Method and system for asynchronous registration of a user equipment in a mobile communication network

Abstract

A method for asynchronous registration of a UE in a mobile communication network is proposed. It comprises sending a first attach request from the UE to a first satellite; storing identification information associated with the UE in the first satellite; sending an attach reject message, comprising a first backoff timer, from the satellite to the UE; sending an authentication information request from the satellite to a ground network; upon successful authentication of the UE by a HSS, sending UE subscription information, including UE authentication vectors, from the ground network to a second satellite; storing the UE subscription information in the second satellite; after expiration of the first backoff timer, sending a second attach request from the UE to the second satellite; and sending a confirmation message indicating successful completion of the registration procedure from the second satellite to the UE. The disclosure also provides a multi-satellite non-terrestrial communication system.

Description

[0001] METHOD AND SYSTEM FOR ASYNCHRONOUS REGISTRATION OF A USER EQUIPMENT IN A MOBILE COMMUNICATION NETWORK

[0002] TECHNICAL FIELD

[0003] The present invention primarily relates to wireless communication systems, such as 3GPP communication systems. Particularly, it relates to a method for asynchronous registration of user equipment (UE) in a mobile communication network utilizing a multi-satellite nonterrestrial communication system. The invention also relates to a multi-satellite system configured to perform the asynchronous registration method.

[0004] BACKGROUND OF THE INVENTION

[0005] Narrowband loT (NB-loT) is a cellular communication technology specifically designed for low-power loT devices that require small amounts of data at regular intervals. While terrestrial cellular networks have driven the adoption of NB-loT, they lack coverage, for example, in rural, remote, and maritime areas. This is where satellite connectivity plays an important role, extending NB-loT coverage to these underserved areas and enabling use cases like global logistics tracking, smart farming, and environmental monitoring.

[0006] NB-loT delay-tolerant applications can benefit from low-density Low-Earth Orbit (LEO) satellite constellations, which are more affordable to deploy compared to large, complex Geostationary Earth Orbit (GEO) or high-density LEO deployments. However, low-density constellations introduce challenges as they cause service and feeder link discontinuities. In Non-Terrestrial Networks (NTNs), where feeder link capacity is limited and ground station availability is scarce, maintaining continuous connections between the satellite constellation and ground stations is not always possible.

[0007] Asynchronous bidirectional data communication is still possible in low-density LEO constellations through a Store and Forward (S&F) mechanism. In essence, S&F allows data to be temporarily buffered at intermediate nodes, in this case, satellites, when connectivity is interrupted. When the satellite re-establishes connectivity with a ground station or the target UE, the stored data is forwarded, ensuring reliable information delivery even in the face of service or feeder link interruptions. This mechanism is particularly beneficial for delay-tolerant loT applications, where timely data delivery is not critical, but reliability is paramount. Support to the S&F mechanism is a topic currently being discussed in the context of the 3rd Generation Partnership Project (3GPP) standardization. For example, the 3GPP TS 22.261 [3] describes the service and operational requirements for 5G systems. This document highlights that a 5G system with support to S&F Satellite operation shall be able to inform a UE whether the S&F Satellite operation is applied.

[0008] The inventors of the present invention recognized the need to reconsider the conventional assumption of continuous connectivity between core components within mobile networks. Fig. 1 illustrates an S&F architecture, previously proposed, in which each satellite is equipped with a regenerative payload that includes an onboard eNB / gNB and a Mobile Mobility Entity (MME). This architecture includes S&F interfaces to maintain service when connectivity with the UE or ground station is unavailable.

[0009] Particularly, the authentication proxy retrieves and stores subscription data from the HSS on the satellite, enabling UE attach procedures without constant connectivity. The user data proxy buffers both Mobile Originated (MO) and Mobile Terminated (MT) traffic on the satellite and ground, ensuring delivery upon reconnection. The UE context proxy synchronizes UE context (e.g., temporary IDs, encryption keys) across satellites, allowing seamless access without repeated attach procedures.

[0010] In previous work efforts, the traditional UE attach procedure has been adapted for NTNs to address feeder link discontinuity. As shown in Fig. 2, this adaptation requires a minimum of four steps to ensure that the satellite can use the S&F interfaces to successfully register the UE within the mobile network [1 , 2],

[0011] Fig. 3 illustrates the signaling flow between UE, satellite, and the ground network (GN) during the four steps of the attach procedure.

