Methods and devices for access control and cell reselection associated with the satellite store and forward operation

Abstract

Methods and devices related to controlling access when a non-terrestrial network has a store and forward capability and a feeder link between an NTN node and a terrestrial satellite gateway node is temporarily unavailable. A wireless communication method (900B) performed by a user equipment (102) in communication with a network entity (104, 112) on a satellite (103) includes receiving (908), from the network entity, a network entity store-and-forward indication indicating that the network entity operates in a store and forward mode when a feeder link from the satellite to a ground satellite gateway is unavailable. The method further includes transmitting (917, 919), to the network entity, a user equipment capability indication indicating whether a non-access stratum of the user equipment is capable of store and forward operation.

Description

Attorney Docket No.: 0683-113-WOMETHODS AND DEVICES FOR ACCESS CONTROL AND CELL RESELECTION ASSOCIATED WITH THE SATELLITE STORE AND FORWARD OPERATIONFIELD 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 embodiments relate to a store and forward (S&F) capability of a non-terrestrial network (NTN) and user equipment (UE) connectivity when a feeder link between an NTN node and a terrestrial satellite gateway node is temporarily unavailable.BACKGROUND

[0002] This background description is provided for the purpose of generally presenting the context in which the embodiments operate. 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] A wireless communication system includes one or more network entities (such as a base station or a core network (CN) device hosting a CN function or module) enabling communication between the CN and a terminal device (referred to as a user equipment (UE)). A base station operates one or more cells to provide coverage (i.e. enable communications) for UEs in a specific area. Existing wireless communication systems and network selection techniques are based primarily on legacy (e.g., 4G, LTE, 5G) terrestrial networks. However, the 3GPP organization has proposed to extend 5G communications to NTNs with 5G new radio (NR) technologies, or with the LTE technologies tailored for the Narrowband Internet-of-Thing (NB-loT) or the enhanced Machine Type Communication (eMTC) technologies.Attorney Docket No.: 0683-113-WO

[0004] An NTN refers to a network, or segment of networks, using radio frequency (RF) resources for communications with an NTN node on board of spaceborne or airborne vehicles (as opposed to devices on the ground). Airborne vehicles include unmanned aircraft systems (UAS), High-Altitude Platform Systems (HAPS), balloons, dirigibles, winged vehicles such as airplane or drones, among other examples. Spaceborne vehicles include a Geostationary Earth Orbit (GEO) satellite (sometimes also referred to as a geosynchronous orbit (GSO) satellite), a Low Earth Orbit (LEO) satellite, a Medium Earth Orbit (MEO) satellite, or a Highly Elliptical Orbit (HEO) satellite, among other examples. The NTN nodes may communicate with one another to form constellations. For simplicity, this document refers to all such vehicles as satellites or NTN nodes.

[0005] In addition to NTN nodes, an NTN can include one or more gateways (sometimes referred to as NTN gateways or sat-gateways). The NTN gateways are ground devices that connect satellites to a public data network. A feeder link refers to a communication link between a sat-gateway and a satellite. A service link refers to a communication link between a satellite and a UE. An NTN may also include inter-satellite links (ISLs) between NTN nodes that form constellations. In normal operation, an operational satellite feeder link is always available and continuously enables the satellite to connect to one or more serving NTN gateways, with sufficient overlap time for the UE to proceed with mobility anchoring and hand-over. Similarly, the satellite ideally maintains service link continuity with the UE. Some NTN deployments provide coverage for UEs in very remote regions. In some instances, even if a UE is under the coverage of a satellite (such as a non-geostationary (NGSO) satellite), that satellite feeder link to an NTN gateway might temporarily become unavailable or inoperable. Thus, the satellite cannot directly connect the UE to services of the core network when the service link and feeder link are not concurrently available. In order to alleviate feeder link unavailability, an NGSO satellite providing services to UEs located in remote areas may operate in a store-and-forward (S&F) mode. NTN nodes with S&F capabilities and / or UEs supporting S&F capabilities may have some opportunities to control service link access between the UE and NTN node before a feeder link changes status.Attorney Docket No.: 0683-113-WOBRIEF DESCRIPTION OF THE DRAWINGS

[0006] 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.

[0007] Fig. 1 A is a block diagram of a wireless communication system in which a UE and a base station perform various techniques for access control and cell reselection associated with the satellite S&F operation.

[0008] Fig. 1 B illustrates a distributed base station with a centralized unit (CU) and a distributed unit (DU) that can operate in the wireless communication system of Fig. 1A.

[0009] Fig. 2A illustrates a protocol stack usable by a UE to communicate with base stations.

[0010] Fig. 2B illustrates a protocol stack usable by a UE to communicate with a CU and a DU of a distributed base station.

[0011] Fig. 3 is a schematic illustration of an NTN node with regenerative payload.

[0012] Fig. 4A illustrates the normal / default satellite operation mode.

[0013] Fig. 4B illustrates the S&F satellite operation mode.

[0014] Fig. 5 is a signal diagram illustrating messages exchanged between a UE and a satellite according to a scenario in which the UE determines whether and how to establish an RRC connection with a cell provided by the satellite operating in the S&F mode.

[0015] Fig. 6 is a signal diagram illustrating messages exchanged between a UE and satellites according to a scenario in which a UE receives a list of cells not operating in the S&F mode and determines to trigger a neighboring cell measurement when the serving cell operates in the S&F mode.

[0016] Fig. 7 a signal diagram illustrating messages exchanged between a UE and satellites according to a scenario in which a UE, which receives information on when the serving cell will start to operate in the S&F mode, determines to trigger a neighboring cell measurement before the serving cell starts to operate in the S&F mode.

[0017] Fig. 8 a signal diagram illustrating messages exchanged between a UE and satellites according to a scenario in which a UE, which receives information on when theAttorney Docket No.: 0683-113-WO serving cell will start to operate in the normal mode (i.e. , when the feeder link will resume) determines to refrain from attempting to access the network until that time.

[0018] Fig. 9A illustrates a flow diagram a method performed by a UE for determining whether to trigger an access attempt in a cell operating in the S&F mode, based on the detailed S&F capability, according to an embodiment.

[0019] Fig. 9B illustrates a flow diagram of a method performed by a UE, for informing the network of UE’s NAS layer support for S&F operation, while conducting an access attempt in the cell operating in the S&F mode, according to an embodiment.

[0020] Fig. 10 illustrates a flow diagram of a method performed by a UE, for determining when to perform an intra-frequency and / or the inter-frequency measurement on a cell supporting the S&F operation, according to an embodiment.

[0021] Fig. 11 illustrates a flow diagram of a method performed by a UE with a full S&F support, for determining when to perform an intra-frequency and / or the interfrequency measurement on a cell supporting the S&F operation, according to an embodiment.

