Conditional handover

Abstract

In some examples, an apparatus comprises at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform receiving handover information comprising at least one handover condition for a cell switch from a first cell to a second cell, and following a cell switch, evaluating the handover condition for a subsequent cell switch from the second cell to a third cell.

Description

[0001] CONDITIONAL HANDOVER

[0002] Technical Field

[0003] Various example embodiments relate generally to conditional handover.

[0004] Background

[0005] Handover (mobility) is a process of transferring an ongoing communication session of a mobile device (e.g., a user equipment (UE)) from one cell to another cell in connected state. The primary motivation behind handover is to ensure seamless connectivity and continuity of service for the user, especially while the user is on the move.

[0006] Summary

[0007] An objective of the present disclosure is to provide support for conditional handover of user equipment for subsequent cell switches in order to reduce overhead associated with new cell switch preparations.

[0008] The foregoing and other objectives are achieved by the features of the independent claims.

[0009] Further implementation forms are apparent from the dependent claims, the description and the Figures.

[0010] A first aspect of the present disclosure provides an apparatus comprising at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform receiving handover information comprising at least one handover condition for a cell switch from a first cell to a second cell, and following a cell switch, evaluating the handover condition for a subsequent cell switch from the second cell to a third cell.

[0011] In an implementation of the first aspect, the at least one memory storing instructions that, when executed by the at least one processor, can cause the apparatus at least to perform determining, whether an early timing advance condition provided as part of the handover information is met for at least one of the second cell and the third cell. The at least one memory storing instructions that, when executed by the at least one processor, can cause the apparatus at least to perform determining, whether an execution condition for a cell switch provided as part of the handover information is met for at least one of the second cell and the third cell.

[0012] In an example, evaluating the handover condition for a subsequent cell switch can comprise evaluating an early timing advance condition for multiple candidate cells. The handover information can comprise information for a condition event relating to a cell switch, wherein the information for the conditional event comprises an event type and at least one condition relating to the event type. The handover information can comprise a consolidated conditional handover configuration, wherein the consolidated conditional handover configuration comprises an event type, at least one condition relating to the event type and set of candidate target cell identifiers.

[0013] The at least one memory storing instructions that, when executed by the at least one processor, can cause the apparatus at least to perform transmitting a Medium Access Control, MAC, control element, CE, message to a serving cell of the apparatus to trigger a cell switch or a subsequent cell switch. The apparatus can comprise user equipment configured to operate in a split radio access network, RAN, architecture comprising a central unit, CU, operatively connected to at least one distributed unit, DU.

[0014] A second aspect of the present disclosure provides an apparatus comprising at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform transmitting a request to a source cell of user equipment for a context modification and conditional handover configuration information, and receiving, from the source cell, at least conditional handover configuration information comprising an early timing advance acquisition condition, and an execution condition associated to at least one candidate cell for a cell switch.

[0015] In an implementation of the second aspect, the at least one memory storing instructions that, when executed by the at least one processor, can cause the apparatus at least to perform transmitting a request to a first target cell for conditional handover configuration information for the first target cell. The at least one memory storing instructions that, when executed by the at least one processor, can cause the apparatus at least to perform transmitting a request to a second target cell for conditional handover configuration information for the second target cell. The at least one memory storing instructions that, when executed by the at least one processor, can cause the apparatus at least to perform generating a conditional handover report configuration, and transmitting the conditional handover report configuration to the source cell of the user equipment. The at least one memory storing instructions that, when executed by the at least one processor, can cause the apparatus at least to perform generating a consolidated conditional handover configuration, wherein the consolidated conditional handover configuration comprises an event type, at least one condition relating to the event type and set of candidate target cell identifiers, and transmitting the consolidated conditional handover configuration to the source cell of the user equipment.

[0016] In an example, the apparatus can comprise a central unit, CU, operatively connected to at least one distributed unit, DU in a split radio access network, RAN, architecture.

[0017] A third aspect of the present disclosure provides a computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following receive handover information comprising at least one handover condition for a cell switch from a first cell to a second cell, and following a cell switch, evaluate the handover condition for a subsequent cell switch from the second cell to a third cell.

[0018] These and other aspects of the invention will be apparent from the embodiment(s) described below.

