Methods, architectures, apparatuses and systems for failure handling for conditional layer-2 mobility

Abstract

Procedures, methods, architectures, apparatuses, systems, devices, and computer program products for failure handling for conditional layer-2 triggered mobility (C-LTM) are disclosed. C-LTM improves robustness compared to network triggered LTM. In C-LTM, a wireless transmit-receive unit (WTRU) is provided with conditions on when to perform LTM, and the WTRU may initiate a LTM procedure without waiting for a cell switch MAC CE, which may not come, or come late, due to signal fading or deterioration. For C-LTM, failure cases may be considered to avoid introducing failures in C-LTM.

Description

METHODS, ARCHITECTURES, APPARATUSES AND SYSTEMS FOR FAILURE HANDLING FOR CONDITIONAL LAYER-2 MOBILITYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 571,866 filed 29-March-2024 which is incorporated herein by reference.BACKGROUND

[0002] The present disclosure is generally directed to the fields of communications, software and encoding, including, for example, to methods, architectures, apparatuses, systems related to failure handling for conditional layer-2 mobility of wireless transmit-receive units.SUMMARY

[0003] There are disclosed embodiments of methods, as described in the following and as claimed in the appended claims.

[0004] There are disclosed embodiments of a device, as described in the following and as claimed in the appended claims.

[0005] Briefly stated, in one embodiment, a wireless transmit / receive unit (WTRU) may receive configuration information related to (e.g., associated with) one or more target cells for conditional layer- 1 and / or layer-2 triggered mobility (C-LTM). The configuration information may include at least one C-LTM condition for performing LTM. The at least one C-LTM condition for performing LTM may include a set of validity conditions associated with performing C-LTM evaluation. The WTRU performs C-LTM evaluation which may include performing measurements on downlink beams of at least one of the one or more target cells, and determining a best downlink beam of a target cell of the one or more target cells. The WTRU may determine that a C-LTM condition is met from the at least one C-LTM condition for performing LTM. The WTRU may determine a validity of the configuration information based on the set of validity conditions. For example, the WTRU may perform random access channel (RACH) - less LTM on the determined best downlink beam in a case of validity of the configuration information. For example, the WTRU may perform RACH-based LTM on a newly determined best downlink beam in a case of invalidity of the configuration information.

[0006] Briefly stated, in one embodiment, a WTRU may receive configuration information related to (e.g., associated with) one or more target cells for C-LTM. The configuration information may include information indicating at least one C-LTM condition for triggering LTM. The WTRU may perform measurements on beams of at least one of the one or more target cells, and determinea best beam of a target cell of the one or more target cells, such as at a time of receiving the configuration information. The WTRU may determine that a C-LTM condition of the at least one C-LTM condition for triggering LTM is met. The WTRU may, at a time of performing C-LTM, determine an invalidity of the configuration information for the best beam determined before the time of performing the C-LTM, and may perform RACH-based LTM on a newly determined best beam.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A more detailed understanding may be had from the detailed description below, given by way of example in conjunction with drawings appended hereto. Figures in such drawings, like the detailed description, are examples. As such, the Figures (FIGs.) and the detailed description are not to be considered limiting, and other equally effective examples are possible and likely. Furthermore, like reference numerals ("ref.") in the FIGs. indicate like elements, and wherein:

[0008] FIG. 1 A is a system diagram illustrating an example communications system;

[0009] FIG. IB is a system diagram illustrating an example wireless transmit / receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1 A;

[0010] FIG. 1C is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communications system illustrated in FIG. 1A;

[0011] FIG. ID is a system diagram illustrating a further example RAN and a further example CN that may be used within the communications system illustrated in FIG. 1 A;

[0012] FIG. 2 is a flow chart of a method according to an embodiment;

[0013] FIG. 3 is a flow chart of a method according to an embodiment; and

[0014] FIG. 4 is a flow chart of a method according to an embodiment.DETAILED DESCRIPTION

[0015] 5GS 5G SystemBFD Beam Failure DetectionCHO Conditional HOCG Configured GrantCSI Channel State InformationCSLRS C Si-Reference SignalCU Centralized UnitDC Dual ConnectivityDCI Downlink Control InformationDL DownlinkHO Hand OverC-LTM (RACH-less) Conditional LTMLI, L2, L3 Layer- 1, Layer-2, Layer-3LCH Logical ChannelLTM Layer-2 Triggered MobilityMCG Master Cell GroupMN Master NodeNW NetworkPDU Protocol Data UnitPSDB PDU Set Delay BudgetRACH Random Access ChannelRLF Radio Link FailureRRC Radio Resource ControlRSRP Reference Signal Received PowerRSRQ Reference Signal Received QualitySCG Secondary Cell GroupSN Secondary NodeSSB Synchronization Signal BlockTA Timing AdvanceTCI Transmission Synchronization IndicatorTRP Transmission / Reception PointUE User EquipmentUL UplinkWTRU Wireless Transmit-Receive Unit

[0016] In the following detailed description, numerous specific details are set forth to provide a thorough understanding of embodiments and / or examples disclosed herein. However, it will be understood that such embodiments and examples may be practiced without some or all of the specific details set forth herein. In other instances, well-known methods, procedures, components and circuits have not been described in detail, so as not to obscure the following description. Further, embodiments and examples not specifically described herein may be practiced in lieu of, or in combination with, the embodiments and other examples described, disclosed or otherwise provided explicitly, implicitly and / or inherently (collectively "provided") herein. Although various embodiments are described and / or claimed herein in which an apparatus, system, device, etc. and / or any element thereof carries out an operation, process, algorithm, function, etc. and / or any portion thereof, it is to be understood that any embodiments described and / or claimed herein assume that any apparatus, system, device, etc. and / or any element thereof is configured to carry out any operation, process, algorithm, function, etc. and / or any portion thereof.

[0017] A symbol ' / ' (e.g., forward slash) may be used herein to represent 'and / or', where for example, 'A / B' may imply 'A and / or B'.

[0018] Example Communications System

[0019] The methods, apparatuses and systems provided herein are well-suited for communications involving both wired and wireless networks. An overview of various types ofwireless devices and infrastructure is provided with respect to FIGs. 1A-1D, where various elements of the network may utilize, perform, be arranged in accordance with and / or be adapted and / or configured for the methods, apparatuses and systems provided herein.

[0020] FIG. 1A is a system diagram illustrating an example communications system 100 in which one or more disclosed embodiments may be implemented. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), singlecarrier FDMA (SC-FDMA), zero-tail (ZT) unique-word (UW) discreet Fourier transform (DFT) spread OFDM (ZT UW DTS-s OFDM), unique word OFDM (UW-OFDM), resource block- filtered OFDM, filter bank multicarrier (FBMC), and the like.

[0021] As shown in FIG. 1A, the communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104 / 113, a core network (CN) 106 / 115, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a "station" and / or a "STA", may be configured to transmit and / or receive wireless signals and may include (or be) a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi- Fi device, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. Any of the WTRUs 102a, 102b, 102c and 102d may be interchangeably referred to as a UE.

[0022] The communications systems 100 may also include a base station 114a and / or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d, e.g., to facilitateaccess to one or more communication networks, such as the CN 106 / 115, the Internet 110, and / or the networks 112. By way of example, the base stations 114a, 114b may be any of a base transceiver station (BTS), a Node-B (NB), an eNode-B (eNB), a Home Node-B (HNB), a Home eNode-B (HeNB), a gNode-B (gNB), a NR Node-B (NR NB), a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0023] The base station 114a may be part of the RAN 104 / 113, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and / or the base station 114b may be configured to transmit and / or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for a wireless service to a specific geographical area that may be relatively fixed or that may change over time. The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in an embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and may utilize multiple transceivers for each or any sector of the cell. For example, beamforming may be used to transmit and / or receive signals in desired spatial directions.

[0024] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0025] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 / 113 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA) and / or High-Speed Uplink Packet Access (HSUPA).

[0026] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE- Advanced (LTE-A) and / or LTE-Advanced Pro (LTE-A Pro).

[0027] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR Radio Access, which may establish the air interface 116 using New Radio (NR).

[0028] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, for instance using dual connectivity (DC) principles. Thus, the air interface utilized by WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to / from multiple types of base stations (e.g., an eNB and a gNB).

[0029] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (Wi-Fi), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 IX, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0030] The base station 114b in FIG. 1 A may be a wireless router, Home Node-B, Home eNode- B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a roadway, and the like. In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish any of a small cell, picocell or femtocell. As shown in FIG. 1 A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the CN 106 / 115.

[0031] The RAN 104 / 113 may be in communication with the CN 106 / 115, which may be any type of network configured to provide voice, data, applications, and / or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have varyingquality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN 106 / 115 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions, such as user authentication. Although not shown in FIG. 1 A, it will be appreciated that the RAN 104 / 113 and / or the CN 106 / 115 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 / 113 or a different RAT. For example, in addition to being connected to the RAN 104 / 113, which may be utilizing an NR radio technology, the CN 106 / 115 may also be in communication with another RAN (not shown) employing any of a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or Wi-Fi radio technology.

[0032] The CN 106 / 115 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and / or the internet protocol (IP) in the TCP / IP internet protocol suite. The networks 112 may include wired and / or wireless communications networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 / 114 or a different RAT.

[0033] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0034] FIG. IB is a system diagram illustrating an example WTRU 102. As shown in FIG. IB, the WTRU 102 may include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and / or other elements / peripherals 138, among others. It will be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0035] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. While FIG. IB depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together, e.g., in an electronic package or chip.

[0036] The transmit / receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in an embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In an embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals, for example. In an embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF and light signals. It will be appreciated that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0037] Although the transmit / receive element 122 is depicted in FIG. IB as a single element, the WTRU 102 may include any number of transmit / receive elements 122. For example, the WTRU 102 may employ MIMO technology. Thus, in an embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0038] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit / receive element 122 and to demodulate the signals that are received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11, for example.

