WO2025035109A1

WO2025035109A1 - Selection of rach procedure to perform for handover execution

Info

Publication number: WO2025035109A1
Application number: PCT/US2024/041748
Authority: WO
Inventors: Brian Martin; Oumer Teyeb; Paul Marinier; Erdem Bala; Keiichi Kubota; Martino M. Freda; Umer Salim; Dylan WATTS
Original assignee: InterDigital Patent Holdings Inc
Current assignee: InterDigital Patent Holdings Inc
Priority date: 2023-08-10
Filing date: 2024-08-09
Publication date: 2025-02-13
Anticipated expiration: 2026-02-10

Abstract

Systems, methods, and instrumentalities are described for selecting a random access channel (RACH) procedure for handover (HO) execution. A wireless transmit/receive unit (WTRU) may receive configuration information from a first cell indicating mobility candidate cells and a conditional handover (CHO) based on timing advance (TA) validity. The WTRU may transmit channel state information (CSI) to the first cell, receive a physical downlink control channel (PDCCH) order, and obtain a TA value. The WTRU may prioritize the first candidate cell for handover and perform a RACH-less handover, sending a reconfiguration complete indication to the first candidate cell.

Description

SELECTION OF RACH PROCEDURE TO PERFORM FOR HANDOVER EXECUTION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of provisional U.S. patent application No. 63/531 ,931 , filed August 10, 2023, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Mobile communications using wireless communication continue to evolve. A fifth generation may be referred to as 5G. A previous (legacy) generation of mobile communication may be, for example, fourth generation (4G) long term evolution (LTE).

SUMMARY

[0003] Systems, methods, and instrumentalities are described herein related to selecting a random access channel (RACH) procedure for performing handover (HO) execution. A wireless transmit/receive unit (WTRU) may receive, from a first cell, configuration information that indicates mobility candidate cells and a first configuration of a first conditional handover (CHO) associated with a first condition for a first random access channel (RACH)-less handover that is based on a first candidate cell timing advance (TA) validity duration. The mobility candidate cells may include at least a first candidate cell and a second candidate cell. The WTRU may transmit a report comprising channel state information (CSI) information to the first cell. The WTRU may receive a physical downlink control channel (PDCCH) order from the first cell. The WTRU may receive, based on the PDCCH order, a first candidate cell TA value for the first candidate cell. The WTRU may perform measurements on the first candidate cell and the second candidate cell. Based on the measurements and based on the first condition being met before expiration of the first candidate cell TA validity duration, the WTRU may prioritize the first candidate cell over the second candidate cell for handover execution. The WTRU may perform a conditional cell switch from the first cell to the first candidate cell by performing the first RACH-less handover. The WTRU may, based on performing the conditional cell switch, send, to the first candidate cell, a reconfiguration complete indication.

[0004] The PDCCH order may include a random access (RA) resource and the first candidate cell TA validity duration. The reconfiguration complete indication may be sent to the first candidate cell in a radio resource control message (RRC). The first candidate cell may include a first target cell, and the second candidate cell may include a second target cell. The WTRU may prioritize the first candidate cell over the second candidate cell for handover execution based on the second candidate cell lacking a second candidate cell TA value, or a second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration.

[0005] Prioritizing the first candidate cell over the second candidate cell for handover execution based on the second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration may include the WTRU receiving a second configuration of a second conditional handover (CHO) associated with a second condition for a random access channel (RACH)-less handover that is based on the second candidate cell timing advance (TA) validity duration. The first condition may be met based on the first candidate cell TA value being valid before expiration of the first candidate cell TA validity duration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 A is a system diagram illustrating an example communications system in which one or more disclosed embodiments may be implemented.

[0007] FIG. 1 B is a system diagram illustrating an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A according to an embodiment.

[0008] FIG. 1 C 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 according to an embodiment.

[0009] FIG. 1 D 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. 1A according to an embodiment.

[0010] FIG. 2 illustrates an example of a measurement model.

[0011] FIG. 3 illustrates an example of LTM using carrier aggregation (CA).

[0012] FIG. 4 illustrates an example of performing an LTM.

[0013] FIG. 5 illustrates an example flowchart for the selection of a RACH procedure to perform for HO execution.

[0014] FIG.6 illustrates an example of triggering a RACH-less handover on a first cell before the completion of a RACH procedure on a second cell.

DETAILED DESCRIPTION

[0015] FIG. 1A is a 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), single-carrier FDMA (SC-FDMA), zero-tail unique-word DFT-Spread OFDM (ZT UW DTS-s OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like.

[0016] As shown in FIG. 1A, the communications system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a RAN 104/113, a ON 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 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.

[0017] 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 to facilitate access to one or more communication networks, such as the CN 106/115, the Internet 110, and/or the other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a gNB, a (e.g., new) radio (NR) NodeB, 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.

[0018] 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 one 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 sector of the cell. For example, beamforming may be used to transmit and/or receive signals in desired spatial directions.

[0019] 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).

[0020] 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 115/116/117 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink (DL) Packet Access (HSDPA) and/or High-Speed uplink (UL) Packet Access (HSUPA).

[0021] 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).

[0022] 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).

[0023] 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).

[0024] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, 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.

[0025] 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 one 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 yet another 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 a picocell or femtocell. As shown in FIG. 1A, 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.

[0026] 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. 1A, 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 a NR radio technology, the CN 106/115 may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

[0027] 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 the 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 104/113 or a different RAT.

[0028] 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.

[0029] FIG. 1 B is a system diagram illustrating an example WTRU 102. As shown in FIG. 1 B, 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 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.

[0030] 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. 1 B 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 in an electronic package or chip.

[0031] 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 one 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 yet another 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.

[0032] Although the transmit/receive element 122 is depicted in FIG. 1 B as a single element, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one 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.

[0033] 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.

[0034] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128. In addition, the processor 118 may access information from, and 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), read-only 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).

[0035] 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.

[0036] 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 locationdetermination method while remaining consistent with an embodiment.

[0037] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (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 peripherals 138 may include one or more sensors, the sensors may be one or more of a gyroscope, an accelerometer, a hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor; an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and/or a humidity sensor.

[0038] 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 UL (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 WRTU 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 UL (e.g., for transmission) or the downlink (e.g., for reception)).

[0039] FIG. 1 C 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, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0040] 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 one 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/or receive wireless signals from, the WTRU 102a. [0041 ] Each of the eNode-Bs 160a, 160b, 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 UL and/or DL, and the like. As shown in FIG. 1 C, the eNode-Bs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0042] The CN 106 shown in FIG. 1 C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (or PGW) 166. While each of the foregoing elements are depicted as part of the CN 106, it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator.

[0043] The MME 162 may be connected to each of the eNode-Bs 160a, 160b, 160c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and/or WCDMA.

[0044] The SGW 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via the S1 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.

[0045] 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.

[0046] 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.

[0047] Although the WTRU is described in FIGS. 1 A-1 D 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. [0048] In representative embodiments, the other network 112 may be a WLAN.

[0049] 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 in to and/or out of the BSS. Traffic to STAs that originates from outside the BSS may arrive through the AP and may be delivered to the STAs. Traffic originating from STAs to destinations outside the BSS may be sent to the AP to be delivered to respective destinations. Traffic between STAs within the BSS may be sent through the AP, for example, where the source STA may send traffic to the AP and the AP may deliver the traffic to the destination STA. The traffic between STAs within a BSS may be considered and/or referred to as peer-to- peer traffic. The peer-to-peer traffic may be sent between (e.g., directly between) the source and destination STAs with a direct link setup (DLS). In certain representative embodiments, the DLS may use an 802.11e DLS or an 802.11 z tunneled DLS (TDLS). A WLAN using an Independent BSS (I BSS) 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.

[0050] When using the 802.11 ac 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.

[0051] 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 nonadjacent 20 MHz channel to form a 40 MHz wide channel.

[0052] Very High Throughput (VHT) STAs may support 20MHz, 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 the Medium Access Control (MAC).

[0053] Sub 1 GHz modes of operation are supported by 802.11af and 802.11 ah. The channel operating bandwidths, and carriers, are reduced in 802.11 af and 802.11 ah relative to those used in 802.11 n, and

802.11 ac. 802.11 af supports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11 ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non- TVWS spectrum. According to a representative embodiment, 802.11 ah may support Meter Type Control/Machine-Type Communications, 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).

[0054] WLAN systems, which may support multiple channels, and channel bandwidths, such as

802.11 n, 802.11 ac, 802.11 af, and 802.11 ah, 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 802.11 ah, 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.

[0055] In the United States, the available frequency bands, which may be used by 802.11 ah, 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

802.11 ah is 6 MHz to 26 MHz depending on the country code.

[0056] FIG. 1 D 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 [0057] 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 one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, gNBs 180a, 108b may utilize beamforming to transmit signals to and/or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a, for example, may use multiple antennas to transmit wireless signals to, and/or receive wireless signals from, the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit 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).

