Channel state information acquisition during cell switch

Abstract

Methods, apparatuses and computer-readable media for cell-switch operation are provided During a cell-switch operation, a user equipment (UE) receives, from a network node of a source cell, a Radio Resource Control (RRC) configuration message for the cell-switch operation having a Channel State Information Reference Signal (CSI-RS) measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells. In response to a first trigger message, the UE processes the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements. The UE receives a cell switch command (CSC) for switching from the source cell to a target cell of the one or more candidate target cells.

Description

CHANNEL STATE INFORMATION ACQUISITION DURING CELL SWITCH TECHNICAL FIELD

[0001] The subject disclosure generally relates to wireless communication systems and, in particular, to early channel state information acquisition. Yet more particularly, the subject disclosure provides methods and apparatuses for performing channel state information reference signal measurements during a cell switch operation.BACKGROUND

[0002] Wireless communication systems, also referred to mobile communication systems, are under constant development. In wireless communication systems, precise synchronization between user equipments (UE) and base stations (BS) is critical for maintaining efficient and reliable communication. This is especially important in mobile networks such as 5G, where devices frequently transition between different cells during mobility events, such as handovers or, generally, cell switches.

[0003] One of the challenges arising is keeping track of the channel quality. Generally, the UE performs lower layer measurements of the channel quality, referred to as channel state information (CSI) acquisition. To this end, network elements transmit reference signals (RS) which the UE measures to determine certain CSI parameters. Acquired CSI is fed back to the network by way of CSI reports. These CSI reports enable the network to schedule the UE appropriately according to current channel conditions.

[0004] Challenges in CSI acquisition arise during cell switch events due to the disruptive impact of a cell switch. Before the cell switch from the source cell to the target cell, future channel conditions with the target cell may remain unknown. After the cell switch, CSI acquisition for the target cell may start from scratch, causing delays until channel-condition aware scheduling.

[0005] Therefore, methods and apparatuses that address these issues and improve channel state information acquisition are presented herein.SUMMARY

[0006] According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims.

[0007] These aspects and features may be implemented in systems, apparatuses, methods, articles and non-transitory computer-readable media depending on the desired configuration. The subject disclosure may be implemented in and used with a number of different types of devices, including but notlimited to cellular phones, tablet computers, wearable computing devices, portable media players, and any of various other computing devices.TERMINOLOGY

[0008] To facilitate understanding on the terminologies in the subject disclosure, the following list of the most relevant abbreviations is provided:3GPP 3rd Generation Partnership Program5G / NG 5thGeneration, Next GenerationAMF Access and Mobility Management FunctionAS Access StratumBB Base BandBWP Bandwidth PartON Core NetworkCMD CommandCRI CSI-RS Resource IndicatorCSC Cell switch CommandCSI Channel State InformationCQI Channel Quality IndicatoreNB LTE Base Station, E-Utran NodeBgNB 5G Base Station, 5G NodeBFR1 / 2 Frequency Range 1 / 2ID IdentifierloT Internet of ThingsHARQ Hybrid automatic repeat requestLI Layer IndicatorLTE Long-Term Evolution (Network)LTM Lower Layer (L1 / L2) Triggered MobilityMG Measurement GapMCS Modulation Coding SchemePDCCH Physical Downlink Control ChannelPMI Precoding Matrix Indicator(P)RACH (Physical) Random Access ChannelPRB Physical Resource BlockRA Random AccessRAN Radio Access NetworkRF Radio FrequencyRl Rank IndicatorRNTI Radio Network Temporary IdentifierRRC Radio Resource ControlRRM Radio Resource ManagementRRS Radio Resource ControlRS Reference SignalRSRP Reference Signal Received PowerSIB System Information BlockSSB Synchronization Signal BlockSSBRI SS / PBCH Resource Block IndicatorTA Timing AdvanceTCI Transmission Configuration IndicatorUE User EquipmentBRIEF DESCRIPTION OF THE DRAWINGS

[0009] A better understanding of the subject disclosure may be obtained when the following detailed description of various embodiments is considered in conjunction with the following drawings, in which:

[0010] FIG. 1 shows a schematic diagram of an example wireless network;

[0011] FIG. 2 shows a schematic diagram of an example wireless device;

[0012] FIG. 3 shows a schematic diagram of an example network node;

[0013] FIG. 4A presents a total time switch delay as known in the prior art.

[0014] FIG. 4B presents a total time switch delay with CSI-RS measurement delay.

[0015] FIG. 5 illustrates a flow chart of a first basic method as described herein.

[0016] FIG. 6 depicts a flow chart of a further basic method as described herein.

[0017] FIG. 7 shown a flow chart of a third basic method as described herein.

[0018] FIG. 8 illustrated times for LTM-RRC-processing.

[0019] FIG. 9 shows times for LTM-RRC-processing together with CSI-RRC-processing.

[0020] FIG. 10 illustrates locations of the target cell CSI-RS within the active BWP of the UE.

[0021] FIG. 11 depicts processing the CSI-RS measurements in relation to the CSC.

[0022] FIG. 12 illustrates examples for application of the methodologies as described herein.GENERAL MOBILE COMMUNICATION ASPECTS

[0023] The examples and embodiments set forth below represent information to enable those skilled in the art to practice the subject disclosure. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the description and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the description.

[0024] In the following description, numerous specific details are set forth. However, it is understood that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of the description. Those of ordinary skill in the art, with the included description, will be able to implement appropriate functionality without undue experimentation.

[0025] References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0026] As used herein, "plurality" means two or more. As used herein, a "set" of items may include one or more of such items. As used herein, whether in the subject disclosure or the claims, the terms "comprising", "including", "carrying", "having", "containing", "involving", and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of' and "consisting essentially of', respectively, are closed or semi-closed transitional phrases with respect to claims. Use of ordinal terms such as "first", "second", "third", etc., in the claims or the subject disclosure to modify an element does not by itself connote any priority, precedence, or order of one element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the elements. As used herein, "and / or" and "at least one of" means that the listed items are alternatives, but the alternatives also include any combination of the listed items.

[0027] Before explaining the examples according to the subject disclosure in detail, certain general principles of a wireless communication system are briefly explained with reference to FIGS. 1 to 3 to assist in understanding the technology underlying the described examples.

[0028] FIG. 1 illustrates an example of a wireless network 100 that may be used for wireless communications. Wireless network 100 includes wireless devices, such as UEs 110 (e.g., 110A-110B), and network nodes, such as radio access nodes 120 (e.g., 120A-120B) (e.g., eNBs, gNBs, etc.),connected to one or more network nodes 130 over an interconnecting network 125. The network 100 may use any suitable deployment scenarios. UEs 110 within coverage area 115 may each be capable of communicating directly with radio access nodes 120 over a wireless or air interface. In some embodiments, UEs 110 may also be capable of communicating with each other via D2D communication.

[0029] As an example, UE 110A may communicate with radio access node 120A over a wireless or air interface. That is, UE 110A may transmit wireless signals to and / or receive wireless signals from radio access node 120A. The wireless signals may contain voice traffic, data traffic, control signals, and / or any other suitable information.

[0030] As used herein, the term "user equipment" (UE) has the full breadth of its ordinary meaning and may refer to any type of wireless device which may communicate with a network node and / or with another UE in a cellular or mobile or wireless communication system. Examples of UE are target device, D2D UE, machine type UE or UE capable of machine-to-machine (M2M) communication, personal digital assistant, tablet, mobile terminal, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, ProSe UE, vehicle-to-vehicle (V2V) UE, V2X UE, MTC UE, eMTC UE, FeMTC UE, UE Cat 0, UE Cat Ml, narrow band loT (NB-loT) UE, UE Cat NB1 , etc. Example embodiments of a UE are described in more detail below with respect to FIG. 2.

[0031] In some embodiments, an area of wireless signal coverage 115 associated with a radio access node 120 may be referred to as a cell. Particularly with respect to the 5thgeneration (5G) / New Radio (NR) mobile communication concepts, beams, such as the herein described multicast radio beams (MRBs) may be used within cells for communication. In some embodiments described herein, the UE 110 may be served by radio access node 120A, which be denoted as source cell. Access node 120B may be a candidate cell for handover / cell switching. If the cell of radio access node 120B is selected as target for handover / cell switching, the cell of radio access node 120B may be denoted as target cell. Although not shown in FIG. 1 , there may be more than one candidate cell provided by more than one other radio access node 120. It is noted that a source cell and target cell may also be provided by the same BS.

[0032] With respect to a beam-based mobile communication system, the radio access node 120 (base station) may transmit a beamformed signal to the UE 110 in one or more transmit directions (transmission beam, Tx beam). The UE 110 may receive the beamformed signal from the base station 120 in one or more receive directions (reception beam, Rx beam). The UE 110 may also transmit a beamformed signal to the base station 120 in one or more directions and the base station 120 may receive the beamformed signal from the UE 110 in one or more directions. The base station 120 and the UE 110 may determine the best receive and transmit directions, e.g., best in the sense of these directions leading to the highest link quality or fulfilling other quality conditions in the most suitable manner, for each of the base station / UE pairs.

[0033] The interconnecting network 125 may refer to any interconnecting system capable of transmitting audio, video, signals, data, messages, etc., or any combination of the preceding. The interconnecting network 125 may include all or a portion of a public switched telephone network (PSTN), a public or private data network, a local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a local, regional, or global communication or computer network such as the Internet, a wireline or wireless network, an enterprise intranet, or any other suitable communication link, including combinations thereof.

[0034] In some embodiments, the network node 130 may be a core network node, managing the establishment of communication sessions and other various other functionalities for UEs 110. Examples of network node 130 may include mobile switching center (MSC), MME, serving gateway (SGW), packet data network gateway (PGW), operation and maintenance (O&M), operations support system (OSS), SON, positioning node (e.g., Enhanced Serving Mobile Location Center, E-SMLC), location server node, MDT node, etc. UEs 110 may exchange certain signals with the network node 130 using the non-access stratum (NAS) layer. In non-access stratum signaling, signals between UEs 110 and the network node 130 may be transparently passed through the radio access network. In some embodiments, radio access nodes 120 may interface with one or more network nodes 130 over an internode interface.

[0035] As used herein, the term "network node" has the full breadth of its ordinary meaning and may correspond to any type of radio access node (or radio network node) or any network node, which may communicate with a UE and / or with another network node in a cellular or mobile or wireless communication system. Examples of network nodes are NodeB, MeNB, SeNB, a network node may belonging to MCG or SCG, base station (BS), multi-standard radio (MSR) radio access node such as MSR BS, eNodeB, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission point, transmission node, RRU, RRH, node in distributed antenna system (DAS), core network node (e.g., MSC, MME, etc.), O&M, OSS, Self-organizing Network (SON), positioning node (e.g., E-SMLC), MDT, test equipment, etc. Example embodiments of a network node are described in more detail below with respect to FIG. 3.

[0036] In some embodiments, radio access node 120 may be a distributed radio access node. The components of the radio access node 120, and their associated functions, may be separated into two main units (or sub-radio network nodes) which may be referred to as the central unit (CU) and the distributed unit (DU). Different distributed radio network node architectures are possible. For instance, in some architectures, a DU may be connected to a CU via dedicated wired or wireless link (e.g., an optical fiber cable) while in other architectures, a DU may be connected a CU via a transport network. Also, howthe various functions of the radio access node 120 are separated between the CU(s) and DU(s) may vary depending on the chosen architecture.

[0037] In some embodiments, radio access nodes 120 may communicate with each other over terrestrial or other connections. The communication between the radio access nodes 120 may, e.g., in a 5G / NR communication system may be achieved by using an Xn interface connecting the radio access nodes 120.

