Methods and devices for feeder link unavailability management

Abstract

Methods and devices embody feeder link unavailability (FLU) management techniques. Before the FLU starts, a network entity (162) transmits (404) FLU assistance information to the UE (102) via a node (104) on a satellite. The FLU assistance information includes FLU timing information and indicates whether the satellite reconnects with the same network entity after the FLU. The radio access network's potential signaling congestion before and after the FLU may be avoided by applying random delays (511) within a maximum time offset received (508) from the network entity, to the FLU-related signaling.

Description

PATENT APPLICATION Attorney Docket No.: 0683-089-WO METHODS AND DEVICES FOR FEEDER LINK UNAVAILABILITY MANAGEMENT FIELD 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 3rd Generation Partnership Project (3GPP) technical specifications (TSs), for example, in the Long Term Evolution (LTE), Fifth Generation (5G), or future 6G communication systems. More particularly, the methods and devices employ techniques for handling feeder link unavailability when at least a part of the radio access network (RAN) node is on a satellite and thus, the service link may remain available. BACKGROUND

[0002] This background description is provided for the purpose of generally presenting the context of the embodiments described later in this document. 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 embodiments of feeder link management techniques described in this document.

[0003] In a non-terrestrial network (NTN), a satellite (i.e., as a drone, balloon, plane, or another suitable apparatus) facilitates the communication between a core network (CN) and users (e.g., a user equipment, (UE)) via a RAN node (also called base station). Portions of a distributed base station or the entire base station may be on the satellite (called collectively RAN-Sat) or in a ground station (which includes a terrestrial satellite-gateway and is connected to or includes a CN entity). The NTN includes feeder links between satellites and ground stations and service links between satellites and user equipment (UE).

[0004] A satellite can belong to one of several types based on altitude, orbit, beam footprint size and movement. When the satellite is not geostationary, its ground coverage area (also called footprint) changes in time. This change may cause disruption of the service link to the UE and / or the feeder link to the ground station thus interruptingPATENT APPLICATION Attorney Docket No.: 0683-089-WO a UE’s communication with the core network (CN). When the feeder link is unavailable while the service link is available, the (portion of) RAN node on the satellite may store mobile originated (MO) data received from the UE over available service link, and later forward the stored MO data to the ground station when the feeder link becomes available again. Some (but not all) (portions of) RAN nodes on the satellite have such a store and forward (S&F) capability. Note that in this document “RAN” may be used instead of “RAN node,” and “RAN-Sat” is used for a RAN node or a portion of a RAN node located on a satellite.

[0005] Conventionally, there is no mechanism to make the UE aware of an upcoming feeder link unavailability (FLU) although the UE is still within the satellite coverage (i.e., the service link is still available and usable), thus, still having an operational service link. The UE’s behavior may be enhanced based on information about the FLU. SUMMARY

[0006] In some embodiments, upon determining that a feeder link employed in the communication via satellite with a UE becomes unavailable, a CN entity (i.e., a wireless communication device hosting a CN function or module, such as, an Access and Mobility Management Function) transmits FLU assistance information towards the UE. The FLU assistance information may include (i) a FLU start time and (ii) a FLU duration or an FLU end time. Alternatively or additionally, the FLU assistance information may include an FLU indication, which indicates, to the UE, an imminent FLU and enables the UE to use default values for the FLU start time and / or the FLU duration if individually- predicted values are not known. The CN entity may also include a configuration update indication when predicting that the satellite will communicate with the CN entity via a feeder link to a different ground station after the FLU ends. The CN entity may determine that the UE has to connect to another ground station after the FLU ends based on (A) a tracking area identity (TAI) list received from the RAN-Sat, or (B) based on (i) local configuration (i.e., satellite’s current and foreseeable location, UE’s location) or (ii) operation and management (O&M) information.PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0007] In order to save power, the UE may switch to a CM-idle state (here CM stands for connection management) or use another power saving technique for at least part of the FLU duration. A RAN node at least partially located on the satellite (a) releases or suspends a first transport network level (TNL) association with an initial ground station before the FLU starts and (b) connects or resumes a second TNL association with a second ground (which may be the initial ground station or another ground station) after the FLU ends. The UE and the CN may be configured to handle a FLU type of unavailability period different from other discontinuous coverage type of unavailability period (e.g. the UE’s moving into discontinuous coverage of a satellite using transparent payload).

[0008] In one embodiment, the CN entity provides CN assistance information using a non-UE specific N2 message to enable a RAN-Sat to adequately handle an upcoming FLU. Based on the CN assistance information, which includes a maximum offset time, the RAN-Sat prepares the UEs connected via the RAN-Sat for the upcoming FLU, using radio resource control (RRC) signaling transmitted with random delays within the maximum offset time, respectively. In another embodiment, upon receiving a UE- specific N2 message including the CN assistance information (e.g., a maximum offset time), the RAN-Sat applies a random delay within the UE-specific maximum offset time before disconnecting the UE and / or transmits the UE-specific maximum offset time. The UE then applies a random delay within UE-specific maximum offset time before stopping the communication via satellite and / or restarting the communication via satellite after the FLU ends. The CN may transmit the FLU assistance information and the UE-specific maximum offset time simultaneously.

[0009] In some other embodiments, the UE requests FLU assistance information from the CN entity (e.g., sends an FLU assistance request). The UE may ask for guidance regarding whether the UE connects to another CN entity after the FLU period. Features similar to the ones described above for the case when the UE does not request FLU assistance information are pertinent for embodiments when the UE sends the FLU assistance request.PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0010] In yet other embodiments, the RAN node broadcasts FLU assistance information using a system information block (SIB), which may be a new SIB or an adjustment to an existing SIB, such as a modified SIB 19 (e.g., including the FLU assistance information in modified parts). The RAN node may also indicate in this SIB whether it provides S&F operation mode. The UE may request guidance upon receiving such an SIB and may adjust its behavior during the FLU period according to the indicated operation mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments of FLU-related techniques and, together with the description, explain these embodiments.

[0012] Fig.1 is a block diagram of a wireless communication system in which a user device, a RAN, and a CN entity associated with an NTN perform FLU-related techniques according to various embodiments.

[0013] Fig.2A is a block diagram of a distributed base station.

[0014] Fig.2B is a block diagram of an example protocol stack usable by a UE to communicate with a CU and a DU of a distributed base station.

[0015] Fig.3A is a block diagram of an example NTN node on a satellite with both a service link between the satellite and the UE, and feeder link between the satellite and the ground station, available to support the normal operation with both links operational.

[0016] Fig.3B is a block diagram of example NTN nodes on satellites with only a service link between the first satellite and a UE and with only a feeder link between the second satellite and a ground station.

[0017] Fig.4 is a signal diagram illustrating FLU management according to an embodiment in which the CN entity hosting the initial AMF provides FLU assistance information to the UE via the RAN serving the UE.

[0018] Fig.5 is a signal diagram illustrating FLU management according to an embodiment in which the CN entity hosting the initial AMF provides a maximum offset time to the RAN.PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0019] Fig.6 is a signal diagram illustrating FLU management techniques according to an embodiment in which the CN entity hosting the initial AMF provides simultaneously the FLU assistance information and the maximum offset time to the UE.

[0020] Fig.7 is a signal diagram illustrating FLU management techniques to an embodiment in which the UE sends a FLU assistance request to the CN.

[0021] Fig.8 is a signal diagram illustrating FLU management techniques according to an embodiment in which the UE sends the FLU assistance request and the CN entity hosting the initial AMF provides a maximum offset time to the RAN-Sat.

[0022] Fig.9 a signal diagram illustrating FLU management techniques according to an embodiment, in which the UE sends a FLU assistance request, and the RAN-Sat forwards simultaneously the FLU assistance information and the maximum time offset to the UE.

[0023] Fig.10 is a flowchart of a wireless communication method performed by a CN entity according to an embodiment.

[0024] Fig.11 is a flowchart of a wireless communication method performed by a UE according to an embodiment.

