Effective TA-based RACH-less CHO evaluation

Abstract

A system, method, and means for obtaining an early timing advance (TA) for a RACH-less conditional handover (CHO) is described herein. A wireless transceiver unit (WTRU) can receive information from a first cell indicating the configuration of a mobility candidate cell and a RACH-less CHO. The WTRU can receive an indication of a conditional cell switchover having a TA value and a TA validity period for the first candidate cell. If the RACH-less CHO condition is met before the expiration of the TA validity period, the WTRU can use the TA value to perform a conditional cell switchover and transmit a reconfiguration complete indication to the first candidate cell.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of U.S. Provisional Application No. 63 / 531,920, filed on August 10, 2023, the disclosure of which is hereby incorporated by reference in its entirety.

Background Art

[0002] Mobile communication using wireless communication has continued to evolve. The fifth generation is sometimes called 5G. Previous (legacy) generations of mobile communication could be, for example, the fourth generation (4G) LTE (Long Term Evolution).

Summary of the Invention

[0003] Systems, methods, and means related to early timing advance (TA) acquisition for random access channel (RACH) - less conditional handover (CHO) are described herein. A wireless transmit - receive unit (WTRU) can receive configuration information indicating a mobility candidate cell and a configuration of a random access channel (RACH) - less conditional handover (CHO) from a first cell. The mobility candidate cell can include at least a first candidate cell, and the configuration of the RACH - less CHO can include at least RACH - less CHO conditions. The WTRU can receive an indication of a conditional cell switch - over that indicates a timing advance (TA) value associated with the conditional cell switch - over and a TA validity period associated with the first candidate cell. Based on the RACH - less CHO conditions being met before the expiration of the TA validity period, the WTRU can perform a conditional cell switch - over from the first cell to the first candidate cell using the RACH - less CHO. Using the RACH - less CHO can include using the TA value. Based on performing the conditional cell switch - over, the WTRU can transmit a re - configuration completion indication to the first candidate cell.

[0004] Conditional cell switching from the first cell to the first candidate cell can be performed based on measurements. The WTRU can perform measurements on the first candidate cell. The WTRU can receive a Physical Downlink Control Channel (PDCCH) order from the first cell. Based on the received PDCCH order, the WTRU can send a preamble to the first candidate cell. The preamble may be associated with a TA value. The first candidate cell may include a target cell. A reconfiguration complete indication can be sent to the first candidate cell in a Radio Resource Control Message (RRC). The TA value may be used in a PUSCH transmission. The RACH-less CHO condition may be met based on the TA value being valid before the expiration of the TA validity period. [Brief explanation of the drawing]

[0005] [Figure 1A] This is a system diagram showing an exemplary communication system capable of carrying out one or more disclosed embodiments. [Figure 1B] This is a system diagram showing an exemplary wireless transceiver unit (WTRU) that may be used in the communication system shown in Figure 1A, according to one embodiment. [Figure 1C] This is a system diagram showing an exemplary radio access network (RAN) and an exemplary core network (CN) that may be used in the communication system shown in Figure 1A according to one embodiment. [Figure 1D] This is a system diagram showing further exemplary RANs and CNs that may be used in the communication system shown in Figure 1A according to one embodiment. [Figure 2] This figure shows an example of a measurement model. [Figure 3] This figure shows an example of LTM using carrier aggregation (CA). [Figure 4] This figure shows an example of LTM execution. [Figure 5] This figure shows an example flowchart for evaluating RACH-less conditional handover (CHO) based on a valid TA. [Figure 6] This figure illustrates an example of evaluating whether to perform recombination based on whether the target cell has a valid TA. [Figure 7] Figure 7 shows an example of evaluating whether to perform reconfiguration based on whether the target cell has a valid TA. [Figure 8] This figure shows an example of deciding whether to use TAG to evaluate CHO in multiple cells. [Figure 9] This figure shows an example flowchart for early TA acquisition via WTRU triggers for RACH-less CHO and / or conditional LTM. [Figure 10] This figure shows an example of triggering early TA acquisition based on conditions evaluated by WTRU, which may be called WTRU-triggered early TA acquisition. [Figure 11] This diagram shows an example flowchart for selecting the RACH procedure to execute for HO execution. [Figure 12] This figure shows an example where a RACH-less handover is triggered in the first cell before the RACH procedure in the second cell is completed. [Modes for carrying out the invention]

[0006] Figure 1A shows an exemplary communication system 100 that can implement one or more disclosed embodiments. The communication system 100 may be a multiple access system that provides content such as voice, data, video, messaging, and broadcast to multiple radio users. The communication system 100 may enable multiple radio users to access such content through the sharing of system resources, including radio bandwidth. For example, the communication system 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 (ZT) unique word (UW) discrete Fourier transform (DFT) spread OFDM (ZT UW DFT-s OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, and filter bank multicarrier (FBMC).

[0007] As shown in Figure 1A, the communication system 100 may include radio transceiver units (WTRUs) 102a, 102b, 102c, and 102d, a radio access network (RAN) 104 / 113, a core network (CN) 106 / 115, a public switched telephone network (PSTN) 108, the internet 110, and other networks 112, but it will be understood that the disclosed embodiments assume any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, and 102d may be any type of device configured to operate and / or communicate in a radio environment. For example, WTRU102a, 102b, 102c, and 102d may all be referred to as “stations” and / or “STAs,” and these may be configured to transmit and / or receive radio signals and may include user equipment (UEs), mobile stations, fixed or mobile subscriber units, subscription-based units, pagers, cellular telephones, personal digital assistants (PDAs), smartphones, laptops, notebooks, personal computers, radio sensors, hotspots or Mi-Fi devices, IoT devices, watches or other wearables, head-mounted displays (HMDs), vehicles, drones, medical equipment and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other radio devices operating in the context of industrial and / or automated processing chains), consumer electronic devices, and devices operating on commercial and / or industrial radio networks. WTRU102a, 102b, 102c, and 102d may all be referred to as UEs interchangeably.

[0008] The communication system 100 may also include base stations 114a and / or base stations 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 CN 106 / 115, the Internet 110, and / or other networks 112. For example, base stations 114a, 114b may be any such device, including a transceiver base station (BTS), NodeB (NB), eNodeB (eNB), home NodeB (HNB), home eNodeB (HeNB), gNodeB (gNB), (e.g., new) radio (NR) NodeB (NR NB), site controller, access point (AP), wireless router, etc. Although base stations 114a and 114b are depicted as single elements, it will be understood that base stations 114a and 114b may contain any number of interconnected base stations and / or network elements.

[0009] Base station 114a may be part of RAN 104 / 113, which may also include other base stations and / or network elements (not shown) such as base station controllers (BSCs), radio network controllers (RNCs), and relay nodes. Base station 114a and / or base station 114b may be configured to transmit and / or receive radio signals on one or more carrier frequencies which may be called cells (not shown). These frequencies may be licensed spectra, unlicensed spectra, or combinations of licensed and unlicensed spectra. Cells can provide coverage for radio services in a particular geographic area which may be relatively fixed or may change over time. Cells may be further divided into cell sectors. For example, a cell associated with base station 114a may be divided into three sectors. Thus, in one embodiment, base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In one embodiment, the base station 114a may employ multiple-input multiple-output (MIMO) technology and may utilize multiple transceivers for each sector of the cell or for any sector of the cell. For example, beamforming may be used to transmit and / or receive signals in a desired spatial direction.

[0010] Base stations 114a, 114b may communicate with one or more WTRUs 102a, 102b, 102c, 102d via an air interface 116 which may be any suitable radio 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).

[0011] More specifically, as described above, the communication system 100 may be a multiple access system and may employ one or more channel access schemes such as CDMA, TDMA, FDMA, OFDMA, and SC-FDMA. For example, base stations 114a and WTRUs 102a, 102b, and 102c in RAN 104 / 113 may implement radio technologies such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) that can establish an air interface 116 using broadband CDMA (WCDMA®). WCDMA may include communication protocols such as High Speed ​​Packet Access (HSPA) and / or Advanced HSPA (HSPA+). HSPA may include High Speed ​​Downlink (DL) Packet Access (HSDPA) and / or High Speed ​​Uplink (UL) Packet Access (HSUPA).

[0012] In one embodiment, base stations 114a and WTRUs 102a, 102b, and 102c can implement radio technologies such as Advanced UMTS Terrestrial Radio Access (E-UTRA), which can establish an air interface 116 using Long-Term Evolution (LTE) and / or LTE Advanced (LTE-A) and / or LTE Advanced Pro (LTE-A Pro).

[0013] In one embodiment, the base station 114a and WTRUs 102a, 102b, and 102c may implement radio technologies such as NR radio access, which can establish an air interface 116 using New Radio (NR).

[0014] In one embodiment, base station 114a and WTRU 102a, 102b, 102c can implement multiple radio access technologies. For example, base station 114a and WTRU 102a, 102b, 102c can implement LTE radio access and NR radio access together, for example, using the dual connectivity (DC) principle. Thus, the air interface utilized by WTRU 102a, 102b, 102c may be characterized by transmissions between multiple types of radio access technologies and / or multiple types of base stations (e.g., eNB and gNB).

[0015] In other embodiments, base stations 114a and WTRUs 102a, 102b, and 102c may implement wireless technologies such as IEEE 802.11 (i.e., WiFi (Wireless Fidelity)), IEEE 802.16 (i.e., WiMAX (Worldwide Interoperability for Microwave Access)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Provisional Standard 2000 (IS-2000), Provisional Standard 95 (IS-95), Provisional Standard 856 (IS-856), GSM (Registered Trademark) (Global System for Mobile communications), GSM Advanced High-Speed ​​Data Rate (EDGE), and GSM EDGE (GERAN).

[0016] The base station 114b in FIG. 1A may be, for example, a wireless router, a home NodeB, a home eNodeB, or an access point, and may utilize any suitable RAT to facilitate wireless connectivity in a local area such as a workplace, home, vehicle, campus, industrial facility, (e.g., an air corridor for use by drones), a road, etc. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a wireless technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a wireless 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 pico cell or a femto cell. 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 need to access the Internet 110 via the CN 106 / 115.

[0017] RAN104 / 113 may communicate with CN106 / 115, which may be any type of network configured to provide voice, data, applications, and / or VoIP services to one or more of WTRU102a, 102b, 102c, and 102d. The data may have various quality of service (QoS) requirements, such as different throughput requirements, latency requirements, fault tolerance requirements, reliability requirements, data throughput requirements, and mobility requirements. CN106 / 115 may provide call control, billing services, mobile location services, prepaid calling, internet connectivity, video distribution, and / or perform high-level security functions such as user authentication. Although not shown in Figure 1A, it should be understood that RAN104 / 113 and / or CN106 / 115 may communicate directly or indirectly with other RANs employing the same RAT as RAN104 / 113 or different RATs. For example, in addition to connecting to RAN104 / 113, which may utilize NR radio technology, CN106 / 115 may also communicate with another RAN (not shown) employing GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

[0018] CN106 / 115 can also function as a gateway for WTRU102a, 102b, 102c, 102d to access PSTN108, the Internet 110, and / or other networks 112. PSTN108 may include a circuit-switched telephone network providing basic telephone services (POTS). The Internet 110 may include a global system of interconnected computer networks and devices using common communication protocols such as TCP, UDP, and / or IP in the TCP / IP Internet Protocol Suite. Network 112 may include wired and / or wireless networks owned and / or operated by other service providers. For example, network 112 may include another CN connected to one or more RANs that may employ the same RAT as RAN104 / 113 or a different RAT.

[0019] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication system 100 may include multimode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks via different wireless links). For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with a base station 114a that may employ a cellular-based wireless technology and with a base station 114b that may employ IEEE 802 wireless technology.

[0020] FIG. 1B is a system diagram showing an example of a WTRU 102. As shown in FIG. 1B, the WTRU 102 may include, among other things, a processor 118, a transceiver 120, a transceiver element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, a non-removable memory 130, a removable memory 132, a power supply 134, a GPS chipset 136, and / or other peripheral devices 138. It will be understood that the WTRU 102 may comprise any sub-combination of the foregoing elements while maintaining consistency with an embodiment.

[0021] The processor 118 may be a general-purpose processor, a dedicated processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, other types of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal encoding, data processing, power control, input / output processing, and / or any other function 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 transceiver element 122. Although the processor 118 and the transceiver 120 are shown in FIG. 1B as separate components, it will be understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0022] The transmitting / receiving element 122 may be configured to transmit and receive signals to and from a base station (e.g., base station 114a) via the air interface 116. For example, in one embodiment, the transmitting / receiving element 122 may be an antenna configured to transmit and / or receive RF signals. In another embodiment, the transmitting / receiving element 122 may be an emitter / detector configured to transmit and / or receive, for example, IR, UV, or visible light signals. In one embodiment, the transmitting / receiving element 122 may be configured to transmit and / or receive both RF signals and optical signals. It will be understood that the transmitting / receiving element 122 may be configured to transmit and / or receive any combination of radio signals.

[0023] In Figure 1B, the transmit / receive element 122 is depicted as a single element, but 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 radio signals via the air interface 116.

[0024] The transceiver 120 may be configured to modulate the signal to be transmitted by the transmitting / receiving element 122 and to demodulate the signal received by the transmitting / receiving element 122. As described above, the WTRU 102 may have multimode capability. Therefore, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11.

[0025] The processor 118 of the WTRU102 may be coupled to a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light-emitting diode (OLED) display unit) and may receive user input data from them. The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. Furthermore, the processor 118 may access information in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132, and store data therein. Non-removable memory 130 may include RAM, ROM, a hard disk, or any other type of memory storage device. Removable memory 132 may include a SIM card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access and store data in memory that is not physically located on the WTRU 102, such as on a server or home computer (not shown).

[0026] The processor 118 may be configured to receive power from the power supply 134 and distribute and / or control power to other components in the WTRU 102. The power supply 134 may be any suitable device for supplying power to the WTRU 102. For example, the power supply 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.), a solar cell, a fuel cell, etc.

