User Equipment, Network Node, and Method in a User Equipment or Network Node

Abstract

The present invention provides a method and associated apparatus for solving or at least mitigating the problem of user equipment (UE) context when the UE moves from one geographical region to another. A communication system (1) is disclosed that includes a non-terrestrial based network part including a plurality of cells, each cell serving at least one coverage area. A UE (3) has a Radio Resource Control (RRC) connection in a first coverage area. When the UE (3) detects, based on location information, that it has moved to a different coverage area, the UE (3) releases the RRC connection based on the location of the UE (3).

Description

[Technical field]

[0001] The present disclosure relates to wireless communication systems and apparatus therefor that operate in accordance with 3rd Generation Partnership Project (3GPP®) standards or equivalent or derived standards. In particular, but not by way of limitation, the present disclosure relates to improvements relating to user equipment (UE) context acquisition / UE redirection in so-called "5G" (or "next generation") systems that employ non-terrestrial parts, including aircraft or satellite network nodes. [Background technology]

[0002] In the 3GPP standards, a NodeB (or "eNB" in LTE, "gNB" in 5G) is a base station through which a communication device (user equipment, or "UE") connects to the core network and communicates with other communication devices or remote servers. A communication device may be, for example, a mobile communication device such as a mobile phone, a smartphone, a smart watch, a personal digital assistant, a laptop / tablet computer, a web browser, an e-reader, etc. Such mobile (or generally stationary) devices are typically operated by a user (and thus they are collectively referred to as user equipment, or "UE"), although IoT devices and similar MTC devices may also be connected to the network. For simplicity, the present application uses the term base station to refer to any such base station and the term mobile device or UE to refer to any such communication device.

[0003] The latest development in the 3GPP standards is the so-called "5G" or "New Radio" (NR) standard, which is an evolving communications technology that is expected to support a variety of applications and services, such as machine type communications (MTC), Internet of Things (IoT) / Industrial IoT (IIoT) communications, vehicular communications and autonomous vehicles, high definition video streaming, smart city services, and / or the like. 3GPP plans to support 5G with the so-called 3GPP Next Generation (NextGen) Radio Access Network (RAN) and 3GPP Next Generation Core (NGC) networks. Various details of 5G networks are described, for example, in the "NGMN 5G White Paper" V1.0 by the Next Generation Mobile Network (NGMN) Alliance, which is available at https: / / www.ngmn.org / 5g-white-paper.html.

[0004] The communication devices of the end users are generally referred to as User Equipment (UE) and may be operated by humans or may consist of automated (MTC / IoT) devices. The base stations of a 5G / NR communication system are generally referred to as New Radio Base Stations ("NR-BS") or "gNBs", although it will be understood that they are more commonly referred to using the term "eNB" (or 5G / NR eNB), which relates to Long Term Evolution (LTE) base stations (also commonly referred to as "4G" base stations). 3GPP Technical Specifications (TS) 38.300 V16.4.0 and TS 37.340 V16.4.0 define, among others, the following nodes: gNB: A node that provides termination of NR user plane and control plane protocols for the UE and is connected to the 5G core network (5GC) via the NG interface. ng-eNB: A node that provides Evolved Universal Terrestrial Radio Access (E-UTRA) user plane and control plane protocol termination for the UE and is connected to the 5GC via the NG interface. en-gNB: A node that provides NR user plane and control plane protocol termination for the UE and functions as a secondary node for E-UTRA-NR Dual Connectivity (EN-DC). NG-RAN node: Either a gNB or a ng-eNB.

[0005] 3GPP is also working on the specification of integrated satellite and terrestrial network infrastructure in the context of 5G. The term Non-Terrestrial Networks (NTN) means a network or a segment of a network that uses aircraft or satellites for communication. Satellite means an artificial satellite in geostationary orbit (GEO) or non-geostationary orbit (NGEO), such as low Earth orbit (LEO), medium Earth orbit (MEO), highly elliptical orbit (HEO). Aircraft means a stratospheric platform (HAP) including unmanned aircraft systems (UAS), including tethered UAS, lighter than air UAS, and heavier than air UAS, all of which typically operate in a quasi-geostationary manner at altitudes between 8 km and 50 km. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] 3GPP Technical Report 38.811 V 15.4.0 [Non-Patent Document 2] 3GPP Technical Report 38.821 V 16.0.0

[0007] Non-Patent Document 1 is a study on New Radio to support such non-terrestrial networks. This study includes, among other things, deployment scenarios of NTNs and related system parameters (architecture, altitude, orbit, etc.) and a description of the adaptation of 3GPP channel models for non-terrestrial networks (propagation conditions, mobility, etc.). Non-Patent Document 2 provides details on NTNs.

[0008] Non-terrestrial networks include: - Facilitating the deployment of 5G services in unserved and underserved areas and improving terrestrial network performance; - Improving service reliability by providing service continuity for user equipment or mobile platforms (e.g. passenger vehicles - aircraft, ships, high-speed trains, buses, etc.); - Improving the availability of services at any location, especially for critical communications and future rail / maritime / air communications; Achieving 5G network scalability by providing efficient multicast / broadcast resources for transmitting data to the network edge or directly to user equipment; is expected.

[0009] NTN Access is typically characterized by (among other things): NTN terminal: This may represent a 3GPP UE or a terminal specific to the satellite system if the satellite does not directly serve the 3GPP UE. -Service link, which means a radio link between the UE and a space / airborne platform (which may be in addition to a radio link with a terrestrial RAN). - Space or airborne platforms. - Gateways that connect satellite or aeronautical access networks to the core network ("NTN Gateways"). It will be understood that in most cases the Gateways are collocated with the base stations. - Feeder link, which means the radio link between the gateway and the space / airborne platform.

[0010] A satellite or aircraft can generate multiple beams over a given area to serve each NTN cell, with the beams forming a typically elliptical footprint on the Earth's surface.

[0011] 3GPP plans to support three types of NTN beams or cells. - Earth-fixed cells (e.g. GEO satellites and HAPS, etc.) that are characterized by at least one beam that always covers the same geographical area; - a quasi-Earth fixed cell characterized by at least one beam that covers a geographic area for a limited period of time and a different geographic area for another period of time (e.g., an NGEO satellite generating a steerable beam); and -Earth-moving cells characterized by at least one beam (e.g., an NGEO satellite generating a fixed beam or a non-moving beam) that at one moment covers one geographical area and at another moment covers a different geographical area.

[0012] When the altitude / azimuth of the satellite or aircraft position is fixed relative to a particular point, e.g., in the case of GEO and UAS, the beam footprint is fixed to the Earth.

[0013] If the satellite orbits the Earth (e.g., LEO) or is in an elliptical orbit around the Earth (e.g., HEO), the beam footprint may move over the Earth with the orbital motion of the satellite or aircraft, or the beam footprint may be temporarily fixed to the Earth, in which case an appropriate beam pointing mechanism (mechanical or electronic steering) can be used to compensate for the satellite or aircraft motion.

[0014] LEO satellites may have steerable beams, where the beams are temporarily directed to a substantially fixed footprint on the ground. In other words, the footprint of the beam (representing the NTN cell) is stationary on the ground for a certain time, and then changes its focal area to another NTN cell (as the satellite moves in orbit). This results in cell changes occurring periodically at discrete intervals, from the cell coverage area / UE point of view. This is because, even if these beams serve the same land area (with the same footprint), different physical cell identifiers (PCIs) and / or synchronization signal / physical broadcast channel (PBCH) blocks (SSBs) must be assigned after each service link change. LEO satellites without steerable beams, as the satellite moves along its orbit, will have their beams (cells) periodically move over the ground in a sweeping motion, resulting in service link changes and therefore cell changes occurring periodically at discrete intervals, as in the case of steerable beams.