[0025] Fig.12 is a flowchart of a wireless communication method performed by a RAN node according to an embodiment.PATENT APPLICATION Attorney Docket No.: 0683-089-WO DETAILED DESCRIPTION OF THE DRAWINGS

[0026] Methods and devices described in this section embody FLU management techniques. A part of a RAN node or the entire RAN may be on the satellite which is then called RAN-Sat. These FLU management techniques impact the UEs and the RANs. After the FLU concludes, the feeder link may change from one ground station to another ground station. A core network (CN) entity anticipating an upcoming FLU transmits FLU assistance information to one or more UEs affected by the FLU. The FLU assistance information may specify various quantities and features relevant to a FLU, such as (but not limited to) the FLU start time and the FLU duration or the FLU end time, and one or more indications. The RAN node forwards the FLU assistance information received from the CN entity to the UE(s). The RAN node may broadcast the FLU assistance information (e.g., using a system information block, SIB) or may forward the FLU assistance information individually to the UE(s) optionally with random delays within a maximum offset time.

[0027] Prior to discussing various embodiments, Fig.1 illustrates a wireless communication system 100 including UE 102, a RAN node 104 (also called RAN-Sat when it is located on satellite 103) and a CN entity 140 hosting one or more CN 110’s functions and / or modules. In some embodiments, one or more functions and / or modules of the CN 110 may also be hosted by a physical device (not shown) on the satellite 103 and use the feeder link (FL) between the satellite 103 and the ground station 107 to communicate with the functions and / or modules of the CN 110 hosted by the CN entity 140, which is on the ground. The UE 102, the RAN 104 and the CN entity 140 are configured to perform FLU management techniques according to various embodiments. The CN 110 may include an evolved packet core (EPC) 111 and / or a fifth generation (5G) core (5GC) 160. Additionally or alternatively, the CN 110 may include a sixth generation (6G) core.

[0028] The RAN 104 is located on satellite 103 covers (i.e., serves UEs located within) a cell 124 and a cell 125, while the RAN 106 covers a cell 126. The cells 124 and 125 may correspond to different satellites but share the same cell identifier. If the RAN 104 is a gNB (i.e., a Next Generation Node B, which is a RAN that supports thePATENT APPLICATION Attorney Docket No.: 0683-089-WO 5G New Radio (NR) radio access technology), then the cells 124 and 125 are NR cells. If the RAN 104 is an eNB (i.e., an evolved NodeB, sometimes abbreviated eNodeB, that is a RAN that manages radio resources and mobility in a cell and sector for LTE) or an ng-eNB (i.e., an enhanced 4G eNodeB that connects to a 5G CN), the cells 124 and 125 are evolved universal terrestrial radio access (E-UTRA) cells. Similarly, if the RAN 106 is a gNB, the cell 126 is an NR cell, and if the RAN 106 is an ng-eNB or eNB, the cell 126 is an E-UTRA cell. The cells 124, 125, 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 RANs (such as 104 and 106), and each of the RANs can cover one, two, three, or any other suitable number of cells. The UE 102 supports a 5G NR (or simply, “NR”) interface and / or an E-UTRA air interface to communicate with the RAN 104 and / or 106.

[0029] Among other components, the EPC 111 can include a Mobility Management Entity (MME) 112, a Serving Gateway (SGW) 114, and a Packet Data Network Gateway (PGW) 116. The MME 112 is configured to manage authentication, registration, paging, and other related functions. The SGW 114 is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc. 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 EPC modules and other functions are described in the 3GPP TSs.

[0030] The 5GC 160 includes an Access and Mobility Management Function (AMF) 162, a Session Management Function (SMF) 164, and a User Plane Function (UPF) 166. The AMF 162 is configured to manage authentication, registration, paging, and other related functions. The SMF 166 is configured to manage PDU sessions. The UPF 162 is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc. The 5GC functions are described in the 3GPP TSs.

[0031] The CN 110 is hosted on one or more physical devices such as the CN entity 140. A CN entity hosts at least one CN function or module. The CN entity includes a processor 142 controlling a receiver 144 and a transmitter 146 (or a transceiver) enabling the CN entity to perform the FLU management methods described below.PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0032] The RAN 104 is equipped with processing hardware 130 that includes one or more general-purpose processors and / or special-purpose processing units such as processor 132. Processor 132 is configured to prepare data that the RAN 104 transmits to the UE 102, to the CN 110, and / or to other RANs (e.g., the RAN 106), and to process data that the RAN 104 receives from the UE 102, the CN 110, and / or to other RANs (e.g., the RAN 106). The processing hardware 130 includes a receiver 134 configured to receive data and a transmitter 136 configured to transmit the data (or a transceiver, not shown, configured to both transmit and receive data). The RAN typically also includes a memory (i.e., computer readable recording medium, not shown) non- transitorily storing executable codes that make the processor 132 controlling the receiver 134 and the transmitter 136 (or a transceiver) to perform the methods related to managing FLU described below. The RAN 106 can include generally similar components (not shown for the sake of simplicity). The RAN 104 may be connected to the MME 112 via an S1 interface, to the AMF 162 via an N2 interface and to the RAN 106 via n X2 or Xn interface. More generally (as illustrated for RAN 106), a RAN may be connected to the CN 110 using an S1 or NG interface. The RANs 104 and 106 also can be interconnected via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes. These interfaces are described in the 3GPP TSs.

[0033] The UE 102 is equipped with processing hardware 150 that includes one or more general-purpose processors and / or special-purpose processing units such as processor 152. The processing hardware 150 also includes a receiver 154 configured to receive data and a transmitter 156 configured to transmit data (or a transceiver configured to both transmit and receive data) via, for example, the RAN 104. The processing hardware 150 typically includes a memory (not shown) that stores executable codes for the processor 152 controlling the receiver 154 and the transmitter 156 (or the transceiver) to perform the methods related to managing FLU described below.

[0034] The RAN 105 supports Integrated Access and Backhaul (IAB) functionality and Non-Terrestrial Network (NTN) functionality interconnecting a ground station 107 and satellite 103.PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0035] The RAN 104 may be a distributed base station as the RAN 270 illustrated in Fig.2A. The distributed RAN 270 includes a central unit (CU) 272 and one or more distributed units (DUs) 274. Similar to processing hardware 130, the CU 272 includes one or more processors and a computer-readable memory storing machine-readable instructions executable on the processor(s). Functionally, the CU 272 may include a packet data convergence protocol (PDCP) controller and an RRC controller as illustrated and discussed below based on Fig.2B. In some implementations, the CU 272 can include a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures. The CU 272 may include one or more CU- CP(s) 272A specialized in managing the control plane traffic and one or more CU-UP(s) 272B specialized in managing user plane traffic.

[0036] Similar to processing hardware 130, each of the DUs 274 also includes one or more processors computer-readable memory storing machine-readable instructions executable on the one or more processors. Functionally, the DU may include a Medium Access Control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure), an RLC controller configured to manage or control one or more RLC operations or procedures, and / or a physical layer controller configured to manage or control one or more physical layer operations or procedures as illustrated and discussed below based on Fig.2B.

[0037] As already mentioned, the CU 272 can include a logical node CU-CP 272A that hosts the control plane part of the PDCP protocol of the CU 272 and a logical node CU-UP 272B that hosts the user plane part of the PDCP protocol and / or Service Data Adaptation Protocol (SDAP) protocol of the CU 272. The CU-CP 272A transmits control information (e.g., RRC messages, F1 application protocol messages), and the CU-UP 272B transmits the data packets (e.g., SDAP PDUs or Internet Protocol packets). The CU-CP 272A is typically connected to multiple CU-UP 272B through an E1 interface. The CU-CP 272A selects the appropriate CU-UP 272B for the requested services for the UE 102. A single CU-UP 272B may connect to multiple CU-CP 272A through the E1 interface. The CU-CP 272A may connect to one or more DU 274s through an F1-C or W1-C (corresponding to 5G and LTE, respectively) interface. The CU-UP 272B canPATENT APPLICATION Attorney Docket No.: 0683-089-WO connect to one or more DU 274 through F1-U or W1-U interfaces under the control of the same CU-CP 272A. In some implementations, one DU 274 can connect to multiple CU-UP 272B under the control of the same CU-CP 272A. In such implementations, the connectivity between the CU-UP 272B and the DU 274 is established by the CU-CP 272A using Bearer Context Management functions. The interfaces E1, F1, and W1 are described in 3GPP technical specifications. From the NTN perspective, the CU may be part of the ground station (e.g., 107) while the DU may be mounted on a satellite (e.g., 103).