[0012] Step 1 :

[0013] • When the UE has visibility with a first satellite, the UE issues an attach request and sends the corresponding identifier (e.g., the International Mobile Subscriber Identity - I MSI) to the MME onboard the satellite.

[0014] • The satellite receives the identifier and verifies if there is an Authentication Vector (AV) for the IMSI identifier. Given that at this time the satellite cannot establish direct communication with the Home Subscriber Server (HSS) for authentication, since the ground station of the ground network is not visible, the satellite issues a provisional rejection message that leaves the UE on standby (i.e., blocks the repetition of the authentication requests).

[0015] • The satellite stores the Authentication Information Request (AIR) and the I MSI identifier in the internal memory until the moment when the ground network becomes visible to the first satellite.

[0016] Step 2:

[0017] • When the satellite and the ground station of the ground network have visibility, the satellite sends the generated AIR with the IMSI identifier of the UE.

[0018] • The ground network receives them and generates an AV and an Updated Location Answer (ULA), if the authentication has been validated by the HSS.

[0019] • The generated AV and ULA are stored in the terrestrial network until a second satellite becomes visible, which may in fact be the same satellite that transmitted the AIR or any other satellite in the constellation.

[0020] Step 3:

[0021] • The ground network sends the AV and the ULA to the second visible satellite or to the first satellite if still visible.

[0022] Step 4:

[0023] • When the UE has visibility with first or second satellite, that would already have received and stored the AV and the ULA from the GN, the UE sends a subsequent attach request to the satellite.

[0024] • The first or second satellite verifies the existence of the credentials for the requesting UE and sends ULA of the UE.

[0025] • The UE is authenticated and can initiate the transmission of data packets.

[0026] In a satellite cell operating in S&F operation mode, if a UE initiates a signaling procedure during a satellite pass, and the procedure cannot be completed within the duration of the pass because some information is missing in the serving satellite (e.g. authentication vectors from the HSS), the initiated procedure should be terminated / suspended with a proper rejection cause. Additionally, the UE should be provided with guidance on when and how to retry, such as "procedure suspended due to S&F operation" with a retry suggestion (e.g. "re-try in ‘X’ minutes" during the next satellite pass where the necessary data may be available). Moreover, in a multi-satellite constellation, it should be possible to initiate or suspend procedures in one satellite and resume or terminate it in another satellite on the same Public Mobile Land Network (PLMN) in order to benefit from reduced latencies.

[0027] While current methods in the state of the art address feeder link discontinuity in signaling procedures between the UE and Non-Terrestrial Networks (NTN), additional innovations are necessary to enable efficient support for S&F operations in multi-satellite environments.

[0028] References:

[0029] [1] T. Kellermann et al., “Novel architecture for cellular loT in future non-terrestrial networks: Store and forward adaptations for enabling discontinuous feeder link operation”, IEEE Access, vol. 10, June 2022.

[0030] [2] WO2023094715 “Method of asynchronous data communication and registration of a user equipment”, June 2023.

[0031] [3] 3GPP TS 22.261 version 19.4.0, 3rd Generation Partnership Project, Technical Specification Group Services and System Aspects, Service requirements for the 5G system, Stage 1 , Release 18, September 2023.

[0032] DESCRIPTION OF THE INVENTION

[0033] An object of the present invention is thus to extend 3GPP UE registration procedures to support S&F operation in a multi-satellite scenario.

[0034] According to a first aspect, a method for asynchronous registration of a UE in a mobile communication network is provided. In a preferred embodiment, the method comprises the steps of: sending a first attach request from a UE to a first satellite, the first attach request comprising identification information associated with the UE; storing the identification information associated with the UE in the first satellite; sending an attach reject message from the first satellite to the UE, the attach reject message comprising a first backoff timer to indicate when the UE can re-attempt an attach request; sending an authentication information request, generated with the stored identification information associated with the UE, from the first satellite to a ground network; upon successful authentication of the UE by a HSS, sending UE subscription information, including authentication vectors of the UE, from the ground network to a second satellite; storing the UE subscription information in the second satellite; after expiration of the first backoff timer, sending a second attach request from the UE to the second satellite, the second attach request comprising identification information associated with the UE; and sending a confirmation message indicating successful completion of the registration procedure from the second satellite to the UE. In some embodiments, at least one of the first attach request and the second attach request further comprise a flag indicating that the UE supports asynchronous operations.

[0035] In some embodiments, if the UE does not support asynchronous operations, the attach reject message sent by the satellite is a definitive reject cause forcing the UE to retry in a next satellite pass.

