Multi-hop conditional switching

Abstract

A system and method for multi-hop conditional switching is disclosed. In the system and the method, the WTRU can be configured with a plurality of condition reconfigurations, and the condition reconfigurations have an implicit or explicit relationship. WTRU behavior related to the reconfigured processing is based on relationships between the configurations. The WTRU may be configured with a multi-hop CHO in which a CHO configuration to a first target cell is associated with another CHO configuration to a second target cell, which may also be further associated with another CHO configuration to a third target cell, and the like. Upon completion of the CHO configuration at the first hop, the WTRU executes an associated HO command, connects to the first target, and begins monitoring a trigger condition of the CHO configuration at a second hop associated with the first target.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 336,650, filed on April 29, 2022, the contents of which are incorporated herein by reference. Background Art

[0003] The main purpose of describing the concept of Conditional Handover (CHO) is to reduce the possibility of Radio Link Failure (RLF) and Handover Failure (HOF). Conventional LTE / NR handovers are usually triggered by measurement reports, even though there is nothing preventing the network from sending a HO command to the WTRU without receiving a measurement report. For example, when the radio signal level / quality (RSRP, RSRQ, etc.) of the neighboring cell becomes better than the primary serving cell (PCell), the WTRU is configured with an A3 event that triggers a measurement report to be sent. The WTRU monitors the serving cell and the neighboring cells and sends measurement reports when the conditions are met. When such a report is received, the network (current serving node / cell) requests the best neighboring cell / node to grant the WTRU (sends a HO request message) by including information about the WTRU context (e.g., configured bearers, WTRU capabilities, etc.).

[0004] If the neighboring cell / node has sufficient resources to accommodate the WTRU, the neighboring cell / node responds with a HO Request Confirmation message. Embedded in this message is the actual HO Command. The HO Command is an RRC reconfiguration message with the (possibly updated) WTRU bearer configuration and information required to access the target cell (e.g., target cell ID, new C-RNTI, target gNB security algorithm identifier for the selected security algorithm, dedicated RACH resources for performing initial random access, etc.). The serving cell / node transparently forwards this HO Command to the WTRU. The WTRU executes the HO Command, resulting in the WTRU connecting to the target cell. Summary of the invention

[0005] A system and method for multi-hop conditional handover are disclosed. In the system and method, a WTRU may be configured with multiple conditional reconfigurations, wherein the conditional reconfigurations have an implicit or explicit relationship between them. The WTRU behavior associated with the processing of the reconfiguration is based on the relationship between the configurations. The WTRU may be configured with multi-hop CHO, wherein a CHO configuration to a first target cell is associated with another CHO configuration to a second target cell, which may also be further associated with yet another CHO configuration to a third target cell, and so on. Upon completion of the CHO configuration at the first hop, the WTRU executes the associated HO command, connects to the first target, and begins monitoring the triggering condition of the CHO configuration at the second hop associated with the first target.

[0006] In the system and method, a WTRU may be configured with a multi-hop CHO configuration with several hops. The WTRU may monitor trigger conditions for a target at multiple levels simultaneously, and if a trigger condition at a level deeper than the current level is met, sequentially execute HO commands (or at least security updates required for each HO) at previous levels before performing CHO at the deeper level. The WTRU may be configured with a multi-hop CHO configuration that is subject to validity time constraints, and monitor trigger conditions only within a specified validity time. The WTRU may be configured with a multi-hop CHO configuration that is subject to start and stop time constraints, and if the condition is not met, the WTRU starts monitoring the trigger conditions for the CHO configuration at a specified start time and stops monitoring at a stop time.

[0007] In the system and method, the WTRU may include receiving one or more multi-hop conditional handover (CHO) configurations associated with multiple hops of a handover (HO), the configurations including at least one parameter of the one or more CHO configurations. The at least one parameter of the one or more CHO configurations may include one or more target cells in a set of target cells associated with a source cell, one or more measurement criteria for HO associated with each hop, and a validity time duration for monitoring one or more criteria for each or a subset of the source cell and the target cell. In the system and method, the WTRU may include determining at least one hop criterion from the received one or more multi-hop CHO configurations. Determining at least one hop criterion may be based on at least one of the multi-hop CHO configuration, the current hop, and the previous hop source cell-target cell pair. In the system and method, the WTRU may include determining at least one candidate target cell from the received one or more multi-hop CHO configurations. Determining at least one target cell may be based on at least one of the following: the multi-hop CHO configuration, the previous hop source-target pair, the current cell, the previous cell. In the system and method, the WTRU may include monitoring at least one hop criterion determined for at least one candidate target cell. In the system and method, the WTRU may include determining that a candidate target cell meets criteria for one or more monitored hop criteria. The target cell that meets the criteria may include meeting a threshold for measurement. The criteria is based on a multi-hop CHO configuration, a current hop, and a previous hop. In the system and method, the WTRU may include sending using resources associated with the determined candidate target cell that meets the criteria. In the system and method, the WTRU may also include triggering a HO associated with the current hop to the determined candidate target cell that meets the criteria. In the system and method, based on the target cell to which the WTRU performs the HO, the WTRU may also include determining and monitoring the next hop criteria for one or more target cells based on the multi-hop CHO configuration associated with the previous hop and the HO. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] A more detailed understanding may be obtained from the following description given by way of example in conjunction with the accompanying drawings, in which like reference numerals indicate like elements, and in which:

[0009] Figure 1A is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented;

[0010] Figure 1B is an example of an embodiment in which Figure 1A A system diagram of an example wireless transmit / receive unit (WTRU) for use within the illustrated communication system;

[0011] Figure 1C is an example of an embodiment in which Figure 1A a system diagram of an example Radio Access Network (RAN) and an example Core Network (CN) used within the illustrated communication system;

[0012] Figure 1D is an example of an embodiment in which Figure 1A A system diagram of another example RAN and another example CN used within the illustrated communication system;

[0013] Figure 2 illustrates a signal diagram for conditional switching configuration and execution;

[0014] Figure 3A The configuration for HO is illustrated;

[0015] Figure 3B Illustrated with Figure 3A A method associated with configuration of HO;

[0016] Figure 4 A diagram illustrating the generation of key hierarchy in 5GS including derivation of security keys in NR;

[0017] Figure 5A illustrates a diagram illustrating a mobile WTRU moving within a specific exemplary coverage scenario of a 5G NR cell;

[0018] Figure 5B Illustrated with Figure 5A Methods of associating exemplary coverage scenarios;

[0019] Figure 6 illustrates a configuration for illustrating a scenario where a message is sent before the WTRU performs a first level CHO;

[0020] Figure 7illustrates a configuration for illustrating a scenario in which the WTRU may exchange one or more RRC messages (e.g., measurement report, UL information transfer, etc.) to cell A using a first security context associated with cell A while the WTRU is monitoring for a CHO trigger;

[0021] Figure 8 illustrates a configuration for illustrating a scenario where a WTRU attempts CHO from cell A to cell B when a trigger for cell A to cell B CHO is met;

[0022] Fig. 9 An enhanced HO request procedure is illustrated;

[0023] Fig.10 illustrates a multi-hop CHO WTRU configuration and HO triggering procedure; and

[0024] Fig.11 Methods that may be implemented by a wireless transmit receive unit (WTRU) are illustrated. DETAILED DESCRIPTION

[0025] A system and method are disclosed. The system and method may be implemented by a wireless transmit receive unit (WTRU). The system may include a transceiver and a processor operably connected to the transceiver. The system and method include: receiving a plurality of multi-hop conditional handover (CHO) configurations, each configuration being associated with a hop criterion for handover (HO); determining at least a first candidate target cell from the received plurality of multi-hop CHO configurations; monitoring at least a first hop criterion for the first candidate target cell, the first hop criterion being associated with at least the first of the plurality of multi-hop CHO configurations; using measurements associated with the first candidate target cell to determine that the first candidate target cell satisfies the first hop criterion; establishing a connection to the determined first candidate target cell; determining at least a second candidate target cell from the received plurality of multi-hop CHO configurations; monitoring at least a second hop criterion for the second candidate target cell, the second hop criterion being associated with at least the second of the plurality of multi-hop CHO configurations; using measurements associated with the second candidate target cell to determine that the second candidate target cell satisfies the second hop criterion; and establishing a connection to the determined second candidate target cell.

[0026] The system and method may include monitoring at least a first hop criterion including the WTRU performing measurements and comparing the measurements taken with the first hop criterion. The system and method may include the first hop criterion and the second hop criterion being the same. The system and method may include a processor and a transceiver, which further operates to transmit using radio resources associated with the determined first candidate target cell based on a connection established with the determined first candidate target cell. The system and method may include a processor and a transceiver, which further operates to transmit using radio resources associated with the determined second candidate target cell based on a connection established with the determined second candidate target cell. The system and method may include a processor and a transceiver, which further operates to monitor at least a third hop criterion for a third candidate target cell, the third hop criterion being associated with at least one of a plurality of multi-hop CHO configurations; using measurements associated with the third candidate target cell to determine that the third candidate target cell meets the third hop criterion; and establishing a connection to the determined third candidate target cell. The systems and methods may include the received multiple multi-hop CHO configurations including one or more of: a set of target cells associated with a source cell per hop; one or more measurement criteria for HO associated with each hop; and a validity time duration for monitoring one or more criteria for each or a subset of the source cell and the target cells. The systems and methods may include the second hop criteria being based on at least one of: the received multiple multi-hop CHO configurations; an established connection to the determined first candidate target cell; and a previously established connection of the WTRU and a previous hop criteria for HO. The systems and methods may include determining that at least the first target cell is based on at least one of: the received multiple multi-hop CHO configurations, the established connection to the determined first candidate target cell, and a previously established connection of the WTRU and a previous hop criteria for HO. The systems and methods may include the first candidate target cell that meets at least the first hop criteria including exceeding a threshold value on a measurement associated with the first target cell.

[0027] Figure 1A1 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 multiple wireless users to access such content through sharing of system resources (including wireless bandwidth). For example, the communication system 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single carrier FDMA (SC-FDMA), zero tail unique word discrete Fourier transform spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, filter bank multi-carrier (FBMC), etc.