[0058] The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using transmissions associated with a scalable numerology. For example, the orthogonal frequency division multiplexing (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., containing varying number of OFDM symbols and/or lasting varying lengths of absolute time).

[0059] 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. [0060] 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 Function (UPF) 184a, 184b, routing of control plane information towards Access and Mobility Management Function (AMF) 182a, 182b and the like. As shown in FIG. 1 D, the gNBs 180a, 180b, 180c may communicate with one another over an Xn interface.

[0061] The CN 115 shown in FIG. 1 D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a 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.

[0062] 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 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 in order 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 machine type communication (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.

[0063] 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, Ethernetbased, and the like.

[0064] 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, 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 multi-homed PDU sessions, handling user plane QoS, buffering downlink packets, providing mobility anchoring, and the like.

[0065] 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 one 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.

[0066] In view of Figures 1A-1 D, and the corresponding description of Figures 1A-1 D, one or more, or all, of the functions described herein with regard to one or more of: WTRU 102a-d, Base Station 114a-b, eNode-B 160a-c, MME 162, SGW 164, PGW 166, gNB 180a-c, AMF 182a-b, UPF 184a-b, SMF 183a-b, DN 185a-b, and/or any other device(s) described herein, may be performed by one or more emulation 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.

[0067] 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 perform testing using over-the-air wireless communications.

[0068] 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 testing 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. [0069] Reference to a timer herein may refer to a time, a time period, a tracking of time, a tracking of a period of time, a combination thereof, and/or the like. Reference to a timer expiration herein may refer to determining that the time has occurred or that the period of time has expired.

[0070] As used herein, the term SpCell may refer to the PCell of the master cell group (MCG) or the Primary SCG Cell (PSCell) of the SCG, for example, depending on whether the MAC entity is associated with the MCG or the SCG.

[0071] Systems, methods, and instrumentalities are described herein related to early timing advance (TA) acquisition for a random access channel (RACH)-less conditional handover (CHO) . A device may (e.g., be configured to) do one or more of the following actions. A wireless transmit/receive unit (WTRU) may perform RACH-less CHO evaluation based on a valid TA. A WTRU may trigger early TA acquisition for RACH-less CHO/conditional L1/L2 triggered mobility (LTM). A WTRU may select a RACH procedure to perform for handover (HO) execution.

[0072] Systems, methods, and instrumentalities are described herein related to a random access channel-less (RACH-less) conditional handover (CHO) evaluation based on valid timing advance (TA). A device may (e.g., be configured to) do one or more of the following actions. A wireless transmit/receive unit (WTRU) may be configured with a conditional handover that is applicable for a given target cell (e.g., only) while the WTRU has a valid TA for the target cell. The WTRU may receive a RACH-less conditional handover configuration that uses the TA validity to determine whether the RACH-less handover and the associated conditions are applicable/valid. The conditional RACH-less handover may be enabled for L1/L2 triggered mobility (LTM), for example, if/when a medium access control (MAC) control element (CE) indicates a TA and a validity duration for RACH-less handover conditional triggering.

[0073] A WTRU may receive a configuration of LTM candidate cells and/or a configuration of RACH-less CHO. The configuration(s) may indicate, for example, one or more of the following: an L3 event for one or more target cells; an L1 measurement-based event; one or more (e.g., specific) measurement resources; RACH-less (e.g., specific) trigger conditions, which may consider (e.g., only) cells with a valid TA; one or more (e.g., specific) resources (e.g., configured grant) to use when executing a conditional LTM (e.g., separate to explicit LTM trigger resources); a CHO configuration, which may include a first condition for execution if/when RACH-less is used (e.g., if/when WTRU has valid TA for this target) and a second condition for execution otherwise. A CHO configuration may include multiple (e.g., two) thresholds, such as one threshold used if/when a WTRU may have TA and another threshold used otherwise. A CHO configuration may include alternati ve/different times to trigger and/or filtering parameters, for example, so that RACH-less can be triggered more quickly. A CHO configuration may include multiple (e.g., two) CHO configurations. For example, cells for which WTRU has TA may be evaluated in the first CHO configuration and other cells may be evaluated in the second CHO configuration. A CHO configuration may include multiple levels (e.g., three or more levels), such as RACH-less, 2-step, 4-step, contention-based random access (CBRA), and contention-free random access (CFRA).

[0074] The WTRU may transmit channel state information (CSI) reporting.

[0075] The WTRU may receive a physical downlink control channel (PDCCH) order. The WTRU may transmit a preamble to a target cell.

[0076] The WTRU may receive conditional cell switch indication, which may include a TA value, a validity time, and/or an indication to perform the cell switch when the CHO condition is met within the validity time.

[0077] In some examples, a WTRU may perform PDCCH reception, preamble transmission, and conditional cell switch indications multiple/several times, for example, to enable CHO to more than one target in parallel.

[0078] In some examples, a WTRU may perform PDCCH reception and preamble transmission multiple/several times, while a conditional cell switch indication may include a TA/CHO enabler for multiple targets.

[0079] In some examples, a WTRU may perform PDCCH reception and preamble transmission on a (e.g., one) target cell within a configured timing advance group (TAG). The acquired TA may enable a RACH-less CHO to a (e.g., any) cell within the TAG.

[0080] FIGS. 6-8 show examples of obtaining a TA. Other examples of obtaining a TA may include, for example, a random access response (RAR) on a target cell, a RAR on a source, and a WTRU maintaining the TA. A MAC CE may or may not be used to “enable” the CHO. A CHO may depend on having the TA, which may be obtained by any method. A configuration may be activated/deactivated, for example, using a MAC CE.

[0081] The WTRU may measure one or more configured target cells. In some examples, the measurements may be performed on (e.g., all) cells within a TAG for which the TA is valid.

[0082] The WTRU may execute LTM (e.g., apply the pre-configured candidate configuration), for example, if the RACH-less CHO condition is met for one or more (e.g., any) of the cells configured with a TA value before the expiry of the validity timer. CHO conditions (e.g., other CHO conditions) may include, for example, a synchronization signal block (SSB), a reference signal received power (RSRP) threshold, a timing comparison, etc. The configured grant (CG) associated with the beam (e.g., best beam) triggering the CHO may be used. A CHO may no longer be valid, and the configuration may be released, for example, if the timer (e.g., TA validity timer) expires. The next CHO evaluation may occur, for example, if/when a new TA command is received. The WTRU may use a second condition (e.g., a different CHO configuration corresponding to a RACH-based CHO for if/when the WTRU does not have a valid TA), for example, if the timer expires.

[0083] The WTRU may send an indication to the target. For example, the WTRU may transmit an RRC complete message on a physical uplink shared channel (PUSCH). The WTRU may use the CG associated with the beam (e.g., best beam) triggering the CHO. The WTRU may monitor for an uplink grant on PDCCH. The WTRU may (e.g., then) transmit data and/or a radio resource control (RRC) complete message.

[0084] An example device may include a processor configured to perform one or more actions. For example, a device may receive, from a first cell, a configuration comprising mobility candidate cells, including first and second candidate cells, and a configuration of random access channel (RACH)-less conditional handover (CHO), including a RACH-less CHO condition. The device may perform, and report measurements of the mobility candidate cells to the first cell. The device may perform random access (RA) to the first candidate cell using an RA resource indicated by the first cell. The device may receive a conditional cell switch indication comprising a timing advance (TA) value and a TA validity time for the first candidate cell. The device may perform the conditional cell switch from the first cell to the first candidate cell if the RACH-less CHO condition is satisfied before the expiration of the TA validity time.

[0085] The configuration may include a configuration of a RACH-based CHO, including a RACH-based CHO condition. The device may perform the conditional cell switch from the first cell to the first candidate cell using RACH-based CHO if the RACH-based CHO condition is satisfied after the expiration of the TA validity time.

[0086] The configuration may indicate a timing advance group (TAG) for the first and second candidate cells (e.g., the TA value and TA validity time apply to the first and second candidate cells). The device may perform the conditional cell switch from the first cell to the second candidate cell if the RACH-less CHO condition is satisfied before the expiration of the TA validity time.

[0087] Systems, Methods, and instrumentalities are described herein related to wireless transmit/receive unit (WTRU) triggered early timing advance (TA) acquisition for random access channel (RACH)-less conditional handover (CHO)Zconditional L1/L2 triggered mobility (LTM). A device may (e.g., be configured to) do one or more of the following actions. A wireless transmit/receive unit (WTRU) may trigger early TA acquisition, which may be used for RACH-less CHO, based on a condition (e.g., in addition to the first condition for triggering the LTM execution). The condition evaluation may be enabled, for example, if/when the WTRU receives a physical downlink control channel (PDCCH) order indicating an RA resource and a validity duration for the RA resource. The WTRU may trigger a random access (RA), for example, if/when the condition is met, for example, to allow TA acquisition for the target. [0088] A WTRU may receive a configuration of LTM candidate cells and/or a configuration of RACH-less CHO (e.g., a first condition). The WTRU may receive a condition (e.g., a second condition) for triggering TA acquisition.

