Methods for improving RLF and re-establishment in NTNs

Abstract

A wireless transmit / receive unit (WTRU) may be configured to receive configuration information. The configuration information may include an indication of a stop time of a first cell and a start time of a second cell. The WTRU may be configured to perform radio link monitoring (RLM) measurements of the first cell. The WTRU may be configured to determine that the first cell is down based on the received indication of the stop time of the first cell. The WTRU may be configured to stop the RLM measurements of the first cell. The WTRU may be configured to initiate a radio resource control (RRC) connection re-establishment procedure to the second cell in response to determining that the first cell is down. The first cell may be a current cell, and the second cell may be a neighbor cell or a target cell. The configuration information may further include a time offset value. (Representative image: Figure 5)

Description

[Technical Field]

[0001] The present disclosure relates to methods for improving RLF and re-establishment in NTNs. [Background technology]

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 410,765, filed September 28, 2022, and U.S. Provisional Patent Application No. 63 / 421,386, filed November 1, 2022, the contents of which are incorporated herein by reference.

[0003] Non-terrestrial networks (NTNs) facilitate the deployment of wireless networks in areas where terrestrial antennas are impractical, for example, due to terrain or cost. Coupled with terrestrial networks, NTNs are intended to enable truly ubiquitous coverage of 5G networks. While initial NTN deployments will support basic calling and texting anywhere in the world, further upgrades coupled with the proliferation of next-generation low-earth-orbit satellites are expected to enable enhanced services such as web browsing. Summary of the Invention

[0004] A wireless transmit / receive unit (WTRU) may be configured to receive configuration information. The configuration information may include an indication of a stop time of a first cell and a start time of a second cell. The WTRU may be configured to perform radio link monitoring (RLM) measurements of the first cell. The WTRU may be configured to determine that the first cell is down based on the received indication of the stop time of the first cell. The WTRU may be configured to stop RLM measurements of the first cell. The WTRU may be configured to initiate a radio resource control (RRC) connection re-establishment procedure to the second cell in response to determining that the first cell is down. The first cell may be a current cell, and the second cell may be a neighbor cell or a target cell. The configuration information may further include a time offset value. The time offset value may be related to the stop time of the first cell. The WTRU may be configured to perform measurements of the second cell on the condition that the second cell started before the first cell was down. Measurements may be performed on the second cell when the first cell stop time is within the received stop time offset value. The WTRU may be configured to delay initiating a connection re-establishment procedure for the second cell before the second cell starts and on the condition that the first cell stops until the second cell starts. Measurements may be performed on the second cell before a radio link failure (RLF) occurs or upon the occurrence of an RLF. The WTRU may be configured to perform RRC connection re-establishment based on the stop time of the first cell and the start time of the second cell. The RRC connection re-establishment may be performed without using a T310 timer expiration. The WTRU may be configured to trigger a radio link failure (RLF) or RRC connection re-establishment on the condition that a cell quality level criterion is met. The cell quality level criterion may include at least one of the measured signal quality of the second cell being above an RSRP threshold or an RSRQ threshold and the measured signal quality of the first cell being below an RSRP threshold or an RSRQ threshold. [Brief explanation of the drawings]

[0005] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which like reference numerals indicate similar elements and in which:

[0006] [Figure 1A] FIG. 1 is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented. [Figure 1B] 1B is a system diagram illustrating an example wireless transmit / receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A, according to an embodiment. [Figure 1C] 1B is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communication system illustrated in FIG. 1A, according to an embodiment. [Figure 1D] 1B is a system diagram illustrating another exemplary RAN and another exemplary CN that may be used within the communication system illustrated in FIG. 1A, according to an embodiment. [Figure 2] FIG. 1 is a diagram illustrating an example of an interface in NTN. [Figure 3] FIG. 1 illustrates an exemplary radio link failure (RLF) and re-establishment procedure. [Figure 4] FIG. 1 illustrates an example of an extended RLF procedure. [Figure 5] FIG. 1 illustrates an example of RLF enhancement for overlapping coverage scenarios. [Figure 6] FIG. 1 illustrates an example method for RLF enhancement for overlapping coverage scenarios. [Figure 7] FIG. 1 illustrates an example of RLF enhancement for discrete changes in coverage scenarios. [Figure 8] FIG. 1 illustrates an exemplary method of RLF enhancement for discrete changes in coverage scenarios. [Figure 9] FIG. 1 illustrates an example of RLF enhancement for a discontinuous coverage scenario. [Figure 10]FIG. 1 illustrates an example method for RLF enhancement for discontinuous coverage scenarios. [Figure 11] FIG. 1 illustrates an exemplary method for RLF enhancement. [Figure 12] FIG. 1 illustrates an exemplary method for RLF / re-establishment. DETAILED DESCRIPTION OF THE INVENTION

[0007] 1A is a diagram illustrating an example communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multiple-access system that provides content, such as voice, data, video, messaging, broadcasts, etc., to multiple wireless users. The communication system 100 may enable multiple wireless users to access such content by sharing system resources, including wireless bandwidth. For example, the communication system 100 may employ one or more channel access methods, such as coded multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tailed unique word discrete Fourier transform spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, filter bank multicarrier (FBMC), and the like.

[0008] 1A, communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network (CN) 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it should be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as stations (STAs), may be configured to transmit and / or receive wireless signals and may include user equipment (UE), mobile stations, fixed or mobile subscriber units, subscription-based units, pagers, cellular phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, wireless 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 wireless devices operating in industrial and / or automated processing chain situations), consumer electronic devices, devices operating in commercial and / or industrial wireless networks, and the like. Any of the WTRUs 102a, 102b, 102c, and 102d may be referred to interchangeably as UEs.

[0009] The communications system 100 may also include a base station 114a and / or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communications networks, such as the CN 106, the Internet 110, and / or other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a NodeB, an eNodeB (eNB), a home NodeB, a home eNodeB, a next generation NodeB such as a gNodeB (gNB), a new radio (NR) NodeB, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it should be understood that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0010] The base station 114a may be part of the RAN 104, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, and the like. The base station 114a and / or base station 114b may be configured to transmit and / or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in the licensed spectrum, the unlicensed spectrum, or a combination of the licensed and unlicensed spectrum. A cell may provide coverage for wireless services for a particular geographic area, which may be relatively fixed or which may change over time. The cell may also be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple-output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming may be used to transmit and / or receive signals in desired spatial directions.

[0011] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communications link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0012] More specifically, as mentioned above, the communication system 100 may be a multiple-access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a and the WTRUs 102a, 102b, 102c in the RAN 104 may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using Wideband CDMA (WCDMA). WCDMA may include communication protocols such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink (DL) Packet Access (HSDPA) and / or High Speed ​​Uplink (UL) Packet Access (HSUPA).

[0013] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE Advanced (LTE-A) and / or LTE Advanced Pro (LTE-A Pro).

[0014] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR radio access, which may establish the air interface 116 using NR.

[0015] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may jointly implement LTE and NR radio access, e.g., using a dual connectivity (DC) principle. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to and from multiple types of base stations (e.g., eNBs and gNBs).

[0016] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a wireless technology such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi)), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0017] 1A may be, for example, a wireless router, a Home Node B, a Home eNode B, or an access point and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a road, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish a picocell or a femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the CN 106.

[0018] The RAN 104 may be in communication with the CN 106, which may be any type of network configured to provide voice, data, application, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have varying Quality of Service (QoS) requirements, such as different throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN 106 may provide call control, charging services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions such as user authentication. Although not shown in FIG. 1A , it should be understood that the RAN 104 and / or CN 106 may communicate directly or indirectly with other RANs employing the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may utilize NR radio technology, the CN 106 may also be in communication with another RAN (not shown) that employs GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

[0019] The CN 106 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network providing 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) of the TCP / IP Internet protocol suite. The networks 112 may include wired and / or wireless communication networks owned and / or operated by other service providers. For example, the network 112 may include other CNs connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0020] Some or all of the WTRUs 102a, 102b, 102c, 102d of the communications system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with a base station 114a that may employ a cellular-based wireless technology and with a base station 114b that may employ an IEEE 802.11 wireless technology.