[0038] Exemplary wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology (RAT). The various development stages of the 3GPP specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE (LTE-A) employs a radio mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a core network known as the Evolved Packet Core (EPC). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features such as user plane Packet Data Convergence / Radio Link Control / Medium Access Control / Physical layer protocol (PDCP / RLC / MAC / PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other RAT examples comprise those provided by base stations of systems that are based on technologies such as WLAN and / or Worldwide Interoperability for Microwave Access (WiMax). A base station may provide coverage for an entire cell or similar radio service area. Core network elements include Mobility Management Entity (MME), Serving Gateway (S-GW) and Packet Gateway (P-GW).

[0039] An example of a suitable communications system is the 5G or NR concept. Network architecture in NR may be similar to that of LTE-A. Base stations of NR systems may be known as next generation Node Bs (gNBs). Changes to the network architecture may depend on the need to support various radio technologies and finer Quality of Service (QoS) support, and some on-demand requirements for QoS levels to support Quality of Experience (QoE) of user point of view. Also network aware services and applications, and service and application aware networks may bring changes to the architecture. Those are related to Information Centric Network (ICN) and User-Centric Content Delivery Network (UC-CDN) approaches. NR may use multiple input-multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates.

[0040] Future networks may utilize network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entitiesthat may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes, or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

[0041] An example 5G core network (CN) comprises functional entities. The CN is connected to a UE via the radio access network (RAN). An UPF (User Plane Function) whose role is called PSA (PDU Session Anchor) may be responsible for forwarding frames back and forth between the DN (data network) and the tunnels established over the 5G towards the UEs exchanging traffic with the data network (DN). The UPF is controlled by an SMF (Session Management Function) that receives policies from a PCF (Policy Control Function). The CN may also include an AMF (Access & Mobility Function).

[0042] Generally, all concepts disclosed herein may be applicable to different communication networks, comprising but not limited to LTE, LTE-A, 5G, 5G advanced, 6G, and other future or already implemented networks.

[0043] FIG. 2 is a schematic diagram of an apparatus for the UE. In an embodiment, the apparatus may comprise the UE, in yet another embodiment the apparatus is comprised in the UE, and in another embodiment the apparatus is the UE. The apparatus may comprise a wireless device. The apparatus may comprise at least one processor 220 and at least memory 230 storing computer program instructions that, when executed by the at least one processor 220, cause the apparatus to carry out the embodiments of the UE 110 described herein. UE 110 includes a transceiver 210, processor 220, memory 230, and a network interface 240. In some embodiments, the transceiver 210 facilitates transmitting wireless signals to and receiving wireless signals from radio access node 120 (e.g., via transmitter(s) (Tx), receiver(s) (Rx) and antenna(s)). The processor 220 executes instructions to provide some or all of the functionalities described herein as being provided by UE 110, and the memory 230 stores the instructions executed by the processor 220. In some embodiments, the processor 220 and the memory 230 form processing circuitry.

[0044] As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog, and / or digital and / or quantum circuitry) and (b) combinations of hardware circuit(s) and software, such as (as applicable): (i) a combination of analog, and / or digital and / or quantum hardware circuit(s) with software / firmware and (ii) any or all portions of hardware processor(s) (including digital signal and / or quantum processor(s)) withsoftware, and memory(ies) that work together to cause an apparatus, such as a mobile device, computing device, or server, to perform various functions) and (c) any or all portions of hardware circuit(s), such as microprocessor(s), processor(s) and / or quantum processor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0045] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0046] The processor 220 may include any suitable combination of hardware to execute instructions and manipulate data to perform some or all of the described functions of UE 110 described herein. In some embodiments, the processor 220 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs) and / or other logic.

[0047] The memory 230 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and / or other instructions capable of being executed by a processor 220. Examples of memory 230 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or or any other volatile or non-volatile, non- transitory computer-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by the processor 220 of UE 110. For example, the memory 230 includes computer program code causing the processor 220 to perform processing according to the methods described herein.

[0048] The network interface 240 is communicatively coupled to the processor 220 and may refer to any suitable device operable to receive input for UE 110, send output from UE 110, perform suitable processing of the input or output or both, communicate to other devices, or any combination thereof. The network interface 240 may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

[0049] Other embodiments of UE 110 may include additional components beyond those shown in FIG. 2 that may be responsible for providing certain aspects of the wireless device’s functionalities, including any of the functionalities described herein and / or any additional functionalities (including anyfunctionality necessary to support the mechanisms according to the subject disclosure). As an example, UE 110 may include input devices and circuits, output devices, and one or more synchronization units or circuits, which may be part of the processor 220. Input devices include mechanisms for entry of data into UE 110. For example, input devices may include input mechanisms, such as a microphone, input elements, a display, etc. Output devices may include mechanisms for outputting data in audio, video and / or hard copy format. For example, output devices may include a speaker, a display, etc.

[0050] In some embodiments, the wireless device UE 110 may comprise a series of modules configured to implement the functionalities of the wireless device described herein. Moreover, in some embodiments, the UE 110 may also comprise means for the functionalities described herein.

[0051] It will be appreciated that the various modules may be implemented as combination of hardware and software, for instance, the processor, memory, and transceiver(s) of UE 110 shown in FIG.2. Some embodiments may also include additional modules to support additional and / or optional functionalities.

[0052] FIG. 3 is a schematic diagram of an example of an apparatus for a radio access node 120 or network node 130. The apparatus may comprise at least one processor 220 and at least memory 230 storing computer program instructions that, when executed by the at least one processor 220, cause the apparatus to carry out the embodiments of the network node 130 or radio access node 120 described herein. The example radio access node 120 or network node 130 may include one or more of a transceiver 310, processor 320, memory 330, and network interface 340. In some embodiments, the transceiver 310 facilitates transmitting wireless signals to and receiving wireless signals from wireless devices, such as UE 110 (e.g., via transmitter(s) (Tx), receiver(s) (Rx), and antenna(s)). The processor 320 executes instructions to provide some or all of the functionalities described herein as being provided by the radio access node 120 or the network node 130, the memory 330 stores the instructions executed by the processor 320. In some embodiments, the processor 320 and the memory 330 form processing circuitry. The network interface 340 may communicate signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), core network nodes or radio network controllers, etc.

[0053] The processor 320 may include any suitable combination of hardware to execute instructions and manipulate data to perform some or all of the described functions of the radio access node 120 or the network node 130, such as those described herein. In some embodiments, the processor 320 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs) and / or other logic.

[0054] The memory 330 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and / or other instructions capable of being executed by a processor 320. Examples of memory 330 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or or any other volatile or non-volatile, non- transitory computer-readable and / or computer-executable memory devices that store information. For example, the memory 330 includes computer program code causing the processor 320 to perform processing according to the methods described herein.

[0055] In some embodiments, the network interface 340 is communicatively coupled to the processor 320 and may refer to any suitable device operable to receive input for the radio access node 120 or the network node 130, send output from the radio access node 120 or the network node 130, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. The network interface 340 may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

[0056] Other embodiments of the radio access node 120 or the network node 130 may include additional components beyond those shown in FIG. 3 that may be responsible for providing certain aspects of the node’s functionalities, including any of the functionalities described herein and / or any additional functionalities (including any functionality necessary to support the solutions described herein). The various different types of radio access nodes or network nodes may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

[0057] Processors, interfaces, and memory similar to those described with respect to FIG. 3 may be included in other nodes (such as UE 110, radio access node 120, etc.). Other nodes may optionally include or not include a wireless interface (such as the transceiver described in FIG. 3).

[0058] In some embodiments, the radio access node 120 or the network node 130 may comprise a series of modules configured to implement the functionalities of the radio access node 120 or the network node 130 described herein. Moreover, in some embodiments, the radio access node 120 or the network node 130 may also comprise means for the functionalities described herein.

[0059] It will be appreciated that the various modules may be implemented as combination of hardware and software, for instance, the processor, memory, and transceiver(s) of the radio access node 120 or the network node 130 shown in FIG. 3. Some embodiments may also include additional modules to support additional and / or optional functionalities.GENERAL ASPECTS OF THE PRESENT DISCLOSURE

[0060] Before referring to FIGs. 5 to 12 describing methods, apparatuses and computer-readable storage media for CSI acquisition during cell switch in detail, some general information on processing and delay times during cell switch operations and the issues arising are given first, with reference to FIGs. 4A and 4B.

[0061] Generally, one type of cell switch operations is L1 / L2 triggered mobility (LTM). As defined in 3GPP TS 38.300, e.g., in version 18.4.0, LTM is a procedure in which a gNB receives L1 or L3 measurement report(s) from a UE 100, and on their basis the gNB 120 may change UE's 120 serving cell by a cell switch command signalled via a MAC CE. The cell switch command indicates an LTM candidate configuration that the gNB 120 previously prepared and provided to the UE 110 through RRC signaling. Then the UE 110 switches to the target configuration according to the cell switch command. The LTM procedure reduces the mobility latency and interruption compared to traditional cell switch operations.

[0062] When configured by the network, it is possible to activate Transmission Configuration Indicator (TCI) states of one or multiple cells that are different from the current serving cell. For instance, the TCI states, also referred to as TCI state activation commands, of the LTM candidate cells are activated in advance before any of those cells become the serving cell. This allows the UE 110 to be DL synchronized with those cells, thereby facilitating a faster cell switch to one of those cells when cell switch is triggered. All the activated TCI states except those received in the cell switch command are deactivated upon LTM cell switch execution. When configured by the network, it is possible to initiate UL TA acquisition (called early TA or early TA) procedure of one or multiple cells that are different from the current serving cells. Further information is to be found in 3GPP TS 38.300, V18.4.0, which is incorporated herein by reference.

[0063] The procedure for LTM is defined in 3GPP TS 38.300 V18.4.0 as follows:1. The UE sends a MeasurementReport message to the gNB. The gNB decides to configure LTM and initiates LTM preparation.2. The gNB transmits an RRCReconfiguration message to the UE including the LTM candidate target cell configurations.3. The UE stores the LTM candidate configurations and transmits an RRCReconfigurationComplete message to the gNB.4a. The UE performs DL synchronization with the LTM candidate cell(s) before receiving the cell switch command. The UE may activate and deactivate TCI states of LTM candidate cell(s), as triggered by the gNB and defined in 3GPP TS 38.133 V18.8.0.4b. The UE may perform UL synchronization with LTM candidate cell(s) before receiving the cell switch command, by using UE-based TA measurement, if configured, and / or by transmitting a preamble towards the candidate cell, as triggered by the gNB by PDCCH order. When UE-based TA measurement is configured, UE acquires the TA value(s) of the candidate cell(s) by measurement. UE performs early TA acquisition with the candidate cell (s) as requested by the network before receiving the cell switch command as specified in clause 9.2.6 and TS 38.133 V18.8.0. This is done via contention-free RA (CFRA) triggered by a PDCCH order from the source cell, following which the UE sends preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the UE does not receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command. The UE does not maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity.5. The UE performs L1 and / or L3 measurements on the configured LTM candidate cell(s) and transmits L1 and / or L3 measurement reports to the gNB. The UE may perform simultaneously L3 measurements for the same SSB. L1 measurement may be performed as long as RRC reconfiguration is applicable. The UE also performs L3 measurement reporting to the gNB, including beam level measurement results on cell(s) which are configured as LTM candidate target cell(s) according to the received network configuration.6. The gNB decides to execute cell switch to a target cell and transmits an LTM cell switch command MAC CE triggering cell switch by including a target configuration ID which indicates the index of the candidate configuration of the target cell, a beam indicated with a TCI state or beams indicated with DL and UL TCI states, and a timing advance command for the target cell, if available. The UE switches to the target cell and applies the candidate configuration indicated by the target configuration ID.7. The UE performs the random access procedure towards the target cell, if UE does not have valid TA of the target cell as specified in clause 5.18.35 of 3GPP TS 38.321.8. The UE completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to target cell. If the UE has performed a RA procedure the UE considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For RACH-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the network has successfully received its first UL data.