[0019] Brief Description of the Drawings

[0020] In order that the present disclosure may be more readily understood, embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

[0021] Figure 1 is a schematic representation of a portion of a split radio access network, according to an example; Figure 2 is a signaling chart, according to an example;

[0022] Figure 3 is a signaling chart, according to an example, which is a continuation of the signaling chart of figure 2;

[0023] Figure 4 is a signaling chart, according to an example, which is a continuation of the signaling chart of figure 3;

[0024] Figure 5 is a signaling chart, according to an example;

[0025] Figure 6 is a signalling chart, according to an example, which is a continuation of the signalling chart of figure 5;

[0026] Figure 7 is a signalling chart, according to an example which is a continuation of the signalling chart of figure 6; and

[0027] Figure 8 is a schematic representation of a machine according to an example.

[0028] Detailed Description

[0029] Example embodiments are described below in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

[0030] Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

[0031] The terminology used herein to describe embodiments is not intended to limit the scope. The articles “a,” “an,” and “the” are singular in that they have a single referent, however the use of the singular form in the present document should not preclude the presence of more than one referent. In other words, elements referred to in the singular can number one or more, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and / or “including,” when used herein, specify the presence of stated features, items, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and / or groups thereof. The term “and / or” is only an association relationship for describing associated objects and represents that three relationships may exist such that A and / or B may indicate that A exists alone, A and B exist at the same time, or B exists alone. The character “ / ” generally represents that the associated objects are in an “or” relationship.

[0032] Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealized or overly formal sense unless expressly so defined herein.

[0033] The following contains specific information related to implementations of the present disclosure. The drawings and their accompanying detailed disclosure are merely directed to implementations. However, the present disclosure is not limited to these implementations. Other variations and implementations of the present disclosure will be obvious to those skilled in the art.

[0034] The phrases “in one implementation,” or “in some implementations,” may each refer to one or more of the same or different implementations. The term “coupled” is defined as connected whether directly or indirectly through intervening components and is not necessarily limited to physical connections. The expression “at least one of A, B and C” or “at least one of the following: A, B and C” means “only A, or only B, or only C, or any combination of A, B and C.”

[0035] The terms “system” and “network” may be used interchangeably.

[0036] For the purposes of explanation and non-limitation, specific details such as functional entities, techniques, protocols, and standards are set forth for providing an understanding of the present disclosure. In other examples, detailed disclosure of well-known methods, technologies, systems, and architectures are omitted so as not to obscure the present disclosure with unnecessary details.

[0037] Persons skilled in the art will immediately recognize that any network function(s) or algorithm(s) disclosed may be implemented by hardware, software or a combination of software and hardware. Disclosed functions may correspond to modules which may be software, hardware, firmware, or any combination thereof.

[0038] A software implementation may include machine- and / or computer- readable and / or executable instructions stored on a machine- and / or computer-readable medium such as memory or other types of storage devices. One or more microprocessors or general- purpose computers with communication processing capability may be programmed with corresponding executable instructions and perform the disclosed network function(s) or algorithm(s).

[0039] The microprocessors or general-purpose computers may include Applications Specific Integrated Circuitry (ASIC), programmable logic arrays, and / or using one or more Digital Signal Processor (DSPs). Although some of the disclosed implementations are oriented to software installed and executing on computer hardware, alternative implementations implemented as firmware or as hardware or as a combination of hardware and software are well within the scope of the present disclosure. The computer readable medium includes but is not limited to Random Access Memory (RAM), Read Only Memory (ROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), flash memory, Compact Disc Read- Only Memory (CD-ROM), magnetic cassettes, magnetic tape, magnetic disk storage, or any other equivalent medium capable of storing computer-readable instructions.

[0040] Examples described may be implemented in a communication network, such as any of the following radio access technologies (RATs): Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GPRS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband- code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, and enhanced LTE (eLTE), 5G (also called NR), or any future RAT such as 6G. Moreover, communication within the communication network may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), and / or Discrete Fourier Transform spread OFDM (DFT-s-OFDM).

[0041] As used herein, the term “network device” or “network node” refers to a node in a communication network via which user equipment may access the network and / or which is capable of controlling radio communication and managing radio resources within a cell. The network node or network device may be referred to as a base station (BS), an access point (AP) or an access node. The network device may be, depending on the applied technology, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, or an aircraft network device.

[0042] Moreover, in connection of split radio access network (RAN), the network device may refer to a centralised unit (CU) of a base station and / or a distributed unit (DU) of a base station. An interface between CU and DU may be referred to as an Fl interface in NR. In the split RAN architecture, node operations may be carried out, at least partly, in the central / centralized unit, CU, (e.g. server, host or node) operationally coupled to the DU, (e.g. a radio head / node). One CU may control one or more DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some embodiments, the DUs may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layers. Other functional splits are possible too. In practice, any processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation.

[0043] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example, a terminal device may be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), or a Mobile Station (MS). The terminal device may include a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, USB dongles, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like.