[0022] Fig. 12 illustrates a flow diagram of a method performed by a UE, for determining when the feeder link will resume or become unavailable, and then acting accordingly, in an embodiment.DETAILED DESCRIPTION OF THE DRAWINGS

[0023] Methods and devices described in this section embody techniques used by a UE and a network entity (e.g., a base station or CN device onboard a satellite) capable of S&F operation for managing access control and cell reselection when the feeder link is temporarily unavailable. The embodiment descriptions in this section refer to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The detailed descriptions do not preclude other embodiments within the scope of the appended claims. The embodiments are not limited to the described configurations but may be extended to other arrangements.

[0024] 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 theAttorney Docket No.: 0683-113-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.

[0025] Different UEs may support the satellite S&F operation in different ways. Some UEs may only support the satellite S&F operation up to a Radio Resource Control (RRC) protocol layer (i.e. , the Access Stratum), while other UEs have a full support including both the Access Stratum and a Non-Access Stratum (NAS) and possibly even higher protocol layers. An NTN node operating in the S&F mode may serve UEs with full S&F support while the UEs are in any RRC state (i.e., RRCJDLE, RRCJNACTIVE, and RRC_CONNECTED). However, an NTN node operating in the S&F mode may be able to serve UEs having only Access Stratum support only while the UEs are in specific RRC states (e.g., RRCJDLE or RRCJNACTIVE). To have better access control over all types of UEs, it is desirable for the UEs to report their detailed S&F capabilities during access attempts, as well as for the NTN node to convey time information regarding the current feeder link status to the served UEs.

[0026] According to some embodiments, a method for wireless communication performed by a UE includes receiving system information from an NTN node, the system information indicating that legacy UEs and UEs not supporting S&F are barred and that satellite / cell(s) covering UE’s location operates in the S&F operation mode. The method further includes selectively initiating an access attempt triggered by a UE upper layer due to uplink data or user activity based on determining whether UE’s NAS is capable of supporting the S&F operation. If UE’s NAS is indeed capable of supporting the S&F operation, the UE conducts the access attempt in the cell, otherwise the UE refrains from conducting the access attempt in the cell.

[0027] According to other embodiments, a method for wireless communication performed by a UE includes receiving system information indicating a timer or a time instance associated with the current feeder link status. The method further includes determining whether the system information indicates that the satellite / cell operates in the S&F operation mode. If the satellite / cell indeed operates in the S&F operation mode, the UE considers that the feeder link will be resumed at the time instance or upon theAttorney Docket No.: 0683-113-WO expiry of the timer, and the UE refrains from attempting to access the network and / or freezing the NAS layer until the feeder link is resumed. Conversely, if the satel lite / cell is not operating in the S&F operation mode, the method further includes the UE considering the feeder link will become unavailable at the time instance or upon the expiry of the timer, and UE triggering the intra-frequency and / or inter-frequency measurement before the feeder link becomes unavailable.

[0028] According to other embodiments described in this document a wireless communication device that includes a communication interface and a processor that controls the communication interface are configured to perform the above-referenced methods.

[0029] Referring first to Fig. 1A, an example wireless communication system 100 includes a UE 102, a base station (BS) 104, a BS 106, and a core network (CN) 110. The BSs 104 and 106 illustrated in Fig. 1A operate in a radio access network (RAN) 105 connected to the CN 110. The CN 110 may include an evolved packet core (EPC) 111 and / or a 5G core (5GC) 160. The CN 110 may also include as a sixth generation (6G) core.

[0030] The BS 104 covers a cell 124, and the BS 106 covers a cell 126. If the BS 104 is a gNB, the cell 124 is an NR cell. If the BS 104 is an ng-eNB or eNB, the cell 124 is an evolved universal terrestrial radio access (E-UTRA) cell. Similarly, if the BS 106 is a gNB, the cell 126 is an NR cell, and if the BS 106 is an ng-eNB or eNB, the cell 126 is an E-UTRA cell. The cells 124 and 126 may be in the same Radio Access Network Notification Areas (RNA) or different RNAs. In general, the RAN 105 may include any number of BSs, and each of the BSs may cover one, two, three, or any other suitable number of cells. The UE 102 supports at least a 5G NR (or simply, “NR”) or an E-UTRA air interface to communicate with the BSs 104 and 106. Each of the BSs 104, 106 may connect to the CN 110 via an interface (e.g., S1 or NG interface). The BSs 104 and 106 also may be interconnected via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes. The interfaces S1 , NG, X2, and Xn are described in the 3GPP TSs.

[0031] Among other components, the EPC 111 typically includes 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,Attorney Docket No.: 0683-113-WO 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 5GC 160 typically includes instances of 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 164 is configured to manage PDU sessions. The UPF 166 is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc.

[0032] As illustrated in Fig. 1A, the BS 104 supports a cell 124, and the BS 106 supports a cell 126. The cells 124 and 126 partially overlap, so that the UE 102 remains connected while selects, reselects, or is handed over from one of the cells 124 and 126 to the other.

[0033] As discussed in detail below, the UE 102 and / or the RAN 105 may utilize the techniques described relative to various embodiments 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.

[0034] The BS 104 is equipped with processing hardware 130 that includes one or more general-purpose processors and / or special-purpose processing units, and a non- transitory computer-readable memory storing instructions that the one or more processors / processing units execute. As illustrated in Fig. 1A, the processing hardware 130 includes a processor 132 to process data that the BS 104 transmits in the downlink direction or receives in the uplink direction. The processing hardware 130 also includes a transmitter 136 configured to transmit the data in the downlink direction and a receiver 134 configured to receive data in the uplink direction. The BS 106 includes generally similar components. In particular, components 140, 142, 144, and 146 of the BS 106 can be similar to the components 130, 132, 134, and 136, respectively.Attorney Docket No.: 0683-113-WO

[0035] The CN 110 (i.e., functions and modules of the CN 110) may be hosted on one or more network entities (NE or NW entity / device) such as 140 illustrated in Fig. 1A. The NE 140 includes processing hardware for exchanging and processing data exchanged wirelessly with other NW devices such as BSs 104 and 106 and the UE 102. Specifically, the processing hardware includes at least one processor 142 (which may be a general-purpose processor or a special-purpose processing unit), a transmitter 146 and a receiver 144 (or a transceiver). The NE device typically also includes a non- transitory computer-readable memory storing machine-readable instructions executable by the processor 142.

[0036] The UE 102 is equipped with processing hardware 150 that includes one or more general-purpose processors and / or special-purpose processing units, and a non- transitory computer-readable memory storing machine-readable instructions executable on the one or more processors and / or processing units. As illustrated in Fig. 1A, the processing hardware 150 includes a processor 152 to process data that the UE 102 transmits in the uplink direction or receives in the downlink direction. The processing hardware 150 also includes a transmitter 156 configured to transmit the data in the downlink direction and a receiver 154 configured to receive the data in the uplink direction.

