Methods, architectures, apparatuses and systems for layer 2 mobility

Abstract

Procedures, methods, architectures, apparatuses, systems, devices, and computer program products for Layer 2 Mobility (LTM). A wireless transmit / receive unit, WTRU, performs measurements of respective downlink beams associated with at least one initial candidate cell for handover, determines, based on the measurements, a selected candidate cell for handover among the at least one initial candidate cell, transmits, using an uplink control channel resource, information indicative of the selected candidate cell as target cell, and transmits information indicating complete handover.

Description

METHODS, ARCHITECTURES, APPARATUSES AND SYSTEMS FOR LAYER 2 MOBILITYCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 572,473, filed April 1, 2024, which is incorporated herein by reference in its entirety.BACKGROUND

[0002] The present disclosure is generally directed to the fields of communications including, for example, methods, architectures, apparatuses, systems directed to Layer 2 Mobility (LTM).SUMMARY

[0003] In a first aspect, the present principles are directed to a method at a wireless transmit / receive unit, WTRU, the method including performing measurements of respective downlink beams associated with at least one initial candidate cell for handover, determining, based on the measurements, a selected candidate cell for handover among the at least one initial candidate cell, transmitting, using an uplink control channel resource, information indicative of the selected candidate cell as target cell, and transmitting information indicating complete handover.

[0004] In embodiments, the method includes determining respective timing advance values for the at least one initial candidate cell for handover, and the information indicative of the selected candidate cell as target cell is transmitted to the selected candidate cell using the uplink control channel resource and the timing advance value of the selected candidate cell.

[0005] In embodiments, the method includes receiving, from the selected candidate cell on a downlink control channel, an indication of an uplink shared channel, wherein information indicating complete handover is transmitted on the uplink shared channel. The information indicative of the selected candidate cell as target cell can be transmitted to a cell currently serving the WTRU. The method can include, in response to transmitting the information indicative of a selected candidate cell as target cell, receiving information indicative of an activation of the uplink shared channel. The uplink shared channel can be associated with a dynamic grant. The uplink shared channel can be associated with a configured grant.

[0006] In embodiments, the selected candidate cell for handover is determined upon occurrence of a trigger event for at least one candidate cell for handover.

[0007] In embodiments, the selected candidate cell is the initial candidate cell whose measured beam quality is the highest of the at least one initial candidate cell.

[0008] In embodiments, the method includes receiving information indicative of the at least one initial candidate cell for handover, the information comprising, for each initial candidate cell forhandover, at least one uplink control channel resource associated with downlink beams, and a condition for performing handover.

[0009] In embodiments, the handover is a layer 2 mobility handover.

[0010] In embodiments, the uplink control channel resource is a scheduling request transmitted to a cell currently serving the WTRU.

[0011] In a second aspect, the present principles are directed to a wireless transmit / receive unit, WTRU, including at least one processor configured to perform measurements of respective downlink beams associated with at least one initial candidate cell for handover, determine, based on the measurements, a selected candidate cell for handover among the at least one initial candidate cell, transmit, using an uplink control channel resource, information indicative of the selected candidate cell as target cell, and transmit information indicating complete handover.

[0012] In embodiments, the at least one processor is configured to determine respective timing advance values for the at least one initial candidate cell for handover, and transmit the information indicative of the selected candidate cell as target cell to the selected candidate cell using the uplink control channel resource and the timing advance value of the selected candidate cell.

[0013] In embodiments, the at least one processor is configured to receive, from the selected candidate cell on a downlink control channel, an indication of an uplink shared channel, wherein information indicating complete handover is transmitted on the uplink shared channel. The information indicative of the selected candidate cell as target cell can be transmitted to a cell currently serving the WTRU. The at least one processor can be configured to, in response to transmitting the information indicative of a selected candidate cell as target cell, receive information indicative of an activation of the uplink shared channel. The uplink shared channel can be associated with a dynamic grant. The uplink shared channel can be associated with a configured grant.

[0014] In embodiments, the at least one processor is configured to determine the selected candidate cell for handover upon occurrence of a trigger event for at least one candidate cell for handover.

[0015] In embodiments, the selected candidate cell is the initial candidate cell whose measured beam quality is the highest of the at least one initial candidate cell.

[0016] In embodiments, the at least one processor is configured to receive information indicative of the at least one initial candidate cell for handover, the information comprising, for each initial candidate cell for handover, at least one uplink control channel resource associated with downlink beams, and a condition for performing handover.

[0017] In embodiments, the handover is a layer 2 mobility handover.

[0018] In embodiments, the uplink control channel resource is a scheduling request transmitted to a cell currently serving the WTRU.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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:

[0020] FIG. 1 A is a system diagram illustrating an example communications system;

[0021] 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;

[0022] 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;

[0023] 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;

[0024] FIG. 2 illustrates a conventional LTM procedure defined in 3GPP TS 38.300 vl8.1.0; and

[0025] FIG. 3 illustrates a flowchart of conditional LTM according to an embodiment of the present principles.DETAILED DESCRIPTION

[0026] 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.

[0027] Example Communications System

[0028] The methods, apparatuses and systems provided herein are well-suited for communications involving both wired and wireless networks. An overview of various types of wireless 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.

[0029] 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.

[0030] 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.

[0031] 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 facilitate access 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.

[0032] 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.

[0033] 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).

[0034] 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 communicationprotocols 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).

[0035] 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).

[0036] 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).

[0037] 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).

[0038] 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.

[0039] 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.

[0040] 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 varying quality 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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 liquidcrystal 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 store data 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).

[0049] 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.

[0050] 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.

[0051] 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 lightsensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and / or a humidity sensor.

[0052] 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)).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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 theWTRUs 102a, 102b, 102c, and the like. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] In representative embodiments, the other network 112 may be a WLAN.