[0027] The processor 118 may also be coupled to a GPS chipset 136 which may be configured to provide location information (e.g., longitude and latitude) about the current location of the WTRU 102. In addition to, or instead of, information from the GPS chipset 136, the WTRU 102 may receive location information from base stations (e.g., base stations 114a, 114b) via the air interface 116 and / or determine its location based on the timing of signals received from two or more nearby base stations. It will be understood that the WTRU 102 may acquire location information by any preferred location determination method while maintaining consistency with the embodiment.

[0028] The processor 118 may also be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functions, and / or wired or wireless connectivity. For example, peripherals 138 may include an accelerometer, e-compass, satellite transceiver, digital camera (for photos and / or videos), Universal Serial Bus (USB) port, vibration device, television transceiver, hands-free headset, Bluetooth® module, frequency modulation (FM) radio unit, digital music player, media player, video game player module, internet browser, virtual reality and / or augmented reality (VR / AR) device, activity tracker, etc. Peripherals 138 may include one or more sensors. The sensors may be one or more of the following: gyroscope, accelerometer, Hall effect sensor, magnetometer, orientation sensor, proximity sensor, temperature sensor, time sensor, geolocation sensor, altimeter, light sensor, touch sensor, magnetometer, barometer, gesture sensor, biosensor, and / or humidity sensor.

[0029] WTRU102 may include a full-duplex radio where the transmission and reception of some or all of the signal (for example, related to a particular subframe for both the uplink (for transmission) and the downlink (for reception)) may occur simultaneously and / or concurrently. The full-duplex radio may include an interference management unit 139 to reduce and / or substantially eliminate self-interference through signal processing via either hardware (e.g., chokes) or a processor (e.g., a separate processor (not shown) or processor 118). In one embodiment, WTRU102 may include a half-duplex radio for the transmission and reception of some or all of the signal (for example, related to a particular subframe for either the uplink (for transmission) or the downlink (for reception)).

[0030] Figure 1C is a system diagram showing RAN104 and CN106 according to one embodiment. As described above, RAN104 employs E-UTRA wireless technology and can communicate with WTRU102a, 102b, and 102c via the air interface 116. RAN104 may also communicate with CN106.

[0031] RAN104 may include eNode-B160a, 160b, and 160c, but it will be understood that RAN104 may include any number of eNode-B while maintaining consistency with the embodiment. Each of eNode-B160a, 160b, and 160c may be equipped with one or more transceivers for communicating with WTRU102a, 102b, and 102c via the air interface 116. In one embodiment, eNode-B160a, 160b, and 160c may implement MIMO technology. Thus, eNode-B160a may, for example, use multiple antennas to transmit radio signals to and receive radio signals from WTRU102a.

[0032] Each of the eNodeB160a, 160b, and 160c may be associated with a specific cell (not shown) and may be configured to handle wireless resource management decisions, handover decisions, user scheduling on uplink (UL) and / or downlink (DL), etc. As shown in Figure 1C, the eNodeB160a, 160b, and 160c may communicate with each other via the X2 interface.

[0033] The CN106 shown in Figure 1C may include a Mobility Management Entity (MME) 162, a Serving Gateway (SGW) 164, and a Packet Data Network (PDN) Gateway (PGW) 166. Although each of the above elements is shown as part of CN106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0034] MME162 may be connected to each of the eNodeB160a, 160b, and 160c within RAN104 via the S1 interface and may act as a control node. For example, MME162 may be responsible for authenticating users of WTRU102a, 102b, and 102c, activating / deactivating bearers, and selecting a specific serving gateway during the initial attachment of WTRU102a, 102b, and 102c. MME162 may provide control plane functionality for switching between RAN104 and other RANs (not shown) employing other radio technologies such as GSM and / or WCDMA.

[0035] SGW164 may be connected to each of the e-nodes B160a, 160b, and 160c in RAN104 via the S1 interface. Generally, SGW164 can route and forward user data packets to and from WTRU102a, 102b, and 102c. SGW164 may perform other functions such as anchoring the user plane during handovers between e-nodes B, triggering paging when DL data is available to WTRU102a, 102b, and 102c, and managing and remembering the context of WTRU102a, 102b, and 102c.

[0036] SGW164 may be connected to PGW166, which can provide WTRU102a, 102b, and 102c with access to a packet-switched network such as the Internet 110 to facilitate communication between WTRU102a, 102b, and 102c and IP-enabled devices.

[0037] CN106 can facilitate communication with other networks. For example, CN106 may provide WTRU102a, 102b, and 102c with access to a circuit-switched network such as PSTN108 to facilitate communication between WTRU102a, 102b, and 102c and conventional fixed communication devices. For example, CN106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between CN106 and PSTN108. Furthermore, CN106 can provide WTRU102a, 102b, and 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers.

[0038] Although the WTRU is shown as a wireless terminal in Figures 1A to 1D, in some typical embodiments, such a terminal may use a wired communication interface with a communication network (for example, temporarily or permanently).

[0039] In a typical embodiment, the other network 112 may be a WLAN.

[0040] A WLAN in Infrastructure Basic Service Set (BSS) mode has an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have access to or interface to a distribution system (DS) or another type of wired / wireless network that carries traffic to and / or from the BSS. Traffic originating outside the BSS and destined for the STA may arrive through the AP and be sent to the STA. Traffic originating from the STA to destinations outside the BSS may be sent to the AP and delivered to their respective destinations. Traffic between STAs within the BSS can be transmitted through the AP, for example, a source STA may send traffic to the AP, and the AP may deliver the traffic to the destination STA. Traffic between STAs within the BSS may be considered or referred to as peer-to-peer traffic. Peer-to-peer traffic can be transmitted (e.g., directly) between a source STA and a destination STA using a Direct Link Setup (DLS). In certain typical embodiments, the DLS may be an 802.11e DLS or an 802.11z Tunnel DLS (TDLS). WLANs using Independent BSS (IBSS) mode may not have access points (APs), and STAs within or using IBSS (e.g., all STAs) may communicate directly with each other. The IBSS communication mode is sometimes referred to as the “ad-hoc” communication mode in this specification.

[0041] When using 802.11ac infrastructure mode or a similar operating mode, an AP can transmit beacons on a fixed channel, such as the primary channel. The primary channel can be of a fixed width (e.g., a wide bandwidth of 20 MHz) or a dynamically set width via signaling. The primary channel may be the operating channel of the BSS and may be used by the STA to establish a connection with the AP. In certain typical embodiments, a carrier-sensing multiple access / collision avoidance scheme (CSMA / CA) may be implemented, for example, in an 802.11 system. In the case of CSMA / CA, the STA, including the AP (e.g., all STAs), can sense the primary channel. If the primary channel is sensed / detected by a particular STA and / or determined to be busy, that particular STA can backoff. One STA (e.g., just one station) can transmit on a given BSS at any time.

[0042] High-throughput (HT) STAs can use a 40MHz wide channel for communication, for example, by combining a primary 20MHz channel with adjacent or non-adjacent 20MHz channels to form a 40MHz wide channel.

[0043] Very high-throughput (VHT) STAs can support channels with widths of 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz. 40 MHz and / or 80 MHz channels can be formed by combining consecutive 20 MHz channels. 160 MHz channels may be formed by combining eight consecutive 20 MHz channels or by combining two discontinuous 80 MHz channels, the latter sometimes referred to as an 80+80 configuration. In the 80+80 configuration, the channel-coded data passes through a segment parser, which splits the data into two streams. Inverse fast Fourier transform (IFFT) processing and time-domain processing can be performed independently on each stream. The streams are mapped to two 80 MHz channels, and the data is transmitted by the transmitting STA. At the receiver of the receiving STA, the above operation for the 80+80 configuration can be reversed, and the combined data can be transmitted to the media access control (MAC).

[0044] Sub-1GHz operating modes are supported by 802.11af and 802.11ah. Channel operating bandwidth and carrier are reduced in 802.11af and 802.11ah compared to those used in 802.11n and 802.11ac. 802.11af supports 5MHz, 10MHz, and 20MHz bandwidths in the TV white space (TVWS) spectrum, while 802.11ah supports 1MHz, 2MHz, 4MHz, 8MHz, and 16MHz bandwidths using the non-TVWS spectrum. According to a typical embodiment, 802.11ah can support meter-type control / machine-type communications (MTC), such as MTC devices in a macro-coverage area. MTC devices may have limited functionality, including support for specific and / or limited bandwidths (e.g., support only). MTC devices may include batteries with battery life exceeding a threshold (e.g., maintaining a very long battery life).

[0045] A WLAN system can support multiple channels and channel bandwidths, including 802.11n, 802.11ac, 802.11af, and 802.11ah, and this WLAN system includes a channel that can be designated as the primary channel. The bandwidth of the primary channel may be equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by an STA from among all STAs operating in a BSS that support the minimum bandwidth operating mode. In the 802.11ah example, even if the AP and other STAs in the BSS support operating modes of 2MHz, 4MHz, 8MHz, 16MHz, and / or other channel bandwidths, the primary channel of an STA (e.g., an MTC-type device) that supports (e.g., only supports) the 1MHz mode may be 1MHz wide. Carrier sensing and / or network allocation vector (NAV) settings may depend on the status of the primary channel. For example, if the primary channel is busy because an STA (which only supports 1MHz operating mode) is transmitting to the AP, a large portion of the frequency band remains idle, and even if it were available, the entire available frequency band can be considered busy.

[0046] In the United States, the usable frequency band for 802.11ah is 902MHz to 928MHz. In South Korea, the usable frequency band is 917.5MHz to 923.5MHz. In Japan, the usable frequency band is 916.5MHz to 927.5MHz. The total usable bandwidth for 802.11ah is 6MHz to 26MHz, depending on the country code.

[0047] Figure 1D is a system diagram showing RAN113 and CN115 according to one embodiment. As described above, RAN113 can employ NR radio technology to communicate with WTRU102a, 102b, and 102c via the air interface 116. RAN113 may also communicate with CN115.

[0048] RAN113 may include gNB180a, 180b, and 180c, but it will be understood that RAN113 may include any number of gNBs while maintaining consistency with one embodiment. Each of gNB180a, 180b, and 180c may include one or more transceivers for communicating with WTRU102a, 102b, and 102c via the air interface 116. In one embodiment, gNB180a, 180b, and 180c can implement MIMO technology. For example, gNB180a and 180b can transmit and / or receive signals to and from WTRU102a, 102b, and 102c using beamforming. Thus, for example, gNB180a can transmit and / or receive radio signals to and from WTRU102a using multiple antennas. In one embodiment, gNB180a, 180b, and 180c can implement carrier aggregation technology. For example, gNB180a can transmit multiple component carriers to WTRU102a (not shown). A subset of these component carriers may be on the unlicensed spectrum, and the remaining component carriers may be on the licensed spectrum. In one embodiment, gNB180a, 180b, and 180c can implement Coordinated Multi-Point (CoMP) technology. For example, WTRU102a can receive coordinated transmissions from gNB180a and gNB180b (and / or gNB180c).

[0049] WTRU102a, 102b, and 102c can communicate with gNB180a, 180b, and 180c using transmissions associated with scalable numerology. For example, orthogonal frequency division multiplexing (OFDM) symbol spacing and / or OFDM subcarrier spacing may vary by different transmissions, different cells, and / or different parts of the radio transmission spectrum. WTRU102a, 102b, and 102c can communicate with gNB180a, 180b, and 180c using subframes or transmit time intervals (TTI) of varying or scalable lengths (e.g., varying numbers of OFDM symbols and / or varying lengths of absolute time duration).

[0050] gNB180a, 180b, and 180c can be configured to communicate with WTRU102a, 102b, and 102c in standalone and / or non-standalone configurations. In a standalone configuration, WTRU102a, 102b, and 102c can communicate with gNB180a, 180b, and 180c without accessing other RANs (e.g., e-nodes B160a, 160b, and 160c). In a standalone configuration, WTRU102a, 102b, and 102c can utilize one or more gNB180a, 180b, and 180c as mobility anchor points. In a standalone configuration, WTRU102a, 102b, and 102c can communicate with gNB180a, 180b, and 180c using signals in unlicensed bands. In a non-standalone configuration, WTRU102a, 102b, and 102c can communicate with gNB180a, 180b, and 180c while also communicating with other RANs such as eNode-B160a, 160b, and 160c. For example, WTRU102a, 102b, and 102c can implement the DC principle to communicate with one or more gNB180a, 180b, and 180c and one or more eNodes B160a, 160b, and 160c almost simultaneously. In a non-standalone configuration, eNodes B160a, 160b, and 160c can act as mobility anchors for WTRU102a, 102b, and 102c, and gNB180a, 180b, and 180c can provide additional coverage and / or throughput to service WTRU102a, 102b, and 102c.

[0051] Each of the gNB180a, 180b, and 180c may be associated with a specific cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, user scheduling in UL and / or DL, support for network slicing, dual connectivity, interworking between NR and E-UTRA, routing of user plane data to user plane functions (UPF) 184a and 184b, access to control plane information, and routing to mobility management functions (AMF) 182a and 182b. As shown in Figure 1D, the gNB180a, 180b, and 180c can communicate with each other via the Xn interface.

[0052] The CN115 shown in Figure 1D may include at least one AMF182a, 182b, at least one UPF184a, 184b, at least one Session Management Function (SMF)183a, 183b, and optionally a Data Network (DN)185a, 185b. Although each of the above elements is shown as part of CN115, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0053] AMF182a, 182b may be connected to one or more gNB180a, 180b, 180c in RAN113 via the N2 interface and function as a control node. For example, AMF182a, 182b may be responsible for user authentication of WTRU102a, 102b, 102c, support for network slicing (e.g., handling different protocol data unit (PDU) sessions with different requirements), selection of specific SMF183a, 183b, management of registration areas, termination of NAS signaling, mobility management, etc. Network slicing may be used by AMF182a, 182b to customize CN support for WTRU102a, 102b, 102c based on the type of service utilized by WTRU102a, 102b, 102c. For example, various network slices can be established for various use cases, such as services that rely on ultra-high reliability low latency (URLLC) access, services that rely on extended large-scale mobile broadband (eMBB) access, and services for machine-type communications (MTC) access. The AMF182 may provide control plane functionality for switching between RAN113 and other RANs (not shown) that use other radio technologies such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies such as Wi-Fi.