[0015] As satellites move in orbit, feeder link changes occur periodically, as do service link changes. Both service and feeder link changes may occur between different base stations / gateways (which may be referred to as "inter-gNB radio link switches") or may occur within the same base station / gateway ("intra-gNB radio link switches"). 3GPP is working on detailed specifications, but envisions that Earth-fixed tracking areas will be used for Earth-fixed and / or mobile cells.

[0016] Groups of cells are assigned to different coverage regions or service / tracking areas, which may correspond to respective geographical regions (such as countries, cities, regions, or similar geographical units). Each cell has an associated “NR Cell Global Identifier (NCGI)”, which consists of the Public Land Mobile Network (PLMN) Identifier (PLMN ID) to which the cell belongs and the NR Cell Identity (NCI) of the cell. A “global gNB identifier” is used to globally identify a gNB and consists of the PLMN ID to which the gNB belongs and the gNB ID (an identifier for identifying a particular gNB within a PLMN). However, nothing precludes a cell served by a gNB from broadcasting its associated PLMN ID contained in the global gNB ID.

[0017] A base station (gNB / NG-RAN node) may control one or more cells serving different geographical regions (e.g., different coverage areas, service areas, tracking areas, or countries). The base station may serve one or more of such geographical regions via a cell having a coverage area (self-print) beyond the borders of adjacent regions. The base station may also serve multiple geographical regions via each cell (in other words, a cell may only serve a single region). When the base station serves multiple geographical regions, it enables each UE to use an Access and Mobility Management Function (AMF) that serves the geographical region in which the UE is located (taking into account the UE's location information, if any). Summary of the Invention [Problem to be solved by the invention]

[0018] A UE may initially establish a Radio Resource Control (RRC) connection over a cell and register with an AMF in one geographical area (e.g., in a first country). The UE may then move to a different geographical area (e.g., in a second country). This may occur when the UE moves across a border (e.g., within the same cell).

[0019] However, the conventional UE context may not be suitable for the region and may not be available to the base station serving the UE in the new area.

[0020] SUMMARY OF THE PRESENT EMBODIMENT The present invention therefore provides a method, and associated apparatus, that overcomes or at least alleviates (at least part of) the problems set forth above.

[0021] For the sake of efficiency of understanding for those skilled in the art, the present invention will be described in detail in the context of 3GPP systems (5G networks including NTN), but the principles of the present invention can also be applied to other systems. [Means for solving the problem]

[0022] In one exemplary aspect, the present invention provides a method performed by a user equipment (UE) configured to communicate over a non-terrestrial network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the method including determining that a current location of the UE is in a coverage area different from the first coverage area, and releasing the RRC connection based on the current location of the UE.

[0023] In one exemplary aspect, the present invention provides a method performed by a network node configured to communicate with a user equipment (UE) via a non-terrestrial based network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the method comprising the steps of receiving from the UE a message initiating a procedure to release a no RRC connection based on a current location of the UE, and sending a message to the UE to release the RRC connection based on the location of the UE.

[0024] In one exemplary aspect, the present invention provides a user equipment (UE) configured to communicate over a non-terrestrial network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the UE comprising means for determining that a current location of the UE is in a coverage area different from the first coverage area, and means for releasing the RRC connection based on the current location of the UE.

[0025] In one exemplary aspect, the present invention provides a network node configured to communicate with a user equipment (UE) via a non-terrestrial network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the network node comprising: means for receiving, from the UE, a message initiating a procedure to release the RRC connection based on a current location of the UE; and means for sending, to the UE, a message to release the RRC connection based on the location of the UE.

[0026] In another exemplary aspect, the present invention provides a user equipment (UE) configured to communicate over a non-terrestrial network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the UE comprising a processor, a transceiver, and a memory storing instructions, and a controller configured to determine that a current location of the UE is in a coverage area different from the first coverage area and release the RRC connection based on the current location of the UE.

[0027] In another exemplary aspect, the present invention provides a network node configured to communicate with a user equipment (UE) via a non-terrestrial based network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the network node comprising a processor, a transceiver and a memory storing instructions, the controller configured to cause the transceiver to receive from the UE a message initiating a procedure to release the RRC connection based on a current location of the UE and to send a message to the UE to release the RRC connection based on the location of the UE.

[0028] Aspects of the invention include corresponding systems, apparatus and computer program products, such as a computer readable storage medium having instructions stored thereon that are operable to program a programmable processor to perform the methods described in any of the above aspects and possibilities or claims, and / or to program a suitably configured computer to provide an apparatus as described in any of the claims.

[0029] Each feature disclosed in this specification (including the claims) and / or shown in the drawings may be incorporated in the present invention independently of (or in combination with) other disclosed and / or illustrated features. In particular, but not by way of limitation, the features of any claim dependent on a particular independent claim may be incorporated in the independent claim in any combination or individually. Effect of the Invention

[0030] SUMMARY OF THE PRESENT EMBODIMENT The present invention provides a method, and associated apparatus, that overcomes or at least alleviates (at least part of) the problems set forth above. [Brief description of the drawings]

[0031] An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG.

[0032] [Figure 1] FIG. 1 illustrates generally a mobile (cellular or wireless) telecommunications system in which exemplary embodiments of the invention may be applied. [Diagram 2] FIG. 2 is a schematic block diagram of a mobile device forming part of the system shown in FIG. [Diagram 3] FIG. 3 is a schematic block diagram of an NTN node (e.g., a satellite / UAS platform) forming part of the system shown in FIG. [Figure 4] FIG. 4 is a schematic block diagram of an access network node (eg a base station) forming part of the system shown in FIG. [Diagram 5] FIG. 5 illustrates diagrammatically two exemplary scenarios in which exemplary embodiments of the present invention can be applied. [Figure 6] FIG. 6 illustrates diagrammatically two exemplary scenarios in which exemplary embodiments of the present invention can be applied. [Figure 7] FIG. 7 is a signaling (timing) diagram illustrating some example ways in which exemplary embodiments of the present invention may be implemented in the scenarios illustrated in FIGS. [Figure 8] FIG. 8 is a signaling (timing) diagram illustrating some example ways in which exemplary embodiments of the present invention may be implemented in the scenarios illustrated in FIGS. [Figure 9] FIG. 9 is a signaling (timing) diagram illustrating some example ways in which exemplary embodiments of the present invention may be implemented in the scenarios illustrated in FIGS. [Figure 10] FIG. 10 is a signaling (timing) diagram illustrating some example ways in which exemplary embodiments of the present invention may be implemented in the scenarios illustrated in FIGS. [Figure 11]FIG. 11 is a signaling (timing) diagram illustrating some example ways in which exemplary embodiments of the present invention may be implemented in the scenarios illustrated in FIGS. [Figure 12] FIG. 12 illustrates generally some exemplary architectural options for providing NTN functionality in the system shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] overview Figure 1 is a schematic diagram of a mobile (cellular or wireless) communication system 1 to which exemplary embodiments of the present invention may be applied. In this communication system 1, users of mobile devices 3 (UE) may communicate with each other and with other users via respective satellites 5 and / or base stations 6 of access network nodes and a data network 7 using an appropriate 3GPP radio access technology (RAT), e.g., E-UTRA and / or 5G RAT. As will be appreciated by those skilled in the art, although for illustrative purposes, three mobile devices 3, one satellite 5 and one base station 6 are shown in Figure 1, the system, when implemented, will typically include other satellite / UAS platforms, base stations / RAN nodes and mobile devices (UE).

