Method, apparatus and computer program

Abstract

There is provided an apparatus, method, and computer program for causing an apparatus to perform: maintaining a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and a candidate cell prior to a mobility event between the apparatus and the candidate cell being triggered; identifying a plurality of candidate cells that have fulfilled one or more of the conditions; selecting a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled; and performing the mobility event with the selected candidate cell.

Description

METHOD, APPARATUS AND COMPUTER PROGRAMFIELD

[0001] The present application relates to selecting a candidate cell from a plurality of candidate cells.BACKGROUND

[0002] A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and / or other nodes by providing carriers between the various entities involved in the communications session. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email), text message, multimedia and / or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

[0003] The communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and / or parameters which shall be used for the connection are also typically defined. One example of a communications system is UTRAN (Universal Mobile Telecommunications Service terrestrial radio access network (e.g., 3G radio)). Other examples of communication systems are the longterm evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology and so-called 5G or New Radio (NR) networks. NR is being standardized by the 3rd Generation Partnership Project (3GPP).SUMMARY

[0004] According to a first aspect, there is provided an apparatus comprising means for: maintaining a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and a candidate cell prior to a mobility event between the apparatus and the candidate cell being triggered; identifying a plurality of candidate cells that have fulfilled one or more of the conditions; selecting a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled; and performing the mobility event with the selected candidate cell.

[0005] According to a second aspect, there is provided an apparatus comprising: at least one processor; and at least one memory comprising code that, when executed by the at least one processor, causes the apparatus to perform: maintaining a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and a candidate ceil prior to a mobility event between the apparatus and the candidate cell being triggered; identifying a plurality of candidate cells that have fulfilled one or more of the conditions; selecting a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled; and performing the mobility event with the selected candidate cell.

[0006] According to a third aspect, there is provided a method for an apparatus, the method comprising: maintaining a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and a candidate cell prior to a mobility event between the apparatus and the candidate cell being triggered; identifying a plurality of candidate cells that have fulfilled one or more of the conditions; selecting a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled; and performing the mobility event with the selected candidate cell.

[0007] According to a fourth aspect, there is provided an apparatus comprising: maintaining circuitry for maintaining a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and acandidate cell prior to a mobility event between the apparatus and the candidate cell being triggered; identifying circuitry for identifying a plurality of candidate cells that have fulfilled one or more of the conditions; selecting circuitry for selecting a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled; and performing circuitry for performing the mobility event with the selected candidate cell.

[0008] The following may apply in respect of any (e.g., one or more, including all) of the above first to fourth aspects.

[0009] The selecting a candidate cell using a set of prioritisation rules may comprise: determining a set of candidate cells from the plurality of candidate cells by: determining, for each candidate cell of a plurality of candidate cells, how many conditions have been fulfilled by that candidate cell; and selecting the set of candidate cells that have fulfilled the most conditions; and selecting a candidate cell from the set of candidate cells.

[0010] The selecting a single candidate cell using a set of prioritisation rules may comprise: determining a set of candidate cells from the plurality of candidate cells by: determining, for each candidate cell of a plurality of candidate cells, which conditions have been fulfilled by that candidate cell, wherein each condition is associated with a respective time; and determining the set of candidate cells by selecting those candidate cells whose total fulfilled conditions are associated with a highest cumulative time; and selecting a candidate cell from the set of candidate cells.

[0011] The set of candidate cells may comprise more than one candidate cell, and the selecting may comprise: comparing respective measured signal qualities of the more than one candidate cell to identify a candidate cell that has the best measured signal quality; and selecting the identified candidate cell as the selected candidate cell.

[0012] The set of candidate cells may comprise a single candidate cell.

[0013] The set of conditions may comprise at least one of: a completion and / or initiation of an uplink time and / or frequency synchronisation procedure with a candidate ceil, or a completion and / or initiation downlink time and / or frequency synchronisation procedure with a candidate cell.

[0014] The set of conditions may comprise at least one of: obtaining an initial downlink time and / or frequency synchronisation with a candidate cell; maintaining a downlink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial downlink time and / or frequency synchronisation with the candidate cell; obtaining an initial path loss estimate for signals communicated between the apparatus and the candidate cell; maintaining a path loss estimate for signals communicated between the apparatus and the candidate cell; obtaining an initial uplink time and / or frequency synchronisation with a candidate cell; maintaining an uplink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial uplink time and / or frequency synchronisation with the candidate cell; initiating and / or completing Abstract Syntax Notation One (ASN. 1 ) decoding of a candidate cell’s radio resource control, RRC, configuration; or initiating and / or completing validity checking of a candidate cell’s RRC configuration.

[0015] The apparatus may maintain at least one property of the one or more actions, wherein the at least one property of the one or more actions may comprise at least one of: a time when said one or more actions was initiated; a time when said one or more actions was completed; a type of reference signal used for said one or more actions; a type of timing acquisition method used for said one or more actions; or a type of transmission configuration indication state corresponding to a candidate cell during said one or more actions.

[0016] The set of conditions may comprise at least one of: obtaining an initial downlink time and / or frequency synchronisation with a candidate cell; or maintaining a downlink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial downlink time and / or frequency synchronisation with the candidate cell, and the prioritisation rules may be further based on a type of reference signal used when the one or more conditions in the set of conditions are fulfilled.

[0017] The prioritisation rules may be configured so that a candidate cell for which downlink time and / or frequency synchronisation is performed using a channel state information reference signal is prioritised for said selection as the selected candidate cell over a candidate cell for which downlink time and / or frequency synchronisation is performed using a synchronisation signal burst.

[0018] The apparatus may be caused to obtain the set of conditions from a serving network access node and / or an operations and management function.

[0019] The apparatus may be caused to obtain, from a network access node, one or more cell switch conditions, wherein a cell switch condition is a condition that causes the apparatus to initiate a cell switch to that candidate cell when that cell switch condition is determined to be fulfilled, wherein the selecting the candidate cell is performed based on a determination that one or more measurements corresponding to candidate cells of the plurality of candidate cells fulfil the one or more cell switch conditions.

[0020] The mobility event may comprise a conditional layer 1 and / or layer 2- triggered mobility event.

[0021] The mobility event may comprise at least one of: a handover event, or a dualconnectivity event.

[0022] According to an aspect, there is provided a non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least the method according to any of the preceding aspects.

[0023] in the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above.DESCRIPTION OF FIGURES

[0024] Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

[0025] Figure 1 shows a representation of a network system according to some example embodiments;

[0026] Figure 2 shows a representation of a control apparatus according to some example embodiments;

[0027] Figure 3 shows a representation of an apparatus according to some example embodiments;

[0028] Figures 4 and 5 illustrate example signalling and / or methods; and

[0029] Figure 6 illustrates example methods that may be performed by an apparatus described herein.DETAILED DESCRIPTION

[0030] The following describes operations that may be performed in relation to selecting one or more ceils out of a plurality of cells for performing a mobility event, such as a cell switch event (e.g., a conditional cell handover).

[0031] In more detail, the following a method in which an apparatus such as a user equipment (UE) is configured with one or more rules for prioritizing a cell for selection. These rules may be configured to prioritise those cells for selection (e.g., make a cell more likely to be selected) that are expected to have a shorter cell switch time than other cells being considered for selection. Stated differently, the rules may be configured to select a cell that the UE is expected to be able to connect to quicker than other cells being considered during the selection.