[0028] like Figure 1A As shown, the communication system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network (CN) 106, a public switched telephone network (PSTN) 108, the Internet 110 and other networks 112, but it should be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d (any of which may be referred to as a station (STA)) may be configured to send and / or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular phone, a personal digital assistant (PDA), a smart phone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable device, a head-mounted display (HMD), a vehicle, a drone, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in an industrial and / or automated process chain environment), a consumer electronic device, a device operating on a commercial and / or industrial wireless network, etc. Any of the WTRUs 102a, 102b, 102c, and 102d may be interchangeably referred to as a UE.

[0029] 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, 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 evolved Node B (eNB), a Home Node B, a Home evolved Node B, a next generation Node B (such as a gNode B (gNB)), a new radio (NR) Node B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0030] The base station 114a may be part of the RAN 104, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), a relay node, etc. The base station 114a and / or the base station 114b may be configured to send and / or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in a licensed spectrum, an unlicensed spectrum, or a combination of licensed and unlicensed spectrums. A cell may provide coverage of wireless services to a specific geographic area, which may be relatively fixed or may change over time. The cell may be further divided into cell sectors. For example, a cell associated with the base station 114a may be divided into three sectors. Therefore, in one embodiment, the base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple-output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming may be used to send and / or receive signals in a desired spatial direction.

[0031] 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).

[0032] More specifically, as noted above, the communication system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology, such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), that may use Wideband CDMA (WCDMA) to establish the air interface 116. 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).

[0033] 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 Advanced LTE (LTE-A) and / or Advanced LTE Pro (LTE-A Pro).

[0034] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology (such as NR radio access) that may establish the air interface 116 using NR.

[0035] 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 together implement LTE radio access and NR radio access, for example using the 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 transmitted to / from multiple types of base stations (e.g., eNBs and gNBs).

[0036] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi)), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), etc.

[0037] Figure 1A The base station 114b in the 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 local areas such as commercial venues, homes, vehicles, campuses, industrial facilities, sky corridors (e.g., for use by drones), roads, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement radio technologies 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 radio technologies such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish a picocell or a femtocell. As Figure 1A As shown, the base station 114b may have a direct connection to the Internet 110. Therefore, the base station 114b may not be required to access the Internet 110 via the CN 106.

[0038] The RAN 104 may be in communication with the CN 106, which may be any type of network configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have different quality of service (QoS) requirements, such as different throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, etc. The CN 106 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions, such as user authentication. Although not described in detail in the specification, the CN 106 may be configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. Figure 1AAlthough not shown in the figure, it will be appreciated that the RAN 104 and / or the CN 106 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may utilize NR radio technology, the CN 106 may also be in communication with another RAN (not shown) that employs GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

[0039] The CN 106 may also act 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 that provides plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and / or the Internet Protocol (IP) in the TCP / IP Internet protocol suite. The networks 112 may include wired communication networks and / or wireless communication networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0040] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication 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 via different wireless links). Figure 1A The illustrated WTRU 102c may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0041] Figure 1B is a system diagram illustrating an example WTRU 102. Figure 1B As shown, 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 appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0042] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), any other type of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal decoding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. Although Figure 1B The processor 118 and the transceiver 120 are depicted as separate components, but it is understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0043] The send / receive element 122 may be configured to send a signal to a base station (e.g., base station 114a) or receive a signal from the base station via an air interface 116. For example, in one embodiment, the send / receive element 122 may be an antenna configured to send and / or receive an RF signal. In an embodiment, the send / receive element 122 may be a transmitter / detector configured to send and / or receive, for example, IR, UV or visible light signals. In another embodiment, the send / receive element 122 may be configured to send and / or receive both RF signals and optical signals. It should be understood that the send / receive element 122 may be configured to send and / or receive any combination of wireless signals.

[0044] Although the transmit / receive element 122 Figure 1B 1 as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0045] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. For example, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11.

[0046] 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 access 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 a memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0047] The processor 118 may receive power from the power source 134, and may be configured to distribute and / or control power to other components in 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 cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0048] The processor 118 may also be coupled to the 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 in lieu of the information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (e.g., base stations 114a, 114b) over the air interface 116 and / or determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by any suitable location-determination method while remaining consistent with an embodiment.

[0049] The processor 118 may also be coupled to other peripherals 138, which may include one or more software modules and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos and / or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, 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, etc. The peripheral device 138 may include one or more sensors. The sensor may be one or more of the following: a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geographic location sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, a humidity sensor, etc.

[0050] The WTRU 102 may include a full-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with specific subframes for both UL (e.g., for transmission) and DL (e.g., for reception)) may be concurrent and / or simultaneous. The full-duplex radio may include an interference management unit for reducing and / or substantially eliminating self-interference via signal processing performed by hardware (e.g., a choke) or via a processor (e.g., a separate processor (not shown) or via the processor 118). In an embodiment, the WTRU 102 may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with specific subframes for both UL (e.g., for transmission) or DL ​​(e.g., for reception)) may be concurrent and / or simultaneous.

[0051] Figure 1C 1 is a system diagram illustrating the RAN 104 and the CN 106 according to one embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0052] The RAN 104 may include evolved Node-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of evolved Node-Bs while remaining consistent with an embodiment. The evolved Node-Bs 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 evolved Node-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the evolved Node-B 160a, for example, may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0053] Each of the evolved Node Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, etc. Figure 1C As shown, the eNode-Bs 160a, 160b, 160c may communicate with one another via an X2 interface.

[0054] Figure 1C The illustrated CN 106 may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (PGW) 166. Although the foregoing elements are depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0055] The MME 162 may be connected to each of the evolved Node-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may serve 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 an 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.

[0056] The SGW 164 may be connected to each of the evolved Node-Bs 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-evolved Node-B handovers, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, and the like.

[0057] The SGW 164 may be connected to the 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.

[0058] 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 land-line communications devices. For example, the CN 106 may include, or may be in communication with, an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired networks and / or wireless networks owned and / or operated by other service providers.

[0059] Although the WTRU Figures 1A to 1D Although described as wireless terminals, it is contemplated that in certain representative embodiments, such terminals may (eg, temporarily or permanently) use a wired communication interface with a communication network.

[0060] In a representative embodiment, the other network 112 may be a WLAN.

[0061] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STA) associated with the AP. The AP may have access or an interface to a distribution system (DS) or another type of wired / wireless network that carries traffic to and / or carries traffic away from the BSS. Traffic originating from outside the BSS and leading to the STA may be reached by the AP and may be delivered to the STA. Traffic originating from the STA and leading to a destination outside the BSS may be transmitted to the AP to be delivered to the corresponding destination. Traffic between STAs within the BSS may be transmitted by the AP, for example, wherein the source STA may transmit traffic to the AP, and the AP may deliver traffic to the target STA. Traffic between STAs within the BSS may be considered and / or referred to as point-to-point traffic. Direct link establishment (DLS) may be used to transmit point-to-point traffic between the source STA and the target STA (e.g., directly between them). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z tunnel DLS (TDLS). A WLAN using an independent BSS (IBSS) mode may not have an AP, and STAs within or using the IBSS (eg, all STAs in the STA) may communicate directly with each other. The IBSS communication mode may sometimes be referred to herein as an "ad-hoc" communication mode.

[0062] When using the 802.11ac infrastructure operating mode or a similar operating mode, the AP may send beacons on a fixed channel (such as a primary channel). The primary channel may be a fixed width (e.g., a 20 MHz wide bandwidth) or a dynamically set width. The primary channel may be a working channel of the BSS and may be used by the STA to establish a connection with the AP. In certain representative embodiments, carrier sense multiple access / collision avoidance (CSMA / CA) may be implemented, for example, in an 802.11 system. For CSMA / CA, a STA (e.g., each STA) (including the AP) may listen to the primary channel. If the primary channel is listened / detected and / or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0063] High throughput (HT) STAs may communicate using a 40 MHz wide channel, for example, via a combination of a primary 20 MHz channel and adjacent or non-adjacent 20 MHz channels to form a 40 MHz wide channel.

[0064] Very high throughput (VHT) STA can support 20MHz, 40MHz, 80MHz and / or 160MHz wide channels. 40MHz channels and / or 80MHz channels can be formed by combining continuous 20MHz channels. 160MHz channels can be formed by combining 8 continuous 20MHz channels, or by combining two non-continuous 80MHz channels (this can be called 80+80 configuration). For 80+80 configuration, after channel coding, the data can pass through a segment parser that can divide the data into two streams. Each stream can be processed by inverse fast Fourier transform (IFFT) and time domain processing separately. These streams can be mapped to two 80MHz channels, and data can be sent by sending STA. At the receiver of the receiving STA, the above-mentioned operation for 80+80 configuration can be reversed, and the combined data can be transmitted to the medium access control (MAC).

[0065] 802.11af and 802.11ah support operating modes below 1GHz. Channel operating bandwidths and carriers are reduced in 802.11af and 802.11ah relative to those used in 802.11n and 802.11ac. 802.11af supports 5MHz, 10MHz, and 20MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1MHz, 2MHz, 4MHz, 8MHz, and 16MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah may support meter type control / machine type communication (MTC), such as MTC devices in macro coverage areas. MTC devices may have certain capabilities, such as limited capabilities, including support for (e.g., only support for) certain bandwidths and / or limited bandwidths. MTC devices may include batteries with battery life above a threshold (e.g., to maintain very long battery life).

[0066] WLAN systems that can support multiple channels and channel bandwidths (such as 802.11n, 802.11ac, 802.11af, and 802.11ah) include channels that can be designated as primary channels. 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 (which supports the minimum bandwidth operation mode) from all STAs operating in the BSS. In the example of 802.11ah, for STAs (e.g., MTC-type devices) that support (e.g., only support) a 1MHz mode, the primary channel may be 1MHz wide, even if the AP and other STAs in the BSS support 2MHz, 4MHz, 8MHz, 16MHz, and / or other channel bandwidth operation modes. Carrier sensing and / or network allocation vector (NAV) settings may depend on the state of the primary channel. If the primary channel is busy, for example, because a STA (which only supports a 1MHz operation mode) is transmitting to the AP, all available bands may be considered busy even if most of the available bands remain idle.

