Methods for enhanced mobility in wireless systems

Abstract

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

Description

[Technical field]

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

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 652,163, filed April 3, 2018, and U.S. Provisional Patent Application No. 62 / 736,290, filed September 25, 2018.

[0003] Mobile communications are evolving incrementally, and mobile networks are on the doorstep of the fifth generation (5G). As with previous generations, new use cases have contributed greatly in setting the requirements for the new systems. The 5G air interface and its New Radio (NR) access technology are expected to enable use cases such as improved broadband performance (IBB), industrial control and communications (ICC), and vehicular applications (V2X), as well as massive machine-type communications (mMTC). Summary of the Invention [Problem to be solved by the invention]

[0004] A method for enhanced mobility in a wireless system is provided. [Means for solving the problem]

[0005] A method, device, and system for communication by a wireless transmit / receive unit (WTRU) associated with a source cell. The WTRU is configured to use a conditional reconfiguration including a trigger condition and a configured target cell. The WTRU detects the occurrence of an impairment event that causes an impairment to the operation of the WTRU in the source cell. If the impairment event satisfies the trigger condition, a reconfiguration is performed with the configured target cell. If the impairment event does not satisfy the trigger condition, a target cell is selected based on a cell selection procedure, and if the WTRU is configured to use a conditional reconfiguration for the selected target cell, a reconfiguration is performed with the selected target cell, and if the WTRU is not configured to use a conditional reconfiguration for the target cell, a reestablishment is performed with the selected target cell.

[0006] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which like reference numbers indicate similar elements and in which: Effect of the Invention

[0007] A method for enhanced mobility in a novel wireless system is provided. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 1 illustrates an example communication system in which one or more disclosed embodiments may be implemented. [Figure 1B] 1A is a system diagram illustrating an example wireless transmit / receive unit (WTRU) that can be used within the communication system of FIG. 1A in accordance with an embodiment. [Figure 1C] FIG. 1B is a system diagram illustrating an example radio access network (RAN) and core network (CN) that can be used within the communication system of FIG. 1A in accordance with an embodiment. [Figure 1D]FIG. 1B is a system diagram illustrating a further example RAN and CN that may be used within the communication system of FIG. 1A in accordance with an embodiment. [Diagram 2] FIG. 1 illustrates handover failure causes associated with mobility signaling problems. [Diagram 3] A cell diagram illustrating CFRA resources that are activated based on association with a serving beam in a source cell. [Figure 4] 1 is a message sequence chart illustrating a configuration mismatch scenario. [Diagram 5] 1 is a message sequence chart illustrating an example procedure for re-establishment including fallback to conditional handover. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] FIG. 1A is a diagram illustrating an example communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communication system 100 may enable the multiple wireless users to access such content through sharing of system resources, including wireless bandwidth. For example, the communication system 100 may utilize one or more channel access methods, such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Zero-tailed Unique Word DFT Spread OFDM (ZT UW DTS-s OFDM), Unique Word OFDM (UW-OFDM), Resource Block Filtered OFDM, and Filter Bank Multi-Carrier (FBMC).

[0010] 1A, the communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a RAN 104, a 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” and / or “STA,” may be configured to transmit and / or receive wireless signals and may include user equipment (UE), mobile stations, fixed or mobile subscriber units, subscription-based units, pagers, cellular phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, wireless sensors, hotspots or Mi-Fi devices, Internet of Things (IoT) devices, watches or other wearables, head mounted displays (HMDs), vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in industrial and / or automated processing chain situations), consumer electronics devices, and devices operating on commercial and / or industrial wireless networks, etc. Any of the WTRUs 102a, 102b, 102c, 102d may be referred to interchangeably as UEs.

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

[0012] The base station 114a may be part of the RAN 104 / 113, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and / or the base station 114b may be configured to transmit and / or receive wireless signals on one or more carrier frequencies, which may be referred to as cells (not shown). These frequencies may be in a licensed spectrum, an unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for wireless services in a particular geographic area, which may be relatively constant or may change over time. A cell may be further divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, one for each sector of the cell. In an embodiment, the base station 114a may utilize multiple-input multiple-output (MIMO) technology and may utilize multiple transceivers for each sector of the cell, e.g., beamforming may be used to transmit and / or receive signals in desired spatial directions.

[0013] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0014] More specifically, as mentioned above, the communication system 100 may be a multiple access system and may utilize one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, and SC-FDMA. For example, the base station 114a in the RAN 104 / 113 and the WTRUs 102a, 102b, 102c may implement a radio technology, such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using Wideband CDMA (WCDMA). WCDMA may include communication protocols, such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink (DL) Packet Access (HSDPA) and / or High Speed ​​Uplink (UL) Packet Access (HSUPA).

[0015] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE), and / or LTE Advanced (LTE-A), and / or LTE Advanced Pro (LTE-A Pro).

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

[0017] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, e.g., using a dual connectivity (DC) principle. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to / from multiple types of base stations (e.g., eNBs and gNBs).

[0018] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a wireless technology such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi)), IEEE 802.16 (i.e., Global Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE), and GSM EDGE (GERAN).

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

[0020] The RAN 104 / 113 may communicate with the CN 106 / 115, which may be any type of network configured to provide voice, data, application, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have various Quality of Service (QoS) requirements, such as different throughput requirements, delay requirements, error resilience requirements, reliability requirements, data throughput requirements, and mobility requirements. The CN 106 / 115 may provide call control, billing services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, and / or perform high-level security functions, such as user authentication. Although not shown in FIG. 1A, it will be appreciated that the RAN 104 / 113 and / or the CN 106 / 115 may communicate directly or indirectly with other RANs that utilize the same RAT as the RAN 104 / 113 or a different RAT. For example, in addition to being connected to the RAN 104 / 113, which may utilize NR radio technology, the CN 106 / 115 may also communicate with another RAN (not shown) that utilizes GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

[0021] The CN 106 / 115 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network providing plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communications protocols, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and / or Internet Protocol (IP) in the TCP / IP Internet protocol suite. The network 112 may include wired and / or wireless communications networks owned and / or operated by other service providers. For example, the network 112 may include another CN connected to one or more RANs that may utilize the same RAT as the RAN 104 / 113 or a different RAT.

