WO2024168483A1

WO2024168483A1 - Enhancement on connected mode mobility

Info

Publication number: WO2024168483A1
Application number: PCT/CN2023/075735
Authority: WO
Inventors: Jarkko Tuomo Koskela; Chunli Wu; Samuli Heikki TURTINEN
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Priority date: 2023-02-13
Filing date: 2023-02-13
Publication date: 2024-08-22
Anticipated expiration: 2025-08-13
Also published as: CN120693918A

Abstract

Example embodiments of the present disclosure relate to enhancements on connected mode mobility. An apparatus receives, from a network device, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover (CHO) event at the apparatus. The apparatus determines whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event. Based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, the apparatus selects a target cell based on a cell selection rule. In this way, the UE mobility and service continuity can be guaranteed regardless of network energy saving (NES) status change of the serving cell. In addition, the implementation of NES features can be improved.

Description

ENHANCEMENT ON CONNECTED MODE MOBILITY

FIELD

Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for connected mode mobility enhancements.

BACKGROUND

Energy saving techniques have been developed at both UE side and network side in 5G NR. In particular, the energy saving implemented in terms of base station (BS) transmission and/or reception is referred to as network energy saving (NES) . It has been proposed various NES modes or statuses designed for different deployment scenarios, network conditions, and so on. During switching of NES status of a serving cell, the UE mobility from that cell may be triggered. That is, it is possible to handover the UEs camped on the serving cells to another cell.

Therefore, it is expected that UE would move out the cell immediately or faster, in order to minimize the service interruptions for the UEs and allow the network to implement energy saving features as fast as possible.

SUMMARY

In general, example embodiments of the present disclosure provide a solution of connected mode mobility enhancements.

In a first aspect of the present disclosure, there is provided an apparatus. The apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, from a network device, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the apparatus; determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.

In a second aspect of the present disclosure, there is provided an apparatus. The apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: transmitting, to a terminal device in a serving cell provided by the apparatus, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and transmitting, to the terminal device, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the terminal device.

In a third aspect of the present disclosure, there is provided a method. The method comprises: receiving, at a terminal device and from a network device, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the terminal device; determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.

In a fourth aspect of the present disclosure, there is provided a method. The method comprises: transmitting, at a network device and to a terminal device in a serving cell provided by the network device, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and transmitting, to the terminal device, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the terminal device.

In a fifth aspect of the present disclosure, there is provided a first apparatus. The apparatus comprises: means for receiving, from a second apparatus, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the first apparatus; means for determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and means for based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.

In a sixth aspect of the present disclosure, there is provided a second apparatus. The apparatus comprises: means for transmitting, to a first apparatus in a serving cell provided by the second apparatus, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and means for transmitting, to the first apparatus, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the first apparatus.

In a seventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform: receiving, from a network device, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the apparatus; determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.

In an eighth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform: transmitting, to a terminal device in a serving cell provided by the apparatus, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and transmitting, to the terminal device, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the terminal device.

In a ninth aspect of the present disclosure, there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, from a network device, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the apparatus; determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.

In a tenth aspect of the present disclosure, there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform: transmitting, to a terminal device in a serving cell provided by the apparatus, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and transmitting, to the terminal device, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the terminal device.

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

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

FIG. 2 illustrates a signaling chart for connected mode mobility in NES cell according to some example embodiments of the present disclosure;

FIG. 3 illustrates a flowchart of a method implemented at a terminal device according to some example embodiments of the present disclosure;

FIG. 4 illustrates a flowchart of a method implemented at a network device according to some example embodiments of the present disclosure;

FIG. 5 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

FIG. 6 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

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

DETAILED DESCRIPTION

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

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

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

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish functionalities of various elements. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

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

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” , means at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

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

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

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

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.

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

As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a Next Generation NodeB (NR NB) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , Integrated Access and Backhaul (IAB) node, a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology. The network device is allowed to be defined as part of a gNB such as for example in CU/DU split in which case the network device is defined to be either a gNB-CU or a gNB-DU.

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

As used herein, the term “control device” refers to any entity/function/device/apparatus for control. In some example embodiments, the control device is device used for implementing domain orchestration, network optimization and network management functions and so on.

