Methods, apparatuses, and computer program products for network slice based conditional fast handover

Abstract

Various example implementations relate to methods and apparatuses for network slice based conditional fast handover An apparatus may be configured to receive, from a source network element, a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, wherein the message comprises a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or more network slice specific configurations associated with one or more network slices supported at the one or more candidate target cells. The apparatus may be configured to evaluate the triggering condition and the slice specific configurations to select at least one target cell of the one or more candidate target cells for the conditional handover. And the apparatus may be configured to initiate a random access procedure to establish a radio resource connection with the selected at least one target cell.

Description

METHODS, APPARATUSES, AND COMPUTER PROGRAM PRODUCTSFOR NETWORK SLICE BASED CONDITIONAL FAST HANDOVERTECHNICAL FIELD

[0001] Various example implementations described herein generally relate to mobility in a wireless communication system, and more particularly, to methods and apparatuses for network slice based conditional fast handover.BACKGROUND

[0002] A wireless communication network (e.g., 5G NR network) may comprise a plurality of base stations (e.g., gNB) that serve one or more cells across a particular area. In case a mobile terminal such as a user equipment (UE) moves within a cell or through different cells (e.g., different radio coverage areas) of one or more gNBs, it is desirable to keep the UE’s traffic uninterrupted. To this end, cell change or switch, for example handover, occurs to maintain connectivity between the UE and the serving radio access network (RAN).Brief Description

[0003] In a first aspect, an example of a terminal device is provided. The terminal device may comprise at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to: receive, from a source network element, a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, wherein the message comprises a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or more network slice specific configurations associated with one or more network slices supported at the one or more candidate target cells;evaluate the triggering condition and the slice specific configurations to select at least one target cell of the one or more candidate target cells for the conditional handover; and initiate a random access procedure to establish a radio resource connection with the selected at least one target cell.

[0004] In a second aspect, an example of a network element serving as a source network element for a conditional handover procedure is provided. The network element may comprise at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network element at least to: receive, from at least one target network element, a baseline configuration for the conditional handover procedure in association with one or more candidate target cells served by the at least one target network element, and one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells; determine for a terminal device, a combined configuration comprising the baseline configuration and the one or more network slice specific configurations; determine, for the terminal device, a message in association with the conditional handover procedure, the message comprising the combined configuration, and at least one triggering condition for the conditional handover procedure; and transmit the message to the terminal device.

[0005] In a third aspect, an example of a network element serving as a target network element for a conditional handover procedure is provided. The network element may comprise at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network element at least to: determine a radio resource control configuration comprising a baseline configuration for the conditional handover procedure in association with one or more candidate target cells served by the network element, and one or more network slice specific configurations associated with one or more slices served in the one or more candidate target cells for the conditional handover procedure; and transmit the radio resource control configuration to a source network element of the conditional handover of a terminal device from the source network element tothe at least one of the one or more candidate target cells.

[0006] Some examples of methods, apparatus, computer readable medium and computer program products are also provided. Such example implementations generally correspond to the example implementations in the above aspects and a repetitive description thereof is omitted here for convenience.

[0007] These and other features and advantages of the present disclosure will be apparent from the following detailed description when read in conjunction with the accompanying drawings, which illustrate, examples of the present disclosure. This disclosure is intended to be read in its entirety such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable unless the context of the disclosure clearly dictates otherwise.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Some example implementations will now be described, by way of nonlimiting examples, with reference to the accompanying drawings.

[0009] Fig. 1 illustrates a deployment of a communication network according to some example implementations of the present disclosure.

[0010] Fig. 2 is a signaling chart of a fast conditional handover procedure, according to some example implementations.

[0011] Fig. 3 illustrates an example of a method for a fast conditional handover procedure.

[0012] Fig. 4 illustrates an example of a method for a fast conditional handover procedure.

[0013] Fig. 5 illustrates an example of a method for a fast conditional handover procedure.

[0014] Fig. 6 illustrates an example of a terminal device.

[0015] Fig. 7 illustrates an example of a network element.DETAILED DESCRIPTION

[0016] Herein below, some examples are described in detail with reference to the accompanying drawings. The following description includes details that clarify various concepts. However, it will be apparent to those skilled in the art that these concepts may also be practiced without these details.

[0017] In the following, various examples will be described using, as an example of an access architecture, a radio access architecture based on long term evolution advanced (LTE-A), new radio (NR, 5G), 5G Advanced, or sixth generation (6G) without restricting to such an architecture, however. It is obvious for a person skilled in the art that the examples may also be applied to other kind of communication networks having suitable means by adjusting parameters and procedures appropriately.

[0018] As used herein, the term “network element” or “network element” may refer to a radio access network (RAN) device. The RAN device may include for example a base station that can provide cells or coverage, through which terminal devices can access the network or receive services. The base station may be implemented as an evolved node B (eNB), a next generation eNB (ng-eNB), a next generation node B (gNB), or a beyond 5G base station. The base station may be embodied as a macro base station, a relay node, or a low power node such as a pico base station or a femto base station. The base station may consist of several distributed network units, such as a baseband unit (BBU), one or more remote radio heads (RRHs) or remote radio units (RRUs). In some architectures, the BBU may be split into a central unit (CU), and one or more distributed units (DUs) such as a server, host or node. The number and functions of these distributed units depend on the selected split RAN architecture.

[0019] As used herein, the term “terminal device” or “user equipment” (UE) may refer to any entities or devices that can wirelessly communicate with the network elements or with each other. Examples of the terminal device can include a mobile phone, a mobile terminal (MT), a mobile station (MS), a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), a computer, a wearabledevice, an on-vehicle communication device, a machine type communication (MTC) device, a device-to-device (D2D) communication device, a vehicle-to- everything (V2X) communication device, a sensor and the like. The term “terminal device” can be used interchangeably with a UE, a user terminal, a mobile terminal, a mobile station, or a wireless device.

[0020] Fig. 1 illustrates a deployment of a communication network according to various example implementations of the present disclosure. As shown, communication network 100 may include a radio access network (RAN) 120 with one or more radio access network elements (e.g., base stations 122, 124) configured to provide cells to interact with UEs 110 (only one is shown), and a core network (CN) 130. In the context of a 5G network, RAN 120 is a next generation radio access network (NG-RAN), and CN 130 is a 5G core network (5GC). In some deployments, base stations 122, 124 may be connected to one another by a network interface, such as an Xn interface. Similarly, the base stations may be connected to CN 130 by a network interface, e.g., a NG interface.

[0021] In operations, UE 110 may be configured to connect to one or more of base stations (or node Bs) 122, 124 according to its radio access technology to thereby access CN 130, or to access an external data network, such as the Internet. For example, UE 110 may camp on a cell served by base station 122 and establish a radio resource control (RRC) connection with base station 122. UE 110 may communicate with base station 122 on uplink (UL) and downlink (DL) channels. Base station 122 may be referred to as a serving base station for UE 110, and base station 124 that is proximate to serving base station 122 may be referred to as a neighboring base station. It should be understood that, although only one neighboring base station is shown, in actual application, there may be more than two neighboring base stations near the serving base station.

[0022] For UE 110 in an RRC connected state, it is generally desirable to keep the UE’s traffic uninterrupted when the UE moves across different cells of one or more base stations 122, 124. To continuously monitor the UE’s radio link condition toward a serving cell and initiate change of the cell such that the UE has the bestpossible link toward a base station, the UE may be configured to measure received signal level and quality from the serving base station as well as a list of configured neighboring cells, and report the results to the serving base station periodically and / or whenever a configured reporting event is met. These measurement may then be evaluated at the serving base station, and may result in a handover (HO) of the UE from the serving cell provided by the serving base station (also referred to as a handover source network element), to a new cell provided by a target base station (also referred to as a handover target network element).