[0037] Fig. 1 B illustrates a distributed base station with a centralized unit (CU) and a distributed unit (DU) that can operate as the BS 104 or 106 in the wireless communication system of Fig. 1A. The BS 170 includes a central unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 includes processing hardware, such as one or more general-purpose processors (e.g., CPUs) and / or special-purpose processing units, and a computer-readable memory storing machine-readable instructions executable on the general-purpose processor(s) and / or special-purpose processing unit(s). The CU 172 may include a Packet Data Convergence Protocol (PDCP) controller, a radio resource control (RRC) controller and / or an RRC inactive controller. The CU 172 may also include a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures.

[0038] Each of the DUs 174 also includes processing hardware that can include one or more general-purpose processors (e.g., CPUs) and / or special-purpose processingAttorney Docket No.: 0683-113-WO units, and a computer-readable memory storing machine-readable instructions executable on the processor(s) and / or processing unit(s). For example, the processing hardware may include a media access control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure), and / or an RLC controller configured to manage or control one or more RLC operations or procedures. The processing hardware may also include a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0039] In some embodiments, the RAN 105 supports Integrated Access and Backhaul (IAB) functionality. In some embodiments, the DU 174 operates as an Integrated Access Backhaul (IAB) node, and the CU 172 operates as an lAB-donor. he RAN 105 supports Non-Terrestrial Network (NTN) functionality.

[0040] In some embodiments, the CU 172 includes a logical node CU-CP 172A that hosts the control plane (CP) part of the PDCP protocol of the CU 172. The CU 172 may also include logical node(s) CU-UP 172B that hosts the user plane (UP) part of the PDCP protocol and / or Service Data Adaptation Protocol (SDAP) protocol of the CU 172. The CU-CP 172A may transmit control information (e.g., RRC messages, F1 application protocol messages), and the CU-UP 172B may transmit the data packets (e.g., SDAP PDUs or Internet Protocol packets).

[0041] The CU-CP 172A may be connected to multiple CU-UP 172B through the E1 interface. The CU-CP 172A selects the appropriate CU-UP 172B for the requested services for the UE 102. In some embodiments, a single CU-UP 172B can connect to multiple CU-CP 172A through the E1 interface. The CU-CP 172A can connect to one or more DU 174s through an F1 -C interface. The CU-UP 172B can connect to one or more DU 174 through the F1-U interface under the control of the same CU-CP 172A. In some embodiments, one DU 174 can connect to multiple CU-UP 172B under the control of the same CU-CP 172A. In such embodiments, the connectivity between a CU-UP 172B and a DU 174 is established by the CU-CP 172A using Bearer Context Management functions. The E1 and F1 interfaces are described in the 3GPP TSs.

[0042] Fig. 2A illustrates, in a simplified manner, a protocol stack 200 usable by a UE (e.g., the UE 102 of Fig. 1A) to communicate with an eNB / ng-eNB base station 230 and a gNB 232 (such as the BSs 104 and / or 106 in Fig. 1A).Attorney Docket No.: 0683-113-WO

[0043] The stack 200 includes a physical layer (PHY) 202A of ELITRA that provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLC sublayer 206A in turn provides RLC channels to an EUTRA PDCP sublayer 208 and, in some cases, to an NR PDCP sublayer 210. Similarly, the NR PHY 202B provides transport channels to the NR MAC sublayer 204B, which in turn provides logical channels to the NR RLC sublayer 206B. The NR RLC sublayer 206B in turn provides data transfer services to the NR PDCP sublayer 210. The NR 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 in Fig. 2A). The UE 102, in some embodiments, supports both the EUTRA and the NR stack as shown in Fig. 2A, to support handover between EUTRA and NR BSs and / or to support DC over EUTRA and NR interfaces. Further, as illustrated in Fig. 2A, the UE 102 can support layering of NR PDCP 210 over EUTRA RLC 206A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0044] The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the PDCP layer 208 or 210) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer 206A or 206B) 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.”

[0045] On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide signaling radio bearers (SRBs) or RRC sublayer (not shown in Fig. 2A) to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0046] Fig. 2B illustrates, in a simplified manner, a protocol stack 250 usable by a UE (e.g., UE 102 in Fig. 1A) to communicate with a CU 232 (e.g., CU 172 in Fig. 1 B) and a DU 174 of a distributed base station. The radio protocol stack 200 may be functionally split as shown by the radio protocol stack 250 in Fig. 2B. The CU at any of the BSs 104Attorney Docket No.: 0683-113-WO or 106 may perform all the control and upper layer functionalities (e.g., RRC 214, SDAP 212, NR PDCP 210), while the lower layer operations (e.g., NR RLC 206B, NR MAC 204B, and NR PHY 202B) are delegated to the DU. To support connection to a 5GC, NR PDCP 210 provides signaling radio bearers (SRBs) to RRC 214, and data radio bearers (DRBs) to SDAP 212.

[0047] Fig. 3 is a schematic illustration of an NTN node with regenerative payload (i.e. , a certain type of NTN deployment in which the signal transmitted between the UE and the terrestrial devices is regenerated at the satellite). The service link between the satellite 304 and the UE 102 carries the Uu interface and the feeder link which enables a Satellite Radio Interface (SRI) carries part of an S1 or an NG interface. The terrestrial sat-gateway 302 placed at one end of the SRI / feeder link serves as an intermediate node forwarding the S1 / NG traffic to and from the CN 110 (and further to the data network 370). In some examples of regenerative satellite payload, part of the MME 114 (i.e., split-MME) or the entire MME 114 is also installed on the satellite 304, and hence feeder link does not carry either the S1 interface or NG interface (it only carries the internal interface within a core network node). Different regenerative satellites may connect to the same CN 110 on the ground, via the same sat-gateway, or via different sat-gateways. In addition, as the UE 102 needs to know its Global Navigation Satellite System (GNSS) position in order to compensate for the time delay and frequency drift occurring when transmitting data / signal to a moving satellite, the UE 102 also needs to obtain / measure the signal emitted from at least one GNSS satellite 308.

[0048] Although the regenerative payload illustrated in Fig. 3 is employed in most embodiments, these techniques may apply to the transparent payload as well. In terms of the satellite moving pattern, there are three types of service links that are supported in NTN: (A) Earth-fixed satellites, which provides beam(s) continuously covering the same geographical area(s) (e.g., the GEO / GSO satellites), (B) Quasi-Earth-fixed satellites, which provides beam(s) covering one geographic area for a limited period and a different geographic area during another period (e.g., LEO / MEO satellites capable of using steerable beams), and (C) Earth-moving satellites, which provides beam(s) whose coverage area slides over the Earth surface (e.g., LEO / MEO satellites using fixed or non-steerable beams). A BS on a LEO / MEO satellite may provide either a quasi-Earth-Attorney Docket No.: 0683-113-WO fixed cell coverage or an Earth-moving cell coverage. A BS on a GEO satellite provides Earth fixed cell coverage.