[0036] In some embodiments, the attach reject message further comprises a list of satellites identifiers to indicate to the UE which satellites to consider for subsequent attempts.

[0037] In some embodiments, the second satellite is the same as the first satellite.

[0038] In some embodiments, the confirmation message comprises a second backoff timer to indicate when the UE can begin user data exchange with satellites operating in a same PLMN.

[0039] In some embodiments, the confirmation message further comprises a list of satellites identifiers to indicate to the UE which satellites to consider for data exchange.

[0040] In some embodiments, before the sending of the first attach request, the UE receives a PLMN and Two-Line Elements (TLEs) of multiple satellites within the same constellation through system information broadcasted by the mobile communication network. Particularly, the system information may be broadcasted via a System Information Block (SIB)32.

[0041] In some embodiments, before the sending of the fist attach request, the UE detects or learns that the first satellite is configured for asynchronous operation based on system information broadcasted by the mobile communication network. Particularly, the system information is broadcasted by the mobile communication network via a system information block (e.g., SIB31 or SIB32).

[0042] According to a second aspect, the present invention provides a multi-satellite non-terrestrial communication system configured to execute the asynchronous registration of a UE within a mobile communication network. In a preferred embodiment, the system comprises a first satellite that comprises a communication unit configured to receive a first attach request from a UE. This attach request contains identification information associated with the UE. The first satellite further comprises a storage unit configured to store this identification information, and a processing unit configured to generate an attach reject message comprising a first backoff timer indicating the period after which the UE can attempt to re-initiate an attach request. Additionally, the communication unit in the first satellite is further configured to send the attach reject message to the UE and an authentication information request, generated using the stored UE information, to a ground network.

[0043] The system also comprises a second satellite equipped with a communication unit configured to receive UE subscription information from the ground network following successful authentication by a Home Subscriber Server (HSS). The subscription information may include authentication vectors of the UE. The second satellite further comprises a storage unit configured to store the UE subscription information. The communication unit of the second satellite is further configured to receive a second attach request from the UE after the first backoff timer expires, the second attach request containing identification information associated with the UE. Moreover, the second satellite further comprises a processing unit that generates a confirmation message, which is transmitted via the communication unit to the UE, indicating successful registration.

[0044] BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The previous and other advantages and features will be more fully understood from the following detailed description of embodiments, with reference to the attached figures, which must be considered in an illustrative and non-limiting manner, in which:

[0046] Fig. 1 shows an S&F architecture where each satellite is equipped with a regenerative payload that includes an onboard eNB / gNB and Core Network functions (e.g. MME).

[0047] Fig. 2 schematically illustrates the steps required for UE attachment with service and feeder link discontinuity with one satellite.

[0048] Fig. 3 illustrates the signaling between UE, satellite, and ground network over the 4 steps of the registration procedure.

[0049] Fig. 4 illustrates the proposed registration procedure under S&F Satellite operation in a multisatellite deployment and roaming scenario (i.e. HSS on ground), according to an embodiment of the present invention.

[0050] DETAILED DESCRIPTION OF THE INVENTION AND OF PREFERRED EMBODIMENTS

[0051] The present invention provides a method for handling asynchronous UE registration procedures in multi-satellite 3GPP-based NTN networks operating in S&F mode incorporating one or more of the following improvements. • Mechanism for the UE to advertise the network that supports S&F: The incorporation of an 'S&F feature supported' flag signaling the device's ability to handle S&F operations in the attach request message.

[0052] • New reject causes for terminating / suspending the Non-Access Stratum (NAS) procedures, such as initial attach procedure: In cases where the UE has not indicated support for S&F, a specific reject code can be used to direct the UE to retry during the next satellite pass.

[0053] • New backoff timers for assisting the UE on subsequent re-attempts in the same or other satellite cells of the same PLMN: A new backoff timer is introduced to manage when the UE can re-attempt the attach procedure. During the duration of this timer value, the UE should not initiate a new attach attempt with any satellite cell operating in S&F mode within the same PLMN.

[0054] • Mechanism for the networks to communicate to the UE which satellites to consider for subsequent attempts and / or user data transfer: Provision of a list of satellite cells or satellite identifiers to inform the UE the appropriate satellites for reattempting or resuming NAS procedures, or initiating data transfer, once the backoff timer ends.

