Methods for enhanced mobility in wireless systems

Abstract

To provide methods for enhanced mobility in wireless systems.SOLUTION: The invention provides methods, devices and systems for communication by a wireless transmit / receive unit (WTRU) associated with a source cell. The WTRU is configured with a conditional reconfiguration which includes a trigger condition and a configured target cell. The WTRU detects occurrence of an impairment event resulting in impairment of operation of the WTRU in the source cell. If the impairment event satisfies the trigger condition, a reconfiguration is performed with the configured target cell. If the impairment event does not satisfy the trigger condition, a target cell is selected based on a cell selection procedure; if the WTRU is configured with a conditional reconfiguration for the selected target cell, a reconfiguration is performed with the selected target cell; and, if the WTRU is not configured with a conditional reconfiguration for the target cell, a reestablishment is performed with the selected target cell.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for enhanced mobility in a wireless system.

Background Art

[0002] Cross-Reference to Related Applications The present application claims benefit based on U.S. Provisional Patent Application No. 62 / 652,163 filed on April 3, 2018 and U.S. Provisional Patent Application No. 62 / 736,290 filed on September 25, 2018.

[0003] Mobile communications has been evolving progressively, and mobile networks are at the gateway of the fifth generation (5G). As with previous generations, new use cases have contributed greatly to setting requirements for the new system. The 5G air interface and its New Radio (NR) access technology are expected to enable use cases such as Improved Broadband Performance (IBB), Industrial Control and Communications (ICC), vehicular applications (V2X), and massive Machine Type Communications (mMTC).

Summary of the Invention

Problem to be Solved by the Invention

[0004] A method for enhanced mobility in a wireless system is provided.

Means for Solving the Problem

[0005] A method, device, and system for communication between a wireless transceiver unit (WTRU) associated with a source cell. The WTRU is configured to use conditional reconfiguration, which includes trigger conditions and a configured target cell. The WTRU detects the occurrence of an impairment event that causes a failure in the operation of the WTRU in the source cell. If the impairment event satisfies the trigger conditions, reconfiguration is performed using the configured target cell. If the impairment event does not satisfy the trigger conditions, a target cell is selected based on a cell selection procedure, and if the WTRU is configured to use conditional reconfiguration for the selected target cell, reconfiguration is performed using the selected target cell; if the WTRU is not configured to use conditional reconfiguration for the target cell, re-establishment is performed using the selected target cell.

[0006] A more detailed understanding can be obtained from the following description, given as an example, in conjunction with the attached drawings, where similar reference numbers in the drawings indicate similar elements. [Effects of the Invention]

[0007] This provides a method for enhanced mobility in novel wireless systems. [Brief explanation of the drawing]

[0008] [Figure 1A] This figure shows an exemplary communication system that can implement one or more disclosed embodiments. [Figure 1B] This is a system diagram showing an exemplary wireless transceiver unit (WTRU) that can be used in the communication system of Figure 1A according to an embodiment. [Figure 1C] This is a system diagram showing exemplary radio access networks (RANs) and core networks (CNs) that can be used within the communication system of Figure 1A according to an embodiment. [Figure 1D]This is a system diagram illustrating further exemplary RANs and CNs that can be used within the communication system of Figure 1A according to an embodiment. [Figure 2] This diagram shows the causes of handover failures, which are associated with mobility signaling problems. [Figure 3] This cell diagram illustrates CFRA resources that are activated based on their association with serving beams in source cells. [Figure 4] This is a message sequence chart illustrating a configuration mismatch scenario. [Figure 5] This is a message sequence chart illustrating an exemplary procedure for re-establishment, including a fallback to a conditional handover. [Modes for carrying out the invention]

[0009] Figure 1A illustrates 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 wireless users. The communication system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communication system 100 may utilize one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), quadrature FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique word DFT spread OFDM (ZT UW DTS-s OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, and filtered bank multicarrier (FBMC).

[0010] As shown in Figure 1A, the communication system 100 may include radio transceiver units (WTRUs) 102a, 102b, 102c, and 102d, a RAN 104, a CN 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, but it will be understood that the disclosed embodiments intend any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, and 102d can be any type of device configured to operate and / or communicate in a radio environment. For example, any of them may be called a “station” and / or “STA,” and WTRU102a, 102b, 102c, and 102d can 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 phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, radio sensors, hotspots or Mi-Fi devices, Internet of Things (IoT) devices, watches or other wearables, head-mounted displays (HMDs), vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other radio devices operating in industrial and / or automated processing chain situations), consumer electronics devices, and devices operating on commercial and / or industrial radio networks. Any of WTRU102a, 102b, 102c, and 102d may be interchangeably referred to as a UE.

[0011] The communication system 100 may also include base stations 114a and / or base stations 114b. Each of the base stations 114a and 114b can be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, and 102d to facilitate access to one or more communication networks, such as CN 106 / 115, the Internet 110, and / or other networks 112. As an example, base stations 114a and 114b may be base transceiver stations (BTS), node B, enode B (eNB), home node B, home enode B, gNB, NR node B, site controller, access point (AP), and wireless router. Although each of the base stations 114a and 114b is depicted as a single element, it will be understood that base stations 114a and 114b may include any number of interconnected base stations and / or network elements.

[0012] 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, sometimes called cells (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for radio services to a particular geographic area that may be relatively constant or may change over time. A cell 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 for each sector of the cell. In embodiments, the base station 114a can utilize multiple-input multiple-output (MIMO) technology and can utilize multiple transceivers for each sector of the cell. For example, beamforming can be used to transmit and / or receive signals in a desired spatial direction.

[0013] Base stations 114a and 114b can communicate with one or more WTRUs 102a, 102b, 102c, and 102d over the air interface 116, and the air interface 116 can 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 can be established using any suitable radio access technology (RAT).

[0014] More specifically, as mentioned above, the communication system 100 can be a multiple access system and can utilize 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 can implement radio technologies such as Universal Mobile Communications System (UMTS) Terrestrial Radio Access (UTRA), which can establish an air interface 116 using broadband CDMA (WCDMA). WCDMA can include communication protocols such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA can include High Speed ​​Downlink (DL) Packet Access (HSDPA) and / or High Speed ​​Uplink (UL) Packet Access (HSUPA).

[0015] In an embodiment, base station 114a and WTRUs 102a, 102b, and 102c can implement radio technologies such as Advanced UMTS Terrestrial Radio Access (E-UTRA) that 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).

[0016] In this embodiment, base station 114a and WTRUs 102a, 102b, and 102c can implement radio technologies such as NR radio access, which can establish an air interface 116 using New Radio (NR).

[0017] In embodiments, base station 114a and WTRUs 102a, 102b, and 102c can implement multiple radio access technologies. For example, base station 114a and WTRUs 102a, 102b, and 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 WTRUs 102a, 102b, and 102c can be characterized by multiple types of radio access technologies, as well as transmissions sent to and from multiple types of base stations (e.g., eNBs and gNBs).

[0018] In other embodiments, base stations 114a and WTRUs 102a, 102b, and 102c can implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi)), IEEE 802.16 (i.e., Global Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Provisional Standard 2000 (IS-2000), Provisional Standard 95 (IS-95), Provisional Standard 856 (IS-856), Global System for Mobile Communications (GSM), High Speed ​​Data Rate for GSM Evolution (EDGE), and GSM EDGE (GERAN).

[0019] The base station 114b in FIG. 1A may be, for example, a wireless router, a home Node B, a home eNode B, or an access point, and any appropriate RAT may be used to facilitate wireless connectivity in a localized area such as an office, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., used by drones), and a roadway. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish a picocell or a femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Accordingly, the base station 114b may not need to access the Internet 110 via the CN 106 / 115.

[0020] RAN104 / 113 can communicate with CN106 / 115, which can be any type of network configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of WTRU102a, 102b, 102c, and 102d. The data may have various Quality of Service (QoS) requirements, including different throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, and mobility requirements. CN106 / 115 can provide call control, billing services, mobile location-based 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 will be understood that RAN104 / 113 and / or CN106 / 115 can communicate directly or indirectly with other RANs utilizing the same or different RAT as RAN104 / 113. For example, in addition to being connected to RAN104 / 113, which may utilize NR radio technology, CN106 / 115 can also communicate with other RANs (not shown) that utilize GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

[0021] CN106 / 115 may also serve as a gateway for WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network that provides plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and / or Internet Protocol (IP) in the TCP / IP Internet protocol suite. The network 112 may include wired and / or wireless communication networks owned and / or operated by other service providers. For example, the network 112 may include another CN connected to one or more RANs that may utilize the same RAT as RAN 104 / 113 or a different RAT.

[0022] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication system 100 may include multi-mode functionality (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different radio links). For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with a base station 114a that may utilize cellular-based radio technology, and to communicate with a base station 114b that may utilize IEEE 802 radio technology.

[0023] Figure 1B is a system diagram illustrating an exemplary WTRU 102. As shown in Figure 1B, the WTRU 102 may include, among other things, a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power supply 134, a Global Positioning System (GPS) chipset 136, and / or other peripherals 138. It will be understood that the WTRU 102 may include any subcombinations of the above elements while maintaining consistency with the embodiment.

[0024] The processor 118 can be a general-purpose processor, a dedicated processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors working with a DSP core, a controller, a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), and a state machine. The processor 118 can perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 can be coupled to the transceiver 120, and the transceiver 120 can be coupled to the transmit / receive element 122. Although Figure 1B depicts the processor 118 and the transceiver 120 as separate components, it will be understood that the processor 118 and the transceiver 120 can be integrated together in an electronic package or chip.

[0025] The transmit / receive element 122 can be configured to transmit signals to or receive signals from a base station (e.g., base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In another embodiment, the transmit / receive element 122 may be a radiator / detector configured to transmit and / or receive, for example, IR, UV, or visible light signals. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF signals and optical signals. It will be understood that the transmit / receive element 122 can be configured to transmit and / or receive any combination of radio signals.