[0049] Store and Forward (S&F) is an operation mode of a 5G system with satelliteaccess, where the 5G system is able to provide some level of service (by storing and forwarding the data) when satellite connectivity (feeder link) is intermittently / temporarily unavailable. In one embodiment, the S&F operation mode provides communication service for UEs under satellite coverage without a simultaneous active feeder link connection to the ground gateway. This S&F operation mode is particularly suitable for delay-tolerant loT services via non-geostationary orbit (NGSO) space segment. For example, a service provider offers a service of remote monitoring of fields by deploying and tracking many battery-powered loT type UEs across the globe. All the loT remote monitoring UEs include a 5G modem that is able to access the satellite network. Some of the UEs are deployed in a remote area where there is no mobile coverage by mobile network operator and only satellite coverage is possible. All loT remote monitoring UEs regularly send information related to the area they are monitoring to the application server of the service provider and sometimes receive new parameters from the application server. In most of the cases, the messages exchanged are delay- tolerant / non-real-time.

[0050] Fig. 4A illustrates 400 the normal / default satellite operation mode in which a delay tolerant UE 102 (e.g., an loT device) exchanges signals and data with data network 370 via satellite 304 and sat-gateway (also called NTN gateway) 302. Here, both the service link between the UE and the satellite and feeder link between the satellite and the gateway 302 are active and available.

[0051] Fig. 4B illustrates the “S&F operation mode” 450. The UE 102 interacts continuously over the service link with the satellite 304, but under “S&F operation mode”, the end-to-end exchange of signaling / data is not achieved in one shot but is now achieved in a two-step procedure. In step A illustrated on the left side of Fig. 4B, the UE 102 and the satellite 304 exchange signaling / data, without the satellite 304 being simultaneously connected to the NTN gateway 302 (i.e. the satellite 304 operates the service link without an active feeder link connection). Later in step B illustrated on the right side of Fig. 4B, when the satellite 304 is closer to NTN gateway 302 (and possiblyAttorney Docket No.: 0683-113-WO further away from UE 102), the connection between the satellite 304 and the NTN gateway 302 is (re)established and hence the uplink data / signal stored on the satellite 304 is forwarded to the data network 370 through the NTN gateway 302. Also in step B, the satellite 304 may store the downlink signal / data for the UE 102 while the service link is interrupted, to later forward the stored data to the UE 102 when the satellite 304 (re)establishes the service link with the UE 102 (e.g., after returning to the same coverage area as in step A possibly by traveling an orbit around the Earth).

[0052] When the feeder link and the service link are not available simultaneously in the S&F operation mode, as shown in Fig. 4B, completing a procedure initiated by the UE 102 and involving the core network would take the time required for the satellite 304 to return to the same coverage area as step A (i.e. , step A - step B - step A).However, the legacy (i.e., pre-5G terrestrial wireless communication systems) timers regulating the procedures involving the core network are not designed / configured for such a long delay and hence it is very likely the UE 102 would consider such a procedure failed due to the expiry of the legacy timer and would restart the procedure repeatedly. Repeating a procedure that is doomed to fail should be avoided, and hence it is better if the UE (at least the RRC and the NAS layers of the UE) is capable of suspending the status and / or the timer of the procedure when the signal / data is stored on the satellite due to the absence of either the service link or the feeder link. For the legacy UEs or the UEs not supporting the S&F operation mode, it is preferable for the BS to bar these UEs from camping on the cells operating in the S&F mode.

[0053] Therefore, 3GPP community has agreed (i) to (re)use the legacy barring bit (i.e., cellBarredNTN) to bar the legacy UEs and UEs not supporting the S&F operation mode and (ii) to use a new “S&F operation” indication broadcasted in the system information to bar the UE supporting the S&F operation when needed. When present, the “S&F operation” indication has two possible settings: ‘1 ’ means the cell is operating in S&F mode and Rel-19 UEs supporting S&F are allowed to access the cell, while ‘0’ means the cell is operating in S&F mode for UEs in RRC_CONNECTED but UEs in RRCJdle state are barred. When the “S&F operation” indication is absent, the UEs supporting S&F follow the legacy barring procedure based on the legacy barring bit.Attorney Docket No.: 0683-113-WORegardless of the presence or absence of the “S&F operation” indication, the legacy UEs and UEs not supporting S&F follow the legacy barring bit.

[0054] However, different UEs may support the satellite S&F operation in different ways. Some UEs may only have the support from the RRC layer for the satellite S&F operation, which means these UEs are only able to read and understand the new “S&F operation” indication in the system information, or other new indications provided in other RRC messages, but are not able to suspend the NAS status or extend the NAS timers due to the unavailability of the feeder link or the service link. Some UEs may have full support including the support from the NAS layer and even higher layers. The NTN node operating in the S&F mode is able to serve the UEs with full S&F support while the UE is in any RRC states (i.e. , RRCJDLE, RRCJNACTIVE, and RRC_CONNECTED). However, the network may allow the UEs having only the AS support for the satellite S&F operation to camp on the S&F cell to receive the paging and ETWS / CMAS (that is, Earthquake and Tsunami Warning System, and Commercial Mobile Alert System) service but does not support these UEs in the connected state. Because the new S&F operation indication introduced by 3GPP does not distinguish the UE having full S&F support from the UE having only limited S&F support (i.e., only RRC support), an admission control mechanism based on UE’s detailed S&F capabilities would better handle the connection requests from all types of UEs.

[0055] The UE with limited S&F support (e.g., AS only) are better served by remaining in the cells operating in the normal mode for as long as possible, even if the UE is allowed to camp on the cell operating in the S&F mode. Camping on a cell having a feeder link is better than camping on the cell having no feeder link even for the UE with full S&F support (if these cells are similar in terms of cell quality) because camping on the cell with feeder link means the real-time ETWS and CMAS notification is always available regardless of the network deployment option (e.g., split-MME or full CN on board), and the mobile terminated (MT) or mobile originated (MO) data thus have a shorter latency (because there is no feeder link interruption). To make it easier for UEs to detect and reselect a cell operating in the normal mode, the network can provide a list of cells (e.g., Physical Cell Identities, PCIs) that are not operating in the S&F mode as part of the cell reselection information / configuration, so that UEs can then prioritize theAttorney Docket No.: 0683-113-WO listed cells in the cell reselection decision. In addition, providing time information (e g., the remaining duration) associated with the current feeder link status is desirable because the UE may use such information to determine the best moment to trigger an inter-frequency and / or intra-frequency measurement.

