Managing a user equipment's access and network selection to a non‑terrestrial network

Abstract

User equipment (UE) may save power and communication resources when applying various techniques selectively considering whether to access a public land mobile network (PLMN) via non-terrestrial network (NTN). The UE (102) receives (706) from a first PLMN, in response to sending (702) an access-request message, an access-reject message providing an NTN-related indication that the UE is not currently allowed to access the first PLMN via an NTN. The UE then refrains (708) from selecting the first PLMN for access via the NTN.

Description

MANAGING A USER EQUIPMENT’S ACCESS AND NETWORK SELECTION TO A NON-TERRESTRIAL NETWORKFIELD OF THE DISCLOSURE

[0001] This document generally describes methods and devices (user equipment, UE, and network entity, NE) operating in wireless communication systems, such as (but not limited to) the ones described in 3rdGeneration Partnership Project (3GPP) technical specifications, known as the Fifth Generation (5G) or Long Term Evolution (LTE) communication systems.BACKGROUND

[0002] This background section is provided for the purpose of generally presenting the context and the technical problems. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that do not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art.

[0003] The 5G technology builds upon the framework developed for LTE terrestrial networks (TNs). However, 5G (as well as LTE) also extend to communications employing non-terrestrial networks (NTNs) tailored for the Narrowband Internet-of-Thing (NB-loT) or the enhanced Machine Type Communication (eMTC) scenarios. In an NTN, a radio frequency (RF) transceiver is mounted on a satellite, an uncrewed aircraft system (UAS) also referred to as drone, balloon, plane, or another suitable apparatus. For simplicity, the discussion below refers to all such apparatuses as satellites. In addition to satellites, an NTN typically includes a satellite gateway (simply referred to as “sat-gateway” or sometimes as “NTN gateway”) that connects the NTN to a public data network, feeder links between sat-gateways and satellites, service links from the satellite to user equipment (i.e., terminal devices that may be mobile), and inter-satellite links (ISL) between satellites when the satellite is part of a satellite constellation.

[0004] A satellite can belong to one of several types based on altitude, orbit, beam footprint size, and beam footprint movement. The types include Low-Earth Orbit (LEO) satellite, Medium-Earth Orbit (MEO) satellite, Geostationary Earth Orbit (GEO) satellite, UAS platform (including High Altitude Platform Station (HAPS)), and High Elliptical Orbit (HEO) satellite. GEO satellites are also known as the Geosynchronous Orbit (GSO) satellites, and LEO / MEO satellites are also known as non-GSO (NGSO) satellites.

[0005] A GSO satellite communicates with one or more sat-gateways deployed over a satellite targeted coverage area (e.g., a region, country, continent, etc.). A non- GSO satellite at different times communicates with one or several serving sat-gateways. An NTN may be designed to provide service link and feeder link continuity between successive serving sat-gateways, with sufficient time duration to proceed with mobility anchoring and hand-over procedures.

[0006] A satellite may support a transparent payload or a regenerative (with on board processing) payload, and typically generates several beams for a given service area bounded by the field of view. The footprints of the beams typically have an elliptic shape and depend on the on-board antenna configuration and the satellite’s elevation angle. For a transparent payload implementation, a satellite applies RF filtering and / or frequency conversion and amplification, and refrains from changing the waveform signal. For a regenerative payload implementation, a satellite applies RF filtering, frequency conversion and amplification, demodulation and decoding, routing, and / or coding / modulation. The regenerative payload approach is effectively equivalent to implementing most of the functions of a base station (e.g., a gNB, that is a 5G Next Generation base station, or an eNB, that is an LTE base station).

[0007] NB-loT and eMTC technologies are expected to be particularly suitable for loT devices operating in remote areas with limited or no terrestrial connectivity. Such loT devices can be used in a variety of industries including, for example, transportation (maritime, road, rail, air) and logistics; solar, oil, and gas harvesting; utilities; farming; environmental monitoring; and mining. To enable loT connectivity, deployment of these technologies uses satellite connectivity to provide coverage beyond terrestrialdeployments. Satellite NB-loT or eMTC is defined in a complementary manner to terrestrial deployments.

[0008] In order to select a public land mobile network, PLMN, a UE scans RF channels according to its capabilities. On each carrier frequency during the scan, the UE searches for the strongest cell and reads its system information (SIB1 ) to find the available PLMNs. After selecting one of the available PLMNs, the UE initiates a cell selection procedure to find a suitable cell of the selected PLMN to camp on and requests access to the selected PLMN via the suitable cell. The selection of a particular PLMN from the available PLMNs may be automatic or manual. An automatic selection may be based on a predefined order (such as, Home PLMN first, else equivalent Home PLMN, else last registered PLMN, and otherwise another PLMN with strong signal) or a UE-established or network-provided order. The PLMN selection may also take into consideration the employed radio access technology, RAT (e.g., a PLMN’s 5G NR RAT may be preferred to its 4G LTE RAT).

[0009] A UE’s access to a PLMN via an NTN cell (i.e., the suitable cell is an NTN cell of the PLMN employing a satellite) may be declined, for example, because the UE has a PLMN subscription without a companion NTN subscription, or the PLMN’s operator has a policy declining a UE’s access for the purpose of encouraging access via the PLMN’s TN. Although an access-reject message may indicate a cause value, currently defined values are insensitive to nuances, such as, the PLMN having both TN and NTN cells as well as 4G, 5G, and possibly future 6G RAT access (to result in 4G- TN, 4G-NTN, 5G-TN, 5G-NTN, 6G-TN, 6G-NTN access to a single PLMN). The cause (e.g., cause value 22) is currently interpreted to instruct the UE to wait a certain time interval (e.g., until after timer T3346 expires) before sending another access-request message to the same PLMN. Currently, it is unclear whether the UE could try to access another PLMN during this time interval (while T3346 is running) or the access reject is particular to the original connectivity attempt (e.g., NTN only such that a PLMN-TN is still available for an access attempt while T3346 is running). The UE may repeat its attempt to access the PLMN via the NTN (e.g., due to PLMN priority and / or PLMN’s NTN signal quality being better than PLMN’s TN signal quality) thereby wasting energy (battery power) and communication resources, while ignoring alternative accessopportunities (via TN cells or another PLMN). Moreover, if a PLMN’s NTN cells are congested, currently the UE receives no indication to access TN cells or other PLMNs.SUMMARY

[0010] According to various embodiments, upon receiving, from a PLMN, an access-reject message providing an NTN-related indication that the UE is not currently allowed to access the PLMN via an NTN, the UE refrains from requesting access to the PLMN via the NTN. The NTN-related indication may be a cause value indicating that UE’s NTN access (to the PLMN or to any PLMN) is forbidden. The NTN-related indication may be a retry indicator indicating whether the UE is allowed to access another PLMN via an NTN. The access-reject message may also include a timer value that the UE then uses to count an NTN-non-access time interval during which not to repeat an access request to the PLMN via an NTN cell.

[0011] The UE may then select a second PLMN, different from the first PLMN to which UE’s access via an NTN has been denied, or may access the first PLMN via a TN. The UE may seek access to the second PLMN via a TN and via an NTN if the second PLMN supports NTN. When the first PLMN supports TN access, the UE may seek access to the first PLMN via TN before seeking access via the second PLMN. The UE may temporarily disable its NTN capability. The UE re-enables its NTN capability when the NTN-non-access time interval expires, when a UE power cycle occurs, when a Universal Subscriber Identity Module (USIM) is unplugged and plugged in, when an airplane mode is turned on and off, or when a USIM or an eSIM (i.e., a digital SIM) changes. When the retry indicator is included in the access-reject message, the UE determines whether UE’s access to a second PLMN via an NTN is allowed based on the retry indicator’s value. The UE may determine that access to a second PLMN via an NTN is allowed when the second PLMN is not a Home PLMN (HPLMN) or an Equivalent HPLMN (EHPLMN).

