiguration.

In block 708, the UE determines that the at least one CHO execution condition for a target PCell is fulfilled, and the UE executes PCell change towards the target PCell.

In block 709, the UE maintains, or stores, at least the SCG configurations. The UE may also maintain (store) the MCG configurations.

In block 710, the UE performs a random-access procedure to the target MN to access the target PCell. In other words, the UE accesses the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled. However, the UE delays accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 711, the target MN initiates an RRC reconfiguration procedure to the UE after the random-access procedure is completed.

In block 712, the UE keeps evaluating the PSCell access conditions of the maintained SCG configurations.

In block 713, the target MN transmits an indication, for example an RRC reconfiguration message, to the UE for releasing at least the maintained SCG configurations. The target MN may also indicate the UE to release the MCG configurations, if they were maintained.

In block 714, the UE deletes, i.e., releases, at least the maintained SCG configurations upon receiving the indication (e.g., RRC reconfiguration message). The UE may also delete the MCG configurations, if the target MN indicated to release the MCG configurations.

In block 715, the target MN releases at least the SCG configurations. The target MN may also release the MCG configurations.

FIG. 8 illustrates a signaling diagram according to an example embodiment. In this example embodiment, the triggering is done from the network side instead of UE- based triggering. Thus, the UE does not have to maintain the configurations, as the configurations are maintained at the network side. In this example embodiment, the configurations may be provided as a conditional PSCell addition change (CPAC) to the UE.

Referring to FIG. 8, in block 801, the source MN transmits a handover request for CHO to a target MN. In other words, the source MN indicates a CHO request with measurements for the target PSCells to the target MN.

In block 802, the target MN prepares the target PSCells (e.g., PSCell-1 and PSCell-2) by transmitting an SN addition request to a target SN.

In block 803, the target SN transmits, to the target MN, an acknowledgement (ACK) to the SN addition request.

In block 804, each SCG configuration for a target PSCell may be configured in a separate CHO configuration at the target MN. For example, the target MN may determine a first CHO configuration for PCell-1 and PSCell-1, and a second CHO configuration for PCell-1 and PSCell-2. Herein a PCell refers to a primary cell of a master cell group, and PSCell refers to a primary cell of a secondary cell group.

In block 805, the target MN transmits, to the source MN, an ACK to the handover request. The target MN also transmits the one or more CHO configurations to the source MN, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 806, the source MN performs RRC reconfiguration to configure the UE with the one or more CHO configurations and related conditions, i.e., the at least one CHO execution condition and the at least one PSCell access condition. In other words, the UE receives the one or more CHO configurations and the related conditions. The CHO configuration(s) may be transmitted with a handover command for conditional handover.

In block 807, the UE transmits an RRC reconfiguration complete message to the source MN to confirm the successful completion of the RRC reconfiguration.

In block 808, the UE determines that the at least one CHO execution condition for a target PCell is fulfilled, and the UE executes PCell change towards the target PCell. For example, the UE may execute the MCG configuration in the first CHO configuration in response to detecting that the at least one CHO execution condition associated with the first CHO configuration is fulfilled.

In block 809, the UE releases, or deletes, the CHO configuration(s) other than the executed one. For example, the UE may delete the second CHO configuration (in case the MCG configuration in the first CHO configuration was executed).

In block 810, the UE performs a random-access procedure to the target MN to access the target PCelL In other words, the UE accesses the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled. However, the UE delays accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

The UE may also transmit an indication to the target MN associated with the target PSCell indicating that the at least one access condition for the target PSCell was not fulfilled when the at least one execution condition was fulfilled.

In block 811, the target MN initiates an RRC reconfiguration procedure to the UE after the random-access procedure is completed. The target MN may also configure the UE to report measurements related to the target PSCells (candidate PSCells). For example, the measurements may comprise reference signal received power (RSRP) measurements and/or reference signal received quality (RSRQ) measurements.

In block 812, the target MN maintains, or stores, the SCG configurations for the target PSCells, even though single connectivity is executed by the UE.

The source MN may maintain the configurations based on a timer. In other words, a timer may be maintained at the network side, and this timer may be started when the UE is connected to the PCell (i.e., a random-access procedure is performed towards the target MN based on CHO configuration). When the timer expires, the target MN releases the configurations. Furthermore, the timer may be stopped when the network uses the maintained configuration to trigger CPAC (i.e., block 813).

