Methods and devices enabling satellite access during temporary feeder link outages

Abstract

Methods and devices maintain continuity of communications during a temporary interruption of a non-terrestrial network connection between a user equipment and the wireless network. After transmitting (602) an uplink non-access stratum message initiating a non-access stratum procedure, the user equipment extends (604) a time interval for completing the non-access stratum procedure upon determining (603) that the temporary interruption is likely to occur during the procedure.

Description

METHODS AND DEVICES ENABLING SATELLITE ACCESS DURING TEMPORARY FEEDER LINK OUTAGESFIELD OF THE DISCLOSURE

[0001] This document generally describes methods and devices operating in wireless communication systems such as (but not limited to) the ones described in Long Term Evolution (LTE) or 5thgeneration (5G) New Radio (NR) standard documents, known as 3rd Generation Partnership Project (3GPP) communication systems. More particularly, the methods and devices enable communication of a user equipment with a nonterrestrial network (NTN) when the connection between a base station (BS) and a core network (CN) is temporarily unavailable.BACKGROUND

[0002] This background description is provided for the purpose of generally presenting the context and current 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 may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0003] The 5G technology relies primarily on legacy terrestrial networks (TNs).However, the 3GPP organization has proposed to extend communications to NTNs with 5G NR or LTE technologies tailored for the Narrowband Intemet-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) such as a drone, a balloon, a plane, or another suitable apparatus. For simplicity, the discussion below refers to all such apparatuses as satellites. In addition to satellites, an NTN can include one or more sat-gateways that connect the NTN to a public data network, feeder links between the sat-gateway(s) and the satellite(s), service links between satellites, and inter-satellite links (ISL) when satellites form constellations.

[0004] A satellite is characterized by its altitude, orbit, and beam footprint size. The types include a Low-Earth Orbit (LEO) satellite, a Medium-Earth Orbit (MEO) satellite, a Geostationary Earth Orbit (GEO) satellite, a UAS platform (including a High AltitudePlatform Station (HAPS)), and a High Elliptical Orbit (HEO) satellite. The GEO satellites are also known as Geosynchronous Orbit (GSO) satellites, and LEO / MEO satellites are also known as non-GSO (NGSO) satellites.

[0005] A GSO satellite can communicate 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 can communicate with different among the one or several serving sat-gateways. An NTN is designed to ensure service and feeder link continuity between successive serving sat-gateways, with sufficient sat-gateway overlap time to proceed with mobility anchoring and hand-over procedures.

[0006] A satellite may support a transparent 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 satellite beams typically have an elliptical shape and depend on the on-board antenna configuration and the satellite’s elevation angle. For a transparent payload embodiment, a satellite may apply RF filtering and / or frequency conversion and amplification but refrains from changing the waveform of the received signal. For a regenerative payload embodiment, a satellite may apply RF filtering, frequency conversion and amplification, demodulation and decoding, routing, and / or coding / modulation. This approach is effectively equivalent to implementing most of the functions of a BS (e.g., a gNB or an eNB).

[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. However, to ensure the required loT connectivity, deployment of these technologies requires satellite connectivity to provide coverage beyond terrestrial deployments. Satellite NB-loT or eMTC is defined in a complementary manner to terrestrial deployments.

[0008] The NTN usage has been specified in 3GPP Release 17, but since then, it has been optimized in Release 18 and commercial deployments are ongoing at the moment. Based on real deployments or deployment plans, 3GPP has identified that further evolution of NTN is needed such as for supporting Store & Forward (S&F) basedon regenerative payload. The S&F NTN operation with regenerative payload allows for delay-tolerant, non-real-time loT NTN services to be offered in areas visited by the satellites but with no need to have NTN gateway infrastructure (e.g. mid-sea, remote areas). Along with support for discontinuous coverage, this S&F NTN operation facilitates cost-effective deployment of loT NTN services and enables an immediate operational service with (1 ) sparse LEO constellations and (2) reduced ground segment infrastructure. Thus, the S&F NTN operation provides support for the 3GPP loT NTN on par with other non-3GPP solutions intended for massive satellite loT, which natively already supports S&F services.

[0009] The satellite-intermediated communication may be temporarily interrupted when the feeder link (between the network devices and the satellite) and / or a UE’s service link (between the satellite and the UE) become(s) unavailable. For example, a BS on a ship providing services to narrowband Internet-of-Things (NB-loT) UEs (e.g., sensors gathering ocean-related information) may temporarily loose its NTN connection to terrestrial CN devices (sometimes called “CN elements” or “CN nodes”). Any outage of UE-CN communications occurring after a UE, or the CN, initiates a non-access stratum (NAS) procedure, but before the NAS procedure is completed, causes waste of energy and communication resources. The NAS is a functional layer in wireless communication systems (such as, but not limited to 5G and LTE) for CN to UE communications. This layer is used to manage the establishment and maintenance of communication sessions with a moving UE. Even if an NTN BS intermediating the UE- CN communications hosts an S&F function, conventional UE and CN may consider that the NAS procedure has failed when respective UE and / or CN NAS timers expire(s).SUMMARY

[0010] Methods and devices operating in a wireless communication system, with a UE communicating with a CN element via an NTN, extend NAS time intervals to accommodate an NTN-based communication’s temporary interruption.

[0011] In some embodiments, a UE extends a time interval for completing a NAS procedure upon determining that a UE-CN communication outage during a NAS procedure is likely. The UE may extend the time interval by inputting, to a NAS timer, a timer value obtained by adding a predetermined value to a regular timer value (i.e., the regular timer value being the value used when the UE-CN communication outage is not likely), by multiplying the regular timer value with a predetermined factor larger than 1 , or by suspending the NAS timer during the UE-CN communication outage. The UE may determine that a UE-CN communication outage is likely based on whether the UE- CN communication employs an NTN, estimating that the UE-CN communication outage is imminent based on ephemeris information, receiving, from a BS serving the UE, an NTN-outage indication, and / or detecting that a store and forward function of a BS serving the UE is enabled.

[0012] In some other embodiments, a CN element connected to a UE via an NTN, extends a time interval for completing a NAS procedure upon determining that a UE-CN communication outage during the NAS procedure is likely.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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.

[0014] Fig. 1 is a block diagram of an example wireless communication system in which a UE, a BS, and a CN element can implement the wireless communication methods according to various embodiments.

[0015] Fig. 2A is a block diagram of a protocol stack usable by the UE of Fig. 1 to communicate via a BS housed by a satellite with a terrestrial CN element, that is, in an NTN of a regenerative type 1 architecture.

[0016] Fig. 2B is a block diagram of another protocol stack according to which the UE of Fig. 1 communicates via a distributed unit (DU) of a BS (the DU being housed by a satellite and a central unit of the BS being on the ground) with a terrestrial CN element, that is, in an NTN of a regenerative type 2 architecture.

[0017] Fig. 3A is a block diagram illustrating a transparent payload NTN architecture.

[0018] Fig. 3B is a block diagram illustrating a regenerative payload (type 1 ) NTN architecture.

[0019] Figs. 4A-4F are signal diagrams illustrating scenarios in which a UE and / or a CN use longer timer values associated with a UE initiated NAS procedure to alleviate the effect of an interrupted feeder link connection between the UE and a CN.

[0020] Figs. 5A, 5B, and 5C are signal diagrams illustrating scenarios in which a CN uses a longer timer value when initiating a NAS procedure to alleviate the effect of an interrupted service link connection between a UE and the CN element.

[0021] Figs. 6A, 6B, and 6C are flowcharts of UE methods for managing foreseeable (likely) feeder link outages according to various embodiments.

[0022] Figs. 7A and 7B are flowcharts of UE methods including a determination as to when to transmit an uplink (UL) NAS message according to some embodiments.

[0023] Figs. 8A, 8B, and 8C are flowcharts of CN methods that include starting a CN NAS timer with a longer timer value to accommodate a foreseeable (likely) UE-CNconnection interruption based on a calculated or known service link outage according to various embodiments.

[0024] Figs. 9A, 9B, and 9C are flowcharts of CN methods that include transmitting a CN-to-BS message to a BS to page a UE according to various embodiments.