[0032] A cell may be considered to have a shorter cell switch time when it is expected to have the shortest handover time, a handover time that is less than a threshold amount, and / or has one of the nth shortest handover times (where n may be any integer configured at the apparatus for this purpose).

[0033] Although this will be discussed in more detail later, the following first presents an example environment in which the presently described techniques may be deployed, with reference to Figures 1 to 3.

[0034] Figure 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented.

[0035] Figure 1 shows an example communication environment 100 in which example embodiments of the present disclosure can be implemented.

[0036] In the communication environment 100, a plurality of communication devices, comprising user devices 110 and 115 (also referred to herein as a “terminal” or “terminal device”) and a network device 120 (also referred to herein as a “network access node”), can communicate with each other. The network device 120 may serve a coverage area, called a ceil 125. The user device 110 may have access to a communication network via the cell 125. In some example embodiments, both theuser device 110 and the network device 120 may be configured to implement a beamforming technique and communicate with each other via a plurality of beams.

[0037] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a mobile device, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), a machine-type communications (MTC) device, 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. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user device”, “user equipment” and “UE” may be used interchangeably.

[0038] As used herein, the term “network device” is used interchangeably with “network access node”, and refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or nonground network device such as a satellite network device, a low earth orbit (LEO)satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0039] In some example embodiments, a link from the network device 120 to the user device 110 or 115 is referred to as a DL, while a link from the user device 110 or 115 to the network device 120 is referred to as a UL. Links are also referred to herein as “channels”. In DL, the network device 120 is a Tx device (or a transmitter), and the user device 110 or 115 is a Rx device (or a receiver). In UL, the user device 110 or 115 is a Tx device (or a transmitter), and the network device 120 is a Rx device (or a receiver). A link between the user device 110 and another user device (not shown) is referred to as a sidelink (SL). In SL, one of the user devices is a Tx device (or a transmitter), and the other of the user devices is a Rx device (or a receiver).

[0040] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1 G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), the sixth generation (6G), and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s- OFDM) and / or any other technologies currently known or to be developed in the future.

[0041] Figure 2 illustrates an example of a control apparatus 200 for causing a network device 120 (such as the network device described in Figure 1 ) to perform its operations. The control apparatus may comprise at least one random access memory (RAM) 211a, at least on read only memory (ROM) 211 b, at least one processor 212, 213 and an input / output interface 214. The at least one processor 212, 213 may be coupled to the RAM 211 a and the ROM 211 b. The at least one processor 212, 213 may be configured to execute an appropriate software code 215. The software code 215 may for example allow to perform one or more steps to perform one or more of the present aspects. The software code 215 may be stored in the ROM 211 b. The control apparatus 200 may be interconnected with another control apparatus 200 controlling another function of the network device. In some embodiments, each function of the network device comprises a control apparatus 200. In some exemplary embodiments, the apparatus 200 may be implemented at the network device 120 or may be the network device 120. References to “code” herein are understood to refer to software code, and vice versa.

[0042] Network devices of an access system may further be categorised into two different types: distributed units (Dlls), and centralised units (CUs).

[0043] A DU provides access node support for lower layers of the protocol stack (such as, for example, the radio link control (RLC), medium access control (MAC), and / or physical layer protocol layers). Each DU is able to support one or more cells, while each cell is able to support one or more beams.

[0044] A CU can support multiple DUs, and provides access node support for higher layers of the protocol stack within an access node (such as, for example, packet data convergence protocol (PDCP), service data adaptation protocol (SDAP), and / or radio resource control (RRC) protocol layers). The interface between a CU and a DU is labelled as an F1 interface. There is a single CU for each gNB, and CU’s belonging to multiple gNB may be implemented using a shared hardware platform.

[0045] A RAN (Radio Access Network) node or network node or access node like e.g. a gNB, base station, a CU or DU or parts thereof may be implemented using e.g. an apparatus with at least one processor and / or at least one memory (with computer-readable instructions (computer program)) configured to support and / or provision and / or process CU and / or DU related functionality and / or features, and / orat least one protocol (sub-)layer of a RAN (Radio Access Network), e.g. layer 2 and / or layer 3.

[0046] The CU and DU parts may e.g., be co-located or physically separated. The DU may even be split further, e.g., into two parts, e.g., one including processing equipment and one including an antenna. Hereinafter, in various example embodiments of the present disclosure, the CU-CP (or more generically, the CU) may also be referred to as a network node that supports at least one of central unit control plane functionality or a layer 3 protocol of a radio access network; and similarly, the DU may be referred to as a network node that supports at least one of distributed unit functionality or the layer 2 protocol of the radio access network.

[0047] A DU supports one or multiple cells, and could thus serve as e.g., a serving cell for a user equipment (UE).

[0048] The following description also provides illustrative examples with reference to dual connectivity (DC) systems. DC systems may comprise a master node and at least one secondary node. It is understood that the presently described principles are not limited to such terminology, and may be applied to other systems having a similar architecture.

[0049] PSCells are a type of cell currently defined in 5G New Radio, along with Primary Cells (PCells), Secondary Cells (SCells) and Special Cells (SpCells). A PCell may be used as part of an initial access between a UE and an access network, and is considered to be a main cell in a master cell group (MCG). A PSCell may be comprised as part of a secondary cell group (SCG). The SpCells and SCells may be in at least one of the MCG and the SCG.

[0050] The cells may be controlled by network nodes. There are a maximum of two different types of network nodes in 5G New Radio: Master nodes (which provide a control plane connection to a core network); and Secondary Nodes (which do not have control plane connections to the core network). It is understood that not all 5G system deployments may comprise a master node and a secondary node. For example, the Master and Secondary nodes may be present in a master node-dual connectivity deployment, but not in a standalone deployment. The Master and Secondary nodes may both provide user plane (e.g. data) connections to the core network. The Master node may control the PCell. In addition to the PCell, the Masternode may control at least one PSCell, although this is not always the case. The Secondary node may control at least one PSCell.

[0051] Figure 3 illustrates an example of a terminal 300, such as the user device 110, 115 illustrated on Figure 1. The terminal 300 may be provided by any device capable of sending and receiving radio signals, such as the user device described herein. The terminal 300 may provide, for example, communication of data for carrying communications. The communications may be one or more of voice, electronic mail (email), text message, multimedia, data, machine data and so on.

[0052] The terminal 300 may receive signals over an air or radio interface 307 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 3 transceiver apparatus is designated schematically by block 306. The transceiver apparatus 306 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

[0053] The terminal 300 may be provided with at least one processor 301 , at least one memory ROM 302a, at least one RAM 302b and other possible components 303 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems (such as a network access system provided by the network device described above in relation to Figures 1 and 2) and other communication devices. The at least one processor 301 is coupled to the RAM 302b and the ROM 302a. The at least one processor 301 may be configured to execute an appropriate software code 308. The software code 308 may for example allow to perform one or more of the present aspects. The software code 308 may be stored in the ROM 302a.