The configurations (e.g., SCG configurations) maintained at the network side (i.e., target MN) may be modified based on information received from the SN(s), i.e., SN modification procedure. The information received from the SN(s) may comprise, for example, network load information, and a change in the network load may be a trigger for the modification. For example, the modification may mean removing a data radio bearer (DRB) from at least one of the maintained SCG configurations. Such a modification may be initiated either by the target MN or by SN.

In block 813, the target MN uses the maintained SCG configurations to configure CPAC to the UE for the target PSCells (e.g., PSCell-1 and PSCell-2). In other words, the target MN determines, based on the secondary cell group configuration, a conditional cell addition change configuration for accessing the target primary cell of the secondary cell group. In block 814, the target MN transmits an RRC reconfiguration message to the UE to configure the CPAC. In other words, the target MN transmits the conditional cell addition change configuration to the UE. The UE may report the measurements to the target MN before the CPAC is configured.

In block 815, the UE transmits an RRC reconfiguration complete message to the target MN to confirm the reception of the CPAC configuration and the measurements to trigger CPAC.

In block 816, the UE evaluates the CPAC condition(s) based on the measurements related to the target PSCells. In other words, the UE may compare the measurements against the CPAC condition(s).

In block 817, the UE determines that the CPAC condition(s) associated with the target PSCell are fulfilled.

In block 818, the UE transmits an RRC reconfiguration complete message to the target MN to confirm the configuration of the PSCell addition.

In block 819, the UE performs a random-access procedure to access the target PSCell.

In block 820, the target MN transmits an SN modification confirmation (RRC reconfiguration complete) message to the target SN.

FIG. 9 illustrates a signaling diagram according to an example embodiment. In this example embodiment, the triggering is done from the network side instead of UE- based triggering. Thus, the UE does not have to maintain the configurations, as the configurations are maintained at the network side. In this example embodiment, the configurations may be provided as a PSCell addition command to the UE, in response to the measurements received from the UE.

Referring to FIG. 9, in block 901, the source MN transmits a handover request for CHO to a target MN. In other words, the source MN indicates a CHO request with measurements for the target PSCells to the target MN.

In block 902, the target MN prepares the target PSCells (e.g., PSCell-1 and PSCell-2) by transmitting an SN addition request to a target SN.

In block 903, the target SN transmits, to the target MN, an acknowledgement (ACK) to the SN addition request.

In block 904, each SCG configuration for a target PSCell may be configured in a separate CHO configuration at the target MN. For example, the target MN may determine a first CHO configuration for PCell-1 and PSCell-1, and a second CHO configuration for PCell-1 and PSCell-2. Herein a PCell refers to a primary cell of a master cell group, and PSCell refers to a primary cell of a secondary cell group.

In block 905, the target MN transmits, to the source MN, an ACK to the handover request. The target MN also transmits the one or more CHO configurations to the source MN, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

In block 906, the source MN performs RRC reconfiguration to configure the UE with the one or more CHO configurations and related conditions, i.e., the at least one CHO execution condition and the at least one PSCell access condition. In other words, the UE receives the one or more CHO configurations and the related conditions. The CHO configuration(s) may be transmitted with a handover command for conditional handover.

In block 907, the UE transmits an RRC reconfiguration complete message to the source MN to confirm the successful completion of the RRC reconfiguration.

In block 908, the UE determines that the at least one CHO execution condition for a target PCell is fulfilled, and the UE executes PCell change towards the target PCell. For example, the UE may execute the MCG configuration in the first CHO configuration in response to detecting that the at least one CHO execution condition associated with the first CHO configuration is fulfilled.

In block 909, the UE releases, or deletes, the CHO configuration(s) other than the executed one. For example, the UE may delete the second CHO configuration (in case the MCG configuration in the first CHO configuration was executed).

In block 910, the UE performs a random-access procedure to the target MN to access the target PCelL In other words, the UE accesses the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled. However, the UE delays accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

The UE may also transmit an indication to the target MN indicating that the at least one access condition for the target PSCell was not fulfilled when the execution condition was fulfilled.