[0063] 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 directlink setup (DLS). In certain representative embodiments, the DLS may use an 802. l ie DLS or an 802.1 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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 in 802.1 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,802.11ah may support meter type control / machine-type communications (MTC), such as MTC devices 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).

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 mayimplement carrier aggregation technology. For example, the gNB 180a may transmit multiple component 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).

[0072] 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).

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Layer 2 Mobility (LTM) in wireless networks was introduced in 3GPP R18. Compared to the conventional Layer 3 mobility, it can provide better handover latency and interruption time.

[0084] LTM is described as follows in 3GPP TS 38.300 vl8.1.0, section 9.2.3.5 [with the explanations of some acronyms added in square brackets],

[0085] "LTM is a procedure in which a gNB receives LI measurement report(s) from a UE, and on their basis the gNB changes UE serving cell by a cell switch command signalled via a MAC CE. The cell switch command indicates an LTM candidate configuration that the gNB previously prepared and provided to the UE through RRC [Radio Resource Control] signalling. Then the UE switches to the target configuration according to the cell switch command. The LTM procedure can be used to reduce the mobility latency as described in Annex G.

[0086] When configured by the network, it is possible to activate TCI [Transmission Configuration Indication] 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 UE to be DL synchronized with those cells, thereby facilitating a faster cell switch to one of those cells when cell switch is triggered.

[0087] 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 UE to perform early TA acquisition of a candidate cell before a cell switch. The early TA acquisition procedure is triggered by PDCCH [Physical Downlink Control Channel] order as specified in clause 9.2.6 or realized through UE-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 UE performs TA measurement for the candidate cells after being configured by RRC but the exact time the UE performs TA measurement is up to UE implementation. The UE 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.

[0088] Depending on the availability of a valid TA value, the UE performs either a RACH-less LTM or RACH-based LTM cell switch. If the TA value is provided in the cell switch command, the UE applies the TA value as instructed by the network. In the case where UE-based TA measurement is configured, but no TA value is provided in the cell switch command, the UE applies the TA value by itself if available. Meanwhile, the UE performs RACH-less LTM cell switchupon receiving the cell switch command. If no valid TA value is available, the UE performs RACH- based LTM cell switch.

[0089] Regardless of whether the UE is configured for UE-based TA measurement for a certain candidate cell, it will still follow the PDCCH order, which includes requesting a random access procedure towards the candidate cells. This also applies to the candidate cells for which the UE is capable of deriving TA values by itself. Additionally, regardless of whether the UE has already performed a random access procedure towards the candidate cells, it will still follow the UE-based measurement configuration if configured by the network.

[0090] For RACH-less LTM, the UE 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 UE 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 UE starts to monitor PDCCH on the target cell for dynamic scheduling. Before RACH-less LTM procedure completion, the UE shall not trigger random access procedure if it does not have a valid PUCCH [Physical Uplink Control Channel] resource for triggered SRs.

[0091] The following principles apply to LTM:

[0092] - Security key is maintained upon an LTM cell switch;

[0093] - Subsequent LTM is supported.

[0094] LTM supports both intra-gNB-DU and intra-gNB-CU inter-gNB-DU mobility. LTM supports both intra-frequency and inter-frequency mobility, including mobility to inter-frequency cell that is not a current serving cell. LTM is supported only for licensed spectrum. The following scenarios are supported:

[0095] - PCell change in non-CA scenario and non-DC scenario;

[0096] - PCell and SCell(s) change in CA scenario;

[0097] - Dual connectivity scenario, PCell and MCG SCell(s) change and intra-SN PSCell and SCG SCell(s) change without MN involvement. LTM for simultaneous PCell and PSCell change is not supported.

[0098] While the UE has stored LTM candidate configurations the UE can also execute any L3 handover command sent by the network. "

[0099] The LTM procedure defined in the document is illustrated FIG. 2 ("Figure 9.2.3.5.2-1. Signalling procedure for LTM" in the document), which will not be described herein.

[0100] However, as stated in 3GPP work item RP -234036: "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.

[0101] 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 gNB s (i.e. inter-CU) then the network will be able gain the benefits of LTM for a far greater number of handovers.

[0102] Layer 3 mobility uses layer 3 measurement reporting which supports UE 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.

[0103] LI measurements for LTM procedures are limited to SSB measurements. Expanding LI measurements to include CSI-RS can address this limitation and can be expected to enable greater throughput on the target cell immediately after cell switch.

[0104] 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. "

[0105] In other words, LTM as introduced in Rel-18 offers short interruption time but without the same level of robustness as conditional L3 mobility procedures such as conditional handover (CHO) and other conditional mobility procedures (CP AC, SCPAC) that were developed to achieve high robustness by enabling the procedure to be executed without necessitating a signalling exchange with source cell beforehand.

[0106] 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 UE needs to be able to perform a Random Access Channel (RACH)-less CHO. Typically, in order to support RACH-less handover the UE needs to have uplink timing information (timing advance) and either needs a configured grant to transmit on the Physical Uplink Shared Channel (PUSCH) directly, or needs to monitor for scheduling on Physical Downlink Control Channel (PDCCH) on the target cell which requires the target cell to be aware of the UE presence (e.g., if the source issues a cell switch command, the target should already be prepared). This can imply significant resource overhead because either all potential conditional LTM candidates should be prepared for as long as the UE is configured to evaluate (and in this case the UE will have to transmit RACH to make the target aware of the UE presence), or configured grants need to be reserved on all potential target cells and beams.

[0107] It will thus be appreciated that there is a desire for resource-efficient conditional LTM with low interruption and latency.

[0108] Briefly speaking, to be described in more detail after, according to the present principles, a UE is configured to perform a conditional LTM, and determines a PUCCH resource on a target cell corresponding to a downlink beam measurement that meets a condition triggering LTM to that target cell, transmits an indication using the PUCCH resource to the target cell that a RACH-less conditional LTM handover is being executed, and receives Downlink Control Information (DCI) scheduling an uplink PUSCH transmission.