[0054] SMF183a and 183b may be connected to AMF182a and 182b in CN115 via the N11 interface. SMF183a and 183b may also be connected to UPF184a and 184b in CN115 via the N4 interface. SMF183a and 183b can select and control UPF184a and 184b and configure the routing of traffic through UPF184a and 184b. SMF183a and 183b can perform other functions such as managing and assigning UE IP addresses, managing PDU sessions, controlling policy enforcement and QoS, and providing downlink data notifications. PDU session types may be IP-based, non-IP-based, Ethernet®-based, etc.

[0055] UPF184a, 184b can be connected to one or more gNB180a, 180b, 180c in RAN113 via the N3 interface, which provides WTRU102a, 102b, 102c with access to packet-switched networks such as the Internet 110 and facilitates communication between WTRU102a, 102b, 102c and IP-enabled devices. UPF184, 184b can perform other functions such as packet routing and forwarding, enforcement of user plane policies, support for multi-homed PDU sessions, processing of user plane QoS, buffering of downlink packets, and providing mobility anchors.

[0056] CN115 can facilitate communication with other networks. For example, CN115 may include, or communicate with, an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between CN115 and PSTN108. Furthermore, CN115 may provide WTRU102a,102b,102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers. In one embodiment, WTRU102a,102b,102c may be connected to local DN185a,185b through UPF184a,184b via an N3 interface to UPF184a,184b and an N6 interface between UPF184a,184b and data networks (DN)185a,185b.

[0057] With regard to Figures 1A to 1D and the corresponding descriptions therein, one or more, or all, of the functions described herein with respect to one or more of the WTRU102a to d, base stations 114a to b, e-nodes B160a to c, MME162, SGW164, PGW166, gNB180a to c, AMF182a to b, UPF184a to b, SMF183a to b, DN185a to b, and / or other devices described herein can 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, emulation devices may be used to test other devices and / or to simulate network and / or WTRU functions.

[0058] Emulation devices can be designed to implement one or more tests of other devices in a lab environment and / or operator network environment. For example, one or more emulation devices can be fully or partially implemented and / or deployed as part of a wired and / or wireless network to perform one, more or all of its functions in order to test other devices in a communications network. One or more emulation devices can be temporarily implemented / deployed as part of a wired and / or wireless network to perform one, more or all of its functions. Emulation devices can be directly coupled to another device for testing purposes and / or can perform tests using wireless communication.

[0059] One or more emulation devices may perform one or more functions (including all functions) without being implemented / deployed as part of a wired and / or wireless communication network. For example, an emulation device may be used in a test scenario in a test lab and / or in a test scenario in a non-deployed (e.g., test) wired and / or wireless communication network to implement testing of one or more components. One or more emulation devices may be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (e.g., which may have one or more antennas) may be used by the emulation device to transmit and / or receive data.

[0060] In this specification, references to a timer may include time, period, tracking of time, tracking of a period of time, or combinations thereof. In this specification, references to timer expiration may include determining that time has elapsed or that a period has expired.

[0061] As used herein, the term SpCell may refer, for example, to a PCell of an MCG or a primary SCG cell (PSCell) of an SCG, depending on whether the MAC entity is associated with a master cell group (MCG) or an SCG.

[0062] Systems, methods, and means relating to early timing advance (TA) acquisition for random access channel (RACH)-less conditional handover (CHO) are described herein. A device can perform (for example, be configured to perform) one or more of the following actions: A wireless transceiver unit (WTRU) can perform a RACH-less CHO evaluation based on a valid TA. A WTRU can trigger early TA acquisition for RACH-less CHO / conditional L1 / L2 trigger mobility (LTM). A WTRU can select a RACH procedure to perform for handover (HO) execution.

[0063] Systems, methods, and means relating to random access channelless (RACH-less) conditional handover (CHO) evaluation based on a valid timing advance (TA) are described herein. A device can perform (for example, be configured to perform) one or more of the following actions: A wireless transceiver unit (WTRU) may be configured with a conditional handover applicable to a given target cell while the WTRU has a valid TA for the target cell (for example, only during that period). The WTRU can receive a RACH-less conditional handover configuration using the TA validity period to determine whether a RACH-less handover and associated conditions are applicable / valid. A conditional RACH-less handover may be enabled for L1 / L2 trigger mobility (LTM), for example, when a media access control (MAC) control element (CE) indicates the TA and validity period of a RACH-less handover conditional trigger.

[0064] A WTRU may receive configurations for LTM candidate cells and / or configurations for RACHless CHOs. A configuration may include, for example, one or more of the following: L3 events for one or more target cells, L1 measurement-based events, one or more (e.g., specific) measurement resources, RACHless (e.g., specific) trigger conditions that may consider cells with valid TAs (e.g., only those cells), one or more (e.g., specific) resources (e.g., configured grants) to use when performing a conditional LTM (e.g., separate from an explicit LTM trigger resource), a CHO configuration that may include a first execution condition when RACHless is used (e.g., when the WTRU has a valid TA for this target), and a second execution condition otherwise. A CHO configuration may include multiple (e.g., two) thresholds, such as one threshold used when the WTRU may have a TA and another threshold used otherwise. A CHO configuration may include alternative / different time and / or filtering parameters to trigger, for example, so that RACHless can be triggered more quickly. A CHO configuration may include multiple (e.g., two) CHO configurations. For example, cells with a WTRU having a TA may be evaluated using a first CHO configuration, while other cells may be evaluated using a second CHO configuration. The CHO configuration can 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).

[0065] WTRU can transmit Channel Status Information (CSI) reports.

[0066] The WTRU can receive physical downlink control channel (PDCCH) orders. The WTRU can send a preamble to the target cell.

[0067] WTRU can receive conditional cell switch instructions, which may include an indication to perform a cell switch when the TA value, validity time, and / or CHO condition are met within the validity time.

[0068] In some cases, the WTRU can execute multiple PDCCH reception, preamble transmission, and conditional cell switching instructions, for example, to enable CHO to multiple targets in parallel.

[0069] In some cases, the WTRU may perform PDCCH reception and preamble transmission multiple times, while the conditional cell switching instruction may include TA / CHO enablers for multiple targets.

[0070] In some examples, a WTRU can perform PDCCH reception and preamble transmission to a target cell (e.g., one) within a configured Timing Advance Group (TAG). The acquired TA may enable RACH-less CHO to any cell (e.g., any) within the TAG.

[0071] Figures 6-8 show examples of obtaining a TA. Other examples of obtaining a TA may include, for example, the Random Access Response (RAR) of the target cell, the RAR of the source cell, and the WTRU that maintains the TA. MAC CE may or may not be used to "enable" CHO. CHO may depend on obtaining a TA, and TA can be obtained by any means. Configurations can be activated / deactivated, for example, using MAC CE.

[0072] WTRU can measure one or more configured target cells. In some examples, the measurement may be performed on (e.g., all) cells within a TAG where TA is enabled.

[0073] A WTRU can perform an LTM (for example, apply a pre-configured candidate configuration) if, for example, a RACH-less CHO condition is met for one or more cells (e.g., any cells) configured with TA values ​​before the expiration of the validity timer. CHO conditions (e.g., other CHO conditions) can include, for example, a synchronous signal block (SSB), a reference signal received power (RSRP) threshold, and a timing comparison. A configured grant (CG) associated with the beam that triggers the CHO (e.g., the best beam) may be used. A CHO may no longer be valid, and the configuration can be released, for example, when a timer (e.g., a TA validity timer) expires. The next CHO evaluation may occur, for example, when a new TA command is received. A WTRU can use a second condition (e.g., a different CHO configuration corresponding to a RACH-based CHO if the WTRU does not have a valid TA) if, for example, the timer has expired.

[0074] A WTRU can transmit indications to a target. For example, a WTRU can transmit an RRC completion message on a physical uplink shared channel (PUSCH). A WTRU can use a CG associated with the beam that triggers the CHO (e.g., the best beam). A WTRU can monitor uplink grants on a PDCCH. A WTRU can transmit (for example, then) data and / or Radio Resource Control (RRC) completion messages.

[0075] An exemplary device may include a processor configured to perform one or more actions. For example, the device may receive from a first cell a configuration including a mobility candidate cell containing a first candidate cell and a second candidate cell, and a configuration for a Random Access Channel (RACH)-less Conditional Handover (CHO) including a RACH-less CHO condition. The device may perform measurements on the mobility candidate cell and report the measurements to the first cell. The device may perform Random Access (RA) to the first candidate cell using the RA resources indicated by the first cell. The device may receive a conditional cell switching indication including the timing advance (TA) value and TA validity period of the first candidate cell. The device may perform a conditional cell switching from the first cell to the first candidate cell if the RACH-less CHO condition is met before the expiration of the TA validity period.

[0076] The configuration may include a RACH-based CHO configuration, which includes RACH-based CHO conditions. The device may use RACH-based CHO to perform a conditional cell switch from the first cell to the first candidate cell if the RACH-based CHO conditions are met after the expiration of the TA validity period.

[0077] The configuration can represent timing advance groups (TAGs) for a first candidate cell and a second candidate cell (for example, the TA value and TA validity period apply to the first and second candidate cells). The device can perform a conditional cell switch from the first cell to the second candidate cell if the RACH-less CHO condition is met before the expiration of the TA validity period.

[0078] Systems, methods, and means relating to triggering early timing advance (TA) acquisition by a wireless transceiver unit (WTRU) for random access channel (RACH)-less conditional handover (CHO) / conditional L1 / L2 triggered mobility (LTM) are described herein. The device can perform (for example, be configured to perform) one or more of the following actions: The wireless transceiver unit (WTRU) can trigger early TA acquisition, which may be used for RACH-less CHO, based on certain conditions (for example, in addition to a first condition for triggering LTM execution). Condition evaluation may be enabled, for example, when the WTRU receives a physical downlink control channel (PDCCH) order indicating an RA resource and the lifetime of the RA resource. The WTRU may, for example, trigger a random access (RA) if the conditions are met, to enable, for example, a target TA acquisition.

[0079] The WTRU can receive the configuration of LTM candidate cells and / or the configuration of RACH-less CHO (e.g., condition 1). The WTRU can receive conditions to trigger TA acquisition (e.g., condition 2).

[0080] WTRU can transmit Channel Status Information (CSI) reports.

[0081] A WTRU can submit a PDCCH order request that enables the WTRU to trigger a TA acquisition / CHO. This request may be based on an event, for example, when a target value is better than a threshold. This request may also be part of a CSI report, such as an event-triggered report.

[0082] A WTRU may receive a PDCCH order that enables the WTRU to trigger a TA acquisition. The PDCCH order may include an RA resource and / or an RA resource lifetime timer. There may be multiple (e.g., two) conditions. The first condition may be for a RACH (e.g., an autonomous RA) for a target. 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 a CHO. The second condition may indicate, for example, a second threshold (e.g., threshold 2) and a valid TA.

[0083] WTRU can perform measurements on a configured target.

[0084] A TA acquisition can be triggered when the TA acquisition conditions (e.g., condition 1) are met. The WTRU can send a PRACH preamble to the target when a TA acquisition is triggered. Requests can 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)) can be used.

[0085] WTRU can receive the TA value and enable RACH-less CHO.

[0086] LTM may be executed (for example, by applying a pre-configured candidate configuration). For example, if the RACH-less CHO condition (for example, the second condition) is met for one or more cells (for example, any cells) configured with TA values ​​before the timer expires. The PDCCH order can disable / enable the LTM configuration.

[0087] A WTRU can transmit indications to a target. For example, a WTRU can transmit a Radio Resource Control (RRC) completion message on a Physical Uplink Shared Channel (PUSCH). A WTRU can use a CG associated with the best beam to trigger a CHO. A WTRU can monitor uplink grants on a PDCCH and (for example, then) transmit data and / or an RRC completion message.

[0088] An exemplary device may include a processor configured to perform one or more actions. For example, the device may receive from a first cell a configuration including a mobility candidate cell containing a first candidate cell, a RACH-less CHO configuration including a Random Access Channel (RACH)-less Conditional Handover (CHO) condition, and a TA Acquisition configuration including a Timing Advance (TA) Acquisition condition. The device may perform measurements on the mobility candidate cell and report the measurements to the first cell. If the TA Acquisition condition is met, the device may perform Random Access (RA) to the first candidate cell using the RA resource indicated by the first cell. The device may receive a conditional cell switching indication including the TA value and TA validity period of the first candidate cell. If the RACH-less CHO condition is met before the expiration of the TA validity period, the device may perform a conditional cell switching from the first cell to the first candidate cell.

[0089] The configuration may include a RACH-based CHO configuration, which includes RACH-based CHO conditions. The device may use RACH-based CHO to perform a conditional cell switch from the first cell to the first candidate cell if the RACH-based CHO conditions are met after the expiration of the TA validity period.

[0090] The configuration can represent timing advance groups (TAGs) for a first candidate cell and a second candidate cell (for example, the TA value and TA validity period apply to the first and second candidate cells). The device can perform a conditional cell switch from the first cell to the second candidate cell if the RACH-less CHO condition is met before the expiration of the TA validity period.

[0091] Systems, methods, and means relating to selecting a Random Access Channel (RACH) procedure for performing a handover (HO) are described herein. A device can perform (for example, be configured to perform) one or more of the following actions: A wireless transceiver unit (WTRU) can prioritize targets for performing L1 / L2 trigger mobility (LTM) depending on whether the WTRU can perform a RACH-less handover. A RACH-less conditional HO (CHO) can provide reduced interruption and / or robustness compared to a handover that utilizes RACH, for example.