[0039] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may access information from, and storedata in, any type of suitable memory, such as the non-removable memory 130 and / or the removable memory 132. The non-removable memory 130 may include random-access memory (RAM), readonly memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0040] The processor 118 may receive power from the power source 134, and may be configured to distribute and / or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like.

[0041] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and / or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0042] The processor 118 may further be coupled to other elements / peripherals 138, which may include one or more software and / or hardware modules / units that provide additional features, functionality and / or wired or wireless connectivity. For example, the elements / peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (e.g., for photographs and / or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, a virtual reality and / or augmented reality (VR / AR) device, an activity tracker, and the like. The elements / peripherals 138 may include one or more sensors, the sensors may be one or more of a gyroscope, an accelerometer, a hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor; an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and / or a humidity sensor.

[0043] The WTRU 102 may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the uplink (e.g., for transmission) and downlink (e.g., for reception) may be concurrent and / or simultaneous. The full duplex radio may include an interference management unit to reduce and or substantially eliminate self-interference via either hardware (e.g., a choke) or signal processing via a processor (e.g., a separate processor (not shown) or via processor 118). In an embodiment, the WTRU 102 may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the uplink (e.g., for transmission) or the downlink (e.g., for reception)).

[0044] FIG. 1C is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0045] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In an embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the eNode-B 160a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

[0046] Each of the eNode-Bs 160a, 160b, and 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink (UL) and / or downlink (DL), and the like. As shown in FIG. 1C, the eNode-Bs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0047] The CN 106 shown in FIG. 1C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (PGW) 166. While each of the foregoing elements are depicted as part of the CN 106, it will be appreciated that any one of these elements may be owned and / or operated by an entity other than the CN operator.

[0048] The MME 162 may be connected to each of the eNode-Bs 160a, 160b, and 160c in the RAN 104 via an SI interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may provide a control plane function forswitching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0049] The SGW 164 may be connected to each of the eNode-Bs 160a, 160b, 160c in the RAN 104 via the SI interface. The SGW 164 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring user planes during inter-eNode-B handovers, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

[0050] The SGW 164 may be connected to the PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0051] The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the CN 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and / or wireless networks that are owned and / or operated by other service providers.

[0052] Although the WTRU is described in FIGs. 1A-1D as a wireless terminal, it is contemplated that in certain representative embodiments that such a terminal may use (e.g., temporarily or permanently) wired communication interfaces with the communication network.

[0053] In representative embodiments, the other network 112 may be a WLAN.

[0054] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have an access or an interface to a distribution system (DS) or another type of wired / wireless network that carries traffic into and / or out of the BSS. Traffic to STAs that originates from outside the BSS may arrive through the AP and may be delivered to the STAs. Traffic originating from STAs to destinations outside the BSS may be sent to the AP to be delivered to respective destinations. Traffic between STAs within the BSS may be sent through the AP, for example, where the source STA may send traffic to the AP and the AP may deliver the traffic to the destination STA. The traffic between STAs within a BSS may be considered and / or referred to as peer-to-peer traffic. The peer-to-peer traffic may be sent between (e.g., directly between) the source and destination STAs with a direct link setup (DLS). In certain representative embodiments, the DLS may use an 802. l ie DLS or an802.1 Iz tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and the STAs (e.g., all of the STAs) within or using the IBSS may communicate directly with each other. The IBSS mode of communication may sometimes be referred to herein as an "ad-hoc" mode of communication.

[0055] When using the 802.1 lac infrastructure mode of operation or a similar mode of operations, the AP may transmit a beacon on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20 MHz wide bandwidth) or a dynamically set width via signaling. The primary channel may be the operating channel of the BSS and may be used by the STAs to establish a connection with the AP. In certain representative embodiments, Carrier sense multiple access with collision avoidance (CSMA / CA) may be implemented, for example in in 802.11 systems. For CSMA / CA, the STAs (e.g., every STA), including the AP, may sense the primary channel. If the primary channel is sensed / detected and / or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0056] High throughput (HT) STAs may use a 40 MHz wide channel for communication, for example, via a combination of the primary 20 MHz channel with an adjacent or nonadj acent 20 MHz channel to form a 40 MHz wide channel.

[0057] Very high throughput (VHT) STAs may support 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz wide channels. The 40 MHz, and / or 80 MHz, channels may be formed by combining contiguous 20 MHz channels. A 160 MHz channel may be formed by combining 8 contiguous 20 MHz channels, or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80 configuration, the data, after channel encoding, may be passed through a segment parser that may divide the data into two streams. Inverse fast fourier transform (IFFT) processing, and time domain processing, may be done on each stream separately. The streams may be mapped on to the two 80 MHz channels, and the data may be transmitted by a transmitting STA. At the receiver of the receiving STA, the above-described operation for the 80+80 configuration may be reversed, and the combined data may be sent to a medium access control (MAC) layer, entity, etc.

[0058] Sub 1 GHz modes of operation are supported by 802.1 laf and 802.11 ah. The channel operating bandwidths, and carriers, are reduced in 802.1 laf and 802.1 lah relative to those used in802.1 In, and 802.1 lac. 802.1 laf supports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV white space (TVWS) spectrum, and 802.1 lah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment,802.1 lah may support meter type control / machine-type communications (MTC), such as MTCdevices in a macro coverage area. MTC devices may have certain capabilities, for example, limited capabilities including support for (e.g., only support for) certain and / or limited bandwidths. The MTC devices may include a battery with a battery life above a threshold (e.g., to maintain a very long battery life).

[0059] WLAN systems, which may support multiple channels, and channel bandwidths, such as 802.1 In, 802.1 lac, 802.11af, and 802.1 lah, include a channel which may be designated as the primary channel. The primary channel may have a bandwidth equal to the largest common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA, from among all STAs in operating in a BSS, which supports the smallest bandwidth operating mode. In the example of 802.1 lah, the primary channel may be 1 MHz wide for STAs (e.g., MTC type devices) that support (e.g., only support) a 1 MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operating modes. Carrier sensing and / or network allocation vector (NAV) settings may depend on the status of the primary channel. If the primary channel is busy, for example, due to a STA (which supports only a 1 MHz operating mode), transmitting to the AP, the entire available frequency bands may be considered busy even though a majority of the frequency bands remains idle and may be available.

[0060] In the United States, the available frequency bands, which may be used by 802.1 lah, are from 902 MHz to 928 MHz. In Korea, the available frequency bands are from 917.5 MHz to 923.5 MHz. In Japan, the available frequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidth available for 802.1 lah is 6 MHz to 26 MHz depending on the country code.

[0061] FIG. ID is a system diagram illustrating the RAN 113 and the CN 115 according to an embodiment. As noted above, the RAN 113 may employ an NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 113 may also be in communication with the CN 115.

[0062] The RAN 113 may include gNBs 180a, 180b, 180c, though it will be appreciated that the RAN 113 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In an embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, gNBs 180a, 180b may utilize beamforming to transmit signals to and / or receive signals from the WTRUs 102a, 102b, 102c. Thus, the gNB 180a, for example, may use multiple antennas to transmit wireless signals to, and / or receive wireless signals from, the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiplecomponent carriers to the WTRU 102a (not shown). A subset of these component carriers may be on unlicensed spectrum while the remaining component carriers may be on licensed spectrum. In an embodiment, the gNBs 180a, 180b, 180c may implement Coordinated Multi-Point (CoMP) technology. For example, WTRU 102a may receive coordinated transmissions from gNB 180a and gNB 180b (and / or gNB 180c).

[0063] The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using transmissions associated with a scalable numerology. For example, OFDM symbol spacing and / or OFDM subcarrier spacing may vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using subframe or transmission time intervals (TTIs) of various or scalable lengths (e.g., including a varying number of OFDM symbols and / or lasting varying lengths of absolute time).

[0064] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non- standalone configuration. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c without also accessing other RANs (e.g., such as eNode-Bs 160a, 160b, 160c). In the standalone configuration, WTRUs 102a, 102b, 102c may utilize one or more of gNBs 180a, 180b, 180c as a mobility anchor point. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non- standalone configuration WTRUs 102a, 102b, 102c may communicate with / connect to gNBs 180a, 180b, 180c while also communicating with / connecting to another RAN such as eNode-Bs 160a, 160b, 160c. For example, WTRUs 102a, 102b, 102c may implement DC principles to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In the non- standalone configuration, eNode-Bs 160a, 160b, 160c may serve as a mobility anchor for WTRUs 102a, 102b, 102c and gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for servicing WTRUs 102a, 102b, 102c.

[0065] Each of the gNBs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, support of network slicing, dual connectivity, interworking between NR and E-UTRA, routing of user plane data towards user plane functions (UPFs) 184a, 184b, routing of control plane information towards access and mobility management functions (AMFs) 182a, 182b, and the like. As shown in FIG. ID, the gNBs 180a, 180b, 180c may communicate with one another over an Xn interface.

[0066] The CN 115 shown in FIG. ID may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one session management function (SMF) 183a, 183b, and at least one Data Network (DN) 185a, 185b. While each of the foregoing elements are depicted as part of the CN 115, it will be appreciated that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0067] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N2 interface and may serve as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling of different protocol data unit (PDU) sessions with different requirements), selecting a particular SMF 183a, 183b, management of the registration area, termination of NAS signaling, mobility management, and the like. Network slicing may be used by the AMF 182a, 182b, e.g., to customize CN support for WTRUs 102a, 102b, 102c based on the types of services being utilized WTRUs 102a, 102b, 102c. For example, different network slices may be established for different use cases such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for MTC access, and / or the like. The AMF 162 may provide a control plane function for switching between the RAN 113 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies such as WiFi.

