Measurements on a set of reference signals in lower-layer triggered mobility (LTM)

Abstract

Example embodiments relate to lower-layer triggered mobility (LTM). For example, a method may comprise receiving, from a network device, first information comprising a lower-layer triggered mobility, LTM, channel state information, CSI, configuration for measuring CSI reference signals, CSI-RS, associated with respective beams of a candidate cell that the first apparatus is capable of being switched to using LTM signalling. The method may also comprise measuring a set of the CSI-RSs in response to at least one of an activated transmission configuration indicator, TCI, state or an early timing advance, TA, acquisition status for reference signals, RSs, associated with the set of the CSI-RSs.

Description

[0001] Lower-Layer Triggered Mobility (LTM)

[0002] Technical Field

[0003] Various example embodiments relate generally to lower-layer triggered mobility (LTM).

[0004] Background

[0005] Lower-layer triggered mobility (LTM) is a cell switch process in which a user equipment's (UE's) serving cell is switched to a target cell in response to a network device transmitting an LTM cell switch command. In 3GPP-Rel 18, the LTM cell switch command is transmitted by media access control (MAC) signalling using MAC control element(s) (MAC-CE). An LTM cell switch decision made by the network device is based on layer 1 (LI) measurements that are performed by the UE and reported to the network device using LI measurement reports. The target cell may be a neighbouring cell of the UE or one of the UE's current serving cells.

[0006] Summary

[0007] According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. The embodiments that do not fall under the scope of the claims are to be interpreted as examples useful for understanding the disclosure.

[0008] According to a first aspect of the invention, there is provided an apparatus comprising at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: receive, from a network device, first information comprising a lower-layer triggered mobility, LTM, channel state information, CSI, configuration for measuring CSI reference signals, CSI- RS, associated with a candidate cell that the first apparatus is capable of being switched to using LTM signalling; and measure a set of the CSI-RSs in response to at least one of: activation of transmission configuration indicator, TCI, state; or an early timing advance, TA, acquisition status, for reference signals, RSs, associated with the set of the CSI-RSs.

[0009] In some embodiments, the first information is received using at least one of: radio resource control, RRC, signaling or media access control, MAC, signaling. In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: report, to the network device, second information comprising the CSI-RS measurements for the candidate cell.

[0010] In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: transmit, to the network device, third information comprising at least an indication that the first apparatus supports the measuring of CSI- RSs for LTM. In some embodiments, the third information further comprises an indication of a number of CSI-RSs measurements the first apparatus supports for the measuring of CSI-RSs for LTM.

[0011] In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: suspend or terminate the measuring of the set of CSI-RSs in response to at least one of: receiving a cell switch command from the network device; receiving a cell handover command from the network device; detecting that a first condition for cell switching is met; completion of cell switch or handover; expiry of a predetermined time period; or receiving a reconfiguration message from the network device. In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: suspend or terminate measuring of a synchronization signal block, SSB, associated with the candidate cell or RSs associated with the set of CSI-RSs. In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: reduce measuring frequency of a synchronization signal block, SSB, associated with the candidate cell or RSs associated with the set of CSI-RSs.

[0012] In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: receive, from the network device, an LTM cell switch command; and switch from a current beam to a new beam for communicating with the candidate cell in response to receiving the LTM cell switch command, wherein the new beam is determined at least partly based on the CSI-RS measurements. In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: determine that a condition for conditional cell switch is met; and switch from a current beam to a new beam for communicating with the candidate cell in response to the condition for conditional cell switch being met, wherein the new beam is determined at least partly based on the CSI-RS measurements. In some embodiments, the new beam is determined by the network device based at least partly on the reported CSI-RS measurements, the LTM cell switch command comprising an indication of the new beam. In some embodiments, the new beam is determined by the first apparatus. In some embodiments, the activated TCI state for the RSs associated with the set of CSI-RSs is received with an LTM cell switch command.

[0013] In some embodiments, the set of CSI-RSs comprises all CSI-RSs associated with the candidate cell, based on the candidate cell being associated with the activated TCI state. In some embodiments, the set of CSI-RSs comprises a subset of the CSI-RS associated with the candidate cell, based on said subset of the CSI-RS being associated with RSs in the activated TCI state. In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: in response to an activation of the TCI state for a different set of RSs, wherein the different set of RSs does not comprise at least one of the previous set of RSs, suspend or terminate the measuring of the CSI-RSs associated with said at least one of the previous set of RSs. In some embodiments, the instructions, when executed by the at least one processor, further cause the first apparatus to: in response to an activation of the TCI state for a different set of RSs, wherein the different set of RSs does not comprise at least one of the previous set of RSs, continue the measuring of the CSI-RSs associated with said at least one of the previous set of RSs unless deactivated.

[0014] In some embodiments, the set of CSI-RSs comprises CSI-RSs associated with RSs for which a physical downlink control channel, PDCCH, ordered random access channel, RACH, transmission has been performed. In some embodiments, the set of CSI-RSs comprises CSI-RSs associated with RSs for which a user device -based early TA estimation has been performed. In some embodiments, the RSs associated with the set of the CSI-RSs comprise the same RSs or different RSs having a quasi-co-location, QCL, relationship with the set of CSI-RSs.

[0015] In some embodiments, the set of CSI-RSs are associated with a resource set configured with a higher layer parameter "repetition."

[0016] In some embodiments, the first apparatus is comprised by a user terminal.

[0017] According to a second aspect of the invention, there is provided a method, comprising: receiving, from a network device, first information comprising a lower-layer triggered mobility, LTM, channel state information, CSI, configuration for measuring CSI reference signals, CSI-RS, associated with a candidate cell that the first apparatus is capable of being switched to using LTM signalling; and measuring a set of the CSI-RSs in response to at least one of: activation of transmission configuration indicator, TCI, state; or an early timing advance, TA, acquisition status, for reference signals, RSs, associated with the set of the CSI-RSs.

[0018] In some embodiments, the second aspect may comprise any feature described in relation to the first aspect.

[0019] According to a third aspect of the invention, there is provided a computer program product or non-transitory computer-readable medium and comprising program instructions, which, when loaded into an apparatus, execute a method comprising: receiving, from a network device, first information comprising a lower-layer triggered mobility, LTM, channel state information, CSI, configuration for measuring CSI reference signals, CSI-RS, associated with a candidate cell that the first apparatus is capable of being switched to using LTM signalling; and measuring a set of the CSI-RSs in response to at least one of: activation of transmission configuration indicator, TCI, state; or an early timing advance, TA, acquisition status, for reference signals, RSs, associated with the set of the CSI-RSs.

[0020] In some embodiments, the third aspect may comprise any feature described in relation to the first aspect.

[0021] According to a fourth aspect of the invention, there is provided an apparatus comprising: means for receiving, from a network device, first information comprising a lower-layer triggered mobility, LTM, channel state information, CSI, configuration for measuring CSI reference signals, CSI-RS, associated with a candidate cell that the first apparatus is capable of being switched to using LTM signalling; and means for measuring a set of the CSI-RSs in response to at least one of: activation of transmission configuration indicator, TCI, state; or an early timing advance, TA, acquisition status, for reference signals, RSs, associated with the set of the CSI-RSs.