[0034] It will be understood that several base stations 6 form a (Radio) Access Network or (R)AN, and several NTN nodes 5 (satellite and / or UAS platforms) form a non-terrestrial based network (NTN). Each NTN node 5 is connected to an appropriate gateway (in this case residing in the base station 6) by means of a so-called feeder link, and to each UE 3 via a corresponding service link. Thus, when the NTN node 5 serves, the mobile device 3 communicates data with the base station 6 via the NTN node 5 by means of an appropriate service link (between the mobile device 3 and the NTN node 5) and a feeder link (between the NTN node 5 and the gateway / base station 6). In other words, the NTN forms part of the (R)AN, but can also provide satellite communication services independently of E-UTRA and / or 5G communication services.

[0035] Although not shown in Figure 1, neighbouring base stations 6 are connected to each other via appropriate inter-base station interfaces (so-called "X2" interfaces, "Xn" interfaces, etc.) and to data network nodes via appropriate interfaces (so-called "S1", "NG-C", "NG-U" interfaces, etc.).

[0036] The data (or core) network 7 (EPC for LTE, NGC for NR / 5G) typically includes logical nodes (or "functions") for supporting communications in the communication system 1 and for (among other things) subscriber management, mobility management, charging, security, and call / session management. For example, the data network 7 in a "next generation" / 5G system includes user plane entities and control plane entities, such as one or more control plane functions (CPFs) and one or more user plane functions (UPFs). A so-called access and mobility management function (AMF) is responsible for handling connection and mobility management tasks for the mobile devices 3. The data network 7 is also connected to other data networks, such as the Internet or a similar Internet Protocol (IP)-based network (not shown in FIG. 1).

[0037] Each NTN node 5 controls several directional beams through which an associated NTN cell is served. In particular, each beam has an associated footprint on the Earth's surface that corresponds to the NTN cell. Each NTN cell (beam) has an associated Physical Cell Identity (PCI) and / or beam identifier. The beam footprint may move as the NTN node 5 moves along its orbit. Alternatively, the beam footprint may be fixed to the Earth, in which case an appropriate beam pointing mechanism (mechanical or electronic steering) may be used to compensate for the movement of the NTN node 5.

[0038] Each cell has an associated "NR Cell Global Identifier" (NCGI), which identifies the cell globally. The NCGI consists of the Public Land Mobile Network (PLMN) Identifier (PLMN ID) to which the cell belongs and the NR Cell Identifier (NCI) of the cell. The PLMN ID contained in the NCGI is the first PLMN ID in the set of PLMN IDs associated with the NR Cell ID in System Information Block Type 1 (SIB1). The "gNB Identifier" (gNB ID) is used to identify a specific gNB within a PLMN. The gNB ID is contained within the NCI of its cell. The "global gNB ID" is used to identify a gNB globally and consists of the PLMN ID to which the gNB belongs and the gNB ID. The Mobile Country Code (MCC) and Mobile Network Code (MNC) are the same as those contained in the NCGI.

[0039] Cells serving a particular geographical area are grouped into a coverage area (e.g., a tracking area) belonging to one PLMN. In this example, different groups of cells serve different countries, although other types of cell groupings are possible.

[0040] The UE 3 establishes an RRC connection with the base station 6 via a cell and also registers with the AMF 9 of the country / area / PLMN served by the base station 6. The UE 3 is thus in a so-called RRC Connected state and the associated UE context is maintained by the serving base station 6-1. Then, when the UE 3 is released and goes into an RRC Inactive state, the RRC connection is interrupted and the associated UE context is stored by the base station 6-1 (which may be referred to as the last / old serving base station of the UE when the UE goes into an RRC Inactive state).

[0041] While in RRC Connected or RRC Inactive state, the UE 3 may move to another coverage area / country. It will be appreciated that this new coverage area / country may be a cell under the control of the same base station 6 or a different base station. The cell may broadcast at least one associated PLMN ID, although some cells are not configured to broadcast such an ID.

[0042] The UE 3 may also be configured (in either the RRC Connected or RRC Inactive state) to monitor its current location and current coverage area / country based on suitable location information, such as Global Navigation Satellite System (GNSS) location information, a mobile country code (for the mobile device), and / or any other suitable positioning information. The current UE context associated with the UE 3 and / or the AMF 9 assigned to the UE 3 may not be suitable in the new coverage area or country. The UE 3 is therefore configured to release the RRC connection by itself or by initiating an appropriate procedure with the network upon detecting that it has moved to a coverage area (new country) different from the coverage area associated with the UE context / current AMF. In effect, by releasing the RRC connection, the UE 3 transitions (from the RRC Inactive or RRC Connected state) to the RRC Idle state.

[0043] If the UE 3 (e.g., in the RRC Connected state) notifies the network that the RRC connection needs to be released due to a change in coverage area, the base station can send the appropriate redirection information to the mobile device 3 to register with a new AMF appropriate for the coverage area / country / PLMN in which the mobile device 3 is currently located.

[0044] User Equipment (UE) FIG. 2 is a block diagram illustrating the main components of the mobile equipment (UE) 3 shown in FIG. 1. As shown in the figure, the UE 3 includes a transceiver circuit 31, which is operable to transmit and receive signals to and from a connected node via one or more antennas 33. Although not necessarily shown in FIG. 2, the UE 3 can of course have all the usual functions of a conventional mobile device (such as a user interface 35), which may be provided by one or any combination of hardware, software and firmware, as appropriate. A controller 37 controls the operation of the UE 3 according to software stored in a memory 39. The software may be pre-installed in the memory 39 and / or downloaded over the communication network 1 or, for example, from a removable data storage device (RMD). The software includes, among others, an operating system 41, a communication control module 43 and a positioning module 45.

[0045] The communication control module 43 processes (generates / sends / receives) signaling messages and uplink / downlink data packets between the UE 3 and other nodes, including the NTN node 5, the (R)AN node 6, and the core network nodes. This signaling may include control signaling related to RRC setup, RRC (re)configuration, RRC resumption, RRC release, and / or redirection to a new AMF / PLMN.

[0046] A positioning module 45 (optional in some UEs) determines the position of the UE 3, for example based on GNSS signals, and also provides position assistance information to other nodes where appropriate.

[0047] NTN Node (Satellite / UAS Platform) FIG. 3 is a block diagram illustrating the main components of the NTN node 5 (satellite / UAS platform) shown in FIG. 1. As shown in the figure, the NTN node 5 includes a transceiver circuit 51, which is operable to transmit and receive signals to and from one or more connected UEs 3 via one or more antennas 53, and to transmit and receive signals to and from other network nodes, such as gateways and base stations (directly or indirectly). A controller 57 controls the operation of the NTN node 5 in accordance with software stored in memory 59. The software may be pre-installed in memory 59 and / or may be downloaded over the communications network 1 or, for example, from a removable data storage device (RMD). The software includes, among other things, an operating system 61 and a communications control module 63.

[0048] The communication control module 63 processes (generates / sends / receives) signals between the NTN node 5 and other nodes, including for example the UE 3, base stations 6, gateways, and core network nodes (via base stations / gateways). This signaling may include control signaling related to RRC setup, RRC (re)configuration, RRC resumption, RRC release, and / or UE redirection to a new AMF / PLMN.

