Non-terrestrial network (NTN) store and forward operation

Abstract

This disclosure provides systems, methods and apparatuses for a Store and Forward (S&F) operation in a non-terrestrial network (NTN). S&F operation is a feature in which an NTN node (101) can provide some service to a user equipment (UE) (102) even though a service link to the UE and a feeder link to the core network (CN 110) are not concurrently available. The NTN node (101) can implement some functionality of a base station (BS) (106) on board a satellite (104). The BS (106) can transmit system information (612) to indicate whether it supports the S&F operation as well as other parameters to manage whether a UE (102) attempts to access BS (106). Aspects of this disclosure enable the BS (106) on a satellite (104) to control timing and coordinate S&F operation with the UE (102) based on current or future availability of a feeder link to the CN (110).

Description

NON-TERRESTRIAL NETWORK (NTN) STORE AND FORWARD OPERATIONRELATED APPLICATION

[0001] This application claims the priority benefit of U.S. Provisional Patent Application Serial No. 63 / 561,541, filed March 5, 2024, and U.S. Provisional Patent Application Serial No. 63 / 557,992, filed February 26, 2024, both entitled “NON- TERRESTRIAL NETWORK (NTN) STORE AND FORWARD OPERATION,” the contents of which are both hereby incorporated by reference herein.TECHNICAL FIELD

[0002] This disclosure relates generally to wireless communication and some aspects relate to a store and forward capability of a non-terrestrial network (NTN) to support user equipment (UE) connectivity when a connection between an NTN node and a core network is periodically unavailable.BACKGROUND

[0003] This background description is provided for the purpose of generally presenting the context of the disclosure. 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.

[0004] A wireless communication system includes one or more network entities (such as a base station) enabling communication for a mobile communication device (referred to as a user equipment (UE)). Each base station operates one or more cells to provide coverage for the UE. Existing wireless communication systems and network selection techniques are based primarily on legacy terrestrial networks. However, the 3rdGeneration Partnership Project (3GPP) organization has proposed to extend 5thGeneration (5G) communications to nonterrestrial networks (NTNs) with 5G new radio (NR) technologies, or with the Long-Term- Evolution (LTE) technologies tailored for the Narrowband Internet-of-Thing (NB-IoT) or the enhanced Machine Type Communication (eMTC) technologies. A non-terrestrial network (NTN) refers to a network, or segment of networks, using radio frequency (RF) resources onboard an NTN node. Example NTN nodes include spaceborne vehicles or airborne vehicles. Airborne vehicles can include unmanned aircraft systems (UAS), High-Altitude Platform Systems (HAPS), balloons, dirigibles, winged vehicles such as airplane or drones, among other examples. Spaceborne vehicles can 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. In some implementations, NTN nodes can form constellations. For simplicity, the discussion below refers to all such apparatuses 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-gateway s). NTN gateways 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 can also include inter-satellite links (ISLs) when multiple NTN nodes form constellations. During normal operation, a satellite has feeder link continuity such that the satellite can connect to one or more serving NTN gateways, with sufficient time duration 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 might not have a feeder link to an NTN gateway. 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. It is desirable for an NGSO satellite to support connectivity for UEs located in remote areas.BRIEF SUMMARY

[0006] The systems, methods, and apparatuses of this disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0007] One innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless communication by a user equipment (UE). The method includes the UE receiving system information from a non-terrestrial network (NTN) node, thesystem information indicating that the NTN node supports a store and forward (S&F) operation. The method further includes the UE establishing a radio resource control (RRC) connection via a service link with the NTN node and communicating a Non-Access Stratum (NAS) message to the NTN node via the service link. The NAS message is associated with a NAS operation between the UE and a core network. The method further includes the UE suspending the RRC connection when the service link is unavailable and maintaining a state of the NAS operation while the RRC connection is suspended.

[0008] Another innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless communication by an NTN node. The method includes the NTN node transmitting system information indicating whether the NTN node supports an S&F operation. The method includes the NTN node establishing an RRC connection via a service link with a UE that supports the S&F operation and receiving a NAS message from the UE via the service link. The NAS message is associated with a NAS operation between the UE and a core network. The method includes the NTN node storing the NAS message while a feeder link between the NTN node and the core network is unavailable and communicating the NAS message to the core network after the feeder link becomes available.

[0009] Another innovative aspect of the subject matter described in this disclosure can be implemented as an apparatus that includes a communication unit and a processing system configured to control the communication unit to implement any one of the above-referenced methods.

[0010] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Like reference numbers and designations in the various drawings indicate like elements. Note that the relative dimensions of the figures may not be drawn to scale. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0012] FIG. 1 shows an example wireless communication system in which a user equipment (UE) communicates via a non-terrestrial network (NTN).

[0013] FIG. 2 shows an example of store and forward (S&F) operation of an NTN node when a service link and a feeder link are occasionally not available concurrently.

[0014] FIG. 3A shows an example wireless communication system implementing an NTN base station (BS) connecting to a satellite via an NTN gateway using a transparent payload implementation.

[0015] FIG. 3B shows an example wireless communication system implementing an NTN BS onboard a satellite using a regenerative payload implementation.

[0016] FIG. 4A shows an example user plane protocol stack in accordance with aspects of this disclosure.

[0017] FIG. 4B shows an example control plane protocol stack in accordance with aspects of this disclosure.

[0018] FIG. 5 shows example radio resource control (RRC) states and example Non-Access Stratum (NAS) states.

[0019] FIG. 6 shows a messaging diagram associated with an S&F operation.

[0020] FIG. 7A shows a messaging diagram of an example scenario in which a UE utilizes the S&F operation and transitions to an inactive / suspended state based on a suspension indication from the network.

[0021] FIG. 7B shows a messaging diagram of an example scenario in which a UE is capable of using the S&F operation and the NTN node provides a timer-extension indication to cause the UE to extend access stratum (AS) or NAS timers until a time when the NTN node expects a feeder link to resume.

[0022] FIG. 8 shows a messaging diagram of an example scenario in which a UE is not capable of supporting the S&F operation and refrains from accessing an NTN node that is capable of the S&F operation.

[0023] FIG. 9A shows a messaging diagram of an example scenario in which a legacy UE is barred from accessing an NTN node even though the NTN node supports the S&F operation for newer types of UEs.

[0024] FIG. 9B shows a messaging diagram of an example scenario in which an NTN node can manage access attempts from a legacy UE that does not support the S&F operation.

[0025] FIG. 10 shows a flow diagram of example operations of a UE to communicate with an NTN node using the S&F operation.

[0026] FIG. 11 shows a flow diagram of example operations of a UE in which the UE suspends or extends relevant AS / NAS timer based on an indication from an NTN node.

[0027] FIG. 12A shows a flow diagram of example operations of a UE that does not support the S&F operation in which the UE determines whether to access an NTN node based on a flag / indicator provided in the system information.

[0028] FIG. 12B shows a flow diagram of example operations of a UE that does not support the S&F operation in which the UE determines whether to access an NTN node based on a time value indicated in the system information.

[0029] FIG. 12C shows a flow diagram of example operations of a UE that does not support the S&F operation in which the UE determines whether to access an NTN node based on a time instance and a threshold value provided by the NTN node.

[0030] FIG. 13A shows a flow diagram of example operations of an NTN node for announcing the S&F operation mode using the cell barring indication and an S&F indication.

[0031] FIG. 13B shows a flow diagram of example operations of an NTN node for announcing the S&F operation mode using the S&F indication.

[0032] FIG. 14 shows a flow diagram of example operations of an NTN node for determining the RRC state of a UE that supports the S&F operation mode.

[0033] FIG. 15A shows a flow diagram of example operations of an NTN node for determining the RRC state of a UE that does not support the S&F operation mode.

[0034] FIG. 15B shows another flow diagram of example operations of an NTN node for determining the RRC state of a UE that does not support the S&F operation mode.

[0035] FIG. 16 shows an example wireless communication system in which more than one NTN node can participate in the S&F operation to enable connectivity for a UE.

[0036] FIG. 17A shows example system information according to aspects of this disclosure.

[0037] FIG. 17B shows an example RRC message according to aspects of this disclosure.

[0038] FIG. 18 shows a block diagram of an example wireless communication system showing hardware features and communication interfaces.DETAILED DESCRIPTION

[0039] The following description is directed to certain implementations for the purpose of describing innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. Some of the examples in this disclosure are based on wireless communication according to the 3rdGeneration Partnership Project (3GPP) wireless standards, such as the 4th generation (4G) Long Term Evolution (LTE) and 5thgeneration (5G) New Radio (NR) standards. However, the described implementations can be implemented in any device, system, or network that is capable of transmitting and receiving radio frequency signals according to any of the wireless communication standards, including any of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 or 802.16 wireless standards, or other known signals that are used to communicate within a wireless, cellular, or internet of things (loT) network, such as a system utilizing 4G, 5G, 6G, WiFi, or future radio technology.

[0040] A user equipment (UE) typically accesses a wireless communication system via a network node of a radio access network (RAN). A non-terrestrial network (NTN) is a type of RAN that includes spaceborne vehicles or airborne vehicles, referred to collectively as NTN nodes or satellites for brevity. An NTN node communicates with the UE via a service link and communicates with a core network via a feeder link to an NTN gateway. The service link is part of an access stratum (AS) between the UE and the NTN node. The UE and the NTN node can implement a radio resource control (RRC) protocol to manage aspects of the service link, such as radio resources, connectivity state, etc. A Non-Access Stratum (NAS) protocol refers to a protocol between the UE and the core network. NAS messages are communicated via a combination of the service link and the feeder link.

[0041] During normal operation, the service link and the feeder link are concurrently available. However, it is possible that a satellite can be temporarily or periodically located in an area where either the service link or the feeder link becomes unavailable. Absent the techniques of this disclosure, the UE might restart NAS operations or RRC operations each time the service link becomes available. These RRC and NAS protocol messages canconsume radio resources and power (both at the UE and the satellite). It is desirable to manage UE connectivity using a combination of a feeder link and service link that might not be concurrently available in some areas and / or at some times.

[0042] This disclosure provides systems, methods and apparatuses for a store and forward (S&F) operation. A satellite implements at least some functionality of a base station (BS), such as an RRC protocol. The satellite can indicate whether it supports the S&F operation by transmitting system information. In the S&F operation, the satellite can buffer or store NAS protocol messages for a feeder link or a service link when such links are unavailable. The satellite can retrieve the stored NAS protocol messages and transmit the NAS protocol messages via the feeder link (for uplink NAS messages) or the service link (for downlink NAS messages) when such links become available. The UE and the satellite can maintain awareness of the NAS status so that NAS operations can be temporarily suspended and subsequently resumed based on availability of the feeder link or the service link. S&F operation (also referred to as S&F operation mode) is a feature of a 5G system with satellite access in which the 5G system can provide some level of service (in storing and forwarding the data) when the end-to-end network connectivity via the satellite is intermittently / temporarily unavailable. The S&F operation mode can provide communication service for UEs under satellite coverage without a simultaneous active feeder link connection to the ground gateway.

[0043] In some aspects, the satellite can transmit system information indicating the satellite's capability for the S&F operation, whether the core network is currently available, a time delay to refrain from RRC operations, or other parameters. A UE can determine whether to initiate RRC operations based on the system information and whether the UE supports the S&F operation. Some aspects of this disclosure enable the satellite to control the RRC state based on predicted availability or unavailability of the feeder link.

[0044] In some aspects, a legacy UE can be in a coverage area of a satellite that supports S&F operation. In the context of this disclosure, a legacy UE is one that does not support S&F operation and does not interpret system information relevant to S&F operation. For example, the legacy UE might implement a previous version of the 3 GPP wireless standards that does not contemplate S&F operation or related information (such as system information or RRC information relevant to S&F capabilities). To mitigate repeated connection attemptsand failures, this disclosure provides techniques to control how the legacy UE interacts with the satellite based on the present or predicted availability of the feeder link.

[0045] Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. An NTN node (such as a satellite) can provide service to a UE in a remote area, even when connectivity between the NTN node and the core network is temporarily unavailable. In some aspects, the protocols and messages of this disclosure can reduce signaling overhead or redundant communications, such as starting and restarting RRC and NAS operations between periods of connectivity. Some techniques of this disclosure can reduce power consumption by a UE and satellite using more efficient suspend and resume operations at the RRC and NAS protocol layers. Advantageously, this disclosure includes techniques to accommodate different capabilities of UEs, such as UEs that do not support the S&F operation.

