Cell reselection based on satellite information for a non-terrestrial network (NTN)

Abstract

This disclosure provides systems, methods and apparatuses where a first satellite (112) transmits (150), to a user equipment (UE) (101) a message including a list of satellite identifiers (IDs) that identifies one or more other satellites that support a store-and-forward (S&F) operation with the first satellite. The UE performs neighbor cell measurements (170) during a radio resource control (RRC) idle state or an RRC inactive state. The UE detects a neighboring cell of a second satellite (122) fulfilling a cell reselection criterion. The UE performs (180) a cell reselection to the second satellite based on a satellite ID of the second satellite and the list of satellite IDs.

Description

Docket No. 14730885900PCTCELL RESELECTION BASED ON SATELLITE INFORMATION FOR A NONTERRESTRIAL NETWORK (NTN)RELATED APPLICATION

[0001] This application claims the priority benefit of U.S. Provisional Patent Application Serial No. 63 / 754,767, filed February 6, 2025, entitled “CELL RESELECTION BASED ON SATELLITE INFORMATION FOR A NON-TERRESTRIAL NETWORK (NTN),” the entire contents of which are hereby incorporated by reference herein.TECHNICAL FIELD

[0002] This disclosure relates generally to wireless communication and some aspects relate to cell reselection based on satellite information for a non-terrestrial network (NTN).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 base stations) 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 (TNs). The 3rdGeneration Partnership Project (3 GPP) organization has proposed to extend 5thGeneration (5G) communications to non-terrestrial 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 on board an NTN node. Example NTN nodes include spaceborne vehicles and airborne vehicles. 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-gateways). NTN gateways connect satellites to a coreDocket No. 14730885900PCTnetwork. 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. During normal operation, a satellite concurrently maintains a feeder link to the NTN gateway and a service link to the UE.

[0006] 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. Depending on a location of the satellite in relation to an NTN gateway and the UE, there might be instances where either the feeder link or the service link can become temporarily unavailable. The 3 GPP has proposed a store-and-forward (S&F) operation to enable partial connectivity when the service link and the feeder link are not concurrently available. In S&F operation, a satellite can buffer (i.e., temporarily storing and then later forwarding) NAS messages until the relevant feeder link or service link becomes available.

[0007] As satellite network deployments continue to expand, more satellites are being deployed to enable coverage for subscribers. In some implementations, a wireless communication system can include multiple NTN nodes. For example, NTN nodes can form constellations or other logical groups that share some common features. It is desirable to enable S&F operation at multiple satellites so that a UE can start a NAS procedure at one satellite and resume the ongoing NAS procedure at another satellite, as long as these satellites are in a same group.BRIEF SUMMARY

[0008] 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.

[0009] One innovative aspect of the subject matter described in this disclosure can be implemented as a method of a user equipment (UE) for wireless communication. The method includes the UE receiving, from a first satellite, a message (such as a non-access stratum (NAS) message) that indicates a list of satellite identifiers (IDs) of one or more other satellites that support a store-and-forward (S&F) operation with the first satellite. The method includes the UE performing neighbor cell measurements during a radio resource control (RRC) idle state or an RRC inactive state. The method includes the UE detecting a neighboring cell of a second satelliteDocket No. 14730885900PCTfulfilling a cell reselection criterion. The method includes the UE performing a cell reselection to the second satellite based on a satellite ID of the second satellite and the list of satellite IDs.

[0010] Another innovative aspect of the subject matter described in this disclosure can be implemented as a method of a first satellite for wireless communication. The method includes the first satellite establishing an RRC connection with a UE. The method includes the first satellite enabling an S&F operation for the UE. The method includes the first satellite communicating, to the UE, a message that indicates a list of satellite identifiers (IDs) identifying at least a second satellite that supports the S&F operation with the first satellite.

[0011] 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.

[0012] 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

[0013] 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.

[0014] FIG. 1 shows an example wireless communication system in which a user equipment (UE) communicates via a non-terrestrial network (NTN) having one or more satellites.

[0015] FIG. 2A illustrates an example of store-and-forward (S&F) operation in contrast to a normal operation mode.

[0016] FIG. 2B shows an example wireless communication system in which a satellite includes onboard non-access stratum (NAS) features.

[0017] FIG. 2C shows an example wireless communication system with multiple satellites participating in an S&F operation mode.

[0018] FIG. 3 shows an example split mobility management entity (MME) deployment.

[0019] FIG. 4 shows example messages that can include a list of satellite IDs for satellites participating in an S&F operation.Docket No. 14730885900PCT

[0020] FIG. 5 shows a messaging diagram of an example scenario in which a UE performs cell reselection based on a list of satellite IDs obtained from a first satellite.

[0021] FIG. 6A shows a messaging diagram of an example scenario in which a UE determines to reselect and camp on a cell of a satellite that is in a list of satellite IDs obtained from the NAS layer.

[0022] FIG. 6B shows a messaging diagram of an example scenario in which a UE determines to bar a cell of a satellite based on the satellite having a satellite ID that is not in a list of satellite IDs.

[0023] FIG. 7 shows a messaging diagram of an example scenario in which a UE manages neighboring cell measurement based on a list of satellite IDs.

[0024] FIG. 8 shows a messaging diagram of an example scenario in which a UE adjusts the cell ranking of a cell in the cell reselection evaluation process, based on a list of satellite IDs obtained from the NAS layer.

[0025] FIG. 9 shows a messaging diagram of an example scenario in which a UE determines whether to perform a tracking area update (TAU) procedure upon moving to a new cell based on the list of satellite IDs obtained from the NAS layer.

[0026] FIG. 10 shows a flow diagram of example operations of a UE for determining whether to reselect and camp on a neighboring cell fulfilling the cell reselection criteria based on a list of satellite IDs intended for the S&F operation.

[0027] FIG. 11 shows a flow diagram of example operations of a UE for performing cell reselection based on a list of satellite IDs obtained from the system information.

[0028] FIG. 12 shows a flow diagram of example operations of a UE for performing cell reselection based on an existing list of satellite IDs in a system information block type 33 (SIB33), where the SIB33 includes flags / indicators to indicate which satellites are in a list of satellite IDs intended for the S&F operation.

[0029] FIG. 13 shows a flow diagram of example operations of a UE for determining how to perform the neighbor cell measurement based on a list of satellite IDs intended for the S&F operation.

[0030] FIG. 14 shows a flow diagram of example operations of a UE for adjusting the rankings of neighboring cells for the cell reselection evaluation purpose based on a list of satellite IDs intended for the S&F operation.Docket No. 14730885900PCT

[0031] FIG. 15 shows a flow diagram of example operations of a UE for determining whether to trigger a TAU procedure upon camping on a new cell based on a list of satellite IDs intended for the S&F operation.

[0032] FIG. 16 is a block diagram illustrating an example user equipment.

[0033] FIG. 17A shows an example control plane protocol stack in accordance with aspects of this disclosure.

[0034] FIG. 17B shows an example user plane protocol stack in accordance with aspects of this disclosure.

[0035] FIG. 18 shows a block diagram of an example wireless communication system showing hardware features and communication interfaces.DETAILED DESCRIPTION

[0036] 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 (3 GPP) 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, sixth generation (6G), WiFi, or future radio technology.

[0037] This disclosure provides systems, methods and apparatuses for managing cell reselection in a wireless communication system having multiple non-terrestrial network (NTN) nodes (referred to as satellites, for brevity). Multiple satellites can participate in a store-and-forward (S&F) operation. A user equipment (UE) and / or a network node of a radio access network (RAN) can use the techniques of this disclosure to manage cell reselection in an NTN based on a list of satellite identifiers (IDs) for satellites that form a group (such as a constellation or logical group) that can coordinate S&F operation. In aspects of this disclosure, satellites can implement the S&F operation with onboard non-access stratum (NAS) features, such as features of a mobilityDocket No. 14730885900PCTmanagement entity (MME). In the examples of this disclosure, a satellite can operate a part of an MME, referred to as an “MME-onboard.” Another part of the MME (i.e., “MME-ground”) can be installed on a ground network node connecting to a satellite gateway. The MME-ground and several satellites with MME-onboard features can be grouped together to offer a complete MME functionality that is able to share and manage the UE context. An on-going NAS procedure can be retained and resumed when the UE switches from one satellite to another, as long as these satellites are in the same group (sometimes referred to as an MME group, S&F group, or other similar terms). In some implementations, the satellites in the same group periodically connect to the same NTN gateway. The satellites in the same group can exchange the UE context in NAS layer via interfaces to the same MME-ground or with each other. The satellites in a group are typically operated by the same operator.

[0038] To allow a UE to switch between satellites without requiring the UE to start over with a new NAS procedure, a satellite can transmit a list of satellite IDs to the UE to inform the UE about other satellites in a group (such as other satellites in the MME group or other satellites that maintain a shared UE context). In accordance with aspects of this disclosure, the UE can use the list of satellite IDs when performing a cell reselection. Cell reselection is performed at the radio resource control (RRC) layer of a UE to reselect and camp on a cell. In some aspects of this disclosure, a UE can obtain the list of satellite IDs in a NAS message and coordinate the RRC layer cell reselection based on the list of satellite IDs.

[0039] This disclosure provides several techniques to inform a UE about the list of satellite IDs. In some aspects, a first satellite can transmit a NAS message (such as from an MME-onboard or relaying a NAS message from an MME-ground) that includes the list of satellite IDs. In some aspects, a first satellite can transmit a system information message (such as a broadcast system information block (SIB)) that includes the list of satellite IDs. In some aspects, the first satellite transmits an RRC message to the UE while the UE is operating in an RRC connected state with the first satellite, where the RRC message is formatted to include the list of satellite IDs. In some aspects, a satellite can transmit a SIB type 33 (SIB33) that includes a list of neighboring satellite information, where the list of neighboring satellite information includes, for each neighboring satellite, a satellite ID and a corresponding flag indicating whether the neighboring satellite is in a same MME group for the S&F operation with the current satellite (e.g., whether the neighboring satellite should be included in the list of satellites for cell reselection to favor satellites in an MME group). A legacy SIB33 might include a list of neighboring satellite information withDocket No. 14730885900PCTsatellite IDs. However, in the context of this application, a “list of satellite IDs” refers to a listing of satellites (by satellite ID) that are in intended for S&F operation as a group. The term “list of satellite IDs” can be replaced with other terms, such as “list of confederated satellites,” “list of satellite IDs intended for the S&F operation,” “list of satellites in an MME group,” “list of S&F coordinating satellites,” or any term that suggests a relationship between satellites that collectively provide a cohesive experience between the UE and a core network. In some aspects, the NAS and the access stratum (AS) can use the same satellite ID for a particular satellite.