[0021] 1B is a system diagram illustrating an example WTRU 102. As shown in FIG. 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 source 134, a global positioning system (GPS) chipset 136, and / or other peripherals 138. It should be understood that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0022] The processor 118 may be a general-purpose processor, a special-purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors in conjunction with a DSP core, a controller, a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. While FIG. 1B depicts the processor 118 and the transceiver 120 as separate components, it should be understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0023] The transmit / receive element 122 may be configured to transmit signals to or receive signals from a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In an embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF and light signals. It should be understood that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0024] 1B as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0025] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As mentioned above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate over multiple RATs, such as NR and IEEE 802.11.

[0026] The processor 118 of the WTRU 102 may be coupled to and receive user input data from 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). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. Additionally, the processor 118 may access information from and store data in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132. The non-removable memory 130 may include random access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as a server or home computer (not shown).

[0027] The processor 118 may receive power from the power source 134 and may be configured to distribute and / or control the power to other components of the WTRU 102. The power source 134 may be any suitable device for providing power to the WTRU 102. For example, the power source 134 may include one or more dry batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like.

[0028] The processor 118 may also be coupled to a GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to or instead of information from the GPS chipset 136, the WTRU 102 may receive location information from base stations (e.g., base stations 114a, 114b) over the air interface 116 and / or determine its location based on the timing of signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0029] The processor 118 may also be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos and / or videos), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, a Bluetooth module, a frequency modulation (FM) radio unit, a digital music player, a media player, a video game player module, an internet browser, a virtual reality and / or augmented reality (VR / AR) device, an activity tracker, and the like. The peripherals 138 may include one or more sensors. The sensor may be one or more of a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, a direction sensor, a proximity sensor, a temperature sensor, a time sensor, a geolocation sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, a humidity sensor, and the like.

[0030] The WTRU 102 may include a full-duplex radio, in which case transmission and reception of some or all of the signals (e.g., associated with a particular subframe on both the UL (e.g., for transmission) and DL (e.g., for reception)) may be parallel and / or simultaneous. The full-duplex radio may include an interference management unit to reduce and or substantially eliminate self-interference by hardware (e.g., a choke) or by signal processing via a processor (e.g., via a separate processor (not shown) or processor 118). In an embodiment, the WTRU 102 may include a half-duplex radio for transmission and reception of some or all of the signals (e.g., associated with a particular subframe on the UL (e.g., for transmission) or DL ​​(e.g., for reception)).

[0031] 1C is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As mentioned above, the RAN 104 may employ E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also communicate with the CN 106.

[0032] The RAN 104 may include eNode-Bs 160a, 160b, and 160c, although it should be understood that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, and 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, and 160c may implement MIMO technology. Thus, the eNode-B 160a may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a, for example.

[0033] Each of the eNode-Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, and the like. As shown in FIG. 1C, the eNode-Bs 160a, 160b, 160c may communicate with each other via an X2 interface.

[0034] 1C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (PGW) 166. While the foregoing elements are depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0035] The MME 162 may be connected to each of the eNode-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may function as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies such as GSM and / or WCDMA.

[0036] The SGW 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to and from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring the user plane during inter-eNode B handovers, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, and the like.

[0037] The SGW 164 may be connected to a PGW 166, which provides the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communication between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0038] The CN 106 may facilitate communication with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communication between the WTRUs 102a, 102b, 102c and traditional landline communication devices. For example, the CN 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may also provide the WTRUs 102a, 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.

[0039] Although the WTRU is depicted in Figures 1A-1D as a wireless terminal, it is contemplated that in some representative embodiments such a terminal may use a wired communication interface (e.g., temporarily or permanently) with the communication network.

[0040] In an exemplary embodiment, the other network 112 may be a WLAN.

[0041] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have access or interface to a distribution system (DS) or another type of wired / wireless network that carries traffic into and / or out of the BSS. Traffic to a STA originating from outside the BSS may arrive through the AP and be delivered to the STA. Traffic originating from a STA to a destination outside the BSS may be sent to the AP for delivery to the respective destination. Traffic between STAs within a BSS may be sent through the AP; for example, a source STA may send traffic to the AP, which then delivers the traffic to the destination STA. Traffic between STAs within a BSS may be considered and / or referred to as peer-to-peer traffic. Peer-to-peer traffic may be sent between (e.g., directly between) a source STA and a destination STA using direct link setup (DLS). In some representative embodiments, the DLS may use 802.11e DLS or 802.11z Tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and STAs within or using an IBSS (e.g., all of the STAs) may communicate directly with each other. The IBSS mode of communication may sometimes be referred to herein as an "ad hoc" mode of communication.

[0042] When using the 802.11ac infrastructure mode of operation or a similar mode of operation, an AP may transmit beacons on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20 MHz wide bandwidth) or a dynamically set width. The primary channel may be the operating channel of the BSS and may be used by STAs to establish a connection with the AP. In some representative embodiments, carrier sense multiple access with collision avoidance (CSMA / CA) may be implemented, for example, in an 802.11 system. In CSMA / CA, STAs (e.g., all STAs), including the AP, may sense the primary channel. If the primary channel is sensed / detected by a particular STA and / or determined to be busy, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0043] High-throughput (HT) STAs may use 40 MHz wide channels for communication, for example, by combining a primary 20 MHz channel with adjacent or non-adjacent 20 MHz channels to form a 40 MHz wide channel.

[0044] A very high throughput (VHT) STA may support 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz wide channels. A 40 MHz and / or 80 MHz channel may be formed by combining contiguous 20 MHz channels. A 160 MHz channel may be formed by combining eight contiguous 20 MHz channels or two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. In the 80+80 configuration, after channel coding, the data may be passed through a segment parser that may split the data into two streams. Inverse fast Fourier transform (IFFT) processing and time-domain processing are performed separately for each stream. The streams may be mapped to two 80 MHz channels, and the data may be transmitted by the transmitting STA. At the receiver of the receiving STA, the above-described operations for the 80+80 configuration may be reversed, and the combined data may be sent to the medium access control (MAC).

[0045] Sub-1 GHz operating modes are supported by 802.11af and 802.11ah. Channel operating bandwidths and carriers are reduced in 802.11af and 802.11ah compared to those used in 802.11n and 802.11ac. 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, while 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to representative embodiments, 802.11ah may support meter-type control / machine-type communication (MTC), such as MTC devices within macro coverage areas. MTC devices may have specific capabilities, for example, limited capabilities including support (e.g., support only) of specific and / or limited bandwidths. MTC devices may include batteries with battery life exceeding a threshold (e.g., to maintain very long battery life).

[0046] WLAN systems that may support multiple channels and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include a channel that may be designated as a primary channel. The primary channel may have a bandwidth equal to the largest common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA that supports the smallest bandwidth operating mode among all STAs operating in the BSS. In an 802.11ah example, the primary channel may be 1 MHz wide for a STA (e.g., an MTC-type device) that supports 1 MHz mode (e.g., only supports 1 MHz), even if the AP and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operating modes. Carrier sensing and / or network allocation vector (NAV) setting may depend on the state of the primary channel. If the primary channel is busy, for example, due to a STA (that only supports 1 MHz operating mode) transmitting to the AP, all available frequency bands may be considered busy even though most of the available frequency bands are idle.

[0047] In the United States, the available frequency bands that may be used with 802.11ah are 902MHz to 928MHz. In South Korea, the available frequency bands are 917.5MHz to 923.5MHz. In Japan, the available frequency bands are 916.5MHz to 927.5MHz. The total available bandwidth for 802.11ah is 6MHz to 26MHz depending on the country code.