[0046] In some implementations, the S&F operation mode can be used for delay-tolerant loT services via non-geostationary orbit (NGSO) satellite services. For example, a service provider can offer a service of remote monitoring of fields by deploying and tracking many low-power or battery-powered loT type UEs (loT UEs) across the globe. The loT UEs can 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 a terrestrial mobile network operator and only satellite coverage is possible. The loT UEs can regularly send uplink information related to the area they are monitoring to an application server and sometimes receive downlink information (such as new parameters) from the application server. The uplink and downlink information can be delay-tolerant such that even periodic or occasional network access is suitable. By supporting S&F operation with the enhancements of this disclosure, the loT UEs can reduce power consumption and maintain RRC / NAS states more efficiently in coordination with the NTN.

[0047] FIG. 1 shows an example wireless communication system 100 in which a UE 102 communicates via an NTN. The NTN extends or augments the service capability of a wireless communication system. An NTN refers to a network, or segment of networks, using radio frequency (RF) resources on board an NTN node 101 (such as a spaceborne vehicle or an airborne vehicle). An NTN node 101 can belong to one of several types based on altitude, orbit, and beam footprint size. FIG. 1 shows an NTN node 101 as a satellite 104. A satellite104 can support a transparent or a regenerative (with on board processing) payload, and typically generates several beams for a given service area bounded by the satellite’s field of view. For a transparent payload implementation, a satellite 104 can apply RF filtering and frequency conversion and amplification, and not change the waveform signal. For a regenerative payload implementation (such as shown in FIG. 1), a satellite 104 can apply RF filtering, frequency conversion and amplification, demodulation and decoding, routing, and coding / modulation. In FIG. 1 the NTN node 101 (e.g., satellite 104) can perform some or all functions of a base station (shown as BS 106) such as managing an RRC protocol.

[0048] An NTN gateway 114 (sometimes also referred to as a “sat-gateway” or “GW”) communicatively couples the satellite 104 to ground components of the example wireless communication system 100 (such as another BS 106', a core network (CN) 110, or other data network resources). In this disclosure, the term BS 106 can refer to either or both of the BS 106' on the ground (when present) or the BS 106 (when onboard the satellite 104). In the example of FIG. 1, the satellite 104, the NTN gateway 114, and the BS 106 form part of a RAN (sometimes referred to as an NTN RAN). In some implementations, the radio access technology for the NTN RAN is based on 5G NR. Alternatively, the radio access technology for the NTN RAN can use an Evolved Universal Terrestrial Radio Access (E-UTRA) air interface for 4G LTE, or another radio access technology such as NB-IoT, among other examples. Any number of RANs can be communicatively coupled to the CN 110. The CN 110 can be implemented as an evolved packet core (EPC), a fifth generation (5G) core (5GC), or a sixth generation (6G) core.

[0049] In this disclosure, the NTN node 101 can refer to the satellite 104, the BS 106 onboard the satellite 104, or collectively to the satellite 104 and the BS 106, such that the phrases or reference numbers can be interchangeable. When the UE 102 is within a coverage area of the satellite 104, the UE 102 can establish a radio connection to the satellite 104 via an NTN cell 117. The NTN cell 117 refers to a coverage area in which the satellite 104 operates as part of a radio network. The radio network can be associated with a footprint on the surface of the Earth or could be deployed in air, space, a spaceship, or other planetary objects. The radio connection between the UE 102 and the satellite 104 can also be referred to as service link 122. When the UE 102 and the BS 106 have established the service link 122, the UE 102 is said to be in an RRC connected (RRC CONNECTED) state. After theUE is in the RRC_CONNECTED state, the UE 102 might send a network registration request or other uplink NAS messages to the CN 110 via the NTN node 101 (e.g., the satellite 104 and the BS 106). The satellite 104 communicates the network registration request or other NAS messages to the CN 110 via a feeder link 124 that communicatively couples the satellite 104 to the NTN gateway 114. The CN 110 determines whether to accept or reject the network registration based on user subscription information. Depending on where the UE 102 is located or what RAN is being accessed, the CN 110 might accept or reject the network registration request. The CN 110 provides the network registration accept / reject or other downlink NAS messages to the satellite 104 via the NTN gateway 114 and feeder link 124. After registering to the CN 110, the UE 102 can release or suspend the radio connection (e.g., service link 122). An RRC idle (RRC IDLE) state refers to a state where the radio connection is released. An RRC inactive (RRC INACTIVE) state refers to a state where the radio connection is suspended.

[0050] During normal operation 125, the satellite 104 is concurrently connected to the UE 102 (via the service link 122) and to the CN 110 (via the feeder link 124 and the NTN gateway 114). During normal operation 125 (sometimes referred to as a default operation mode), signaling and data exchange between a UE 102 with satellite access and the CN 110 includes both the service link 122 and the feeder link 124 being available simultaneously. Hence, at the time when the UE 102 interacts over the service link 122 with the satellite 104, there is a continuous end-to-end connectivity path between the UE 102 and the CN 110.

[0051] There may be some times when one of the links 122 or 124 becomes unavailable. For example, when the satellite 104 is in a first position 125A, the satellite 104 might have a service link 122 to the UE 102 but no feeder link 124 to the NTN gateway 114. The first position 125A is referred to as “Position A” for reference purposes in this disclosure. As an example, the first position 125 A might be over a remote area, such as the middle of an ocean, a sparsely populated area, or any location in which the satellite 104 cannot directly communicate with the NTN gateway 114. In another position (referred to as a second position 125B or “Position B”), the satellite 104 might have a feeder link 124 to the NTN gateway 114 but no service link 122 to the UE 102. For example, the UE 102 might remain located at the remote area while the satellite 104 has moved to the second position 125B where the satellite 104 can establish the feeder link 124 to the NTN gateway 114. In accordance with aspects ofthis disclosure, the NTN node 101 (e g., the satellite 104 and / or the BS 106) can implement an S&F operation. The S&F operation can be implemented on any type of spaceborne / airborne vehicle with RRC protocol functionality that is capable of managing S&F operations of a NAS protocol.

[0052] FIG. 2 shows an example 200 of S&F operation of an NTN node when a service link and a feeder link are occasionally not available concurrently. During S&F operation mode, end-to-end exchange of signaling / data (such as NAS message) is not achieved by concurrently available service link 122 and feeder link 124. Rather, the exchange of signaling / data is achieved in multiple steps, such as a first step for Position A and a second step for Position B. When the satellite 104 is at Position A (first position 125A), the signaling / data exchange between the UE 102 and the satellite 104 takes place, without the satellite 104 being simultaneously connected to the NTN gateway 114 (i.e., the satellite 104 is able to operate the service link 122 without an active feeder link 124 connection). Later, at Position B (second position 125B), when the satellite 104 is closer to NTN gateway 114 (and is further away from the UE 102), the connection between the satellite 104 and the NTN gateway 114 is established and hence the uplink data / signal stored on the satellite 104 can now be forwarded to the CN 110 through the NTN gateway 114. At Position B, the satellite 104 also receives and stores the downlink signal / data from the CN 110 for subsequent transmission to the UE 102. In a later step (such as a third step), the stored downlink data / signal is forwarded to the UE 102, such as when the satellite 104 travels back to Position A (first position 125A). In some implementations, the satellite 104 repeatedly traverses to the first position 125 A and the second position 125B at different times based on an orbit. For example, the satellite 104 can travel a circuit across a region of the Earth and return back to the first position 125A. Alternatively, or additionally, the satellite 104 can travel between multiple locations that include the first position 125A and the second position 125B.

[0053] It should be clear that the locations of Position A and Position B are not necessarily fixed. In some implementations, the UE 102 can be at a static location. Alternatively, the UE 102 can be mobile such that the third step (e.g., forwarding downlink NAS messages to the UE 102) might occur at a different position (not shown) other than Position A. The reference to Position A and Position B are for illustrative purposes to indicate that the satellite 104 can alternate between instances where the feeder link 124 is unavailable or the servicelink 122 is unavailable. The NTN node (e.g., satellite 104) stores (e.g., buffers) uplink NAS messages that the NTN node 101 receives from the UE 102 when the feeder link 124 is unavailable. In the S&F operation, when the feeder link 124 becomes available, the NTN node 101 can forward the buffered uplink NAS messages to the CN 110. Similarly, the NTN node 101 can store downlink NAS messages that the NTN node 101 receives from the CN 110 when the service link 122 is unavailable. When the service link 122 becomes available, the NTN node 101 can transmit the downlink NAS messages to the UE 102.

[0054] When the feeder link 124 and service link 122 are not available simultaneously, completing a procedure initiated by the UE 102 and involving the CN 110 could take more time than usually expected for the procedure (such as a NAS operation). For example, the satellite 104 might take a while to travel a complete circuit (i.e., position A to position B and back to Position A). Legacy timers for the procedures (e.g., NAS operations) involving the core network are not designed / configured for such a long delay and hence it is likely the UE 102 would consider such a procedure to have failed due to the expiry of a timer. If the UE 102 considers the procedure failed, the UE 102 might repeatedly restart the procedure, consuming additional power and radio resources. It is desirable to prevent repeating a procedure that is doomed to fail.

[0055] In accordance with aspects of this disclosure, the UE 102 (and the CN 110) can suspend the status and / or the timer of the procedure when using the S&F operation. For a legacy UE (e.g., a UE that does not support the S&F operation) it might be better for the NTN node to prevent access attempts from the legacy UE when a feeder link 124 is unavailable. This disclosure provides techniques (such as system information) to inform UEs regarding whether the NTN node supports the S&F operation. Furthermore, the system information can be formatted to enable S&F operation for some UEs (that support the S&F operation) and also prevent access requests by other UEs (that do not support S&F operation).

[0056] FIG. 3A is a block diagram of an example wireless communication system 300A implementing a BS 106' (on the ground) connecting to a satellite 104 via an NTN gateway using a transparent payload implementation. The example wireless communication system 300A uses one type of NTN deployment referred to as transparent payload architecture, which involves an NTN gateway 114 and a “transparent” satellite 104 for extending the range of a Uu interface. The Uu interface refers to the link between the UE 102 and a base station. Insome implementations, the satellite 104 implements a frequency conversion and an RF amplifier in both the uplink and downlink directions. With that being said, the satellite 104 function is similar to that of an analogue RF repeater. As a result, the satellite 104 repeats the Uu radio interface from a feeder link 124 (between the NTN gateway 114 and the satellite 104) to the service link 122 (between the satellite 104 and the UE 102) in the downlink direction and vice versa in the uplink direction. The Satellite Radio Interface (SRI) on the feeder link is the Uu interface, and the NTN gateway 114 supports functions to forward the signal of the Uu interface. The NTN gateway 114 can be placed at the same site as the BS 106' location, or can be connected to the BS 106' at a distance via a wired link. It is also possible to connect more than one NTN gateway 114 to a BS 106'. Different transparent satellites may be connected to the same base station on the ground, via the same NTN gateway, or via different NTN gateways. FIG. 3A also shows a data network 310 that is accessible via the CN 110.

[0057] In addition to the NTN node (e.g., satellite 104), the UE 102 can receive signals from other satellites. For example, the UE 102 can receive signals from a global navigation satellite system (GNSS), such as GNSS satellite 301. The UE 102 can obtain or measure the signals emitted from the GNSS satellite 301 to determine the UE's position. Based on the UE's position, the UE 102 can compensate for time and / or frequency drift when transmitting or receiving signals to or from the satellite 104, particularly when the satellite 104 is an NGSO satellite.

[0058] FIG. 3B illustrates a block diagram of an example wireless communication system 300B implementing an NTN BS 106 onboard a satellite 104 using a regenerative payload implementation. The BS 106 can perform some or all of the functions of a base station, including those described with reference to BS 106 or BS 106' in this disclosure. The service link (labeled Uu interface) is shown between the UE 102 and the BS 106. In the example of FIG. 3B, the feeder link from the BS 106 to the NTN gateway 114 can be referred to as the SRI. In this example, the SRI is a transport link between the NTN gateway 114 and the satellite 104 that carries traffic for the Ng (or SI) interface. The NTN gateway 114 at one end of the SRI serves as an intermediate node forwarding the Sl / Ng traffic to and from the CN 110. The Ng interface from the BS 106 includes a portion over the SRI (shown as Ngover SRI) and a portion on the ground. Different regenerative satellites can connect to the same CN 110 on the ground, via the same NTN gateway 114, or via different NTN gateways.