[0040] In some implementations, a UE can use the list of satellite IDs to qualify a candidate cell after performing neighbor cell measurements. For example, when a UE detects a candidate cell that fulfills a cell reselection criteria and access criteria, the UE can obtain the SIB type 31 (SIB31) from the candidate cell to determine the satellite ID of the satellite providing the candidate cell. The UE can determine whether to reselect and camp on the cell based on whether the satellite ID is included in the list of satellite IDs. In some implementations, the UE bars access to a candidate cell for a period of time (e.g., 5, 10, 30 seconds, among other examples if the candidate cell is associated with a satellite ID that is not in the list of satellite IDs. Alternatively, if no candidate cells have a satellite ID in the list of satellite IDs, the UE may determine to camp on the cell and / or proactively perform a tracking area update (TAU) and / or restart the NAS procedure.

[0041] In some implementations, the UE can save power and time by performing neighbor cell measurements based on the list of satellite IDs. For example, when triggering intra-frequency or inter-frequency cell measurements, the UE can prioritize measurements on candidate frequencies that are associated with satellites having satellite IDs in the received list of satellite IDs. In some implementations, the UE can perform neighbor cell measurements only on frequencies associated with the list of satellite IDs. In some implementations, the UE can calculate timing for satellites in the list of satellite IDs and perform neighbor cell measurements based on the timing for candidate cells. For example, this can reduce extraneous processing overhead for timing calculations on satellites that are not in the list of satellite IDs. In some implementations, the UE increases or maximizes the cell reselection priorities (i.e., CellReselectionPriority ::= INTEGER (0...7)) of candidate frequencies that are associated with satellites having satellite IDs in the received list of satellite IDs, by e g., adding a constant or a configurable value to these cell reselection priorities capped by 7.Docket No. 14730885900PCT

[0042] In some implementations, the UE can detect candidate cells from multiple satellites and adjust a cell ranking to favor a neighboring cell from a satellite in the list of satellite IDs. Alternatively, or additionally, a cell reselection criterion can be adjusted to favor satellites that are in the received list of satellite IDs. When the UE selects and camps on a cell provided by a satellite that is not in the list of satellite IDs, the LTE can proactively perform a TAU regardless of a tracking area code (TAC) of the neighboring cell so that the MME (i.e., MME-ground and one or more MME-onboard parts) can be informed that the UE is camped on a cell from a satellite that is not part of a group coordinated S&F operation.

[0043] Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. A network operator can provide a more cohesive coverage by operating multiple satellites in a group that shares UE context and onboard NAS functionality. Similarly, a UE can enjoy the benefits of satellite coverage and S&F operation that is coordinated among multiple satellites in a group. The UE can adjust cell reselection techniques to favor cells from satellites in a list of satellite IDs intended for the S&F operation. By camping on satellites in the group MME, the UE can save time and power by resuming an on-going NAS procedure instead of restarting the NAS procedure each time the UE reselects a different cell. Some techniques of this disclosure enable the UE to obtain a list of satellite IDs at a NAS layer (e.g., from an MME) and use that list of satellite IDs when performing a cell reselection at the RRC layer.

[0044] FIG. 1 shows an example wireless communication system 100A in which a UE 101 communicates via an NTN having one or more satellites. An 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 (such as a spaceborne vehicle or an airborne vehicle). 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. An NTN node can belong to one of several types based on altitude, orbit, and beam footprint size. An NTN can also include inter-satellite links (ISLs), such as when multiple NTN nodes form constellations and communicate directly between the NTN nodes.Docket No. 14730885900PCT

[0045] FIG. 1 shows an NTN node 111 as a first satellite 112. The NTN node 111 also includes at least part of a first BS 114 and a first MME-onboard 118 that are carried in the first satellite 112. For brevity, references to the NTN node 111 or the first satellite 112 can interchangeably refer to the satellite itself as well as all onboard features of the first satellite 112. A first satellite 112 can support a transparent or a regenerative (with on board processing for an integrated or distributed base station) 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 first satellite 112 can apply RF filtering and frequency conversion and amplification, and not change the waveform signal provided by a ground BS 134 (sometimes also referred to as an NTN BS). For a regenerative payload implementation (such as shown in FIG. 1), a first satellite 112 can apply RF filtering, frequency conversion and amplification, demodulation and decoding, routing, and coding / modulation. In FIG. 1, the NTN node 111 (e.g., first satellite 112) can perform some or all functions of a base station (shown as first BS 114) such as managing an RRC protocol as well as some or all features of an MME (shown as first MME-onboard 118).

[0046] An NTN gateway 132 (sometimes also referred to as a “sat-gateway” or “GW”) communicatively couples the first satellite 112 to ground components of the example wireless communication system 100A (such as ground BS 134 (when present), a core network (CN) 131, or other data network resources). In this disclosure, the term first BS 114 can refer to either or both of the ground BS 134 on the ground (when present), a portion of a distributed BS (e.g., a Central Unit or a Distributed Unit), or the first BS 114 (when onboard the first satellite 112). In the example of FIG. 1, the first satellite 112, the NTN gateway 132, and the first BS 114 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 131. The CN 131 can be implemented as an evolved packet core (EPC), a 5G core (5GC), or a 6G core.

[0047] When the UE 101 is in-coverage (e.g., within a coverage area) of the first satellite 112, the UE 101 can establish a radio connection to the first satellite 112 via an NTN cell 117. The NTN cell 117 refers to a coverage area in which the first satellite 112 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 connectionDocket No. 14730885900PCTbetween the UE 101 and the first satellite 112 is referred to as a service link. When the UE 101 and the first BS 114 have established the service link 113A, the UE 101 is said to be in an RRC connected (RRC CONNECTED) state. After the UE 101 is in the RRC CONNECTED state, the UE 101 might send a network registration request or other uplink NAS messages to the CN 131 (or the first MME-onboard 118) via the NTN node 111. When the feeder link 115A that communicatively couples the first satellite 112 to the NTN gateway 132 is available, the first satellite 112 communicates the network registration request or other NAS messages to the CN 131 via the feeder link 115 A. The CN 131 determines whether to accept or reject the network registration based on user subscription information. Depending on where the UE 101 is located or what RAN is being accessed, the CN 131 might accept or reject the network registration request. After registering with the CN 131, the UE 101 can release or suspend the radio connection (e.g., service link 113A). An RRC idle (RRC IDLE) state refers to a state where the radio connection is released. An RRC inactive (RRC IN ACTIVE) state refers to a state where the radio connection remains configured but is suspended.

[0048] During normal operation (sometimes referred to as a default operation mode), the first satellite 112 is concurrently connected to the UE 101 (via a service link) and to the CN 131 (via a feeder link and the NTN gateway 132). In the normal operation, the signaling and data exchange between a UE 101 with satellite access and the CN 131 includes both the service link and the feeder link both being available such that the UE 101 has an end-to-end path to the CN 131. However, there may be some times when one of the links becomes unavailable. For example, when the first satellite 112 is in a first position 119A, the first satellite 112 might have a service link 113A to the UE 101 but no feeder link 115A to the NTN gateway 132. As an example, the first position 119A might be over a remote area, such as the middle of an ocean, a sparsely populated area, or any location in which the first satellite 112 cannot directly communicate with the NTN gateway 132. In another position (referred to as a second position 119B), the first satellite 112 might have a feeder link 115B to the NTN gateway 132 but no service link 113B to the UE 101. For example, the UE 101 might remain located at a remote area while the first satellite 112 has moved to the second position 119B where the first satellite 112 can establish the feeder link 115B to the NTN gateway 132.

[0049] In some instances, even if a UE is in the coverage area of a satellite (such as a non-geostationary (NGSO) satellite), the satellite may be unable to directly connect the UE to services of the core network due to an unavailable feeder link. RRC and NAS procedures haveDocket No. 14730885900PCTtraditionally been designed for terrestrial network (TN) connectivity where presence of AS and NAS connection options might be consistent. The UE and the satellite would unnecessarily consume radio resources and power if they restart RRC and NAS procedures each time service and feeder link continuity is restored. To enable intermittent feeder / service link connectivity, the 3 GPP has introduced a store and forward (S&F) operation. The S&F operation mode can provide some level of service (in storing and forwarding the data) when end-to-end connectivity is intermittently / temporarily unavailable. The S&F operation mode is particularly useful for delay-tolerant loT services via NGSO space segment. For example, a service provider offers a service of remote monitoring of fields by deploying and tracking many battery-powered loT type UEs across the globe. The loT remote monitoring UEs can include a modem that is able to access the satellite network. In some implementations, the S&F operation enables delay-tolerant, non-real-time NTN services to be offered in areas visited by a satellite having intermittent access to an NTN gateway infrastructure. The S&F operation can support discontinuous coverage, cost-effective deployment of loT NTN services and rapid deployment options. In some implementations, the S&F operation enables a service provider to deploy wireless coverage using sparse LEO constellations and reduced ground segment infrastructure. It is expected that the S&F operation can support NTN solutions on par with other non-3GPP solutions intended for massive satellite loT.

[0050] During S&F operation mode, end-to-end exchange of signaling / data (such as NAS message) is not achieved by concurrently available service link and feeder link. Rather, the exchange of signaling / data is achieved in multiple steps, such as a first step at the first position 119A and a second step at the second position 119B. In some deployments, the CN 131 can provide downlink signa / data to another satellite (such as the second satellite 122 shown in FIG.1) instead of (or in addition to) the first satellite 112. The second satellite 122 might move to a position that will provide a service link 123 to the UE 101 earlier than the first satellite 112 moving back to the first position 119A.

[0051] As shown in FIG. 1, the second satellite 122 can also include onboard components, such as a second BS 124 and a second MME-onboard 128, collectively referred to as the second satellite 122 or a second NTN node 121. The CN 131 can provide DL NAS messages to the second satellite 122 via a feeder link 125 from the NTN gateway 132 (or another NTN gateway, not shown) to the second satellite 122. Alternatively, or additionally, the second satellite 122 and the first satellite 112 can coordinate S&F operation (such as UE context, NAS messaging,Docket No. 14730885900PCTMME-onboard data) via an inter-satellite link (shown as ISL 129). The first MME-onboard 118, the second MME-onboard 128, and the MME-ground 138 can collectively form an MME-group. From the perspective of the NAS layer in the UE 101, the MME-group may appear to behave as a single MME performing all the functions of an MME that would normally be present only in the CN 131.

[0052] When the UE 101 selects the NTN cell 117 and communicates with the first satellite 112 (at first position 119A), the UE 101 may begin a NAS procedure (such as a network registration, tracking area update, or other MME-related procedure). However, when the first satellite 112 moves to the second position 119B, the NTN cell 117 is no longer available and the UE 101 performs a cell reselection. Absent the techniques of this disclosure, the UE 101 might select a cell provided by another satellite (not shown) that does not have an MME-onboard or that does not coordinate the S&F operation in an MME-group. The other satellite might be unaware of the ongoing NAS procedure and S&F operation. Thus, extra signaling, delay, and power would be consumed.

