RLF and reconstruction improvement method in NTN

Abstract

A wireless transmit / receive unit (WTRU) may be configured to receive configuration information, which 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 on a first cell. The WTRU may be configured to determine that the first cell has stopped based on the received indication of the stop time of the first cell. The WTRU may be configured to stop RLM measurements on the first cell. The WTRU may be configured to initiate a radio resource control (RRC) connection reestablishment procedure on the second cell in response to a determination that the first cell has stopped. 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 also include a time offset value.

Description

[0001] Related Applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 410,765, filed on September 28, 2022, and U.S. Provisional Application No. 63 / 421,386, filed on November 1, 2022, the contents of which are incorporated herein by reference. Background Art

[0003] Non-terrestrial networks (NTNs) facilitate the deployment of wireless networks in areas where land-based antennas are not practical, e.g., due to geography or cost. It is envisioned that, coupled with terrestrial networks, NTNs will enable truly ubiquitous coverage of 5G networks. Initial NTN deployments support basic talking and texting anywhere in the world; however, further updates, along 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 for a first cell and a start time for a second cell. The WTRU may be configured to perform radio link monitoring (RLM) measurements on the first cell. The WTRU may be configured to determine that the first cell has stopped based on the received indication of the stop time for the first cell. The WTRU may be configured to stop the RLM measurements on the first cell. The WTRU may be configured to initiate a radio resource control (RRC) connection reestablishment procedure on the second cell in response to determining that the first cell has stopped. The first cell may be a serving cell, and the second cell may be an adjacent 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 on the second cell under the condition that the second cell has started and before the first cell stops. 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 the connection reestablishment procedure on the second cell under the condition that the first cell stops before the second cell starts and until the second cell starts. Measurements may be performed on the second cell before or at the occurrence of a radio link failure (RLF). The WTRU may be configured to perform RRC connection reestablishment based on the stop time of the first cell and the start time of the second cell. RRC connection reestablishment may be performed without using the expiration of a T310 timer. The WTRU may be configured to trigger a radio link failure (RLF) or RRC connection reestablishment under the condition that a cell quality level criterion is met. The cell quality level criterion may include at least one of the following: the measured signal quality of the second cell is higher than an RSRP or RSRQ threshold, and the measured signal quality of the first cell is lower than an RSRP or RSRQ threshold. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0006] Figure 1A is a system diagram illustrating an example communication system in which one or more of the disclosed embodiments may be implemented;

[0007] Figure 1B is, in accordance with one embodiment, a system diagram illustrating an example wireless transmit / receive unit (WTRU) that may be used within Figure 1A the illustrated communication system;

[0008] Figure 1C is, in accordance with one embodiment, a diagram illustrating that may be used within Figure 1ASystem diagram of an example radio access network (RAN) and an example core network (CN) used within the illustrated communication system;

[0009] Figure 1D According to one embodiment, it illustrates that it can be in Figure 1A System diagram of another example RAN and another example CN that can be used within the illustrated communication system;

[0010] Figure 2 Shows an example of an interface in NTN;

[0011] Figure 3 Shows an example of a radio link failure (RLF) and reconstruction process;

[0012] Figure 4 Shows an example of an enhanced RLF process;

[0013] Figure 5 Shows an example of RLF enhancement for an overlapping coverage scenario;

[0014] Figure 6 Shows an example method of RLF enhancement for an overlapping coverage scenario;

[0015] Figure 7 Shows an example of RLF enhancement for discrete changes in a coverage scenario;

[0016] Figure 8 Shows an example method of RLF enhancement for discrete changes in a coverage scenario;

[0017] Figure 9 Shows an example of RLF enhancement for a discontinuous coverage scenario;

[0018] Figure 10 Shows an example method of RLF enhancement for a discontinuous coverage scenario;

[0019] Figure 11 Shows an example method for RLF enhancement; and

[0020] Figure 12 Shows an example method of RLF / reconstruction. Detailed Description

[0021] Figure 1AFIG. is a diagram illustrating an example communication system 100 in which one or more of the disclosed embodiments may be implemented. The communication system 100 may be a multi-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 code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique word discrete Fourier transform spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, filter bank multi-carrier (FBMC), etc.

[0022] As Figure 1A shown, the communication 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 will be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d (any of which may be referred to as a station (STA)) may be configured to transmit and / or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular phone, a personal digital assistant (PDA), a smart phone, a laptop computer, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable device, a head-mounted display (HMD), a vehicle, a drone, a medical device and application (e.g., remote surgery), an industrial device and application (e.g., a robot and / or other wireless devices operating in the context of an industrial and / or automation processing chain), a consumer electronic device, a device operating on a commercial and / or industrial wireless network, etc. Any of the WTRUs 102a, 102b, 102c, and 102d may be interchangeably referred to as a UE.

[0023] The communication system 100 may also include base station 114a and / or base station 114b. Each of base stations 114a, 114b may be any type of device configured to facilitate access to one or more communication networks (such as CN 106, Internet 110, and / or other networks 112) by wirelessly engaging with at least one of WTRUs 102a, 102b, 102c, 102d. By way of example, base stations 114a, 114b may be base transceiver stations (BTSs), Node Bs, eNode Bs (eNBs), home Node Bs, home eNodeBs, next-generation Node Bs (such as gNode Bs (gNBs)), New Radio (NR) Node Bs, site controllers, access points (APs), wireless routers, etc. Although each of base stations 114a, 114b is depicted as a single element, it will be understood that base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0024] Base station 114a may be part of RAN 104, which may also include other base stations and / or network elements (not shown), such as base station controllers (BSCs), radio network controllers (RNCs), relay nodes, etc. 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 cells (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for wireless services to a specific geographical area, which may be relatively fixed or may change over time. A cell may also be divided into cell sectors. For example, the cell associated with base station 114a may be divided into three sectors. Thus, in one embodiment, base station 114a may include three transceivers, i.e., one transceiver corresponding to each sector of the cell. In one embodiment, base station 114a may employ multiple-input multiple-output (MIMO) technology and may use multiple transceivers for each sector of the cell. For example, beamforming may be used to transmit and / or receive signals in a desired spatial direction.

[0025] Base stations 114a, 114b may communicate with one or more of WTRUs 102a, 102b, 102c, 102d via air interface 116, which may be any suitable wireless communication link (such as radio frequency (RF), microwave, centimeter wave, millimeter wave, infrared (IR), ultraviolet (UV), visible light, etc.). Air interface 116 may be established using any suitable radio access technology (RAT).

[0026] More specifically, as described above, the communication system 100 can be a multiple access system and can employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base stations 114a and the WTRUs 102a, 102b, 102c in the RAN 104 can implement radio technologies such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), and the UMTS UTRA can use Wideband CDMA (WCDMA) to establish the air interface 116. WCDMA can include communication protocols such as High Speed Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA can include High Speed Downlink (DL) Packet Access (HSDPA) and / or High Speed Uplink (UL) Packet Access (HSUPA).

[0027] In one embodiment, the base stations 114a and the WTRUs 102a, 102b, 102c can implement radio technologies such as Evolved UMTS Terrestrial Radio Access (E-UTRA), and the E-UTRA technology can use Long Term Evolution (LTE) and / or Advanced LTE (LTE-A) and / or Pro LTE-A (LTE-A Pro) to establish the air interface 116.

[0028] In one embodiment, the base stations 114a and the WTRUs 102a, 102b, 102c can implement radio technologies such as NR radio access, and the NR radio access can use NR to establish the air interface 116.

[0029] In one embodiment, the base stations 114a and the WTRUs 102a, 102b, 102c can implement multiple radio access technologies. For example, the base stations 114a and the WTRUs 102a, 102b, 102c can implement LTE radio access and NR radio access together, such as using the Dual Connectivity (DC) principle. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c can be characterized by multiple types of radio access technologies and / or transmissions to / from multiple types of base stations (e.g., eNBs and gNBs).

[0030] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as, for example, 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 Rate for GSM Evolution (EDGE), GSM EDGE (GERAN), etc.

[0031] In Figure 1A the base station 114b 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 to facilitate wireless connectivity in a local area (such as a business premise, a home, a vehicle, a campus, an industrial facility, an air corridor (such as for drones), a road, etc.). 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 one 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 (such as WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-Advanced Pro, NR, etc.) to establish a picocell or a femtocell. As Figure 1A shown, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not need to access the Internet 110 via the CN 106.