[0068] The SMF 183a, 183b may be connected to an AMF 182a, 182b in the CN 115 via an N11 interface. The SMF 183a, 183b may also be connected to a UPF 184a, 184b in the CN 115 via an N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b and configure the routing of traffic through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating UE IP address, managing PDU sessions, controlling policy enforcement and QoS, providing downlink data notifications, and the like. A PDU session type may be IP -based, non-IP based, Ethernet-based, and the like.

[0069] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, e.g., to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPF 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multihomed PDU sessions, handling user plane QoS, buffering downlink packets, providing mobility anchoring, and the like.

[0070] The CN 115 may facilitate communications with other networks. For example, the CN 115 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 115 and the PSTN 108. In addition, the CN 115 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and / or wireless networks that are owned and / or operated by other service providers. In an embodiment, the WTRUs 102a, 102b, 102c may be connected to a local Data Network (DN) 185a, 185b through the UPF 184a, 184b via the N3 interface to the UPF 184a, 184b and an N6 interface between the UPF 184a, 184b and the DN 185a, 185b.

[0071] In view of FIGs. 1 A-1D, and the corresponding description of FIGs. 1 A-1D, one or more, or all, of the functions described herein with regard to any of: WTRUs 102a-d, base stations 114a- b, eNode-Bs 160a-c, MME 162, SGW 164, PGW 166, gNBs 180a-c, AMFs 182a-b, UPFs 184a- b, SMFs 183a-b, DNs 185a-b, and / or any other element(s) / device(s) described herein, may be performed by one or more emulation elements / devices (not shown). The emulation devices may be one or more devices configured to emulate one or more, or all, of the functions described herein. For example, the emulation devices may be used to test other devices and / or to simulate network and / or WTRU functions.

[0072] The emulation devices may be designed to implement one or more tests of other devices in a lab environment and / or in an operator network environment. For example, the one or more emulation devices may perform the one or more, or all, functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network in order to test other devices within the communication network. The one or more emulation devices may perform the one or more, or all, functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The emulation device may be directly coupled to another device for purposes of testing and / or may performing testing using over-the-air wireless communications.

[0073] The one or more emulation devices may perform the one or more, including all, functions while not being implemented / deployed as part of a wired and / or wireless communication network. For example, the emulation devices may be utilized in a testing scenario in a testing laboratory and / or a non-deployed (e.g., testing) wired and / or wireless communication network in order to implement testing of one or more components. The one or more emulation devices may be test equipment. Direct RF coupling and / or wireless communications via RF circuitry (e.g., which may include one or more antennas) may be used by the emulation devices to transmit and / or receive data.

[0074] 3GPP has agreed to a work item on mobility enhancement in Release 19 (Rel-19). The justification for the work is as follows:

[0075] Layer 2 mobility (LTM) was introduced in Rel-18 and can offer improvements in handover latency and interruption time compared to Layer 3 based mobility. However, LTM as introduced in Rel-18 also has a number of limitations compared to Layer 3 mobility. This Rel-19 work item aims to remove a number of these limitations.

[0076] LTM operation is only supported for mobility between cells of the same gNB (same CU). Depending on the deployment of the network this may significantly limit the opportunities to use LTM. By enabling LTM operation between cells of different gNBs (i.e., inter-CU) then the network will be able gain the benefits of LTM for a far greater number of handovers.

[0077] Layer 3 mobility uses layer 3 measurement reporting which supports WTRU evaluated events for triggering of measurement reports and reduces signalling overhead compared to periodic measurement reporting. Such event triggering is not supported by the LI measurements that are used for LTM mobility.

[0078] LI measurements for LTM procedures are limited to SSB measurements. Expanding LI measurements to include CSLRS can address this limitation and can be expected to enable greater throughput on the target cell immediately after cell switch.

[0079] Layer 3 mobility has evolved over several releases. Conditional handover (CHO) and other conditional mobility procedures (CP AC, SCPAC) were developed to achieve high robustness by enabling the procedure to be executed without necessitating a signalling exchange with source cell beforehand. LTM as introduced in Rel-18 offers short interruption time but not with the same level of robustness as the conditional L3 mobility procedures. In Rel-19, enhancements should be specified so that the system can benefit from both the high robustness and short interruption.

[0080] Overview

[0081] LTM is a procedure in which a gNB receives LI measurement report(s) from a WTRU, and on their basis a gNB changes the WTRU’s serving cell by a cell switch command signaled via a MAC CE. The cell switch command indicates an LTM candidate configuration that the gNB previously prepared and provided to the WTRU through RRC signalling. Then the WTRU switches to the target configuration according to the cell switch command.

[0082] When configured by the network, it is possible to activate TCI states of one or multiple cells that are different from the current serving cell. For instance, the TCI states of the LTM candidate cells can be activated in advance before any of those cells become the serving cell. This allows the WTRU to be DL synchronized with those cells, thereby facilitating a faster cell switch to one of those cells when cell switch is triggered.

[0083] When configured by the network, it is possible to initiate UL TA acquisition (called early TA) procedure of one or multiple cells that are different from the current serving cells. If the cell has the same NTA as the current serving cells or NTA=0, early TA acquisition procedure is not required. The network may request the WTRU to perform early TA acquisition of a candidate cell before a cell switch. The early TA acquisition procedure is triggered by PDCCH order or realized through WTRU-based TA measurement as configured by RRC. In the former case, the gNB to which the candidate cell belongs calculates the TA value and sends it to the gNB to which the serving cell belongs. The serving cell sends the TA value in the LTM cell switch command MAC CE when triggering LTM cell switch. In the latter case, the WTRU performs TA measurement for the candidate cells after being configured by RRC but the exact time the WTRU performs TA measurement is up to WTRU implementation. The WTRU applies the TA value measured by itself and performs RACH-less LTM upon receiving the cell switch command. The network may also send a TA value in the LTM cell switch command MAC CE without early TA acquisition.

[0084] Depending on the availability of a valid TA value, the WTRU performs either a RACH- less LTM or RACH-based LTM cell switch. If the TA value is provided in the cell switch command, the WTRU applies the TA value as instructed by the network. In the case where WTRU- based TA measurement is configured, but no TA value is provided in the cell switch command, the WTRU applies the TA value by itself if available. Meanwhile, the WTRU performs RACH- less LTM cell switch upon receiving the cell switch command. If no valid TA value is available, the WTRU performs RACH-based LTM cell switch.

[0085] Regardless of whether the WTRU is configured for WTRU-based TA measurement for a certain candidate cell, it will still follow the PDCCH order, which includes requesting a random access (RA) procedure towards the candidate cells. This also applies to the candidate cells for which the WTRU is capable of deriving TA values by itself. Additionally, regardless of whether the WTRU has already performed a random access procedure towards the candidate cells, it will still follow the WTRU-based measurement configuration if configured by the network.

[0086] For RACH-less LTM, the WTRU accesses the target cell using either a configured grant or a dynamic grant. The configured grant is provided in the LTM candidate configuration, and the WTRU selects the configured grant occasion associated with the beam indicated in the cell switch command. Upon initiation of LTM cell switch to the target cell, the WTRU starts to monitor PDCCH on the target cell for dynamic scheduling. Before RACH-less LTM procedure completion, the WTRU shall not trigger random access procedure if it does not have a valid PUCCH resource for triggered SRs.

[0087] Conditional LTM Failure Handling

[0088] Conditional LTM improves the robustness compared to NW triggered LTM. L3 conditional handover (CHO) and other conditional mobility procedures (CP AC, SCPAC) were developed to achieve high robustness by enabling the procedure to be executed without necessitating a signalling exchange with source cell beforehand. In C-LTM, the WTRU is provided with conditions on when to perform LTM and may initiate the LTM procedure without waiting for the cell switch MAC CE, which may not come (or may come late) due to signal fading or deterioration.

[0089] However, to support conditional LTM with a short interruption time and with the robustness enabled by avoiding signalling exchange with the source cell beforehand, the WTRU may need to perform RACH-less HO. Specifically, it is expected that the WTRU be provided with a CG resource and possibly a TA as part of the conditional configuration. Because of the time limitation associated with the TA and the CG (e.g., the best SSB may change between the time the CG was configured and the fulfilment of the C-LTM conditions), conditional LTM failure cases need to be considered. In particular, there may be cases where resources for RACH-less HO were configured in the C-LTM configuration, but cannot be performed at the time of execution (e.g., TA expiry, the best SSB changing, CG no more available, etc.). These scenarios may be handled to avoid introducing failures in C-LTM.

[0090] C-LTM Modification following change in C-LTM Configuration Validity

[0091] Embodiments are described herein for C-LTM procedure in the context of a C-LTM configuration. However, they should be equally applicable to any conditional mobility procedure, such as CHO, in which a configuration for evaluating and performing a mobility procedure to a (pre)configured cell, beam, TRP is being performed, but aspects related to the configuration may change with time or may relate to conditions that change with time or change at execution.

[0092] It should also be noted that the term validity here is mainly referring some parts of the C- LTM configuration, specifically resource configurations that are needed to perform RACH less C- LTM such as TA to apply towards the target cell for UL transmission, configured grants to use for sending the C-LTM complete message or subsequent UL messages, etc., and not related to the actual configuration that the WTRU has to apply upon C-LTM execution to the target (e.g., full RRC reconfiguration message, delta RRC reconfiguration message, or / and a reference configuration to be applied whenever a LTM switch is performed, etc., ). Furthermore, the terminology "change in validity" can be considered interchangeable with the considering the configuration being invalid in the sense mentioned above.

[0093] C-LTM Validity Determination during C-LTM Evaluation

[0094] A WTRU may determine a (change in) validity of a C-LTM configuration during C-LTM evaluation.

[0095] A WTRU may be provided with a C-LTM configuration consisting of at least a target cell configuration and a set of conditions for triggering C-LTM. As with CHO, the WTRU may perform C-LTM execution upon one or more C-LTM conditions being satisfied.