Although functionalities described herein can be performed, in various example embodiments, in a fixed and/or a wireless network node, in other example embodiments, functionalities may be implemented in a user equipment apparatus (such as a cell phone or tablet computer or laptop computer or desktop computer or mobile IoT device or fixed IoT device) . This user equipment apparatus can, for example, be furnished with corresponding capabilities as described in connection with the fixed and/or the wireless network node (s) , as appropriate. The user equipment apparatus may be the user equipment and/or or a control device, such as a chipset or processor, configured to control the user equipment when installed therein. Examples of such functionalities include the bootstrapping server function and/or the home subscriber server, which may be implemented in the user equipment apparatus by providing the user equipment apparatus with software configured to cause the user equipment apparatus to perform from the point of view of these functions/nodes.

It has been proposed to facilitate the mobility of UE by means of conditional handover (CHO) , when NES status of the serving cell changes. The CHO is defined as a handover (HO) that is executed by the UE when one or more handover execution conditions are met. In particular, the CHO configuration may contain a configuration of at least one CHO candidate cell managed by at least one candidate gNB and execution condition (s) generated by the source gNB. The UE may start evaluating at least one execution condition upon receiving a CHO configuration. Before any CHO execution condition is satisfied, upon reception of HO command (without CHO configuration) , the UE executes the HO procedure, regardless of any previously received CHO configuration. Once a HO is executed, the UE may stop evaluating the at least one execution condition.

In an example scenario, a UE is configured with at least one CHO event that is to be triggered based on NES state and/or some NES cell specific CHO conditions. In particular, the NES status or NES mode change of a cell may trigger CHO. However, it is not always possible to have a CHO condition met at the time NES status changes, since the CHO candidates may not fulfil the quality requirements set in the CHO configuration. According to the existing CHO mechanism, if none of the candidate cells fulfil the CHO condition, it will delay the UE getting out of the cell until radio link failure (RLF) is declared, which could take a very long time (e.g., seconds, tens of seconds, etc. ) . In this case, the service continuity will be impacted, and thus the implementation outlook of NES features is lowered down.

Thus, there is a need for enhancements on connected mode mobility for the case where CHO is to be triggered based on a certain NES state or a NES state change. The enhanced mechanism is expected to ensure that the UE can get out from the serving cell.

Example Environment

FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. The communication environment 100 may be a communication network supporting NES features. The communication network 100 includes a terminal device 110 and a network device 120. Hereinafter, the terminal device 110 and the network device 120 may be also referred to as UE 110 and gNB 120, respectively.

In the communication network 100, there are a plurality of cells 12 to 18 for providing the radio coverage. As shown in FIG. 1, the terminal device 110 is located within the cell 12 and served by the network device 120. In other words, the cell 12 is a serving cell of the terminal device 110. The terminal device 110 may be in an RRC_CONNECTED mode with mobility among the cells 12 to 18. It should be understood that the cells 14 to 18 may or may not be provided by the network device 120. Thus, the embodiments of the present disclosure are not limited in this regard.

The network device 120 may provide more than one cell, which includes the serving cell 12. For sake of energy saving, the network device 120 may control the operation state of the cells. For example, the network device 120 may control the cell 12 to switch between a normal state or a non-NES state and a NES state. The cell 12 may be also controlled to switch among different NES states. Furthermore, the network device 120 may control the cell 12 to be turned off or barred for the terminal device 110. In a case where the operation state of the serving cell 12 changes to a certain NES state, an off state or a barred state, the terminal device 110 may need to hand over from the serving cell 12 or another cell.

To facilitate the mobility of the terminal device 110, the network device 120 may configure the terminal device 110 with at least one CHO event triggered based on an operation state change of the serving cell 12. The at least one CHO event may be configured for at least one candidate cell. For example, the at least one CHO event may involve a group of candidate cells 14 to 18 that are prepared for the potential handover. In addition, the CHO event may be associated with a CHO condition. If at least one of the candidate cells fulfils the CHO condition, the terminal device 110 may select a target cell from the at least one candidate cell. If no candidate cell fulfils the CHO condition, the terminal device 110 may select a target cell based on a cell selection rule, which will be discussed in detail below.