[0032] The RAN 104 may communicate with the CN 106, which may be any type of network configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have varying Quality of Service (QoS) requirements, such as different throughput requirements, latency requirements, fault tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, etc. The CN 106 may provide call control, billing services, location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform advanced security functions such as user authentication. Although in Figure 1AAlthough not shown, it will be understood that RAN 104 and / or CN 106 can communicate directly or indirectly with other RANs that employ the same RAT as RAN 104 or a different RAT. For example, in addition to being connected to RAN 104 that can utilize NR radio technology, CN 106 can also communicate with another RAN (not shown) that employs GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

[0033] CN 106 can also act as a gateway for WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 can include a circuit-switched telephone network that provides plain old telephone service (POTS). The Internet 110 can include a global system of interconnected computer networks and devices that use common communication protocols (such as the Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and / or Internet Protocol (IP) in the TCP / IP Internet protocol family). The networks 112 can include wired and / or wireless communication networks owned and / or operated by other service providers. For example, the networks 112 can include another CN connected to one or more RANs, and the one or more RANs can employ the same RAT as RAN 104 or a different RAT.

[0034] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication system 100 can include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d can include multiple transceivers for communicating with different wireless networks via different wireless links). For example, Figure 1A the illustrated WTRU 102c can be configured to communicate with a base station 114a (which can employ a cellular-based radio technology) and communicate with a base station 114b (which can employ IEEE 802 radio technology).

[0035] Figure 1B is a system diagram of an exemplary WTRU 102. As Figure 1B shown, the WTRU 102 can include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keyboard 126, a display / touchpad 128, a non-removable memory 130, a removable memory 132, a power supply 134, a Global Positioning System (GPS) chipset 136, and / or other peripheral devices 138, etc. It will be understood that the WTRU 102 can include any sub-combination of the foregoing elements while remaining consistent with the embodiments.

[0036] The processor 118 can be a general-purpose processor, a dedicated processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated 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, etc. The processor 118 can perform signal encoding, data processing, power control, input / output processing, and / or any other functions that enable the WTRU 102 to operate in a wireless environment. The processor 118 can be coupled to a transceiver 120, which can be coupled to a transmit / receive element 122. Although Figure 1B the processor 118 and the transceiver 120 are depicted as separate components, it will be understood that the processor 118 and the transceiver 120 can be integrated together in an electronic package or chip.

[0037] The transmit / receive element 122 can be configured to transmit signals to or receive signals from a base station (such as base station 114a) via the air interface 116. For example, in one embodiment, the transmit / receive element 122 can be an antenna configured to transmit and / or receive RF signals. In one embodiment, the transmit / receive element 122 can be a transmitter / detector configured to transmit and / or receive signals such as IR, UV, or visible light signals. In yet another embodiment, the transmit / receive element 122 can be configured to transmit and / or receive both RF and optical signals. It will be understood that the transmit / receive element 122 can be configured to transmit and / or receive any combination of wireless signals.

[0038] Although the transmit / receive element 122 is depicted as a single element in Figure 1B the WTRU 102 can include any number of transmit / receive elements 122. More specifically, the WTRU 102 can employ MIMO technology. Thus, in one embodiment, the WTRU 102 can include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals via the air interface 116.

[0039] The transceiver 120 can be configured to modulate the signals to be transmitted by the transmit / receive element 122 and demodulate the signals received by the transmit / receive element 122. As described above, the WTRU 102 can have multi-mode capabilities. Thus, the transceiver 120 can include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs (such as NR and IEEE 802.11).

[0040] The processor 118 of the WTRU 102 may be coupled to a speaker / microphone 124, a keyboard 126, and / or a display / touchpad 128 (such as a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit), and may receive user input data from these devices. The processor 118 may also output user data to the speaker / microphone 124, the keyboard 126, and / or the display / touchpad 128. In addition, the processor 118 may access information from any type of suitable memory (such as non-removable memory 130 and / or removable memory 132), and store data to these memories. 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, etc. In other embodiments, the processor 118 may access information from a memory that is not physically located on the WTRU 102 (such as on a server or a home computer (not shown)), and store data to these memories.

[0041] The processor 118 may receive power from a power supply 134, and may be configured to distribute and / or control power to other components in the WTRU 102. The power supply 134 may be any suitable device for powering the WTRU 102. For example, the power supply 134 may include one or more dry cells (such as nickel cadmium (NiCd), nickel zinc (NiZn), nickel metal hydride (NiMH), lithium ion (Li-ion), etc.), a solar cell, a fuel cell, etc.

[0042] The processor 118 may also be coupled to a GPS chipset 136, which may be configured to provide location information (such as longitude and latitude) regarding the current location of the WTRU 102. As a supplement or replacement to the information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (such as base stations 114a, 114b) via an air interface 116 and / or determine its location based on the signal timing received from two or more nearby base stations. It will be understood that the WTRU 102 may obtain location information by any suitable location determination method while remaining consistent with the embodiments.

[0043] The processor 118 may also be coupled to other peripheral devices 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 peripheral devices 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 console module, an Internet browser, a virtual reality and / or augmented reality (VR / AR) device, an activity tracker, etc. The peripheral devices 138 may include one or more sensors. The sensors may be one or more of a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, a humidity sensor, etc.

[0044] The WTRU 102 may include a full-duplex radio, for which the transmission and reception of some or all signals (e.g., associated with a specific subframe for both UL (e.g., for transmission) and DL (e.g., for reception)) may be concurrent and / or simultaneous. The full-duplex radio may include an interference management unit to reduce and / or substantially eliminate self-interference via hardware (e.g., a choke) or via signal processing by a processor (e.g., a separate processor (not shown) or via the processor 118). In one embodiment, the WTRU 102 may include a half-duplex radio, for which the transmission and reception of some or all signals (e.g., associated with a specific subframe for UL (e.g., for transmission) or DL (e.g., for reception)).

[0045] Figure 1C is a system diagram illustrating the RAN 104 and the CN 106 according to one embodiment. As described above, the RAN 104 may communicate with the WTRU 102a, 102b, 102c via the air interface 116 using E-UTRA radio technology. The RAN 104 may also communicate with the CN 106.

[0046] The RAN 104 may include eNode-Bs 160a, 160b, 160c, although it will be understood that the RAN 104 may include any number of eNode-Bs while remaining consistent with the embodiments. Each of the eNode-Bs 160a, 160b, 160c may include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c via the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, for example, the eNode-B 160a may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0047] Each of the eNode-Bs 160a, 160b, 160c may be associated with a specific cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, user scheduling in the UL and / or DL, etc. As Figure 1C shown, the eNode-Bs 160a, 160b, 160c may communicate with each other via the X2 interface.

[0048] Figure 1C The CN 106 shown may include a Mobility Management Entity (MME) 162, a Serving Gateway (SGW) 164, and a Packet Data Network (PDN) Gateway (PGW) 166. Although the above elements are depicted as part of the CN 106, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0049] The MME 162 may be connected to each of the eNode-Bs 162a, 162b, 162c in the RAN 104 via the S1 interface and may act as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, activation / deactivation of bearers, selection of a specific serving gateway during the initial attachment of the WTRUs 102a, 102b, 102c, etc. The MME 162 may provide control plane functions for interworking between the RAN 104 and other RANs (not shown) employing other radio technologies such as GSM and / or WCDMA.

[0050] The SGW 164 can be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via the S1 interface. The SGW 164 can generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 can perform other functions, such as anchoring the user plane during an inter-eNodeB handover, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, etc.

[0051] The SGW 164 can be connected to the PGW 166, which can provide the WTRUs 102a, 102b, 102c with access to a packet switched network (such as the Internet 110) to facilitate communication between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0052] The CN 106 can facilitate communication with other networks. For example, the CN 106 can provide the WTRUs 102a, 102b, 102c with access to a circuit switched network (such as the PSTN 108), thereby facilitating communication between the WTRUs 102a, 102b, 102c and traditional landline communication devices. For example, the CN 106 can include or communicate with an IP gateway (such as an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 can provide the WTRUs 102a, 102b, 102c with access to other networks 112, which can include other wired and / or wireless networks owned and / or operated by other service providers.

[0053] Although the WTRU is described as a wireless terminal in Figures 1A - 1D it is contemplated that in some representative embodiments, such a terminal can use (e.g., temporarily or permanently) a wired communication interface with the communication network.

[0054] In a representative embodiment, the other network 112 can be a WLAN.

[0055] In a Wireless Local Area Network (WLAN) in Infrastructure Basic Service Set (BSS) mode, there can be an Access Point (AP) for the BSS and one or more Stations (STAs) associated with the AP. The AP can have access or an interface to a Distribution System (DS) or another type of wired / wireless network that carries traffic into and / or out of the BSS. Traffic destined for an STA from outside the BSS can reach the STA through the AP and can be delivered to the STA. Traffic originating from an STA destined for a destination outside the BSS can be transmitted to the AP for delivery to the respective destination. Traffic between STAs within the BSS can be transmitted through the AP. For example, the source STA can transmit traffic to the AP, and the AP can deliver the traffic to the destination STA. Traffic between STAs within the BSS can be considered and / or referred to as peer-to-peer traffic. Peer-to-peer traffic can be transmitted between the source STA and the destination STA (e.g., directly between the source STA and the destination STA) using Direct Link Setup (DLS). In some representative embodiments, DLS can use 802.11e DLS or 802.11z Tunnel DLS (TDLS). A WLAN using Independent BSS (IBSS) mode may not have an AP, and STAs within the IBSS or using the IBSS (e.g., all STAs) can communicate directly with each other. Communication in IBSS mode can sometimes be referred to in this document as an "ad-hoc" communication mode.