[0067] In the United States, the available frequency band for 802.11ah is 902MHz to 928MHz. In South Korea, the available frequency band is 917.5MHz to 923.5MHz. In Japan, the available frequency band is 916.5MHz to 927.5MHz. The total bandwidth available for 802.11ah is 6MHz to 26MHz, depending on the country code.

[0068] Figure 1D1 is a system diagram illustrating the RAN 104 and the CN 106 according to one embodiment. As noted above, the RAN 104 may employ NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0069] The RAN 104 may include gNBs 180a, 180b, 180c, though it will be appreciated that the RAN 104 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, 180b may utilize beamforming to send signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a may, for example, use multiple antennas to send wireless signals to and / or receive wireless signals from the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, gNB 180a may transmit multiple component carriers to WTRU 102a (not shown). A subset of these component carriers may be on unlicensed spectrum, while the remaining component carriers may be on licensed spectrum. In an embodiment, gNBs 180a, 180b, 180c may implement coordinated multi-point (CoMP) technology. For example, WTRU 102a may receive coordinated transmissions from gNB 180a and gNB 180b (and / or gNB 180c).

[0070] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with parameter sets that may be scalable. For example, OFDM symbol spacing and / or OFDM subcarrier spacing may vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using subframes or Transmission Time Intervals (TTIs) of varying or scalable lengths (e.g., containing varying numbers of OFDM symbols and / or varying absolute time lengths over time).

[0071] 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 while not accessing other RANs (e.g., such as the eNodeBs 160a, 160b, 160c). In a standalone configuration, the WTRUs 102a, 102b, 102c may use one or more of the gNBs 180a, 180b, 180c as mobility anchors. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate / connect with the gNB 180a, 180b, 180c while also communicating / connecting with another RAN, such as the eNode-B 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 eNode-Bs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNode-B 160a, 160b, 160c may act as a mobility anchor for the WTRUs 102a, 102b, 102c, and the gNB 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0072] Each of the gNBs 180a, 180b, 180c may be associated with a specific cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in UL and / or DL, support of network slicing, interworking between DC, NR, and E-UTRA, routing of user plane data towards a user plane function (UPF) 184a, 184b, routing of control plane information towards an access and mobility management function (AMF) 182a, 182b, etc. Figure 1D As shown, gNBs 180a, 180b, and 180c may communicate with each other via an Xn interface.

[0073] Figure 1D The illustrated CN 106 may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one session management function (SMF) 183a, 183b, and possible data networks (DNs) 185a, 185b. Although the aforementioned elements are depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0074] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via the N2 interface and may act as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRU 102a, 102b, 102c, support of network slicing (e.g., handling of different protocol data unit (PDU) sessions with different requirements), selecting a specific SMF 183a, 183b, management of registration areas, termination of non-access stratum (NAS) signaling, mobility management, etc. The AMF 182a, 182b may use network slicing in order to customize CN support for the WTRU 102a, 102b, 102c based on the type of services utilized by the WTRU 102a, 102b, 102c. For example, different network slices may be established for different use cases, such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for MTC access, etc. The AMF 182a, 182b may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies, such as WiFi.

[0075] The SMF 183a, 183b may be connected to the AMF 182a, 182b in the CN 106 via the N11 interface. The SMF 183a, 183b may also be connected to the UPF 184a, 184b in the CN 106 via the N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b, and configure the traffic routing through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating UE IP addresses, managing PDU sessions, controlling policy implementation and QoS, providing DL data notification, etc. The PDU session type may be IP-based, non-IP-based, Ethernet-based, etc.

[0076] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via the 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 UPF 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering DL packets, providing mobility anchoring, etc.

[0077] The CN 106 may facilitate communications with other networks. For example, the CN 106 may include or may communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired networks and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to the DNs 185a, 185b via the UPFs 184a, 184b via the N3 interfaces to the UPFs 184a, 184b and the N6 interfaces between the UPFs 184a, 184b and the local DNs 185a, 185b.

[0078] Given that Figures 1A to 1D as well as Figures 1A to 1D In accordance with the corresponding description of the present invention, one or more or all of the functions described herein with reference to one or more of the following items may be performed by one or more simulation devices (not shown): WTRU 102a-102d, base station 114a-114b, evolved Node B 160a-160c, MME 162, SGW 164, PGW 166, gNB 180a-180c, AMF 182a-182b, UPF 184a-184b, SMF 183a-183b, DN 185a-185b and / or any other device described herein. The simulation device may be one or more devices configured to mimic one or more or all of the functions described herein. For example, the simulation device may be used to test other devices and / or simulate network and / or WTRU functions.

[0079] The simulation device may be designed to implement one or more tests of other devices in a laboratory environment and / or in an operator network environment. For example, one or more simulation devices may perform one or more functions or all functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network in order to test other devices within the communication network. One or more simulation devices may perform one or more functions or all functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The simulation device may be directly coupled to another device for the purpose of testing and / or performing tests using over-the-air wireless communications.

[0080] One or more simulation devices can perform one or more (including all) functions without being implemented / deployed as part of a wired and / or wireless communication network. For example, the simulation device can be used in a test scenario in a test laboratory and / or a non-deployed (e.g., testing) wired and / or wireless communication network to implement testing of one or more components. One or more simulation devices can be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (e.g., which can include one or more antennas) can be used by the simulation device to send and / or receive data.

[0081] The main purpose of describing the concept of Conditional Handover (CHO) is to reduce the possibility of Radio Link Failure (RLF) and Handover Failure (HOF). Conventional LTE / NR handovers are usually triggered by measurement reports, even though there is nothing preventing the network from sending a HO command to the WTRU without receiving a measurement report. For example, when the radio signal level / quality (RSRP, RSRQ, etc.) of the neighboring cell becomes better than the primary serving cell (PCell), the WTRU is configured with an A3 event that triggers a measurement report to be sent. The WTRU monitors the serving cell and the neighboring cells and sends measurement reports when the conditions are met. When such a report is received, the network (current serving node / cell) requests the best neighboring cell / node to grant the WTRU (sends a HO request message) by including information about the WTRU context (e.g., configured bearers, WTRU capabilities, etc.).

[0082] If the neighboring cell / node has sufficient resources to accommodate the WTRU, the neighboring cell / node responds with a HO Request Confirmation message. Embedded in this message is the actual HO Command. The HO Command is an RRC reconfiguration message with the (possibly updated) WTRU bearer configuration and information required to access the target cell (e.g., target cell ID, new C-RNTI, target gNB security algorithm identifier for the selected security algorithm, dedicated RACH resources for performing initial random access, etc.). The serving cell / node transparently forwards this HO Command to the WTRU. The WTRU executes the HO Command, resulting in the WTRU connecting to the target cell.

[0083] CHO differs from conventional handover in two main aspects: multiple handover targets are prepared (compared to only one target in the conventional case); and the WTRU does not perform CHO immediately as in the case of conventional handover. Instead, the WTRU is configured with a trigger condition (a set of radio conditions), and when / if the trigger condition is met, the WTRU performs a handover towards one of the targets.

[0084] The CHO command may be sent when the radio conditions on the current serving cell are still good, thereby reducing two major failure points in traditional handovers. The two major failure points include the WTRU's failure to send measurement reports on time (e.g., if the link quality to the current serving cell drops below an acceptable level when the measurement report is triggered) and the failure to receive a handover command (e.g., if the link quality to the current serving cell drops below an acceptable level after the WTRU has sent a measurement report but before it has received a HO command).

[0085] The trigger conditions for CHO may be based on the radio quality of the serving cell and the neighboring cells, similar to the conditions used in traditional NR / LTE for triggering measurement reports. For example, the WTRU may be configured with CHO with a trigger condition similar to A3 and an associated HO command. The WTRU may monitor the current cell and the serving cell, and when the A3 trigger condition is met, the WTRU may execute the associated HO command to switch the connection to the target cell instead of sending a measurement report.

[0086] Figure 2 A signal diagram 200 for conditional switching configuration and execution is illustrated. Figure 2 2, for simplicity, only one target node 275 is configured for CHO. When operating with a source node 255, the WTRU 225 may be configured with other potential target nodes 275. At 210, the source node 255 may initiate a CHO request with the potential target node 275. At 220, the potential target node 275 may confirm the CHO request to the source node 255. At 230, the source node 255 may provide the CHO configuration to the WTRU 225. At 240, the WTRU 225 monitors the CHO conditions for the target cell candidates. If the CHO conditions are met, the WTRU 225 may perform HO at 250. At 260, the WTRU 225 may send a CHO confirmation to the potential target node 275 (which is in the process of being switched to). At 270, the potential target node 275 operates to switch the path and provide the WTRU 225 context release.

[0087] As will be appreciated, the network may prepare several CHO candidates and provide multiple CHO configurations to the WTRU 225, each CHO configuration corresponding to a particular CHO candidate. The WTRU 225 may monitor trigger conditions for different CHO configurations and may perform CHO towards a target that satisfies the trigger conditions (such as a first target to be satisfied). While performing CHO, the WTRU 225 may delete / release other CHO configurations. The network may release resources reserved for the WTRU 225 at candidate CHO targets other than the candidate CHO target to which the WTRU 225 is switched.

[0088] Another benefit of CHO is the elimination of unnecessary reestablishment in the event of a radio link failure. For example, if the WTRU 225 is configured with multiple CHO targets, and the WTRU 225 experiences RLF before the triggering conditions with any of the targets are met, conventional operation would result in an RRC reestablishment procedure that would incur a significant outage time for the WTRU's bearers. However, in the case of CHO, if the WTRU 225 eventually arrives at a cell with which the WTRU 225 has CHO associated after detecting RLF (i.e., a target cell has been prepared for the WTRU), the WTRU 225 executes a HO command associated with that target cell instead of continuing with a full reestablishment procedure.