[0049] Base Station / Gateway (Access Network Node) FIG. 4 is a block diagram illustrating the main components of the gateway 6 (base station (gNB) or similar access network node) shown in FIG. 1. As shown in the figure, the gateway / gNB 6 includes a transceiver circuit 71, which is operable to transmit and receive signals to and from one or more connected UEs 3 via one or more antennas 73, and also to transmit and receive signals to and from other network nodes (directly or indirectly) via a network interface 75. Signals may be transmitted and received directly and / or via the NTN node 5, as appropriate, to and from one or more UEs 3. The network interface 75 typically includes a suitable base station-base station interface (e.g., X2 / Xn, etc.) and a suitable base station-core network interface (e.g., S1 / NG-C / NG-U, etc.). The controller 77 controls the operation of the base station 6 in accordance with software stored in the memory 79. This software may be pre-installed in the memory 79 and / or may be downloaded via the communication network 1 or, for example, from a removable data storage device (RMD). The software includes, among other things, an operating system 81 and a communication control module 83.

[0050] The communication control module 83 processes (generates / sends / receives) signals between the base station 6 and other nodes, including the UE 3, the NTN node 5, and core network nodes, etc. This signaling may include control signaling related to RRC setup, RRC (re)configuration, RRC resumption, RRC release, and / or UE redirection to a new AMF / PLMN.

[0051] Detailed Description With reference to the scenarios shown in FIGS. 5 and 6, some exemplary procedures (solutions 1 to 3) performed by the nodes of the system shown in FIG. 1 will be described.

[0052] Specifically, in the scenario shown in Figure 5, base station 6 (gNB) serves multiple countries or coverage areas via its cell ("Cell A" in Figure 5), which broadcasts an identifier of each PLMN associated with the country or coverage area it serves via that cell. In Figure 6, base station 6 controls cells in different countries or coverage areas, and each cell broadcasts at least one identifier of at least one PLMN it serves. Base station 6 connects to different AMFs 9-1 and 9-2, which serve respective PLMNs 8-1 and 8-2 in different countries / areas.

[0053] In the above mentioned scenario, the UE 3 establishes an RRC connection with the base station via a cell and registers with the AMF of the relevant country / region / PLMN. In the example shown in Fig. 5 and Fig. 6, the UE 3 (initially) establishes an RRC connection via "Cell A" of the base station 6 and registers with the AMF 9-1 of "Coverage Area X" or "Country X" (PLMN 8-1). Thus, in this case, the UE 3 is in a so-called RRC Connected state and the relevant UE context is maintained by the serving base station 6. Then, when the UE 3 is released and goes to RRC Inactive state, the RRC connection is interrupted and the relevant UE context is stored by the base station 6 (which may be referred to as the last / old serving gNB of the UE when the UE goes to RRC Inactive state).

[0054] Later, in RRC Inactive or RRC Connected state, the UE 3 may move to another coverage area (within the same cell in FIG. 5 or in a new cell in FIG. 6), in this example the cell serving the new coverage area belongs to the same base station 6.

[0055] In order to prevent an inappropriate UE context from being used in a new country or new area, multiple nodes of the system are configured to perform one or more of the following solutions:

[0056] Solution 1 FIG. 7 is a signaling (timing) diagram illustrating an example of an exemplary method for a UE to transition to RRC Idle in the scenario described above.

[0057] Initially, the UE 3 is in an RRC Connected state and has an RRC connection with a base station 6 (e.g., a gNB of an NG-RAN). The UE 3 is registered with an AMF 9-1 (denoted as "Old AMF" in FIG. 7). The base station 6 and the AMF 7-1 serve the UE's current coverage area (e.g., "Country X" in FIG. 5 and FIG. 6).

[0058] In step S1, the serving base station 6 (RAN node) sends appropriate parameters for suspending the UE's RRC connection to the UE 3. In this example, the base station 6 generates and sends to the UE 3 a suitably formatted "RRCRelease" message containing the appropriate suspended configuration.

[0059] The UE 3 transitions to the RRC Inactive state based on the received configuration. The relevant UE context is stored in the base station 6. The UE context is associated with or valid for the coverage area (country) served by the AMF 9-1 in which the UE 3 is currently registered.

[0060] During the RRC Inactive state, the UE 3 monitors its location (e.g., by performing periodic location measurements, by monitoring signal conditions of nearby cells, and / or by monitoring system information transmitted in nearby cells). In this example, the UE 3 determines its current location using the GNSS, MCC, etc.

[0061] It will be appreciated that each cell of the system serves at least one coverage area / country. The cells of the system broadcast (e.g., in associated system information) information identifying the respective coverage area / country that they serve (e.g., based on associated PLMN and / or MCC). This information may be a list of PLMN identifiers and associated MCCs. Furthermore, a cell may broadcast information identifying / related to the borders of at least one coverage area associated with the cell as part of the system information or via higher layers. This information may be provided as map data, etc. The UE 3 may be configured to detect whether a cell supports multiple coverage areas (countries) under the control of different PLMNs based on the PLMN identifiers / MCCs broadcasted in the cell.

[0062] When the UE 3 detects (at step S3) that it has moved to a different coverage area (new country) than the coverage area served by the AMF 9-1 in which the UE 3 is currently registered, the UE 3 releases the RRC connection, as generally shown in step S5. As can be seen, in this case the UE 3 releases the RRC connection itself, and the UE 3 transitions to an RRC Idle state (step S7). It will be appreciated that the new coverage area may be served by the same cell as the old coverage area, in other words the UE 3 may be in the same cell (e.g. in "cell A" in FIG. 5).

[0063] On the network side, since the UE 3 is in RRC Idle state (meaning that the UE does not resume the RRC connection and does not update its location information within a certain time), the serving base station 6 and the old serving AMF 9-1 perform an appropriate UE context release procedure (step S8) to release the stale UE context and release resources of the base station 6. For example, the UE context stored in the network may be released after expiry of an appropriate timer (e.g. the "T310" timer, whose value is given by the information element PeriodicRNAU-TimerValue, or any suitable timer).

[0064] Solution 2 The first option of solution 2 is based on steps S1 to S7 described above with reference to FIG. 7, while the second and third options are illustrated in FIG.

[0065] In the first option, after the UE 3 releases the RRC connection (step S5), it determines (step S10) which PLMN, if any, to use in the current coverage area. The UE 3 selects a suitable PLMN and proceeds to register with the new AMF 9-2 associated with the coverage area (or country) in which the UE 3 is currently located.

[0066] More specifically, the UE 3 selects an appropriate PLMN based on information it holds (e.g., a list of PLMNs and corresponding coverage areas). Since the newly selected PLMN is served by the new AMF 9-2, the UE 3 performs an appropriate RRC setup procedure (via the serving base station 6) in the new coverage area and registers with the new AMF 9-2, as generally shown in steps S12 and S13 of FIG. 7. In this case, it will be appreciated that the UE context release procedure with the base station 6 may be performed after (or in response to) the RRC setup (step S12) or registration of the UE 3 with the new AMF 9-2. In other words, step S8 may be performed after steps S12 / S13, regardless of whether the relevant timer (e.g., T310 timer) is still running in the base station 6 / old AMF 9-1. The UE context release procedure may be initiated by the base station 6 or the new AMF 9-2 towards the old AMF 9-1 (or the old serving base station 6, if different).