[0089] The WTRU may transmit channel state information (CSI) reporting.

[0090] The WTRU may transmit a request for a PDCCH order enabling the WTRU triggered TA acquisition/CHO. The request may be based on an event, for example, target is better than threshold. The request may be part of CSI reporting, for example, event-triggered reports.

[0091] The WTRU may receive the PDCCH order enabling WTRU-triggered TA acquisition. The PDCCH order may include an RA resource and/or an RA resource validity timer. There may be multiple (e.g., two) conditions. A first condition may be for a RACH to the target (e.g., an autonomous RA). The first condition may indicate, for example, a first threshold (threshold 1) and a valid physical random access channel (RACH) (PRACH) resource. The second condition may be to trigger the CHO. The second condition may indicate, for example, a second threshold (e.g., threshold 2) and a valid TA.

[0092] The WTRU may perform measurements on configured target(s).

[0093] The TA acquisition may be triggered if the TA acquisition condition (e.g., first condition) is met. The WTRU may transmit a PRACH preamble to the target if/when the TA acquisition is triggered. A request may be sent for a new PDCCH order. For example, if a PRACH resource becomes invalid (e.g., expires), a different PRACH resource (e.g., contention-based random access (CBRA)) may be used.

[0094] The WTRU may receive a TA value, enabling RACH-less CHO.

[0095] LTM may be executed (e.g., applying the pre-configured candidate configuration). For example, if the RACH-less CHO condition (e.g., second condition) is met for one or more (e.g., any) of the cells configured with a TA value before the expiry of the timer. A PDCCH order may disable/enable an LTM configuration.

[0096] The WTRU may send an indication to a target. For example, the WTRU may transmit a radio resource control (RRC) complete message on a physical uplink shared channel (PUSCH). The WTRU may use the CG associated with the best beam triggering the CHO. The WTRU may monitor for an uplink grant on PDCCH and (e.g., then) transmit data and/or an RRC complete message.

[0097] An example device may include a processor configured to perform one or more actions. For example, a device may receive, from a first cell, a configuration comprising mobility candidate cells, including a first candidate cell, a configuration of random access channel (RACH)-less conditional handover (CHO), including a RACH-less CHO condition, and a configuration for timing advance (TA) acquisition, including a TA acquisition condition. The device may perform, and report measurements of the mobility candidate cells to the first cell. The device may perform random access (RA) to the first candidate cell using an RA resource indicated by the first cell if the TA acquisition condition is satisfied. The device may receive a conditional cell switch indication comprising a TA value and a TA validity time for the first candidate cell. The device may perform the conditional cell switch from the first cell to the first candidate cell if the RACH-less CHO condition is satisfied before the expiration of the TA validity time.

[0098] The configuration may include a configuration of a RACH-based CHO, including a RACH-based CHO condition. The device may perform the conditional cell switch from the first cell to the first candidate cell using RACH-based CHO if the RACH-based CHO condition is satisfied after the expiration of the TA validity time.

[0099] The configuration may indicate a timing advance group (TAG) for the first and second candidate cells (e.g., the TA value and TA validity time apply to the first and second candidate cells). The device may perform the conditional cell switch from the first cell to the second candidate cell if the RACH-less CHO condition is satisfied before the expiration of the TA validity time.

[0100] Systems, methods, and instrumentalities are described herein related to selecting a random access channel (RACH) procedure for performing handover (HO) execution. A device may (e.g., be configured to) do one or more of the following actions. A wireless transmit/receive unit (WTRU) may prioritize which target to execute L1/L2 triggered mobility (LTM) towards, for example, depending on whether the WTRU may perform a RACH-less handover. A RACH-less conditional HO (CHO) may provide reduced interruption and/or robustness, for example, compared to a handover utilizing a RACH.

[0101] A WTRU may receive a configuration of LTM candidate cells and/or a configuration of CHO. A CHO configuration may include separate execution conditions, for example, depending on whether the WTRU has a valid timing advance (TA) or not (e.g., separate thresholds). A CHO configuration may include one or more conditions related to the remaining validity time (e.g., a first condition when the remaining validity time is above a threshold, and a second condition otherwise). A CHO configuration may include configuration of a type of RACH procedure to perform and/or conditions for selecting the type of RACH procedure to perform, for example depending on remaining TA validity time.

[0102] The WTRU may transmit channel state information (CSI) reporting.

[0103] The WTRU may receive a physical downlink control channel (PDCCH) order. The WTRU may transmit a preamble to a first target cell.

[0104] The WTRU may receive a TA value for the first cell.

[0105] The WTRU may perform measurement(s) on the configured LTM target(s), which may include at least the first cell, and may include a second cell (e.g., without a valid TA value). A second cell may have a valid TA with a remaining TA validity time, which may be less than the first cell’s remaining TA validity time. [0106] The WTRU may select the first cell. The WTRU may execute the CHO (e.g., RACH-less LTM execution) to the first cell based on a prioritization rule, for example, if the cell switch criteria is met for the first cell and the second cell. Example selection conditions/prioritization rules may include, for example, one or more of the following: an indication whether TA is valid or invalid; an indication to select the target with the longest remaining TA validity time; an indication to select the target configured for RACH-less as a priority over a target not configured for RACH-less; a selection condition may include an offset to the CHO criteria, for example, a cell configured for RACH-less may have a lower reference signal received power (RSRP) threshold; a selection condition may apply a shorter time to trigger (TTT) to the CHO criteria if the cell is configured for RACH-less; selection of the first cell may include aborting a reconfiguration procedure towards the second cell (e.g., abort and perform RACH-less to the first cell, for example, if the WTRU is performing preamble retransmission to perform a RACH procedure for HO to the second cell); and/or a selection prioritization rule may be applied if/when a conditional reconfiguration criteria is met for multiple cells or if multiple cells are performing different types of reconfiguration (e.g., an explicit reconfiguration versus a conditional reconfiguration).

[0107] The WTRU may send an indication to a target (first cell). For example, the WTRU may transmit a radio resource control (RRC) complete message on PUSCH. The WTRU may use the configured grant (CG) associated with the best beam triggering the CHO. The WTRU may monitor for an uplink grant on PDCCH. The WTRU may transmit data and/or an RRC complete message.

[0108] An example device may include a processor configured to perform one or more actions. For example, a device may receive, from a first cell, a configuration that may comprise mobility candidate cells, including first and second candidate cells, a configuration of random access channel (RACH)-less conditional handover (CHO), including a RACH-less CHO condition, and a configuration for cell switch prioritization. The device may perform, and report measurements of the mobility candidate cells to the first cell. The device may perform random access (RA) to the mobility candidate cells using an RA resource indicated by the first cell. The device may receive a first conditional cell switch indication comprising a timing advance (TA) value and a TA validity time for the first candidate cell. The device may receive a second conditional cell switch indication to the second candidate cell. The device may prioritize the first conditional cell switch over the second conditional cell switch based on the cell switch prioritization. The device may perform the first conditional cell switch from the first cell to the first candidate cell if the RACH- less CHO condition is satisfied before the expiration of the TA validity time.

[0109] The cell switch prioritization may prioritize the first conditional cell switch over the second conditional cell switch, for example, by prioritizing RACH-less CHO over RACH-based CHO and/or by prioritizing the remaining TA validity time. [0110] A WTRU (e.g., in RRC_CONNECTED) may measure multiple beams, for example, including at least one measurement of a cell. The measurement results (e.g., power values) may be averaged, for example, to derive the cell quality. The WTRU may be configured to consider a subset of the detected beams, for example, based on the determined cell quality. Filtering may occur at multiple (e.g., two) levels, such as at the physical layer to derive beam quality and at the RRC level to derive cell quality from multiple beams. Cell quality from beam measurements may be derived in the same way for the serving cell (s) and for the non-serving cell(s). Measurement reports may include the measurement results of the X best beams, for example, if the WTRU is configured to do so by the gNB. A corresponding high-level measurement model is shown in FIG. 2.

[0111] FIG. 2 illustrates an example of a measurement model.

[0112] Inter-cell L1/2 triggered mobility (LTM) may be implemented. Inter-cell beam management may be used to manage beams, for example, for carrier aggregation (CA). Cell change/addition may be supported, for example, as described herein.

[0113] L1/L2 based inter-cell mobility may be used for mobility latency reduction. Multiple candidate cells may be configured and maintained to allow fast application of configurations for candidate cells (e.g., in RAN2, RAN3). Dynamic switching among candidate serving cells (e.g., including a special cell (SpCell) and a secondary cell (SCell)) may be implemented based on L1/L2 signaling (e.g., in RAN2, RAN1). Inter-cell beam management may include, for example, L1 measurement and reporting and beam indication (e.g., in RAN1 , RAN2). Timing Advance management may be provided (e.g., in RAN1 , RAN2). CU-DU interface signaling may be provided to support L1/L2 mobility, if needed (e.g., in RAN3). L1/L2 based inter-cell mobility may be applicable to one or more of the following scenarios: standalone (e.g., carrier aggregation (CA) and NR-DC case with serving cell change within one configured grant (CG)); intra-DU case and intra- CU inter-DU case (e.g., applicable for standalone and CA); both intra-frequency and inter-frequency; both FR1 and FR2; and/or source and target cells may be synchronized or non-synchronized.