It is to be understood that the number of devices and their connections shown in FIG. 1 are only for the purpose of illustration without suggesting any limitation. The communication network 100 may include any suitable number of devices configured to implementing example embodiments of the present disclosure. Although not shown, it would be appreciated that one or more additional devices and connections may be deployed in the communication network 100.

Communications in the communication environment 100 may be implemented according to any proper communication protocol (s) , comprising, but not limited to, cellular communication protocols of the first generation (1G) , the second generation (2G) , the third generation (3G) , the fourth generation (4G) , the fifth generation (5G) , the sixth generation (6G) , and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA) , Frequency Division Multiple Access (FDMA) , Time Division Multiple Access (TDMA) , Frequency Division Duplex (FDD) , Time Division Duplex (TDD) , Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Division Multiple (OFDM) , Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and/or any other technologies currently known or to be developed in the future.

Work Principle and Example Signaling for Communication

Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

Reference is now made to FIG. 2, which illustrates a signaling chart for connected mode mobility in the NES cell according to some example embodiments of the present disclosure. As shown in FIG. 2, the process 200 involves the terminal device 110 and the network device 120. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling flow 200.

As previously described, the terminal device 110 may be in RRC_CONNECTED mode and served in the cell 12. The network device 120 supports NES features. Accordingly, the cell 12 provided by the network device 120 may operate in at least one NES state. In some cases, the cell 12 may be switch between more than one NES state. Additionally, the network device 120 may control the cell 12 to be turned off or barred for NES UE.

In some example embodiments, the network device 120 may transmit 205 a configuration of the at least one CHO event to the terminal device 110. The at least one CHO event is configured for at least one candidate cell, such as, cells 14 to 18 as shown in FIG. 1. In this case, the candidate cells 14 to 18 may be prepared for potential HO from the serving cell 12.

The at least one CHO event may be triggered based on an operation state change of the serving cell 12. For example, the at least one CHO event may be triggered based on a target operation state of the serving cell 12. Such a configuration of the at least one CHO event may be, for example, indicated via a RRC Reconfiguration message. In the context of the embodiments, the target operation state may refer to one of the following: an off state, a barred state, a NES state, etc.

In some example embodiments, the at least one CHO event may comprise an event of triggering handover based on NES, triggerHObasedOnNES.

In some example embodiments, the network device 120 may transmit 210 a configuration of a cell selection rule. The cell selection rule may be used if no CHO event configured for the at least one candidate cell fulfils the CHO condition. It should be noted that the concept “cell selection rule” is different from the concept of “radio quality criterion” . The concept of the cell selection rule indicates a selection of the target cell via either a re-establishment or a CHO procedure based on the operation state of the serving cell changing to the target operation state, while the concept of radio quality criterion is specified by at least one of the following factors, signal strength, signal quality, PLMN selection, service type, etc.

It should be understood that for the sake of description, in the example embodiments, the cell selection rule is described as being configured separately from the CHO events. However, in some other example embodiments, such a cell selection rule may be configured as a part of the CHO events, or considered as one of the CHO events, but is used in case of the rest of the configured CHO events not fulfilling the CHO condition. Therefore, the present disclosure is not limited in this regard.

In a case where the operation state change, the network device 120 transmits 215 an indication related to an operation state change of the serving cell 12. The indication triggers the at least one CHO event at the terminal device 110. Such an indication may be, for example, indicated via a NESState indication.

In some example embodiments, the indication related to the operation state change of the serving cell 12 may be a first indication indicating that the operation state changes to an off state. For example, in a case where the cell 12 is turned off, the network device 120 may transmit the first indication to the terminal device 110.

In some example embodiments, the indication related to the operation state change of the serving cell 12 may be a second indication indicating that the operation state changes to a target NES state. For example, in a case where the cell is changed to a certain NES state, the network device 120 may transmit the second indication to the terminal device 110.

In some example embodiments, the indication related to the operation state change of the serving cell 12 may be a third indication indicating that the operation state changes to a barred state. For example, in a case where the cell 12 is barred for UE, the network device 120 may transmit the third indication to the terminal device 110.

Upon determining the operation state change based on the indication, the terminal device 110 determines 220 whether the at least one CHO event configured for at least one candidate cell fulfils the CHO condition associated with the CHO event. If at least one CHO event fulfils the CHO condition, the terminal device 110 may perform CHO from the serving cell 12 to a corresponding candidate cell that is configured with the CHO event. By way of example, if a CHO event configured for the cell 14, among the candidate cells 14 to 18, fulfils the CHO condition, the termina device 110 may perform CHO from the serving cell 12 to the target cell 14.