[0067] FIG. 8 is a signaling (timing) diagram that illustrates two options (option 2 and option 3) for registering to a new AMF after transitioning the UE to RRC Idle.

[0068] In a second option, when the UE 3 moves to a new coverage area / country different from the one it was previously registered in, the serving RAN node 6 indicates to the UE 3 whether the UE 3 is allowed to release the RRC connection itself or not. In this example, this indication is sent in an RRCRelease message including the suspended configuration parameters (step S1), but any other suitable message (any suitable RRC message, system information block, etc.) may be used.

[0069] In step S1, the serving base station 6 configures an appropriate UE release configuration using one or more appropriate information elements (IEs) so that the UE 3 can release itself when the UE 3 moves (crosses the boundary) into a new coverage area different from the area where the UE 3 was previously registered. For example, the RRCRelease message may include a UE release configuration (e.g., uEReleaseAllowedIndication IE, uEReleaseLocationIndication IE, etc.) indicating whether the UE 3 can release the RRC connection. The information element may include a "TRUE" / "FALSE" value (or "1" / "0") depending on the appropriate configuration, and may be set to "TRUE" / "1" if the UE 3 is allowed to release the RRC connection, and set to "FALSE" / "0" otherwise.

[0070] For example, the RRCRelease message (described in 3GPP Technical Specification 38.331) may contain the following information elements: RRCRelease-vxyz-IEs ::= SEQUENCE { uEReleaseAllowedIndication ENUMERATED {true} OPTIONAL, -- Need N nonCriticalExtension SEQUENCE {} OPTIONAL }

[0071] The uEReleaseLocationIndication field (if present) can be defined as a field that indicates to the UE that the UE should trigger an RRC release (i.e., release the UE itself and transition to RRC Idle) when the UE moves to a new coverage area under the control of a new AMF different from the AMF on which the UE registered.

[0072] In step S2, the UE 3 transitions to an RRC Inactive state and monitors its location (at least at the coverage area level). If the UE 3 determines (in step S3) based on its location information and / or information identifying / related to the border of at least one coverage area associated with its cell, that the UE 3 has moved to a coverage area (new country) different from the coverage area served by the AMF 9-1 in which the UE 3 is currently registered, the UE 3 initiates a procedure to release the RRC connection, as shown in step S4.

[0073] Specifically, if the release configuration allows the UE 3 to do so (e.g., uEReleaseAllowedIndication IE or uEReleaseLocationIndication IE is included in the RRCRelease message and is set to "TRUE"), the UE 3 triggers its own release (transition to the RRC Idle state) by sending an appropriate indicator to the serving base station 6. For example, the UE 3 can send an information element (e.g., uEReleaseIndication IE) indicating that the UE 3 is requesting an RRC connection release. This information element can be included in an appropriately formatted RRCResumeRequest message. The UE 3 may include an appropriate cause value in the RRCResumeRequest message to indicate to the network that the UE 3 is requesting release of the RRC connection due to the UE's current location (e.g. cause value for "UE Release due to location", cause value for "UE movement into a new location / new coverage area", cause value for "Release due to UE preference", and / or cause value for "UE Release due to Allowance").

[0074] Advantageously, the network can timely release (in step S8) the associated UE context based on the message (and any information elements contained therein) from the UE 3. In step S9, the base station 6 ensures that the UE 3 is allowed to release the old RRC connection by generating and sending an appropriate signalling message (e.g. an RRCRelease message).

[0075] As generally shown in step S11, the UE 3 transitions to the RRC Idle state only after it has indicated to the network that it has moved to a new coverage area (or country).

[0076] The third option is also shown in Fig. 8, which is a variant of the second option. As can be seen, steps S1-S4 and step S8 are substantially the same as the second option. However, in this example, as shown in step S9, when the UE 3 enters the RRC Idle state, the base station 6 also provides appropriate redirection information to assist the UE 3 to register with an appropriate AMF serving the UE's new coverage area. This information may include, for example, a list of PLMNs served by the UE's current cell and corresponding coverage area, and / or a list of AMFs (at least one AMF) serving the UE's current coverage area (or country).

[0077] The redirection information is included in the RRCRelease message (sent in step S9) and the UE 3 selects an appropriate PLMN based on this information. Once the UE 3 releases the old RRC connection (step S11), the UE 3 initiates an appropriate RRC setup procedure in the new coverage area (via the base station 6) and registers with the new AMF 9-2 serving that coverage area, as shown in steps S12 and S13 of Figure 8.

[0078] Solution 3 Even if the UE 3 is in the RRC Connected state, the UE 3 may be configured to release its RRC connection or to initiate a procedure to release the RRC connection. Figures 9 to 11 show diagrammatically some possible ways to release the UE's RRC connection when the UE 3 moves to a new coverage area (or country).

[0079] A first option for solution 3 is shown in Figure 9. This option is similar to the first option for solution 2 described above with reference to Figure 7. However, as generally shown in step S1, in this example, the UE 3 has an active RRC connection to the network (e.g., gNB in ​​NG-RAN, etc.), so the UE 3 remains in the RRC Connected state (step S2). As described above, the UE 3 is registered with the AMF 9-1 (labeled "Old AMF" in Figure 9) serving the UE's current coverage area. The associated UE context is maintained in the base station 6 serving the UE 3. This UE context is associated with or valid for the coverage area (country) served by the AMF 9-1 in which the UE 3 is currently registered.

[0080] While in the RRC Connected state, the UE 3 monitors its location (e.g., by performing periodic location measurements, by monitoring signal conditions of nearby cells, and / or by monitoring system information transmitted in nearby cells, including the current serving cell). In this example, the UE 3 determines its current location using GNSS, MCC, etc.

[0081] When the UE 3 detects (at step S3) that it has moved to a coverage area (new country) other than the coverage area served by the currently registered AMF 9-1, the UE 3 releases the RRC connection, as generally shown in step S5. As can be seen, in this case, the UE 3 releases the RRC connection by itself without exchanging signaling messages with the network, and the UE 3 transitions to an RRC Idle state (step S7). It will be appreciated that both the old coverage area and the new coverage area are served by the same cell (e.g., "Cell A" in FIG. 5).

[0082] On the network side, since the UE 3 is in RRC Idle state (meaning that the UE does not resume the RRC connection and does not update its location information within a predetermined time), the base station 6 and the old serving AMF 9-1 perform an appropriate UE context release procedure (step S8) and release the UE context associated with the UE 3 (e.g., by expiry of an appropriate "T310" timer, etc.).

[0083] Next, in step S10, the UE 3 determines which PLMN, if any, to use for the current coverage area. As generally shown in steps S12 and S13 of Figure 9, the UE 3 selects a suitable PLMN and proceeds to register with the new AMF 9-2 associated with the coverage area (or country) in which the UE 3 is currently located, which includes a suitable RRC setup procedure in the new coverage area (via the serving base station 6). The suitable PLMN may be selected based on information held by the UE 3 (e.g. a list of PLMNs and corresponding coverage areas). It will be appreciated that a UE context release procedure (step S8) with the base station 6 may be performed after (or in response to) the RRC setup (step S12) or registration of the UE 3 with the new AMF 9-2 (step S13).

[0084] Figures 10 and 11 are signalling (timing) diagrams which illustrate, in schematic form, some additional options for transitioning the UE 3 from an RRC Connected state to an RRC Idle state when the UE 3 moves to a new coverage area (new country). Options 2 and 4 are similar to option 2 described above with reference to Figure 8, and options 3 and 5 are similar to option 3 of Figure 8. However, in Figures 10 and 11, the UE 3 is in an RRC Connected state when the UE 3 initiates the procedure to release the RRC connection.