[0022] In some embodiments, the fourth aspect may comprise any feature described in relation to the first aspect.

[0023] Drawings

[0024] In the following, the invention will be described in greater detail with reference to the embodiments and the accompanying drawings, in which:

[0025] Figure 1 illustrates an example of a communication network to which examples disclosed herein may be applied; Figure 2 illustrates a signalling diagram illustrating an example of lower layer triggered mobility;

[0026] Figure 3 is a schematic diagram relating to LTM CSI reporting configurations which may be useful for understanding example embodiments.

[0027] Figure 4 is a schematic view of beams associated with candidate cells which may be useful for understanding example embodiments;

[0028] Figure 5 is a schematic view of network device beams and user device beams which may be useful for understanding example embodiments;

[0029] Figure 6 illustrates an example of a method according to some example embodiments; Figure 7 illustrates a signalling flow diagram according to some example embodiments; Figure 8 illustrates a signalling flow diagram according to some example embodiments; and

[0030] Figure 9 illustrates an example of an apparatus.

[0031] Detailed Description

[0032] The following embodiments are exemplary. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Further, when a particular feature, structure, or characteristic is described in connection of an embodiment, it is within the knowledge of one skilled in the art to apply such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. It shall be understood that although the terms "first," "second" and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0033] For the purposes of the present disclosure, the phrases "at least one of A or B", "at least one of A and B", and "A and / or B" means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0034] Embodiments described may be implemented in a communication network, such as any of the following radio access technologies (RATs): Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, and enhanced LTE (eLTE), 5G (also called NR), or any future RAT such as 6G. Moreover, communication within the communication network may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), and / or Discrete Fourier Transform spread OFDM (DFT-s-OFDM).

[0035] As used herein, the term "network device" or "network node" refers to a node in a communication network via which user equipment may access the network and / or which is capable of controlling radio communication and managing radio resources within a cell. The network node or network device may be referred to as a base station (BS), an access point (AP) or an access node. The network device may be, depending on the applied technology, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, or an aircraft network device.

[0036] Moreover, in connection of split radio access network (RAN), the network device may refer to a centralised unit (CU) of a base station and / or a distributed unit (DU) of a base station. An interface between CU and DU may be referred to as an Fl interface in NR. In the split RAN architecture, node operations may be carried out, at least partly, in the central / centralized unit, CU, (e.g. server, host or node) operationally coupled to the DU, (e.g. a radio head / node). One CU may control one or more DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some embodiments, the DUs may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layers. Other functional splits are possible too. In practice, any processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation. The term "terminal device" refers to any end device that may be capable of wireless communication. By way of example, a terminal device may be referred to as a communication device, user equipment (UE), user device, a Subscriber Station (SS), or a Mobile Station (MS). The terminal device may include a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, USB dongles, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like.

[0037] A term "resource", as used herein, may refer to radio resources in time domain, in frequency domain, in space domain, and / or in code domain. Some examples of resources include e.g. a physical resource block (PRB), a radio frame, a subframe, a time slot, a subband, a frequency region, a sub-carrier, a beam, etc. The term "transmission" and / or "reception" may refer to wirelessly transmitting and / or receiving via a wireless propagation channel on radio resources.

[0038] Figure 1 illustrates an example of a communication network to which examples disclosed herein may be applied. The communication network or a cellular communication network may comprise a network node 110 providing one or more cells, such as cell 100, and a network node 112 providing one or more other cells, such as cell 102. Each cell may be, e.g., a macro cell, a micro cell, femto, or a pico cell, for example. The cell may define a coverage area or a service area of the corresponding access node.

[0039] The network node 110 may provide a user equipment (UE) 120 (one or more UEs) with wireless access to the communication network. The wireless access may comprise downlink (DL) communication from the network node to the UE 120 and uplink (UL) communication from the UE 120 to the network node. Examples of uplink channels comprise physical uplink control channel (PUCCH) for transmitting control information and physical uplink shared channel (PUSCH) for transmitting data towards the network. Examples of downlink channels comprise physical downlink control channel (PDCCH) for transmitting control information and physical downlink shared channel (PDSCH) for transmitting data towards the user equipment.

[0040] There may be a plurality of UEs 120, 122 in the system. Each of them may be served by the same or by different network nodes 110, 112. UE may be configured with dual connectivity (DC), wherein the UE, e.g. UE 120, may be connected to multiple network nodes 110, 112. The UEs 120, 122 may communicate with each other, in case device- to-device (D2D) communication interface is established between them via a so-called sidelink (SL). Such D2D communications may be referred to as machine-to-machine, peer-to-peer (P2P) communications, or vehicle-to-vehicle (V2V), for example.

[0041] In the case of multiple network nodes in the communication network, the network nodes may be connected to each other via an interface. LTE specifications call such an interface as X2 interface. An interface between an LTE node and a 5G node, or between two 5G nodes may be called Xn interface.

[0042] The network nodes 110 and 112 may be further connected via another interface to a core network 116 of the communication network. The LTE specifications specify the core network as an evolved packet core (EPC), and the core network may comprise e.g. a mobility management entity (MME) and a gateway node. The MME may handle mobility of terminal devices in a tracking area encompassing a plurality of cells and handle signalling connections between the terminal devices and the core network. The gateway node may handle data routing in the core network and to / from the terminal devices. The 5G specifications specify the core network as a 5G core (5GC). The 5G core may comprise e.g. an access and mobility management function (AMF) and a user plane function / gateway (UPF) and other functions. The AMF may handle termination of non- access stratum (NAS) signalling, NAS ciphering & integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. The UPF node may support packet routing and forwarding, packet inspection and quality of service (QoS) handling, for example.

[0043] In 3GPP R.el-18, a new mobility mechanism was introduced, namely lower layer- triggered mobility (LTM), which aims to reduce interruption time during handover.

[0044] The overall procedure for LTM is illustrated in the signalling diagram in Figure 2, with reference to the network components schematically illustrated in Figure 1. Figure 2 is taken from Figure 9.2.3.5.2-1 of TS38.300vl8. As described in TS38.300vl8, 9.2.3.5.2, the procedure for LTM is as follows:

[0045] In Step 1 of Figure 2 the UE, for example the UE 120 sends a MeasurementReport message to the gNB 110, which provides access to the source cell 100. The gNB 110 decides to configure LTM and initiates LTM preparation.

[0046] In Step 2 of Figure 2, the gNB 110 transmits an RRCReconfigu ration message to the UE 120 including the LTM candidate configurations.

[0047] In Step 3 of Figure 2 the UE 120 stores the LTM candidate configurations and transmits an RRCReconfigurationComplete message to the gNB 110.

[0048] In Step 4a of Figure 2, the UE 120 performs DL synchronization with the candidate cell(s) 102 before receiving the cell switch command.