Otherwise, if no CHO event configured for the at least one candidate cell fulfils the CHO condition, the terminal device 110 selects 225 a target cell based on a cell selection rule.

In some example embodiments where no CHO event configured for the at least one candidate cell fulfils the CHO condition, the terminal device 110 may declare a radio link failure (RLF) based on the cell selection rule. Accordingly, the terminal device 110 may trigger the RRC re-establishment procedure. The terminal device 110 may then select the target cell via the re-establishment procedure.

In this case, UE may immediately, or with small delay, perform RRC re-establishment, e.g., by declaring RLF, which will trigger UE cell selection and RRC Re-establishment procedure to be triggered. As one option, in this case, the RLF cause may be set to ‘HO failure’ .

Additionally, or alternatively, the cell selection rule may further comprise prioritizing the at least one candidate cell configured with the CHO event during the re-establishment procedure. Therefore, in performing re-establishment, the terminal device 110 may prioritize the candidate cells 14 to 18 that are configured with CHO since those cells have been prepared by the network.

In some example embodiments where no CHO event configured for the at least one candidate cell fulfils the CHO condition, the terminal device 110 may determine whether the at least one CHO event configured for the at least one at least one candidate cell fulfils a radio quality criterion. In the embodiments of the present disclosure, the radio quality criterion is used for evaluating the radio quality of a cell. In particular, the radio quality may be characterized by at least one of the following factors, signal strength, signal quality, PLMN selection, service type, etc. It should be understood that the radio quality criterion may or may not be part of a cell selection criterion.

If at least one CHO event configured for at least one candidate cell fulfils the radio quality criterion, the terminal device 110 may perform CHO to one of the at least one candidate cell.

In this way, the UE falls back to consider the cell selection threshold as a CHO condition threshold, if none of the configured conditions are met. If at least one candidate cell configured with CHO event (e.g., the cell 18) fulfils the radio quality criterion, the terminal device 110 may select that cell (e.g., the cell 18) as the target cell and perform CHO to the target cell. Additionally, or alternatively, the UE may further indicate or report a successful CHO to the target cell 18 without fulfilling the CHO condition. For example, such an indication or report may be transmitted in a RRC ReconfigurationComplete message.

In some example embodiments, the re-establishment or CHO with the cell selection threshold may be limited to the case where the NES state is changed to turn off the cell 12 or where the cell 12 is indicated as barred for the terminal device 110. For other NES state changes, the terminal device 110 may still stay in the serving cell 12 if CHO condition is not fulfilled.

In some example embodiments, a list of cells or frequencies which should be prioritized for cell selection in a case where no CHO condition is fulfilled may be configured by the network. To this end, the network device 120 may transmit at least one of a configuration of a candidate cell list or a configuration of a candidate frequency list to be prioritized for cell selection due to no CHO condition being fulfilled. The target cell is selected from the candidate cell list or associated with one of the candidate frequency list. Furthermore, the candidate cell list and/or the candidate frequency list may be event specific.

To implement the CHO event that is triggered based on the indication related to the operation state change (e.g., the NES status change or cell barred) , new events that are triggered based on the indication of NES status change or cell barred may be added, or alternatively, at least one extra condition may be appended to existing events. An example extension is shown below for an event. It should be understood that the example extension is also applicable to any event.

Table 1. example event and/or conditions

The example trigger shown above may be configured for the event triggerHObasedOnNES, which is to be triggered if UE received a NES indication and some of the candidate cells fulfils all the criteria (e.g., radio criteria) .

It might happen that no event triggers CHO, even if the serving cell 12 is changed to the “NES state” . However, it does not make sense to stay on the current cell. In this case, the terminal device 110 may perform forced RRC re-establishment. This configuration could be also event specific, that is, only if a specific CHO event is configured with (see triggerReestablishment) parameter in the above example shown in table 1, it would trigger RRC re-establishment by the terminal device 110.