[0064] FIG.4A illustrates the resulting total cell switch delay, which is written as specified in subclause 6.3.1.3 of 3GPP 38.133 V18.8.0, herein incorporated by reference:TLTM-interrupt - Tl_TM-RRC-processing + Tl_TM-processing + Tfirst-RS + TRS-proc + TLTM-IUWith:• TLTM-RRC-processing being the time for ASN.1 decoding and validity / compliance check for the RRC configuration of the LTM target cell indicated in the LTM cell switch command;• TLTM-processmg being the time for UE processing, consisting of applying the target cell parameters and L1 / L2 change;• Tfirst-RS being the time for fine time tracking and acquiring full timing information of the target cell;• TRS-PTOC being the time for SSB processing; and• TLTM-IU as the interruption uncertainty during LTM cell switch.

[0065] The LTM procedure as set forth by TS 38.133 V18.8.0 prescribes certain definitions and conditions for the UE behavior for the various delay times. Inter alia, when LTM-RRC-processing has already been performed, i.e. TLTM-RRC-processing = 0, when the UE supports ltm-FastProcessingConfig-r18 capability, and• the number of LTM candidate cell configurations does not exceed maxNumberConfigs-r18 and the number of the configured serving cells and the cells in the LTM configuration does not exceed maxNumberStoredConfigCells-r18, or• when the following conditions for the target cell are fulfilled:o the UE has received a LTM candidate cell TCI state activation command for the target cell at least 13 Milliseconds after an HARQ before the LTM cell switch command, i. e , THARQ + 13 Milliseconds before an LTM CSC, and / oro the UE has received a PDCCH order for early RACH for the target cell at least NT.2+10 Milliseconds before the LTM cell switch command, where NT,2 is defined in section 8.1 of TS 38.213, ando the number of LTM candidate cells for which TCI state(s) were activated or PDCCH order was received before the cell switch command does not exceed maxNumberConfigs-r18, and the total number of serving cells and the cells in the LTM configuration for which TCI state(s) were activated or PDCCH order was received before the cell switch does not exceed maxNumberStoredConfigCells-r18.

[0066] Furthermore, ltm-FastProcessingConfig-r18 indicates whether the UE supports fast processing of LTM candidate cell RRC configuration. This capability signalling comprises the following parameters:• maxNumberStoredConfigCells-r18 indicating the maximum number of serving cell(s) and candidate cell(s), including serving SpCell(s), serving SCell(s) in MCG and SCG, SpCell in LTM candidate configurations and Scell(s) in LTM candidate configurations for MCG and SCG, that UE can store the configurations.• maxNumberConfigs-r18 representing the maximum number of LTM candidate configuration for which the UE can perform early ASN.1 decoding and validity check, as described in TS 38.133.

[0067] A UE supporting this capability also indicates support of ltm-MAC-CE-JointTCI-r18 or Itm-MAC-CE-SeparateTCI-r18. UE shall set the capability values for maxNumberStoredConfigCells-r18 and maxNumberConfigs-r18 consistently for all bands. These capability values represent the maximum number across all the supported bands. The conditions for fast processing of an LTM candidate cell RRC configuration is defined in clause 6.3 in TS 38.133 V18.8.0 which is incorporated herein by reference.

[0068] Otherwise, TLTM -RRC-processing equals to 10 Milliseconds (ms).

[0069] On a further note, when the UE supports ltm-FastUE-Processing-r18 capability, the value of TLTM-processing equals to:• fr1-r18 for Frequency Range 1 (FR1) to Frequency range 2 (FR1) LTM cell switch, with fr1-r18 specified in section 6.3.1.3. of T38.133 V18.8.0, being incorporated by reference;• fr2-r18 for FR2 to FR2 LTM cell switch.• fr1-AndFR2-r18 for FR1 to FR2 and FR2 to FR1 LTM cell switch with fr1-AndFR2-r18 specified in section 6.3.1.3. of T38.133 V18.8.0 being incorporated by reference.

[0070] Furthermore, the value of TLTM -processing equals to:• 20 ms for FR1 to FR1 and FR2 to FR2 LTM cell switch.• 40 ms for FR1 to FR2 and FR2 to FR1 LTM cell switch.

[0071] Moreover, no fine time tracking and acquiring full timing information of the target cell and no SSB processing is performed, i.e. Tfirst-Rs = 0 and TRs-Proc= 0, when:• the target TCI state indicated in the LTM cell switch command is in the serving cell active TCI state list, or• the UE is configured with LTM L1 intra- and / or inter-frequency measurements for the target cell, ando the target TCI state in the cell switch command is in the LTM candidate cell active TCI state list, and;o the time between receiving the LTM candidate cell TCI state activation MAC-CE and the cell switch command is at least TCI state activation delay stated in TS 38.133 V18.8.0, subclause 8.25.3 ando the time between receiving the LTM candidate cell TCI state activation MAC-CE and the cell switch command is not more than TCI state activation delay stated in TS 38.133 V18.8.0, subclause 8.25.3 + 160 Milliseconds (ms), oro the measurement period of the SSB associated to target TCI state is not larger than 160 ms after the LTM candidate cell TCI state activation MAC-CE is received, or• The target cell is an FR1 cell, and the UE is not configured with LTM L1 intra- and / or interfrequency measurements for the target cell, ando The target TCI state in the cell switch command is in the LTM candidate cell active TCI state list, and■ the time between receiving the LTM candidate cell TCI state activation MAC-CE and the cell switch command is at least TCI state activation delay stated in TS 38.133 V18.8.0, subclause 8.25.3, and not more than TCI state activation delay stated in TS 38.133 V18.8.0, subclause 8.25.3 + 480 ms (longer L3 measurement delay may be expected for 480 ms after TCI state activation delay stated in TS 38.133 V18.8.0, subclause 8.25.3), or■ the time between the latest PDCCH ordered RACH preamble transmission on the target cell and the cell switch command is not more than 160 ms.

[0072] Additionally, Tfirst-Rs is the time to the first SSB transmission on the target cell after performing CSC, LTM-RRC-processing and LTM-processing, i.e. after Tcmd +TLTM-RRC -processing + TLTM -processing.

[0073] The present methodologies specifically concern CSI-RS for CSI acquisition as opposed to measuring reference signals for power measuring. CSI acquisition refers to acquiring one or more of the measurement quantities: CQI, PMI, LI, CRI, Rl. Thus, the CSI acquisition or CSI-RS measurements comprise acquiring the measurement quantities of least one of a• Channel Quality Information (CQI);• Precoding Matrix Indicator (PMI);• CSI-RS Resource Indicator (CRI);• SS / PBCH Resource Block Indicator (SSBRI);• Layer Indicator (LI);• Rank Indicator (Rl).

[0074] The cell switch delay as currently specified by TS 38.133 V18.8.0 considers only SSB based reference signal, which is used for performing DL synchronization with the target cell / TCI state if the target TCI state is not active at the time of cell switch. Hence, no CSI-RS for CSI acquisition is taken into accountin the cell switch delay currently. When a UE is configured with CSI acquisition after the cell switch, it is undefined how and when the UE should start the CSI acquisition except that CSI acquisition is supposed to start at some point after cell switch command.

[0075] In the following, methods and apparatuses are provided to perform CSI acquisition after the cell switch command with minimal extension to the cell switch interruption, and when to start the CSI acquisition process during the cell switch. The present methodologies aim at facilitating efficient cell switch in terms of delay as well as improved network-UE interoperation.

[0076] The method provides UE behavior and requirements related to the UE early CSI acquisition, and on the network side transmitting CSI-RS for CSI acquisition early so that the reporting is possible. On the network side, when the starting point of the CSI-RS measurements by the UE is known, the method as provided enables the network to transmit early procedure trigger, such as the first and the second trigger, or the cell switch command in relation to the CSI-RS measurement resource. The network therefore considers the UE pre-processing capabilities, the CSI frequency location and UE capabilities. The network optimizes either the CSI-RS transmission or the transmission of the cell switch command to provide the UE more time to perform the CSI measurement. The outcome of this procedure is that the network receives the CSI-reporting faster and is able to schedule UE with higher MCS earlier. In embodiments, the CSI-RS measurement delay being added to the total time switch delay as shown in FIG. 4B is divided into three delay components:TcSI - TcSI-RRC-processing + TcSI-measurement + TcSI-processingWith:• Tcsi as the time for the first CSI-RS measurement (CSI acquisition) from the target cell;• Tcsi-RRc-processing as the processing delay associated with the CSI-RS measurement configuration processing (CSI-RRC processing);• Tcsi-measurement as the time for performing the (actual) CSI-RS measurements;• Tcsi-processing as the time for UE CSI processing based on UE CSI processing capability.CSI-RS MEASUREMENT CONFIGURATION PROCESSING

[0077] FIG. 5 is a flow chart of the basic method according to the disclosure. The method is performed by a user equipment (e.g. UE 110, 110A, 11 A). The UE receives 20, from a network node 120, 120A, 120B of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal,CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells. The UE processes 22, in response to a first trigger message 21, the CSI-RS measurement configuration to store 23 the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment. The UE receives 24 a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate target cells.

[0078] In some embodiments, the CSC may be an in-band message (e.g. MAC CE) originating, or not originating from MAC layer. In other words, the origin of the message carrying the CSC may be from another user plane layer. Similarly, the CSC command may be ASN.1 message, for instance RRC message.

[0079] In some embodiments, processing the CSI-RS measurement configuration comprises an RRC-layer processing to transform the CSI-RS measurement configuration into a lower layer configuration. This addresses the aspect that the behavior of the UE 110 in terms of CSI acquisition is controlled by a lower layer configuration (the CSI-RS measurement configuration) obtained during the configuration processing activities. In some embodiments, the lower layer configuration comprises a layer 1 and / or layer 2 configuration. This makes the CSI-RS measurement configuration readily available, and in shorter time than without pre-processing, for starting CSI acquisition once the second trigger message (measurement trigger) is received by the UE 110.

[0080] In some embodiments, processing the CSI-RS measurement configuration is performed together with early / fast-RRC-processing capability where an RRC configuration of the target cell 21 associated with the CSC and going to be indicated in the CSC (e.g. LTM candidate cell configuration 51 shown by FIG. 12), is processed before the cell switch command, when conditions apply, when the user equipment supports a cell switch configuration processing capability, e.g. when the UE supports e.g. Itm-FastProcessingConfig-r18. This enables the processing of the CSI-RS measurement configuration under the same conditions as the LTM RRC-configuration according to the ltm-FastProcessingConfig-r18 capability, resulting that after the cell switch, TCSI-RS -processing = 0 and TLTM -RRC-processing = 0, when the CSI-RS measurement configuration and the RRC configuration have already been processed beforehand.

[0081] In some embodiments, processing the CSI-RS measurement configuration comprises at least one of decoding the RRC configuration message, validating content of the RRC configuration message, checking the RRC configuration message for misconfigured parameters, extracting parts of the RRC configuration (e.g. the CSI-RS acquisition config based on the direct / indirect indication in the trigger). This processing is performed before the UE 110 stores the processed configuration to memory, such as a permanent memory or buffered to an operating memory. The UE may store the configuration into a format in the memory where the processed configuration is in machine readable format (i.e. , theUE can access the processed configuration very fast to perform lower lawyer CSI-RS measurements without significant delay in response to a trigger). When the second (measurement) trigger is then received, the UE 110 loads the processed CSI-RS measurement configuration from the memory and applies the loaded lower layer CSI-RS measurement configuration to the CSI measurement engine.