[0012] A network entity (NE), in a PLMN that receives an access-request message from a UE via an NTN, provides an NTN-related indication in an access-rejectmessage, the NTN-related indication indicating that the UE is not currently allowed to access the PLMN (or any PLMN) via the NTN.

[0013] The UE may determine whether a selected PLMN supports NTN access before sending an access-request message based on a list of PLMN identifiers of PLMNs to which UE’s access via an NTN is forbidden. The UE may update this list by adding the selected PLMN’s identifier upon receiving an access-reject message with an NTN-related indication.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments.

[0015] Fig. 1 is a block diagram of a wireless communication system in which a UE and an NE use various techniques for managing PLMN access via an NTN, according to various embodiments.

[0016] Fig. 2 is a block diagram of an NTN architecture implementing transparent payload, usable in the wireless communication system illustrated in Fig. 1.

[0017] Fig. 3 illustrates an exemplary user plane protocol stack usable for UE communications to / from a CN with the architecture of Fig. 2.

[0018] Fig. 4 illustrates an exemplary control plane protocol stack usable for UE communications to / from a CN with the architecture of Fig. 2.

[0019] Fig. 5 illustrates an example scenario in which a UE has satellite coverage during certain time periods separated by intervals of non-coverage.

[0020] Fig. 6 is a signal diagram illustrating techniques for managing PLMN access according to various embodiments.

[0021] Fig. 7 is a flow diagram illustrating a UE method for managing PLMN access upon receiving an access-reject message providing an NTN-related indication that the UE is not currently allowed to access a PLMN via an NTN cell, according to an embodiment.

[0022] Fig. 8 is a flow diagram illustrating a UE method for managing PLMN access after access to a PLMN via an NTN is rejected according to an embodiment.

[0023] Fig. 9 is a flow diagram illustrating a UE method for managing PLMN access after access to a PLMN via an NTN is rejected according to another embodiment.

[0024] Fig. 10 is a flow diagram illustrating a UE method for managing PLMN access after access to a PLMN via an NTN is rejected, depending on whether the PLMN supports TN access according to an embodiment.

[0025] Fig. 11 is a flow diagram illustrating a UE method for managing PLMN access after access to a PLMN via an NTN is rejected, when the PLMN supports TN access according to an embodiment.

[0026] Fig. 12 is a flow diagram illustrating a UE method for managing PLMN access after access to a PLMN via an NTN is rejected, depending on a retry indicator according to an embodiment.

[0027] Fig. 13 is a flow diagram illustrating a UE method for managing PLMN access after access to a PLMN via an NTN is rejected depending on whether an access reject message is received from a HPLMN or an EHPLMN according to an embodiment.

[0028] Fig. 14 is a flow diagram illustrating an NE method of rejecting access via an NTN according to an embodiment.

[0029] Fig. 15 is a flow diagram illustrating a UE method for managing PLMN access depending on whether a selected PLMN supports NTN access according to an embodiment.

[0030] Fig. 16 is a flow diagram illustrating a UE method for managing PLMN access using a list of PLMNs that the UE should not access via an NTN according to an embodiment.

[0031] Fig. 17 is a flow diagram illustrating a UE method for managing PLMN access using and updating a list of PLMNs the UE cannot access via an NTN according to an embodiment.

[0032] Fig. 18 is a flow diagram illustrating a UE method for updating a list of PLMNs that the UE cannot access via an NTN depending on a cause value included in an access-reject message according to an embodiment.

[0033] Fig. 19 is a flow diagram illustrating a UE method for updating a list of PLMNs that the UE cannot access via an NTN depending on whether the UE receives an access reject message via a satellite according to an embodiment.DETAILED DESCRIPTION OF THE DRAWINGS

[0034] Methods and devices described in this section embody techniques related to managing PLMN selection after a UE’s access to a PLMN via an NTN cell is rejected.

[0035] The embodiment descriptions in this section refer to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The detailed descriptions do not preclude other embodiments within the scope of the appended claims. The embodiments are not limited to the described configurations but may be extended to other arrangements.

[0036] Reference throughout this section to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0037] As discussed in more detail below, a UE and a NE may cooperatively operate to solve the above-identified problems related to the UE’s PLMN access via an NTN. In various scenarios and embodiments described hereinafter, a PLMN (i.e. , an NE thereof) that rejects a UE’s access request via an NTN conveys, to the UE, an NTN- related indication, which specifies that the UE is not currently allowed to access the PLMN via an NTN. Before discussing various embodiments of the NTN-related indication and related methods, FIG. 1 provides a brief description of a wireless communication system that supports the later-described methods for managing a PLMN selection after UE’s access via an NTN is rejected.

[0038] The wireless communication system 100 includes a UE 102 that may be connected to a core network (CN) 110 via base station (BS) 104 and a radio access network (RAN) 105, and to a CN 109 via BS 106 and a RAN 103. The CN 110 may include an evolved packet core (EPC) 111 and (or) a 5G core (5GC) 160. The CN 110 may also be or include a sixth generation (6G) core or another wireless network core (not shown). The RAN 105 and the CN 110 pertain to a PLMN 108, while the RAN 103 and the CN 109 pertain to a PLMN 107. The BS 104 and RAN 105 communicate with UEs via one or more satellites (as suggested by the satellite icon), the PLMN 108 thus supporting UE access via an NTN cell 124. The BS 106 and RAN 103 communicate with UEs using terrestrial equipment (as suggested by the tower icon the PLMN 107 thus supporting UE’s access via a TN cell 126.

[0039] If the BS 104 is a gNB, the NTN cell 124 is an NR (i.e., New Radio) cell. If the BS 104 is an ng-eNB (i.e., an eNB that can communicate with a 5GC) or an eNB, the NTN cell 124 is an evolved universal terrestrial radio access (E-UTRA) cell.Similarly, if the BS 106 is a gNB, the TN cell 126 is an NR cell, and if the BS 106 is an ng-eNB or eNB, the TN cell 126 is an E-UTRA cell. The cells 124 and 126 can be in the same Radio Access Network Notification Areas (RNA) or different RNAs. Each of the RANs 103 and 105 may include any number of BSs, and each of the BSs can cover one or more cells. The UE 102 supports at least one of a 5G NR (or simply, “NR”) or E- UTRA air interface to communicate with the BSs 104 and / or 106. The BS 104 may connect to the CN 110 via an interface (e.g., S1 or NG interface) and to other BSs in RAN 105 via an interface (e.g., X2 or Xn interface) for interconnecting RAN nodes.Similarly, the BS 106 can connect to the CN 109 via an interface (e.g., S1 or NG interface) to other BSs in RAN 103 via an interface (e.g., X2 or Xn interface) for interconnecting RAN nodes.

[0040] Among other components, the EPC 111 may include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, and a Home Subscriber Server (HSS) 116. The SGW 112 in general is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME 114 is configured to manage authentication, registration, paging, and other related functions. The HSS 116 is a master database of subscriber information (such as user identification, security,location, and subscription profile) acting as a central repository of information for network nodes. The 5GC 160 includes (among other components) a User Plane Function (UPF) 162, an Access and Mobility Management Function (AMF) 164, and User Data Management (UDM) 166. The UPF 162 is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the UDM 166 is similar to HSS, but it is cloud-native and designed for 5G specifically. Similarly, the CN 110 is able to connect to BSs supporting NR cells and / or EUTRA cells.