[0054] The processor, storage and other relevant control apparatus can be provided on an appropriate circuit board and / or in chipsets. This feature is denoted by reference 304. The device may optionally have a user interface such as key pad 305, touch sensitive screen or pad, combinations thereof or the like. Optionally one or more of a display, a speaker and a microphone may be provided depending on the type of the device.

[0055] In some exemplary embodiments, the terminal 300 may be an apparatus comprising at least one processor and at least one memory storing instructions that,when executed by the at least one processor, cause a user device 110, 115 to perform examples or embodiments described in this document.

[0056] In any telecoms technology (2G, 3G, 4G or 5G), mobility-related decisions may be performed by a network access node based on measurement reports received from the UE and / or by a UE that has been preconfigured with one or more conditions that, when fulfilled, allow the UE to initiate handover from a source cell (also referred to herein as a serving cell) to a candidate cell. These are referred to herein as network initiated handover and conditional handover herein.

[0057] For network initiated handover, a network access node may determine, from the measurement report(s) that the UE is to be handed over from a current serving cell to a candidate cell that can provide better service to the UE than the serving cell, and signal an instruction to the UE to perform that handover. The measurement report(s) may comprise one or more measurement metrics obtained by a UE that indicates a signal quality of one or more cells. There are multiple measurement metrics (e.g., Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Signal to Interference and Noise Ratio (SINR)), multiple times (e.g., periodic, event triggered, etc.) and multiple ways in which a UE may measure a signal quality of the UE’s serving cell and neighbor cells.

[0058] For conditional handover, a network access node may determine that the UE is likely to handover in the near future. The network access node may subsequently provide the UE with some monitoring and cell switch execution conditions for determining when the UE is to handover to at least one of a plurality of candidate cells as part of a conditional mobility event.

[0059] Stated differently, for conditional handover methods, a network access node configures a UE with one or more cell switch execution conditions that, when fulfilled, causes the UE to attempt a handover from its current serving cell to a new serving cell. These are known as conditional handovers as handover is performed when one or more conditions are fulfilled at the UE. These conditions are also referred to as “cell switch execution conditions” and / or “conditional handover configuration” herein, and it is understood that these expressions are used interchangeably.

[0060] In general, a conditional handover event may be considered to be a procedure in which a UE is configured with (e.g., via signalling from a networkaccess node) a conditional handover configuration. The conditional handover configuration comprises a set of cell switch execution conditions per candidate cell. When the UE determines that at least one of those cell switch execution conditions have been fulfilled, the UE initiates handover to the candidate cell.

[0061] For example, Layer 3 (L3) conditional handover (e.g., network protocol layer conditional handover) is a procedure in which a network configures a UE with one or more signal threshold-based conditions for one or more cells. The UE performs signal-based measurements on signals transmitted by those cells to evaluate the signal threshold-based conditions. In the event of a signal threshold-based condition for a cell becoming met (e.g., when the measured strength of a signal from a cell exceeds a threshold amount configured at the threshold, executes conditional handover without a handover command to this cell.

[0062] All of the above-mentioned mobility procedures were defined by 3GPP in respect of layer 3 mobility procedures.

[0063] In addition to these layer-3 mobility procedures, Rel-18 considered layer 1 / layer 2 (L1 / L2)-triggered mobility (LTM) procedures. Layer 1 refers to a physical layer. Layer 2 refers to a media access control (MAC) layer.

[0064] Rel-18 LTM is a mobility procedure where the network configures the UE with up to 8 candidate cells, and eventually sends a cell switch command to the UE to perform cell switch to one of those cells. Cell switch decision may be based on L1 or L3 measurements reported by the UE.

[0065] In contrast to layer 3 (L3) mobility procedures, in which the handover between two cells is decided by a radio resource control (RRC) layer, LTM is performed by the MAC layer. As such, the procedure is terminated in a Distributed Unit (DU) in the CU-DU model of a gNB.

[0066] One of the key goals of LTM was to reduce the interruption caused by the cell switch from the L3 handover. This may be achieved through several different “early” procedures (e.g., through several different procedures that may be performed before the LTM mobility operation is completed). An “early procedure” may be considered to be a procedure that is performed with or in respect of a target cell that is used for a later cell switch procedure and that is performed before a cell switch communication is transmitted (e.g., before a cell switch command issignalled). The early procedures are also referred to herein as “early actions” and / or “preparation actions”. These early procedures include one or more of:• Early downlink synchronization of a UE with a candidate cell (e.g., through early transmission configuration indication (TCI) state activation);• Early uplink synchronization of a UE with a candidate cell (e.g., through physical downlink control channel (PDCCH) ordered random access channel (RACH)-based timing advance estimation or UE-based timing advance estimation); or• Early Abstract Syntax Notation One (ASN. 1 ) decoding and validity checking of a candidate cell’s radio resource control configuration (RRC).

[0067] With respect to early downlink synchronisation, Rel-18 LTM supports early DL synchronization through early TCI state activation for one or more candidate cells before the cell switch command would ordinarily be sent.

[0068] In more detail, a network access node sends a candidate cell specific medium access control-control element (MAC-CE) to a UE to activate one or more TCI states for a candidate cell for downlink synchronisation. When the network wants to activate TCI states for more than one candidate cell, the network may send a separate MAC-CE for each of those cells. Based on receiving a TCI state activation MAC-CE (e.g., in response to receiving a TCI state activation), the UE performs downlink synchronization using a reference signal corresponding to the TCI states indicted in the TCI state activation, such as a synchronisation signal burst (SSB) and / or a tracking reference signal (TRS) associated to the target TCI state(s).

[0069] When a TCI state of a candidate cell is considered active and the UE has downlink synchronization of that TCI state, the cell switch delay associated with performing a switch to that cell switch does not comprise any time for downlink synchronization as this has already been performed. When a TCI state is not on the active TCI state list and / or when the UE does not have target synchronization of the TCI state of a candidate cell, the UE is afforded time to perform downlink synchronization during the cell switch procedure, which makes that cell switch longer compared to when the TCI state is considered active and the UE has downlink synchronisation of that TCI state.

[0070] For conditional LTM, different ways of early TCI state activation may be considered. For example, the Rel-18 non-conditional LTM mechanism can be usedto activate a TCI state (e.g., the network sends a TCI state activation command, and the UE activates TCI state(s) accordingly before receiving a cell switch command). As another example, the UE may autonomously perform TCI state activation. This latter method may be contingent on (e.g., performed in response to) the fulfilment of one or more conditions and / or the detection of one or more events.

[0071] Analogous to the downlink case, a cell switch may be performed faster for those cases in which a UE already has a timing advance (TA) value for its target candidate cell.