[0059] In some implementations, a first portion of the base station functionality (shown as BS 106) can be implemented on the satellite 104 while a second portion of the base station functionality (shown as BS 106') can be implemented at a ground entity. For example, in a disaggregated network, BS 106 can be divided into two components: the Distributed Unit (DU) and Centralized Unit (CU). In an example, the BS 106 can operate as a DU that handles baseband processing, including RF signal processing and modulation / demodulation. The BS 106' can be an example CU that manages higher-layer tasks like resource management, scheduling, and network optimization.

[0060] Although examples of this disclosure are based on the regenerative payload architecture illustrated in FIG. 3B, the techniques of this disclosure can apply to the transparent payload architecture as well, particularly where the transparent satellite 104 includes some subset or limited features for S&F operation (such as a capability to maintain coordinated states of RRC and NAS protocols).

[0061] In terms of the satellite moving pattern, there are three types of service links that are supported in NTN:• Earth-fixed: provisioned by beam(s) continuously covering the same geographical areas all the time (e.g., the case of Geostationary Earth Orbit or Geosynchronous Orbit (GEO / GSO) satellites)• Quasi-Earth-fixed: provisioned by beam(s) covering one geographic area for a limited period and a different geographic area during another period (e g., the case of Low Earth Orbit or Medium Earth Orbit (LEO / MEO) satellites capable of using steerable beams), or• Earth-moving: provisioned by beam(s) whose coverage area slides over the Earth surface (e.g., the case of LEO / MEO satellites using fixed or non-steerable beams).

[0062] With LEO / MEO satellites, the BS 106 can provide either quasi-Earth-fixed cell coverage or Earth-moving cell coverage. With GEO satellites, the BS 106 can provide Earth fixed cell coverage.

[0063] FIG. 4A shows an example user plane protocol stack in accordance with aspects of this disclosure. FIG. 4A includes a visual representation of the NTN portion of user planeprotocol stack 400 A involving the UE 102, the satellite 104, the NTN gateway 1 14, and a CN 110. The example CN 110 in FIG. 4A can illustrate a user plane function (UPF) of the 5GC. If the CN 110 is a EPC, the features of CN 110 can be performed by a serving gateway (SGW) function. In FIG. 4A, the NTN BS 106 is onboard the satellite 104. In the illustrated example in FIG. 4A, the BS 106 is a 5G NR base station, referred to as a gNB. In an alternative implementation, the B S 106 can use E-UTRA for 4G LTE and can be referred to as an evolved base station (eNB).

[0064] The diagram of the NTN user plane protocol stack 400A shows the NR-Uu interface (e.g., via a service link) between the satellite 104 (e.g., the BS 106) and the UE 102. When the BS 106 is an eNB, the user interface is referred to as LTE-Uu instead of NR-Uu. The diagram of the NTN user plane protocol stack 400A shows the Ng-U interface (e.g., via a feeder link) between the satellite 104 (e.g., BS 106) and the CN 110 via the NTN gateway 114. When the BS 106 is an eNB, the user interface is referred to as Sl-U instead of Ng-U.

[0065] On the UE 102, the user plane protocol stack 400A includes protocol layers for the Packet Data Unit (PDU), the Service Data Adaptation Protocol (SDAP), the Packet Data Convergence Protocol (PDCP), the Radio Link Control (RLC) protocol, the Medium Access Control (MAC), and Physical Layer (PHY). The satellite 104 also implements the SDAP, PDCP, RLC, MAC, and PHY layers. However, user data (e.g., PDU messages) are passed through the satellite 104 (via the lower layer protocols) to the PDU on the CN 110. If the radio access technology for the NTN RAN is E-UTRA or NB-IoT, the SDAP layer may not exist.

[0066] FIG. 4B shows an example control plane protocol stack 400B in accordance with aspects of this disclosure. The diagram of the NTN control plane protocol stack 400B shows the NR-Uu interface (e.g., via a service link) between the satellite 104 (e.g., the BS 106) and the UE 102. The NR-Uu includes a radio resource control (RRC) protocol in addition to the PDCP, RLC, MAC, and PHY layers. The UE 102 and the BS 106 serve as endpoints of the RRC 402 and the RRC 404, respectively. The RRC protocol can have one of a plurality of different states associated with the RRC connection. For example, the RRC connection can have an RRC state 422 of RRC IDLE, RRC CONNECTED, or RRC INACTIVE as described with reference to FIG. 1 and further described with reference to FIG. 5. In accordance with some implementations of this disclosure, the RRC state 422 can also be asuspended state such that the UE 102 and the BS 106 can suspend and restore the RRC connection depending on whether the UE 102 is currently in a coverage area of the satellite 104 (such as “Position A” of FIGs. 1 and 2)

[0067] The Ng-C interface is between the BS 106 and the CN 110. The example CN 110 in FIG. 4B can illustrate operation of an access and mobility function (AMF) of the 5GC. In 3GPP standards (e.g., the 3GPP technical specification (TS) 24.501 version 18.4.0), refer to an N1 interface. The diagram of the NTN control plane protocol stack 400B shows the N1 interface between the NAS layer 403 of the UE 102 and the NAS layer 413 of the CN 110. The N1 interface links the UE 102 and the AMF of the CN 110 via an access network. In FIG. 4B, the access network includes the NTN (such as the satellite 104, BS 106) coupled by the NTN gateway 114. In normal operation 125, and in traditional implementations of regenerative satellite access, the satellite 104 does not participate in the N1 interface other than to relay communications through the lower layers of the protocol stacks of the NR-Uu and Ng-C interfaces. In accordance with aspects of this disclosure, the satellite 104 can perform an S&F operation 425. During the S&F operation 425, the satellite 104 can maintain awareness of the NAS state 423. Example NAS states are further described with reference to FIG. 5. In some aspects, the S&F operation 425 includes a coordination of the RRC state 422 and the NAS state 423 such that they can be saved and resumed depending on availability of the NR-Uu interface and the Ng-C interface.

[0068] As with FIG. 4A, the example illustrated in FIG. 4B shows the BS 106 as a gNB. However, FIG. 4B could be modified to describe a scenario in which the BS 106 is an eNB. The CN 110 can illustrate operation of a mobility management entity (MME) of an EPC. For example, if the radio access technology for the NTN RAN is E-UTRA or NB-IoT, the Ng-U interface can be referred to as an SI -MME interface. The Nr-Uu can be referred to as an LTE-Uu interface.

[0069] FIG. 4B shows the S&F operation 425 as part of the satellite 104. However, alternatively, or additionally, the BS 106 (or even the NTN gateway 114) can perform some or all of the S&F operation 425. For example, the NTN gateway 114 can include a combination of nodes or functions, some of which are implemented in proximity to the satellite 104 and some of which are implemented in proximity to the CN 110. The S&F operation 425 (implemented by whichever NTN node or nodes) can maintain a status of theRRC state 422 and the NAS state 423 in association with a particular UE (such as the UE 102). The satellite 104 can maintain the status by any combination of local memory, messaging, or other protocols (not shown).

[0070] FIG. 5 shows example RRC states 522 and example NAS states 523. The RRC states 522 include the RRC IDLE 505, RRC CONNECTED 595, and RRC INACTIVE 535 states. Typically, a UE begins in the RRC IDLE 505 state and transitions to the RRC CONNECTED 595 state when it has established a radio connection to an access network (such as an NTN RAN). The RRC INACTIVE 535 state refers to a feature in which the RRC connection is suspended but RRC configurations and status are maintained by the UE and the access network so that the RRC connection can quickly return to the RRC CONNECTED 595 state (or else transition to the RRC IDLE 505 state when the RRC connection is released).

[0071] The NAS states 523 can include various connection management (CM) states. Connection management refers to the initiating and terminating of a NAS signaling connection between a UE and the core network (e.g., an AMF or an MME) via an N1 interface. CM states can include the CM idle state (CM-IDLE 508) and the CM connected state (CM- CONNECTED 509). In a traditional deployment, the CM-CONNECTED state refers to a state in which the UE has a NAS signaling connection with the core network (e g., the AMF or MME) via an N1 interface. A NAS signaling connection uses an RRC connection between the UE and the access network and a UE-specific association via a feeder link between the access network and the core network. Thus, under a traditional definition of the CM states, a UE in CM-IDLE 508 state has no NAS signaling connection established with the AMF over Nl, and a UE in CM-CONNECTED 509 does have a NAS signaling connection with the AMF over N 1. Upon completion of a NAS signaling procedure, the AMF may decide to release the NAS signaling connection with the UE. The AMF may keep a UE CM state in the AMF in CM-CONNECTED 509 state until the UE de-registers from the core network. A UE in CM- CONNECTED 509 state can be in the RRC CONNECTED 595 or the RRC INACTIVE 535 states.

[0072] FIG. 5 shows some example combinations of states that might occur during normal operation (such as normal operation 125 of FIG. 1). In the first example 515A, the UE is in the RRC IDLE 505 and CM-IDLE 508 states. In the second example 515B, the UE transitions to the RRC_CONNECTED 595 but the core network is not yet connected, the CMstate is CM-IDLE 508. In the third example 515C, the UE has an RRC connection (RRC_CONNECTED 595) to the access network and a NAS signaling connection (CM- CONNECTED 509) to the AMF or MME. However, as described with reference to FIG. 1, this is possible when the feeder link (Ng-C or SI -MME interface) and the service link (Nr- Uu or LTE-Uu interface) are concurrently available. A fourth example 515D shows the UE can be in RRC INACTIVE 535 state while the CM state is still CM-CONNECTED 509. Typically, the RRC INACTIVE 535 state is used for power saving techniques in which the access network can wake up the UE or the UE can periodically wake up to monitor for paging or downlink control information.

[0073] The bottom portion of FIG. 5 shows some examples of different combinations of the RRC and NAS states in accordance with aspects of this disclosure. In a first example 525A, a service link is available but the feeder link is unavailable (e.g., “Position A” of FIG. 2). The UE can be in the RRC IDLE 505, RRC CONNECTED 595, or RRC INACTIVE 535 states. However, because the feeder link is not available, the UE does not immediately transition from the CM-IDLE 508 state to the CM-CONNECTED 509 state because the N1 interface is not active. Instead, the NTN performs an S&F operation 501. The NAS state might be referred to as being in a NAS suspended state 518. The NAS suspended state 518 can be referred to by a variety of terms, such as CM suspended (CM- SUSPENDED). Alternatively, or additionally, the NAS suspended state 518 can be a modification of the CM-IDLE or CM- CONNECTED state where operations are delayed or occasionally interrupted by the lack of concurrent feeder and service links. The NTN can also cause the UE to enter an RRC suspended state 536 while the NTN node moves from Position A to Position B (as shown in the example of FIG. 2). The RRC suspended state 536 can be referred to by a variety of terms such as the RRC INACTIVE, a new name (e.g., RRC SUSPENDED), or a modification of the RRC IDLE state or RRC CONNECTED state where operations are delayed or occasionally interrupted.

[0074] In a second example 525B, a service link is unavailable and the feeder link is available (e.g., “Position B” of FIG. 2). The UE can be in an RRC suspended state (such as RRC_INACTIVE). The NTN performs an S&F operation 501 to send NAS messaging to the CN, which is similar to the CM-CONNECTED 509 except that the NTN relays stored UE messages for the N1 interface. In some examples, the NTN can cause the NAS state to changefrom the CM-IDUE 508 to the CM-CONNECTED 509 based on sending the stored uplink NAS messages.

[0075] The S&F operation 501 can coordinate the RRC states 522 and the NAS states 523 based on availability of the service link and the feeder link. For example, for a particular UE, the NTN node or the UE (or both) can maintain a status of the RRC state and the NAS state so that the NTN node or the UE (or both) can alternate between RRC suspended 536 and NAS suspended 518 states depending on whether the NTN node is at Position A or Position B. Although examples of the S&F operation described in this disclosure are based on NAS states 423 (CM state), the techniques of this disclosure can also apply to uplink and downlink user data. For example, the NTN node can perform S&F operations for PDU session management and / or data network communications (e.g., PDU packets).