[0056] When using 802.11ac infrastructure operation mode or a similar operation mode, the AP can send beacons on a fixed channel (e.g., the primary channel). The primary channel can be of a fixed width (e.g., 20 MHz bandwidth) or dynamically set width. The primary channel can be the operating channel of the BSS and can be used by STAs to establish a connection with the AP. In some representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) can be implemented, for example, in an 802.11 system. For CSMA / CA, STAs (e.g., each STA) (including the AP) can listen to the primary channel. If the primary channel is sensed / detected and / or determined to be busy by a particular STA, that particular STA can back off. Only one STA (e.g., only one station) can transmit at any given time in a given BSS.

[0057] High Throughput (HT) STAs can communicate using a channel with a width of 40 MHz, for example, by combining the primary 20 MHz channel with an adjacent or non-adjacent 20 MHz channel to form a 40 MHz wide channel.

[0058] A very high throughput (VHT) STA can support channels with widths of 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz. 40 MHz and / or 80 MHz channels can be formed by combining consecutive 20 MHz channels. A 160 MHz channel can be formed by combining eight consecutive 20 MHz channels or by combining two non - consecutive 80 MHz channels, which can be referred to as an 80 + 80 configuration. For the 80 + 80 configuration, the data after channel coding can be fed through a segment parser that can divide the data into two streams. Inverse fast Fourier transform (IFFT) processing and time - domain processing can be performed on each stream separately. The streams can be mapped to two 80 MHz channels, and the data can be transmitted by the transmitting STA. At the receiver of the receiving STA, the above operations for the 80 + 80 configuration can be reversed, and the combined data can be transferred to the media access control (MAC).

[0059] Sub - 1 GHz operation modes are supported by 802.11af and 802.11ah. Compared to the channel operation bandwidths and carriers used in 802.11n and 802.11ac, the channel operation bandwidths and carriers in 802.11af and 802.11ah are reduced. 802.11af supports bandwidths of 5 MHz, 10 MHz, and 20 MHz in the TV white space (TVWS) spectrum, and 802.11ah supports bandwidths of 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz using non - TVWS spectrum. According to a representative embodiment, 802.11ah can support meter - type control / machine - type communication (MTC), such as MTC devices in a macro - coverage area. MTC devices can have certain capabilities, such as limited capabilities including supporting (e.g., only supporting) certain and / or restricted bandwidths. MTC devices can include a battery with a battery life higher than a threshold (e.g., to maintain an extremely long battery life).

[0060] A WLAN system (e.g., 802.11n, 802.11ac, 802.11af, and 802.11ah) that can support multiple channels and channel bandwidths includes a channel that can be designated as a primary channel. The primary channel can have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel can be set and / or restricted by the STA that supports the minimum bandwidth operation mode among all STAs operating in the BSS. In the example of 802.11ah, for an STA (e.g., an MTC type device) that supports (e.g., only supports) the 1 MHz mode, the primary channel can be 1 MHz wide, even if the AP and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operation modes. Carrier sensing and / or network allocation vector (NAV) settings can depend on the state of the primary channel. If the primary channel (e.g., due to an STA that only supports the 1 MHz operation mode transmitting to the AP) is busy, then all available bands can be considered busy even if most of the available band remains idle.

[0061] In the United States, the available band for 802.11ah is from 902 MHz to 928 MHz. In Korea, the available band is from 917.5 MHz to 923.5 MHz. In Japan, the available band is from 916.5 MHz to 927.5 MHz. Depending on the country code, the total available bandwidth for 802.11ah is 6 MHz to 26 MHz.

[0062] Figure 1D FIG. is a system diagram illustrating RAN 104 and CN 106 according to an embodiment. As described above, RAN 104 can communicate with WTRUs 102a, 102b, 102c via air interface 116 using NR radio technology. RAN 104 can also communicate with CN 106.

[0063] The RAN 104 may include gNBs 180a, 180b, 180c, but it will be understood that the RAN 104 may include any number of gNBs while remaining consistent with the embodiments. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c via the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, the gNBs 180a, 108b may utilize beamforming to transmit signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, for example, the gNB 180a may use multiple antennas to transmit wireless signals to the WTRU 102a and / or receive wireless signals from the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers (not shown) to the WTRU 102a. A subset of the component carriers may be on unlicensed spectrum, while the remaining component carriers may be on licensed spectrum. In an embodiment, the gNBs 180a, 180b, 180c may implement coordinated multi-point (CoMP) technology. For example, the WTRU 102a may receive coordinated transmissions from the gNB 180a and the gNB 180b (and / or gNB 180c).

[0064] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with scalable numerology. For example, the OFDM symbol spacing and / or the OFDM subcarrier spacing may vary according to different transmissions, different cells, and / or different portions of the radio transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using subframes or transmission time intervals (TTIs) of various or scalable lengths (e.g., containing a varying number of OFDM symbols and / or an absolute time of continuously varying length).

[0065] gNBs 180a, 180b, 180c can be configured to communicate with WTRUs 102a, 102b, 102c in stand-alone configuration and / or non-stand-alone configuration. In stand-alone configuration, WTRUs 102a, 102b, 102c can communicate with gNBs 180a, 180b, 180c without accessing another RAN (e.g., eNode-Bs 160a, 160b, 160c for example). In stand-alone configuration, WTRUs 102a, 102b, 102c can utilize one or more of gNBs 180a, 180b, 180c as a mobility anchor. In stand-alone configuration, WTRUs 102a, 102b, 102c can communicate with gNBs 180a, 180b, 180c using signals in the unlicensed band. In non-stand-alone configuration, WTRUs 102a, 102b, 102c can communicate / connect with gNBs 180a, 180b, 180c while also communicating / connecting with another RAN (e.g., eNode-Bs 160a, 160b, 160c). For example, WTRUs 102a, 102b, 102c can implement the DC principle to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In non-stand-alone configuration, eNode-Bs 160a, 160b, 160c can act as the mobility anchor for WTRUs 102a, 102b, 102c, and gNBs 180a, 180b, 180c can provide additional coverage and / or throughput for serving WTRUs 102a, 102b, 102c.

[0066] Each of gNBs 180a, 180b, 180c can be associated with a specific cell (not shown) and can be configured to handle radio resource management decisions, handover decisions, user scheduling in UL and / or DL, support for network slicing, DC, interworking between NR and E-UTRA, routing of user plane data to user plane functions (UPFs) 184a, 184b, routing of control plane information to access and mobility management functions (AMFs) 182a, 182b, etc. As Figure 1D shown, gNBs 180a, 180b, 180c can communicate with each other via the Xn interface.

[0067] Figure 1DThe illustrated CN 106 may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one session management function (SMF) 183a, 183b, and may include data networks (DN) 185a, 185b. Although the foregoing elements are depicted as part of CN 106, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0068] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via the N2 interface and may act 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 specific SMF 183a, 183b, managing the registration area, terminating non-access stratum (NAS) signaling, mobility management, etc. The AMF 182a, 182b may use network slicing in order to customize the CN support for the WTRUs 102a, 102b, 102c based on the type of service utilized by the WTRUs 102a, 102b, 102c. For example, different network slices may be established for different use cases, such as services that rely on ultra-reliable low-latency (URLLC) access, services that rely on enhanced massive mobile broadband (eMBB) access, services for machine type communication (MTC) access, etc. The AMF 182a, 182b may provide control plane functions for exchange between the RAN 104 and other RANs (not shown) that employ other radio technologies (e.g., LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies such as WiFi).

[0069] The SMF 183a, 183b may be connected to the AMF 182a, 182b in the CN 106 via the N11 interface. The SMF 183a, 183b may also be connected to the UPF 184a, 184b in the CN 106 via the N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b and configure the routing of traffic through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating UE IP addresses, managing PDU sessions, controlling policy enforcement and QoS, providing DL data notifications, etc. The PDU session type may be IP-based, non-IP-based, Ethernet-based, etc.

[0070] UPF 184a and 184b can be connected to one or more of gNBs 180a, 180b, and 180c in RAN 104 via the N3 interface. The N3 interface can provide access to a packet-switched network (such as the Internet 110) for WTRU 102a, 102b, and 102c to facilitate communication between WTRU 102a, 102b, and 102c and IP-enabled devices. UPF 184a and 184b can perform other functions, such as routing and forwarding data packets, enforcing user-plane policies, supporting multi-homed PDU sessions, handling user-plane QoS, buffering DL data packets, providing mobility anchoring, etc.