[0085] It will be appreciated that steps S1-S3 are common to all the options shown in Figures 10 and 11. As shown in step S1, the UE 3 is initially in an RRC Connected state. Thus, the UE 3 has an RRC connection with a base station 6 (e.g. a gNB in ​​an NG-RAN) and the UE 3 is registered with an AMF 9-1 serving the UE's current coverage area (e.g. "Country X" in Figures 5 and 6).

[0086] In step S2, the serving base station 6 configures an appropriate UE release configuration using one or more appropriate information elements (IEs) so that the UE 3 can release itself when the UE 3 moves (crosses the border) into a new coverage area different from the area in which it was previously registered. In this example, the UE release configuration is sent to the UE 3 in an appropriately formatted RRCReconfiguration message. For example, the message may include a uEReleaseAllowedIndication IE or a uEReleaseLocationIndication IE, similar to the information elements included in the RRCRelease message of step S1 of FIG. 8.

[0087] The UE3 monitors its location (at least at the coverage area level) and if it determines (in step S3) based on the UE3's location information and / or information identifying / related to the boundary of at least one coverage area associated with the cell, that the UE3 has moved to a coverage area (new country) different from the coverage area provided by the AMF9-1 in which the UE3 is currently registered, the UE3 initiates a procedure to release the RRC connection, as shown in step S5.

[0088] In option 2, step S5 includes the UE 3 sending an indication (in this case a new RRC message) that the UE 3 is releasing the RRC connection due to a change in location. In effect, the UE 3 triggers itself to release and move to the RRC Idle state. Specifically, the UE 3 sends this indication to the serving base station 6 if the release configuration allows the UE 3 to do so (e.g., the RRCReconfiguration message includes a uEReleaseAllowedIndication IE or a uEReleaseLocationIndication IE set to "TRUE"). As described with reference to step S4 of FIG. 8, the RRC message may include an information element (e.g., a uEReleaseIndication IE) indicating that the UE 3 is requesting an RRC connection release. The RRC message may also include an appropriate cause value indicating to the network that UE3 is requesting release of the RRC connection due to the UE's current location (e.g. a cause value indicating "UE Release due to location", a cause value indicating "UE movement into a new location / new coverage area", a cause value indicating "Release due to UE preference", and / or a cause value indicating "UE Release due to Allowance").

[0089] Advantageously, the network can timely release the associated UE context (step S8) based on the message (and any information elements contained therein) from the UE 3. In step S9, the base station 6 ensures that the UE 3 is allowed to release its old RRC connection by generating and sending an appropriate signalling message (e.g. an RRCRelease message).

[0090] As generally shown in step S11, the UE 3 transitions to the RRC Idle state only after it has indicated to the network that it has moved to a new coverage area (or country).

[0091] Now referring to option 3 of Figure 10, steps S5 and S8 are the same as above. However, in this case, the base station 6 also provides appropriate redirection information to assist the UE 3 in registering with an appropriate AMF serving the UE's new coverage area. This information may include, for example, a list of PLMNs served by the UE's current cell and corresponding coverage area, and / or a list of AMFs (at least one AMF) serving the UE's current coverage area (or country).

[0092] The redirection information is included in the RRCRelease message (sent in step S9) and the UE 3 selects an appropriate PLMN based on this information. Once the UE 3 releases the old RRC connection (step S11), the UE 3 (via the base station 6) initiates an appropriate RRC setup procedure in the new coverage area and registers with the new AMF 9-2 serving that coverage area, as shown in steps S12 and S13 of Figure 10.

[0093] Option 4 and Option 5 are substantially the same as Option 2 and Option 3, respectively. However, as shown in Figure 11, the message sent by UE3 in step S5 may include a UEAssistanceInformation message to trigger the release of the RRC connection (to transition to the RRC Idle state). Essentially, UE3 can use the UE Assistance Information message to indicate the desired RRC state (in this case, the RRC Idle state) to the network.

[0094] The UE's preferred RRC state may be indicated by means of the information element preferredRRC-State in the UE assistance information message. If the UE 3 wishes to be released from the RRC Connected state and transition to the RRC Idle state, the information element preferredRRC-State may be set to the value "idle". Alternatively, if the UE 3 wishes to be released from the RRC Connected state and transition to the RRC Inactive state, it may indicate the value "inactive". If appropriate, the value "connected" may be used if the UE wishes to revert a previous indication to remain in the RRC Connected state. The value "outOfConnected" may be used to indicate that the UE 3 wishes to release the RRC Connected state and has no preferred RRC state to transition to. Thus, the state of the UE in step S11 may depend on the UE's preferences, i.e. the value of the information element preferredRRC-State.

[0095] advantage The above solution can prevent the use of inappropriate UE context in a new country or area, and can also reduce signaling overhead caused by failures when a UE attempts to access a cell in a new coverage area.

[0096] Modifications and Alternatives Detailed embodiments have been described above. As will be appreciated by those skilled in the art, many modifications and alternatives to the above-described embodiments are possible while still benefiting from the invention embodied therein. By way of example, some of these many alternatives and modifications will be described.

[0097] It will be appreciated that the above-described embodiments are applicable to both 5G New Radio and LTE systems (E-UTRAN). A base station (gateway) supporting E-UTRAN / 4G protocols is referred to as an "eNB", and a base station supporting next-generation / 5G protocols is referred to as a "gNB". It will be appreciated that some base stations can be configured to support both 4G and 5G protocols, and / or other 3GPP or non-3GPP communication protocols.

[0098] 3GPP Technical Report 38.857 V1 7 Section 10.1 of RRC_INACTIVE provides further information on positioning of UEs in RRC_INACTIVE state. In summary, the following positioning techniques are considered: -Downlink (DL), uplink (UL), and downlink and uplink positioning methods; UE-based and UE-assisted positioning means; -Support for UE positioning for UEs in RRC_inactive state; Possible options include a Downlink Positioning Reference Signal (DL-PRS) or a Downlink Positioning Reference Signal and Synchronization Signal Block (SSB); - Support for gNB location measurement for UE in RRC_inactive state. To enable positioning of a UE in RRC_INACTIVE state, the following methods may be used: -Uplink reference signals for uplink measurements (e.g., Sounding Reference Signals (SRS), Physical Random Access Channel (PRACH) preambles for positioning); Signaling and procedures to support the transmission of assistance data, configuration of downlink positioning reference signals, downlink reference signals for positioning resource configuration, and measurement reporting, which may be developed based on extensions of existing signaling and procedures (e.g., existing two-step and / or four-step physical random access channel procedures, paging procedures, small data communications, etc.).

[0099] For downlink positioning in RRC_INACTIVE the following procedures can be used: -If the UE is in RRC_INACTIVE, reporting of downlink positioning reference signal measurements and / or position estimation performed in RRC_INACTIVE; When the UE is in RRC_INACTIVE, the measurement of the downlink positioning reference signal and / or the reporting of the position estimation performed in RRC_INACTIVE is enabled by extending small data communication in RRC_INACTIVE; - on-demand system information request in RRC_INACTIVE for transmission of assistance data by broadcast in RRC_INACTIVE; -ProvideAssistanceData in RRC_CONNECTED for configuration of downlink positioning reference signals used in downlink positioning in RRC_INACTIVE; -RequestLocationInformation may be sent in RRC_CONNECTED for downlink positioning reference signal measurements or location estimation performed in RRC_INACTIVE.