[0092] The WTRU may receive configurations for LTM candidate cells and / or configurations for the CHO. The CHO configuration may include separate execution conditions (e.g., separate thresholds) depending, for example, whether the WTRU has a valid timing advance (TA). The CHO configuration may include one or more conditions related to the remaining validity period (e.g., a first condition if the remaining validity period is greater than a threshold, and a second condition otherwise). The CHO configuration may include configurations for the type of RACH procedure to execute and / or conditions for selecting the type of RACH procedure to execute, depending on the remaining TA validity period.

[0093] WTRU can transmit Channel Status Information (CSI) reports.

[0094] The WTRU can receive the Physical Downlink Control Channel (PDCCH) order. The WTRU can send a preamble to the first target cell.

[0095] WTRU can receive the TA value for the first cell.

[0096] WTRU can perform measurements on a configured LTM target, which may include at least a first cell and a second cell (e.g., one without a valid TA value). The second cell may have a valid TA with a remaining TA validity period, which may be shorter than the remaining TA validity period of the first cell.

[0097] The WTRU can select the first cell. Based on prioritization rules, the WTRU can perform a CHO (e.g., RACH-less LTM execution) on the first cell if, for example, the cell switching criteria are met for both the first and second cells. Exemplary selection criteria / prioritization rules may include, for example, one or more of the following: an indication of whether a TA is enabled or disabled; an indication for selecting the target with the longest remaining TA validity period; an indication for selecting a target configured for RACH-less as a priority over targets not configured for RACH-less; selection criteria may include an offset to the CHO criterion, for example, a cell configured for RACH-less may have a lower Reference Signal Received Power (RSRP) threshold; selection criteria may apply a shorter trigger time (TTT) to the CHO criterion if a cell is configured for RACH-less, and the selection of a first cell may include aborting a reconfiguration procedure toward a second cell (e.g., if a WTRU is performing a preamble retransmission to perform a RACH procedure for HO toward a second cell, for example, aborting and performing RACH-less toward the first cell); and / or selection prioritization rules may apply if conditional reconfiguration criteria are met for multiple cells / or if multiple cells are performing different types of reconfiguration (e.g., explicit and conditional reconfiguration).

[0098] The WTRU can transmit indications to the target (first cell). For example, the WTRU can transmit a Radio Resource Control (RRC) completion message on the PUSCH. The WTRU can use a configured grant (CG) associated with the best beam to trigger the CHO. The WTRU can monitor uplink grants on the PDCCH. The WTRU can transmit data and / or RRC completion messages.

[0099] An exemplary 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 include a mobility candidate cell containing a first candidate cell and a second candidate cell, and a RACH-less CHO configuration that includes a Random Access Channel (RACH)-less Conditional Handover (CHO) condition. The device may perform measurements on the mobility candidate cell and report the measurements to the first cell. The device may perform Random Access (RA) to the mobility candidate cell using the RA resources indicated by the first cell. The device may receive a first conditional cell switching indication that includes the Timing Advance (TA) value and TA validity period of the first candidate cell. The device may receive a second conditional cell switching indication to the second candidate cell. The device may prioritize the first conditional cell switching over the second conditional cell switching based on cell switching priorities. The device may perform a first conditional cell switching from the first cell to the first candidate cell if the RACH-less CHO condition is met before the expiration of the TA validity period.

[0100] Cell switching prioritization can take precedence over a second conditional cell switching by, for example, prioritizing RACH-less CHOs over RACH-based CHOs and / or prioritizing the remaining TA validity period.

[0101] A WTRU (e.g., a WTRU in the RRC_CONNECTED state) can measure multiple beams, for example, including at least one measurement of a cell. The measurement results (e.g., power values) can be averaged to derive cell quality, for example. The WTRU can be configured to consider a subset of detected beams based on the determined cell quality, for example. Filtering can be performed 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 can be derived in the same way for serving and non-serving cells. The measurement report can include measurement results for X best beams, for example, if the WTRU is configured to do so by gNB. The corresponding high-level measurement model is shown in Figure 2.

[0102] Figure 2 shows an example of a measurement model.

[0103] Inter-cell L1 / L2 trigger mobility (LTM) may be implemented. Inter-cell beam management can be used, for example, to manage beams for carrier aggregation (CA). Cell changes / additions may be supported, for example, as described herein.

[0104] L1 / L2-based inter-cell mobility may be used to reduce mobility latency. Multiple candidate cells may be configured and maintained (e.g., in RAN2, RAN3) to enable rapid application of configurations to candidate cells. Dynamic switching between candidate serving cells (e.g., including special cells (SpCell) and secondary cells (SCell)) may be performed based on L1 / L2 signaling (e.g., in RAN2, RAN1). Inter-cell beam management may include, for example, L1 measurements 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 as 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., NR-DC case with carrier aggregation (CA) and serving cell changes within a single configured grant (CG)); in-DU case and inter-CU case (e.g., applicable to standalone and CA); both in-frequency and inter-frequency; both FR1 and FR2; and / or source and target cells may be synchronized or asynchronous.

[0105] L1 / L2-based mobility can utilize inter-cell beam management in in-DU and / or in-frequency scenarios. The serving cell may remain unchanged (e.g., there may be no possibility of changing the serving cell using L1 / L2-based mobility). CA may be used to aggregate multiple CCs into one band by utilizing available bandwidth (e.g., in an FR2 deployment). These CCs can be transmitted on the same analog beam pair (e.g., gNB beam and WTRU beam). WTRU may consist of TCI states (e.g., 64 TCI states) for receiving PDCCH and PDSCH. TCI states (e.g., each TCI state) may include a reference signal (RS) or synchronization signal block (SSB) that the WTRU can refer to to set its beam. The SSB may be associated with a non-serving PCI. MAC signaling ("TCI state indication for WTRU-specific PDCCH MAC CE") can activate the TCI states of CORESET / PDCCH. Reception of PDSCH from a non-serving cell may be supported by MAC CE indicating TCI states associated with the non-serving physical cell identifier (PCI). MAC signaling ("TCI States Activation / Deactivation for WTRU-specific PDSCH") can activate a subset of TCI states (e.g., up to eight TCI states) for PDSCH reception. Downlink control information (DCI) can indicate one or more TCI states. "Integrated TCI states" may be supported by different update mechanisms (e.g., DCI-based), for example, with or without multi-transmit / receive point (TRP) support.

[0106] L1 / L2 trigger mobility (LTM) can improve handover latency. L3 handover or conditional handover may involve the WTRU transmitting a measurement report using RRC signaling (e.g., initially). The network may provide further measurement configurations and / or conditional handover configurations (e.g., in response). The network may provide a configuration for a target cell (e.g., for conventional handovers) after the WTRU has reported using RRC signaling that the cell meets configured radio quality criteria. Conditional handovers (CHOs) can reduce the handover failure rate (e.g., for conventional handovers) due to delays in the transmission of measurement reports and reception of RRC reconfigurations provided by the network. A CHO may include pre-determining and receiving target cell configurations and / or metrics that can be used to determine when the WTRU can trigger a CHO configuration. Unconditional and conditional handovers implemented as L3 methods may be delayed for the transmission of measurement reports and reception of target configurations.

[0107] LTM enables rapid application of candidate cell configurations, including dynamic switching between SCells and primary cell (PCell) switching (e.g., switching roles between SCells and PCells), without performing RRC signaling. Inter-CU cases may include relocation of Packet Data Convergence Protocol (PDCP) anchors. RRC-based approaches may support inter-CU handovers.

[0108] L3 handover allows the WTRU to release currently active SCells before completing the handover to the target cell within the coverage area of ​​the new site. Released SCells may be added again after the handover is successful (e.g., only after success), which can reduce throughput during the handover. The LTM may enable CA behavior (e.g., instantaneously) when the serving cell changes.

[0109] Figure 3 shows an example of LTM operation. Candidate cell groups may be configured by RRC. Dynamic switching between PCell and SCell can be achieved using L1 / L2 signaling.

[0110] Figure 3 shows an example of LTM using CA.

[0111] Figure 4 shows an example of an LTM procedure (e.g., a baseline LTM procedure). As shown in Figure 4, this specification describes an example of an LTM procedure.

[0112] In reference numeral 1, the WTRU can send a measurement message (e.g., a MeasurementReport message) to the gNB. The gNB can decide to use the LTM. The gNB can begin preparing the LTM candidate.

[0113] In reference numeral 2, the gNB may send a configuration message (e.g., an RRCReconfiguration message) to the WTRU that includes the configuration of one or more LTM candidate target cells.

[0114] In reference numeral 3, the WTRU can store the configuration of the LTM candidate target cell. The WTRU can send a completion message (e.g., an RRCReconfigurationComplete message) to the gNB.

[0115] In reference numeral 4, the WTRU can, for example, perform downlink (DL) synchronization and timing advance (TA) acquisition with a candidate target cell before receiving an LTM cell switch command. DL synchronization of the candidate cell before receiving the cell switch command may be supported, for example, based on SSB. TA acquisition of the candidate cell before receiving the LTM cell switch command may be supported, for example, based on a PDCCH ordered RACH. The PDCCH order may be triggered by a source cell (for example, only by a source cell).

[0116] In reference 5, the WTRU can perform L1 measurements on the configured LTM candidate target cells. The WTRU can send lower-layer measurement reports to the gNB. Lower-layer measurement reports can be delivered via L1 or MAC.

[0117] In reference 6, the gNB can decide to perform an LTM cell switch to the target cell. The gNB can send a MAC CE that triggers the LTM cell switch, for example, by including a candidate configuration index of the target cell. The WTRU can switch to the configuration of the LTM candidate target cell.

[0118] In reference to 7, the WTRU can, for example, perform a random access procedure toward the target cell if the TA is unavailable.

[0119] In reference numeral 8, the WTRU can indicate to the target cell that the LTM cell switchover has been successfully completed. After the WTRU has switched to the target cell, an uplink signal or message can indicate that the LTM cell switchover has been successfully completed.

[0120] RACH-less LTM may be performed. A WTRU can perform early TA acquisition with a candidate cell before receiving a cell switch command. Early TA acquisition can be performed, for example, via contention-free random access (CFRA) triggered by a PDCCH order from the source cell, after which the WTRU can send a preamble to the candidate cell. Information identifying the allocated CFRA resource can be indicated in the PDCCH order, for example, to enable sharing of preamble resources among multiple WTRUs in the RRC configuration. The source gNB can (for example, dynamically) indicate which WTRU will use the resource at any given time. A WTRU may not receive RAR, for example, to minimize data interruption to the source cell due to CFRA to the candidate cell. The source cell may trigger preamble retransmission / power ramping, for example, using a different PDCCH order, if the preamble was not received. A WTRU can perform RACH-less handover, for example, if the candidate cell's TA value is indicated in the cell switch command.

[0121] L1 / L2 triggered mobility (LTM) procedures can improve mobility latency by, for example, pre-configuring multiple target cells before handover, early DL / UL synchronization (sync) of target cells, L1 measurement reports, MAC CE indicating cell switching, etc. Conditional LTM can improve robustness. Conditional LTM can be performed using one or more of the following: L1-based conditions for triggering HO, LTM candidate cell configuration applied at trigger time, RACH-less CHO, and / or beam refinement before CHO. LTM preparation procedures can be configured so that the WTRU can perform RACH-less CHO (e.g., L3 or L1 triggered CHO) by enabling CHO using a TA acquisition procedure.

[0122] Where used herein, “perform an LTM” or “perform an LTM procedure” may mean performing one or more (e.g., all) actions related to an LTM, as may be shown or illustrated in the figures, which may include, for example, early synchronization in DL and / or UL to one or more candidate cells, performing L1 measurements and / or reporting to one or more candidate cells, switching between candidate cells (e.g., performing a handover) (for example, “perform an LTM” may mean that the WTRU moves / switches between multiple candidate cells during the procedure).

[0123] One or more candidate cell sets may be a group of multiple RRC configurations corresponding to one or more candidate SpCell and / or SCell handover configurations. 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 candidate cell configuration (e.g., each candidate cell configuration) may include a candidate configuration identifier. A candidate cell group (e.g., each candidate cell group) may include a candidate cell group identifier. Grouping may be performed in RRC. Switching between different sets of candidate cells (e.g., if grouping is performed in RRC) may involve updating a serving cell index or a candidate configuration index, which can be used to reference (e.g., specific) indexes in L1 and MAC signaling. For example, a MAC CE triggering a reconfiguration may include a candidate configuration index that informs the WTRU which cells are undergoing reconfiguration.

[0124] One or more candidate cell groups can be configured as a single list or group of candidate cell configurations in the RRC. Grouping may occur, for example, during the early sync or LTM execution phase rather than the configuration phase, meaning that a set of candidate cells may be considered a single group in terms of, for example, the RRC configuration list or group, while the cells selected for early sync, L1 measurement, and LTM execution may rely on further grouping into multiple subsets of the overall candidate cell list. Grouping itself cannot be modeled in the RRC using candidate configuration identifiers, but grouping can be performed as part of the early sync or LTM execution procedure.

[0125] LTM candidate configurations can be applied to types of pre-configured cell information. For example, a WTRU may be configured with one or more conditional reconfigurations such as a conditional handover (CHO), a conditional PSCell addition (CPA), and / or a conditional PSCell modification (CPC), which may be effective before and / or after a cell modification, and / or effective in one or more cells.

[0126] L1 measurements can include, for example, measurements of reference signal received power (RSRP) and received signal strength indicator (RSSI), which can be performed by WTRUs of cells, beams, sets of cells, and / or sets of beams. L1 measurements may be similar to L3 measurements reported in Radio Resource Management (RRM), although they differ in filtering, measured reference signals, reporting mechanisms, etc.