[0056] Next, several example scenarios in which a UE and / or a RAN perform the techniques for supporting S&F operation mode are discussed with reference to Figs. 5- 8. Similar events in Figs. 5-8 are labeled with reference numbers that have the same lower-order digits. For example, event 504 is similar to event 704 and 804, event 508 is similar to events 608 and 808, event 634 is similar to events 734, and event 516A is similar to event 516B and event 816. For brevity, similar events are not discussed in detail in each instance, but the discussion of a certain event with reference to one of the figures also applies to similar events in other figures.

[0057] Fig. 5 a signal diagram 500 illustrating messages exchanged between a UE 102 and a satellite (i.e. , a BS 104 or a network entity hosting a CN function or module such as MME 112) according to a scenario in which the UE determines whether and how to establish an RRC connection with a cell provided by the satellite supporting the S&F mode. Initially, the UE 102, which has only the RRC support for the S&F operation (i.e., capable of acquiring and decoding the S&F related information included in the system information or in the RRC message), stays 502 in an idle state and camps on an NTN cell provided by the BS 104 (through satellite 304). The satellite 304 may also house a part of MME of an entire MME 112 installed on it. When the BS 104 (or the satellite 304) still connects to the NTN gateway 302 via the feeder link, the UE 102 receives 504 the system information including a legacy NTN barring indication (i.e., cellBarredNTN) equal to ‘notBarred’.

[0058] Because the satellite 304 is an NGSO satellite, at a certain point in time, the feeder link becomes unavailable 506 because the satellite 304 is outside a communication range of the NTN gateway 302. The UE 102 the receives 508 the system information including the legacy NTN barring indication (i.e., cellBarredNTN) equal to ‘Barred, and also an S&F operation indication equal to ‘1 ’. Because the RRC layer of the UE 102 is capable of acquiring and decoding the S&F related information, the UE 102 considers itself as ‘supporting the S&F operation’, and hence remains onAttorney Docket No.: 0683-113-WO the cell provided by the BS 104 (via the satellite 304). While camping on the cell provided by the BS 104 (via the satellite 304), the UE 102 may (optionally as suggested by the dashed lines) receive 510 a paging message, or receive 512 ETWS or a CMAS notification from the BS 104, even if the BS (or the satellite 304) does not have a feeder link toward the NTN gateway 302. In one embodiment, the BS / MME 104 / 114 having no feeder link available may generate an ETWS / CMAS notification or a paging message based on the source provided by other UEs served by the BS / MME 104 / 114.

[0059] Later, the arrival of UL data or the user activity triggers 514 UE’s NAS layer to connect to the network, that is, triggers the RRC layer to establish an RRC connection with the BS 104. However, the arrival of UL data or the user activity may selectively trigger the RRC layer to establish the RRC connection with the BS 104 depending on UE’s actual RRC status. After the event 514, UE behavior depends on whether the UE 102 supports the full S&F operation in the NAS layer or not.

[0060] In the first alternative (i.e., Alt-A box in Fig. 5), the UE 102 does not support the full S&F operation in the NAS layer, and hence while transmitting 516A the RRCConnectionRequest message (or the RRCConnectionResumeRequest message or the RRCConnectionReestablishmentRequest message) to the BS 104, the UE 102 also includes an S&F capability indication in MSG3 containing the RRCConnectionRequest message (or the RRCConnectionResumeRequest message or the RRCConnectionReestablishmentRequest message). This S&F capability indication indicates that the UE 102 does not support the S&F operation in the NAS layer. In order to transmit the RRCConnectionRequest message to the BS 104, the UE 102 may need to initiate a Random Access (RA) procedure with the BS 104 to obtain an uplink grant for transmitting the RRCConnectionRequest message. In one embodiment, the S&F capability indication is included in a MAC CE transmitted together with theRRCConnectionRequest message (or the RRCConnectionResumeRequest message or the RRCConnectionReestablishmentRequest message). In another embodiment, the S&F capability indication is transmitted within the RRC message (i.e., a new field / parameter as the S&F capability indication of the RRCConnectionRequest, the RRCConnectionResumeRequest, or the RRCConnectionReestablishmentRequest message). In response to the RRCConnectionRequest message and the S&F capabilityAttorney Docket No.: 0683-113-WO indication, the BS 104 transmits 518 an RRCConnectionReject message to the UE 102 to reject the connection establishment request. The reason for rejecting the connection establishment request may be that the satellite 304 does not have the full CN installed on it (otherwise the BS 104 may accept the connection establishment request).

[0061] In the second alternative (i.e. , Alt-B box in Fig. 5), the UE 102 does support the full S&F operation in the NAS layer, and hence while transmitting 516B the RRCConnectionRequest message (or the RRCConnectionResumeRequest message or the RRCConnectionReestablishmentRequest message) to the BS 104, the UE 102 also includes an S&F capability indication in MSG3 containing the RRCConnectionRequest message (or the RRCConnectionResumeRequest message or the RRCConnectionReestablishmentRequest message). Here, the S&F capability indication indicates the UE 102 does support the S&F operation in the NAS layer. In response to the RRCConnectionRequest message and the S&F capability indication, the BS 104 transmits 520 an RRCConnectionSetup message to the UE 102 to accept the connection establishment request. In response to the RRCConnectionSetup message, the UE 102 transmits 522 an RRCConnectionSetupComplete message to the BS 104 to complete the RRC connection establishment procedure. After that, the UE 102 moves 524 to the RRC_CONNECTED state, and then the UE NAS initiates an attach procedure by transmitting 526 a NAS Attach Request message to the MME 112. In response to the NAS Attach Request message, the MME 112 transmits 528 a NAS Attach Accept message to the UE 102 to complete the NAS Attach procedure. After that, the UE 102 starts transmitting 530 the UL data to the network.

[0062] In the third alternative (i.e., Alt-C box in Fig. 5), the UE 102 does not support the full S&F operation in the NAS layer, and hence refrains 532 from attempting to access the network (i.e., refrains from initiating a random access procedure and transmitting the RRCConnectionRequest, the RRCConnectionResumeRequest, or the RRCConnectionReestablishmentRequest message to the BS 104).

[0063] Fig. 6 is a signal diagram 600 illustrating messages exchanged between a UE 102 and satellites 304 and 306 housing BS 104 and MME 112 and BS 106 and MME 118 respectively, according to a scenario in which the UE receives a list of cells not operating in the S&F mode and determines to trigger a neighboring cell measurementAttorney Docket No.: 0683-113-WO when the serving cell operates in the S&F mode. Steps 502, 504, and 506 have been described relative to Fig. 5. The UE 102 receives 608 the system information including (i) the legacy NTN barring indication (i.e. , cellBarredNTN) equal to ‘Barred, (ii) an S&F operation indication equal to ‘1 ’, and (iii) a list of cells not operating in the S&F mode.