[0076] FIG. 6 shows a messaging diagram 600 associated with an S&F operation. The diagram 600 shows communications and operations of the UE 102, the NTN node 101 (including the BS 106 and the satellite 104), and the CN 110. The NTN node 101 communicates with the UE 102 via the service link 122 (when available) and communicates with the CN 110 via the feeder link 124 to the NTN gateway 114 (when available).

[0077] In the example of FIG. 6, the UE 102 might start in an idle 605 state (such as RRC IDLE with CM-IDLE or RRC INACTIVE with CM-IDLE). When the NTN node 101 is at the first position 125A ("Position A"), the Sl / NG connection breaks 610, meaning the feeder link 124 is unavailable. However, at the first position 125A, the UE 102 is within coverage of the NTN node 101 and can receive system information 612 from the NTN node 101. The system information 612 can indicate, for example, that the NTN node 101 supports S&F operation. If the UE 102 also supports the S&F operation (meaning the UE 102 can implement techniques of this disclosure which use the S&F operation of the NTN node 101), the UE 102 establishes an RRC connection to the NTN node 101. For example, the UE 102 performs one or more RRC operations 620 with the BS 106 to transition to an RRC connected state 625. The UE 102 can also transmit uplink NAS or PDU messages to the BS 106 (shown as NAS and / or PDU operations (service link messages) 630). As an example, the uplink NAS messages 630 can include a NAS attach request message. However, because the feeder link 124 is not available at the first position 125A, the NAS / PDU operations 630 might not be completed at this stage. Instead, the NTN node 101 can store the uplink NAS or PDUmessages. The UE 102 can then transition to an RRC suspended state 635 (such as RRC INACTIVE, RRC SUSPENDED, etc.). In some implementations, the NTN node 101 transmits a downlink RRC message (not shown) to cause the UE 102 to transition to the RRC suspended state 635. In some implementations, the UE 102 would normally start a timer to determine when a failure of the NAS or PDU operations occurs during a normal operation. However, for the S&F operation, the UE 102 might extend, delay, pause, or stop such timers because the UE 102 is aware that the NTN node 101 is using an S&F operation. Later, when the satellite 104 moves (or the UE 102 moves), the UE is out of satellite coverage 640.

[0078] However, at the second position 125B ("Position B"), the Sl / NG connection resumes 650, meaning the feeder link 124 is available. The NTN node 101 can transmit uplink NAS / PDU messages 660 to the CN 110 via the feeder link 124. The NTN node 101 can also receive downlink NAS / PDU messages 660 from the CN 110. Because the service link 122 is not available at the second position 125B, the NTN node 101 stores the downlink NAS / PDU messages. Later, the Sl / NG connection breaks 670 when the satellite 104 moves (or an intermediate node of the NTN gateway 114 moves) such that the feeder link 124 becomes unavailable.

[0079] At a later time, the NTN node 101 might return to the first position 125 A (or to a position where the UE 102 is located) such that the UE is within satellite coverage 680. The NTN node 101 can establish the service link 122 by resuming the RRC connection 690. In some implementations, resuming the RRC connection can include transitioning from the RRC INACTIVE (or the RRC SUSPENDED or even the RRC IDLE) state to the RRC_CONNECTED state (shown as connected 695 state). The NTN node 101 then resumes the NAS / PDU operations 696 that were initiated at event 630. For example, the NTN node 101 can transmit downlink NAS / PDU messages.

[0080] After transmitting downlink NAS / PDU messages (operations 696), the UE 102 can return (shown as arrow 626) to event 630 where the UE 102 can transmit further uplink NAS / PDU messages. In some implementations, the pattern from events 630 to 696 can repeat multiple times as the satellite 104 moves between the first position 125 A and the second position 125B. Through the cycles of the first position 125A and the second position 125B, the NTN node 101 can maintain status of the RRC state and NAS state of the UE 102. In some implementations, the NTN node 101 can proxy or mimic the NAS state (e.g., CM-CONNECTED or CM-IDLE) when communicating with the UE 102. Alternatively, or additionally, the NTN node 101 can proxy or mimic the RRC state when communicating to the CN 110.

[0081] The remaining Figures of this disclosure include several example scenarios in which a UE and / or an NTN node perform techniques for supporting S&F operation mode. Generally speaking, similar events are labeled with reference numbers that have the same lower-order (ones and tens) digits. For example, events 612, 712, 812, 912A, and 912B describe alternative examples of system information. For brevity, similar events are not discussed in detail in each Figure, but the discussion of a certain event with reference to one of the figures also applies to similar events in other figures.

[0082] FIG. 7A shows a messaging diagram 700A of an example scenario in which a UE utilizes the S&F operation and transitions to an inactive / suspended state based on a suspension indication from the network. A UE 102 capable of supporting the S&F operation mode initially stays in the idle 605 state and camps on an NTN cell provided by the BS 106 (through satellite 104). In this example, the satellite 104 is an NGSO satellite. At a certain point of time, the Sl / NG connection breaks 610 because the satellite 104 is beyond the reachable distance from the NTN gateway 114. The UE 102 receives the system information 712. In the example of FIG. 7A, the system information 712 includes a barring indicator (referred to as a “cellBarred" indicator, and a flag / indication indicating the BS 106 supports the S&F operation mode. The cellBarred indicator is a bit that informs UEs whether a cell is barred (cellBarred indicator = "barred") or not barred (cellBarred indicator = "not barred"). As described further with reference to FIG. 9A and FIG. 9B, the cellBarred indicator is a legacy indication that can be used to manage whether a legacy UE (e.g., a UE that does not support the S&F operation) can access the cell of the BS 106. A UE that does support the S&F operation mode might disregard the cellBarred indicator. For example, the UE 102 might proceed with an RRC connection regardless of whether the cellBarred indicator in the system information 712 indicates “barred” or “notBarred.”

[0083] The UE 102 determines to establish the RRC connection with the BS 106, and hence transmits an RRC Connection Request message 720 to the BS 106. In order to transmit an RRC Connection Request message to the BS 106, the UE 102 may need to initiate a Random Access (RA) procedure with the BS 106 to obtain an uplink grant for transmitting the RRCConnection Request message. A random access procedure may be referred to as a random access channel (RACH) procedure. A Type-1 random access procedure may be referred to as a 4-step RACH. The Type-1 random access procedure includes a protocol of up to four messages (referred to as MSG1, MSG2, MSG3, and MSG4). To begin the Type-1 random access procedure, a UE 102 transmits a random access preamble in a first message (MSG1) via a physical random access channel (PRACH). The NTN node 101 responds to the MSG1 by transmitting a second message (MSG2) via a physical downlink shared channel (PDSCH). The MSG2 is also referred to as a random access response (RAR) transmission. In some instances, the MSG2 indicates scheduled resources (in a physical uplink shared channel (PUSCH)) for the UE 102 to use for transmission of a third message (MSG3). When applicable, the UE 102 transmits the MSG3 via the PUSCH resources granted by the network entity. In response to the MSG3, the NTN node 101 transmits a fourth message (MSG4). The MSG4 is also referred to as a contention resolution transmission. It is noted that the MSG3 and the MSG4 might not be needed. For example, the UE 102 can include a small data transmission with the random access preamble in the MSG1 and the NTN node 101 can include a response in the MSG2. Alternatively, the UE 102 and the NTN node 101 can use a Type-2 random access procedure (referred to as a 2-step RACH) which uses fewer messages.

[0084] In some implementations, the RRC Connection Request message 720 includes an indication that the UE is capable of using the S&F operation mode. In some implementations, the indication is transmitted within the RRC message in a MSG3 grant. Alternatively, the indication can be transmitted via an uplink MAC control element (CE) in the MSG3 grant. Upon receiving the RRC Connection Request message, the BS 106 accepts the request and transmits an RRC Connection Setup message 722 to the UE 102. The UE 102 can acknowledge the reception of the RRC Connection Setup message 722 by transmitting an RRC Connection Setup Complete message 724 to the BS 106. After the RRC connection setup is complete, the UE 102 transitions to the RRC_CONNECTED state (connected 625). Although in the example 700A the UE 102 performs the RRC Connection Establishment procedure in order to enter the RRC CONNECTED state, the UE 102 may perform an RRC Connection Reestablishment or an RRC Connection Resume procedure instead, and indicates it is capable of using the S&F operation mode in the RRC Connection Reestablishment Request or in the RRC Connection Resume Request message.

[0085] After entering the RRC CONNECTED state, the UE 102 attempts to attach / register to the CN 110 by transmitting an uplink NAS message (e.g., NAS Attach Request 730) to the BS 106. In some implementations, the message transmitted at event 730 can be a Tracking Area Update (TAU) Request message if the UE 102 attempts to update its tracking area with the CN 110. Because there is no Sl / NG interface established between the BS 106 and the CN 110, the BS 106 stores the uplink NAS message. The BS 106 transmits a RRC Connection Release message 732 to the UE 102. In some implementations, the RRC Connection Release message 732 can include a cause value to inform the UE 102 that the Sl / NG connection is unavailable. For example, the cause value can indicate that the core network is disconnected, that a feeder link of the NTN node is unavailable, an S&F operation indication, or any indication that the UE 102 can interpret to mean that the BS 106 will use S&F operation for the uplink NAS message.

[0086] In some implementations, the RRC Connection Release message 732 can indicate a time, duration, or other condition to cause the UE 102 to suspend the RRC connection for a period of time. The period of time can be based on a duration, a time, or a timer value, among other examples. For example, the time / duration can be based on when the satellite 104 expects to return to a location (e.g., Position A of FIG. 2) where it can communicate with the UE 102 after making a pass past the NTN gateway 114. Although described as an RRC Connection Release message 732, the RRC message at event 732 can be a new RRC message used to cause the UE 102 to transition to the RRC suspended state 635. In some implementations, BS 106 can transmit the cause value and the time instance via a MAC CE or a Downlink Control Information (DCI) instead via an RRC message 732.

[0087] In the RRC suspended state 635, the UE suspends its RRC / NAS timers / status and keeps / stores the RRC / NAS context. As an example, the UE 102 can enter the RRC INACTIVE state, or transition to a state that does not require the UE 102 to monitor the physical downlink control channel (PDCCH) addressed to UE’s radio network temporary identifiers (RNTIs) configured for the RRC CONNECTED state. In some implementations, when UE 102 transitions to the RRC_INACTIVE state, the periodical RAN-based Notification Area (RNA) update timer is configured to be infinite on both the UE 102 and network sides.

[0088] After that, the satellite 104 moves such that the UE is out of satellite coverage 640. Later, the Sl / NG connection resumes 650 when the satellite 104 has moved to a position that is reachable from the NTN gateway 114. With the Sl / NG interface being established, the BS 106 can now forward the stored NAS message to the CN 110. In an example where the stored NAS message is a NAS Attach Request, the BS 106 transmits an S1AP Initial UE message 760 containing the NAS Attach Request message to the CN 110. In response to the SIAP Initial UE message 760, the CN 110 transmits an Initial Context Setup Request message 762 to the BS 106, and may forward the downlink data 764 (for the UE 102) to the BS 106.

[0089] The BS 106 may start paging the UE 102. However, because the connection between the BS 106 and UE 102 is not concurrently available, the BS 106 can store the downlink NAS message and / or the downlink data 764 for later transmission to the UE 102. In some implementations, the BS 106 or CN 110 (or both) can pause / suspend (such as a NAS suspended mode 518 of FIG. 5) transactions regarding the UE 102 between the BS 106 and the CN 110 based on the S&F operation. The Sl / NG connection between the BS 106 and CN 110 breaks 670 when the satellite 104 has moved away from the NTN gateway 114.

[0090] Later, the UE 102 is within the coverage of the satellite 104 again (at event 680), and hence it may receive the RAN paging or the CN paging message 781 including the identity of the UE 102 from the BS 106. Upon receiving the RAN paging or the CN paging message 781 or upon reaching the time indicated in event 732, the UE 102 starts initiating an RRC Connection Resume procedure 790 with the BS 106. In some implementations, instead of performing an RRC Connection Resume procedure at event 790, the UE 102 performs an RRC Connection Reestablishment procedure, an RRC Connection Establishment procedure, or another procedure to resume all the suspended RRC / NAS timers and status and re-synchronize with the BS 106. After the RRC connection has been re- established / established / resumed / recovered (shown as connected 695), the UE 102 receives the downlink NAS message 796 (e.g., NAS Attach Accept) from the CN 110. For example, the downlink NAS message 796 can be a response (stored and forwarded by the BS 106) in response to the uplink NAS message at event 730. The UE 102 may also receive the downlink data 798 stored and forwarded by the BS 106.