[0109] FIG. 3 illustrates a flowchart of a method of conditional LTM according to an embodiment of the present principles.

[0110] In step S302, the UE receives, from the network (e.g., the source cell, Cell A), information indicative of a configuration of one or more LTM candidate cells including PUCCH resources (e.g., Scheduling Request (SR) resource) that are associated with downlink beams (e.g., Synchronization Signal Block) and a condition for performing LTM execution (i.e., an LTM trigger).

[0111] The LTM trigger may be based on any of those detailed in section "LTM Execution Trigger" hereinafter. The PUCCH resource may include an element in Uplink Control Information (UCI) for CHO indication (in addition to SR, Channel-Quality Indicator (CQI), etc.) or may use SR with a specific resource configuration. The configuration may include type 2 Configured Grant (CG) on target, associated with the downlink beams or PUCCH resources.

[0112] In step S304, the UE performs measurements on downlink beams from one or more configured LTM candidates (i.e., target cell, Cell B), evaluates the measurements and determines (e.g., calculates) a Timing Advance (TA) value for a target cell (e.g., receive Media Access Control Control Element (MAC CE) or perform UE based measurement). The TA can be determined in different ways, as described in section "Early TA acquisition" hereinafter; in brief, the TA can be a fixed value in the RRC configuration (e.g., if the target cell is co-located on the same physical location), provided in a MAC CE, following a UE transmission to the target cell, target cells communicates this to the source cell, or estimated by the UE based on measurements.

[0113] In case a configured condition for executing LTM is met for an LTM candidate cell, in step S306, the UE determines a PUCCH resource based on the best quality downlink beam (i.e., the beam causing the condition to be met).

[0114] In step S308, the UE transmits an indication using the determined PUCCH resource and the determined TA. The indication can for example include measurement event ID or otherinformation in the UCI. The PUCCH resource is specific for the UE to complete a conditional LTM, so it may implicitly indicate the conditional LTM.

[0115] In step S310, the UE receives PDCCH scheduling information. The beam information for the PDCCH is implicitly known, for example due to its Quasi Co-Location (QCL) relationship with the best beam corresponding to the determined PUCCH resource.

[0116] In step S312, the UE transmits information indicative of RRC Reconfiguration complete on the indicated PUSCH resource (for example indicated by CG, preconfigured by RRC, or dynamic grant, received in a DCI on PDCCH).

[0117] It will be appreciated that the method can enable RACH-less conditional LTM handover without the need to perform signalling on the source cell and without the need to reserve dedicated preamble or PUSCH resource on the target cell. The UE obtains uplink timing ahead of attempting the conditional handover. The method can provide lower latency and better robustness, as well as faster beam refinement in case CSI-RS can be measured.

[0118] Perform LTM

[0119] In this document, "perform LTM" or "perform LTM procedures" refers to performing steps described in FIG. 3. Specifically, early synchronization in DL and / or UL to one or more of the candidate cells, performing LI measurements and reporting on one or more of the candidate cells, switching (i.e. performing handover) between candidate cells. The UE can move / switch between multiple candidate cells during the procedure.

[0120] Candidate cell sets

[0121] The one or more candidate cell sets may be groups of more than one RRC configuration corresponding to a handover configuration for one or more candidate SpCells and optionally SCells. This may be modelled or received as one or more complete RRC Reconfiguration messages, one or more cell group configurations, or one or more cell configurations. Each of the candidate cell configurations may include a candidate configuration identifier, and each of the candidate cell groups may include a candidate cell group identifier. If the grouping is performed at RRC, the switching between different sets of candidate cells may include updating the serving cell indexes or candidate configuration indexes which are used in LI and MAC signalling to refer to specific indexes (for example a MAC CE triggering the reconfiguration may include a candidate configuration index informing the UE which cell to perform the reconfiguration to).

[0122] The one or more candidate cell groups may be configured as a single list or group of candidate cell configurations at RRC. The grouping may occur at the early synchronisation or LTM execution phase rather than at the configuration phase. This means that the candidate cell set may be considered as a single group in terms of a RRC configuration list or group, while the cellsselected for performing early sync, LI measurements, and LTM execution depend on a further grouping into multiple subsets of the overall candidate cell list. In other words, instead of grouping at RRC using candidate configuration identifiers, the grouping is executed as part of the early sync or the LTM execution procedure.

[0123] Throughout the description, when referring to an LTM candidate configuration, this may apply to any type of preconfigured cell information. For example, a UE may be configured with one or more conditional reconfigurations such as conditional handover (CHO), conditional PSCell addition (CPA) or conditional PSCell change (CPC) which are valid before and / or after a cell change, or valid in certain cells.

[0124] LI measurement

[0125] A LI measurement may include measurement of Reference Signal Received Power (RSRP), Received Signal Strength Indicator (RS SI), etc., performed by a UE of a cell, beam, set of cells, or set of beams. Such a LI measurement may be similar to L3 measurements reported in Radio Resource Management (RRM), with differences in the filtering, reference signals measured, reporting mechanisms, etc.

[0126] LI measurement can apply also to RRM reporting

[0127] Herein, measurements typically refer to LI measurements for LTM. However, in certain embodiments, measurements may also refer to RRM / L3 measurements, as well as other measurements (e.g., measurements of speed, location, height, traffic, etc.).

[0128] LTM cell switch can apply also to any type of handover execution

[0129] Herein, the LTM cell switch refers to Ll / 2-triggered mobility, whereby a preconfigured RRC configuration is applied when the UE receives an indication using MAC CE or when a certain condition is met at the UE. However, certain embodiments may also apply to an RRC reconfiguration, an RRC conditional reconfiguration, as well as any other type of mobility procedure.