[0114] L1/L2 based mobility may utilize inter-cell beam management for intra-DU and intra-frequency scenarios. The serving cell may remain unchanged (e.g., there is no possibility to change the serving cell using L1/2 based mobility). CA may be used (e.g., in FR2 deployments), for example, to exploit the available bandwidth, for example, to aggregate multiple CCs in one band. The CCs may be transmitted with the same analog beam pair (e.g., gNB and WTRU beams). The WTRU may be configured with TCI states (e.g., 64) for the reception of PDCCH and PDSCH. A (e.g., each) TCI state may include, for example, a reference signal (RS) or synchronization signal block (SSB) that the WTRU may refer to for setting its beam. An SSB may be associated with a non-serving PCI. MAC signaling (“TCI state indication for WTRU-specific PDCCH MAC CE”) may activate the TCI state for a CORESET/PDCCH. Reception of PDCCH from a non-serving cell may be supported by a MAC CE indicating a TCI state associated with a non-serving physical cell identity (PCI). MAC signaling (“TCI States Activation/Deactivation for WTRU- specific PDSCH”) may activate a subset of (e.g., up to eight (8)) TCI states for PDSCH reception. Downlink control information (DCI) may indicate one or more TCI states. A “unified TCI state” may be supported, for example, with a different updating mechanism (e.g., DCI-based), for example, with or without multiTransmission / Reception Point (TRP) support.

[0115] L1/L2 triggered mobility (LTM) may improve handover latency. An L3 handover or conditional handover may involve the WTRU (e.g., first) sending a measurement report using RRC signaling. The network may (e.g., in response) provide a further measurement configuration and/or a conditional handover configuration. The network may (e.g., for conventional handover) provide a configuration for a target cell, for example, after the WTRU reports using RRC signaling that the cell meets a configured radio quality criteria. A conditional handover (CHO) may reduce the handover failure rate (e.g., of conventional handovers) due to the delay in sending a measurement report and receiving an RRC reconfiguration provided by the network. A CHO may involve determining/receiving, in advance, a target cell configuration and/or a measurement criteria that may be used to determine when the WTRU may trigger the CHO configuration. Non-conditional and conditional handover implemented as L3 methods may be delayed due to the sending of measurement reports and receiving of target configurations.

[0116] LTM may allow a fast application of configurations for candidate cells, for example, including dynamically switching between SCells and switching of the primary cell (PCell) (e.g., switching the roles between SCell and PCell) without performing RRC signaling. An inter-CU case may involve the relocation of the packet data convergence protocol (PDCP) anchor. An RRC based approach may be used to support an inter-CU handover.

[0117] L3 handovers may release any currently active SCell(s) before the WTRU completes the handover to a target cell in the coverage area of a new site. Released SCells may be added back (e.g., only) after successful handover, which may lead to throughput degradation during handover. LTM may enable CA operation to be enabled (e.g., instantaneously) upon serving cell change.

[0118] FIG. 3 shows an example of an LTM operation. A candidate cell group may be configured by RRC. A dynamic switch of PCell and SCell may be achieved using L1/2 signaling.

[0119] FIG. 3 illustrates an example of LTM using CA.

[0120] FIG. 4 illustrates an example of performing an LTM (e.g., a baseline LTM procedure). As shown in FIG. 4, an example procedure for LTM is described herein.

[0121] At 1 , the WTRU may send a measurement message (e.g., MeasurementReport message) to the gNB. The gNB may decide to use LTM. The gNB may initiate LTM candidate preparation. [0122] At 2, the gNB may transmit a configuration message (e.g., a RRCReconfiguration message) to the WTRU, for example, including the configuration of one or multiple LTM candidate target cells.

[0123] At 3, the WTRU may store the configuration of LTM candidate target cell(s). The WTRU may transmit a complete message (e.g., an RRCReconfigurationComplete message) to the gNB.

[0124] At 4, the WTRU may perform downlink (DL) synchronization and timing advance (TA) acquisition with candidate target cell(s), for example, before receiving the LTM cell switch command. DL synchronization for candidate cell(s) before a cell switch command may be supported, for example, based on SSB. TA acquisition of candidate cell(s) before an LTM cell switch command may be supported, for example, based on PDCCH ordered RACH. The PDCCH order may be triggered (e.g., only) by a source cell.

[0125] At 5, the WTRU may perform L1 measurements on the configured LTM candidate target cell(s). The WTRU may transmit lower-layer measurement reports to the gNB. The lower-layer measurement reports may be carried on L1 or MAC.

[0126] At 6, the gNB may decide to execute an LTM cell switch to a target cell. The gNB may transmit a MAC CE triggering LTM cell switch, for example, by including the candidate configuration index of the target cell. The WTRU may switch to the configuration of the LTM candidate target cell.

[0127] At 7, the WTRU may perform a random access procedure towards the target cell, for example, if TA is not available.

[0128] At 8, the WTRU may indicate successful completion of the LTM cell switch towards the target cell. An uplink signal or message after the WTRU has switched to the target cell may indicate the successful completion of the LTM cell switch.

[0129] RACH-less LTM may be performed. A WTRU may perform early TA acquisition with candidate cell(s) before receiving the cell switch command. Early TA acquisition may be done via contention-free random access (CFRA) triggered by a PDCCH order from the source cell, for example, following which the WTRU may send a preamble to a candidate cell. The information that identifies the allocated CFRA resource may be indicated in the PDCCH order, for example, to enable shared preamble resources among multiple WTRUs in the RRC configuration. The source gNB may (e.g., dynamically) indicate which WTRU uses the resource at any specific time. A WTRU may not receive a RAR, for example, to minimize the data interruption of the source cell, for example, due to CFRA towards the candidate cell(s). The source cell may trigger a preamble retransmission/power ramping, for example, using another PDCCH order, for example, if the preamble was not received. The WTRU may perform a RACH-less handover, for example, if the TA value of the candidate cell is indicated in the cell switch command. [0130] The L1/2 triggered mobility (LTM) procedure may improve mobility latency, for example, by preconfiguring multiple target cells before handover, early DL/UL synchronization (sync) of target cells, L1 measurement reports, MAC CE to indicate cell switch, etc. Conditional LTM may improve robustness. Conditional LTM may be implemented with one or more of the following: an L1 based condition for triggering the HO; LTM candidate cell configurations applied upon trigger; RACH-less CHO; and/or beam refinement ahead of CHO. LTM preparation procedures may be configured to enable the WTRU to perform a RACH-less CHO (e.g., L3 or L1 triggered CHO), for example, using a TA acquisition procedure to enable CHO.

[0131] As used herein, “perform LTM” or “perform LTM procedures” may refer to performing one or more (e.g., all) operations related to LTM, as may be described or shown in figures, such as early synchronization in DL and/or UL to one or more of the candidate cells, performing L1 measurements and/or reporting on one or more of the candidate cells, switching (e.g., performing handover) between candidate cells (e.g., “Perform LTM” may mean that the WTRU moves/switches between multiple candidate cells during the procedure).

[0132] 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/or SCells. This may be modeled or received as one or more complete RRC Reconfiguration messages, one or more cell group configurations, and/or one or more cell configurations. A (e.g., each) candidate cell configuration may include a candidate configuration identifier. A (e.g., each) candidate cell group may include a candidate cell group identifier. The grouping may be performed at RRC. The switching between different sets of candidate cells may (e.g., if the grouping is performed at RRC) include updating the serving cell indexes or candidate configuration indexes, which may be used in L1 and MAC signaling to refer to (e.g., specific) indexes. For example, a MAC CE triggering the reconfiguration may include a candidate configuration index informing the WTRU which cell to perform the reconfiguration.

[0133] 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 sync or LTM execution phase, for example, rather than the configuration phase, which may mean that the candidate cell set may be considered as a single group, for example, in terms of an RRC configuration list or group, while the cells selected for performing early sync, L1 measurements, and LTM execution may depend on a further grouping into multiple subsets of the overall candidate cell list. The grouping itself may not be modeled at RRC using candidate configuration identifiers, but the grouping may be executed as part of the early sync or the LTM execution procedure. [0134] An LTM candidate configuration may apply to a type of preconfigured cell information. For example, a WTRU may be configured with one or more conditional reconfigurations, such as conditional handover (CHO), conditional PSCell addition (CPA), and/or conditional PSCell change (CPC), which may be valid before and/or after a cell change, and/or valid in one or more cells.