[0026] In Figure 1B, the transmit / receive element 122 is depicted as a single element, but the WTRU 102 can include any number of transmit / receive elements 122. More specifically, the WTRU 102 can utilize MIMO technology. Therefore, in one embodiment, the WTRU 102 can include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving radio signals over the air interface 116.

[0027] The transceiver 120 can be configured to modulate the signal to be transmitted by the transmit / receive element 122 and to demodulate the signal received by the transmit / receive element 122. As mentioned above, the WTRU 102 can have multimode capabilities. Therefore, the transceiver 120 can include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11.

[0028] The processor 118 of the WTRU102 can 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 can receive user input data from them. The processor 118 can also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 can retrieve information from any type of suitable memory, such as non-removable memory 130 and / or removable memory 132, and store data in them. Non-removable memory 130 can include random access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. Removable memory 132 can include subscriber identification module (SIM) cards, memory sticks, and secure digital (SD) memory cards, etc. In other embodiments, the processor 118 can obtain information from memory located on a server or home computer (not shown), which is not physically located on the WTRU 102, and can store data in it.

[0029] The processor 118 can receive power from the power supply 134 and can be configured to distribute power to and / or control power to other components within the WTRU 102. The power supply 134 can be any suitable device for powering 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, and a fuel cell.

[0030] The processor 118 can also be coupled to a GPS chipset 136, which can be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or instead of, the information from the GPS chipset 136, the WTRU 102 can receive location information from base stations (e.g., base stations 114a, 114b) on the air interface 116 and / or determine its own location based on the timing of signals received from two or more nearby base stations. It will be understood that the WTRU 102 can acquire location information using any suitable location determination method while maintaining consistency with the embodiments.

[0031] The processor 118 can be further coupled to other peripherals 138, which may include one or more software modules and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, peripherals 138 may include an accelerometer, e-compass, satellite transceiver, digital camera (for photos and / or video), Universal Serial Bus (USB) port, vibration device, TV 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, and activity tracker. Peripherals 138 may include one or more sensors, which 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, barometer, gesture sensor, biometric sensor, and / or humidity sensor.

[0032] WTRU102 may include a full-duplex radio where the transmission and reception of some or all of the signals (e.g., associated with specific subframes for both UL (e.g., for transmission) and downlink (e.g., for reception)) can be in parallel and / or simultaneous. The full-duplex radio may include an interference management unit 139 to reduce and / or substantially eliminate self-interference via hardware (e.g., chokes) or via signal processing via a processor (e.g., a separate processor (not shown) or processor 118). In embodiments, WTRU102 may include a half-duplex radio for the transmission and reception of some or all of the signals (e.g., associated with specific subframes for either UL (e.g., for transmission) or downlink (e.g., for reception).

[0033] Figure 1C is a system diagram illustrating RAN104 and CN106 according to an embodiment. As mentioned above, RAN104 can communicate with WTRU102a, 102b, and 102c over the air interface 116 using E-UTRA radio technology. RAN104 can also communicate with CN106.

[0034] RAN104 may include e-nodes B160a, 160b, and 160c, but it will be understood that RAN104 may include any number of e-nodes B while maintaining consistency with the embodiment. Each of the e-nodes B160a, 160b, and 160c may include one or more transceivers for communicating with WTRU102a, 102b, and 102c over the air interface 116. In one embodiment, e-nodes B160a, 160b, and 160c can implement MIMO technology. Thus, e-node B160a may, for example, use multiple antennas to transmit radio signals to and / or receive radio signals from WTRU102a.

[0035] Each of the e-nodes B160a, 160b, and 160c can be associated with a specific cell (not shown) and configured to handle wireless resource management decisions, handover decisions, and user scheduling in UL and / or DL. As shown in Figure 1C, the e-nodes B160a, 160b, and 160c can communicate with each other over the X2 interface.

[0036] 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 (or PGW) 166. Although each of the above elements is depicted as part of CN106, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0037] The MME162 can connect to each of the e-nodes B160a, 160b, and 160c within RAN104 via the S1 interface and can act as a control node. For example, the MME162 can 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. The MME162 can provide control plane functionality for exchanges between RAN104 and other RANs (not shown) utilizing other radio technologies such as GSM and / or WCDMA.

[0038] The SGW164 can connect to each of the e-nodes B160a, 160b, and 160c within RAN104 via the S1 interface. The SGW164 can generally route and forward user data packets to and from WTRU102a, 102b, and 102c. The SGW164 can also perform other functions, such as anchoring the user plane during e-node B handovers, triggering paging when DL data is available to WTRU102a, 102b, and 102c, and managing and remembering the context of WTRU102a, 102b, and 102c.

[0039] SGW164 can connect to PGW166, which in turn provides WTRU102a, 102b, and 102c with access to packet-switched networks such as the Internet 110, facilitating communication between WTRU102a, 102b, and 102c and IP-enabled devices.

[0040] CN106 can facilitate communication with other networks. For example, CN106 can provide WTRU102a, 102b, and 102c with access to circuit-switched networks such as PSTN108, thereby facilitating communication between WTRU102a, 102b, and 102c and conventional fixed-line 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. In addition, 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.

[0041] In Figures 1A to 1D, the WTRU is described as a wireless terminal, but in a typical embodiment, such a terminal is intended to be able to use a wired communication interface with a communication network (e.g., temporarily or permanently).

[0042] In a typical embodiment, the other network 112 can be a WLAN.

[0043] A WLAN in Infrastructure Basic Service Set (BSS) mode may have access points (APs) for the BSS and one or more stations (STAs) associated with the APs. APs may have access to or interfaces with a distribution system (DS) or another type of wired / wireless network that carries traffic within and / or outside the BSS. Traffic originating from outside the BSS to an STA can arrive through an AP and be delivered to the STA. Traffic originating from an STA to a destination outside the BSS can be sent to an AP for delivery to its respective destination. Traffic between STAs within the BSS can be sent through an AP; for example, a source STA can send traffic to an AP, which can then deliver the traffic to a destination STA. Traffic between STAs within the BSS can be considered and / or sometimes referred to as peer-to-peer traffic. Peer-to-peer traffic can be sent (e.g., directly) between a source STA and a destination STA using a Direct Link Setup (DLS). In one typical embodiment, the DLS may be an 802.11e DLS or an 802.11z tunnel DLS (TDLS). A WLAN using Independent BSS (IBSS) mode may not have APs, and STAs within or using IBSS (e.g., all STAs) can communicate directly with one another. Communication in IBSS mode is sometimes referred to herein as “ad hoc” mode communication.

[0044] When using 802.11ac infrastructure mode operation or a similar mode operation, an AP can transmit beacons on a fixed channel, such as a primary channel. The primary channel can be of a fixed width (e.g., 20 MHz bandwidth) or a dynamically set width via signaling. The primary channel can be the operating channel of the BSS and can be used by an STA to establish a connection with the AP. In one typical embodiment, for example, in an 802.11 system, carrier sense multiple access / collision avoidance (CSMA / CA) can be implemented. In the case of CSMA / CA, an STA, including the AP (e.g., any STA), 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. Within a given BSS, at any given time, one STA (e.g., just one STA) can transmit.

[0045] 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.

[0046] Ultra-high throughput (VHT) STAs can support 20MHz, 40MHz, 80MHz, and / or 160MHz wide channels. 40MHz and / or 80MHz channels can be formed by combining consecutive 20MHz channels. 160MHz channels can be formed by combining eight consecutive 20MHz channels, or by combining two discontinuous 80MHz channels, sometimes referred to as an 80+80 configuration. In the 80+80 configuration, data can pass through a segment parser that, after channel encoding, can split the data into two streams. Each stream can be separately subjected to inverse fast Fourier transform (IFFT) processing and time-domain processing. The streams can be mapped onto two 80MHz channels, and the data can be transmitted by the transmitting STA. At the receiver of the receiving STA, the operation described above for the 80+80 configuration can be reversed, and the combined data can be transmitted to the medium access control (MAC).

[0047] Sub-GHz mode operation is 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, such as machine-type communications (MTC) devices in macro coverage areas. MTC devices may have limited functionality, including support for certain bandwidths and / or limited bandwidths (e.g., only support for those). MTC devices may include batteries with a battery life exceeding a threshold (e.g., to maintain a very long battery life).

[0048] A WLAN system that can support multiple channels and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, includes a channel that can be designated as the primary channel. The primary channel may have a bandwidth equal to the largest common operating bandwidth supported by all STAs within the BSS. The bandwidth of the primary channel can be set and / or limited by the STA that supports the minimum bandwidth operating mode among all STAs operating within the BSS. In the case of 802.11ah, even if APs and other STAs within the BSS support 2MHz, 4MHz, 8MHz, 16MHz, and / or other channel bandwidth operating modes, the primary channel may be 1MHz wide for an STA (e.g., an MTC type device) that supports (e.g., only) the 1MHz mode. 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, the majority of the available frequency band remains idle, and even if it could be available, the entire available frequency band can be considered busy.

[0049] In the United States, the available frequency band for use with 802.11ah is from 902 MHz to 928 MHz. In South Korea, the available frequency band is from 917.5 MHz to 923.5 MHz. In Japan, the available frequency band is from 916.5 MHz to 927.5 MHz. The total bandwidth available for 802.11ah is from 6 MHz to 26 MHz, depending on national regulations.

[0050] Figure 1D is a system diagram showing RAN113 and CN115 according to an embodiment. As mentioned above, RAN113 can communicate with WTRU102a, 102b, and 102c over air interface 116 using NR radio technology. RAN113 can also communicate with CN115.