[0038] Fig.2B illustrates, in a simplified manner, an example protocol stack according to which a UE (e.g., UE 102) can communicate with a DU (e.g., DU 274) and a CU (e.g., CU 172). This protocol stack includes a physical layer (PHY) 202, which provides transport channels to a MAC sublayer 204, which in turn provides logical channels to the RLC sublayer 206. The RLC sublayer 206 in turn provides RLC channels to a PDCP sublayer 210. The PDCP sublayer 210 in turn can provide data transfer services to Service Data Adaptation Protocol (SDAP) 212 or a radio resource control (RRC) sublayer (not shown). The UE 102, in some implementations, supports both the EUTRA and the NR stack, to support handover between EUTRA and NR RANs and / or to support DC over EUTRA and NR interfaces. The UE 102 can support layering of NR PDCP over EUTRA RLC, and SDAP sublayer 212 over the NR PDCP sublayer 210. The PDCP sublayer 208 receives packets (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the PDCP layer) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer) that can be referred to as protocol data units (PDUs). On a control plane, the PDCP sublayer 208 can provide signaling radio bearers (SRBs) or RRC sublayer to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the PDCP sublayer can provide Data Radio Bearers (DRBs) to support data exchange such as SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0039] The CU 272 provides the control and upper layer functionalities (e.g., RRC 214, SDAP 212, PDCP 210), while the lower layer operations (e.g., RLC 206, MAC 204,PATENT APPLICATION Attorney Docket No.: 0683-089-WO and PHY 202) are delegated to the DU 274. Thus the CU and DU may incorporate respective layer or sublayer controllers.

[0040] Figs.3A and 3B illustrate RANs (104, 104A, 104B) located on satellites (103, 103A, and 103B, respectively). The RANs may be base stations or base station components (e.g., a DU that can connect to a CU integrated in the ground station). The UE 102’s access to a RAN on the satellite may operate in the normal / default satellite operation mode when both service link and feeder link are available (as in Fig.3A) and in a Store and Forward (S&F) satellite operation mode when only service link is available as illustrated in Fig.3B. In addition, the RAN-Sat (104, 104A, 104B) may connect to the one or more CN 110’s functions and / or modules in different network entities (141, 143). For example, the RAN-Sat 104A may connect to the functions and / or modules 112 / 162 of CN 110 hosted by a ground CN entity 140 or to similar AMF or MME hosted by a network entity (NE) 141 located on satellite 103A or an NE 143 located on satellite 103B. Note that, as suggested in Fig.3B, a satellite 103A with RAN node 104A and CN entity 141 on board without available feeder link may communicate with one or more other satellite 103B over one or more inter-satellite links (ISL), the satellite 103B being out of the range for providing service link to the UE. In some scenarios as shown in FIG.3B, none of satellites 103A and 103B has an operative feeder link to the ground station 107 and, thus, they cannot forward communication traffic to the CN entity 140 on the ground. In other scenarios, when the service link between the RAN-Sat 104A and the UE is available but the feeder link from the satellite 103A to the ground is unavailable, the communication traffic is forwarded via the ISL to the satellite 103B and later the satellite 103B’s reestablishes a feeder link to the ground station 107. The presence of another RAN 104B in this scenario is not required (i.e., satellite 103B may be operated with transparent payload).

[0041] Note that, although the methods discussed below operate in 5G system, equivalent embodiments can be implemented in LTE, 6G, or other similar systems. Additionally, the description mostly refers to a RAN or portion of RAN or portion of CN entity or a whole EPC / 5GC located on the satellite (RAN-Sat) corresponding to a regenerative payload architecture, but some of the FLU management techniques applyPATENT APPLICATION Attorney Docket No.: 0683-089-WO also scenarios in which the RAN is on the ground (i.e., to a transparent payload architecture).

[0042] Figs.4-6 are signal diagram illustrating FLU management techniques initiated by a CN entity such as 140 (i.e., a network-initiated provision of FLU assistance information) and Figs.7-9 are signal diagram illustrating FLU management techniques initiated by a UE. In the scenarios illustrated in these signal diagrams, the RAN serving the UE is on the satellite and they are represented by a single entity RAN-Sat 104. Further, after the FLU, the RAN-Sat 104 may connect to another ground station, another cell, and another CN entity. For simplicity and in order to illustrate functionality (not physical location or distinction), the ground station providing satellite gateway functionality and the CN entity hosting the AMF (which may be collocated or a single device or two physically distinct connected devices) are represented by the AMF. That is, in Fig.4-9, the initial AMF 162 represents the initial ground station and CN entity providing satellite gateway and AMF functionality before the FLU, and the target AMF 163 represents the target ground station and a second CN entity providing satellite gateway and AMF functionality after the FLU. If the ground station does not change, then the initial AMF 162 and the target AMF 163 are the same functional entity.

[0043] The FLU assistance information includes one or more of the following: (A) a FLU indication (explicit or implicit indication that the feeder link is or will become unavailable), (B) a FLU start time (which might default to “immediately”), (C) a FLU end time or a FLU duration (which might have a default timer value), (D) an unavailability type (e.g., an FLU or discontinuous coverage with a service link disruption regardless of whether the feeder link is also unavailable), (E) satellite ephemeris data and ground station location (so that UE can assess the type of feeder link unavailability), (F) an S&F support indication (when the RAN-Sat supports store and forward operation mode), (G) an S&F activation indication (when the RAN-Sat has the S&F activated during a feeder link disruption), and / or (H) a configuration update indication (to trigger a UE registration procedure for an AMF update after the satellite service link and / or feeder link become available).PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0044] The UE may receive the FLU assistance information via a configuration update command (CUC) message (as illustrated in Figs.4-6), or via a registration accept message (as illustrated in Figs.7-9), or via a system information block (SIB) that the RAN broadcasts in the FLU-affected area. Upon receiving the FLU assistance information, a UE applies a configuration update and might apply various methods to reduce power consumption while its feeder link (and / or service link) is (are) unavailable. One of these techniques (illustrated in the figures) is to switch to the CM-idle state for the FLU duration measured using an FLU timer. This configuration update may depend on the UE’s permissions and / or capabilities and whether the RAN-Sat has indicated S&F capabilities or S&F activation. For example, the configuration update may set new extended DRX (eDRX) parameters and timers. Also, a UE may perform a registration update after the feeder link recovers and a CN entity hosting the AMF changes (e.g., a separate target AMF, a new Tracking Area Identity (TAI)). Prior to the FLU or after the FLU ends, random delays of FLU-related messages to / from served UEs or individual UEs reduce signaling overload on the RAN.

[0045] Fig.4 illustrates that the CN entity executing an AMF provides FLU assistance information to the UE via a RAN on a satellite. In Fig.5, the CN entity also provides a maximum offset time to the RAN. In Fig.6, the CN entity provides a UE-specific maximum offset time. These techniques start from the premise of the CN entity detecting an upcoming FLU while the UE is still in the NTN coverage (i.e., both the feeder link and the service link are operational). The FLU may be due to RAN-Sat mobility. Some of these techniques also can be applied when the feeder link remains available, but the UE is out of NTN coverage (i.e., the service link becomes unavailable), in a scenario known as discontinuous coverage. Similar techniques may be applied when both the service link and the feeder link become unavailable. In these signal diagrams, the UE does not use communication via RAN-Sat operated in S&F operation mode during a FLU period (i.e., an assumption for highlighting the FLU- related techniques). For example, when the RAN-Sat does not support S&F operation, or the UE is not allowed to use FLU-compatible services such as short message service (SMS), cellular Internet of Things (CIoT), delay tolerant services via RAN-Sat for storePATENT APPLICATION Attorney Docket No.: 0683-089-WO and forward during FLU, the UE may initiate a power saving mechanism (e.g., enters CM-idle state) and starts an FLU timer to maintain the CM-idle state during FLU.

[0046] Fig.4 illustrates UE, RAN-Sat, and CN entity behavior in a FLU scenario. According to this embodiment the CN (i.e., the initial AMF) provides FLU assistance information to the UE via the RAN serving the UE.