[0048] 1D is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As mentioned above, the RAN 104 may employ NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also communicate with the CN 106.

[0049] The RAN 104 may include gNBs 180a, 180b, and 180c, although it should be understood that the RAN 104 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, and 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, and 180c may implement MIMO technology. For example, the gNB 180a, 180b may utilize beamforming to transmit signals to and / or receive signals from the gNBs 180a, 180b, and 180c. Thus, the gNB 180a may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a, for example. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be in the unlicensed spectrum, and the remaining component carriers may be in the licensed spectrum. In an embodiment, the gNBs 180a, 180b, 180c may implement coordinated multipoint (CoMP) technology. For example, the WTRU 102a may receive coordinated transmissions from the gNBs 180a and 180b (and / or 180c).

[0050] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with scalable numerical values. For example, the OFDM symbol spacing and / or OFDM subcarrier spacing may vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using subframes or transmission time intervals (TTIs) of varying or scalable lengths (e.g., including different numbers of OFDM symbols and / or lasting for varying absolute time lengths).

[0051] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c without also accessing other RANs (e.g., eNode-Bs 160a, 160b, 160c, etc.). In a standalone configuration, the WTRUs 102a, 102b, 102c may utilize one or more of the gNBs 180a, 180b, 180c as mobility anchor points. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in unlicensed bands. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate / connect with a gNB 180a, 180b, 180c while also communicating / connecting with another RAN, such as an eNode-B 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement a DC principle to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNode-Bs 160a, 160b, 160c may act as a mobility anchor for the WTRUs 102a, 102b, 102c, and the gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0052] Each of the gNBs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users during UL and / or DL, support for network slicing, DC, interworking between NR and E-UTRA, routing of user plane data towards user plane functions (UPFs) 184a, 184b, routing of control plane information towards access and mobility management functions (AMFs) 182a, 182b, and the like. As shown in FIG. 1D, the gNBs 180a, 180b, 180c may communicate with each other via an Xn interface.

[0053] 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. While the foregoing elements are depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0054] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via an N2 interface and may function as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, supporting network slicing (e.g., handling different protocol data unit (PDU) sessions with different requirements), selecting a particular SMF 183a, 183b, managing registration realms, terminating non-access stratum (NAS) signaling, mobility management, and the like. Network slicing may be used by the AMF 182a, 182b to customize the CN support of the WTRUs 102a, 102b, 102c based on the type of service being utilized by the WTRUs 102a, 102b, 102c. For example, different network slices may be established for different use cases, such as services relying on Ultra-Reliable Low Latency (URLLC) access, services relying on enhanced Massive Mobile Broadband (eMBB) access, services for MTC access, and the like. The AMF 182a, 182b may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies, such as WiFi.

[0055] The SMFs 183a, 183b may be connected to the AMFs 182a, 182b in the CN 106 via an N11 interface. The SMFs 183a, 183b may also be connected to the UPFs 184a, 184b in the CN 106 via an N4 interface. The SMFs 183a, 183b may select and control the UPFs 184a, 184b and configure the routing of traffic through the UPFs 184a, 184b. The SMFs 183a, 183b may perform other functions, such as managing and allocating UE IP addresses, managing PDU sessions, controlling policy enforcement and QoS, providing DL data notification, and the like. PDU session types may be IP-based, non-IP-based, Ethernet-based, and the like.

[0056] The UPFs 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks such as the Internet 110 to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPFs 184, 184b may perform other functions such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering DL packets, providing mobility anchors, and the like.

[0057] The CN 106 may facilitate communication with other networks. For example, the CN 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to the local DNs 185a, 185b via the UPFs 184a, 184b via an N3 interface with the UPFs 184a, 184b and an N6 interface between the UPFs 184a, 184b and the DNs 185a, 185b.

[0058] 1A-1D and the corresponding description thereof, one or more, or all, of the functions described herein with respect to one or more of the WTRUs 102a-d, base stations 114a-b, eNode-Bs 160a-c, MME 162, SGW 164, PGW 166, gNBs 180a-c, AMFs 182a-b, UPFs 184a-b, SMFs 183a-b, DNs 185a-b, and / or any other devices described herein may be performed by one or more emulation devices (not shown). The emulation devices may be one or more devices configured to emulate one or more, or all, of the functions described herein. For example, the emulation devices may be used to test other devices and / or to simulate network and / or WTRU functionality.

[0059] The emulation device may be designed to perform one or more tests of other devices in a lab environment and / or an operator network environment. For example, one or more emulation devices may perform one or more or all functions while fully or partially implemented and / or deployed as part of a wired and / or wireless communications network to test other devices in a communications network. One or more emulation devices may perform one or more or all functions while temporarily implemented / deployed as part of a wired and / or wireless communications network. The emulation device may be directly coupled to another device for testing and / or to perform testing using over-the-air wireless communications.

[0060] The one or more emulation devices may perform one or more functions (including all functions) while not implemented / deployed as part of a wired and / or wireless communications network. For example, the emulation devices may be utilized in test scenarios in a test lab and / or in a non-deployed (e.g., test) wired and / or wireless communications network to perform testing of one or more components. The one or more emulation devices may be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (which may include, e.g., one or more antennas) may be used by the emulation devices to transmit and / or receive data.

[0061] A basic NTN includes an airborne or satellite-based platform that transmits signals from terrestrial gNBs to WTRUs and vice versa via a gateway (GW). Current NR NTNs support Power Class 3 WTRUs with omnidirectional antennas and linear polarization, or very small aperture antenna (VSAT) terminals with directional antennas and circular polarization. Support for LTE-based narrowband IoT (NB-IoT) and eMTC-type devices is standardized. Regardless of device type, all current NTN WTRUs are assumed to be Global Navigation Satellite System (GNSS) capable.

[0062] Aircraft or satellite-borne platforms are classified in terms of orbit, with current standardization focusing on low Earth orbit (LEO) satellites with an altitude range of 300–1500 km and geostationary Earth orbit (GEO) satellites with an altitude of 35,786 km. Other platform classifications, such as medium Earth orbit (MEO) satellites with an altitude range of 7000–25000 km and high altitude platform stations (HAPS) with an altitude range of 8–50 km, are implicitly assumed to be supported. Satellite platforms are further classified as having "transparent" or "regenerative" payloads. Transparent satellite payloads perform frequency conversion and RF amplification on both the uplink and downlink, potentially connecting multiple transparent satellites to a single terrestrial gNB. Regenerative satellite payloads can implement either a complete gNB onboard the satellite or a gNB distributed unit (DU). Regenerative payloads may perform digital processing of the signal, including demodulation, decoding, re-encoding, re-modulation, or filtering.

[0063] Figure 2 shows the radio interface of an NTN. The NTN may include a core network (CN), a gNB, a gateway (GW), satellites (e.g., SAT1 and SAT2), and a WTRU. The NTN may include a feeder link, which may be a wireless link between the GW and the satellites (e.g., feeder link SAT1 and feeder link SAT2). The NTN may include a service link, which may be a radio link between the satellites and the WTRU. The NTN may include an inter-satellite link (ISL), which may be a transport link between the satellites. The ISL is supported only by regenerative payloads and may be a 3GPP radio interface or a proprietary optical interface.

[0064] Depending on the satellite payload configuration, a different 3GPP air interface may be used for each air link. For transparent payloads, the NR-Uu air interface may be used for both the service link and the feeder link. For regenerative payloads, the NR-Uu interface may be used for the service link and the Satellite Radio Interface (SRI) may be used for the feeder link. Detailed user plane / control plane (UP / CP) protocol stacks for each payload configuration can be found in 3GPP TR38.821 sections 5.1 and 5.2.