[0051] RAN113 may include gNB180a, 180b, and 180c, but it will be understood that RAN113 may include any number of gNBs while maintaining consistency with the embodiment. Each of the gNB180a, 180b, and 180c may include one or more transceivers for communicating with WTRU102a, 102b, and 102c over the air interface 116. In one embodiment, the gNB180a, 180b, and 180c can implement MIMO technology. For example, the gNB180a and 180b can use beamforming to transmit signals to and / or receive signals from the gNB180a, 180b, and 180c. Thus, the gNB180a can, for example, use multiple antennas to transmit radio signals to and / or receive radio signals from the WTRU102a. In embodiments, gNB180a, 180b, and 180c can implement carrier aggregation techniques. For example, gNB180a can transmit multiple component carriers to WTRU102a (not shown). A subset of these component carriers may be on the unlicensed spectrum, while the remaining component carriers may be on the licensed spectrum. In embodiments, gNB180a, 180b, and 180c can implement multipoint coordination (CoMP) techniques. For example, WTRU102a can receive coordinated transmissions from gNB180a and gNB180b (and / or gNB180c).

[0052] WTRU102a, 102b, and 102c can communicate with gNB180a, 180b, and 180c using transmissions associated with scalable numerology. For example, OFDM symbol intervals and / or OFDM subcarrier intervals can vary for 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 (TTIs) of varying or scalable lengths (e.g., containing varying numbers of OFDM symbols and / or lasting for varying absolute times).

[0053] The gNB180a, 180b, and 180c can be configured to communicate with WTRU102a, 102b, and 102c in standalone and / or non-standalone configurations. In standalone configurations, WTRU102a, 102b, and 102c can communicate with gNB180a, 180b, and 180c without accessing other RANs (e.g., e-nodes B160a, 160b, and 160c). In standalone configurations, WTRU102a, 102b, and 102c can use one or more of the gNB180a, 180b, and 180c as mobility anchor points. In standalone configurations, WTRU102a, 102b, and 102c can communicate with gNB180a, 180b, and 180c using signals within the unlicensed band. In a non-standalone configuration, WTRU102a, 102b, and 102c can communicate with and connect to other RANs such as e-nodes B160a, 160b, and 160c, while also communicating with and connecting to other RANs. For example, WTRU102a, 102b, and 102c can implement DC principles to communicate substantially simultaneously with one or more gNB180a, 180b, and 180c, and one or more e-nodes B160a, 160b, and 160c. In a non-standalone configuration, e-nodes B160a, 160b, and 160c can act as mobility anchors for WTRU102a, 102b, and 102c, while gNB180a, 180b, and 180c can provide additional coverage and / or throughput to serve WTRU102a, 102b, and 102c.

[0054] Each of the gNB180a, 180b, and 180c can be associated with a specific cell (not shown) and can 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, and routing of control plane information to access and mobility management functions (AMF) 182a and 182b, etc. As shown in Figure 1D, the gNB180a, 180b, and 180c communicate with each other on the Xn interface. The CN115 shown in Figure 1D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. Although each of the above elements is depicted as a part of CN115, it will be understood that any of these elements may be owned and / or operated by an entity different from the CN operator.

[0055] AMF182a and 182b can connect to one or more of gNB180a, 180b, and 180c within RAN113 via the N2 interface and can act as control nodes. For example, AMF182a and 182b can be responsible for authenticating users of WTRU102a, 102b, and 102c, supporting network slicing (e.g., handling different PDU sessions with different requirements), selecting specific SMF183a and 183b, managing registration areas, terminating NAS signaling, and mobility management. Network slicing can be used by AMF182a and 182b to customize CN support for WTRU102a, 102b, and 102c based on the type of services utilized by WTRU102a, 102b, and 102c. For example, different network slices can be established for different use cases, such as services that rely on ultra-high reliability low latency (URLLC) access, services that rely on high-speed high-capacity mobile broadband (eMBB) access, and / or services for machine-type communications (MTC) access. The AMF182a and 182b can provide control plane functionality for exchange between RAN113 and other RANs (not shown) that utilize other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies like WiFi.

[0056] SMF183a and 183b can connect to AMF182a and 182b in CN115 via the N11 interface. SMF183a and 183b can also connect to UPF184a and 184b in CN115 via the N4 interface. SMF183a and 183b can select and control UPF184a and 184b and configure routing of traffic through them. 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 can be IP-based, non-IP-based, and Ethernet-based, among others.

[0057] UPF184a and 184b can connect to one or more of the gNB180a, 180b, and 180c in RAN113 via the N3 interface, providing WTRU102a, 102b, and 102c with access to packet-switched networks such as the Internet 110, facilitating communication between WTRU102a, 102b, and 102c and IP-enabled devices. UPF184a and 184b can perform other functions such as routing and forwarding packets, enforcing user plane policies, supporting multihoming PDU sessions, handling user plane QoS, buffering downlink packets, and providing mobility anchoring.

[0058] 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. In addition, CN115 can 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 can connect to local data networks (DN) 185a, 185b through UPF184a, 184b via an N3 interface to UPF184a, 184b, and an N6 interface between UPF184a, 184b and DN185a, 185b.

[0059] In view of Figures 1A to 1D and their corresponding descriptions, one or more or all of the functions described herein relating 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 any other devices described herein may be performed by one or more emulation devices (not shown). An emulation device may be one or more devices configured to emulate one or more or all of the functions described herein. For example, an emulation device may be used to test other devices and / or to simulate network and / or WTRU functions.

[0060] Emulation devices can be designed to perform one or more tests of other devices in a laboratory environment and / or an operator network environment. For example, one or more emulation devices can perform one, more, or all functions, fully or partially implemented and / or deployed as part of a wired and / or wireless network, to test other devices in a communication network. One or more emulation devices can perform one, more, or all functions, temporarily implemented / deployed as part of a wired and / or wireless network. Emulation devices can be directly coupled to another device for the purpose of performing tests and / or can perform tests using over-the-air radio communication.

[0061] One or more emulation devices can 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 can be used in a test scenario, in a test laboratory and / or in an undeployed (e.g., test) wired and / or wireless communication network, to perform testing of one or more components. One or more emulation devices can be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (e.g., including one or more antennas) can be used by the emulation device to transmit and / or receive data.

[0062] As explained above, fifth-generation (5G) air interfaces and their New Radio (NR) access technology are expected to enable use cases such as improved broadband performance (IBB), industrial control and communications (ICC), and vehicle-to-vehicle (V2X) applications, as well as massive machine-type communications (mMTC).

[0063] Some such use cases may require support for ultra-reliable low transmission delay (URLLC) communications. Air interface delays as small as 1 ms RTT may require support for TTI between 100 μs and 250 μs, for example. Some such use cases may require ultra-low access delays (e.g., the time from initial system access to the completion of transmission of the first user plane data unit). For example, some ICC and V2X use cases may require end-to-end (e2e) delays of less than 10 ms.

[0064] Furthermore, some such use cases may require support for ultra-reliable transmission (URC). Transmission reliability may need to be far better than what is possible with legacy LTE systems. For example, a possible target could be close to 99.999% transmission success and service availability. Another consideration may be support for mobility speeds in the range of 0 to 500 km / h. Some ICC and V2X use cases may require packet loss rates of less than 10e-6.

[0065] Some use cases may require support for MTC operation, including narrowband operation. The NR air interface can efficiently support narrowband operation (e.g., using less than 200 kHz), extended battery life (e.g., up to 15 years of autonomy), and minimal communication overhead for small and infrequent data transmissions (e.g., at low data rates in the range of 1 to 100 kbps) with access delays ranging from a few seconds to several hours.

[0066] Orthogonal Frequency Division Multiplexing (OFDM) can be used as the basic signal format for data transmission in both LTE and IEEE 802.11. OFDM can efficiently divide the spectrum into multiple parallel orthogonal subbands. Each subcarrier is shaped in the time domain using a rectangular window, resulting in a sinc-shaped subcarrier in the frequency domain. OFDM may require strict control of frequency synchronization and uplink timing alignment within the duration of the cyclic prefix to maintain orthogonality between signals and minimize intercarrier interference. This strict synchronization may be unsuitable in systems where a WTRU is simultaneously connected to multiple access points. Additional power reductions may also be applied to uplink transmissions to comply with the spectral emission requirements of adjacent bands. This may be particularly relevant in the presence of fragmented spectral aggregation for WTRU transmissions.

[0067] In some cases, the shortcomings of conventional cyclic prefix (CP) OFDM (CP-OFDM) can be addressed by more stringent radio front-end requirements for implementation, for example, when operating with large amounts of continuous spectrum that do not require aggregation. CP-based OFDM transmission schemes can also result in a downlink physical layer for 5G that is similar to that of legacy systems (e.g., with modified pilot signal density and location).

[0068] While other waveform candidates can be considered for Flexible 5G Networks (5gFLEX), conventional OFDM remains a possible candidate for 5G systems, for example, for downlink transmission schemes. In some cases, 5gFLEX radio access can be characterized by a very high degree of spectral flexibility, enabling deployment in different frequency bands with different characteristics. 5gFLEX can include different and / or variable-sized available spectra, including different duplex configurations, as well as continuous and discontinuous spectral assignments in the same or different bands. 5gFLEX can also support variable timing modes, such as support for multiple TTI lengths and / or support for asynchronous transmission.

[0069] 5gFLEX can support both TDD and FDD redundancy schemes. For FDD operation, spectral aggregation can be used to support auxiliary downlink operation. FDD operation can support both full-duplex and half-duplex FDD operation. For TDD operation, DL / UL allocation can be dynamic (i.e., it may not be based on a fixed DL / UL frame configuration). For example, the length of the DL or UL transmission interval can be set for each transmission opportunity.

[0070] In some cases, increased path loss at higher frequencies (e.g., above 6 GHz) can be compensated for using beamforming. In some cases, higher beamforming gain can be achieved by using multiple (e.g., a relatively larger number) antenna elements.