[0047] At 402, the initial AMF 162 determines (1) that FLU is about to happen and (2) whether the UE 102 needs to perform mobility registration update due to the change of the CN entity (and AMF) after reconnecting via another feeder link (i.e., another ground station). The AMF 162 determines item that FLU is about to happen (i.e., (1) above) based on the local configuration information (e.g., satellite’s current and foreseeable location, UE’s location), the ephemeris data from (a) operations and maintenance (i.e., O&M, as defined in 3GPP TSs), and / or (b) FLU information received from the RAN-Sat 104. The initial AMF 162 determines whether the UE changes the AMF after FLU ends (i.e., (2) above) based on: a new TAI list after FLU received, for example, in an N2 message from the RAN-Sat 104, and / or based on the local configuration (e.g., satellite’s current and foreseeable location, UE’s location) or the O&M. Note that N2 is a control plane interface between a 5G RAN and the 5GC as illustrated in Fig.1.

[0048] Upon determining that the feeder link is going to become unavailable, the initial AMF 162 then triggers 404 UE configuration update procedures to the impacted UEs (only UE 102 illustrated) by sending configuration update command (CUC) messages via respective RANs (only RAN-Sat 104 shown). The UE configuration update procedure configures the recipient UE for handling UE‘s state (such as a power saving state) during the FLU. The CUC message includes FLU assistance information and / or may include a configuration update indication. When the CUC message includes the configuration update indication, the UE performs a mobility registration update (MRU) after the FLU ends. When the CUC message does not include the configuration update indication, the UE reconnects to the initial AMF after the FLU ends (i.e., the target AMF is the same functional entity as the initial AMF).

[0049] In one embodiment, the UE receives 404 the FLU assistance information as a newly defined information element (IE) including FLU duration, and / or FLU start time. InPATENT APPLICATION Attorney Docket No.: 0683-089-WO another embodiment, the UE receives the FLU assistance information included in another newly defined IE conveying an FLU indication that signals to the UE that FLU is imminent and making the UE to apply a default value (depending on the implementation) of the FLU duration, which starts immediately. According to yet another embodiment, if both the UE and network indicate support of the unavailability period mechanism, the FLU assistance information includes an unavailability period duration corresponding to the feeder link unavailability period duration and / or start of the unavailability period corresponding to the start time of the FLU.

[0050] When determining that a change of AMF is needed after the FLU (e.g., due to service area change), the initial AMF 162 includes a configuration update indication in the CUC message to direct the UE 102 to perform an MRU procedure after FLU ends (e.g., the FLU timer tolling the FLU duration expires). When determining that no change of AMF is needed after the FLU, the initial AMF 162 does not include the configuration update indication in the CUC message to the UE 102.

[0051] In response to the CUC message, the UE 102 sends 406 a configuration update completed message to the initial AMF 162 via the RAN-Sat 104. In an optional step 408, the initial AMF 162 may send an N2 message to notify the RAN-Sat 104 that the 5GC functions completed preparations for the feeder link switchover for the UE 102.

[0052] Then, at step 410A, the UE 102 stores the FLU assistance information, and uses it (for example, to learn when the FLU starts), and (B) optionally enters a power saving mode (e.g., a CM-idle state with CM standing for connection management, which reflects the states for NAS signaling connections between the UE and an AMF) based on the local UE configuration or on detecting an RRC disconnection from the RAN-Sat 104. Alternatively, the UE 102 may send a deregistration request to the network (i.e., to the initial AMF 162 via the RAN-Sat 104). Further, at 410C, the UE 102 starts an FLU timer to toll the FLU duration (that is, the FLU timer expires at the end of the FLU duration). For example, a UE that does not operate in S&F mode starts the FLU timer and enters in a CM-idle state.

[0053] In step 412, the RAN-Sat 104, the initial AMF 162 and a target AMF 163 (when hosted by a CN entity other than the initial AMF 162) perform feeder linkPATENT APPLICATION Attorney Docket No.: 0683-089-WO management as follows. When FLU starts, the RAN-Sat 104 and the initial AMF 162 release or suspend an N2 connection with a first transport network layer (TNL) association. After the FLU ends, the RAN-Sat 104 may resume N2 connection with the second TNL association to the initial AMF 162 or may connect to a different target AMF 163.

[0054] In Fig.4, steps 414, 416, and 418 are optional (as suggested by using dashed line) and correspond to a scenario in which, after the FLU, the UE 102 uses a feeder link to a target AMF 163 other than the initial AMF 162. The UE 102 sends 414 a registration request according to one of the following options. According to Option 1 (which does not correspond to the scenario illustrated in Fig.4), when the UE has not received the configuration update indication in step 404, the UE 102 sends a service request (SR) message for returning from CM-idle state to CM-connected state, to the initial AMF or to the target AMF. According to Option 2, when the UE has received the configuration update indication in step 404, the UE 102 sends a registration request message (as defined in the 3GPP TSs) to initiate an MRU to the target AMF after returning from CM-idle state to CM-connected state. The UE 102 sends this registration request message after FLU ends (e.g., the FLU timer expires) and, optionally, also after a random time interval (that can be measured by the same FLU timer or another timer) based on the local UE configuration. According to Option 3, the UE 102 sends an initial registration request message to the RAN-Sat 104 if the UE has deregistered during FLU. The RAN-Sat 104 then selects the initial AMF or the target AMF and forwards the registration request to the selected AMF.

[0055] The step 416 covers registration procedure steps for UE authentication, identification, subscription information retrieval, and updating UE context for various 5GC functions as described, for example, in 3GPP TS 23.502. During these steps, the target AMF 163 retrieves the UE context from the initial AMF 162 (e.g., the initial AMF 162 responds with an Namf_Communication_UEContextTransfer response message to an Namf_Communication_UEContextTransfer request message received from the target AMF 163, the Namf_Communication_UEContextTransfer messages being described in the 3GPP TSs). The registration procedure employs other CN functionsPATENT APPLICATION Attorney Docket No.: 0683-089-WO such as the policy and control function (PCF), the unified data management (UDM), and the authentication server function (AUSF) as described in the 3GPP TSs.

[0056] In step 418, the target AMF 163 sends a registration accept message to the UE 102 concluding the registration procedure initiated at the step 414.

[0057] The UE 102 then initiates 420 a service request procedure (e.g., as described in the 3GPP TSs) to re-establish one or more PDU sessions for the UE returning from the CM-idle state or initiates a PDU Session establishment procedure to request a new service after registering in steps 414-418.

[0058] Current 3GPP TS 23.501 describes support for unavailability period by a UE and the network (AMF) due to satellite access discontinuous coverage. According to the following embodiments, this existing unavailability period mechanism is improved to support FLU. In some embodiments, when the unavailability period is caused by the FLU, the unavailability period duration includes N2 interface disconnection / suspension with a first AMF via a first feeder link, and N2 interface reconnection / resume with a second AMF via a second feeder link. Here, the first and the second AMF may be the same AMF (i.e., the initial AMF and the target AMF are the same functional entities) or different AMFs (e.g., the initial AMF and the target AMF are different functional entities). Thus, a UE that supports the unavailability period feature carries specific procedures before and after the FLU.

[0059] When both the UE and the network indicate support of unavailability period mechanism due to discontinuous coverage and / or FLU, the AMF determines the UP- related parameters as follows: (1) the unavailability period duration is set based on the FLU duration if known, (2) the start of the unavailability period is set based on the start time of the FLU if known; and (3) the unavailability type indicates discontinuous coverage or FLU as appropriate and allowed (depending on UE and network capabilities to differentiate). In one embodiment (Option 1), the unavailability type for FLU is a new unavailability type different from the discontinuous coverage unavailability type. In another embodiment (Option 2), the unavailability type for FLU is the same as the discontinuous coverage type (i.e., feeder link unavailability is intentionally combined with service link unavailability). Note that in contrast to the FLU, the service link isPATENT APPLICATION Attorney Docket No.: 0683-089-WO definitely unavailable in case of discontinuous coverage. In case of a transparent payload architecture, either the service link or the feeder link being unavailable has same effect, the situation being adequately indicated as discontinuous coverage.