[0041] As illustrated in Fig. 1 , the BS 104 supports the NTN cell 124, and the BS 106 supports the TN cell 126. Note that the NTN cell 124 has a shape corresponding to the footprint of the satellite beams, which, unlike cell TN 126, may project on different areas at different times. The cells 124 and 126 may partially overlap, so that the UE 102 can select, reselect, or hand over from one of the cells 124 and 126 to the other. The BS 104 and BS 106 may support an X2 or Xn interface to directly exchange messages or information.

[0042] According to an embodiment illustrated in Fig. 1 , the BS 104 is equipped with processing hardware 130 that includes one or more general-purpose or special purpose processing units such as processor 134 and a non-transitory computer- readable memory (CRM) 136 storing instructions that the one or more processors execute. The processor 134 is configured to process data that the BS 104 transmits in the downlink direction, or data that the BS 104 receives in the uplink direction. The processing hardware 130 also includes a transceiver 132 configured to transmit data in the downlink direction and to receive data in the uplink direction. The CRM 136 stores executable codes (such as an NTN access manager) for the processor 134 to perform methods according to embodiments described in this section using the transceiver 132. The BS 106 includes generally similar components.

[0043] The UE 102 is equipped with processing hardware 140 that can include one or more general-purpose processors and / or special-purpose processing units, such as, processor 144, and non-transitory CRM 146 storing machine-readable instructions executable on the one or more processors and / or special-purpose processing units.The processor 144 is configured to prepare data that the UE 102 transmits in the uplink direction, or to process data that the UE 102 receives in the downlink direction. The processing hardware 140 also includes a transceiver 142 configured to transmit data in the uplink direction and to receive data in the downlink direction. The non-transitory CRM 146 is configured to store executable codes enabling the processor 144 to perform various techniques described in this section using the transceiver 142.

[0044] Fig. 2 illustrates a certain type of NTN deployment 200 referred to as transparent payload architecture, which involves a satellite (i.e. , NTN) gateway 204 and a “transparent” satellite 201 for extending the range of an air interface (Uu) from BS 104 to the UE 102. The satellite 201 implements a frequency conversion and a RF amplifier in both the uplink and downlink directions. The satellite function is similar to that of an analogue RF repeater. As a result, the satellite 201 repeats the signals received via the Uu radio interface from the feeder link (between the NTN gateway 204 and the satellite 201) to the service link (between the satellite 201 and the UE 102) in the downlink direction and vice versa in the uplink direction. The satellite radio interface on the feeder link is the Uu, and the NTN gateway 204 supports all necessary functions to forward the signal of the Uu interface. The NTN gateway 204 may be collocated with the BS (e.g., eNB, gNB) 104, or may be connected to the BS 104 via a wired link. It is also possible to connect more than one NTN gateway to a BS. Different transparent satellites may be connected to the same BS on the ground, via the same NTN gateway, or via different NTN gateways.

[0045] Next, Fig. 3 illustrates an NTN user-plane protocol stack involving the UE 102, the satellite 201 , the NTN gateway 204, the BS 104, and the EPC SGW 112 (or 5GC UPF 162). The NTN user-plane protocol stack is similar to that of the terrestrial network (TN), except for two additional nodes, the satellite 201 and the NTN gateway 204, operating between the CN and the UE. In this figure, PDU stands for packet data unit layer, SDAP stands for the service data adaptation protocol, PDCP is the package data convergence protocol, RLC is the radio link control layer, MAC is the medium access control layer, and PHY is the physical layer. The interface between BS 104 and 5GC UPF includes GTP-U (GPRS tunneling protocol user plane), UDP (user datagram protocol), IP (Internet protocol) layer, L2 (layer 2, MAC) and L1 (layer 1 , PHY).

[0046] Similarly, the NTN control plane protocol stack illustrated in Fig. 4 is also analogous to that of the terrestrial network counterpart but involves additional nodes 201 and 204. In this figure, NAS stands for non-access stratum layer, RRC is the resource radio control layer, PDCP, RLC, MAC and PHY having same significance as discussed relative to Fig. 3. The interface between BS 104 and 5GC AMF includes NGAP (Next Generation Application Protocol) and SCPT (stream control transmission protocol) in addition to IP, L2 and L1 specified relative to Fig. 3.

[0047] Referring generally to Figs. 1 -4, NTN supports at least three types of service links NTN, described in terms of satellite movement patterns: (i) Earth-fixed: provisioned by beam(s) continuously covering the same geographical areas all the time (e.g., the case of GEO / GSO satellites); (ii) Quasi-Earth-fixed: provisioned by beam(s) covering one geographic area for a limited period and a different geographic area during another period (e.g., the case of LEO / MEO satellites capable of using steerable beams); and (iii) Earth-moving: provisioned by beam(s) whose coverage area slides over the Earth surface (e.g., the case of LEO / MEO satellites using fixed or nonsteerable beams). With LEO / MEO satellites, a BS can provide either quasi-Earth-fixed cell coverage or Earth-moving cell coverage. With GEO satellites, the BS can provide Earth fixed cell coverage.

[0048] Although the transparent payload architecture illustrated in Fig. 2 is the current focus of the 3GPP development, the regenerative payload architecture that places some of the BS functions on the satellite is a foreseeable NTN deployment. In such an architecture, the Uu only exists between the satellite and the UE. In general, the techniques described in this section may be applied for both the transparent payload architecture and the regenerative payload architecture.

[0049] Fig. 5 illustrates an example scenario 500 in which the UE 102 may experience discontinuous coverage from an NTN due, for example, to a sparse satellite constellation deployment. Successive positions (at ti , t2, ts, and t4) of satellite 201 are illustrated on top of Fig. 5, and successive positions (at same ti , t2, ts, and t4) of satellite 501 are illustrated on bottom of Fig. 5 (in a UE-centric perspective). In the scenario 500, the UE 102 is within a first coverage zone served by a satellite 201 from ti to t2, and within a second coverage zone served by satellite 501 from t3 to t4. In the periodbetween t2 to ts, however, the UE 102 is not served by any satellite. When a UE 102 loses coverage by a serving cell, the UE 102 starts searching for another suitable cell to camp on. However, in the scenario illustrated in Fig. 5, even if the UE 102 starts searching for other cells immediately after t2, if there is no TN coverage, the UE 102 is unable to find another NTN cell. Moreover, the cell search may last a long time, as the time period between t2 to t3 can vary from tens of minutes to hours. Therefore, the cell search causes extra, unnecessary power consumption in the UE 102. To reduce power consumption at the UE in such scenarios as the one depicted in Fig. 5, the UE 102 may benefit from refraining from performing cell search during an NTN-non-access period while the UE is not within coverage of any satellite.

[0050] In some scenarios, the UE 102 in a connected state (e.g., RRC_CONNECTED state) communicates with a RAN (e.g., RAN 105) via the satellite 201 and detects radio link failure on the service link with the satellite 201 because the UE 102 is out of coverage of the satellite 201 (e.g., in the period between t2 to t3). In response to the radio link failure, the UE 102 initiates an RRC connection reestablishment procedure (e.g., in accordance with 3GPP technical specification 38.331 ).

[0051] Next, several example scenarios that involve several components of Fig. 1 and relate to UE receiving an NTN-access reject message with an NTN-related indication are discussed with reference to Fig 6. In this figure time flows from top to bottom, an earlier action (i.e., a box along a vertical line linked to a device) or signal (i.e. , horizontal arrow from one vertical line to another) being illustrated above a later action or signal.