[0065] NTN satellites can support multiple cells. Each cell can contain one or more satellite beams. Satellite beams cover a terrestrial footprint similar to a terrestrial cell, which can range from 100 to 1,000 km in diameter for LEO deployments and 200 to 3,500 km in diameter for GEO deployments. The beam footprint for GEO deployments remains fixed relative to the Earth, while for LEO deployments, the area covered by the beam / cell changes over time due to satellite movement. This beam movement can be classified as "Earth-moving," where the LEO beam moves continuously across the Earth, or "Earth-fixed," where the beam is pointed to remain covering a fixed location until a new cell overtakes the coverage area with discrete and coordinated changes.

[0066] Due to the altitude and beam diameter of the NTN platform, the round trip time (RTT) and maximum differential delay can be significantly larger than those of terrestrial systems. In a typical transparent NTN deployment, the RTT can range from 25.77 ms (LEO at 600 km altitude) to 541.46 ms (GEO), and the maximum differential delay can range from 3.12 ms to 10.3 ms. Because the transparent configuration includes both the service link and the feeder link, the RTT of the regenerative payload can be approximately half that of the transparent payload, while the RTT of the regenerative payload considers only the service link. To minimize the impact on the existing NR system (e.g., to avoid preamble ambiguity or to appropriately time the receive window), the WTRU may perform timing pre-correction before the first access.

[0067] The timing pre-correction procedure may require the WTRU to obtain its position via GNSS and the feeder link (or common) delay and satellite positions via satellite ephemeris data. The satellite ephemeris data is periodically broadcast as system information and includes satellite speed, direction, and velocity. The WTRU may then estimate the distance, i.e., delay, from the satellite and then add the feeder link delay component to obtain the complete WTRU-gNB RTT, which may then be used to offset timers, receive windows, or timing relationships. Frequency compensation is assumed to be performed by the network.

[0068] Other important enhancements in NTN relate to WTRU mobility and measurement reporting. The RSRP difference between cell center and cell edge is less pronounced than in terrestrial systems. This, combined with much larger areas of cell overlap, makes traditional measurement-based mobility less reliable in NTN environments. New conditional handover and measurement reporting triggers are being introduced, depending on location and time, and details are to be confirmed. Enhanced mobility is particularly interesting in LEO deployments, where even stationary WTRUs are expected to perform mobility approximately every 7 seconds due to satellite movement, depending on deployment characteristics.

[0069] The Radio Link Failure (RLF) and re-establishment procedure is summarized in Figure 3. While in the RRC_CONNECTED state, the WTRU may perform Radio Link Monitoring (RLM) with the serving cell. The WTRU may be configured with timers and counters to use when evaluating RLF and performing radio link recovery or re-establishment. When N310 consecutive "out of sync" indications are detected from L1 (RLM) at the RRC, a timer may be started with a period or duration T310. While T310 continues, the WTRU may attempt to recover the radio link with the serving cell. If N311 consecutive "in sync" indicators are received from L1 at the RRC, the WTRU may consider the radio link to be restored and resume normal operation, continuing RLM with the serving cell. If T310 expires, the WTRU may consider this an RLF. When an RLF is detected, a timer is started with a period or duration T311, and the WTRU may perform a cell search to determine whether there is a suitable cell available on which the WTRU may perform RRC connection re-establishment. If timer T311 expires before the WTRU finds a suitable cell, the WTRU may enter RRC_IDLE mode with cause "RRC connection failure." If the WTRU finds a suitable cell, which may include the original cell, this cell may be selected, T311 may be stopped, T301 may be started, and the RRC connection re-establishment procedure may be initiated. If timer T301 expires before the RRC connection re-establishment is complete, the WTRU may enter idle mode with cause "RRC connection failure."

[0070] An RLF may occur, for example, when the WTRU goes out of coverage (e.g., enters a tunnel or moves to a rural area outside of cellular coverage). An RLF may occur, for example, as a result of a handover being initiated too late, whereby an RLF is detected in the serving cell before the handover can be completed. The first part of the procedure in FIG. 3 (N310, T310, N311) gives the WTRU an opportunity to recover the radio link in case of a temporary problem. The second part of the procedure after T310 expiration allows the WTRU to attempt to re-establish the connection to the same cell or a different cell without having to completely release the connection.

[0071] NB-IoT relies on RLF and re-establishment to implement mobility in RRC_CONNECTED because measurement reporting or handover is not supported. The reason for this is that when NB-IoT was first standardized, it targeted the use case of stationary devices such as power meters. However, mobile devices soon appeared on the market (e.g., rental bicycles that use NB-IoT for communication). When an RLF is detected (e.g., after T310 expires), the WTRU may perform a cell search and then re-establish to a suitable cell. For moving devices, it was determined that using the existing RLF procedure is inefficient because measurements are not performed on neighboring cells before an RLF occurs. The delay caused by the WTRU having to perform a cell search to find a suitable cell causes a significant interruption, during which the WTRU is both unreachable (e.g., by paging) and unable to communicate (e.g., send uplink reports). To reduce this interruption, the RLF procedure has been enhanced for NB-IoT. This enhancement is summarized in Figure 4.

[0072] Neighbor cell measurements in RRC_CONNECTED before RLF were introduced to reduce the cell detection time and therefore the overall re-establishment time when an RLF occurs. If measurements are performed before an RLF occurs, the target cell may be known and re-establishment can be performed more quickly during T311 (i.e., no cell search is required).

[0073] Neighbor cell measurements can be triggered when the RSRP measured at the serving cell falls below a configured threshold and the delta RSRP (when the RSRP changes) is greater than the delta threshold within a configured time period, as defined in 3GPP TS36.331 clause 5.5.8 (Measurements in NB-IoT) as follows: Upon entering RRC_CONNECTED mode, the UE: 1> If neighCellMeasCriteria is present in SystemInformationBlockType3-NB: 2> NRSRP Ref Set ,to the most recent result of the serving cell measurement used for cell selection / reselection evaluation; 2> If the mitigation monitoring criteria defined in TS36.304[4] are not met: 3> Start T326 with value t-MeasureDeltaP; It shall be. While in RRC_CONNECTED mode, after performing measurements, the UE shall: 1> In the following, we use the NRSRP measurement value of the measured carrier and the nrs-PowerOffsetNonAnchor corresponding to the measured carrier; 1> If neighCellMeasCriteria is present in SystemInformationBlockType3-NB: 2>(NRSRP Ref -If (NRSRP-PowerOffsetNonAnchor)) > s-MeasureDeltaP: 3> NRSRP RefSet (NRSRP - nrs - PowerOffsetNonAnchor); 3> Start or resume T326 with the value t - MeasureDeltaP; 1> If neighCellMeasCriteria does not exist in SystemInformationBlockType3 - NB, or 1> If T326 is in execution: 2> If (NRSRP - nrs - PowerOffsetNonAnchor) < s - MeasureIntra, perform in - band measurements defined in TS36.133

[16] ; 2> If (NRSRP - nrs - PowerOffsetNonAnchor) < s - MeasureInter, perform inter - band measurements defined in TS36.133

[16] shall be the case.

[0074] In IoT - NTN, it is proposed to introduce the above - mentioned procedure. However, NTN deployment is not the same as that of the terrestrial network (TN). There are several scenarios to be considered. The target cell coverage may overlap with the source cell coverage as in TN (e.g., GEO) (overlapping coverage scenario). Cell A may switch to Cell B at a given time (e.g., geostationary scenario) (discrete change scenario). Cell A may disappear before Cell B appears (discontinuous coverage scenario). RSRP - based triggers may be less effective in NTN cells compared to terrestrial networks due to more uniform RSRP measurements across the cell. In NTN, it can be more reliably known whether a cell change has occurred or there is a temporary radio link problem. Time - based information may be considered to include the current cell stop time and the target cell start time, as well as location - based information (the WTRU can estimate the cell change time).

[0075] A time-based trigger may be used to initiate measurements. A distance-based trigger may be used to initiate measurements. However, if this is based only on the serving cell, this may not be sufficient to ensure that the WTRU can measure the target cell at the correct or optimal time, or to trigger the RLF at the correct or optimal time in all scenarios.