[0060] When the service link is available, the unavailability type may be indicated as a FLU unavailability type or as a discontinuous coverage unavailability type. In one embodiment, when the AMF provides only a unavailability period duration and the service link is available, the UE applies the FLU duration immediately or after a short default start time interval. In another embodiment, when the AMF provides only a unavailability period start time for the FLU and the service link is available, the UE applies a default FLU duration based on the UE implementation, the local configuration, or information received in a system information block (SIB) prior to the start time. In yet another embodiment, when the AMF provides only an Unavailability Type and the service link is available, the UE applies a FLU duration based on the UE implementation, the local configuration, or SIB information received before the FLU start time. In a UE implementation, the UE applies the FLU duration immediately or after a short default start time.

[0061] When the unavailability of the service link and unavailability of the feeder link overlap, the FLU may be indicated using a discontinuous coverage unavailability type or an FLU unavailability type. In this case (i.e., the unavailability of the service link and of the feeder link overlap), (A) the unavailability period start time may be selected to be the earlier of the unavailability period start time for discontinuous coverage and the unavailability period start time for the FLU, and (B) the unavailability period duration may be selected so that its end time is the latest between the unavailability period end time corresponding to the discontinuous coverage and the unavailability period end time corresponding to the FLU. Here, the UE calculates the unavailability period end times as sums of the respective unavailability period start times and unavailability period durations.

[0062] Fig.5 is a signal diagram illustrating techniques related to FLU according to an embodiment in which the CN entity executing the initial AMF provides FLU assistance information and a maximum offset time to the UE. The description of stepsPATENT APPLICATION Attorney Docket No.: 0683-089-WO 402-406 and 410-420 is omitted these steps being previously described above relative to Fig.4. In the signal diagram of Fig 5, the initial AMF 162 provides 508 a maximum offset time to the RAN. The maximum offset time may be a UE-specific maximum offset time or a FLU-related (non-UE-specific) maximum offset time. This CN assistance information (e.g., the maximum offset time) improves the FLU-related RRC signaling by implementing RAN’s overload control in a UE-specific manner at RRC level in the former case (i.e., using the UE-specific maximum offset time) described below, or in a non-UE specific manner at RRC level in the latter case (i.e., using the FLU-related specific maximum offset time).

[0063] Thus, when, in step 508, the initial AMF 162 sends an N2 message including a UE-specific maximum offset time to the RAN-Sat 104, the UE-specific maximum offset time refers to a specific RAN-served UE (in this case, the UE 102). Then, in step 511, the RAN-Sat 104 (1) determines a random timer value within the UE-specific maximum offset time for the UE and (2) disconnects the UE’s RRC connection when the random timer value expires. Alternatively, the RAN-Sat 104 instructs the UE 102 to enter RRC_Inactive state when the random timer value expires.

[0064] When the initial AMF 162 sends 508 a non-UE specific N2 message including a FLU-related maximum offset time to RAN-Sat, the FLU-related maximum offset time applied to all UEs currently served via the feeder link that becomes unavailable. Then, at 511, the RAN determines a random timer value within the FLU-related maximum offset time for each of the UEs and disconnects a UE’s RRC connection when the respective UE’s random timer value expires. Alternatively, the RAN-Sat 104 instructs a served UE (such as, UE 102) to enter in an RRC_Inactive state when the UE’s random timer value expires. Additionally, after FLU ends, the UE may send the registration request (e.g., step 414) after the UE’s random timer value expires.

[0065] Fig.6 is a signal diagram illustrating techniques related to FLU according to an embodiment in which the CN entity executing an AMF provides FLU assistance information and a maximum offset time to the UE via the CUC command message. The description of steps 402,406, 408, 412, 414, and 416-420 is omitted, these steps being previously described above relative to Fig.4.PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0066] In step 604, upon determining that a change of the AMF is needed after FLU, the initial AMF 162 includes a maximum offset time besides the FLU assistance information in the CUC message to the UE. Upon receiving the maximum offset time in the CUC message, in step 609, the UE 102 determines a random timer value within the maximum offset time, and (2) in anticipation to entering the CM-idle state (or other power saving mechanism), requests an RRC disconnection or sends a deregistration request message to the RAN-Sat 104 when the random timer value expires. Step 614 is similar to step 414, but the UE 102 initiates a registration request procedure for mobility registration update after the FLU ends and the random timer value expires.

[0067] Fig.7 is a signal diagram illustrating techniques related to FLU according to an embodiment in which the UE sends a FLU assistance request upon receiving an SIB including FLU information. The RAN-Sat 104 broadcasts 722 a SIB indicating an upcoming FLU based on ephemeris data locally configured at the RAN-Sat or on O&M. Note that the SIB is not UE-specific. The UE 102 then calculates 724 that FLU is about to happen based on the information in the SIB and potentially other variables such as the UE location, and requests 726 FLU assistance from the initial AMF 162.

[0068] The SIB information may indicate an FLU area range using ephemeris information (e.g., as described in 3GPP TS 38.331). In this case, the UE calculates FLU duration and / or FLU start time based on its location within the FLU area range. Alternatively, the SIB information specifies the FLU duration and / or start time. The UE may request 726 FLU assistance by including an FLU assistance request in a registration request message. In one embodiment (Option 1), this registration request message includes the FLU duration, and the FLU start time that the UE has determined based on the SIB information. In another embodiment (Option 2), the registration request message includes a FLU indication signaling that AMF guidance is needed in view of the imminent FLU. In yet another embodiment (Option 3), the registration request message includes the UE-calculated FLU duration, the FLU start time, and the unavailability type (e.g., FLU type if supported by the UE and the network).

[0069] The initial AMF 162 responds to UE’s registration request message, based on the local configuration, the information received from the RAN-Sat, and / or O&M ifPATENT APPLICATION Attorney Docket No.: 0683-089-WO available. The initial AMF 162 determines 728 whether the UE has to change the AMF after FLU ends based on (Option1) an N2 message received from RAN-Sat specifying a TAI list pertinent after FLU, and / or (Option2) the local configuration (satellite’s current and foreseeable location, UE’s location) or O&M. The initial AMF 162 then sends 730 a registration accept message including FLU assistance information to the RAN-Sat 104. The FLU assistance information may be provided (Option1) via a new IE including the FLU duration and / or the FLU start time, (Option2) via a new IE including a FLU indication signaling that the UE is about to experience FLU and applies a default FLU duration that is based on the UE implementation and / or the local configuration (satellite’s current and foreseeable location, UE’s location) and the UE considers that the FLU starts immediately, or (Option 3) when both the UE and network support of the unavailability period, the FLU assistance information specifies an unavailability period duration based on the FLU duration and / or an unavailability period start time based on the FLU start time.

[0070] Upon determining that the UE has to change the AMF after the FLU (e.g., due to service areas change), the initial AMF 162 includes a feeder link update indication in the registration accept message to direct the UE to perform an MRU after FLU ends (e.g., the FLU timer expires). Upon determining that the UE does not have to change the AMF after the FLU, the initial AMF 162 does not include feeder link update indication in the registration accept message to the UE.

[0071] As previously discussed, the FLU assistance information may be provided by reusing and enhancing the unavailability period mechanism described in 3GPP TS 23.501. That is, when the unavailability period is caused by the FLU, in addition to the FLU duration, the unavailability period duration includes a first time interval for an N2 interface disconnection with a first AMF via a first feeder link, and a second time interval for an N2 interface reconnection with a second AMF via a second feeder link. Here, the first AMF and the second AMF may be the same (initial) AMF or different AMFs (i.e., the initial AMF and the target AMF respectively). The UE supporting the unavailability period feature supports the procedures before and after FLU. If both the UE and the network indicate unavailability period feature support due to discontinuous coveragePATENT APPLICATION Attorney Docket No.: 0683-089-WO and / or FLU, the AMF determines the unavailability period parameters as follows. (1) The unavailability period duration is set based on FLU duration if known. (2) The unavailability period start time is set based on the FLU start time if known. The unavailability type indicates the discontinuous coverage type or the FLU type. In one embodiment (Option1), the FLU type is a new unavailability type different from the discontinuous coverage unavailable period (DCUP) type due to unavailable service link. In another embodiment (Option2), the DCUP type is used for both FLU and DCUP regardless of whether the service link or the feeder link is unavailable.