In block 911, the target MN initiates an RRC reconfiguration procedure to the UE after the random-access procedure is completed. The target MN may also configure the UE to report measurements related to the target PSCells (candidate PSCells).

In block 912, the target MN maintains, or stores, the SCG configurations for the target PSCells, even though single connectivity is executed by the UE.

The source MN may maintain the configurations based on a timer. In other words, a timer may be maintained at the network side, and this timer may be started when the UE is connected to the PCell (i.e., a random-access procedure is performed towards the target MN based on CHO configuration). When the timer expires, the target MN releases the configurations. Furthermore, the timer may be stopped when the network uses the maintained configuration to trigger PSCell addition (i.e., block 914).

The configurations maintained at the network side (i.e., target MN) may be modified using information received from the SN(s), i.e., SN modification procedure. Such modification can be initiated either by the target MN or by SN.

In block 913, the UE transmits a measurement report to the target MN to report the measurements related to the target PSCells.

In block 914, in case the measurement condition to add any of the PSCells is fulfilled based on the measurement report, the target MN uses the maintained SCG configurations to trigger PSCell addition to the UE for the PSCell, for which the measurement condition was fulfilled.

In block 915, the target MN transmits an RRC reconfiguration message to the UE, wherein the RRC reconfiguration message comprises the PSCell addition command. The PSCell addition command may also be referred to as a cell addition change configuration for the target primary cell (PSCell) of the secondary cell group. The difference between the PSCell addition command and the CPAC configuration is that the PSCell addition command does not involve any conditions, whereas the CPAC configuration involves one or more conditions to be fulfilled.

In block 916, the UE transmits an RRC reconfiguration complete message to the target MN to confirm the successful completion of the RRC reconfiguration.

In block 917, the UE performs a random-access procedure to access the target PSCell based on the PSCell addition command.

In block 918, the target MN transmits an SN modification confirmation (RRC reconfiguration complete) message to the target SN.

FIG. 10 illustrates a flow chart according to an example embodiment of a method performed by an apparatus. For example, the apparatus may be, or comprise, or be comprised in, a user device. The user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal, terminal device, or user equipment (UE). The user device may correspond to one of the user devices 100, 102 of FIG. 1, or to the user device 203 of FIG. 2.

Referring to FIG. 10, in block 1001, one or more configurations for a conditional handover are received, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group.

In block 1002, the target primary cell of the master cell group is accessed upon detecting that the at least one execution condition is fulfilled. Herein the accessing may mean performing a random-access procedure with the target primary cell. The randomaccess procedure may also be referred to as a random-access channel (RACH) procedure or a physical random-access channel (PRACH) procedure.

In block 1003, accessing the target primary cell of the secondary cell group is delayed based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

FIG. 11 illustrates a flow chart according to an example embodiment of a method performed by an apparatus. For example, the apparatus may be, or comprise, or be comprised in, a network element of a radio access network, for example the target master node described above. The network element may correspond to the access node 104 of FIG. 1, or to the master node 201 of FIG. 2.

Referring to FIG. 11, in block 1101, one or more configurations for a conditional handover of a user device are determined, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group.

In block 1102, the one or more configurations are transmitted, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

The blocks, related functions, and information exchanges (messages) described above by means of FIGS. 3-11 are in no absolute chronological order, and some of them may be performed simultaneously or in an order differing from the described one. Other functions can also be executed between them or within them, and other information may be sent, and/or other rules applied. Some of the blocks or part of the blocks or one or more pieces of information can also be left out or replaced by a corresponding block or part of the block or one or more pieces of information.

As used herein, “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.

FIG. 12 illustrates an example of an apparatus 1200 comprising means for performing one or more of the example embodiments described above. For example, the apparatus 1200 may be an apparatus such as, or comprising, or comprised in, a user device. The user device may correspond to one of the user devices 100, 102 of FIG. 1. The user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal, terminal device, or user equipment (UE).

The apparatus 1200 comprises at least one processor 1210. The at least one processor 1210 interprets instructions (e.g., computer program instructions) and processes data. The at least one processor 1210 may comprise one or more programmable processors. The at least one processor 1210 may comprise programmable hardware with embedded firmware and may, alternatively or additionally, comprise one or more application-specific integrated circuits (ASICs).