[0044] A term “resource”, as used herein, may refer to radio resources in time domain, in frequency domain, in space domain, and / or in code domain. Some examples of resources include e.g. a physical resource block (PRB), a radio frame, a subframe, a time slot, a subband, a frequency region, a sub-carrier, a beam, etc. The term “transmission” and / or “reception” may refer to wirelessly transmitting and / or receiving via a wireless propagation channel on radio resources.

[0045] Certain acronyms and / or abbreviations may be used herein, such as for example:

[0046] TA - Timing Advance

[0047] TCI state - The IE TCI-State associates one or two DL reference signals with a corresponding quasi-colocation (QCL) type.

[0048] In all the handover types until Release 17 of the 3rd Generation Partnership Project (3GPP), a serving cell change is triggered by layer 3 (L3) measurements and is done by radio resource control (RRC) signalling for a change of primary cell (PCell) and primary secondary cell (PSCell). All cases require reconfiguration of upper layers (e.g., RRC or PDCP) and / or resetting of lower layers (e.g., MAC and / or PHY) which leads to longer latency, larger overhead and longer interruption time than, e.g., beam level mobility.

[0049] Release 18 has introduced layer 1 (Ll) / L2 based mobility also known as lower layer triggered mobility (LTM) to enable a serving cell change via L1 / L2 signalling, while keeping configuration of the upper layers and / or minimizing changes of configuration of the lower layers. This helps to reduce latency, overhead and interruption time during handover. LTM supports both intra-distributed unit (DU) and intra-central unit (CU)- inter-DU mobility.

[0050] Release 19 introduce conditional LTM (C-LTM) as an enhancement to the Release 18 LTM procedure. In C-LTM a UE can autonomously execute a cell switch to a candidate cell based on some network-configured conditions.

[0051] As noted above, LTM enables mobility using lower-layer signalling to reduce overhead and interruption time. LTM supports the use of dual connectivity and carrier aggregation which makes it useful for services requiring high bitrate and short mobility interruption. LTM can also be used for the higher frequency bands above 7 GHz, together with beamforming.

[0052] In a split radio access network architecture, the gNB is separated into a gNB Central Unit (gNB-CU) and one or more gNB Distributed Units (gNB-DU). LTM supports both intra- DU and inter-DU mobility without changing the gNB-CU. A single gNB-DU may control many cells and a gNB-CU may be connected to many gNB-DUs. LTM therefore works for large areas with many cells even with the intra-gNB-CU limitation.

[0053] For Release 19 C-LTM the procedures defined in Release 18 LTM, which were based on network-triggered cell switch, are to be enhanced to support UE-autonomous cell switch triggering. Furthermore, while multiple target cells / beams can be prepared (in the case of LTM), provisions should be kept for facilitating subsequent cell switches instead of implementing fresh preparations.

[0054] For example, in working group discussions relating to conditional cell switching and subsequent conditional LTM, the conditional events and their mapping needs to be configured for each of the LTM candidate cells. The condition and its mapping to candidate cells can be included in the LTM configuration structure similarly to, e.g., SCPAC. However, in SCPAC the conditions are mapped to a L3 measurement ID that does not have candidate cells included in the measurement object. In LTM, the reportconfigurations are mapped to a resource-configuration that comprises candidate-ID and beam information.

[0055] According to an example, to support subsequent C-LTM, the C-LTM related parameters such as an event definition and list of candidates / beams can be introduced within the given resource set in an LTM Report configuration within each candidate RRC configuration. This may include a modification of a report configuration whenever a candidate cell is modified in the LTM configuration. In the SCPAC approach only the candidate ID can be mapped and this requires further changes to include beam specific information.

[0056] According to an example, there is provided apparatus and methods for implementing inter-DU, intra-CU conditional handover in which handover conditions for a UE are evaluated after a cell switch in order to implement a subsequent inter-DU, intra-CU conditional handover according to the same

[0057] Figure 1 is a schematic representation of a portion of a split radio access network, according to an example. In the example of figure 1 gNB 101 is separated into a gNB Central Unit (gNB-CU) 103 and two gNB Distributed Units (gNB-DU), gNB-DUl 105 and gNB-DU2 107. gNB-DUl 105 supports cells 109 (Cell 1) and 111 (Cell 2), whilst gNB-DU2 107 supports cells 113 (Cell 3) and 115 (Cell 5). gNB-DUl 105 and / or gNB-DU2 107 may support more or less cells than those depicted. That is, the gNB-Dus 105, 107 may control many cells and the gNB-CU 103 may be connected to more gNB-DUs than depicted.