[0025] Figs. 10A and 10B are flowcharts of CN methods that include determining when to transmit a DL NAS message in response to a UL NAS message received from a UE according to some embodiments.

[0026] Figs. 11 A and 11 B are flowcharts of BS methods responding to a connection between a BS and a CN being interrupted according to a couple of embodiments.

[0027] Figs. 12A and 12B are flowcharts of other BS methods according to some embodiments.

[0028] Fig. 13 is a flowchart of a UE method that includes suspending a NAS timer according to an embodiment.

[0029] Fig. 14 is a flowchart of a CN method that includes suspending a NAS timer according to an embodiment.DETAILED DESCRIPTION OF THE DRAWINGS

[0030] As discussed in more detail below, a UE and / or a CN element (or device) connected via an NTN can use the techniques described in this section to mitigate the effect of temporary feeder link outages.

[0031] Fig. 1 is a block diagram an example wireless communication system 100 in which a UE 102, base stations (BS) 104 and 106, and a CN 110 can implement the wireless communication methods according to various embodiments. The CN is a set of interconnected modules (as they are called in LTE) or functions (as called in 5G) designed to provide services to end users (i.e. , UEs). The CN functions or modules are housed by one or more CN devices (also called “CN elements” or CN nodes”) that are hardware support for the CN. The BSs and the CN devices are network devices (unlike the UEs).

[0032] The BSs 104 and 106 in Fig. 1 are connected to the CN via a radio access network (RAN) 105. The BS 104 uses satellite 103 to communicate with UE’s such as102 and / or with the CN 110. The CN 110 can be implemented as an evolved packet core (EPC) 111 or a fifth generation (5G) core (5GC) 160, for example. The CN 110 can also be implemented as a sixth generation (6G) core and future evolutions.

[0033] In Fig. 1 , the BS 104 covers an NTN cell 124 via satellite 103, and the BS 106 covers a terrestrial network (TN) cell 126. If the BS 104 is a gNB, the NTN cell 124 is a new radio (NR) NTN cell. If the BS 104 is an ng-eNB or eNB, the NTN cell 124 is an evolved universal terrestrial radio access (E-LITRA) NTN cell. Similarly, if the BS 106 is a gNB, the TN cell 126 is an NR TN cell, and if the BS 106 is an ng-eNB or eNB, the TN cell 126 is an E-LITRA TN cell. The cells 124 and 126 can be in the same Radio Access Network Notification Areas (RNA) or different RNAs. In general, the RAN 105 can include any number of terrestrial and non-terrestrial BSs, and each of the BSs can cover one, two, three, or any other suitable number of cells. The UE 102 can support at least a 5G NR (or simply, “NR”) or E-UTRA air interface to communicate with the BSs 104 and 106. Each of the BSs 104 and 106 connect to the CN 110 via an interface (e.g., S1 or NG interface). The BSs 104 and 106 also can be interconnected via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes.

[0034] Among other modules, the EPC 111 can include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, and a Packet Data Network Gateway (PGW) 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 PGW 116 provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and / or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The 5GC 160 includes a User Plane Function (UPF) 162 and an Access and Mobility Management Function (AMF) 164, and / or Session Management Function (SMF) 166. Generally speaking, 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 SMF 166 is configured to manage PDU sessions.

[0035] As illustrated in Fig. 1 , the BS 104 supports a cell 124, and the BS 106 supports a cell 126. The cells 124 and 126 can partially overlap, so that the UE 102 canselect, reselect, or hand over from one of the cells 124 and 126 to the other. To directly exchange messages or information, the BS 104 and BS 106 can support an X2 or Xn interface. In general, the CN 110 can connect to any suitable number of terrestrial and / or non-terrestrial BSs supporting NR cells and / or EUTRA cells. As discussed in detail below, the UE 102 and / or the RAN 105 may utilize the techniques of this disclosure when the radio connection between the UE 102 and the RAN 105 is suspended, e.g., when the UE 102 operates in an inactive or idle state of the protocol for controlling radio resources between the UE 102 and the RAN 105. For clarity, the examples below refer to the RRCJNACTIVE or RRCJDLE state of the RRC protocol.

[0036] The BS 104 is equipped with hardware and software 130 that can include one or more general-purpose processors (e.g., CPUs) and a non-transitory computer- readable memory storing instructions that the one or more general-purpose processors execute. Additionally, or alternatively, the processing hardware 130 can include special-purpose processing units. The hardware and software 130 in an example embodiment include a processor 132 to process data that the BS 104 transmits in the downlink direction, or process data the BS 104 receives in the uplink direction. The hardware and software 130 also include a receiver 134 configured to receive data in the uplink direction, and a transmitter 136 configured to transmit data in the downlink direction. The hardware and software 130 may include an RRC controller 138 configured to implement procedures and messaging at the RRC sublayer of the protocol communication stack and a store and forward function or module 139. The BS 106 can include generally similar components.

[0037] The UE 102 is equipped with hardware and software 150 that can include one or more general-purpose processors such as CPUs, non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general- purpose processors, and / or special-purpose processing units. The hardware and software 150 in an example embodiment include a processor 152 to process data that the UE 102 transmits in the uplink direction, or data the UE 102 receives in the downlink direction. The hardware and software 150 also include a receiver 154 configured to receive data in the uplink direction, and a transmitter 156 configured to transmit data in the downlink direction. The hardware and software 150 may further include an RRCcontroller 158 to implement procedures and messaging at the RRC sublayer of the protocol communication stack and a NAS timer 159.

[0038] As already mentioned above, the CN 110 is hosted by one or more CN devices (alternatively called “elements” or “nodes”). Fig. 1 illustrates hardware 140 of such a CN element. Hardware 140 includes a processor 142, a receiver 144, a transmitter 146, and a NAS timer 148.

[0039] Fig. 2A illustrates a block diagram of a protocol stack 200A usable by the UE 102 of Fig. 1 to communicate via a BS 204 with a CN 110. This protocol stack corresponds to a regenerative NTN architecture employing a complete BS on the satellite (i.e., a satellite gNB) known as a regenerative typel architecture (with its feeder link using an S1 -MME / S1-U (LTE) interface or an NG-C / NG-U (5G) interface, also called backhaul). The stack 200A includes a physical (PHY) layer 202 that provides transport channels to a MAC sublayer 204, which in turn provides logical channels to an RLC sublayer 206. The RLC sublayer 206 provides RLC channels to a PDCP sublayer 208 that in turn can provide data transfer services to a radio resource control (RRC) sublayer 210, an Internet Protocol (IP) layer and / or a Service Data Adaptation Protocol (SDAP) sublayer (not shown in this figure). The PDCP sublayer 208 receives packets (e.g., from the RRC sublayer 210, the SDAP sublayer, or the IP layer, layered directly or indirectly over the PDCP layer 208) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer 206) that can be referred to as protocol data units (PDUs). Except where the difference between SDUs and PDUs is relevant, this disclosure for simplicity refers to both SDUs and PDUs as “packets”. In some embodiments, the PHY layer 202, MAC sublayer 204, RLC sublayer 206, PDCP sublayer 208, RRC sublayer 210 are EUTRA layers or sublayers. In other embodiments, the PHY layer 202, MAC sublayer 204, RLC sublayer 206, PDCP sublayer 208, RRC sublayer 210 are NR layers or sublayers.

[0040] The RRC sublayer 210 provides data transfer services to a Non-Access- Stratum (NAS) layer 212. The NAS layer 212 includes a mobility management (MM) sublayer and / or a session management (SM) sublayer. In some embodiments, the MM sublayer is an EPS MM (EMM) sublayer. In other embodiments, the MM sublayer is a 5G MM (5GMM) sublayer. In some embodiments, the SM sublayer is an EPS SM(ESM) sublayer. In other embodiments, the SM sublayer is a 5G SM (5GSM) sublayer. The NAS layer being transparent to the BS, when the BS 204 (i.e. , gNB or eNB 104 or 106) receives UL NAS PDUs from the UE 102, the BS forwards the UL NAS PDUs to the ON 110 without processing the UL NAS PDUs, and when the BS receives DL NAS PDUs from the CN 110, the BS forwards the DL NAS PDUs to the UE 102 without processing the DL NAS PDUs.