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

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

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

[0025] The transmit / receive element 122 can be configured to transmit signals to or receive signals from a base station (e.g., base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 can be an antenna configured to transmit and / or receive RF signals. In an embodiment, the transmit / receive element 122 can be an emitter / detector configured to transmit and / or receive, for example, 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 light signals. It will be appreciated that the transmit / receive element 122 can be configured to transmit and / or receive any combination of wireless signals.

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

[0027] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and demodulate signals received by the transmit / receive element 122. As mentioned above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, such as, for example, NR and IEEE 802.11.

[0028] The processor 118 of the WTRU 102 may be coupled to and may receive user input data from a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may obtain information from and store data in any type of suitable memory, such as a non-removable memory 130 and / or a removable memory 132. The non-removable memory 130 may include a random access memory (RAM), a read only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as located on a server or home computer (not shown).

[0029] The processor 118 may receive power from the power source 134 and may be configured to distribute and / or control power to other components within the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

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

[0031] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photos and / or videos), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, a Bluetooth module, a frequency modulation (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, a virtual reality and / or augmented reality (VR / AR) device, an activity tracker, and the like. The peripherals 138 may include one or more sensors, which 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 barometer, a gesture sensor, a biometric sensor, and / or a humidity sensor.

[0032] The WTRU 102 may include a full-duplex radio where the transmission and reception of some or all of the signals (e.g., associated with a particular subframe for both the UL (e.g., for transmission) and the downlink (e.g., for reception)) may be parallel and / or simultaneous. The full-duplex radio may include an interference management unit 139 to reduce and / or substantially eliminate self-interference via hardware (e.g., a choke) or via signal processing via a processor (e.g., a separate processor (not shown) or the processor 118). In an embodiment, the WTRU 102 may include a half-duplex radio for the transmission and reception of some or all of the signals (e.g., associated with a particular subframe for either the UL (e.g., for transmission) or the downlink (e.g., for reception).

[0033] 1C is a system diagram illustrating the RAN 104 and the CN 106, according to an embodiment. As mentioned above, the RAN 104 can communicate with the WTRUs 102a, 102b, 102c over the air interface 116 using E-UTRA radio technology. The RAN 104 can also communicate with the CN 106.

[0034] The RAN 104 may include eNodeBs 160a, 160b, 160c, although it will be understood that the RAN 104 may include any number of eNodeBs while remaining consistent with an embodiment. The eNodeBs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNodeBs 160a, 160b, 160c may implement MIMO technology. Thus, the eNodeB 160a, for example, may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0035] Each of the eNodeBs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, etc. As shown in FIG 1C, the eNodeBs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0036] 1C may include a Mobility Management Entity (MME) 162, a Serving Gateway (SGW) 164, and a Packet Data Network (PDN) Gateway (or PGW) 166. Although each of the above elements is depicted as part of the CN 106, it will be understood that any of these elements may be owned and / or operated by an entity different from the CN operator.

[0037] The MME 162 may be connected to each of the eNodeBs 160a, 160b, 160c in the RAN 104 via an 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, bearer activation / deactivation, selecting a particular serving gateway during initial attach of the WTRUs 102a, 102b, 102c, etc. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0038] The SGW 164 may be connected to each of the eNodeBs 160a, 160b, 160c in the RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring the user plane during inter-eNodeB handover, triggering paging when DL data is available to the WTRUs 102a, 102b, 102c, as well as managing and storing the context of the WTRUs 102a, 102b, 102c.

[0039] The SGW 164 may be connected to a PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0040] The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional landline communications devices. For example, the CN 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers.

[0041] Although in Figures 1A-1D the WTRU is described as a wireless terminal, it is contemplated that in certain representative embodiments such a terminal may use a wired communications interface (e.g., temporarily or permanently) with the communications network.

[0042] In an exemplary embodiment, the other network 112 may be a WLAN.

[0043] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have access or interface to a distribution system (DS) or another type of wired / wireless network that carries traffic within and / or outside the BSS. Traffic to a STA originating from outside the BSS may arrive through the AP and be delivered to the STA. Traffic originating from a STA to a destination outside the BSS may be sent to the AP for delivery to the respective destination. Traffic between STAs in the BSS may be sent through the AP, e.g., a source STA may send traffic to the AP, which may deliver the traffic to the destination STA. Traffic between STAs in the BSS may be considered and / or referred to as peer-to-peer traffic. Peer-to-peer traffic may be sent (e.g., directly) between a source STA and a destination STA using a direct link setup (DLS). In one representative embodiment, the DLS may use 802.11e DLS or 802.11z Tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and STAs (e.g., all of the STAs) in or using an IBSS may communicate directly with each other. IBSS mode communication is sometimes referred to herein as an "ad-hoc" mode of communication.

[0044] When using 802.11ac infrastructure mode of operation or a similar mode of operation, the AP may transmit beacons on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20 MHz wide bandwidth) or a width dynamically set via signaling. The primary channel may be an operating channel of the BSS and may be used by STAs to establish a connection with the AP. In one representative embodiment, for example, in an 802.11 system, carrier sense multiple access / collision avoidance (CSMA / CA) may be implemented. With CSMA / CA, STAs (e.g., every STA), including the AP, may sense the primary channel. If the primary channel is sensed / detected by a particular STA and / or determined to be busy, the particular STA may back off. Within a given BSS, one STA (e.g., only one STA) may transmit at any given time.

[0045] High-throughput (HT) STAs may use a 40 MHz wide channel for communication, for example, via combining a primary 20 MHz channel with adjacent or non-adjacent 20 MHz channels to form a 40 MHz wide channel.