[0053] In accordance with aspects of this disclosure, when the UE 101 is in the NTN cell 117 of the first satellite 112, the first satellite 112 can provide a list of satellite IDs that participate in the S&F operation (shown at block 150). The UE 101 can use the list of satellite IDs to obtain neighbor cell measurements 170 for satellites in the list of satellite IDs and perform a cell reselection (block 180) based on the list of satellite IDs. For example, the UE 101 might obtain neighbor cell measurements 170 for a cell (not shown) provided by the second satellite 122 when the second satellite 122 arrives at a position to provide a coverage area for the UE 101. The UE 101 can reselect the cell of the second satellite 122 and continue or complete the on-going NAS procedure with the second MME-onboard 128 using the S&F operation.

[0054] FIG.2A illustrates an example of S&F operation in contrast to a normal operation mode. In the examples shown in FIG. 2A, an example wireless communication system operates in a normal operation mode 200A of signaling and data exchange between a UE 101 with satellite access and the remote data network. In the normal / default operation mode shown in FIG. 2A, signaling and data exchange between a UE 101 with satellite access and the remote data network (via CN 131) uses both the service and feeder links, perhaps simultaneously. When both the service link and feed link are available, the UE 101 interacts over the service link with the first satellite 112 and there is a continuous end-to-end connectivity path between the UE 101 and the CN 131 via the service link and the feeder link.Docket No. 14730885900PCT

[0055] In the example shown in FIG. 2A, example wireless communication system operates in an S&F operation mode 200B. In the S&F operation mode, the end-to-end exchange of signaling / data between aUE 101 with satellite access and the remote data network is not achieved as a single atomic communication, but is instead achieved in a two-step procedure, referred to as “step A” and “step B.” In step A, the UE 101 and the satellite 112 exchange control signaling and / or data, where the satellite 112 does not have a feeder link to the NTN gateway 132 For example, in step A, the satellite 112 can operate the service link with the UE 101 and does not have an active feeder link connection with the NTN gateway 132. In step B, when the satellite 112 is closer to the NTN gateway 132 (and is further away from UE 101), the connection between the satellite 112 and the feeder link between NTN gateway 132 can be established. In step B, the uplink data / signal stored on the satellite 112 (from step A) can now be forwarded to the CN 131 via the NTN gateway 132. In step B, the satellite 112 can store downlink control signaling and / or data for the UE 101. In this situation, the stored downlink data / signal can be forwarded to the UE 101 later when the satellite 112 is once again able to communicate with the UE 101 (e.g., the satellite 112 travels a complete orbit around the Earth and is back to the same position again as in step A).

[0056] FIG. 2B shows an example wireless communication system 201 in which a satellite includes onboard NAS features. In the example of FIG. 2B, first satellite 112 includes an NTN BS (shown as first BS 114) implementing a regenerative payload. A satellite implementing with an NTN BS implementing a regenerative payload is sometimes referred to as a “regenerative satellite.” The first BS 114 can perform some or all of the functions of a base station, including those described with reference to first BS 114 or ground BS 134 in this disclosure. The service link enables a Uu interface between the UE 101 and the first BS 114. In the example of FIG. 2B, the feeder link from the first BS 114 to the NTN gateway 132 can be referred to as the satellite radio interface (SRI). In this example, the SRI is a transport link between the NTN gateway 132 and the first satellite 112 that carries traffic for the Ng (or SI, when part of the first BS 114 is implemented in a ground unit) interface. The NTN gateway 132 at one end of the SRI serves as an intermediate node forwarding the Sl / Ng traffic to and from the data network 230 via CN 131. The Ng interface from the first BS 114 includes a portion over the SRI (referred to as “Ng over SRI”) and a portion on the ground. The first MME-onboard 118 can implement at least part of a NAS protocol for mobility, user subscription and / or access to the data network 230, in coordination with an MME-ground (not shown).Docket No. 14730885900PCT

[0057] In some implementations, a first portion of the base station functionality (shown as first BS 114) can be implemented on the first satellite 112 while a second portion of the base station functionality can be implemented at a ground entity (e.g., FIG. 1, ground BS 134). For example, in a disaggregated network, first BS 114 can be divided into two components: the Distributed Unit (DU) and Centralized Unit (CU). In an example, the first BS 114 can operate as a DU that handles baseband processing, including RF signal processing and modulation / demodulation. The ground BS 134 can be an example CU that manages higher-layer tasks such as resource management, scheduling, and network optimization.

[0058] In some examples of the regenerative satellite payload architecture shown in FIG. 2B, part of the MME (e.g., MME-onboard 118) in a split-MME architecture or the entire MME is installed on the “regenerative” satellite (e.g., satellite 112). In such examples, the feeder link does not carry either the SI interface or the NG interface. Instead, the feeder link carries the internal interface within a core network node (e.g., CN 131). Different regenerative satellites can connect to the same CN 131 on the ground, via the same NTN gateway (e.g., NTN gateway 132), or via different NTN gateways.

[0059] In some aspects, the UE 101 compensates for time and frequency drift while transmitting control signals and / or data to a moving satellite using its global navigations satellite system (GNSS) position. The UE 101 may obtain its GNSS position via a signal obtained or measured from at least one GNSS satellite 212.

[0060] Although examples of this disclosure are based on the regenerative payload architecture illustrated in FIG. 2B, the techniques of this disclosure can apply to a transparent payload architecture as well, particularly where the transparent first satellite 112 includes some subset or limited features for S&F operation (such as a capability to maintain coordinated states of RRC and NAS protocols).

[0061] The NTN can support different types of service links, depending on the satellite moving pattern. In some examples, there are three types of service links that are supported in an 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), orDocket No. 14730885900PCT• 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 respect to LEO / MEO satellites, the first BS 114 can provide either quasi-Earth-fixed cell coverage or Earth-moving cell coverage. With respect to GEO satellites, the first BS 114 can provide Earth fixed cell coverage.

[0063] FIG. 2C shows an example wireless communication system 202 with multiple satellites participating in an S&F operation mode. The example of FIG. 2C includes the UE 101, first satellite 112, second satellite 122, NTN gateway 132, CN 131, and optionally, a second NTN gateway 232.

[0064] Different regenerative satellites (e.g., first satellite 112 and second satellite 122 as shown in FIG. 2C) can connect to the same CN 131 on the ground, via the same NTN gateway 132, or via different NTN gateways (e.g., NTN gateway 232). At various times, the UE 101 can be within a coverage area of the first satellite 112. In some point, the first satellite 112 might move away from the UE 101 so that the UE 101 is not in coverage (referred to as “out-of-coverage condition”) of the first satellite 112. In some scenarios, the second satellite 122 (e.g., having an onboard second BS 124 if the second satellite 122 is using a regenerative payload implementation) moves toward the location of the UE 101. Depending on the movements of the first satellite 112, the second satellite 122, and the UE 101, it is possible for UE 101 to have intermittent periods of in-coverage and out-of-coverage from the first satellite 112 and / or the second satellite 122.

[0065] In the example shown in FIG. 2C, first satellite 112 and second satellite 122 implement a split-MME architecture and are configured to participate as a group in S&F operations. For instance, first satellite 112 and second satellite 112 may be included in a list of satellite IDs indicating a group of satellites that participate as a group in S&F operations.

[0066] In the example of FIG. 2C, the first satellite 112 is moving away from the UE 101 and towards the NTN gateway 132. The second satellite 122 is moving towards the UE 101 and away from the NTN gateway 132. At an initial time, the UE 101 may be in the coverage area of the first satellite 112 and out of the coverage area of the second satellite 122. The NTN gateway 132 may be out of the coverage area of the first satellite 112 and in the coverage area of the second satellite 122. At this initial time, the first satellite 112 may store data and control signaling received from UE 101 and forward the data and control signaling to the CN 131 when the CN 131 is within the coverage area of first satellite 112. Similarly, the second satellite 122 may storeDocket No. 14730885900PCTdata and control signaling received from the CN 131 viaNTN gateway 132 and forward the data and control signaling to the UE 101 when the UE 101 is within the coverage area of the second satellite 122.

[0067] FIG. 3 shows an example split MME deployment 300. The example shown in FIG. 3 includes the UE 101, two NTN nodes 111 and 121, and the CN 131. NTN node 111, NTN node 121, and an CN 131. In the example shown in FIG. 3, the UE 101 communicates with a first satellite (e.g., first satellite 112) that is moving away from the UE 101, and a second satellite (e.g., second satellite 122) that is moving toward the UE 101. The first satellite 112 implements the first BS 114 and the first MME-onboard 118. The second satellite 122 implements the second BS 124 and the second MME-onboard 128. The CN 131 implements MME-ground 138. Collectively, the first MME-onboard 118, the second MME-onboard 128, and the MME-ground 138 can be referred to as an MME 338. The UE 101 can communicate with the MME 338 (i.e., any of the first MME-onboard 118, the second MME-onboard 128, or the MME-ground 138) using NAS messages that would traditionally be communicated between the UE 101 and MME of a core network.

[0068] The UE 101 includes a physical (PHY) layer 302, an RRC layer 304, and a NAS layer 308. The NAS layer 308 coordinates NAS protocol messaging with the MME 338 via an N1 interface. The Uu interface refers to the RRC layer protocol between the RRC layer 304 of the UE and a BS (such as the first BS 114 or the second BS 124). The N1 interface and the Uu interface are illustrated as separate connections for reference. However, the N1 interface typically is carried by the Uu interface, which in turn is carried over a PHY layer connection between the UE 101 and the first satellite 112 (or the second satellite 122).

[0069] The MME 338 is split into two functions, MME-onboard and MME-ground. MME-onboard includes the MME portions that are onboard the first satellite 112 and the second satellite 122 (e.g., the first MME-onboard 118 and the second MME-onboard 128, respectively). In some examples, an MME-onboard communicates with its respective BS via and SI -MME interface.

[0070] MME-ground is part of the MME 338 that is implemented on the ground network (e.g., MME-ground 138). MME-ground handles interfaces towards various CN functions Examples of such interfaces and CN functions include the S6a interface towards the home subscriber system (HSS), SGd interface towards short message service-gateway mobile switching center (SMS-GMSC), interworking mobile switching center (IWMSC), and / or SMS Router, T6a interface towards service capability exposure function (SCEF), T6ai interface towards interworkingDocket No. 14730885900PCTfunction-SCEF (IWF-SCEF), and / or Sil interface towards servicing gateway (SGW) among others. In some implementations, one MME-ground 138 instance can be associated with one or multiple MME-onboard instances. In some implementations, an MME group includes at least one MME-onboard that in charge of handling the SI interface with the onboard eNB and at least one MME-ground that is in charge of handling the rest of interfaces towards other CN functions.

[0071] The MME-ground (e.g., MME-ground 138) together with the set of MME-onboard instances (e.g., first MME-onboard 118 and second MME-onboard 128) deployed in the set of satellites can behave jointly as a single MME entity (e.g., MME 338). The UE context is synchronized between MME-ground and MME-onboard. Each MME-onboard instance is associated with a different satellite identifier (ID) (referring to the satellite ID of the satellite that carries the respective MME-onboard). For example, the first MME-onboard 118 is associated with the first satellite ID 311 of the first satellite 112 and the second MME-onboard 128 is associated with the second satellite ID 321 of the second satellite 122.