[0135] An L1 measurement may include a measurement of, for example, reference signal received power (RSRP), received signal strength indicator (RSSI), etc, which may be performed by a WTRU of a cell, beam, set of cells, and/or set of beams. An L1 measurement may be similar to L3 measurements reported in radio resource management (RRM), with differences in the filtering, reference signals measured, reporting mechanisms, etc.

[0136] An L1 measurement may apply to RRM reporting. Measurements may refer to L1 measurements for LTM, but may (e.g., also) apply (e.g., as described herein) to RRM/L3 measurements and/or other measurements (e.g., measurements of speed, location, height, traffic, etc.).

[0137] LTM cell switch may apply to other types (e.g., any type) of handover execution. An LTM cell switch may refer to L1/2 triggered mobility, which may involve a preconfigured RRC configuration applied if/when the WTRU receives an indication (e.g., using MAC CE) or if/when a condition is met at the WTRU. LTM cell switch may also apply (e.g., as described herein) to an RRC reconfiguration, an RRC conditional reconfiguration, and/or (e.g., any) other type(s) of mobility procedure.

[0138] As described herein, early timing advance (TA) acquisition may be used for a random access channel (RACH)-less conditional handover (CHO). For example, a WTRU may perform a RACH-less CHO evaluation based on a valid TA. A WTRU may trigger early TA acquisition for RACH-less CHO/conditional L1/L2 triggered mobility (LTM). A WTRU may select a RACH procedure to perform for handover (HO) execution. Implementation of examples described herein may provide improved robustness with reduced interruption and latency. A WTRU with a valid TA acquired before cell change criteria is met may (e.g., immediately) trigger the RACH-less LTM handover when the criteria is met, for example, without the delay associated with reporting measurements and receiving an explicit cell switch command. In some examples, the network may prepare multiple cells with a TA value for RACH-less CHO. A WTRU may trigger a cell switch to the best cell based on evaluation, for example, without reporti ng/receiving an explicit trigger.

[0139] An LTM candidate configuration may be determined, provided, or received. A gNB (e.g., a CU in a CU/DU split architecture, where RRC may reside in CU) may configure potential LTM candidates, for example, using RRC signaling. A WTRU may receive LTM candidate configurations, for example, using an RRC Reconfiguration message, for example, during the “LTM preparation” phase shown in FIG. 4. The WTRU may store the LTM candidate configurations to apply later, for example, upon receiving an indication using L1/2 signaling (e.g., MAC CE) to perform a cell switch, for example, in the “LTM execution” phase shown in FIG. 4.

[0140] The configuration of potential LTM candidates may include candidate sets, such as a first set that may be suitable for a first path (for example, a WTRU in a vehicle that turns left and takes first road) and a second set that may e.g., be suitable for a second path (e.g., WTRU in a vehicle that turns right and takes second road).

[0141] One or more (e.g., some or all) of the candidate set information may be broadcast in system information. A WTRU may enable the pre-configuration of the broadcast configurations, for example, based on (e.g., upon) receiving an indication in dedicated signalling (e.g., RRC Reconfiguration) that refers to the broadcast of one or more configurations (e.g., using an index or identifier).

[0142] A configuration may include all or a subset of the potential cells in an area, such as (e.g., all) cells belonging to the CU with which the WTRU is currently connected, or cells within a (e.g., particular) geographical area. The cells may not have been detected or measured by the WTRU yet but may be configured in advance. A WTRU may (e.g., after the initial configuration of LTM candidate configurations) receive an update to the configuration to modify, add, remove, and/or replace one or more (e.g., any) part of the LTM candidate configurations.

[0143] A WTRU may receive an indication to enable or disable one or more (e.g., some or all) of the LTM configurations. LTM may be disabled, for example, if it is predicted that the WTRU mobility would be better handled using L3 (e.g., RRC measurement report, RRC reconfiguration, conditional reconfiguration). LTM may be enabled (e.g., a previously configured and disabled LTM configuration may be re-enabled), for example, if it is predicted that LTM would better suit the WTRU mobility.

[0144] A configuration may be based on a prediction model internal to, and determined by, the network (e.g., gNB). The prediction may, for example, be based on what the NW prediction model determines to be the WTRU’s most likely path(s).

[0145] Candidate cell configurations may include all or part of the information necessary to complete a reconfiguration (e.g., handover) to the candidate cell, such as channel configurations (e.g., PRACH, DPCCH, DPSCH), CORESET, bandwidth part (BWP), security parameters, L2 parameters (e.g., MAC, radio link control (RLC), PDCP), radio bearer configurations, a combination thereof, and or the like.

[0146] LTM execution trigger may refer to a condition for performing LTM (e.g., a conditional handover trigger or measurement report trigger). An LTM execution trigger may be configured or indicated by the network to the WTRU or estimated/determined by the WTRU.

[0147] A trigger may be based on one or more of the following: time; a radio quality measurement or predicted radio quality of one or more of the serving cells or target cells; a position; and/or an L3 measurement event; an L1 measurement event or condition; a predicted event; an (e.g., explicit) indication from the network; a measured, predicted, or estimated throughput, error rate, buffer status, or QoS parameter; and/or an evaluation metric.

[0148] Time may be indicated by one or more of the following: absolute or relative time measured time at a WTRU, a system frame number (SFN), and/or a subframe number.

[0149] A radio quality measurement or predicted radio quality of one or more of the serving cells or target cells may include, for example, one or more of the following: RSRP (e.g., beam or cell), RSRQ (e.g., beam or cell), cri-RI-PMI-channel quality indicator (CQI) (cri-RI-PMI-CQI), cri-RI-i1, cri-RI-i1-CQI, cri-RI- CQI, cri-RSRP, ssb-lndex-RSRP, and/or cri-RI-LI-PMI-CQI.

[0150] A position may be indicated, for example, by one or more of the following: an area (e.g., defined by a reference point and radius) or a range of coordinates, and/or a distance threshold from a reference location.

[0151] An (e.g., any) L3 measurement event, may include, for example, one or more of the following: Event A1 (e.g., serving becomes better than threshold); Event A2 (e.g., serving becomes worse than threshold); Event A3 (e.g., neighbor becomes offset better than SpCell); Event A4 (e.g., neighbor becomes better than threshold); Event A5 (e.g., SpCell becomes worse than thresholdl and neighbor becomes better than threshold2); Event A6 (e.g., neighbor becomes offset better than SCell); Event B1 (e.g., inter RAT neighbor becomes better than threshold); and/or Event B2 (e.g., PCell becomes worse than thresholdl and inter RAT neighbor becomes better than threshold2).

[0152] An L1 measurement event or condition may be, for example, any event defined that utilizes L1 beam measurements to evaluate whether a criteria or condition is met.

[0153] A predicted event may be, for example, any event using any measurement quantity that may be associated with measured or predicted CSI information.

[0154] An (e.g., explicit) indication from the network may be received by a WTRU. For example, a WTRU may enable CSI reporting based on an explicit indication (e.g., a MAC CE) received from the network. The WTRU may (e.g., then) execute an LTM cell switch upon receiving a second MAC CE from the network.

[0155] An evaluation metric may be, for example, a time-to-trigger, a hysteresis, an offset (e.g., a radio quality measurement offset), and/or a measurement filtering configuration.

[0156] A trigger may include one or more conditions under which a WTRU is allowed to perform an (e.g., any) action related to LTM. For example, the WTRU may perform one or more of the following procedures: early TA acquisition; switching off CSI reporting; switching on or updating the CSI reporting configuration; performing LTM cell switch; monitoring PDCCH on a target cell; performing BFR or RLM on a target cell; and/or activating or deactivating certain SCells.

[0157] Early TA acquisition may occur, for example, based on a trigger. For example, a WTRU may trigger a RACH to a target LTM cell. A WTRU may receive a TA value in an RAR. An RAR may be received from, for example, a target cell or via a source cell. A WTRU may receive a TA value in a MAC CE triggering the cell switch. A WTRU may perform power ramping and preamble retransmission on the target, for example, if a RAR/MAC CE is not received.

[0158] CSI reporting may be switched off, for example, based on a trigger. A WTRU may be allowed to or requested to, switch off CSI reporting, for example, to reduce reporting overhead in the uplink. The CSI reporting may be reduced, for example, rather than switched off. For example, the number of cells or beams reporting may be reduced, and/or the reporting frequency may be reduced. A WTRU may resume CSI reporting, for example, if/when the condition is no longer met.

[0159] A CSI reporting configuration may be switched on and/or updated, for example, based on a trigger. For example, a WTRU may (e.g., be required to) perform and/or report CSI measurements on one or more (e.g., a subset) of the LTM candidate cells during the window.

[0160] An LTM cell switch may be performed, for example, based on a trigger. One or more conditions or criteria may indicate if/when the WTRU may be allowed to trigger an LTM cell switch.

[0161] PDCCH may be monitored on a target cell, for example, based on a trigger. A WTRU 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.