[0071] In some cases, analog and / or hybrid beamforming can be used to reduce implementation costs (for example, by reducing the number of RF chains). Analog and / or hybrid beams can be multiplexed in time. Beamforming can be applied to one or more of the synchronous, PBCH, and control channels to provide cell-wide coverage. The term beam sweep can refer to the transmission and / or reception of beamformed channels that are multiplexed in time and / or frequency and / or space.

[0072] The term "reference signal" can refer to any signal, preamble, or system signature that can be received and / or transmitted by a WTRU for one or more of the purposes described herein. Different reference signals can be defined for beam management in DL and UL. For example, DL beam management may use a channel status information reference signal (CSI-RS), demodulation reference signal (DMRS), synchronization signal (SS), or other suitable signal. UL beam management may use a sounding reference signal (SRS), DMRS, preamble transmission associated with random access channel (RACH), or other suitable signal.

[0073] After receiving a reconfiguration message implicitly or explicitly associated with a condition (i.e., a conditional reconfiguration), the WTRU can verify and store the reconfiguration, begin monitoring the condition (i.e., trigger condition), and apply the reconfiguration when the trigger condition is satisfied. For example, a WTRU may receive a Radio Resource Control (RRC) connection reconfiguration having one or more of the mobility information elements and conditional mobility information elements. The WTRU may receive one of the information elements for each candidate target cell. A WTRU can be configured to use multiple conditional reconfigurations associated with multiple target cells. Conditional reconfigurations are sometimes referred to as conditional handovers (CHOs), and these terms are used interchangeably herein.

[0074] Detaching reconfiguration transmission from the application of reconfiguration can improve the reliability of control signals. For example, control signaling can be transmitted when the quality of the radio link is better. Another advantage of this technique is that the response time between a fault event (e.g., measurement) and a corrective action (e.g., reconfiguration with mobility) can be shorter. In legacy methods, the WTRU may first need to detect the fault event, report the event to the network, wait for a network response, process the network response, and then take corrective action. Such delays can prevent the execution of mobility reconfiguration in the correct time under rapidly degrading radio conditions. In contrast, conditional reconfiguration can facilitate the WTRU benefiting from controlled autonomy. In such cases, the network can configure how fault events should be detected and what corrective actions should be taken, while the WTRU can decide when to take corrective action. This can enable faster response times, which can facilitate sparse transmission and / or measurement of reference signals and increase power savings in the network and / or WTRU.

[0075] The cell can be configured to use an auxiliary uplink (SUL). The SUL can extend the coverage of a WTRU operating at a higher frequency by switching the UL to a lower band when the WTRU is far from the gNB. In some cases, the SUL may include a cell having a DL carrier associated with two separate UL carriers. In some implementations, the separate UL carriers may include a regular UL (RUL) which can be in a higher frequency band (where the DL carrier is also located, for example) and a SUL which can be in a lower frequency band.

[0076] SUL can be configured for both primary cells (PCells) (e.g., in NR standalone mode) and PSCells in NR-NR DC or dual connectivity between LTE and NR (i.e., non-standalone (NSA) mode or NR DC (EN-DC)). WTRU can use either RUL or SUL to perform initial access to the cell. SUL configurations can be broadcast by the cell with minimum SI. If the DL quality of a serving cell falls below a threshold, WTRU may choose SUL for initial access.

[0077] In some cases, when a WTRU is RRC connected (e.g., in the RRC_CONNECTED state), multiple separate operating modes are possible for a SUL. In an exemplary operating mode, the RRC can configure the WTRU to use two ULs, one of which is a full UL configuration and the other is an SRS configuration. When the full UL configuration is provided to the carrier, the WTRU can perform UL control, UL data, SRS, PRACH, etc. When only the SRS configuration is provided to the carrier, the WTRU can perform only SRS transmission. In this exemplary operating mode, the WTRU can use the fully configured UL configuration for all control and data transmission on the uplink and transmit SRS on other, not fully configured uplinks. RRC reconfiguration can be used to provide the full UL configuration to different carriers and to switch between UL data between different ULs. In another exemplary operating mode, the RRC can configure two ULs, both of which are fully configured ULs. In some implementations, signaling (e.g., MAC CE, or DCI) can enable the WTRU to switch between two UL configurations. In another exemplary mode of operation, the RRC can configure two ULs that are used together. This mode of operation assumes that a push transmission for a single serving cell cannot occur simultaneously for both ULs.

[0078] As described above, the NR interface can support a wide range of use cases with diverse service requirements. For example, mMTC use cases may require power-efficient services with low overhead and low data rates. URLLC use cases may require very high reliability. Extended mobile broadband (eMBB) use cases may require high data rates. The NR interface can support diverse WTRU capabilities, including low-power, low-bandwidth WTRUs, WTRUs capable of transmitting with very wide bandwidth (e.g., 80 MHz), and WTRUs using high frequencies (e.g., 6 GHz and above). In such use cases, WTRUs may be in various mobility scenarios (e.g., stationary / fixed, high-speed trains, etc.). The NR interface may require an architecture that is flexible enough to adapt to diverse deployment scenarios (e.g., standalone, non-standalone supported by different air interfaces, centralized, virtualized, and delivery over ideal / non-ideal backhaul).

[0079] In such scenarios, frequent handover failures and / or wireless link failures may occur. For example, such failures may be due to a rapid deterioration in the quality of the serving cell over a short period of time. Methods and devices that can overcome these problems and improve the reliability of control signaling are described herein.

[0080] WTRUs can perform re-establishment procedures to recover from critical error conditions affecting the operation of a serving cell. However, re-establishment procedures can incur costs such as increased downtime and data loss. Enhanced re-establishment procedures can be provided to facilitate acceptable downtime in critical error scenarios.

[0081] Figure 2 illustrates the causes of handover failures associated with mobility signaling problems. The radio link condition may rapidly deteriorate within the source cell before the Handover Command (HOC) is received by the WTRU, and a Radio Link Failure (RLF) may be declared. The WTRU can then perform a re-establishment toward the target cell. The HOC may not be received in a timely manner for one or more reasons. The WTRU may not transmit measurement reports quickly enough (e.g., while a suitable neighbor cell is available) due to uplink radio link degradation. The WTRU may not receive the Handover Command due to downlink radio link degradation. If the WTRU receives a Handover Command for a suitable target cell before declaring an RLF, while the link with the source cell is still functioning correctly, a re-establishment and service interruption can be avoided.

[0082] Figure 2 illustrates a handover failure case associated with a mobility signaling problem. The WTRU measurement process 200 begins when a measurement event 205 is detected by the WTRU. After a time interval 210 (tracked, for example, by the WTRU's timer), the WTRU sends a measurement report 215 to the network (e.g., to or via the gNB). After the measurement report is sent to the network, the WTRU waits for a time period 220 while the network prepares a handover command 225. After the WTRU receives the handover command 225, it performs the handover based on the handover command 225. The handover requires an execution time 230. From the WTRU's perspective, handover completion 235 can occur, for example, when RACH is completed in the target cell of the handover.

[0083] Exemplary RLF240 illustrates an exemplary handover failure case in which an RLF occurs before the WTRU can send measurement report 215. In this example, the WTRU detects a radio link problem during time interval 245 (e.g., when the maximum number of lag indications is received from the lower layer). After detecting the radio link problem 250, the WTRU waits for time interval 255 (tracked using an RLF timer, e.g., T310, to rule out transient issues, e.g.) before declaring RLF 260. Since the WTRU has determined that the radio link with the network has failed (time X) before it sends measurement report 215, the WTRU does not send measurement report 215 and instead attempts to re-establish its connection with the network during time interval 265 (tracked using a timer, e.g., T311, e.g.). If the WTRU is unable to re-establish its connection within time interval 265, it enters idle state 270.

[0084] Exemplary RLF275 illustrates an exemplary handover failure case in which an RLF occurs after the WTRU sends measurement report 215 but before it receives a handover command 225. In this example, the WTRU detects a radio link problem during time interval 280 (e.g., when the maximum number of missync indications is received from the lower layer). After detecting the radio link problem 285, the WTRU waits for time interval 290 (tracked using an RLF timer, e.g., T310, to rule out transient issues) before declaring RLF295. Since the radio link with the network has failed (time Y) before the WTRU can receive the handover command 225, the WTRU does not perform a handover and instead attempts to re-establish its connection with the network during time interval 296 (tracked using a timer, e.g., T311). If the WTRU is unable to re-establish its connection within time interval 296, it enters an idle state 297.

[0085] Legacy RRC re-establishment can result in increased latency and downtime for active services in a WTRU. RRC re-establishment procedures can include WTRU-based mobility triggered by one or more conditions (e.g., critical error conditions), such as radio link failure (e.g., expiration of an RLF timer (e.g., T310)), random access failure, maximum number of radio link control (RLC) retransmissions, or integrity check failure. However, initiating an RRC re-establishment procedure can result in a data radio bearer (DRB) suspension. In some embodiments, after the completion of the re-establishment procedure for a target cell, the DRB may not resume until the WTRU receives a first RRC reconfiguration from the network. The downtime from DRB suspension to resumption can be considerable, potentially resulting in data loss.

[0086] In some embodiments, the WTRU can determine, as a function of a failure event, whether to initiate a re-establishment procedure or a conditional reconfiguration procedure. The WTRU can be configured to monitor various events that cause failures to the operation of the serving cell. Failure events may include, for example, one or more of the following from the Radio Link Monitoring (RLM) process: lower-layer problem indications (e.g., RLF timer (e.g., T310) expiration), random access problem indications, indications that the maximum RLC retransmission has been reached, indications that beam recovery has failed and / or no candidate beams have been found, reconfiguration failures (e.g., the WTRU is unable to follow a received reconfiguration command), integrity check failures, handover failures, etc. After detecting one or more such failure events, the WTRU can be configured to determine whether to perform a re-establishment procedure or a conditional reconfiguration procedure. The decision can be made as a function of a particular failure event or type of failure event.