[0072] When the UE 101 initiates a NAS procedure (e.g., a UL NAS message) that needs an interaction with a core network node on the ground, the MME-onboard (e.g., the first MME-onboard 118 and / or the second MME-onboard 128) store the UL NAS message if the feeder link is not available and later synchronizes with the MME-ground (e.g., MME-ground 138) when the feeder link becomes available. The MME-ground executes the procedure with the ground network nodes and synchronizes the UE context with the MME-onboard when the feeder link becomes available. The MME-ground stores a DL NAS message when the feeder link is unavailable and transfers the DL NAS message to the MME-onboard (e.g., first MME-onboard 118 and / or second MME-onboard 128) when the feeder link for either satellite becomes available. The MME-ground can determine the satellite that will serve the UE 101 next and send the DL NAS message to the corresponding MME-onboard. As noted above, in the example of FIG. 3 the first satellite 112 is moving away from the UE 101 and the second satellite 122 is moving towards the UE 101. The MME-ground 138 can determine that the second satellite 122 will serve the UE 101 next. The MME-ground 138 can send the DL NAS message to the second MME-onboard 128 when the feeder link to the second satellite 122 is available. If the service link to the UE 101 is unavailable, the second MME-onboard 128 can store the DL NAS message for transfer to the UE 101 when the service link becomes available.

[0073] In some situations, a procedure such as the NAS ATTACH or the Tracking Area Update (TAU) procedure perhaps cannot be completed during the coverage of a single satelliteDocket No. 14730885900PCTimplementing a split-MME architecture. In some aspects, the MME 338 (e.g., any of the first MME-onboard 118, the second MME-onboard 128, or the MME-ground 138) provides a list of satellite IDs to the UE 101 identifying subsequent satellite(s) with which the UE 101 may resume the NAS ATTACH or TAU procedure. The UE 101 may receive the list of satellite IDs via the NAS layer 308. The UE 101 can reselect and camp on a cell provided by a satellite whose satellite ID is within the list of satellite IDs. In some aspects, the UE 101 can prioritize 380 cell reselection to the satellites in the list of satellite IDs that are intended for S&F operation.

[0074] FIG. 4 shows example messages that can include a list of satellite IDs for satellites participating in an S&F operation. As discussed above with respect to FIG. 1, a satellite (e.g., FIG. 1, first satellite 112) can communicate the list of satellite IDs to the UE 101 to inform the UE 101 about satellites that participate as a group in store-and-forward operations. The satellite can provide the list of satellite IDs to the UE 101 using various messaging.

[0075] In some aspects, the satellite can provide the list of satellite IDs to the UE 101 using non-access stratum (NAS) message 451, from MME-onboard. In some aspects, the satellite can provide the list of satellite IDs to the UE 101 using a NAS message 452, from MME-ground. In some aspects, the satellite can provide the list of satellite IDs to the UE 101 using a system information block (SIB) message 453 that includes the list of satellite IDs. In some aspects, the satellite can provide the list of satellite IDs to the UE 101 using an RRC message 454 from the satellite when the UE is operating in an RRC connected state with the satellite.

[0076] In some aspects, the first satellite 112 can provide the list of satellite IDs to the UE 101 using a SIB33456 populated with the list of neighboring satellite information including, for each neighboring satellite, a satellite ID and a corresponding flag indicating whether the neighboring satellite is in the list of satellite IDs for a store-and-forward group.

[0077] FIG. 5 to FIG. 9 are message flow diagrams illustrating example scenarios in which a UE and / or a RAN perform the techniques of this disclosure for a cell reselection procedure using a list of satellite IDs. FIG. 10 to FIG. 15 are flow chart diagrams showing example operations of a UE, satellite, or core network. Generally speaking, similar elements in FIG. 5 to FIG. 15 are labeled with reference numbers that have the same lower-order digits to represent similar features. For example, message 651 is similar to message 751, and message 771 A is similar to message 871. For brevity, similar elements are not discussed in detail in each instance, but the discussion of a certain element with reference to one of the figures also applies to similar elements in other figures. Further, in some cases, various acknowledgements for messagesDocket No. 14730885900PCTillustrated in FIG. 5 to FIG. 9 may be implemented to ensure reliable operations for performing a cell reselection procedure and are not illustrated for the sake of illustration clarity.

[0078] FIG. 5 shows a messaging diagram 500 of an example scenario in which a UE performs cell reselection based on a list of satellite IDs obtained from a first satellite. The example of FIG. 5 continues the examples of FIG. 3 discussed above. Similar to the example of FIG. 3, the example of FIG. 5 includes the UE 101, the first satellite 112, and the second satellite 122. FIG.5 also shows other satellites 512 and 522 that are not part of a split-MME or shared S&F operation. The first satellite 112 and the second satellite 122 implement first BS 114 and second BS 124, respectively. The first satellite 112 and second satellite 122 also implement first MME-onboard 118 and second MME-onboard 128, respectively, that, with MME-ground 138, form MME 338.

[0079] The example of FIG. 5 starts with UE 101 being in communication with the first satellite 112. At bracket 550, the first satellite 112 communicates a message (e.g., from the first BS 114 and / or the first MME-onboard 118) including a list of satellite IDs to the LTE 101. In some implementations, the message is a system information message, an RRC message, or NAS message (e.g., from an MME-onboard or an MME-ground). The list of satellite IDs indicates satellites that are configured to participate as a group in S&F operations. In the example of FIG.5, the list of satellite IDs includes the satellite ID of the second satellite 122, but does not include the satellite IDs of other satellites 512 or 522.

[0080] The UE 101 performs a cell reselection 580, for example, when the first satellite 112 moves such that UE 101 is no longer in (or will soon no longer be in) the coverage area of the first satellite 112. As part of the cell reselection 580, the UE selects a new satellite to communicate with. In this example, the UE 101 may be in the coverage areas of second satellite 122, other satellite 512, and other satellite 522. The UE 101 can reselect the cell associated with second satellite 122 based on the satellite ID of second satellite 122 being in the list of satellite IDs while the other satellite 512 and the other satellite 522 are not in the list of satellite IDs. After the cell reselection 580, the UE 101 communicates with second BS 124 and second MME-onboard 128 of the second satellite 122.

[0081] In some implementations, the UE 101 performs a cell selection instead of cell reselection in the event 580, and selects the NTN cell associated with second satellite 122 based on the satellite ID of second satellite 122 being in the list of satellite IDs. For example, the UE can obtain the list of satellite IDs from a previous serving cell (e.g., any of the messages describedDocket No. 14730885900PCTin bracket 550). The UE 101 can store the list of satellite IDs in a memory for subsequent use during a cell selection procedure. The UE 101 can maintain the list of satellite IDs in the memory when the UE 101 enters an RRC idle state. When performing a cell selection procedure in the same PLMN as the previous serving cell, the UE 101 can prioritize selection of cells from satellites in the list of satellite IDs. In some implementations, the UE 101 can obtain one or more lists of satellite IDs for one or more MME groups in at least one NTN of a PLMN. In some implementations, the UE 101 is preconfigured or provisioned with at least one list of satellite IDs. When performing a cell selection, the UE can preferentially select a cell from a satellite based on the satellite having a satellite ID in any stored list of satellite IDs supporting S&F operation as a group.

[0082] FIG. 6A shows a messaging diagram 600 of an example scenario in which a UE determines to reselect and camp on a cell of a satellite that is in a list of satellite IDs obtained from the NAS layer. The example of FIG. 6A starts with the UE 101 in RRC_CONNECTED state 645 and connected to the first BS 114 implemented on the first satellite 112. The first satellite 112 also implements the first MME-onboard 118. In some aspects, the first MME-onboard 118 may be a split-MME. In some aspects, the first MME-onboard 118 may be a full MME.

[0083] When the service link between the UE 101 and the first satellite 112 is still available, the UE 101 initiates a NAS attach procedure 646 with the first MME-onboard 118. The first MME-onboard 118 transmits a NAS message 651 (e.g., ATTACH ACCEPT message or TAU ACCEPT message) including a list of satellite IDs intended for the S&F operation to the UE 101. Later, the UE 101 transitions to the RRC IDLE or RRC INACTIVE state 665. In some aspects, the UE 101 can enter the RRC IDLE or RRC IN ACTIVE state 665 upon receiving an RRC connection release message 661 from the first BS 114. In some aspects, theUE 101 autonomously transitions to the RRC IDLE or RRC INACTIVE state 665 upon the expiry of a data inactivity timer.

[0084] While the UE 101 is in the idle or inactive state, the UE 101 can obtain measurements of the serving and / or neighboring cell for use in a cell reselection evaluation. In some aspects, the measurements are intra-frequency and / or inter-frequency measurements. In some aspects, the measurements are based on the measurement rules defined in 3GPP technical specification (TS) 36.304.Docket No. 14730885900PCT

[0085] In the example of FIG. 6A, at block 672, the UE 101 detects a neighboring cell while performing the neighboring cell measurement where the measurement results indicate that the neighboring cell fulfills the cell reselection criteria. The detected neighboring cell becomes the target cell for the cell reselection. In some implementations, at block 673, the UE 101 acquires a SIB type 1 (SIB 1) from the target cell and determines that access to the cell is not restricted based on the information in the SIB1. For example, the PLMN ID(s) and the barring indication(s) acquired from SIB1 can indicate that the UE is not restricted from access to the cell. In some implementations, the UE 101 detects a neighboring cell while performing the neighboring cell measurement where the measurement results indicate that the neighboring cell fulfills a cell selection criterion. The detected neighboring cell becomes the target cell for the cell selection.

[0086] At block 680, the UE 101 acquires a SIB31 containing the satellite assistance information for the target cell. Based on the information in the SIB31, the UE 101 can determine the satellite ID of the second satellite 122 providing the target cell. In the example of FIG. 6A, the UE 101 determines (at block 681 A) that the satellite ID of the second satellite 122 providing the target cell is one of the satellite IDs provided in the list of satellite IDs in the NAS message 651 (e.g., one of the satellite IDs intended for the S&F operation). At block 685, the UE 101 determines to reselect (or select) and camp on the target cell.