[0096] A WTRU may further be provided with one or more conditions for evaluating the validity of a C-LTM configuration. Specifically, upon receiving the C-LTM configuration (time Tl), or some configured or defined time after receiving the configuration (time T2), the WTRU may start evaluating the validity of the C-LTM configuration. Evaluating the validity of C-LTM configuration at T2 may consist of any of (a-c): a) Determining whether one or more parts of the C-LTM evaluation conditions are still valid; b) Determining whether one or more parts of the target cell configuration are still valid; c) Determining whether properties of the target cell determined at the WTRU after reception of the configuration are still valid.

[0097] A WTRU may determine that a change in the validity occurs based on detecting one or more of the following (a-c): a) Change in the cell level signal quality of the target cell or of another measurement associated with the target cell, for example, measurement of a beam (e.g., SSB) associated with the target cell; b) A time has elapsed since the reception of the C-LTM configuration without execution; c) A time has elapsed since the determination, by the WTRU after reception of the C-LTM configuration, of a property associated with the target cell.

[0098] Change in Quality of the Target

[0099] A WTRU may perform measurements of the target cell in the C-LTM configuration. Target cell measurements may consist of cell level RSRP / RSRQ / etc. The WTRU may perform such target cell measurements as part of the C-LTM evaluation conditions. A WTRU may further perform beam level measurements (SSB or CSLRS) associated with the target cell. A WTRU may perform beam level CSLRS measurements associated with the target cell, possibly reporting such measurements to the source cell as part of normal LTM procedure. A WTRU may determine a change in target cell quality as a condition associated with any of the aforementioned measurements. Specifically, the following embodiment may be generalized to apply to any of the aforementioned measurements.

[0100] According to an embodiment, a change in the quality of the target may consist of detecting a change in SSB measurements of one or more SSB measurements associated with a target cell. Specifically, the WTRU may be configured with conditions, thresholds, etc. for determining the change in validity based on SSB measurements of the target cell.

[0101] According to an embodiment, determination may be based on a change of the best SSB. For example, the condition may be satisfied if the best SSB of the target cell changes during C- LTM evaluation. Change of best SSB may be based on a second SSB becoming better in quality than the initial best SSB, possibly by at least a threshold, possibly for at least a time to trigger. Such threshold, time to trigger, etc. may be configured in the C-LTM configuration.

[0102] According to an embodiment, determination may be based on the change in the measurements of the best SSB. For example, the condition may be satisfied if the quality of the best SSB changes by at least a threshold during the C-LTM evaluation. For example, the condition may be satisfied if the quality of the best SSB falls below a threshold during the C-LTM evaluation. For example, the condition may be satisfied if the quality of the best SSB relative to some other measurement (e.g., another SSB, another N SSBs, an average of N other SSBs, etc.).

[0103] According to another embodiment, determination may be based on the change in quality of a number of beams associated with the target. For example, if the quality of the N best beams changes by a threshold, or the quality of the N best beams fall below a threshold, the condition may be satisfied.

[0104] In each of the aforementioned examples, change in quality is measured relative to an initial (first) measurement of the SSB(s). Specifically, for the case of a change in the best SSB by at least a threshold, the WTRU may determine a first measurement of the best SSB at a specific time Tl, and may determine, by a second measurement, during the duration of C-LTM evaluation T2 where T2 > Tl, whether the best SSB changes (diminishes) by at least a threshold relative to the measurement made at time Tl . In the aforementioned examples, the measurement made at time Tl may consist of any of the following (a-c): a) A measurement determined by the WTRU and / or reported to the network, at a specific time instant, possibly following configuration of the C-LTM, for example (al-a3): al) A specific (e.g., the first) measurement determined and / or reported after reception of the C- LTM configuration; a2) A specific (e.g., the first) measurement determined and / or reported after reception of the TA, possibly associated with that SSB, from the network; a3) A specific (e.g., the first) measurement determined and / or reported after determination, by the WTRU of the TA, possibly associated with that SSB.b) A measurement determined by the WTRU and / or reported to the network which may have occurred during the evaluation period, for example, the maximum value of the measured and / or reported quality of the SSB over the C-LTM evaluation time, or over a configured subset of time within the C-LTM evaluation time. c) A function of the measurements determined and / or reported by the WTRU of the quality of the SSB over the evaluation period, for example, the average value, possibly weighted with some configured coefficients, of the measured and / or reported quality of the SSB taken over the C-LTM evaluation time, or a subset of the C-LTM evaluation time.

[0105] A time elapsed since the reception of the C-LTM configuration

[0106] According to an embodiment, a WTRU may be configured with one or more parameters in a C-LTM configuration which are valid only for a configured period of time. Specifically, part of the C-LTM configuration may expire a configured time after reception of C-LTM configuration. For example, the WTRU may be provided with different parts of the C-LTM configuration that expire at different times.

[0107] For example, the WTRU may be provided with the best SSB of each target cell as part of the C-LTM configuration, along with an associated time. If the time following reception of the C- LTM configuration expires prior to execution of the C-LTM, or prior to any conditions configured with the C-LTM being satisfied, the WTRU may determine that the validity of the best SSB parameter has changed during evaluation.

[0108] For example, the WTRU may be provided with a TA value, possibly associated with a particular SSB, as part of the C-LTM configuration along with an associated time. If the time following reception of the C-LTM configuration expires prior to execution of the C-LTM, or prior to any conditions configured with the C-LTM being satisfied, the WTRU may determine that the validity of the TA parameter has changed during evaluation.

[0109] For example, the WTRU may be provided with a CG resource, possibly associated with a particular SSB, as part of the C-LTM configuration along with an associated time. If the time following reception of the C-LTM configuration expires prior to execution of the C-LTM, or prior to any condition configured with the C-LTM being satisfied, the WTRU may determine that the validity of the TA parameter has changed during evaluation.

[0110] For example, the WTRU may be provided with a condition for triggering C-LTM (e.g., Ax event) which has a time-limited validity. If the time following reception of the C-LTM configuration expires (i.e., exceeds the validity period), and possibly if the condition which triggered C-LTM configuration is associated with the time limited event, the WTRU may performan action defined herein associated with error handling. Specifically, the WTRU may consider that the validity of the C-LTM configuration has changed.[OHl] A time elapsed since the determination of a property associated with the target cell

[0112] According to an embodiment, a WTRU may be configured to receive a value for a property associated with a target cell during C-LTM evaluation. For example, the WTRU may receive a C-LTM configuration by RRC signaling. Following reception of the C-LTM configuration, and during C-LTM evaluation, the WTRU may receive a new or updated value for a parameter, where such parameter may be any of (a-d): a) Best SSB associated to a target cell; b) TA, possibly associated to one or more SSB, to be used for uplink transmission to the target cell; c) TCI state associated to a target cell; d) CG for transmission to the target cell, possibly associated with one or more SSB.

[0113] The WTRU may receive a new or updated value for any of the above parameters from the source cell (e.g., via RRC message, MAC CE, DCI, etc.,). Alternatively, the WTRU may determine its own value for one of the above properties. For example, the WTRU may perform measurements for determination of the TA. For example, the WTRU may select the TCI state or subset of the TCI states. For example, the WTRU may select a CG, possibly among multiple CGs associated with the same and / or different SSBs.

[0114] A WTRU may determine that the validity of a C-LTM configuration (or of the specific parameter in question) has changed if a configured time has expired since the last reception and / or determination of the specific parameter.

[0115] C-LTM Validity Determination at C-LTM execution

[0116] A WTRU may determine a (change in) validity of a C-LTM configuration at C-LTM execution.

[0117] The WTRU may be configured with conditions, thresholds, etc. to determine whether the validity of a C-LTM configuration has changed, where such conditions can be determined at the execution of C-LTM. Specifically, when a measurement that triggers C-LTM execution is met, the WTRU may be configured to evaluate a condition. If the condition is met, the WTRU may determine that the C-LTM configuration has changed.

[0118] A WTRU may determine C-LTM validity at C-LTM execution (at T2) based on one or a combination of any of the following factors, to a measure of the following factor compared to a threshold or to another factor (a-h):a) Time between C-LTM execution and a resource (e.g., a CG resource) of a beam (or the comparison of such between different beams); b) Cell or beam quality measured at C-LTM execution; c) Cell or beam quality measurements determined at any time during C-LTM evaluation; d) The properties of data available for transmission, such as (dl-d2): dl) the QoS of data, possibly available for transmission (dla-dlb): dla) For example, the LCH or LCG associated with data available for transmission; dlb) For example, the delay budget associated with buffered data (e.g., PSDB). d2) The buffer status at the WTRU. e) The time to perform a RACH procedure; f) Time between C-LTM execution and when C-LTM validity is expected to change following C- LTM execution (fl -f2): fl) For example, this may be in terms of a measure of a number of slots (fla-flb): fl a) e.g., the number of slots following C-LTM execution during which a configured CG with time limited validity is expected to remain valid; fib) e.g., the number of slots following C-LTM execution during which a provided / determined TA is expected to remain valid. f2) For example, this may be in terms of a measure of a number of CG occasions (f2a-f2b): f2a) e.g., the number of CG occasions following C-LTM execution during which a configured CG with time limited validity is expected to remain valid; f2b) e.g., the number of CG occasions following C-LTM execution during which a TA with time limited validity is expected to remain valid. g) Time between C-LTM execution and confirmation that C-LTM was executed successfully h) An action (as defined section 4.1.3) is triggered associated with C-LTM validity change during C-LTM evaluation is triggered but does not complete before C-LTM execution is triggered.

[0119] C-LTM validity at execution may be determined based on CG resource timing.

[0120] In one family of embodiments, the WTRU may determine a change in C-LTM validity at execution based on the timing of CG resources with respect to the execution.

[0121] In one embodiment, the WTRU may determine a change in C-LTM validity at execution if the time until the next CG occasion after the execution is larger than a threshold.