[0087] In some embodiments, the WTRU is configured to use conditional reconfiguration for any target cell (i.e., a suitable target cell exists—there is at least one target cell for which conditional reconfiguration exists), and if the target cell satisfies cell selection criteria (e.g., the quality of the target cell exceeds a predefined threshold), the WTRU can execute the conditional reconfiguration procedure after detecting a first subset of failure events. The first subset of failure events may include one or more indications of lower-layer problems from the RLM process (e.g., T310 expiration), random access problems, indications that the maximum RLC retransmission has been reached, beam recovery has failed, and / or no candidate beams have been found.

[0088] In some embodiments, the WTRU may perform a re-establishment procedure after detecting a second subset of failure events. The second subset of failure events may include one or more of the following: reconfiguration failure (e.g., the WTRU receives a handover command but is unable to follow the contents of the handover command), integrity check failure, and handover failure. The WTRU may also perform a re-establishment procedure after detecting a first set of failure events if the WTRU is not configured to use conditional reconfiguration for any target cell (i.e., no suitable target cell exists), or if the target cell associated with conditional reconfiguration does not satisfy the cell selection criteria.

[0089] In some embodiments, the WTRU may initiate a handover procedure if a re-establishment is triggered for a cell for which a conditional reconfiguration exists (i.e., the WTRU is configured to use a conditional reconfiguration that targets that cell). The WTRU may be configured to use a conditional reconfiguration for one or more target cells. While the WTRU monitors the trigger conditions associated with the target cells, it may detect failure events, such as a first or second set of the failure events described above. Based on the detected failure events, the WTRU may trigger a re-establishment procedure.

[0090] The re-establishment procedure may include performing cell selection to select the appropriate cell. In one example, as a result of cell selection, the WTRU may select a cell for which a conditional reconfiguration exists (e.g., the WTRU has received a conditional reconfiguration for a cell that has not yet expired). If the WTRU selects a cell for which a conditional reconfiguration exists, the WTRU may assume that the trigger condition has been met for that cell (i.e., the WTRU can trigger a conditional handover instead of the re-establishment procedure). In another example, if the WTRU selects a cell for which a conditional reconfiguration does not exist (e.g., all conditional reconfigurations for the cell have expired, or no conditional reconfiguration has been configured for the cell), the WTRU can trigger the re-establishment procedure. In the case of a conditional handover, the DRB can be restarted after the WTRU sends a reconfiguration completion, so this scheme can help reduce downtime in some cases. In addition, the WTRU can be configured to use a dedicated random access resource for conditional reconfigurations, which further reduces delay / downtime.

[0091] During the cell selection procedure, the WTRU may prioritize cells configured for conditional handover (i.e., cells for which the WTRU has received a conditional handover configuration that designates the cell as a target cell). For example, the WTRU may be configured to add a positive offset (i.e., a positive bias when evaluating the cell selection criteria, e.g., a positive bias on the RSRP or RSRQ measurement) to target cells for which conditional reconfiguration exists (i.e., cells for which the WTRU has received a conditional handover configuration that designates the cell as a target cell). Alternatively, the WTRU may be configured to select target cells for which conditional reconfiguration exists if the quality of the target cell (e.g., RSRP or RSRQ value) exceeds a predefined threshold.

[0092] A WTRU can be configured to use conditional reconfiguration for two or more target cells. A WTRU can be configured to use further rules for prioritizing target cells among multiple target cells. For example, a WTRU may prefer the target cell with the highest priority (or relatively higher priority). In some embodiments, priority can be explicitly configured by the network as part of conditional reconfiguration. In some embodiments, priority can be implicitly determined by the WTRU based on trigger conditions, such as target cells whose offset / threshold is smaller compared to the serving cell. For example, a WTRU can be configured to trigger a conditional handover of that of a serving cell to any of multiple target cells having an RSRP or RSRQ value that exceeds that of a serving cell by a threshold amount or by a maximum amount. A WTRU may prefer a target cell to which a dedicated random access preamble has been assigned. A WTRU may prefer a target cell to which a SUL configuration is used. A WTRU may prefer one or more target cells that have been configured most recently, or a target cell with the highest validity timer value (e.g., the one with the longest remaining validity).

[0093] As described above, a Conditional Handover (CHO), or Enhanced Re-establishment Procedure, can be triggered by the detection of a lower-layer problem. A lower-layer problem that triggers a CHO can be associated with one or more of the following events, namely, one or more of the following: T310 expiration, RA access problem indications from the MAC while T300, T301, T304, or T311 are inactive, or indications from the RLC indicating that maximum retransmission has been reached. T300 is a timer that, while active, indicates that the WTRU is engaged in an ongoing RRC connection setup procedure. T301 is a timer that, while active, indicates that the WTRU is waiting for a re-establishment response. T304 is a timer that, while active, indicates that the WTRU is engaged in an ongoing handover procedure. T311 is a timer that, while active, indicates that the WTRU is engaged in an ongoing re-establishment procedure.

[0094] The WTRU can be configured to use timer and / or radio link failure (RLF) related parameter values ​​(e.g., maximum number of transmissions, and N3xx values, where N310 is a counter tracking the number of out-of-sync indications from lower layers, and N311 is a counter tracking the number of in-sync indications from lower layers; T310 is started when N310 exceeds a threshold, and T310 is stopped when N311 exceeds a threshold) or their offsets, which can trigger an RLF. The parameters can be the same as, or similar to, parameters commonly used in monitoring functions (e.g., RLM, HARQ, etc.). For example, the WTRU can be configured to use values ​​that can trigger conditional mobility or enhanced re-establishment procedures before the WTRU otherwise determines that a radio link failure has occurred. In some implementations, this can avoid triggering RLF and re-establishment procedures.

[0095] CHO triggering based on detection of lower-layer problems can depend on the SUL configuration. For example, if a WTRU configured to use CHO is configured to use SUL in a serving cell, the WTRU can only execute CHO when T310 expires. Otherwise, the WTRU can execute CHO when a trigger for RLF associated with any cause (e.g., an indication of an RLM problem, the maximum number of HARQ retransmissions, a RACH failure, etc.) occurs. For example, the WTRU may consider the occurrence of beam fault recovery as a trigger.

[0096] If the WTRU is configured to use the SUL and attempts to perform the RA procedure on the RUL are unsuccessful, the WTRU can indicate a random access problem to a higher layer. After this indication is received by the RRC (e.g., upon reception), the WTRU can start a timer and, if the measured DL reference signal received power (RSRP) falls below a threshold, can perform the RA procedure on the SUL. If the RA procedure on the SUL is successful, the WTRU can transmit an indication to the RRC layer. The WTRU can stop its timer upon or after receiving an indication from the MAC layer indicating a successful RA procedure on the SUL. Upon or after the expiration of this timer, the WTRU can perform a CHO.

[0097] If the WTRU is configured to use SUL, when an RLF is triggered, the WTRU can report Master Cell Group Radio Link Failure (MCG-RLF) information over the SUL link instead of initiating a re-establishment. The WTRU can trigger a handover on the best cell with the CHO. The MCG-RLF report may include the most recent measurement of the target cell that triggered the CHO, or the best cell among them. The source gNB can transmit these results to the target cell. The target cell can release uncontested random access (CFRA) resources associated with beams with RSRP lower than a configured threshold and an indication showing the beam where the WTRU is most likely to attempt an RA procedure. The target can also configure the WTRU to use the beam with the highest reported measurement result (e.g., CSI-RS configuration).

[0098] After a successful handover to the target cell is completed, the target cell can send an indication to the source cell that the handover was successful. Based on this indication, the source cell can notify other prepared candidate cells to release the configuration associated with this WTRU (e.g., a dedicated RACH resource). CHO can be triggered in RRC_CONNECTED mode based on the detection of lower-layer problems. A new timer for Layer 1 problem detection, or an offset to T310, can be set to facilitate triggering a handover based on an existing CHO command before an RLF is triggered, upon its expiration. A new timer in MAC, or an offset to the beam fault recovery timer, smaller than the beam fault recovery timer, can be set to trigger a handover based on an existing CHO command before the expiration indication for T310 to higher layers. For example, a maximum number of preamble retransmissions, or an offset to ra-PreambleTx-Max, smaller than ra-PreambleTx-Max, can be set to trigger a handover before declaring an RLF. A number of consecutive mis-sync indications from lower layers, smaller than N313, or an offset relative to N313, can be set to trigger a handover based on an existing CHO command before the RLF is declared.

[0099] In some embodiments, the CHO trigger is associated with multiple measurements. For example, the WTRU can be configured to use a CHO trigger condition associated with a specific measurement. In some examples, the WTRU can be configured to use a trigger condition that includes two or more measurements. One or more measurements may include, for example, RSRP, reference signal reception quality (RSRQ), and / or signal-to-interference noise ratio (SINR). An example of a trigger condition that includes two or more measurements may require both that a first measurement of the candidate cell is better than the serving cell or a first absolute threshold, and that a second measurement of the candidate cell is better than the serving cell or a second absolute threshold. Different combinations of the first and second measurements may be possible, for example, RSRP and RSRQ, RSRP and SINR, RSRQ and SINR, etc. In some examples, the WTRU can be configured to use a trigger condition that includes three or more measurements, for example, RSRP, RSRQ, and SINR, etc.

[0100] In cases where multiple cells simultaneously satisfy the trigger condition, the WTRU can be configured to prioritize target cells based on the metric associated with the trigger condition. For example, the WTRU can be configured to prioritize candidate cells with the highest SINR. In another example, the WTRU can be configured to prioritize candidate cells with the highest RSRQ. In some examples, the WTRU can be configured to use a priority order associated with the trigger condition such that some trigger conditions take precedence over others. For example, the WTRU can be configured to prioritize trigger conditions based on SINR and / or RSRQ over trigger conditions based on RSRP.