[0087] FIG. 6B shows a messaging diagram of an example scenario in which a UE determines to bar a cell of a satellite (shown as other satellite 512) based on the satellite having a satellite ID that is not in a list of satellite IDs. The scenario illustrated in FIG. 6B is similar to that illustrated in FIG. 6A and starts with the same operations and messages. FIG. 6B differs from FIG. 6A in that FIG. 6B shows the scenario where the UE detects a neighboring cell from the other satellite 512 instead of the second satellite 122. At block 681B, the UE 101 determines that the satellite ID of the other satellite 512 providing the detected target cell is not within the list of satellite IDs intended for the S&F operation. At block 688, the UE 101 bars the target cell as a candidate cell for cell reselection (or cell selection) for X seconds. In some aspects, the value X can be a constant value (e.g., 300). In some aspects, the value of X can be predefined in a 3GPP specification. In some aspects, the value of X can be a configurable value provided by the core network or the NTN. In some implementations, the UE 101 releases (or undoes) the barring on the target cell if the UE 101 is conducting an emergency call or if the target cell is the only cell fulfilling the cell reselection criteria.Docket No. 14730885900PCT

[0088] FIG. 7 shows a messaging diagram 700 of an example scenario in which a UE manages neighboring cell measurement based on a list of satellite IDs. The elements of FIG. 7 include corresponding elements described in the examples of FIG. 6A and FIG. 6B. FIG. 7 includes an example optional feature in which the UE 101 can refrain from performing neighboring cell measurements for cells provided by satellites that are not in the list of satellite IDs provided by the first satellite 112.

[0089] In this example, the first MME-onboard 118 transmits a list of satellite IDs that includes the satellite ID for second satellite 122 and does not include the satellite IDs for other satellite 512 and other satellites 522. In the RRC idle or RRC inactive state 665, the UE 101 triggers intra-frequency and / or inter-frequency neighbor cell measurement (at block 770). In some aspects, the intra-frequency and / or inter-frequency cell measurement may be performed based on rules or heuristics defined in 3GPP TS 36.304, section 5.2.4.2. However, rather than obtaining neighbor cell measurements for all available frequencies, the UE 101 can limit the neighbor cell measurements to only those frequencies and / or timing associated with satellites in the list of satellite IDs from message 751.

[0090] For example, at block 771A, the UE 101 can perform neighbor cell measurement only on one or more frequencies that are associated with one or more satellites included in the list of satellite IDs received via message 751. In some aspects, the UE 101 acquires the frequency information of each frequency to be measured from a SIB type 3 (SIB3) and / or a SIB type 5 (SIB5), where the frequency information identifies satellites (based on satellite IDs) that are associated with the frequency. The UE performs the neighbor cell measurement only on the frequencies that are associated with at least one satellite ID that also appears in the list of satellite IDs intended for the S&F operation. In this example, the UE 101 performs neighbor cell measurement for second satellite 122 and does not perform neighbor cell measurement for the other satellites 512 and 522.

[0091] Alternatively, or additionally, at block 771B, the UE 101 can perform the neighbor cell measurement only at a timing determined for satellites in the list of satellite IDs. For example, the UE 101 acquires from SIB3 and / or SIB5 indications of satellite IDs associated with the frequency or frequencies to be measured. The UE considers timing for only the satellite IDs that are also included in the list of satellite IDs in message 751. The UE 101 calculates a propagation delay per satellite information corresponding to the satellite ID. In some aspects, the satellite information includes the satellite ephemeris and / or common timing advance obtained from aDocket No. 14730885900PCTSIB33. The UE 101 can determine the timing(s) at which the UE 101 performs the neighbor cell measurements based on the calculated propagation delay(s).

[0092] Based on the neighbor cell measurements (i.e., according to block 771A and / or block 771B), the UE 101 detects a neighboring cell provided by second satellite 122. The remaining elements 672 to 685 are as described with respect to FIG. 6A.

[0093] FIG. 8 shows a messaging diagram 800 of an example scenario in which a UE adjusts the cell ranking of a cell in the cell reselection evaluation process based on a list of satellite IDs obtained from the NAS layer. The elements 645 to 770 in FIG. 8 are the same as corresponding numbered elements in FIG. 6A and FIG. 7. However, FIG. 8 differs from FIG. 7 in that the UE 101 does not limit neighbor cell measurements to only those frequencies associated with satellites in the list of satellite IDs. Instead, the UE 101 performs neighbor cell measurements on multiple frequencies obtained from a SIB3 and / or SIB5 without limiting the measured frequencies based on the list of satellite IDs. At block 871, the UE 101 performs neighbor cell measurement on all frequencies (or multiple frequencies) listed in SIB3 and / or SIB5. As shown in FIG. 8, the UE 101 obtains neighbor cell measurements for the cells provided by the second satellite 122 as well as the other satellites 512 and 522.

[0094] At block 872A, the UE 101 detects a first neighboring cell associated with the second satellite 122 in the list of satellite IDs when the measurement results indicate that the first neighboring cell fulfills the cell reselection criteria. The first neighboring cell becomes a candidate target cell for cell reselection. At block 872B, the UE 101 detects a second neighboring cell associated with a satellite (e.g., the other satellite 512 or 522) that is not in the list of satellite IDs when the measurement results indicate that the second neighboring cell fulfills the cell reselection criteria. The detected second neighboring cell also becomes a candidate target cell for the cell reselection.

[0095] After detecting candidate target cells, at block 874, the UE 101 calculates cell rankings for the candidate target cells. In some aspects, the cell ranking of a cell is based, at least in part, on the ranking heuristics defined in 3GPP TS 36.304. The UE 101 calculates the cell ranking of the first neighboring cell (Rni) and the cell ranking of the second neighboring cell Rn2). In some aspects, the UE 101 lowers the value of Rn2 by a value A (i.e., Rn2 = Rn2 - A) because the second neighboring cell is provided by a satellite that is not in the list of satellite IDs. Alternatively, or additionally, the UE 101 can increase the value of Rni because the first neighboring cell is provided by a second satellite 122 that is in the list of satellite IDs. The adjustment(s) to cellDocket No. 14730885900PCTranking(s) make it less likely for the UE 101 to reselect and camp on the second neighboring cell because a satellite ID that is not within the list of satellite IDs provided in message 751. The value A can be a fixed value defined in the 3GPP specifications, or can be a configurable value provided by the network (e.g., via a dedicated RRC message or via the system information).

[0096] Although the description of FIG. 8 refers to adjusting the cell ranking by a value A, the 101 can use other techniques of adjusting the cell ranking. For example, the UE 101 can adjust a criterion or parameter (e.g., signal received level (Srxlev) or signal quality level (Squal)) to impact the cell ranking.

[0097] FIG. 9 shows a messaging diagram 900 of an example scenario in which a UE determines whether to perform a TAU procedure upon moving to a new cell. The example scenario of FIG. 9 includes UE 101, a first NTN node 111 including first satellite 112 that implements first BS 114 and first MME-onboard 118, and a second NTN node 931 including other satellite 512 that implements third BS 934 and third MME-onboard 938. The scenario illustrated in FIG. 9 begins with the same elements 645 to 673 as described with FIG. 6B. In the example of FIG. 6B, the UE 101 bars the neighboring cell of the other satellite 512 because the other satellite 512 is not in the list of satellite IDs obtained from message 651. However, there may be instances in which the UE 101 does not bar the neighboring cell, such as when no suitable neighboring cell from the list of satellite IDs has been detected, the UE 101 determines that the second satellite 122 will not arrive within a threshold time, or a timer for an on-going S&F operation will expire. Forthose or other reasons, the UE 101 may determine to reselect and camp on the other satellite 512 (at block 685).

[0098] At block 992, the UE 101 performs a TAU procedure after reselecting the neighboring cell of the other satellite 512 because the satellite ID of the neighboring cell is not included in the list of satellite IDs received by theUE 101 in message 651. For example, the UE 101 performs a TAU procedure with the MME (i.e., either a core network MME or a third MME-onboard 938 that is not in the MME-group that includes the first MME-onboard 118). In some aspects, the UE 101 obtains the satellite ID of the neighbor cell via a SIB31 and determines that the satellite ID of the other satellite 512 is not in the list of satellite IDs for the original MME-group. In some aspects, the UE 101 performs the TAU procedure regardless of whether the tracking area identity (TAI) of the neighboring cell is identical to, or different from, the TAI of the previous serving cell (e.g., the original cell corresponding to first BS 114). The TAU procedure 992 will eventually trigger a UE context switch between the original MME (e.g., first MME-onboard 118)Docket No. 14730885900PCTand the new MME (e.g., third MME-onboard 938 of the core network MME). FIG. 9 shows the example where the other satellite 512 is another NTN node that also includes a third BS 934 and a third MME-onboard 938. Alternatively, the other satellite 12 might be from a different NTN or be associated with a split-MME other than the split-MME that includes the first MME-onboard 118.

[0099] FIG. 10 through FIG. 15 are flow diagrams describing example UE operations for methods for cell reselection. The operations can be performed, for example, by the UE 101 of FIG. 1 through FIG. 9.

[0100] FIG. 10 shows a flow diagram of example operations of a UE for determining whether to reselect and camp on a neighboring cell fulfilling the cell reselection criteria based on a list of satellite IDs intended for the S&F operation. At block 1045, and as described above with respect to FIG. 6A, element 645, the UE operates in the RRC connected state and is connected to a satellite (e.g., first satellite 112 of FIG. 1) having a BS node (e.g., eNB) and a full or partial network node (e.g., a full or partial MME) installed on the satellite.

[0101] At block 1051, and as further described with respect to FIG. 5 element 550 and FIG. 6A and FIG. 6B, element 651, the UE receives, from the network node, a message including a list of satellite IDs intended for S&F operation. FIGs. 4-5 describe how this message may be sent via either a NAS or an RRC protocol layer message, and FIGs. 6-9 show NAS message examples.

[0102] At block 1065, and as further described with respect to FIG. 6A and FIG. 6B, message 665, the UE transitions to an idle state (e.g., RRC IDLE or RRC INACTIVE).

[0103] At block 1072, and as further described with respect to FIG. 6A and FIG. 6B, block 672, the UE detects a neighboring cell while performing a neighboring cell measurement, where the measurement results indicate that the neighboring cell fulfills cell reselection criteria. The detected neighboring cell becomes the target cell for the cell reselection.

[0104] At optional block 1073, and as further described with respect to FIG. 6A and FIG. 6B, element 673, the UE acquires a SIB1 from the neighboring cell and determines that access to the neighboring cell is not restricted based on information provided in the SIB1.

[0105] At block 1080, and as further described with respect to FIG. 6A and FIG. 6B, element 680, the UE acquires a SIB31 from the neighboring cell. The UE can determine the satellite ID of the neighboring cell based on information in the SIB31.Docket No. 14730885900PCT

[0106] At block 1081, and as further described with respect to FIG. 6A, element 681 A and FIG.6B, element 68 IB, the UE determines if the satellite ID of the satellite corresponding to the neighboring cell is included in the list of satellite IDs intended for S&F operation obtained at block 1051.

[0107] If the satellite ID is in the list of satellite IDs intended for S&F operation ("YES" branch of block 1081), then at block 1085, and as further described with respect to FIG. 6A, block 685, the UE determines to reselect and camp on the neighboring cell.

[0108] If the satellite ID is not in the list of satellite IDs intended for S&F operation ("NO" branch of block 1081), then at block 1088, and as further described with respect to FIG. 6B, block 688, the UE bars the neighboring cell as a candidate for cell reselection for A seconds. In some aspects, the value A can be a constant value (e.g., 300 seconds), a value that is predefined in a 3GPP specification, or a configurable value provided by the network.