[0082] In some embodiments, the first trigger message is at least one of the following: the RRC configuration message; a Transmission Control Indicator, TCI, state activation command; an Early Random Access Channel, RACH, procedure trigger message; a Layer 1 or Layer 3 event triggered measurement report; a Measurement activation / deactivation trigger message; or the CSC. This specifically triggers when the UE should start processing the RRC CSI-RS measurement configuration to render the configuration readily available for performing CSI acquisition in response to the second trigger (measurement trigger).

[0083] In some embodiments, the TCI state activation command comprises a Lower Layer Triggered Mobility Transmission Control Information, LTM TCI activation, Medium Access Control, MAC, Control Element, CE 54, as shown in FIG. 12 (described in further detail below). This specifically triggers the CSI-RS measurement configuration processing when the UE performs DL synchronization with the LTM candidate cell(s).

[0084] In some embodiments, the RACH procedure trigger message comprises at least one of a: Physical Downlink Control Channel, PDCCH, order message 57, as shown in FIG. 12; Medium Access Control, MAC, Control element, CE, Timing Advance, TA, command. This specifically triggers the CSI-RS measurement configuration processing when the UE 110 performs UL synchronization with the LTM candidate cell(s).

[0085] In some embodiments, the measurement activation / deactivation trigger message comprises: CSI-RS activation / deactivation in-band signaling; a MAC control element. This also specifically triggers when the UE should start the CSI-RS measurement configuration processing.

[0086] In some embodiments, the cell-switch operation comprises a mobility procedure such as a Lower Layer Triggered Mobility (LTM) procedure or an RRC Triggered Mobility procedure. The LTM procedure enables the UE 110 to perform a serving cell change via L1 / L2 signaling, while keeping configuration of the upper layers and / or minimizing changes of configuration of the lower layers, as already mentioned above.

[0087] In some embodiments, the method further comprises, in response to the second trigger message, loading the stored CSI-RS measurement configuration to perform the lower layer CSI-RS measurements. This enables the measurement triggering of the (actual) CSI-RS measurement process of e.g. the CSI-parameters CQI, PMI, CRI, SSBRI, LI, Rl and / or L1-RSRP from the CSI-RS measurement configuration and to schedule said measurement either e.g. before or after the CSC, as described infurther detail below. Enabling the measurement triggering is understood in the sense that when the network transmits the trigger, the network may transmit the reference signal towards the UE after a known delay from the trigger. This guarantees that the UE is ready to receive the CSI-RS.

[0088] In some embodiments, processing the CSI-RS measurement configuration processing is performed upon receiving the RRC configuration message when the number of configured CSI reference signals for measurement, CSI-RS, for the candidate cell is smaller or equal to a maximum number of configured CSI-RS for measurement.

[0089] In some embodiments, the second trigger message comprises at least one of the following: a Transmission Control Element, TCI, state activation command; an Early Random Access Channel, RACH, procedure message; or the CSC. This enables the triggering of the (actual) CSI-RS measurement process of the CSI-parameters either at DL or UL synchronization or after the CSC.

[0090] In some embodiments, processing the CSI-RS measurement configuration is performed upon receiving the CSC, and simultaneously while the UE is performing TiTM-RRc-processing. This allows the network to transmit the CSI-RS after the TLTM -RRC-processing duration. This may be supported with or without ltm-FastProcessingConfig-r18 capability.

[0091] As derivable from the above, in same scenarios, one and the same trigger message may constitute the first trigger (for processing the RRC CSI-RS measurement configuration) and the second trigger (for starting the CSI acquisition). For example, as also set out further below with reference to FIG.12, the TCI state activation command or the Early RACH procedure may trigger both, CSI-RS measurement configuration processing and, afterwards, CSI acquisition. Another example may be the CSC which may trigger RRC CSI-RS measurement configuration processing in some embodiments, and also trigger CSI-RS acquisition (cf. FIG. 7 showing the case of CSI-RS measurements after the cell switch). In this example, the first trigger message 21 and the CSC reception 24 coincide, meaning that processing 22 and storing 23 occur after the CSC 24. In other scenarios, the first and second trigger are given by separate messages, e.g. the first trigger message may be the RRC configuration message and the second trigger message may be the CSC. This may be the case if e.g. the LTM cell switch procedure does not feature an early downlink or uplink synchronization routine (cf. FIG. 12 discussed below).

[0092] FIG. 8 visualizes different options processing of the RRC configuration in response to different first trigger messages as described above, such as the RRC configuration message; a Transmission Control Indicator, TCI, state activation command; an Early Random Access Channel, RACH, procedure trigger message. FIG. 8 also shows that when the RRC-configuration has already been processed before the CSC, the TuM-RRe-processing = 0 after the CSC. FIG. 9 visualizes the relation between processing the LTM candidate cell configuration included in the RRC configuration message (time component TLTM RRc-processing) and processing the CSI-RS measurement configuration for CSI acquisitionincluded in the RRC configuration (time component Tcsi-RRc-processing). Depending on the first trigger message, Tcsi-RRc-processing may follow TLTM -RRC-processing without further delay time components in between, i.e. both RRC configurations are processed together.CSI-RS MEASUREMENTS BEFORE CELL SWITCH COMMAND

[0093] According to one aspect of the present disclosure, a method performed by a user equipment (UE) is provided. The UE 110 is in a cell-switch operation from a source cell to a target cell. The method includes at least the activities shown by the flow chart of FIG. 6 and optionally further activities.

[0094] The UE 110 receives in 30, a trigger message which causes the UE 110 to perform lower layer CSI-RS measurements in dependency of conditions to be determined by the UE 110. The UE 110 determines these conditions for performing the lower layer CSI-RS, measurements in 31. The conditions prescribe more specifically when, in the time domain, the UE 110 performs the lower layer CSI-RS measurements, as shown in 32. According to the present aspect, the UE performs the lower layer CSI-RS measurements of the target cell based on the determined conditions and a CSI-RS measurement configuration stored at the UE 110 for the CSI measurements relating to the target cell before receiving the CSC. The UE 110 receives the CSC in 33.

[0095] Generally, the behavior of the UE 110 in the present aspect is controlled by a lower layer configuration (the CSI-RS measurement configuration) obtained during the configuration processing activities described above, in particular with reference to FIG. 5. In a typical scenario, it is assumed that the UE 110 has performed the activities of FIG. 5 before the activities of FIG. 6 are performed. However, a likewise typical scenario is that the first trigger message causing the UE 110 to perform the activities of FIG. 5 has not yet received beforehand, i.e. the trigger message shown in box 30 of FIG. 6 may also be the first trigger message of box 21 in FIG. 5. In other words, if the UE 110 has not yet performed TCSI-RRC-processmg, the UE shall process the CSI-RS measurement configuration (FIG. 5) in response to the trigger message 30. More specifically, the UE 110 may process the CSI-RS measurement configuration before the first CSI-RS associated with the trigger message 30.

[0096] Generally, the trigger message 30 enables the UE 110 to "know" which of the typically multiple candidate target cells will become the target cell selected by the network, even before the UE 110 receives the CSC. Thus, the UE 110 being aware of the future target cell even before the actual cell switch is enabled to perform lower layer CSI measurements before the cell switch, at least under certain conditions. If these conditions allow performing the lower layer CSI-RS measurements before the CSC, the overall cell switch and the UE operation in the target cell is rendered more efficiently. For example, performing the lower layer CSI-RS measurements based on CSI-RS transmitted by the target cell in an early phase before the cell switch shortens the time until the UE 110 is able to send an initial CSI-RSmeasurement report to the target cell after the cell switch which, in turn, enables the target cell to schedule the UE 110 more appropriately according to the physical channel conditions of the UE 110 vis-a-vis the target cell.

[0097] Accordingly, after receiving the CSC in 33, the UE 110 may prepare a CSI measurement report and transmit the CSI measurement report to the target cell. The UE 110 may then be scheduled (e.g. receive a DCI message with a downlink or uplink grant) by the network (target cell) based on the CSI measurement report earlier than in traditional procedures.

[0098] These activities likewise constitute functionalities of the UE 110, implemented by way of processor-readable and processor-executable instructions stored in a memory of the UE 110, equipping the UE 110 with the aforementioned functionalities. Likewise, these activities may be embodied as a computer-readable storage medium which, when executed by a computer (e.g. a processor of the computer such as a processor of the UE 110), cause the computer to perform the described activities.

[0099] As mentioned above, the activities are performed by the UE 110 during a cell switch operation. In some embodiments, the cell switch operation comprises a mobility procedure such as a Lower Layer Triggered Mobility (LTM) procedure as currently specified by 3GPP TS 38.133 V18.8.0. Thus, in such embodiments, the activities constitute an extension of the LTM procedure, being able to render the performance of the LTM procedure more efficiently. In some embodiments, the cell switch operation comprises an RRC Triggered Mobility (RTM) procedure. Accordingly, in these embodiments, the cell switch command is an RTM cell switch command.

[0100] In some embodiments, the trigger message comprises a Transmission Control Element, TCI, state activation command for a TCI state activation. In such embodiments, when the cell switch operation is or features an LTM procedure, the TCI state activation command comprises a Lower Layer Triggered Mobility Transmission Control Information, LTM TCI activation, Medium Access Control, MAC, Control Element, CE.

[0101] In some embodiments, the trigger message comprises an Early Random Access Channel, RACH, procedure trigger message for transmitting an uplink RACH message. In such embodiments, the RACH procedure trigger message comprises at least one of a Physical Downlink Control Channel, PDCCH, ordered RACH message or a Medium Access Control, MAC, Control element, CE, Timing Advance, TA, command.

[0102] Both options, the TCI state activation command and the Early RACH procedure trigger message, may inform the UE 110 of the identity of the target cell before the source cell issues the CSC to the UE 110. The UE 110 is thus enabled to utilize the time between the trigger message and the CSC for early CSI-RS measurements of the target cell, depending on one ore more conditions.

[0103] In some embodiments, the conditions comprise whether a CSI-RS of the target cell is within or partially contained within an active bandwidth part, BWP, of the UE 110. This ensures that the UE 110 has a certain minimum amount of CSI-RS transmitted by the target cell available while still utilizing the active BWP in the source cell. Performing the measurement within the active bandwidth part allows UE 110 to measure without needing to retune the RF chain.

[0104] Thus, with reference to FIG. 6, in such embodiments, the UE 110 determines whether or not the CSI-RS of the target cell is located with the active BWP of the UE 110 at least to a certain extent. For example, the CSI-RS of the target cell may be defined as being partially within active BWP if at least a given threshold number of Physical Resource Blocks (PRBs) of the CSI-RS are within the active BWP of the UE 110. For example, in some embodiments, the threshold number of PRBs may be 48 PRB. Thus, the condition of the CSI-RS being partially contained within the active BWP of the UE 110 is fulfilled when at least 48 PRBs of the CSI-RS are within the active BWP of the UE 110.

[0105] This condition is visualized in FIG. 10. The current active BWP of the UE 110 being still with the source cell is defined by the two horizontal lines in the frequency domain (y axis). Several possibilities of the amount (in terms of PRBs) and location of the CSI-RS of the target cell relative to the active BWP of the UE 110 with the source cell are shown. For example, the CSI-RS of the target cell may be completely located within the active BWP of the UE 110 as shown by option D. If such CSI-RS is completed located inside the active BWP, the condition "is within an active BWP" is fulfilled, irrespective of the amount of PRBs constituting the CSI-RS.