[0052] Referring first to Fig. 6, in a scenario 600, a UE 102 communicates with a CN 110 via a RAN 105 including the satellite 201 . CN 110 and RAN 105 belong to PLMN 108. In this scenario, the UE 102 selects 601 the PLMN 108 during a legacy PLMN selection process. The UE 102, which operates in a connected state within coverage of the satellite 201 , transmits 602 an UL NAS message (i.e., an accessrequest message) to the CN 110 (e.g., the MME 114 of EPC or AMF 164 for 5GC) via the RAN 105 and the satellite 201. For example, in some embodiments, the connected state is an ECM-CONNECTED state or EMM-CONNECTED state for an MME 114(here ECM stands for EPS connection management and EMM, for EPS mobility management, EPS being the acronym of evolved packet system). In other embodiments, the connected state is a 5GCM-CONNECTED state or 5GMM-C0NNECTED state in the case of the AMF 164 (here 5GCM stands for 5GS connection management and 5GMM, for 5GS mobility management, 5GS being the acronym of 5G system). In yet other embodiments, the connected state is an RRC_CONNECTED state.

[0053] When the CN 110 receives the UL NAS message, the CN 110 determines 604 that the UE 102 is not allowed to access an NTN (i.e. , the UE 102 is not allowed to access the CN 110 and / or RAN 105 via a satellite) in the PLMN 108 based on the subscription, the operator’s policy, or in view of an imminent lack of satellite coverage. In some embodiments, the PLMN 108 is a registered PLMN (RPLMN hereafter) for the UE 102. In some embodiments, the UE 102 is not allowed to access an NTN because the CN 110 determines that the UE 102 does not subscribe to NTN services based on subscription data for the UE 102. In the case that the CN 110 is an EPC 111 , when the MME 114 receives 602 the UL NAS message, if the MME 114 does not have subscription data for the UE 102, the MME 114 might transmit a first message to a network node (e.g., HSS 116) to obtain subscription data for the UE 102. In response, the network node transmits a second message including subscription data for the UE 102 to the MME 114. The MME 114 may then determine that the UE 102 is not allowed to access an NTN based on the subscription data. In the case that the CN 110 is a 5GC 160, when the AMF 164 receives 602 the UL NAS message, if the AMF 164 does not have subscription data for the UE 102, the AMF 164 might transmit a first message to a network node (e.g., UDM 166) to obtain subscription data for the UE 102. In response, the network node transmits a second message including subscription data for the UE 102 to the AMF 164. The AMF 164 may determine that the UE 102 is not allowed to access an NTN based on the subscription data. In some embodiments, the UE 102 is not allowed to access an NTN because the CN 110 determines that the operator of the CN 110 has a policy for the UE 102 not to be allowed accessed via an NTN (e.g., because cheaper TN is available, or NTN is overloaded above a predetermined traffic threshold). The operator’s policy may be configured in the MME 114 in the case that theCN 110 is an EPC 111. The operator’s policy may be configured in the AMF 164 in the case that the CN 110 is a 5GC 160.

[0054] The CN 110 (e.g., an NE operating as the MME or executing the AMF) further determines 604 whether the UE 102 is allowed to access NTN in other PLMNs. In some embodiments, such a determination should be made only by the HPLMN or an EHPLMN (e.g., a NE of the HPLMN or the EHPLMN). If the PLMN associated with the CN 110 is neither an HPLMN nor an EHPLMN, the CN 110 may check with the HPLMN of the UE 102 whether the restriction on NTN is only for the registered PLMN or for all PLMNs. In some embodiments, subscription data may indicate whether the UE 102 is allowed to access an NTN for a registered PLMN or for every PLMN.

[0055] Upon determining that the UE 102 is not allowed to access an NTN, the CN 110 generates a DL NAS message including a cause value and transmits 606 the DL NAS message to the UE 102 via the RAN 105 and the satellite 201 . The cause value indicates that the UE 102 cannot use NTN services (i.e., the UE 102 is not allowed to access an NTN). In some embodiments, the CN 110 may include a timer value corresponding to an NTN-non-access time interval during which the UE 102 is prohibited from using a satellite access (i.e., the NTN). In some embodiments, the DL NAS message 706 further includes a retry indicator indicating whether the UE 102 can retry to access an NTN in the other PLMNs. In some embodiments, the retry indicator indicates to the UE 102 also whether the UE 102 is allowed to access an NTN in the other PLMN than the PLMN 108. In some embodiments, the retry indicator also indicates whether the restriction on using NTN also applies to the equivalent PLMNs of the PLMN 108.

[0056] In some embodiments, the UL NAS message and the DL NAS message are a Registration Request message and a Registration Reject message, respectively, as such messages are defined in 3GPP technical specifications. In other embodiments, the UL NAS message and the DL NAS message are an Attach Request message and an Attach Reject message, respectively, as such messages are defined in 3GPP technical specifications. In yet other embodiments, the UL NAS message and the DL NAS message are a Tracking Area Update Request message and a Tracking Area Update Reject message, respectively, as such messages are defined in 3GPP technicalspecifications. In yet other embodiments, the UL NAS message and the DL NAS message are a Service Request message and a Service Reject message, respectively, as such messages are defined in 3GPP technical specifications.

[0057] Upon receiving 606 the access-reject message (i.e. , the DL NAS message), the UE 102 starts refraining 608 from selecting the PLMN 108 with NTN access. If the access-reject message includes a timer value, the UE 102 refrains temporarily from selecting the PLMN 108 with NTN access, for an NTN-non-access time interval corresponding to the timer value as suggested by the vertical arrow drawn on a side of box 608 in Fig. 6. If the PLMN 108 supports TN access, the UE 102 may seek first a suitable TN cell of the PLMN 108 before (if unsuccessful in finding a suitable TN cell of the PLMN 108) seeking another PLMN. In scenario 600, the UE 102 selects 610 a PLMN 107, that is, another PLMN with TN access.

[0058] After receiving 606 the DL NAS message or after selecting 610 another PLMN with TN access, the UE 102 may disable 612 its NTN capability, e.g., for the PLMN 108 and / or other PLMNs, depending on the type of access-reject indication. Disabling the NTN capability is optional as suggested by the dashed line of box 612. In some embodiments, disabling 612 UE’s NTN capability includes turning off the entire UE’s radio capability for NTN. In some embodiments, disabling 612 UE’s NTN capability excludes the UE’s ability to receive Cell Broadcast Service (CBS) messages. In some embodiments, the disabling 612 UE’s NTN capability is temporary, that is, the UE 102 refrains from accessing NTN cells in the PLMN 108 while a condition lasts (e.g., while a timer is running). If the DL NAS message received 606 includes a timer value for measuring an NTN-non-access time interval, the UE 102 starts a timer (e.g., an NTN access prohibit timer) with the received timer value concurrently with disabling UE’s NTN capability.

[0059] In some embodiments, disabling 612 NTN capability is based on a retry indicator included in the DL NAS message the UE receives 606. If the retry indicator indicates that the UE 102 is allowed to access an NTN in another PLMN, the UE 102 disables NTN capability only for the PLMN 108 and may re-enable the NTN capability after selecting the PLMN 107. In some embodiments, if a timer value is also provided in the DL NAS message 606, the UE 102 starts the timer (e.g., an NTN access prohibittimer) with the received timer value and sets the applicability of the timer based on the retry indicator. If the retry indicator indicates that the UE 102 is allowed to access an NTN in another PLMN, the UE 102 stops the timer when the UE 102 selects a second PLMN 107 different than the PLMN 108. If the retry indicator indicates that the UE 102 is not allowed to access an NTN in any PLMN, the UE 102 keeps the timer running when the UE 102 selects the second PLMN 107.