[0091] FIG. 7B shows a messaging diagram 700B of an example scenario in which a UE is capable of using the S&F operation and the NTN node provides a timer-extension indicationto cause the UE to extend AS or NAS timers when a feeder link is expected to resume. The message diagram in FIG. 7B is similar to that in FIG. 7A, with the differences discussed below. After receiving the uplink NAS message 730 from the UE 102, the BS 106 determines to keep the UE 102 in the RRC CONNECTED state for extra time until the BS 106 resumes the Sl / NG connection with the CN 110. For example, the BS 106 might be aware that the feeder link (e.g., Sl / NG) connection resumes 650 before the service link breaks. The BS 106 can store the uplink NAS message while waiting for the Sl / NG connection to resume.

[0092] The BS 106 transmits an RRC Connection Reconfiguration message 733 including a timer-extension indicator and optionally including cell discontinuous reception (c-DRX) configuration to the UE 102. In some implementations, the timer-extension indicator is included in another dedicated RRC message other than the RRC Connection Reconfiguration message 733. Alternatively, the BS 106 can transmit the timer-extension indicator via a downlink MAC CE or via a DCI. In another alternative, the BS 106 can transmit the timerextension indicator in system information such as in system information block type 1 (SIB1) or a new SIB type. Based on the timer-extension indicator, the UE 102 extends or suspends (block 736) certain AS and / or NAS timers. For example, the UE 102 can suspend or extend a data inactivity timer and / or a NAS timer used to determine the failure of the NAS Attach procedure.

[0093] Later, after the BS 106 has resumed the Sl / NG interface (650) with the CN 110 (i.e., the feeder link between the satellite 104 and the NTN gateway 114 has been established), the BS 106 forwards the stored NAS message to the CN 110 and the rest of the transactions (such as events 760, 762, 764, 796 and 798) among the BS 106, the UE 102, and CN 110 take place in the connected 625 state as normal. Upon receiving the downlink NAS message forwarded by the BS 106, the UE 102 can resume (block 797) the suspended AS / NAS timers or restore the extended AS / NAS timers. In one implementation, the UE 102 resumes or restores the suspended or extended AS / NAS timers based on receiving an indicator (not shown) from the BS 106, where the indicator can be transmitted in a dedicated RRC message, in a downlink MAC CE, in a DCI, or in system information.

[0094] FIG. 8 shows a messaging diagram 800 of an example scenario in which a UE is not capable of supporting the S&F operation and refrains from accessing an NTN node that is capable of the S&F operation. The message diagram in FIG. 8 is similar to that in FIG. 7A,with the differences discussed below. After the Sl / NG connection breaks 610, the BS 106 transmits system information 812 including: a) a barring bit (i.e., cellBarred) with the value equal to "barred" or "notBarred" , b) a flag / indication indicating the BS 106 supports S&F operation mode, and optionally c) a time value before which the UE not capable of supporting the S&F operation mode shall refrain from performing the RRC Connection Establishment / Re-establishment / Resume procedure with the BS 106. Thus, system information 812 is similar to system information 712 with the addition of a time value that can be interpreted by the UE 102 even though the UE 102 (in the example of FIG. 8) does not support S&F operation.

[0095] Upon receiving the system information 812, at block 820, the UE 102 (which is not capable of supporting the S&F operation mode) refrains, for a period of time based on the time value in the system information 812, from performing RRC connection establishment with BS 106 based on the UE 102 being not capable of S&F. In some implementations, the BS 106 sets the time value based on when the Sl / NG connection to the CN 110 is resumed / recovered. In some implementations, the time value can be omitted from the system information 812. In such cases the UE 102 (which does not support for S&F operation) refrains (block 820) from performing the RRC Connection Establishment / Re- establishment / Resume procedure with BS 106 until the UE 102 receives updated system information (not shown) that indicates that the cell is not barred and / or that the Sl / NG connection is available.

[0096] In some implementations, the time value indicated in the system information 812 can indicate a duration, a timer, a time instance, or a time instance plus a duration. After the time period associated with the time value has passed, the UE 102 can initiate an RRC Connection Establishment procedure with the BS 106 by transmitting an RRC Connection Request message 821 to the BS 106. The UE 102 can include an indication in the RRC Connection Request message or in an uplink MAC CE transmitted together with the RRC Connection Request message, which indicates the UE 102 is not capable of supporting the S&F operation mode.

[0097] In response to the RRC Connection Request message 821, the BS 106 can determine to accept the connection request when the feeder link is available. In some implementations, the BS 106 can determine whether to accept the RRC connection request based on whetherthe feeder link will remain available for a sufficient duration. In the example of FIG. 8, the BS 106 decides to accept the RRC Connection Request 821 and transmits an RRC Connection Setup message 722 to the UE 102. In a scenario where the BS 106 determines to reject the connection request (such as a determination that the feeder link will not remain available for a sufficient duration), the BS 106 might transmit an RRC Connection Reject message (not shown) to the UE.

[0098] After the RRC connection is established (connected 625), the UE 102 initiates and completes a NAS procedure (shown at events 730, 760, 762, 764, 796, and 798) with the CN 110 before the Sl / NG connection breaks 670 between the BS 106 and the CN 110, for example, due to satellite movement. Once the BS 106 loses its Sl / NG connection to the CN 110, the BS 106 may transmit an RRC Connection Release message 899 to the UE 102 to cause the UE 102 to transition to the RRC IDLE or RRC INACTIVE state (not shown). Although in the example 800 the UE 102 performs the RRC Connection Establishment procedure in order to enter the RRC CONNECTED state, the UE 102 may perform an RRC Connection Reestablishment or an RRC Connection Resume procedure instead, and indicates it is not capable of using the S&F operation mode in the RRC Connection Reestablishment Request or in the RRC Connection Resume Request message

[0099] FIG. 9A shows a messaging diagram 900A of an example scenario in which a legacy UE 902 is barred from accessing an NTN node even though the NTN node supports the S&F operation for newer types of UEs. The message diagram in FIG. 9A is similar to that in FIG. 8, with the differences discussed below. The UE 902 can be similar to UE 102 except that UE 902 does not support the S&F operation. In some examples, UE 102 can implement a newer version of the 3GPP technical specifications (such as Release 19 or later), while the legacy UE 902 implements an earlier version of the 3GPP technical specifications (such as release 18 or earlier). Because the UE 902 does not support the S&F operation and implements an earlier version of the 3GPP technical specifications, the UE 902 might not interpret the available system information related to this feature. The technique in FIG. 9A can prevent the UE 902 from consuming power or spectrum resources until such time that the Sl / NG connection resumes 650.

[0100] The BS 106 can update system information based on the availability of the feeder link. For example, when the Sl / NG connection breaks 610, the system information 912A(such as a SIB1) includes the barring bit (i.e., cellBarred) equal to "barred." The BS 106 can also include in SIB1 a flag / indication indicating the BS 106 supports the S&F operation mode and a time value as described with system information 812 (from FIG. 8), so that the flag / indication and the time value can be interpreted by a non-legacy UE (e.g., UE 102). Because the UE 902 is a legacy UE, the UE 902 may not attempt to establish / re- establish / resume the RRC connection with the BS 106, until the barring bit becomes ‘ notBarring" , which, in this example, occurs at the time when the Sl / NG connection between the BS 106 and CN 110 is resumed / recovered 650. When the legacy UE 902 attempts to establish / re-establish / resume the RRC connection 954 with the BS 106, the BS 106 may either accept the connection request, or reject the connection, depending on whether the feeder link will remain for a sufficient duration for the UE 902 to complete RRC and NAS related operations (such as events 722, 724, 730, 760, 762, 764, 796, and 798.

[0101] FIG. 9B shows a messaging diagram 900B of an example scenario in which an NTN node can manage access attempts from a legacy UE that does not support the S&F operation. The message diagram in FIG. 9B is similar to that in FIG. 9A, with the differences discussed below. After the Sl / NG interface between the BS 106 and CN 110 breaks 610, the BS 106 still configures system information 912B (e.g., SIB 1) to set the barring bit (i.e., cellBarred) as "notBarred." Based on the cell being “notBarred,” the legacy UE 102 transmits an RRC Connection Request message 920 in an attempt to establish the RRC connection with the BS 106.

[0102] Upon receiving the RRC Connection Request message 920, the BS 106 determines to reject the connection request based on a determination that the Sl / NG connection toward the CN 110 is currently unavailable. The BS 106 transmits an RRC Connection Reject message 921 to the UE 902, where the RRC Connection Reject message 921 may include an extendWaitTime information element (IE). The extendWaitTime IE prevents the UE 902 from further attempting to establish the connection with the BS 106 for a duration indicated in the extendWaitTime IE. In some implementations, a new IE other than the extendWaitTime IE is included in the RRC Connection Reject message 921 to prevent the UE 902 from accessing the cell for a duration longer than the maximum duration configurable in the extendWaitTime IE. In some implementations, the BS 106 sets the time in the extendWaitTime IE or the new IE based on a time when the Sl / NG connection to the CN 110 will be resumed / recovered.

[0103] FIG. 10 shows a flow diagram of example operations 1000 of a UE to communicate with an NTN node using the S&F operation. For example, a UE (e.g., UE 102) can perform the operations 1000 to connect to a BS (e.g., BS 106) operating in the S&F operation mode. The example operations 1000 are similar to those described with reference to FIG. 7A. Initially, at block 1005, the UE operates in the idle or inactive state, and is capable of supporting the S&F operation mode. At block 1012, the UE receives, from a BS, the system information indicating the BS supports the S&F operation mode. In some implementations, the system information also indicates that the cell is barred which implies that the feeder link is interrupted 610. By knowing the BS supports the S&F operation mode, the UE determines to access the cell even though the cell is indicated as barred. At block 1020, the UE transmits to the BS an uplink (UL) common control channel (CCCH) service data unit (SDU) (e.g., an RRC Connection Request, an RRC Connection Reestablishment Request, or an RRC Connection Resume Request message) indicating the UE is capable of supporting the S&F operation mode. In some implementations, the UE indicates the capability of supporting the S&F operation mode in an uplink MAC CE transmitted together with the uplink CCCH SDU.

[0104] At block 1022, the UE receives, from the BS, a downlink (DL) dedicated control channel (DCCH) SDU (e.g., an RRC Connection Setup, an RRC Connection Reestablishment, or an RRC Connection Resume message) in response to the UL CCCH SDU, where the DL DCCH SDU causes the UE to transition to the RRC CONNECTED state. After entering the RRC_CONNECTED state, the UE initiates a NAS procedure (e.g., a NAS Attach or a TAU update procedure) and transmits to the CN, at block 1030, a NAS message (e.g., a NAS Attach Request or a TAU Request message). At block 1032, the UE receives, from the BS, an RRC Connection Release message including a cause value indicating ‘CN is disconnected’, and optionally indicating a time value. The time value can be indicated as a timer, a duration, or a time instance plus a duration. In some implementations, the RRC Connection Release message includes an identity (e.g., UE Resume ID or inactive RNTI (LRNTI)) that is used to identify the UE in the RRC INACTIVE state. An I-RNTI can also be referred to as an RRC INACTIVE state RNTI. In response to the RRC Connection Release message, at block 1035, the UE enters an RRC suspended state (such as the RRC_INACTIVE state with an infinite RNA update timer or RRC SUSPENDED state).

[0105] At block 1081 , the UE may receive a paging message (e.g., a RAN paging or a CN paging message) including the UE’s ID (e.g., UE’s Resume ID or s-temporary mobile subscriber identity (s-TMSI)). In response to the paging message including UE’s ID, the UE initiates, at block 1090, an RRC Connection Resume or an RRC Connection Establishment procedure with the BS. Alternatively, if the UE does not receive a paging message including UE’s ID, but has received a time value in the RRC Connection Release message, the UE initiates an RRC Connection Resume or an RRC Connection Establishment procedure with the BS after a period of time based on the time value indicated in the RRC Connection Release message. After the RRC Connection is resumed / established, the UE receives from the CN, at block 1096, a NAS message (e.g., a NAS Attach Accept or a TAU Accept message) in response to the NAS message transmitted at block 1030.