[0023] A conventional handover procedure, e.g., basic handover (BHO or simply a handover, HO) may start with an UE transmitting a measurement report (MR) indicating relevant measurements for one or more cells provided by one or more handover candidate target base station(s) to its serving base station (e.g. base station 122). Upon reception of such a measurement report, the source serving base station may decide to initiate the handover procedure, e.g., based on the content of the measurement report and possible other information such as loading information, and initiate a handover preparation in which the serving base station sends a handover request with a current configuration of UE 110 to the handover candidate target base station (e.g. base station 124) controlling a target cell. In some cases, the handover request may be sent over an Xn interface between the handover source serving base station and the handover candidate target base station. In case there is no Xn interface between these two base stations, the handover candidate target base station may be accessed over an access and mobility management function (AMF) in core network 130.

[0024] If the preparation is successful, i.e. candidate target base station 124 accepts the handover request, the handover source base station may send to UE 110, a handover command that may comprise configuration for initial access to the target cell. As soon as UE 110 receives the handover command, it may attempt to obtain downlink and uplink synchronization with handover candidate target base station 124, and thereafter complete the handover procedure.

[0025] In the case of a conditional handover (CHO), UE 110 may be configuredwith a CHO command containing the target cell configuration and one or more CHO conditions for carrying out the handover to one or more cells. This condition may, for example, comprise a condition of a measured reference signal received power (RSRP), or reference signal received quality (RSRQ) for the serving cell falling below a predefined threshold, and / or the RSRP / RSRQ of the target cell being above a given threshold. Upon receipt of the handover command, UE 110 may not immediately try to access the target cell. Instead, UE 110 may monitor or evaluate if the CHO condition is met for a specific target cell, and only then attempt to access the target cell.

[0026] The CHO enables UE 110 to execute the handover without the need of serving base station 122 to trigger the handover execution. Compared to conventional BHO, CHO may reduce the number of handover failure (HOF) and / or radio link failure (REF) during handover as target cell(s) of handover candidate target base station 124 may be prepared earlier, and UE 110 may start handover execution as soon as a CHO condition is met. As a drawback, in CHO, decoupling handover preparation and execution may lead to unnecessary handover preparation and inefficient dedicated resource reservation at the network. Additionally, during CHO preparations, the UE may be configured with information on multiple target cells and may thus face an issue with selecting one or some of target cells for handover among multiple target cells meeting the handover condition. Moreover, as the service demand of the UE may change, there may be a mismatch at execution time.

[0027] Example implementations of the present disclosure provide support for enhanced and fast mobility use cases, such as inter-node handover or the like. Some example implementations provide fast conditional handover procedures that employ a baseline radio resource control (RRC) configuration and one or more network slice-specific configurations to save time and resources used in preparing a target cell.

[0028] Fig. 2 is a signaling chart of a fast conditional handover procedure, according to some examples. As shown, an example network infrastructure utilizedfor the CHO procedure comprises at least UE 110, source network element 122, and at least one target network element 124. In some examples, the source network element and target network element may serve one or more cells, and each cell may support one or more network slices.

[0029] Referring to Fig. 2, at 202, target network element 124 may determine (e.g. generate) and share an RRC configuration for the CHO with handover source network element 122, without a previous handover request from the handover source network element. The RRC configuration may be sent to the source network element in a RAN node configuration update message (e.g., an Xn NG-RAN node Configuration Update message), or any other suitable (existing or new) message. The source network element may, at 204, send a corresponding acknowledgement message (e.g., RAN node configuration update ACK) back to the handover candidate target network element.

[0030] RRC configuration determined by the handover candidate target network element may comprise a baseline configuration for a CHO procedure in association with one or more candidate target cells supported or served by target network element 124, and one or more network slice-specific configurations associated with one or more network slices served in the one or more candidate target cells for the CHO. One or more network slice-specific configurations may be associated with one or more network slice groups served in the one or more candidate target cells for the CHO. One or more network slice groups can be in the form of network slice access stratum (AS) groups (NS AG). The RRC configuration may be divided into these two parts to reduce its size and thereby load requirements. The first part may be a cell specific part, e.g., common for each of the multiple candidate target cells served by target network element 124, and the second part may be network slicespecific. With this configuration information, source network element 122 may be aware of the network slice support of the potential target cells and enable a slicebased CHO for UE 110.

[0031] In some examples, a baseline configuration may comprise a pool (list) of one or more cell radio network temporary identifiers (C-RNTIs) that can beused / controlled (to assign to UE 110) by handover source network element 122 in case of handover to a radio cell provided / controlled (e.g., served) by handover target network element 124. The pool of C-RNTIs may be predetermined, preconfigured or pre-reserved at the handover candidate target network element. Any one of the C-RNTIs selected (by source network element 122) from this pool and assigned to UE 110 may be later readily recognizable by the handover candidate target network element during any suitable subsequent process.

[0032] In some examples, a baseline configuration may further comprise a pool (list) of one or more random access preambles (herein also referred to as RACH preambles) that can be used for a CHO procedure. The pool of RACH preambles, aka PRACH preambles, may also be predetermined, preconfigured or pre-reserved at handover candidate target network element 124. Any one of the preambles selected (by source network element 122) from this pool and assigned to UE 110 may be later recognizable by the handover candidate target network element during the subsequent synchronization / random access process.

[0033] In some examples, a network slice specific configuration may comprise an identifier (ID) of the one or more network slices served in the one or more candidate target cells of target network element 124. For example, the identifier (ID) may comprise network slice selection assistance information (NSSAI), single-NSSAI (S-NSSAI), slice service type (SST), or slice differentiator (SD). In addition, or alternatively, the network slice specific configuration may comprise an identifier of a slice group, for example, a network slice access stratum group identifier (NS AG ID).

[0034] In some examples, a network slice-specific configuration may further comprise a network slice-specific baseline configuration associated with a respective slice identifier or slice group identifier. For example, the network slice specific baseline configuration may comprise a dedicated resource for the network slice or the slice group, a radio bearer associated with the network slice, and / or quality of service (QoS) parameters associated with the network slice or bearer. With this configuration information, source network element 122 may be aware ofwhich candidate target cell(s) will most likely best serve UE 110, and thus may be able to prioritize specific target cells for the conditional handover execution.

[0035] In some examples, a network slice-specific configuration may be provided to source network element 122 for each cell of target network element 124. As target network element 124 may provide more than one candidate target radio cell, it may be configured to generate RRC configurations for respective ones of its target radio cells. These RRC configurations may be transmitted to source network element 122 as separate suitable messages, or as a single (e.g., aggregated or the like) suitable message. In addition to or alternatively, when network slices served in the candidate target cells of target network element 124 are at least substantially equivalent (e.g., same) in a tracking area (TA) or a cell group, network slice specific configurations associated with one or more network slices served in the candidate target cells may be provided on a TA basis or a cell group basis to reduce signaling overhead.

[0036] At 206, source network element 122 may configure UE 110 with measurement and reporting configuration, for example, through explicit signaling (e.g., RRCReconfiguration) to the UE, based on the measConfig parameter of the information element (IE) MeasConfig. Then, at 208, UE 110 may perform a radio resource management (RRM) measurement for one or more neighboring radio cells and send a measurement report indicating relevant measurements for one or more candidate target cells provided (e.g., served) by target network element 124.

[0037] At 210, source network element 122 may determine a combined configuration that comprises a part of or all the baseline configuration (received from target network element 124) and one or more network slice specific configurations usable for UE 110 to select an appropriate target cell during CHO execution.

[0038] In some examples, network slice specific configurations (also referred to herein as modified network slice specific configurations) may be determined based on the network slice specific configuration(s) received from target network element 124 (also referred to herein as first network slice specific configuration), andsecond network slice specific configuration(s) associated with the network slice(s) used by UE 110 (e.g., currently required by UE 110 and supported at source network element 122). For example, based on the first and second configurations, source network element 122 may be aware which network slice(s) required by UE 110 can be supported by which candidate target cell(s) served by target network element 124, and thus may determine the modified network slice specific configuration(s) in association with these network slice(s). For different UEs, depending on the supported network slice(s), the modified network slice specific configuration(s) will vary. In other words, the modified configuration is UE specific which depends on the combination of network slices the UE requires or uses. In an example, if the first network slice specific configuration is received on a slice group basis, the determined modified network slice configuration can be also for a slice group, e.g., an NSAG.