[0122] In one embodiment, the WTRU may determine a change in C-LTM validity at execution if the time until the next CG resource of one CG is at least a threshold number of slots larger than the time until the next CG resource of another CG, where the threshold may be 0. The first CG resource may correspond to the CG resource associated with one SSB (e.g., the best SSB) whilethe second CG resource may correspond to the CG associated with another SSB (e.g., another SSB of the same target cell whose measurements meet some configured criteria).

[0123] C-LTM validity at execution may be determined based on cell or beam measurements at C-LTM execution.

[0124] According to a family of embodiments, the WTRU may determine a change in C-LTM validity at execution based on cell or beam measurements at C-LTM execution.

[0125] According to an embodiment, the WTRU may determine a change in C-LTM validity at execution if the cell measurements are below a threshold at execution.

[0126] According to an embodiment, the WTRU may determine a change in C-LTM validity at execution if the beam measurements (e.g., SSB) are below a threshold at execution.

[0127] C-LTM Validity at execution may be determined based on cell or beam measurements during C-LTM evaluation.

[0128] In one family of embodiments, the WTRU may determine a change in C-LTM validity at execution based on cell or beam measurements during C-LTM evaluation.

[0129] In one embodiment, the WTRU may determine a change in C-LTM validity at execution if the cell or beam measurements associated with the target were determined to be below a threshold at any time during C-LTM evaluation.

[0130] C-LTM validity at execution may be determined based on properties of the data.

[0131] In one family of embodiments, the WTRU may determine a change in C-LTM validity at execution based on properties of the data.

[0132] In one embodiment, the WTRU may determine a change in C-LTM validity at execution based on the QoS of any available data at execution.

[0133] In one embodiment, the WTRU may determine a change in C-LTM validity at execution if the buffer status, possibly associated with one or more logical channels or LCGs, is above a threshold.

[0134] In one embodiment, the WTRU may determine a change in C-LTM validity at execution if the remaining PSDB of data at the WTRU is less than a threshold.

[0135] In one embodiment, the WTRU may determine a change in C-LTM validity at execution if the amount of data for which the remaining PSDB is less than a first threshold is above a second threshold.

[0136] C-LTM validity at execution may be determined based on remaining time of validity of C-LTM configuration.

[0137] In one family of embodiments, the WTRU may determine a change in C-LTM validity at execution based on remaining time of validity of a C-LTM configuration at the time of C-LTM execution.

[0138] In one embodiment, the WTRU may determine a change in the C-LTM validity if the remaining validity time associated with a CG is less than a threshold at the time of execution.

[0139] In one embodiment, the WTRU may determine a change in the C-LTM validity if the remaining validity time associated with the TA is less than a threshold at the time of C-LTM execution.

[0140] In one embodiment, the WTRU may determine a change in the C-LTM validity if the number of CG occasions configured within the time period after C-LTM execution while the TA is still considered valid (based on a TA timer, possibly provided in the C-LTM configuration).

[0141] C-LTM Validity at execution may be determined based on time until confirmation that C-LTM succeeds.

[0142] In one family of embodiments, the WTRU may determine a change in C-LTM validity at execution based on time until C-LTM succeeds.

[0143] In one embodiment, the WTRU may determine a change in C-LTM validity if C-LTM is executed and is not confirmed prior to configured time following execution.

[0144] C-LTM validity evaluation action may be triggered and not completed before C-LTM execution.

[0145] In one family of embodiments, the WTRU may determine a change in C-LTM validity at execution based on having previously triggered an action (defined in section "Actions Associated with change of C-LTM configuration validity") as a result of a change of C-LTM validity during C-LTM evaluation, and the action is not completed before execution of C-LTM.

[0146] In one embodiment, a WTRU may trigger TA measurement during C-LTM evaluation due to conditions described in section "C-LTM Validity Determination during C-LTM Evaluation". If TA measurement is not complete and the WTRU triggers C-LTM execution, the WTRU is assumed to have detected a change in validity of C-LTM at execution.

[0147] C-LTM validity at execution may involve a combination of factors.

[0148] A WTRU may use a combination of the above factors to determine C-LTM validity at execution, where combination may consist of AND, OR of conditions, comparison of different factors, or comparison of the same factor associated with different properties of the target.

[0149] According to an embodiment, the WTRU may determine a change in C-LTM validity if the time until the next CG resource, possibly associated with the best SSB, is larger than the time required to perform RACH following execution of C-LTM.

[0150] According to an embodiment, the WTRU may determine a change in C-LTM validity if the time until the next CG resource is larger than a first threshold, and the PSDB associated with data available for transmission at the WTRU is less than a second threshold.

[0151] For example, the WTRU may determine a change in C-LTM validity if C-LTM execution is has not been successfully confirmed after at least a configured time period following C-LTM execution, and the WTRU has data available for transmission associated with a particular LCH.

[0152] Actions associated with change of C-LTM configuration validity

[0153] A WTRU may perform one or multiple actions based on any of the conditions associated with determination of a change of C-LTM configuration validity, either during evaluation or execution. Such actions may be any of the actions described below.

[0154] A WTRU may performs different mobility procedure upon change in C-LTM validity. In one family of embodiments, the WTRU may perform a different mobility procedure than what is indicated in the C-LTM configuration in the case a change in C-LTM configuration validity is determined during evaluation or execution. This may consist of any of the following: a) Performing RACH-based C-LTM instead of RACH-less C-LTM; b) Performing CHO instead of executing C-LTM; c) Triggering re-establishment instead of performing C-LTM; d) Waiting for an LTM command or a HO command instead of performing C-LTM.

[0155] In one embodiment, if the WTRU detects a change in the best SSB during C-LTM evaluation, and the C-LTM configuration indicates to perform a RACH-less C-LTM, the WTRU may perform RACH-based C-LTM instead at execution of the C-LTM in case the selected target is the same as the target in which the best SSB changed. A WTRU may further determine to change from RACH-less to RACH-based if the new SSB is not configured with a CG. Specifically, upon detection of a change of the best SSB for a target during C-LTM evaluation, the WTRU may select a new SSB for the target. If the new SSB is not configured with a CG, the WTRU may perform RACH-based C-LTM upon execution.

[0156] In another embodiment, if the WTRU is configured with RACH-less C-LTM, and if at least a threshold time has elapsed following enabling a CG associated with the best SSB of a target cell before C-LTM execution, the WTRU may perform RACH-based C-LTM instead of RACH- less C-LTM. Otherwise (i.e., if the C-LTM execution is triggered prior to the expiry of the CG validity timer), it may perform RACH-less LTM.

[0157] In another embodiment, if the WTRU is configured with RACH-less C-LTM, and if at least a threshold time associated with a C-LTM condition has elapsed following reception of C- LTM configuration, the WTRU may perform CHO. The WTRU may further perform CHO onlyin the case where the conditions associated with the CHO are satisfied, either prior to timer expiry, or at or following timer expiry.

[0158] A WTRU may triggers a RACH procedure or TA measurement. In one family of embodiments, a WTRU may trigger RACH transmission or TA measurement upon a change in validity of C-LTM configuration.

[0159] According to an embodiment, if the WTRU detects a change in the best S SB of a target during C-LTM evaluation, the WTRU may select a new SSB and perform RACH transmission to the target in order to initiate reception of a new TA. The WTRU may assume, upon selection of the new SSB, that the C-LTM configuration for the target is invalid. If the new TA is received prior to C-LTM execution, the WTRU may assume that the C-LTM configuration is valid. The WTRU may then perform RACH-based C-LTM instead of RACH-less C-LTM if C-LTM is triggered to the said target and the C-LTM configuration is still invalid at the time of triggering the execution.

[0160] According to an embodiment, if a validity timer associated with a TA expires during C- LTM evaluation, the WTRU may trigger a TA measurement. If the triggered TA measurement is not completed at the time C-LTM execution is triggered, the WTRU may perform RACH-based LTM instead of RACH-less LTM.

[0161] A WTRU may triggers a report to the source or target cell.

[0162] In one family of embodiments, the WTRU may trigger a report to the source cell or to the target cell. Such a report may contain any of the following: a) Identity of a (new) SSB or beam; b) Beam or cell measurement; c) TA measurement performed by the WTRU; d) Target Cell ID.

[0163] For example, if the best SSB changes during C-LTM evaluation, the WTRU may select a new SSB and send the new SSB to the network.

[0164] Handling Multiple Target Cells

[0165] In one embodiment, the WTRU may be configured to prioritize one target cell over another for C-LTM execution depending on the availability of resources for RACH less C-LTM execution at the two targets.

[0166] In one embodiment, a WTRU may execute a C-LTM to target cell A instead of target cell B, even though cell B may have a better signal level than cell A, if the WTRU has determined that the TA towards cell B has expired or is going to expire, while the TA towards cell A is still fresh (i.e., valid for longer duration).

[0167] In one embodiment, a WTRU may execute a C-LTM to target cell A instead of target cell B, even though cell B may have a better signal level than cell A, if the WTRU has determined that the CG resources towards cell B has expired while the CG resources towards cell A are still valid, or the next CG occasion towards target cell B is scheduled later than the next CG occasion in cell B (E.g., by more than a certain time duration).

[0168] In one embodiment, the prioritization described above may further be constrained by a relative threshold between the two target cells. For example, cases above, the WTRU may still be configured to execute the C-LTM using RACH towards target B, even though it was possible to perform RACH less C-LTM towards target A, if the signal level of target B is better than that of target A by more than a certain threshold.

[0169] In one embodiment, the prioritization described above may further be constrained by an absolute threshold of the target cell. For the example cases above, the triggering of the RACH less C-LTM towards cell A instead of the RACH based C-LTM towards cell B can be performed as long as cell A's signal level is above a certain threshold. For example, this threshold can be different from the C-LTM triggering threshold for the target cell.