[0046] A Very High Throughput (VHT) STA can support 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz wide channels. The 40 MHz and / or 80 MHz channels can be formed by combining contiguous 20 MHz channels. The 160 MHz channel can be formed by combining eight contiguous 20 MHz channels or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80 configuration, the data, after channel encoding, can pass through a segment parser that can split the data into two streams. Inverse Fast Fourier Transform (IFFT) processing and time domain processing can be performed separately for each stream. The streams can be mapped onto two 80 MHz channels and the data can be transmitted by the transmitting STA. At the receiver of the receiving STA, the operations described above for the 80+80 configuration can be reversed and the combined data can be transmitted to the Medium Access Control (MAC).

[0047] Sub-1 GHz mode operation is supported by 802.11af and 802.11ah. Channel operating bandwidths and carriers are reduced in 802.11af and 802.11ah compared to those used in 802.11n and 802.11ac. 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah can support meter type control / machine type communication, such as machine type communication (MTC) devices in macro coverage areas. MTC devices can have limited functionality, including, for example, support of (e.g., only) a certain bandwidth and / or limited bandwidth. MTC devices can include a battery with a battery life above a threshold (e.g., to maintain a very long battery life).

[0048] A WLAN system, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, that may support multiple channels and channel bandwidths, includes a channel that may be designated as a primary channel. The primary channel may have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA that supports a minimum bandwidth operating mode among all STAs operating in the BSS. In an 802.11ah example, for a STA (e.g., an MTC type device) that supports (e.g., only supports) the 1 MHz mode, the primary channel may 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 operating modes. Carrier sensing and / or network allocation vector (NAV) setting may depend on the status of the primary channel. For example, if the primary channel is busy because a STA (that only supports a 1 MHz mode of operation) is transmitting to the AP, the entire available frequency band may be considered busy, even though most of the available frequency band may remain idle and available.

[0049] In the United States, the available frequency bands that can be used by 802.11ah are 902MHz to 928MHz. In South Korea, the available frequency bands are 917.5MHz to 923.5MHz. In Japan, the available frequency bands are 916.5MHz to 927.5MHz. The total available bandwidth for 802.11ah is 6MHz to 26MHz, depending on country regulations.

[0050] 1D is a system diagram illustrating the RAN 113 and the CN 115 according to an embodiment. As mentioned above, the RAN 113 may communicate with the WTRUs 102a, 102b, 102c over the air interface 116 utilizing NR radio technology. The RAN 113 may also communicate with the CN 115.

[0051] The RAN 113 may include gNBs 180a, 180b, 180c, although it will be understood that the RAN 113 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, the gNBs 180a, 108b may utilize beamforming to transmit signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a may transmit wireless signals to and / or receive wireless signals from the WTRU 102a using multiple antennas, for example. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation techniques. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on an unlicensed spectrum, while the remaining component carriers may be on a licensed spectrum. In an embodiment, the gNBs 180a, 180b, 180c may implement coordinated multipoint (CoMP) techniques. For example, the WTRU 102a may receive coordinated transmissions from the gNBs 180a and 180b (and / or gNB 180c).

[0052] The WTRUs 102a, 102b, 102c can communicate with the gNBs 180a, 180b, 180c using transmissions associated with a scalable numerology. For example, the OFDM symbol spacing and / or OFDM subcarrier spacing can vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c can communicate with the gNBs 180a, 180b, 180c using subframes or transmission time intervals (TTIs) of different or scalable lengths (e.g., including different numbers of OFDM symbols and / or lasting for different lengths of absolute time).

[0053] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c without accessing other RANs (e.g., eNodeBs 160a, 160b, 160c). In a standalone configuration, the WTRUs 102a, 102b, 102c may utilize one or more of the gNBs 180a, 180b, 180c as mobility anchor points. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in unlicensed bands. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate / connect to a gNB 180a, 180b, 180c while also communicating / connecting to another RAN, such as the eNodeBs 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement the DC principle to communicate with one or more gNBs 180a, 180b, 180c and one or more eNodeBs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNodeBs 160a, 160b, 160c may act as mobility anchors for the WTRUs 102a, 102b, 102c, and the gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0054] Each of the gNBs 180a, 180b, 180c can be associated with a particular cell (not shown) and can be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, support for network slicing, dual connectivity, interworking between NR and E-UTRA, routing of user plane data to User Plane Functions (UPFs) 184a, 184b, and routing of control plane information to Access and Mobility Management Functions (AMFs) 182a, 182b, etc. As shown in FIG. 1D, the gNBs 180a, 180b, 180c communicate with each other over the Xn interface. The CN 115 shown in Figure 1D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. Although each of the above elements is depicted as part of the CN 115, it will be understood that any of these elements may be owned and / or operated by an entity different from the CN operator.

[0055] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N2 interface and may 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 PDU sessions with different requirements), selecting a particular SMF 183a, 183b, managing registration areas, terminating NAS signaling, and mobility management, etc. Network slicing may be used by the AMF 182a, 182b to customize CN support for the WTRUs 102a, 102b, 102c based on the type of service utilized by the WTRUs 102a, 102b, 102c. Different network slices may be established for different use cases, such as, for example, services relying on ultra-reliable low latency (URLLC) access, services relying on eMBB access, and / or services for machine type communication (MTC) access, etc. The AMF 182a, 182b may provide a control plane function for switching between the RAN 113 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies such as WiFi.

[0056] The SMFs 183a, 183b can be connected to the AMFs 182a, 182b in the CN 115 via an N11 interface. The SMFs 183a, 183b can also be connected to the UPFs 184a, 184b in the CN 115 via an N4 interface. The SMFs 183a, 183b can select and control the UPFs 184a, 184b and configure the routing of traffic through the UPFs 184a, 184b. The SMFs 183a, 183b can perform other functions such as managing and assigning UE IP addresses, managing PDU sessions, controlling policy enforcement and QoS, and providing downlink data notification. The PDU session types can be IP-based, non-IP-based, Ethernet-based, etc.

[0057] The UPFs 184a, 184b may connect to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPFs 184a, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homing PDU sessions, handling user plane QoS, buffering downlink packets, as well as providing mobility anchoring.

[0058] The CN 115 may facilitate communication with other networks. For example, the CN 115 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 115 and the PSTN 108. In addition, the CN 115 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may connect to local data networks (DNs) 185a, 185b through the UPFs 184a, 184b via an N3 interface to the UPFs 184a, 184b and an N6 interface between the UPFs 184a, 184b and the DNs 185a, 185b.