[0071] CN 106 can facilitate communication with other networks. For example, CN 106 can include or communicate with an IP gateway (such as an IP Multimedia Subsystem (IMS) server) that serves as an interface between CN 106 and the PSTN 108. In addition, CN 106 can provide access to other networks 112 for WTRU 102a, 102b, and 102c, and the other networks 112 can include other wired and / or wireless networks owned and / or operated by other service providers. In one embodiment, WTRU 102a, 102b, and 102c can be connected to local DNs 185a and 185b via the N3 interface to UPF 184a and 184b and the N6 interface between UPF 184a and 184b and DNs 185a and 185b.

[0072] In view of Figure 1A —1D and Figure 1A —the corresponding description of 1D, one or more or all of the functions related to one or more of the following descriptions herein can be performed by one or more emulation devices (not shown): WTRU 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 (one or more) devices described herein. The emulation devices can be one or more devices configured to emulate one or more or all of the functions described herein. For example, the emulation devices can be used to test other devices and / or simulate network and / or WTRU functions.

[0073] The simulation device can be designed to implement one or more tests on other devices in a laboratory environment and / or an operator network environment. For example, one or more simulation devices can perform one or more or all functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network, in order to test other devices within the communication network. One or more simulation devices can perform one or more or all functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The simulation device can be directly coupled to another device for testing and / or performing tests using over-the-air wireless communication.

[0074] One or more simulation devices can perform one or more (including all) functions while not being implemented / deployed as part of a wired and / or wireless communication network. For example, the simulation device can be utilized in a test scenario in a test laboratory and / or a non-deployed (e.g., test) wired and / or wireless communication network to implement tests on one or more components. One or more simulation devices can be test devices. The simulation device can send and / or receive data using direct RF coupling and / or wireless communication via an RF circuit (e.g., which can include one or more antennas).

[0075] The basic NTN includes an over-the-air or space-borne platform that transmits signals from a land-based gNB to a WTRU via a gateway (GW) and vice versa. Current NR NTN supports WTRUs with omnidirectional antennas and linear polarization at power class 3, or very small aperture terminal (VSAT) terminals with directive antennas and circular polarization. Support for LTE-based narrowband IoT (NB-IoT) and eMTC type devices has been standardized. Regardless of the device type, it is assumed that all current NTN WTRUs have global navigation satellite system (GNSS) capabilities.

[0076] Airborne or spaceborne platforms are classified by orbit. Current standardization focuses on low Earth orbit (LEO) satellites with altitude ranges of 300 - 1500 km and geostationary orbit (GEO) satellites at an altitude of 35,786 km. Other platform classifications (such as medium Earth orbit (MEO) satellites with altitude ranges of 7000 - 25000 km and high altitude platform stations (HAPS) at altitudes of 8 - 50 km) are assumed to be implicitly supported. Satellite platforms are also classified as having either a "transparent" payload or a "regenerative" payload. A transparent satellite payload performs frequency conversion and RF amplification in both the uplink and downlink, where multiple transparent satellites may be connected to a land-based gNB. A regenerative satellite payload can implement a complete gNB or gNB distributed unit (DU) on the satellite. The regenerative payload can perform digital processing on the signal, including demodulation, decoding, re-encoding, re-modulation, and / or filtering.

[0077] Figure 2 The radio interface of NTN is shown. NTN can include a core network (CN), gNB, gateway (GW), satellites (such as SAT 1 and SAT 2), and WTRU. NTN can include a feeder link, which can be a wireless link between the GW and the satellite (such as feeder link SAT1 and feeder link SAT2). NTN can include a service link, which can be a radio link between the satellite and the WTRU. NTN can include an inter-satellite link (ISL), which can be a transmission link between satellites. The ISL is only supported by regenerative payloads and can be a 3GPP radio or a proprietary optical interface.

[0078] Depending on the satellite payload configuration, different 3GPP radio interfaces can be used for each radio link. In a transparent payload, the NR-Uu radio interface can be used for both the service link and the feeder link. For a regenerative payload, the NR-Uu interface can be used on the service link, and a satellite radio interface (SRI) can be used for the feeder link. The detailed user plane / control plane (UP / CP) protocol stacks for each payload configuration can be found in Sections 5.1 and 5.2 of 3GPP TR 38.821.

[0079] NTN satellites can support multiple cells. Each cell can include one or more satellite beams. The satellite beams cover a footprint on the Earth, such as a terrestrial cell, and can range in diameter from 100 - 1000 km in LEO deployments and from 200 - 3500 km in GEO deployments. The beam footprint in GEO deployments remains fixed relative to the Earth, and the area covered by the beam / cell in LEO deployments changes over time due to satellite movement. This beam movement can be classified as "Earth-moving", where the LEO beam continuously moves across the Earth, or as "Earth-fixed", where the beam is steered to maintain coverage of a fixed location until a new cell exceeds the footprint with discrete and coordinated changes.

[0080] Due to the altitude and beam diameter of the NTN platform, the round-trip time (RTT) and maximum differential delay can be significantly greater than those of terrestrial systems. In a typical transparent NTN deployment, the RTT can range from 25.77 ms (LEO @ 600 km altitude) to 541.46 ms (GEO), and the maximum differential delay can range from 3.12 ms to 10.3 ms. The RTT of a regenerative payload can be approximately half of the RTT of a transparent payload, as the transparent configuration includes both a service link and a feeder link, while the RTT of a regenerative payload only considers the service link. To minimize the impact on existing NR systems (e.g., to avoid preamble ambiguity or to properly time the receive window), the WTRU can perform timing pre-compensation prior to initial access.

[0081] The timing pre-compensation process may require the WTRU to obtain its position via GNSS and the feeder link (or common) delay and satellite position via satellite ephemeris data. The satellite ephemeris data is broadcast periodically in the system information and includes satellite velocity, direction, and rate. The WTRU can then estimate the distance to the satellite, thereby estimating the delay, and then add the feeder link delay component to obtain the complete WTRU-gNB RTT, which can then be used to offset timers, receive windows, or timing relationships. Assume that frequency compensation is performed by the network.

[0082] Other key enhancements in NTN relate to WTRU mobility and measurement reporting. The difference in RSRP between the cell center and the cell edge is not as pronounced as in terrestrial systems. This, combined with much larger areas of cell overlap, results in traditional measurement-based mobility becoming less reliable in the NTN environment. New conditional handovers and measurement reporting triggers are introduced that depend on location and time, the details of which need to be confirmed. Enhanced mobility is of particular concern in LEO deployments, where, due to satellite movement, even stationary WTRUs are expected to perform mobility approximately every 7 seconds, depending on the deployment characteristics.

[0083] In Figure 3 summarizes the Radio Link Failure (RLF) and reconstruction procedures. When in the RRC_CONNECTED state, the WTRU can perform Radio Link Monitoring (RLM) on the serving cell. The WTRU can be configured with timers and counters for use when evaluating RLF and performing radio link recovery or reconstruction. When the RRC detects N310 consecutive "out-of-sync" indications from L1 (RLM), a timer with length or duration T310 can be started. While T310 is running, the WTRU can attempt to restore the radio link on the serving cell. If the RRC receives N311 consecutive "in-sync" indicators from L1, then the WTRU can consider the radio link to be restored and can continue normal operation and continue RLM on the serving cell. If T310 expires, then the WTRU can consider it an RLF. When an RLF is detected, a timer with length or duration T311 can be started, and the WTRU can perform a cell search to determine if there is an available suitable cell on which the WTRU can perform RRC connection reconstruction. If the timer T311 expires before the WTRU finds a suitable cell, then the WTRU can enter the RRC_IDLE mode with the cause of "RRC connection failure". If the WTRU does find a suitable cell (which can include the original cell), then that cell can be selected, T311 can be stopped, T301 can be started, and the RRC connection reconstruction procedure can be started. If the timer T301 expires before the RRC connection reconstruction is complete, then the WTRU can enter the idle mode with the cause of "RRC connection failure".

[0084] RLF can occur, for example, when the WTRU leaves coverage (e.g., enters a tunnel or moves to a rural area outside of cellular coverage). RLF can occur, for example, as a result of a too-late handover, whereby an RLF is detected on the serving cell before the handover can be completed. Figure 3The first part of the procedure (N310, T310, N311) is intended to allow the WTRU the opportunity to recover the radio link in case of a temporary problem. After T310 expires, the second part of the procedure is intended to allow the WTRU to attempt to re - establish a connection on the same cell or another cell without having to fully release the connection.