[0060] In some embodiments, the UE 102 stores the PLMN identifier (ID) of the current PLMN 108 in a list of PLMN IDs in order to deprioritize the PLMN 108 during the PLMN selection. The UE 102 may store and manage such a list in a non-volatile memory, its Universal Subscriber Identity Module (USIM), or an eSIM (i.e. , a digital SIM). The list of PLMN IDs may be dedicated to the PLMNs with no NTN access (i.e., forbidden satellite use). In yet other embodiments, the UE 102 stores the PLMN ID and RAT type in a list of no-access PLMNs or a list of no-NTN-access PLMNs. The RAT type information may be NR, E-UTRA, NTN access E-UTRA, NTN access NR, etc. In some embodiments, the UE 102 maintains the list entries (PLMN ID or PLMN ID and RAT type) until a power cycle occurs (e.g., the UE 102 is switched off and on), a USIM cycle or change occurs, or when airplane mode is turned on and off. In yet other embodiments, the UE 102 maintains the entries for a specific duration (e.g., 12 hours), which can be configured by the operator or the manufacturer of the UE 102 or can be pre-defined as a default value. In yet other embodiments, the UE 102 maintains the list entries for a duration that the CN 110 provides to the UE 102 within the DL NAS message.

[0061] In the network selection procedure, if the UE 102 selects a PLMN whose PLMN ID (or PLMN ID and RAT type) is stored in the list of no-NTN-access PLMNs as a candidate for the PLMN selection, the UE 102 only searches one or more carrier frequencies of one or more frequency bands defined for TN access. In the network selection procedure, if the UE 102 selects a PLMN whose PLMN ID (or PLMN ID and RAT type) is not stored in the list of no-NTN-access PLMNs as a candidate for the PLMN selection, the UE 102 might search one or more carrier frequencies of one or more frequency bands defined for TN access and / or one or more carrier frequencies of one or more frequency bands defined for NTN access. During the network selection, theUE 102 likely finds and selects a suitable cell of the selected PLMN or PLMN and RAT combination.

[0062] During the PLMN selection, the UE 102 may consider candidate PLMNs or candidate PLMN and RAT combinations depending on the retry indicator included in the access-reject (DL NAS) message received 606 from the CN 110. If the retry indicator indicates that the UE 102 is allowed to use an NTN in other PLMNs, the UE 102 may consider candidate PLMNs with NTN access during the PLMN selection process. If the retry indicator indicates that the UE 102 is not allowed to use NTN access in any PLMN, the UE 102 does not consider PLMNs with NTN RAT types or deprioritizes such PLMN and RAT combinations during the PLMN selection.

[0063] Even when the retry indicator is absent in the DL NAS message, the UE 102 may consider an implicit NTN-related indication. If the UE 102 receives the DL NAS message from the HPLMN or EHPLMN, the UE 102 may consider that use of an NTN to access any PLMNs is forbidden (as if the retry indicator indicates that the UE 102 is not allowed to access an NTN in any PLMNs). Conversely, if the UE 102 receives the DL NAS message from a PLMN other than its HPLMN or an EHPLMN, the UE 102 may consider itself allowed to use an NTN to access HPLMN, EHPLMN, and / or another PLMN (as if the retry indicator indicates that the UE 102 is allowed to use an NTN to access other PLMNs).

[0064] After selecting 610 the PLMN 107, the UE 102 transmits 614 a UL NAS message to the CN 109 via the BS 106 of RAN 103 and a TN cell (as suggested by the tower icon) of the PLMN 107. In response, the CN 109 transmits 616 a DL NAS message to the UE 102 providing an access-accept indication to the UE 102. In some embodiments, if the TN cell in the PLMN 107 is a 5G NR cell, the UL NAS message 614 and the DL NAS message 616 are a Registration Request message and a Registration Accept message, respectively. In other embodiments, if the TN cell in the PLMN 107 is an LTE cell, the UL NAS message 614 and the DL NAS message 616 are an Attach Request message and an Attach Accept message, respectively. In yet other embodiments, if the cell in the PLMN 107 is an LTE cell, the UL NAS message 614 and the DL NAS message 616 are a Tracking Area Update Request message and a Tracking Area Update Accept message, respectively.

[0065] Later, the UE 102 may (i.e. , optionally as suggested by the dashed line of the box) re-enable UE’s NTN access capability for the PLMN 108 or for all PLMNs (not shown in Fig. 6 but assumed to be an action concurrent or shortly before 618). In some embodiments, the UE 102 re-enables UE’s NTN capability when a power cycle, USIM cycle, or the like occurs (e.g., the UE 102 is switched off and on, the USIM is changed, or airplane mode is turned on and off). In yet other embodiments, the UE 102 reenables the NTN capability when the NTN-non-access time interval corresponding to the timer value expires (as suggested by the vertical arrow starting at 608 level and ending at 618 level in Fig. 6).

[0066] In some embodiments, the UE 102 updates the list of PLMN IDs (or PLMN IDs and RAT types) by removing the entry corresponding to the PLMN ID of the PLMN 108 when the NTN-non-access time interval corresponding to the timer value expires, a power cycle occurs, a USIM cycle or change occurs, or airplane mode is turned on and off. In some embodiments, the UE 102 deletes the list (i.e., the list is no longer valid) when a power cycle occurs, a USIM cycle or change occurs, or airplane mode is turned on and off.

[0067] After re-enabling the NTN capability for PLMN 108 or for all PLMNs, the UE 102 may resume 618 selecting the PLMN 108 in the context of removing any restriction on the NTN access or by re-prioritizing the PLMN 108. The UE 102 may reselect 618 an NTN cell of the PLMN 108, which may be provided via another satellite 501 (although in other scenarios the NTN cell may still be provided via satellite 201 ). The UE 102 may then transmit 620 a UL NAS message to the CN 110 via the NTN cell and the RAN 105. In response, the CN 110 may transmit 622 a DL NAS message to the UE 102 via the RAN 105 and the NTN cell. Depending on embodiment, the UL NAS message 620 may be similar to the UL NAS message transmitted at 602 or 614, and the DL NAS message 622 may be similar to the DL NAS message transmitted at 606 or 616. For example, if the CN 110 still determines that the UE 102 is not allowed to access an NTN (e.g., because the UE 102’s subscription data indicates UE 102 is not allowed to access the CN 110 and / or RAN 105 via a satellite), the CN 110 includes the same cause value or retry indicator in the DL NAS message 622 as in the DL message transmitted at 606. In another example, if the CN 110 determines that the UE 102 isallowed access via an NTN, the CN 110 grants 622 the UE 102 access as in the DL NAS message transmitted at 616.

[0068] Figs. 7-19 are flowcharts of methods performed by a UE (such as, UE 102) or an NE (such as, a CN NE performing as an MME or an AMF) related to managing PLMN selection after a UE’s access via an NTN is rejected according to various embodiments. Each of these methods can be implemented using processing hardware as illustrated in Fig. 1 , in a setup similar to the one illustrated in Fig. 2, using protocol stacks as the ones illustrated in Figs. 3 and 4, optionally in a scenario in which the UE temporary lacks satellite coverage as illustrated in Fig. 5. Many of the features illustrated in Figs. 7-19 may be combined as discussed relative to Fig. 6. Similar steps are similarly labeled (e.g., 706, 806, 1006, 1106, etc.) and individual descriptions are therefore omitted.