[0170] In one embodiment, the prioritization described above may be dependent on the QoS requirements of one or more active bearers of the WTRU. For example, the WTRU may be configured to prioritize a C-LTM of a target cell towards which it can perform a RACH less C- LTM, even if there is another target cell that has a better radio quality but the resource for executing RACH less C-LTM towards that cell are not available (e.g., TA has expired, no CGs available, etc.,). In another example, the WTRU may be configured to prioritize RACH based C-LTM towards a cell with the best radio quality, even though there is another cell towards which RACH less C-LTM can be executed, if it has active radio bearers that are not delay sensitive but have more data rate requirements, or if the overall UL or DL activity level of the WTRU is above a certain level (e.g., UL / DL data rates). This could prevent from increasing the interference level of the network (i.e., if there is a lot of UL / DL data associated with the WTRU, it is very important to ensure the WTRU is connected to the best cell and not just a good cell, to make sure the interference level of the network will not become too much.)

[0171] In one embodiment, the WTRU may be configured to perform RACH towards multiple target cells at the same time for early TA acquisition. For example, based on L1 / L3 measurements, the network may predict more than one target cell to be the next candidate for C-LTM execution. Based on this, the network may send to the WTRU one or more PDCCH orders to trigger RACH to the multiple cells. The network then may send to the WTRU a MAC CE that indicates TA values (e.g., absolute TA values to each cell, relative TA values as compared to the current serving cellwhere the MAC CE is being received, relative TA values between the concerned candidate cells, etc.,).

[0172] In one embodiment, the WTRU may be configured with type 1 CG resource configurations along with the C-LTM configurations, and can consider the CG resources to be available / activated for a configured time duration or number of configured CG occasions.

[0173] In one embodiment, the WTRU may be configured with type 2 CG resource configurations along with the C-LTM configurations, and it will consider the CG resources to be activated if it receives an indication (e.g., a PDCCH order) to perform RACH towards the concerned target cell or receives a TA value to apply towards the cell (e.g., a MAC CE from the source cell).

[0174] In one embodiment, the WTRU may be configured to consider the type 2 CG resources (e.g., after being activated due to the reception of a PDCCH order as described in the embodiment above) also for a certain configured time duration or number of configured CG occasions.

[0175] In one embodiment, the WTRU may be configured with both type 1 and type 2 CG resources. For example, type 1 CGs that the WTRU can consider already activated upon the reception of the C-LTM configuration (for a certain configured time duration or CG occasions) and type 2 CG resources that can be considered to be available / activated only after the type 1 CG are no more available and / or WTRU has received a PDCCH order to perform a TA towards the concerned cell and / or the WTRU has received the TA value to apply to the target cell.

[0176] In one embodiment, the WTRU may be configured with an indication regarding which cells are co-located (e.g., which target cells are co-located, which target cells are co-located with the source cell, etc.,), and this way, it will know no TA acquisition is required to perform RACH less C-LTM towards the target cells that are co-located with the source cell, or it can apply a TA value provided regarding one target cell for another target cell.

[0177] Thus, according to an embodiment of a method implemented by a WTRU, the WTRU, which is configured to perform RACH-less conditional LTM (C-LTM) on an SSB, falls back to RACH-based LTM, based on the quality of the SSB configured in the RACH-less LTM.

[0178] The WTRU configured to perform RACH-less conditional LTM (C-LTM) on an SSB falls back to RACH-based LTM based on the quality of the SSB configured in the RACH-less LTM.In a first step, the WTRU receives a configuration of one or more C-LTM target cells (i.e., the WTRU receives a C-LTM target cell configuration per C-LTM target cell of the one or more C- LTM target cells) and a condition for performing LTM execution. The configuration / condition may comprise:a) the condition may comprise a list of possible conditions e.g., conditional event Ax, RLF / BFD on the source cell, etc. The term 'Ax' is a legacy term for a measurement event configuration (e.g., an RSRP of a SBB of a cell becomes better or worse than a threshold); b) a C-LTM target cell configuration may include a configured grant resource on the target, associated with one or more downlink beams / SSBs of the target cell; c) a set of associated error conditions and corresponding configuration associated with C-LTM evaluation and with C-LTM execution, e.g., threshold time between the fulfilment of the C-LTM triggering conditions and next CG availability.

[0179] In a second step, the WTRU may perform and may evaluate measurements of the downlink beams on one or more of the configured LTM targets, and may determine an SSB beam and / or cell quality for selection of a best beam and / or cell at the time of C-LTM configuration.

[0180] In a third step, the WTRU may determine a TA value for a target cell (e.g., based on reception of a MAC CE; according to an embodiment, the MAC CE may comprise the TA value). NB for 'a' target cell may be, for example, for the selected beam of the selected target cell. According to embodiments, the MAC CE may be a cell switch command, while in the presently described embodiment, there is no explicit cell switch command, the WTRU makes the cell switch decision on its own.

[0181] In a fourth step, if the validity of the configured C-LTM configuration changes during C- LTM evaluation (e.g., the RSRP of the best SSB drops by at least a configured threshold compared to the value reported at TA value determination or the WTRU determines that the best SSB has changed), the WTRU may select another SSB.

[0182] In a fifth step, if C-LTM execution is triggered after the change in validity during C-LTM evaluation determined in the fourth step, the WTRU performs RACH-based LTM on the target cell to the other SSB selected in the fourth step (i.e., the SSB falls back to RACH-based LTM based on the quality of the SSB configured in the RACH-less LTM); otherwise, the WTRU performs RACH-less LTM on the target cell to the original selected SSB.

[0183] FIG. 2 is a method for failure handling for conditional LTM (C-LTM) according to an embodiment.

[0184] In 201, the WTRU receives a C-LTM configuration via RRC message from the network. The configuration may indicate a specific mobility procedure to be performed (e.g., RACH-less LTM).

[0185] In 202, the WTRU performs measurements of the beams of one or more target cell or of each target cell in the C-LTM configuration and determines the best beam (e.g., SSB). In someembodiments, step 202 may be combined with step 201, and the WTRU may receive an indication of the best beam from the network, possibly with the C-LTM configuration.

[0186] In 203, the WTRU performs TA determination on the best beam selected in step 202. Step 203 may involve reporting the best beam to the network to receive the TA. Alternatively, step 203 may involve determination of the TA by the WTRU itself. In some embodiments, step 203 can be combined with step 201, and the network may send the TA, possibly associated with an indication of the best beam, to the WTRU, possibly as part of the C-LTM configuration.

[0187] In 204, the WTRU performs evaluation of the C-LTM conditions (e.g., the Ax' conditions). This evaluation of the C-LTM conditions for triggering C-LTM may be initiated immediately after step 201, after step 202, or after step 203. During evaluation of the C-LTM conditions, if a condition associated with validity of the C-LTM configuration is met, the WTRU may perform certain actions in step 204a associated with detection of a change in the validity of the C-LTM configuration, as described herein in section "Actions associated with change of C- LTM configuration validity".

[0188] In step 204a, the WTRU may optionally perform certain actions related to a change in the validity of the C-LTM configuration. Specifically, the WTRU may select a new SSB. Additionally, the WTRU may optionally perform actions towards restoring the validity of the C-LTM configuration. Such actions may or may not complete prior to the initiation of step 205. In case the actions complete, the WTRU can consider the validity of the C-LTM configuration to be restored by such actions.

[0189] Upon C-LTM conditions being satisfied, the WTRU performs C-LTM execution in step 205. At C-LTM execution, if a condition associated with validity of the C-LTM configuration is met (i.e., the configuration is considered not valid (invalid)), the WTRU may perform actions associated with an invalid C-LTM configuration as in step 205b. Specifically, the WTRU may perform a modified mobility procedure compared to the one initially configured in the C-LTM configuration. Otherwise, the WTRU may perform normal C-LTM as in 205a.

[0190] FIG. 3 is a flowchart of an embodiment of a method for failure handling for conditional LTM. The method 300 is implemented by a wireless transmit-receive unit (WTRU) in a network. The method may comprise:In 301, receiving configuration information related to one or more target cells for conditional layer- 2 mobility (C-LTM) and comprising at least one C-LTM condition for triggering LTM;In 302, performing measurements on beams of at least one of the one or more target cells, and determining (e.g. at a time Tl) a (e.g., first) best beam of a target cell of the one or more target cells, e.g., at a time of (after, upon) receiving the configuration information;In 303, determining (e.g., at a time Tl' > Tl) that a C-LTM condition of the at least one C-LTM condition for triggering LTM is met; andIn 304, at a time of performing C-LTM (e.g., at a time T2 > Tl'), determining invalidity of the configuration information for the (e.g., first) best beam determined before the time of performing the C-LTM, and performing random access channel (RACH) - based LTM on a newly (e.g., a second, another) determined best beam.

[0191] According to an embodiment of the method, the method comprises determining a timing advance (TA) value for the target cell, and the invalidity of the configuration information is determined based on a second reference signal received power (RSRP) of the best beam dropping by at least a configured threshold compared to a first reference signal received power of the best beam determined at (a time of) (the) determining of the timing advance value for the target cell.

[0192] According to an embodiment of the method, the invalidity of the configuration information is determined by the WTRU on determining that the best beam has changed.

[0193] According to an embodiment of the method, the timing advance value is determined by the WTRU by reporting the best beam to the network and receiving the timing advance value for the reported best beam from the network.

[0194] According to an embodiment of the method, the timing advance value is determined from the configuration information.

[0195] According to an embodiment of the method, the timing advance value is determined from a cell switch command received from a serving cell.

[0196] According to an embodiment of the method, invalidity of the configuration information is determined based on an elapsed time between receiving the configuration information and the time of performing C-LTM.

[0197] According to an embodiment of the method, invalidity of the configuration information is determined based on an elapsed time since determining, by the WTRU after receiving the configuration information, of a property associated with the target cell.