The at least one processor 1210 is coupled to at least one memory 1220. The at least one processor is configured to read and write data to and from the at least one memory 1220. The at least one memory 1220 may comprise one or more memory units. The memory units may be volatile or non-volatile. It is to be noted that there may be one or more units of non-volatile memory and one or more units of volatile memory or, alternatively, one or more units of non-volatile memory, or, alternatively, one or more units of volatile memory. Volatile memory may be for example random-access memory (RAM), dynamic random-access memory (DRAM) or synchronous dynamic randomaccess memory (SDRAM). Non-volatile memory may be for example read-only memory (ROM), programmable read-only memory (PROM), electronically erasable programmable read-only memory (EEPROM), flash memory, optical storage or magnetic storage. In general, memories may be referred to as non-transitory computer readable media. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM). The at least one memory 1220 stores computer readable instructions that are executed by the at least one processor 1210 to perform one or more of the example embodiments described above. For example, non-volatile memory stores the computer readable instructions, and the at least one processor 1210 executes the instructions using volatile memory for temporary storage of data and/or instructions. The computer readable instructions may refer to computer program code.

The computer readable instructions may have been pre-stored to the at least one memory 1220 or, alternatively or additionally, they may be received, by the apparatus, via an electromagnetic carrier signal and/or may be copied from a physical entity such as a computer program product. Execution of the computer readable instructions by the at least one processor 1210 causes the apparatus 1200 to perform one or more of the example embodiments described above. That is, the at least one processor and the at least one memory storing the instructions may provide the means for providing or causing the performance of any of the methods and/or blocks described above. In the context of this document, a “memory” or “computer-readable media” or “computer-readable medium” may be any non-transitory media or medium or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

The apparatus 1200 may further comprise, or be connected to, an input unit 1230. The input unit 1230 may comprise one or more interfaces for receiving input. The one or more interfaces may comprise for example one or more temperature, motion and/or orientation sensors, one or more cameras, one or more accelerometers, one or more microphones, one or more buttons and/or one or more touch detection units. Further, the input unit 1230 may comprise an interface to which external devices may connect to.

The apparatus 1200 may also comprise an output unit 1240. The output unit may comprise or be connected to one or more displays capable of rendering visual content, such as a light emitting diode (LED) display, a liquid crystal display (LCD) and/or a liquid crystal on silicon (LCoS) display. The output unit 1240 may further comprise one or more audio outputs. The one or more audio outputs may be for example loudspeakers.

The apparatus 1200 further comprises a connectivity unit 1250. The connectivity unit 1250 enables wireless connectivity to one or more external devices. The connectivity unit 1250 comprises at least one transmitter and at least one receiver that may be integrated to the apparatus 1200 or that the apparatus 1200 may be connected to. The at least one transmitter comprises at least one transmission antenna, and the at least one receiver comprises at least one receiving antenna. The connectivity unit 1250 may comprise an integrated circuit or a set of integrated circuits that provide the wireless communication capability for the apparatus 1200. Alternatively, the wireless connectivity may be a hardwired application-specific integrated circuit (ASIC). The connectivity unit 1250 may also provide means for performing at least some of the blocks of one or more example embodiments described above. The connectivity unit 1250 may comprise one or more components, such as: power amplifier, digital front end (DFE), analog-to-digital converter (ADC), digital-to-analog converter (DAC), frequency converter, (de) modulator, and/or encoder/decoder circuitries, controlled by the corresponding controlling units. It is to be noted that the apparatus 1200 may further comprise various components not illustrated in FIG. 12. The various components may be hardware components and/or software components.

FIG. 13 illustrates an example of an apparatus 1300 comprising means for performing one or more of the example embodiments described above. For example, the apparatus 1300 may be an apparatus such as, or comprising, or comprised in, a network element of a radio access network. The network element may correspond to the access node 104 of FIG. 1. The network element may also be referred to, for example, as a network node, a master node, a target master node, a source master node, a radio access network (RAN) node, a next generation radio access network (NG-RAN) node, a NodeB, an eNB, a gNB, a base transceiver station (BTS), a base station, an NR base station, a 5G base station, an access node, an access point (AP), a relay node, a repeater, an integrated access and backhaul (IAB) node, an IAB donor node, a distributed unit (DU), a central unit (CU), a baseband unit (BBU), a radio unit (RU), a radio head, a remote radio head (RRH), or a transmission and reception point (TRP).