[0064] In response to the S&F operation indication being equal to 1 and to the list of cells not operating in the S&F mode, the UE 102 determines 634 to trigger an intrafrequency and / or inter-frequency measurement on neighboring cells. In another embodiment, the UE 102 determines to trigger the intra-frequency and / or interfrequency measurement in response to the reception of the S&F operation indication equal to 1 . The UE 102 then performs 636 the intra-frequency and / or the interfrequency measurement only on the cells listed in 608. Alternatively (i.e., in another embodiment), the UE 102 may perform the intra-frequency and / or the inter-frequency measurement also on cells not included in the cell list.

[0065] Based on the intra-frequency and / or the inter-frequency measurement results, the UE 102 detects 638 a cell provided by another BS 106 via another satellite 306, this detected cell being one of the cells listed in the system information provided to the UE 102 in the event 608. To prioritize the cells listed in the system information over the cells operating in the S&F mode, the UE 102 calculates the ranking Rnof the detected cell (for example as described in TS 36.304, section 5.2.4.6) and increases the cell ranking Rnby a value A. The value A may be a fixed value defined in the specification or a dynamic value configured by the network through the system information or through a dedicated RRC message (e.g., an RRCConnectionRelease message). Alternatively (i.e., in another embodiment), instead of increasing the cell ranking Rnof the detected cell, the UE 102 decreases the serving cell ranking Rs(which may also be calculated as described in TS 36.304) when the serving cell is operating in the S&F mode. Yet in another embodiment, the UE 102 determines to reselect the detected cell immediately as long as the detected cell is one of the cells listed in the event 608 and fulfills a cell selection criterion (for example, as defined in TS 36.304 section 5.2.3.2).

[0066] The UE 102 then ranks all the detected cells (including the serving and neighboring cells) based on the measurement results and frequency priorities and determines to reselect the detected cell provided by the BS 106. The UE 102 thenAttorney Docket No.: 0683-113-WO acquires and checks 640 the system information provided by the BS 106 and to determine whether the legacy NTN barring bit of the detected cell indicates ‘notBarred’. Assuming that indeed the legacy NTN barring bit of the detected cell indicates ‘notBarred, the UE 102 reselects 642 the detected cell provided by the BS 106 and starts downlink synchronizing with this cell.

[0067] Although in this scenario the BS 104 provides a list of cells not operating in S&F mode in the event 608, in other embodiments, the BS 104 may also provide a list of satellite identities, or a list of frequencies not operating in the S&F mode. If the BS 104 provides a list of frequencies not operating in the S&F mode, the UE 102 considers all the satellites / cel Is using these frequencies and not operating in the S&F mode.

[0068] Fig. 7 is a signal diagram illustrating messages exchanged between a UE and satellites according to a scenario in which a UE, which receives information on when the serving cell will start to operate in the S&F mode, determines to trigger a neighboring cell measurement before the serving cell starts to operate in the S&F mode. The signal diagram in Fig. 7 is similar to that in Fig. 6, with the differences discussed below. Before the feeder link becomes unavailable 506 because the satellite 304 is beyond the communication range of the NTN gateway 302, the BS 104 broadcasts 704 the system information including (i) a first timer or a first time instance and (ii) a list of cells not operating in the S&F mode. Here, the first timer or the first time instance indicates the moment when the serving cell will start to operate in the S&F mode. In one embodiment, the first time instance indicates an absolute time (e.g., a coordinated universal time (UTC) value, or a System Frame Number (SFN) plus a sub-frame index) at which the feeder link will become unavailable. In another embodiment, the first timer indicates a remaining time (e.g., number of slots, number of subframes, milliseconds, or seconds) during which the feeder link remains available.

[0069] Before the serving cell starts to operate in the S&F mode (e.g., X time units before), the UE 102 determines 734 to trigger an intra-frequency and / or inter-frequency measurement on neighboring cells. Here the value X may be configured by the network or depends on the UE implementation. In another embodiment, the UE 102 selectively determines 734 to trigger the intra-frequency and / or inter-frequency measurement X time units before the serving cell starts to operate in the S&F mode depending onAttorney Docket No.: 0683-113-WO whether the UE 102 has received the list of cells not operating in the S&F mode. The UE 102 then performs 636 the intra-frequency and / or the inter-frequency measurement on the neighboring cells, and steps 638, 640 and 642 as in Figure 6.

[0070] Fig. 8 a signal diagram 800 illustrating messages exchanged between a UE and satellites according to a scenario in which a UE, which receives information on when the serving cell will start to operate in the normal mode (i.e., when the feeder link will resume), determines to refrain from attempting to access the network until that time. This Fig. 8 is a potential implementation of Fig. 6 Alternative C. Initially, a UE 102 having the RRC support for the S&F operation (i.e., capable of acquiring and decoding the S&F related information included in the system information or in the RRC message) stays 502 in the idle state and camps on an NTN cell provided by the BS 104 (through satellite 304). The satellite 304 may also carry a part of MME of an entire MME 112. While the satellite 304 still has the feeder link available, the UE 102 receives 804 the system information including (i) the legacy NTN barring indication (i.e., cellBarredNTN) equal to ‘notBarred, and (i) a first timer or time instance associated with the current feeder link status (i.e., feeder is available). In one embodiment, the first time instance indicates an absolute time (e.g., UTC time, or an SFN plus a sub-frame index) at which the feeder link will become unavailable. In another embodiment, the first timer indicates the remaining time (e.g., number of slots, number of subframes, milliseconds, or seconds) for which the feeder link will remain available. Upon acquiring the first timer or the first time instance, the UE 102 knows when the serving cell will start operating in the S&F mode.

[0071] Because the satellite 304 is an NGSO satellite, at a certain point of time, the feeder link becomes unavailable 506 because the satellite 304 is beyond the NTN gateway 302’s communication range. The UE 102 then receives 808 the system information including (i) the legacy NTN barring indication (i.e., cellBarredNTN) equal to ‘Barred, an S&F operation indication equal to T, and (ii) a first timer or time instance as described with respect to Fig. 7 and a second timer or time instance. In one embodiment, the second time instance indicates an absolute time (e.g., a UTC time, or an SFN plus a sub-frame index) at which the feeder link will resume. In another embodiment, the second timer indicates a remaining time (e.g., number of slots, numberAttorney Docket No.: 0683-113-WO of subframes, milliseconds, or seconds) for which the feeder link will remain unavailable. Upon acquiring the second timer or the second time instance, the UE 102 knows when the serving cell will start operating in the normal mode (i.e., not in the S&F mode), and hence determines 844 to refrain from attempting to access the network and / or freeze the NAS layer until the feeder link is resumed.

[0072] Later, at the time when the feeder link is resumed 846 (i.e., is again available), the UE 102 stops 848 refraining from attempting to access the network, and / or unfreezes the NAS layer. The UE 102 may then receive 850 the system information including (a) the legacy NTN barring indication (i.e., cellBarredNTN) equal to ‘notBarred, and (b) a third timer or time instance associated with the current feeder link status (i.e., feeder is available). After that, the UE may initiate 816 an RRC connection establishment procedure when triggered by the UL traffic or user activity.