[0058] According to an example, a UE 117 is initially in an active state in Cell 2 111 of gNB- DUl 105. In an LTM scenario, in which both intra-DU and inter-DU mobility is supported without changing the gNB-CU, UE 117 may switch cells. For example, UE 117 can switch from Cell 2 111 to Cell 3 113 (i.e., inter-DU mobility), or between Cell 2 111 to Cell 1 109 (i.e., intra-DU mobility). In C-LTM the network can send a handover command to the UE 117 with a condition and the UE 117 applies the handover command when the condition is satisfied. According to an example, UE 117 can receive handover information comprising at least one handover condition for a cell switch from a first cell to a second cell. Following a cell switch, UE 117 can continue to evaluate the handover condition for a subsequent cell switch from the second cell to a third cell. That is, after UE 117 has moved to a target Cell through Cell Switch using C-LTM, there is provision for one or more subsequent autonomous C-LTM switches so that UE 117 can move further to different target Cells using the previously supplied handover conditions. As such, no RRC Reconfiguration is required to be sent to UE 117 from the network for any subsequent cell change.

[0059] With reference to figure 1, following an initial cell switch of UE 117 from Cell 2 111 to Cell 3 113, UE 117 continues to evaluate the handover conditions that were provided (and from which the C-LTM handover from Cell 2 111 to Cell 3 113 was predicated). If it determines that the conditions are met, UE 117 may autonomously perform a subsequent cell switch from, e.g., Cell 3 113 to Cell 4 115. Further evaluation of the handover conditions may then lead UE 117 to autonomously perform a subsequent cell switch from Cell 4 115 to, e.g., Cell 1 109.

[0060] Figure 2 is a signaling chart, according to an example. At 1, a L3 measurement report is received by a source DU 105 from UE 117. At 2, the source DU 105 transmits an uplink (UL) RRC message to CU 103 containing the L3 Measurement Report from the UE 117. After receipt of the L3 Measurement Report, the CU 103 analyzes the report and triggers LTM candidate preparation (3). At 4, a UE context setup request is sent from the CU 103 to Target DU1 107 with at least one candidate cell. In an example, an indication is added in this message to obtain a C-LTM Report Configuration from DU1 107. Accordingly, at 5, a UE context setup response is sent from Target DU1 107 to CU 103 with a C-LTM Report Configuration comprising:

[0061] 1. Early TA acquisition condition (optional)

[0062] 2Execution condition for candidate cells and beams

[0063] At 6, the UE context setup request is sent from CU 103 to a Target DU2 201 with the candidate Cell. An indication is added in this message to obtain a C-LTM Report Configuration from the DU 201. In the example of figure 2, target DU1 (which is also show in figure 1) and target DU2 201 are both connected to the same CU 103 so that cell switching is intra-CU / gNB and inter-DU.

[0064] At 7, a UE context setup response is sent from Target DU2 201 to CU 103 with a C-LTM Report Configuration comprising:

[0065] 1. Early TA acquisition condition (optional)

[0066] 2Execution condition for candidate cells and beams

[0067] At 8, a UE context modification request is sent from CU 103 to Source DU 105 with an indication to obtain a C-LTM Report Configuration from source DU 105. In response, at 9, a UE context modification response is sent from source DU 105 to CU 103 with a C- LTM Report Config comprising:

[0068] 1. Early TA acquisition condition (optional)

[0069] 2Execution condition for candidate cells and beams.

[0070] CU 103 therefore obtains a UE context setup response with a C-LTM Report Configuration from the target / candidate DUs.

[0071] At 10, CU 103 generates an RRC Reconfiguration to be sent to UE 117 with a C-LTM report configuration generated on the basis of the received UE Context Setup Responses and the UE Context Modification Response. CU 103 can then send (11) a downlink (DL) RRC message containing the RRC Reconfiguration to source DU 105.

[0072] According to an example, for each candidate cell a Configuration for a prepared cell received from the DUs is included and a C-LTM Report Configuration comprising:

[0073] 1. Early TA acquisition condition (optional)

[0074] 2. Execution condition for candidate cells and beams

[0075] At 12, the RRC Reconfiguration (with the above configuration) is sent from the Source- DU 105 to UE 117. In an example, for each candidate cell, the following information is therefore received by UE 117: For each candidate cell, a configuration of prepared cell received by UE 117 from DUs of the CU 103, and a C-LTM Report Configuration comprising:

[0076] 1. Early TA acquisition condition (optional)

[0077] 2. Execution condition for candidate cells and beams

[0078] An RRC Reconfiguration Complete message is sent (13) from UE 117 to Source-DU 105, and, at 14 an UL RRC message transfer containing the RRC Reconfiguration Complete message is sent from the Source-DU 105 to CU 103.