[0106] FIG. 11 shows a flow diagram of example operations 1100 of a UE (e.g., UE 102) in which the UE suspends or extends relevant AS / NAS timers based on an indication from a BS (e.g., BS 106). The example operations 1100 are similar to those described with reference to FIG. 7B. The flow diagram in FIG. 11 is similar to that in FIG. 10, with the differences discussed below. After the UE has transmitted (block 1030) a NAS message to the CN, the UE receives from the BS, at block 1133, a timer-extension / suspension indicator with a first value (such as ‘ 1 ’), and optionally an RRC Connection Reconfiguration message including a c-DRX configuration. In some implementations, the timer-extension / suspension indicator indicates other values than ‘ 1’ . In response to the timer-extension / suspension indicator, the UE remains, at block 1136, in the RRC CONNECTED state by suspending or extending certain AS / NAS timers relevant to the RRC state transition (e.g., the RRC data inactivity timer). After that, the UE receives from the CN, at block 1096, a NAS message (e.g., a NAS Attach Accept or a TAU Accept message) in response to the NAS message transmitted at block 1030.

[0107] At block 1191, the UE may receive, from the BS, the timer-extension / suspension indicator with a second value (such as ‘0’), or with the value opposite to the value indicated at block 1133. In response to the NAS message received at block 1096, or the timer- extension / suspension indicator received at block 1 191 , the UE resumes or shortens, at block 1193, the relevant AS / NAS timers that have been suspended or extended earlier at block 1136.

[0108] FIG. 12A shows a flow diagram of example operations 1200A of a UE (e.g., UE 102 or UE 902) that does not support the S&F operation in which the UE determines whether to access an NTN node based on a flag / indicator provided in the system information. The example operations 1200 A are similar to those described with reference to FIG. 8. Initially, at block 1205, the UE operates in the idle or inactive state, and is not capable of supporting the S&F operation mode. At block 1212A, the UE receives, from a BS, the system information including a fl ag / indi cation indicating the BS supports the S&F operation mode. At block 1220A, because the cell supports the S&F operation mode and the UE does not support S&F operation, the UE refrains from establishing / reestablishing / resuming the RRC connection with the BS. At block 1213, the UE receives, from the BS, system information. The system information may not include the flag / indication indicating the BS supports S&F operation mode. Alternatively, or additionally, the UE receives system information that includes the flag / indication indicating the BS supports S&F operation mode without being able to interpret the flag / indication indicating the BS supports S&F operation mode. In some implementations, the UE knows the BS does not support the S&F operation mode at block 1213, upon receiving the system information including a flag / indication indicating the BS does not support the S&F operation mode. Based on the BS not supporting the S&F operation mode, the UE might attempt to access the cell based on normal operation. For example, at block 1221A, the UE transmits, to the BS, an UL CCCH SDU indicating the UE is not capable of supporting the S&F operation mode. In some implementations, the UE indicates the UE is not capable of supporting the S&F operation mode by not sending a flag / indication indicating the UE is capable of supporting S&F in the UL CCCH SDU. In other words, a missing flag / indication regarding S&F support means that the UE is not capable of supporting S&F. After that, the UE receives from the BS, at block 1222, a DL DCCH SDU in response to the UL CCCH SDU, which transitions the UE to the connected state, to the idle state, or to the inactive state.

[0109] FIG. 12B shows a flow diagram of example operations 1200B of a UE (e.g., UE 102 or UE 902) that does not support the S&F operation in which the UE determines whether to access an NTN node based on a time value indicated in the system information. Initially, at block 1205, the UE operates in the idle or inactive state, and is not capable of supporting the S&F operation mode. At block 1212B, the UE receives from a BS, system informationindicating a time value before which the UE shall refrain from performing the RRC connection establishment / re-establishment / resume with the BS. At block 1220B, the UE refrains from establishing / reestablishing / resuming the RRC connection with the BS until after a timer period associated with the time value indicated in 1212B. After the time period, at block 1221B, the UE transmits, to the BS, an UL CCCH SDU indicating the UE is not capable of supporting S&F as described with respect to FIG. 12A. The rest of the procedure in FIG. 12B is the same as that in FIG. 12A.

[0110] FIG. 12C shows a flow diagram of example operations 1200C of a UE (e.g., UE 102 or UE 902) that does not support the S&F operation in which the UE determines whether to access an NTN node based on a time instance and a threshold value provided by the NTN node. Initially, at block 1205, the UE operates in the idle or inactive state, and is not capable of supporting the S&F operation mode. At block 1212C, the UE receives, from a BS, system information indicating a time duration upon which the connection to CN will remain. In some implementations, the system information can also indicate whether the BS supports S&F operation. At block 1219, the UE determines whether the connection to CN will remain for a duration longer than a threshold value based on the time duration indicated in block 1212C. The threshold value can be pre-defined in the 3GPP specifications (i.e., a value hardcoded within the UE), or can be configured by the BS through a previously-received dedicated RRC message (not shown). If the decision at block 1219 is negative ("No"), the UE does not access the cell and then the flow returns back to the beginning of the flow diagram (block 1205). On the other hand, if the decision at block 1219 is positive ("Yes"), the flow proceeds to the block 1221A and the rest of the procedure is the same as that in FIG. 12A.

[0111] FIG. 13A shows a flow diagram of example operations 1300A of an NTN node for announcing the S&F operation mode using the cell barring indication and an S&F indication. The example operations 1300A can describe operations of the NTN node 101 (e.g., BS 106) as described with reference to FIG. 9A. The operations 1300A enable a BS (e.g., BS 106 in this disclosure) to announce the S&F operation mode using the cell barring indication and an S&F indication. Initially, at block 1310, the BS releases or suspends the connection to the CN based on the NTN gateway being beyond a reachable distance from the BS on an NGSO satellite. At block 1312A, the BS transmits system information indicating the cell is barred (due to the feeder link interruption 610) and the BS supports the S&F operation mode. Later,at block 1350, the BS establishes or resumes the connection to CN based on the NTN gateway now being within a reachable distance from the BS. At block 1352, the BS transmits system information indicating the cell is not barred due to the feeder link resumption 650.

[0112] FIG. 13B shows a flow diagram of example operations 1300B of an NTN node for announcing the S&F operation mode using the S&F indication. The operations of FIG. 13B are the same as FIG. 13 A, except that FIG. 13B includes block 1312B instead of block 1312A. At block 1312B, the BS transmits system information including a flag / indicator indicating that the BS supports the S&F operation mode based on determination the NTN gateway being beyond a reachable distance from the BS on an NGSO satellite. In block 1352, the BS can omit the flag / indicator because the BS has a connection to the CN and currently does not need to activate the S&F operation. Another difference between FIG. 13B and FIG. 13 A is that the system information in block 1312B can indicate that the cellBarred indicator is “not barred" when the BS supports S&F operation.

[0113] FIG. 14 shows a flow diagram of example operations 1400 of an NTN node for determining the RRC state of a UE (e.g., UE 102) that supports the S&F operation mode. The operations 1400 can be implemented by a BS (e.g., BS 106 in this disclosure). Initially, at block 1410, the BS releases or suspends the connection to the CN when, for example, the NTN gateway is beyond a reachable distance from the BS on an NGSO satellite. See connection interruption 610 of FIGs. 6, 7A, 7B, 8, 9A and 9B. At block 1420, the BS receives, from a UE, an uplink CCCH SDU indicating the UE is capable of supporting the S&F operation mode. See operations 620, 720 of FIGs. 6, 7A and 7B. In some implementations, at block 1420, the BS receives from a UE an uplink MAC CE transmitted together with an uplink CCCH SDU, where the uplink MAC CE indicates the UE is capable of supporting the S&F operation mode. In response to the uplink CCCH SDU, the BS transmits to the UE, at block 1422, a DL DCCH SDU in response to the UL CCCH SDU. See operation 722 in FIGs. 7A and 7B. The DL DCCH SDU causes the UE to transition to the connected state (e.g., RRC_CONNECTED). See operation 625 in FIGs. 6, 7A, and 7B (see operations 630, 730 in FIGs. 6, 7A, and 7B). At block 1430, the BS receives, from the UE, an uplink NAS message.

[0114] At block 1431, the BS determines whether the connection to the core network will resume before the satellite moves to a location where the on-board BS cannot serve the UE. If the determination at the block 1431 is negative ("NO") (i.e., the connection to the corenetwork will not resume before the satellite stops serving the UE), the flow proceeds to the block 1432. At block 1432, the BS transmits to the UE an RRC Connection Release message including a cause value indicating ‘CN is disconnected’, and optionally including a time value (such as described with reference to FIG. 7A). On the other hand, if the determination at the block 1431 is positive ("YES") (i.e., the connection to the core network will resume before the satellite stops serving the UE), the flow proceeds to the block 1433. At block 1433, the BS transmits to the UE a timer-extension / suspension indicator with value ‘ 1’, and optionally an RRC Connection Reconfiguration message including a c-DRX configuration (such as described with reference to FIG. 7B). Later, at block 1491, after resuming the connection with the core network, the BS may transmit to the UE the timer-extension / suspension indicator with value ‘0.'

[0115] FIG. 15A shows a flow diagram of example operations 1500A of an NTN node for determining the RRC state of a UE that does not support the S&F operation mode. The operations 1500A can be implemented by a BS (e.g., BS 106 in this disclosure) in an NTN node. Initially, at block 1550, the BS establishes or resumes the connection to the core network when the NTN gateway is within a reachable distance from the BS on an NGSO satellite. See operation 650. At block 1521, the BS receives, from a UE, an UL CCCH SDU indicating the UE is not capable of supporting the S&F operation mode. See message 821. At block 1525 A, the BS determines whether the connection to CN will break before the satellite stops serving the UE. If the determination at block 1525A is negative ("NO") (i.e., the connection to CN will not break before the satellite stops serving the UE), the flow proceeds to block 1522. At block 1522, the BS transmits, to the UE, a DL DCCH SDU in response to the UL CCCH SDU, which transitions the UE to the RRC CONNECTED state (such as described with reference to FIG. 8). On the other hand, if the determination at the block 1525 A is positive ("YES") (i.e., the connection to CN will break before the satellite stops serving the UE), the BS transmits to the UE, at block 1594, a DL DCCH SDU in response to the uplink CCCH SDU, which transitions the UE to the RRC IDLE or the RRC INACTIVE sate.

[0116] FIG. 15B shows another flow diagram of example operations 1500B of an NTN node for determining the RRC state of a UE that does not support the S&F operation mode. FIG. 15B is similar to FIG. 15A, except that FIG. 15B includes block 1525B instead of block 1525 A after receiving an UL CCCH SDU from a UE. At block 1525B, the BS determineswhether the connection to the core network will remain for a duration shorter than a threshold value. The threshold value at the decision block 1525B can a configurable value (configured by network vendors or operators) or a fix value hardcoded in the BS.

[0117] FIG. 16 shows an example wireless communication system 1600 in which more than one NTN node can participate in the S&F operation to enable connectivity for a UE 102. FIG. 16 shows two NTN nodes (represented by satellite 104 and satellite 1604). Although not illustrated, each of the satellites 104 and 1604 can include a BS (similar to BS 106). In the example of FIG. 16, a first NTN node (satellite 104) is traveling in one direction (such as east-ward) and a second NTN node (e.g., satellite 1604) is traveling in a different direction (such as west-ward). In some implementations, the satellites could be traveling in any variety of directions, or even in the same direction but separated by some distance. The satellites 104 and 1604 can be communicatively coupled by an inter-satellite link (ISL 1623). In some implementations, the ISL 1623 can enable an X2 or Xn interface between base stations onboard the satellites. The satellites 104 and 1604 can communicate information about the UE 102 via the ISL 1623. In accordance with aspects of this disclosure, the satellites 104 and 1604 can exchange information regarding an S&F operation. For example, when the service link 122 breaks because the satellite 104 moves away from the first position 125 A the satellite 104 may have stored uplink NAS messages from the UE 102. When the feeder link 124 becomes available, the satellite 104 can provide the uplink NAS messages to the CN 110. The CN 110 can respond with downlink NAS messages which are stored at the satellite 104 in accordance with the S&F operation. The satellite 104 can transfer the downlink NAS messages to the satellite 1604 via the ISL 1623 based on a determination that the satellite 1604 will encounter the first position (shown at 1625 A) sooner than the initial satellite 104 will return to the first position. Alternatively, or additionally, the CN 110 can transmit the downlink NAS messages, the paging message, and / or the information about the S&F operation directly to the satellite 1604. When the satellite 1604 reaches the first position 1625 A, the satellite 1604 can resume the service link 1622 based on the previously-suspended service link 122. All other operations and features of this disclosure (such as those described with reference to FIG. 2, FIG. 6, FIG. 7A, FIG. 7B, etc.) can be implemented using two NTN nodes (e.g., satellite 104 and satellite 1604) where the operations described for BS 106 aresplit to between BSs in each of the NTN nodes and the ISL 1623 providing coordinated between the different NTN nodes.