[0130] LTM Candidate configuration

[0131] The gNB (e.g. a CU in case of CU / DU split architecture - note: RRC resides in Central Unit (CU)) configures potential LTM candidates using RRC signalling. In one embodiment, the UE receives information indicative of the LTM candidate configurations using an RRC Reconfiguration message, for example during the "LTM preparation" phase illustrated in FIG. 2. The UE may store the LTM candidate configurations to apply later upon receiving an indication using Ll / 2 signalling (e.g., MAC CE) to perform a cell switch, for example in the "LTM execution" phase illustrated in FIG. 2.

[0132] In one embodiment, the configuration of potential LTM candidates may include candidate sets, for example a first set that may be suitable for a first path (for example, a UE turns left and takes the first road) and a second set that may be suitable for a second path (e.g. UE turns right and takes the second road).

[0133] In one embodiment, some or all of the candidate set information is broadcast in system information, and the UE enables the pre-configuration of these broadcast configurations upon receiving an indication in dedicated signalling (e.g., RRC Reconfiguration) which refers to the broadcast of one or more configurations (e.g., using an index or identifier).

[0134] In one embodiment, the configuration may include all or a subset of the potential cells in a specific area (for example all cells belonging to the CU with which the UE is currently connected or cells within a particular geographical area). These cells may still have to be detected or measured by the UE but are configured in advance. In one embodiment, after the initial configuration of LTM candidate configurations, the UE may receive an update to the configuration to modify, add, remove, or replace any part of the LTM candidate configurations.

[0135] In one embodiment, the UE may receive an indication to enable or disable some or all of the LTM configurations. For example, if it is predicted that the UE mobility would be better handled using L3 (e.g., RRC measurement report, RRC reconfiguration, conditional reconfiguration) then LTM may be disabled. On the other hand, if it is predicted that LTM would better suit the UE mobility then LTM may be enabled (e.g., a previously configured and disabled LTM configuration may be re-enabled).

[0136] The configuration may in one embodiment be based on a prediction model internal to, and determined by, the network (e.g., gNB). This prediction may, for example, be based on what the NW prediction model determines to be the UEs most likely paths.

[0137] In some embodiments, the candidate cell configurations contain all or part of the information necessary to complete a reconfiguration (e.g. handover) to the candidate cell, such as channel configurations (e.g. Physical Random-Access Channel (PRACH), PDCCH, PDSCH), CORESET, Bandwidth Part (BWP), security parameters, L2 parameters (E.g. MAC, RLC, Packet Data Convergence Protocol (PDCP)), radio bearer configurations, and so on.

[0138] LTM Execution Trigger

[0139] Herein, LTM execution trigger refers to a condition for performing LTM (e.g. a conditional handover trigger or measurement report trigger), which is either configured or indicated by the network to the UE, or estimated / determined by the UE.

[0140] A trigger may be based on one or more of time (e.g., absolute or relative time measured time at UE, System Frame Number (SFN), and subframe number), radio quality measurement orpredicted radio quality one or more of the serving cells or target cells (e.g., RSRP (beam or cell), Reference Signal Received Quality (RSRQ) (beam or cell), cri-RI-PMI-CQI, cri-RI-il, cri-RI-il- CQI, cri-RI-CQI, cri-RSRP, ssb-Index-RSRP, and cri-RI-LI-PMI-CQI), position (e g., an area (e.g. defined by reference point and radius) or range of coordinates, and a distance threshold from a reference location), a L3 measurement event (e.g., Event Al (Serving becomes better than threshold), Event A2 (Serving becomes worse than threshold), Event A3 (Neighbor becomes offset better than SpCell), Event A4 (Neighbor becomes better than threshold), Event A5 (SpCell becomes worse than threshold 1 and neighbor becomes better than threshold2), Event A6 (Neighbour becomes offset better than SCell), Event B 1 (Inter RAT neighbour becomes better than threshold), and Event B2 (PCell becomes worse than threshold 1 and inter RAT neighbor becomes better than threshold2), a LI measurement event or condition (for example any event defined which utilizes LI beam measurements to evaluate whether a criteria or condition is met), a predicted event (for example using any of the measurement quantities previously listed in this paragraph), an explicit indication from the network (for example, the UE may enable CSI reporting based on an explicit indication (e.g. a MAC CE) received from the network, and then execute LTM cell switch upon receiving a second MAC CE from the network), a measured, predicted, or estimated throughput, error rate, buffer status, or QoS parameter, and an evaluation metric (for example a time-to-trigger, a hysteresis, offset (e.g. a radio quality measurement offset), or a measurement filtering configuration).

[0141] The trigger may include one or more conditions under which the UE is allowed to perform actions related to LTM. For example, the UE may perform one or more of the following procedures.

[0142] Early TA acquisition

[0143] In a first embodiment, the UE may trigger a RACH to a target LTM cell. In a first example, the UE may receive a TA value in a Random-Access Response (RAR), for instance from the target cell, or via the source cell. In a second example, the UE may receive a TA value in a MAC CE triggering the cell switch. In a third example, the UE may perform power ramping and preamble retransmission on the target if a RAR / MAC CE is not received.

[0144] In a second embodiment, the UE may acquire the TA value of a candidate LTM cell by measurement, and trigger when complete, the UE may support and be configured with UE-based TA measurement, whereby the UE acquires the TA value(s) of the candidate cell(s) by measurement.

[0145] Switching off CSI reporting. The UE may be allowed, or required, to switch off CSI reporting to reduce reporting overhead in the uplink. The CSI reporting may be reduced rather thanswitched off (for example, reduced number of cells or beams reporting, or a reduced reporting frequency). The UE may resume CSI reporting when the condition is no longer met.