[0079] According to example, at 15, UE 117 evaluates if early TA condition in ReportConfig of the sourceDUConfig is met for any Candidate.

[0080] Figure 3 is a signaling chart, according to an example. The signaling in figure 3 is a continuation of that from that of figure 2. With reference to figure 3, at 1, DL Synchronization is performed with the candidate Cells. If (at 2) early TA acquisition condition (received at 9 in figure 2) is met at UE 117 for target DU1 113 then preamble (i.e., a TA Preamble received at step 9 in figure 2) is sent (3) to candidate cells for early TA acquisition.

[0081] At 4, an execution condition received in the Report Configuration of source DU 105 is met for Target DU1 113. Accordingly, at 5 to 14 of figure 3, a Cell switch procedure to move to a cell of target DU1 107 is executed and path switch procedure is completed.

[0082] However, according to an example, UE 117 continues to evaluate if early TA condition in ReportConfig of the CandidateConfig of DU1 is met for any Candidate.

[0083] Figure 4 is a signaling chart, according to an example. The signaling in figure 4 is a continuation of that from that of figure 3. Similarly to that described with reference to figure 3, at 1, DL Synchronization is performed with the candidate Cells. If (at 2) early TA acquisition condition (received at 9 in figure 2) is met at UE 117 for target DU2 201 then preamble (i.e., a TA Preamble received at step 9 in figure 2) is sent (3) to candidate cells for early TA acquisition.

[0084] At 4, an execution condition received in the Report Configuration of source DU 105 is met for Target DU2 201. Accordingly, at 5 to 14 of figure 4, a Cell switch procedure to move to a cell of target DU2 is executed and path switch procedure is completed. As such, following a cell switch of UE 117, handover conditions can continue to be evaluated by UE 117 such that, if the conditions are met, UE 117 can autonomously perform a subsequent cell switch without the need for an RRC Reconfiguration to be sent to UE 117 from the network for the subsequent cell change.

[0085] In the example described with reference to figures 2 to 4, CU 103 fetches the Report Configuration for a subsequent Cell change for UE 117 (from the Target DUs) when fetching the Configuration from the Target DUs. UE 117 picks up SSB information of candidate cells from the LTM-Candidate-cells.

[0086] The LTM-Report-Config information element in the RRC Configuration message of each LTM-Candidate has, according to an example, the following new information element:

[0087] - A Conditional Event containing: o A List of Resource-config-IDs [comprising candidate cells and beams], o An Event-type. o A Condition to select beam within candidate.

[0088] Figure 5 is a signaling chart, according to an example. At 1 of figure 5, a L3 Measurement Report is received by source DU 105 from UE 117. An UL RRC message is sent from Source DU 105 to CU 103 containing the above received L3 Measurement Report. At 3, CU 103 analyses the L3 Measurement Report and triggers LTM candidate preparation for UE 117. At 4, a UE context setup request is sent from CU 103 to Target DU1 113 with candidate cells. At 5, a UE context setup response is sent from Target DU1 113 to CU 103. The UE context response indicates the Report-Config-ID to be used for C-LTM and the condition(s) for beams within Candidate cells (which, in an example, can be used for a subsequent Cell Switch case).

[0089] At 6, a UE context setup request is sent from CU 103 to Target DU1 113 with candidate Cells. At 7, a UE context setup response is sent from Target DU2 201 to CU 103 indicating the Report-Config-ID to be used for C-LTM and the condition(s) for beams within Candidate cells (which, in an example, can be used for a subsequent Cell Switch case).

[0090] At 8, a UE context modification request is sent from CU 103 to the Source DU 105. At 9, a UE context modification response is sent from Source DU 105 to CU 103 indicating the Report-Config-ID to be used for C-LTM, and the condition(s) for beams within Candidate cells (to be used for a current Cell Switch case).

[0091] According to an example, on the basis of the information received by the CU 103 from the DUs, at 10, CU 103 generates an RRC Reconfiguration with a common C-LTM Configuration for all candidates, which includes the following information:

[0092] • Event-type

[0093] • Condition to select the candidate

[0094] • EarlyTA condition (optional)

[0095] • Execution condition

[0096] • List of Candidate-IDs

[0097] • List of Candidate Configurations of all Target DUS

[0098] • include subsequent-LTM structure in corresponding LTMCandidateConfig

[0099] • include the Flag "Conditional -Exec" and "Report-needed-prior-execution".