[0073] Fig. 9A is a flow diagram of a method 900A performed by a UE (e.g., UE 102) for determining whether to trigger an access attempt in a cell operating in the S&F mode, based on detailed S&F capability. Initially, at 902, the UE operates in the idle or inactive state and camps on an NTN cell. The UE is capable 903 of supporting the S&F operation in the RRC layer (i.e., the UE is capable of acquiring and decoding the S&F related information included in the system information or in the RRC message). The UE then receives 908, from the network (e.g., from the BS providing the serving cell), system information indicating the legacy NTN barring indication indicating that UEs not supporting S&F are barred (i.e., cellBarredNTN = ‘Barred’) and an indication that the satellite / cell is operating in the S&F operation mode (i.e., S&F operation = 1 ). Later, UE’s upper layer (e.g., a NAS layer) triggers 914 an network access attempt, due to UL data or user activity.

[0074] The UE then determines 909 whether the UE NAS is capable of supporting the S&F operation (e.g., the UE NAS is able to extend / suspend the NAS timers and / or suspend the NAS state machine due to the unavailability of the feeder link or service link). If the determination at the decision block 909 is positive (i.e., the “YES” branch of 909), the UE triggers 916 an access attempt in the cell (e.g., by initiating a random access procedure in the cell and transmitting an RRCConnectionRequest message, an RRCConnectionResumeRequest message, or anAttorney Docket No.: 0683-113-WORRCConnectionReestablishmentRequest message to the network). However, if the determination at the decision block 909 is negative (i.e. , “NO” branch of 909), the UE refrains 932 from attempting to access the network (e.g., refrains from initiating a random access procedure in the cell).

[0075] Fig. 9B a flow diagram of a method 900B performed by a UE, for informing the network of UE’s NAS layer support for S&F operation, while conducting an access attempt in the cell operating in the S&F mode, according to an embodiment. The method 900B is similar to method 900A, with the differences discussed below. After steps 902, 903, 908, and 914, the UE determines at the decision block 909, whether the UE NAS is capable of supporting the S&F operation (e.g., the UE NAS is able to extend / suspend the NAS timers and / or suspend the NAS state machine due to the unavailability of the feeder link or service link). If the determination at the decision block 909 is positive (i.e., the “YES” branch of 909), the UE transmits 917 to the BS, an RRCConnectionRequest, an RRCConnectionResumeRequest, or an RRCConnectionReestablishmentRequest message, together with a UE capability indication indicating the UE NAS is capable of supporting the S&F operation. However, if the determination at the decision block 909 is negative (i.e., the “NO” branch of 909), the UE transmits 919 to the BS, an RRCConnectionRequest, an RRCConnectionResumeRequest, or an RRCConnectionReestablishmentRequest message, together with a UE capability indication indicating the UE NAS is not capable of supporting the S&F operation.

[0076] Fig. 10 is a flow diagram of a method 1000 performed by a UE (e.g., UE 102), for determining when to perform an intra-frequency and / or the inter-frequency measurement on a cell supporting the S&F operation according to an embodiment. After steps 902 and 903 described relative to Fig. 9A, at the decision block 1008A, the UE determines whether the UE has received system information indicating that the satellite / cell operates in the S&F operation mode (i.e., S&F operation = 1 ) from the BS (which provides the serving cell). If the determination at the decision block 1008A is negative (i.e., the “NO” branch of 1008A), the UE returns to step 902 and 903. However, if the determination at the decision block 1008A is positive (i.e., the “YES” branch of 1008A), the UE triggers 1034 an intra-frequency and / or inter-frequency measurement, ifAttorney Docket No.: 0683-113-WO the UE has not done so already. Prior to step 1034, the UE may receive 1008B again system information from the BS, this system information including a list of cells not operating in S&F mode.

[0077] After obtaining the measurement results, the UE may increase 1038 a detected cell ranking Rnby a value A, if the detected cell is not operating in S&F mode (i.e., if the detected cell is within the list of cells provided in 1008B). The value A may be a fix value defined in the specifications or may be a dynamic value configured by the network. The UE then performs 1041 a cell reselection evaluation based on the cell rankings and the frequency priorities of the detected cells and the serving cell.

[0078] Fig. 11 is a flow diagram of a method 1000 performed by a UE (e.g., UE 102) with full S&F support, for determining when to perform an intra-frequency and / or interfrequency measurement on a cell supporting the S&F operation according to an embodiment. The method 1100 is similar to method 1000, with the differences discussed below. Here, the UE is capable 905 of supporting the S&F operation in both NAS and RRC layer. On the “YES” branch of 1008A, instead of step 1008B in Fig. 10, the UE determines, at decision block 1108B, whether the UE has received the system information including a list of cells not operating in S&F mode. If the determination at the decision block 1008B is positive (i.e., the “YES” branch of 1108B), steps 1034, 1038 and 1041 follow as in method 1000 illustrated in Fig. 10. However, if the determination at the decision block 1008B is negative (i.e., the “YES” branch of 1108B), then the UE repeats step 902 and the steps following 902.

[0079] Fig. 12 is a flow diagram of a method 1200 performed by a UE (e.g., UE 102), for determining when the feeder link will resume or become unavailable, and then acting accordingly. After steps 902 and 903, the UE receives 1204A, from the network (e.g. BS providing the serving cell), system information indicating a timer or a time instance associated with the current feeder link status. In one embodiment, time instance indicates an absolute time (e.g., a UTC time, or an SFN plus a sub-frame index) at which the current feeder link status (i.e., feeder link is available or unavailable) will change. In another embodiment, the timer indicates a remaining time (e.g., number of slots, number of subframes, milliseconds, or seconds) for which the current feeder link status (i.e., feeder link is available or unavailable) is maintained. In some embodiments,Attorney Docket No.: 0683-113-WO the timer indicating the remaining time associated with the current feeder link status is a value that would change every time when receiving system information. The changes of the timer value should neither result in system information change notifications nor in a modification of systemlnfoValueTag in S I B 1 . The UE should only need to acquire the timer once and then maintain and elapse the timer value automatically by itself.

[0080] After that, the UE determines at 1205 whether the UE has received from the BS the system information indicating the satellite / cell is operating in the S&F operation mode (i.e., S&F operation - 1 ). If the result of the determination at the decision block 1205 is positive (i.e., the “YES” branch of 1205), the UE considers 1243 that the feeder link will be resumed at the time instance or when the timer expires. The UE then refrains 1244 from attempting to access the network and / or freezes the NAS layer until the feeder link is resumed.