[0076] The measurement trigger may be based on both the current cell service time and the next cell service time. The trigger for neighbor cell measurements may be based on the time the serving cell is about to stop (e.g., based on the parameter t-service) and the target cell start time (e.g., based on the parameter t-serviceStart). The measurement may be initiated (e.g., simply started) when the target cell is available (i.e., the WTRU takes into account both the source cell coverage time and the target cell coverage time). If the cell 1 stop time is later than the cell 2 start time (scenario 1: overlapping coverage), the measurement may be made before the RLF (e.g., a configurable time offset before cell 1 stops). If the cell 1 stop time is equal to the cell 2 start time (scenario 2: discrete change), the measurement may be made at the RLF. If cell 1 stops before cell 2 starts, the measurement may be made at a time after the RLF (scenario 3: discontinuous coverage).

[0077] The re-establishment trigger may be based on both the current cell service time and the next cell service time. The current cell stop time (e.g., based on the parameter t-service) combined with the future cell start time (e.g., based on the parameter t-serviceStart) may be used as a trigger to perform RRC connection re-establishment instead of using T310 expiration / RLF to trigger RRC connection re-establishment. The out-of-sync count and T310 may be reduced or eliminated if cell 1 goes down, but the out-of-sync count and T310 may be performed when cell 1 is not down (for legacy RLF recovery). T311 may start when the current cell goes down and the next cell starts.

[0078] If possible, it makes sense for the WTRU to start measuring future cells shortly before losing coverage of the current cell to enable the WTRU to change cells more quickly when coverage is lost (similar to the use of an RSRP threshold in NB-IoT that indicates the WTRU is reaching a cell edge), but in NTN networks, the WTRU should also take into account the start time of the incoming cell to ensure that the WTRU does not attempt to measure future cells before they are available (thus wasting measurement effort and consuming power unnecessarily). By considering both the stop time of the current cell and the start time of the incoming / future cell, a single solution can address various scenarios in NTN. The current cell stop time may be provided, for example, using the parameter “t-service.” The current cell stop time may be provided by the serving cell. The current cell stop time may be provided in system information (e.g., a system information block (SIB)) and / or radio resource control (RRC) signaling. The next cell start time may be provided, for example, using the parameter “t-serviceStart.” The next cell start time may be provided by the serving cell. The next cell start time may be provided in system information (e.g., a system information block (SIB)) and / or radio resource control (RRC) signaling.

[0079] Current RLF procedures in LTE and NR are designed to provide the WTRU with sufficient time to recover the radio link to the current cell in the event of a temporary radio link problem. In a TN, it is difficult for the WTRU to determine whether loss of synchronization is due to a temporary radio link problem or a change in cell or coverage conditions. In an NTN, the stop time of the current cell and the start time of a neighboring cell can be utilized (e.g., using the parameter “t-Service” provided in the system information) to determine whether loss of synchronization is due to a cell change or an underlying radio condition problem. Therefore, rather than using existing procedures (e.g., counting N310 out-of-sync conditions and then waiting for T310 to expire before declaring RLF), time information (e.g., the stop time of the current cell and / or the start time of the next cell) can be used to reduce or completely eliminate N310 and T310 based directly on the time information to trigger RLF. The term “triggering RLF” can refer to triggering RLF-related procedures, such as those that perform cell search and RRC re-establishment. This may be done without considering a failed radio link in the traditional sense, e.g., instead of "trigger RLF" "trigger RRC re-establishment" or "trigger cell search" may be used.

[0080] 5 shows an example of RLF enhancements for an overlapping coverage scenario. A WTRU may start in a first cell (e.g., cell 1) and move to a second cell (e.g., cell 2). In this example, there are periods when the WTRU is in the coverage of both cell 1 and cell 2, similar to what is expected in a TN. The WTRU may receive time information related to when cell 1 stopped and when cell 2 started. The WTRU may receive a time offset (e.g., X seconds) related to the stop time of cell 1. Prior to this time offset of the stop time of cell 1, the WTRU is not required to perform measurements on cell 2. The WTRU may receive one or more radio quality thresholds, e.g., an RSRP threshold and an RSRP delta threshold.

[0081] Because cell 2 coverage begins before cell 1 coverage ends, the WTRU may perform measurements on cell 2 when the time is within a time offset (e.g., X seconds) of the cell 1 stop time. This measurement may be triggered before the RLF occurs due to cell 1 coverage outage, but the trigger for the measurement may include the stop time of the current cell (i.e., cell 1) and the start time of the next cell (i.e., cell 2). In this case, the WTRU may perform measurements after cell 2 appears and before cell 1 stops, which may ensure that cell 2 is detected and measured, and therefore may speed up or eliminate cell search time after the RLF.

[0082] In addition to measurement triggers, re-establishment may also be triggered using cell coverage time information. The WTRU may continue to perform RLM and out-of-sync indication counting until cell 1 goes down, and may use the T310 timer to attempt to restore the radio link to cell 1 if an out-of-sync condition is detected. If cell 1 is known to be down or is known to go down before T310 expires, there may be no need to count out-of-sync indications or start T310 to attempt to restore the radio link to cell 1. Rather, the WTRU may immediately trigger RLF for cell 1 (or re-establishment for cell 2) without using T310 based on the cell 1 stop time, or based on the detection of a single or reduced number of out-of-sync indications. The WTRU may take into account the start time of cell 2 when triggering re-establishment. This is primarily for other scenarios, since in this scenario cell 2 is already started, and therefore RLF / re-establishment may be triggered immediately when cell 1 goes down.

[0083] When a re-establishment procedure is triggered, the WTRU may utilize a separate or scaled T311 that may be shorter than the T311 used for re-establishment due to a conventionally triggered RLF because the target cell is already known, detected, and measured, so much of the time allowed for in T311 is not required.

[0084] 5, measurements may be triggered when cell 2 is available and the WTRU is within a time offset (e.g., X seconds) of the cell 1 outage time. RLF / re-establishment may be triggered directly at cell 1 outage without using T310.

[0085] In an example, the WTRU may trigger RLF / re-establishment before the stop time of cell 1. For example, RLF / re-establishment may be triggered immediately at the expected start time of cell 2. Alternatively, the WTRU may start measurements immediately at the expected start time of cell 2 and trigger RLF / re-establishment when cell 2 is detected and / or when a cell quality level criterion is met. The cell quality level criterion may be, for example, that the measured signal quality of cell 2 is above an RSRP and / or RSRQ threshold and / or that the measured signal quality of cell 1 is below an RSRP and / or RSRQ threshold.

[0086] 6 shows an example method 600 for RLF enhancement for an overlapping coverage scenario. A WTRU may be within the current coverage of a first cell (e.g., cell 1) and may move into the coverage of a second cell (e.g., cell 2). There may be a period of time during which the WTRU is in the overlapping coverage of both cell 1 and cell 2.

[0087] The WTRU may receive configuration information (610). The configuration information may indicate time information indicating when cell 1 stopped and cell 2 started. The configuration information may indicate a time offset value (e.g., X seconds) associated with the stop time of cell 1. The configuration information may indicate one or more radio quality thresholds, e.g., an RSRP threshold and an RSRP delta threshold. The configuration information may be received in one message or multiple messages. The configuration information may be provided, for example, as system information or may be provided as RRC-only signaling. The configuration information may include position information of current and neighboring satellites that the WTRU may use to estimate the current cell stop time and next cell start time without explicit time indications.

[0088] The WTRU may perform measurements on cell 2 (620). The WTRU may perform measurements based on a trigger condition. The trigger condition may be before the RLF. The measurements may be triggered based on a serving cell RSRP threshold and / or an RSRP delta threshold. For example, a measurement may be triggered if the serving cell RSRP is above the RSRP threshold or below the RSRP threshold. A measurement may be triggered based on the stop time of cell 1 and the start time of cell 2. A measurement may be triggered on the condition that cell 1 is within a time offset (e.g., X seconds) of the outage and cell 2 is available or in WTRU coverage. A measurement may be triggered based on an RSRP threshold, cell 1 is within a time offset of the outage, and cell 2 is available. In this case, the WTRU may perform measurements after cell 2 appears and before cell 1 goes out; this measurement may ensure that cell 2 is detected and measured, and therefore may speed up or eliminate cell search time after the RLF.