According to some example embodiments of the present disclosure, there is provided a solution of connected mode mobility. With the solution, the connected mode UEs can be handed over after the serving cell is turned off. In other words, the mobility of the connected mode UEs is independent of the operation state change of the serving cell. Thus, the UE autonomous mobility enables a faster cell off, and signaling to HO each UE individually can be avoided.

It should be understood that some of the steps in process 200 are optional or can be omitted, and the order of the steps is given for an illustrative purpose. Thus, the embodiments of the present disclosure are not limited in this regard.

The example descriptions on the embodiments of the present disclosure as well as possible standardization impacts and information model in the standards are shown as below. However, it should be understood that the details, values, configurations in the following description are given as example implementations, not limitations to the embodiments of the present disclosure.

Example Methods

FIG. 3 illustrates a flowchart of a method 300 implemented at a terminal device according to some example embodiments of the present disclosure. For example, the terminal device may include a UE. For the purpose of discussion, the method 300 will be described from the perspective of the terminal device 110 in FIG. 1.

At block 310, the terminal device 110 receives, from a network device 120, an indication related to an operation state change of the serving cell 12. The indication may trigger at least one CHO event at the terminal device 110.

In some example embodiments, the at least one CHO event may be configured by the network. In these embodiments, the terminal device 110 may receive, from the network device 120, a configuration of the at least one CHO event configured for the at least one candidate cell. The at least one CHO event configured for the at least one candidate cell may be triggered based on a target operation state of the serving cell 12.

In some example embodiments, the terminal device 110 may receive, from the network device 120, a configuration of the cell selection rule. The cell selection rule may be used if no CHO event configured for the at least one candidate cell fulfils the CHO condition.

In some example embodiments, the indication related to an operation state change of the serving cell 12 may comprise at least one of the following: a first indication indicating that the operation state changes to an off state, a second indication indicating that the operation state changes to a target network energy saving state, or a third indication indicating that the operation state changes to a barred state.

At block 320, the terminal device 110 determines whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event.

At block 330, based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, the terminal device 110 selects a target cell based on a cell selection rule.

In some example embodiments, the cell selection rule may comprise a rule for selecting the target cell via one of a re-establishment or a CHO procedure based on the operation state changing to a target operation state for the serving cell 12. In this case, the target operation state may comprise one of the following: an off state, a barred state, a target NES state.

In some example embodiments, the rule for selecting the target cell may comprise: based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, triggering a RRC re-establishment; and selecting the target cell via the re-establishment procedure.

In some example embodiments, the rule for selecting the target cell may further comprise: based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, declaring a radio link failure that triggers the re-establishment procedure.

In some example embodiments, the cell selection rule may further comprise prioritizing the at least one candidate cell during the re-establishment procedure.

In some example embodiments, the rule for selecting the target cell comprises: based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, determining whether the at least one CHO event configured for the at least one at least one candidate cell fulfils a radio quality criterion; and based on determining that the at least one candidate cell fulfils the radio quality criterion, performing CHO to one of the at least candidate cell.

In some example embodiments, the method 300 may further comprise: transmitting, to the network device 120, a report of a successful CHO to the target cell without fulfilling the CHO condition.

In some example embodiments, the method 300 may further comprise: receiving, from the network device 120, at least one of a configuration of a candidate cell list or a configuration of a candidate frequency list to be prioritized for cell selection due to no CHO condition being fulfilled, wherein the target cell is selected from the candidate cell list or associated with one of the candidate frequency list.

In some example embodiments, the at least one CHO event may comprise an event of triggering handover based on network energy saving, triggerHObasedOnNES.

In some example embodiments, the terminal device 110 may be in an RRC_CONNECTED mode.

FIG. 4 illustrates a flowchart of an example method 400 implemented at a network device in accordance with some example embodiments of the present disclosure. For example, the network device may include a gNB. For the purpose of discussion, the method 400 will be described from the perspective of the network device 120 in FIG. 1.

At 410, the network device 120 transmits, to a terminal device 110 in a serving cell 12 provided by the network device 120, a configuration of a cell selection rule. The cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition.

At 420, the network device 120 transmits, to the terminal device 110, an indication related to an operation state change of the serving cell. The indication triggers at least one CHO event at the terminal device 110.

In some example embodiments, the method 400 may further comprise: transmitting, to the terminal device 110, a configuration of the at least one CHO event configured to the at least one candidate cell, the at least one CHO event configured for the at least one candidate cell is triggered based on a target operation state of the serving cell.