[0039] In some examples, a modified network slice specific configuration may comprise an identifier of at least one of the one or more network slices or a network slice group (e.g., network slice(s) used by UE 110 and simultaneously supported at one candidate target cell or tracking area), and a network slice specific parameter associated with the at least one network slice or network slice group. The identifier of the network slice may be, as discussed earlier, e.g., an S-NSSAI or an NSAG ID. The network slice specific parameter may be applied by UE 110 during CHO evaluation for indicating a priority of the one or more candidate target cells. For example, source network element 122 may decide to prioritize a certain candidate target cell by defining a larger slice specific parameter, e.g., a larger cell individual offset (CIO) for a high-priority network slice and / or the candidate target cell that supports a high-priority network slice. By this way, a modified network slice specific configuration forwarded to UE 110 may be aligned with UE’s need and / or target cell configuration, thus facilitating the CHO evaluation and execution.

[0040] At 212, based on the measurement report(s) received from UE 110, source network element 122 may decide to initiate a handover procedure as a fast CHO procedure. In this regard, source network element 122 may determine to apply aconventional HO procedure or CHO procedure, such as based on measurement report and radio service quality. Likewise, source network element 122 may determine to apply a conventional CHO procedure or a fast CHO procedure, such as based on one or more service reliability requirements (e.g., QoS on reliability), one or more service delay requirements (e.g., expected QoS on delay), one or more slice requirements (e.g., based on service level agreements, SLAs), or the like.

[0041] When source network element 122 decides that a fast CHO procedure should be initiated, it may carry out CHO preparations for the handover of UE 110 to one or more candidate target cells. For example, source network element 122 may determine (e.g., configure) for UE 110 a message in association with the CHO procedure. The message may comprise, e.g., the combined configuration as discussed earlier, and at least one triggering condition for the CHO procedure. The triggering condition may define when the UE should (autonomously) execute the CHO, e.g., based on the radio condition of the candidate target cell in comparison to that of the source cell (e.g., signal strength / quality information, etc.)

[0042] It shall be understood that although operation 212 is illustrated as taking place after operation 210, this is given for an illustrative purpose and not limiting. For example, operation 212 may be carried out in parallel to operation 210.

[0043] In some examples, handover candidate target network element 124 may determine a change in a baseline RRC configuration, or network slice specific configurations. For example, either or both of a pool of RACH preambles or a pool of C-RNTIs may be updated, such as after some of RACH preambles and / or C- RNTIs have been used / occupied, freed, reconfigured, or the like. In these instances, handover candidate target network element 124 may generate an updated baseline RRC configuration according to the change and share the updated baseline RRC configuration with handover source network element 122. Additionally, handover candidate target network element 124 may determine a change with respect to the availability and / or priority information on the network slices served in one or more candidate target cells. For example, one or more network slices may become unavailable, one or more new network slices may be created, or one or moreparameters of a network slice may be modified by the network slice provider or network operator. In these instances, handover candidate target network element 124 may generate an updated network slice specific configuration according to the change and share the updated network slice specific configuration with handover source network element 122.

[0044] Alternatively, or in addition to, source network element 122 may request updated information from target network element 124. For example, as illustrated in Fig. 2, at 214, source network element 122 may transmit, to target network element 124, a request for updated information on the network slice(s) served in one or more candidate target cells provided by target network element 124. In response to the request, target network element 124 may determine the updated information on the network slices (if any), and at 216, transmit the updated information to source network element 122 over an Xn interface. Upon receiving the updated information, source network element 122 may, at 218, update a combined configuration based on the updated information.

[0045] Then, at 220, source network element 122 may transmit an RRC reconfiguration message with the combined configuration to UE 110. The combined configuration may comprise (part or all of) the baseline RRC configuration obtained from target network element 124 at operation 202 (or operation 216). For example, the combined configuration may comprise a C-RNTI selected from the pool of C-RNTIs, and optionally a RACH preamble selected from the pool of reserved RACH preambles by the source network element.

[0046] The combined configuration may further comprise other suitable configuration / information for UE 110 to evaluate and execute the fast conditional handover. For example, the combined configuration may comprise at least one triggering condition (e.g., a radio condition) for a conditional handover to one or more candidate target cells, and one or more network specific configurations associated with a network slice(s) supported at the candidate target cell(s) to facilitate UE 110 to select the best candidate target cell.

[0047] In some examples, network slice specific configurations may includepriority information indicating a respective priority level of each of the network slices that are currently used by UE 110. For example, source network element 122 may, based on its awareness of network slice status (e.g., network slice availability, priority, etc.) at each candidate target cell and / or TA, determine a slice specific parameter (e.g., a CIO) for indicating a priority level of each of the network slices used by UE 110. A respective priority level may be associated with a slice group, e.g., NSAG.

[0048] Before, after or in parallel with the CHO command message sent to UE 110, source network element 122 may initiate UE specific preparation at each candidate target cell. For example, at 222, source network element 122 may transmit a UE- related configuration to handover candidate target network element 124 (candidate target cell). The UE-related configuration sent to the handover candidate target network element may comprise information similar / relevant to or the same as that sent to UE 110, which may comprise the RACH preamble and C-RNTI selected from the respective pools by source network element 122. The handover information may also comprise UE context information. In some examples, the handover candidate target network element may also be notified about the user plane configuration (e.g., DRB related configuration) of the UE at the source network element.

[0049] In some examples, handover information may comprise network slice(s) used by UE (e.g., currently active in source network element 122) until the CHO execution. This allows target network element 124 to release respective resources once the UE is handed over to the target cell, if a part of the network slices is not supported. In some examples, the handover information may further comprise network slice(s) supported by UE 110 but may not be supported at source network element 122. This facilitates target network element 124 to configure additional network slices supported by UE 110 but not configured in the current serving cell. This handover information may be pr epared / generated by source network element 122 and transmitted (sent) to the candidate target cell in a suitable (existing or newly introduced) message or as separate messages.

[0050] Upon receipt of the RRC reconfiguration message, UE 110 may store the network slice specific configuration. At 224, the UE may monitor and evaluate CHO triggering conditions with respect to one or more candidate target cells. For example, based on the radio link quality measurements, UE 110 may determine one or more candidate target cells satisfy the triggering condition, when the link quality of a candidate target cell becomes a predetermined offset better than that of the serving cell of source network element 122.

[0051] Upon determining that a triggering condition associated with one or more candidate target cells has been satisfied, UE 110 may select a candidate target cell towards which to carry out a conditional handover. In some examples, UE 110 may prioritize at least one of the determined one or more candidate target cells based on the received network slice specific configurations of the one or more candidate target cells. For example, with the slice specific parameter (e.g., CIO) associated with each network slice supported by the one or more candidate target cells, UE 110 may be aware which candidate target cell can best support the high-priority network slice(s) of UE 110, and, accordingly, select such a candidate target cell from the list of candidate target cells. This will help ensure an efficient and reliable handover.

[0052] Then, UE 110 may start CHO execution towards the selected candidate target cell. In some examples, UE 110 may be configured to obtain DL and UL synchronization and initiate a random access procedure to establish an RRC connection with the selected at least one target cell which is, e.g., provided by target network element 124. The random access procedure may be a 4-step random access or a 2-step random access. Taking the 4-step random access as an example, this may comprise the UE at 226 obtaining DL and UL synchronization and RACH access to the target cell. In the RACH access, the UE may apply / use the RACH preamble selected from the respective pools by source network element 122 and received by UE 110 at operation 220. At 228, target network element 124 may transmit to the UE a random access response (RAR) message (also referred to as Msg2) in response to reception of the preamble. Upon successful reception of RAR,UE 110 may at 230 transmit a RRC reconfiguration complete message (Msg3) including a C-RNTI selected from the respective pools by source network element 122 and received by UE 110 at operation 220. In some examples, with the received C-RNTI, target network element 124 may at 232, transmit a request to source network element 122 for retrieving whether there is any update on UE context information. As a response, source network element 122 may, at 234, transmit a new UE context information to target network element 124.