[0041] On a control plane, the PDCP sublayer 208 can provide signaling radio bearers (SRBs) to the RRC sublayer 210 to exchange RRC messages or NAS messages (e.g., MM messages and / or SM messages), for example. On a user plane, the PDCP sublayer 208 can provide Data Radio Bearers (DRBs) to support user plane data exchange. User plane data exchanged on the PDCP sublayer 208 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0042] Fig. 2B illustrates an example protocol stack 200B similar to the protocol state 200A, according to which the UE of Fig. 1 communicates via a distributed unit (DU) of a BS (the DU being housed by a satellite and a central unit of the BS being on the ground) with a terrestrial CN element, that is, in an NTN of a regenerative type 2 architecture. The NAS layer is made of portion 212A and portion 212B. The NAS layer portion 212A utilizes user links (i.e., links between UEs and satellite) and the NAS layer portion 212B utilizes feeder links (i.e., links between the satellite and a terrestrial RAN device, such as, a satellite gateway) any of these links may be temporarily interrupted which disrupts ongoing UE-to / from-CH communications. In this case, the NAS layer is not transparent to the BS 204 (i.e., gNB or eNB 104 or 106). When the BS 204 receives a UL NAS PDU from the UE 102, the BS 204 may process the UL NAS PDU and then transmits a DL NAS PDU to the UE 102.

[0043] Fig. 3A illustrates a transparent payload architecture 300, in which UEs, such as the UE 102, communicate with a terrestrial BS 104 using user links 312 to the satellite 103 and a feeder link 314 from the satellite 103 to the gateway 302. In case of a NAS procedure, the BS 104 intermediates UE’s communications with a CN element 140, which may also be connected to a data network 316.

[0044] Fig. 3B illustrates a regenerative payload architecture 300, in which UEs such as the UE 102 communicate via user links 312 with the BS 104 on the satellite 103. Incase of a NAS procedure, the BS 104 then communicates with the CN element 140 via a feeder link 314 and the satellite gateway 302. In case of a NAS procedure, the BS 104 intermediates UE’s communications with the CN element 140 which may be connected to a data network 316. For NAS procedure-related communications, the BS 104 implements a Radio Frequency (RF) filtering, a RF amplifier, and a frequency conversion in both the uplink and / or downlink directions. As a result, the BS 104 communicates with the UE 102 via the satellite 103 and the Uu radio interface (user links 312A) in the downlink direction and vice versa in the uplink direction. The BS 104 communicates with the CN 110 via a feeder link 314 (between the NTN gateway 302 and the satellite 103) and another link (not labled) between the NTN gateway 302 and the CN 140. The NTN gateway 302 can be placed at the same site as the CN 140 location or be connected to the CN 110 at a distance via a wired link or a wireless link. If the BS 104 is a complete BS this arrangement is known as a regenerative typel architecture with its feeder link using an S1 -MME / S1 -U (LTE) interface or an NG-C / NG- II (5G) interface (also called backhaul). If the BS 104 is only a portion of the BS (e.g., a distributed unit, DU), this arrangement is known as a regenerative type2 architecture with a feeder link using an F1 interface (also called midhaul).

[0045] The UE’s satellite-intermediated communication as illustrated in Figs. 3A and 3B may be temporarily interrupted when the feeder link and / or a UE’s service link become(s) unavailable. An outage of UE-CN communications occurring after a UE, or the CN, initiates a non-access stratum (NAS) procedure, but before the NAS procedure is completed, may causes waste of energy and communication resources even if the BS intermediating the UE-CN communications uses a store-and-forward function. Therefore, methods and devices according to various embodiments operating in a wireless communication system, with a UE communicating with a CN element via an NTN, extend NAS time intervals to accommodate an NTN-based communication’s temporary interruption.

[0046] Figs. 4A-5C illustrate several example scenarios in which a BS such as the BS 104 on satellite 103 operating in the wireless communication system 100 illustrated in Fig. 1 communicates with a UE such as the UE 102 and the CN 110. Figures 6A-14 are flowcharts of UE, BS, or CN methods according to various embodiments. Similarevents and actions in Figs. 4A-14 are labeled with similar reference numbers (e.g., event 402 of Figs. 4A-4E is similar to event 502 of Figs. 5A-5C, event 602 of Figs. 6A- 6C, event 702 in Figs. 7A and 7B, event 802 in Figs. 8A-8C), with differences discussed where appropriate. With the exception of the differences shown in the figures and discussed below, any of the alternative embodiments discussed with respect to a particular event (e.g., for messaging and processing) may apply to events labeled with similar reference numbers in other figures. Note also that time flows from top to bottom of the figures, that is events illustrated higher in a scenario occur earlier than events illustrated lower therein.

[0047] Fig. 4A illustrates an example scenario 400A, in which the BS 104 communicates with the UE 102 via the satellite 103 and with the CN 110 (i.e., one or more CN modules or CN functions executed by a CN element such as 140) via the NTN gateway 302. The UE 102 communicates with the BS 104 via a satellite cell (e.g., cell 124) operated by the BS 104 via the satellite 103. The BS 104 may detect a connection between the CN 110 and the BS 104 is interrupted 406, for example, due to the satellite 103 temporarily being out of range of the NTN gateway 302. The UE, which receives an indication from the BS that the connection is interrupted or may be interrupted, the UE 102 initiates 402 a NAS procedure and starts 404 a UE NAS timer with a longer timer value than a normal timer value (e.g., specified in a 3GPP specification such as 24.301 or 24.501 ) so that the UE is able to handle failure of the NAS procedure or transmission of the first UL NAS message. In some implementations, the UE 102 determines or is preconfigured to use the longer timer value when the UE 102 performs the NAS procedure via a satellite with regenerative payload, regardless of whether the UE 102 knows the BS 104 is not currently connected to the CN 110. In other implementations, UE 102 determines to use the longer timer value based on system information (received at 401 ) or preconfigured information (as described relative to the flow diagram in Fig. 6C). In yet other implementations, the UE 102 receives system information from the BS 104 before initiating the NAS procedure. The system information may indicate the UE 102 to use longer timer values for NAS procedure(s) or NAS message(s). Thus, the UE 102 starts 404 the timer with the longer timer value based on the system information. If the system information does not include suchindication, the UE 102 uses a normal timer value for the UE NAS timer. In some implementations, the system information indicates a multiplier to be applied to the normal timer value (i.e. , the longer timer value = multiplier * normal timer value). The BS 104 can set the multiplier such that to ensure that the longer timer value is going to be long enough to accommodate the time of the interrupted connections between the BS 104 and the CN 110 and / or between the UE 102 and the BS 104. In yet other implementations, the system information indicates the longer timer value.

[0048] In response to initiating the NAS procedure, the UE 102 transmits 408 a first UL NAS message to the BS 104. In some embodiments, the UE 102 initiates 402 the NAS procedure while operating in an idle state (e.g., an RRCJDLE state) with or without a suspended RRC connection or in an inactive state (e.g., an RRCJNACTIVE state) with a suspended RRC connection. If the UE 102 operates in the idle state, the UE 102 may perform an RRC connection establishment procedure with the BS 104 to transition to a connected state (e.g., an RRC_CONNECTED state). As a result of the RRC connection establishment procedure, the UE 102 enters the connected state and establishes an SRB (e.g., SRB1 ). If the UE 102 operates in the idle state with a suspended RRC connection or in the inactive state, the UE 102 may perform an RRC connection resume procedure to transition to the connected state. As a result of the RRC connection resume procedure, the UE 102 enters the connected state and resumes one or more suspended SRBs (e.g., SRB1 , SRB2) and / or one or more suspended DRBs. After the UE 102 enters the connected state, the UE 102 transmits the first UL NAS message via the established or resumed SRB (e.g., SRB1 ) to the BS 104. For example, the UE 102 transmits an RRC message including the first UL NAS message to the BS 104. The RRC message may be an RRC connection setup complete message, an RRC setup complete message, an RRC connection resume complete message, or an RRC resume complete message. In some other embodiments, the UE 102 transmits the first UL NAS message to the BS 104 without entering the connected state. In such cases, the UE 102 neither performs an RRC connection establishment procedure nor an RRC connection resume procedure. In one embodiment, the UE 102 transmits an RRC message (e.g., an RRCEarlyDataRequest) including the first UL NAS message to the BS 104. In another embodiment, the UE 102includes an RRC connection resume request message and the first UL NAS message in a UL MAC PDU and transmits the UL MAC PDU to the BS 104. In yet another embodiment, the UE 102 includes an RRC resume request message and the first UL NAS message in a UL MAC PDU and transmits the UL MAC PDU to the BS 104.