[0198] According to an embodiment of the method, the (first, second) best beam is determined based on at least one of the following beam level measurements: a synchronization signal block (SSB) measurement; a channel state information reference signal (CSLRS) measurement.

[0199] The present disclosure also relates to a wireless transmit-receive unit (WTRU) in a network, the WTRU comprising at least one processor, wherein the at least one processor is configured to: receive configuration information related to one or more target cells for conditional layer-2 mobility (C-LTM) and comprising at least one C-LTM condition for triggering LTM;perform measurements on beams of at least one of the one or more target cells, and determine (e.g. a time Tl) a (first) best beam of a target cell of the one or more target cells, e.g., at a time of (after, upon) receiving the configuration information; determine (e.g., at a time Tl' > Tl) that a C-LTM condition of the at least one C-LTM condition for triggering LTM is met; and at a time of performing C-LTM (e.g., at a time T2 > Tl'), determine invalidity of the configuration information for the best beam determined before the time of performing the C-LTM, and to perform random access channel (RACH) - based LTM on a newly (e.g., second, another) determined best beam.

[0200] According to an embodiment of the WTRU, the at least one processor is configured to determine a timing advance (TA) value for the target cell, and to determine the invalidity of the configuration information based on a second reference signal received power of the best beam dropping by at least a configured threshold compared to a first reference signal received power of the best beam determined at (a time of) (the) determining of the timing advance value for the target cell.

[0201] According to an embodiment of the WTRU, the at least one processor is configured to determine the invalidity of the configuration information on determining that the best beam has changed.

[0202] According to an embodiment of the WTRU, the at least one processor is configured to determine the timing advance value by reporting the best beam to the network and by receiving the timing advance value for the reported best beam from the network.

[0203] According to an embodiment of the WTRU, the at least one processor is configured to determine the timing advance value from the configuration information.

[0204] According to an embodiment of the WTRU, the at least one processor is configured to determine the timing advance value from a cell switch command received from a serving cell.

[0205] According to an embodiment of the WTRU, the at least one processor is configured to determine invalidity of the configuration information based on an elapsed time between receiving the configuration information and the time of performing C-LTM.

[0206] According to an embodiment of the WTRU, the at least one processor is configured to determine invalidity of the configuration information based on an elapsed time since determining, by the at least one processor after receiving the configuration information, of a property associated with the target cell.

[0207] According to an embodiment of the WTRU, the at least one processor is configured to determine the best beam based on at least one of the following beam level measurements: asynchronization signal block (SSB) measurement; a channel state information reference signal (CSI-RS) measurement.

[0208] There is also disclosed a method, implemented by a wireless transmit-receive unit (WTRU) in a network. The method may comprise: a) receiving configuration information related to one or more target cells for conditional layer-2 mobility (C-LTM) and comprising at least one C-LTM condition for triggering LTM; b) performing measurements on beams of at least one of the one or more target cells, and determine a best beam of a target cell of the one or more target cells, at a time of receiving the configuration information; c) determining that a validity of the configuration information has changed during the measurements, selecting another best beam, and perform random access channel (RACH) - based LTM on the target cell to the selected another best beam.

[0209] There is also disclosed a WTRU in a network, comprising at least one processor configured to: a) receive configuration information related to one or more target cells for conditional layer-2 mobility (C-LTM) and comprising at least one C-LTM condition for triggering LTM; b) perform measurements on beams of at least one of the one or more target cells, and determine a best beam of a target cell of the one or more target cells, at a time of receiving the configuration information; and c) determine that a validity of the configuration information has changed during the measurements, select another best beam, and perform random access channel (RACH) - based LTM on the target cell to the another best beam.

[0210] FIG. 4 is a flow chart of a method according to an embodiment. The method 400, implemented by a wireless transmit-receive unit (WTRU) in a network, may comprise: Receiving (401) configuration information related to one or more target cells for conditional layerl-2 triggered mobility (C-LTM), the configuration information comprising at least one C-LTM condition for performing LTM, the at least one C-LTM condition for performing LTM comprising a set of validity conditions associated with performing C-LTM evaluation; Performing (402) C- LTM evaluation, comprising performing measurements on downlink beams of at least one of the one or more target cells, and determining a best downlink beam of a target cell of the one or more target cells; Determining (403) that a C-LTM condition is met from the at least one C-LTM condition for performing LTM; Determining (404) validity of the configuration information based on the set of validity conditions; Performing (405) random access channel (RACH) - less LTM on the determined best downlink beam in case of validity of the configuration information; andPerforming (406) RACH - based LTM on a newly determined best downlink beam in case of invalidity of the configuration information.

[0211] According to an embodiment of the method, the set of validity conditions comprises at least one of: reference signal received power of the determined best downlink beam dropping below a configured threshold; and expiration of a validity timer associated with a timing advance (TA) value comprised in the configuration information.

[0212] According to an embodiment, the method comprises determining a timing advance (TA) value for the target cell, wherein the invalidity of the configuration information is determined based on a second reference signal received power (RSRP) of the determined best downlink beam dropping by at least a configured threshold compared to a first RSRP of the best downlink beam determined at determining of the TA value for the target cell.

[0213] According to an embodiment of the method, the invalidity of the configuration information is determined by the WTRU on determining that the best downlink beam has changed.

[0214] According to an embodiment of the method, the TA value is determined by the WTRU by reporting the best downlink beam to the network and receiving the TA value for the reported best downlink beam from the network.

[0215] According to an embodiment of the method, the TA value is determined from the configuration information.

[0216] According to an embodiment, of the method, the TA value is determined from a cell switch command received from a serving cell.

[0217] According to an embodiment of the method, invalidity of the configuration information is determined based on an elapsed time between receiving the configuration information and the time of performing C-LTM.

[0218] According to an embodiment of the method, invalidity of the configuration information is determined based on an elapsed time since determining, by the WTRU after receiving the configuration information, of a property associated with the target cell.

[0219] According to an embodiment of the method, the best downlink beam is determined based on at least one of the following beam level measurements: synchronization signal block measurement; and channel state information reference signal measurement.

[0220] There is also disclosed and described a WTRU in a network. The WTRU comprising at least one processor. The at least one processor is configured to: receive configuration information related to one or more target cells for conditional layer-2 mobility (C-LTM) and comprising at least one C-LTM condition for triggering LTM; perform measurements on beams of at least one of the one or more target cells, and determine a best beam of a target cell of the one or more targetcells, at a time of receiving the configuration information; determine that a C-LTM condition of the at least one C-LTM condition for triggering LTM is met; and at a time of performing C-LTM, determine invalidity of the configuration information for the best beam determined before the time of performing the C-LTM, and to perform random access channel (RACH) - based LTM on a newly determined best beam.

[0221] According to an embodiment, the at least one processor is configured to determine a timing advance (TA) value for the target cell, and to determine the invalidity of the configuration information based on a second reference signal received power of the best beam dropping by at least a configured threshold compared to a first reference signal received power of the best beam determined at determining of the TA value for the target cell.

[0222] According to an embodiment, the at least one processor is configured to determine the invalidity of the configuration information on determining that the best beam has changed.

[0223] According to an embodiment, the at least one processor is configured to determine the timing advance value by reporting the best beam to the network and by receiving the timing advance value for the reported best beam from the network.

[0224] According to an embodiment, the at least one processor is configured to determine the timing advance value from the configuration information.

[0225] According to an embodiment, the at least one processor is configured to determine the timing advance value from a cell switch command received from a serving cell.

[0226] According to an embodiment, the at least one processor is configured to determine invalidity of the configuration information based on an elapsed time between receiving the configuration information and the time of performing C-LTM.

[0227] According to an embodiment, the at least one processor is configured to determine invalidity of the configuration information based on an elapsed time since determining, by the at least one processor after receiving the configuration information, of a property associated with the target cell.

[0228] According to an embodiment, the at least one processor is configured to determine the best beam based on at least one of the following beam level measurements: synchronization signal block measurement; and channel state information reference signal measurement.

[0229] Although features and elements are provided above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations may be made without departing from its spirit and scope, as will be apparent to those skilled in the art. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly provided as such. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods or systems.

[0230] The foregoing embodiments are discussed, for simplicity, with regard to the terminology and structure of wireless communication capable devices, (e.g., radio wave emitters and receivers). However, the embodiments discussed are not limited to these systems but may be applied to other systems that use other forms of electromagnetic waves or non-electromagnetic waves such as acoustic waves.

[0231] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used herein, the term "video" or the term "imagery" may mean any of a snapshot, single image and / or multiple images displayed over a time basis. As another example, when referred to herein, the terms "user equipment" and its abbreviation "UE", the term "remote" and / or the terms "head mounted display" or its abbreviation "HMD" may mean or include (i) a wireless transmit and / or receive unit (WTRU); (ii) any of a number of embodiments of a WTRU; (iii) a wireless-capable and / or wired-capable (e.g., tetherable) device configured with, inter alia, some or all structures and functionality of a WTRU; (iii) a wireless-capable and / or wired-capable device configured with less than all structures and functionality of a WTRU; or (iv) the like. Details of an example WTRU, which may be representative of any WTRU recited herein, are provided herein with respect to FIGs. 1 A-1D. As another example, various disclosed embodiments herein supra and infra are described as utilizing a head mounted display. Those skilled in the art will recognize that a device other than the head mounted display may be utilized and some or all of the disclosure and various disclosed embodiments can be modified accordingly without undue experimentation. Examples of such other device may include a drone or other device configured to stream information for providing the adapted reality experience.

[0232] In addition, the methods provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer- readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

[0233] Variations of the method, apparatus and system provided above are possible without departing from the scope of the invention. In view of the wide variety of embodiments that can be applied, it should be understood that the illustrated embodiments are examples only, and should not be taken as limiting the scope of the following claims. For instance, the embodiments provided herein include handheld devices, which may include or be utilized with any appropriate voltage source, such as a battery and the like, providing any appropriate voltage.