[0085] NB - IoT relies on RLF and re - establishment to perform mobility in RRC_CONNECTED as measurement reports or handovers are not supported. The reason is that when NB - IoT was initially standardized, it targeted use cases of fixed devices such as power meters. However, mobile devices quickly entered the market (e.g., bike rentals communicating using NB - IoT). Once an RLF is detected (e.g., after T310 expires), the WTRU can perform a cell search and then perform a re - establishment to a suitable cell. For mobile devices, the use of the existing RLF procedure was determined to be inefficient as no measurements were performed on neighboring cells before the RLF occurred. The delay caused by the WTRU having to perform a cell search to detect a suitable cell results in significant interruptions during which the WTRU is neither reachable (e.g., by paging) nor able to communicate (e.g., send an uplink report). To reduce the interruptions, the RLF procedure was enhanced for NB - IoT. The enhancements are summarized in Figure 4 In

[0086] To reduce the cell detection time and thus the total re - establishment time when an RLF occurs, neighboring cell measurements in RRC_CONNECTED before RLF are introduced. If measurements are performed before the RLF occurs, then the target cell can be known and the re - establishment can be performed faster during T311 (i.e., no cell search is required).

[0087] Neighboring cell measurements can be triggered when the RSRP of the serving cell measurement is below a configured threshold and the delta RSRP (if the change in RSRP is greater than the delta threshold within a configured time period). This is defined in section 5.5.8 of 3GPP TS 36.331 (Measurements in NB - IoT) as follows:

[0088] When transitioning to RRC_CONNECTED mode, the UE shall:

[0089] 1> If neighCellMeasCriteria exists in SystemInformationBlockType3 - NB:

[0090] 2> Set the NRSRP RefSet to the latest result of the serving cell measurement for cell selection / reselection evaluation;

[0091] 2> If the relaxed monitoring criteria defined in TS 36.304 [4] are not met:

[0092] 3> Start T326 with the value t-MeasureDeltaP;

[0093] When in RRC_CONNECTED mode, after performing the measurement, the UE shall:

[0094] 1> Use the NRSRP measurement for the measured carrier and nrs-PowerOffsetNonAnchor corresponding to the measured carrier hereinafter;

[0095] 1> If neighCellMeasCriteria exists in SystemInformationBlockType3-NB:

[0096] 2> If (NRSRP Ref -(NRSRP-PowerOffsetNonAnchor)) > s-MeasureDeltaP:

[0097] 3> Set NRSRP Ref =(NRSRP - nrs-PowerOffsetNonAnchor);

[0098] 3> Start or restart T326 with the value t-MeasureDeltaP;

[0099] 1> If neighCellMeasCriteria does not exist in SystemInformationBlockType3-NB; or

[0100] 1> If T326 is running:

[0101] 2> If (NRSRP - nrs-PowerOffsetNonAnchor) < s-MeasureIntra, perform intra-frequency measurement as defined in TS36.133

[16] ;

[0102] 2> If (NRSRP - nrs-PowerOffsetNonanchor) < s-MeasureInter, perform inter-frequency measurement as defined in TS 36.133

[16] .

[0103] In IoT-NTN, the introduction of the above process is proposed. However, NTN deployment is different from that of the terrestrial network (TN). There are several scenarios to consider. The target cell coverage can overlap with the source cell coverage, similar to TN (e.g., GEO) (overlapping coverage scenario). Cell A can be switched to Cell B at a given time (e.g., earth-fixed scenario) (discrete change scenario). Cell A can disappear before Cell B appears (discontinuous coverage scenario). Compared with the terrestrial network, due to more uniform RSRP measurements across cells, RSRP-based triggers may be less effective in NTN cells. It can be more deterministically known in NTN whether a cell change has occurred or whether there is a temporary radio link problem. Time-based information can be considered, including 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).

[0104] Time-based triggers can be used to initiate measurements. Distance-based triggers can be used to initiate measurements. However, if this is based only on the serving cell, then this may not be sufficient to ensure that the WTRU can measure the target cell at the correct or optimal time in all scenarios, or trigger RLF at the correct or optimal time.

[0105] Measurement triggers can be based on both the current cell service time and the next cell service time. The trigger for measuring adjacent cells can be based on the time when the serving cell is going to stop (e.g., based on the parameter t-service) and the target cell start time (e.g., based on the parameter t-serviceStart). When the target cell is available (i.e., the WTRU considers both the source and target cell coverage times), measurements can be initiated (e.g., only initiated). In the case where the cell 1 stop time is later than the cell 2 start time (Scenario 1: overlapping coverage), the measurement can occur before RLF (e.g., at a configurable time offset before cell 1 stops). In the case where the cell 1 stop time is equal to the cell 2 start time (Scenario 2: discrete change), the measurement can occur at the time of RLF. If cell 1 stops before cell 2 starts (Scenario 3: discontinuous coverage), the measurement can occur at a time after RLF.

[0106] The reconstruction trigger can be based on both the current cell service time and the next cell service time. The combination of the current cell stop time (e.g., based on the parameter t-service) and the future cell start time (e.g., based on the parameter t-serviceStart) can be used as a trigger for performing RRC connection reconstruction, instead of using T310 expiration / RLF to trigger RRC connection reconstruction. In the case where cell 1 stops, the out-of-sync count and T310 can be reduced or removed. However, when cell 1 has not stopped (for traditional RLF recovery), the out-of-sync count and T310 can be performed. When the current cell stops and the next cell starts, T311 can be started.

[0107] Although it makes sense to start measuring the future cell (if possible) within a short period before the WTRU loses coverage of the current cell so that the WTRU can change cells faster when coverage is lost (similar to using the RSRP threshold in NB-IoT to indicate that the WTRU has reached the cell edge), in the NTN network, to ensure that the WTRU does not attempt to measure the future cell before it is available (thus wasting measurement effort and unnecessarily consuming power), the WTRU should also consider the start time of the newly arrived cell. By considering the stop time of the current cell and the start time of the newly arrived / future cell, a single solution can handle various scenarios in NTN. The parameter "t-service" can be used, for example, to provide the current cell stop time. The current cell stop time can be provided by the serving cell. The current cell stop time can be provided in the system information (e.g., system information block (SIB)) and / or radio resource control (RRC) signaling. The parameter "t-serviceStart" can be used, for example, to provide the next cell start time. The next cell start time can be provided by the serving cell. The next cell start time can be provided in the system information (e.g., system information block (SIB)) and / or radio resource control (RRC) signaling.

[0108] The current RLF procedures in LTE and NR are designed to provide the WTRU with sufficient time to recover the radio link on the current cell in the case of a temporary radio link problem. For TN, it is difficult for the WTRU to determine whether the out-of-synchronization is due to a temporary radio link problem or a change in the cell or coverage situation. For NTN, the stop time of the current cell and the start time of the neighboring cell (e.g., using the parameter "t-Service" provided in the system information) can be utilized to determine whether the out-of-synchronization is due to a cell change or a potential radio condition problem. Therefore, time information (e.g., the current cell stop time and / or the next cell start time) can be used to reduce or completely eliminate N310 and T310, and directly trigger RLF based on the time information, instead of using the existing procedures (e.g., counting the N310 out-of-synchronization indication before declaring RLF and then waiting for T310 to expire). The term "trigger RLF" can refer to triggering a process related to RLF that will perform, for example, cell search and RRC reconstruction. This can be done without considering a failed radio link in the traditional sense. For example, instead of "trigger RLF", "trigger RRC reconstruction" or "trigger cell search" can be used.

[0109] Figure 5 An example of RLF enhancement in an overlapping coverage scenario is shown. The WTRU can start on a first cell (e.g., cell 1) and move to a second cell (e.g., cell 2). In this example, there is a period during which the WTRU is in the coverage of both cell 1 and cell 2, similar to what is expected in TN. The WTRU can receive time information regarding when cell 1 stops and when cell 2 starts. The WTRU can receive a time offset (e.g., X seconds) related to the stop time of cell 1. Before this time offset time of the stop time of cell 1, the WTRU does not need to perform measurements on cell 2. The WTRU can receive one or more radio quality thresholds, such as an RSRP threshold and an RSRP difference threshold.

[0110] Since the coverage of cell 2 starts before the coverage of cell 1 ends, when the time is within the time offset (e.g., X seconds) of the stop time of cell 1, the WTRU can perform measurements on cell 2. The measurement can be triggered before RLF occurs due to the stop of cell 1 coverage, but the trigger for the measurement can 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 can perform measurements after cell 2 appears and before cell 1 stops, which can ensure that cell 2 has been detected and measured, and thus can accelerate or eliminate the cell search time after RLF.