[0127] L1 measurements may be applied to RRM reports. While the measurements may represent L1 measurements of the LTM, they may also be applied to RRM / L3 measurements and / or other measurements (e.g., measurements of speed, position, height, traffic volume, etc.) (as described herein, for example).

[0128] LTM cell switching can be applied to other types of handover executions (e.g., any type). LTM cell switching can indicate L1 / L2 triggered mobility, which may include pre-configured RRC configurations that are applied when a WTRU receives an indication (e.g., using MAC CE) or when conditions are met at the WTRU. LTM cell switching can also be applied to RRC reconfiguration, RRC conditional reconfiguration, and / or other types of mobility procedures (e.g., as described herein).

[0129] As described herein, early timing advance (TA) acquisition can be used for random access channel (RACH)-less conditional handover (CHO). For example, a WTRU can perform a RACH-less CHO evaluation based on a valid TA. A WTRU can trigger early TA acquisition for RACH-less CHO / conditional L1 / L2 trigger mobility (LTM). A WTRU can select the RACH procedure to execute for handover (HO) execution. Implementations of the examples described herein can reduce interruptions and latency and improve robustness. A WTRU with a valid TA acquired before the cell change criterion is met can trigger a RACH-less LTM handover (e.g., immediately) without the delay associated with reporting a measurement and receiving an explicit cell switch command, if the criterion is met. In some examples, a network can prepare multiple cells with TA values ​​for RACH-less CHO. A WTRU can trigger a cell switch to the optimal cell based on the evaluation, for example, without reporting / receiving an explicit trigger.

[0130] LTM candidate configurations can be determined, provided, or received. A gNB (e.g., a CU in a CU / DU partition architecture where an RRC may reside within a CU) can configure potential LTM candidates, for example, using RRC signaling. A WTRU can receive LTM candidate configurations, for example, during the "LTM preparation" phase shown in Figure 4, using RRC reconfiguration messages. A WTRU can store LTM candidate configurations for later application, for example, when it receives an indication to perform a cell switch using L1 / L2 signaling (e.g., MAC CE) during the "LTM execution" phase shown in Figure 4.

[0131] The configuration of potential LTM candidates may include a first set of candidates that may be suitable for a first route (e.g., the WTRU of a vehicle turning left and traveling on a first road), and a second set of candidates that may be suitable for a second route (e.g., the WTRU of a vehicle turning right and traveling on a second road).

[0132] One or more (e.g., some or all) of the candidate set information may be broadcast in the system information. A WTRU can enable pre-configuration of broadcast configurations based on receiving (e.g., upon receiving) an indication in dedicated signaling (e.g., RRC reconfiguration) that indicates the broadcast of one or more configurations (e.g., using an index or identifier).

[0133] The configuration may include all (e.g., all) cells belonging to the CU to which the WTRU is currently connected, or all or a subset of potential cells within an area, such as cells within a specific geographical area. These cells may not yet have been discovered or measured by the WTRU, but may be pre-configured. The WTRU may receive configuration updates to modify, add, delete, and / or replace one or more parts (e.g., any parts) of the LTM candidate configuration (e.g., after the initial configuration of the LTM candidate configuration).

[0134] A WTRU may receive an indication to enable or disable one or more (e.g., some or all) LTM configurations. LTM may be disabled, for example, if WTRU mobility is expected to be better handled using L3 (e.g., RRC measurement reporting, RRC reconstruction, conditional reconstruction). LTM may be enabled, for example, if LTM is expected to be more suitable for WTRU mobility (e.g., a previously configured and disabled LTM configuration may be re-enabled).

[0135] The configuration may be based on a predictive model located within the network (e.g., gNB), and may be determined by the network (e.g., gNB). The prediction may be based, for example, on what the NW predictive model has determined to be the most likely path for the WTRU.

[0136] The candidate cell configuration may include all or some of the information necessary to complete the reconfiguration to the candidate cell (e.g., handover), such as channel configuration (e.g., PRACH, DPCCH, DPSCH), CORESET, bandwidth portion (BWP), security parameters, L2 parameters (e.g., MAC, radio link control (RLC), PDCP), radio bearer configuration, and combinations thereof.

[0137] An LTM execution trigger can indicate the conditions for performing an LTM (e.g., a conditional handover trigger or a measurement report trigger). The LTM execution trigger may be configured by the network and directed from the network to the WTRU, or it may be estimated and determined by the WTRU.

[0138] Triggers can be based on one or more of the following: time; radio quality measurement or predicted radio quality of one or more serving or target cells; location; and / or L3 measurement events; L1 measurement events or conditions; predicted events; (e.g., explicit) indications from the network; measured, predicted, or estimated throughput, error rate, buffer status, or QoS parameters; and / or evaluation metrics.

[0139] Time may be indicated by one or more of the following: absolute time or relative time, time measured in WTRU, system frame number (SFN), and / or subframe number.

[0140] The radio quality measurement or predicted radio quality of one or more 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-Index-RSRP, and / or cri-RI-LI-PMI-CQI.

[0141] A location may be indicated by, for example, one or more of the following: an area (defined, for example, by a reference point and radius), or a range of coordinates, and / or a distance threshold from the reference location.

[0142] An (for example) arbitrary L3 measurement event may include one or more of the following: Event A1 (e.g., Serving cell is better than the threshold), Event A2 (e.g., Serving cell is worse than the threshold), Event A3 (e.g., Neighbor offset is better than SpCell), Event A4 (e.g., Neighbor is better than the threshold), Event A5 (e.g., SpCell is worse than threshold 1 and Neighbor is better than threshold 2), Event A6 (e.g., Neighbor offset is better than SCell), Event B1 (e.g., Inter-RAT neighbor is better than the threshold), and / or Event B2 (e.g., PCell is worse than threshold 1 and Inter-RAT neighbor is better than threshold 2).

[0143] An L1 measurement event or condition can be any event defined to utilize L1 beam measurements to evaluate whether a criterion or condition is met.

[0144] The predicted event could be any event using any quantifiable quantity that may be associated with the measured or predicted CSI information.

[0145] Indications from the network (e.g., explicit) may be received by the WTRU. For example, the WTRU may enable CSI reporting based on an explicit indication (e.g., MAC CE) received from the network. When the WTRU receives a second MAC CE from the network, it may (e.g., subsequently) perform an LTM cell switchover.

[0146] The evaluation metrics may include, for example, trigger time, hysteresis, offset (e.g., wireless quality measurement offset), and / or measurement filtering configuration.

[0147] A trigger can include one or more conditions that allow a WTRU to perform any action related to the LTM (e.g., any action). For example, a WTRU could perform one or more of the following: early TA acquisition, switching off CSI reporting, switching on or updating CSI reporting configuration, performing LTM cell switching, monitoring PDCCH on the target cell, performing BFR or RLM on the target cell, and / or activating or deactivating a specific SCell.

[0148] Early TA acquisition may occur based on triggers, for example. For instance, a WTRU can trigger a RACH to a target LTM cell. The WTRU can receive the TA value in the RAR. The RAR can be received, for example, from the target cell or via the source cell. The WTRU can receive the TA value in the MAC CE, which triggers a cell switchover. If the RAR / MAC CE is not received, the WTRU can perform power ramping and preamble retransmission on the target, for example.

[0149] CSI reporting can be switched off, for example, based on a trigger. WTRUs may be permitted or required to switch off CSI reporting, for example, to reduce reporting overhead in the uplink. CSI reporting may be reduced rather than switched off, for example. For example, the number of cells or beams reporting may be reduced and / or the reporting frequency may be reduced. WTRUs may restart CSI reporting, for example, when the conditions are no longer met.

[0150] The CSI reporting configuration can be switched on and / or updated based on triggers, for example. For instance, a WTRU can perform and / or report a CSI measurement on one or more LTM candidate cells (e.g., a subset) during a window (e.g., it can be requested to do so).

[0151] LTM cell switching can be performed, for example, based on a trigger. One or more conditions or criteria can indicate whether and when a WTRU may be allowed to trigger an LTM cell switch.

[0152] PDCCH can be monitored on the target cell, for example, based on a trigger. WTRU can be configured to schedule PDSCH to initiate a cell switching procedure, or to monitor the target cell for DCIs indicating one or more actions on the target cell.

[0153] Beam failure recovery (BFR) or radio link monitoring (RLM) can be performed on the target cell, for example, based on a trigger. The WTRU can be configured to monitor beam failure detection (BFD) resources on the target cell and / or to perform RLM on the target cell during a window.

[0154] A cell (e.g., SCell) can be activated or deactivated, for example, based on a trigger. A WTRU can consist of one or more (e.g., a specific) SCells, which may be active or deactivated during a window.

[0155] RACH-less CHO and early TA acquisition may be performed. The WTRU may, for example, perform an early TA acquisition procedure using a candidate cell before receiving a cell switching command and / or before triggering a conditional reconfiguration, in order to enable a 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 perform PDCCH reception and uplink transmission (for example, instead) using an already provided TA.

[0156] Early TA acquisition can be performed, for example, using contention-free random access (CFRA) triggered by a PDCCH order from the source cell. WTRUs can then (for example) send a preamble to candidate cells. Information identifying the allocated CFRA resource can be indicated in the PDCCH order, for example, to allow sharing of preamble resources among multiple WTRUs in the RRC configuration. The source gNB can (for example, dynamically) indicate which WTRUs can use the resource at any given time.

[0157] Early TA acquisition can be performed, for example, based on receiving a MAC CE indicating that a RACH transmission will be performed on the target cell (e.g., upon reception).

[0158] Early TA acquisition can be achieved, for example, by sending a contention-based random access (CBRA) preamble.

[0159] In some cases, the WTRU may not receive the RAR, which can minimize data interruptions in the source cell, for example, due to a CFRA to a candidate cell. The source cell may trigger preamble retransmission / power ramping, for example, by using a different PDCCH order if the preamble was not received. The TA may be provided from the target cell to the source cell. The TA can be provided to the WTRU, for example, within a MAC CE that triggers a cell switchover, or by enabling a conditional LTM to one or more target cells.

[0160] In some cases, a WTRU can receive the TA value from the target cell in a Random Access Response (RAR). In some cases, a WTRU can receive the TA value from the source cell in a Random Access Response (RAR). If a WTRU does not receive an RAR in response to the transmission of a preamble (for example, within a given time), it can retransmit the preamble using higher transmit power, for example.

[0161] In some cases, a WTRU can store received TA values ​​for later use, for example, if a reconfiguration trigger occurs. A WTRU can store TA values ​​for a certain period (e.g., an expiration timer), which can, or may be, trigger a new TA acquisition procedure when the time expires.

[0162] In some cases, a WTRU can receive and / or store multiple TA values, and these values ​​may be associated with multiple cells.

[0163] A WTRU can perform a RACH-less handover, for example, when a cell switch to a candidate cell is triggered, if the WTRU stores a valid TA value for that candidate cell. Cell switches can be triggered, for example, by the network (e.g., using an explicit cell switch command) or by the WTRU (e.g., when trigger conditions are met). For example, the WTRU can perform an LTM (e.g., apply a pre-configured RRC configuration to a new SpCell) based on determining that the measured radio quality of the target cell exceeds a threshold (e.g., once determined).

[0164] A WTRU can determine the TA Validity. A WTRU can determine that a received / stored TA is valid based, for example, on one or more of the following: a validity timer pre-configured to be used with the TA value, a validity timer received with the TA value, conditions relating to the DL cell timing of the source cell and the DL cell timing of the candidate cell where the TA is received / stored, conditions relating to the DL cell timing of the candidate cell, conditions relating to WTRU mobility, and / or conditions relating to WTRU location.

[0165] WTRU can determine if a received / stored TA is valid based on the DL cell timing conditions of the source cell and the candidate cell where the TA is received / stored. For example, WTRU can consider a TA valid if the difference between the DL cell timings of the source cell and the candidate cell is smaller than a configured threshold. For example, WTRU can consider a TA valid if the difference between the DL cell timings of the source cell and the candidate cell is within a configured range.

[0166] WTRU can determine if a received / stored TA is valid, for example, based on the DL cell timing conditions of a candidate cell. WTRU can consider a TA valid if, for example, the difference in DL cell timing of the target cell at the time of TA reception does not exceed a (e.g., configured) value / range compared to the current DL cell timing of the same target cell.

[0167] WTRU can determine if a received / stored TA is valid, for example, based on conditions related to WTRU mobility. WTRU can consider a TA valid if, for example, the TA is static or below a (e.g., configured) speed threshold.

[0168] A WTRU can determine whether a received / stored TA is valid based, for example, on conditions related to the WTRU's location. For instance, if a WTRU determines that its location has not changed by more than a certain configured threshold (e.g., x meters) since acquiring the TA, the WTRU can consider the TA valid.

[0169] As described herein, a random access channelless (RACH-less) conditional handover (CHO) evaluation may be based on a valid timing advance (TA). A device may perform (for example, be configured to perform) one or more of the following actions: A wireless transceiver unit (WTRU) may be configured to perform a conditional handover applicable to a given target cell (e.g., only) if the WTRU has a valid TA for the target cell, which can provide a RACH-less conditional handover configuration that uses the validity period of the TA to determine whether a RACH-less handover and associated conditions may be used. A conditional RACH-less handover may be enabled for L1 / L2 trigger mobility (LTM) when, for example, a media access control (MAC) control element (CE) indicates the TA and validity period of a RACH-less handover conditional trigger.

[0170] A WTRU may receive configurations for LTM candidate cells and / or configurations for RACHless CHOs. A configuration may include, for example, one or more of the following: L3 events for one or more target cells, L1 measurement-based events, one or more (e.g., specific) measurement resources, RACHless (e.g., specific) trigger conditions that may consider cells with valid TAs (e.g., only those cells), one or more (e.g., specific) resources (e.g., configured grants) to use when performing a conditional LTM (e.g., separate from an explicit LTM trigger resource), a CHO configuration that may include a first execution condition when RACHless is used (e.g., when the WTRU has a valid TA for this target), and a second execution condition otherwise. A CHO configuration may include multiple (e.g., two) thresholds, such as one threshold used when the WTRU has a TA and another threshold used otherwise. A CHO configuration may include alternative / different time and / or filtering parameters to trigger, for example, so that RACHless can be triggered more quickly. A CHO configuration may include multiple (e.g., two) CHO configurations. For example, cells with a WTRU having a TA may be evaluated using a first CHO configuration, while other cells may be evaluated using a second CHO configuration. The CHO configuration can 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).