[0053] Target network element 124 may determine (e.g. generate) any supplementary configuration based on the UE-related configuration received at operation 222 or operation 234 for UE 110 to complete the conditional handover. Target network element 124 may at 236 provide this supplementary configuration in an RRC reconfiguration message (e.g., Msg4) to UE 110 to complete the handover procedure.

[0054] In some examples, an RRC reconfiguration message may further comprise additional information on one or more network slices served in the target cell, or information on one or more network slices used by UE 110 but not served in the target cell. Alternatively, the additional information may also be provided in the RAR message at operation 228. The additional information may be configured to indicate the network slice(s) admitted by the target cell, and the network slice(s) that is supported at UE 110 but not supported at the target cell. For example, target network element 124 may determine a change bitmap to indicate the supported network slice(s), as well as the network slice(s) that the target cell cannot support. For those non-admitted network slice(s), in an example, target network element 124 may further determine and provide network slice specific redirection information, e.g., on one or more cells that support the non-admitted network slice(s). With this redirection information, UE 110 may select a suitable cell for redirection in case it does not prefer to complete the handover with the currently selected target cell.

[0055] It should be appreciated that, in the foregoing, one or more operations may be carried out simultaneously, and / or one or more operations may be carried out ina different order. Additionally, or alternatively, some operations (e.g., operations 214, 232) may be optional, and / or additional operations may be carried out. The forgoing examples are not limiting.

[0056] Fig. 3 illustrates method 300 for a fast conditional handover procedure more detailed examples of which are described above by means of Fig. 2. Method 300 may be carried out by a terminal device, e.g., UE 110 as discussed above.

[0057] Referring to Fig. 3, method 300 may comprise receiving, from a source network element, a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, as shown at 310. The message may comprise a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or more network slice specific configurations associated with one or more network slices supported at the one or more candidate target cells.

[0058] In some examples, the baseline configuration of the one or more candidate target cells may comprise a pools of random access preambles and a pool of cell radio network temporary identifiers (C-RNTIs). In some examples, the one or more network slice specific configurations may comprise an identifier (ID) of at least one of the one or more network slices or a network slice group, and a network slice specific parameter associated with the at least one of the one or more network slices or the network slice group.

[0059] Method 300 may comprise, at 320, evaluating the triggering condition and the slice specific configurations to select at least one target cell of the one or more candidate target cells for the conditional handover.

[0060] In some examples, a triggering condition may be based on radio measurements, such as measured RSRP. UE 110 may determine one or more candidate target cells that satisfy the at least one triggering condition based on radio link quality measurements in association with the one or more candidate target cells.

[0061] In some examples, UE 110 may further prioritize one or more of the candidate target cell(s) based on the one or more network slice specific 1configurations of the one or more candidate target cells. As such, UE 110 may select a candidate target cell that can best support the network slice used or required by the UE.

[0062] If at least one target cell satisfies a corresponding CHO condition, at 330, UE 110 may be configured to initiate a random access procedure to establish a radio resource connection (RRC) with the selected at least one target cell, in order to be successfully connected to the target cell provided by the target network element(s).

[0063] Method 330 may further comprise, at 340, receiving, from the target network element supporting the at least one target cell, a reconfiguration message comprising a supplementary configuration for the terminal device to complete the conditional handover, and at least one of: information on one or more network slices served in the at least one target cell, or information on one or more network slices used by the at least one terminal device but not served in the at least one target cell.

[0064] Fig. 4 illustrates a method 400 for a fast conditional handover procedure, more detailed examples of which are described above by means of Fig. 2. Method 400 may be carried out by a network element, e.g., source network element 122 as discussed above.

[0065] Method 400 may comprise receiving, from at least one target network element, a baseline configuration for a conditional handover procedure in association with one or more candidate target cells served by the at least one target network element, and one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells, as shown at 410.

[0066] In some examples, in case the one or more network slices served in the one or more candidate target cells are at least substantially equivalent in a tracking area or a cell group, one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells are received on a basis of the tracking area or the cell group. In some examples the oneor more network slice specific configurations associated with one or more network slices used by the terminal device comprise a slice specific parameter for indicating a priority of the one or more candidate target cells.

[0067] Then, source network element 122 may at 420, determine for a terminal device, a combined configuration comprising the baseline configuration and the one or more network slice specific configurations. At 430, source network element 122 may further determine, for the terminal device, a message in association with the conditional handover procedure, the message comprising the combined configuration, and at least one triggering condition for the conditional handover procedure.

[0068] Optionally, method 400 may comprise, transmitting to the at least one target network element, a request for updated information on the one or more network slices served in the one or more candidate target cells; receiving from the at least one target network element, the updated information, and updating the combined configuration based on the updated information, as shown at blocks 440 through 460. Alternatively, or in addition, source network element 122 may receive the update information on the network slices from neighboring network elements without a request, e.g., over an Xn interface.

[0069] In some examples, updated information may comprise availability or priority information on the one or more network slices served in the one or more candidate target cells.

[0070] At 470, source network element 122 may transmit the message to the terminal device, for example, via a RRC reconfiguration message.

[0071] In some examples, method 400 may further comprise transmitting, to the at least one target network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device, as shown at 480. Any update information on the network slice of the terminal device may be included in the configuration information. This enables and facilitates a network slice specific initial access.

[0072] Fig. 5 illustrates an example of method 500 for a fast conditional handover procedure, more detailed examples of which are described above by means of Fig. 2. Method 500 may be carried out by a network element, e.g., target network element 124 as discussed above.

[0073] Method 500 may comprise determining a radio resource control configuration, as shown at 510. In an example, the configuration may comprise a baseline configuration for a conditional handover procedure in association with one or more candidate target cells served by the network element, and one or more network slice specific configurations associated with one or more slices served in the one or more candidate target cells for the conditional handover procedure.

[0074] Then, target network element 124 may at 520, transmit the radio resource control configuration to a source network element of the conditional handover of a terminal device from the source network element to the at least one of the one or more candidate target cells. In some examples, the baseline configuration and the network slice specific configuration may be transmitted to the source network element in a single message (e.g., RAN node configuration update message). In other examples, the baseline configuration and the network slice specific configuration may be transmitted in separate messages, such as one message for the baseline configuration, and one message for the network slice specific configuration.

[0075] In some examples, method 500 may comprise receiving, from the source network element, a request for updated information on the one or more network slices, and transmitting, to the source network element, the updated information, as shown at 530 and 540, respectively.

[0076] In some examples, method 500 may further comprise, at 550, receiving, from the source network element, configuration information on the terminal device, which may comprise context information on the terminal device, and information on one or more network slices used by the terminal device; at 560, determining a supplementary configuration for the terminal device to complete the conditional handover; and at 570, transmitting a reconfiguration message to the terminal device.The configuration message may comprise the supplementary configuration, and at least one of: information on the one or more network slices served in the at least one target cell, or information on the one or more network slices used by the terminal device but not served in the target cell. In an example, the above information may be used by the terminal device to determine (e.g., identify) the network slice(s) admitted by the target cell, and the network slice(s) that is unsupportive at the target cell.

[0077] According to example implementations of the present disclosure, a telecommunications system 100, and its components such as a UE 110, network element 212, 214, and CN 130, may be implemented by various means. Means for implementing the system and its components may comprise hardware, firmware, software, or combinations thereof. In some examples, one or more apparatuses may be configured to function as or otherwise implement the system and its components shown and described herein. In examples involving more than one apparatus, the respective apparatuses may be connected to or otherwise in communication with one another in a number of different manners, such as directly or indirectly via a wired or wireless network or the like.