[0111] In addition to measurement triggers, cell coverage time information can also be used to trigger a reconstruction. Until cell 1 stops, the WTRU can continue to perform RLM, asynchronous indication counting, and if an asynchronous situation is detected, use the T310 timer to attempt to restore the radio link on cell 1. If it is known that cell 1 has stopped, or if it is known that cell 1 will stop before T310 expires, then it may not be necessary to perform asynchronous indication counting or start T310 to attempt to restore the radio link on cell 1. Instead, the WTRU can trigger an RLF (or reconstruction to cell 2) on cell 1 immediately based on the stop time of cell 1 without using T310, or based on the detection of a single or reduced number of asynchronous indications. The WTRU can consider the start time of cell 2 when triggering the reconstruction. This is mainly for other scenarios where cell 2 has started so that an RLF / reconstruction can be triggered immediately when cell 1 stops.

[0112] When triggering the reconstruction process, the WTRU can utilize a separate or scaled T311, which can be shorter than the T311 used for reconstruction due to an RLF triggered in a conventional manner, because most of the time allowed by T311 is not needed since the target cell is already known, detected, and measured.

[0113] In Figure 5 the scenario where cell 2 is available and the WTRU is within a time offset (e.g., X seconds) of the stop time of cell 1, measurements can be triggered. The RLF / reconstruction can be triggered directly without T310 when cell 1 stops.

[0114] In an example, the WTRU can trigger an RLF / reconstruction before the stop time of cell 1. For example, an RLF / reconstruction can be triggered immediately at the expected start time of cell 2. Alternatively, the WTRU can start measurements immediately at the expected start time of cell 2 and trigger an RLF / reconstruction when cell 2 is detected and / or when the cell quality level criteria are met. The cell quality level criteria can be, for example, that the measured signal quality of cell 2 is higher than the RSRP and / or RSRQ thresholds, and / or the measured signal quality of cell 1 is lower than the RSRP and / or RSRQ thresholds.

[0115] Figure 6 An example method 600 for enhancing RLF in an overlapping coverage scenario is shown. The WTRU can be in the current coverage of a first cell (e.g., cell 1) and can move into the coverage of a second cell (e.g., cell 2). There can be a period of time when the WTRU is in the overlapping coverage of both cell 1 and cell 2.

[0116] The WTRU may receive configuration information 610. The configuration information may indicate time information that indicates when cell 1 stops and when cell 2 starts. The configuration information may indicate a time offset value (e.g., X seconds) related to the stop time of cell 1. The configuration information may indicate one or more radio quality thresholds, such as an RSRP threshold and an RSRP difference threshold. The configuration information may be received in one message or multiple messages. The configuration information may be provided, for example, in system information or may be provided in RRC dedicated signaling. The configuration information may include the position information of the current satellite and adjacent satellites, and the WTRU may use this position information to estimate the current cell stop time and the next cell start time instead of an explicit time indication.

[0117] The WTRU may perform measurements 620 on cell 2. The WTRU may perform the measurements when a triggering condition occurs. The triggering condition may be before RLF. The measurements may be triggered based on a serving cell RSRP threshold and / or an RSRP difference threshold. For example, if the serving cell RSRP is higher or lower than the RSRP threshold, then the measurements may be triggered. The measurements may be triggered based on the stop time of cell 1 and the start time of cell 2. The measurements may be triggered under the condition that cell 1 is within a time offset (e.g., X seconds) of stopping and cell 2 is available or within the WTRU coverage. The measurements may be triggered based on the RSRP threshold, cell 1 is within the time offset of stopping, and cell 2 is available. In this case, the WTRU may perform the measurements after cell 2 appears and before cell 1 stops, which may ensure that cell 2 has been detected and measured and thus may accelerate or eliminate the cell search time after RLF.

[0118] Until cell 1 stops, the WTRU may continue to perform RLM, asynchronous indication counting, and if an asynchronous situation is detected, use the T310 timer to attempt to restore the radio link on cell 1. If it is known that cell 1 has stopped, or if it is known that cell 1 will stop before T310 expires, then it may not be necessary to perform asynchronous indication counting or start T310 to attempt to restore the radio link on cell 1.

[0119] A WTRU may trigger or declare a Radio Link Failure (RLF) 630. The WTRU may trigger or declare an RLF on cell 1 (or re-establishment to cell 2) based on the cell 1 stop time and without using T310. T310 may not need to be started because it is known that cell 1 has stopped and the WTRU cannot regain synchronization with cell 1. The WTRU may trigger an RLF on cell 1 (or re-establishment to cell 2) based on detecting a single or reduced number of out-of-sync indications. The WTRU may trigger an RLF before the stop time of cell 1. For example, the 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 may trigger an RLF 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 higher than the RSRP and / or RSRQ thresholds, and / or the measured signal quality of cell 1 is lower than the RSRP and / or RSRQ thresholds. The WTRU may start the T311 timer upon RLF.

[0120] A 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 consider the start time of cell 2 when triggering re-establishment. Since cell 2 has started, an RLF / re-establishment may be triggered immediately when cell 1 stops. The re-establishment may be triggered without T310. The WTRU may trigger re-establishment before the stop time of cell 1. For example, the 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 may 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 higher than the RSRP and / or RSRQ thresholds, and / or the measured signal quality of cell 1 is lower than the RSRP and / or RSRQ thresholds.

[0121] When triggering the re-establishment procedure, the WTRU may utilize a separate or scaled T311 timer which may be shorter for re-establishment than the T311 used for an RLF triggered in the conventional manner because most of the time allowed by T311 is not needed since the target cell (i.e., cell 2) has already been known, detected, and measured.

[0122] Figure 7 An example of RLF enhancement in a discrete change of the coverage scenario is shown. In Figure 7 which is similar to Figure 5, the WTRU is initiated on cell 1 and moves to cell 2. However, in this example, there is a discrete time when the current / serving cell (e.g., cell 1) stops and the newly arrived / target cell (e.g., cell 2) starts. This can be the case, for example, in some geostationary cell scenarios where a satellite beams to cells in a fixed geographical area and when one satellite moves away, a newly arrived satellite starts providing coverage to that geographical area.

[0123] In Figure 7 , for measurements, similar to Figure 5 , the WTRU can consider both the stop time of cell 1 and the start time of cell 2. In this scenario, the main trigger for measurement is the start time of cell 2. The measurement is not triggered before RLF because cell 2 is not available before RLF. The measurement of the target cell starts at the cell 1 stop time / cell 2 start time. Similar to the example in Figure 5 , in this example, the WTRU can use the cell 1 stop time to optimize or accelerate the reconstruction process even if the measurement is not yet available because the WTRU can immediately trigger RLF / reconstruction without N310 and T310. In this scenario, T311 can be reduced compared to the value used for normal RLF. However, because the time includes performing measurements on the newly arrived cell 2, the time can be longer than the time used in the scenario in Figure 5 to take it into account.

[0124] In Figure 7 , the RLF / reconstruction and the measurement of the target cell are triggered at the time of both the stop of cell 1 and the start of cell 2.

[0125] Figure 8 Illustrates an example method 800 for RLF enhancement in a discrete change of a coverage scenario. The WTRU can be in the current coverage of a first cell (e.g., cell 1) and can move to the coverage of a second cell (e.g., cell 2). There can be a period of time when the WTRU is in the overlapping coverage of both cell 1 and cell 2. When cell 1 stops and cell 2 starts, there can be a discrete time.

[0126] The WTRU can receive configuration information 810. The configuration information can indicate time information that indicates when cell 1 stops and when cell 2 starts. The configuration information can indicate one or more radio quality thresholds, such as an RSRP threshold and an RSRP difference threshold. The configuration information can be received in one message or multiple messages. The configuration information can be provided, for example, in system information or can be provided in RRC dedicated signaling. The configuration information can include the position information of the current satellite and adjacent satellites, which the WTRU can use to estimate the current cell stop time and the next cell start time instead of an explicit time indication.

[0127] The WTRU may trigger or declare an RLF 820. The WTRU may trigger or declare the RLF at the time when cell 1 stops and cell 2 starts. The WTRU may trigger or declare the RLF based on detecting a single or reduced number of out-of-sync indications after the time when cell 1 stops and cell 2 starts. The WTRU may start the T311 timer upon RLF.

[0128] The WTRU may perform measurements 830 on cell 2. The measurements 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 measurements is the start time of cell 2. The measurements are not triggered prior to RLF because cell 2 is not available prior to RLF.

[0129] The WTRU may trigger and / or perform a reconstruction procedure 840. Similar to Figure 5 the example in which the WTRU may use the cell 1 stop time to optimize or accelerate the reconstruction procedure even if the measurements are not yet available because the WTRU may immediately trigger the RLF / reconstruction without N310 and T310. In this example, T311 may be reduced compared to the value used for normal RLF, however the time may be longer than that used in the scenario of Figure 5 to take it into account because the time includes performing measurements on the newly arrived cell 2. The reconstruction procedure may be triggered at the time when cell 1 stops and cell 2 starts.