[0146] Performing LTM cell switch. There are conditions or criteria under which the UE is allowed to trigger LTM cell switch.

[0147] Monitoring PDCCH on a target cell. The UE may be configured to monitor on a target cell for a DCI scheduling PDSCH or indicating one or more actions on the target cell, for example to initiate the cell switch procedure.

[0148] Performing BFR or RLM on a target cell. The UE may be configured to monitor Beam Failure Detection (BFD) resources on a target cell or to perform Radio Link Monitoring (RLM) on a target cell during the window.

[0149] Activating or deactivating certain SCells. The UE may be configured with one or more specific SCells which should be active or not active during the window.

[0150] RACH-less CHO and early TA acquisition

[0151] To enable RACH-less conditional handover (CHO), whereby the UE is not required to send a random access preamble or perform a random access procedure on the target cell following a reconfiguration trigger, but rather whereby the UE performs PDCCH reception and uplink transmission using the TA already provided, the UE may perform an early TA acquisition procedure with a candidate cell(s) before receiving the cell switch command or before triggering a conditional reconfiguration.

[0152] In one embodiment, early TA acquisition may be performed using contention-free random access (CFRA) triggered by a PDCCH order from the source cell, following which the UE may send a preamble towards a candidate cell. The information that identifies the allocated CFRA resource may be indicated in the PDCCH order to enable shared preamble resource among multiple UEs in the RRC configuration. The source gNB dynamically indicates which UE uses the resource at any specific time.

[0153] In one embodiment, early TA acquisition may be performed upon receiving a MAC CE indicating to perform a RACH transmission on a target cell.

[0154] In one embodiment, this may be performed by transmitting using a contention-based random access (CBRA) preamble.

[0155] In one embodiment, and in order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the UE does not receive RAR at all. The source cell may trigger a preamble retransmission / power ramping using another PDCCH order, e.g. if the preamble was not received. In this case, the TA may be provided from the target cell to the source cell, andprovided to the UE in a MAC CE triggering cell switch or enabling conditional LTM to one or more target cells.

[0156] In one embodiment, the UE may receive a TA value from the target cell in a randomaccess response (RAR). In one embodiment, the UE may receive a TA value from the source cell in a random-access response (RAR). If the UE does not receive a RAR in response to transmitting the preamble (e.g., within a prescribed time), the UE may retransmit a preamble using a higher transmission power.

[0157] In one embodiment, the UE may store the received TA value to be used later when a reconfiguration trigger occurs. The UE may store the TA value for a limited period of time (e.g., a validity timer) and may trigger or be triggered to perform a new TA acquisition procedure when the time expires.

[0158] In one embodiment, the UE may receive and / or store multiple TA values respectively associated with more than one cell.

[0159] In one embodiment the UE may obtain the TA value of the target cell by measurement.

[0160] If the UE has stored a valid TA value of a candidate cell when a cell switch is triggered towards that candidate cell (either triggered by the NW using an explicit cell switch command, or triggered by the UE upon meeting a trigger condition), then the UE performs a RACH-less handover. For example, the UE may execute LTM (e.g. apply a pre-configured RRC configuration to a new SpCell) upon determining that a measured radio quality of the target cell is above a threshold.

[0161] The UE may support and be configured with UE-based TA measurement, whereby the UE acquires the TA value(s) of the candidate cell(s) by measurement. If the cell switch command does not contain a TA value, and the UE has acquired a TA measurement, the UE performs a RACH-less handover if it has been configured to do so by RRC.

[0162] TA Validity

[0163] The UE may determine a received / stored TA to be valid based upon any one of a validity timer pre-configured to be used with TA value, a validity timer received with the TA value, a condition on the DL cell timing of the source cell and the DL cell timing of the candidate cell for which TA is received / stored (e.g., the UE may consider the TA valid while the difference of the DL cell timing of the source and candidate cell is less than a configured threshold; the UE may consider the TA valid while the difference of the DL cell timing of the source and candidate cell is within a configured range), a condition on the DL cell timing of the candidate cell (e.g., the UE may consider the TA valid if the difference of the DL cell timing of the target cell at the time of the TA reception is not different by more than a certain configured value / range than the currentDL cell timing of the same target cell), a condition on the UE mobility (e.g., a UE may consider the TA valid if it is static (not moving) or moving below a certain configured speed threshold), a condition on the UE location (e.g., a UE may consider the TA valid if it has determined that it has not changed its location by more than a certain configured threshold (e.g., x meters) after the TA acquisition), and a condition that a UE-based TA measurement is available and a cell quality or beam quality measurement is above a threshold.

[0164] UE based TA calculation report

[0165] In one embodiment, the UE may trigger an event when a UE-based TA acquisition has been completed, and may for example transmit a MAC CR, CSI, or other uplink indication to the source cell or the candidate cell when a TA has been obtained based on UE measurement.

[0166] In one embodiment, the UE may trigger an event based on a measurement criterion (e.g. RSRP or any of the other triggers listed above) and may send the corresponding report only if a TA has additionally been obtained, for example a TA is available due to a prior UE-based TA acquisition. In one embodiment, a report or an LTM execution trigger caused due to a measurement-based event or trigger may be delayed until a UE-based TA acquisition is completed. That is, a measurement event (e.g. a beam RSRP is above a threshold) may cause the UE to initiate a UE-based TA acquisition, and the trigger is executed when both the measurement event is satisfied and the TA has been obtained.

[0167] In one embodiment, in response to receiving a report from the UE (e.g. UE-based TA acquisition has been performed and a beam or cell measurement is above a threshold), the network may transmit to the UE a command to enable conditional LTM evaluation, for example in a MAC CE. The UE may receive the command and may, based on the content of the command, enable conditional LTM evaluation based on determination of one or more measurement conditions.