[0072] With respect to early uplink synchronisation, Rel-18 LTM supports early uplink synchronization (also referred to herein as timing advance (TA) acquisition through at least one of: i. Physical downlink control channel (PDCCH) ordered random access channel (RACH transmission): In this example, a network access node provides a PDCCH order to the UE for a candidate cell, and the UE performs RACH transmission on that cell before the cell switch. The target candidate network access node (e.g., the network access node providing that candidate cell) uses this transmission to determine a timing advance value for that UE, and sends the TA value to the source network access node (which in turn provides the TA value to the UE in a cell switch command). The UE may apply the TA value for the first uplink transmission on the candidate cell, and hence performs RACH- less cell switch. ii.UE autonomous TA estimation: In this example, the network access node configures UE to autonomously estimate the TA for one or more candidate cells. When the UE receives a cell switch command for one of those candidate cell without a TA value, the UE applies the UE estimated TA for the first UL transmission and hence perform RACH-less cell switch. iii. Preconfigured value: In this example, the network access node provides a serving cell TA value and / or provide a zero TA value (TA=0) in the cell switch command, which also leads to RACH-less cell switch; or iv.lf none of the above apply, the UE performs RACH-based cell switch. Stated differently, the UE performs a RACH procedure after receiving the cell switch command.

[0073] Tim ing Advance (TA) is a command sent by network access node to a UE to cause the UE to adjust its uplink transmission timing in order to synchronise uplink reception from multiple UE. The TA value comprised in a TA command indicates an amount of time by which the UE should adjust its uplink transmissions in order to synchronise in time with a cell provided by a network access node. Stated differently, TA can be used a network access node to control the timings of uplink transmissions made by multiple UE so that the network access node receives uplink transmissions in a timing aligned manner, which reduces the likelihood of interference.

[0074] With respect to early ASN.1 decoding and validity checking, during the LTM preparation phase, the UE may receive the RRC configurations of the candidate cells (see below discussion in respect of Figure 4). The RRC configuration of a candidate is only used when the UE switches to this candidate. In legacy mobility procedures other than LTM, such as L3 conditional handover, after the cell switch is triggered, the UE must process this configuration and check that it is valid and can be applied to the UE. This procedure takes time, which is added to the interruption time of the cell switch. Therefore, it is beneficial to perform this procedure before the cell switch is triggered. Since processing multiple candidate RRC configurations before a cell switch requires additional processing power and memory at the UE, a UE may have the capability to perform this procedure for a limited number of candidate cells. Performing early ASN.1 decoding and validity check for a candidate cell may be triggered by receiving a TCI state activation command or PDCCH order for said candidate cell by the network or may be triggered autonomously by the UE, e.g., upon performing UE-based TA acquisition.

[0075] For conditional LTM, at least one of i) to iii) may be performed in advance of the UE determining that a cell switch execution condition has been fulfilled.

[0076] A primary benefit of LTM compared to L3 handover and L3 conditional handover is that the interruption during the handover execution can be reduced substantially as the UE does not need to perform higher layer reconfiguration (e.g., RRC reconfiguration, and / or packet data convergence protocol (PDCP) reconfiguration). Moreover, for some scenarios, the UE can perform a more generalised handover scheme (known as Random Access Channel (RACH)-less) to connect the candidate cell than would otherwise be used. This may be especiallyuseful in Frequency Range 2 (FR2), which is a frequency range defined by 3GPP to occupy part of the frequency spectrum in which the channel conditions are expected to change more rapidly compared to Frequency Range 1 (FR1 ). This is because the more rapidly changing conditions can lead to more frequent handover for UE operating in FR2 than those operating in FR1 . More frequent handovers are associated with an increase in unnecessary handover.

[0077] Therefore, if a handover can be avoided, it would lead to less interruption and savings in signalling and processing in the network.

[0078] It is expected that Rel-19 will introduce a conditional LTM (CLTM) procedure as an enhancement to the Rel-18 LTM procedure. Stated differently, it is expected that Rel-19 will introduce a conditional LTM in which a UE will autonomously execute cell switch to one of the candidate cells based on the fulfilment of one or more network-configured cell switch execution conditions.

[0079] In CLTM, the UE will be configured with a set of CLTM cell switch execution conditions, which the UE will evaluate to determine whether a cell switch to the corresponding candidate cell should be executed in an analogous way to L3 conditional handover.

[0080] When the CLTM cell switch execution conditions for two or more candidates are triggered (e.g., fulfilled) simultaneously, one of these candidates will be selected for cell switch execution. It is expected that this selection will be performed by selecting a candidate cell from a plurality of candidate cells that has the best measured signal quality of all of the candidate cells. This is similar to the procedure used in L3 conditional handover (see, for example, TS38.331 , clause 5.3.5.13.5).

[0081] However, the following recognizes that this type of candidate cell selection may not result in an optimal choice of cell to switch to. This may be, for example, as a result of the selected cell not being as far advanced for cell switch as other candidate cells in the plurality of candidate cells. Stated differently, the selected cell may be at an earlier stage of preparation for handover relative to another cell that may still fulfil communication service requirements for the UE. In such a case, selecting a cell based on signal quality may potentially result in a higher cell switch interruption time.

[0082] The following aims to address one or more of the above-mentioned issues.

[0083] In more detail, the following discloses the use of one or more rules that prioritize selection of certain candidate cells to which the UE is to perform a CLTM cell switch. These rules will be referred to herein as “prioritization rules”, although it is understood that they may simply be labelled as “rules”.

[0084] The prioritization rules may be based on a set of actions that the UE may perform prior to and during the evaluation of CLTM cell switch execution conditions. These actions may have been performed prior to a cell switch being initiated with the aim of reducing the interruption time during cell switch. This set of actions may comprise one or more of the above-mentioned early procedures, although it is understood that the presently described techniques are not limited to only those above-mentioned early procedures. Instead and / or in addition, the set of actions may comprise one or more procedures that are used when performing a cell switch to a candidate cell.

[0085] For example, such actions may include one or more of:• performing and maintaining downlink synchronization with a candidate cell,• obtaining and keeping track of a path loss estimate between a UE and a candidate cell,• performing and maintaining uplink synchronization with a candidate cell, or• performing early ASN.1 decoding and validity check of a candidate cell’s radio resource control (RRC) configuration.

[0086] With respect to performing and keeping track of a path loss estimate between a UE and a candidate cell, the following is noted. A path loss estimate is used by a UE to determine the UE’s transmit power for performing its initial uplink transmission to the target cell. When the UE does not have this estimate, when the cell switch is triggered, the UE may make measurements of reference signals to acquire this estimate in order to determine its initial uplink transmission power. Measuring these reference signals takes time and may add to the interruption time of the cell switch.

[0087] It is understood that some or all of these prioritization rules may be set as a condition for selecting a candidate cell for handover. It is further understood that these prioritization rules represent methods that are performed for assisting with a fast cell switch, and that other rules may be generated based on any other methods that are performed for assisting with a fast cell switch.