[0130] Figure 9 An example of RLF enhancement in a discontinuous coverage scenario is shown. In Figure 9 similar to Figure 5 and Figure 7 the WTRU starts on cell 1 and moves to cell 2. In this example, there is a coverage gap (i.e., a time gap) between the stop of cell 1 and the start of cell 2.

[0131] In Figure 9 similar to the example in Figure 7 measurements may not be started prior to RLF / reconstruction because cell 2 is not yet available. In this example, the WTRU may wait for the duration of the coverage gap before performing the measurements (i.e., the WTRU waits until cell 2 becomes available).

[0132] Compared with Figure 5 and 7Similar to the example in , the WTRU may trigger or declare RLF immediately when Cell 1 stops. However, in this example, an additional waiting time is used before the measurement and reconstruction processes. The waiting time may be implemented after detecting / triggering RLF due to Cell 1 stop and before starting T311 / measurement / reconstruction, or the waiting time may be implemented before triggering RLF / reconstruction. Either way, the WTRU does not need to perform out-of-sync counting (N310) or attempt to regain synchronization with Cell 1 during T310. The RLF / reconstruction process trigger is thus based on the Cell 1 stop and Cell 2 start times.

[0133] In Figure 9 the example of, similar to Figure 7 the example in , T311 may be shorter than the T311 used for normal RLF reconstruction, but longer than the value that can be used in the example in Figure 5 because measurements have not been performed before RLF, but the target cell is still known to the WTRU / UE. In this example, similar to other examples, the measurement and RLF / reconstruction are based on both the current cell stop time and the next cell start time. RLF can be directly triggered without T310, but in this example, the Cell 2 start time is the main factor triggering the start of the process in addition to skipping T310 and stopping RLM on Cell 1 based on the Cell 1 stop time.

[0134] Figure 10 Figure 1000 shows an example method for RLF enhancement in a discontinuous coverage scenario.

[0135] Figure 10 Figure 1000 shows an example method for RLF enhancement in a discontinuous coverage scenario. The WTRU may be in the current coverage of a first cell (e.g., Cell 1) and may move to the coverage of a second cell (e.g., Cell 2). There may be a time period (coverage gap) between the stop of Cell 1 and the start of Cell 2.

[0136] The WTRU may receive configuration information 1010. The configuration information may indicate time information that indicates when Cell 1 stops and when Cell 2 starts. The configuration information may indicate one or more radio quality thresholds, such as an RSRP threshold and an RSRP difference threshold. The configuration information may be received in one message or multiple messages. The WTRU may determine the coverage gap based on the Cell 1 stop time and the Cell 2 start time. The configuration information may be provided, for example, in system information or may be provided in RRC dedicated signaling. The configuration information may include the position information of the current satellite and adjacent satellites, and the WTRU may use this position information to estimate the current cell stop time and the next cell start time instead of an explicit time indication.

[0137] The WTRU may trigger or declare RLF 1020. The WTRU may trigger or declare RLF at the time when the cell 1 stops. The WTRU may trigger or declare RLF based on detecting a single or reduced number of out-of-sync indications after the time when the cell 1 stops.

[0138] The WTRU may perform measurements 1030 on cell 2. The measurements may be triggered after 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 the cell 2 start time). The WTRU may start the T311 timer when cell 2 becomes available (i.e., at the cell 2 start time).

[0139] The WTRU may trigger and / or perform a reconstruction procedure 1040. Similar to Figure 7 the example in Figure 5 T311 may be shorter than the T311 used for normal RLF reconstruction, but longer than the value that can be used in the example in

[0140] Figure 11 An example flowchart of the enhanced RLF / reconstruction procedure is shown.

[0141] The WTRU may receive configuration information 1105. The configuration information may indicate the stop time of the current cell / serving cell (e.g., cell 1), the start time of the next cell / newly arrived cell (e.g., cell 2), and a time offset value (e.g., X seconds) with respect to the stop time of cell 1. If the time offset value is before the stop of cell 1, the time offset value may be used to determine when to start the measurements. The configuration information may be provided, for example, in the system information or may be provided in RRC dedicated signaling. The configuration information may include other criteria, such as an RSRP threshold for determining when to start the measurements or for determining the length of the coverage gap. The configuration information may include the position information of the current satellite and adjacent satellites, which the WTRU may use to estimate the stop time of the current cell and the start time of the next cell instead of an explicit time indication.

[0142] The WTRU may determine whether the time until the stop of the current cell is within the received time offset value 1105. If not, the WTRU may continue radio link monitoring until the time until the stop of the current cell is within the received time offset value.

[0143] If the time to the stop of the current cell is within the received time offset value, the WTRU may determine whether the next cell has been started 1115. If the next cell has not been started, the WTRU may determine whether the current cell has stopped 1140.

[0144] If the start time of the next cell has passed and the next cell has been started, the WTRU may perform measurements on the next cell 1120. The measurements may be used to detect and determine the cell quality level.

[0145] The WTRU may determine whether the current cell has stopped 1125. Until the current cell stops, the WTRU may perform measurements on the next cell.

[0146] When the current cell stops, the WTRU may trigger an RLF on the current cell and stop RLM 1130. The WTRU may trigger an RLF and stop RLM on the current cell without the timer T310 to attempt to restore the radio link on the current cell.

[0147] The WTRU may start a timer T311 with a shorter (e.g., shortest) value 1135. The WTRU may perform an RRC reestablishment procedure 1170.

[0148] If the WTRU determines that the next cell has not been started, the WTRU may determine whether the current cell has stopped 1140. If the current cell has stopped, the WTRU may trigger an RLF without the timer T310 1145. If the current cell has not stopped, the WTRU determines whether the next cell has been started 1115.

[0149] If the current cell has stopped and the next cell has not been started before that time, the WTRU may trigger an RLF without using the timer T310 and may stop RLM on the current cell to attempt to restore the radio link on the current cell 1145.

[0150] The WTRU may determine whether the next cell has been started 1150. If the next cell has not been started, the WTRU may wait 1155 and make another determination as to whether the next cell has been started 1150. The waiting time may be the duration of the coverage gap (e.g., in a discontinuous scenario). If the next cell has been started, the WTRU may start a timer T311 with a longer value 1160. The longer value may be longer relative to the T311 value from 1135.

[0151] The WTRU may start measurements on the next cell 1165.

[0152] The WTRU may perform an RRC reestablishment procedure 1170.

[0153] In Figure 11 the example, the WTRU may determine the current cell stop time and the next cell start time to determine when to initiate measurements on the next cell, when to trigger RLF (and stop RLM on the current cell), and when to perform a reconstruction on the next cell.

[0154] The new T311 value may be signaled explicitly, or the new T311 value may be determined by applying an offset, or the new T311 value may be scaled depending on when the measurement is performed (i.e., before or after RLF). If the measurement has been performed, the new T311 value may be shorter. The new T311 value may be used (e.g., only used) to attempt a reconstruction on the indicated next NTN cell. When the new T311 expires, the WTRU may fallback to the legacy RLF procedure. That is, the WTRU may perform a cell search for other cells and use the legacy T311 timer that triggers an RRC connection failure upon expiration.

[0155] The WTRU may report whether the reconstruction was triggered due to a true RLF or due to a time-based trigger. This may be indicated using a new RRC reconstruction cause. This may be indicated using a new explicit indication in an uplink message. This may be logged and reported to the network at a later time, e.g., as part of an RLF report for MDT / SON. The WTRU may report whether a fallback has occurred (i.e., whether the new T311 was first applied due to the expiration of the previous cell stop time, but then the WTRU failed to reconstruct to the new cell within the (new) T311). This may occur if the WTRU reconstructs to any new cell (including the original cell or the failed cell) within the legacy T311 timer.

[0156] Some randomization may be applied to the reconstruction time to avoid multiple WTRUs simultaneously initiating random access to perform a reconstruction due to the previous cell stopping for multiple WTRUs simultaneously and / or the new cell starting for multiple WTRUs simultaneously. The WTRU may generate the reconstruction 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 selecting any value in a range, e.g., 0 - 100 percent, comparing it to a threshold, and selecting one time if the random value is below the threshold and another time if the random value is above the threshold.

[0157] In an example where the WTRU triggers a re-establishment after the WTRU appears in cell 2 but before cell 1 stops, the WTRU may apply randomization to the re-establishment trigger time. This temporally spreads the re-establishment attempts from multiple WTRUs to minimize RACH and / or CN signaling congestion. The WTRU may, for example, calculate a random time within a time window that starts at the point where cell 2 starts and ends at the point where cell 1 stops (i.e., during a time period where it is known that both cell 1 and cell 2 provide coverage).

[0158] 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 may select a semi-random value from within a uniform distribution calculated within that range.