[0106] In other options, the CSI-RS of the target cell is partially contained in the active BWP of the UE 110 in the source cell. Whether or not the condition "partially contained within an active BWP" is fulfilled then depends on the number of PRBs of the CSI-RS which are inside the active BWP. As mentioned above, the threshold number is e.g. 48 PRBs. If the number of PRBs of the CSI-RS is 48 PRBs or more (as shown in options A and C of FIG. 10), the condition "partially contained within an active BWP" is deemed to be fulfilled. Otherwise, e.g. if the overlap between the CSI-RS and the active BWP is less than e.g. 48 PRBs, as shown by option B of FIG. 10, the UE 110 determines that the condition is not fulfilled and the CSI-RS is partially outside the active BWP. The CSI-RS of the target cell may also be located completely outside of the active BWP (option E), in which case the UE 110 determines that the condition is not fulfilled and the CSI-RS is fully outside the active BWP.

[0107] In response to the CSI measurement trigger message (also referred to as second trigger above), the presence of the conditions control the behavior of the UE 110 as follows.

[0108] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements from the first CSI-RS after the TCI state activation when the CSI-RS is within or partially contained within the active BWP.

[0109] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements at the next CSI-RS after the TCI state activation when the CSI-RS is within or partially contained within the active BWP.

[0110] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements at the next measurement gap associated with the CSI-RS after the TCI state activation, when the CSI RS is fully or partially outside the active BWP.

[0111] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements from the first CSI-RS, after the Early RACH procedure trigger message, such as the Physical Downlink Control Channel, PDCCH, ordered RACH message or, more specifically, the uplink RACH message when the CSI-RS is within or partially contained within the active BWP.

[0112] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements from the first CSI-RS, after the Early RACH procedure trigger message or, more specifically, the uplink RACH message, such as the Physical Downlink Control Channel, PDCCH, ordered RACH message and an interruption related Radio Frequency, RF, retuning when the CSI-RS is within or partially contained within the active BWP.

[0113] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements at the next measurement gap when the CSI-RS is fully or partially outside the active BWP.

[0114] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements at the next measurement gap after the PDCCH ordered RACH or, more specifically, the uplink RACH message when the CSI-RS is fully or partially outside the active BWP.

[0115] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements at the next measurement gap after the PDCCH ordered RACH or, more specifically, the uplink RACH message and an interruption related Radio Frequency, RF, retuning when the CSI-RS is fully or partially outside the active BWP.

[0116] In some embodiments, other or further conditions may be defined, may be determined by the UE 110 in response to the trigger message and may then control the behavior of the UE 110 in terms of timing of the lower layer CSI-RS measurements of the target cell.

[0117] In some embodiments, after having performed the lower layer CSI-RS measurements, the UE 110 further processing the lower layer CSI-RS measurements to prepare a CSI measurement report to be transmitted to the target cell after the CSC. As mentioned above, the time utilized for processing the CSI-RS measurements is denoted as Tcsi-processing. As visualized in FIG. 11, in some embodiments, the UE 110 processes the obtained lower layer CSI-RS measurements without further time delay after performing the lower layer CSI-RS measurements based on a processing capability of the userequipment. Hence, Tcsi-processing may be located after Tcsi-measurement without any additional time delay utilized for other operations of the UE 110.

[0118] In some embodiments, the UE 110 may perform lower layer CSI-RS measurements before the CSC, in response to a trigger message and based on one or more conditions as described above, and may additionally determine whether or not the amount of obtained CSI-RS measurements is sufficient for preparing a CSI measurement report during Tcsi-processing. When the amount of obtained CSI-RS measurements is sufficient, the UE may directly proceed to Tcsi-processing after the CSC without performing further CSI-RS measurements. Otherwise, if the amount of obtained CSI-RS is not sufficient, the UE 110 may perform additional CSI-RS measurements after the CSC and then proceed to Tcsi-processing.

[0119] More specifically, in such embodiments, the UE 110 may determine that an amount of CSI-RS before receiving the CSC is sufficient for a CSI measurement report. If this is the case, the UE 110 omits further lower layer CSI-RS measurements after receiving the CSC and transmitting the CSI measurement report to the target cell after receiving the CSC based on the lower layer CSI-RS measurements performed before receiving the CSC.

[0120] On the other hand, the UE 110 may determine that an amount of CSI-RS before receiving the CSC is insufficient for a CSI measurement report. If this is the case, the UE 110 performs further lower layer CSI-RS measurements after receiving the CSC and transmitting the CSI measurement report to the target cell after receiving the CSC based on the lower layer CSI-RS measurements performed before receiving the CSC and on the further lower layer CSI-RS measurements performed after receiving the CSC.

[0121] The methodologies of performing the lower layer CSI-RS measurements before the cell switch can be summarized as follows:

[0122] If the UE has not yet performed TCSI-RRC -processing, the UE shall perform TCSI-RRC -processing based on the measurement trigger (before the first CSI-RS associated with the measurement trigger).

[0123] If the UE has performed CSI-RRC-processing (Tcsi-RRc-processing - 0), the UE shall start the CSI-RS measurements at the first CSI-RS after the measurement trigger.

[0124] In one example, the trigger is TCI state activation. In one example, after TCI state activation, the UE 110 shall perform TCSI-RRC -processing, and if the CSI-RS is within or partially (e.g. N PRBs) contained within active BWP, the UE 110 shall start CSI-RS measurement from the first CSI-RS after the TCI state activation. In one example, if the TCI state is activated, and Tcsi-RRc-processing = 0 (meaning that the CSI-RS measurement configuration has already been processed beforehand and, hence, no time is needed for the activities of FIG. 5 anymore), and if the CSI-RS is within or partially (e.g. N PRBs) contained within active BWP, the UE shall start CSI-RS measurements at the next CSI-RS after the TCI state activation. In one example, if the TCI state is activated, and Tcsi-RRc-processing = 0, and if the CSI-RS is fully or partially(e.g. N PRBs) outside of the active BWP, the UE shall start CSI-RS measurements at the next measurement gap associated with CSI-RS after the TCI state activation. The N may be, for instance 48 or other positive integer.

[0125] In one example, the trigger is PDCCH ordered RACH (Tcsi-RRc-processing = 0 ms or x ms depending if the conditions for processing the CSI-RS measurement configuration were met or not, see above with reference to FIG. 5). In one example, after PDCCH ordered RACH, and if the CSI-RS is within or partially (e.g. N PRBs) contained within active BWP, the UE shall start CSI-RS measurement from the first CSI-RS:- After PDCCH ordered RACH transmission associated with the PDCCH order RACH,- After PDCCH ordered RACH transmission + interruption related RF retuning after PDCCH ordered RACH transmission.

[0126] In one example, PDCCH order RACH is received, and if the CSI-RS is fully or partially (e.g. N PRBs) outside of the active BWP, the UE shall start CSI-RS measurements:- At the next measurement gap,- At the next measurement gap after PDCCH ordered RACH transmission,- At the next measurement gap after PDCCH ordered RACH transmission + interruption related RF retuning after PDCCH ordered RACH transmission.CSI MEASUREMENTS AFTER CELL SWITCH COMMAND

[0127] According to one aspect of the present disclosure, a method performed by a user equipment (UE) is provided. The UE 110 is in a cell-switch operation from a source cell to a target cell. The method includes at least the activities shown by the flow chart of FIG. 7 and optionally further activities.

[0128] The UE 110 receives in 40, a cell switch command which causes the UE 110 to perform lower layer CSI-RS measurements in dependency of conditions to be determined by the UE 110. The UE 110 determines these conditions for performing the lower layer CSI-RS, measurements in 41. The conditions prescribe more specifically when, in the time domain, the UE 110 performs the lower layer CSI-RS measurements, as shown in 42. According to the present aspect, the UE performs the lower layer CSI-RS measurements of the target cell based on the determined conditions and a CSI-RS measurement configuration stored at the UE 110 for the CSI measurements relating to the target cell after receiving the CSC in box 40. Hence, the CSC serves as the trigger (also referred to as second trigger message above) to perform the lower layer CSI-RS measurements.

[0129] Generally, similar to the activities before cell switch described above with reference to FIG.6, the behavior of the UE 110 in the present aspect is controlled by a lower layer configuration (the CSI-RS measurement configuration) obtained during the configuration processing activities described above,in particular with reference to FIG. 5. It is assumed that the UE 110 has typically performed the activities of FIG. 5 before the cell switch command is received, i.e. before the start of the procedure of FIG. 7. However, as described above as well, in some situations, processing the CSI-RS measurement configuration is triggered by the CSC and thus may also occur after the CSC.

[0130] After having performed the lower layer CSI-RS measurements (= CSI acquisition), the UE 110 may prepare a CSI measurement report and transmit the CSI measurement report to the target cell. The UE 110 may then be scheduled (e.g. receive a DCI message with a downlink or uplink grant) by the network (target cell) based on the CSI measurement report earlier than in traditional procedures.

[0131] These activities likewise constitute functionalities of the UE 110, implemented by way of processor-readable and processor-executable instructions stored in a memory of the UE 110, equipping the UE 110 with the aforementioned functionalities. Likewise, these activities may be embodied as a computer-readable storage medium which, when executed by a computer (e.g. a processor of the computer such as a processor of the UE 110), cause the computer to perform the described activities.

[0132] As mentioned above, the activities are performed by the UE 110 during a cell switch operation. In some embodiments, the cell switch operation comprises a mobility procedure such as a Lower Layer Triggered Mobility (LTM) procedure as currently specified by 3GPP TS 38.133 V18.8.0 and described in detail above. Thus, in such embodiments, the activities constitute an extension of the LTM procedure, being able to render the performance of the LTM procedure more efficiently. Accordingly, in these embodiments, the cell switch command is an LTM cell switch command. In some embodiments, the cell switch operation comprises an RRC Triggered Mobility (RTM) procedure. Accordingly, in these embodiments, the cell switch command is an RTM cell switch command.

[0133] In some embodiments, similar to what has been described above with reference to FIG. 6, the one or more conditions comprise whether a CSI-RS of the target cell is within or partially contained within an active bandwidth part, BWP, of the UE 110. This ensures that the UE 110 sees a certain minimum amount of CSI-RS transmitted by the target cell.

[0134] Thus, with reference to FIG. 7, in such embodiments, the UE 110 determines whether or not the CSI-RS of the target cell is located with the active BWP of the UE 110 at least to a certain extent. For example, the CSI-RS of the target cell may be defined as being partially within the active BWP if at least a given threshold number of Physical Resource Blocks (PRBs) of the CSI-RS are within the active BWP of the UE 110. For example, in some embodiments, the threshold number of PRBs may be 48 PRB. Thus, the condition of the CSI-RS being partially contained within the active BWP of the UE 110 is fulfilled when at least 48 PRBs of the CSI-RS are within the active BWP of the UE 110.

[0135] This condition is visualized in FIG. 10. To avoid repetitions, it is referred to the description of FIG. 10 already given above.

[0136] In response to the CSI measurement trigger message, namely the CSC (also referred to as second trigger above), the presence of the conditions control the behavior of the UE 110 as follows.

[0137] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements at the first CSI-RS after the CSC when the CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment.

[0138] In some embodiments, the UE 110 performs the lower layer CSI-RS measurements after processing target cell parameters and layer 1 / layer 2, Lower Layer Triggered Mobility processing, when the CSI-RS is fully or partially outside the active BWP of the user equipment.

[0139] Moreover, in some embodiments, the one or more conditions comprise whether a Transmission Control Indicator, TCI, state activation command was received by the UE 110. As mentioned above with reference to FIG. 5 and FIG. 6, the TCI state activation command is an optional message of the LTM procedure which may occur before the cell switch command.