[0078] At least part of method 300 with respect to Fig. 2 and 3 may be carried out by an apparatus comprising means for performing functions corresponding operations of the method. Similarly, at least part of method 400 or method 500 described with respect to Figs. 2, 4 and / or 5 may be carried out by an apparatus comprising means for performing functions corresponding operations of the method. Examples of a suitable apparatus may comprise a gNB, or any suitable apparatus, such as a server, host or node.

[0079] Fig. 6 illustrates an example of terminal device 600. Referring to Fig. 6, terminal device 600 may comprise one or more processors 610, one or more memories 620 and one or more transceivers 630 interconnected through one or more buses 640. One or more buses 640 may be address, data, or control buses, and may include any interconnection mechanism such as series of lines on a motherboard or integrated circuit, fiber, optics or other optical communicationequipment, and the like. Each of one or more transceivers 630 may comprise a receiver and a transmitter, which are connected to one or more antennas 650. Terminal device 600 may wirelessly communicate with a network element e.g. a base station through one or more antennas 650. One or more memories 620 may include instructions 622 which, when executed by one or more processors 610, may cause terminal device 600 to perform operations relating to UE 110 described above by means of Fig. 2 and 3.

[0080] Fig. 7 illustrates an example of network element 700. Referring to Fig. 7, network element 700 may comprise one or more processors 710, one or more memories 720, one or more transceivers 730 and one or more network interfaces 760 interconnected through one or more buses 740. One or more buses 740 may be address, data, or control buses, and may include any interconnection mechanism such as a series of lines on a motherboard or integrated circuit, fiber, optics or other optical communication equipment, and the like. Each of one or more transceivers 730 may comprise a receiver and a transmitter, which are connected to one or more antennas 750. Network element 700 may operate as a source network element, or a target network element for terminal device 600 in a handover procedure. Network element 700 may wirelessly communicate with terminal device 600 through one or more antennas 750. One or more network interfaces 760 may provide wired or wireless communication links through which network element 700 may communicate with other network elements, entities, elements or functions. For example, network element 700 may communicate with a core network (not shown) via backhaul connections. One or more memories 720 may include instructions 722 which, when executed by one or more processors 710, may cause network element 700 to perform operations relating to base station 122, 124 described above by means of Fig. 2, 4 and / or 5.

[0081] One or more processors 610, 710 discussed above may be of any appropriate type that is suitable for the local technical network, and may include one or more of general purpose processors, special purpose processor, microprocessors, a digital signal processor (DSP), one or more processors in aprocessor based multi-core processor architecture, as well as dedicated processors such as those developed based on Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuit (ASIC). One or more processors 610, 710 may be configured to control other elements of the terminal / network elements and operate in cooperation with them to implement the procedures discussed above.

[0082] One or more memories 620, 720 may include at least one storage medium in various forms, such as a transitory memory and / or a non-transitory memory. The transitory memory may include, but not limited to, for example, a random access memory (RAM) or a cache. The non-transitory memory may include, but not limited to, for example, a read only memory (ROM), a hard disk, a flash memory, and the like. The term “non-transitory”, as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM). Further, one or more memories 620, 720 may include but not limited to an electric, a magnetic, an optical, an electromagnetic, an infrared, or a semiconductor system, apparatus, or device or any combination of the above.

[0083] It would be understood that blocks in the drawings may be implemented in various manners, including software, hardware, firmware, or any combination thereof. In some embodiments, one or more blocks may be implemented using software and / or firmware, for example, machine-executable instructions stored in the storage medium. In addition to or instead of machine-executable instructions, parts or all of the blocks in the drawings may be implemented, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field- Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application-Specific Standard Products (ASSPs), System-on-Chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), etc.

[0084] Some example implementations further provide program instruction or instructions which, when executed by one or more processors, may cause a device or apparatus to perform the procedures described above. The program instructionfor carrying out procedures of the example implementations may be in source code form, object code form, or in some intermediate form. The program instruction may be provided to one or more processors or controllers of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program instruction, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program instruction may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[0085] Some example implementations further provide a computer program product or a computer readable medium having the program instruction or instructions stored therein. The computer readable medium may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but is not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0086] As will be appreciated, any suitable instructions may be loaded onto a computer, a processing circuitry, or other programmable apparatus from a memory or a computer-readable medium to produce a particular machine, such that the particular machine becomes a means for implementing the functions specified herein. The instructions may also be stored in a computer readable medium thatcan direct a computer, a processing circuitry or other programmable apparatus to function in a particular manner to thereby generate a particular machine or particular article of manufacture. In some examples, the instructions stored in the computer readable medium may produce an article of manufacture, where the article of manufacture becomes a means for implementing functions described herein. The instructions may be retrieved from a computer readable medium and loaded into a computer, processing circuitry or other programmable apparatus to configure the computer, processing circuitry or other programmable apparatus to execute operations to be performed on or by the computer, processing circuitry or other programmable apparatus.

[0087] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0088] As explained above and reiterated below, the present disclosure comprises, without limitation, the following example implementations.

[0089] Example 1. 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: receive, from a source network element, a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, wherein the message comprises a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or more network slice specific configurations associated with one or more network slices supported at the one or more candidate target cells; evaluate the triggering condition and the slice specific configurations to select at least one target cell of the one or more candidate target cells for the conditional handover; and initiate a random access procedure to establish a radio resource connection with the selected at least one target cell.

[0090] Example 2. The apparatus of example 1, wherein the one or more network slice specific configurations comprise an identifier of at least one of the one or more network slices or a network slice group, and a network slice specific parameter associated with the at least one of the one or more network slices or the network slice group.

[0091] Example 3. The apparatus of example 1 or 2, wherein the evaluating the triggering condition and the slice specific configurations to select the at least one target cell for the conditional handover further comprises: determining one or more candidate target cells that satisfy the at least one triggering condition associated with the one or more candidate target cells, based on radio link quality measurements in association with the one or more candidate target cells; and prioritizing one or more of the one or more candidate target cells based on the one or more network slice specific configurations of the one or more candidate target cells.

[0092] Example 4. The apparatus of any of examples 1 to 3, wherein the apparatus further being caused to: receive, from the target network element supporting the at least one target cell, a reconfiguration message comprising a supplementary configuration for the terminal device to complete the conditional handover, and at least one of: information on one or more network slices served in the at least one target cell, or information on one or more network slices used by the at least one terminal device but not served in the at least one target cell.

[0093] Example 5. An apparatus comprising: means for receiving, from a source network element, a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, wherein the message comprises a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or more network slice specific configurations associated with one or more network slices supported at the one or more candidate target cells; means for evaluating the triggering condition and the slice specific configurations to select atleast one target cell of the one or more candidate target cells for the conditional handover; and means for initiating a random access procedure to establish a radio resource connection with the selected at least one target cell.

[0094] Example 6. The apparatus of example 5, wherein the one or more network slice specific configurations comprise an identifier of at least one of the one or more network slices or a network slice group, and a network slice specific parameter associated with the at least one of the one or more network slices or the network slice group.

[0095] Example 7. The apparatus of example 5 or 6, wherein the means for evaluating the triggering condition and the slice specific configurations to select at least one target cell for the conditional handover further comprises: means for determining one or more candidate target cells that satisfy the at least one triggering condition associated with the one or more candidate target cells, based on radio link quality measurements in association with the one or more candidate target cells; and means for prioritizing one or more of the one or more candidate target cells based on the one or more network slice specific configurations of the one or more candidate target cells.