[0059] In view of Figures 1A-1D and the corresponding description thereof, one or more or all of the functions described herein with respect to one or more of the WTRUs 102a-d, base stations 114a-b, eNodeBs 160a-c, MME 162, SGW 164, PGW 166, gNBs 180a-c, AMFs 182a-b, UPFs 184a-b, SMFs 183a-b, DNs 185a-b, and / or any other devices described herein may be performed by one or more emulation devices (not shown). The emulation devices may be one or more devices configured to emulate one or more or all of the functions described herein. For example, the emulation devices may be used to test other devices and / or to simulate network and / or WTRU functions.

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

[0061] The one or more emulation devices can perform one or more functions, including all functions, without being implemented / deployed as part of a wired and / or wireless communication network. For example, the emulation devices can be utilized in a test lab and / or in a test scenario in a non-deployed (e.g., test) wired and / or wireless communication network to perform testing of one or more components. The one or more emulation devices can be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (which may include, for example, one or more antennas) can be used by the emulation devices to transmit and / or receive data.

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

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

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

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

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

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

[0068] For flexible 5G networks (5gFLEX), other waveform candidates can be considered, however, conventional OFDM remains a possible candidate for 5G systems, e.g., for downlink transmission schemes. In some cases, 5gFLEX radio access can be characterized by a very high degree of spectrum flexibility, enabling deployment in different frequency bands with different characteristics. 5gFLEX can include different and / or variable sizes of available spectrum, including different duplex configurations, as well as contiguous and non-contiguous spectrum allocations in the same or different bands. 5gFLEX can also support variable timing aspects, such as support for multiple TTI lengths and / or support for asynchronous transmission.

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

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

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

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

[0073] After receiving a reconfiguration message that is implicitly or explicitly associated with a condition (i.e., a conditional reconfiguration), the WTRU may verify and store the reconfiguration, start monitoring the condition (i.e., a trigger condition), and apply the reconfiguration when the trigger condition is satisfied. For example, the WTRU may receive a radio resource control (RRC) connection reconfiguration having one or more of a mobility information element and a conditional mobility information element. The WTRU may receive one of the information elements, one for each candidate target cell. The WTRU may be configured with multiple conditional reconfigurations associated with multiple target cells. A conditional reconfiguration may also be referred to as a conditional handover (CHO), and these terms are used interchangeably herein.

[0074] Decoupling the reconfiguration transmission from the application of the reconfiguration can improve the reliability of the control signaling. For example, the control signaling can be transmitted when the quality of the radio link is better. Another advantage of this approach can be a shorter reaction time between a failure event (e.g., measurement) and a corrective action (e.g., reconfiguration with mobility). In a legacy method, the WTRU may first need to detect a failure event, report the event to the network, wait for a network response, process the network response, and take a corrective action. Such a delay may prevent the execution of a mobility reconfiguration at the right time under rapidly deteriorating radio conditions. In contrast, a conditional reconfiguration can facilitate the WTRU to benefit from controlled autonomy. In such a case, the network can configure how to detect a failure event and which corrective action to perform, while the WTRU can decide when to perform the corrective action. This can enable a faster reaction time, which can facilitate sparse transmission and / or measurement of reference signals, and can increase power savings in the network and / or the WTRU.

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

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

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

[0078] As described above, the NR interface can support a wide range of use cases with different service requirements. For example, mMTC use cases may require power-efficient services with low overhead and low data rates. URLLC use cases may require very high reliability. Enhanced Mobile Broadband (eMBB) use cases may require high data rates. The NR interface can support a variety of WTRU capabilities, such as low-power, low-bandwidth WTRUs, WTRUs capable of very wide bandwidth (e.g., 80 Mhz) transmissions, and WTRUs using high frequencies (e.g., 6 Ghz and above). In such use cases, the WTRUs may be in different mobility scenarios (e.g., stationary / fixed, high-speed trains, etc.). The NR interface may require an architecture that is flexible enough to be adapted to different deployment scenarios (e.g., standalone, non-standalone with assistance from different air interfaces, centralized, virtualized, and distribution over ideal / non-ideal backhaul).

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

[0080] The WTRU may perform a re-establishment procedure to recover from a severe error condition that affects operation in the serving cell. However, the re-establishment procedure may come at the cost of increased downtime and data loss. An enhanced re-establishment procedure may be provided to facilitate tolerable downtime in severe error scenarios.

[0081] FIG. 2 illustrates handover failure causes associated with mobility signaling problems. Radio link conditions may deteriorate rapidly in the source cell before a handover command (HOC) is received by the WTRU, and a radio link failure (RLF) may be declared. The WTRU may perform re-establishment towards the target cell. Due to one or more reasons, the HOC may not be received on time. The WTRU may not send a measurement report early enough (e.g., while a suitable neighbor cell is available) due to uplink radio link degradation. The WTRU may not receive the handover command due to downlink radio link degradation. If the WTRU receives a handover command for a suitable target cell before declaring the RLF, while the link with the source cell has not yet failed, re-establishment and service interruption may be avoided.

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

[0083] Example RLF 240 illustrates an example handover failure case in which an RLF occurs before the WTRU can transmit a measurement report 215. In this example, the WTRU detects a radio link problem during time interval 245 (e.g., when a maximum number of out-of-sync indications is received from lower layers). After detecting 250 a radio link problem, the WTRU waits for time interval 255 (e.g., tracked with an RLF timer, such as T310, to rule out transient problems) before declaring an RLF 260. Because the WTRU determined that the radio link with the network failed (time X) before it transmitted the measurement report 215, the WTRU does not transmit the measurement report 215 and instead attempts to re-establish its connection with the network during time interval 265 (tracked with a timer, such as T311). If the WTRU is unable to re-establish its connection within time interval 265, it enters an idle state 270.