[0140] In some of these embodiments, the UE 110 may perform the lower layer CSI-RS measurements after starting fine time tracking when the TCI state activation command was not received.

[0141] In some embodiments, other or further conditions may be defined, may be determined by the UE 110 in response to the trigger message and may then control the behavior of the UE 110 in terms of timing of the lower layer CSI-RS measurements of the target cell.

[0142] In some embodiments, after having performed the lower layer CSI-RS measurements as shown by FIG. 7, the UE 110 further processes the lower layer CSI-RS measurements to prepare a CSI measurement report to be transmitted to the target cell after the CSC. As mentioned above, the time utilized for processing the CSI-RS measurements is denoted as Tcsi-processing. As visualized in FIG. 11, in some embodiments, the UE 110 processes the obtained lower layer CSI-RS measurements without further time delay after performing the lower layer CSI-RS measurements based on a processing capability of the user equipment. Hence, Tcsi-processing may be located after Tcsi-measurement without any additional time delay utilized for other operations of the UE 110.

[0143] The methodologies of performing the lower layer CSI-RS measurements after the cell switch can be summarized as follows:

[0144] In one example, if TCI state is activated before the cell switch command, but the CSI-RS measurements are triggered based on cell switch command, and CSI-RS is within or partially (e.g. N PRBs) contained in the active BWP, the UE 110 shall start the CSI-RS measurements at the first CSI-RS after the Tcmd processing. The total delay D is:DLTM - Tcmd+TcSI+Tl_TM-interruptwhich corresponds toDLTM - Tcmd+TcSI-RRC-processing+TcSI-measurement+TcSI-processing+Tl_TM-RRC-processing+Tl_TM-processing+Tfirst-RS+TRS -proc + TLTM-IU

[0145] Furthermore, Tcsi-RRc-processing - 0 if the DE has processed CSI configuration as explained above with reference to FIG. 5.

[0146] If CSI-RS is outside of partially outside of the active BWP, the UE 110 starts the CSI measurements after TuM-processing. The delay D is then:DLTM = Tcmd + TCSI-RRC -processing+TcSI-measurement+TcSI-processing + TLTM-RRC -processing + TLTM -processing + TLTM-IU

[0147] In another example, if the TCI state is not activated, the CSI-RS measurements are started after fine time tracking. The delay D is thenDLTM = Tcmd + TLTM-RRC -processing + TLTM -processing + Tfirst-RS + TRS -proc + Tcsi +TLTM-IU

[0148] Generally, CSI processing (Tcsi-processing) follows the CSI-RS measurements (Tcsi-measurement). TcSI-processing is considered in the above examples as a separate component as it may be variable and depending on UE processing capability. UE capability signalling may be used to determine the duration Of TcSI-processing.

[0149] If TLTM -RRC-processing 0 (TLTM -RRC-processing > 0, e.g. because the UE 110 does not support Itm-fastProcessingConfig-r18 capability, and the CSI-RS measurement configuration is provided outside of the LTM candidate cell configuration (e.g., in a message LTM-Config or in a message LTM-Candidate, but outside of Itm-CandidateConfig), and the CSI-RS is fully within or partially within (at least N PRBs) of the active BWP, the UE shall start the CSI-RS measurements after the Tcmd.

[0150] The previous description has focused on the perspective of the UE 110, but it is understood that the network (such as the network elements providing the source cell and the target cell) perform likewise activities as the network (specifically the network element constituting the target cell) is arranged to provide CSI-RS at times expected by the UE 110 according to the trigger messages and conditions described above. Accordingly, when the network transmits the trigger, the network may transmit the CSI-RS towards the UE 110 after a known delay from the trigger. This enables the UE 110 to be ready to receive the CSI-RS efficiently and at an earliest possible time during the cell switch operation, rendering the cell switch operation more efficiently. Thus, generally, depending on the trigger of Tcsi-RRc-processing in relation to the cell switch command and the one or more conditions described above, the target cell transmits the CSI-RS e.g. at the first available slot after the Tcsi-RRc-processing. If the CSI-RS is periodic, the source cell transmits the cell switch command in relation to the periodicity of the first slot of the CSI-RS. Thus, network commands and reference signals facilitate early and efficient CSI acquisition by the UE 110 during cell switch.OVERALL ASPECTS

[0151] FIG. 12 shows an exemplary message sequence chart of an overall cell switch operation which may be a result of the various aspects described above, depending on the trigger messages and conditions. FIG. 12 specifically depicts an LTM cell switch procedure. Other types of cell switch procedure envisaged herein may deviate in detail, but may have similar general functions and message exchanges.

[0152] The LTM cell switch procedure starts with the provision of an LTM candidate cell configuration 51 by the network element constituting the source cell 120A. The candidate target cells may have been selected by the network based on Layer 3 measurement reports 50 transmitted by the UE 110 beforehand.

[0153] To prepare the actual cell switch, the UE 110 utilizes the LTM candidate cell configuration 51 to perform neighboring cell measurements such as SSB measurements 52. The aim of these neighboring measurements is to support target cell selection by the network. Typically, the network selects the target cell among multiple candidate target cells which likely provides the best channel quality to the UE, i.e. which the UE 110 sees which maximum receive power among the candidate target cells. The result of the neighboring cell measurements 52 is one or more measurement reports 53. Depending on the LTM candidate cell configuration, these measurement reports 53 include Layer 1 , Layer 3, SSB and / or CSI-RS beam level measurement results.

[0154] Typically, according to the present methodologies, the LTM candidate cell configuration 51 includes the RRC CSI-RS measurement configuration enabling the UE to perform CSI-RS acquisition with the target cell 120B, once the target cell 120B has been selected and the UE 110 has been informed of the identity of the target cell. Thus, generally, Tcsi-RRc-processing may occur after the reception of message carrying the LTM candidate cell configuration 51 and additionally the RRC CSI-RS measurement configuration for the candidate target cells, among which is also the target cell selected later by the network.

[0155] At some point of the LTM cell switch procedure, the network determines the target cell 120B among the candidate target cells to which the UE 110 is going to switch to. The LTM cell switch procedure provides several early synchronization options which are utilized for early CSI acquisition as already described above and now visualized in FIG. 12.

[0156] In the case of an early downlink synchronization option, TCSI-RRC -processing is triggered by the LTM TCI activation MAC CE 54 which, inter alia, informs the UE 110 of the identity of the target cell 120B. The UE 110 is therefore triggered to process the CSI-RS measurement configuration at 55. Depending on further conditions such as the location of the CSI-RS of the target cell relative to the active BWP of the UE 110 in the source cell 120A, the UE 110B may also perform the CSI-RS measurements without further delay in 56, i.e. TcSI-measurement follows Tcsi -RRC-processing.

[0157] Likewise, in the case of an early uplink synchronization option, TCSI-RRC -processing is triggered by the PDDCH order 57 which instructs the UE 110 to transmit a RACH preamble 58 to the target cell 120B and thus informs the UE 110 of the identity of the target cell 120B. The UE 110 is therefore triggered to process the CSI-RS measurement configuration at 59, i.e. after transmitting the RACH preamble 58. Depending on further conditions such as the location of the CSI-RS of the target cell relative to the active BWP of the UE 110 in the source cell 120A, the UE 110B may also perform the CSI-RS measurements without further delay in 60, i.e. TcSI-measurement follows Tcsi -RRC-processing.

[0158] At some point, the network element hosting the source cell 120A transmits the LTM cell switch command (CSC) 61 to the UE 110, causing the UE 110 to perform the actual switch from the source cell 120A to the target cell 120B. This is the latest occasion at which the UE 110 is informed about the identity of the target cell 120B, namely if neither early downlink nor early uplink synchronization have been performed. In this situation preferably, Tcsi-RRc-processing has nevertheless been performed before the CSC 61 , e.g. triggered by the LTM candidate cell configuration message 51. As the target cell 120B was not yet determined at this earlier point, the UE 110 may have processed a RRC CSI-RS measurement configuration for each of the candidate target cells indicated in the LTM candidate cell configuration 51. As a consequence, also a prepared CSI-RS measurement configuration at lower layer (Layer 1) can be available in the UE memory when the CSC 61 is received, meaning that Tcsi-RRc-processing = 0 at this point of time at 62 (no time still needs to be spent for processing the CSI-RS measurement configuration to enable CSI acquisition).

[0159] Accordingly, in such situation, the UE 110 is enabled to perform CSI-RS measurements in 63 right away after Tcmd, depending on conditions as described above with respect to FIG. 7. Hence, here, the order of the delay time components is TCSI-RRC -processing 0 Tcmd 0 TcSI-measurement 0 TcSI-processing.

[0160] The cell switch procedure then ends, shown by 64, with the UE 110 transmitting a CSI-RS measurement report indicating the acquired CSI, and potentially being scheduled early according to current channel conditions with the target cell 120B.

[0161] In summary, the UE 110 shown in FIG. 12 may be equipped with the following functionalities: The UE 110 may receive, from a network node of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal, CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells. In response to a first trigger message, the UE 110 may process the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment. The UE 110 may then receive a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate targetcells. The UE 110 may determine, in response to receiving the trigger message, conditions for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements. The UE 110 may then perform, before receiving a cell switch command, CSC, for switching from the source cell to the target cell, the lower layer CSI-RS measurements of the target cell based on the determined conditions and a CSI-RS measurement configuration stored at the user equipment for the CSI measurements relating to the target cell. Alternatively or additionally, the UE 110 may perform, after receiving the CSC, the lower layer CSI-RS measurements based on the determined conditions and the CSI-RS measurement configuration stored at the user equipment for performing the lower layer CSI-RS measurements relating to the target cell

[0162] A condensed summary of some of the aspects and options described above may be given by:Tcsi is the time for the first CSI acquisition from the target cell:—TcSI - TcSI-RRC-processing+TcSI-measurement+TcSI-processingi- Alternative 1 : When CSI-RS resource is fully or at least 48 PRBs are within of the active BWP, Tcsi is the time to the first CSI-RS transmission and processing from the target cell after Tcmd; - Alternative 2: When CSI-RS resource is fully or at least 48 PRBs are within of the active BWP, Tcsi is the time to the first CSI-RS transmission and processing from the target cell after Tcmd,+T|_TM-Processing;- When CSI-RS resource does not have at least 48 PRBs within active BWP, Tcsi is the time to the first CSI-RS transmission and processing from the target cell after Tcmd+T|_TM-Processing;o TCSI-RRC -processing is the processing delay associated with the CSI configuration processing (e.g., ASN.1 validation and decoding),■ Alternative 1 : Where Tcsi-RRc-processing = 0 when TLTM -RRC-processing - 0;■ Alternative 2: Where Tcsi-RRc-processing = 0 if UE supports Early CSI-RS processing capability, and• TCI state associated with the CSI measurement is activated x ms ago, or• PDCCH ordered RACH associated with the SSB index QCL-D with CSI-RS has been transmitted x ms ago;■ Otherwise, Tcsi -RRC-processing - 2 FTIS;O TcSI-processing is the time for UE CSI-processing based on UE CSI processing capability.

[0163] The herein described procedures may be applied per model or per functionality level or across models or functionalities of a given entity, e.g., as a UE feature. It should be understood that theapparatuses described herein 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 whilst embodiments have been described in relation to LTE or 5G similar principles may be applied in relation to other networks and communication systems (e.g., future 3GPP mobile communication systems like 6G or other mobile communication systems) where cell switching is present. 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.

[0165] It is also noted herein that while the above describes exemplary embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the subject disclosure. In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the subject 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 subject disclosure is not limited thereto. While various aspects of the subject 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.