[0088] The selection of one or more candidate cells may be performed in dependence on how many of the above-mentioned actions have been completed and / or initiated. For example, a candidate cell that has performed (e.g., completed and / or initiated) more actions may be selected (e.g., prioritized) over candidate cells that have performed fewer actions. Further, where multiple candidate cells have performed exactly the same number of actions, a single candidate cell to which the UE will perform cell switch may be selected. This may be useful when the actions are treated as taking the same and / or similar amounts of time to complete, as it may simplify a selection procedure. This is illustrated in the following example in which the following prioritization rules may be defined.The UE shall:1> if more than one triggered LTM candidates for which preparation actions 1-4 have been performed exist:2> select one of the triggered LTM candidates as the selected candidate for conditional LTM cell switch execution;1> else if only one triggered LTM candidate for which preparation actions 1- 4 have been performed exists:2> consider the triggered LTM candidate as the selected candidate for conditional LTM cell switch execution;1> else if more than one triggered LTM candidates for which preparation actions 1-3 have been performed exist:2> select one of the triggered LTM candidates as the selected candidate for conditional LTM cell switch execution;1> else if only one triggered LTM candidate for which preparation actions 1- 3 have been performed exists:2> consider the triggered LTM candidate as the selected candidate for conditional LTM cell switch execution;1> else if more than one triggered LTM candidates for which preparation action 1 has been performed exist:2> select one of the triggered LTM candidate as the selected candidate for conditional LTM cell switch execution;1> else if only one triggered LTM candidate for which preparation action 1 has been performed exists:2> consider the triggered LTM candidate as the selected candidate for conditional LTM cell switch execution;1> else if more than one triggered LTM candidates exist:2> select one of the triggered LTM candidates as the selected candidate for conditional LTM cell switch execution;1> else if only one triggered LTM candidate exists:2> consider the triggered LTM candidate as the selected candidate for conditional LTM cell switch execution;

[0089] It is understood that this is merely one method by which the prioritisation rules may be applied, and that more or fewer actions may be considered when determining how to select a cell. For example, in general, the prioritisation rules may be configured so as to identify which one(s) of the candidate cells is (are) likely to be the quickest to switch to than others of the candidate cells.

[0090] For example, each action may be associated with respective one or more delay times, where the delay times each represent a way in which that action may be performed and / or a dynamic characteristic of that action. For example, an action may be associated with one or more delay times corresponding to different types of reference signals, different types of signalling conditions, different types of reference signal configurations, etc. In such a case, a UE may be configured with prioritization rules that enable the UE to select a candidate cell corresponding to a shortest estimated cell switch time based on how each action of the set of actions is expected to be performed with respect to that candidate cell (and / or has been performed with respect to that candidate cell) and the corresponding delay time(s) associated therewith. For example, in an example comprising 5 actions, the prioritisation rules may determine that a first candidate cell that has completed actions 2, 3, and 5 is an equally valid selection for completing a cell switch procedure as a second candidate cell that has completed actions 1 , 2, 3, and 4 when actions 1 and 4 cumulatively take the same time to complete as action 5.

[0091] The prioritisation rules may additionally and / or alternatively be able to be factor in (e.g., account for) scenarios in which different actions may be performed simultaneously (e.g., contemporaneously and / or in parallel) rather than serially. Forexample, in an example comprising 5 actions, the prioritisation rules may determine that a first candidate cell that has completed actions 1 , 2 and 3 is an equally valid selection for completing a cell switch procedure as a second candidate cell that has completed actions 1 , 2, 3, and 4 when actions 4 and 5 may be performed simultaneously.

[0092] It is further understood that the candidate cell may be selected based on a property (e.g., a characteristic) of the procedure used with and / or by a candidate cell when fulfilling one or more of the actions.

[0093] For example, a respective time of execution of one or more of the above actions may be used as a prioritization criterion.

[0094] As another example, the downlink synchronization-based prioritization may be further categorized based on the reference signal type. For example, the prioritization may be configured to prioritize more those procedures and signaling that are expected to be more accurate than other procedures and signaling. This will be illustrated using channel state information reference signal (CSI-RS) and synchronization signal burst (SSB) reference signals, where CSI-RS-based synchronization is assumed to provide finer synchronization in terms of frequency and / or spatial domain than SSB-based synchronization.

[0095] For example, downlink synchronization using a channel state information reference signal (CSI-RS) may be prioritized over DL synchronization using a synchronization signal burst (SSB).

[0096] As another example, downlink synchronization may be achieved by activating appropriate transmission configuration indication (TCI) states . For example, a cell with activation of a TCI state associated with a CSI-RS may be prioritized over another cell with activation of a TCI state associated with an SSB.

[0097] As another example, uplink synchronization-based prioritization may be further categorized based on a time advance (TA) acquisition technique used. For example, TA acquired via RACH-based mechanism may be prioritized over the TA acquired via UE-based TA mechanism.

[0098] At least one illustration of example signalling that may be performed in an implementation example of the presently described methods is now illustrated with respect to Figures 4 and 5, with Figure 6 more generally illustrating examplemethods that may be performed by apparatus described herein (including an apparatus as illustrated with respect to Figures 4 and 5).

[0099] Figure 4 illustrates signalling that may be performed when configuring a LJE with cell switch execution conditions for configuring the UE to perform condition LTM-based mobility events (e.g., a cell switch) from a cell of a source DU to another cell of a target DU. For clarity and brevity throughout the following, the terms “DU” and “cell” will be used interchangeably. In contrast, Figure 5 illustrates signalling that may be performed when the UE is configured to perform conditional LTM, and further illustrates when the UE may utilise the presently described prioritisation rules for selecting a candidate cell.

[0100] Figure 4 illustrates signalling that may be performed between a UE 401 , a source DU 402, a first target DU 403, a second target DU 404, and a CU 405. Prior to 4001 , the UE is configured to connect to a network via the source DU 402. Stated differently, the UE is configured to connect to a core network via the source DU 402.

[0101] During 4001 , the UE 401 signals the source DU 402. This signalling may comprise an L3 measurement report. The measurement report may comprise information specified in a measurement reporting configuration. The measurement report may comprise an indication of measurements made of the UE’s radio environment that indicate a state of that radio environment. The report may have been triggered because a signal provided by a neighbour cell may have become better than a signal provided by the serving cell, indicating that the UE is in the cell border area. The way measurements, measurement triggers, and measurement reporting is set up for RRC is explained in 3GPP TS 38.331 section 5.5.1 .

[0102] During 4002, the source DU 402 forwards the measurement report received during 4001 to the CU 405. The signalling of 4002 may be comprised in an uplink radio resource control message transfer service message.

[0103] During 4003, the CU 405 determines, based on the received measurement report of 4002, that a handover (e.g., a cell switch) is to be performed such that the UE is switched away from the source DU to another DU.

[0104] During 4004, the CU 405 signals the first target DU 403. This signalling may comprise a UE context setup request. A purpose of this UE context setup request is to cause a UE context (e.g., security keys, UE capabilities, etc.) to be established at the first target DU 403 in respect of the UE.

[0105] During 4005, the first target DU 403 signals the CU 405. This signalling may comprise a UE context setup response. This signalling may comprise a DU to CU container for communicating between a DU and a CU.

[0106] The signalling of 4004 to 4005 is similarly performed in respect of the other target DUs. This is illustrated with respect to 4006 to 4007 for the second target DU, although it is understood that there may be more DUs.

[0107] During 4006, the CU 405 signals the second target DU 404. This signalling may comprise a UE context setup request. A purpose of this UE context setup request is to cause a UE context (e.g., security keys, UE capabilities, etc.) to be established at the second target DU 403 in respect of the UE.

[0108] During 4007, the second target DU 404 signals the CU 405. This signalling may comprise a UE context setup response. This signalling may comprise a DU to CU container for communicating between a DU and a CU.

[0109] When a UE context changes, this may be signalled to the DUs using a UE context modification request. This is illustrated with respect to the first target DU only, although it is understood that the same signalling may be provided in respect of the other target DUs.