[0089] The WTRU may continue to perform RLM and out-of-sync indication counting until cell 1 goes down, and if an out-of-sync condition is detected, may use the T310 timer to attempt to restore the radio link to cell 1. If cell 1 is known to be down or is known to go down before T310 expires, it may not be necessary to count out-of-sync indications or start T310 to attempt to restore the radio link to cell 1.

[0090] The WTRU may trigger or declare a radio link failure (RLF) (630). The WTRU may immediately trigger or declare RLF for cell 1 (or re-establishment for cell 2) without using T310 based on the cell 1 stop time. Because cell 1 is known to be down and the WTRU cannot regain synchronization to cell 1, T310 may not need to be started. The WTRU may trigger RLF for cell 1 (or re-establishment for cell 2) based on detection of a single or reduced number of out-of-sync indications. The WTRU may trigger RLF before the stop time of cell 1. For example, RLF may be triggered immediately at the expected start time of cell 2. The WTRU may start measurements immediately at the expected start time of cell 2 and trigger RLF when cell 2 is detected and / or when cell quality level criteria are met. The cell quality level criterion may be, for example, that the measured signal quality of cell 2 is above the RSRP and / or RSRQ threshold and / or that the measured signal quality of cell 1 is below the RSRP and / or RSRQ threshold. The WTRU may start the T311 timer with the RLF.

[0091] The WTRU may trigger and / or perform a re-establishment procedure (640). The re-establishment procedure may be triggered using cell coverage time information. The WTRU may take into account the start time of cell 2 when triggering re-establishment. Because cell 2 has already started, RLF / re-establishment may be triggered immediately when cell 1 stops. Re-establishment may be triggered without using T310. The WTRU may trigger re-establishment before the stop time of cell 1. For example, re-establishment may be triggered immediately at the expected start time of cell 2. The WTRU may start measurements immediately at the expected start time of cell 2 and trigger re-establishment when cell 2 is detected and / or when a cell quality level criterion is met. The cell quality level criterion may be, for example, that the measured signal quality of cell 2 is above an RSRP and / or RSRQ threshold and / or that the measured signal quality of cell 1 is below an RSRP and / or RSRQ threshold.

[0092] When a re-establishment procedure is triggered, the WTRU may utilize a separate or scaled T311 timer that may be shorter than the T311 used for re-establishment due to a conventionally triggered RLF because the target cell (i.e., cell 2) is already known, detected, and measured, so much of the time allowed for in T311 is not required.

[0093] 7 shows an example of RLF enhancement during a discrete change in coverage scenario. In FIG. 7, similar to FIG. 5, the WTRU starts in cell 1 and moves to cell 2. However, in this example, there are discrete times when the current / serving cell (e.g., cell 1) stops and the incoming / target cell (e.g., cell 2) starts. This may be the case, for example, in some terrestrial fixed cell scenarios where satellites radiate cells to a fixed geographic area and one satellite moves away and an incoming satellite begins providing coverage to that geographic area.

[0094] In FIG. 7, similar to FIG. 5, for measurements, the WTRU may take into account both the cell 1 stop time and cell 2 start time. In this scenario, the main trigger for measurements is the cell 2 start time. Because cell 2 is not available before the RLF, measurements are not triggered in advance of the RLF. Measurements on the target cell begin at the cell 1 stop time / cell 2 start time. Similar to the example of FIG. 5, in this example, the WTRU may trigger RLF / re-establishment immediately without using N310 and T310, so may use the cell 1 stop time to optimize or expedite the re-establishment procedure even if measurements are not yet available. In this scenario, T311 may be reduced compared to the value used for normal RLF, but because time includes performing measurements on incoming cell 2, this time may be longer than that used in the scenario of FIG. 5 to take this into account.

[0095] In the scenario of FIG. 7, the RLF / re-establishment and target cell measurements are triggered at the time when cell 1 goes down and cell 2 starts.

[0096] 8 shows an example method 800 of RLF enhancement in discrete changes of coverage scenarios. A WTRU may be within the current coverage of a first cell (e.g., cell 1) and may move into the coverage of a second cell (e.g., cell 2). There may be periods when the WTRU is in the overlapping coverage of both cell 1 and cell 2. There may be discrete times when cell 1 stops and cell 2 starts.

[0097] The WTRU may receive configuration information (810). The configuration information may indicate time information indicating when cell 1 stopped and cell 2 started. The configuration information may indicate one or more radio quality thresholds, e.g., an RSRP threshold and an RSRP delta threshold. The configuration information may be received in one message or multiple messages. The configuration information may be provided, for example, as system information or may be provided as RRC-only signaling. The configuration information may include position information of current and neighboring satellites that the WTRU may use to estimate the current cell stop time and the next cell start time, rather than an explicit time indication.

[0098] The WTRU may trigger or declare RLF (820). The WTRU may trigger or declare RLF at the time cell 1 stops and cell 2 starts. The WTRU may trigger or declare RLF based on the detection of a single or reduced number of out-of-sync indications after the time cell 1 stops and cell 2 starts. The WTRU may start a T311 timer with RLF.

[0099] The WTRU may perform 830 measurements on cell 2. This measurement may be triggered based on the stop time of cell 1 and the start time of cell 2. In this scenario, the main trigger for the measurement is the start time of cell 2. Because cell 2 is not available before the RLF, the measurement is not triggered ahead of the RLF.

[0100] The WTRU may trigger and / or perform a re-establishment procedure (840). Similar to the example of FIG. 5, in this example, the WTRU may use the cell 1 stop time to optimize or expedite the re-establishment procedure, even if measurements are not yet available, because the WTRU may immediately trigger RLF / re-establishment without using N310 and T310. In this example, T311 may be reduced compared to the value used for normal RLF, but because time includes performing measurements on incoming cell 2, this time may be longer than that used in the scenario of FIG. 5 to take this into account. The re-establishment procedure may be triggered at the time cell 1 stops and cell 2 starts.

[0101] Figure 9 shows an example of RLF enhancement for a discontinuous coverage scenario. In Figure 9, similar to Figures 5 and 7, a WTRU starts in cell 1 and moves to cell 2. In this example, there is a coverage gap (i.e., a time gap) between stopping cell 1 and starting cell 2.

[0102] In Figure 9, measurements may not be initiated before RLF / re-establishment because cell 2 is not yet available, similar to the example of Figure 7. In this example, the WTRU may wait for the duration of the coverage gap before performing measurements (i.e., the WTRU waits until cell 2 becomes available).

[0103] 5 and 7, the WTRU may immediately trigger or declare RLF when cell 1 goes down, but in this example, an additional wait time is used before proceeding with the measurement and re-establishment procedure. This wait time may be implemented after RLF is detected / triggered due to cell 1 outage and before T311 / measurement / re-establishment begins, or it may be implemented before triggering RLF / re-establishment. In either case, the WTRU does not need to perform an out-of-sync count (N310) or attempt to regain synchronization with cell 1 during T310. Therefore, the triggering of the RLF / re-establishment procedure is based on the cell 1 stop time and cell 2 start time.

[0104] In the example of Figure 9, as with the example of Figure 7, T311 is shorter than that used for normal RLF re-establishment, although it may be longer than the value used in the example of Figure 5 because measurements are not performed before RLF and the target cell is known to the WTRU. In this example, as with the other examples, measurements and RLF / re-establishment are based on both the current cell stop time and the next cell start time. While RLF may be triggered directly without T310, in this example, the cell 2 start time, which is based on the cell 1 stop time, is the main factor that triggers the initiation of the procedure, apart from skipping T310 and stopping the RLF for cell 1.