[0166] Example embodiments of the subject 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 carryout embodiments. The one or more computer-executable components may be at least one software code or portions of it.

[0167] Further in this regard it should be noted that any blocks of the logic flow as in the figures may represent program processes, or interconnected logic circuits, blocks and functions, or a combination of program processes 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 mediasuch 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. 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).

[0168] 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 (ASICs), FPGA, gate level circuits and processors based on multi-core processor architecture, as non-limiting examples.

[0169] Example embodiments of the subject disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by 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.

[0170] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0171] The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of the subject 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 appended claims. However, all such and similar modifications of the teachings of this disclosure will still fall within the scope of the subject disclosure as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.CLAUSES1. A user equipment comprising:- at least one processor; and- at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment, during a cell-switch operation, at least to:- receive, from a network node of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal, CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells;- in response to a first trigger message, process the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment;- receive a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate target cells.The user equipment of clause 1 , wherein the instructions cause the user equipment, when executed by the at least one processor, to process the CSI-RS measurement configuration by an RRC-layer processing to transform the CSI-RS measurement configuration into a lower layer configuration. The user equipment of clause 1 or clause 2, wherein the instructions cause the user equipment, when executed by the at least one processor to process the CSI-RS measurement configuration together with processing an RRC configuration of the target cell indicated in the CSC, when the user equipment supports a cell switch configuration processing capability.The user equipment of any one of clauses 1 to 3, wherein the instructions cause the user equipment, when executed by the at least one processor, to process the CSI-RS measurement configuration by at least one of decoding the RRC configuration message, validating content of the RRC configuration message, checking the RRC configuration message for misconfigured parameters.The user equipment of any one of clauses 1 to 4, wherein the first trigger message is at least one of the following:- the RRC configuration message;- a Transmission Control Indicator, TCI, state activation command;- an Early Random Access Channel, RACH, procedure trigger message;- a Layer 1 or Layer 3 event triggered measurement report;- a Measurement activation / deactivation trigger message; or- the CSC.The user equipment of clause 5, wherein the TCI state activation command comprises a Lower Layer Triggered Mobility Transmission Control Information, LTM TCI activation, Medium Access Control, MAC, Control Element, CE.7. The user equipment of clause 5, wherein the Early RACH procedure trigger message comprises at least one of a:- Physical Downlink Control Channel, PDCCH, order message;- Medium Access Control, MAC, Control element, CE, Timing Advance, TA, command.8. The user equipment of clause 5, wherein the Measurement activation / deactivation trigger message comprises:- CSI-RS activation / deactivation in-band signaling;- a MAC control element.9. The user equipment of any one of clauses 1 to 8, wherein the cell-switch operation comprises a Lower Layer Triggered Mobility procedure.10. The user equipment of any one of clauses 1 to 9, further comprising, in response to the second trigger message, loading the stored CSI-RS measurement configuration to perform the lower layer CSI-RS measurements.11. The user equipment of any one of clauses 1 to 10, wherein processing the CSI-RS measurement configuration is performed upon receiving the RRC configuration message when the number of configured CSI reference signals for measurement, CSI-RS, for the candidate cell is smaller or equal to a maximum number of configured CSI-RS for measurement.12. The user equipment of any one of clauses 1 to 11 , wherein the second trigger message comprises at least one of the following:- a Transmission Control Element, TCI, state activation command;- an Early Random Access Channel, RACH, procedure message; or- the CSC.13. A method performed by a user equipment in a cell-switch operation, the method comprising:- receiving, from a network node of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal, CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells;- in response to a first trigger message, processing the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment;- receiving a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate target cells.14. The method of clause 13, wherein processing the CSI-RS measurement configuration comprises an RRC-layer processing to transform the CSI-RS measurement configuration into a lower layer configuration.15. The method of clause 1 or clause 2, wherein processing the CSI-RS measurement configuration is performed together with processing an RRC configuration of thetarget cell indicated in the CSC, when the user equipment supports a cell switch configuration processing capability.16. The method of any one of clauses 13 to 15, wherein processing the CSI-RS measurement configuration comprises at least one of decoding the RRC configuration message, validating content of the RRC configuration message, checking the RRC configuration message for misconfigured parameters.17. The method of any one of clauses 13 to 16, wherein the first trigger message is at least one of the following:- the RRC configuration message;- a Transmission Control Indicator, TCI, state activation command;- an Early Random Access Channel, RACH, procedure trigger message;- a Layer 1 or Layer 3 event triggered measurement report;- a Measurement activation / deactivation trigger message; or- the CSC.18. The method of clause 17, wherein the TCI state activation command comprises a Lower Layer Triggered Mobility Transmission Control Information, LTM TCI activation, Medium Access Control, MAC, Control Element, CE.19. The method of clause 17, wherein the RACH procedure trigger message comprises at least one of:- a Physical Downlink Control Channel, PDCCH, order message;- a Medium Access Control, MAC, Control element, CE, Timing Advance, TA, command. 20. The method of clause 17, wherein the Measurement activation / deactivation trigger message comprises:- CSI-RS activation / deactivation in-band signaling;- a MAC control element.21. The method of any one of clauses 13 to 20, wherein the cell-switch operation comprises a Lower Layer Triggered Mobility procedure.22. The method of any one of clauses 13 to 21, further comprising, in response to the second trigger message, loading the stored CSI-RS measurement configuration to perform the lower layer CSI-RS measurements.23. The method of any one of clauses 13 to 22, wherein processing the CSI-RS measurement configuration is performed upon receiving the RRC configuration message when the number of configured CSI reference signals for measurement, CSI-RS, for the candidate cell is smaller or equal to a maximum number of configured CSI-RS for measurement.24. The method of any one of clauses 13 to 23, wherein the second trigger message comprises at least one of the following:- a Transmission Control Element, TCI, state activation command;- an Early Random Access Channel, RACH, procedure message; or- the CSC.25. A computer program product comprising instructions which, when executed by a processor of a user equipment, cause the user equipment to perform any one of the method of clauses 13 to 24.26. A user equipment comprising:- at least one processor; and- at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment during a cell-switch operation at least to:- determine, in response to receiving a trigger message, conditions for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements;- perform, before receiving a cell switch command, CSC, for switching from the source cell to the target cell, the lower layer CSI-RS measurements of the target cell based on the determined conditions and a CSI-RS measurement configuration stored at the user equipment for the CSI measurements relating to the target cell;- receive the CSC.27. The user equipment of clause 26, wherein the trigger message comprises:- a Transmission Control Element, TCI, state activation command for a TCI state activation; or - an Early Random Access Channel, RACH, procedure trigger message for transmitting an uplink RACH message.28. The user equipment of clause 27, wherein the TCI state activation command comprises a Lower Layer Triggered Mobility Transmission Control Information, LTM TCI activation, Medium Access Control, MAC, Control Element, CE.29. The user equipment of clause 27, wherein the RACH procedure trigger message comprises at least one of:a Physical Downlink Control Channel, PDCCH, ordered RACH message; or a a Medium Access Control, MAC, Control element, CE, Timing Advance, TA, command.The user equipment of any one of clauses 27 to 29, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements from the first CSI-RS after the TCI state activation when the CSI-RS is within or partially contained within the active BWP.The user equipment of any one of clauses 27 to 29, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements at the next CSI-RS after the TCI state activation when the CSI-RS is within or partially contained within the active BWP.The user equipment of any one of clauses 27 to 29, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements at the next measurement gap associated with the CSI-RS after the TCI state activation, when the CSI RS is fully or partially outside the active BWP.The user equipment of any one of clauses 27 to 29, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements from the first CSI-RS, after the uplink RACH message when the CSI-RS is within or partially contained within the active BWP.The user equipment of any one of clauses 27 to 29, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements from the first CSI-RS, after the uplink RACH message and an interruption related Radio Frequency, RF, retuning when the CSI-RS is within or partially contained within the active BWP.The user equipment of any one of clauses 27 to 29, 33 and 34, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements at the next measurement gap when the CSI- RS is fully or partially outside the active BWP.The user equipment of any one of clauses 27 to 29, 33 and 34, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements at the next measurement gap after the uplink RACH message when the CSI-RS is fully or partially outside the active BWP.The user equipment of any one of clauses 27 to 29, 33 and 34, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements at the next measurement gap after the uplink RACH message and an interruption related Radio Frequency, RF, retuning when the CSI-RS is fully or partially outside the active BWP.The user equipment of any one of clauses 30 to 37, wherein the condition of the CSI-RS being partially contained within the active BWP of the user equipment is fulfilled when at least 48 Physical Resource Blocks, PRBs, of the CSI-RS are within the active BWP of the user equipment.The user equipment of any one of clauses 26 to 38, wherein the instructions, when executed by the at least one processor, cause the user equipment to process the lower layer CSI-RS measurements after performing the lower layer CSI-RS measurements based on a processing capability of the user equipment.The user equipment of any one of clauses 26 to 39, wherein the instructions, when executed by the at least one processor, cause the user equipment to:- determine that an amount of CSI-RS before receiving the CSC is sufficient for a CSI measurement report;- omit further lower layer CSI-RS measurements after receiving the CSC and transmitting the CSI measurement report to the target cell after receiving the CSC based on the lower layer CSI-RS measurements performed before receiving the CSC.The user equipment of any one of clauses 26 to 39, wherein the instructions, when executed by the at least one processor, cause the user equipment to:- determine that an amount of CSI-RS before receiving the CSC is insufficient for a CSI measurement report;- perform further lower layer CSI-RS measurements after receiving the CSC and transmitting the CSI measurement report to the target cell after receiving the CSC based on the lower layer CSI-RS measurements performed before receiving the CSC and on the further lower layer CSI-RS measurements performed after receiving the CSC.42. The user equipment of any of one clauses 26 to 41, wherein the cell-switch operation comprises a Lower Layer Triggered Mobility procedure.43. A method performed by a user equipment in a cell-switch operation from a source cell to a target cell, the method comprising:- determining, in response to receiving a trigger message, conditions for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements;- performing, before receiving a cell switch command, CSC, for switching from the source cell to the target cell, the lower layer CSI-RS measurements of the target cell based on the determined conditions and a CSI-RS measurement configuration stored at the user equipment for the CSI measurements relating to the target cell;- receiving the CSC.44. The method of clause 43, wherein the trigger message comprises:- a Transmission Control Element, TCI, state activation command for a TCI state activation; or - an Early Random Access Channel, RACH, procedure trigger message for transmitting an uplink RACH message.45. The method of clause 44, wherein the TCI state activation command comprises a Lower Layer Triggered Mobility Transmission Control Information, LTM TCI activation, Medium Access Control, MAC, Control Element, CE.46. The method of clause 44, wherein the RACH procedure trigger message comprises at least one of:- a Physical Downlink Control Channel, PDCCH, ordered RACH message; or a- a Medium Access Control, MAC, Control element, CE, Timing Advance, TA, command. 47. The method of any one of clauses 44 to 46, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements from the first CSI-RS after the TCI state activation when the CSI-RS is within or partially contained within the active BWP.48. The method of any one of clauses 44 to 46, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements at the next CSI-RS after the TCI state activation when the CSI-RS is within or partially contained within the active BWP.The method of any one of clauses 44 to 46, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements at the next measurement gap associated with the CSI-RS after the TCI state activation, when the CSI RS is fully or partially outside the active BWP.The method of any one of clauses 44 to 46, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements from the first CSI-RS, after the uplink RACH message when the CSI-RS is within or partially contained within the active BWP.The method of any one of clauses 44 to 45, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements from the first CSI-RS, after the uplink RACH message and an interruption related Radio Frequency, RF, retuning when the CSI-RS is within or partially contained within the active BWP.The method of any one of clauses 42 to 44, 50 and 51 , wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements at the next measurement gap when the CSI- RS is fully or partially outside the active BWP.The method of any one of clauses 42 to 44, 50 and 51 , wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements at the next measurement gap after the uplink RACH message when the CSI-RS is fully or partially outside the active BWP.The method of any one of clauses 42 to 44, 50 and 51 , wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements at the next measurement gap after the uplink RACH message and an interruption related Radio Frequency, RF, retuning when the CSI-RS is fully or partially outside the active BWP.55. The method of any one of clauses 47 to 54, wherein the condition of the CSI-RS being partially contained within the active BWP of the user equipment is fulfilled when at least 48 Physical Resource Blocks, PRBs, of the CSI-RS are within the active BWP of the user equipment.56. The method of any one of clauses 43 to 55, further comprising processing the lower layer CSI-RS measurements after performing the lower layer CSI-RS measurements based on a processing capability of the user equipment.57. The method of any one of clauses 43 to 56, further comprising- determining that an amount of CSI-RS before receiving the CSC is sufficient for a CSI measurement report;- omitting further lower layer CSI-RS measurements after receiving the CSC and transmitting the CSI measurement report to the target cell after receiving the CSC based on the lower layer CSI- RS measurements performed before receiving the CSC.58. The method of any one of clauses 43 to 56, further comprising- determining that an amount of CSI-RS before receiving the CSC is insufficient for a CSI measurement report;- performing further lower layer CSI-RS measurements after receiving the CSC and transmitting the CSI measurement report to the target cell after receiving the CSC based on the lower layer CSI-RS measurements performed before receiving the CSC and on the further lower layer CSI- RS measurements performed after receiving the CSC.59. The method of any of one clauses 43 to 58, wherein the cell-switch operation comprises a Lower Layer Triggered Mobility procedure.60. A computer program product comprising instructions which, when executed by a processor of a user equipment, cause the user equipment to perform the method of any one of clauses 43 to 59.61. A network element comprising:- at least one processor; and- at least one memory storing instructions that, when executed by the at least one processor, cause the network element at least to:- determine, in response to transmitting a trigger message to a user equipment, conditions of the user equipment for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements;- transmitting, before transmitting a cell switch command, CSC, for switching the user equipment from a source cell to a target cell, a CSI-RS based on the determined conditions;- transmit the CSC to the user equipment.A user equipment comprising:- at least one processor; and- at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment during a cell-switch operation at least to:- receive a cell switch command, CSC, for switching from the source cell to the target cell; - determine conditions for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements;- perform, after receiving the CSC, the lower layer CSI-RS measurements based on the determined conditions and a CSI-RS measurement configuration stored at the user equipment for performing the lower layer CSI-RS measurements relating to the target cell.The user equipment of clause 62, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements at the first CSI-RS after the CSC when the CSI- RS is within or partially contained within an active bandwidth part, BWP, of the user equipment. The user equipment of clause 62 or clause 63, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to:- perform the lower layer CSI-RS measurements after processing target cell parameters and layer 1 / layer 2, Lower Layer Triggered Mobility processing, when the CSI-RS is fully or partially outside the active BWP of the user equipment.The user equipment of clause 63 or clause 64, wherein the condition of the CSI-RS being partially contained within the active BWP of the user equipment comprises that at least 48 Physical Resource Blocks, PRBs, of the CSI-RS are within the active BWP of the user equipment.The user equipment of any one of clauses 62 to 65, wherein the conditions comprise whether a Transmission Control Indicator, TCI, state activation command was received by the user equipment, and the instructions, when executed by the at least one processor, cause the user equipment to: - perform the lower layer CSI-RS measurements after starting fine time tracking when the TCI state activation command was not received.The user equipment of any one of clauses 62 to 66, wherein the instructions, when executed by the at least one processor, cause the user equipment to process the lower layer CSI-RS measurements after performing the lower layer CSI-RS measurements based on a processing capability of the user equipment.The user equipment of any of one clauses 62 to 67, wherein the cell-switch operation comprises a Lower Layer Triggered Mobility procedure.A method performed by a user equipment in a cell-switch operation from a source cell to a target cell, the method comprising:- receiving a cell switch command, CSC, for switching from the source cell to the target cell; - determining conditions for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements;- performing, after receiving the CSC, the lower layer CSI-RS measurements based on the determined conditions and a CSI-RS measurement configuration stored at the user equipment for performing the lower layer CSI-RS measurements relating to the target cell.The method of clause 69, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises:- performing the lower layer CSI-RS measurements at the first CSI-RS after the CSC when the CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment.The method of clause 69 or clause 70, wherein the conditions comprise whether a CSI-RS is within or partially contained within an active bandwidth part, BWP, of the user equipment, and the method further comprises- performing the lower layer CSI-RS measurements after processing target cell parameters and layer 1 / layer 2, Lower Layer Triggered Mobility processing, when the CSI-RS is fully or partially outside the active BWP of the user equipment.The method of clause 70 or clause 71, wherein the condition of the CSI-RS being partially contained within the active BWP of the user equipment comprises that at least 48 Physical Resource Blocks, PRBs, of the CSI-RS are within the active BWP of the user equipment.The method of any one of clauses 69 to 72, wherein the conditions comprise whether a Transmission Control Indicator, TCI, state activation command was received by the user equipment, and the method further comprises- performing the lower layer CSI-RS measurements after starting fine time tracking when the TCI state activation command was not received.The method of any one of clauses 69 to 73, further comprising processing the lower layer CSI-RS measurements after performing the lower layer CSI-RS measurements based on a processing capability of the user equipment.75. The method of any of one clauses 69 to 74, wherein the cell-switch operation comprises a Lower Layer Triggered Mobility procedure.76. A computer program product comprising instructions which, when executed by a processor of a user equipment, cause the user equipment to perform the method of any one of clauses 69 to 75.77. A network element comprising:- at least one processor; and- at least one memory storing instructions that, when executed by the at least one processor, cause the network element at least to:- determine conditions of a user equipment for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements;- transmit, after a cell switch command, CSC, for switching the user equipment from a source cell to the target cell, a CSI-RS based on the determined conditions.78. A user equipment comprising:- at least one processor; and- at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment, during a cell-switch operation, at least to:- receive, from a network node of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal, CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells;- in response to a first trigger message, process the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment;- receive a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate target cells;- determine, in response to receiving the trigger message, conditions for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements;- perform, before receiving a cell switch command, CSC, for switching from the source cell to the target cell, the lower layer CSI-RS measurements of the target cell based on the determined conditions and a CSI-RS measurement configuration stored at the user equipment for the CSI measurements relating to the target cell; and- perform, after receiving the CSC, the lower layer CSI-RS measurements based on the determined conditions and the CSI-RS measurement configuration stored at the user equipment for performing the lower layer CSI-RS measurements relating to the target cell.79. The user equipment of clause 78, wherein the instructions, when executed by the at least one processor, cause the user equipment to perform the method of any one of clauses 14 to 24, 44 to 59, 70 to 75.80. A method performed by a user equipment in a cell-switch operation from a source cell to a target cell, the method comprising:- receiving, from a network node of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal, CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells;- in response to a first trigger message, processing the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment; - receiving a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate target cells;- determining, in response to receiving the trigger message, conditions for performing lower layer Channel State Information Reference Signal, CSI-RS, measurements;- performing, before receiving a cell switch command, CSC, for switching from the source cell to the target cell, the lower layer CSI-RS measurements of the target cell based on the determined conditions and a CSI-RS measurement configuration stored at the user equipment for the CSI measurements relating to the target cell; and- performing, after receiving the CSC, the lower layer CSI-RS measurements based on the determined conditions and the CSI-RS measurement configuration stored at the user equipment for performing the lower layer CSI-RS measurements relating to the target cell.81. The method of clause 80, further comprising the method of any one of clauses 14 to 24, 44 to 59, 70 to 75.