[0118] FIG. 17A shows a diagram 1700A with example system information 1712 according to aspects of this disclosure. The example system information 1712 can include a cellBarred indicator 1713A, a flag / indicator indicating support for S&F operation 1713B, a CN connected status 1713C, a time value 1713D for a UE to refrain from RRC operations, or a time duration 1713E in which the CN will remain connected. For example, the cellBarred indicator 1713 A can indicate “barred” or “not barred” as described with reference to various Figures of this disclosure. The flag / indicator indicating support for S&F operation 1713B can be a field, bit, or IE. In some implementations, the support for S&F operation 1713B is an extension of the cellBarred indicator 1713A. Alternatively, or additionally, example system information 1712 can include the support for S&F operation 1713B only when the CN is not presently connected and the BS supports the S&F operation. When included, the CN connected status 1713C can inform the UE whether the BS currently has a feeder link (e.g., Sl / NG connection) or any communication path through which the BS can communicate with the CN. In some implementations, the example system information 1712 indicates a time duration 1713E in which the CN will remain connected to enable the UE to determine whether the time duration is sufficient for the UE to complete a NAS procedure. For UEs that do not support S&F operation, the example system information 1712 can include a time value 1713D for UE to refrain from RRC operations 1713D. The time value can enable the UE to conserve power and radio resources for a period of time when the BS knows the CN will not be available.

[0119] FIG. 17B shows a diagram 1700B with an example RRC message 1731 according to aspects of this disclosure. In various examples, the example RRC message 1731 can include a cause code 1732A, a suspend timer value 1732B, a timer-extension indicator 1732C, or an extended WaitTme IE 1732D. For example, the cause value 1732A can be any of the cause values described with reference to FIG. 7A. In some implementations, the cause value 1732A is a new cause code that is specific to S&F operation and which causes the UE to enter an RRC suspended state (such as RRC INACTIVE or RRC SUSPENDED). The suspend timer value 1732B can be an indicator, a value from a lookup table, a time instance, a duration, a timer initialization parameter, or any other information which informs the UE to suspend theRRC connection for a period of time. The timer-extension indicator 1732C can be an indicator that informs the UE to wait longer than normal AS / NAS timers. In some implementations, the timer-extension indicator 1732C can cause the UE to suspend or stop AS / NAS timers that would normally be active during RRC_CONNECTED and CM-CONNECTED states. The example RRC message 1731 can include an extendedWaitTme IE as described with reference to FIG. 9B.

[0120] FIG. 18 shows a block diagram of an example wireless communication system 1800 showing hardware features and communication interfaces. The depicted hardware configurations may omit certain components well-understood to be frequently implemented in such electronic devices, such as displays, peripherals, power supplies, and the like. The wireless communication system 1800 includes the same elements as described with reference to FIG. 1, including the UE 102, the BS 106, the satellite 104, and the CN 110. In some implementations, the UE 102 can support at least a 5G NR (or simply, “NR”) or E-UTRA air interface to communicate with the BS 106. The BS 106 connects to the CN 110 via an interface (e g., SI or NG interface). The BS 106 can connect to other base stations (including the BS 106' or the BS 1816) via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes.

[0121] The BS 106 is equipped with processing hardware 1806 that can include a receiver 1807B configured to receive data in the uplink direction. The processing hardware 1806 can also include a transmitter 1807A configured to transmit data in the downlink direction. The processing hardware further can one or more general-purpose processor(s) 1807C (e g., CPUs) and a non-transitory computer-readable memory (CRM) 1807D storing instructions that the one or more general-purpose processors execute. Additionally, or alternatively, the processing hardware 1806 can include special-purpose processing units. The processor 1807C may include, for example, one or more central processing units, graphics processing units (GPUs), or other application-specific integrated circuits (ASICs), and the like. CRM 1807D may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory usable to store device data of the BS 106. The satellite 104 can include processing hardware 1804, such as a transmitter 1805 A, a receiver 1805B, a processor 1805C, and CRM 1805D (similar to components 1806, 1807A, 1807B, 1807C and1807D of the BS 106). Tn some implementations, the components 1805 A, 1805B, 1805C and 1805D are shared or commonly implemented with the components 1807A, 1807B, 1807C and 1807D. The BS 1816 can include generally similar components (not shown) as the processing hardware 1806.

[0122] The UE 102 is equipped with processing hardware 1802 that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory 1803D storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. The processing hardware 1802 can also include a transmitter 1803 A configured to transmit data in the downlink direction. Further processing hardware can include a receiver 1803B configured to receive data in the uplink direction. The processing hardware 1802, in an example implementation, includes a processor 1803C to process data that the UE 102 will transmit in the uplink direction or process data received by UE 102 in the downlink direction. The processor(s) 1803C may include, for example, one or more central processing units, GPUs, or other ASICs, and the like. To illustrate, the processor(s) 1803C may include an application processor (AP) utilized by the UE 102 to execute an operating system and various user-level software applications, as well as one or more processors utilized by modems or a baseband processor. The CRM 1803D may include any suitable memory or storage device such as RAM, SRAM, DRAM, NVRAM, ROM, Flash memory, SSD or other mass-storage devices, and the like useable to store one or more sets of executable software instructions and associated data that manipulate the one or more processor(s) 1803C and other components of the processing hardware 1802 to perform the various functions described herein and attributed to the UE 102. The sets of executable software instructions include, for example, an operating system (OS) and various drivers (not shown), and various software applications (not shown), which are executable by processor(s) 1803C to enable user-plane communication, control-plane signaling, and user interaction with the UE 102.

[0123] The CN 110 can be an Evolved Packet Core (EPC) and / or a 5G core (5GC). Among other components, the EPC can include a Serving Gateway (SGW), a Mobility Management Entity (MME), a Home Subscriber Server (HSS), and a Packet Data Network Gateway (PGW). The SGW in general is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME is configured to manage authentication,registration, paging, and other related functions. The PGW 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 includes a User Plane Function (UPF), a Unified Data Management (UDM), an Access and Mobility Management Function (AMF), and / or Session Management Function (SMF). Generally speaking, the UPF is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF is configured to manage authentication, registration, paging, and other related functions, and the SMF is configured to manage PDU sessions. The HSS and the UDM store and maintain subscription information regarding the UE 102. The CN 110 can be implemented by one or more processing elements (shown as processing hardware 1810). The processing hardware 1810 can include a transmitter 1811A, a receiver 181 IB, a processor 1811C, and a CRM 181 ID, similar to corresponding components described with reference to processing hardware 1802, 1804, and 1806.

[0124] The transmitters 1803 A, 1805A, 1807A, and 1811A and receivers 1803B, 1805B, 1807B, and 181 IB are examples of a communication unit. The processors 1803C, 1805C, 1807C, and 1811C can also be referred to as a processing system. Other examples of a communication unit and a processing system are possible, including some examples that are commonly used in a wireless communication system. The BS 106, UE 102, satellite 104, and CN 110 can include other components not illustrated in FIG. 18. For example, the BS 106 can include an S&F operation unit to perform any of the functions described in this disclosure. The S&F operation unit can be implemented by a processing system and communication unit. Similarly, the UE 102 can include a system information interpretation unit capable of interpreting any of the example system information described in this disclosure. The UE 102 can also include an RRC management unit that can operate an RRC IN ACTIVE or RRC SUSPENDED based on information from the BS 106 to transition to an RRC suspended state. The system information interpretation unit and / or the RRC management unit can be implemented by a processing system and communication unit of the UE 102.

[0125] FIG. 1 through FIG. 18 and the operations described herein are examples meant to aid in understanding example implementations and should not be used to limit the potential implementations or limit the scope of the claims, some implementations may performadditional operations, fewer operations, operations in parallel or in a different order, and some operations differently.

[0126] The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects. While the aspects of the disclosure have been described in terms of various examples, any combination of aspects from any of the examples is also within the scope of the disclosure. The examples in this disclosure are provided for pedagogical purposes. Alternatively, or in addition to the other examples described herein, examples include any combination of the following implementation options (enumerated as clauses for clarity).

[0127] CLAUSES

[0128] Clause 1 : A method for wireless communication by a user equipment (UE) (102), the method comprising: receiving system information (612, 712, 812, 912A, 912B, 1712) from a non-terrestrial network (NTN) node (101, 104, 106), the system information indicating that the NTN node supports a store and forward (S&F) operation; establishing a radio resource control (RRC) connection via a service link with the NTN node; communicating a Non-Access Stratum (NAS) message to the NTN node via the service link, the NAS message associated with a NAS operation between the UE and a core network; suspending the RRC connection when the service link is unavailable; and maintaining a state of the NAS operation while the RRC connection is suspended.

[0129] Clause 2: The method of clause 1, wherein the suspending the RRC connection includes: receiving an RRC message including an indicator or cause value associated with suspending the RRC connection; and suspending the RRC connection based on the indicator or cause value.

[0130] Clause 3: The method of clause 2, wherein the indicator or cause value includes one or more of: a cause value indicating that the core network is disconnected, a cause value indicating that a feeder link of the NTN node is unavailable, or a timer value indicating a duration to suspend the RRC connection.

[0131] Clause 4: The method of any one of clauses 1 to 3, wherein the suspending the RRC connection includes: storing the state of the NAS operation in a memory of the UE; and entering an RRC inactive state or RRC suspended state.

[0132] Clause 5: The method of any one of clauses 1 to 4, further comprising: resuming the RRC connection and the NAS operation when the service link becomes available.

[0133] Clause 6: The method of any one of clauses 1 to 5, further comprising: determining that the service link is available based on at least one of: system information from the NTN node, a paging message from the NTN node, ephemeris information about the NTN node and location information about the UE, or expiration of a timer previously configured by the NTN node.

[0134] Clause 7: The method of any one of clauses 1 to 6, further comprising: receiving, from the NTN node, an RRC message with a timer-extension indicator; maintaining the RRC connection in a connected state; and suspending or extending a timer associated with the NAS operation based on the timer-extension indicator.

[0135] Clause 8: The method of any one of clauses 1 to 7, further comprising: disregarding a cellBarred indicator of the system information when the system information indicates that the NTN node supports the S&F operation.

[0136] Clause 9: A method for wireless communication by a non-terrestrial network (NTN) node (104, 106), the method comprising: transmitting system information (612, 712, 812, 912A, 912B, 1712), the system information indicating whether the NTN node supports a store and forward (S&F) operation; establishing a radio resource control (RRC) connection via a service link with a user equipment (UE) (102) that supports the S&F operation; receiving a Non-Access Stratum (NAS) message from the UE via the service link, the NAS message associated with a NAS operation between the UE and a core network; storing the NAS message while a feeder link between the NTN node and the core network is unavailable; and communicating the NAS message to the core network after the feeder link becomes available.

[0137] Clause 10: The method of clause 9, further comprising: suspending the RRC connection when the service link is unavailable; maintaining a configuration of the RRC connection while the service link is unavailable; and resuming the RRC connection based on the configuration when the service link becomes available.

[0138] Clause 1 1 : The method of clause 10, wherein the suspending the RRC connection includes: transmitting an RRC message to the UE including an indicator or cause value associated with suspending the RRC connection, wherein the indicator or cause value includes at least one of: a cause value indicating that the core network is disconnected, a cause value indicating that a feeder link of the NTN node is unavailable, or a timer value for a duration to suspend the RRC connection.

[0139] Clause 12: The method of any one of clauses 9 to 11, further comprising: transmitting a paging message to the UE when the service link becomes available, or transmitting a timer value to the UE to indicate a duration after which NTN node expects the service link to become available.