[0055] • New backoff timers to back-off UE interactions with the network after the UE has completed a NAS procedure (e.g. attach) that has resulted in a modification of the UE context in the satellite and there is a need for UE context distribution or synchronization with modification in any of the satellites: A new backoff timer can be included as part of the NAS attach acceptance message to the UE to indicate a proper time when the UE can attempt user data transmission / reception in any satellite. This timer is needed to allow for the network to properly synchronize the updated UE context among the satellite constellation and to avoid the situation where the UE is trying to interact with a satellite with an outdated context, which could lead to abnormal situations (e.g., forced detach, etc.).

[0056] A multi-satellite non-terrestrial communication system in which the satellites are equipped with specific components to facilitate the asynchronous registration of UEs within a mobile communication network is also proposed.

[0057] In an embodiment, the system comprises a first satellite equipped with a communication unit, for example an onboard eNB, configured to receive a first attach request from a UE. The first satellite further comprises a storage unit, such as a computer memory, to store the UE's identification information, and a processing unit as part of an onboard Core Network (CN) element. This processing unit is configured to generate an attach reject message containing a first backoff timer, indicating when the UE can retry the attach request.

[0058] In some embodiments, the communication unit of the first satellite can also comprise a communication interface between the onboard CN element and the ground CN element to send an authentication information request, based on the stored UE information, to a ground network.

[0059] Moreover, the system may also comprise at least one additional satellite (or second satellite) comprising a communication unit configured to receive UE subscription information in the onboard CN element, including AVs, from the ground network after successful authentication by an HSS. The second satellite further comprises a storage unit for storing the UE subscription information and a processing unit, as part of the onboard CN element, which generates a confirmation message indicating successful completion of the registration procedure. The communication unit (e.g., the onboard eNB) is further configured to send the confirmation message to the UE.

[0060] In some embodiments, the second satellite can be the same as the first satellite, if the first satellite remains within communication range of the ground network following the successful authentication of the UE by the HSS.

[0061] Likewise, the CN functionalities can be distributed between the satellites and the ground network. The onboard CN element deployed on the satellites is not restricted to a complete MME, as depicted in the architecture of Fig. 1 , but may instead encompass only a subset of MME functions required for handling specific 3GPP interfaces. The ground network element comprises the remaining core network functions, which interact with other 3GPP core network components (e.g., S / P-GW, SCEF, HSS) through standardized 3GPP interfaces.

[0062] Fig. 3 illustrates a preferred embodiment of the proposed registration method. In this embodiment, without loss of generality, the procedure involves three different satellites (SAT#i, SAT#j, SAT#k) to highlight the facts that the execution of the attach procedure can be initiated in one satellite and completed in another and that, after the attach completion, user data transmission should be possible via any of the three satellites.

[0063] In this embodiment, it is assumed that the HSS with the subscription information (including the E-UTRAN AVs needed for completing the attach procedure) is on the ground, as it could be the case of a roaming scenario. Moreover, in this embodiment, the method begins with the UE powered on and searching for a network to register with. In this scenario, the UE is unable to find its home PLMN via terrestrial networks and initiates a search for a cell in a satellitebased PLMN.

[0064] In Step 01 , as a first satellite SAT#i enters the UE's communication range, the UE detects the satellite cell. During this detection, the UE receives the PLMN and TLEs of multiple satellites within the constellation through system information broadcasted by the mobile communication network, for example, through a SIB32. Additionally, the UE can also learn from the information broadcasted by the mobile communication network, such as, but not limited to, a SIB31 or SIB32, that the detected first satellite operates in S&F satellite mode. In Step 02, the UE initiates the network attach procedure by sending an attach request to the first satellite SAT#i. In some embodiments, in the attach request, the UE can signal that it supports the S&F feature by including an S&F feature-supported flag in its network capabilities.

[0065] Next, in Step 03, the first satellite SAT#i rejects the initial attach procedure due to the lack of onboard subscription data, such as E-UTRAN authentication vectors (AVs), and the absence of an active feeder link to retrieve such data from the ground network. If the UE has indicated support for S&F, the first satellite SAT#i sends an attach reject message with a S&F-specific reject cause and includes a backoff timer (S&F Timer#1). This timer prevents the UE from initiating another attach attempt with any other satellite in the same PLMN operating in S&F mode. If the UE does not support S&F, the first satellite SAT#i can use a different reject cause, such as network congestion, to delay the UE’s next attach attempt. Alternatively, the satellite can provide a definitive reject cause, forcing the UE to retry in a next satellite pass. Additionally, the first satellite SAT#i stores information about the attach attempt internally and will retrieve the missing data when ground network connectivity is reestablished.