[0049] In Step 4b of Figure 2, when the UE-based TA measurement is configured, the UE 120 acquires the TA value(s) of the candidate cell(s) 102 by measurement. The UE 120 performs early TA acquisition with the candidate cell(s) 102 as requested by the network before receiving the cell switch command as specified in clause 9.2.6. This is done via CFRA triggered by a PDCCH order from the source cell 100, following which the UE 120 sends preamble towards the indicated candidate cell 102. In order to minimize the data interruption of the source cell 100 due to CFRA towards the candidate cell(s) 102, the UE 120 does not receive a random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell 102 is instead indicated in the cell switch command. The UE 120 does not maintain the TA timer for the candidate cell 102 and relies on network implementation to guarantee the TA validity.

[0050] In Step 5 of Figure 2 the UE 120 performs LI measurements on the configured candidate cell(s) 102 and transmits LI measurement reports to the source gNB 110. LI measurements should be performed as long as the RRC reconfiguration (from step 2) is applicable.

[0051] In Step 6 of Figure 2, the gNB 110 decides to execute a cell switch from the source cell 100 to the candidate or target cell 102 and transmits a MAC CE triggering cell switch by including the candidate configuration index of the target cell 102. The UE 120 then switches to the target cell 102 and applies the configuration indicated by candidate configuration index.

[0052] In Step 7 of Figure 2 the UE 120 performs the random access procedure towards the target cell 102, if the UE 120 does not have a valid TA of the target cell 102 as specified in clause 6.1.3 of TS 38.321[6].

[0053] In Step 8 of Figure 2, the UE 120 completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to the gNB 112 providing access to the target cell 102.

[0054] If the UE 120 has performed a RA procedure in Step 7 of Figure 2 then the UE 120 considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed.

[0055] For RACH-less LTM, the UE 120 considers that the LTM cell switch execution is successfully completed when the UE 120 determines that the network has successfully received its first UL data.

[0056] As seen above, in LTM, early TA acquisition, i.e. TA acquisition before handover / cell switch, can be performed in the following ways:

[0057] Firstly, the network can order the UE 120 to perform random access (RA) preamble transmission to a candidate cell 102. The candidate cell 102 uses the received RA preamble to estimate the TA and provides the TA estimate to the source cell 100. When the source cell 100 decides to trigger the cell switch, it provides the estimated TA value along with the cell switch command.

[0058] Secondly, during LTM preparation, the network can configure the UE 120 to perform UE-based TA measurements. UE-based TA measurements may be performed based on the TA of the serving cell 100 and the measured time difference between the candidate cell 102 and the serving cell 100. After being configured, the UE 120 is assumed to obtain a TA measurement before a cell switch command is issued by the gNB 110 providing access to the source cell 100.

[0059] Another purpose served by random access is that the target gNB 112 is notified about the presence of the UE 120 and resources for the UE's subsequent transmissions are provided to the UE 120. Hence, when RACH-less LTM cell switch is performed, a mechanism is required to support the initial transmission of the UE 120 to the target cell 102. A mechanism that supports this purpose is the provisioning of configured grants, which consist of sets of resources in the candidate / target cell that the UE 120 may use if / when it performs its initial transmission after handover / cell switch to the target cell 102. An alternative to this mechanism is to provide an access notification from the source cell 100 to the target cell 102, so that the target cell 102 can then provide a dynamic grant to the UE 120 for the target cell 102.

[0060] A similar RACH-less approach has also been proposed for baseline and conditional handover (BHO / CHO) as well to facilitate fast cell switch.

[0061] To summarise, 3GPP Rel-18 LTM is a cell switch procedure where the serving cell of the UE 120 is switched by the gNB 110 using an LTM cell switch command. The LTM cell switch command may be delivered using MAC CE and hence not using RRC signalling as an L3 -based handover. The LTM cell switch decision at the gNB 110 may be based on reported LI measurements and may also be based on beam level, L3, measurements.

[0062] 3GPP Rel-19 will introduce conditional LTM as an enhancement to the Rel-18 LTM. In conditional LTM, switching the UE's serving cell will be triggered autonomously by the UE based on evaluation of one or more network configured conditional LTM conditions. In the event of at least one of such conditions being met for a candidate cell, the UE will initiate a conditional cell switch without reception of a cell switch command from the network. Details of the conditional LTM are up to 3GPP Rel-19 work.

[0063] According to 3GPP Rel-18, measurements on candidate cells are performed using synchronization signal blocks (SSBs) transmitted by the candidate cells; for this purpose, a SSB configuration for the candidate cells is provided in advance to the UE 120.

[0064] Prior to a cell switch decision, the gNB 110 may optionally activate one or more transmission configuration indication (TCI) states for the candidate cells. When a TCI state for a candidate cell is activated, the UE 120 may perform time / frequency synchronization using reference signals, RSs, associated with the activated TCI states. The UE 120 may also perform early UL synchronization before the cell switch if requested to by the gNB 110 through the abovementioned ordered or UE-based timing advance (TA) estimation configuration.

[0065] Information about measurement resources, for example the SSBs transmitted by the candidate cells, may be provided to the UE 120 for performing measurements on relatively wide beams.

[0066] The UE 120 may also be provided with a reporting configuration in order that the UE is configured to report the SSB measurements for the candidate cells to the gNB 110. In 3GPP Rel-18, periodic and semi-persistent reporting on the PUCCH, semi-persistent reporting on the PUSCH, and aperiodic reporting on the PUSCH are supported.

[0067] Referring to Figure 3, the UE 120 may also be configured with one or more LTM channel state information (CSI) reporting configurations (LTM-CSI-ReportConfig) 310.

[0068] Each LTM CSI reporting configuration 310 may comprise an LTM CSI resource configuration (LTM-CSI-ResoureConfig) 320 comprising information related to resources to be used for channel measurements, e.g., Ll-RSRP measurements.

[0069] For each LTM CSI reporting configuration 320, the UE 120 may be configured to report measurements on M relatively narrow beams for the candidate cells. For example, each LTM CSI reporting configuration 320 may comprise an LTM CSI resource setting (LTM- CSI-ResourceConfig) which may comprise a configuration of an LTM-CSI-SSB- ResourceSet (LTM-CSI-SSB-ResourceSet) including a list of SS / PBCH block indices (LTM-CSI-SSB-REsourceList) 340 and a list of Z LTM candidate IDs (LTM- CandidatelDList) 350 which refer to the candidate cells associated with the SS / PBCH block indices.

[0070] For each candidate cell, the UE 120 may determine (i) time domain behaviour of an SS / PBCH block resource from ssb-Periodicity and ssb-PositionsInBurst and (ii) frequency domain behaviour of an SS / PBCH block resource by higher layer parameters subCarrierSpacing, ssbFrequency. For each candidate cell, the LTM CSI reporting configuration 320 may be provided with the current serving cell's configuration wherein each reporting configuration comprises an indication of an LTM CSI resource configuration and other parameters relating to the reporting, e.g., timing of uplink resources to transmit reports. An LTM CSI resource configuration 320 may also contain a set of SSB indices from multiple candidate cells, and placed in a common LTM configuration, e.g., in LTM-Config. A detailed configuration of each SSB of a candidate cell indicated in an LTM CSI resource configuration 320 is provided in LTM-SSB-Config under the LTM-Candidate information element (IE). For each candidate cell, the LTM Candidate IE comprises the configuration and / or information needed by the UE 120 prior to cell switching, e.g., SSB information for LTM SSB measurements. The LTM- Candidate IE may also comprise a list of non-zero power (NZP) CSI RS resources currently used to provide information for activation of TCI states associated with tracking a RS (a type of CSI-RS) and the same may be used for LTM CSI-RS measurements. An LTM-Candidate IE may also comprise an RRC container (ServingCellConfig) comprising all configuration information needed by the UE 120 when the UE switches to the candidate cell from the current serving cell in response to receiving a cell switch command. In other words, the ServingCellConfig provided under the LTM-Candidate IE comprises configuration information needed to perform regular serving cell operation within the candidate cell.