[0168] Beam refinement on a target cell before or during handover

[0169] The UE may perform beam refinement on a target cell before or during a handover and before the UE accesses the target cell, such that a UE first performs measurement of SSB resources, then selects a subset of CSI-RS resources to measure based on the SSB measurements (e.g., based on the best SSB measured). Then the UE may perform measurements on the selected subset of CSLRS resource and determine a best CSI-RS resource. The selected best CSI-RS resource can be indicated before a handover takes place (e.g., to a source cell) or upon initial access (e.g., to a target cell), rather than performing the beam refinement only after a connection to a target cell is completed.

[0170] Reporting CSI-RS measurements

[0171] The UE may report the measurements of the subset of CSI-RS resources using CSI reporting on PUCCH to the source cell. The report may alternatively be transmitted using a MAC CE, an RRC measurement report, or any other type of uplink signaling. The report may contain one or more of RSRP (beam or cell), RSRQ (beam or cell), cri-RI-PMI-CQI, cri-RI-il, cri-RI-il- CQI, cri-RI-CQI, cri-RSRP, ssb-Index-RSRP, and cri-RI-LI-PMI-CQI.

[0172] Enabling CSI-RS measurements

[0173] The UE may determine, based on a trigger, a subset of CSI-RS to measure. For example, the UE may determine based on a pre-configured association (e.g., configured by RRC) between SSB and CSI-RS resources. The UE may determine a best SSB, based on an indication of an SSB or from performed SSB measurements.

[0174] The subset of CSI-RS may be indicated explicitly in a random access response (e.g., using a pointer to one of multiple subsets) or may be indicated implicitly (e.g., the UE enables a subset of CSI-RS depending on a reported or indicated SSB when the RAR is received). The UE may alternatively enable the subset of CSI-RS measurements when the UE receives a PDCCH order triggering early TA acquisition, while the RAR or MAC CE containing a TA in response to the PRACH preamble transmission for TA acquisition activates the configured grant.

[0175] The CSI-RS measurements may be configured temporarily. For example, the UE may activate CSI-RS measurements for a certain time period, or a certain number of reports, which may be configured or predefined. The UE may deactivate CSI-RS measurements, for example, when a best SSB changes, or when a SSB or CSI-RS measurement goes below a threshold.

[0176] Configured grant activation

[0177] The UE may receive an indication to activate a grant from either a source or a target cell. This may for example be a type 2 configured grant, whereby the first cell configures the grant, and the second cell activates the grant, an explicit grant (a direct indication of the grant to use), a pointer to one or more preconfigured grants (e.g. previously configured by RRC).

[0178] An indication of the grant may be a pointer to a configured grant corresponding to a reported SSB or may be a set of configured grants corresponding to multiple CSI-RS associated with a reported SSB.

[0179] The configured grant activation may be received in a PDCCH order (e.g., triggering TA acquisition), in a MAC CE (e.g., triggering LTM), or in a RAR (e.g., received from the source or the target, containing a TA value to use for RACH-less handover).

[0180] The UE may autonomously activate a configured grant based on a condition, for example, any of the LTM execution triggers already listed.

[0181] Determining a PUCCH resource to transmit on

[0182] In addition to LTM candidate configurations and downlink measurement resource configuration (e.g., SSB, CSI-RS), the UE may be configured with PUCCH resources for one or more LTM candidates, for example in an RRC Reconfiguration message. The PUCCH resources for an LTM candidate may be configured with an association with one or more downlink measurement resources. For example, one or more PUCCH resources may be associated with each of the downlink measurement resources, such that at least one PUCCH resource may be selected based on identifying a best measurement resource.

[0183] The UE may determine, based on downlink measurements, a best one or more beams (e.g., SSB, CSLRS measurement) in a candidate LTM cell. The UE may then select a corresponding PUCCH resource to use based on the association with the best measured beam. In some embodiments, the UE selects the PUCCH resource autonomously based on the best measured beam. In some embodiments, the UE reports measurements to a source cell (e.g., CSI report, MAC CE, or RRC measurement report), then receives an indication (e.g., in a MAC CE) of a target beam. Based on the indicated target beam the UE may then select an associated PUCCH resource. The indication of PUCCH resource may be provided explicitly by the source cell, for example in a MAC CE providing a TA value to the UE. The UE may determine the PUCCH to use based on a PDCCH order from the source cell (for example, a PDCCH order which may indicate to the UE to perform a RACH transmission to a target cell for the purpose of TA measurement may include an indication of a downlink beam, and that downlink beam may be associated with a PUCCH resource.

[0184] When the condition is met for performing a handover, the UE may then transmit on the determined PUCCH resource. This enables the target gNB to know that the condition for cell switch was met, and for which beam the gNB should schedule further transmissions. The gNB may then respond and transmit a DCI to the UE. The UE may receive a DCI which either activates a configured grant (e.g., type2 CG) or may explicitly schedule the UE to perform transmission and / or reception (e.g., transmit a RRC Reconfiguration complete message on PUSCH).

[0185] The PUCCH configuration may be a new type of uplink control information, used specifically for indicating a conditional LTM trigger has been met. The uplink control information may include a payload portion used for indicating information related to the event, for example event ID, source cell, cells or beams above a threshold (e.g., 1 bit per beam, measured to be above a configured threshold), timing information (e.g., synchronization information) or cell quality information (e.g., CQI of the target cell, or beam RSRP of the best one or more beams).

[0186] The PUCCH may alternatively be a scheduling request using one of the known formats and using a specific resource configuration. The PUCCH SR may be multiplexed with other uplink control information, for example a SR may be sent multiplexed with a CQI.

[0187] In some embodiments, the association between PUCCH resource and downlink beams may be controlled dynamically. For example, the UE may receive a configuration of multiple potential associations for a particular cell (e.g., multiple SSB vs. PUCCH associations) and then receive one or more indications (e.g., in a MAC CE) to indicate which are active or enabled at any particular time.