[0089] Figure 3A A configuration for HO 300 is illustrated. Figure 3B Illustrated with Figure 3A The method 350 associated with the configuration of the HO 300. Figure 3A , Figure 3B , at 355, the WTRU 305 moves in the RRC_CONNECTED state in cell A 310. At 360, the WTRU 305 receives a CHO configuration from the NG-RAN node A 315. This may include a list of target cells (B, C, D) at 365 and cell evaluation criteria at 370, which in one embodiment may be per cell. At 375, the WTRU 305 may evaluate the criteria according to the measurement configuration. At 380, when the criteria are met, the WTRU 305 may trigger a HO. For example, as the WTRU 305 moves at 345, cell B 320, cell C 330, and cell D 340 may be monitored. When the movement causes the WTRU 305 to measure that the criteria are met for one cell (cell B 320, cell C 330, and cell D 340), a HO to that cell may be triggered.

[0090] The CHO configuration may be configured with a WTRU configuration. In NR, each measurement configuration is identified by a unique measID and is associated with a measObject and a reportConfig. Tables 1-3 below illustrate information elements (IEs) for configuring a WTRU with measurements and measurement reports (included within an RRC reconfiguration message).

[0091] Table 1 - MeasIdToAddModList information elements

[0092]

[0093] Table 2 - MeasObjectToAddModList information elements

[0094]

[0095] Table 3 - ReportConfigToAddModList information elements

[0096]

[0097] The CHO configuration (or more precisely, conditional reconfiguration) may be provided to the WTRU using an RRC message containing lcondReconfigToAddModList, which is defined as follows:

[0098]

[0099] Where condExecutionCond-r16 is the execution condition that needs to be satisfied in order to trigger the execution of the conditional reconfiguration given by MeasID, ie, the binding of a specific measurement object and reporting configuration linked to a specific cell ID.

[0100] When a specific CHO trigger criterion is set for CHO instead of measurement reporting, the specific CHO trigger criterion may be defined by the reporting criterion.

[0101] In one example, IE ReportConfigNR may look like this:

[0102]

[0103] and where condExecutionCond-r16 is defined as

[0104]

[0105] In practical applications, this means that two events may be used as triggers for the WTRU to trigger CHO, including CondEvent A3: conditional reconfiguration candidate may be better than the offset of PCell / PSCell, and CondEvent A5: PCell / PSCell may be worse than absolute threshold 1, and conditional reconfiguration candidate may be better than another absolute threshold 2. The criteria for an event may be met for the duration specified in the timeToTrigger parameter before the criteria are considered met and the WTRU performs a conditional reconfiguration evaluation.

[0106] Figure 4 A diagram 400 is illustrated of the generation of a key hierarchy in 5GS including the derivation of security keys in NR. The keys generated by the key hierarchy are described below. The key hierarchy may include the following keys: K AUSF 403, K SEAF 408, K AMF 413, K NASint 418, K NASenc 423.K N3IWF 428, K gNB 433, K RRCint 438, K RRCenc 443, K UPint 448 and K UPenc 453. While many of these key hierarchies are understood, the following discussion is relevant to the access layer.

[0107] The NG-RAN key consists of the keys obtained by ME and AMF from K AMF K obtained from 413 gNB 433. When performing horizontal or vertical key derivation, K gNB 433 is further derived by ME and source gNB. K gNB 433 is used as K between ME and ng-eNB eNB .

[0108] The UP service key consists of the key obtained by ME and gNB from K gNB K obtained from 433 UPenc 453, which is used to protect UP services using a specific encryption algorithm, and ME and gNB from K gNB K obtained from 433 UPint 448, which is used to protect UP services between ME and gNB using a specific integrity algorithm.

[0109] The key for RRC signaling consists of K gNB K obtained from 433 RRCint438, which is used to protect RRC signaling using a specific integrity algorithm, and K derived by ME and gNB from KgNB RRCenc 443, which is used to protect RRC signaling using a specific encryption algorithm.

[0110] The intermediate keys include NH derived by the ME and AMF to provide forward security, and K derived by the ME and NG-RAN (i.e., gNB or ng-eNB) when performing horizontal or vertical key derivation. NG-RAN *(If the target is gNB, then K gNb *, or K if the target is an eNB eNB *).

[0111] Whenever an initial AS security context needs to be established between the WTRU and the gNB, the AMF and the WTRU derive K gNB 433 and the next hop parameter (NH). K gNB 433 and NH from K AMF 413. The NH link counter (NCC) is associated with each K gNB 433 is associated with the NH parameter. Each K gNB 433 is associated with the NCC corresponding to the NH value derived from it. gNB 433 Directly from K AMF 413 is derived and is subsequently considered to be associated with a virtual NH parameter having an NCC value equal to 0. At initial setup, the derived NH value is associated with an NCC value of 1. At handover, the K used between the WTRU and the target gNB gNB 433 basis (called K gNB *) is from the currently active K gNB 433 or derived from the NH parameters. If K gNB * is from the currently active K gNB 433, it is called horizontal key derivation and is indicated to the WTRU without increasing the NCC. gNB * is derived from the NH parameter, then the derivation is called vertical key derivation and is indicated to the WTRU and the NCC is increased. Finally, when the new K gNB 433 and later based on K gNB 433 gets K RRCint 438, K RRCenc 443, K UPint 448 and K UPenc 453.

[0112] Using such a key, we have K shared with the WTRU. gNBThe gNB with knowledge of 433 cannot calculate any previous K that has been used between the same WTRU and a previous gNB gNB 433, thus providing backward security. Similarly, with K shared with the WTRU gNB The gNB with knowledge of 433 cannot predict any future K that will be used between the same WTRU and another gNB after n or more handovers. gNB 433 (because the NH parameter can only be calculated by WTRU and AMF).

[0113] In case of handover with vertical key derivation, NH is used as K in the target gNB. gNB 433 is further bound to the target PCI and its frequency ARFCN-DL. In the case of a switch with a horizontal key, the currently active K gNB 433 is used as K in the target gNB gNB 433 is further bound to the target PCI and its frequency ARFCN-DL. That is, when K gNB At 433, the PCI and ARFCN (ie, the absolute frequency of the SSB of the target cell) are used as input to a security key derivation function (KDF).

[0114] Provides the WTRU with a baseline security key (e.g., K gNB 433. NH), the WTRU uses this baseline security key to derive the actual security keys used for encryption and integrity protection in the UL and decryption and integrity verification in the DL, both for the UP and CP. The derivation of these keys may use cell-specific information such as the PCI and frequency used in the cell.

[0115] When a WTRU is handed over, the security keys need to be updated (ie, both the target and the WTRU may start using the updated keys), and this is one of the main functions of the handover procedure.

[0116] When a WTRU is configured with CHO, this means that the CHO candidate cells have performed admission control and reserved the resources required to accommodate the WTRU. Because the WTRU is given radio condition related criteria that need to be met before it performs CHO, the NW node does not know exactly when the WTRU will perform CHO. Therefore, the target node needs to keep the relevant resources reserved until the WTRU is switched (i.e., the CHO conditions are met and the WTRU executes a CHO command) or the source instructs the target to release the resources (for example, if there are multiple CHO targets, when the WTRU performs CHO to one of the targets, that particular target node will notify the source node, and the source will communicate with the remaining targets to cancel the CHO and release the resources reserved for that WTRU).

[0117] The more target cells are prepared, the higher the probability of preventing RLF / HOF and the WTRU can connect to the best target cell. However, preparing multiple target cells is resource intensive and in some embodiments, the number of simultaneous CHO configurations / monitorings that the WTRU can perform is limited to 8 (maxNrofCondCells). Therefore, the network may compromise and limit the number of CHO targets (e.g., based on load conditions).

[0118] Handover (whether HO or CHO based on measurement reports) is a one-hop system / decision involving one source node / cell and a target node / cell. Since the source node can only know its own neighboring cells and some knowledge of where the WTRU is directed (e.g., measurement reports or some WTRU location / track information, if available), the source node can provide the WTRU with a one-hop HO / CHO configuration.

[0119] Figure 5A FIG500 illustrates a mobile WTRU moving within a specific exemplary coverage scenario of a 5G NR cell. For this discussion, it is assumed that all cells belong to different base stations. Under the current 3GPP specification, a WTRU 505 in cell A 510 may receive multiple CHO configurations for hop 1 (one CHO configuration involving each neighboring cell of cell A 510, i.e., cell B 520, cell D 540, and cell F 560). If the CHO trigger condition for cell B 520 is met, and the WTRU 505 switches to cell B 520. At HO, the WTRU 505 deletes the CHO configuration towards cell D 540 and cell F 560. If CHO is to be used (again) when in cell B 520, the WTRU 505 has to be provisioned with additional CHO configurations when in cell B 520, this time possibly involving cell A 510, cell C 530, cell D 540, cell E 550, cell F 560, and cell G 570. This process is repeated after each CHO execution (i.e., CHO is performed to one candidate target, all other CHO configurations are released, the new serving cell / node provides the WTRU 505 with new CHO configurations associated with the neighbors of the new serving cell, etc.).

[0120] This approach may provide a reasonable / practical way to perform the handover if the network does not know the trajectory of the WTRU 505. However, if the network can predict / estimate the trajectory of the WTRU 505 (e.g., based on AI / ML techniques, possibly with some feedback information from the WTRU 505), limiting the CHO configuration to only one hop is suboptimal, e.g., for failure scenarios, as the signaling overhead and trajectory information are not used to the maximum extent.

[0121] For failure scenarios, CHO towards the target may fail for several reasons (e.g. RA failure due to RACH congestion). Reestablishment may be triggered when a failure occurs (unless the cell reselection after the failure is to another CHO candidate cell, in which case CHO to that target is performed).

[0122] However, from a signaling and WTRU performance perspective, a better solution may be to keep the WTRU 505 in the source cell (e.g., if conditions toward the source cell are still good enough) or immediately perform a CHO to a neighboring cell of the source cell or target cell, as described herein.

[0123] For signaling overhead, when a WTRU switches from a source cell to a target cell, there may be multiple cells that are neighbors of both cells. Soon after the HO, the WTRU 505 may need to switch cells again. In the absence of this example, other configurations may be released. Additionally or alternatively, when a cell switch fails soon after performing a HO and there are other configurations for the WTRU 505 to perform, using two cells may be beneficial.