[0159] The WTRU may calculate a time range based on the time of detecting and measuring cell 2 and the expected stop time of cell 1.

[0160] The WTRU may consider service, bearer, or traffic characteristics when determining the time to trigger RLF / re-establishment. For example, if the WTRU has an ongoing data exchange (e.g., sending or receiving), then the WTRU may delay declaring RLF until the time the data exchange ends, or until the time cell 1 stops. The WTRU may use a data inactivity timer to determine when the data exchange stops, such as a DRX inactivity timer. If the WTRU is configured with delay-tolerant services, the WTRU may trigger re-establishment earlier (e.g., once cell 2 starts). If the WTRU has delay-sensitive services, then re-establishment may be delayed to take advantage of cell 1 availability for as long as possible.

[0161] In some examples, the WTRU may additionally consider NTN network measurements. 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 measurements on the TN to try and find a suitable cell that may be faster, or that is selected when NTN re-establishment fails. In some examples, TN measurements may only be triggered during an expected coverage gap. In some examples, once RLF is triggered, the WTRU may perform TN measurements. In some examples, TN measurements may only be performed if an NTN cell has not been successfully selected within the (new) T311 time.

[0162] In some examples, more than one target NTN cell may be provided to the WTRU. In such a case, the WTRU may consider the start times of all of these target cells and perform measurements on those cells in accordance with their respective start times. If more than one cell is provided as a target, T311 may be adjusted.

[0163] As an alternative or supplement to the start and stop times of the current cell and neighboring cells, the WTRU may use distance- or location-based criteria. 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 the location measured by the WTRU (e.g., using GNSS) to a network-configured reference point. The reference point may indicate a location within cell 1, for example. 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 the location measured by the WTRU (e.g., using GNSS) to a network-configured reference point. The reference point may indicate a location within cell 2, for example.

[0164] The WTRU may monitor one or more distances and may perform an action if, for example, the distance meets / exceeds / falls below a distance threshold criterion. The distance threshold may be based on, for example, one or more of the following: the WTRU-satellite distance; the distance between the WTRU and the center of the satellite cell; the distance between the WTRU and the satellite coverage area; the distance between the WTRU and a ground-based gNB; the distance between the WTRU and the ground coverage edge; and the distance between the WTRU and a reference point.

[0165] Figure 12 An example method of enhanced RLF / re-establishment 1200 is shown. The WTRU may receive configuration information 1210. The configuration information may indicate time information that indicates the stop time of a first cell and the start time of a second cell. The first cell may be the 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) related to the stop time of the first cell. The configuration information may indicate one or more radio quality thresholds, such as an RSRP threshold and an RSRP difference threshold. The configuration information may be received in one message or multiple messages. The configuration information may be provided, for example, in system information or may be provided in RRC dedicated signaling. The configuration information may include the location information of the current satellite and neighboring satellites, which the WTRU may use to estimate the current cell stop time and the next cell start time instead of an explicit time indication.

[0166] The WTRU may perform radio link monitoring (RLM) 1220 of the first cell. The WTRU may determine that the first cell has stopped (1230). The determination that the first cell has stopped may be based on received information indicating the stop time of the first cell. The WTRU may stop RLM measurements on the current cell 1240. The WTRU may initiate a radio resource control (RRC) connection re-establishment procedure on the second cell in response to the determination that the first cell has stopped 1250.

[0167] The WTRU may perform measurements on a second cell. The measurements on the second cell may be performed under the condition that the first cell has stopped and the second cell has been started. The measurements on the second cell may be performed when the current cell stop time is within the received stop time offset value. Under the condition that the first cell stops before the second cell is started, the WTRU may delay initiating a connection reestablishment procedure on the second cell and until the second cell is started. The measurements on the second cell may be performed before a radio link failure (RLF) occurs. The measurements on the second cell may be performed when the RLF occurs. The WTRU may perform RRC connection reestablishment based on the stop time of the first cell and the start time of the second cell. The RRC connection reestablishment may be performed without the expiration of the T310 timer. The WTRU may trigger RLF or RRC connection reestablishment when the cell quality level criteria are met. The cell quality level criteria may include that the measured signal quality of the second cell is higher than the RSRP or RSRQ threshold. The cell quality level criteria may include that the measured signal quality of the first cell is lower than the RSRP or RSRQ threshold.

[0168] Although the features and elements have been described above in specific combinations, those of ordinary skill in the art will understand that each feature or element may be used alone or in any combination with other features and elements. Additionally, the methods described herein may be implemented in a computer program, software, or firmware that is incorporated into a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (sent 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 storage devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM discs and digital versatile discs (DVDs). A processor associated with the software may be used to implement a radio frequency transceiver used in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

1. A method implemented by a wireless transmit / receive unit (WTRU), the method comprising: Receiving configuration information, wherein the configuration information includes an indication of a stop time of a first cell and a start time of a second cell; Performing radio link monitoring (RLM) measurements on the first cell; Determining that the first cell has stopped based on the received indication of the stop time of the first cell; Stopping the RLM measurements on the first cell; And In response to the determination that the first cell has stopped, initiating a radio resource control (RRC) connection reestablishment procedure on the second cell.

2. The method according to claim 1, wherein the first cell is a current cell, and the second cell is an adjacent cell or a target cell.

3. The method according to any one of claims 1 to 2, wherein the configuration information further includes a time offset value, wherein the time offset value is related to the stop time of the first cell.

4. The method according to any one of claims 1 to 3, further comprising: Performing measurements on the second cell before the first cell stops and under the condition that the second cell has started.

5. The method according to any one of claims 1 to 4, wherein the measurements on the second cell are performed when the stop time of the first cell is within the received stop time offset value.

6. The method according to any one of claims 1 to 5, further comprising: Delaying the initiation of the connection reestablishment procedure on the second cell under the condition that the first cell stops before the second cell starts and until the second cell starts.

7. The method according to any one of claims 1 to 6, wherein the measurements on the second cell are performed before the occurrence of a radio link failure (RLF) or at the time of the occurrence of the RLF.

8. The method according to any one of claims 1 to 7, further comprising: Performing RRC connection reestablishment based on the stop time of the first cell and the start time of the second cell.

9. The method according to any one of claims 1 to 8, wherein the RRC connection reestablishment is performed without the expiration of the T310 timer.

10. The method according to any one of claims 1 to 9, further comprising: Triggering a radio link failure (RLF) or an RRC connection reestablishment under the condition that a cell quality level criterion is met, wherein the cell quality level criterion includes at least one of the following: the measured signal quality of the second cell is higher than an RSRP or RSRQ threshold, and the measured signal quality of the first cell is lower than an RSRP or RSRQ threshold.

11. A wireless transmit / receive unit (WTRU) comprising: A transceiver; And A processor, wherein: The transceiver is configured to receive configuration information, wherein the configuration information includes 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 on the first cell; The processor is further configured to determine that the first cell has stopped based on the received indication of the stop time of the first cell; The processor is further configured to stop the RLM measurement on the first cell; and The processor is further configured to initiate a radio resource control (RRC) connection reestablishment procedure on the second cell in response to the determination that the first cell has stopped.

12. The WTRU according to claim 11, wherein the first cell is the current cell, and the second cell is an adjacent cell or a target cell.

13. The WTRU according to any one of claims 11 to 12, wherein the configuration information further includes a time offset value, and the time offset value is related to the stop time of the first cell.

14. The WTRU according to any one of claims 11 to 13, wherein: The processor is further configured to perform a measurement on the second cell before the first cell stops and under the condition that the second cell has been started.

15. The WTRU according to any one of claims 11 to 14, wherein the measurement on the second cell is performed when the stop time of the first cell is within the received stop time offset value.

16. The WTRU according to any one of claims 11 to 15, wherein: The processor is further configured to delay initiating the connection reestablishment procedure on the second cell under the condition that the first cell stops before the second cell starts and until the second cell starts.

17. The WTRU according to any one of claims 11 to 16, wherein the measurement on the second cell is performed before the occurrence of a radio link failure (RLF) or at the time of the occurrence of the RLF.

18. The WTRU according to any one of claims 11 to 17, wherein: The processor is further configured to perform RRC connection reestablishment based on the stop time of the first cell and the start time of the second cell.

19. The WTRU according to any one of claims 11 to 18, wherein the RRC connection reestablishment is performed without the expiration of the T310 timer.

20. The WTRU according to any one of claims 11 to 19, wherein: The processor is further configured to trigger a radio link failure (RLF) or an RRC connection reestablishment under the condition that a cell quality level criterion is met, and the cell quality level criterion includes at least one of the following: the measured signal quality of the second cell is higher than an RSRP or RSRQ threshold, and the measured signal quality of the first cell is lower than an RSRP or RSRQ threshold.

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