[0188] Further details regarding the method illustrated in FIG. 3 will now be provided.

[0189] In step S302, the UE receives, from the network (e.g., BS), information indicative of a configuration. Upon reception of the information, the UE may configure itself accordingly.

[0190] The information may for example be received in a RRC Reconfiguration message. The information may identify LTM candidates. The information may also identify PUCCH resources (e.g., SR resource) associated with downlink beams (e.g., SSB) and a condition for performing LTM execution (e.g. any trigger described in "LTM Execution Trigger"). In some embodiments, the event ID associated with the conditional reconfiguration determines the PUCCH resource to select (e.g. if more than one event is configured with a conditional reconfiguration, the UE may select the associated PUCCH).

[0191] The PUCCH resource may additionally depend on one or more of timing information (e.g., SFN of the target cell, a time during which the event was satisfied, or in case of multiple events requiring to be satisfied, a time between the first and the second event being met (e.g. a first event may be defined based on cell quality, and a second event may be defined based on beam quality)), a priority associated with cells or beams, a priority associated with ongoing services or data, latency or throughput requirement, CG availability, and an explicit indication in DCI or MAC CE (e.g., Preconfigure the PUCCH resources, and dynamic indication of which resources are enabled or active).

[0192] In step S304, the UE performs measurements on downlink beams, evaluates the measurements and determines a TA value for a target cell. Based on the configuration in step S302, the UE performs measurements of the configured candidate cells and / or beams (e.g. as described in "LTM Execution Trigger"). The TA value can be determined as described in "RACH-less CHO and early TA acquisition".

[0193] In case a configured condition for executing LTM is met for an LTM candidate cell, i.e., in case a trigger is met, in step S306, the UE determines, based on its configuration, a PUCCHresource. The PUCCH resource can, as mentioned, be associated with the beam which has been determined to have the best signal quality (e.g., beam RSRP).

[0194] In step S308, the UE transmits an indication using the determined PUCCH resource. The indication can convey that a condition has been met for LTM cell switch, and indicate to the network (e.g., BS and / or gNB) the best beam(s) and the condition that has been met.

[0195] In step S310, the UE receives an indication on PDCCH. For example, the received indication may indicate PDCCH scheduling information. Based on the PUCCH indication in step S308, the UE monitors for and receives an indication on PDCCH. The PDCCH indication may include one or more of a dynamic scheduling providing a grant to transmit RRC complete message, a type 2 CG activation and an indication of beam refinement (e.g., one or more CSI-RS to measure and report ahead of or during the transmission of a handover completion message).

[0196] In step S312, the UE transmits information indicative of RRC Reconfiguration complete on the indicated PUSCH resource (CG or dynamic).

[0197] In some embodiments, if the grant is sufficient, the UE may cancel the SR based on reception of a PDCCH scheduling an uplink transmission (e.g., for a subsequent transmission following the RRC complete message, or for the transmission of the RRC complete message, or for activation of a configured grant).

[0198] In some embodiments, a conditional trigger may occur for more than one beam or cell (for example, if the trigger condition is met when the measured signal quality goes above a threshold. In this embodiment, the UE may attempt to send an SR (or other PUCCH indication) to one cell (e.g. the best cell or the cell with the best beam).

[0199] In some embodiments, the UE may determine that the attempted cell has failed (e.g., due to no response within a certain time) and may then proceed to send an SR to another cell (e.g., the second best cell).

[0200] In some embodiments, if the UE does not receive a response on the first cell, the UE may send on PUCCH resources corresponding to a plurality (e.g., all) of the other cells or beams satisfying a condition.

[0201] In some embodiments, the UE may send to one or multiple targets based on certain criteria, such as relative measurements (e.g., if one cell or beam has a measured signal quality which is better than the second best cell by a relative quality threshold, then the UE may transmit to one cell only, otherwise the UE may send on more than one cell), or such as the periodicity of a corresponding PUCCH resource (for example if the PUCCH resources are configured with a relatively long periodicity then the UE may transmit on cells according to which SR resources are available sooner).

[0202] In some embodiments, the UE may monitor multiple PDCCH resources corresponding to the multiple PUCCH resources which the UE transmitted on.

[0203] In some embodiments, the UE may attempt PUCCH transmission once, or for a limited number of times (e.g., N times), or until expiry of a timer, before determining RACH-less conditional Handover (HO) has failed, and therefore transmit a random access preamble instead.

[0204] In some embodiments, the UE may be configured with an additional condition for selecting whether to perform RACH-less CHO, or performing a RACH based CHO, or for reporting LI measurement reporting to the source cell. For example, if the cell quality of a target is above a threshold and / or a TA value is available, then perform RACH-less CHO; conversely, if below the threshold, then perform RACH-based CHO.

[0205] In some embodiments, the UE may determine based on a QoS characteristic of traffic or configured services whether to perform RACH-less conditional LTM or another mobility method.

[0206] In some embodiments, a TA validity time threshold determined whether to transmit on PUCCH or on RACH (e.g., if the TA is about to expire, then use RACH based handover).

[0207] In some embodiments, the selected PUCCH resources may be configured on a source cell. That is, different PUCCH resources correspond to different target cells and beams, and the UE indicated the condition has been met to the source cell before attempting to receive PDCCH or use a CG for PUSCH transmission on the target cell.

[0208] In some embodiments, the UE indicates using a PUCCH resource or a MAC CE to the source cell and receives activation of a (e.g., type 2) configured grant in the target cell from the source cell before the UE performs cell switch. In some solutions, the UE may determine whether to transmit on a PUCCH resource on the target, or whether to transmit an indication on the source, based on a condition (e.g., measured signal quality of the source cell). In some solutions, once a configured grant selected or activated on the target / best beam, the UE may determine whether the configured grant is within a certain time. If the configured grant is determined to be within the certain time, then the reconfiguration complete can be transmitted using the configured grant. If the configured grant is not within the certain time, then the RRC complete may be indicated to the source cell (e.g., using a PUCCH Resource or MAC CE).