[0124] With the current CHO mechanism, the WTRU 505 must release the CHO configuration to these neighboring cells when CHO is performed, and must receive the CHO configuration for these neighboring cells from the target cell. Figure 5A 500, the WTRU 505 releases the CHO configuration towards cell D 540 and cell F 560 when switching to cell B 520, and is then again provided with the CHO configuration towards cell D 540 and cell F 560. The new CHO configuration may involve unnecessary signaling and processing on the network side (e.g., cell A 510 notifies cell D 540 and cell F 560 to reserve resources for the WTRU 505 and then releases the resources, cell B 520 notifies cell D 540 and cell F 560 to reserve resources again, etc.).

[0125] By adopting AI / ML techniques in the RAN, the network can have a more accurate prediction of the trajectory of the WTRU. The network can estimate very accurately when the WTRU exactly needs to be handed over and to which specific cell the WTRU needs to be handed over. In the case of only one-hop handover, such trajectory information can be used only at one cell at a time, instead of a more optimal handover configuration that can be used by the WTRU for a longer duration as the WTRU traverses several cells. The current CHO mechanism defined in 3GPP only allows for suboptimal one-hop CHO from the perspective of WTRU / network signaling overhead and WTRU performance. The present system and method for implementing multi-hop CHO are disclosed. In order to configure multi-hop CHO, the network can use the information it may have about the predicted WTRU trajectory, the current and predicted network resources at the target node, etc. A person of ordinary skill in the art will understand the details of how the network can collect this information. In the description of the solution below, the terms "level", "depth" and "hop" are used interchangeably.

[0126] A WTRU may be configured with multiple conditional reconfigurations with implicit or explicit relationships between the conditional reconfigurations (or portions thereof). The WTRU behavior associated with the processing of the reconfigurations (or portions thereof) may be based on the relationships between the configurations. In one solution, the WTRU may receive multiple conditional reconfigurations and explicit relationships between the conditional reconfigurations. For example, the explicit relationship may be configured by signaling a link between identifiers associated with each conditional reconfiguration. The links may be sequential or parallel. In another solution, the WTRU may receive multiple conditional reconfigurations and implicit relationships between the conditional reconfigurations. For example, the implicit relationship may be configured by signaling sequential conditional reconfigurations as a list within an AddModList information element.

[0127] The WTRU may receive multiple conditional reconfigurations with a sequential relationship between the conditional reconfigurations. In one solution, the WTRU may be configured with a first conditional reconfiguration, a second conditional reconfiguration, and a sequential relationship between the first conditional reconfiguration and the second conditional reconfiguration. When a sequential relationship is configured, the WTRU may consider the second conditional reconfiguration valid only after the successful application of the first conditional reconfiguration.

[0128] The WTRU may receive multiple conditional reconfigurations where the execution conditions have different relationships with the RRC reconfiguration of a single conditional reconfiguration. The conditional reconfiguration may have two parts - an execution condition and an RRC reconfiguration - where the WTRU may be configured to apply the RRC reconfiguration when the execution condition is met. In one solution, the WTRU may receive a first conditional reconfiguration and a second conditional reconfiguration - where different relationships may be configured between the execution conditions and the RRC reconfigurations contained in the first conditional reconfiguration and the second conditional reconfiguration. In one example, the WTRU may be configured with a sequential relationship between the execution conditions in the first conditional reconfiguration and the execution conditions in the second conditional reconfiguration. In such an example, after the successful application of the RRC configuration associated with the first conditional reconfiguration, the WTRU may begin monitoring the execution conditions associated with the second conditional reconfiguration. In another example, the WTRU may be configured with a parallel relationship between the execution conditions in the first conditional reconfiguration and the execution conditions in the second conditional reconfiguration. In such an example, the WTRU may begin monitoring the execution conditions associated with the second conditional reconfiguration at the same time as it begins monitoring the execution conditions associated with the first conditional reconfiguration.

[0129] One or more of the solutions described herein may be extended to N number of conditional reconfigurations. Each conditional reconfiguration may have a sequential relationship with one other conditional reconfiguration (or a portion thereof) - resulting in N-1 sequential relationships. This may be extended to the case where a first conditional reconfiguration may have a sequential relationship with N other conditional reconfigurations (or portions thereof). When the first conditional reconfiguration succeeds, the N other conditional reconfigurations (or portions thereof) may become valid.

[0130] From the WTRU's perspective, there may be a baseline multi-hop CHO configuration configured. The WTRU may be configured with a CHO configuration associated with sequential HO towards several cells, i.e., comprising several levels / hops. The WTRU monitors the triggering conditions of the target cells at the same level / hop of the CHO configuration. When the conditions for one of the target cells are met, the WTRU may perform CHO associated with that target cell while maintaining the CHO configuration in the next level associated with the selected candidate cell and releasing the other CHO configurations.

[0131] The following is about Figure 5A One such example configuration is provided. Generally, this type of configuration may be referred to as a baseline multi-hop CHO configuration. This configuration may be provided to the WTRU 505 when the WTRU 505 is in a source cell S (not shown):

[0132] 1.CHO configuration A:

[0133] Target cell: Cell A 510

[0134] Trigger condition (e.g. Cond A3 event with threshold_A)

[0135] HO command_A

[0136] 2.CHO Configuration B

[0137] Target cell: Cell B 520

[0138] Trigger condition (e.g., cond A3 event with threshold_B)

[0139] HO command_B

[0140] 3.CHO configuration C

[0141] Target cell: Cell C 530

[0142] Trigger condition (e.g., cond A3 event with threshold_C)

[0143] HO command_C

[0144] 2.CHO configuration D

[0145] Target cell: Cell D 540

[0146] Trigger condition (e.g., cond A3 event with threshold_D)

[0147] HO command_D

[0148] 3.CHO configuration E

[0149] Target cell: Cell E 550

[0150] Trigger condition (e.g., cond A3 event with threshold_E_1)

[0151] HO command_E

[0152] 1.CHO configuration F:

[0153] Target cell: Cell F 560

[0154] Trigger condition (e.g. Cond A3 event with threshold_F)

[0155] HO command_F

[0156] 2.CHO configuration G

[0157] Target cell: Cell G 570

[0158] Trigger condition (e.g., cond A3 event with threshold_G)

[0159] HO command_G

[0160] The WTRU 505 may start monitoring the radio conditions for cell A 510 and cell F 560 (i.e., the first hop target cell in the multi-hop CHO configuration). If a CHO is performed towards cell A 510, the WTRU 505 may perform a CHO towards cell A 510 and may maintain the second level CHO configuration associated with cell A 510. That is, after the HO towards cell A 510, the CHO configuration at the WTRU 505 becomes:

[0161] 1.CHO Configuration B

[0162] Target cell: Cell B 520

[0163] Trigger condition (e.g., cond A3 event with threshold_B)

[0164] HO command_B

[0165] 2.CHO configuration C

[0166] Target cell: Cell C 530

[0167] Trigger condition (e.g., cond A3 event with threshold_C)

[0168] HO command_C

[0169] 1.CHO configuration D

[0170] Target cell: Cell D 540

[0171] Trigger condition (e.g., cond A3 event with threshold_D)

[0172] HO command_D

[0173] 2.CHO configuration E

[0174] Target cell: Cell E 550

[0175] Trigger condition (e.g., cond A3 event with threshold_E_1)

[0176] HO command_E

[0177] The WTRU 505 may begin monitoring trigger conditions for the second hop target cell B 520 and cell D 540, and so on.

[0178] A baseline multi-hop CHO configuration can be introduced by including a reference from one conditional reconfiguration to another. An example is shown below:

[0179]

[0180] For the baseline multi-hop CHO example above, the CHO configuration for cell B 520 may include the ID of the CHO configuration for cell A 510, and so on.

[0181] The WTRU 505 may monitor trigger conditions for more than one hop at a time. The WTRU 505 may not necessarily follow the predicted trajectory, so the trigger conditions associated with multi-hop CHO may not be satisfied sequentially at each level. For example, the WTRU 505 may have been configured with a CHO configuration from cell A 510 to cell B 520 to cell C 530, such as expected to follow trajectory 1 515, but its trajectory may change from the predicted trajectory 1 515, and a handover may be performed directly from cell A 510 to cell C 530 to accommodate the actual trajectory.

[0182] In one solution, the triggering conditions for a WTRU with configured multi-hop CHO to monitor a target cell are more than one hop / level (e.g., all target cells at all levels, the depth of levels to be monitored indicated in the CHO configuration, etc.). Figure 5A , if depth 2 is included in the configuration, the WTRU 505 may simultaneously monitor cell A 510, cell B 520, cell D 540, cell F 560, and cell G 570 at the source cell. Similarly, if depth level 3 is included (or indicated to monitor all levels), the WTRU may also monitor cell C 530 and cell E 550. It may be configured such that not specifying a depth is equivalent to depth level 1.

[0183] If the trigger condition is met towards a cell at a level deeper than the current level, the WTRU may not be able to immediately execute the HO command associated with that target. Figure 5A520, and the WTRU 505 is monitoring the third level (i.e., monitoring all target cells A 510, B 520, C 530, D 540, E 550, F 560, and G 570). If the conditions for cell C 530 are met, the WTRU 505 may attempt to directly execute the HO command associated with cell C 530. Doing so may result in failure due to security reasons. This is because the HO command_C should be executed after the WTRU has been handed over to cell A 510 and then to cell B 520. Since at least the security key needs to be updated at each HO command, the WTRU 505 may not be able to compile the HO command_C while only having the security information of the source cell.

[0184] When a WTRU 505 having multi-hop CHO configured and also configured to monitor more than one hop determines that a trigger condition is met at a level deeper than the first level, the CHO configuration may be performed sequentially until that level is reached. For the above example, if the conditions of cell C 530 are met, the WTRU 505 may execute HO command_A and HO command_B before executing HO command_C.

[0185] The WTRU 505 may refrain from performing random access and may send the HO complete message only to the final target (ie, skipping the RA and sending the complete message to the intermediate target).