[0162] Beam failure recovery (BFR) or radio link monitoring (RLM) may be performed on a target cell, for example, based on a trigger. A WTRU may be configured to monitor beam failure detection (BFD) resources on a target cell and/or perform RLM on a target cell during the window.

[0163] Cells (e.g., SCells) may be activated or deactivated, for example, based on a trigger. A WTRU may be configured with one or more (e.g., specific) SCells, which may be active or inactive during the window.

[0164] RACH-less CHO and early TA acquisition may be performed. A WTRU may perform an early TA acquisition procedure with candidate cell(s) before receiving the cell switch command and/or triggering a conditional reconfiguration, for example, to enable RACH-less conditional handover. The WTRU may avoid sending a random access preamble or performing a random access procedure on the target cell following a reconfiguration trigger. The WTRU may (e.g., instead) perform PDCCH reception and uplink transmission using the TA already provided. [0165] Early TA acquisition may be performed, for example, using contention-free random access (CFRA) triggered by a PDCCH order from the source cell. The WTRU may (e.g., then) send a preamble to a candidate cell. The information that identifies the allocated CFRA resource may be indicated in the PDCCH order, for example, to enable a shared preamble resource among multiple WTRUs in the RRC configuration. The source gNB may (e.g., dynamically) indicate which WTRU may use the resource, for example, at any specific time.

[0166] Early TA acquisition may be performed, for example, based on, (e.g., upon) receiving a MAC CE indicating to perform a RACH transmission on a target cell.

[0167] Early TA acquisition may be performed, for example, by transmitting using a contention-based random access (CBRA) preamble.

[0168] In some examples, a WTRU may not receive a RAR, which may minimize the data interruption of the source cell, for example, due to CFRA towards the candidate cell(s). A source cell may trigger preamble retransmission/power ramping, for example, using another PDCCH order, for example, if the preamble was not received. The TA may be provided from the target cell to the source cell. The TA may be provided to the WTRU, for example, in a MAC CE triggering cell switch, or by enabling conditional LTM to one or more target cells.

[0169] In some examples, a WTRU may receive a TA value from the target cell in a random access response (RAR). In some examples, the WTRU may receive a TA value from the source cell in a random access response (RAR). The WTRU may retransmit a preamble, for example, using a higher transmission power, for example, if the WTRU does not receive a RAR in response to transmitting the preamble (e.g., within a prescribed amount of time).

[0170] In some examples, a WTRU may store the received TA value to be used later, for example, if/when a reconfigure trigger occurs. The WTRU may store the TA value for a limited period of time (e.g., a validity timer), which may trigger or be triggered to perform a new TA acquisition procedure, for example, when the time expires.

[0171] In some examples, the WTRU may receive and/or store multiple TA values, which may be associated with more than one cell.

[0172] The WTRU may perform a RACH-less handover, for example, if the WTRU has stored a valid TA value of a candidate cell, for example, when a cell switch is triggered towards that candidate cell. A cell switch may be triggered, for example, by the NW (e.g., using an explicit cell switch command) or by the WTRU (e.g., upon meeting a trigger condition). For example, the WTRU may execute LTM (e.g., apply a pre-configured RRC configuration to a new SpCell) based on (e.g., upon) determining that a measured radio quality of the target cell is above a threshold. [0173] A WTRU may determine TA Validity. A WTRU may determine a received/stored TA to be valid, for example, based on one or more of the following: a validity timer pre-configured to be used with a 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; a condition on the DL cell timing of the candidate cell; a condition on the WTRU mobility; and/or a condition on the WTRU location.

[0174] A WTRU may determine a received/stored TA to be valid, based on 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. A WTRU may consider the TA valid, for example, while the difference in the DL cell timing of the source and candidate cell is less than a configured threshold. A WTRU may consider the TA valid, for example, while the difference in the DL cell timing of the source and candidate cell is within a configured range.

[0175] A WTRU may determine a received/stored TA to be valid, for example, based on a condition on the DL cell timing of the candidate cell. A WTRU may consider the TA valid, for example, 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 (e.g., configured) value/range than the current DL cell timing of the same target cell.

[0176] A WTRU may determine a received/stored TA to be valid, for example, based on a condition on the WTRU mobility. A WTRU may consider the TA valid, for example, if it is static or below a (e.g., configured) speed threshold.

[0177] A WTRU may determine that a received/stored TA is valid for example, based on a condition on the WTRU location. A WTRU may consider the TA valid, for example, if the WTRU has determined that it has not changed its location by more than a certain configured threshold (e.g., x meters) after the TA acquisition.

[0178] As described herein, a random access channel (RACH) procedure may be selected and used to perform a handover (HO) execution. A device may (e.g., be configured to) do one or more of the following actions. A wireless transmit/receive unit (WTRU) may prioritize which target to execute L1/L2 triggered mobility (LTM) towards, for example, depending on whether the WTRU may perform a RACH-less handover. A RACH-less conditional HO (OHO) may provide reduced interruption and/or robustness, for example, compared to a handover utilizing a RACH.

[0179] A WTRU may receive a configuration of LTM candidate cells and/or a configuration of CHO. A CHO configuration may include separate execution conditions, for example, depending on whether the WTRU has a valid timing advance (TA) or not (e.g., separate thresholds). A CHO configuration may include one or more conditions related to the remaining validity time (e.g., a first condition when the remaining validity time is above a threshold, and a second condition otherwise). A CHO configuration may include the configuration of a type of RACH procedure to perform and/or conditions for selecting the type of RACH procedure to perform, for example, depending on the remaining TA validity time.

[0180] The WTRU may transmit channel state information (CSI) reporting.

[0181] The WTRU may receive a physical downlink control channel (PDCCH) order. The WTRU may transmit a preamble to a first target cell.

[0182] The WTRU may receive a TA value for the first cell.

[0183] The WTRU may perform measurement(s) on the configured LTM target(s), which may include at least the first cell, and may include a second cell (e.g., without a valid TA value). A second cell may have a valid TA with a remaining TA validity time, which may be less than the first cell's remaining TA validity time. [0184] The WTRU may select the first cell. The WTRU may execute the CHO (e.g., RACH-less LTM execution) to the first cell based on a prioritization rule, for example, if the cell switch criteria are met for the first cell and the second cell. Example selection conditions/prioritization rules may include, for example, one or more of the following: an indication whether TA is valid or invalid; an indication to select the target with the longest remaining TA validity time; an indication to select the target configured for RACH-less as a priority over a target not configured for RACH-less; a selection condition may include an offset to the CHO criteria, for example, a cell configured for RACH-less may have a lower reference signal received power (RSRP) threshold; a selection condition may apply a shorter time to trigger (TTT) to the CHO criteria if the cell is configured for RACH-less; selection of the first cell may include aborting a reconfiguration procedure towards the second cell (e.g., abort and perform RACH-less to the first cell, for example, if the WTRU is performing preamble retransmission to perform a RACH procedure for HO to the second cell); and/or a selection prioritization rule may be applied if/when a conditional reconfiguration criteria is met for multiple cells or if multiple cells are performing different types of reconfiguration (e.g., an explicit reconfiguration versus a conditional reconfiguration).

[0185] The WTRU may send an indication to a target (first cell). For example, the WTRU may transmit a radio resource control (RRC) complete message on PUSCH. The WTRU may use the configured grant (CG) associated with the best beam triggering the CHO. The WTRU may monitor for an uplink grant on PDCCH. The WTRU may (e.g., then) transmit data and/or an RRC complete message.

[0186] FIG. 5 illustrates an example flowchart for the selection of a RACH procedure to perform the HO execution.

[0187] As shown in FIG. 5, at 1 , a WTRU may receive a configuration of LTM candidate cells and a configuration of RACH-less conditional handover for (e.g., at least) a first target cell. The configuration(s) may be received, for example, in an RRC reconfiguration message. The RACH-less conditional handover configuration may include, for example, one or more trigger conditions (e.g., as described herein). A WTRU may (e.g., also) receive an indication of a prioritization criteria to determine which type of handover to execute should the LTM execution trigger criteria be met for more than one target cell. A conditional handover may, for example, use a first criteria when a condition is met and a second criteria when a condition is not met. For example, a first radio quality measurement threshold may be used if/when a valid TA is stored, and a second threshold may be used otherwise.

[0188] At 2, the WTRU may transmit CSI reporting for the configured target cells or beams.

[0189] At 3, the WTRU may receive a PDCCH order enabling the WTRU-triggered TA acquisition (e.g., preamble transmission to target). The PDCCH order may include one or more of the following: an indication identifying a random access resource, a condition (e.g., a second condition), and/or a validity time during which the WTRU-triggered TA acquisition may be evaluated.

[0190] At 4, the WTRU may receive a TA value for the first cell (e.g., after a PDCCH order to transmit a preamble to a target cell).

[0191] At 5, the WTRU may perform measurements on the configured one or more target cells or beams, which may include (e.g., at least) the first cell and a second cell. The second cell may not be configured for RACH-less reconfiguration (e.g., RACH-less has not been enabled for the second cell, or RACH-less has been configured, but no valid TA value is stored, or a condition to execute RACH-less has not been met).