[0084] Example RLF 275 illustrates an example handover failure case in which an RLF occurs after the WTRU transmits measurement report 215 but before it receives handover command 225. In this example, the WTRU detects a radio link problem during time interval 280 (e.g., when a maximum number of out-of-sync indications is received from lower layers). After detecting a radio link problem 285, the WTRU waits for time interval 290 (e.g., tracked with an RLF timer, such as T310, for example, to rule out transient problems) before declaring an RLF 295. Because the radio link with the network failed (time Y) before the WTRU was able to receive handover command 225, the WTRU does not perform a handover but instead attempts to re-establish its connection with the network during time interval 296 (tracked with a timer, such as T311, for example). If the WTRU is unable to re-establish its connection within time interval 296, it enters an idle state 297.

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

[0086] In some embodiments, the WTRU may determine whether to initiate a re-establishment procedure or a conditional reconfiguration procedure as a function of a failure event. The WTRU may be configured to monitor various events that result in failure to the operation in the serving cell. The failure events may include, for example, one or more of a lower layer problem indication from a radio link monitoring (RLM) process (e.g., an RLF timer (e.g., T310) expiry), a random access problem indication, an indication that a maximum RLC retransmission has been reached, an indication that beam recovery has failed and / or a candidate beam is not found, a reconfiguration failure (e.g., the WTRU is unable to follow a received reconfiguration command), an integrity check failure, a handover failure, etc. The WTRU may be configured to determine whether to perform a re-establishment procedure or a conditional reconfiguration procedure after detecting one or more of such failure events. The decision may be made as a function of a particular failure event or a type of failure event.

[0087] In some embodiments, the WTRU may perform a conditional reconfiguration procedure after detecting a first subset of failure events if the WTRU is configured to use conditional reconfiguration for any target cell (i.e., there is a suitable target cell - there is at least one target cell for which a conditional reconfiguration exists) and the target cell satisfies a cell selection criterion (e.g., the quality of the target cell is above a predefined threshold). The first subset of failure events may include one or more of an indication of a lower layer problem from the RLM process (e.g., T310 expiration), an indication of a random access problem, an indication that maximum RLC retransmissions have been reached, an indication that beam recovery has failed and / or a candidate beam cannot be found, etc.

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

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

[0090] The re-establishment procedure may include performing cell selection to select a suitable cell. In one example, as a result of the cell selection, the WTRU may select a cell for which a conditional reconfiguration exists (e.g., the WTRU has received a conditional reconfiguration for the cell that has not expired). If the WTRU selects a cell for which a conditional reconfiguration exists, the WTRU may assume that a trigger condition is satisfied for that cell (i.e., the WTRU may trigger a conditional handover instead of a re-establishment procedure). In another example, if the cell selection results in the WTRU selecting a cell for which a conditional reconfiguration does not exist (e.g., all conditional reconfigurations for the cell have expired or no conditional reconfiguration is configured for the cell), the WTRU may trigger a re-establishment procedure. In the case of a conditional handover, this scheme may help reduce interruption time in some cases, since the WTRU may resume the DRB after sending a reconfiguration complete. In addition, the WTRU may be configured to use a dedicated random access resource for the conditional reconfiguration, which further reduces the delay / interruption time.

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

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

[0093] As described above, a conditional handover (CHO), or enhanced re-establishment procedure, may be triggered by detection of a lower layer problem. The lower layer problem that triggers a CHO may be associated, for example, with one or more of the following events: T310 expiration, an RA access problem indication from the MAC while T300, T301, T304, T311 are not running, or an indication from the RLC indicating that maximum re-transmissions have been reached. T300 is a timer that, while running, indicates that the WTRU is engaged in an ongoing RRC connection setup procedure. T301 is a timer that, while running, indicates that the WTRU is waiting for a re-establishment response. T304 is a timer that, while running, indicates that the WTRU is engaged in an ongoing handover procedure. T311 is a timer that, while running, indicates that the WTRU is engaged in an ongoing re-establishment procedure.

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

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

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

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

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

[0099] In some embodiments, the CHO trigger is associated with multiple measurement quantities. For example, the WTRU may be configured to use a CHO trigger condition associated with a particular measurement quantity. In some examples, the WTRU may be configured to use a trigger condition including two or more measurement quantities. The one or more measurement quantities may include, for example, RSRP, Reference Signal Received Quality (RSRQ), and / or Signal to Interference and Noise Ratio (SINR). An example of a trigger condition including two or more measurement quantities may require both a first measurement quantity of a candidate cell to be better than the serving cell or a first absolute threshold and a second measurement quantity of a candidate cell to be better than the serving cell or a second absolute threshold. Different combinations of the first and second measurement quantities may be possible. For example, RSRP and RSRQ, RSRP and SINR, RSRQ and SINR, etc. In some examples, the WTRU may be configured to use a trigger condition including three or more measurement quantities, for example, RSRP, RSRQ, and SINR, etc.

[0100] For cases where multiple cells simultaneously satisfy a trigger condition, the WTRU may be configured to prioritize target cells based on measurements associated with the trigger condition. For example, the WTRU may be configured to prioritize a candidate cell with the highest SINR. In another example, the WTRU may be configured to prioritize a candidate cell with the highest RSRQ. In some examples, the WTRU may be configured to use priorities associated with the trigger conditions such that some trigger conditions are prioritized over others. For example, the WTRU may be configured to prioritize trigger conditions based on SINR and / or RSRQ over RSRP-based trigger conditions.

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

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

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

[0104] Some embodiments include prioritization associated with the trigger conditions. In some embodiments, the WTRU may be configured to use one or more candidate cells for CHO, and each candidate cell may be associated with one or more trigger conditions resulting in multiple trigger conditions for the execution of CHO. It may occur that more than one trigger condition is satisfied at a given time. In some examples, the WTRU may be configured to use rules to determine which target cell to CHO to when these satisfied trigger conditions are associated with different candidate cells. Exemplary rules may include prioritization, or a combination of prioritization, based on best beam, based on number of good beams, and / or based on availability of dedicated resources. For prioritization based on best beam, the WTRU may be configured to select the candidate cell that has the best beam for the WTRU (e.g., in terms of RSRP, RSRQ, or SINR). For prioritization based on number of good beams, the WTRU may be configured to select the candidate cell that has the most good beams for the WTRU, and a good beam may be defined in terms of a measurement quantity (e.g., RSRP, RSRQ, or SINR) above a preconfigured threshold. For prioritization based on availability of dedicated resources to the WTRU, the WTRU may be configured to select a candidate cell that has availability above a minimum threshold (e.g., in terms of RSRP, RSRQ, or SINR) and is associated with available dedicated resources (e.g., CFRA). Alternatively, the WTRU may be configured to select a candidate cell that has the most CFRA resources associated with a good beam.