[0186] The WTRU 505 may perform a Figure 5A 510 and cell B 520 in the above example illustrated in FIG. 5 and sends a HO Complete message, but includes an indication that this is only a temporary HO. For example, when target A receives such an indication, target A may release the resources it has reserved for the WTRU and notify the source cell to release the resources for the WTRU. This may ensure that target A does not send any reconfiguration to the WTRU while potentially changing the WTRU context and interrupting the multi-hop handover process.

[0187] The WTRU may perform security-related configuration of HO commands from intermediate targets (eg, A and B in the above example) before performing a HO command to the final target.

[0188] For a WTRU using a multi-hop CHO configuration with timing constraints, as described above, configuring CHO towards several targets in the network is very resource intensive, such as by using a conventional CHO configuration or in the multi-hop CHO proposed herein.

[0189] The WTRU may be configured with a CHO configuration (e.g., a multi-hop CHO configuration), and the CHO configuration may include an associated validity time. The validity time indicates a time period or duration of validity of the configuration. The validity time may identify a time period or duration during which the network marks resources as available at the corresponding target cell to grant the WTRU. That is, when a specified duration has passed after receiving the configuration, the WTRU may delete / release that portion of the configuration.

[0190] Provides how validity time can be introduced into Figure 5A An example of a baseline multi-hop CHO:

[0191] 1.CHO configuration A:

[0192] Target cell: Cell A 510

[0193] Trigger condition (e.g. Cond A3 event with threshold_A)

[0194] Validity time: t_A

[0195] HO command_A

[0196] 2.CHO Configuration B

[0197] Target cell: Cell B 520

[0198] Trigger condition (e.g., cond A3 event with threshold_B)

[0199] Validity time: t_B

[0200] HO command_B

[0201] 3.CHO configuration C

[0202] Target cell: Cell C 530

[0203] Trigger condition (e.g., cond A3 event with threshold_C)

[0204] Validity time: t_C

[0205] HO command_C

[0206] 2.CHO configuration D

[0207] Target cell: Cell D 540

[0208] Trigger condition (e.g., cond A3 event with threshold_D)

[0209] Validity time: t_D

[0210] HO command_D

[0211] 3.CHO configuration E

[0212] Target cell: Cell E 550

[0213] Trigger condition (e.g., cond A3 event with threshold_E_1)

[0214] Validity time: t_E

[0215] HO command_E

[0216] 1.CHO configuration F:

[0217] Target cell: Cell F 560

[0218] Trigger condition (e.g. Cond A3 event with threshold_F)

[0219] Validity time: t_F

[0220] HO command_F

[0221] 2.CHO configuration G

[0222] Target cell: Cell G 570

[0223] Trigger condition (e.g., cond A3 event with threshold_G)

[0224] Validity time: t_G

[0225] HO command_G

[0226] If the WTRU monitors the first level target, and assuming that the above configuration is received all at once, the WTRU may start timers with values ​​t_A and t_F during which the conditions of cell A and cell F are monitored respectively. For example, if t_F is shorter than t_A and the timer associated with t_A expires before the triggering condition for cell A or cell F is met, the WTRU may delete the CHO configuration for cell F and the second hop configuration for cell G associated with cell F, and continue to monitor the triggering condition for cell A.

[0227] Similarly, if t_A is shorter than t_F and the timer associated with t_A expires before the trigger condition for cell A or cell F is met, the WTRU may delete the CHO configuration for cell A, the second level CHO configuration for cell B and cell D, and the third level configuration for cell C and cell E, but keep monitoring the trigger condition for cell F.

[0228] In the following examples, the validity times of the second level and deeper levels may be interpreted in several ways. The validity time of a given level may be considered after the conditions of the previous level are met. For example, in the above configuration, the WTRU may start a timer associated with t_B after a CHO is performed towards cell A and cell B has become the first level target. The validity times of all levels may be considered from the receipt of the configuration. For example, for the above configuration, assuming that the configuration is received all at once, the WTRU may start timers associated with all targets. When each timer expires, the WTRU may delete the relevant configuration and any configuration that depends on that configuration.

[0229] In one solution, the interpretation of the validity time in one of the above ways is included as part of the CHO configuration or indicated to the WTRU in another dedicated signaling, or indicated to all WTRUs via SIB signaling. In one solution, the interpretation of the validity time in one of the above ways is explicitly specified in the 3GPP standard.

[0230] In one solution, the WTRU may stop monitoring conditions for a target when the validity timer associated with the target has expired. The WTRU may maintain the configuration and the configuration in the deeper level associated with the target and start monitoring conditions for the next level. For example, when the validity timer for target A expires, the WTRU may stop monitoring conditions for cell A and start monitoring trigger conditions for cell B and start a timer with validity time t_B. If this also expires, the WTRU may stop monitoring conditions for cell B and start monitoring conditions for cell c and start a timer with validity time t_C. If the conditions for cell C are met, the WTRU may execute HO command_A, followed by HO command_B, followed by HO command_C (or other variants discussed in the previous subsection when executing a CHO command at a hop different from the current hop). This step-by-step monitoring of the targets (i.e., monitoring at only one level and considering the next level only when the validity time of the highest level has expired) may ensure that the WTRU remains compliant with the limit of a maximum of 8 CHO candidates that the WTRU may monitor simultaneously. One possible way to introduce validity time in a multi-hop CHO configuration in a conditional reconfiguration IE is shown below:

[0231]

[0232] The WTRU may use a time-based multi-hop CHO configuration with timing constraints. In one solution, the multi-hop CHO configuration may include timing information including the start time and end time of a given CHO configuration. Figure 5A Example:

[0233] 1.CHO configuration A:

[0234] Target cell: Cell A 510

[0235] Trigger condition (e.g. Cond A3 event with threshold_A)

[0236] Validity time: [t_A1, t_A2]

[0237] HO command_A

[0238] 2.CHO Configuration B

[0239] Target cell: Cell B 520

[0240] Trigger condition (e.g., cond A3 event with threshold_B)

[0241] Validity time: [t_B1, t_B2]

[0242] HO command_B

[0243] 3.CHO configuration C

[0244] Target cell: Cell C 530

[0245] Trigger condition (e.g., cond A3 event with threshold_C)

[0246] Validity time: [t_C1, t_C2]

[0247] HO command_C

[0248] 2.CHO configuration D

[0249] Target cell: Cell D 540

[0250] Trigger condition (e.g., cond A3 event with threshold_D)

[0251] Validity time: [t_D1, t_D2]

[0252] HO command_D

[0253] 3.CHO configuration E

[0254] Target cell: Cell E 550

[0255] Trigger condition (e.g., cond A3 event with threshold_E_1)

[0256] Validity time: [t_E1, t_E2]

[0257] HO command_E

[0258] 1.CHO configuration F:

[0259] Target cell: Cell F 560

[0260] Trigger condition (e.g. Cond A3 event with threshold_F)

[0261] Validity time: [t_F1, t_F2]

[0262] HO command_F

[0263] 2.CHO configuration G

[0264] Target cell: Cell G 570

[0265] Trigger condition (e.g., cond A3 event with threshold_G)

[0266] Validity time: [t_G1, t_G2]

[0267] HO command_G

[0268] For a WTRU monitoring the first level target as described above, t_A1 is 1 second and t_A2 may be 3 seconds. Assuming the above configuration is received all at once, the WTRU may start monitoring the conditions for target A after 1 second has passed from the reception of the configuration, and if the conditions for target A are not met after 3 seconds have passed from the reception of the configuration, the WTRU may delete the CHO configuration for cell A 510 and the second level CHO configuration for cell B 520 and cell D 540, and the third level configuration for cell C 530 and cell E 550.

[0269] In another example, t_A2 may be configured relative to t_A1 so that the duration of monitoring for a trigger of that particular configuration is not an absolute time from the receipt of the configuration. That is, for the above example where t_A1 is set to 1 second and t_A2 is set to 3 seconds, this may be equivalent to starting monitoring the conditions of cell A 510 after 1 second from the receipt of the configuration and continuing to do so for another 3 seconds.

[0270] A start time may be included in a given CHO configuration, indicating that the WTRU may start monitoring conditions for that particular CHO configuration from this time, and may keep monitoring until the conditions are met or the network sends explicit signaling to release the configuration. Including an end time may be equivalent to the validity time based solution described above.

[0271] In the above solution, the time-related information (validity time, start time, end time) can be a relative time (e.g., seconds, milliseconds, etc.) from the receipt of the configuration. Solutions are also envisioned in which the time-related information can be absolute time values. For example, the validity time can specify an exact time of day (e.g., HH:MM:SS:ms) when the configuration becomes invalid. Similarly, the start time and end time can be specified using an exact time of day. A mixture of these two timing mechanisms - relative time and absolute time - can be used (e.g., a "start time" specified as an absolute time in day format, an "end time" specified as a time interval duration, e.g., in milliseconds).

[0272] The WTRU may use a cyclic configuration from cell A 510 to cell B 520, from cell B 520 to cell A 510, etc. The WTRU may be configured with a multi-hop CHO configuration where the second level is actually a CHO configuration back to the source cell, where the second level CHO may have two different thresholds. Figure 5A (CHO configuration received when in cell A 510).

[0273] 1.CHO configuration A:

[0274] Target cell: Cell A 510

[0275] Trigger condition (e.g. Cond A3 event with threshold_A)

[0276] Validity time: [t_A1, t_A2]

[0277] HO command_A

[0278] 2.CHO Configuration B

[0279] Target cell: Cell B 520

[0280] Trigger condition (e.g., cond A3 event with threshold_B)

[0281] Validity time: [t_B1, t_B2]

[0282] HO command_B

[0283] 3.CHO Configuration A

[0284] Target cell: Cell A 510

[0285] Trigger condition 1 (e.g., cond A3 event with threshold_A1)

[0286] Trigger condition 1 (e.g., cond A3 event with threshold_A2)

[0287] HO command_A

[0288] If the first CHO is successful, the WTRU may HO to cell B 520 and start monitoring the first trigger condition (i.e., threshold_A1) for HO from cell B 520 back to cell A 510. If the HO is successful, the above-described procedure may be used to handle the HO, where the second level CHO is for another cell instead of the source cell. If a failure occurs during the execution of the first CHO towards cell B 520 (e.g., RA to cell B 520 cannot be performed), the WTRU may check whether at least the second trigger condition (i.e., threshold_A2) for HO back to cell A 510 is met. If the second trigger condition for HO back to cell A 510 is met, the WTRU may perform CHO back towards the source cell A 510. In the described solution of multi-hop CHO configuration returning to the source, when the source cell receives an RRC message from the WTRU after the configuration of the CHO, confusion may arise regardless of whether the message is sent before the WTRU has performed the first level CHO (e.g., before the conditions for the first CHO are met) or after the WTRU has performed the second level CHO (e.g., the first CHO has failed and the second threshold of the failure condition is met and the WTRU wants to return to cell A 510).