The apparatus 1300 may comprise, for example, a circuitry or a chipset applicable for realizing one or more of the example embodiments described above. The apparatus 1300 may be an electronic device comprising one or more electronic circuitries. The apparatus 1300 may comprise a communication control circuitry 1310 such as at least one processor, and at least one memory 1320 storing instructions 1322 which, when executed by the at least one processor, cause the apparatus 1300 to carry out one or more of the example embodiments described above. Such instructions 1322 may, for example, include a computer program code (software), wherein the at least one memory and the computer program code (software) are configured, with the at least one processor, to cause the apparatus 1300 to carry out one or more of the example embodiments described above. The at least one processor and the at least one memory storing the instructions may provide the means for providing or causing the performance of any of the methods and/or blocks described above.

The processor is coupled to the memory 1320. The processor is configured to read and write data to and from the memory 1320. The memory 1320 may comprise one or more memory units. The memory units may be volatile or non-volatile. It is to be noted that there may be one or more units of non-volatile memory and one or more units of volatile memory or, alternatively, one or more units of non-volatile memory, or, alternatively, one or more units of volatile memory. Volatile memory may be for example random-access memory (RAM), dynamic random-access memory (DRAM) or synchronous dynamic random-access memory (SDRAM). Non-volatile memory may be for example read-only memory (ROM), programmable read-only memory (PROM), electronically erasable programmable read-only memory (EEPROM), flash memory, optical storage or magnetic storage. In general, memories may be referred to as non- transitory computer readable media. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM). The memory 1320 stores computer readable instructions that are executed by the processor. For example, non-volatile memory stores the computer readable instructions and the processor executes the instructions using volatile memory for temporary storage of data and/or instructions.

The computer readable instructions may have been pre-stored to the memory 1320 or, alternatively or additionally, they may be received, by the apparatus, via an electromagnetic carrier signal and/or may be copied from a physical entity such as a computer program product. Execution of the computer readable instructions causes the apparatus 1300 to perform one or more of the functionalities described above.

The memory 1320 may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and/or removable memory. The memory may comprise a configuration database for storing configuration data. For example, the configuration database may store a current neighbour cell list, and, in some example embodiments, structures of the frames used in the detected neighbour cells.

The apparatus 1300 may further comprise a communication interface 1330 comprising hardware and/or software for realizing communication connectivity according to one or more communication protocols. The communication interface 1330 comprises at least one transmitter (Tx) and at least one receiver (Rx) that may be integrated to the apparatus 1300 or that the apparatus 1300 may be connected to. The communication interface 1330 may provide means for performing some of the blocks for one or more example embodiments described above. The communication interface 1330 may comprise one or more components, such as: power amplifier, digital front end (DFE), analog-to-digital converter (ADC), digital-to-analog converter (DAC), frequency converter, (de) modulator, and/or encoder/decoder circuitries, controlled by the corresponding controlling units.

The communication interface 1330 provides the apparatus with radio communication capabilities to communicate in the cellular communication system. The communication interface may, for example, provide a radio interface to one or more user devices. The apparatus 1300 may further comprise another interface towards a core network such as the network coordinator apparatus or AMF, and/or to the access nodes of the cellular communication system.

The apparatus 1300 may further comprise a scheduler 1340 that is configured to allocate radio resources. The scheduler 1340 may be configured along with the communication control circuitry 1310 or it may be separately configured.

It is to be noted that the apparatus 1300 may further comprise various components not illustrated in FIG. 13. The various components may be hardware components and/or software components.

As used in this application, the term “circuitry” may refer to one or more or all of the following: a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry); and b) combinations of hardware circuits and software, such as (as applicable): i) a combination of analog and/or digital hardware circuit(s) with software/firmware and ii) any portions of hardware processor(s) with software (including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone, 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 (for example 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.

The techniques and methods described herein maybe implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatus(es) of example embodiments may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), graphics processing units (GPUs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chipset (for example procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case, it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and/or complemented by additional components in order to facilitate the achievements of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept may be implemented in various ways. The embodiments are not limited to the example embodiments described above, but may vary within the scope of the claims. Therefore, all words and expressions should be interpreted broadly, and they are intended to illustrate, not to restrict, the example embodiments.