[0071] Referring back to FIG. 2, in order to trigger a cell change in step 6, the serving DU may indicate a TCI state which may include quasi-co-location (QCL) information for receiving on the PDCCH / PDSCH from the target cell (DL reception) and / or for transmitting on PUSCH (UL transmission). The QCL information may comprise the RS and QCL type (type = typeA, typeB, typeC and type D), and a bandwidth part (bwp) where the RS is located. Definitions of the QCL types are provided in TS 38.214. For switching a serving beam, options that are allowed for QCL information include:

[0072] (1) qcl-Typel: referencesignal = Tracking RS (TRS) index where TRS is a special configuration of CSI-RS index (see below) and qcl-Type = A, qcl-Type2 (applicable only in FR2): referencesignal = same TRS index and qcl-Type = D;

[0073] (2) qcl-Typel: referencesignal = Tracking RS (TRS) index and qcl-Type = A, qcl- Type2 (applicable only in FR2): referencesignal = CSI-RS index and qcl-Type = D.

[0074] The configuration of a CSI-RS resource is provided in TS 38.331. In particular, the IE NZP-CSI-RS-Resource is used to configure NZP CSI-RSs transmitted in a candidate cell where the IE is included, and which the UE 120 may be configured to measure. A change of configuration between periodic, semi-persistent or aperiodic for an NZP-CSI- RSs may not be supported without a release and add. For a CSI-RS resource, they may be an SSB-index which serves as a source RS for QCL information (given by qcl- InfoPeriodicCSI-RS) which may point to a TCI state which may further point to its QCL source RS. This may be performed either directly or indirectly via a QCL chain reference. In the case of a direct QCL reference, a SSB may be configured as the QCL source of the CSI-RS. In the case of an indirect QCL reference, a CSI-RS may have another CSI-RS as the QCL reference where the reference CSI-RS has an SSB as its QCL reference.

[0075] Given that an SSB may typically be transmitted using a relatively wide beam compared with CSI-RSs, which may be associated with relatively narrow beams, multiple CSI-RSs may be associated with the same source SSB index.

[0076] Figure 4, for example, illustrates that a first SSB, SSB1, serves as a source RS for QCL information of CSI-RS1, CSI-RS2, CSI-RS3 and CSI-RS4, and a second SSB, SSB2, serves a source RS for QCL information of CSI-RS5, CSI-RS6, CSI-RS7 and CSI-RS8.

[0077] For a CSI-RS resource in an NZP-CSI-RS-ResourceSet configured with a higher layer parameter "trs-info" and without the higher layer parameter "repetition" the UE 120 will expect that a TCI state indicates one of the following QCL types: typeA with a CSI-RS resource in a NZP-CSI-RS-ResourceSet configured with higher layer parameter "trs-info" and, when applicable, typeD with the same CSI-RS resource, or typeA with a CSI-RS resource in a NZP-CSI-RS-ResourceSet configured with higher layer parameter "trs-info" and, when applicable, typeD with an SS / PBCH block, where SS / PBCH block may have a PCI different from the PCI of the serving cell. The UE may assume centre frequency, SCS and SFN offset are the same for SS / PBCH block from the serving cell and SS / PBCH block having a PCI different from the serving cell; typeA with a CSI-RS resource in a NZP-CSI-RS-ResourceSet configured with higher layer parameter "trs-info" and, when applicable, typed with a CSI-RS resource in a NZP-CSI-RS-ResourceSet configured with higher layer parameter "repetition"; or typeB with a CSI-RS resource in a NZP-CSI-RS-ResourceSet configured with higher layer parameter "trs-info" when typed is not applicable.

[0078] For a CSI-RS resource with the "repetition" flag set, transmissions are transmitted in the cell for the purpose of allowing receive beam alignment, also known as a P-3 procedure, for which the UE 120 is served by that cell. Such CSI-RS transmissions are usually transmitted on a CSI-RS beam which is reported by the UE 120.

[0079] Referring to Figure 5, the gNB 110 may transmit a CSI-RS resource set with "repetition" flag set, meaning that the UE 120 can assume that the CSI-RS resources in the CSI-RS resource set are transmitted using the same gNB DL transmit beam. The UE 120 may use this CSI-RS resource set to quickly evaluate the quality with different UE receive beams. In order to reduce overhead on the gNB side with such a procedure, this type of CSI-RS transmission (i.e., a set of CSI-RSs with the "repetition" flag set may be transmitted as aperiodic CSI-RS where only a few transmit beams are selected for this procedure.

[0080] For a CSI-RS resource in an NZP-CSI-RS-ResourceSet configured with "repetition" flag set, the UE 120 can assume that a TCI State indicates one of the following quasi colocation type(s): typeA with a CSI-RS resource in a NZP-CSI-RS-ResourceSet configured with higher layer parameter trs-Info and, when applicable, typeD with the same CSI-RS resource, or typeA with a CSI-RS resource in a NZP-CSI-RS-ResourceSet configured with higher layer parameter trs-Info and, when applicable, typeD with a CSI-RS resource in a NZP-CSI-RS-ResourceSet configured with higher layer parameter repetition, or typeC with an SS / PBCH block and, when applicable, typeD with the same SS / PBCH block, the reference RS may additionally be an SS / PBCH block having a PCI different from the PCI of the serving cell. The UE 120 can assume center frequency, SCS, SFN offset are the same for SS / PBCH block from the serving cell and SS / PBCH block having a PCI different from the serving cell.

[0081] For a periodic CSI-RS resource in an NZP-CSI-RS-ResourceSet configured with higher layer parameter trs-Info, the UE 120 may assume that a TCI State indicates one of the following quasi co-location type(s): typeC with an SS / PBCH block and, when applicable, typeD with the same SS / PBCH block where SS / PBCH block may have a PCI different from the PCI of the serving cell. The UE 120 can assume center frequency, SCS, SFN offset are the same for SS / PBCH block from the serving cell and SS / PBCH block having a PCI different from the serving cell, or typeC with an SS / PBCH block and, when applicable, typeD with a CSI-RS resource in an NZP-CSI-RS-ResourceSet configured with higher layer parameter repetition, where SS / PBCH block may have a PCI different from the PCI of the serving cell. The UE 120 can assume center frequency, SCS, SFN offset are the same for SS / PBCH block from the serving cell and SS / PBCH block having a PCI different from the serving cell.