[0171] WTRU can transmit Channel Status Information (CSI) reports.

[0172] The WTRU can receive physical downlink control channel (PDCCH) orders. The WTRU can send a preamble to the target cell.

[0173] A WTRU can receive a conditional cell switching indication, which may include a TA value, a validity period, and / or an instruction to perform a cell switching if the CHO condition is met within the validity period.

[0174] In some cases, the WTRU can execute PDCCH reception, preamble transmission, and conditional cell switching instructions multiple times, for example, to perform CHO to multiple targets in parallel.

[0175] In some cases, the WTRU may perform PDCCH reception and preamble transmission multiple times, while the conditional cell switching instruction may include TA / CHO enablers for multiple targets.

[0176] In some examples, a WTRU can perform PDCCH reception and preamble transmission to a target cell (e.g., one) within a configured Timing Advance Group (TAG). The acquired TA may enable RACH-less CHO to any cell (e.g., any) within the TAG.

[0177] Figures 6-8 show examples of obtaining a TA. Other examples of obtaining a TA may include, for example, the Random Access Response (RAR) of the target cell, the RAR of the source cell, and the WTRU that maintains the TA. MAC CE may or may not be used to "activate" CHO. CHO may depend on obtaining a TA, and TA can be obtained by any means. Configurations can be activated / deactivated, for example, using MAC CE.

[0178] WTRU can measure one or more (e.g., configured) target cells. In some examples, the measurement may be performed on (e.g., all) cells within a TAG where TA is enabled.

[0179] The WTRU can perform an LTM (for example, apply a pre-configured candidate configuration) if, for example, the RACH-less CHO condition is met for one or more cells (e.g., any cells) configured with TA values ​​before the expiration of the validity period timer. CHO conditions (e.g., other CHO conditions) can include, for example, a synchronous signal block (SSB), a reference signal received power (RSRP) threshold, and a timing comparison. A configured grant (CG) associated with the beam that triggers the CHO (e.g., the best beam) can be used. The CHO may no longer be valid, and the configuration can be released, for example, when a timer (e.g., a TA validity period timer) expires. The next CHO evaluation may occur, for example, when a new TA command is received. The WTRU can use a second condition (e.g., a different CHO configuration corresponding to a RACH-based CHO if the WTRU does not have a valid TA) if, for example, the timer has expired.

[0180] A WTRU can transmit indications to a target. For example, a WTRU can transmit an RRC completion message on a physical uplink shared channel (PUSCH). A WTRU can use a CG associated with the beam that triggers the CHO (e.g., the best beam). A WTRU can monitor uplink grants on a PDCCH. A WTRU can transmit (for example, then) data and / or Radio Resource Control (RRC) completion messages.

[0181] Figure 5 shows an example flowchart for RACH-less CHO assessment based on effective TA.

[0182] As shown in Figure 5, in reference numeral 1, the WTRU can receive configurations for LTM candidate cells and RACHless Conditional Handovers. These configurations can be received, for example, in an RRC reconfiguration message. A RACHless Conditional Handover (CHO) configuration may include, for example, one or more of the following: one or more trigger conditions (e.g., as described herein), a condition that considers only cells with valid TAs (e.g., only those cells) (e.g., as part of an evaluation of one or more trigger conditions), specific resources, e.g., configured grants (CGs) used when performing a conditional LTM which may be separate from (e.g., explicit) LTM trigger resources, measurement resources (e.g., an indication of a specific set of SSB or CSI-RS resources to measure and evaluate), and / or CHO configuration conditions.

[0183] In some examples, a CHO configuration may include a first execution condition for when RACHless is used (e.g., when the WTRU has a valid TA for the target) and a second execution condition for when it is not. The trigger conditions may be, for example, multiple (e.g., two) radio quality thresholds or multiple (e.g., two) values ​​corresponding to one or more trigger conditions (e.g., as described herein). For example, the first trigger condition may be used when the WTRU has a valid TA for a particular target cell, and the second trigger condition may be used when it is not. The first and second trigger conditions may be, for example, separate trigger times or filtering parameters, measurement evaluations, or parameters related to the execution of a measurement. For example, a RACHless handover may be triggered more quickly by shortening the trigger time. The first and second trigger conditions may be, for example, multiple CHO configurations. For example, cells where the WTRU has a TA may be evaluated according to the first configuration, and other cells may be evaluated according to the second configuration. The first and second trigger conditions may include three or more conditions, such as conditions that determine which type of RACH procedure to perform, such as RACH-less, 2-step, 4-step, CBRA, or CFRA.

[0184] As shown in Figure 5, in reference numeral 2, the WTRU can transmit a CSI report about the configured target cell or beam.

[0185] In code 3, the WTRU can receive the PDCCH order and send a preamble to the target cell (for example, an early synchronization procedure to enable the target gNB to determine the TA value of the WTRU).

[0186] In reference numeral 4, the WTRU may receive one or more indications for performing a conditional LTM cell switchover, which may include an indication for a target cell / beam or cell / beam, a TA value, an expiration period, and / or a CHO condition that is met within the expiration period.

[0187] In reference numeral 5, the WTRU can measure one or more configured target cells or beams. For example, the CSI report may be turned off during the measurement time because the WTRU evaluates the conditional cell switching conditions based on the measurement.

[0188] In reference 6, the LTM can be executed, for example, if the RACH-less CHO condition is met for any cell configured with TA values ​​before the expiration of the validity period timer (for example, a pre-configured candidate configuration can be applied). For example, if the timer (e.g., the TA validity period timer) expires, the CHO may be considered invalid and the configuration may be released. If a new TA command is received, the next CHO evaluation can be performed. The WTRU may use a second condition (e.g., a different CHO configuration corresponding to a RACH-based CHO when the WTRU does not have a valid TA) (for example, if the TA validity period timer expires).

[0189] In reference numeral 7, the WTRU may send an indication to the target cell, for example, an RRC completion message on the PUSCH. This indication may be sent, for example, by using a CG associated with the best beam to trigger the CHO, or by monitoring an uplink grant (e.g., a dynamic grant) on the PDCCH and sending data and / or an RRC completion message on the PUSCH.

[0190] WTRU can, for example, determine whether and / or when to perform a cell switchover based on the use of the Timing Advance validity period.

[0191] Figure 6 illustrates an example of evaluating whether to perform a reconfiguration based on whether the target cell has a valid TA. Figure 6 shows an exemplary procedure in which the WTRU consists of an LTM and a RACH-less conditional handover. The RACH-less CHO can be provided, for example, in an RRC configuration. The TA can be determined, for example, in a gNB, by performing an early TA acquisition procedure that can be triggered, for example, by a PDCCH order from the target cell. The WTRU can send a random access preamble to one or more target cells. One or more target cells can determine / estimate the TA. One or more target cells can provide the determined / estimated TA to the source cell. The WTRU can receive a MAC CE, which may include at least one TA value and an indication of the TA validity period, in order to enable a RACH-less CHO. The MAC CE may indicate one or more target cells for which a conditional reconfiguration is being evaluated, or the target cells may be pre-configured (for example, as part of a CHO configuration). The MAC CE may also indicate which CHO configuration (e.g., conditional reconfiguration ID) to evaluate. A WTRU may evaluate conditional reconfiguration using one or more trigger conditions (such as those described herein) until the CHO's validity period expires (for example, based on the TA validity period). A WTRU may perform reconfiguration to a determined target cell (e.g., perform an LTM) using a RACH-less handover procedure if the conditions are met before the expiration date. Performing a conditional reconfiguration (e.g., performing a conditional LTM or RACH-less L3CHO) may depend on the trigger conditions and whether the WTRU has a valid TA for the evaluated target cell. While a WTRU has a valid TA for a given target cell, it may use RACH-less CHO evaluation conditions (e.g., only) for that cell. A WTRU may release or deactivate the conditional reconfiguration evaluation if, for example, the expiration date has passed.Conditional reconfiguration can be reactivated, for example, when the WTRU receives a new TA value for a cell (e.g., by performing another early TA acquisition procedure).

[0192] A WTRU can consist of a conditional reconfiguration for evaluation. A WTRU can evaluate a conditional reconfiguration. A WTRU can use one or more trigger conditions (e.g., as described herein) for evaluation. A WTRU can also consist of a conditional PDCCH order, for example, showing U random access parameters to one or more target cells in the WTRU. A WTRU can execute the conditional PDCCH order (e.g., if the condition is met) and send a random access preamble to the target cell that satisfies the condition. A WTRU can receive the TA value of a target cell (e.g., from a serving cell or target cell). A WTRU can then execute a conditional LTM. A WTRU can execute a conditional LTM and, for example, after the LTM execution, send a random access preamble to the cell.

[0193] A separate condition can be used to determine whether to perform a handover based on whether a valid TA is stored.

[0194] Figure 7 illustrates an example of evaluating whether to perform a reconfiguration based on whether the target cell has a valid TA. Figure 7 shows an exemplary procedure in which the WTRU consists of an LTM and a RACH-less conditional handover. As shown in Figure 7, the WTRU can receive first and second conditional handover (CHO) execution conditions, which may use one or more trigger conditions (such as those described herein). The WTRU may evaluate whether to perform a reconfiguration based on the first condition, for example, if the WTRU has a valid TA for a given target cell. The WTRU may evaluate whether to perform a reconfiguration based on the second condition, for example, if it does not. The WTRU may evaluate based on the first condition until the expiration of the TA validity period, and then evaluate based on the second condition after the expiration of the TA validity period. The CHO configuration may remain valid, for example, until a cell switchover is performed.

[0195] WTRU can use Timing Advance Groups (TAGs) to determine whether to evaluate CHO in multiple cells.

[0196] Figure 8 shows an example of using a TAG to determine whether to evaluate CHO on multiple cells. As shown in Figure 8, a WTRU can consist of one or more Timing Advance Groups (TAGs). This configuration can be received, for example, in an RRC configuration that provides an LTM candidate configuration and / or a CHO configuration. Cells belonging to the same TAG can use (for example, are expected to use) the same TA value (for example, the cells may be physically located in the same place). The WTRU can receive the TAs corresponding to the cells in the TAG (for example, in a MAC CE). The WTRU can use the TA values ​​to enable CHO evaluation on one or more of the cells in the TAG (for example, any cell or all cells). For example, the WTRU may currently be active on a first cell (for example, cell A). The WTRU can then perform RACH on a second cell (for example, cell B). A WTRU can perform a RACH-less CHO on a third cell (e.g., cell C), provided that the WTRU has a valid TA for the TAG which includes the second and third cells (e.g., cells B and C).

[0197] A RACH-less CHO evaluation based on a valid TA can improve robustness while reducing interruptions. WTRU can trigger a RACH-less LTM handover (e.g., immediately) if conditions are met. Multiple cells can be configured with RACH-less CHO TA values. WTRU can trigger a RACH-less CHO to the optimal cell based on the evaluation, for example, without reporting / receiving an explicit trigger.

[0198] As described herein, a wireless transceiver unit (WTRU) can trigger an early timing advance (TA) acquisition for Random Access Channel (RACH)-less conditional handover (CHO) / conditional L1 / L2 triggered mobility (LTM). The device can perform (for example, be configured to perform) one or more of the following actions: The wireless transceiver unit (WTRU) can trigger an early TA acquisition that may be used for RACH-less CHO based on certain conditions (for example, in addition to a first condition for triggering LTM execution). Condition evaluation may be enabled, for example, when the WTRU receives a physical downlink control channel (PDCCH) order indicating an RA resource and the lifetime of the RA resource. The WTRU may, for example, trigger a random access (RA) if the conditions are met to enable, for example, a target TA acquisition.

[0199] The WTRU can receive the configuration of LTM candidate cells and / or the configuration of RACH-less CHO (e.g., condition 1). The WTRU can receive conditions to trigger TA acquisition (e.g., condition 2).

[0200] WTRU can transmit Channel Status Information (CSI) reports.

[0201] A WTRU can submit a PDCCH order request that enables the WTRU to trigger a TA acquisition / CHO. This request may be based on an event that could indicate, for example, that the target is above a threshold. This request may be part of a CSI report, for example, an event-triggered report.

[0202] A WTRU may receive a PDCCH order that enables the WTRU to trigger a TA acquisition. The PDCCH order may include RA resources and / or RA resource lifetime timers. There may be multiple (e.g., two) conditions. The first condition may be about a RACH (e.g., an autonomous RA) for a target. The first condition may indicate, for example, a first threshold (threshold 1) and a valid physical RACH (PRACH) resource. The second condition may be to trigger a CHO. The second condition may indicate, for example, a second threshold (e.g., threshold 2) and a valid TA.

[0203] WTRU can perform measurements on a configured target.

[0204] A TA acquisition can be triggered when the TA acquisition conditions (e.g., condition 1) are met. The WTRU can send a PRACH preamble to the target when a TA acquisition is triggered. For example, if a PRACH resource becomes invalid (e.g., expires), a request for a new PDCCH order can be sent. A different PRACH resource (e.g., contention-based random access (CBRA)) can be used (e.g., as an alternative).

[0205] WTRU can receive the TA value and enable RACH-less CHO.

[0206] LTM can be executed, for example, if the RACH-less CHO condition (e.g., the second condition) is met for one or more cells (e.g., any cells) composed of TA values ​​before the timer expires (for example, it may be executed by applying a pre-configured candidate configuration). The PDCCH order can disable / enable the LTM configuration.