[0049] Because the connection between the CN 110 and the BS 104 is interrupted (i.e., the CN 110 is unreachable), the BS 104 stores 410 the first UL NAS message. The feeder link connection between the CN 110 and the BS 104 is then recovered 412. For example, the BS 104 may detect the connection is recovered after the satellite 103 enters the range of the NTN gateway 302 and reconnects to the NTN gateway 302. After the connection is recovered, the BS 104 forwards 414 the first UL NAS message to the CN 110 (e.g., the MME 114 or the AMF 164). In some embodiments, the BS 104 includes the first UL NAS message in a first BS-to-CN message and transmits the first BS-to-CN message to the CN 110 at the event 414. The first BS-to-CN message may be an S1 Application Protocol (S1AP) message. Alternatively, the first BS-to-CN message may be an NG Application Protocol (NGAP) message.

[0050] The CN 110 responds to the UL NAS message 414 by transmitting 416 a DL NAS message to the BS 104. In some embodiments, the CN 110 includes the DL NAS message in a CN-to-BS message and transmits the CN-to-BS message to the BS 104 at the event 416. The CN-to-BS message may be an S1AP message. Alternatively, the CN-to-BS message may be an NGAP message.

[0051] Upon receiving 414 the first UL NAS message or transmitting 416 the DL NAS message, the CN 110 may start 415 a CN NAS timer with a normal timer value specified in a 3GPP specification (e.g., 24.301 or 24.501 ). Upon receiving the DL NAS message 416 from CN 110, the BS 104 transmits / forwards 418 the DL NAS message to the UE 102, e.g., via the SRB (e.g., SRB1 ). The UE 102 then stops 424 the UE NAS timer in response to receiving the DL NAS message. In some embodiments, the UE 102 may transmit 420 a second UL NAS message to the BS 104 in response to receiving 418 the DL NAS message (this operation is optional as suggested by using dashed line). In such cases, the BS 104 transmits 422 the second UL NAS message to the CN 110. The CN 110 stops 425 the CN NAS timer in response to receiving the second UL NAS message. In some embodiments, the BS 104 includes the second UL NASmessage in a second BS-to-CN message and transmits the second BS-to-CN message to the CN 110 at the event 422. In some embodiments, the second BS-to-CN message is a S1AP message. In other embodiments, the second BS-to-CN message is a NGAP message.

[0052] In some scenarios or embodiments, when the BS 104 receives 416 the DL NAS message from CN 110, the BS 104 cannot reach the LIE 102 because the UE 102 is not in coverage of the BS 104. The BS 104 may determine that the UE 102 is not reachable based on location of the satellite 103 and / or location of the UE 102. In such cases, the BS 104 stores the DL NAS message until the UE 102 is reachable. The BS 104 may later determine that the UE 102 is reachable based on location of the satellite 103 and / or location of the UE 102. In response to determining that the UE 102 is reachable, the BS 104 transmits 418 or attempts to transmit the DL NAS message to the UE 102. In such cases, the CN 110 may start the CN NAS timer with an extended timer value instead of the normal timer value, similar to the cases described in Figs. 4C, 4D, or 5A. In some implementations, the CN 110 determines or is preconfigured to use the extended timer value while connecting to the BS 104 via the satellite 103, because the BS 104 may have already lost the connection with the UE 102 when the CN 110 connects to the BS 104. In other implementations, the CN 110 determines to use or uses the extended timer value for the UE 102 because the CN 110 determines that the BS 104 may have already lost the connection with the UE 102 when the BS 104 connects to the CN 110. When the BS 104 receives the DL NAS message and the UE 102 is reachable, the BS 104 forwards the DL NAS message to the UE 102.

[0053] In some scenarios or embodiments, when the BS 104 receives 422 the second UL NAS message, the connection between the BS 104 and the CN 110 may be interrupted as described for the event 406. In such cases, the BS 104 stores the second UL NAS message until the connection is recovered as described for the events 410 and 412. In such cases, upon transmitting the DL NAS message, the CN 110 may start the CN NAS timer with a normal timer value plus an additional time value, similar to the cases described above and in Figs. 4C, 4D, or 5A. When the BS 104 receives the second UL NAS message and the connection between the BS 104 and the CN 110 is available or recovered, the BS 104 forwards the second UL NAS message to the CN110. Because the longer timer value applies to the CN NAS timer, the CN NAS timer is still running when the CN 110 receives the second UL NAS message. In both Fig. 4A and Fig. 4B, the longer timer value at the UE 102 accommodates certain potential connection interruptions and recoveries.

[0054] In some embodiments, the UE-initiated NAS procedure is an attach procedure, and the first UL NAS message, the DL NAS message, and the second UL NAS message are an Attach Request message, an Attach Accept message, and an Attach Complete message, respectively. In other embodiments, the UE-initiated NAS procedure is a tracking area update procedure, and the first UL NAS message, the DL NAS message, and the second UL NAS message are a Tracking Area Update Request message, a Tracking Area Update Accept message, and a Tracking Area Update Complete message, respectively. In such cases, the UE NAS timer is T3410, and the CN NAS timer is a T3450.

[0055] In other embodiments, the UE-initiated NAS procedure is a registration procedure and the first UL NAS message, the DL NAS message, and the second UL NAS message are a Registration Request message, a Registration Accept message, and a Registration Complete message, respectively. In such cases, the UE NAS timer is T3510, and the CN NAS timer is a T3550.

[0056] In yet other embodiments, the UE-initiated NAS procedure is a service request procedure, the first UL NAS message and the DL NAS message being a Service Request message and a Service Accept message, respectively. In such cases, the second UL NAS message is omitted. The UE NAS timer may be T3417 or T3517 as described in 3GPP technical specifications. In some embodiments, the UE-initiated NAS procedure is a control plane service request procedure, and the first UL NAS message and the DL NAS message are a Control Plane Service Request message and a Service Accept message, respectively. In such cases, the second UL NAS message is omitted.

[0057] In some embodiments, the UE-initiated NAS procedure is a packet data network (PDN) connectivity procedure, and the first UL NAS message, the DL NAS message, and the second UL NAS message are a PDN Connectivity Request message, an Activate Default EPS Bearer Context Request message, and an Activate Default EPS Bearer Context Accept message, respectively. In some embodiments, the UE NAStimer is T3482 and / or the CN NAS timer is T3485 as described in 3GPP technical specifications. In other embodiments, the UE-initiated NAS procedure is a bearer resource allocation procedure, and the first UL NAS message, the DL NAS message and the second UL NAS message are a Bearer Resource Allocation Request message, an Activate Dedicated EPS Bearer Context Request message and an Activate Dedicated EPS Bearer Context Accept message, respectively. The UE NAS timer may be T3480 and / or the CN NAS timer may be T3485. In yet other embodiments, the UE- initiated NAS procedure is a bearer resource allocation procedure, and the first UL NAS message, the DL NAS message, and the second UL NAS message are a Bearer Resource Allocation Request message, a Modify EPS Bearer Context Request message, and a Modify EPS Bearer Context Accept message, respectively. In some embodiments, the UE NAS timer is T3480 and / or the CN NAS timer is T3486. In yet other embodiments, the UE-initiated NAS procedure is a bearer resource modification procedure, and the first UL NAS message, the DL NAS message and the second UL NAS message are a Bearer Resource Modification Request message, an Activate Dedicated EPS Bearer Context Request message and an Activate Dedicated EPS Bearer Context Accept message, respectively. In some embodiments, the UE NAS timer is T3481 and / or the CN NAS timer is T3485. In yet other embodiments, the UE- initiated NAS procedure is a bearer resource modification procedure, and the first UL NAS message, the DL NAS message and the second UL NAS message are a Bearer Resource Modification Request message, a Modify EPS Bearer Context Request message and a Modify EPS Bearer Context Accept message, respectively. In some embodiments, the UE NAS timer is T3481 and / or the CN NAS timer is T3486.