[0109] FIG. 11 shows a flow diagram 1100 of example operations of a UE for performing cell reselection based on a list of satellite IDs obtained from the system information. The flow diagram 1100 is similar to the flow diagram 1000 of FIG. 10. Flow diagram 1100 differs from flow diagram 1000 in that the UE obtains 1153 the list of the satellite IDs intended for the S&F operation while the UE is in the idle or inactive state (block 1065), and the list of satellite IDs is obtained from the system information instead of from a NAS (or RRC) message. The list of satellite IDs obtained at block 1153 can be different from the existing list of satellite IDs broadcast in SIB33. For example, the satellite IDs broadcast in SIB33 are provided for the purpose of adjusting the measurement timing and covers as many neighboring satellites as possible. In some implementations, the list of satellite IDs in block 1153 can be included as an additional information element of the SIB33, or another SIB, and refers to the “list of satellite IDs” indicating those satellites that are part of a group (such as an MME-group or S&F operation group).

[0110] FIG. 12 shows a flow diagram 1200 of example operations of a UE for performing cell reselection based on an existing list of neighboring satellite information in a SIB33, where the SIB33 includes flags or indicators to indicate which satellites are in a list of satellite IDs intended for the S&F operation. The flow diagram 1200 of FIG. 12 is similar to the flow diagram 1100 of FIG. 11, except that the SIB33 does not include a separate “list of satellite IDs.” Instead, the SIB33 is modified so that the list of neighboring satellite information includes a flag / indicator for various satellites that are intended for S&F operation in coordination with the satellite thatDocket No. 14730885900PCTtransmits the SIB33. At block 1256, the UE obtains the list of neighboring satellite information from the SIB33. In some aspects, the neighboring satellite information includes, for a satellite in the neighboring satellite information, a flag or indication associated with the satellite, where the flag or indication is used to indicate whether or not the associated satellite is intended for the S&F operation. In some implementations, the UE generates the list of satellite IDs based on the neighboring satellite information (which includes the satellite ID and corresponding flag / indication).[OHl] At block 1281, the UE determines whether the target cell (e.g., a neighboring cell fulfilling the cell reselection criteria and is not restricted for access) is intended for S&F operation, based on the flag or indication associated to the satellite ID of the target cell.

[0112] FIG. 13 shows a flow diagram 1300 of example operations of a UE for determining how to perform the neighbor cell measurement based on a list of satellite IDs intended for the S&F operation. Blocks 1045, 1051, and 1065 of flow diagram 1300 have been described above with respect to FIG. 10 and omitted from the description of FIG. 13 for brevity.

[0113] At block 1371A, and as described above with respect to FIG. 7, block 771A, the UE optionally performs the neighboring cell measurement only on the frequencies that are listed in SIB3 and SIB5 and that are associated to at least one of the satellite IDs intended for the S&F operation. In some implementations, the UE first acquires the frequency information of each frequency to be measured from SIB3 and / or SIB5, where the frequency information also includes a list of satellite IDs that are associated with the frequency. The UE then performs the neighbor cell measurement only on the frequencies that are associated with at least one satellite ID that also appears in the list of satellite IDs intended for the S&F operation.

[0114] At block 1371B, and as described above with respect to FIG. 7, block 771B, the UE optionally performs the neighboring cell measurement only at the timing(s) determined based on the propagation delays estimated or calculated for those satellites corresponding to the satellite IDs appearing in both SIB3 (or SIB5) and the list of satellite IDs intended for the S&F operation.

[0115] FIG. 14 shows a flow diagram 1400 of example operations of a UE for adjusting the rankings of neighboring cells for the cell reselection evaluation purpose based on a list of satellite IDs intended for the S&F operation. Blocks 1045, 1051, and 1065 have been described above with respect to FIG. 10 and will not be further described here.

[0116] At block 1471A, and as described above with respect to FIG. 8, block 871 the UE performs neighboring cell measurement on the frequencies listed in SIB3 and / or SIB5. In someDocket No. 14730885900PCTaspects, the UE first acquires the frequency information of each frequency to be measured from SIB3 and / or SIB5, where the frequency information also includes a list of satellite IDs that are associated with the frequency.

[0117] At block 1471B, and similar to FIG. 7, block 771B and FIG. 13, block 1371B, the UE performs measurement at the timing(s) determined based on the propagation delays estimated / calculated for those satellites referred by the satellite IDs associated with the frequencies identified in SIB3 and / or SIB5. Block 147 IB differs from block 77 IB and block 1371B in that block 1471B performs measurements on satellites identified via SIB3 and / or SIB5, while blocks 771B and 1371B perform measurements on satellites identified in a list of satellites provided to the UE by the network via a NAS or RRC message.

[0118] At block 1472, and similar to FIG. 6, block 672, the UE detects a neighboring cell associated with a satellite ID. In some aspects, the UE determines the neighboring cell is associated with a satellite ID because the UE detects the neighboring cell on the frequency associated with the satellite ID and also at the timing derived based on a propagation delay estimated or calculated based on the same satellite ID.

[0119] At block 1081, and as described above with respect to FIG. 10, block 1081, the UE determines whether the satellite ID of the neighboring cell is included in the list of satellite IDs intended for the S&F operation (e.g., the list obtained at block 1051). If the neighboring cell is included in the list of satellite IDs intended for the S&F operation ("YES" branch of block 1081), then at block 1474A, and similar to FIG. 8, block 874, the UE calculates the cell ranking of the neighboring cell. Block 1474A is different from block 1474B in that the UE does not adjust the cell ranking. If the neighboring cell is not included in the list of satellite IDs intended for the S&F operation ("NO" branch of block 1081), then at block 1474B, and as described above with respect to FIG. 8, block 874, the UE calculates the cell ranking of the neighboring cell ( / / ») and lowers the cell ranking of the neighboring cell by a value A (i.e., Rn= R» - A). Alternatively, or additionally, the UE can adjust input parameters for the cell ranking calculations to effectively lower the cell ranking of the neighboring cell. Although FIG. 14 describes lowering the cell ranking of a neighboring cell not in the list of satellite IDs (block 1474B), a similar result can be achieved by raising the cell ranking of a neighboring cell that is in the list of satellite IDs (e.g., modifying block 1474B to include raising the cell ranking).

[0120] FIG. 15 shows a flow diagram 1500 of example operations of a UE for determining whether to trigger a TAU procedure upon camping on a new cell based on a list of satellite IDsDocket No. 14730885900PCTintended for the S&F operation. The flow diagram 1500 includes blocks 1045, 1051, 1065, and 1072, which have been described above with respect to FIG. 10, and will not be further described here.

[0121] At block 1585, and as described above with respect to FIG. 6, block 685, the UE determines to reselect and camp on the neighboring cell.

[0122] At block 1080, and as described above with respect to FIG. 6A and FIG. 6B, element 680, the UE acquires a SIB31 from the neighboring cell. The UE obtains the satellite ID of the neighboring cell from the SIB31.

[0123] At block 1581, and as described above with respect to FIG. 10, block 1081, the UE determines whether the satellite ID of the neighboring cell is included in the list of satellite IDs intended for the S&F operation. If the satellite ID of the neighboring cell is included in the list of satellite IDs intended for the S&F operation ("YES" branch of block 1581), then at block 1592A, performs a TAU procedure based on the tracking area code (TAC) value of the neighboring cell (i.e., the UE follows the legacy behavior). If the satellite ID of the neighboring cell is included in the list of satellite IDs intended for the S&F operation ("NO" branch of block 1581), then at block 1592B, and as described above with respect to FIG. 9, block 992, the UE determines to perform a TAU procedure regardless of the TAC value of the neighboring cell.

[0124] FIG. 16 is a block diagram illustrating an example user equipment. Note that the depicted hardware configurations represent the processing components and communication components of a UE 1601 (such as the UE 101 described herein). 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.

[0125] The UE 1601 includes antennas 1611 A, a radio frequency front end (RF front end) 161 IB, and radio-frequency transceivers (e.g., an LTE transceiver 1603A and a 5G NR transceiver 1603B) for communicating with a network entity (such as an NTN node). The RF front end 161 IB includes one or more modems configured for the corresponding RAT(s) employed (for example, 5G NR, one or more analog-to-digital converters (ADCs), one or more digital-to-analog converters (DACs), signal processors, and the like. In the example illustrated in FIG. 16, the RF front end 161 IB of the UE 1601 may couple or connect the LTE transceiver 1603 A, and the 5G NR transceiver 1603B to the antennas 1611 A to facilitate various types of wireless communication. The RF front end 161 IB operates, in effect, as a physical (PHY)Docket No. 14730885900PCTtransceiver interface to conduct and process signaling between the one or more processor(s) 1603C and antennas 1611 A so as to facilitate various types of wireless communication.

[0126] The antennas 1611 A of the UE 1601 may include an array of multiple antennas that may be tuned to one or more frequency bands associated with a corresponding RAT. The antennas 1611A and the RF front end 161 IB may be tuned to, and / or be tunable to, one or more frequency bands defined by the 3 GPP LTE and 5G NR communication standards and implemented by the LTE transceiver 1603A, and / or the 5G NR transceiver 1603B. Additionally, the antennas 1611A, the RF front end 161 IB, the LTE transceiver 1603 A, and / or the 5GNR transceiver 1603B may be configured to support beamforming for the transmission and reception of communications with an NTN node (e.g., the first BS 114 and first satellite 112). By way of example and not limitation, the antennas 1611A and the RF front end 161 IB may be implemented for operation in sub-gigahertz bands, sub-6 GHz bands, and / or above 6 GHz bands that are defined by the 3GPP LTE and 5G NR communication standards.

[0127] The UE 1601 also includes processor(s) 1603C and computer-readable storage media (CRM) 1603D. The processor(s) 1603C may include, for example, one or more central processing units, graphics processing units (GPUs), or other application-specific integrated circuits (ASIC), and the like. To illustrate, the processor(s) 1603C may include an application processor (AP) utilized by the UE 1601 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 of the RF front end 161 IB.

[0128] CRM 1603D 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), Flash memory, solid-state drive (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) 1603C and other components of the UE 1601 to perform the various functions described herein and attributed to the UE 1601. 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) 1603C to enable user-plane communication, control-plane signaling, and user interaction with the UE 1601.

[0129] In accordance with aspects of this disclosure, the UE 1601 implements a NAS layer 1608 (similar to NAS layer 308) and an RRC layer 1604 (similar to RRC layer 304). The UE 1601Docket No. 14730885900PCTcan implement the NAS layer 1608 and the RRC layer 1604 using hardware and / or software -such as using a special-purpose processor or by a combination of a processor with computer readable instructions. The RRC layer 1604 can process communications from a lower layer (such as the physical and media access control layers (shown as PHY / MAC 1602)) and the NAS layer 1608. In some implementations, the UE 1601 maintains a list of satellite IDs 1650 in coordination with the NAS layer 1608 and RRC layer 1604. In some aspects, the UE 1601 may maintain the list of satellite IDs 1650 in computer readable media / memory 1603D.