[0082] For an aperiodic CSI-RS resource in an NZP-CSI-RS-ResourceSet configured with higher layer parameter trs-Info, the UE 120 shall expect that a TCI-State indicates qcl-Type set to typeA with a periodic CSI-RS resource in an NZP-CSI-RS-ResourceSet configured with higher layer parameter trs-Info and, when applicable, qcl-Type set to typed with the same periodic CSI-RS resource.

[0083] LTM under 3GPP-Rel 18 may offer improvements in terms of handover latency and interruption time as compared with L3-based mobility. 3GPP-Rel 19 aims to remove certain limitations of 3GPP-Rel 18 including enabling CSI-RS measurements for LTM procedures.

[0084] Example embodiments relate generally to beam management in this context. Example embodiments may, for example, involve performing certain CSI-RS measurements for LTM to derive or select a UE (narrow) beam that the UE 120 switches to upon receiving from the gNB 110 a cell switch command, thereby to increase throughput. Example embodiments may also take into account UE power requirements for measuring CSI- RSs and this may involve measuring not all CSI-RSs at the same time to conserve UE power.

[0085] Figure 6 is a flow diagram showing operations 600 that may be performed by one or more example embodiments. The operations 600 may be performed by hardware, software, firmware or a combination thereof. The operations 600 may be performed by one, or respective, means, a means being any suitable means such as one or more processors or controllers in combination with computer-readable instructions provided on one or more memories. The operations 600 may, for example, be performed by a user device, for example the UE 120 of Figure 1. The order of operations 600 is not necessarily indicative of their order of processing or performance.

[0086] A first operation 610 may comprise receiving, from a network device, first information comprising a lower-layer triggered mobility, LTM, channel state information, CSI, configuration for measuring CSI reference signals, CSI-RS, associated with respective beams of a candidate cell that the first apparatus is capable of being switched to using LTM signalling.

[0087] A second operation 620 may comprise measuring a set of the CSI-RSs in response to at least one of an activated transmission configuration indicator, TCI, state, or an early timing advance, TA, acquisition status, for reference signals, RSs, associated with the set of the CSI-RSs.

[0088] Optionally, as indicated by broken lines, a third operation 630 may comprise reporting, to the network device, second information comprising the CSI-RS measurements for the candidate cell.

[0089] In some example embodiments, the first information may be received using at least one of RRC signalling or MAC signalling.

[0090] In some example embodiments, another operation may comprise transmitting, to the network device, third information comprising at least an indication that the first apparatus supports the measuring of CSI-RSs for LTM. The third information may further comprise an indication of a number of CSI-RSs measurements the first apparatus supports for the measuring of CSI-RSs for LTM.

[0091] In some example embodiments, another operation may comprise terminating the measuring of the set of CSI-RSs in response to at least one of: receiving a cell switch command from the network device; receiving a cell handover command from the network device; detecting that a first condition for cell switching is met; completion of a cell switch or handover; expiry of a predetermined time period; or receiving a reconfiguration message from the network device.

[0092] In some example embodiments, the candidate cell may be selected from a plurality of candidate cells. The selection may be based on SSB-based (e.g., LI or L3) measurements on respective SSBs associated with, for example transmitted by, the plurality of candidate cells. In some example embodiments, if the UE is configured to perform SSB-based (e.g., LI or L3) measurements on an SSB associated with the candidate cell or any cell or RS associated with the CSI-RSs, for example which act as the source of the CSI-RSs, another operation may comprise terminating LI or L3 measurement of said SSB(s). In some example embodiments, instead of terminating measuring, another operation may comprise reducing a measuring frequency of said SSB(s).

[0093] In some example embodiments, other operations may comprise receiving, from the network device, an LTM cell switch command, and switching from a current beam to a new beam for communicating with the candidate cell in response to receiving the LTM cell switch command, wherein the new beam is determined based on the CSI-RS measurements.

[0094] In the case of conditional cell switch, other operations may comprise determining that a condition for conditional cell switch is met, and switching from a current beam to a new beam for communicating with the candidate cell in response to the condition for conditional cell switch being met, wherein the new beam is determined at least partly based on the CSI-RS measurements.

[0095] In some example embodiments, the new beam may be determined by the network device based on the reported CSI-RS measurements, wherein the LTM cell switch command comprises an indication of the new beam. In some example embodiments, as an alternative, the new beam may be determined by the first apparatus. Determining the new beam, which may be termed a "best beam" in the sense that it may be assumed to be the beam for which the CSI-RS measurements are most optimal or most meet a predetermined condition, may require measuring multiple instances of the CSI-RS.

[0096] In some example embodiments, the activated TCI state for the RSs associated with the set of CSI-RSs is received with an LTM cell switch command.

[0097] In some example embodiments, the set of CSI-RSs comprises all CSI-RSs associated with the candidate cell, or SSB, based on the candidate cell being associated with the activated TCI state. In some example embodiments, as an alternative, the set of CSI-RSs may comprise a subset of the CSI-RS associated with the candidate cell, or SSB, based on said subset of the CSI-RS being associated with RSs in the activated TCI state.

[0098] In some example embodiments, in response to an activation of the TCI state for a different set of RSs, wherein the different set of RSs does not comprise at least one of the previous set of RSs, another operation may comprise terminating the measuring of the CSI-RSs associated with said at least one of the previous set of RSs. In some example embodiments, as an alternative, the measuring of the CSI-RSs associated with said at least one of the previous set of RSs may be continued unless deactivated, for example in an activation / deactivation message from the network device.

[0099] In some example embodiments, and related to early TA acquisition status, the set of CSI-RSs may comprise CSI-RSs associated with RSs for which a physical downlink control channel, PDCCH, ordered random access channel, RACH, transmission has been performed. The RS information, for example RS index and SSB index, to be used for the RACH preamble transmission may be provided in the PDCCH order.

[0100] In some example embodiments, and also related to early TA acquisition status, the set of CSI-RSs may comprise CSI-RSs associated with RSs for which a user device -based early TA estimation has been performed. The RS may be used to determine timing of the candidate cell which is used to determine the receive timing difference between the current (serving) cell and the candidate cell to derive the TA for the candidate cell.

[0101] In some example embodiments, the RSs associated with the set of the CSI-RSs comprise the same RSs or different RSs having a quasi-co-location, QCL, relationship with the set of CSI-RSs.

[0102] In some example embodiments, the determined set of CSI-RSs may be associated with a configuration without repetition, e.g., without a repetition flag set (without repetition = ON or with repetition = OFF) in the associated configuration as described above.

[0103] Some example embodiments will now be described with reference to Figures 7 and 8.

[0104] Figure 7 illustrates a signalling diagram of an example embodiment wherein measuring the set of CSI-RSs is performed in response to TCI state activation. Figure 7 indicates signaling and messaging flow between various devices including a UE 702 and a source DU 704, target DU 706 and source CU 708 of a network node, collectively a gNB, wherein the flow is arranged into a preparation, early synchronization, execution phase and completion phases which is for ease of explanation.