[0058] In some embodiments, the UE-initiated NAS procedure is a PDU session establishment procedure, and the first UL NAS message and the DL NAS message are a PDU Session Establishment Request message and a PDU Session Establishment Accept message, respectively. In such cases, the second UL NAS message may be omitted. In some embodiments, the UE NAS timer is T3580. In other embodiments, the UE-initiated NAS procedure is a PDU session modification procedure, and the first UL NAS message, the DL NAS message and the second UL NAS message are a PDU Session Modification Request message, a PDU Session Modification Commandmessage, and a PDU Session Modification Complete message, respectively. In some embodiments, the UE NAS timer is T3581 and / or the CN NAS timer is T3591 . In yet other embodiments, the UE-initiated NAS procedure is a PDU session release procedure, and the first UL NAS message, the DL NAS message and the second UL NAS message are a PDU Session Release Request message, a PDU Session Release Command message, and a PDU Session Release Complete message, respectively. In some embodiments, the UE NAS timer is T3582 and / or the CN NAS timer is T3592.

[0059] If the UE 102 starts the UE NAS timer with a normal timer value based on Table 10.2.1 and / or Table 10.3.1 in 3GPP specification 24.301 or 24.501 , the UE NAS timer might expire before the UE 102 receives a DL NAS message in response to the first UL NAS message. For example, in the case of the attach procedure or the tracking area update procedure, the UE NAS timer may be timer T3410 and the normal timer value for T3410 is 15 seconds as specified in 3GPP specification 24.301 . If the UE 102 starts T3410 with 15 seconds and the time period between the event 408 and the event 412 is longer than 15 seconds, the UE 102 does not receive the DL NAS message before the UE NAS timer expires. Upon expiry of T3410, the UE 102 terminates the NAS procedure (i.e. , the attach procedure or the tracking area update procedure) and determines that the UE 102 fails the NAS procedure.

[0060] Therefore, instead of applying the normal timer value to the UE NAS timer, the UE 102 at the event 404 starts the UE NAS timer with the longer timer value that accommodates the connection interruption between the BS 104 and the CN 110. In some cases, the longer timer value should be long enough to accommodate not only the connection interruption time between the BS 104 and the CN 110 but also the connection interruption time between the BS 104 and the UE 102. For example, the connection between the BS 104 and the UE 102 is interrupted because the UE 102 is out of coverage of the satellite 103. Because the longer timer value applies to the UE NAS timer, the UE NAS timer is still running when the UE 102 receives the DL NAS message. Thus, the extended timer value ensures that the UE 102 completes the NAS procedure with the CN 110. For example, in the case of the attach procedure or the tracking area update procedure, the UE 102 starts T3410 with a longer timer value toaccommodate the connection interruption time between the BS 104 and the CN 110 and / or the connection interruption time between the BS 104 and the UE 102.

[0061] In some embodiments, the longer timer value is predetermined based on the maximum predicted interruption time between the BS 104 and the CN 110 and / or the maximum predicted interruption time between the UE 102 and the BS 104. In some embodiments, the longer timer values are different for different UE-initiated NAS procedures or for different UL NAS messages. In other embodiments, at least some of the longer timer values for some of the UE-initiated NAS procedures or for some of the UL NAS messages are the same and the reset are different. In some embodiments, the longer timer value(s) are specified in one or more 3GPP specifications (e.g., 3GPP specification 24.301 and / or 24.501 ). In other embodiments, the BS 104 broadcasts the longer replacement timer value(s) or the extension timer values via the satellite 103.

[0062] The scenario 400B illustrated in Fig. 4B is similar with the one in Fig. 4A except that the connection between the BS 104 and the CN 110 is interrupted after the UL NAS message 408 is received 414 by the CN 110. In Figs. 4A and 4B, events 402, 404 and 408 may be grouped within a UE procedure 492 that includes UE initiating UL NAS procedure, starting UE NAS timer with longer value than a normal (i.e., nominal or standard-specified) value, and transmitting the UL NAS message.

[0063] Unlike the scenarios illustrated in Figs. 4A and 4B, in the scenario 400C illustrated in Fig. 4C, the CN 110 starts 415 a CN NAS timer with a longer timer value than a normal timer value, to accommodate a foreseeable (likely) connection interruption 406. Note that while a connection interruption is always possible, a foreseeable (likely) interruption is anticipated / predicted (e.g., based on the satellite orbital pattern). However, some possible interruptions cannot be predicted (e.g., clouds or other hardware disruption requiring rebooting, etc.).

[0064] Different from the scenario illustrated in Fig. 4C in which the UE 102 transmits 420 the second UL NAS message while the connection is interrupted, according to the scenario 400D in Fig. 4D, the UE 102 transmits 420 the second UL NAS message after the connection between the CN and the BS is recovered 412. In both Fig. 4C and Fig. 4D, the longer timer value at the CN 110 accommodates foreseeable (likely) connection interruptions and recoveries.

[0065] In the scenario 400E illustrated in Fig. 4E, the UE 102 starts 405 the LIE NAS timer with a normal timer value. Upon receiving 408 an UL NAS message while the connection between the CN and the BS is interrupted, the BS 104 stores 410 the first UL NAS message, but transmits 418 the DL NAS message to the UE 102. Thus, the BS 104 emulates the CN response. Upon receiving the DL NAS message (e.g., a ‘Service Accept’ message) generated by the BS 104 instead of the DL NAS message from the CN via the satellite 103 in Figs. 4A-4D, the UE 102 stops 424 the UE NAS timer. After the connection between the CN and the BS is recovered 412, the BS 104 forwards 419 the first UL NAS message to the CN 110. The CN 110 then refrains 421 from transmitting a DL NAS message (such as the DL NAS messages 416, 418 in Figs. 4A- 4D) in response to the first UL NAS message.

[0066] In the scenario 400F illustrated in Fig. 4F, after starting 405 the UE NAS timer with a normal value, the UE 102 sends 409 a service request to the BS 104. A radio bearer establishment 421 then occurs between the UE 102 and the BS 104 after the BS 104 stores 410 the UL NAS message. The UE 102 then stops 424 the UE NAS timer and transmits 426 UL data via a data radio bearer (DRB) established at 421 . Thus, in this scenario, the radio bearer establishment 421 (instead of receiving 418 the DL NAS message from the CN via the satellite 103 in Figs. 4A-4D) triggers the UE to stop 424 the UE NAS timer. The BS 104 stores 410 the service request and 411 the UL data until the connection between the CN and the BS is recovered 412. The BS 104 then sends 419 the service request message to the CN 110 followed by transmitting 428 the UL data to the CN 110, where the service request message may include a ‘store and forward’ indication.

[0067] Next, Fig. 5A illustrates a scenario 500A, in which the BS 104 communicates with the UE 102 via the satellite 103 and communicates with the CN 110 via the NTN gateway 302. Initially, the CN 110 (e.g., the MME 114 or the AMF 164) initiates 502 a NAS procedure with the UE 102. In response to initiating the NAS procedure, the CN 110 transmits 516 a DL NAS message to the BS 104. In response to initiating the NAS procedure or transmitting the DL NAS message, the CN 110 starts 504 a CN NAS timer to handle failure of the NAS procedure or transmission of the DL NAS message. The CN 110 starts the CN NAS timer with a longer timer value than a normal timer value toaccommodate a foreseeable (likely) connection interruption time between the BS 104 and the CN 110 and / or a foreseeable (likely) connection interruption time between the UE 102 and the BS 104. In some implementations, the CN 110 is preconfigured to use the longer timer value because the BS 104 may lose the connection with the UE 102 when the CN 110 connects to the BS 104. In other implementations, the CN 110 determines to use or uses the longer timer value for the UE 102 while communicating with the BS 104 via the satellite 103, because the CN 110 determines that the BS 104 may lose the connection with the UE 102 when the BS 104 connects to the CN 110. Yet in some implementations, the CN 110 determines to use or uses the longer timer value for the UE 102 while communicating with the BS 104 via the satellite 103, because the CN 110 determines that the BS 104 may lose the connection with the CN 110 when the BS 104 communicates with the UE 102. The BS 104 stores 530 the DL NAS message because the UE 102 is 594 out of coverage of the satellite 103. In some embodiments, the BS 104 may determine that the UE 102 is out of the satellite 103’s coverage based on location of the satellite 103 and / or a last known or a predicted location of the UE 102. After BS 104 receiving the DL NAS message from the CN 110, the connection between the CN 110 and the BS 104 might be interrupted 506.