[0072] When the service link is available during the FLU, the unavailability type is indicated as FLU (according to option1) in the first embodiment, or as discontinuous coverage unavailability type according to option2) in the second embodiment. In this case, when the AMF provides only unavailability period duration, the UE applies the FLU duration immediately or after a short default start time. Also, when the AMF provides only an unavailability period start time for the FLU, the UE applies a FLU duration based on the UE implementation, the local configuration, or the SIB information received before the FLU start time. When the AMF provides only the unavailability type, the UE may apply immediately or a short default start time a FLU duration based on the UE implementation, the local configuration, or the SIB information received before the FLU start time.

[0073] When the service link unavailability and the feeder link unavailability overlap, the enhanced unavailability period mechanism operates as follows. The unavailability type may indicate a discontinuous coverage type (option 1) or an FLU type (option 2). In this case (i.e., the unavailability of the service link and of the feeder link overlap), (A) the unavailability period start time may be selected to be the earlier of the unavailability period start time for discontinuous coverage and the unavailability period start time for the FLU, and (B) the unavailability period duration may be selected so that its end time to be the latest between the unavailability period end time corresponding to the discontinuous coverage and the unavailability period end time corresponding to the FLU. Here, the UE calculates the unavailability period end times as sums of the respective unavailability period start times and unavailability period durations.PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0074] As illustrated in Fig.7, the initial AMF 162 sends an N2 message including the FLU assistance information to RAN-Sat 104, which then forwards 732 the FLU assistance information to the UE in a registration accept message. The steps 726-732 are the basis of the registration procedure 725.

[0075] Similar to Figs.5 and 7, Fig.8 is a signal diagram illustrating techniques related to FLU according to an embodiment, in which the UE sends a FLU assistance request upon receiving an SIB including FLU information, and the CN entity executing an initial AMF provides a maximum offset time to the RAN-Sat. In the context of Fig.7’s steps 722-728, and 732 (described relative to Fig.7), the initial AMF 162 includes a maximum offset time in the N2 message it sends 830 to the RAN-Sat 104. The steps 726, 728, 830, and 732 are the basis of the registration procedure 825.

[0076] This maximum offset time may be a UE-specific maximum offset time or a non-UE specific maximum offset time. The RAN-Sat 104 handles 511 the maximum offset time as described relative to Fig.5 thereby providing overload control at RRC level.

[0077] Similar to Figs.6 and 7, Fig.9 is a signal diagram illustrating techniques related to FLU according to an embodiment, in which the UE sends a FLU assistance request upon receiving an SIB including FLU information, and the RAN-Sat forwards the maximum time offset it received from the initial AMF to the UE together with the FLU assistance information. In the context of Fig.8’s steps 722-728, and 830 (described relative to Figs.7 and 8), the RAN-Sat 162 forwards 932 the maximum offset time received 830 in the N2 message into the registration accepted message it sends to the UE 102. The steps 726, 728, 830, and 932 are the basis of the registration procedure 925.

[0078] Various aspects related to the SIB that the RAN-Sat broadcasts at 732 are now described in more detail. The SIB includes FLU-related information enabling the UE to determine location (affected area) and duration for the current or the upcoming FLU (e.g., satellite ephemeris information). For example, FLU-related information in the SIB may include an FLU indication and a (remaining) FLU duration for an ongoing FLU or an upcoming FLU. When the FLU indication is “active,” the FLU is ongoing at thePATENT APPLICATION Attorney Docket No.: 0683-089-WO serving and / or neighboring cells and the FLU duration is the remaining duration of the ongoing FLU.

[0079] In another example, the FLU-related information in the SIB includes an FLU start time and an FLU end time or an FLU duration. When the FLU start time is zero, the FLU is ongoing.

[0080] In yet another example, the FLU-related information in the SIB satellite ephemeris information enabling the UE to determine the range (i.e., area affected) by the FLU or directly conveying this range.

[0081] The SIB may be a new SIB or an SIB already defined in the 3GPP TSs (e.g., SIB19) providing FLU-related information for a specific time period and / or location. When the FLU-related information is included in the new SIB or SIB19, this information is excluded when determining changes in system information, that is it should neither result in system information change notifications nor in a modification of valueTag in SIB1.

[0082] In one embodiment, the RAN broadcasts the FLU-related information as a new SIB having the following structure.PATENT APPLICATION Attorney Docket No.: 0683-089-WO new SIB (new) SIB ::= SEQUENCE { fl-unavailability-info FL-unavailability -info OPTIONAL, -- Need R lateNonCriticalExtension OCTET STRING OPTIONAL, ... }

[0083] In another embodiment, the RAN broadcasts the FLU-related information embedded in SIB 19 ntn-Config component as illustrated next. SIB19 ::= SEQUENCE { (new) fl-unavailability-info FL-unavailability-info OPTIONAL, -- Need R ntn-Config-r17 NTN-Config-r17 OPTIONAL, -- Need R ntn-NeighCellConfigList-r17 NTN-NeighCellConfigList-r17 OPTIONAL, -- Need R ... }

[0084] In yet another embodiment, the RAN broadcasts the FLU-related information embedded into the NTN-Config at serving cell and / or NTN-NeighCellConfigList at neighboring cells as illustrated next. SIB19 ::= SEQUENCE { ntn-Config-(new) NTN-Config-(new) OPTIONAL, -- Need R ntn-NeighCellConfigList-(new) NTN-NeighCellConfigList-(new) OPTIONAL, -- Need R ... }PATENT APPLICATION Attorney Docket No.: 0683-089-WO NTN-NeighCellConfigList-(new)::= SEQUENCE (SIZE(1..maxCellNTN-r17)) OF NTN-NeighCellConfig-(new) NTN-NeighCellConfig-(new) ::= SEQUENCE { ntn-Config-(new) NTN-Config-(new) OPTIONAL, -- Need R carrierFreq-r17 ARFCN-ValueNR OPTIONAL, -- Need R physCellId-r17 PhysCellId OPTIONAL -- Need R } NTN-Config-(new) ::= SEQUENCE { (new) fl-unavailability-info FL-unavailability-info OPTIONAL, -- Need R epochTime-r17 EpochTime-r17 OPTIONAL, -- Need R ntn-UlSyncValidityDuration-r17 ENUMERATED{ s5, s10, s15, s20, s25, s30, s35, s40, s45, s50, s55, s60, s120, s180, s240, s900} OPTIONAL, -- Need R cellSpecificKoffset-r17 INTEGER(1..1023) OPTIONAL, -- Need R kmac-r17 INTEGER(1..512) OPTIONAL, -- Need R ta-Info-r17 TA-Info-r17 OPTIONAL, -- Need R ntn-PolarizationDL-r17 ENUMERATED {rhcp,lhcp,linear} OPTIONAL, -- Need R ntn-PolarizationUL-r17 ENUMERATED {rhcp,lhcp,linear} OPTIONAL, -- Need R ephemerisInfo-r17 EphemerisInfo-r17 OPTIONAL, -- Need R ta-Report-r17 ENUMERATED {enabled} OPTIONAL, -- Need R ... }

[0085] In one embodiment, the RAN broadcasts the FLU-related information using an existing SIB (e.g. SIB19) with NTN-Config containing FL unavailability event information indicated in EphemerisInfo IE. The FL unavailability event information indicates the UEs that the satellite is undergoing or will undergo a FLU during a specific time period and at a specific location as indicated in satellite ephemeris data. Thus, the FLU-related information may include an FLU indication, which indicates to the UEs that satellite thatPATENT APPLICATION Attorney Docket No.: 0683-089-WO is subject to ephemeris information is undergoing FLU. For example, the FLU-related information may include an FLU indication and a remaining FL unavailability period duration, which indicate to the UEs that the satellite is undergoing an FLU lasting the remaining FLU duration. When the FLU-related information includes an FLU start time of FL unavailability event and an FLU end time or FLU duration, the FLU-related information indicates to the UEs that communications via the satellite will be affected by an FLU beginning at the estimated FLU start time and lasting until the estimated FLU end time or lasting for the estimated FLU duration.