[0096] Example 8. The apparatus of any of examples 5 to 7, wherein the apparatus further means for receiving, from the target network element supporting the at least one target cell, a reconfiguration message comprising a supplementary configuration for the terminal device to complete the conditional handover, and at least one of: information on one or more network slices served in the at least one target cell, or information on one or more network slices used by the at least one terminal device but not served in the at least one target cell.

[0097] Example 9. A method comprising: receiving, from a source network element, a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, wherein the message comprises a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or morenetwork slice specific configurations associated with one or more network slices supported at the one or more candidate target cells; evaluating the triggering condition and the slice specific configurations to select at least one target cell of the one or more candidate target cells for the conditional handover; and initiating a random access procedure to establish a radio resource connection with the selected at least one target cell.

[0098] Example 10. The method of example 9, wherein the one or more network slice specific configurations comprise an identifier of at least one of the one or more network slices or a network slice group, and a network slice specific parameter associated with the at least one of the one or more network slices or the network slice group.

[0099] Example 11. The method of example 9 or 10, wherein the evaluating the triggering condition and the slice specific configurations to select the at least one target cell for the conditional handover further comprises: determining one or more candidate target cells that satisfy the at least one triggering condition associated with the one or more candidate target cells, based on radio link quality measurements in association with the one or more candidate target cells; and prioritizing one or more of the one or more candidate target cells based on the one or more network slice specific configurations of the one or more candidate target cells.

[0100] Example 12. The method of any of examples 9 to 11, wherein the method further comprises: receive, from the target network element supporting the at least one target cell, a reconfiguration message comprising a supplementary configuration for the terminal device to complete the conditional handover, and at least one of: information on one or more network slices served in the at least one target cell, or information on one or more network slices used by the at least one terminal device but not served in the at least one target cell.

[0101] Example 13. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processor, causes an apparatus at least to: receive, from a source network element,a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, wherein the message comprises a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or more network slice specific configurations associated with one or more network slices supported at the one or more candidate target cells; evaluate the triggering condition and the slice specific configurations to select at least one target cell of the one or more candidate target cells for the conditional handover; and initiate a random access procedure to establish a radio resource connection with the selected at least one target cell.

[0102] Example 14. The computer-readable storage medium of example 13, wherein the one or more network slice specific configurations comprise an identifier of at least one of the one or more network slices or a network slice group, and a network slice specific parameter associated with the at least one of the one or more network slices or the network slice group.

[0103] Example 15. The computer-readable storage medium of example 13 or 14, wherein the apparatus caused to evaluate the triggering condition and the slice specific configurations to select the at least one target cell for the conditional handover further comprises the apparatus caused to: determine one or more candidate target cells that satisfy the at least one triggering condition associated with the one or more candidate target cells, based on radio link quality measurements in association with the one or more candidate target cells; and prioritize one or more of the one or more candidate target cells based on the one or more network slice specific configurations of the one or more candidate target cells.

[0104] Example 16. The computer-readable storage medium of any of examples 13 to 15, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processor, causes the apparatus to further receive, from the target network element supporting the at least one target cell, a reconfiguration message comprising a supplementary configuration for the terminal device to complete the conditional handover, and atleast one of: information on one or more network slices served in the at least one target cell, or information on one or more network slices used by the at least one terminal device but not served in the at least one target cell.

[0105] Example 17. An apparatus comprising means for carrying out the method of any of examples 9 to 12.

[0106] Example 18. A computer-readable medium comprising instructions that, in response to execution by at least one processor, causes an apparatus to carry out the method of any of examples 9 to 12.

[0107] Example 19. A computer-readable storage medium comprising instructions that, in response to execution by at least one processor, causes an apparatus to carry out the method of any of examples 9 to 12.

[0108] Example 20. A computer program comprising instructions that, in response execution by at least on processor, causes an apparatus to carry out the method of any of examples 9 to 12.

[0109] Example 21. 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: receive, from at least one target network element, a baseline configuration for the conditional handover procedure in association with one or more candidate target cells served by the at least one target network element, and one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells; determine for a terminal device, a combined configuration comprising the baseline configuration and the one or more network slice specific configurations; determine, for the terminal device, a message in association with the conditional handover procedure, the message comprising the combined configuration, and at least one triggering condition for the conditional handover procedure; and transmit the message to the terminal device.

[0110] Example 22. The apparatus of example 21, wherein in case the one or more network slices served in the one or more candidate target cells are at least substantially equivalent in a tracking area or a cell group, the one or more networkslice specific configurations associated with one or more network slices served in the one or more candidate target cells are received on a basis of the tracking area or the cell group.

[0111] Example 23. The apparatus of example 21 or 22, wherein the one or more network slice specific configurations associated with one or more network slices used by the terminal device comprise a slice specific parameter for indicating a priority of the one or more candidate target cells.

[0112] Example 24. The apparatus of any of examples 21 to 23, wherein the apparatus further being caused to: transmit to the at least one target network element, a request for updated information on the one or more network slices served in the one or more candidate target cells; receive from the at least one target network element, the updated information, and update the combined configuration based on the updated information.

[0113] Example 25. The apparatus of example 24, wherein the updated information comprises availability or priority information on the one or more network slices served in the one or more candidate target cells.

[0114] Example 26. The apparatus of any of examples 21 to 25, wherein the apparatus further being caused to: transmit to the at least one target network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device.

[0115] Example 27. An apparatus comprising: means for receiving, from at least one target network element, a baseline configuration for a conditional handover procedure in association with one or more candidate target cells served by the at least one target network element, and one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells; means for determining for a terminal device, a combined configuration comprising the baseline configuration and the one or more network slice specific configurations; means for determining, for the terminal device, a message in association with the conditional handover procedure, themessage comprising the combined configuration, and at least one triggering condition for the conditional handover procedure; and means for transmitting the message to the terminal device.

[0116] Example 28. The apparatus of example 27, wherein in case the one or more network slices served in the one or more candidate target cells are at least substantially equivalent in a tracking area or a cell group, the one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells are received on a basis of the tracking area or the cell group.

[0117] Example 29. The apparatus of example 27 or 28, wherein the one or more network slice specific configurations associated with one or more network slices used by the terminal device comprise a slice specific parameter for indicating a priority of the one or more candidate target cells.

[0118] Example 30. The apparatus of any of examples 27 to 29, wherein the apparatus further comprises: means for transmitting to the at least one target network element, a request for updated information on the one or more network slices served in the one or more candidate target cells; means for receiving from the at least one target network element, the updated information; and means for updating the combined configuration based on the updated information.

[0119] Example 31. The apparatus of example 30, wherein the updated information comprises availability or priority information on the one or more network slices served in the one or more candidate target cells.

[0120] Example 32. The apparatus of any of examples 27 to 31, wherein the apparatus further comprises means for transmitting, to the at least one target network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device.

[0121] Example 33. A method comprising: receiving, from at least one target network element, a baseline configuration for a conditional handover procedure in association with one or more candidate target cells served by the at least one targetnetwork element, and one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells; determining for a terminal device, a combined configuration comprising the baseline configuration and the one or more network slice specific configurations; determining, for the terminal device, a message in association with the conditional handover procedure, the message comprising the combined configuration, and at least one triggering condition for the conditional handover procedure; and transmitting the message to the terminal device.

[0122] Example 34. The method of example 33, wherein in case the one or more network slices served in the one or more candidate target cells are at least substantially equivalent in a tracking area or a cell group, the one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells are received on a basis of the tracking area or the cell group.

[0123] Example 35. The method of example 33 or 34, wherein the one or more network slice specific configurations associated with one or more network slices used by the terminal device comprise a slice specific parameter for indicating a priority of the one or more candidate target cells.

[0124] Example 36. The method of any of examples 33 to 35, wherein the method further comprises: transmitting to the at least one target network element, a request for updated information on the one or more network slices served in the one or more candidate target cells; receiving from the at least one target network element, the updated information, and updating the combined configuration based on the updated information.

[0125] Example 37. The method of example 36, wherein the updated information comprises availability or priority information on the one or more network slices served in the one or more candidate target cells.