In some example embodiments, the indication related to an operation state change of the serving cell may comprise at least one of the following: a first indication indicating that the operation state changes to an off state, a second indication indicating that the operation state changes to a target network energy saving state, or a third indication indicating that the operation state changes to a barred state.

In some example embodiments, the cell selection rule may indicate at least one of the following: a selection of a target cell via a re-establishment procedure based on the operation state of the serving cell changing to a target operation state, a selection of the target cell via a CHO procedure based on the operation state of the serving cell changing to the target operation state and a radio quality criterion, prioritizing at least one candidate cell configured with the CHO event during the selection of the target cell.

In some example embodiments, the target operation state may comprise one of the following: an off state, a barred state, a target NES state.

In some example embodiments, the method 400 may further comprise: receiving, from the terminal device 110, a report of a successful CHO to the target cell without fulfilling the CHO condition.

In some example embodiments, the method 400 may further comprise: transmitting, to the terminal device 110, at least one of a configuration of a candidate cell list or a configuration of a candidate frequency list to be prioritized for cell selection due to no CHO condition being fulfilled, wherein the target cell is selected from the candidate cell list or associated with one of the candidate frequency list.

In some example embodiments, the at least one CHO event comprises an event of triggering handover based on network energy saving, triggerHObasedOnNES.

In some example embodiments, a first apparatus capable of performing any of the method 300 (for example, the terminal device 110 in FIG. 1) may comprise means for performing the respective operations of the method 300. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the terminal device 110 in FIG. 1.

In some example embodiments, the first apparatus comprises: means for receiving, from a second apparatus, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the first apparatus; means for determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and means for based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.

In some example embodiments, the first apparats further comprises: means for receiving, from the second apparatus, a configuration of the at least one CHO event configured for the at least one candidate cell, the at least one CHO event configured for the at least one candidate cell is triggered based on a target operation state of the serving cell.

In some example embodiments, the first apparats further comprises: means for receiving, from the second apparatus, a configuration of the cell selection rule, the cell selection rule is used if no CHO event configured for the at least one candidate cell fulfils the CHO condition.

In some example embodiments, the indication related to an operation state change of the serving cell comprises at least one of the following: a first indication indicating that the operation state changes to an off state, a second indication indicating that the operation state changes to a target network energy saving state, or a third indication indicating that the operation state changes to a barred state.

In some example embodiments, the cell selection rule comprises a rule for selecting the target cell via one of a re-establishment or a CHO procedure based on the operation state changing to a target operation state for the serving cell, wherein the target operation state comprises one of the following: an off state, a barred state, a target network energy saving state.

In some example embodiments, the rule for selecting the target cell further comprises: based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, triggering a RRC re-establishment; and selecting the target cell via the re-establishment procedure.

In some example embodiments, the rule for selecting the target cell further comprises: based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, declaring a radio link failure that triggers the re-establishment procedure.

In some example embodiments, the cell selection rule further comprises prioritizing the at least one candidate cell during the re-establishment procedure.

In some example embodiments, the first apparatus further comprises: means for transmitting, to the second apparatus, a report of a successful CHO to the target cell without fulfilling the CHO condition.

In some example embodiments, the first apparatus further comprises: means for receiving, from the second apparatus, at least one of a configuration of a candidate cell list or a configuration of a candidate frequency list to be prioritized for cell selection due to no CHO condition being fulfilled, wherein the target cell is selected from the candidate cell list or associated with one of the candidate frequency list.

In some example embodiments, the first apparatus comprises a terminal device in an RRC_CONNECTED mode.

In some example embodiments, a second apparatus capable of performing any of the method 400 (for example, the network device 120 in FIG. 1) may comprise means for performing the respective operations of the method 400. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the network device 120 in FIG. 1.

In some example embodiments, the second apparatus comprises: means for transmitting, to a first apparatus in a serving cell provided by the second apparatus, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and means for transmitting, to the first apparatus, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the first apparatus.

In some example embodiments, the second apparatus further comprises: means for transmitting, to the first apparatus, a configuration of the at least one CHO event configured to the at least one candidate cell, the at least one CHO event configured for the at least one candidate cell is triggered based on a target operation state of the serving cell.