[0086] In another embodiment, the FLU-related information is an FLU location determined based on the satellite ephemeris information. In this case, the FLU-related information may include a satellite ephemeris range of the FLU. For an ongoing FLU, the satellite ephemeris range remains the same or can be changed based on current ephemeris info. EphemerisInfo-(new) ::= CHOICE { (new) fl-unavailability-info FL-unavailability-info OPTIONAL, -- Need R positionVelocity-r17 PositionVelocity-r17, orbital-r17 Orbital-r17 }

[0087] In some embodiments, the UE determines whether to request FLU assistance information based on other information the RAN-Sat broadcasts via SIB. In one embodiment, the RAN-Sat includes information about its operation mode in the broadcasted SIB. For example, an FLU with S&F operation mode indicates that only limited delay tolerant services are allowed during FLU. Further, an FLU without S&F operation mode indicates that RAN-Sat does not enable or support S&F mode during FLU. Further yet, a normal operation mode indicates that both service link and feeder link are available. Alternatively, the normal operation mode is not included being the default mode (i.e., when no other mode is specified).

[0088] In some embodiments, the UE determines whether to initiate power saving mechanisms during the FLU. In one embodiment, the UE determines to initiate a powerPATENT APPLICATION Attorney Docket No.: 0683-089-WO saving mechanism when the RAN-Sat does not support S&F operation (i.e., FLU without S&F operation mode). In another embodiment, the UE determines to initiate a power saving mechanism when, although the RAN-Sat operates in S&F mode (i.e., FLU with S&F operation mode), the UE is not allowed to use SMS, CIoT, delay tolerant services via RAN-Sat during FLU. The SMS, CIoT, delay tolerant services are called FLU compatible services. In yet another embodiment, the UE determines to initiate a power saving mechanism when, although the RAN-Sat operates in S&F mode and the UE is allowed to use SMS, CIoT, delay tolerant services via RAN-Sat for store and forward during FLU, the UE does not use these services.

[0089] Fig.10 is a flowchart of a wireless communication method 1000 performed by a CN entity (such as 140 in Fig.1, or 162 in Figs.4-9) communicating with a UE (e.g., 102) via a satellite (e.g., 103 in Figs.1 and 3A), according to an embodiment. The method 1000 includes determining 1002 (corresponding, for example, to 402 in Figs 4- 6) when a feeder link between an initial ground station connected to the CN entity and the satellite becomes unavailable. The method 1000 further includes transmitting 1004, towards the UE, FLU assistance information about a FLU disrupting a service link between the CN entity and the satellite. Step 1004 corresponds to step 404 in Figs.4 and 5, 604 in Fig.6, 730 in Fig.7, and 830 in Figs.8 and 9.

[0090] Fig.11 is a flowchart of a wireless communication method 1100 performed by a UE (e.g., 102 in Figs.1-9) connected to a CN (110) via a satellite (103). The method 1100 optionally includes the UE determining 1124 that the feeder link is about to become unavailable and transmitting 1126 a FLU assistance request. The steps 1124 and 1126 correspond to steps 724 and 726 in Figs 7-9. The method 1100 further includes receiving 1132 FLU assistance information about a FLU disrupting communication between the CN and the satellite. The step 1132 corresponds to 404, 604, 732 and 932 in Fig.4-9, respectively. The method 1100 then includes decision block 1134, in which the UE inquires (1) whether the RAN-Sat provides S&F, and (2) whether there is any active FLU-compatible service. When the UE determines that the RAN-Sat does not provide S&F (i.e., 1=No) or that, while the RAN-Sat provides S&F (i.e., 1=Yes), the UE has no active FLU-compatible services (i.e., 2=No), the UEPATENT APPLICATION Attorney Docket No.: 0683-089-WO optionally applies 1138 a power saving technique during the FLU. The step 1138 corresponds to step 410B in Figs.4-9. When the UE determines that the RAN-Sat provides S&F (i.e., 1=Yes) and the UE has a (at least one) active FLU-compatible service (i.e., 2=Yes), then the UE remains 1136 active, applying no power saving mechanism,

[0091] Fig.12 is a flowchart of a wireless communication method 1200 performed by a RAN-Sat (e.g., 104 in Figs.1-9) connected to a CN (110) via a feeder link. The method 1200 includes forwarding to a UE served by the RAN node, feeder link unavailability, FLU, assistance information received from the CN. The step 1204 corresponds to 404 in Figs.4 and 5, 604 in Fig.6, 732 in Figs.7 and 8, and 932 in Fig.9. The method 1200 then includes decision block 1250 representing the inquiry as to whether the satellite reconnects to the CN via the initial feeder link or connected to the CN via another feeder link after the FLU. When the response to this inquiry is positive (i.e., Y branch of 1250), the method 1200 further includes releasing 1252 a connection with the CN before the FLU starts. When the response to this inquiry is negative (i.e., N branch of 1250), the method 1200 further includes suspending 1254 a connection with the CN before the FLU starts.

[0092] According to example 1, a wireless communication method (such as, method 1000) performed by a CN (e.g.,110) entity (e.g., 140) communicating with a UE (e.g., 102) via a satellite (e.g., 103) includes: (A) determining (e.g., 1002, 402) when a feeder link between an initial ground station (e.g., 107) connected to the CN entity and the satellite becomes unavailable, (B) transmitting (e.g., 1004, 404, 730, 830), towards the UE, (FLU) assistance information about a FLU disrupting the feeder link between the CN entity and the satellite. The CN entity may host an AMF and / or an SMF. At least a portion of a RAN node serving the UE may be located on the satellite.

[0093] The determining step of the method according to example 1 may include predicting whether, after the FLU, the satellite will communicate via the initial ground station after the FLU, and further the method may include selectively including a configuration update indication in the FLU assistance information based on a result ofPATENT APPLICATION Attorney Docket No.: 0683-089-WO the predicting. The predicting step may use information related to tracking area identifiers, local configuration, and / or operation and maintenance.

[0094] The FLU assistance information transmitted towards the UE may include: (i) a FLU start time, and (ii) a FLU duration or a FLU end time. The FLU assistance information may alternatively include a FLU indication enabling the UE to use a first default value for a FLU start time and second default value for a FLU duration when actual respective values are not known. The FLU assistance information may include a first unavailability period type for the FLU different from a discontinuous coverage unavailability period (DCUP) type that occurs when a service link between the satellite and the UE is unavailable. When the FLU overlaps the DCUP, the FLU assistance information may include an unavailability period start time that is an earlier time between a FLU start time and a DCUP start time, and an unavailability period duration or an unavailability period end time corresponding to a later time between a FLU end time and a DCUP end time.

[0095] The FLU assistance information may be transmitted using a UE configuration update command message. The wireless communication method according to example 1 may further include receiving, from the UE, an FLU assistance request, the FLU information being then transmitted in response to the FLU assistance request. The FLU assistance request may be received in a registration request message, and the transmitting the FLU information may then be included in a registration accept message.

[0096] The wireless communication method of example 1 may further include transmitting a maximum offset time. The CN entity may also indicate that the maximum offset time is a UE-specific maximum offset time associated with the UE or that the maximum offset time is associated with UEs connected to the satellite.

[0097] According to example 2, a wireless communication method (e.g., 1100) performed by a UE (e.g., 102) connected to a CN (e.g., 110) via a satellite (e.g., 103) includes: (A) receiving (e.g., 1132, 404, 732, 932) FLU assistance information about an FLU disrupting a feeder link between the CN and the satellite, and (B) applying (e.g., 1138, 410B) a power saving mechanism during the FLU. The power saving mechanism may include at least one of deregistration, radio resource control, RRC,PATENT APPLICATION Attorney Docket No.: 0683-089-WO disconnection, release, or suspension. The FLU assistance information may be received in an SIB. The SIB may be an SIB19 having the FLU assistance information embedded in an NTN-Config part or an NTN-NeighCellConfig part thereof.

[0098] The method of example 2 may further include transmitting a FLU assistance request before the receiving of the FLU assistance information. The FLU assistance request may be triggered by detecting the FLU affecting the UE based on information in an initial SIB with satellite-related information.