[0101] In some embodiments, the CHO trigger is associated with multiple reference signal types. For example, the WTRU can be configured to use a CHO trigger condition based on a measurement associated with a particular RS type. The RS type can be, for example, SSB or CSI-RS. In some examples, the WTRU can be configured to use multiple trigger conditions, each involving two or more reference signal types. For example, the WTRU can be configured to use one trigger condition based on a measurement associated with SSB, and another trigger condition based on a measurement associated with CSI-RS. Such trigger conditions can be associated with the same or different candidate cells and / or frequencies.

[0102] In cases where multiple cells simultaneously satisfy the trigger conditions, the WTRU can be configured to prioritize target cells based on the reference signal type associated with each trigger condition. For example, the WTRU can be configured to prioritize candidate cells with the most good beams based on SSB. In this context, a good beam can refer to a beam associated with an SSB whose RSRP exceeds a pre-configured threshold (e.g., RSRP-Threshold-SSB). In another example, the WTRU can be configured to prioritize candidate cells with the most good beams based on CSI-RS. In this context, a good beam can refer to a beam associated with a CSI-RS whose RSRP exceeds a pre-configured threshold (e.g., RSRP-Threshold-CSI-RS). In some examples, the WTRU can be configured to determine which reference signal type to prioritize based on the type of service. For example, if the WTRU is configured to prefer reliability, the WTRU can prioritize trigger conditions associated with SSB as the RS type. Similarly, if the WTRU is configured to prefer lower latency or higher throughput, the WTRU may prefer trigger conditions based on CSI-RS as the RS type.

[0103] Some embodiments include implicit and / or default CHO candidates. In some cases, the implicit configuration of CHO candidates can facilitate the reduction of RRC signaling overhead. In some implementations, a WTRU may, by default, assume that cells with certain characteristics are CHO candidates. For example, a WTRU may consider all secondary cells (Scells) configured for the WTRU as implicit CHO candidates. In another example, a WTRU may consider only those activated Scells as implicit CHO candidates. In yet another example, a WTRU may configure whether an Scell ​​should be considered a default CHO candidate during the addition or modification of an Scell. In yet another example, a WTRU may assume that a primary Scell ​​(PScell) is an implicit CHO candidate. In yet another example, a WTRU may consider any cell in an SCG as an implicit CHO candidate. In yet another example, a WTRU may configure whether an Scell ​​should be considered a default CHO candidate during the addition or modification of an SCG or during cell group configuration. In another example, WTRU can be configured to prioritize implicit CHO candidates (for example, over explicit CHO candidates) during CHO execution.

[0104] Some embodiments include prioritization associated with trigger conditions. In some embodiments, the WTRU can be configured to use one or more candidate cells for a CHO, each candidate cell can be associated with one or more trigger conditions that result in multiple trigger conditions for performing a CHO. It is possible that two or more trigger conditions are satisfied within a given time. In some examples, the WTRU can be configured to use rules for determining which target cell to CHO to when these satisfied trigger conditions are associated with different candidate cells. Exemplary rules may include prioritization, or combinations of prioritization, based on the best beam, based on the number of good beams, and / or based on the availability of dedicated resources. For prioritization based on the best beam, the WTRU can be configured to select candidate cells that have the best beam with respect to the WTRU (e.g., with respect to RSRP, RSRQ, or SINR). For prioritization based on the number of good beams, the WTRU can be configured to select candidate cells that have the most good beams with respect to the WTRU, and a good beam can be defined with respect to a metric (e.g., RSRP, RSRQ, or SINR) that exceeds a pre-configured threshold. Regarding prioritization of WTRUs based on the availability of dedicated resources, the WTRU can be configured to select candidate cells that have availability exceeding a minimum threshold (e.g., with respect to RSRP, RSRQ, or SINR) and are associated with available dedicated resources (e.g., CFRA). Alternatively, the WTRU can be configured to select candidate cells that have the most CFRA resources associated with a good beam.

[0105] In some cases, the WTRU can be configured to prioritize CHO reliability. For example, the WTRU can be configured to select the cell with the best cell quality and / or beam quality from among candidate cells. In some cases, the WTRU can be configured to prioritize CHO delay. For example, the WTRU can select a cell with available CFRA resources from among candidate cells. The term "available" indicates that the beam (i.e., the reference signal) associated with the CFRA resource configuration meets the minimum threshold (e.g., with respect to RSRP, RSRQ, and / or SINR).

[0106] Some embodiments implement CFRA effectiveness in the target cell as a function of the serving beam in the source cell. Some embodiments provide a CHO command that indicates the CFRA resource to be activated based on the serving beam in the source cell. For example, a WTRU may receive a CHO command that includes multiple configurations of dedicated RACH resources for some or all of the SSB / CSI-RS in the target cell. Furthermore, the WTRU may be configured to use an association between the serving beam and a group of beams in the target cell. In some examples, the WTRU may select a beam to use CFRA in the target cell only if it is associated with the serving beam (or best beam) in the serving cell.

[0107] A serving cell uses a Target Cell Identifier (TCI) state to communicate which beam should be used (for example, for physical downlink control channel (PDCCH) monitoring or DL ​​data). Indications indicating CFRA resources to be activated based on the serving beam in the source cell can be based on the TCI state. For example, when a WTRU executes a handover command in a target cell, it can consider only CFRA resources for beams in the target cell that are linked to the beam indicated in the TCI state. A WTRU can be configured to assume that only CFRA resources in the target cell beam linked to the current serving cell beam (i.e., based on the TCI state) are valid. This implicit activation of CFRA resources based on pre-configured linkages can have the advantage of minimizing frequent signaling.

[0108] Figure 3 is a cell diagram illustrating CFRA resources that are activated based on their association with serving beams in source cell 300. In Figure 3, the WTRU in source cell 300 is configured to use the association between serving beam 305 and beams 310, 315, and 320 in the first target cell 325. When the WTRU performs CHO in target cell 325, only the CFRA resources for beams 310, 315, and 320 are activated based on their association with serving beam 305, as shown in the TCI state. The CFRA resources for beams 330 and 335 are not activated because they are not associated with serving beam 305.

[0109] Since the timing of conditional reconfiguration can be determined by the WTRU, the RRC configuration used by the WTRU in the target cell is ambiguous and may lead to handover failures.

[0110] Figure 4 is a message sequence chart illustrating an exemplary configuration mismatch scenario. In the example in Figure 4, WTRU400 can first receive a conditional reconfiguration 420 for target gNB405 from source gNB410. Source gNB410 can determine the conditional reconfiguration 420 based on adjustments 425 that can be made on the Xn interface. Xn adjustments 425 can be based on handover preparation signaling. The conditional reconfiguration 420 can include various parameters, including trigger conditions and RRC configurations that are applied in the target cell associated with target gNB405 when the trigger conditions occur. In some implementations, the parameters can include logical identifiers associated with the target cell RRC configuration. In step 430, WTRU400 can begin monitoring for trigger conditions for a time T1. During time T1, WTRU can still be connected to the serving cell associated with source gNB410 and can receive different types of RRC signaling from source gNB410. Such RRC signaling from source gNB410 can affect the stored conditional reconfiguration 420 in WTRU400, and therefore can affect the configuration of WTRU400 applied in the source cell associated with source gNB410. Whenever the conditional configuration 420 of the WTRU applicable to the target operation is updated, source gNB410 may also need to reconcile with target gNB405. For example, source gNB410 may need to reconcile both WTRU400 and target gNB405 so that the RRC configuration 420 is consistent between the WTRU and the target gNB.

[0111] Since the timing of conditional reconfiguration is determined by the WTRU, there may be cases where the WTRU autonomously triggers a handover while reconfiguration with the source cell is in progress. This can result in a configuration mismatch in the target cell, leading to a failure of the handover procedure. In other words, the target gNB may be uncertain about the RRC configuration last used in the source cell. For example, WTRU400 may receive one or more reconfigurations in the source cell during time T1. It may not be clear to the target gNB whether the WTRU was able to receive / apply those reconfigurations before triggering the CHO. In this example, source gNB410 determines an update 435 for conditional reconfiguration 420 based on adjustment 440 on the Xn interface and sends the update 435 to WTRU400. The update 435 may include one or more changes to parameters in conditional reconfiguration 420 (e.g., a different target cell RRC configuration, a different RACH configuration, a different radio bearer configuration, a different security configuration, or one or more different conditions). If the parameters of conditional reconfiguration 420 include an identifier (e.g., an ID number), update 435 includes a different identifier. WTRU400 does not receive update 435, as illustrated in Figure 4. In step 445, WTRU400 determines that the trigger condition specified in conditional reconfiguration 420 has been satisfied and initiates the random access procedure 450 with target eNB405. A configuration mismatch occurs here, in that WTRU400 triggered the random access procedure 450 based on conditional reconfiguration 420 and not on update 435.

[0112] A WTRU can send an indication that is associated with a target cell and shows its configuration. For example, a WTRU can be configured to send an indication that is associated with a target cell and shows its RRC configuration. The indication can be sent in the target cell with the first message after a random access procedure. The indication can be sent in the target cell with the first RRC message. The indication can include an identity (e.g., an identifier, ID number, or other parameters as described above) associated with the conditional reconfiguration message applied by the WTRU. For example, the indication can include a transaction identifier corresponding to the most recent RRC reconfiguration message, including the conditional reconfiguration message associated with the target cell. The indication can be an identity associated with the last RRC configuration used in the source gNB. For example, the indication can be a transaction identifier corresponding to the most recent RRC reconfiguration message successfully received and applied by the WTRU in the source gNB.

[0113] A WTRU can be configured to send an indication with the MAC CE along with the initial RRC message. For example, the initial RRC message can be both encrypted and integrity protected using the configuration indicated by the MAC CE. A WTRU can also be configured to send an indication within the RRC message. For example, a WTRU can send an indication as part of the transaction identifier in the RRC reconfiguration completion message. The RRC message can be integrity protected only.