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

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

[0107] The serving cell uses the target cell identifier (TCI) status to communicate which beam to use (e.g., for physical downlink control channel (PDCCH) monitoring or DL ​​data). An indication of the CFRA resources to be activated based on the serving beam in the source cell can be based on the TCI status. For example, when the WTRU executes a handover command in the target cell, it can consider only CFRA resources for beams in the target cell that are linked to the beams indicated in the TCI status. The WTRU can be configured to assume that only CFRA resources in the target cell beams that are linked to the current serving cell beam (i.e., based on the TCI status) are valid. This implicit activation of CFRA resources based on a preconfigured linkage can have the advantage of minimizing frequent signaling.

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

[0109] Since the timing of the conditional reconfiguration may be determined by the WTRU, the RRC configuration used by the WTRU in the target cell may be ambiguous, resulting in a handover failure.

[0110] FIG. 4 is a message sequence chart illustrating an example configuration mismatch scenario. In the example of FIG. 4, the WTRU 400 may first receive a conditional reconfiguration 420 for the target gNB 405 from the source gNB 410. The source gNB 410 may determine the conditional reconfiguration 420 based on an adjustment 425 that may be made on the Xn interface. The Xn adjustment 425 may be based on handover preparation signaling. The conditional reconfiguration 420 may include various parameters, including a trigger condition and an RRC configuration to be applied at a target cell associated with the target gNB 405 if the trigger condition occurs. In some implementations, the parameters may include a logical identifier associated with the target cell RRC configuration. The WTRU 400 may begin monitoring for the trigger condition at step 430 for a time T1. During the time T1, the WTRU may still be connected to a serving cell associated with the source gNB 410 and may receive different types of RRC signaling from the source gNB 410. Such RRC signaling from the source gNB 410 may affect the stored conditional reconfiguration 420 at the WTRU 400, and therefore the configuration of the WTRU 400 that is applied in the source cell associated with the source gNB 410. The source gNB 410 may also need to coordinate with the target gNB 405 whenever the WTRU's conditional configuration 420 applicable to target operation is updated. For example, the source gNB 410 may need to coordinate both the WTRU 400 and the target gNB 405 so that the RRC configuration 420 is consistent between the WTRU and the target gNB.

[0111] Since the timing of the conditional reconfiguration is determined by the WTRU, there may be cases where the WTRU autonomously triggers handover while a reconfiguration with the source cell is in progress. This may result in a configuration mismatch in the target cell, resulting in a failure of the handover procedure. In other words, the target gNB may be uncertain about the RRC configuration last used in the source cell. For example, the WTRU 400 may receive one or more reconfigurations in the source cell during time T1. It may not be clear to the target gNB whether the WTRU was able to receive / apply those reconfigurations or not before triggering the CHO. In this example, the source gNB 410 determines updates 435 to the conditional reconfiguration 420 based on the adjustment 440 over the Xn interface and sends the updates 435 to the WTRU 400. The updates 435 may include one or more changes to parameters in the conditional reconfiguration 420 (e.g., a different target cell RRC configuration, a different RACH configuration, a different radio bearer configuration, a different security configuration, a different condition or conditions, etc.). If the parameters of the conditional reconfiguration 420 include an identifier (e.g., an ID number), then the update 435 includes a different identifier. The WTRU 400 does not receive the update 435, as illustrated in FIG. 4. At step 445, the WTRU 400 determines that the triggering conditions indicated in the conditional reconfiguration 420 have been satisfied and initiates a random access procedure 450 with the target eNB 405. Now, a configuration mismatch has occurred, in that the WTRU 400 triggered the random access procedure 450 based on the conditional reconfiguration 420 and not based on the update 435.

[0112] The WTRU may transmit an indication indicating its configuration associated with the target cell. For example, the WTRU may be configured to transmit an indication indicating its RRC configuration associated with the target cell. The indication may be transmitted in a first message after a random access procedure in the target cell. The indication may be transmitted with the first RRC message in the target cell. The indication may include an identity (e.g., an identifier, ID number, or other parameters as described above) associated with a conditional reconfiguration message applied by the WTRU. For example, the indication may include a transaction identifier corresponding to the latest RRC reconfiguration message, including the conditional reconfiguration message associated with the target cell. The indication may be an identity associated with the last used RRC configuration at the source gNB. For example, the indication may be a transaction identifier corresponding to the latest RRC reconfiguration message successfully received and applied by the WTRU at the source gNB.

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

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

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

[0116] The WTRU may be configured to transmit two response messages in response to the conditional reconfiguration message. The WTRU may be configured to transmit a first message to the source cell upon receipt of a conditional reconfiguration including mobility. The WTRU may be configured to transmit a second message to the target cell upon execution of a conditional reconfiguration including mobility. The first message may be a MAC Control Element having a predefined Logical Channel Identification (LCID). The MAC CE may indicate a transaction identifier of a corresponding RRC message including the conditional reconfiguration. The first message may be an RRC response message indicating successful reception of the conditional reconfiguration message. If the WTRU is unable to comply with the conditional reconfiguration, the WTRU may transmit a failure cause in the RRC response message. The second message may be an RRC reconfiguration complete message.

[0117] The measurement may be sent too late, which may not allow the network to prepare and send the handover command in time. The time to trigger the measurement may be a function of the radio link quality in the source cell. For example, the time to trigger (TTT) may be a function of one or more of the following: Block Error Rate (BLER) of resources configured for radio link monitoring, the number of out-of-sync (OOS) cases, the number of beam failure cases detected in the source cell, the quality of the serving cell (RSRP, RSRQ, SINR), the quality of the best beam in the source cell or base, and the RS provided for the active TCI state for the PDCCH.