[0126] Example 38. The method of any of examples 33 to 37, wherein the method further comprises transmitting, to the at least one target network element, configuration information on the terminal device, wherein the configurationinformation comprises context information on the terminal device, and information on one or more network slices used by the terminal device.

[0127] Example 39. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processor, causes an apparatus at least to: receive, from at least one target network element, a baseline configuration for the conditional handover procedure in association with one or more candidate target cells served by the at least one target network element, and one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells; determine for a terminal device, a combined configuration comprising the baseline configuration and the one or more network slice specific configurations; determine, for the terminal device, a message in association with the conditional handover procedure, the message comprising the combined configuration, and at least one triggering condition for the conditional handover procedure; and transmit the message to the terminal device.

[0128] Example 40. The computer-readable storage medium of example 39, wherein in case the one or more network slices served in the one or more candidate target cells are at least substantially equivalent in a tracking area or a cell group, the one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells are received on a basis of the tracking area or the cell group.

[0129] Example 41. The computer-readable storage medium of example 39 or 40, wherein the one or more network slice specific configurations associated with one or more network slices used by the terminal device comprise a slice specific parameter for indicating a priority of the one or more candidate target cells.

[0130] Example 42. The computer-readable storage medium of any of examples 39 to 41, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processor, causes the apparatus to further transmit to the at least one target network element, a request for updated information on the one or more network slices served in the one ormore candidate target cells; determine, for the terminal device, a message in association with the conditional handover procedure, the message comprising the combined configuration, and at least one triggering condition for the conditional handover procedure; and transmit the message to the terminal device.

[0131] Example 43. The computer-readable storage medium of example 42, wherein the updated information comprises availability or priority information on the one or more network slices served in the one or more candidate target cells.

[0132] Example 44. The computer-readable storage medium of any of examples 39 to 43, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processor, causes the apparatus to further transmit, to the at least one target network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device.

[0133] Example 45. An apparatus comprising means for carrying out the method of any of examples 33 to 38.

[0134] Example 46. A computer-readable medium comprising instructions that, in response to execution by at least one processor, causes an apparatus to carry out the method of any of examples 33 to 38.

[0135] Example 47. A computer-readable storage medium comprising instructions that, in response to execution by at least one processor, causes an apparatus to carry out the method of any of example 33 to 38.

[0136] Example 48. A computer program comprising instructions that, in response to execution by at least on processor, causes an apparatus to carry out the method of any of examples 33 to 38.

[0137] Example 49. 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: determine a radio resource control configuration comprising a baseline configuration for the conditional handover procedure in association with one or more candidate target cells served by the network element,and one or more network slice specific configurations associated with one or more slices served in the one or more candidate target cells for the conditional handover procedure; and transmit the radio resource control configuration to a source network element of the conditional handover of a terminal device from the source network element to the at least one of the one or more candidate target cells.

[0138] Example 50. The apparatus of example 49, wherein the apparatus further being caused to: receive, from the source network element, a request for updated information on the one or more network slices, and transmit, to the source network element, the updated information.

[0139] Example 51. The apparatus of example 49 or 50, wherein the apparatus further being caused to: receive, from the source network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device; determine a supplementary configuration for the terminal device to complete the conditional handover; and transmit, to the terminal device, a reconfiguration message comprising the supplementary configuration, and at least one of: information on the one or more network slices served in the at least one target cell, or information on the one or more network slices used by the terminal device but not served in the target cell.

[0140] Example 52. An apparatus comprising: means for determining a radio resource control configuration comprising a baseline configuration for a conditional handover procedure in association with one or more candidate target cells served by the network element, and one or more network slice specific configurations associated with one or more slices served in the one or more candidate target cells for the conditional handover procedure; and transmitting the radio resource control configuration to a source network element of the conditional handover of a terminal device from the source network element to the at least one of the one or more candidate target cells.

[0141] Example 53. The apparatus of example 52, wherein the apparatus further comprises: means for receiving, from the source network element, a request forupdated information on the one or more network slices, and transmitting, to the source network element, the updated information.

[0142] Example 54. The apparatus of example 52 or 53, wherein the apparatus further comprises: means for receiving, from the source network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device; means for determining a supplementary configuration for the terminal device to complete the conditional handover; and means for transmitting, to the terminal device, a reconfiguration message comprising the supplementary configuration, and at least one of: information on the one or more network slices served in the at least one target cell, or information on the one or more network slices used by the terminal device but not served in the target cell.

[0143] Example 55. A method comprising: determining a radio resource control configuration comprising a baseline configuration for a conditional handover procedure in association with one or more candidate target cells served by the network element, and one or more network slice specific configurations associated with one or more slices served in the one or more candidate target cells for the conditional handover procedure; and transmitting the radio resource control configuration to a source network element of the conditional handover of a terminal device from the source network element to the at least one of the one or more candidate target cells.

[0144] Example 56. The method of example 55, wherein the method further comprises: receiving, from the source network element, a request for updated information on the one or more network slices, and transmitting, to the source network element, the updated information.

[0145] Example 57. The method of example 55 or 56, wherein the method further comprises: receiving, from the source network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slicesused by the terminal device; determining a supplementary configuration for the terminal device to complete the conditional handover; and transmitting, to the terminal device, a reconfiguration message comprising the supplementary configuration, and at least one of: information on the one or more network slices served in the at least one target cell, or information on the one or more network slices used by the terminal device but not served in the target cell.

[0146] Example 58. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processor, causes an apparatus at least to: determine a radio resource control configuration comprising a baseline configuration for the conditional handover procedure in association with one or more candidate target cells served by the network element, and one or more network slice specific configurations associated with one or more slices served in the one or more candidate target cells for the conditional handover procedure; and transmit the radio resource control configuration to a source network element of the conditional handover of a terminal device from the source network element to the at least one of the one or more candidate target cells.

[0147] Example 59. The computer-readable storage medium of example 58, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processor, causes the apparatus to further receive, from the source network element, a request for updated information on the one or more network slices, and transmit, to the source network element, the updated information.

[0148] Example 60. The computer-readable storage medium of example 58 or 59, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processor, causes the apparatus to further receive, from the source network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device; determine a supplementaryconfiguration for the terminal device to complete the conditional handover; and transmit, to the terminal device, a reconfiguration message comprising the supplementary configuration, and at least one of: information on the one or more network slices served in the at least one target cell, or information on the one or more network slices used by the terminal device but not served in the target cell.

[0149] Example 61. An apparatus comprising means for carrying out the method of any of examples 55 to 57.

[0150] Example 62. A computer-readable medium comprising instructions that, in response to execution by at least one processor, causes an apparatus to carry out the method of any of examples 55 to 57.

[0151] Example 63. A computer-readable storage medium comprising instructions that, in response to execution by at least one processor, causes an apparatus to carry out the method of any of examples 55 to 57.

[0152] Example 64. A computer program comprising instructions that, in response to execution by at least one processor, causes an apparatus to carry out the method of any of examples 55 to 57.

[0153] Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

[0154] Although the subject matter has been described in a language that is specific to structural features and / or method actions, it is to be understood the subject matterdefined in the appended claims is not limited to the specific features or actions described above. On the contrary, the above-described specific features and actions are disclosed as an example of implementing the claims.

[0155] Some abbreviations that may be found in the description and / or in the figures are herewith defined as follows:ACK AcknowledgementAMF Access and Mobility Management FunctionCHO Conditional HandoverCN Core NetworkCIO Cell individual OffsetC-RNTI Cell Radio Network Temporary IdentifierDL DownlinkHOF Handover FailureID identifierDRB Data Radio BearerNR New RadioNSAG Network Slice AS GroupRACH Random Access ChannelRAN Radio Access NetworkRAR Random Access ResponseRLF Radio Link FailureRRC Radio Resource ControlRRM Radio Resource ManagementRSRP reference signal received powerS-NSSAI Single Network Slice Selection Assistance InformationTA Tracking AreaUE User EquipmentUL Uplink

Claims

CLAIMS:

1. A terminal device, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to: receive, from a source network element, a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, wherein the message comprises a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or more network slice specific configurations associated with one or more network slices supported at the one or more candidate target cells; evaluate the triggering condition and the slice specific configurations to select at least one target cell of the one or more candidate target cells for the conditional handover; and initiate a random access procedure to establish a radio resource connection with the selected at least one target cell.