[0110] During 4008, the CU 405 signals the first target DU 403. This signalling may comprise a UE context modification request. A purpose of this UE context modification request is to modify a UE context (e.g., security keys, UE capabilities, etc.) maintained at the first target DU 403 in respect of the UE.

[0111] During 4009, the first target DU 403 signals the CU 405. This signalling may comprise a UE context modification response. This signalling may comprise a DU to CU container for communicating between a DU and a CU and indicate whether the user context was successfully modified at the first target DU.

[0112] During 4010, the CU generates a radio resource control (RRC) reconfiguration for the UE 401. This RRC reconfiguration may comprise a measurement reporting configuration for layer 1 cell change operations, and configurations of any prepared target DUs on which those measurements are to be performed (e.g., the first and second target DUs in the present example). This generation may be based on the UE context setup responses received during 4004 and 4006. The generation RRC reconfiguration may comprise one or more of:1 ) CSI resource and reporting configurations for one or more of the target DUs;2) RRC Configurations of the target Dlls;3) Early sync configuration of the target DUs; or4) C-LTM configuration of the target DUs (e.g., including conditional cell switch execution conditions).

[0113] During 4011 , the CU 403 signals the source DU 402. This signalling may comprise the RRC reconfiguration generated during 4010. This signalling may be provided using a downlink RRC message transfer message.

[0114] During 4012, the source DU 402 signals the UE 401. This signalling may comprise the RRC reconfiguration of 4010.

[0115] During 4013, after the UE 401 has successfully updated its RRC configuration based on the received RRC reconfiguration of 4012, the UE 401 signals the source DU 402. This signalling may comprise an acknowledgement that the RRC reconfiguration of 4011 has been successfully configured at the UE.

[0116] During 4014, the source DU 401 signals the CU 405 an uplink RRC message to confirm that the RRC reconfiguration has been successfully configured. From 4014, the method proceeds to 5001 of Figure 5.

[0117] Figure 5 illustrates the same signalling entities as depicted in Figure 4 and so will use the same labelling as those entities in Figure 4.

[0118] During 5001 , the UE 401 starts evaluating the conditional cell switch execution conditions for the each of the target DUs to determine whether the UE may perform handover (or some other mobility event) to either of those DUs.

[0119] During 5002, the UE 401 signals an L1 and / or L3 measurement report to the CU 405 via the source DU 402. This signalling may comprise a measurement report that was generated in accordance with the RRC reconfiguration received during 4012. 5002 may be performed repeatedly (e.g., when the RRC reconfiguration configures the UE 401 to make periodic measurement reports).

[0120] During 5003, and based on at least one measurement report received during 5002, the source DU 402 and / or the CU 405 may determine to cause the UE to synchronize with one or more of the candidate cells in time and / or frequency in advance of a potential cell switch being triggered by the UE. Stated differently, the source DU 402 and / or the CU 405 may determine to perform early sync (e.g., TCI activation (for downlink synchronization) and / or timing advance acquisition (for uplink synchronization)) for the first and second target DUs.

[0121] During 5004, the source DU 402 signals the UE 401. This signaling may comprise a TCI state activation command for the first target DU. The UE 401 may become downlink synchronized with the first target DU 403 using this TCI state information of 5004.

[0122] During 5005, the source DU 402 signals the UE 401. This signaling may comprise a TCI state activation command for the first target DU. The UE 401 may become downlink synchronized with the second target DU 404 using this TCI state information of 5005.

[0123] During 5006, the source DU 402 signals the UE 401. This signaling may comprise a physical downlink control channel order for early timing advance acquisition for the first target DU 403.

[0124] During 5007, the first target DU 403 signals timing advance information for its cell to the CU 405.

[0125] During 5008, the CU 405 provides this timing advance information to the UE 401 via the source DU 402. The UE 401 may become uplink synchronized with the first target DU 403 using this timing advance information of 5008.

[0126] During 5009, the UE 401 starts and / or continues to determine whether the conditional cell switch execution conditions have been fulfilled (e.g., as described in relation to 5001 ) until during 5010, the UE determines that the conditional cell switch execution conditions configured via the signalling of 4012 have been fulfilled for both the first and second target DUs.

[0127] During 5011 , the UE selects a single target DU from the target DUs that fulfil the conditional cell switch execution conditions (e.g., the first and second target DUs in the present example). This selection is performed using the presently described prioritization rules.

[0128] For example, in the example of Figure 5, the UE has performed both downlink and uplink synchronization with the first target DU 403, but only downlink synchronization with the second target DU 404. Based on the prioritization rule provided in the example above, the UE therefore selects the first target DU 404 for performing a conditional cell switch instead of the second target DU 404 as it will be a shorter cell switch time for connecting to the first target DU that it would be for the second target DU 404 as a result of more of the pre-cell switch procedures being completed when the UE makes its handover decision.

[0129] Based on this selection, the UE 401 initiates a cell switch to the selected first target DU 403. This signalling may be performed using a RACH-less conditional cell switch as the UE is uplink synchronized with the first target DU.

[0130] When this cell switch is completed, the UE 401 signals an RRC reconfiguration complete message to the first target DU 403 during 5012, for the first target DU to forward to the CU 405 during 5013. This signalling comprises an indication that the UE 401 has completed its switch to the first target DU 403.

[0131] Based on this signalling, the CU 405 signals a UE context release command to the source DU 402 during 5014, which causes the source DU to release its UE context for the UE 401 . Subsequently, the source DU 402 (which is no longer serving the UE) signals the CU 405 to confirm that the UE context has been released during 5015, and the CU 405, the source DU 403 and the first target DU 403 perform a path switch during 5016 (e.g., cause communications for the UE to be routed through the first target DU 403 instead of through the source DU 402).

[0132] Figure 6 illustrates a method that may be performed by an apparatus. The apparatus may be as described in relation to Figure 3. For example, the apparatus may be comprised in or be a user equipment.

[0133] The method of Figure 6 may be performed, for example, during 5009. However, it is understood that the presently described method is not limited to being performed in only that context. In particular, the presently described method may be implemented in any configuration in which an apparatus is configured to select a candidate cell (e.g., a target DU and / or one or more cells provided by the target DU) out of a plurality of candidate cells for use in completing a mobility event (e.g., a cell switch, a handover, a dual connectivity procedure, etc.).

[0134] During 601 , the apparatus maintains a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and a candidate cell prior to a mobility event between the apparatus and the candidate cell being triggered. The presently described conditions may be as described above.

[0135] A cell may be considered to be a candidate cell when the apparatus is configured to performed one or more measurements on that cell in advance of a mobility event between the apparatus and a candidate cell being triggered (e.g., cell switch and / or handover).

[0136] The set of conditions may comprise a single condition. The set of conditions may comprise a plurality of conditions.

[0137] During 602, the apparatus identifies a plurality of candidate cells that have fulfilled one or more of the conditions.

[0138] Stated differently, during 602, the apparatus identifies a plurality of candidate cells that have completed at least part of one or more of the above-mentioned early procedures, preparation actions and / or early actions. Stated differently, during 602, the apparatus identifies a plurality of candidate cells that have at least initiated one more procedures that are to be performed between the apparatus and those candidate cells prior to the mobility event being triggered.