[0289] Figure 5B Illustrated with Figure 5A Method 545 of associating an exemplary coverage scenario. Figure 3A and 3B , at 555, the WTRU 505 moves in a RRC_CONNECTED state in a cell A 510. At 565, the WTRU 510 is configured with a target cell list. The configuration may include receiving a CHO configuration from a NG-RAN node. The target cell list may include target cells (B, C, D, E, F, G) and may provide cell evaluation criteria, which may be each cell in one embodiment. At 575, the WTRU 505 may monitor the cell evaluation criteria of at least one cell in the target cell list, may monitor all cells in the target cell list, or a subset of the cells in the target cell list. At 585, when the criteria of at least one cell in the target cell list are met, the WTRU 510 may trigger a HO to the at least one cell. For example, when the WTRU 510 moves to cell B 520, cell C 530 and cell D 540 may be monitored. When the mobility causes the WTRU to measure a cell (cell B 520, cell C 530, and cell D 540) the criteria are met, a HO to that cell may be triggered. For example, cell B 520 may be triggered.

[0290] Once a HO is triggered (such as to cell B 520), the WTRU 510 may monitor the cell evaluation criteria of at least one other cell in the target cell list at 595. The list may now include the remaining cells in the list (cell C 530 and cell D 540 in this example), may add additional cells in addition to the cells in the list, and may also include the cell from which the WTRU moved (e.g., cell A 510), as described in detail above. At 597, the WTRU 510 may trigger a HO to the at least one other cell in the target cell list when the criteria of the at least one other cell in the target cell list are met. For example, cell C 530 and cell D 540 may be monitored when the WTRU 510 moves in cell B 520. The HO to another cell, such as cell C 530, may then cause the method 545 to continue to iterate across the remaining cells in the list at 595 and 597. Again as described above, the list may now include the remaining cells in the list (cell D 540 in this example), additional cells may be added in addition to the cells in the list, and may also include the cell from which the WTRU moved (e.g., cell A 510, cell B 520), as described in detail above.

[0291] Figure 6 Configuration 600 is illustrated to illustrate the scenario of whether a message is sent before the WTRU 605 performs a first level CHO 610. It is assumed that if the first CHO 610 is successful, the target cell B 630 can inform the source cell A 620, thereby alleviating the confusion situation. The initial steps occur when the WTRU 605 receives a multi-hop CHO configuration, such as first from cell A 620 to cell B 630, and second from cell B 630 to cell A 620.

[0292] Figure 7 The configuration 700 is illustrated to illustrate a scenario where, while the WTRU 705 is monitoring for a CHO trigger (i.e., monitoring criteria for cell B), the WTRU 705 may exchange one or more RRC messages 710 (e.g., measurement reports, UL information transfers, etc.) to cell A 720 using a first security context associated with cell A 720. This may occur when the CHO criteria have not yet been met.

[0293] Figure 8Configuration 800 is illustrated to illustrate a scenario where a WTRU 805 attempts a CHO from cell A 820 to cell B 830 when a trigger for cell A to cell B CHO is met. The attempted CHO fails (e.g., due to a RACH failure in cell B 830). Note that at this point, the WTRU 805 has already applied the first HO command, and therefore the security context is updated. The WTRU 805 then applies a second CHO configuration from cell B 830 to cell A 820 (if the second trigger condition is met as described above), which further updates the security context. In this case, the WTRU 805 sends one or more RRC messages 810 (e.g., RRC Reconfiguration Complete, etc.) to cell A 820 using the latest security context to integrity protect and cipher the messages.

[0294] exist Figure 7 In the scenario 700, the source node (cell A 720) may not experience problems because the received RRC message is integrity protected and encrypted using the current security configuration at cell A 720. Figure 8 In the scenario 800 of FIG. 8 , the security context of the WTRU 805 at the network is different than the security context used at the WTRU 805. The integrity verification of the RRC message 810 (e.g., HO Complete message) sent from the WTRU 805 at the network may fail, and the message may be either discarded by the network or the network may trigger some failure handling procedures. The WTRU 805 may not be able to correctly decode any UP message from cell A 820, and if a CP message (e.g., RRC message 810) is sent from cell A 820, the integrity verification of the message may fail, which is considered as RLF and may trigger a re-establishment.

[0295] In one solution, the WTRU may be configured to transmit an indication to the source cell (e.g., in a MAC CE) that it has performed a second CHO after the first CHO has failed (e.g., before the second CHO is performed or before a reconfiguration complete message is sent after multiplexing with the same message at the MAC level). In this way, the network knows that it must use the second security context for the WTRU going forward.

[0296] In one solution, the WTRU may be configured to store the first security configuration used in cell A, even after the conditions for CHO to cell B have been met, and if the HO to cell B is not successful, revert the security context to the old security context and not perform a second CHO at all. The WTRU may send an indication / report (e.g., an RRC message such as WTRU Assistance Information) to the network indicating that a failure has occurred during the first CHO.

[0297] The network aspects of the handover may be considered. In one solution, the handover process on the network side is enhanced to facilitate multi-hop CHO, where the source node sends a handover request message to the target node, which may indicate other targets of the multi-hop CHO. For example, if the network wants to configure CHO from cell A to cell B to cell C, and from cell A to cell B to cell D, the network may perform the following operations (for simplicity, assuming that the cells belong to different gNBs).

[0298] Cell A sends a HO request to cell B, indicating a multi-hop CHO with other target cells C and D. Cell B performs admission control on the WTRU.

[0299] If the admission control is successful, cell B prepares a HO command for the first hop. Cell B may send a HO request to cell C and cell D, indicating CHO (cell B may forward the WTRU context to cell C and cell D after applying the delta configuration that may have been included in the HO command for the first hop). Cell C and cell D may perform admission control and respond to cell B with a HO Preparation Failure message (if they cannot admit the WTRU) or a HO Request ACK including a HO command for the second hop. Cell B sends a response to cell A. For example, if admission at B fails, a HO Preparation Failure message is sent in response.

[0300] If admission at cell B has been successful, but the second level has failed for both cell C and cell D, a HO request ACK message including a first hop HO command for cell B and an indication that the second level HO was not successful is sent in response. The WTRU may receive a legacy CHO configuration for cell B.

[0301] If admission at cell B, cell C, and cell D has been successful, a HO request ACK message may be sent in response. The message may include a first level HO command for cell B and a second level HO command for both cell C and cell D. The WTRU may receive 2 multi-hop CHO configurations (cell A to cell B to cell C, cell A to cell B to cell D).

[0302] If admission at cell B and cell C has been successful, but not to cell D, a HO request ACK message may be sent in response. The message may include a first level HO command for cell B and a second level HO command for cell C and an indication that the second level HO to cell D has not been successful. The WTRU may receive 1 multi-hop CHO configuration (cell A to cell B to cell C).

[0303] If admission at cell B and cell D has been successful, but not to cell C, a HO request ACK message may be sent in response. The message may include a first level HO command for cell B and a second level HO command for cell D and an indication that the second level HO to cell C has not been successful. The WTRU may receive 1 multi-hop CHO configuration (A to B to D).

[0304] In one solution, the network configures the WTRU with a multi-hop CHO configuration with an associated validity time. The network may determine the validity time for each handover target using information such as the predicted WTRU trajectory and the predicted resource requirements at the network. The target node is also aware of the validity time and may release these if the target node does not receive a HO complete message within the validity time associated with the CHO configuration for that node / cell.

[0305] In one solution, after a source node has configured a WTRU with a multi-CHO configuration, where the second level CHO is a HO back to the source, the source node performs double decoding of RRC messages received from the WTRU on an as-needed basis. That is, the source node may first use the first security context (e.g., the security context used in the source cell when the CHO configuration was sent to the WTRU) to integrity verify and decrypt the received RRC messages. If the integrity verification fails, the source node may try the second security context and may declare RLF and initiate reestablishment if this fails.

[0306] In one solution, the WTRU refrains from performing random access and sends a HO completion message only to the final target (ie, skips the RA and sends a completion message to an intermediate target).

[0307] An exemplary process for WTRU configuration is provided. For the network resource reservation discussed above, Fig. 9 An enhanced HO request process 900 is illustrated. At 905, the source gNB 910 sends a HO request to the target gNB 920, as described herein. The target gNB 920 performs admission control at 915 by evaluating whether the WTRU can be accommodated in the future compared to a conventional instant evaluation. The target gNB 920 sends a HO request ACK to the source gNB 910 at 925.

[0308] Fig.10A multi-hop CHO WTRU configuration and HO triggering process 1000 is illustrated. At 1005, the source gNB 1020 infers that the multi-hop CHO configuration is the best mobility strategy for the WTRU 1010. At 1015, the source gNB 1020 performs an enhanced HO request process as described herein. At 1025, the source gNB 1020 provides the multi-hop configuration as described herein to the WTRU 1010. At 1035, the WTRU 1010 evaluates the radio conditions for a specific cell / level. At 1045, the WTRU 1010 triggers a CHO type HO to the target cell. At 1055, the WTRU 1010 evaluates the radio conditions for a specific cell / level for the second hop, as described herein. At 1065, the WTRU 1010 triggers a CHO type HO to the target cell for the second hop. The triggering of the CHO type HO to the target cell may include the WTRU 1010 establishing a connection with the target cell. As will be appreciated by one of ordinary skill in the art, this may include the necessary sending and receiving of messages and registration within a cell if necessary.