[0068] When the UE 102 is back 596 in the satellite coverage (a situation that the BS 104 may determine based on a current location of the satellite 103 and / or a current or correctly predicted location of the UE 102), the BS 104 transmits 518 the DL NAS message to the UE 102. In response to the DL NAS message, the UE 102 transmits 520 a UL NAS message to the BS 104. In some scenarios, the UE 102 may again be 599 out of the satellite 103’s coverage after transmitting the UL NAS message. If the connection between the BS 104 and the CN 110 is interrupted (e.g., event 506), the BS 104 stores 510 the UL NAS message until the connection between the BS 104 and the CN 110 is recovered 512. After the connection between the BS 104 and the CN 110 is recovered 512 or if the connection between the BS 104 and the CN 110 has remained available throughout, the BS 104 transmits 522 the UL NAS message to the CN 110. The CN 110 stops 525 the CN NAS timer in response to receiving the UL NAS message. Thus, the extended timer value of the CN NAS timer accommodates one or both potential interruptions 594, 506 and their subsequent recoveries 596, 512.

[0069] In the scenario 500B illustrated in Fig. 5B, the CN 110 starts the CN NAS timer with a normal value, but if determining 593 that the UE is out of satellite coverage, the CN 110 suspends 595 the CN NAS timer. When determining 597 that the UE is back in satellite coverage, the CN 110 resumes 598 the CN NAS timer running.

[0070] The scenario 500C illustrated in Fig. 5C differs from the scenario 500A in Fig. 5A in that instead of transmitting 516 a DL NAS message, the CN 110 transmits 517 a CN-to-BS paging. Subsequently, instead of transmitting 518 a DL NAS message, the BS 104 transmits 519 an UE Paging. After stopping 525 the CN NAS timer in responds to receiving 514 the UL NAS message forwarded by the BS 104, the CN 110 transmits 516 a DL NAS message to the BS 104, which then forwards 518 the DL NAS message to the UE 102. Similar to Fig. 5A, the extended timer value of the CN NAS timer accommodates one or both potential interruptions 594, 506.

[0071] Figs. 6A-14 are flowcharts of methods that can be implemented in a UE (e.g., the UE 102), a CN (e.g. the CN 110, MME 114, AMF 164, or SMF 166) or a BS (e.g., the BS 104). The descriptions of scenarios illustrated in Figs. 4A-5B may apply to Figs. 6A-14. Each of these methods can be implemented using processing hardware such as one or more processors to execute instructions stored on a non-transitory computer- readable medium such as computer memory.

[0072] Figs. 6A-C are flowcharts of UE methods for managing foreseeable (likely) feeder link outages according to various embodiments. Referring first to Fig. 6A, a method 600A may be executed by a suitable UE (e.g., the UE 102), the method including using a longer timer value for a UE NAS timer in order to accommodate a UE-CN connection interruption. The method 600A includes transmitting 602 a first UL NAS message, determining 603 when a UE-CN communication outage is likely, and then starting 604 a UE NAS timer with a longer timer value than a normal timer value in response to transmitting the first UL NAS message. The method 600A further includes receiving 618 a DL NAS message in response to the first UL NAS message, stopping 624 the UE NAS timer in response to receiving the DL NAS message, and then optionally (as suggested by using dashed line) transmitting 620 a second UL NAS message in response to the DL NAS message. Thus, the method of Fig. 6A corresponds to the UE 102 behavior of Fig. 4A.

[0073] Fig. 6B is a flow diagram of a UE method 600B similar to the method 600A, except for differences now described. The method 600B begins with the UE camping 601 on a cell (e.g., a satellite cell) and receiving system information via the cell. After transmitting 602 a first UL NAS message, the UE determines 640 whether system information indicates that a store and forward function is enabled. If indeed the system information indicates that the cell enables store and forward function (i.e. , “Yes” branch of 640), the UE starts 604 a UE NAS timer with a longer timer value than a normal timer value in response to transmitting the UL NAS message. Otherwise (i.e., “No” branch of 640), the UE starts 605 the UE NAS timer with the normal timer value in response to transmitting the UL NAS message. Regardless which timer value is used when starting the UE NAS timer, the UE then receives 618 a DL NAS message in response to the first UL message, stops 624 the UL NAS timer in response to receiving the DL NAS message, and, optionally, transmits 620 a second UL NAS message in response to the DL NAS message. Thus, this method augments the method illustrated in Fig. 6A accounting for situations when a base station on the satellite does not provide a store and forward function.

[0074] Fig. 6C is a flow diagram of a UE method 600C similar to the method 600B, except that, in method 600C, the UE determines 641 whether a CN is unreachable instead of determining whether the system information indicates a store and forward information being enabled at 640 in Fig. 6B. The determinations 640 and 641 may occur shortly before or after (as illustrated) 602before starting the NAS timer. If the UE determines that a CN is unreachable (i.e., ‘Yes’ branch of 641 ), the UE starts 604 the UE NAS timer with a longer timer value. Otherwise (i.e., ‘No’ branch of 641 ), the UE starts 603 the UE NAS timer with a normal timer value. In some embodiments, the UE determines whether the CN is reachable based on the system information. For example, the system information may include an indicator (e.g., a field or an information element) that indicates that the CN is unreachable, and, if the CN is reachable, the system information does not include the indicator. In other embodiments, the system information includes time information indicating when the CN is unreachable. The time information may include a time (e.g., absolute time) and / or a duration. If the time of initiating the NAS procedure is within the time interval, the UE determines that the CN isunreachable. Otherwise, if the time of initiating the NAS procedure is outside the time interval, the UE determines that the CN is reachable.

[0075] In yet other alternative embodiments, the UE receives a dedicated message including the time information from the CN when the UE connects to the CN via the BS or another BS (e.g., BS 106). The dedicated message may be a NAS message or an Internet Protocol (IP) packet. The UE may receive a dedicated message (e.g., a RRC message) including the time information from the BS when the UE connects to the BS. Alternatively, the UE may be preconfigured (e.g., during manufacturing) with the time information.

[0076] In some embodiments, the system information includes location information (e.g., ephemeris information) indicating positions (i.e., trajectory) of a satellite when the CN is unreachable. The satellite operates the cell or a BS on the satellite operates the cell. The satellite may be a satellite with regenerative payload. If a current position of the satellite is located o a certain portion of the trajectory, the UE determines that the CN is unreachable. Otherwise, if the position of the satellite is located outside the trajectory, the UE determines that the CN is reachable. In some alternative embodiments, the UE receives a dedicated message (e.g., a NAS message) including the location information from the CN when the UE connects to the CN via the BS or another BS (e.g., BS 106). The dedicated message may be a NAS message or an IP packet. The UE may receive a dedicated message (e.g., an RRC message) including the location information from the BS when the UE connects to the BS. Alternatively, the UE may be preconfigured (e.g., during manufacturing) with the location information. In some alternative embodiments, the UE may receive the system information from a terrestrial cell (e.g., cell 126).