[0100] It will be appreciated that the UE may be configured to calculate its position using any of the techniques described above and the UE may provide position assistance information accordingly.

[0101] In the above description, the RRCRelease message and the RRCReconfiguration message include a UEReleaseAllowedIndication IE or a uEReleaseLocation Indication IE to indicate to the UE that the UE is allowed to release the RRC connection when the UE crosses a boundary, however, it will be appreciated that the release configuration may be provided using any other suitable message and / or any other suitable information element.

[0102] [Table 1]

[0103] It will be appreciated that there may be various architectural options for implementing NTN in a 5G system, some of which are shown diagrammatically in FIG. 12. A first option is an NTN characterized by an access network serving UEs, based on bent-pipe payloads and terrestrial (satellite hub or gateway level) gNBs and satellites / aircraft. A second option is an NTN characterized by an access network serving UEs, based on gNBs and satellites / aircraft. A third option is an NTN characterized by an access network providing relay nodes, based on bent-pipe payloads and satellites / aircraft. A fourth option is an NTN characterized by an access network providing relay nodes, based on gNBs and satellites / aircraft. It will be appreciated that other architectural options may be employed, for example a combination of two or more of the above options. Alternatively, the relay node may include a satellite / UAS.

[0104] In the above description, for ease of understanding, the UE, NTN nodes (satellite / UAS platforms), and access network nodes (base stations) are described as having a number of separate modules (such as a communications control module). While these modules may be provided in this manner for certain applications, such as when an existing system is modified to implement the present invention, in other applications, such as systems designed from the outset with the features of the present invention, these modules may not be identified as separate entities because they are integrated into the overall operating system or code. These modules may also be implemented in software, hardware, firmware, or a combination thereof.

[0105] Each controller may include any suitable form of processing circuitry, including (but not limited to) one or more hardware implemented computer processors, microprocessors, central processing units (CPUs), arithmetic logic units (ALUs), input / output (IO) circuitry, internal memory / cache (program and / or data), processing registers, communication buses (e.g., control buses, data buses and / or address buses), direct memory access (DMA) facilities, hardware or software implemented counters, pointers and / or timers, etc.

[0106] In the above-described embodiment, a number of software modules have been described. As will be appreciated by those skilled in the art, the software modules may be provided in compiled or uncompiled form and may be provided to the UE, NTN node, and access network node (base station) as a signal, via a computer network or a recording medium. Furthermore, the functionality performed by some or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred in order to facilitate updating the functionality of the UE, NTN node, and access network node (base station).

[0107] The above described embodiments may also be applied to "non-mobile" or typically fixed UEs. The above mentioned mobile devices may comprise MTC / IoT devices etc.

[0108] The method performed by the UE may further include obtaining information identifying at least one public land mobile network (PLMN) and / or at least one mobile country code (MCC) associated with at least one respective coverage area served by a current cell of the UE, and determining that a current location of the UE is in a coverage area different from the first coverage area based on the obtained information (e.g., system information).

[0109] The method performed by the UE may further include obtaining information regarding a boundary of at least one coverage area served by a current cell of the UE, and determining, based on the information regarding the boundary, that a current location of the UE is in a coverage area different from the first coverage area.

[0110] The method performed by the UE may further include receiving information indicating that the UE is allowed to release the RRC connection based on the location of the UE (e.g., an information element "uEReleaseAllowedIndication" or "uEReleaseLocationIndication"), which may be received in an RRCRelease message or an RRCReconfiguration message.

[0111] Releasing the RRC connection includes the UE sending information to the network node indicating that it is requesting an RRC connection release (e.g. using an information element uEReleaseIndication) and / or indicating the desired RRC state (e.g. using an information element preferredRRC-State). This information may be included in an RRC message (e.g. an RRCResumeRequest message or an UEAssistanceInformation message). This information may include a cause value indicating the cause of releasing the RRC connection (e.g. a cause value for "UE Release due to location", a cause value for "UE movement into a new location / new coverage area", a cause value for "Release due to UE preference", and / or a cause value for "UE Release due to Allowance").

[0112] The method performed by the UE may further include setting up an RRC connection via cells serving different coverage areas and selecting a PLMN and / or core network node for mobility management associated with the coverage area based on a list of PLMNs and corresponding coverage areas maintained by the UE.

[0113] The method performed by the UE may further include receiving information for redirecting the UE to a PLMN and / or a core network node for mobility management associated with a location of the UE, and setting up an RRC connection via a cell serving a different coverage area based on the information for redirecting the UE. The method may include receiving an RRCRelease message or an RRCReject message including the information for redirecting the UE to an AMF / PLMN associated with the location of the UE.

[0114] Determining that the current location of the UE is in a coverage area different from the first coverage area may be based on at least one of a Global Navigation Satellite System (GNSS) based position and an MCC associated with the UE.

[0115] The method performed by the network node may further include triggering a release of a UE context associated with the first coverage area after receiving the message from the UE.

[0116] The method performed by the network node may further include transmitting information identifying at least one Public Land Mobile Network (PLMN) and / or at least one Mobile Country Code (MCC) associated with at least one respective coverage area served by a cell of the network node.

[0117] The method performed by the network node may further comprise the step of transmitting information to the UE regarding a boundary of at least one coverage area served by a cell of the network node.

[0118] The method performed by the network node may further comprise the step of sending information to the UE indicating that the UE is allowed to release the RRC connection based on the location of the UE (e.g. in the RRCReconfiguration message or using the "uEReleaseAllowedIndication" or "uEReleaseLocationIndication" information element).

[0119] The method performed by the network node may further include the step of transmitting information to the UE for redirecting the UE to a PLMN and / or a core network node for mobility management associated with a location of the UE.

[0120] The method performed by the network node may include sending an RRCRelease message or an RRCReject message to the UE to redirect the UE to an AMF / PLMN associated with the UE's location.

[0121] The RRC connection associated with the first coverage area may be a suspended RRC connection or an active RRC connection.

[0122] Various other variations will be apparent to those skilled in the art and will not be described in further detail herein.

[0123] The program includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray® disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, the transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other form of propagated signal.

[0124] This application claims the benefit of priority to UK Patent Application No. 2105402.8, filed April 15, 2021, and UK Patent Application No. 2106477.9, filed May 6, 2021, the disclosures of which are incorporated herein by reference in their entireties.