[0105] Preparation (Steps 0 to 12 of Figure 7)

[0106] In Step 0 of Figure 7, the UE 702 indicates to the source CU 708 its capability to support CSI-RS measurements for LTM. The UE 702 may also indicate a number (e.g., maximum number) of CSI-RS measurements the UE may perform for candidate cells for LTM cell change purposes.

[0107] In Step 1 of Figure 7, the UE 702 may transmit to the source DU 704 an L3 measurement report associated with an associated SSB index which may be used for configuring CSI-RS measurements.

[0108] In Step 2 of Figure 7, the source DU 704 may perform an UL RRC message transfer to the source CU 708 comprising an L3 measurement report with the associated SSB index.

[0109] In Step 3 of Figure 7, the source CU 708 may determine a best candidate cell (potential target cell) based on selecting the N best SSB measurements.

[0110] The source CU 708 may configure the corresponding CSI-RSs which have a QCL relationship with the determined SSB index for the candidate cell. This operation is performed based on the prior indication (Step 0) that the UE 702 supports CSI-RS measurements for LTM.

[0111] In Step 4 of Figure 7, a context setup process is initiated whereby the source CU 708 transmits a UE context setup request to the target DU 706 for the candidate cell.

[0112] In Step 5 of Figure 7, the target DU 606 responsively transmits a UE context setup response to the source CU 708.

[0113] In Step 6 of Figure 7, the source CU 708 responsively transmits a UE context modification request to the source DU 704. In Step 7 of Figure 7, the source DU 704 responsively transmits a UE context modification response to the source CU 708.

[0114] In Steps 8 to 10 of Figure 7, the source CU 708 compiles and generates RRC configurations for the UE 702, wherein the UE stores the LTM configuration including the candidate cell for LTM cell change and the configuration of CSI-RS measurements for respective (narrow) beams of the candidate cell. However, CSI-RS measurements are not started at this time.

[0115] For example, in Step 8 of Figure 7, the source CU 708 generates an RRC reconfiguration comprising a measurement configuration of an LI cell change and a configuration for prepared candidate cells, including said identified candidate cell.

[0116] For example, in Step 9 of Figure 7, the source CU 708 transmits a DL message transfer with an RRC message to the source DU 704.

[0117] For example, in Step 10 of Figure 7, the source DU 704 responsively transmits an RRC reconfiguration to the UE 702.

[0118] In Step 11 of Figure 7, the UE 702 responsively transmits a RRC reconfiguration complete message to the source DU 704 to indicate its reconfiguration.

[0119] In Step 12 of Figure 7, the source DU 704 responsively transmits an UL message transfer message to the source CU 708.

[0120] Early Synchronization (Steps 13 to 20 of Figure 7)

[0121] In Step 13 of Figure 7, the UE 702 may perform DL synchronization with the candidate cell. For example, the source DU 704 may transmit a TCI state activation command to the UE 702. The UE 702 may responsively activate certain TCI state(s) of the candidate cell and start to track its timing to ensure synchronization with the candidate cell.

[0122] In Step 14 of Figure 7, the UE 702 may determine, or select, a set of CSI-RSs which comprise, or have a QCL relationship with, the RSs associated with the activated TCI state(s) of the candidate cell obtained in Step 13 and linked to the SSB of the candidate cell. The UE 702 may be instructed to track the SSB of the candidate cell. In one option, the UE 702 may, instead of tracking the SSB of the candidate cell, determine, or select, those CSI-RSs associated with the tracked SSB and measure said CSI-RSs to determine a best narrow beam. For example, and referring to Figure 4, it will be seen that CSI-RS1 to CSI-RS4 are associated with the SSB-1 and hence the UE 702 may track CSI-RS1 to CSI-RS4 (instead of SSB-1) to determine a best narrow beam. Being able to measure CSI-RSs of the target cell verifies that the UE 702 is synchronized with the candidate cell.

[0123] In another option, the UE 702 may track the SSB of the target cell as well as measuring those CSI-RSSs associated with said SSB and measure said CSI-RSs to derive a best narrow beam.

[0124] The best narrow beam may be used by the UE 702 after receiving a cell switch command.

[0125] In Step 15 of Figure 7, and prior to receiving a cell switch command, the UE 702 may responsively perform CSI-RS measurements for the determined set of CSI-RSs.

[0126] In Step 16 of Figure 7, the UE 702 may suspend or terminate performing CSI-RS measurements in response to a condition, for example at least one of receiving a cell switch command, receiving a cell handover command, detecting that a first predetermined condition for cell switching is met, completion of cell switch or handover, expiry of a predetermined (e.g., network configured) time period, or receiving a reconfiguration message (e.g., RRC reconfiguration message).

[0127] Steps 17 to 20 of Figure 7 relate to the UE 702 performing an early UL synchronization (TA estimate) via a PDCCH order.

[0128] For example, in Step 17 of Figure 7, the UE 702 may receive from the source DU 704 a PDCCH order.

[0129] For example, in Step 18 of Figure 7, the UE 702 may responsively perform a RACH transmission to the target DU 706.

[0130] For example, in Step 19 of Figure 7, the target DU 706 may responsively determine, with the source CU 708, a TA for the UE 702. For example, in Step 20 of Figure 7, the source CU 608 may responsively transmit the determined TA to the source DU 704.

[0131] Execution (Steps 21 to 27 of Figure 7)

[0132] In Step 21 of Figure 7, the UE 702 may transmit a (LI) measurement report to the source DU 704 based on the measured set of CSI-RSs.

[0133] In Step 22 of Figure 7, the source DU 704 may determine a serving cell change, which could be a SSB or CSI-RS as configured in step 10 of Figure 7. The source DU 704 may determine the candidate cell based on the measurement report.

[0134] In Step 23 of Figure 7, the source DU 704 may transmit a cell switch command to the UE 702, for example a MAC CE cell change command, which may comprise the TA of the candidate cell. The source DU 704 may use the reported measurements to select the best (narrow) beam to be used by, or configured at, the UE 702 for the candidate cell.

[0135] In one option, the best beam may be indicated in the cell switch command and the UE 702 may immediately use the best beam for subsequent UL transmissions or for receiving the first DL transmission.

[0136] In this case, and in Step 24 of Figure 7, the UE 702 and target DU 706 may perform a RACH or RACH-less process.

[0137] In Step 25 of Figure 7, the UE 602 may transmit a RRC reconfiguration complete message to the target DU 706 to indicate completion of handover.

[0138] In another option, the best beam may not be indicated in the cell switch command in Step 23 of Figure 7. The cell switch command may, however, indicate that the UE 702 is to use a CSI-RS beam. The UE 702 may responsively determine the best narrow beam based on its own CSI-RS measurements which it uses for the first UL transmission or for receiving the first DL transmission. The UE 702 may report the determined best beam to the target DU 706. Optionally, the source DU 704 may determine the candidate cell and the UE 702 may determine the best beam.

[0139] In Step 26 of Figure 7, the target DU 706 may transmit an UL RRC message transfer to the source CU 708.

[0140] In Step 27 of Figure 7, the target DU 706 may transmit an access notification to the source CU 708.