[0105] FIG. 10 illustrates an example method 1000 for RLF enhancement for discontinuous coverage scenarios.

[0106] 10 shows an example method 1000 of RLF enhancement for a discontinuous coverage scenario. A WTRU may be within the current coverage of a first cell (e.g., cell 1) and may move into the coverage of a second cell (e.g., cell 2). There may be a period (coverage gap) between cell 1 stopping and cell 2 starting.

[0107] The WTRU may receive configuration information (1010). The configuration information may indicate time information indicating when cell 1 stopped and cell 2 started. The configuration information may indicate one or more radio quality thresholds, e.g., an RSRP threshold and an RSRP delta threshold. The configuration information may be received in one message or multiple messages. The WTRU may determine a coverage gap based on the cell 1 stop time and cell 2 start time. The configuration information may be provided, for example, as system information or may be provided as RRC-dedicated signaling. The configuration information may include position information of current and neighboring satellites that the WTRU may use to estimate the current cell stop time and the next cell start time, rather than an explicit time indication.

[0108] The WTRU may trigger or declare RLF (1020). The WTRU may trigger or declare RLF at the time that cell 1 goes down. The WTRU may trigger or declare RLF based on the detection of a single or reduced number of out-of-sync indications after the time that cell 1 goes down.

[0109] The WTRU may perform measurements on cell 2 (1030). The measurements may be triggered after the RLF. The measurements may be triggered after the duration of the coverage gap. The measurements may be triggered when cell 2 becomes available (i.e., at cell 2 start time). The WTRU may start a T311 timer when cell 2 becomes available (i.e., at cell 2 start time).

[0110] The WTRU may trigger and / or perform a re-establishment procedure 1040. As with the example of Figure 7, T311 may be shorter than that used for normal RLF re-establishment, but may be longer than that which may be used in the example of Figure 5 because measurements are not performed before the RLF and the target cell is known to the WTRU. In this example, measurements and RLF / re-establishment are based on both the current cell stop time and the next cell start time.

[0111] FIG. 11 shows an exemplary flow chart of an enhanced RLF / re-establishment procedure.

[0112] The WTRU may receive configuration information (1105). The configuration information may indicate a current cell / serving cell (e.g., cell 1) stop time, a next cell / incoming cell (e.g., cell 2) start time, and a time offset value (e.g., X seconds) for the cell 1 stop time. The time offset value may be used to determine when to start measurements, if it is before cell 1 stops. The configuration information may be provided, for example, as system information or may be provided as RRC-dedicated signaling. The configuration information may include other criteria, such as RSRP thresholds, for determining when to start measurements or for determining the length of a coverage gap. The configuration information may include position information of the current and neighboring satellites, which the WTRU may use to estimate the current cell stop time and next cell start time rather than an explicit time indication.

[0113] The WTRU may determine whether the time until the current cell goes down is within the received time offset value 1105. If not, the WTRU may continue radio link monitoring until the time until the current cell goes down is within the received time offset value.

[0114] If the time until the current cell stops is within the received time offset value, the WTRU may determine whether the next cell has started 1115. If the next cell has not started, the WTRU may determine whether the current cell has stopped 1140.

[0115] If the start time of the next cell has passed and the next cell has started, the WTRU may perform measurements on the next cell 1120. The measurements may be used to detect and determine the cell quality level.

[0116] The WTRU may determine whether the current cell is out of service 1125. The WTRU may perform measurements on the next cell until the current cell is out of service.

[0117] When the current cell goes down, the WTRU may trigger the RLF and stop the RLM of the current cell 1130. The WTRU may trigger the RLF and stop the RLM of the current cell without using timer T310 and attempt to recover the radio link to the current cell.

[0118] The WTRU may start timer T311 with the shorter (eg, shortest) value 1135. The WTRU may perform an RRC re-establishment procedure 1170.

[0119] If the WTRU determines that the next cell has not started, the WTRU may determine whether the current cell is down 1140. If the current cell is down, the WTRU may trigger an RLF without using timer T310 1145. If the current cell is not down, the WTRU determines whether the next cell has started 1115.

[0120] If the current cell is down and the next cell has not started before this time, the WTRU may trigger the RLF, stop the RLM of the current cell without using timer T310, and attempt to recover the radio link of the current cell (1145).

[0121] The WTRU may determine 1150 whether the next cell has started. If the next cell has not started, the WTRU may wait 1155 and make another determination 1150 whether the next cell has started. The wait time may be the duration of the coverage gap (e.g., in a discontinuous scenario). If the next cell has started, the WTRU may start timer T311 with a longer value 1160. This longer value may be longer than the T311 value from 1135.

[0122] The WTRU may start measuring the next cell (1165).

[0123] The WTRU may perform an RRC re-establishment procedure (1170).

[0124] In the example of FIG. 11, the WTRU may determine both the stop time of the current cell and the start time of the next cell to determine when to start measurements on the next cell, when to trigger RLF (and stop RLM for the current cell), and when to perform re-establishment of the next cell.

[0125] The new T311 value may be explicitly signaled, or it may be determined by applying an offset, or it may be scaled depending on when the measurement is performed (i.e., before or after RLF). If the measurement has already been performed, the new T311 value may be short. The new T311 value may be used (e.g., simply used) to attempt re-establishment with the indicated next NTN cell. Once the new T311 expires, the WTRU may fall back to the legacy RLF procedure. That is, the WTRU may perform cell search for other cells and use the legacy T311 timer, which triggers an RRC connection failure upon expiration.

[0126] The WTRU may report whether the re-establishment was triggered due to an actual RLF or a time-based trigger. This may be indicated using a new RRC re-establishment cause. This may be indicated using a new explicit indication in the uplink message. This may be logged, for example, as part of the RLF report used for MDT / SON and later reported to the network. The WTRU may report whether a fallback occurred (i.e., whether a new T311 was initially applied due to the expiration of a previous cell outage time, but the WTRU subsequently failed to re-establish a new cell within the (new) T311). This may occur if the WTRU re-establishes to any new cell, including the original cell or the failed cell, within the legacy T311 timer.

[0127] To prevent many WTRUs from simultaneously initiating random access to perform re-establishment due to the previous cell going down for many WTRUs and / or the new cell starting up for many WTRUs, some randomization may be applied to the re-establishment time. The WTRU may generate the re-establishment time based on the next cell start time and a semi-random value. The semi-random value may be based on the WTRU-ID. The semi-random value may include, for example, selecting a value in the range of 0 to 100 percent, comparing it to a threshold, and selecting one time if the random value is below the threshold and the other time if the random value is above the threshold.

[0128] In an example where a WTRU triggers re-establishment after cell 2 appears but before cell 1 goes down, the WTRU may apply randomization to the re-establishment trigger time. This spreads out re-establishment attempts by multiple WTRUs over time to minimize RACH and / or CN signaling congestion. The WTRU may, for example, calculate a random time within a time window starting when cell 2 starts and ending when cell 1 goes down (i.e., during the time when coverage is known to be provided by both cell 1 and cell 2).

[0129] The WTRU may determine or calculate a time range based on the stop time of cell 1 and the start time of cell 2, and select a semi-random value from within the calculated uniform distribution range within this range.

[0130] The WTRU may calculate a time range based on the time that cell 2 was detected and measured and the expected outage time of cell 1.

[0131] The WTRU may take service, bearer, or traffic characteristics into account when determining when to trigger RLF / re-establishment. For example, if the WTRU has an ongoing data exchange (e.g., transmission or reception), the WTRU may delay declaring RLF until the data exchange has finished or until Cell 1 has stopped. The WTRU may use a data inactivity timer (e.g., a DRX inactivity timer) to determine when the data exchange will stop. If the WTRU is configured with delay-tolerant services, the WTRU may trigger re-establishment sooner, for example, as soon as Cell 2 starts. If the WTRU has delay-sensitive services, re-establishment may be delayed to take advantage of Cell 1 availability for as long as possible.