[0192] At 6, the LTM may be executed (e.g., the preconfigured candidate configuration may be applied) towards the first cell based on a prioritization criteria, for example, if the cell switch criteria are met for the first cell and the second cell.

[0193] At 7, the WTRU may send an indication to the target cell, for example, an RRC Complete message on PUSCH, which may be performed, for example, using the CG associated with the beam (e.g., the best beam) triggering the CHO or by monitoring for an uplink grant (e.g., dynamic grant) on PDCCH to transmit data and/or RRC complete on PUSCH.

[0194] Prioritization criteria may include, for example, one or more of the following: a criterion to execute one type of handover (e.g., to execute a RACH-less handover rather than a RACH-based handover or to execute an explicit handover request rather than a conditional one); a criterion based on whether a cell has a valid TA or not or whether a cell was configured for RACH-less or not by RRC; a criterion to select a cell with the longest TA validity time; a criterion based on an absolute or relative radio quality threshold; a timebased criterion; an event-based criterion; and/or a criterion based on the availability of configured grants.

[0195] Prioritization criteria may include a criterion based on an absolute or relative radio quality threshold. For example, a RACH-less handover may be executed as long as the cell configured for RACH- less (e.g., with a valid TA) meets the LTM cell switch trigger criteria has a radio quality measurement that is (e.g., at least) within X dB of the radio quality measurement criteria of a cell that is not configured for RACH-less (e.g., without a valid TA) that meets the LTM cell switch criteria.

[0196] Prioritization criteria may include a time-based criterion. For example, if the cell configured for RACH-less (e.g., with a valid TA) meets the LTM cell switch trigger criteria within a certain time after a cell that is not configured for RACH-less.

[0197] Prioritization criteria may include an event-based criterion. For example, if the cell configured for RACH-less (e.g., with a valid TA) meets the LTM cell switch trigger criteria before a certain event within a procedure used by a cell that is not configured for RACH-less (e.g., before a successful random access response is received, or before a handover completion is transmitted).

[0198] Prioritization criteria may include a criterion based on the availability of configured grants. For example, a WTRU may choose a second cell over a first cell if the first and second cells both fulfill the CHO conditions, the first cell is marginally better than the second cell in terms of radio signal level, but one or more configured grant resources are available on the second cell while there are no valid/activated configured grants on the first cell. For example, a WTRU may choose a second cell even if a first cell has a better radio quality if active configured grants are available on both cells, but the grants on the second cell occur earlier or there are more configured grant occasions (e.g., the CG configuration on the second cell has shorter periodicity, etc.).

[0199] FIG.6 illustrates an example of triggering a RACH-less handover on a first cell before the completion of a RACH procedure on a second cell. FIG. 6 shows an example where a conditional RACH- less handover execution takes priority over the completion of a RACH-based reconfiguration. As shown in FIG. 6, LTM may be configured while a WTRU is connected to cell A, for example, along with a configuration for RACH-less handover to cell B. The WTRU may receive (e.g., during the LTM preparation phase) a PDCCH order to transmit a random access preamble to cell B. The WTRU may (e.g., then) receive a cell switch indication (e.g., in a MAC CE) from Cell A, which may indicate a TA value for cell B and a validity time for enabling RACH-less CHO to cell B. The WTRU may receive (e.g., while the WTRU is performing measurements and evaluation of cell B for a conditional LTM execution) an LTM cell switch indication for Cell C, which does not include a TA value (e.g., indicating to perform a RACH-based handover). The WTRU may determine a CHO condition that enables a RACH-based handover is met for cell C. The WTRU may initiate the reconfiguration to cell C and start performing the random access procedure (e.g., PRACH preamble transmission and retransmission with power ramping). Meanwhile, the conditional LTM criteria may be met for cell B. The WTRU may terminate the reconfiguration to cell C and perform a RACH-less handover using LTM to cell B. [0200] Higher priority RACH-less reconfiguration may take place even after another reconfiguration starts, or if the conditions for executing a RACH-less reconfiguration and a RACH-based reconfiguration occur in parallel (e.g., at the same time, or before completion of one or the other procedure).

[0201] Prioritizing a target cell to execute LTM based on a RACH-less handover may reduce interruption, for example, because a RACH-less reconfiguration may be completed more quickly and/or may have a configured grant to perform a UL transmission.

[0202] Systems, methods, and instrumentalities are described herein related to selecting a random access channel (RACH) procedure for performing handover (HO) execution. A wireless transmit/receive unit (WTRU) may receive, from a first cell, configuration information that indicates mobility candidate cells and a first configuration of a first conditional handover (CHO) associated with a first condition for a first random access channel (RACH)-less handover that is based on a first candidate cell timing advance (TA) validity duration. The mobility candidate cells may include at least a first candidate cell and a second candidate cell. The WTRU may transmit a report comprising channel state information (CSI) information to the first cell. The WTRU may receive a physical downlink control channel (PDCCH) order from the first cell. The WTRU may receive, based on the PDCCH order, a first candidate cell TA value for the first candidate cell. The WTRU may perform measurements on the first candidate cell and the second candidate cell. Based on the measurements and based on the first condition being met before expiration of the first candidate cell TA validity duration, the WTRU may prioritize the first candidate cell over the second candidate cell for handover execution. The WTRU may perform a conditional cell switch from the first cell to the first candidate cell by performing the first RACH-less handover. The WTRU may, based on performing the conditional cell switch, send, to the first candidate cell, a reconfiguration complete indication.

[0203] The PDCCH order may include a random access (RA) resource and the first candidate cell TA validity duration. The reconfiguration complete indication may be sent to the first candidate cell in a radio resource control message (RRC). The first candidate cell may include a first target cell, and the second candidate cell may include a second target cell. The WTRU may prioritize the first candidate cell over the second candidate cell for handover execution based on the second candidate cell lacking a second candidate cell TA value, or a second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration.

[0204] Prioritizing the first candidate cell over the second candidate cell for handover execution based on the second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration may include the WTRU receiving a second configuration of a second conditional handover (CHO) associated with a second condition for a random access channel (RACH)-less handover that is based on the second candidate cell timing advance (TA) validity duration. The first condition may be met based on the first candidate cell TA value being valid before expiration of the first candidate cell TA validity duration.

[0205] Systems, methods, and instrumentalities are described herein related to early timing advance (TA) acquisition for a random access channel (RACH)-less conditional handover (CHO) . A device may (e.g., be configured to) do one or more of the following actions. A wireless transmit/receive unit (WTRU) may perform RACH-less CHO evaluation based on a valid TA. A WTRU may trigger early TA acquisition for RACH-less CHO/conditional L1/L2 triggered mobility (LTM). A WTRU may select a RACH procedure to perform for handover (HO) execution.

[0206] Systems, methods, and instrumentalities are described herein related to selecting a random access channel (RACH) procedure for performing handover (HO) execution. A device may (e.g., be configured to) do one or more of the following actions. A wireless transmit/receive unit (WTRU) may prioritize which target to execute L1/L2 triggered mobility (LTM) towards, for example, depending on whether the WTRU may perform a RACH-less handover. A RACH-less conditional HO (CHO) may provide reduced interruption and/or robustness, for example, compared to a handover utilizing a RACH.

[0207] A WTRU may receive a configuration of LTM candidate cells and/or a configuration of CHO. A CHO configuration may include separate execution conditions, for example, depending on whether the WTRU has a valid timing advance (TA) or not (e.g., separate thresholds). A CHO configuration may include one or more conditions related to the remaining validity time (e.g., a first condition when the remaining validity time is above a threshold, and a second condition otherwise). A CHO configuration may include configuration of a type of RACH procedure to perform and/or conditions for selecting the type of RACH procedure to perform, for example depending on remaining TA validity time.

[0208] The WTRU may transmit channel state information (CSI) reporting.

[0209] The WTRU may receive a physical downlink control channel (PDCCH) order. The WTRU may transmit a preamble to a first target cell.

[0210] The WTRU may receive a TA value for the first cell.

[0211] The WTRU may perform measurement(s) on the configured LTM target(s), which may include at least the first cell, and may include a second cell (e.g., without a valid TA value). A second cell may have a valid TA with a remaining TA validity time, which may be less than the first cell’s remaining TA validity time.