[0209] In some embodiments, one PUCCH resource may correspond to multiple downlink beams or cells. For example, a PUCCH resource in one cell belonging to one DU may be used to indicate the beam quality of any cell belonging to that DU. The PUCCH indication would in this case include an explicit indication of the best beam or cell.

[0210] In some embodiments, multiple thresholds may be provided which need to be satisfied before performing certain steps. For example, a first threshold may be used for determiningwhether to transmit a PUCCH indication to the target cell, which may activate a configured grant. A second threshold may be used to determine when to complete the cell switch and transmit using the configured grant.

[0211] 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 as illustrations 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.

[0212] The foregoing embodiments are discussed, for simplicity, with regard to the terminology and structure of infrared capable devices, i.e., infrared 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.

[0213] 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 headmounted 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.

[0214] 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 computer or 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.

[0215] 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.

[0216] 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."

[0217] 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 databits. 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.

[0218] 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, which exist 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.

[0219] 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.

[0220] 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 trade-offs. 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.

[0221] 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 someaspects 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 skill of 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.).

[0222] 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.

[0223] 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 maybe 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.

[0224] 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.

[0225] 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 havingskill 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 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.). 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".

[0226] 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.

[0227] 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.

[0228] 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 at a wireless transmit / receive unit, WTRU, the method comprising: performing measurements of respective downlink beams associated with at least one initial candidate cell for handover; determining, based on the measurements, a selected candidate cell for handover among the at least one initial candidate cell; transmitting, using an uplink control channel resource, information indicative of the selected candidate cell as target cell; and transmitting information indicating complete handover.

2. The method of claim 1, comprising: determining respective timing advance values for the at least one initial candidate cell for handover; and wherein the information indicative of the selected candidate cell as target cell is transmitted to the selected candidate cell using the uplink control channel resource and the timing advance value of the selected candidate cell.

3. The method of claim 1 or 2, comprising: receiving, from the selected candidate cell on a downlink control channel, an indication of an uplink shared channel; and wherein information indicating complete handover is transmitted on the uplink shared channel.

4. The method of claim 3, wherein the information indicative of the selected candidate cell as target cell is transmitted to a cell currently serving the WTRU.

5. The method of claim 4, comprising: in response to transmitting the information indicative of a selected candidate cell as target cell, receiving information indicative of an activation of the uplink shared channel.

6. The method of any one of claims 3-5, wherein the uplink shared channel is associated with a dynamic grant.

7. The method of any one of claims 3-5, wherein the uplink shared channel is associated with a configured grant.

8. The method of any one of claims 1-7, wherein the selected candidate cell for handover is determined upon occurrence of a trigger event for at least one candidate cell for handover.

9. The method of any one of claims 1-8, wherein the selected candidate cell is the initial candidate cell whose measured beam quality is the highest of the at least one initial candidate cell.

10. The method of any one of claims 1-9, comprising: receiving information indicative of the at least one initial candidate cell for handover, the information comprising, for each initial candidate cell for handover, at least one uplink control channel resource associated with downlink beams, and a condition for performing handover.

11. The method of any one of claims 1-10, wherein the handover is a layer 2 mobility handover.

12. The method of any one of claims 1-3, wherein the uplink control channel resource is a scheduling request transmitted to a cell currently serving the WTRU.

13. A wireless transmit / receive unit, WTRU, comprising at least one processor configured to: perform measurements of respective downlink beams associated with at least one initial candidate cell for handover; determine, based on the measurements, a selected candidate cell for handover among the at least one initial candidate cell; transmit, using an uplink control channel resource, information indicative of the selected candidate cell as target cell; and transmit information indicating complete handover.

14. The WTRU of claim 13, wherein the at least one processor is configured to: determine respective timing advance values for the at least one initial candidate cell for handover; and transmit the information indicative of the selected candidate cell as target cell to the selected candidate cell using the uplink control channel resource and the timing advance value of the selected candidate cell.

15. The WTRU of claim 13 or 14, wherein the at least one processor is configured to: receive, from the selected candidate cell on a downlink control channel, an indication of an uplink shared channel; and wherein information indicating complete handover is transmitted on the uplink shared channel.

16. The WTRU of claim 15, wherein the information indicative of the selected candidate cell as target cell is transmitted to a cell currently serving the WTRU.

17. The WTRU of claim 16, wherein the at least one processor is configured to: in response to transmitting the information indicative of a selected candidate cell as target cell, receive information indicative of an activation of the uplink shared channel.

18. The WTRU of any one of claims 15-17, wherein the uplink shared channel is associated with a dynamic grant.

19. The WTRU of any one of claims 15-17, wherein the uplink shared channel is associated with a configured grant.

20. The WTRU of any one of claims 13-19, wherein the at least one processor is configured to determine the selected candidate cell for handover upon occurrence of a trigger event for at least one candidate cell for handover.

21. The WTRU of any one of claims 13-20, wherein the selected candidate cell is the initial candidate cell whose measured beam quality is the highest of the at least one initial candidate cell.

22. The WTRU of any one of claims 13-21, wherein the at least one processor is configured to: receive information indicative of the at least one initial candidate cell for handover, the information comprising, for each initial candidate cell for handover, at least one uplink control channel resource associated with downlink beams, and a condition for performing handover.

23. The WTRU of any one of claims 13-22, wherein the handover is a layer 2 mobility handover.

24. The WTRU of any one of claims 13-15, wherein the uplink control channel resource is a scheduling request transmitted to a cell currently serving the WTRU.

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