2. The terminal device of claim 1, wherein the one or more network slice specific configurations comprise an identifier of at least one of the one or morenetwork slices or a network slice group, and a network slice specific parameter associated with the at least one of the one or more network slices or the network slice group.

3. The terminal device of claim 1 or 2, wherein the evaluating the triggering condition and the slice specific configurations to select the at least one target cell for the conditional handover further comprises: determining one or more candidate target cells that satisfy the at least one triggering condition associated with the one or more candidate target cells, based on radio link quality measurements in association with the one or more candidate target cells; and prioritizing one or more of the one or more candidate target cells based on the one or more network slice specific configurations of the one or more candidate target cells.

4. The terminal device of any of claims 1 to 3, the terminal device further being caused to: receive, from the target network element supporting the at least one target cell, a reconfiguration message comprising a supplementary configuration for the terminal device to complete the conditional handover, and at least one of: information on one or more network slices served in the at least one target cell, orinformation on one or more network slices used by the at least one terminal device but not served in the at least one target cell.

5. A network element serving as a source network element for a conditional handover procedure, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network element at least to: receive, from at least one target network element, a baseline configuration for the conditional handover procedure in association with one or more candidate target cells served by the at least one target network element, and one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells; determine for a terminal device, a combined configuration comprising the baseline configuration and the one or more network slice specific configurations; determine, for the terminal device, a message in association with the conditional handover procedure, the message comprising the combined configuration, and at least one triggering condition for the conditional handover procedure; and transmit the message to the terminal device.

6. The network element of claim 5, wherein in case the one or more network slices served in the one or more candidate target cells are at least substantially equivalent in a tracking area or a cell group, the one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells are received on a basis of the tracking area or the cell group.

7. The network element of claim 5 or 6, wherein the one or more network slice specific configurations associated with one or more network slices used by the terminal device comprise a slice specific parameter for indicating a priority of the one or more candidate target cells.

8. The network element of any of claims 5 to 7, the network element further being caused to: transmit to the at least one target network element, a request for updated information on the one or more network slices served in the one or more candidate target cells; receive from the at least one target network element, the updated information, and update the combined configuration based on the updated information.

9. The network element of claim 8, wherein the updated information comprises availability or priority information on the one or more network slices served in the one or more candidate target cells.

10. The network element of any of claims 5 to 9, the network element further being caused to: transmit, to the at least one target network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device.

11. A network element serving as a target network element for a conditional handover procedure, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network element at least to: determine a radio resource control configuration comprising a baseline configuration for the conditional handover procedure in association with one or more candidate target cells served by the network element, and one or more network slice specific configurations associated with one or more slices served in the one or more candidate target cells for the conditional handover procedure; andtransmit the radio resource control configuration to a source network element of the conditional handover of a terminal device from the source network element to the at least one of the one or more candidate target cells.

12. The network element of claim 11, the network element further being caused to: receive, from the source network element, a request for updated information on the one or more network slices, and transmit, to the source network element, the updated information.

13. The network element of claim 11 or 12, further being caused to: receive, from the source network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device; determine a supplementary configuration for the terminal device to complete the conditional handover; and transmit, to the terminal device, a reconfiguration message comprising the supplementary configuration, and at least one of: information on the one or more network slices served in the at least one target cell, or information on the one or more network slices used by the terminal device but not served in the target cell.

14. A method comprising: receiving, from a source network element, a message in association with a conditional handover for conditional handover to one or more candidate target cells supported by one or more target network elements, wherein the message comprises a baseline configuration of the one or more candidate target cells, at least one triggering condition for the conditional handover to the one or more candidate target cells, and one or more network slice specific configurations associated with one or more network slices supported at the one or more candidate target cells; evaluating the triggering condition and the slice specific configurations to select at least one target cell of the one or more candidate target cells for the conditional handover; and initiating a random access procedure to establish a radio resource connection with the selected at least one target cell.

15. The method of claim 14, wherein the one or more network slice specific configurations comprise an identifier of at least one of the one or more network slices or a network slice group, and a network slice specific parameter associated with the at least one of the one or more network slices or the network slice group.

16. The method of claim 14 or 15, wherein the evaluating the triggering condition and the slice specific configurations to select the at least one target cell for the conditional handover further comprises: determining one or more candidate target cells that satisfy the at least one triggering condition associated with the one or more candidate target cells, based on radio link quality measurements in association with the one or more candidate target cells; and prioritizing one or more of the one or more candidate target cells based on the one or more network slice specific configurations of the one or more candidate target cells.

17. The method of any of claims 14 to 16, further comprising: receive, from the target network element supporting the at least one target cell, a reconfiguration message comprising a supplementary configuration for the terminal device to complete the conditional handover, and at least one of: information on one or more network slices served in the at least one target cell, or information on one or more network slices used by the at least one terminal device but not served in the at least one target cell.

18. A method comprising: receiving, from at least one target network element, a baseline configuration for a conditional handover procedure in association with one or more candidatetarget cells served by the at least one target network element, and one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells; determining for a terminal device, a combined configuration comprising the baseline configuration and the one or more network slice specific configurations; determining, for the terminal device, a message in association with the conditional handover procedure, the message comprising the combined configuration, and at least one triggering condition for the conditional handover procedure; and transmitting the message to the terminal device.

19. The method of claim 18, wherein in case the one or more network slices served in the one or more candidate target cells are at least substantially equivalent in a tracking area or a cell group, the one or more network slice specific configurations associated with one or more network slices served in the one or more candidate target cells are received on a basis of the tracking area or the cell group.

20. The method of claim 18 or 19, wherein the one or more network slice specific configurations associated with one or more network slices used by the terminal device comprise a slice specific parameter for indicating a priority of the one or more candidate target cells.

21. The method of any of claims 18 to 20, further comprising: transmitting to the at least one target network element, a request for updated information on the one or more network slices served in the one or more candidate target cells; receiving from the at least one target network element, the updated information, and updating the combined configuration based on the updated information.

22. The method of claim 21, wherein the updated information comprises availability or priority information on the one or more network slices served in the one or more candidate target cells.

23. The method of any of claims 18 to 22, further comprising: transmitting, to the at least one target network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device.

24. A method comprising: determining a radio resource control configuration comprising a baseline configuration for a conditional handover procedure in association with one or more50candidate target cells served by the network element, and one or more network slice specific configurations associated with one or more slices served in the one or more candidate target cells for the conditional handover procedure; and transmitting the radio resource control configuration to a source network element of the conditional handover of a terminal device from the source network element to the at least one of the one or more candidate target cells.

25. The method of claim 24, further comprising: receiving, from the source network element, a request for updated information on the one or more network slices, and transmitting, to the source network element, the updated information.

26. The method of claim 24 or 25, further comprising: receiving, from the source network element, configuration information on the terminal device, wherein the configuration information comprises context information on the terminal device, and information on one or more network slices used by the terminal device; determining a supplementary configuration for the terminal device to complete the conditional handover; and transmitting, to the terminal device, a reconfiguration message comprising the supplementary configuration, and at least one of: information on the one or more51network slices served in the at least one target cell, or information on the one or more network slices used by the terminal device but not served in the target cell.

27. An apparatus, comprising means for carrying out the method of any of claims 14 to 26.

28. A computer program product embodied in at least a computer readable medium comprising instructions for causing an apparatus at least to carry out the method of any of claims 14 to 26.52

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