[0100] In an example, this "Report-needed-prior-execution" helps the serving DU know the report that triggers the C-LTM.

[0101] At 11, CU 103 sends the above generated RRC Reconfiguration message to the Source DU 105 in a DL RRC message transfer. The Source DU 105 sends (12) the received RRC Reconfiguration to UE 117. The RRC Reconfiguration sent to UE 117 from Source DU 105 comprises the following parameters:

[0102] • Event-type

[0103] • Condition to select the candidate

[0104] • EarlyTA condition (optional)

[0105] • Execution condition

[0106] • List of Candidate-IDs

[0107] List of Candidate Configurations of all Target DUS • include subsequent-LTM structure in corresponding LTMCandidateConfig

[0108] • include the Flag "Conditional -Exec" and "Report-needed-prior-execution".

[0109] At 13, an RRC Reconfiguration Complete message is sent from UE 117 to Source DU 105, and an UL RRC message transfer containing the RRC Reconfiguration Complete message is sent (14) from the Source DU 105 to CU 103.

[0110] The UE 117 evaluates if early an TA condition available in ReportConfig of Source DU 105 (if condition is present) is met for any Candidate cell.

[0111] Figure 6 is a signalling chart, according to an example. The signalling in figure 6 is a continuation of that from that of figure 5. At 1 of figure 6, DL Synchronization is done with the candidate Cells. If an early TA acquisition condition is met (2) for Target DU1 113, TA acquisition is performed (3).

[0112] At 4, an execution condition in ReportConfig of Source DU 105 is met for the Target DU1 113. UE sends (6) a report that triggers the C-LTM to Source DU 105 using MAC- CE (if "Report-needed-prior-execution" is set to true). UE 117 initiates (7) a Random access process (if needed) towards a target cell of target DU1 113, and at 8, a cell switch is triggered by UE 117 to the target cell of target DU1 113. An RRC Reconfiguration Complete message is sent (9) from UE 117 to Target DU1 113, and an UL RRC message transfer is performed (10) from Target DU1 113 to CU 103. At 11, an access notification is performed from Target DU1 113 to CU 103. At 12, a no UE context release command is sent from CU 103 to the source DU 105. At 13, a UE context Modification Request is sent from CU 103 to the Source DU 105, and a UE context Modification Response is sent (14) from the Source DU 105 to CU 103. At 15, there is a path switch for UE 117.

[0113] At 16, UE 117 replaces the Cond-LTM-Configuration structure with the same structure of LTM-Subsequent-cond-config in CandidateLTMConfig of Target DU1 113, and UE 117 continues the evaluation if early TA condition in ReportConfig of Target DU1 113 (if condition is present) is met for any candidate.

[0114] Figure 7 is a signalling chart, according to an example. The signalling in figure 7 is a continuation of that from that of figure 6. At 1 of figure 7, DL Synchronization is performed with the candidate Cells. If an early TA acquisition condition is met for Target DU1 113 (2) TA acquisition is performed (3). At 4, if an execution condition in ReportConfig of Target DU1 113 is met for the Target DU2 201 UE 117 sends (6) the report that triggers the C-LTM to Target DU1 113 using MAC-CE (if "Report-needed-prior-execution" is set to true). Then, UE 117 performs a Random access process (if needed, 7) towards a Target Cell of Target DU2 201. At 8, a cell switch is triggered by UE 117 to the Target Cell of Target DU2 201, and an RRC Reconfiguration Complete message is sent (9) from UE 117 to Target DU2 201.

[0115] At 10, an UL RRC message is transferred from Target DU2 201 to CU 103, and an access notification is sent (11) from Target DU2 201 to CU 103. At 12, a no UE context release command is sent from CU 103 to the Target DU1 113. At 13, a UE context Modification Request is sent from CU 103 to the Target DU1 113, and a UE context Modification Response is sent (14) from the Target DU1 113 to CU 103. At 15, there is a path switch for UE 117.

[0116] Accordingly, each DU indicates to the CU 103 the Report-Config-ID to be used for C- LTM. The Report-config in the Candidate-RRC message can include a flag: Conditional- Execution. Furthermore, a flag: Report-needed-prior-execution can be included to aid the serving DU to know the report that triggers the C-LTM for UE 117.