[0130] In accordance with aspects of this disclosure, the UE 1601 implements an S&F operation module 1609. The S&F operation module 1609 may implement one or more of the techniques of the disclosure. For example, the S&F operation module 1609 can store a NAS state or information about an on-going NAS procedure that is pending a NAS response from a satellite that provides the S&F operation mode. In some aspects, the S&F operation module 1609 may reside in computer readable media / memory 1603D.

[0131] FIG. 17A shows an example control plane protocol stack 1700A in accordance with aspects of this disclosure. The diagram of the NTN control plane protocol stack 1700A shows the NR-Uu interface (e.g., via a service link) between the first satellite 112 (e g., the first BS 114) and the UE 101. The NR-Uu includes a radio resource control (RRC) protocol in addition to the PDCP, RLC, MAC, and PHY layers. The UE 101 and the first BS 114 serve as endpoints of the RRC layer 304 and the RRC 1714, 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 1704 of RRC IDLE, RRC CONNECTED, or RRC INACTIVE as described with reference to FIG. 1. In accordance with some implementations of this disclosure, the RRC state 1704 can also be a suspended state such that the UE 101 and the first BS 114 can suspend and restore the RRC connection depending on whether the UE 101 is currently in a coverage area of the first satellite 112.

[0132] The Ng-C interface is between the first BS 114 and the CN 131. The example CN 131 in FIG. 17A can illustrate the operation of an AMF of the 5GC. The diagram of the NTN control plane protocol stack 1700A shows an N1 interface between the NAS layer 308 of the UE 101 and the NAS layer 1738 of the CN 131. The N 1 interface links the UE 101 and the AMF of the CN 131 via an access network. In FIG. 17A, the access network includes the NTN (such as the first satellite 112, first BS 114) coupled by the NTN gateway 132. In normal operation, and in traditional implementations of regenerative satellite access, the first satellite 112 does notDocket No. 14730885900PCTparticipate 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 some implementations, the first satellite 112 can perform an S&F operation 1709. During the S&F operation 1709, the first satellite 112 can temporarily buffer or maintain UL NAS messages or DL NAS messages for a NAS procedure between the NAS layer 308 and the NAS entity 1738.

[0133] The example illustrated in FIG. 17A shows the first BS 114 as a gNB. However, FIG.17A could be modified to describe a scenario in which the first BS 114 is an evolved base station (eNB). The CN 131 can illustrate the 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-C interface can be referred to as an SI -MME interface. The Nr-Uu can be referred to as an LTE-Uu interface.

[0134] FIG. 17A shows the S&F operation 1709 as part of the first satellite 112. However, alternatively, or additionally, the first BS 114 (or even the NTN gateway 132) can perform some or all of the S&F operation 1709. For example, the NTN gateway 132 can include a combination of nodes or functions, some of which are implemented in proximity to the first satellite 112 and some of which are implemented in proximity to the CN 110. The S&F operation 1709 (implemented by whichever NTN node or nodes) can maintain a status of the RRC state 1704 and the NAS mode 1708 in association with a particular UE (such as the UE 101). The first satellite 112 can maintain the status by any combination of local memory, messaging, or other protocols (not shown).

[0135] In accordance with aspects of this disclosure, an MME-onboard can implement all or part of the S&F operation 1709. The MME-onboard can coordinate with an MME-ground to collectively implement the features of the NAS entity 1738.

[0136] FIG. 17B shows an example user plane protocol stack 1700B in accordance with aspects of this disclosure. FIG. 17B includes a visual representation of the NTN portion of user plane protocol stack 1700B involving the UE 101, the first satellite 112, the NTN gateway 132, and a CN 131. The example CN 131 in FIG. 17B can illustrate a user plane function (UPF) of the 5GC. If the CN 131 is an EPC, the features of CN 131 can be performed by a serving gateway (SGW) function. In FIG. 17B, the NTN first BS 114 is onboard the first satellite 112. In the illustrated example in FIG. 17B, the first BS 114 is a 5G NR base station, referred to as a gNB. In an alternative implementation, the first BS 114 can use E-UTRA or NB-IoT and can be referred to as an eNB.Docket No. 14730885900PCT

[0137] The diagram of the NTN user plane protocol stack 1700B shows the NR-Uu interface (e.g., via a service link) between the first satellite 112 (e.g., the first BS 114) and the UE 101. When the first BS 114 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 1700B shows the Ng-U interface (e.g., via a feeder link) between the first satellite 112 (e.g., first BS 114) and the CN 131 via the NTN gateway 132. When the first BS 114 is an eNB, the user interface is referred to as Sl-U instead of Ng-U.

[0138] On the UE 101, the user plane protocol stack 1700B includes protocol layers for the user-plane Protocol 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 first satellite 112 also implements the SDAP, PDCP, RLC, MAC, and PHY layers. However, user data (e.g., PDU messages) are passed through the first satellite 112 (via the lower layer protocols) to the PDU on the CN 131. If the radio access technology for the NTN RAN is E-UTRA or NB-IoT, the SDAP layer may not exist. In some alternative implementations, user plane PDUs may be exchanged between the UE 101 and the CN 131 via the N1 interface or the control plane protocol stack 1700A. In such cases, the user plane protocol state may not exist.

[0139] 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 101, the first BS 114, the first satellite 112, and the CN 131. In some implementations, the UE 101 can support at least a 5G NR (or simply, “NR”) or E-UTRA air interface to communicate with the first BS 114. The first BS 114 connects to the CN 131 via an interface (e.g., SI or NG interface). The first BS 114 can connect to other base stations (including the ground BS 134 or the BS 1814 operating a TN cell 1817) via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes.

[0140] The first BS 114 is equipped with processing hardware 1804 that can include a receiver 1805B configured to receive data in the uplink direction. The processing hardware 1804 can also include a transmitter 1805 A configured to transmit data in the downlink direction. The processing hardware further can one or more general-purpose processor(s) 1805C (e.g., CPUs) and a non-Docket No. 14730885900PCTtransitory computer-readable memory (CRM) 1805D storing instructions that the one or more general-purpose processors execute. Additionally, or alternatively, the processing hardware 1804 can include special -purpose processing units. The processor 1805C 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 1805D 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 first BS 114. The first satellite 112 can include processing hardware 1812, such as a transmitter 1812A, a receiver 1812B, a processor 1812C, and CRM 1812D (similar to components 1804, 1805A, 1805B, 1805C and 1805D of the first BS 114). In some implementations, the components 1812A, 1812B, 1812C and 1812D are shared or commonly implemented with the components 1805A, 1805B, 1805C and 1805D. The BS 1814 can include similar components (not shown) as the processing hardware 1804.

[0141] The CN 131 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 101. The CN 131 can be implemented by one or more processing elements (shown as processing hardware 1831). The processing hardware 1831 can include a transmitter 1832A, a receiver 1832B, a processor 1832C, and a CRM 1832D, similarly, to corresponding components described with reference to processing hardware 1812 and 1804.

[0142] The transmitters 1802A, 1812A, 1805 A, and 1832A and receivers 1802B, 1812B, 1805B, and 1832B are examples of a communication unit. The processors 1802C, 1812C, 1805C,Docket No. 14730885900PCTand 1832C 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 first BS 114, UE 101, first satellite 112, and CN 131 can include other components not illustrated in FIG. 18.

[0143] 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 perform additional operations, fewer operations, operations in parallel or in a different order, and some operations differently. Alternatively, or in addition to the other examples described herein, examples include any combination of the following enumerated example implementation options (referred to as clauses for clarity).

[0144] Clause 1: A method of a user equipment (UE) (101) for wireless communication, the method comprising: receiving, from a first satellite (112), a message (150, 451, 452, 453, 454, 453, 550, 651, 1051, 1153, 1256) that indicates a list of satellite identifiers (IDs) of one or more other satellites that support a store-and-forward (S&F) operation with the first satellite; performing neighbor cell measurements (170, 770, 771A, 771B, 871, 1371A, 1371B, 1471A, 1471B) during a radio resource control (RRC) idle state or an RRC inactive state; detecting (672, 872A, 872B, 1072, 1472) a neighboring cell of a second satellite (122) fulfilling a cell reselection criterion; and performing (180, 380, 580, 1081, 1181, 1281, 1581) a cell reselection to the second satellite based on a satellite ID (321) of the second satellite and the list of satellite IDs.

[0145] Clause 2: The method of clause 1, further comprising, prior to the performing neighbor cell measurements: performing at least part of a non-access stratum (NAS) procedure (646) with the first satellite; and transitioning to the RRC idle state or the RRC inactive state (665, 1065) based on an RRC connection release message (661), expiration of an inactivity timer, or loss of signal with the first satellite.

[0146] Clause 3: The method of clause 1 or 2, wherein the performing the cell reselection includes: camping (685, 1085) on the neighboring cell when the satellite ID of the second satellite is within the list of satellite IDs; or barring (688, 1088) the neighboring cell when the satellite ID is not within the list of satellite IDs.

[0147] Clause 4: The method of any one of clauses 1 to 3, wherein the performing the neighbor cell measurements includes: obtaining system information that includes frequency information of one or more frequencies for the neighbor cell measurements, the frequency informationDocket No. 14730885900PCTcorresponding to satellite IDs associated with the one or more frequencies; and determining (771 A, 1371 A, 1471 A) which frequencies to measure based on the satellite IDs associated with the one or more frequencies and the list of satellite IDs.

[0148] Clause 5: The method of clause 4, wherein the performing the neighbor cell measurements includes: performing the neighbor cell measurements on frequencies associated with satellite IDs in the list of satellite IDs; or refraining from performing neighbor cell measurements on other frequencies associated with satellite IDs that are not in the list of satellite IDs.

[0149] Clause 6: The method of any one of clauses 1 to 5, wherein the performing neighbor cell measurements includes: obtaining satellite information associated with one or more satellites; and performing (771B, 1371B, 1471B) the neighbor cell measurements at a timing based on the satellite information associated with satellites having satellite IDs in the list of satellite IDs.

[0150] Clause 7: The method of any one of clauses 1 to 6, wherein the performing neighbor cell measurements includes: calculating neighbor cell measurement timing based on at least one of propagation delay, satellite ephemeris, or timing advance information for the satellites having satellite IDs in the list of satellite IDs; or refraining from calculating neighbor cell measurement timing for other satellites associated with other satellite IDs not in the list of satellite IDs.

[0151] Clause 8: The method of any one of clauses 1 to 7, wherein the neighboring cell of the second satellite is a first neighboring cell, and wherein the performing the cell reselection includes: detecting a second neighboring cell associated with a third satellite (512) having a third satellite ID not in the list of satellite IDs; and calculating (874, 1474A, 1474B) a cell ranking of the first neighboring cell and the second neighboring cell, where the calculating includes reducing the cell ranking of the second neighboring cell based on the list of satellite IDs not including the third satellite ID.