[0207] A WTRU can transmit indications to a target. For example, a WTRU can transmit a Radio Resource Control (RRC) completion message on a Physical Uplink Shared Channel (PUSCH). A WTRU can use a CG associated with the best beam to trigger a CHO. A WTRU can monitor uplink grants on a PDCCH and (for example, then) transmit data and / or an RRC completion message.

[0208] Figure 9 shows an exemplary flowchart of early TA acquisition via WTRU trigger for RACH-less CHO and / or conditional LTM.

[0209] As shown in Figure 9, in reference numeral 1, the WTRU can receive configurations for LTM candidate cells, configurations for RACH-less conditional handover using a first condition, and / or WTRU configurations for early TA acquisition triggered by the WTRU using a second condition. These configurations can be received, for example, in an RRC reconfiguration message.

[0210] A RACH-less conditional handover configuration may provide a first condition which may include one or more of the following (e.g., its indications): one or more trigger conditions (e.g., as described herein); a condition which considers cells (cells only) having a valid TA (e.g., as part of the evaluation of one or more trigger conditions); one or more resources, e.g., configured grants (CGs) used when performing a conditional LTM which may be separate from an explicit LTM trigger resource; one or more measurement resources (e.g., a set of SSB or CSI-RS resources for measurement and evaluation).

[0211] Early TA acquisition via WTRU trigger may be provided with a second condition which may include one or more of the following: one or more trigger conditions (e.g., as described herein); one or more resources such as a dedicated preamble (e.g., CFRA) or RA resource used when sending a preamble to a target cell; and / or timer conditions that take into account WTRU trigger acquisition (e.g., RA preamble trigger) such as random access via WTRU trigger ordered by PDCCH and any associated trigger or resource being valid at a given time value.

[0212] As shown in Figure 9, in reference numeral 2, the WTRU can transmit a CSI report about the configured target cell or beam.

[0213] In reference numeral 3, the WTRU may send a request for the provision of a PDCCH order for WTRU-triggered TA acquisition (e.g., RA resource, etc.). This request may be based on a third condition, such as using one or more trigger conditions (e.g., as described herein). The WTRU may, for example, first determine that the cell has adequately high radio quality (e.g., above a threshold) and trigger a request to constitute WTRU-triggered TA acquisition.

[0214] In reference numeral 4, the WTRU can receive a PDCCH order that enables TA acquisition (sending a preamble to the target) triggered by the WTRU. The PDCCH order may include one or more of the following: an indicator that identifies the random access resource, a condition (e.g., a second condition), and / or a validity period during which TA acquisition triggered by the WTRU can be evaluated.

[0215] In reference numeral 5, the WTRU can measure one or more configured target cells or beams. The measurements may include (for example, at least) measurements on a resource associated with an uplink RA resource configured to evaluate RA by WTRU triggering (e.g., SSB or CSI-RS). The WTRU can perform measurements on one or more configured target cells or beams. Since the WTRU evaluates conditional TA acquisition conditions based on the measurements, for example, the CSI report can be turned off during the measurement time.

[0216] In reference numeral 6, if the TA acquisition conditions (e.g., the second condition) are met, the early TA acquisition procedure may be triggered. The preamble may be sent to the target cell where the conditions are met. In reference numeral 6, if the beam / SSB / CSI-RS resource measurement on the cell or on the cell exceeds the radio quality threshold, the early synchronization procedure may be triggered to allow the target gNB to determine the TA value of the WTRU.

[0217] In reference numeral 7, the WTRU may receive one or more indicators for performing a conditional LTM cell switchover, which may include an indicator for the target cell / beam, a TA value, an expiration period, and / or an indicator for performing a cell switchover if the CHO condition is met within the expiration period.

[0218] In reference 8, for example, if the RACH-less CHO condition is met for one or more cells (e.g., any cells) that are composed of TA values ​​before the expiration of the validity period timer, the LTM can be executed (e.g., a pre-configured candidate configuration can be applied). The CHO may no longer be valid, and the configuration can be released, for example, when a timer (e.g., a TA validity period timer) expires. The next CHO evaluation may occur, for example, 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 if the WTRU does not have a valid TA) if the timer expires.

[0219] In reference numeral 9, the WTRU can send indications to the target cell, such as an RRC completion message on the PUSCH, which may be done by, for example, triggering the CHO using a CG associated with a beam (e.g., the best beam), or by monitoring an uplink grant (e.g., a dynamic grant) on the PDCCH and sending data and / or an RRC completion message on the PUSCH.

[0220] Figure 10 shows an example of triggering early TA acquisition based on conditions evaluated in WTRU, which can be referred to as WTRU-triggered early TA acquisition.

[0221] A WTRU may consist of conditions for triggering the TA acquisition procedure. A WTRU may be triggered (e.g., explicitly) for a target gNB to send a random access preamble, for example, in MAC CE, to determine the TA value provided to the WTRU by the source cell, enabling evaluation of a conditional RACH-less handover.

[0222] As shown in Figure 10, the WTRU can receive an indication (e.g., PDCCH order) which may enable the evaluation of conditions for sending a random access preamble to a target cell (e.g., to trigger an early TA acquisition procedure). The WTRU can consist of an RA validity timer, indicated, for example, as part of a pre-configuration step (e.g., in RRC reconfiguration) or as part of an indication that enables the evaluation of TA acquisition trigger conditions. The RA validity timer is used to determine how long the indicated random access resource (e.g., for sending an RA preamble) is valid, and indicates the time over which the WTRU can evaluate the conditions to conditionally trigger a random access preamble. The WTRU can, for example, send a random access preamble to the target using the configured RA resource if the conditions are met before the RA validity period expires. The NW can enable (e.g., subsequently) a RACH-less conditional LTM cell switching or an explicit RACH-less LTM cell switching by, for example, providing the acquired TA value in an LTM cell switching MAC CE.

[0223] In some cases, the TA value may be received by the WTRU at a MAC CE that may differ from the cell switching MAC CE. The WTRU may receive an acknowledgment message that does not include the TA value (for example, when sending a random access preamble) but indicates to the WTRU that the random access preamble has been received (or not received). The TA value can then be sent to the WTRU at the MAC CE, e.g., the cell switching MAC CE. The acknowledgment message can be sent, for example, in a DCI, as a sequence, etc.

[0224] A WTRU may transmit a random access preamble but may not receive a timing advance (TA) value within a defined time window. A WTRU may transmit a random access preamble but may not receive an acknowledgment message, or the acknowledgment message may indicate that the random access preamble was not received. A WTRU may retransmit a random access preamble on the same resources (for example, in these cases) if the RA lifetime timer is still running. A WTRU may use power that is a larger offset value than the power used in the previous transmission (for example, for retransmission). Transmit power adjustments (for example, as described herein) may be applied to a second retransmission and / or further retransmissions. The value of the offset power may be configured. Whether a WTRU can increase the PRACH transmit power for retransmission may be configured (e.g., enable / disable power increase for PRACH retransmission) and / or indicated in PDCCH order.

[0225] Early TA acquisition via WTRU triggers for RACH-less CHO and / or conditional LTM can reduce interruptions (e.g., by allowing WTRU to trigger RACH for early TA acquisition) and / or reduce CSI reporting (e.g., WTRU can turn off CSI reporting during conditional assessment).

[0226] As described herein, a Random Access Channel (RACH) procedure may be selected and used to perform a Handover (HO) execution. The device may perform (for example, be configured to perform) one or more of the following actions: A Wireless Transceiver Unit (WTRU) may prioritize targets for performing L1 / L2 Trigger Mobility (LTM) depending on whether the WTRU can perform a RACH-less handover. A RACH-less Conditional HO (CHO) may, for example, provide reduced interruption and / or robustness compared to a handover utilizing RACH.

[0227] The WTRU may receive configurations for LTM candidate cells and / or configurations for the CHO. The CHO configuration may include separate execution conditions (e.g., separate thresholds) depending, for example, whether the WTRU has a valid timing advance (TA). The CHO configuration may include one or more conditions related to the remaining validity period (e.g., a first condition if the remaining validity period is greater than a threshold, and a second condition otherwise). The CHO configuration may include configurations for the type of RACH procedure to execute and / or conditions for selecting the type of RACH procedure to execute, depending on the remaining TA validity period.

[0228] WTRU can transmit Channel Status Information (CSI) reports.

[0229] The WTRU can receive the Physical Downlink Control Channel (PDCCH) order. The WTRU can send a preamble to the first target cell.

[0230] WTRU can receive the TA value for the first cell.

[0231] WTRU can perform measurements on a configured LTM target, which may include at least a first cell and a second cell (e.g., one without a valid TA value). The second cell may have a valid TA with a remaining TA validity period, which may be shorter than the remaining TA validity period of the first cell.

[0232] The WTRU can select the first cell. Based on prioritization rules, the WTRU can perform a CHO (e.g., RACH-less LTM execution) on the first cell if, for example, the cell switching criteria are met for both the first and second cells. Exemplary selection criteria / prioritization rules may include, for example, one or more of the following: an indication of whether a TA is enabled or disabled; an indication for selecting the target with the longest remaining TA validity period; an indication for selecting a target configured for RACH-less as a priority over targets not configured for RACH-less; selection criteria may include an offset to the CHO criterion, for example, a cell configured for RACH-less may have a lower Reference Signal Received Power (RSRP) threshold; selection criteria may apply a shorter trigger time (TTT) to the CHO criterion if a cell is configured for RACH-less, and the selection of a first cell may include aborting a reconfiguration procedure toward a second cell (e.g., if a WTRU is performing a preamble retransmission to perform a RACH procedure for HO toward a second cell, for example, aborting and performing RACH-less toward the first cell); and / or selection prioritization rules may apply if conditional reconfiguration criteria are met for multiple cells / or if multiple cells are performing different types of reconfiguration (e.g., explicit and conditional reconfiguration).

[0233] The WTRU can transmit indications to the target (first cell). For example, the WTRU can transmit a Radio Resource Control (RRC) completion message on the PUSCH. The WTRU can use a configured grant (CG) associated with the best beam to trigger the CHO. The WTRU can monitor uplink grants on the PDCCH. The WTRU can transmit data and / or RRC completion messages (for example, then).

[0234] Figure 11 shows an exemplary flowchart for selecting the RACH procedure to perform the HO execution.

[0235] As shown in Figure 11, in reference numeral 1, the WTRU can receive the configuration of an LTM candidate cell and the configuration of a RACH-less conditional handover for (e.g., at least) a first target cell. The configuration 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). The WTRU may also receive indications of prioritization criteria for determining which type of handover to perform when the LTM execution trigger criteria are met for two or more target cells. The conditional handover may, for example, use a first criterion when the condition is met and a second criterion when the condition is not met. For example, a first radio quality measurement threshold may be used if a valid TA is stored, and a second threshold may be used otherwise.

[0236] In reference numeral 2, the WTRU may transmit a CSI report about the configured target cell or beam.

[0237] In reference numeral 3, the WTRU may receive a PDCCH order that enables WTRU-triggered TA acquisition (e.g., sending a preamble to a target). The PDCCH order may include one or more of the following: an indicator that identifies a random access resource, a condition (e.g., a second condition), and / or a validity period during which WTRU-triggered TA acquisition can be evaluated.

[0238] In reference 4, the WTRU can receive the TA value of the first cell (for example, after the PDCCH order that sends the preamble to the target cell).

[0239] In reference numeral 5, the WTRU can perform measurements on one or more configured target cells or beams, which may include (for example) at least a first cell and a second cell. The second cell may not be configured for RACH-less reconstruction (for example, RACH-less may not be enabled for the second cell, or RACH-less may be configured but no valid TA values ​​are stored, or the conditions for performing RACH-less may not be met).

[0240] In reference numeral 6, the LTM can be executed toward the first cell based on prioritization criteria, for example, if the cell switching criteria for the first and second cells are met (for example, a pre-configured candidate configuration may be applied).

[0241] In reference numeral 7, the WTRU can send indications to the target cell, such as an RRC completion message on the PUSCH, which may be done by, for example, triggering the CHO using a CG associated with a beam (e.g., the best beam), or by monitoring an uplink grant (e.g., a dynamic grant) on the PDCCH and sending data and / or an RRC completion message on the PUSCH.

[0242] Prioritization criteria may include, for example, one or more of the following: criteria for performing one type of handover (e.g., criteria for performing a RACH-less handover rather than a RACH-based handover, or criteria for performing an explicit handover request rather than a conditional one); criteria based on whether a cell has a valid TA or whether a cell has been configured by the RRC for RACH-less handovers; criteria for selecting a cell with the longest TA lifespan; criteria based on absolute or relative wireless quality thresholds; time-based criteria; event-based criteria; and / or criteria based on the availability of configured grants.

[0243] Prioritization criteria may include criteria based on absolute or relative radio quality thresholds. For example, a RACH-less handover may be performed as long as a cell configured for RACH-less (e.g., having a valid TA) satisfies the LTM cell switching trigger criterion and has radio quality measurements that are within (e.g., at least) XdB of the radio quality measurement criterion of a cell not configured for RACH-less (e.g., not having a valid TA) that satisfies the LTM cell switching criterion.

[0244] Prioritization criteria can include time-based criteria. For example, a cell configured for RACH-less (e.g., having a valid TA) may meet the LTM cell switching trigger criteria within a certain time period after a cell not configured for RACH-less.

[0245] Prioritization criteria can include event-based criteria. For example, if a cell configured for RACH-less (e.g., having a valid TA) meets the LTM cell switching trigger criteria before a specific event in a procedure used by a cell not configured for RACH-less (e.g., before a successful random access response is received, or before a handover complete message is sent).

[0246] Prioritization criteria may include criteria based on the availability of configured grants. For example, a WTRU may choose cell 2 over cell 1 if both cell 1 and cell 2 meet the CHO conditions, and cell 1 is slightly better than cell 2 in terms of radio signal level, but one or more configured grant resources are available in cell 2 and cell 1 has no valid / activated configured grants. For example, a WTRU may choose cell 2 even if cell 1 has better radio quality if active configured grants are available on both cells, but grants occur earlier on cell 2 or there are more configured grant opportunities (e.g., CG configurations on cell 2 have shorter periodicity).