[0117] According to an example, with reference to figures 2 to 4, CU 103 sends a Report Configuration comprising the Condition and Event Type of DUs transparently (i.e., in the corresponding candidate configuration structure as received from DUs). Thus, an information element in the LTM-Report-Configuration in the RRC Configuration of each LTM-Candidate will comprise:

[0118] • A Conditional Event comprising: o A List of Resource-config-ID [Consists of candidate-cell and beams], o An Event-type. o A Condition to select beam within candidate

[0119] According to an example, with reference to figures 5 to 7, CU 103 intervenes and constructs the Conditional Configuration comprising the Condition and Event Type for Subsequent Cell Changes (there are two relevant information elements, i.e., the Cond- LTM-Configuration and the LTM-Subsequent-cond-configuration in the relevant RRC Reconfiguration message). Thus, an LTM-Candidate-configuration will comprise a subsequent-LTM structure similar to that of the Service Communication Proxy and Access Control (SCPAC). An Event type and list of candidate IDs is provided, and the LTM-CSI-Resource-configuration does not include resources to align with candidates needed for C-LTM. When UE 117 evaluates this event and the condition is met, the UE 117 can select the candidate from the set of candidates meeting the condition. If two candidates meet same condition the best beam within the resource-set will decide the execution condition. Each DU can indicate to the CU the Report-Config-ID to be used for C-LTM. The Report-configuration in the Candidate-RRC message can include the Flag: Conditional-Exec. Furthermore, a Flag: Report-needed-prior-execution can be included to aid the serving DU to know the report that triggers the C-LTM.

[0120] In the context of the Release 18 network energy saving feature, conditional evaluation is linked to a network energy saving (NES) mode of the serving cell. That is, conditional evaluation for events will be triggered when the serving cell is in a NES mode. Similar triggering can be considered for Cellular Low Power Wide Area (LPWA) technologies (CLTM), where criteria such as availability of timing advance and early downlink synchronization may be used. This way, LTM can benefit from the increased robustness of conditional cell switch execution without compromising on interruption time during cell switch.

[0121] If the network wants to allow conditional LTM to be triggered towards the candidate cells for which early TA acquisition and TCI state activation is completed, the event definition need not include candidate resource set information. It can be implicitly formed on completion of the above steps.

[0122] To allow the network to start the early TA and early TCI state activation at an appropriate time prior to CLTM, the network may configure separate LTM events with event parameters for A3 slightly earlier than the events defined as condition for CLTM. Alternatively additional offset for early reporting for the condition can be used to indicate that DU to start the early sync related actions for CLTM.

[0123] Examples in the present disclosure can be provided as methods, systems or machine- readable instructions, such as any combination of software, hardware, firmware or the like. Such machine-readable instructions may be included on a computer readable storage medium (including but not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0124] The present disclosure is described with reference to flow charts and / or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. In some examples, some blocks of the flow diagrams may not be necessary and / or additional blocks may be added. It shall be understood that each flow and / or block in the flow charts and / or block diagrams, as well as combinations of the flows and / or diagrams in the flow charts and / or block diagrams can be realized by machine readable instructions.

[0125] The machine-readable instructions may, for example, be executed by a machine such as a general-purpose computer, a platform comprising user equipment such as a smart device, e.g., a smart phone, a special purpose computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing apparatus may execute the machine-readable instructions. Thus, modules of apparatus may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term 'processor' is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate set etc. The methods and modules may all be performed by a single processor or divided amongst several processors.

[0126] Such machine-readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode. For example, the instructions may be provided on a non-transitory computer readable storage medium encoded with instructions, executable by a processor.

[0127] Figure 8 is a schematic representation of a machine according to an example. The machine 800 can be, e.g., a system or apparatus, network node, user equipment, or parts thereof. The machine 800 comprises a processor 803, and a memory 805 to store instructions 802, executable by the processor 803. The machine comprises a storage 809 that can be used to store data 811.

[0128] In an example, the instructions 807, executable by the processor 803, can cause the machine 800 (e.g., a UE 117) to receive handover information comprising at least one handover condition for a cell switch from a first cell to a second cell, and following a cell switch, evaluate the handover condition for a subsequent cell switch from the second cell to a third cell.

[0129] In another example, the instructions 807, executable by the processor 803, can cause the machine 800 (e.g., a CU 103) to transmit a request to a source cell of user equipment for a context modification and conditional handover configuration information, and receive, from the source cell, at least conditional handover configuration information comprising an early timing advance acquisition condition, and an execution condition associated to at least one candidate cell for a cell switch.

[0130] Accordingly, the machine 800 can implement a method for conditional handover, such as conditional handover in a split radio access network, RAN, architecture comprising a central unit, CU, operatively connected to at least one distributed unit, DU.