[0309] Fig.11 A method 1100 that may be implemented by a WTRU is illustrated. The method 1100 includes receiving, at 1110, one or more multi-hop conditional handover (CHO) configurations associated with a multi-hop of a handover (HO), the configurations including at least one parameter of the one or more CHO configurations. The at least one parameter of the one or more CHO configurations may include one or more target cells in a set of target cells associated with a source cell, one or more measurement criteria for the HO associated with each hop, and a validity time duration for monitoring the one or more criteria for each or a subset of the source cell and the target cell.

[0310] The method 1100 includes determining at least one hopping criterion from the received one or more multi-hop CHO configurations at 1120. Determining at least one hopping criterion at 1120 may be based on at least one of the multi-hop CHO configuration, a current hop, and a previous hop source cell-target cell pair.

[0311] The method 1100 includes determining at least one candidate target cell from the received one or more multi-hop CHO configurations at 1130. The determining of at least one target cell at 1130 may be based on at least one of: a multi-hop CHO configuration, a previous hop source-target pair, a current cell, a previous cell.

[0312] The method 1100 includes monitoring at least one hop criterion determined for at least one candidate target cell at 1140. The method 1100 includes determining that the candidate target cell satisfies criteria for one or more monitored hop criteria at 1150. The target cell satisfying the criteria at 1150 may include satisfying a threshold on the measurement. The criteria is based on a multi-hop CHO configuration, a current hop, and a previous hop.

[0313] The method 1100 includes, at 1160, transmitting using resources associated with the determined candidate target cell that meets the criteria.

[0314] The method 1100 may also include, at 1170 , triggering a HO associated with the current hop to the determined candidate target cell that meets the criteria.

[0315] Based on the target cell to which the WTRU performs a HO, the method 1100 may also include, at 1180, determining and monitoring next hop criteria for one or more target cells according to a multi-hop CHO configuration associated with a previous hop and the HO.

[0316] For example, the method may include: receiving a plurality of multi-hop conditional handover (CHO) configurations, each configuration being associated with a hop criterion for handover (HO); determining a first candidate target cell from the received plurality of multi-hop CHO configurations; monitoring a first hop criterion for the first candidate target cell, the first hop criterion being associated with at least a first one of the plurality of multi-hop CHO configurations; using measurements associated with the first candidate target cell to determine that the first candidate target cell satisfies the first hop criterion; establishing a connection to the determined first candidate target cell; determining a second candidate target cell from the received plurality of multi-hop CHO configurations; monitoring a second hop criterion for the second candidate target cell, the second hop criterion being associated with at least a second one of the plurality of multi-hop CHO configurations; using measurements associated with the second candidate target cell to determine that the second candidate target cell satisfies the second hop criterion; and establishing a connection to the determined second candidate target cell. The method may include releasing the connection to the determined first candidate target cell.

[0317] In this example, the method may include monitoring the first hop criterion including the WTRU performing measurements and comparing the measurements taken with the first hop criterion. The method may include the first hop criterion and the second hop criterion being the same. The method may include transmitting using radio resources associated with the determined first candidate target cell based on a connection established with the determined first candidate target cell. The method may include transmitting using radio resources associated with the determined second candidate target cell based on a connection established with the determined second candidate target cell. The method may include: monitoring a third hop criterion for a third candidate target cell, the third hop criterion being associated with at least one of a plurality of multi-hop CHO configurations; determining using measurements associated with the third candidate target cell that the third candidate target cell satisfies the third hop criterion; and establishing a connection to the determined third candidate target cell. The method may include the received plurality of multi-hop CHO configurations including one or more of: a set of target cells associated with a source cell per hop; one or more measurement criteria for HO associated with each hop; and a validity time duration for monitoring one or more criteria for each or a subset of the source cell and the target cell. The method may include basing the second hop criteria on at least one of: a received plurality of multi-hop CHO configurations; an established connection to the determined first candidate target cell; and a previously established connection of the WTRU and a previous hop criteria for HO. The method may include determining the first target cell based on at least one of: a received plurality of multi-hop CHO configurations; an established connection to the determined first candidate target cell; and a previously established connection of the WTRU and a previous hop criteria for HO. The method may include the first candidate target cell satisfying the first hop criteria comprising exceeding a threshold on a measurement associated with the first target cell.

[0318] Although features and elements are described above in specific combinations, it will be understood by those of ordinary skill in the art that each feature or element may be used alone or in any combination with other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (sent via 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 built-in 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 may be used to implement a radio frequency transceiver for a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

1. A method implemented by a wireless transmit receive unit (WTRU), the method comprising: receiving a plurality of multi-hop conditional handover (CHO) configurations, each configuration being associated with a hop criterion for handover (HO); determining a first candidate target cell from the received multiple multi-hop CHO configurations; monitoring a first hop criterion for the first candidate target cell, the first hop criterion being associated with at least a first one of the plurality of multi-hop CHO configurations; determining, using measurements associated with the first candidate target cell, that the first candidate target cell satisfies the first hopping criterion; Establishing a connection to the determined first candidate target cell; determining a second candidate target cell from the received multiple multi-hop CHO configurations; monitoring a second hopping criterion for the second candidate target cell, the second hopping criterion being associated with at least a second one of the plurality of multi-hop CHO configurations; determining, using measurements associated with the second candidate target cell, that the second candidate target cell satisfies the second hopping criterion; as well as A connection is established to the determined second candidate target cell.

2. The method according to claim 1, wherein: Monitoring at least a first hop criterion includes the WTRU performing measurements and comparing the measurements to the first hop criterion.

3. The method according to claim 1, wherein: The first hop standard and the second hop standard are the same.

4. The method according to claim 1, further comprising: Based on the connection established with the determined first candidate target cell, the transmission is performed using radio resources associated with the determined first candidate target cell.

5. The method according to claim 1, further comprising: Based on the connection established with the determined second candidate target cell, the transmission is performed using radio resources associated with the determined second candidate target cell.

6. The method according to claim 1, further comprising: monitoring a third hopping criterion for a third candidate target cell, the third hopping criterion being associated with at least a third one of the plurality of multi-hop CHO configurations; using measurements associated with the third candidate target cell to determine that the third candidate target cell satisfies the third hopping criterion; as well as A connection is established to the determined third candidate target cell.

7. The method according to claim 1, wherein: The received multiple multi-hop CHO configurations include one or more of the following: A set of target cells associated with a source cell per hop; one or more measurement criteria for HO associated with each hop; and A validity time duration for monitoring one or more criteria for each or a subset of the source cell and the target cell.

8. The method according to claim 1, wherein: The second hop criterion is based on at least one of the following: Multiple multi-hop CHO configurations received; A connection established to the determined first candidate target cell; and A previously established connection of the WTRU having an associated previous hop criteria for HO.

9. The method according to claim 1, wherein: Determining the first candidate target cell from among the received plurality of multi-hop CHO configurations is based on at least one of: the received plurality of multi-hop CHO configurations, a current connection, and a previously established connection of the WTRU having an associated previous hop criteria for HO.

10. The method according to claim 1, wherein: The first candidate target cell satisfying the first hopping criterion includes measurements associated with the first candidate target cell exceeding a threshold.

11. A wireless transmit receive unit (WTRU), the WTRU comprising: Transceiver; and a processor operatively connected to the transceiver, the processor and the transceiver operating to: receiving a plurality of multi-hop conditional handover (CHO) configurations, each configuration being associated with a hop criterion for handover (HO); determining a first candidate target cell from the received multiple multi-hop CHO configurations; monitoring a first hop criterion for the first candidate target cell, the first hop criterion being associated with at least a first one of the plurality of multi-hop CHO configurations; determining, using measurements associated with the first candidate target cell, that the first candidate target cell satisfies the first hopping criterion; Establishing a connection to the determined first candidate target cell; determining a second candidate target cell from the received multiple multi-hop CHO configurations; monitoring a second hopping criterion for the second candidate target cell, the second hopping criterion being associated with at least a second one of the plurality of multi-hop CHO configurations; determining, using measurements associated with the second candidate target cell, that the second candidate target cell satisfies the second hopping criterion; as well as A connection is established to the determined second candidate target cell.

12. The WTRU of claim 11 wherein: Monitoring a first hop criterion includes the WTRU performing measurements and comparing the measurements to the first hop criterion.

13. The WTRU of claim 11 wherein: The first hop standard and the second hop standard are the same.

14. The WTRU of claim 11 wherein: The processor and the transceiver further operate to transmit using radio resources associated with the determined first candidate target cell based on the connection established with the determined first candidate target cell.

15. The WTRU of claim 11 wherein: The processor and the transceiver further operate to transmit using radio resources associated with the determined second candidate target cell based on the connection established with the determined second candidate target cell.

16. The WTRU of claim 11 wherein: The processor and the transceiver are further operable to: monitoring a third hopping criterion for a third candidate target cell, the third hopping criterion being associated with one of the plurality of multi-hop CHO configurations; using measurements associated with the third candidate target cell to determine that the third candidate target cell satisfies the third hopping criterion; as well as A connection is established to the determined third candidate target cell.

17. The WTRU of claim 11 wherein: The received multiple multi-hop CHO configurations include one or more of the following: A set of target cells associated with a source cell per hop; one or more measurement criteria for HO associated with each hop; and A validity time duration for monitoring one or more criteria for each or a subset of the source cell and the target cell.

18. The WTRU of claim 11 wherein: The second hop criterion is based on at least one of the following: Multiple multi-hop CHO configurations received; A connection established to the determined first candidate target cell; and A previously established connection of the WTRU with a previous hop criteria for HO.

19. The WTRU of claim 11 wherein: Determining the first candidate target cell from among the received plurality of multi-hop CHO configurations is based on at least one of: the received plurality of multi-hop CHO configurations, a current connection, and a previously established connection of the WTRU having an associated previous hop criteria for HO.

20. The WTRU of claim 11 wherein: The first candidate target cell satisfying the first hopping criterion includes measurements associated with the first candidate target cell exceeding a threshold.

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