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

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

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

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

[0122] The validity of the measurement results and the subsequent decision to send an indication to the NW indicating a radio link problem may be determined by the WTRU. The decision to send this indication may be based on whether previous measurement reports sent to the NW are still valid.

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

[0124] The assessment of this condition may be based on layer 1 measurements. In order to send the indication as soon as possible, layer 3 filtering may not be applied.

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

[0126] For example, an event may have recently triggered a report, but the network may not have decided to handoff the WTRU towards the target cell (e.g., because the serving cell is still strong enough.) If the WTRU begins to experience radio link problems while measuring that the target cell that triggered the most recent measurement report still satisfies the reporting conditions, the WTRU may send an indication of link degradation and the validity of the previous measurement report.

[0127] If the WTRU measures that the neighbor cell quality is x dB higher than the serving cell and the link with the serving cell suddenly deteriorates (e.g., based on RLM evaluation), the WTRU may send an indication as soon as one of the radio link failure triggers defined above is achieved, regardless of whether the WTRU is configured with reporting events. This indication may include the identity of the best measured neighbor cell. This indication may include the best beam ID in the target cell.

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

[0129] Some embodiments provide for updating beam measurements for delta CHO reconfiguration. Delta CHO reconfiguration refers to an incremental update to an existing CHO. For example, the delta CHO may indicate different resources than the existing CHO. Some embodiments include transmitting a beam ID and receiving a delta CHO reconfiguration. For example, the WTRU may receive CHO commands for multiple target cells and may monitor a best beam associated with the target cell.

[0130] In some examples, the WTRU may be configured with a measurement event that is triggered when the quality of the best beam in the target cell, or the average quality of a group of best beams, drops below a threshold. When the measurement event is triggered, the WTRU sends a measurement report to the gNB. The measurement report may include quality measurements (e.g., RSRP, RSRQ, or SINR) of all beams in the target cell, an identification of the new best detected beam that exceeds a threshold, a beam identity of the beam, or a combination thereof. In response to the measurement report, the WTRU may receive a delta reconfiguration for the CHO command of the target cell that includes new dedicated RACH resources for the target cell associated with the indicated beam.

[0131] If the WTRU is experiencing radio link problems in an active UL-DL BWP pair and a measurement report is triggered based on the conditions described above, the WTRU may not be able to successfully transmit a report in the current active UL BWP. It may also not be able to receive a subsequent handover command in the active DL BWP. Thus, in some implementations, if a measurement report is triggered based on any of the criteria described above, the WTRU may autonomously switch the active UL / DL BWP to one of the RRC-configured UL / DL BWPs that is experiencing less restrictive radio conditions. In TDD, the WTRU may perform this switching based on a set of configured CSI-RS and / or SSB resources that it has measured. In FDD, the WTRU may switch its active UL BWP based on an estimated path loss from a measured DL reference signal (i.e., a reference signal associated with a measurement object). The WTRU may switch both UL and DL BWPs, or only one BWP, based on the measurement results and the path loss estimate.

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

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

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

[0135] Some embodiments include multiple CHO commands for the same target cell id. For example, in some embodiments, multiple first active UL and DL BWPs are configured in the target cell selection based on measurements. For example, the WTRU may receive multiple conditional reconfiguration commands for the same target cell id, but with different first active UL and DL BWPs, including different sets of candidate beams for RACH (synchronization signal block (SSB) and / or channel state information reference signal (CSI-RS)). If a CHO execution condition for a given target is satisfied (e.g., Ax event), the WTRU may select a configuration based on the CHO command configured to use, for example, the first active DL BWP for which the best reference signal (SSB and / or CSI-RS) was measured. Example events that satisfy the CHO execution condition for a given target include Ax events, where A1 indicates that the serving cell has become better than a threshold (e.g., in terms of RSRP, or RSRQ, or SINR for the WTRU), A2 indicates that the serving cell has become worse than a threshold, A3 indicates that the neighbor cell has become better than the SpCell by an offset, A4 indicates that the neighbor cell has become better than a threshold, A5 indicates that the SpCell has become worse than a first threshold and the neighbor cell has become better than a second threshold, and A6 indicates that the neighbor cell has become better than the SCell by an offset.

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

[0137] If the handover command is sent or received too early or too late, a handover failure may occur. Measurements that can indicate to the NW the exact path of the WTRU and its associated mobility progress in the source and target cells can assist the NW in sending the handover command with appropriate timing.

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

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

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

[0141] The WTRU may be configured to use a CHO associated with one or more target cells, and if one or more target cells satisfy handover execution criteria, the WTRU may monitor the PDCCH of a different target cell before executing a handover command.

[0142] The pre-configured target cell may send a signal (e.g., DCI) in a dedicated CORESET for the WTRU configured to use CHO. The source cell may inform the target cell about the identity of the WTRU configured to use CHO commands.

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

[0144] Before executing the handover command, the WTRU can obtain further information regarding the uplink robustness at the target cell by transmitting an SRS-like signal. If the signal is successfully received or if the measurement results associated with the uplink signal are above a configured threshold, the target cell can send an indication to the WTRU through the source cell. This indication can trigger the actual handover execution on the target cell.

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

[0146] The WTRU may initiate access using resources of a cell that is not the serving cell. This may enable the WTRU to perform mobility procedures while it has limited, but at least sufficient, configuration to initiate access and / or to be identified in the non-serving cell. For example, the configuration may include, at a minimum, the serving frequency and cell identity, etc. The identification may be based on a configured identity for the WTRU, possibly a RAN area specific identity. The mobility procedures may be generally referred to as forward mobility procedures or uplink mobility procedures.

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

[0148] The following description includes modifications to conventional systems in support of conditional handover.

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

[0150] [Table 1]

[0151] Table 2 includes example steps that a WTRU may perform to initiate a conditional reconfiguration.