[0077] Figs. 7A and 7B are flowcharts of UE methods including a determination as to whether to transmit an uplink (UL) NAS message according to some embodiments. These methods can be implemented in a suitable UE (e.g., the UE 102). Referring now to Fig. 7A, the method 700A first includes camping 701 on a cell and receiving system information via the cell (701 being similar to 601 in Fig. 6B). The method 700A then includes the UE initiating 702 an NAS procedure to transmit a UL NAS message. The UE then determines 740 (which is similar to 640) whether the system informationindicates that the store and forward function is enabled. If indeed the system information indicates that the store and forward function is enabled (i.e. , “Yes” branch of block 740), the UE transmits 708 the UL NAS message in response to the initiation (similar to event 408). Otherwise (i.e., “No” branch of block 640), the UE transmits 748 the UL NAS message when the system information indicates that the store and forward function (e.g., event 420) is disabled. In some embodiments, when a BS operating the cell reconnects to a CN, the BS may disable the store and forward function. In such cases, the BS may update the system information to indicate that store and forward function is disabled on the cell and broadcast the updated system information via the cell. In such cases, the UE may receive (i.e., re-read) the updated system information broadcast on the cell and determine that the cell disables the store and forward function.

[0078] Fig. 7B is a flow diagram of a method 700B similar to the method 700A, except that method 700B includes determination 741 as to whether the CN is reachable instead of the determination 740 as to whether the store and forward function is enabled. If the UE determines that a CN is unreachable (i.e., “Yes” branch of 741), the UE transmits 749 the UL NAS message when the CN is reachable. Otherwise (i.e., “No” branch of 741 ), the UE transmits 708 the UL NAS message in response to 702. Examples and embodiments described for Fig. 6C can apply to Fig. 7B.

[0079] Figs. 8A, 8B, and 8C are flowcharts of CN methods that include starting a CN NAS timer with a longer timer value to accommodate a foreseeable (likely) UE-CN connection interruption based on a calculated or known service link outage according to various embodiments. These CN methods can be implemented in a suitable CN device (e.g., the CN 110, AMF 164, SMF 166, or MME 114 hosted by a CN element such as 140). The method 800A illustrated in Fig. 8A includes starting 804 a CN NAS timer with a longer-than-normal timer value to accommodate a predicted (foreseeable, likely) UE-CN connection interruption. The CN can predict an upcoming interruption of its connection with a UE based on the distance between the UE and the BS (i.e., the satellite) forwarding the NAS message, where the distance between the UE and the BS can be calculated based on UE’s position and the ephemeris information of the satellite.

[0080] The method 800A begins with the CN transmitting 802 a DL NAS message for a UE, to a BS. The CN then determines 803 that a UE-CN communication outage is likely to occur during a NAS procedure, and, therefore, starts 804 a CN NAS timer with a longer timer value than a normal timer value. The method 800A further includes receiving 822 a UL NAS message in response to the DL NAS message and stopping 825 the CN NAS timer in response to receiving the UL NAS message.

[0081] Fig. 8B is a flow diagram of a CN method 800B similar to the method 800A, except for the presence of the determination 840 and event 805. The CN determines 840 whether the BS enables a store and forward function. If indeed the BS enables the store and forward function (i.e. , “Yes” branch of block 840), the CN starts 804 a CN NAS timer with a longer timer value than a normal timer value in response to transmitting the DL NAS message. This extended timer value accommodates a predicted delay in view of using the store-and-forward function. Otherwise (i.e., “No” branch of block 840), the CN starts 805 the CN NAS timer with the normal timer value in response to transmitting the DL NAS message (e.g., as in 505). Regardless of which timer value is used, the method 800B further includes the above-described receiving 820 and stopping 825.

[0082] In some embodiments, the CN determines that the BS enables the store and forward function based on a BS-to-CN message received from the BS. If the CN does not receive from the BS an indication that the BS enables the store and forward function, or receives an indication from the BS indicating that the BS disables the store and forward function, the CN determines that the BS does not enable (or disables) the store and forward function, respectively. In other embodiments, the CN determines that the BS enables the store and forward function if the BS was unreachable before transmitting the DL NAS message. Otherwise, if the BS has never been unreachable before transmitting the DL NAS message, the CN determines that the BS does not enable (or disables) the store and forward function.

[0083] Fig. 8C is a flow diagram of another CN method 800C similar to the methods 800A and 800B, except that in the method 800C the CN determines 839 whether the UE operates in a non-serving area instead of determinations 840 in Fig. 8B (i.e., method 800B). If the CN determines 839 that the UE indeed operates in a non-serving area (i.e.,“Yes” branch of 839), the CN starts 804 the CN NAS timer using a longer timer value. Otherwise (i.e. , “No” branch of 839), the CN starts 805 the CN NAS timer using a normal timer value. The CN may receive information of the UE’s location from the UE, e.g., in a UL NAS message. The UL NAS message may be one of the UL NAS messages described above. Based on the information, the CN determines whether the UE operates in a non-serving area.

[0084] Figs. 9A, 9B, and 9C are flowcharts of CN methods that include transmitting a CN-to-BS message to a BS to page a UE according to various embodiments. Referring next to Fig. 9A, a CN method 900A can be implemented in a suitable CN (e.g., the CN 110, AMF 164, SMF 166, or MME 114 hosted by a CN element 140) and includes starting a CN NAS timer with a longer timer value to accommodate a UE-CN connection interruption. This flow diagram corresponds to the signal diagram of Fig. 5B. The method 900A begins with the CN transmitting 917 of a CN-to-BS message to a BS to page a UE, followed by determining 903 that a UE-CN communication outage is imminent, and starting 904 a CN NAS timer with a longer timer value than a normal timer value upon transmitting the CN-to-BS message. The method 900A then includes receiving 922 a UL NAS message from the UE in response to paging the UE and stopping 925 the CN NAS timer in response to receiving the UL NAS message. The CN-to-BS message may be a S1AP Paging message, a NGAP Paging message or a Service Request message. The UL NAS message may be a Control Plane Service Request message.

[0085] Fig. 9B is a flow diagram of another CN method 900B similar to the method 900A, except that method 900B includes a determination 940 as to whether the BS enables a store and forward function. If indeed the BS enables the store and forward function (i.e., “Yes” branch of 940), the CN starts 904 a CN NAS timer with a longer timer value than a normal timer value in response to paging the UE. Otherwise (i.e., “No” branch of 940), the CN starts 905 the CN NAS timer with the normal timer value in response to paging the UE. Regardless of which timer value is used when starting the CN NAS timer, the method 900A further includes receiving 9922 a UL NAS message from the UE in response to paging the UE and stopping 925 the CN NAS timer in response to 922. Examples and embodiments described for Fig. 8B can apply to Fig.9B. The extended timer value supports any delay created by the store and forward function.

[0086] Fig. 9C is a flow diagram of an example method 900C similar to the methods 900A and 900B, except that method 900C includes a determination 939 as to whether the UE operates in a non-serving area instead of the determination 940 in Fig. 9B. If the CN determines 939 that the indeed UE operates in a non-serving area (i.e. , “Yes” branch of 939), the CN starts 904 a CN NAS timer with a longer timer value than a normal timer value in response to paging the UE. Otherwise (i.e., “No” branch of 939), the CN starts 905 the CN NAS timer with the normal timer value in response to paging the UE. The extended timer value accommodates potential user link disruptions when a UE operates outside a serving area.

[0087] Figs. 10A and 10B are flowcharts of CN methods that include determining when to transmit a DL NAS message in response to a UL NAS message received from a UE according to some embodiments. These CN methods can be implemented in a suitable CN (e.g., the CN 110, AMF 164, SMF 166, or MME 114 hosted by a CN element 140). The method 1000A begins with the CN receiving 1014 a UL NAS message of a UE from a BS, followed by determining 1040 whether the BS enables a store and forward function. If the BS does not enable the store and forward function (“No” branch of 1040), the CN transmits 1016 a DL NAS message to the BS in response to the UL NAS message. Otherwise (i.e., if the BS enables the store and forward function (“Yes” branch of block 1040), the CN transmits 1047 the DL NAS message to the BS in response to the UL NAS message after the BS disables the store and forward function. In other words, the CN skips transmitting the DL NAS message (as in 421 ) until the BS disables the store and forward function.