[0234] Moreover, in the embodiments provided above, processing platforms, computing systems, controllers, and other devices that include processors are noted. These devices may include at least one Central Processing Unit ("CPU") and memory. In accordance with the practices of persons skilled in the art of computer programming, reference to acts and symbolic representations of operations or instructions may be performed by the various CPUs and memories. Such acts and operations or instructions may be referred to as being "executed," "computer executed" or "CPU executed."

[0235] One of ordinary skill in the art will appreciate that the acts and symbolically represented operations or instructions include the manipulation of electrical signals by the CPU. An electrical system represents data bits that can cause a resulting transformation or reduction of the electrical signals and the maintenance of data bits at memory locations in a memory system to thereby reconfigure or otherwise alter the CPU's operation, as well as other processing of signals. The memory locations where data bits are maintained are physical locations that have particular electrical, magnetic, optical, or organic properties corresponding to or representative of the data bits. It should be understood that the embodiments are not limited to the above-mentioned platforms or CPUs and that other platforms and CPUs may support the provided methods.

[0236] The data bits may also be maintained on a computer readable medium including magnetic disks, optical disks, and any other volatile (e.g., Random Access Memory (RAM)) or non-volatile (e.g., Read-Only Memory (ROM)) mass storage system readable by the CPU. The computer readable medium may include cooperating or interconnected computer readable medium, whichexist exclusively on the processing system or are distributed among multiple interconnected processing systems that may be local or remote to the processing system. It should be understood that the embodiments are not limited to the above-mentioned memories and that other platforms and memories may support the provided methods.

[0237] In an illustrative embodiment, any of the operations, processes, etc. described herein may be implemented as computer-readable instructions stored on a computer-readable medium. The computer-readable instructions may be executed by a processor of a mobile unit, a network element, and / or any other computing device.

[0238] There is little distinction left between hardware and software implementations of aspects of systems. The use of hardware or software is generally (but not always, in that in certain contexts the choice between hardware and software may become significant) a design choice representing cost versus efficiency tradeoffs. There may be various vehicles by which processes and / or systems and / or other technologies described herein may be effected (e.g., hardware, software, and / or firmware), and the preferred vehicle may vary with the context in which the processes and / or systems and / or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and / or firmware vehicle. If flexibility is paramount, the implementer may opt for a mainly software implementation. Alternatively, the implementer may opt for some combination of hardware, software, and / or firmware.

[0239] The foregoing detailed description has set forth various embodiments of the devices and / or processes via the use of block diagrams, flowcharts, and / or examples. Insofar as such block diagrams, flowcharts, and / or examples include one or more functions and / or operations, it will be understood by those within the art that each function and / or operation within such block diagrams, flowcharts, or examples may be implemented, individually and / or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In an embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), and / or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, may be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and / or writing the code for the software and or firmware would be well within the skillof one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein may be distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a CD, a DVD, a digital tape, a computer memory, etc., and a transmission type medium such as a digital and / or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.).

[0240] Those skilled in the art will recognize that it is common within the art to describe devices and / or processes in the fashion set forth herein, and thereafter use engineering practices to integrate such described devices and / or processes into data processing systems. That is, at least a portion of the devices and / or processes described herein may be integrated into a data processing system via a reasonable amount of experimentation. Those having skill in the art will recognize that a typical data processing system may generally include one or more of a system unit housing, a video display device, a memory such as volatile and non-volatile memory, processors such as microprocessors and digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices, such as a touch pad or screen, and / or control systems including feedback loops and control motors (e.g., feedback for sensing position and / or velocity, control motors for moving and / or adjusting components and / or quantities). A typical data processing system may be implemented utilizing any suitable commercially available components, such as those typically found in data computing / communication and / or network computing / communication systems.

[0241] The herein described subject matter sometimes illustrates different components included within, or connected with, different other components. It is to be understood that such depicted architectures are merely examples, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality may be achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated may also be viewed as being "operably connected", or "operably coupled", to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being "operably couplable" to each other to achieve the desired functionality.Specific examples of operably couplable include but are not limited to physically mateable and / or physically interacting components and / or wirelessly interactable and / or wirelessly interacting components and / or logically interacting and / or logically interactable components.

[0242] With respect to the use of substantially any plural and / or singular terms herein, those having skill in the art can translate from the plural to the singular and / or from the singular to the plural as is appropriate to the context and / or application. The various singular / plural permutations may be expressly set forth herein for sake of clarity.

[0243] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, where only one item is intended, the term "single" or similar language may be used. As an aid to understanding, the following appended claims and / or the descriptions herein may include usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim including such introduced claim recitation to embodiments including only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and / or "an" should be interpreted to mean "at least one" or "one or more"). The same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems thathave A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and / or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B." Further, the terms "any of' followed by a listing of a plurality of items and / or a plurality of categories of items, as used herein, are intended to include "any of," "any combination of," "any multiple of," and / or "any combination of multiples of the items and / or the categories of items, individually or in conjunction with other items and / or other categories of items. Moreover, as used herein, the term "set" is intended to include any number of items, including zero. Additionally, as used herein, the term "number" is intended to include any number, including zero. And the term "multiple", as used herein, is intended to be synonymous with "a plurality".

[0244] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0245] As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein may be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like includes the number recited and refers to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.

[0246] Moreover, the claims should not be read as limited to the provided order or elements unless stated to that effect. In addition, use of the terms "means for" in any claim is intended to invoke 35 U.S.C. §112, 6 or means-plus-function claim format, and any claim without the terms "means for" is not so intended.

Claims

CLAIMSWhat is claimed is:

1. A method, implemented by a wireless transmit-receive unit (WTRU), the method comprising: receiving configuration information related to one or more target cells for conditional layerl-2 triggered mobility (C-LTM), the configuration information comprising at least one C-LTM condition for performing LTM, and the at least one C-LTM condition for performing LTM comprising a set of validity conditions associated with performing C-LTM evaluation; performing C-LTM evaluation, comprising performing measurements on downlink beams of at least one of the one or more target cells, and determining a best downlink beam of a target cell of the one or more target cells; determining that a C-LTM condition is met from the at least one C-LTM condition for performing LTM; determining validity of the configuration information based on the set of validity conditions; performing random access channel (RACH) - less LTM on the determined best downlink beam in case of validity of the configuration information; and performing RACH - based LTM on a newly determined best downlink beam in case of invalidity of the configuration information.

2. The method of claim 1, wherein the set of validity conditions comprises at least one of: reference signal received power of the determined best downlink beam dropping below a configured threshold; and expiration of a validity timer associated with a timing advance (TA) value comprised in the configuration information.

3. The method of claim 1, comprising determining a timing advance (TA) value for the target cell, wherein the invalidity of the configuration information is determined based on a second reference signal received power (RSRP) of the determined best downlink beam dropping by at least a configured threshold compared to a first RSRP of the best downlink beam determined at determining of the TA value for the target cell.

4. The method of claim 1, wherein the invalidity of the configuration information is determined by the WTRU on determining that the best downlink beam has changed.

5. The method of claim 3, wherein the TA value is determined by the WTRU by reporting the best downlink beam to a network and receiving the TA value for the reported best downlink beam from the network.

6. The method of claim 3, wherein the TA value is determined from the configuration information.

7. The method according to claim 3, wherein the TA value is determined from a cell switch command received from a serving cell.

8. The method according to claim 1, wherein invalidity of the configuration information is determined based on an elapsed time between receiving the configuration information and the time of performing C-LTM.

9. The method according to claim 1, wherein invalidity of the configuration information is determined based on an elapsed time since determining, by the WTRU after receiving the configuration information, of a property associated with the target cell.

10. The method according to claim 1, wherein the best downlink beam is determined based on at least one of the following beam level measurements: synchronization signal block measurement; and / or channel state information reference signal measurement.

11. A wireless transmit-receive unit (WTRU), the WTRU comprising at least one processor, wherein the at least one processor is configured to: receive configuration information related to one or more target cells for conditional layer-2 mobility (C-LTM) and comprising at least one C-LTM condition for triggering LTM; perform measurements on beams of at least one of the one or more target cells, and determine a best beam of a target cell of the one or more target cells, at a time of receiving the configuration information; determine that a C-LTM condition of the at least one C-LTM condition for triggering LTM is met; and at a time of performing C-LTM, determine invalidity of the configuration information for the best beam determined before the time of performing the C-LTM, and to perform random access channel (RACH) - based LTM on a newly determined best beam.

12. The WTRU of claim 11, wherein the at least one processor is configured to determine a timing advance (TA) value for the target cell, and to determine the invalidity of the configuration information based on a second reference signal received power of the best beam dropping by at least a configured threshold compared to a first reference signal received power of the best beam determined at determining of the TA value for the target cell.

13. The WTRU of claim 11, wherein the at least one processor is configured to determine the invalidity of the configuration information on determining that the best beam has changed.

14. The WTRU of claim 12, wherein the at least one processor is configured to determine the TA value by reporting the best beam to a network and by receiving the TA value for the reported best beam from the network.

15. The WTRU according to claim 12, wherein the at least one processor is configured to determine the TA value from the configuration information.

16. The WTRU according to claim 12, wherein the at least one processor is configured to determine the TA value from a cell switch command received from a serving cell.

17. The WTRU according to claim 11, wherein the at least one processor is configured to determine invalidity of the configuration information based on an elapsed time between receiving the configuration information and the time of performing C-LTM.

18. The WTRU according to claim 11, wherein the at least one processor is configured to determine invalidity of the configuration information based on an elapsed time since determining, by the at least one processor after receiving the configuration information, of a property associated with the target cell.

19. The WTRU according to claim 11, wherein the at least one processor is configured to determine the best beam based on at least one of the following beam level measurements: synchronization signal block measurement; and / or channel state information reference signal measurement.

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