[0139] The plurality of candidate cells may comprise more than one cell that are provided by a same network access node (e.g., by a same DU). The plurality of candidate cells may comprise cells that are respectively provided by different network access nodes.

[0140] During 603, the apparatus selects a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled.

[0141] During 604, the apparatus performs the mobility event with the selected candidate cell. Stated differently, during 604, the apparatus may cause the selected candidate cell to become a serving cell of the apparatus.

[0142] The apparatus may release a serving cell of the apparatus (e.g., may no longer receive services through that serving cell) based on the apparatus performing the mobility event with the selected candidate ceil.

[0143] For example, the apparatus may perform a handover to the selected candidate cell from a current serving cell of the apparatus. For example, the apparatus may perform a cell switch to receive one or more services through the selected candidate cell instead of a current serving cell of the apparatus.

[0144] The selecting a candidate cell using a set of prioritisation rules may be configured in one or more of a plurality of different ways.

[0145] For example, the selecting the candidate cell using a set of prioritisation rules may be configured by determining a set of candidate cells from the plurality of candidate cells by: determining, for each candidate cell of a plurality of candidate cells, how many conditions have been fulfilled by that candidate cell; and selectingthe set of candidate cells that have fulfilled the most conditions; and selecting a candidate cell from the set of candidate cells. The set of candidate cells may correspond to a set of candidate cells that are associated with a shortest cell switch time.

[0146] In this example, the each of the actions corresponding to their respective condition is treated as having a same cell switch delay. For example, when the time saved for cell switch by each of the actions is considered to be n ms (where n may be any number), then the candidate cells that are determining to have fulfilled the most actions is considered to have “saved” the most time for a cell switch, and so cell switch may be completed sooner than for those cells that did not save as much time.

[0147] However, it is understood that in other methods, different timings may be associated with different conditions, with different methods for fulfilling a condition, and / or with different dynamic conditions.

[0148] For example, when the action is downlink synchronisation, the timing associated for this action may vary based on the signals used for synchronisation and / or a signal quality associated with any of those signals. Further, it may be that one or more actions may, on average, take a lot longer to complete than another of the actions. Therefore, when a condition for those one or more actions is considered fulfilled, this may be considered to have “saved” a larger amount of time than when conditions for the another of the actions have been fulfilled.

[0149] Such variations in “saved” timing between these different actions may be accounted for by a set of prioritisation rules that accounts for such differences.

[0150] For example, the selecting a single candidate cell using a set of prioritisation rules may comprise: determining a set of candidate cells from the plurality of candidate cells by: determining, for each candidate cell of a plurality of candidate cells, which conditions have been fulfilled by that candidate cell, wherein each condition is associated with a respective time; and determining the set of candidate cells by selecting those candidate cells whose total fulfilled conditions are associated with a highest cumulative time. The apparatus may subsequently select a candidate cell from the set of candidate cells. The set of candidate cells may correspond to a set of candidate cells that are associated with a shortest cell switch time.

[0151] In any (e.g., one or more including all) of the above-mentioned examples, the set of candidate cells may comprise more than one candidate cell, and the selecting a candidate cell out of the plurality of candidate cells may comprise: comparing respective measured signal qualities of the more than one candidate cell to identify a candidate cell that has the best measured signal quality; and selecting the identified candidate cell as the selected candidate cell.

[0152] Alternatively, in any of the above-mentioned examples, the set of candidate cells may comprise a single candidate cell.

[0153] The set of conditions may comprise at least one of: a completion and / or initiation of an uplink time and / or frequency synchronisation procedure with a candidate cell, or a completion and / or initiation downlink time and / or frequency synchronisation procedure with a candidate cell.

[0154] The set of conditions (and / or the actions associated therewith) may comprise at least one of: obtaining an initial downlink time and / or frequency synchronisation with a candidate cell; maintaining a downlink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial downlink time and / or frequency synchronisation with the candidate cell; obtaining an initial path loss estimate for signals communicated between the apparatus and the candidate cell; maintaining a path loss estimate for signals communicated between the apparatus and the candidate cell; obtaining an initial uplink time and / or frequency synchronisation with a candidate cell; maintaining an uplink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial uplink time and / or frequency synchronisation with the candidate cell; initiating and / or completing Abstract Syntax Notation One (ASN. 1 ) decoding of a candidate cell’s radio resource control, RRC, configuration; or initiating and / or completing validity checking of a candidate cell’s RRC configuration.

[0155] The apparatus may maintain, for each action of one or more of the actions, at least one respective property (e.g., a characteristic) of the one or more actions. The at least one respective property may comprise at least one of: a time when said one or more actions was initiated; a time when said one or more actions was completed; a type of reference signal used for said one or more actions; a type of timing acquisition method used for said one or more actions; or a type of transmission configuration indication state corresponding to a candidate cell duringsaid one or more actions. The selecting a candidate cell may be performed based on the at least one respective property.

[0156] As discussed above, the prioritisation rules may be further based on a property (e.g., a characteristic) of the action corresponding to one of said conditions. This is illustrated in the following downlink reference signal example, although it is understood that the presently described method is not limited to only this example, and that other combinations of conditions (and / or the corresponding actions to those conditions) and a respective property for a condition are possible.

[0157] For example, when the set of conditions comprises at least one of: obtaining an initial downlink time and / or frequency synchronisation with a candidate cell; or maintaining a downlink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial downlink time and / or frequency synchronisation with the candidate cell, the prioritisation rules may be are further based on a type of reference signal used when the one or more conditions in the set of conditions are fulfilled.

[0158] In this particular example, the prioritisation rules may be configured so that a candidate cell for which downlink time and / or frequency synchronisation is performed using a channel state information reference signal is prioritised for said selection as the selected candidate cell over a candidate cell for which downlink time and / or frequency synchronisation is performed using a synchronisation signal burst.

[0159] Stated differently, the prioritisation rules may be based on a type of reference signal used for performing a downlink time and / or frequency synchronisation with the candidate ceil, such that candidate cells for which synchronisations are performed using reference signals that provide finer (e.g., more accurate) synchronisation (e.g., CSI-RS) are prioritised over those candidate cells for which synchronisations are performed using reference signals that provide less fine (e.g., less accurate) synchronisation (e.g., SSB).

[0160] The apparatus may obtain the set of conditions from a serving network access node and / or an operations and management function. The apparatus may have been configured with the set of conditions by a network operator.

[0161] As illustrated by the above example of Figures 4 to 5, the presently described techniques may be deployed during a cell switch procedure. For example, theapparatus may obtain, from a network access node, one or more cell switch conditions, wherein a cell switch condition is a condition that causes the apparatus to initiate a cell switch to that candidate cell when that cell switch condition is determined to be fulfilled. The selecting the candidate cell may be performed based on a determination that one or more measurements corresponding to candidate cells of the plurality of candidate cells fulfil the one or more cell switch conditions. Stated differently, the selecting the candidate cell may be performed in response to a determination that one or more measurements corresponding to candidate cells of the plurality of candidate cells fulfil the one or more cell switch conditions.