Claims

1. An apparatus comprising at least one processor, and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus at least to: receive one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; access the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

2. The apparatus according to claim 1, further being caused to: store at least the secondary cell group configuration; start a timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period; and access the target primary cell of the secondary cell group based on the stored secondary cell group configuration upon detecting that the at least one access condition is fulfilled before the timer expires.

3. The apparatus according to claim 1, further being caused to: start a timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period; determine that the at least one access condition is not fulfilled within the time period; and transmit, to a target master node associated with the target primary cell, an indication indicating that the at least one access condition was not fulfilled within the time period.

4. The apparatus according to claim 1, further being caused to: start a timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period; and apply the secondary cell group configuration based on detecting that the at least one access condition is fulfilled before the timer expires.

5. The apparatus according to claim 1, further being caused to: start a timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period; and apply the master cell group configuration and the secondary cell group configuration based on detecting that the at least one access condition is fulfilled within the time period.

6. The apparatus according to claim 1, further being caused to: store at least the secondary cell group configuration; start a timer upon detecting that the at least one execution condition for the conditional handover is fulfilled, wherein the timer is configured to expire after a time period; and delete at least the secondary cell group configuration upon determining that the at least one access condition is not fulfilled within the time period.

7. The apparatus according to claim 1, further being caused to: store at least the secondary cell group configuration; and delete at least the secondary cell group configuration upon receiving an indication to release at least the secondary cell group configuration.

8. The apparatus according to claim 1, further being caused to: transmit, to a target master node associated with the target primary cell, an indication indicating that the at least one access condition was not fulfilled when the at least one execution condition was fulfilled; receive, from the target master node, a configuration for reporting measurements related to the target primary cell of the secondary cell group; report, to the target master node, the measurements related to the target primary cell of the secondary cell group; receive, from the target master node, based on the reporting, a cell addition change configuration for the target primary cell of the secondary cell group; and access the target primary cell of the secondary cell group based on the cell addition change configuration.

9. An apparatus comprising at least one processor, and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus at least to: determine one or more configurations for a conditional handover of a user device, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; transmit the one or more configurations, wherein the one or more configurations indicate to delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

10. The apparatus according to claim 9, further being caused to: receive, from the user device, an indication indicating that the at least one access condition was not fulfilled when the at least one execution condition was fulfilled; determine, based on the secondary cell group configuration, a conditional cell addition change configuration for accessing the target primary cell of the secondary cell group; and transmit the conditional cell addition change configuration to the user device.

11. The apparatus according to claim 9, further being caused to: receive, from the user device, an indication indicating that the at least one access condition was not fulfilled when the at least one execution condition was fulfilled; transmit, to the user device, a configuration for reporting measurements related to the target primary cell of the secondary cell group; receive, from the user device, a report comprising the measurements related to the target primary cell of the secondary cell group; and transmit, to the user device, based on the report, a cell addition change configuration for accessing the target primary cell of the secondary cell group.

12. The apparatus according to any of claims 9-11, further being caused to: store at least the secondary cell group configuration; start a timer upon detecting that the user device is connected to the target primary cell, wherein the timer is configured to expire after a time period; and release at least the secondary cell group configuration when the timer expires.

13. The apparatus according to any of claims 9-12, further being caused to: modify the secondary cell group configuration based on information received from a secondary node associated with the target primary cell of the secondary cell group.

14. A method comprising: receiving one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; accessing the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delaying accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.

15. A non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receive one or more configurations for a conditional handover, wherein a configuration of the one or more configurations comprises at least a master cell group configuration for a target primary cell of a master cell group and a secondary cell group configuration for a target primary cell of a secondary cell group, and wherein the configuration is associated with at least one execution condition for the conditional handover and at least one access condition for the target primary cell of the secondary cell group; access the target primary cell of the master cell group upon detecting that the at least one execution condition is fulfilled; and delay accessing the target primary cell of the secondary cell group based on determining that the at least one access condition is not fulfilled upon detecting that the at least one execution condition for the conditional handover is fulfilled.