[0141] Completion (Steps 28 to 30 of Figure 7)

[0142] In Step 28 of Figure 7, the source CU 708 may transmit a UE context release command to the source DU 704.

[0143] In Step 29 of Figure 7, the source CU 708 may transmit a UE context release complete message to the source DU 704.

[0144] In Step 30 of Figure 7, a path switch is performed.

[0145] Figure 8 illustrates a signalling diagram of an example embodiment, wherein measuring the set of CSI-RSs is performed based on an early TA acquisition status.

[0146] Figure 8 indicates signaling and messaging flow between the various devices already described for Figure 7, including the UE 702 and the source DU 704, target 7U 706 and source CU 708 of the network node, e.g. collectively a gNB, wherein the flow is arranged into a preparation, early synchronization, execution phase and completion phases which is for ease of explanation.

[0147] Preparation (Steps 0 to 12 of Figure 8)

[0148] Steps 1 to 12 of Figure 8 may correspond to Steps 1 to 12 of Figure 7.

[0149] Early Synchronization (Steps 13 to 21 of Figure 8)

[0150] In Step 13 of Figure 8, the UE 702 may perform DL synchronization with candidate cells. For example, the gNB may transmit a TCI state activation command to the UE 702. The UE 702 may responsively activate certain TCI states of the candidate cell upon request from the source DU 704 by starting to track the timing of the candidate cell to ensure synchronization with the candidate cell.

[0151] Steps 14 to 17 of Figure 8 relate to the UE 702 performing an early UL synchronization (TA estimate) via a PDCCH order.

[0152] For example, in Step 14 of Figure 8, the UE 702 may receive from the source DU 704 a PDCCH order.

[0153] For example, in Step 15 of Figure 8, the UE 702 may responsively perform a RACH transmission to the target DU 706.

[0154] For example, in Step 16 of Figure 8, the target DU 706 may responsively determine, with the source CU 708, a TA for the UE 702.

[0155] For example, in Step 17 of Figure 8, the source CU 708 may responsively transmit the determined TA to the source DU 704.

[0156] In Step 18 of Figure 8, the UE 702 may determine a set of CSI-RSs that have a QCL relationship with the early TA acquisition status. In the case of a PDCCH ordered TA acquisition the relevant SSB is that which the UU 702 links with the RA preamble. In the alternative case of UE-based TA estimation, the relevant SSB is that which the UE 702 estimates the TA to come from.

[0157] In Step 19 of Figure 8, the UE 702 may modify or suspend or terminate measuring the relevant SSB, for example LI measurements, if configured to do so. An example of modifying the measuring of the relevant SSB may comprise reducing the SSB measurement frequency. In the case of UE-based TA estimation, the UE may modify the SSM measurement only if the UE has reached an above-threshold confidence level in its estimation of the TA.

[0158] In Step 20 of Figure 8, which may be performed at substantially the same time as Step 19 is performed, the UE 702 may perform CSI-RS measurements for the determined set of CSI-RSs.

[0159] In Step 21 of Figure 8, the UE 702 may suspend or terminate performing the CSI-RS measurements in response to a condition, for example at least one of receiving a cell switch command, receiving a cell handover command, detecting that a first predetermined condition for cell switching is met, expiry of a predetermined time period (which may be configured by the gNB), or receiving a reconfiguration message.

[0160] Execution (Steps 22 to 28 of Figure 8)

[0161] In Step 22 of Figure 8, the UE 702 may transmit a (LI) measurement report to the source DU 704 based on the measured set of CSI-RSs.

[0162] In Step 23 of Figure 8, the source DU 704 may determine a serving cell change, which could be a SSB or CSI-RS. The source DU 704 may determine the candidate cell based on the measurement report.

[0163] In Step 24 of Figure 8, the source DU 704 may transmit a cell switch command to the UE 702, for example a MAC CE cell change command, which may comprise the TA of the target cell. The source DU 704 may use the measurements of the measurement report to select a best beam to be used or configured by the UE 702 within the target cell after cell switch.

[0164] In one option, the best beam may be indicated in the cell switch command and the UE 702 may immediately use the best beam for subsequent UL transmissions or for receiving the first DL transmission.

[0165] In this case, and in Step 25 of Figure 8, the UE 702 and target DU 706 may perform a RACH or RACH-less process.

[0166] In Step 26 of Figure 8, the UE 702 may transmit a RRC reconfiguration complete message to the target DU 706 to indicate completion of handover.

[0167] In another option, the best beam may not be indicated in the cell switch command in Step 24 of Figure 8. The cell switch command may, however, indicate that the UE 702 is to use a narrow (CSI-RS) beam. The UE 702 may responsively determine the best narrow beam based on its own CSI-RS measurements for the first UL transmission or for receiving the first DL transmission. The UE 702 may report the determined best beam to the target DU 706. Optionally, the source DU 704 may determine the candidate cell and the UE 702 may determine the best beam.

[0168] In Step 27 of Figure 8, the target DU 706 may transmit an UL RRC message transfer to the source CU 708.

[0169] In Step 28 of Figure 8, the target DU 706 may transmit an access notification to the source CU 708.

[0170] Completion (Steps 29 to 31 of Figure 8)

[0171] In Step 29 of Figure 8, the source CU 708 may transmit a UE context release command to the source DU 704.

[0172] In Step 30 of Figure 8, the source CU 708 may transmit a UE context release complete message to the source DU 704.

[0173] In Step 31 of Figure 8, a path switch is performed.

[0174] In summary, example embodiments are applicable to LTM beam management procedures wherein greater throughputs can be achieved by performing LTM measurements on selected CSI-RSs of a candidate cell corresponding to relatively narrow beams compared with the relatively wider beam associated with the SSB of said candidate cell. By measuring CSI-RSs in advance of receiving a cell switch command, and on a determined set of CSI-RSs based on the activated TCI state(s) and / or early TA acquisition status, UEs are enabled to switch (for example immediately) to a new UE beam for greater throughput. The determined set of CSI-RSs to measure may be a limited number (not all CSI-RSs) and hence UE power may also be conserved.

[0175] Example Apparatus

[0176] Fig. 9 shows, by way of example, a block diagram of an apparatus 10. The apparatus 10 comprises, for example, at least one processor 12 and at least one memory 14 storing instructions 15 that, when executed by the at least one processor, cause the apparatus 10 at least to perform the method or methods as disclosed herein, and any of the embodiments thereof. In an example, the at least one memory and the instructions (e.g. a computer program code, software), are configured, with the at least one processor, to cause the apparatus 10 to perform the method or methods as disclosed herein, and any of the embodiments thereof.

[0177] A processor 12 may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with example embodiments described herein. As used in this application, the term "circuitry" may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a user equipment, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0178] The memory 14 may be implemented using any suitable data storage technology. The memory may comprise a database for storing data. The memory 14 may be at least in part external to apparatus 10 but accessible to apparatus 10.

[0179] The instructions 15 may be comprised in a computer readable medium or a non- transitory computer readable medium. A 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. random access memory, RAM, vs. read only memory, ROM).