Claims

48CLAIMS1. A user equipment comprising:- at least one processor; and- at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment, during a cell-switch operation, at least to:- receive, from a network node of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal, CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells;- in response to a first trigger message, process the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment;- receive a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate target cells.

2. The user equipment of claim 1 , wherein the instructions cause the user equipment, when executed by the at least one processor, to process the CSI-RS measurement configuration by an RRC-layer processing to transform the CSI-RS measurement configuration into a lower layer configuration.

3. The user equipment of claim 1 or claim 2, wherein the instructions cause the user equipment, when executed by the at least one processor to process the CSI-RS measurement configuration together with processing an RRC configuration of the target cell indicated in the CSC, when the user equipment supports a cell switch configuration processing capability.

4. The user equipment of any one of claims 1 to 3, wherein the instructions cause the user equipment, when executed by the at least one processor, to process the CSI-RS measurement configuration by at least one of decoding the RRC configuration message, validating content of the RRC configuration message, checking the RRC configuration message for misconfigured parameters.

5. The user equipment of any one of claims 1 to 4, wherein the first trigger message is at least one of the following:49- the RRC configuration message;- a Transmission Control Indicator, TCI, state activation command;- an Early Random Access Channel, RACH, procedure trigger message;- a Layer 1 or Layer 3 event triggered measurement report;- a Measurement activation / deactivation trigger message; or- the CSC.

6. The user equipment of claim 5, wherein the TCI state activation command comprises a Lower Layer Triggered Mobility Transmission Control Information, LTM TCI activation, Medium Access Control, MAC, Control Element, CE.

7. The user equipment of claim 5, wherein the Early RACH procedure trigger message comprises at least one of a:- Physical Downlink Control Channel, PDCCH, order message;- Medium Access Control, MAC, Control element, CE, Timing Advance, TA, command.

8. The user equipment of claim 5, wherein the Measurement activation / deactivation trigger message comprises:- CSI-RS activation / deactivation in-band signaling;- a MAC control element.

9. The user equipment of any one of claims 1 to 8, wherein the cell-switch operation comprises a Lower Layer Triggered Mobility procedure.

10. The user equipment of any one of claims 1 to 9, further comprising, in response to the second trigger message, loading the stored CSI-RS measurement configuration to perform the lower layer CSI-RS measurements.

11. The user equipment of any one of claims 1 to 10, wherein processing the CSI-RS measurement configuration is performed upon receiving the RRC configuration message when the number of configured CSI reference signals for measurement, CSI-RS, for the candidate cell is smaller or equal to a maximum number of configured CSI-RS for measurement.5012. The user equipment of any one of claims 1 to 11 , wherein the second trigger message comprises at least one of the following:- a Transmission Control Element, TCI, state activation command;- an Early Random Access Channel, RACH, procedure message; or- the CSC.

13. A method performed by a user equipment in a cell-switch operation, the method comprising:- receiving, from a network node of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal, CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells;- in response to a first trigger message, processing the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment;- receiving a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate target cells.

14. A computer program product comprising instructions which, when executed by a processor of a user equipment, cause the user equipment to- receive, from a network node of a source cell, a Radio Resource Control, RRC, configuration message for the cell-switch operation, the RRC configuration message comprising a Channel State Information Reference Signal, CSI-RS, measurement configuration for performing lower layer CSI measurements relating to one or more candidate target cells;- in response to a first trigger message, process the CSI-RS measurement configuration to store the CSI-RS measurement configuration in a format suitable for performing, in response to a second trigger message, lower layer CSI-RS measurements by the user equipment;- receive a cell switch command, CSC, for switching from the source cell to a target cell of the one or more candidate target cells.

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