[0114] For RRC reconfiguration procedures involving a serving cell, the WTRU may send an RRC reconfiguration complete message to the source cell. For RRC reconfiguration procedures involving mobility, the WTRU may not send an RRC response message to the source cell, but may send an RRC reconfiguration complete message to the target cell. For example, in Figure 4, WTRU 400 sends a reconfiguration complete message 455 to target gNB 405 after the random access procedure 450. This may be desirable because the WTRU stops sending to the source cell after receiving the RRC reconfiguration message involving mobility. The reconfiguration complete message 455 may include an identity (e.g., identifier, ID number, or other parameters) associated with the conditional reconfiguration message applied by the WTRU, as described above.

[0115] In the case of conditional reconfiguration involving mobility, the WTRU may remain in the source cell after receiving the RRC reconfiguration message. Unlike normal RRC reconfiguration with mobility, the WTRU may be required to notify the source cell of the successful reception of the conditional reconfiguration.

[0116] A WTRU can be configured to send two response messages in response to a conditional reconfiguration message. The WTRU can be configured to send a first message to the source cell upon receiving a conditional reconfiguration that includes mobility. The WTRU can be configured to send a second message to the target cell upon execution of a conditional reconfiguration that includes mobility. The first message may be a MAC control element with a predefined logical channel identifier (LCID). The MAC CE may indicate the transaction identifier of the corresponding RRC message that includes the conditional reconfiguration. The first message may be an RRC response message indicating successful receipt of the conditional reconfiguration message. If the WTRU is unable to comply with the conditional reconfiguration, the WTRU may send the cause of failure in the RRC response message. The second message may be an RRC reconfiguration completion message.

[0117] Sending measurements too late can prevent the network from preparing and sending handover commands in time. The time to trigger a measurement can be a function of the radio link quality at the source cell. For example, the trigger time (TTT) can be a function of one or more of the following: the block error rate (BLER) of the resource configured for radio link monitoring, the number of out-of-sync (OOS) instances, the number of beam fault instances detected at the source cell, the quality of the serving cell (RSRP, RSRQ, SINR), the best beam quality at the source cell or base, and the RS provided for the active TCI state for PDCCH.

[0118] The configured time for triggering a measurement object may be ignored, and a measurement report is sent immediately by the WTRU when certain conditions regarding the measurement result or radio link in the source cell are met. For example, when a measurement event condition is met, the WTRU can send the available measurement report as soon as the RLF timer starts.

[0119] The TTT in the measurement report can be a function of the propagation conditions experienced by the WTRU in the serving cell during a previous time period. The TTT can also be a function of the number of RLF timer start instances during a past time period. For example, if the RLF timer started at least x times during a previous y time period, the WTRU can be assigned a lower TTT. The values ​​x and y can be configurable.

[0120] If a WTRU detects a wireless link problem while recently reported measurements are still valid, the WTRU can notify the network to take action based on the results of previously transmitted measurement reports (e.g., prepare and send a handover command).

[0121] The trigger for sending an indication can be based on any of the conditions described above.

[0122] The validity of the measurement results and the subsequent decision to transmit an indication to the NW indicating a wireless link problem can be determined by the WTRU. This decision to transmit the indication may be based on whether previous measurement reports transmitted to the NW are still valid.

[0123] The validity of the measurement results can be determined by the WTRU based on whether the target cell that triggered the report still satisfies the measurement reporting conditions when the WTRU needs to send an indication.

[0124] This condition can be evaluated based on Layer 1 measurements. Layer 3 filtering may not be applied in order to send indications as quickly as possible.

[0125] The validity of the measurement results can be determined based on the elapsed time between the last report and the moment the WTRU needs to send the indication. If multiple measurement reports have been sent recently and only a subset of target cells are still suitable for handover, the WTRU may include the identity of the appropriate target cells within the indication.

[0126] For example, an event may have recently triggered a report, but the network did not decide to hand off the WTRU to the target cell (for example, because the serving cell is still strong enough). If the WTRU measures that the target cell that triggered the most recent measurement report is still meeting the reporting conditions, but it has started to experience wireless link problems, the WTRU can transmit an indication of link degradation and the validity of the previous measurement report.

[0127] If the WTRU measures that the neighbor cell quality is x dB higher than that of the serving cell, and that the link with the serving cell has suddenly deteriorated (for example, based on RLM evaluation), the WTRU may immediately transmit an indication as soon as one of the previously defined radio link failure triggers is met, regardless of whether the WTRU is configured to use reporting events. This indication may include the identity of the best-measured neighbor cell. This indication may include the best beam ID in the target cell.

[0128] A WTRU can be configured to use multiple measurement objects associated with sets of CSI-RS and / or SSB belonging to different bandwidth portions (BWPs). These measurement objects can be associated with a reporting configuration. The reporting configuration may further include conditions for reporting measurements based on radio links monitored in the currently active DL BWP (i.e., L1 measurements) or source cell measurement results (i.e., L3 measurements). The conditions can be one of the triggers described above.

[0129] Some embodiments provide updates to beam measurement results for delta CHO reconstruction. Delta CHO reconstruction refers to incremental updates to existing CHOs. For example, a delta CHO may indicate a different resource than the existing CHO. Some embodiments include transmitting beam IDs and receiving delta CHO reconstructions. For example, a WTRU may receive CHO commands for multiple target cells and monitor the best beam associated with the target cells.

[0130] In some cases, the WTRU can be configured to use a measurement event that is triggered when the quality of the best beam in the target cell, or the average quality of a group of best beams, falls below a threshold. When a measurement event is triggered, the WTRU sends a measurement report to the gNB. The measurement report may include quality measurements of all beams in the target cell (e.g., RSRP, RSRQ, or SINR), identification of any new best detected beams that exceed the threshold, beam identity, or a combination of these. In response to the measurement report, the WTRU may receive a delta reconstruction for the target cell's CHO command, including a new dedicated RACH resource for the target cell associated with the indicated beam.

[0131] If a WTRU is experiencing a radio link problem in an active UL-DL BWP pair, and a measurement report is triggered based on the conditions described above, the WTRU may be unable to successfully transmit the report in the currently active UL BWP. It may also be unable to receive subsequent handover commands in the active DL BWP. Therefore, in some implementations, if a measurement report is triggered based on any of the criteria described above, the WTRU may autonomously switch the active UL / DL BWP to one of the RRC-configured UL / DL BWPs experiencing less restrictive radio conditions. In TDD, the WTRU may perform this switching based on the configured set of CSI-RS and / or SSB resources it has measured. In FDD, the WTRU may switch its active UL BWP based on the estimated path loss from the measured DL reference signal (i.e., the reference signal associated with the measurement object). Based on the measurement results and path loss estimate, the WTRU may switch both the UL and DL BWPs, or just one of them.

[0132] After any BWP switchover, the WTRU can send a measurement report to the network. Where appropriate, the measurement report may also include the identity of the DL BWP that the WTRU autonomously switched to. Based on the received measurement report, the WTRU may receive a handover command in the DCI for the BWP to switch to the new activated DL BWP or another DL / UL BWP. If the measurement results associated with the new activated DL / UL BWP are acceptable, no action may be taken.

[0133] The WTRU can be configured to use a handover command that includes multiple configured UL and DL BWPs in the target cell. The WTRU can send a measurement report associated with each BWP. When executing a handover command, the WTRU can perform a measurement on a reference signal and, depending on its associated dedicated configuration, select the BWP associated with the best reference signal.

[0134] For example, the WTRU can select the first active BWP in order of dedicated configuration, and then in order of beam quality associated with each BWP. If this reference signal is associated with a dedicated configuration (i.e., a CFRA resource), the WTRU can select the BWP associated with the best measured reference signal; otherwise, it can select the second-best BWP carrying the second-best beam associated with a dedicated PRACH resource, and so on.

[0135] Some embodiments include multiple CHO commands for the same target cell ID. For example, in some embodiments, multiple first active UL and DL BWPs are configured in target cell selection based on measurements. For example, a WTRU may receive multiple conditional reconfiguration commands for the same target cell ID, but with different first active UL and DL BWPs, including different sets of candidate beams for RACH (Synchronization Signal Block (SSB) and / or Channel State Information Reference Signal (CSI-RS)). If the CHO execution conditions for a given target are satisfied (e.g., an Ax event), the WTRU may select a configuration based on a CHO command configured to use, for example, the first active DL BWP from which the best reference signal (SSB and / or CSI-RS) was measured. An exemplary event that satisfies the CHO execution conditions for a given target includes an Ax event, where A1 indicates that the serving cell has improved (e.g., with respect to RSRP, RSRQ, or SINR for WTRU), A2 indicates that the serving cell has deteriorated below the threshold, A3 indicates that the neighboring cell has improved by an offset compared to the SpCell, A4 indicates that the neighboring cell has improved above the threshold, A5 indicates that the SpCell has deteriorated below the first threshold and the neighboring cell has improved above the second threshold, and A6 indicates that the neighboring cell has improved by an offset compared to the SCell.

[0136] Some embodiments include the selection of a first active UL / DL BWP or carrier in target cell selection based on the RACH configuration. For example, the WTRU may select a CHO command configured to use a first active UL BWP (and paired DL BWP) configured to use one or more CFRA resources associated with the best measured DL beam or one or more. The WTRU may be configured to use multiple uplink carriers in the target cell associated with different CFRA resources, and the WTRU may select carriers for performing RACH from among carriers that exceed a minimum quality threshold, for example, based on the earliest availability of the CFRA resources.

[0137] If a handover command is sent or received too early or too late, a handover failure may occur. Measurements that can show the network the precise path of the WTRU and the progress of its associated mobility in the source and target cells can assist the network in sending handover commands at the appropriate time.

[0138] A new type of measurement event can be associated with the gradient of measurements in the source and target cells. For example, a measurement report can be triggered if the source cell quality has decreased by at least "x" dB over the past time period "y", while the quality of the adjacent cell has increased by at least "z" dB over the same period. This can provide an indication to the network that the WTRU is moving away from cell A and approaching cell B, while also informing the network about the radio link conditions experienced in both cells.