[0069] Fig. 7 is a flow diagram illustrating a UE method 700 for managing PLMN access upon receiving an access-reject message providing an NTN-related indication that the UE is not currently allowed to access a PLMN via an NTN, according to an embodiment. A UE such as UE 102 in Figs. 1-6, sends 702 an access-request message to a first PLMN (e.g., PLMN 108) via a satellite (e.g., 201 ) that forwards signals to and from an NTN cell (e.g., 124). The UE then receives 706, from the first PLMN, an access-reject message providing an NTN-related indication that the UE is not currently allowed to access the first PLMN via an NTN. Note that steps 702 and 706 correspond to signal exchanged between the UE 102 and PLMN 108 at 602 and 606 in Fig. 6 and may be implemented in various ways as discussed relative to Fig. 6. In one embodiment, the NTN-related indication is a cause value included in the access-reject message, where the cause value is specific for indicating lack of NTN access (for the first PLMN only or for any PLMNs). In another embodiment, the NTN-related indication is a retry indicator (which indicates no-NTN-access for the first PLMN or for any PLMN) included in the access-reject message separate from the cause value. Yet in another embodiment, the NTN-related indication is the receiving of the access-reject message via the NTN cell.

[0070] In view of the NTN-related indication, the UE refrains 708 from selecting the first PLMN via NTN. Optionally, if the access-reject message includes a timer valuethereby indicating that UE’s lack of NTN access to the first PLMN is temporary, the UE starts a timer setup with the timer value to count an NTN-non-access time interval. The UE then performs 709 a PLMN selection. The result of the PLMN selection is selecting 710 a second PLMN (e.g., PLMN 107) other than the first PLMN via NTN. If the UE’s lack of NTN access to the first PLMN was temporary, the UE performs 718 a PLMN selection without excluding the first PLMN-NTN access after the NTN-non-access time interval (measured by UE’s timer) expires.

[0071] Fig. 8 is a flow diagram illustrating a UE method 800 for managing PLMN access after access to a PLMN via an NTN is rejected according to another embodiment. UE’s actions and features of steps 802, 806, 808, 809, and 810 are similar to the ones discussed above relative to steps 702, 706, 708, 709, and 710. After selecting the second PLMN, the UE scans 811 one or more TN and / or NTN carrier frequencies seeking a suitable cell of the second PLMN. The UE may find and select 813A a cell of the second PLMN on a scanned TN carrier frequency or may find and select 813B a cell of the second PLMN on a scanned NTN carrier frequency. If a suitable cell is found at 813A or 813B, the UE sends 814 an access-request message to the second PLMN via the selected (suitable) cell.

[0072] Fig. 9 is a flow diagram illustrating a UE method 900 for managing PLMN access after access to a PLMN via an NTN is rejected according to another embodiment. The UE performs steps 802, 806, 808, 809, and 810 before determining 920 whether the second PLMN supports NTN access. If the second PLMN supports NTN access (“Yes” branch of step 920), the UE performs steps 811 (i.e. , scans one or more TN and / or NTN carrier frequencies), 813A, 813B, and 815. If the second PLMN does not supports NTN access (“No” branch of step 920), the UE may (optionally as suggested by the dashed line) disable 921 the UE’s NTN capability. The UE then scans 922 only one or more TN carrier frequencies and, if finding and selecting 813A a suitable TN cell, sends 814 an access-request message to the second PLMN via the selected TN cell.

[0073] Fig. 10 is a flow diagram illustrating a UE method 1000 for managing PLMN access after access to a PLMN via an NTN is rejected, depending on whether the PLMN supports TN access, according to an embodiment. Figs. 10-13 no longerillustrate a step corresponding to steps 702 or 802, but such a step is implicit. The UE receives 1006, from a first PLMN (e.g., 108), an access-reject message including a cause value indicating NTN access is not allowed and a timer value. Note that the cause value is one way that a NE (e.g., a CN node that operated as an MME or performs AMF, or a base station) can provide the NTN-related indication that the UE is not currently allowed to access the first PLMN via an NTN; other ways (e.g., a retry indication) are not excluded. Also note that presence and use of the timer value is not a required feature but rather an illustration of this feature that may be combined with other features of the methods illustrated in Figs. 7-13 and 15-19. The UE refrains 1008 from selecting the first PLMN with NTN access while the NTN access prohibit timer is running.

[0074] The UE then determines 1024 whether the first PLMN supports TN access. If the first PLMN supports TN access (i.e., “Yes” branch of step 1024), the UE performs steps 1022 and 1013A (similar to steps 922 and 913A) and then performs step 1015A a registration procedure or a tracking area update procedure (which are nonlimiting embodiments of an access-request message) with the first PLMN via the selected TN cell. If the first PLMN does not support TN access (i.e., “No” branch of step 1024), the UE performs steps 809, 810, and 811 followed by steps 813A and / or 813B, and finally step 814.

[0075] Fig. 11 is a flow diagram illustrating a UE method 1100 for managing PLMN access after access to a PLMN via an NTN is rejected and the PLMN supports TN access, according to an embodiment. Method 1100 is similar to method 1000 except in method 1100 it is known that the first PLMN supports TN access, and the UE is scanning 1122 one or more TN carrier frequencies. If the UE finds a suitable cell of the first PLMN on the scanned TN carrier frequencies (i.e., “Yes” branch of step 1125), the UE selects 1127 the suitable cell and performs 1115A a registration procedure or a tracking area update procedure with the first PLMN via the selected cell. If the UE does not find a suitable cell of the first PLMN on the scanned TN carrier frequencies (i.e., “No” branch of step 1125), the UE performs steps 809, 810, and 811 , followed by steps 813A and / or 813B, and finally step 815.

[0076] Fig. 12 is a flow diagram illustrating a UE method 1200 for managing PLMN access after access to a PLMN via an NTN is rejected, depending on a retry indicator according to an embodiment. The UE receives 1206, from a core NE (i.e. , an NE pertaining to the PLMN’s core), an access-reject message including a retry indicator that indicates that UE’s NTN access is not currently allowed. The UE then determines 1230 whether the retry indicator is set to a first predetermined value or to a second predetermined value. If the retry indicator has the first value, then the UE 1232 determines that UE’s NTN access in another PLMN may be allowed. If the retry indicator has the second value, then the UE 1232 determines that UE’s NTN access in any PLMN is not allowed.

[0077] Fig. 13 is a flow diagram illustrating a UE method 1300 for managing PLMN access after access to a PLMN via an NTN is rejected depending on whether an access reject message is received from a HPLMN or an EHPLMN according to an embodiment. After receiving 1306, from a core NE, an access-reject message via an NTN cell, the UE determines 1340 whether the access-reject message has been received from the HPLMN or EHPLMN. If the access-reject message has indeed been received from the HPLMN or an EHPLMN (i.e., “Yes” branch of step 1340), then the UE determines that UE’s NTN access in another PLMNs may be allowed. However, if the access-reject message has not been received from the HPLMN or an EHPLMN (i.e., “No” branch of step 1340), then the UE determines 1334 that UE’s NTN access in any PLMN is not allowed.

[0078] Fig. 14 is a flow diagram illustrating an NE method 1400 of rejecting access via an NTN according to an embodiment. The NE receives 1452 an accessrequest message from a UE. During optional steps 1454, 1456, and 1458, the NE retrieves UE’s subscription data from another (second) network node (entity) as previously described with reference to Fig. 6. The NE may transmit 1454 a first message to the second network node to request subscription data for the UE. The second network node may be an HSS or an UDM depending on core network’s technology. In response to the first message, the NE receives 1456 a second message, from the second network node, the second message including the subscription data for the UE. The NE then determines 1458 that the UE is not allowed to use NTN based onthe subscription data. Note that the NE may alternatively determine that the UE is not currently allowed to access the first PLMN via an NTN based on policy, traffic, or due to an imminent lack of NTN coverage.