[0125] Additional Notes For example, some or all of the above exemplary embodiments may be described as follows, but are not limited to the following: (Appendix 1) 1. A method performed by a user equipment (UE) configured to communicate over a non-terrestrial network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the method comprising: determining that a current location of the UE is in a coverage area different from a first coverage area; releasing the RRC connection based on a current location of the UE; A method comprising: (Appendix 2) obtaining first information identifying at least one Public Land Mobile Network (PLMN) and / or at least one Mobile Country Code (MCC) associated with at least one respective coverage area served by a current cell of the UE; 2. The method of claim 1, wherein the determination is made based on the first information. (Appendix 3) obtaining second information regarding a boundary of at least one coverage area served by a current cell of the UE; 3. The method of claim 1 or 2, wherein the determination is based on the second information. (Appendix 4) The method according to any one of Supplementary Notes 1 to 3, further comprising a step of receiving third information indicating that the UE is permitted to release the RRC connection based on a location of the UE. (Appendix 5) The method according to claim 4, wherein the third information is included in an RRC Release message or an RRC Reconfiguration message. (Appendix 6) Releasing the RRC connection includes transmitting fourth information to a network node; The method according to any one of Supplementary Note 1 to 5, wherein the fourth information indicates at least one of an indication that the UE is requesting RRC connection release and a desired RRC state. (Appendix 7) The method of claim 6, wherein the fourth information is included in an RRC message. (Appendix 8) 8. The method according to claim 6 or 7, wherein the fourth information includes a cause value indicating a cause for releasing the RRC connection. (Appendix 9) establishing an RRC connection via a cell serving the different coverage area; selecting a public land mobile network and / or core network node for mobility management associated with the coverage area based on a list of public land mobile networks and corresponding coverage areas that the UE has; The method according to any one of claims 1 to 8, further comprising: (Appendix 10) receiving fifth information for redirecting the UE to a public land mobile network and / or core network node for mobility management associated with a location of the UE; establishing an RRC connection via a cell serving the different coverage area based on the information for redirecting the UE; The method according to any one of claims 1 to 8, further comprising: (Appendix 11) The method of claim 10, further comprising receiving an RRCRelease message or an RRCReject message including the fifth information. (Appendix 12) 12. The method according to any one of claims 1 to 11, wherein the step of determining that the current location of the UE is in a coverage area different from the first coverage area is based on at least one of a Global Navigation Satellite System (GNSS) based position and a mobile country code associated with the UE. (Appendix 13) 1. A method performed by a network node configured to communicate with a user equipment (UE) via a non-terrestrial based network comprising a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the method comprising: receiving, from the UE, a first message initiating a procedure to release an RRC connection based on a current location of the UE; sending a second message to the UE to release the RRC connection based on a location of the UE; A method comprising: (Appendix 14) 14. The method of claim 13, further comprising: triggering a release of a UE context associated with the first coverage area after receiving the first message from the UE. (Appendix 15) 15. The method of claim 13 or 14, further comprising transmitting first information identifying at least one Public Land Mobile Network (PLMN) and / or at least one Mobile Country Code (MCC) associated with at least one respective coverage area served by a cell of the network node. (Appendix 16) 16. The method of any one of Supplementary Notes 13 to 15, further comprising the step of transmitting to the UE second information relating to a boundary of at least one coverage area served by a cell of the network node. (Appendix 17) The method according to any one of Supplementary Notes 13 to 16, further comprising the step of transmitting to the UE third information indicating that the UE is permitted to release the RRC connection based on a location of the UE. (Appendix 18) The first message includes fourth information. The method according to any one of Supplementary Note 13 to 17, wherein the fourth information indicates at least one of an indication that the UE is requesting RRC connection release and a desired RRC state. (Appendix 19) 19. The method of claim 18, wherein the fourth information is included in an RRC message. (Appendix 20) 20. The method of claim 18 or 19, wherein the fourth information includes a cause value indicating a cause for releasing the RRC connection. (Appendix 21) The method according to any one of Supplementary Notes 13 to 20, further comprising a step of sending to the UE fifth information for redirecting the UE to a public land mobile network and / or a core network node for mobility management related to a location of the UE. (Appendix 22) 22. The method of claim 21, further comprising the step of sending an RRCRelease message or an RRCReject message to the UE, the RRCReject message including the fifth information. (Appendix 23) 1. A user equipment (UE) configured to communicate over a non-terrestrial network including a plurality of cells, the UE having a RRC connection associated with a first coverage area; means for determining that a current location of the UE is in a coverage area different from a first coverage area; means for releasing an RRC connection based on a current location of the UE; Equipped with UE. (Appendix 24) 1. A network node configured to communicate with a user equipment (UE) via a non-terrestrial network comprising a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area; means for receiving, from the UE, a message for initiating a procedure for releasing an RRC connection based on a current location of the UE; means for transmitting a message to the UE to release an RRC connection based on a location of the UE; A network node comprising: (Appendix 25) A computer-readable non-transitory storage medium having a program stored thereon, the program being executed by a user equipment (UE) configured to communicate over a non-terrestrial network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the program being configured to, for the UE: determining that a current location of the UE is in a coverage area different from the first coverage area; releasing the RRC connection based on the current location of the UE; A non-transitory computer-readable storage medium. (Appendix 26) 1. A computer-readable non-transitory storage medium having a program stored thereon, the program being executed by a network node configured to communicate with a user equipment (UE) via a non-terrestrial network including a plurality of cells, the UE having a radio resource control (RRC) connection associated with a first coverage area, the program being configured to cause the network node to: receiving, from the UE, a message initiating a procedure to release the RRC connection based on a current location of the UE; sending a message to the UE to release the RRC connection based on a location of the UE; A non-transitory computer-readable storage medium. [Explanation of symbols]

[0126] 1 Mobile communication systems 3. User Equipment 5 satellites 6. Gateway 7 Data Network

Claims

1. A User Equipment (UE) configured to communicate over a non-terrestrial network, comprising: means for receiving a message to suspend a Radio Resource Control (RRC) connection for the first coverage area; means for determining that a current location of the UE is in a coverage area different from the first coverage area; means for receiving first information indicating that the UE is authorized to release the suspended RRC connection based on the location of the UE; means for releasing the suspended RRC connection based on the current location of the UE and first information; A UE equipped with the above.

2. The first information is included in an RRC Release message or an RRC Reconfiguration message. The UE of claim 1.

3. means for obtaining second information indicative of a Public Land Mobile Network (PLMN) and / or a Mobile Country Code (MCC) for the different coverage areas; The determining means is configured to determine based on the second information. The UE according to claim 1 or 2.

4. means for obtaining third information regarding boundaries of the different coverage areas; The determining means is configured to determine based on the third information. The UE according to claim 1 or 2.

5. The releasing means includes: The UE is requesting an RRC connection release; and Priority RRC State and transmitting fourth information indicating at least one of the following: The UE according to claim 1 or 2.

6. the fourth information includes a cause value indicating a reason for releasing the suspended RRC connection; The UE of claim 5.

7. 1. A network node configured to communicate with a User Equipment (UE) via a non-terrestrial based network, comprising: means for transmitting a message to the UE to suspend a Radio Resource Control (RRC) connection for a first coverage area; means for transmitting first information indicating that the UE is authorized to release the suspended RRC connection based on a current location of the UE; means for receiving a first message from the UE, the first message initiating a procedure for releasing the suspended RRC connection based on a current location of the UE and first information; means for transmitting a second message to the UE to release the suspended RRC connection based on the current location of the UE; A network node comprising:

8. 1. A method in a User Equipment (UE) configured to communicate over a non-terrestrial based network, comprising: receiving a message to suspend a Radio Resource Control (RRC) connection for the first coverage area; determining that a current location of the UE is in a coverage area different from the first coverage area; receiving first information indicating that the UE is authorized to release the suspended RRC connection based on the location of the UE; Releasing the suspended RRC connection based on the current location of the UE and first information; A method comprising:

9. 1. A method in a network node arranged to communicate with User Equipment (UE) via a non-terrestrial based network, comprising: sending a message to the UE to suspend a Radio Resource Control (RRC) connection for a first coverage area; transmitting first information indicating that the UE is authorized to release the suspended RRC connection based on a current location of the UE; receiving a first message from the UE that initiates a procedure to release the suspended RRC connection based on a current location of the UE; sending a second message to the UE to release the suspended RRC connection based on the current location of the UE and the first information; A method comprising:

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