[0132] In some examples, the WTRU may further take TN network measurements into account. For example, if the current cell is within X seconds before the stop time but the next NTN cell is not yet available, the WTRU may trigger a measurement of TN to try or find a suitable cell that can be selected more quickly, or if NTN re-establishment fails. In some examples, the TN measurement may be triggered only if a coverage gap is expected. In some examples, the WTRU may perform TN measurements after an RLF is triggered. In some examples, the TN measurement may be performed only if an NTN cell has not been successfully selected within a (new) T311 time.

[0133] In some examples, more than one target NTN cell may be provided to the WTRU. In this case, the WTRU may take into account the start times of all of these target cells and perform measurements on these cells according to their respective start times. T311 may be adjusted when more than one cell is provided as a target.

[0134] The WTRU may use distance or location-based criteria instead of, or in addition to, the start and stop times of the current and neighboring cells. In an example, in addition to, or as an alternative to, the stop time of cell 1, the WTRU may use a criterion that compares its measured location (e.g., using GNSS) to a reference point set by the network. The reference point may, for example, indicate a location within cell 1. In an example, in addition to, or as an alternative to, the start time of cell 2, the WTRU may use a criterion that compares its measured location (e.g., using GNSS) to a reference point set by the network. The reference point may, for example, indicate a location within cell 2.

[0135] The WTRU may monitor one or more distances and, for example, take action if the distance meets / exceeds / falls below a distance threshold criterion. The distance threshold may be based, for example, on one or more of the following: WTRU-satellite distance, WTRU-satellite cell center distance, WTRU-satellite footprint distance, WTRU-terrestrial-based gNB distance, distance between the WTRU and the terrestrial coverage edge, and distance between the WTRU and a reference point.

[0136] FIG. 12 shows an example method 1200 for enhanced RLF / re-establishment. A WTRU may receive 1210 configuration information. The configuration information may indicate time information indicating a stop time of a first cell and a start time of a second cell. The first cell may be a current cell in which the WTRU is in coverage. The second cell may be a neighboring cell (target cell). The configuration information may indicate a time offset value (e.g., X seconds) associated with the stop time of the first cell. The configuration information may indicate one or more radio quality thresholds, e.g., an RSRP threshold and an RSRP delta threshold. The configuration information may be received in one message or multiple messages. The configuration information may be provided, for example, as system information or as RRC-dedicated signaling. The configuration information may include current and neighboring satellite position information that the WTRU may use to estimate the current cell stop time and next cell start time rather than an explicit time indication.

[0137] The WTRU may perform radio link monitoring (RLM) of the first cell 1220. The WTRU may determine that the first cell is down 1230. The determination that the first cell is down may be based on received information indicating an outage time of the first cell. The WTRU may stop RLM measurements of the current cell 1240. In response to determining that the first cell is down, the WTRU may initiate a radio resource control (RRC) connection re-establishment procedure to the second cell 1250.

[0138] The WTRU may perform measurements on the second cell. The measurements on the second cell may be before the first cell stops and may be conditional on the second cell starting. Measurements may be performed on the second cell when the current cell stop time is within the received stop time offset value. The WTRU may delay initiation of a connection re-establishment procedure for the second cell before the second cell starts and on the condition that the first cell stops until the second cell starts. Measurements may be performed on the second cell before a radio link failure (RLF) occurs. Measurements may be performed on the second cell upon the occurrence of an RLF. The WTRU may perform RRC connection re-establishment based on the stop time of the first cell and the start time of the second cell. The RRC connection re-establishment may be performed without using a T310 timer expiration. The WTRU may trigger an RLF or RRC connection re-establishment on the condition that a cell quality level criterion is met. The cell quality level criteria may include the measured signal quality of the second cell being above an RSRP or RSRQ threshold. The cell quality level criteria may include the measured signal quality of the first cell being below an RSRP or RSRQ threshold.

[0139] While features and elements are described above in particular combinations, those skilled in the art will understand that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware embodied in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted via 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, and optical media such as magneto-optical media, CD-ROM disks, and digital versatile disks (DVDs). A processor associated with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

1. 1. A method implemented by a wireless transmit / receive unit (WTRU), comprising: receiving configuration information, the configuration information including an indication of a stop time of a first cell and a start time of a second cell; performing radio link monitoring (RLM) measurements of the first cell; determining that the first cell is down based on the received indication of a down time of the first cell; and Stopping the RLM measurement of the first cell; Initiating a radio resource control (RRC) connection re-establishment procedure to the second cell in response to determining that the first cell is down; and A method comprising:

2. The method of claim 1 , wherein the first cell is a current cell and the second cell is a neighboring cell or a target cell.

3. The method of claim 1 or 2, wherein the configuration information further comprises a time offset value, the time offset value being relative to the stop time of the first cell.

4. 4. The method of claim 1, further comprising performing measurements of the second cell before the first cell stops and on the condition that the second cell has started.

5. The method of claim 1 , wherein the measurement is performed for the second cell when the first cell stop time is within a received time offset value of stop.

6. 6. The method of claim 1, further comprising: delaying initiation of the connection re-establishment procedure for the second cell on condition that the first cell stops before and until the second cell starts.

7. The method of claim 1 , wherein the measurements are performed for the second cell before or upon occurrence of a radio link failure (RLF).

8. The method of claim 1 , further comprising: performing an RRC connection re-establishment based on the stop time of the first cell and the start time of the second cell.

9. The method according to claim 1 , wherein the RRC connection re-establishment is performed without using a T310 timer expiry.

10. 10. The method of claim 1, further comprising: triggering a radio link failure (RLF) or an RRC connection re-establishment on the condition that a cell quality level criterion is met, the cell quality level criterion comprising at least one of a measured signal quality of the second cell being above an RSRP or RSRQ threshold and a measured signal quality of the first cell being below an RSRP or RSRQ threshold.

11. 1. A wireless transmit / receive unit (WTRU), comprising: A transceiver; a processor; Equipped with the transceiver is configured to receive configuration information, the configuration information including an indication of a stop time of a first cell and a start time of a second cell; the processor is configured to perform radio link monitoring (RLM) measurements of the first cell; The processor is further configured to determine that the first cell is out of service based on the received indication of an outage time of the first cell; the processor is further configured to stop the RLM measurement of the first cell; the processor is further configured to initiate a radio resource control (RRC) connection re-establishment procedure to the second cell in response to determining that the first cell is down. WTRU.

12. The WTRU of claim 11 , wherein the first cell is a current cell and the second cell is a neighbor cell or a target cell.

13. The WTRU of claim 11 or 12, wherein the configuration information further includes a time offset value, the time offset value being relative to the stop time of the first cell.

14. 14. The WTRU of claim 11, wherein the processor is further configured to perform measurements of the second cell before the first cell stops and on the condition that the second cell has started.

15. The WTRU of claim 11 , wherein the measurement is performed for the second cell when the first cell stop time is within a received stop time offset value.

16. 16. The WTRU of claim 11, wherein the processor is further configured to delay initiating the connection re-establishment procedure for the second cell on condition that the first cell stops before and until the second cell starts.

17. The WTRU of claim 11 , wherein the measurements are performed on the second cell before or upon occurrence of a radio link failure (RLF).

18. 18. The WTRU of claim 11, wherein the processor is further configured to perform RRC connection re-establishment based on the stop time of the first cell and the start time of the second cell.

19. The WTRU of claim 11 , wherein the RRC connection re-establishment is performed without using a T310 timer expiration.

20. 20. The WTRU of claim 11, wherein the processor is further configured to trigger a radio link failure (RLF) or an RRC connection re-establishment on condition that a cell quality level criterion is met, the cell quality level criterion including at least one of a measured signal quality of the second cell being above an RSRP or RSRQ threshold and a measured signal quality of the first cell being below an RSRP or RSRQ threshold.

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