[0152] Clause 9: The method of any one of clauses 1 to 8, further comprising: determining (992, 1592B) whether to perform a tracking area update (TAU) procedure (992) based on a tracking area code (TAC) value of the neighboring cell when the satellite ID of the neighboring cell is within the list of satellite IDs.

[0153] Clause 10: The method of any one of clauses 1 to 9, further comprising: camping (685) on a third satellite (512) associated with a third satellite ID that is not within the list of satellite IDs; and performing (992) a tracking area update (TAU) based on the camping on the third satellite when the list of satellite IDs does not include the third satellite ID.Docket No. 14730885900PCT

[0154] Clause 11 : The method of any one of clauses 1 to 9, wherein the performing the cell reselection includes: acquiring (680, 980, 1080) a system information block (SIB) type 31 (SIB31) from the neighboring cell, the SIB31 including the satellite ID of the second satellite; and determining whether to reselect the neighboring cell based, at least in part, on whether the satellite ID of the second satellite is within the list of satellite IDs.

[0155] Clause 12: The method of any one of clauses 1 to 11, wherein the message that indicates the list of satellite IDs includes at least one of: a non-access stratum (NAS) message (451) from a first mobility management entity (MME) (118) on-board the first satellite; a NAS message (452) from an MME-ground (138) associated with a core network; a system information block (SIB) message (453); or an RRC message (454) from the first satellite when the UE is operating in an RRC connected state with the first satellite.

[0156] Clause 13: The method of any one of clauses 1 to 12, wherein the message that indicates the list of satellite IDs includes: a SIB type 33 (SIB33) (456) that includes a list of neighboring satellite information, the list of neighboring satellite information including, for each neighboring satellite, a satellite ID and a corresponding flag indicating whether the neighboring satellite supports the S&F operation; and wherein the list of satellite IDs is based on satellite IDs where the corresponding flags indicate that the neighboring satellite supports the S&F operation.

[0157] Clause 14: The method of any one of clauses 1 to 13, wherein the first satellite and the second satellite are in a same mobility management entity (MME) group that includes satellites that: periodically connect to a same NTN gateway; and exchange a UE context in a non-access stratum (NAS) layer via interfaces to a same MME-ground or each other.

[0158] Clause 15: A method of a first satellite (112) for wireless communication, the method comprising: establishing a radio resource control (RRC) connection with a user equipment (UE) (101); enabling a store and forward (S&F) operation for the UE; and communicating, to the UE, a message (150, 451, 452, 453, 454, 453, 550, 651, 1051, 1153, 1256) that indicates a list of satellite identifiers (IDs) identifying at least a second satellite (122) that supports the S&F operation with the first satellite.

[0159] Clause 16: The method of clause 15, wherein the message that indicates the list of satellite IDs includes at least one of: a non-access stratum (NAS) message from a first MME-onboard (118) on-board the first satellite; an RRC message from the first satellite to the UE when the UE and the first satellite are operating in an RRC connected state; a system information block (SIB) message that includes the list of satellite IDs; or a SIB type 33 (SIB33) that includes a listDocket No. 14730885900PCTof neighboring satellite information, the list of neighboring satellite information including, for each neighboring satellite, a satellite ID and a corresponding flag indicating whether the neighboring satellite supports the S&F operation.

[0160] Clause 17: The method of clause 15 or 16, wherein the first satellite and the second satellite are in a same mobility management entity (MME) group that includes satellites that: periodically connect to a same NTN gateway; and exchange a UE context in a non-access stratum (NAS) layer via interfaces to a same MME-ground or each other.

[0161] Clause 18: 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 17.

[0162] Aspects of the subject matter described in this disclosure can be implemented as a computer-readable medium having stored therein instructions which, when executed by a processor, causes the processor to perform any one of the above-mentioned functionalities. Aspects of the subject matter described in this disclosure can be implemented as a system having means for implementing any one of the above-mentioned functionalities. Aspects of the subject matter described in this disclosure can be implemented as an apparatus having one or more processors configured to perform one or more operations from any one of the above-mentioned functionalities.

[0163] 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 orblock 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.

[0164] 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,Docket No. 14730885900PCTquantity, 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.

[0165] 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.

[0166] As used herein, the terms “user device”, “user equipment” (for example, UE 101), “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 mediaDocket No. 14730885900PCTdevices, 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.

[0167] 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 and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0168] 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 specialpurpose processors.

[0169] 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.”

[0170] 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 toDocket No. 14730885900PCTcover 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.

[0171] 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 concept of “only B.” An expression of “(A) B” or “B (A)” may include the concept of “A+B” or “B+A.”

[0172] 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.

[0173] 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.

[0174] 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, or combinations 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.

[0175] 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 codeDocket No. 14730885900PCTin the form of instructions or data structures. Combinations of the above should also be included within the scope of storage media.

[0176] 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.

[0177] 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 a claimed 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.

[0178] 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.

[0179] 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 combinationDocket No. 14730885900PCTof aspects from any of the examples is also within the scope of the disclosure. The examples in this disclosure are provided for pedagogical purposes.

Claims

Docket No. 14730885900PCTCLAIMSWhat is claimed is:

1. A method of a user equipment (UE) (101) for wireless communication, the method comprising:receiving, from a first satellite (112), a message (150, 451, 452, 453, 454, 453, 550, 651, 1051, 1153, 1256) that indicates a list of satellite identifiers (IDs) of one or more other satellites that support a store-and-forward (S&F) operation with the first satellite;performing neighbor cell measurements (170, 770, 771A, 771B, 871, 1371A, 1371B, 1471 A, 147 IB) during a radio resource control (RRC) idle state or an RRC inactive state;detecting (672, 872A, 872B, 1072, 1472) a neighboring cell of a second satellite (122) fulfilling a cell reselection criterion; andperforming (180, 380, 580, 1081, 1181, 1281, 1581) a cell reselection to the second satellite based on a satellite ID (321) of the second satellite and the list of satellite IDs.

2. The method of claim 1, further comprising, prior to the performing the neighbor cell measurements:performing at least part of a non-access stratum (NAS) procedure (646) with the first satellite; andtransitioning to the RRC idle state or the RRC inactive state (665, 1065) based on an RRC connection release message (661), expiration of an inactivity timer, or loss of signal with the first satellite.

3. The method of claim 1 or 2, wherein the performing the cell reselection includes:camping (685, 1085) on the neighboring cell when the satellite ID of the second satellite is within the list of satellite IDs; orbarring (688, 1088) the neighboring cell when the satellite ID is not within the list of satellite IDs.

4. The method of any one of claims 1 to 3, wherein the performing the neighbor cell measurements includes:obtaining system information that includes frequency information of one or more frequencies for the neighbor cell measurements, the frequency information corresponding to satellite IDs associated with the one or more frequencies; andDocket No. 14730885900PCTdetermining (771A, 1371A, 1471A) which frequencies to measure based on the satellite IDs associated with the one or more frequencies and the list of satellite IDs.

5. The method of any one of claims 1 to 4, wherein the performing the neighbor cell measurements includes:performing the neighbor cell measurements on frequencies associated with satellite IDs in the list of satellite IDs; orrefraining from performing neighbor cell measurements on other frequencies associated with satellite IDs that are not in the list of satellite IDs.

6. The method of any one of claims 1 to 5, wherein the performing neighbor cell measurements includes:obtaining satellite information associated with one or more satellites; and performing (771B, 1371B, 1471B) the neighbor cell measurements at a timing based on the satellite information associated with satellites having satellite IDs in the list of satellite IDs.

7. The method of any one of claims 1 to 6, wherein the performing neighbor cell measurements includes:calculating neighbor cell measurement timing based on at least one of propagation delay, satellite ephemeris, or timing advance information for the satellites having satellite IDs in the list of satellite IDs; orrefraining from calculating neighbor cell measurement timing for other satellites associated with other satellite IDs not in the list of satellite IDs.

8. The method of any one of claims 1 to 7, wherein the neighboring cell of the second satellite is a first neighboring cell, and wherein the performing the cell reselection includes:detecting a second neighboring cell associated with a third satellite (512) having a third satellite ID not in the list of satellite IDs; andcalculating (874, 1474A, 1474B) a cell ranking of the first neighboring cell and the second neighboring cell, where the calculating includes reducing the cell ranking of the second neighboring cell based on the list of satellite IDs not including the third satellite ID.Docket No. 14730885900PCT9. The method of any one of claims 1 to 8, further comprising:determining (992, 1592B) whether to perform a tracking area update (TAU) procedure (992) based on a tracking area code (TAC) value of the neighboring cell when the satellite ID of the neighboring cell is within the list of satellite IDs.

10. The method of any one of claims 1 to 9, further comprising:camping (685) on a third satellite (512) associated with a third satellite ID that is not within the list of satellite IDs; andperforming (992) a tracking area update (TAU) based on the camping on the third satellite when the list of satellite IDs does not include the third satellite ID.

11. The method of any one of claims 1 to 9, wherein the performing the cell reselection includes:acquiring (680, 980, 1080) a system information block (SIB) type 31 (SIB31) from the neighboring cell, the SIB31 including the satellite ID of the second satellite; and determining whether to reselect the neighboring cell based, at least in part, on whether the satellite ID of the second satellite is within the list of satellite IDs.

12. The method of any one of claims 1 to 11, wherein the message that indicates the list of satellite IDs includes at least one of:a non-access stratum (NAS) message (451) from a first mobility management entity (MME) (118) on-board the first satellite;a NAS message (452) from an MME-ground (138) associated with a core network; a system information block (SIB) message (453);an RRC message (454) from the first satellite when the UE is operating in an RRC connected state with the first satellite; ora SIB type 33 (SIB33) (456) that includes a list of neighboring satellite information, the list of neighboring satellite information including, for each neighboring satellite, a satellite ID and a corresponding flag indicating whether the neighboring satellite supports the S&F operation, wherein the list of satellite IDs is based on satellite IDs where the corresponding flags indicate that the neighboring satellite supports the S&F operation.

13. A method of a first satellite (112) for wireless communication, the method comprising: establishing a radio resource control (RRC) connection with a user equipment (UE) (101); enabling a store and forward (S&F) operation for the UE; andDocket No. 14730885900PCTcommunicating, to the UE, a message (150, 451, 452, 453, 454, 453, 550, 651, 1051, 1153, 1256) that indicates a list of satellite identifiers (IDs) identifying at least a second satellite (122) that supports the S&F operation with the first satellite.

14. The method of claim 13, wherein the first satellite and the second satellite are in a same mobility management entity (MME) group that includes satellites that:periodically connect to a same NTN gateway; andexchange a UE context in a non-access stratum (NAS) layer via interfaces to a same MME-ground or each other.

15. An apparatus, comprising:a communication unit; anda 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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