[0079] The NE determines 1460 whether the UE is allowed to use NTN to access other PLMNs based on the subscription data. If the UE is allowed to use NTN to access other PLMNs (i.e., “Yes” branch of step 1460) the NE transmits 1464 an access-reject message indicating that NTN services are not currently allowed but that NTN services are (or rather may be) allowed to the UE in other PLMNs. If the UE is not allowed to use NTN to access other PLMNs (i.e., “No” branch of step 1460) the NE transmits 1462 an access-reject message indicating that NTN services are not allowed to the UE in any PLMN.

[0080] Fig. 15 is a flow diagram illustrating a UE method 1500 for managing PLMN access depending on whether a selected PLMN supports NTN access according to an embodiment. The UE selects 1572 a PLMN during a PLMN selection procedure. The UE then determines 1574 whether the selected PLMN supports NTN access. For example, the UE may determine whether the selected PLMN’s ID is in a list of PLMNs with forbidden NTN access. If the selected PLMN supports NTN access (“Yes” branch of step 1574), the UE searches 1576 for a suitable NTN or TN cell for the selected PLMN. If the selected PLMN does not support NTN access (“No” branch of step 1574), the UE refrains 1508 from searching an NTN cell for the selected PLMN and, optionally, searches 1513A a suitable TN cell for the selected PLMN. Alternative to 1513A, the UE may repeat the PLMN selection procedure excluding the selected PLMN.

[0081] Fig. 16 is a flow diagram illustrating a UE method 1600 for managing PLMN access using a list of PLMNs that the UE is currently not allowed to access via NTN according to an embodiment. First the UE obtains 1680 a forbidden PLMN list specifically for NTN access. The entries in this list may be PLMN IDs or PLMN IDs and RAT type information. After selecting 1674 a PLMN during a PLMN selection procedure, the UE determines 1677 whether the selected PLMN’s ID is in the forbidden PLMN list. If the selected PLMN’s ID is an entry (or field of an entry) in the forbidden PLMN list (i.e., the “Yes” branch of step 1677), then the UE refrains 1608 from searching an NTN cell for the selected PLMN, and may (i.e., optionally) search 1613A aTN cell for the selected PLMN. Otherwise, if the selected PLMN’s ID is not in an entry (or field of an entry) in the forbidden PLMN list (i.e. , the “No” branch of step 1677), then the UE searches 1613B a suitable TN or NTN cell for the selected PLMN.

[0082] In some embodiments, if the UE neither finds a suitable TN cell nor a suitable NTN cell from any PLMN, the UE might search an NTN cell of a PLMN in the forbidden PLMN list in order to perform an emergency attach or emergency registration for one or more emergency services (e.g., emergency call).

[0083] Fig. 17 is a flow diagram illustrating a UE method 1700 for managing PLMN access and updating a list on PLMNs that the UE cannot access via NTN according to an embodiment. Initially, the UE maintains 1781 a first PLMN list for forbidden NTN access PLMNs, and a second PLMN for no (TN and NTN) access PLMNs. The UE performs steps 1702 and 1706 which are similar to previously described steps 702 and 706. The UE then determines 1782 whether the UE is allowed to access the PLMN via a TN. In some embodiments, the UE makes the determination 1782 based on the access-reject message. If the access-reject message indicates that the UE is not allowed to access the PLMN via a TN, the UE determines that the UE is not allowed to access the PLMN via a TN. Otherwise, if the access-reject message does not indicate that the UE is not allowed to access the PLMN via a TN, the UE determines that the UE is allowed to access the PLMN via a TN. If the UE is indeed allowed to access the PLMN via a TN (i.e., “Yes” branch of step 1782), then the UE adds the PLMN’s ID to the first list. If the UE is not allowed to access the PLMN via a TN (i.e., “No” branch of step 1782), then the UE adds the PLMN’s ID to the second list.

[0084] Fig. 18 is a flow diagram illustrating a UE method 1800 for updating a list on PLMNs that the UE cannot access via NTN depending on a cause value included in an access reject message according to an embodiment. The UE receives 1806 an access-reject message including a cause value from a PLMN via a satellite (i.e., an NTN cell). The UE determines 1890 whether the cause value is a first values or a second value. If the cause value is a first value (e.g., 61 ) the UE adds 1884 the PLMN ID of the PLMN to a first PLMN list for PLMNs without NTN access. If the cause value is a second value (e.g., 63) the UE adds 1886 the PLMN ID of the PLMN to a second PLMN list for no access PLMNs.

[0085] Fig. 19 is a flow diagram illustrating a UE method 1900 for updating a list on PLMNs that the UE cannot access via NTN depending on whether the UE receives an access reject message via a satellite according to an embodiment. After receiving an access-reject message, the UE determines 1992 whether the access-reject message has been received via an NTN cell. If indeed the access-reject message has been received via an NTN cell (i.e. , “Yes” branch of step 1992), then the UE adds 1984 the PLMN ID of the PLMN to a first list of PLMNs without NTN access. If the access-reject message has not been received via an NTN cell (i.e., “No” branch of step 1992), then the UE adds 1986 the PLMN ID of the PLMN to a second list of no access PLMNs.

[0086] According to an example, a UE method (e.g., 700) performed by a UE (e.g., 102) for managing UE access and a PLMN selection, includes: (i) sending (e.g., 702), to a first PLMN via an NTN cell, an access-request message, (ii) receiving (e.g., 706), from the first PLMN, in response to the access-request message, an access-reject message providing an NTN-related indication that the UE is not currently allowed to access the first PLMN via an NTN, and (iii) refraining (e.g., 708) from selecting the first PLMN for access via the NTN in response to the NTN-related indication.

[0087] The NTN-related indication may be an NTN-specific cause value included in the access-reject message. The NTN-specific cause value may indicate that the UE is not allowed to use NTN services for accessing the first PLMN only. Alternatively, the NTN-specific cause value may indicate that the UE is not allowed to use NTN services for accessing any PLMN.

[0088] The NTN-related indication may be a retry indicator included in the access-reject message. The retry indicator may further indicate whether the UE is allowed to use NTN services in for accessing other PLMN than the first PLMN.

[0089] The NTN-related indication may be the receiving of the access-reject message via the NTN cell.

[0090] The access-reject message may include a timer value, and then the refraining is temporary for an NTN-non-access time interval corresponding to the timer value. The UE method may further include disabling UE’s NTN capability during the NTN-non-access time interval. Alternatively or additionally, the UE method may further include reselecting the first PLMN after the NTN-non-access time interval expires.

[0091] The access-request message and the access-reject message may be NAS messages. For example, the access-request message is a Registration Request, and the access-reject message is a Registration Reject as defined in 3GPP technical specifications. In another example, the access-request message is an Attach Request and the access-reject message is an Attach Reject message as defined in 3GPP technical specifications. In yet another example, the access-request message is a Tracking Area Update (TAU) Request and the access-reject message is a TAU Reject message as defined in 3GPP technical specifications.

[0092] The UE method may further include (i) selecting a second PLMN after receiving the access-reject message, and (ii) scanning one or more terrestrial network, TN, frequencies and / or NTN frequencies for a suitable cell of the second PLMN. The method may further include (iii) finding and selecting the suitable cell of the second PLMN during the scanning and (iv) sending another access-request message to the second PLMN via the suitable cell. Alternatively or additionally, the UE method may also include limiting the scanning to the one or more TN frequencies when the second PLMN does not support the NTN access.