[0212] The WTRU may select the first cell. The WTRU may execute the CHO (e.g., RACH-less LTM execution) to the first cell based on a prioritization rule, for example, if the cell switch criteria are met for the first cell and the second cell. Example selection conditions/prioritization rules may include, for example, one or more of the following: an indication whether TA is valid or invalid; an indication to select the target with the longest remaining TA validity time; an indication to select the target configured for RACH-less as a priority over a target not configured for RACH-less; a selection condition may include an offset to the CHO criteria, for example, a cell configured for RACH-less may have a lower reference signal received power (RSRP) threshold; a selection condition may apply a shorter time to trigger (TTT) to the CHO criteria if the cell is configured for RACH-less; selection of the first cell may include aborting a reconfiguration procedure towards the second cell (e.g., abort and perform RACH-less to the first cell, for example, if the WTRU is performing preamble retransmission to perform a RACH procedure for HO to the second cell); and/or a selection prioritization rule may be applied if/when a conditional reconfiguration criteria is met for multiple cells or if multiple cells are performing different types of reconfiguration (e.g., an explicit reconfiguration versus a conditional reconfiguration).

[0213] The WTRU may send an indication to a target (first cell). For example, the WTRU may transmit a radio resource control (RRC) complete message on PUSCH. The WTRU may use the configured grant (CG) associated with the best beam triggering the CHO. The WTRU may monitor for an uplink grant on PDCCH. The WTRU may transmit data and/or an RRC complete message.

[0214] An example device may include a processor configured to perform one or more actions. For example, a device may receive, from a first cell, a configuration that may comprise mobility candidate cells, including first and second candidate cells, a configuration of random access channel (RACH)-less conditional handover (CHO), including a RACH-less CHO condition, and a configuration for cell switch prioritization. The device may perform, and report measurements of the mobility candidate cells to the first cell. The device may perform random access (RA) to the mobility candidate cells using an RA resource indicated by the first cell. The device may receive a first conditional cell switch indication comprising a timing advance (TA) value and a TA validity time for the first candidate cell. The device may receive a second conditional cell switch indication to the second candidate cell. The device may prioritize the first conditional cell switch over the second conditional cell switch based on the cell switch prioritization. The device may perform the first conditional cell switch from the first cell to the first candidate cell if the RACH- less CHO condition is satisfied before the expiration of the TA validity time.

[0215] The cell switch prioritization may prioritize the first conditional cell switch over the second conditional cell switch, for example, by prioritizing RACH-less CHO over RACH-based CHO and/or by prioritizing the remaining TA validity time.

[0216] Systems, methods, and instrumentalities are described herein related to selecting a random access channel (RACH) procedure for performing handover (HO) execution. A wireless transmit/receive unit (WTRU) may receive, from a first cell, configuration information that indicates mobility candidate cells and a first configuration of a first conditional handover (CHO) associated with a first condition for a first random access channel (RACH)-less handover that is based on a first candidate cell timing advance (TA) validity duration. The mobility candidate cells may include at least a first candidate cell and a second candidate cell. The WTRU may transmit a report comprising channel state information (CSI) information to the first cell. The WTRU may receive a physical downlink control channel (PDCCH) order from the first cell. The WTRU may receive, based on the PDCCH order, a first candidate cell TA value for the first candidate cell. The WTRU may perform measurements on the first candidate cell and the second candidate cell. Based on the measurements and based on the first condition being met before expiration of the first candidate cell TA validity duration, the WTRU may prioritize the first candidate cell over the second candidate cell for handover execution. The WTRU may perform a conditional cell switch from the first cell to the first candidate cell by performing the first RACH-less handover. The WTRU may, based on performing the conditional cell switch, send, to the first candidate cell, a reconfiguration complete indication.

[0217] The PDCCH order may include a random access (RA) resource and the first candidate cell TA validity duration. The reconfiguration complete indication may be sent to the first candidate cell in a radio resource control message (RRC). The first candidate cell may include a first target cell, and the second candidate cell may include a second target cell. The WTRU may prioritize the first candidate cell over the second candidate cell for handover execution based on the second candidate cell lacking a second candidate cell TA value, or a second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration.

[0218] Prioritizing the first candidate cell over the second candidate cell for handover execution based on the second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration may include the WTRU receiving a second configuration of a second conditional handover (CHO) associated with a second condition for a random access channel (RACH)-less handover that is based on the second candidate cell timing advance (TA) validity duration. The first condition may be met based on the first candidate cell TA value being valid before expiration of the first candidate cell TA validity duration.

[0219] Although features and elements described above are described in particular combinations, each feature or element may be used alone without the other features and elements of the preferred embodiments, or in various combinations with or without other features and elements.

[0220] Although the implementations described herein may consider 3GPP specific protocols, it is understood that the implementations described herein are not restricted to this scenario and may be applicable to other wireless systems. For example, although the solutions described herein consider LTE, LTE-A, New Radio (NR) or 5G specific protocols, it is understood that the solutions described herein are not restricted to this scenario and are applicable to other wireless systems as well. [0221] The processes described above may be implemented in a computer program, software, and/or firmware incorporated in a computer-readable medium for execution by a computer and/or processor. Examples of computer-readable media include, but are not limited to, electronic signals (transmitted over wired and/or wireless connections) and/or 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, but not limited to, internal hard disks and removable disks, magneto-optical media, and/or optical media such as compact disc (CD)-ROM disks, and/or digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, terminal, base station, RNC, and/or any host computer.

Claims

1 . A wireless transmit/receive unit (WTRU) comprising: a processor configured to: receive, from a first cell, configuration information that indicates mobility candidate cells and a first configuration of a first conditional handover (CHO) associated with a first condition for a first random access channel (RACH)-less handover that is based on a first candidate cell timing advance (TA) validity duration, wherein the mobility candidate cells comprise at least a first candidate cell and a second candidate cell; transmit a report comprising channel state information (CSI) information to the first cell; receive a physical downlink control channel (PDCCH) order from the first cell; receive, based on the PDCCH order, a first candidate cell TA value for the first candidate cell; perform measurements on the first candidate cell and the second candidate cell; based on the measurements and based on the first condition being met before expiration of the first candidate cell TA validity duration, prioritize the first candidate cell over the second candidate cell for handover execution; perform a conditional cell switch from the first cell to the first candidate cell by performing the first RACH-less handover; and based on performing the conditional cell switch, send, to the first candidate cell, a reconfiguration complete indication.

2. The WTRU of claim 1 , wherein the PDCCH order comprises a random access (RA) resource and the first candidate cell TA validity duration.

3. The WTRU of claim 1 , wherein the reconfiguration complete indication is sent to the first candidate cell in a radio resource control message (RRC).

4. The WTRU of claim 1 , wherein the first candidate cell comprises a first target cell and the second candidate cell comprises a second target cell.

5. The WTRU of claim 1 , wherein the processor is further configured to prioritize the first candidate cell over the second candidate cell for handover execution based on the second candidate cell lacking a second candidate cell TA value, or a second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration.

6. The WTRU of claim 5, wherein the processor configured to prioritize the first candidate cell over the second candidate cell for handover execution based on the second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration comprises the processor being configured to: receive a second configuration of a second conditional handover (CHO) associated with a second condition for a random access channel (RACH)-less handover that is based on the second candidate cell timing advance (TA) validity duration.

7. The WTRU of claim 1 , wherein the first condition is met based on the first candidate cell TA value being valid before expiration of the first candidate cell TA validity duration.

8. A method for a wireless transmit/receive unit (WTRU) comprising: receiving, from a first cell, configuration information that indicates mobility candidate cells and a first configuration of a first conditional handover (CHO) associated with a first condition for a first random access channel (RACH)-less handover that is based on a first candidate cell timing advance (TA) validity duration, wherein the mobility candidate cells comprise at least a first candidate cell and a second candidate cell; transmitting a report comprising channel state information (CSI) information to the first cell; receiving a physical downlink control channel (PDCCH) order from the first cell; receiving, based on the PDCCH order, a first candidate cell TA value for the first candidate cell; performing measurements on the first candidate cell and the second candidate cell; based on the measurements and based on the first condition being met before expiration of the first candidate cell TA validity duration, prioritizing the first candidate cell over the second candidate cell for handover execution; performing a conditional cell switch from the first cell to the first candidate cell by performing the first RACH-less handover; and based on performing the conditional cell switch, sending, to the first candidate cell, a reconfiguration complete indication.

9. The method of claim 8, wherein the PDCCH order comprises a random access (RA) resource and the first candidate cell TA validity duration.

10. The method of claim 8, wherein the reconfiguration complete indication is sent to the first candidate cell in a radio resource control message (RRC).

11 . The method of claim 8, wherein the first candidate cell comprises a first target cell and the second candidate cell comprises a second target cell.

12. The method of claim 8, wherein the method further comprises prioritizing the first candidate cell over the second candidate cell for handover execution based on the second candidate cell lacking a second candidate cell TA value, or a second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration.

13. The method of claim 12, wherein prioritizing the first candidate cell over the second candidate cell for handover execution based on the second candidate cell TA validity duration of the second candidate cell being less than the first candidate cell TA validity duration comprises: receiving a second configuration of a second conditional handover (CHO) associated with a second condition for a random access channel (RACH)-less handover that is based on the second candidate cell timing advance (TA) validity duration.

14. The method of claim 8, wherein the first condition is met based on the first candidate cell TA value being valid before expiration of the first candidate cell TA validity duration.