[0131] Such machine-readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer-implemented processing, thus the instructions executed on the computer, or other programmable devices provide an operation for realizing functions specified by flow(s) in the flow charts and / or block(s) in the block diagrams.

[0132] Further, the teachings herein may be implemented in the form of a computer or software product, such as a non-transitory machine-readable storage medium, the computer software or product being stored in a storage medium and comprising a plurality of instructions, e.g., machine readable instructions, for making a computer device implement the methods recited in the examples of the present disclosure.

[0133] In some examples, some methods can be performed in a cloud-computing or networkbased environment. Cloud-computing environments may provide various services and applications via the Internet. These cloud-based services (e.g., software as a service, platform as a service, infrastructure as a service, etc.) may be accessible through a web browser or other remote interface of the user equipment for example. Various functions described herein may be provided through a remote desktop environment or any other cloud-based computing environment.

[0134] While various embodiments have been described and / or illustrated herein in the context of fully functional computing systems, one or more of these exemplary embodiments may be distributed as a program product in a variety of forms, regardless of the particular type of computer-readable-storage media used to actually carry out the distribution. The embodiments disclosed herein may also be implemented using software modules that perform certain tasks. These software modules may include script, batch, or other executable files that may be stored on a computer-readable storage medium or in a computing system. In some embodiments, these software modules may configure a computing system to perform one or more of the exemplary embodiments disclosed herein. In addition, one or more of the modules described herein may transform data, physical devices, and / or representations of physical devices from one form to another.

[0135] The preceding description has been provided to enable others skilled in the art to best utilize various aspects of the exemplary embodiments disclosed herein. This exemplary description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible without departing from the spirit and scope of the instant disclosure. The embodiments disclosed herein should be considered in all respects illustrative and not restrictive. Reference should be made to the appended claims and their equivalents in determining the scope of the instant disclosure.

Claims

22CLAIMS1. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving handover information comprising at least one handover condition for a cell switch from a first cell to a second cell; and following a cell switch, evaluating the handover condition for a subsequent cell switch from the second cell to a third cell.

2. The apparatus of claim 1, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: determining, whether an early timing advance condition provided as part of the handover information is met for at least one of the second cell and the third cell.

3. The apparatus of claim 1 or 2, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: determining, whether an execution condition for a cell switch provided as part of the handover information is met for at least one of the second cell and the third cell.

4. The apparatus of any preceding claim, wherein evaluating the handover condition for a subsequent cell switch comprises evaluating an early timing advance condition for multiple candidate cells.

5. The apparatus of any preceding claim, wherein the handover information comprises information for a condition event relating to a cell switch, wherein the information for the conditional event comprises an event type and at least one condition relating to the event type.

6. The apparatus of any of claims 1 to 4, wherein the handover information comprises a consolidated conditional handover configuration, wherein the consolidated conditional handover configuration comprises an event type, at least one condition relating to the event type and set of candidate target cell identifiers.

7. The apparatus of any preceding claim, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: transmitting a Medium Access Control, MAC, control element, CE, message to a serving cell of the apparatus to trigger a cell switch or a subsequent cell switch.

8. The apparatus of any preceding claim, wherein the apparatus comprises user equipment configured to operate in a split radio access network, RAN, architecture comprising a central unit, CU, operatively connected to at least one distributed unit, DU.

9. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: transmitting a request to a source cell of user equipment for a context modification and conditional handover configuration information; and receiving, from the source cell, at least conditional handover configuration information comprising an early timing advance acquisition condition, and an execution condition associated to at least one candidate cell for a cell switch.

10. The apparatus of claim 9, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: transmitting a request to a first target cell for conditional handover configuration information for the first target cell.

11. The apparatus of claim 9 or 10, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: transmitting a request to a second target cell for conditional handover configuration information for the second target cell.

12. The apparatus of any of claims 9 to 11, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: generating a conditional handover report configuration; and transmitting the conditional handover report configuration to the source cell of the user equipment.

13. The apparatus of any of claims 9 to 11, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: generating a consolidated conditional handover configuration, wherein the consolidated conditional handover configuration comprises an event type, at least one condition relating to the event type and set of candidate target cell identifiers; and transmitting the consolidated conditional handover configuration to the source cell of the user equipment.

14. The apparatus of any of claims 9 to 13, wherein the apparatus comprises a central unit, CU, operatively connected to at least one distributed unit, DU in a split radio access network, RAN, architecture.

15. A computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receive handover information comprising at least one handover condition for a cell switch from a first cell to a second cell; and25 following a cell switch, evaluate the handover condition for a subsequent cell switch from the second cell to a third cell.

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