[0081] However, if the determination at the decision block 1205 is negative (i.e., the “NO” branch of 1205), the UE considers 1233 that the feeder link will become unavailable at the time instance or when the timer expires. The UE then triggers 1234 an intra-frequency and / or inter-frequency measurement before the feeder link becomes unavailable, if it has not done so already. Note that prior to triggering the measurement, the UE may receive 1240B, from the network system information including a list of cells not operating in S&F mode. After obtaining the measurement results, the UE may increase 1238 a detected cell ranking Rnby a value A, if the detected cell is not operating in S&F mode (i.e., if the detected cell is within the list of cells received at 1204B). The value A may be a fix value defined in the specifications, or may be a dynamic value configured by the network.

[0082] The following description may be applied to the description above. The description for one of the above figures may apply to another of the above figures. Examples, embodiments, and methods described above may be combined, if there is no conflict. An event or block described above may be optional or omitted. For example, an event or block with dashed lines in the figures may be optional. The description described from the perspective of the receiving node also applies to the sending node. For example, a description that a receiving node (e.g., DU) receives a message from a sending node (e.g., CU) may be replaced by the sending node sending a message toAttorney Docket No.: 0683-113-WO the receiving node. Similarly, a description that a receiving node (e.g., CU) receives a message from a sending node (e.g., DU) may be replaced by the sending node sending a message to the receiving node.

[0083] In some embodiments, the term “message” is used and may be replaced by “information element (IE)”, and vice versa. In some embodiments, the term “IE” is used and may be replaced by “field”, and vice versa. In some embodiments, the term “configuration” may be replaced by “configurations” or “configuration parameters”, and vice versa. In some embodiments, the term “LTM command” may be replaced by “serving cell change command”, “Layer 1 / Layer 2 LTM cell switch command”, “lower layer switching command” or “lower layer serving cell change command”. In some embodiments, “some” means “one or more”. In some embodiments, “at least one” means “one or more”. In some embodiments, the “DU configuration” may be replaced by “cell group configuration”. In some embodiments, the “cell index” may be replaced with “serving cell index”, “LTM cell index”, “special cell (SpCell) index”, “PCell index” or “PSCell index”. In some embodiments, the “serving” may be replaced by “source”. In some embodiments, the “measurement report” may be replaced by “measurement result(s)” or “CSI report”. In some embodiments, the “early TA acquisition” may be replaced by “early UL timing synchronization” or “early UL synchronization”. In some embodiments, the “early TA acquisition on a / the candidate cell” may be replaced by “early UL timing synchronization with a / the candidate cell” or “early UL synchronization with a / the candidate cell”. In some embodiments, “include” may be replaced by “comprise”. In some embodiments, the “RACH configuration” described above for early UL synchronization may be replaced by “early UL synchronization configuration”.

[0084] A user device in which the techniques of this document may be performed (e.g., the UE 102) may 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 userAttorney Docket No.: 0683-113-WO device may operate as an internet-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device may include one or more general- purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0085] Certain embodiments are described in this document 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 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.

[0086] When implemented in software, the techniques may be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software may be executed by one or more general-purpose processors or one or more special-purpose processors.

[0087] Reference throughout this document to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0088] Numerical adjectives “first”, “second”, and “third” do not imply any order (are not ordinals) but are markers to distinguish separate instances of similar elements.Attorney Docket No.: 0683-113-WOReferences to the singular (e.g., “a” or “an”, “the”) should include the plural unless clearly indicated otherwise.

[0089] 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.

[0090] Upon reading this document, those of skill in the art will appreciate additional and alternative structural and functional designs for handling mobility between BSs 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.

Claims

Attorney Docket No.: 0683-113-WOWhat is claimed is:1 . A wireless communication method (900B) performed by a user equipment, UE, (102) in communication with a network entity, NE, (104, 112) on a satellite (103), the method comprising: receiving (908), from the NE, an NE store-and-forward indication indicating that the NE operates in a store and forward mode when a feeder link from the satellite to a ground satellite gateway is unavailable; and transmitting (917, 919), to the NE, a UE capability indication indicating whether a non-access stratum, NAS, of the UE is capable of store and forward (SandF) operation.

2. The wireless communication method of claim 1 , further comprising: when the NAS of the UE is capable of SandF operation, performing a NAS procedure with the NE while the feeder link is unavailable.

3. The wireless communication method of claim 1 or 2, further comprising: receiving, from the NE, system information indicating a timer or a time instance associated with the feeder link being unavailable.

4. The wireless communication method of claim 3 wherein the system information is a system information block 1 , SIB1 , broadcasted by the NE.

5. The wireless communication method of claim 3 or 4, further comprising: freezing a NAS procedure according to the timer or the time instance while the feeder link is unavailable.

6. The wireless communication method of any of claims 1 to 5, further comprising: attempting to reconnect to the NE when an uplink data transmission is required while the feeder link is unavailable.Attorney Docket No.: 0683-113-WO7. The wireless communication method of any of claims 1 to 5, further comprising: if the transmitting the UE capability indication indicated the NAS of the UE is incapable of the SandF operation, refraining from attempting to connect to the NE when an uplink data transmission is required while the feeder link is unavailable.

8. The wireless communication method of any of claims 1 to 7, further comprising: when the feeder link is unavailable, performing an intra-frequency measurement and / or an inter-frequency measurement to select a new serving cell.

9. The wireless communication method of claim 8, further comprising: while the performing of the intra-frequency measurement and / or an interfrequency measurement, detecting a non-SandF cell unable to operate in the store and forward mode when the feeder link is unavailable; modifying a cell ranking of the non-SandF cell; and selecting the new serving cell using cell rankings including the modified cell ranking of the non-SandF cell.

10. The wireless communication method of claim 9, wherein the modifying the cell ranking of the non-SandF cell increases the cell ranking of the non-SandF cell with a predetermined value.

11. A wireless communication method (500) performed by a network entity, NE, (104, 112) on a satellite (103), the method comprising: transmitting (508), to a user equipment, UE, (102) connected to the NE, an NE store-and-forward indication indicating that the NE operates in a store and forward mode when a feeder link from the satellite to a ground satellite gateway is unavailable; andAttorney Docket No.: 0683-113-WO receiving (516A, 516B), from the UE, a UE capability indication indicating whether a non-access stratum, NAS, of the UE is capable of store and forward (SandF) operation.

12. The wireless communication method of claim 11 , further comprising: transmitting system information indicating a timer or a time instance associated with the feeder link being unavailable.

13. The wireless communication method of claim 12, wherein the system information is a system information block 1 , SIB1 , broadcasted by the NE.

14. The wireless communication method of any of claims 11 to 13, further comprising: selectively accepting a request to reconnect from the UE depending on the UE capability indication.

15. A wireless communication device (102, 104, 112) including a communication interface (134, 136, 144, 146, 154, 156) and a processor (132, 142, 152) that controls the communication interface and is configured to perform a method as recited in claims 1 to 14.

Images