In some example embodiments, the cell selection rule indicates at least one of the following: a selection of a target cell via a re-establishment procedure based on the operation state of the serving cell changing to a target operation state, a selection of the target cell via a CHO procedure based on the operation state of the serving cell changing to the target operation state and a radio quality criterion, prioritizing at least one candidate cell configured with the CHO event during the selection of the target cell.

In some example embodiments, the target operation state comprises one of the following: an off state, a barred state, a target network energy saving state.

In some example embodiments, the second apparatus further comprises: means for receiving, from the first apparatus, a report of a successful CHO to the target cell without fulfilling the CHO condition.

In some example embodiments, the second apparatus further comprises: means for transmitting, to the first apparatus, at least one of a configuration of a candidate cell list or a configuration of a candidate frequency list to be prioritized for cell selection due to no CHO condition being fulfilled, wherein the target cell is selected from the candidate cell list or associated with one of the candidate frequency list.

FIG. 5 is a simplified block diagram of a device 500 that is suitable for implementing example embodiments of the present disclosure. The device 500 may be provided to implement an electronic device, for example, the terminal device 110, the network devices 112 to 130 as shown in FIG. 1. As shown, the device 500 includes one or more processors 510, one or more memories 520 coupled to the processor 510, and one or more communication modules 540 coupled to the processor 510.

The communication module 540 is for bidirectional communications. The communication module 540 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 540 may include at least one antenna.

The processor 510 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 500 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 520 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 524, an electrically programmable read only memory (EPROM) , a flash memory, a hard disk, a compact disc (CD) , a digital video disk (DVD) , an optical disk, a laser disk, and other magnetic storage and/or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 522 and other volatile memories that will not last in the power-down duration.

A computer program 530 includes computer executable instructions that are executed by the associated processor 510. The instructions of the program 530 may include instructions for performing operations/acts of some example embodiments of the present disclosure. The program 530 may be stored in the memory, e.g., the ROM 524. The processor 510 may perform any suitable actions and processing by loading the program 530 into the RAM 522.

The example embodiments of the present disclosure may be implemented by means of the program 530 so that the device 500 may perform any process of the disclosure as discussed with reference to FIG. 1 to FIG. 4. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some example embodiments, the program 530 may be tangibly contained in a computer readable medium which may be included in the device 500 (such as in the memory 520) or other storage devices that are accessible by the device 500. The device 500 may load the program 530 from the computer readable medium to the RAM 522 for execution. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory, ” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs.ROM) .

FIG. 6 shows an example of the computer readable medium 600 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 600 has the program 530 stored thereon.

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

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

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

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

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

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

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

Claims

An apparatus, comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

receiving, from a network device, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the apparatus;

determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and

based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.
The apparatus of claim 1, wherein the apparatus is further caused to perform:

receiving, from the network device, a configuration of the at least one CHO event configured for the at least one candidate cell, the at least one CHO event configured for the at least one candidate cell is triggered based on a target operation state of the serving cell.
The apparatus of claim 1, wherein the apparatus is further caused to perform:

receiving, from the network device, a configuration of the cell selection rule, the cell selection rule is used if no CHO event configured for the at least one candidate cell fulfils the CHO condition.
The apparatus of claim 1, wherein the indication related to an operation state change of the serving cell comprises at least one of the following:

a first indication indicating that the operation state changes to an off state,

a second indication indicating that the operation state changes to a target network energy saving state, or

a third indication indicating that the operation state changes to a barred state.
The apparatus of claim 1, wherein the cell selection rule comprises a rule for selecting the target cell via one of a re-establishment or a CHO procedure based on the operation state changing to a target operation state for the serving cell,

wherein the target operation state comprises one of the following: an off state, a barred state, a target network energy saving state.
The apparatus of claim 5, wherein the rule for selecting the target cell comprises:

based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, triggering a RRC re-establishment; and

selecting the target cell via the re-establishment procedure.
The apparatus of claim 6, wherein the rule for selecting the target cell further comprises:

based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, declaring a radio link failure that triggers the re-establishment procedure.
The apparatus of claim 6, wherein the cell selection rule further comprises prioritizing the at least one candidate cell during the re-establishment procedure.
The apparatus of any of claims 1 to 5, wherein the rule for selecting the target cell comprises:

based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, determining whether the at least one CHO event configured for the at least one at least one candidate cell fulfils a radio quality criterion;

based on determining that the at least one candidate cell fulfils the radio quality criterion, performing CHO to one of the at least candidate cell.
The apparatus of claim 9, wherein the apparatus is further caused to perform:

transmitting, to the network device, a report of a successful CHO to the target cell without fulfilling the CHO condition.
The apparatus of any of claims 1 to 5, wherein the apparatus is further caused to perform:

receiving, from the network device, at least one of a configuration of a candidate cell list or a configuration of a candidate frequency list to be prioritized for cell selection due to no CHO condition being fulfilled, wherein the target cell is selected from the candidate cell list or associated with one of the candidate frequency list.
The apparatus of any of claims 1 to 11, wherein the at least one CHO event comprises an event of triggering handover based on network energy saving, triggerHObasedOnNES.
The apparatus of any of claims 1 to 12, wherein the apparatus comprises a terminal device in an RRC_CONNECTED mode.
An apparatus, comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

transmitting, to a terminal device in a serving cell provided by the apparatus, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and

transmitting, to the terminal device, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the terminal device.
The apparatus of claim 14, wherein the apparatus is further caused to perform:

transmitting, to the terminal device, a configuration of the at least one CHO event configured to the at least one candidate cell, the at least one CHO event configured for the at least one candidate cell is triggered based on a target operation state of the serving cell.
The apparatus of claim 14 or claim 15, wherein the indication related to an operation state change of the serving cell comprises at least one of the following:

a first indication indicating that the operation state changes to an off state,

a second indication indicating that the operation state changes to a target network energy saving state, or

a third indication indicating that the operation state changes to a barred state.
The apparatus of claim 14, wherein the cell selection rule indicates at least one of the following:

a selection of a target cell via a re-establishment procedure based on the operation state of the serving cell changing to a target operation state,

a selection of the target cell via a CHO procedure based on the operation state of the serving cell changing to the target operation state and a radio quality criterion,

prioritizing at least one candidate cell configured with the CHO event during the selection of the target cell.
The apparatus of claim 17, wherein the target operation state comprises one of the following: an off state, a barred state, a target network energy saving state.
The apparatus of claim 17, wherein the apparatus is further caused to perform:

receiving, from the terminal device, a report of a successful CHO to the target cell without fulfilling the CHO condition.
The apparatus of claim 17, wherein the apparatus is further caused to perform:

transmitting, to the terminal device, at least one of a configuration of a candidate cell list or a configuration of a candidate frequency list to be prioritized for cell selection due to no CHO condition being fulfilled, wherein the target cell is selected from the candidate cell list or associated with one of the candidate frequency list.
The apparatus of any of claims 14 to 20, wherein the at least one CHO event comprises an event of triggering handover based on network energy saving, triggerHObasedOnNES.
A method comprising:

receiving, at a terminal device and from a network device, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the terminal device;

determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and

based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.
A method comprising:

transmitting, at a network device and to a terminal device in a serving cell provided by the network device, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and

transmitting, to the terminal device, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the terminal device.
A first apparatus comprising:

means for receiving, from a second apparatus, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the first apparatus;

means for determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and

means for based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.
A second apparatus comprising:

means for transmitting, to a first apparatus in a serving cell provided by the second apparatus, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and

means for transmitting, to the first apparatus, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the first apparatus.
A computer readable medium comprising program instructions for causing an apparatus to perform:

receiving, from a network device, an indication related to an operation state change of a serving cell, the indication triggering at least one conditional handover, CHO, event at the apparatus;

determining whether the at least one CHO event configured for at least one candidate cell fulfils a CHO condition associated with the CHO event; and

based on determining that no CHO event configured for the at least one candidate cell fulfils the CHO condition, selecting a target cell based on a cell selection rule.
A computer readable medium comprising program instructions for causing an apparatus to perform:

transmitting, to a terminal device in a serving cell provided by the apparatus, a configuration of a cell selection rule, wherein the cell selection rule is used if no CHO event configured for at least one candidate cell fulfils a CHO condition; and

transmitting, to the terminal device, an indication related to an operation state change of the serving cell, the indication triggering at least one CHO event at the terminal device.