[0093] The UE method may further include disabling UE’s NTN capability for a predetermined time interval when the second PLMN does not support the NTN access.

[0094] The UE method may further include scanning at least one TN frequency when the first PLMN supports TN access, wherein if a suitable TN cell of the first PLMN is found during the scanning, sending a TN access request to the first PLMN via the suitable TN cell.

[0095] The UE method may also include determining that the UE is allowed to use NTN services in another PLMN when the first PLMN is a home public land mobile network, HPLMN, or an equivalent HPLMN as defined in 3GPP technical specifications. The UE method may further include (a) maintaining a first list of network identifiers corresponding to PLMNs that do not support UE’s NTN access, and (b) adding a network identifier of the first PLMN to the first list upon receiving the access-reject message when the NTN-related indication further indicates that the UE is lastingly not allowed to access the first PLMN via the NTN. The UE method may further include adding a network identifier of the first PLMN to a second list upon when the access-reject message indicates that UE’s access to the first PLMN via both a terrestrial network, TN, and the NTN is forbidden.

[0096] A wireless communication device (e.g., 102) comprising a transceiver (142), a processor (144), and computer-readable storage media (146) storing executable instructions for the processor to perform any one of UE methods described above, using the transceiver.

[0097] According to another example, an NE method (e.g., 1400) performed by an NE of a PLMN for managing a UE access via an NTN includes: (i) receiving (e.g., 1452) an access-request message from a UE via an NTN cell, and (ii) transmitting (e.g., 1462, 1464) an access-reject message providing an NTN-related indication that the UE is not currently allowed to access the PLMN via the NTN.

[0098] The NTN-related indication may be a cause value, which is included in the access-reject message. The cause value may further indicate that the UE is not allowed to use NTN services for accessing the PLMN specifically. The cause value may further indicate that the UE is not allowed to use NTN services for accessing any PLMN.

[0099] The NTN-related indication may be a retry indicator included in the access-reject message. The retry indicator may further indicate whether the UE is allowed to use NTN services in for accessing other PLMN than the PLMN.

[0100] The access-reject message may include a timer value to enable the UE to refrain from resubmitting the access-request message to the PLMN via an NTN, for an NTN-non-access time interval corresponding to the timer value.

[0101] The NE method may further include retrieving subscription data for the UE from another NE, wherein the transmitting of the access-reject message is triggered by determining, based on the subscription data, that the UE is not entitled to use communicate with the PLMN via the NTN cell. Here, the NE may be a Mobility Management Entity, MME, and the other NE may be a Home Subscriber Server, HSS, as defined in 3GPP technical specifications. Alternatively, the NE may perform an Access and Mobility Management Function (AMF), and the other NE may perform Unified Data Management (UDM) as defined in 3GPP technical specifications.

[0102] The access-request message and the access-reject message may be NAS messages. For example, the access-request message may be a RegistrationRequest, and the access-reject message may be a Registration Reject as defined in 3GPP technical specifications. In another example, the access-request message is an Attach Request and the access-reject message is an Attach Reject message as defined in 3GPP technical specifications. In yet another example, the access-request message is a TAU Request and the access-reject message is a TAU Reject message as defined in 3GPP technical specifications.

[0103] A wireless communication device (e.g., 104) comprising a transceiver (132), a processor (134), and computer-readable storage media (136) storing executable instructions for the processor to perform any one of UE methods described above, using the transceiver.

[0104] Generally speaking, description for one of the above figures can apply to another of the above figures. Examples, embodiments and methods described above can be combined, if there is no conflict. An event or block described above can be optional or omitted. For example, an event or block with dashed lines in the figures can be optional. In some embodiments, “message” is used and can be replaced by “information element (IE)”, and vice versa. In some embodiments, “IE” is used and can be replaced by “field”, and vice versa. In some embodiments, “configuration” can be replaced by “configurations” or “configuration parameters”, and vice versa. In some embodiments, “capability” can be replaced by “capabilities”.

[0105] A user device in which the techniques of this disclosure can be implemented (e.g., the UE 102) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an internet-of-things (loT) device or a mobile- internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0106] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules may be software modules (e.g., code, or machine-readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0107] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software can be executed by one or more general-purpose processors or one or more special-purpose processors.

Claims

WHAT IS CLAIMED IS:1 . A method (700) performed by a user equipment (102), UE, for managing UE access and a public land mobile network, PLMN, selection, the method comprising: sending (702), to a first PLMN via a non-terrestrial network, NTN, cell, an accessrequest message; receiving (706), from the first PLMN, in response to the access-request message, an access-reject message including an NTN-specific cause value indicating the UE is not currently allowed to access the first PLMN via an NTN; and refraining (708) from selecting the first PLMN for access via the NTN in response to the NTN-related indication.

2. The method of claim 1 , further comprising: maintaining a first list of network identifiers corresponding to PLMNs that do not support UE’s NTN access; and adding a network identifier of the first PLMN to the first list upon receiving the access-reject message.

3. The method of claim 1 or 2, wherein the refraining is temporary for an NTN-non-access time interval corresponding to a timer value.

4. The method of claim 3, further comprising: reselecting the first PLMN after the NTN-non-access time interval expires.

5. The method of any of claims 1 to 4, further comprising: selecting a second PLMN from one or more available PLMN for access, in response to the receiving of the access-reject message including an NTN-specific cause value indicating the UE is not currently allowed to access the first PLMN via an NTN, wherein the one or more available PLMN include the first PLMN via a terrestrial network.

6. The method of any of claims 1 to 5, wherein the access-request message and the access-reject message are Non Access stratum, NAS, messages.

7. The method of claim 6, wherein the access-request message is a Registration Request, an Attach Request or a Tracking Area Update Request as defined in 3GPP technical specifications.

8. A method (1400) performed by a network entity, NE, of a PLMN for managing user equipment, UE, access via a non-terrestrial network, NTN, the method comprising: receiving (1452) an access-request message from a UE via an NTN cell; and transmitting (1462, 1464) an access-reject message including an NTN-specific cause value that indicates the UE is not currently allowed to access the PLMN via the NTN.

9. The method of claim 8, wherein the access-reject message includes a timer value to enable the UE to refrain from resubmitting the access-request message to the PLMN via an NTN, for an NTN-non-access time interval corresponding to the timer value.

10. The method of claim 8 or 9, further comprising: retrieving subscription data for the UE from an other NE, wherein the transmitting of the access-reject message is triggered by determining, based on the subscription data, that the UE is not entitled to use communicate with the PLMN via the NTN cell.11 . The method of claim 10, wherein the NE is a Mobility Management Entity, MME, and the other NE is a Home Subscriber Server, HSS, as defined in 3GPP technical specifications.

12. The method of claim 10, wherein the NE performs an Access and Mobility management Function, AMF, and the other NE performs Unified Data Management, UDM, as defined in 3GPP technical specifications.

13. The method of any of claims 8 to 12, wherein the access-request message and the access-reject message are Non Access stratum, NAS, messages.

14. The method of claim 13, wherein the access-request message is a Registration Request, an Attach Request or a Tracking Area Update Request as defined in 3GPP technical specifications.

15. A wireless communication device (102, 104) comprising a transceiver (132, 142), a processor (134, 144), and computer-readable storage media (136, 146) storing executable instructions for the processor to perform any one of methods recited in claims 1-14, using the transceiver.

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