[0140] Clause 13: The method of any one of clauses 9 to 12, further comprising: transmitting, to the UE, an RRC message with a timer-extension indicator, wherein the timerextension indicator is based on a determination that the feeder link is presently unavailable and expected to become available within a time duration associated with the timer-extension indicator; and maintaining the RRC connection in a connected state.

[0141] Clause 14: The method of any one of clauses 9 to 13, wherein the system information further includes a cellBarred indicator, the method further comprising: populating the cellBarred indicator with a “barred” value to cause one or more UEs that do not support the S&F operation to refrain from establishing RRC connections with the NTN node, wherein the NTN node permits RRC connections from one or more UEs that support the S&F operation; or populating the cellBarred indicator with a “notbarred” value to enable the one or more UEs that do not support the S&F operation to establish RRC connections with the NTN node.

[0142] Clause 15: The method of any one of clauses 9 to 14, wherein the system information further includes a wait time value indicating a delay for one or more UEs that do not support the S&F operation to refrain from establishing RRC connections with the NTN node, and wherein the wait time value is a based on a duration after which NTN node expects the feeder link to become available.

[0143] Clause 16: An apparatus, comprising: a communication unit; and a processing system configured to control the communication unit to implement any one of the methods of any one of clauses 1 to 15.

[0144] Another innovative aspect of the subject matter described in this disclosure can be implemented as a machine-readable medium having processor-readable instructions stored therein that, when executed by a processing system of a UE or an NTN node, cause the UE or the NTN node to implement any one of the above clauses.

[0145] Another innovative aspect of the subject matter described in this disclosure can be implemented as an apparatus. The apparatus may include means for implementing any one of the above clauses.

[0146] The following additional considerations may apply to the foregoing and the following discussions. Generally speaking, description for one of the above figures can apply to another of the above figures. Any event or block described above can be optional. For example, an event or block with dashed lines can be optional. In some implementations, “message” is used and can be replaced by “information element (IE),” and vice versa. In some implementations, “IE” is used and can be replaced by “field,” and vice versa. In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters,” and vice versa. In some implementations, “some” means “one or more.” In some implementations, “at least one” means “one or more.” The “eNB” can be replaced by “base station,” “gNB,” “6G base station,” “evolved gNB,” or 6G gNB. “MME” can be replaced by AMF or evolved AMF or 6G AMF. “Core network (CN)” can be replaced by EPC, 5GC or 6GC.

[0147] Some examples of this disclosure refer to RRC messages for illustrative purposes. In the various figures and descriptions, some RRC messages can be replaced by other examples. For example, “RRC Connection Request message” can be replaced by “RRC Setup Request message.” “RRC Connection Setup message” can be replaced by “RRC Setup message.” “RRC Connection Setup Complete message” can be replaced by “RRC Setup Complete message.” “RRC Connection Reconfiguration message” can be replaced by “RRC Reconfiguration message.” “RRC Connection Reestablishment Request message” can be replaced by “RRC Reestablishment Request message.” “RRC Connection Reestablishment message” can be replaced by “RRC Reestablishment message.” “RRC Connection Reestablishment Complete message” can be replaced by “RRC Reestablishment Complete message.” “RRC Connection Resume Request message” can be replaced by “RRC Resume Request message.” “RRC Connection Resume message” can be replaced by “RRC Resumemessage.” “RRC Connection Resume Complete message” can be replaced by “RRC Resume Complete message.” “NAS Attach Request message” or “TAU Request message” can be replaced by “Registration Request message.” “NAS Attach Accept message” or “TAU Accept message” can be replaced by “Registration Accept message.”

[0148] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this specification belongs. The terms “first,” “second,” and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The use of terms “including,” “comprising” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings and can include electrical connections or couplings, whether direct or indirect. Furthermore, terms “circuit” and “circuitry” and “control unit” may include either a single component or a plurality of components, which are either active and / or passive and are connected or otherwise coupled together to provide the described function. In addition, the term operationally coupled as used herein includes wired coupling, wireless coupling, electrical coupling, magnetic coupling, radio communication, software based communication, or combinations thereof.

[0149] Some or all of the foregoing or the following implementations can be jointly combined or formed to be a new or another one implementation. The foregoing or the following techniques can be used to solve at least (but not limited to) the issue(s) or scenario(s) mentioned in this disclosure. Any two or more than two of the foregoing or the following paragraphs, (sub)-bullets, points, actions, or claims described in each method / technique / implementation may be combined logically, reasonably, and properly to form a specific method. Any sentence, paragraph, (sub)-bullet, point, action, or claim described in each of the foregoing or the following technique(s) / implementation(s) / concept(s) may be implemented independently and separately to form a specific method. Dependency, such as “based on,” “more specifically,” “where” or etc., in technique(s) / implementation(s) / concept(s) mentioned in this disclosure is just one possible implementation which would not restrict the specific method.

[0150] As used herein, the terms “user device”, “user equipment” (for example, UE 102), “wireless communication device”, “mobile communication device”, “communication device”, or “mobile device” refer to any one or all of cellular telephones, smartphones, portable computing devices, personal or mobile multi-media players, laptop computers, tablet computers, smartbooks, Internet-of-Things (loT) devices, palm-top computers, wireless electronic mail receivers, multimedia Internet enabled cellular telephones, wireless gaming controllers, display sub-systems, driver assistance systems, vehicle controllers, vehicle system controllers, vehicle communication system, infotainment systems, vehicle telematics systems or subsystems, vehicle display systems or subsystems, vehicle data controllers, point- of-sale (POS) terminals, health monitoring devices, drones, cameras, media-streaming dongles or another personal media devices, wearable devices such as smartwatches, wireless hotspots, femtocells, broadband routers or other types of routers, and similar electronic devices which include a programmable processor and memory and circuitry configured to perform operations as described herein. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an internet-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0151] Certain techniques are described in this disclosure as including logic or a number of components or modules. Modules can be software modules (e.g., code, or machine-readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g., as encompassed within a general -purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated andpermanently configured circuitry, or in temporarily configured circuitry (e. , configured by software) may be driven by cost and time considerations.

[0152] 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.

[0153] As used herein, the terms “component” and “module” are intended to be broadly construed as hardware, firmware, or a combination of hardware and software. As used herein, a processor is implemented in hardware, firmware, or a combination of hardware and software. As used herein, the phrase “based on” is intended to be broadly construed to mean “based at least in part on.”

[0154] As used herein, a phrase referring to a list of items separated by “or” refers to any combination of those items, including single members. For example, “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.

[0155] In this disclosure, an expression of “X / Y” may include meaning of any of the following: “X or Y” or “X and Y” or “X and / or Y." An expression of “(A) B” or “B (A)” may include the concept of “only B.” An expression of “(A) B” or “B (A)” may include the concept of “A+B” or “B+A.”

[0156] In this disclosure, the term "can" indicates a capability, or alternatively indicates a possible implementation option. The term "may" indicates a permission or a possible implementation option. The term "might" indicates a possible utilization of an implementation option.

[0157] Some aspects are described herein in connection with thresholds. As used herein, satisfying a threshold may refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, or the like.

[0158] The various illustrative components, logic, logical blocks, modules, circuits, operations and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, orcombinations of hardware, firmware or software, including the structures disclosed in this specification and the structural equivalents thereof. The interchangeability of hardware, firmware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware, firmware or software depends upon the particular application and design constraints imposed on the overall system.

[0159] As described above, some aspects of the subject matter described in this specification can be implemented as software. For example, various functions of components disclosed herein, or various blocks or steps of a method, operation, process or algorithm disclosed herein can be implemented as one or more modules of one or more computer programs. Such computer programs can include non-transitory processor-executable or computer-executable instructions encoded on one or more tangible processor-readable or computer-readable storage media for execution by, or to control the operation of, a data processing apparatus including the components of the devices described herein. By way of example, and not limitation, such storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store program code in the form of instructions or data structures. Combinations of the above should also be included within the scope of storage media.

[0160] Various modifications to the implementations described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.

[0161] Additionally, various features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. As such, although features may be described above as acting in particular combinations, and even initially claimed as such, one or more features from aclaimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0162] The drawings may schematically depict one or more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

Claims

CLAIMSWhat is claimed is:

1. A method for wireless communication by a user equipment (UE) (102), the method comprising: receiving system information (612, 712, 812, 912A, 912B, 1712) from a non-terrestrial network (NTN) node (101, 104, 106), the system information including a store and forward (S&F) operation indication that indicates the NTN node supports the S&F operation; establishing a radio resource control (RRC) connection via a service link with the NTN node; communicating a Non-Access Stratum (NAS) message to the NTN node via the service link, the NAS message associated with a NAS operation between the UE and a core network; and maintaining a state of the NAS operation based on the S&F operation indication when the service link becomes unavailable.

2. The method of claim 1, further comprising: receiving an RRC message including an indicator or cause value associated with suspending the RRC connection; and suspending the RRC connection based on the indicator or cause value.

3. The method of claim 2, wherein the indicator or cause value includes one or more of: a cause value indicating that the core network is disconnected, a cause value indicating that a feeder link of the NTN node is unavailable, or a timer value indicating a duration to suspend the RRC connection.

4. The method of claim 2 or 3, wherein the suspending the RRC connection includes: storing the state of the NAS operation in a memory of the UE; and entering an RRC inactive state or RRC suspended state.

5. The method of any one of claims 1 to 4, further comprising: resuming the NAS operation when the service link becomes available.

6. The method of any one of claims 1 to 5, further comprising: determining that the service link is available based on at least one of: system information from the NTN node, a paging message from the NTN node, ephemeris information about the NTN node and location information about theUE, or expiration of a timer previously configured by the NTN node.

7. The method of any one of claims 1 to 6, further comprising: disregarding a cellBarred indicator of the system information when the system information includes the S&F operation indication.

8. The method of any one of claims 1 to 7, further comprising: receiving, from the NTN node, a time duration for which the NTN node connection to the core network will remain; and determining to communicate the NAS message based on the time duration being greater than a threshold.

9. A method for wireless communication by a non-terrestrial network (NTN) node (104, 106), the method comprising: transmitting system information (612, 712, 812, 912A, 912B, 1712), the system information including a store and forward (S&F) operation indication that indicates the NTN node supports the S&F operation; establishing a radio resource control (RRC) connection via a service link with a user equipment (UE) (102) that supports the S&F operation; receiving a Non-Access Stratum (NAS) message from the UE via the service link, the NAS message associated with a NAS operation between the UE and a core network; storing the NAS message while a feeder link between the NTN node and the core network is unavailable; and communicating the NAS message to the core network after the feeder link becomes available.

10. The method of claim 9, further comprising: suspending the RRC connection when the service link is unavailable; maintaining a configuration of the RRC connection while the service link is unavailable; and resuming the RRC connection based on the configuration when the service link becomes available.

11. The method of claim 10, wherein the suspending the RRC connection includes: transmitting an RRC message to the UE including an indicator or cause value associated with suspending the RRC connection, wherein the indicator or cause value includes at least one of: a cause value indicating that the core network is disconnected, a cause value indicating that a feeder link of the NTN node is unavailable, or a timer value for a duration to suspend the RRC connection.

12. The method of any one of claims 9 to 11, further comprising: transmitting a paging message to the UE when the service link becomes available, or transmitting a timer value to the UE to indicate a duration after which NTN node expects the service link to become available.

13. The method of any one of claims 9 to 12, further comprising: transmitting, to the UE, an RRC message with a timer-extension indicator, wherein the timer-extension indicator is based on a determination that the feeder link is presently unavailable and expected to become available within a time duration associated with the timer-extension indicator; and maintaining the RRC connection in a connected state.

14. The method of any one of claims 9 to 13, wherein the system information further includes a cellBarred indicator, the method further comprising: populating the cellBarred indicator with a “barred” value to cause one or more UEs that do not support the S&F operation to refrain from establishing RRC connections with the NTN node, wherein the NTN node permits RRC connections from one or more UEs that support the S&F operation; orpopulating the cellBarred indicator with a “notbarred” value to enable the one or more UEs that do not support the S&F operation to establish RRC connections with the NTN node.

15. An apparatus, comprising: a communication unit; and a processing system configured to control the communication unit to implement any one of the methods of any one of claims 1 to 14.

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