[0099] The method of example 2 may further include receiving a maximum offset time and then waiting for a random time interval that is less than the maximum offset time before the applying the power saving technique and / or before attempting to re- establish network services after the FLU. The UE may receive the maximum offset time and the FLU assistance information simultaneously. The FLU assistance information may include (i) a FLU start time, and (ii) a FLU duration or a FLU end time. Alternatively, the FLU assistance information may include an FLU indication enabling the UE to use a first default value for a FLU start time and / or a second default value for a FLU duration when an actual respective value is not known. The FLU assistance information may include a configuration update indication signaling whether, after the FLU, the satellite connects to a target ground station different from an initial ground station to which the satellite is connected before the FLU. The method may then further include initiating a registration procedure after the FLU when the configuration update indication indicates that the satellite connects to the target ground station after the FLU.

[0100] The method of example 2 may further include initiating (e.g., 4020) re- establishment of services provided by the CN before the FLU.

[0101] According to example 3, a wireless communication method (e.g., 1200) performed by a RAN node (e.g., 104) having at least a part located on a satellite (e.g., 103), the RAN node communicating with a CN (e.g., 110) via a feeder link includes: (A) forwarding (e.g., 1204), to a UE served by the RAN node, FLU assistance information received from the CN, and (B) selectively releasing or suspending (e.g., 1250, 1252, 1254) a connection with the CN before a FLU indicated in the FLU assistance information starts. This method may further include determining whether the satellitePATENT APPLICATION Attorney Docket No.: 0683-089-WO connects to the CN via another feeder link after the FLU ends, and, when the determined that the satellite connects via the other feeder link after the FLU ends, suspend the connection, otherwise the RAN release the connection. The method of example 3 may further include receiving a maximum offset time from the CN. When the maximum offset time is associated with the UE, the RAN node transmits the FLU assistance information and the maximum offset time to the UE. When the maximum offset time is not UE-specific, the RAN node generates random delays for UEs connected to the RAN node, respectively, and forwards the FLU assistance information to each of the UEs after waiting for a time interval corresponding to one of the random delays, respectively. The RAN node may broadcast the FLU assistance information in an SIB. The RAN node may forward, to the CN, a FLU assistance request received from the UE.

[0102] The methods of examples 1, 2, and 3 may be performed by a wireless communication device (e.g., 102, 104, 140) including a processor and a transceiver.

[0103] The above description related to one of the figures may apply to another figure. An event or action described indicated as optional (e.g., using dashed lines) may be omitted. In some instances, the term “message” can be replaced by “information element (IE)”, and vice versa. In some instances, the term “configuration” means “one or more configurations” or “configuration parameters”, and vice versa.

[0104] A UE performing the above-described FLU-related techniques 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 UE 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 (IoT) device or a mobile-internet device (MID). Depending on the type, the UE 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.PATENT APPLICATION Attorney Docket No.: 0683-089-WO

[0105] Some embodiments described in this section include logic circuits, components or modules. The modules may be software modules (e.g., code, or machine-readable instructions stored on a non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible physical unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module may 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.

[0106] 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.

[0107] Upon reading this disclosure, those of skill in the art will appreciate still additional and alternative structural and functional designs for handling mobility between LTM candidate cells or cells of different NNs through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

[0108] 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 thePATENT APPLICATION Attorney Docket No.: 0683-089-WO 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.

[0109] Numerical adjectives “first”, “second”, and “third” do not imply any order (are not ordinals) but are markers to distinguish separate instances of similar elements. References to the singular (e.g., “a” or “an”, “the”) should include the plural unless clearly indicated otherwise.

[0110] 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, b only, 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.

[0111] Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. The methods or flowcharts may be implemented in a computer program, software or firmware tangibly embodied in a computer-readable storage medium for execution by a specifically programmed computer or processor.

Claims

PATENT APPLICATION Attorney Docket No.: 0683-089-WO WHAT IS CLAIMED IS:

1. A wireless communication method performed by a user equipment, UE, (102) connected to a core network, CN, (110) via a satellite (103), the method comprising: receiving (1132, 404, 604, 732, 932) feeder link unavailability, FLU, assistance information about a FLU disrupting a feeder link between the CN and the satellite, the FLU assistance information including a store-and-forward indication signaling that the UE is allowed to use delay tolerant services during the FLU, and selectively applying (1138, 410B), based on the FLU assistance information, a power saving mechanism during the FLU.

2. The wireless communication method of claim 1, wherein the power saving mechanism includes at least one of deregistration, radio resource control, RRC, disconnection, release, or suspension.

3. The wireless communication method of claim 1 or 2, wherein the receiving of the FLU assistance information includes receiving a system information block, SIB, with the FLU assistance information.

4. The method of any of claims 1 to 3, further comprising: transmitting a FLU assistance request before the receiving of the FLU assistance information.

5. The wireless communication method of any of claims 1 to 5, further comprising: receiving a maximum offset time; and waiting for a random time interval that is less than the maximum offset time before the applying the power saving technique and / or before attempting to re-establish network services after the FLU.PATENT APPLICATION Attorney Docket No.: 0683-089-WO 6. The wireless communication method of any of claims 1 to 5, wherein the FLU assistance information includes: a FLU start time, and a FLU duration or a FLU end time, or an FLU indication enabling the UE to use a first default value for a FLU start time and / or a second default value for a FLU duration.

7. The wireless communication method of any of claims 1 to 6, wherein the FLU assistance information includes a configuration update indication signaling whether the satellite connects to a target ground station after the FLU, the target station being different from an initial ground station to which the satellite is connected before the FLU, the method further comprising: initiating a registration procedure after the FLU when the configuration update indication indicates that the satellite connects to the target ground station after the FLU and initiating (4020) re-establishment of services provided by the CN before the FLU.

8. A wireless communication method performed by a radio access network, RAN, node (104) having at least a part located on a satellite (103), the RAN node communicating with a core network, CN, (110) via a feeder link, the method comprising: transmitting (404, 604, 732, 932), to a UE (102) served by the RAN node, feeder link unavailability, FLU, assistance information about a FLU disrupting a feeder link between the CN and the satellite, the FLU assistance information including a store-and- forward indication signaling that the UE is allowed to use delay tolerant services during the FLU.

9. The wireless communication method of claim 8, further comprising: determining whether the satellite connects to the CN via another feeder link after the FLU,PATENT APPLICATION Attorney Docket No.: 0683-089-WO wherein, when the determining indicates that the satellite connects via the other feeder link after the FLU, the RAN suspends a connection with the CN before a FLU indicated in the FLU assistance information starts, otherwise the RAN releases the connection with the CN before the FLU starts.

10. The wireless communication method of claim 8 or 9, further comprising: receiving a maximum offset time from the CN, wherein when the maximum offset time is associated with the UE, transmitting the FLU assistance information and the maximum offset time to the UE, and when the maximum offset time is not UE-specific, generating random delays for UEs connected to the RAN node, respectively, and transmitting the FLU assistance information to each of the UEs after waiting for a time interval corresponding to one of the random delays, respectively.

11. The wireless communication method of any of claims 8 to 10, wherein the transmitting, to the UE, the FLU assistance information comprises broadcasting a system information block including the FLU assistance information.

12. The wireless communication method of any of claims 8 to 11, further comprising at least one of: forwarding, to the CN, a FLU assistance request received from the UE; and receiving the FLU assistance information from the CN.

13. A wireless communication method (1000) performed by a core network, CN, (110) entity (140) communicating with a user equipment, UE, (102) via a satellite (103), the method comprising: determining (1002, 402) when a feeder link between an initial ground station (107) connected to the CN entity and the satellite becomes unavailable; andPATENT APPLICATION Attorney Docket No.: 0683-089-WO transmitting (1004, 404, 730, 830), towards the UE, feeder link unavailability, FLU, assistance information about a FLU disrupting the feeder link between the CN entity and the satellite.

14. The wireless communication method of claim 13, wherein the determining includes predicting whether, after the FLU, the satellite will communicate via the initial ground station after the FLU, based on information related to tracking area identifiers, local configuration, and / or operation and maintenance. and the method further comprises: selectively including a configuration update indication in the FLU assistance information based on a result of the predicting.

15. The wireless communication method of claim 13 or 14, wherein the CN entity hosts an Access and Mobility Management Function and / or a Session Management Function.

16. A wireless communication device (102, 104, 140) including a processor and a transceiver configured to perform a method as specified in any of claims 1 to 15.

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