[0088] Fig. 10B is a flow diagram of a CN method 1000B similar to the method 1000A, except that method 1000B includes determining 1039 whether the UE operates in a non-serving area instead of the determination 1040 as to whether the BS enables a store and forward function. If the CN determines 1039 that the UE operates in a nonserving area (i.e., “Yes” branch of 1039), the CN performs the transmitting 1016. Otherwise (i.e., “No” branch of 1039), the CN transmits 1048 a DL message to the BS after detecting that the UE no longer operates in the non-serving area. The CN maydetect that the UE no longer operates in the non-serving area based on the distance between the UE and the BS (i.e. , the satellite) forwarding the NAS message (e.g., the distance is shorter than a threshold value). The CN calculates this distance based on UE position information and the ephemeris information of the satellites.

[0089] Figs. 11 A and 11 B are flowcharts of BS methods responding to the feeder link (i.e., the connection between a BS and a CN) being interrupted according to some embodiments. The method 1100A in Fig. 11A begins with the BS communicating 1160 with a CN, followed by the BS determining 1106 that the CN is temporarily unavailable, before receiving 1108 UL data from the UE. When later the BS determines 1112 that the CN is reachable, the BS transmits 1114 the UL data to the CN.

[0090] The method 1100B in Fig. 11 B is similar to the method 1100A except that 1160 and 1106 are omitted and the receiving 1108 of the UL data from the UE is followed by a determination 11 1 as to whether the CN is reachable. If the BS determines that the CN is reachable (i.e., “Yes” branch of 1141 ), the CN transmits 1162 the UL data to the CN. Otherwise (i.e., “No” branch of 1141 ), the method 1100B loops back to 1141 waiting for the CN to become reachable.

[0091] Figs. 12A and 12B are flowcharts of other BS methods according to some embodiment. The methods 1200A and 1200B begin with the BS (e.g., 104) communicating 1254 RRC messages with a UE (e.g., 102) and processing 1256 these RRC messages. The method 1200A illustrated in Fig. 12A continues with the CN receiving 1208 a UL NAS message from the UE, generating 1258 a DL NAS message in response to the UL NAS message, and transmitting 1222 the DL NAS message to the UE in response to the UL NAS message.

[0092] In the method 1200B illustrated in Fig. 12B, after the receiving of the UL NAS message from the UE, the BS determines 1241 whether the CN is reachable. If the CN is indeed reachable (i.e., “Yes” branch of 1241 ), the CN transmits 1214 the UL NAS message to the CN. Otherwise (i.e., “No” branch of 1241 ), the method 1200B continues with 1258 (thus emulating the CN response to the UL NAS message) followed by 1218 as in the method 1200A.

[0093] Fig. 13 is a flowchart of a CN method 1300 according to another embodiment. The method 1300 starts with the CN transmitting 1308 a DL NAS message to a BS via asatellite, followed by starting 1305 a UE-related CN NAS timer with the normal timer value. If at 1395 the UE determines that the UE is out of the satellite coverage (i.e., “Yes” branch), the CN suspends 1360 the UE-related CN NAS timer (i.e., stops the timer without resetting it). If initially or later the CN determines 1395 that the UE is back in the satellite coverage (i.e., “No” branch), the CN resumes 1362 running the UE- related CN NAS timer.

[0094] Fig. 14 is a flowchart of a CN method 1 00 according to an embodiment. The method 1400 begins with the CN transmitting 1416 a DL NAS message to a BS and starting 1405 a CN NAS timer with the normal timer value in response to transmitting the DL NAS message. Upon then determining 1407 that the feeder link (i.e., the connection between the BS and the CN) is interrupted (i.e., “Yes” branch), the CN suspends 1495 the CN NAS timer. Then when later determining 1407 that the connection between the BS and the CN is recovered (i.e., “No” branch), the CN resumes 1498 the CN NAS timer.

[0095] The following description may be applied to the description above.

[0096] 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, the “longer timer value” and the “normal timer value” can be replaced by a first timer value and a second timer value respectively. In some embodiments, the “normal timer value” can be replaced by a “legacy timer value”. In some embodiments, the “function” can be replaced by a “feature”. The “longer timer value” can be replaced by “extended timer value”.

[0097] As used herein, a phrase referring to “at least one of” or “one or more of” a list of items refers to any combination of those items, including single members. For example, “at least one of: a, b, or c” is intended to cover the possibilities of: a only, bonly, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c.

[0098] 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 mediastreaming 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.

[0099] 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.

[0100] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular softwareapplication, 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 wireless communication method (600A) performed by a user equipment, UE, (102) connected to a core network, CN, element (140) via a non-terrestrial network (NTN), the method comprising: transmitting (602) an uplink non-access stratum, NAS, message; determining (603) that a LIE-CN communication outage is likely to occur during a NAS procedure initiated by the uplink NAS message; and extending (604) a time interval for completing the NAS procedure in response to the determining.

2. The wireless communication method of claim 1 , wherein the LIE-CN communication outage is due to an interruption of a feeder link used by UE-CN communications.

3. The wireless communication method of claim 1 or 2, wherein the extending comprises: inputting an extended timer value to a NAS timer, the extended timer value being obtained by adding a predetermined additional value to a normal timer value used when the UE-CN communication outage is not foreseeable, or by multiplying the normal timer value with a predetermined factor larger than 1 with, or suspending the UE NAS timer during the UE-CN communication outage.

4. The wireless communication method of any of claims 1 to 3, wherein the determining comprises at least one of: estimating that the UE-CN communication outage is imminent based on ephemeris information, receiving, from a base station serving the UE, an indication that the CN is unreachable, or detecting that a store and forward function of a base station serving the UE is enabled.

5. A user equipment, UE, (102) comprising a transceiver (156, 154), and a processor (152) configured to perform any one of methods in claims 1-4, using the transceiver.

6. A wireless communication method (800A) performed by a core network, CN, element (140) connected to a user equipment, UE, (102) via a non-terrestrial network (NTN), the method comprising: transmitting (802) a downlink message; determining (803) that a UE-CN communication outage is likely to occur before receiving an uplink non-access stratum, NAS, message triggered by the downlink message; and extending (804) a time interval for receiving the uplink NAS message.

7. The wireless communication method of claim 6, wherein the determining comprises at least one of: determining that a base station intermediating the UE-CN communications has enabled a store and forward function, determining whether the UE is located in a non-serving area, or determining that a feeder link between the CN element and a base station serving the UE is interrupted.

8. The wireless communication method of claim 6 or 7, wherein the extending comprises: starting a CN NAS timer; and suspending the CN NAS timer during the UE-CN communication outage.

9. A wireless communication method (1000A, 1000B) performed by a core network, CN, (110) element connected to a user equipment, UE, (102) via a nonterrestrial network (NTN), the method comprising: receiving (1014), from the UE, an uplink non-access stratum, NAS, message;determining (1039, 1040) whether a CN-LIE communication is temporarily interrupted; and transmitting (1047, 1048) a downlink NAS message responding to the uplink NAS message with a delay when the CN-UE communication is temporarily interrupted according to the determining.

10. The wireless communication method of claim 9, wherein the determining comprises at least one of: determining (1040) whether a base station serving the UE has enabled a store and forward function, or determining (1039) whether the UE operates in a non-serving area.

11. A wireless communication method (1100A, 1100B) performed by a base station, BS, (104) intermediating communications between a core network, CN, element (140) and a user equipment, UE, (102) via a non-terrestrial network (NTN), the method comprising: receiving (1108), from the UE, a message for the CN element; determining (1106) that the CN element is temporarily unreachable; and forwarding (1114) the message received from the UE to the CN element when the CN element is reachable.

12. The wireless communication method of claim 11 , wherein the message includes uplink data, and the method further comprises: storing the uplink data until the CN element is reachable.

13. The wireless communication method of claim 11 , wherein the message is an uplink non-access stratum, NAS, message, and the method further comprises: transmitting, to the UE, a downlink NAS message responding to the message.

14. The wireless communication method of claim 13, wherein the forwarding comprises:transmitting, to the CN element, an indication that the BS has responded to the message.

15. A network device (104, 140) comprising a transceiver (136, 134, 146, 144) able to communicate with another network device via a non-terrestrial network (NTN), and a processor (132, 142) configured to perform any one of methods in claims 6-14, using the transceiver.

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