[0247] Figure 12 illustrates an example where a RACH-less handover is triggered on the first cell before the completion of the RACH procedure on the second cell. Figure 12 also illustrates an example where the execution of a conditional RACH-less handover takes precedence over the completion of a RACH-based reconfiguration. As shown in Figure 12, the LTM can be configured, for example, with the configuration of a RACH-less handover to cell B while the WTRU is connected to cell A. The WTRU can receive a PDCCH order to send a random access preamble to cell B (e.g., during the LTM preparation phase). The WTRU can receive a cell switching indication from cell A (e.g., in MAC CE), which may indicate the TA value of cell B and the validity period for enabling a RACH-less CHO to cell B. The WTRU can receive an LTM cell switching indication for cell C (e.g., while the WTRU is performing measurements and evaluations of cell B for a conditional LTM execution), which does not include a TA value (e.g., indicating that a RACH-based handover will be performed). The WTRU can determine that the CHO condition is met, enabling a RACH-based handover to cell C. The WTRU can initiate reconfiguration to cell C and start executing random access procedures (e.g., sending and retransmitting the PRACH preamble via power ramping). Meanwhile, the conditional LTM condition may be met for cell B. The WTRU can terminate reconfiguration to cell C and perform a RACH-less handover to cell B using the LTM.

[0248] A higher-priority RACH-less reconfiguration may be performed even after another reconfiguration has been initiated, or if the conditions for performing both a RACH-less reconfiguration and a RACH-based reconfiguration occur in parallel (e.g., simultaneously, or before the completion of one or the other).

[0249] Prioritizing target cells to perform LTM based on RACH-less handover can reduce disruptions, for example, because RACH-less reconfiguration may complete more quickly and / or have configured grants to perform UL transmission.

[0250] Systems, methods, and means relating to early timing advance (TA) acquisition for Random Access Channel (RACH)-less conditional handover (CHO) are described herein. A wireless transceiver unit (WTRU) can receive configuration information from a first cell indicating a mobility candidate cell and the configuration of a Random Access Channel (RACH)-less conditional handover (CHO). The mobility candidate cell includes at least a first candidate cell, and the configuration of the RACH-less CHO may include at least a RACH-less CHO condition. The WTRU can receive an indication of a conditional cell switch, indicating a timing advance (TA) value associated with the conditional cell switch and a TA validity period associated with the first candidate cell. Based on the RACH-less CHO condition being met before the expiration of the TA validity period, the WTRU can use the RACH-less CHO to perform a conditional cell switch from the first cell to the first candidate cell. Using the RACH-less CHO may include using the TA value. Based on the execution of a conditional cell switch, the WTRU can send a reconfiguration complete indication to the first candidate cell.

[0251] Conditional cell switching from the first cell to the first candidate cell can be performed based on measurements. The WTRU can perform measurements on the first candidate cell. The WTRU can receive a Physical Downlink Control Channel (PDCCH) order from the first cell. Based on the received PDCCH order, the WTRU can send a preamble to the first candidate cell. The preamble may be associated with a TA value. The first candidate cell may include a target cell. A reconfiguration complete indication can be sent to the first candidate cell in a Radio Resource Control Message (RRC). The TA value may be used in a PUSCH transmission. The RACH-less CHO condition may be met based on the TA value being valid before the expiration of the TA validity period.

[0252] Systems, methods, and means relating to early timing advance (TA) acquisition for random access channel (RACH)-less conditional handover (CHO) are described herein. A device can perform (for example, be configured to perform) one or more of the following actions: A wireless transceiver unit (WTRU) can perform a RACH-less CHO evaluation based on a valid TA. A WTRU can trigger early TA acquisition for RACH-less CHO / conditional L1 / L2 triggered mobility (LTM). A WTRU can select a RACH procedure to perform for handover (HO) execution.

[0253] Systems, methods, and means relating to random access channelless (RACH-less) conditional handover (CHO) evaluation based on a valid timing advance (TA) are described herein. A device can perform (for example, be configured to perform) one or more of the following actions: A wireless transceiver unit (WTRU) may be configured with a conditional handover applicable to a given target cell while the WTRU has a valid TA for the target cell (for example, only during that period). The WTRU may receive a RACH-less conditional handover configuration that uses TA validity to determine whether a RACH-less handover and associated conditions are applicable / valid. A conditional RACH-less handover may be enabled for L1 / L2 trigger mobility (LTM), for example, when a media access control (MAC) control element (CE) indicates the TA and validity of a RACH-less handover conditional trigger.

[0254] A WTRU may receive configurations for LTM candidate cells and / or configurations for RACHless CHOs. A configuration may include, for example, one or more of the following: L3 events for one or more target cells, L1 measurement-based events, one or more (e.g., specific) measurement resources, a RACHless configuration that may consider cells with valid TAs (e.g., only those cells), a CHO configuration that may include specific trigger conditions, one or more (e.g., specific) resources (e.g., configured grants) used when performing a conditional LTM (e.g., separate from explicit LTM trigger resources), a first execution condition when RACHless is used (e.g., when the WTRU has a valid TA for this target), and a second execution condition otherwise. The CHO configuration is used when the WTRU may have a TA. A CHO configuration can include multiple (e.g., two) thresholds, such as one threshold used for certain conditions and another threshold used for other conditions. A CHO configuration can include alternative / different time and / or filtering parameters to trigger, for example, so that RACHless can be triggered more quickly. A CHO configuration can include multiple (e.g., two) CHO configurations. For example, cells with WTRU having TA may be evaluated with a first CHO configuration, and other cells with a second CHO configuration. A CHO configuration can include multiple levels (e.g., three or more levels), such as RACHless, 2-step, 4-step, contention-based random access (CBRA), and contention-free random access (CFRA).

[0255] WTRU can transmit Channel Status Information (CSI) reports.

[0256] The WTRU can receive physical downlink control channel (PDCCH) orders. The WTRU can send a preamble to the target cell.

[0257] WTRU can receive conditional cell switching indicators which may include indicators for performing a cell switching when the TA value, expiration period, and / or CHO condition are met within the expiration period.

[0258] In some cases, the WTRU can perform PDCCH reception, preamble transmission, and conditional cell switching indication multiple times, for example, to enable CHO to multiple targets in parallel.

[0259] In some examples, a WTRU can perform PDCCH reception and preamble transmission multiple times, while a conditional cell switching indication can include TA / CHO enablers for multiple targets.

[0260] In some examples, a WTRU can perform PDCCH reception and preamble transmission to a target cell (e.g., one) within a configured Timing Advance Group (TAG). The acquired TA may enable RACH-less CHO to any cell (e.g., any) within the TAG.

[0261] Figures 6-8 show examples of obtaining a TA. Other examples of obtaining a TA may include, for example, the Random Access Response (RAR) of the target cell, the RAR of the source cell, and the WTRU that maintains the TA. MAC CE may or may not be used to "activate" CHO. CHO may depend on obtaining a TA, and TA can be obtained by any means. Configurations can be activated / deactivated, for example, using MAC CE.

[0262] WTRU can measure one or more configured target cells. In some examples, the measurement may be performed on (e.g., all) cells within a TAG where TA is enabled.

[0263] The WTRU can perform an LTM (for example, apply a pre-configured candidate configuration) if, for example, the RACH-less CHO condition is met for one or more cells (e.g., any cells) configured with TA values ​​before the expiration of the validity period timer. CHO conditions (e.g., other CHO conditions) can include, for example, synchronization signal (SS) blocks (SSB), reference signal received power (RSRP) thresholds, timing comparisons, etc. A configured grant (CG) associated with the beam that triggers the CHO (e.g., the best beam) can be used. The CHO may no longer be valid, and the configuration can be released, for example, when a timer (e.g., a TA validity period timer) expires. The next CHO evaluation may occur, for example, when a new TA command is received. The WTRU can use a second condition (e.g., a different CHO configuration corresponding to a RACH-based CHO if the WTRU does not have a valid TA) if, for example, the timer has expired.

[0264] A WTRU can transmit indications to a target. For example, a WTRU can transmit an RRC completion message on a physical uplink shared channel (PUSCH). A WTRU can use a CG associated with the beam that triggers the CHO (e.g., the best beam). A WTRU can monitor uplink grants on a PDCCH. A WTRU can transmit (for example, then) data and / or Radio Resource Control (RRC) completion messages.

[0265] An exemplary device may include a processor configured to perform one or more actions. For example, the device may receive from a first cell a configuration including a mobility candidate cell containing a first candidate cell and a second candidate cell, and a configuration for a Random Access Channel (RACH)-less Conditional Handover (CHO) including a RACH-less CHO condition. The device may perform measurements on the mobility candidate cell and report the measurements to the first cell. The device may perform Random Access (RA) to the first candidate cell using the RA resources indicated by the first cell. The device may receive a conditional cell switching indication including the timing advance (TA) value and TA validity period of the first candidate cell. The device may perform a conditional cell switching from the first cell to the first candidate cell if the RACH-less CHO condition is met before the expiration of the TA validity period.

[0266] The configuration may include a RACH-based CHO configuration, which includes RACH-based CHO conditions. The device may use RACH-based CHO to perform a conditional cell switch from the first cell to the first candidate cell if the RACH-based CHO conditions are met after the expiration of the TA validity period.

[0267] The configuration can represent timing advance groups (TAGs) for a first candidate cell and a second candidate cell (for example, the TA value and TA validity period apply to the first and second candidate cells). The device can perform a conditional cell switch from the first cell to the second candidate cell if the RACH-less CHO condition is met before the expiration of the TA validity period.

[0268] Although the features and elements described above are described in specific combinations, each feature or element may be used alone without other features and elements of the preferred embodiment, or in various combinations with or without other features and elements.

[0269] While the implementations described herein may take into account 3GPP-specific protocols, it should be understood that the implementations described herein are not limited to this scenario and are applicable to other wireless systems as well. For example, while the solutions described herein take into account LTE, LTE-A, New Radio (NR), or 5G-specific protocols, it should be understood that the solutions described herein are not limited to this scenario and are applicable to other wireless systems as well.

[0270] The above processes may be executed by computer programs, software, and / or firmware embedded in computer-readable media for execution by a computer and / or processor. Examples of computer-readable media include, but are not limited to, electronic signals (transmitted via wired and / or wireless connections) and / or computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random access memory (RAM), registers, 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 discs and / or digital multipurpose discs (DVDs)). Processors combined with software may be used to implement radio frequency transceivers used in WTRUs, UEs, terminals, base stations, RNCs, or any host computer.

Claims

1. A wireless transceiver unit (WTRU), Receiving configuration information from a first cell indicating the configuration of a mobility candidate cell and a random access channel (RACH)-less conditional handover (CHO), wherein the mobility candidate cell includes at least the first candidate cell, and the RACH-less CHO configuration includes at least the RACH-less CHO condition. Receiving an indication of a conditional cell switch that shows the timing advance (TA) value associated with the conditional cell switch and the TA validity period associated with the first candidate cell, Based on the fact that the RACHlessCHO condition is met before the expiration of the TA validity period, a conditional cell switch from the first cell to the first candidate cell is performed using the RACHlessCHO, wherein the use of the RACHlessCHO includes the use of the TA value. Based on the execution of the conditional cell switching, a reconfiguration completion indication is sent to the first candidate cell, A WTRU equipped with a processor configured to perform the following.

2. The WTRU according to claim 1, wherein the conditional cell switching from the first cell to the first candidate cell is performed based on a measurement, and the processor is further configured to perform the measurement on the first candidate cell.

3. The aforementioned processor, Receiving a physical downlink control channel (PDCCH) order from the first cell, Based on the received PDCCH order, a preamble is transmitted to the first candidate cell, wherein the preamble is associated with the TA value. The WTRU according to claim 1, further configured to perform the following:

4. The WTRU according to claim 1, wherein the first candidate cell includes a target cell.

5. The WTRU according to claim 1, wherein the reconstruction completion indication is transmitted to the first candidate cell in a radio resource control message (RRC).

6. The TA value is the WTRU according to claim 1, used for PUSCH transmission.

7. The WTRU according to claim 1, wherein the RACH-less CHO condition is satisfied on the basis that the TA value is valid before the expiration of the TA validity period.

8. A method for a wireless transceiver unit (WTRU), Receiving configuration information from a first cell indicating the configuration of a mobility candidate cell and a random access channel (RACH)-less conditional handover (CHO), wherein the mobility candidate cell includes at least the first candidate cell, and the RACH-less CHO configuration includes at least the RACH-less CHO condition. Receiving an indication of a conditional cell switch that shows the timing advance (TA) value associated with the conditional cell switch and the TA validity period associated with the first candidate cell, Based on the fact that the RACHlessCHO condition is met before the expiration of the TA validity period, a conditional cell switch from the first cell to the first candidate cell is performed using the RACHlessCHO, wherein the use of the RACHlessCHO includes the use of the TA value. Based on the execution of the conditional cell switching, a reconfiguration completion indication is sent to the first candidate cell, A method that includes this.

9. The method according to claim 8, wherein the conditional cell switching from the first cell to the first candidate cell is performed on a measurement, and the method further comprises performing the measurement on the first candidate cell.

10. The aforementioned method, Receiving a physical downlink control channel (PDCCH) order from the first cell, Based on the received PDCCH order, a preamble is transmitted to the first candidate cell, wherein the preamble is associated with the TA value. The method according to claim 8, further comprising:

11. The method according to claim 8, wherein the first candidate cell includes a target cell.

12. The method according to claim 8, wherein the reconstruction completion indication is transmitted to the first candidate cell in a radio resource control message (RRC).

13. The method according to claim 8, wherein the TA value is used in PUSCH transmission.

14. The method according to claim 8, wherein the RACH-less CHO condition is satisfied based on the TA value being valid before the expiration of the TA validity period.

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