[0180] For example, the apparatus 10 is a terminal device, such as the UE of Figures 1, 2, 7 and 8. As another example, the apparatus is comprised in such a terminal device, e.g. as a chipset configured to control the terminal device. The apparatus 10 may be caused or configured to perform at least the method of Fig. 6 and / or any one or more of the embodiments described.

[0181] The apparatus may comprise one or more entities of any of protocol layers, such as a MAC entity, an RRC entity, an RLC entity, a PDCP entity or a PHY entity. In some embodiments, the entity is configured to perform at least the method of Fig. 6 and / or any one or more of the embodiments described.

[0182] The apparatus 10 comprises a radio interface 16. The radio interface 16 may provide the apparatus 10 with communication capabilities. The radio interface 16 may comprise a receiver configured to receive information in accordance with at least one cellular or non-cellular standard. The radio interface 16 may comprise a transmitter configured to transmit information in accordance with at least one cellular or non-cellular standard. The receiver may comprise more than one receiver. The transmitter may comprise more than one transmitter. The radio interface 16 may comprise a transceiver configured to receive and transmit information in accordance with at least one cellular or non-cellular standard. The transceiver may comprise more than one transceiver.

[0183] The apparatus 10 may comprise a user interface 18 comprising, for example, at least one of a keypad, a microphone, a touch display, a display, a speaker, etc. The user interface 18 may be used to control the apparatus by the user. The user interface 18 may be external to the apparatus 10. For example, the apparatus 10 may be connected to another device, such as a computer, either via wireless or wired connection, and the apparatus 10 is controlled by the user via the computer.

[0184] In an embodiment, at least some of the processes described herein may be carried out by an apparatus comprising means for carrying out at least some of the described processes. Means for performing method steps as disclosed herein may include software and / or hardware components of the apparatus 10. For example, the at least one processor 12, the memory 14, and the computer program code form means for carrying out the method or methods as disclosed herein, and any of the embodiments thereof. As used herein the term "means" is to be construed in singular form, i.e. referring to a single element, or in plural form, i.e. referring to a combination of single elements. Therefore, terminology "means for [performing A, B, C]", is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C. Further, terminology "means for performing A, means for performing B, means for performing C" is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C.

[0185] Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.

Claims

Claims1. A first apparatus, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: receive, from a network device, first information comprising a lower-layer triggered mobility, LTM, channel state information, CSI, configuration for measuring CSI reference signals, CSI-RS, associated with a candidate cell that the first apparatus is capable of being switched to using LTM signalling; and measure a set of the CSI-RSs in response to at least one of: activation of transmission configuration indicator, TCI, state; or an early timing advance, TA, acquisition status, for reference signals, RSs, associated with the set of the CSI-RSs.

2. The first apparatus of claim 1, wherein the first information is received using at least one of: radio resource control, RRC, signaling or media access control, MAC, signaling.

3. The apparatus if claim 1 or claim 2, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to: report, to the network device, second information comprising the CSI-RS measurements for the candidate cell.

4. The first apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to: transmit, to the network device, third information comprising at least an indication that the first apparatus supports the measuring of CSI-RSs for LTM.

5. The first apparatus of claim 4, wherein the third information further comprises an indication of a number of CSI-RSs measurements the first apparatus supports for the measuring of CSI-RSs for LTM.

6. The first apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to:suspend or terminate the measuring of the set of CSI-RSs in response to at least one of: receiving a cell switch command from the network device; receiving a cell handover command from the network device; detecting that a first condition for cell switching is met; completion of cell switch or handover; expiry of a predetermined time period; or receiving a reconfiguration message from the network device.

7. The first apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to: suspend or terminate measuring of a synchronization signal block, SSB, associated with the candidate cell or RSs associated with the set of CSI-RSs.

8. The first apparatus of any of claims 1 to 6, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to: reduce measuring frequency of a synchronization signal block, SSB, associated with the candidate cell or RSs associated with the set of CSI-RSs.

9. The first apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to: receive, from the network device, an LTM cell switch command; and switch from a current beam to a new beam for communicating with the candidate cell in response to receiving the LTM cell switch command, wherein the new beam is determined at least partly based on the CSI-RS measurements.

10. The first apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to: determine that a condition for conditional cell switch is met; and switch from a current beam to a new beam for communicating with the candidate cell in response to the condition for conditional cell switch being met, wherein the new beam is determined at least partly based on the CSI-RS measurements.

11. The first apparatus of claim 9 or claim 10, wherein the new beam is determined by the network device based at least partly on the reported CSI-RS measurements, the LTM cell switch command comprising an indication of the new beam.

12. The first apparatus of claim 9 or claim 10, wherein the new beam is determined by the first apparatus.

13. The first apparatus of any preceding claim, wherein the activated TCI state for the RSs associated with the set of CSI-RSs is received with an LTM cell switch command.

14. The first apparatus of any preceding claim, wherein the set of CSI-RSs comprises all CSI-RSs associated with the candidate cell, based on the candidate cell being associated with the activated TCI state.

15. The first apparatus of any of claims 1 to 13, wherein the set of CSI-RSs comprises a subset of the CSI-RS associated with the candidate cell, based on said subset of the CSI-RS being associated with RSs in the activated TCI state.

16. The first apparatus of claim 14 or claim 15, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to: in response to an activation of the TCI state for a different set of RSs, wherein the different set of RSs does not comprise at least one of the previous set of RSs, suspend or terminate the measuring of the CSI-RSs associated with said at least one of the previous set of RSs.

17. The first apparatus of claim 14 or claim 15, wherein the instructions, when executed by the at least one processor, further cause the first apparatus to: in response to an activation of the TCI state for a different set of RSs, wherein the different set of RSs does not comprise at least one of the previous set of RSs, continue the measuring of the CSI-RSs associated with said at least one of the previous set of RSs unless deactivated.

18. The first apparatus of any preceding claim, whereinthe set of CSI-RSs comprises CSI-RSs associated with RSs for which a physical downlink control channel, PDCCH, ordered random access channel, RACH, transmission has been performed.

19. The first apparatus of any preceding claim, wherein the set of CSI-RSs comprises CSI-RSs associated with RSs for which a user device -based early TA estimation has been performed.

20. The first apparatus of any preceding claim, wherein the RSs associated with the set of the CSI-RSs comprise the same RSs or different RSs having a quasi-co-location, QCL, relationship with the set of CSI-RSs.

21. The first apparatus of any preceding claim, wherein the set of CSI-RSs are associated with a resource set configured with a higher layer parameter "repetition."22. The first apparatus of any preceding claim, wherein the first apparatus is comprised by a user terminal.

23. A method, comprising: receiving, from a network device, first information comprising a lower-layer triggered mobility, LTM, channel state information, CSI, configuration for measuring CSI reference signals, CSI-RS, associated with a candidate cell that the first apparatus is capable of being switched to using LTM signalling; and measuring a set of the CSI-RSs in response to at least one of: an activated transmission configuration indicator, TCI, state; or an early timing advance, TA, acquisition status, for reference signals, RSs, associated with the set of the CSI-RSs.

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