[0162] The mobility event may comprise a conditional layer 1 and / or layer 2- triggered mobility event. The mobility event may comprise at least one of: a handover event, or a dual-connectivity event.

[0163] It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and / or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

[0164] It is noted that references in the above to “obtaining” (and the like) may be read interchangeably with “receiving”, and that references in the above to “providing” (and the like) may be ready interchangeably with “transmitting”.

[0165] It is noted that whilst some embodiments have been described in relation to 5G networks, similar principles can be applied in relation to other networks and communication systems. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

[0166] It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

[0167] 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 atleast any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0168] In general, the various embodiments may be implemented in hardware or special purpose circuitry, software, logic or any combination thereof. Some aspects of the disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0169] As used herein, the term “circuitry” may refer to one or more or all of the following:(a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and(b) combinations of hardware circuits and software, such as (as applicable):(i) a combination of analog and / or digital hardware circuit(s) with software / firmware and(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.”

[0170] This definition of circuitry applies to all uses of this term herein, including in any claims. As a further example, as used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integratedcircuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0171] The embodiments of this disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and / or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer-executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

[0172] Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media.

[0173] 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).

[0174] The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

[0175] Various example embodiments of the disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits isby and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0176] The scope of protection sought for various example embodiments of the disclosure is set out by the independent claims. The example embodiments and features thereof, if any, described in this disclosure that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various example embodiments of the disclosure.

[0177] The foregoing description has provided, by way of non-limiting and illustrative examples, a full and informative description of the various example embodiments of this disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the claims. However, all such and similar modifications of the teachings will still fail within the various example embodiments of the disclosure as set forth in the claims. By way of nonlimiting and illustrative example, there is a further example embodiment comprising a combination of one or more example embodiments with any of the other example embodiments previously discussed.

Claims

CLAIMS1 ) An apparatus comprising means for: maintaining a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and a candidate cell prior to a mobility event between the apparatus and the candidate cell being triggered; identifying a plurality of candidate cells that have fulfilled one or more of the conditions; selecting a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled; and performing the mobility event with the selected candidate cell.2) An apparatus as claimed in claim 1 , wherein the means for selecting a candidate cell using a set of prioritisation rules further comprises means for: determining a set of candidate cells from the plurality of candidate cells by: determining, for each candidate cell of a plurality of candidate cells, how many conditions have been fulfilled by that candidate cell; and selecting the set of candidate cells that have fulfilled the most conditions; and selecting a candidate cell from the set of candidate cells.3) An apparatus as claimed in claim 1 , wherein the means for selecting a single candidate cell using a set of prioritisation rules further comprises means for: determining a set of candidate cells from the plurality of candidate cells by:35determining, for each candidate cell of a plurality of candidate cells, which conditions have been fulfilled by that candidate cell, wherein each condition is associated with a respective time; and determining the set of candidate cells by selecting those candidate cells whose total fulfilled conditions are associated with a highest cumulative time; and selecting a candidate cell from the set of candidate cells.4) An apparatus as claimed in any of claims 2 to 3, wherein the set of candidate cells comprises more than one candidate cell, and the means for selecting further comprises means for: comparing respective measured signal qualities of the more than one candidate cell to identify a candidate cell that has the best measured signal quality; and selecting the identified candidate cell as the selected candidate cell.5) An apparatus as claimed in any of claims 2 to 3, wherein the set of candidate cells comprises a single candidate cell.6) An apparatus as claimed in any preceding claim, wherein the set of conditions comprises at least one of: a completion and / or initiation of an uplink time and / or frequency synchronisation procedure with a candidate cell, or a completion and / or initiation downlink time and / or frequency synchronisation procedure with a candidate cell.7) An apparatus as claimed in any preceding claim, wherein the set of conditions comprises at least one of: obtaining an initial downlink time and / or frequency synchronisation with a candidate cell; maintaining a downlink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial downlink time and / or frequency synchronisation with the candidate cell;obtaining an initial path loss estimate for signals communicated between the apparatus and the candidate cell; maintaining a path loss estimate for signals communicated between the apparatus and the candidate cell; obtaining an initial uplink time and / or frequency synchronisation with a candidate cell; maintaining an uplink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial uplink time and / or frequency synchronisation with the candidate cell; initiating and / or completing Abstract Syntax Notation One (ASN. 1 ) decoding of a candidate cell’s radio resource control, RRC, configuration; or initiating and / or completing validity checking of a candidate cell’s RRC configuration.8) An apparatus as claimed in any preceding claim, further comprising means for maintaining at least one property of the one or more actions, wherein the at least one property of the one or more actions comprises at least one of: a time when said one or more actions was initiated; a time when said one or more actions was completed; a type of reference signal used for said one or more actions; a type of timing acquisition method used for said one or more actions; or a type of transmission configuration indication state corresponding to a candidate cell during said one or more actions.9) An apparatus as claimed any preceding claim, wherein the set of conditions comprises at least one of: obtaining an initial downlink time and / or frequency synchronisation with a candidate cell; or maintaining a downlink time and / or frequency synchronisation with a candidate cell subsequent to said obtaining the initial downlink time and / or frequency synchronisation with the candidate cell,and wherein the prioritisation rules are further based on a type of reference signal used when the one or more conditions in the set of conditions are fulfilled.10)An apparatus a claimed in claim 9, wherein the prioritisation rules are configured so that a candidate cell for which downlink time and / or frequency synchronisation is performed using a channel state information reference signal is prioritised for said selection as the selected candidate cell over a candidate cell for which downlink time and / or frequency synchronisation is performed using a synchronisation signal burst.11 )An apparatus as claimed in any preceding claim, comprising means for obtaining the set of conditions from a serving network access node and / or an operations and management function.12)An apparatus as claimed in any preceding claim, further comprising means for: obtaining, from a network access node, one or more cell switch conditions, wherein a cell switch condition is a condition that causes the apparatus to initiate a cell switch to that candidate cell when that cell switch condition is determined to be fulfilled, wherein the selecting the candidate cell is performed based on a determination that one or more measurements corresponding to candidate cells of the plurality of candidate cells fulfil the one or more cell switch conditions.13)An apparatus as claimed in any preceding claim, wherein the mobility event comprises a conditional layer 1 and / or layer 2-triggered mobility event.14)An apparatus as claimed in claim 13, wherein the mobility event comprises at least one of: a handover event, or a dual-connectivity event.)A method comprising: maintaining, by an apparatus, a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and a candidate cell prior to a mobility event between the apparatus and the candidate cell being triggered identifying, by the apparatus, a plurality of candidate cells that have fulfilled one or more of the conditions; selecting, by the apparatus, a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled; and performing, by the apparatus, the mobility event with the selected candidate cell. )A computer program comprising instructions which, when the program is executed by a computer of an apparatus, cause the apparatus to perform: maintaining a set of conditions, wherein each condition corresponds to one or more actions to be performed between the apparatus and a candidate cell prior to a mobility event between the apparatus and the candidate cell being triggered identifying a plurality of candidate cells that have fulfilled one or more of the conditions; selecting a candidate cell from said plurality of candidate cells using a set of prioritisation rules, wherein said prioritisation rules are based on the one or more conditions being fulfilled; and performing the mobility event with the selected candidate cell.

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