[0139] When the target cell satisfies the criteria described above, it can trigger periodic measurement reports of the target cell results (e.g., using high periodicity) to assist the NW in configuring and transmitting handover commands and to assist the target cell in preparing a dedicated beam for RACH.

[0140] Another reason for handover failure may be that the gNB is unable to decode UL signals (e.g., msg1, msg3) during the random access procedure in the target cell, or that the WTRU is unable to decode DL signals (e.g., msg2, msg4) within the PDCCH. If the WTRU is able to monitor the PDCCH and / or successfully transmit uplink signals before executing the handover command, it can assist the WTRU in deciding whether to initiate action on the target cell and safely suspend the connection with the source cell.

[0141] A WTRU can be configured to use a CHO associated with one or more target cells. If one or more target cells satisfy the handover execution criteria, the WTRU can monitor the PDCCH of different target cells before executing a handover command.

[0142] A pre-configured target cell can transmit signals (e.g., DCI) in a dedicated CORESET for a WTRU configured to use CHO. A source cell can notify the target cell of the identity of the WTRU configured to use CHO commands.

[0143] The WTRU can receive a conditional handover command to receive a configuration for the search space associated with this particular CORESET in potential target cells. The WTRU can then select and execute the handover command only on target cells where it was able to decode the DCI.

[0144] Before executing a handover command, the WTRU can obtain further information about the uplink robustness of the target cell by transmitting a signal similar to the SRS. If the signal is successfully received, or if the measurement result associated with the uplink signal exceeds a configured threshold, the target cell can send an indication to the WTRU through the source cell. This indication can trigger the actual handover execution on the target cell.

[0145] The WTRU can be configured to use one or more triggers, as described above, in addition to any triggers related to legacy measurement events and conditional handovers, to perform one or more of the following actions: The WTRU can send measurement reports to the serving cell. The WTRU can perform conditional handovers.

[0146] A WTRU can initiate access using resources from a cell that is not the serving cell. This allows a WTRU to perform a mobility procedure while it has configurations that are limited but sufficient to initiate access and / or be identified in the non-serving cell. For example, the configurations may include, at a minimum, serving frequency and cell identity. Identification may be based on a configured identity for the WTRU, possibly a RAN area-specific identity. Mobility procedures are sometimes commonly referred to as forward mobility procedures or uplink mobility procedures.

[0147] A WTRU can be configured to perform a specific action when a trigger condition is met. The configuration can be explicit (e.g., configured as part of a measurement object linked to the trigger) or implicitly based on serving cell quality and / or the status of the RLM process.

[0148] The following description includes changes to the legacy system in supporting conditional handovers.

[0149] Table 1 includes exemplary steps that the WTRU can perform upon receiving an RRC reconfiguration message.

[0150] [Table 1]

[0151] Table 2 includes exemplary steps that the WTRU can take to initiate a conditional reconfiguration.

[0152] [Table 2]

[0153] Table 3 includes exemplary steps that the WTRU can take to perform conditional reconfiguration.

[0154] [Table 3]

[0155] Table 4 includes exemplary steps that a WTRU may take to process the expiration of T380.

[0156] [Table 4]

[0157] Table 5 includes exemplary steps that the WTRU can take to delete a stored reconfiguration.

[0158] [Table 5]

[0159] Table 6 includes exemplary steps that the WTRU can perform to detect RLF.

[0160] [Table 6]

[0161] As described above, the RRCReconfiguration message can be a command to modify an RRC connection. It can convey information for measurement configuration, mobility control, radio resource configuration (including RB, MAC main configuration, and physical channel configuration), and security configuration. Table 7 contains an example format of the RRCReconfiguration message.

[0162] [Table 7]

[0163] The ConditionalReconfig information element can be used to configure trigger conditions and parameters associated with conditional reconfiguration. Table 8 shows the structure of the ConditionalReconfig information element.

[0164] [Table 8]

[0165] The variable VarConditionalReconfigList can contain information about one or more target cells for which a triggering condition is monitored. Table 9 shows the format of the VarConditionalReconfigList variable.

[0166] [Table 9]

[0167] Figure 5 is a message sequence chart illustrating an exemplary procedure for re-establishment, including fallback to CHO. In the example in Figure 5, WTRU500 receives message 505 (e.g., an RRC reconfiguration message) from source gNB510, which includes a conditional reconfiguration for gNB1515. WTRU500 may receive message 505, for example, after it has connected to source gNB510. The conditional reconfiguration may include a trigger condition and a configuration to be applied in gNB1515 if the trigger condition occurs. The trigger condition may include, for example, whether the quality of source gNB510 is lower than the quality of gNB1515 (e.g., with respect to RSRP, RSRQ, or SINR for WTRU). In step 520, WTRU500 begins monitoring for the trigger condition. At condition 525, when WTRU500 detects a failure event, it may or may not satisfy the trigger condition. If the detected fault satisfies the trigger condition 530, WTRU500 performs a conditional reconstruction from message 505 using gNB1515 in step 535. If the detected fault does not satisfy the trigger condition 525 (for example, there was an RLF with source gNB510), WTRU500 enters an enhanced re-establishment procedure 540. In the enhanced re-establishment procedure 540, WTRU performs cell selection in step 545. For example, WTRU may select a cell based on one or more of any suitable criteria, such as the highest signal quality, the highest number of beams detectable by WTRU, and whether the cell has a valid CHO. If the selected cell has a valid (e.g., unexpired) CHO configuration (which may be the configuration from message 505 or a different configuration) under condition 550, WTRU 500 performs a CHO on the selected cell (e.g., gNB1515 in this example) in step 555, even if the condition for conditional reconfiguration is not satisfied.Under condition 550, if the selected cell does not have a valid (e.g., not expired) CHO configuration, WTRU500 performs a re-establishment procedure with the selected cell (e.g., gNB2570 in this example) in step 560. In this example, WTRU500 does not perform a handover to gNB2570 because it is not configured for handover.

[0168] While features and elements are described above in specific combinations, those skilled in the art will understand that each feature or element can be used alone or in any combination with other features and elements. In addition, the methods described herein can be implemented in computer programs, software, or firmware contained within a computer-readable medium for execution by a computer or processor. Examples of computer-readable mediums include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital multi-purpose disks (DVDs). A radio frequency transceiver can be implemented using a processor associated with software for use in a WTRU, UE, terminal, base station, RNC, or any host computer. [Industrial applicability]

[0169] This invention can be used for wireless communication. [Explanation of Symbols]

[0170] 100 Communication Systems 102, 102a~102d 104 RAN 106 Core Network 108 PSTN 110 Internet 112 Other Networks 114a, 114b base station 118 processors 120 Transmitter / Receiver 122 Antenna 140a~140c Node B 160 WLAN

Claims

1. A method for communication by a wireless transceiver unit (WTRU) associated with a source cell, Steps include detecting the trigger conditions for a conditional handover configuration (CHO configuration), In response to the trigger condition, the steps include executing CHO on the target cell of CHO, A step in which, in response to completing the CHO, the stored configuration of the CHO represents the trigger condition and includes removing an entry from a conditional reconfiguration variable stored on the WTRU. A method for providing this.

2. The method according to claim 1, wherein completing the CHO comprises completing the random access procedure to the target cell of the CHO.

3. The method according to claim 1, wherein the step of deleting the stored configuration of the CHO includes deleting an entry from the VarConditionalReconfig variable.

4. The method according to claim 1, wherein the step of deleting the stored configuration of the CHO includes deleting entries of the CHO that match the trigger conditions.

5. The method according to claim 1, wherein the step of deleting the stored configuration of the CHO includes deleting an entry that matches the measID corresponding to the trigger condition of the CHO.

6. The method according to claim 1, wherein the step of deleting the stored configuration of the CHO includes deleting the entry that matches the target cell of the CHO.

7. The method according to claim 1, wherein the step of deleting the stored configuration of the CHO includes deleting an entry that matches the spCell variable corresponding to the target cell of the CHO.

8. The method according to claim 1, wherein the trigger condition includes a threshold quality of the source gNB.

9. The method according to claim 1, wherein the trigger condition for the CHO configuration includes a radio link fault (RLF).

10. A wireless transceiver unit (WTRU) associated with a source cell, Transmitter and receiver, Processor and Equipped with, The transceiver and the processor are configured to detect the trigger conditions for a conditional handover configuration (CHO configuration). The transceiver and the processor are configured to execute CHO on the target cell of CHO after detecting the trigger condition. The transceiver and the processor are configured to delete the stored configuration of the CHO in response to completing the CHO, the stored configuration of the CHO representing the trigger condition, and deleting the stored configuration of the CHO includes deleting entries from the conditional reconfiguration variables stored on the WTRU. WTRU.

11. The WTRU according to claim 10, wherein completing the CHO includes completing the random access procedure to the target cell of the CHO.

12. Deleting the stored configuration of the CHO includes deleting an entry from the VarConditionalReconfig variable in the WTRU according to claim 10.

13. The WTRU according to claim 10, wherein deleting the stored configuration of the CHO includes deleting the entry of the CHO that matches the trigger condition.

14. The WTRU according to claim 10, wherein deleting the stored configuration of the CHO includes deleting an entry that matches the measID corresponding to the trigger condition of the CHO.

15. The WTRU according to claim 10, wherein deleting the stored configuration of the CHO includes deleting the entry matching the target cell of the CHO.

16. The WTRU according to claim 10, wherein deleting the stored configuration of the CHO includes deleting an entry that matches the spCell variable corresponding to the target cell of the CHO.

17. The trigger condition includes a threshold quality of the source gNB, according to claim 10.

18. The WTRU according to claim 10, wherein the trigger condition for the CHO configuration includes a radio link fault (RLF).

Images