[0152] [Table 2]

[0153] Table 3 includes example steps that a WTRU may take to perform a conditional reconfiguration.

[0154] [Table 3]

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

[0156] [Table 4]

[0157] Table 5 includes example steps that the WTRU may perform to delete a stored reconfiguration.

[0158] [Table 5]

[0159] Table 6 includes example steps that a WTRU may perform to detect an RLF.

[0160] [Table 6]

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

[0162] [Table 7]

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

[0164] [Table 8]

[0165] The variable VarConditionalReconfigList may contain information about one or more target cells for which triggering conditions are to be monitored. Table 9 shows the format of the VarConditionalReconfigList variable.

[0166] [Table 9]

[0167] FIG. 5 is a message sequence chart illustrating an example procedure for re-establishment including fallback to CHO. In the example of FIG. 5, the WTRU 500 receives a message 505 (e.g., an RRC reconfiguration message) from the source gNB 510 including a conditional reconfiguration for the gNB 1 515. The WTRU 500 may receive the message 505, for example, after it connects to the source gNB 510. The conditional reconfiguration may include a trigger condition and a configuration to be applied at the gNB 1 515 if the trigger condition occurs. The trigger condition may include, for example, whether the quality of the source gNB 510 is lower than the quality of the gNB 1 515 (e.g., in terms of RSRP, RSRQ, or SINR for the WTRU). The WTRU 500 begins monitoring the trigger condition at step 520. A condition 525 under which the WTRU 500 detects a failure event may or may not satisfy the trigger condition. In condition 530 where the detected failure satisfies the triggering condition, the WTRU 500 performs a conditional reconfiguration from message 505 with the gNB1 515 in step 535. In condition 525 where the detected failure does not satisfy the triggering condition (e.g., there has been an RLF with the source gNB 510), the WTRU 500 enters an enhanced re-establishment procedure 540. In the enhanced re-establishment procedure 540, the WTRU performs cell selection in step 545. For example, the WTRU may select a cell based on one or more of any suitable criteria, such as highest signal quality, highest number of beams detectable by the WTRU, and whether the cell has a valid CHO. In the condition 550 where the selected cell has a valid (e.g., unexpired) CHO configuration (which may be the configuration from message 505 or may be a different configuration), the WTRU 500 performs CHO for the selected cell (e.g., in this example, gNB1 515) in step 555, even if the conditions for conditional reconfiguration are not satisfied.In the condition 550 where the selected cell does not have a valid (e.g., unexpired) CHO configuration, the WTRU 500 performs a re-establishment procedure with the selected cell (e.g., in this example, gNB2 570) in step 560. In this example, the WTRU 500 does not perform a handover to gNB2 570 because it is not configured for handover.

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

[0169] The present invention can be used in wireless communication. [Explanation of symbols]

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

Claims

1. 1. A method for communication by a wireless transmit / receive unit (WTRU) associated with a source cell, comprising: detecting a radio link failure (RLF); performing a cell selection procedure and selecting a cell after detecting the RLF; in response to the selected cell being a candidate for a conditional handover configuration (CHO configuration), performing a conditional handover configuration (CHO) to the selected cell; A method for providing the above.

2. The method of claim 1 , wherein the CHO configuration includes a configured target cell.

3. The method of claim 1 , wherein the CHO configuration includes a trigger condition.

4. The method of claim 3 , wherein the trigger condition includes a threshold quality of a source gNB.

5. The method of claim 1 , wherein the CHO configuration includes a trigger condition different from the RLF.

6. The method of claim 1 , wherein the CHO configuration is different from the RLF.

7. in response to the selected cell being associated with the CHO configuration, performing the CHO to the selected cell regardless of whether a trigger condition for the CHO is satisfied. The method of claim 1 further comprising:

8. responsive to the selected cell being associated with the CHO configuration, performing the CHO to the selected cell based on a trigger condition different from a trigger condition of the CHO. The method of claim 1 further comprising:

9. In response to the selected cell being associated with a different CHO configuration, performing the CHO to the selected cell under the condition that the CHO is valid; The method of claim 1 further comprising:

10. In response to the selected cell being associated with a different CHO configuration, performing the CHO to the selected cell, provided that the CHO has not expired; The method of claim 1 further comprising:

11. A wireless transmit / receive unit (WTRU) associated with a source cell, A transceiver; Processor and Equipped with the transceiver and the processor are configured to detect a radio link failure (RLF); The transceiver and the processor are configured to perform a cell selection procedure and select a cell after detecting the RLF; The transceiver and the processor are configured to perform a conditional handover configuration (CHO) to the selected cell in response to the selected cell being a candidate for a conditional handover configuration (CHO configuration); The transceiver and the processor are configured to perform a re-establishment procedure on a condition that the selected cell is not associated with the CHO configuration. W.T.R.U.

12. The WTRU of claim 11 , wherein the CHO configuration includes a configured target cell.

13. The WTRU of claim 11 , wherein the CHO configuration includes a trigger condition.

14. The WTRU of claim 13, wherein the trigger condition includes a threshold quality of a source gNB.

15. The WTRU of claim 11 , wherein the CHO configuration includes a trigger condition different from the RLF.

16. The WTRU of claim 11 , wherein the CHO configuration is different from the RLF.

17. 12. The WTRU of claim 11, wherein the transceiver and the processor are configured to, in response to the selected cell being associated with the CHO configuration, perform the CHO to the selected cell regardless of whether a trigger condition for the CHO is met.

18. 12. The WTRU of claim 11, wherein the transceiver and the processor are configured to, in response to the selected cell being associated with the CHO configuration, perform the CHO to the selected cell based on a trigger condition different from a trigger condition of the CHO.

19. 12. The WTRU of claim 11, wherein the transceiver and the processor are configured to, in response to the selected cell being associated with a different CHO configuration, perform the CHO to the selected cell under a condition where the CHO is valid.

20. 12. The WTRU of claim 11, wherein the transceiver and the processor are configured to, in response to the selected cell being associated with a different CHO configuration, perform the CHO to the selected cell, provided that the CHO has not expired.

Images