[0066] In Step 04, a second satellite (SAT#j), also operating in S&F mode and lacking subscription data, comes within communication range of the UE. Since the second satellite SAT#j belongs to the same PLMN and the S&F Timer#1 has not expired, the UE does not attempt another attach procedure. In Step 04a, once S&F Timer#1 expires, the UE becomes eligible to reattempt the attach procedure in any upcoming satellite cell within the same PLMN.

[0067] In Step 05, the second SAT#i reconnects to the ground network through the feeder link. In Step 06, the onboard CN element of the first satellite SAT#i exchanges information with the CN element on the ground regarding the previous attach attempt by the UE. In Step 07, the ground CN element communicates with the HSS of the UE's home PLMN. Particularly, the latter is executed via the S6a interface, using the I MSI to retrieve the UE's subscription information, including the E-UTRAN AVs. In Step 08, the E-UTRAN AVs are uploaded and stored in the onboard CN element of the first satellite SAT#i.

[0068] In Step 09, a third satellite (SAT#k) gets connected to the ground network. Since the third SAT#k will soon fly over the UE's location, the E-UTRAN AVs for the UE are also uploaded and stored in the third satellite SAT#k’s onboard CN element.

[0069] In Step 10, the third satellite SAT#k comes within the communication range of the UE. In Step 11 , the UE detects SAT#k’s satellite cell and reattempts the attach procedure, as S&F Timer#1 has expired. In Step 12, authentication and security setup procedures are completed successfully, as the third satellite SAT#k now has the required subscription data for the UE. In Step 13, a confirmation message, such as a NAS attach accept message, is sent to indicate the acceptance of the network attach, and a new UE / Network Management Entity (MME) context is created. As part of the NAS attach accept message, the network provides the UE with a new timer (S&F Timer#2). This timer prevents the UE from attempting any data transmission until the HSS location update is complete, and the UE / MME context is replicated across other satellites. In Step 14, the UE sends the NAS attach complete message and sets S&F Timer#2.

[0070] In Step 15, the third satellite SAT#k connects to the ground network, allowing the ground CN element to learn about the new UE / MME context. In Step 16, the ground CN element initiates a location update procedure with the HSS to register the UE. Once the update is complete, all subscriber information is successfully retrieved from the HSS.

[0071] In Step 17, the second satellite SAT#j connects to the ground network, and the new UE / MME context is uploaded and stored in the second satellite SAT#j.

[0072] In Step 18, the second satellite SAT#i comes back into communication range of the UE, but the UE refrains from initiating data transmission because S&F Timer#2 has not expired. In Step 18a, S&F Timer#2 expires, and the UE is now free to begin user data transmission or reception with any upcoming satellite in the PLMN.

[0073] In Step 19, the second satellite SAT#j comes within the communication range of the UE. In Step 20, user data transmission can be initiated through the second satellite SAT#j as the updated UE context is now synchronized.

[0074] The description of the method provided herein is intended for exemplification purposes only and should not be construed as limiting the scope of the invention. The features described are not necessarily required to be employed together, and may be utilized independently or in various combinations. Different embodiments and combinations of the described elements may be implemented without departing from the spirit and scope of the invention, allowing for a range of potential applications tailored to specific needs or environments. While the concepts presented are described within the context of a 4G / LTE architecture, they are equally applicable to other generations of mobile communication networks, such as 5G / NR and future technologies. This is because the principles of the invention can be extended to equivalent network entities and interfaces in these technologies. The examples provided herein are solely for illustration and do not limit the scope of the invention. The scope of the present invention is defined in the following set of claims.

Claims

CLAIMS1. A method for asynchronous registration of a user equipment (UE) in a mobile communication network, the method comprising the steps of: sending a first attach request from a UE to a first satellite, the first attach request comprising identification information associated with the UE; storing the identification information associated with the UE in the first satellite; sending an attach reject message from the first satellite to the UE, the attach reject message comprising a first backoff timer to indicate when the UE can re-attempt an attach request; sending an authentication information request, generated with the stored identification information associated with the UE, from the first satellite to a ground network; upon successful authentication of the UE by a Home Subscriber Server (HSS), sending UE subscription information, including authentication vectors of the UE, from the ground network to a second satellite; storing the UE subscription information in the second satellite; after expiration of the first backoff timer, sending a second attach request from the UE to the second satellite, the second attach request comprising identification information associated with the UE; and sending a confirmation message indicating successful completion of the registration procedure from the second satellite to the UE.

2. The method according to claim 1 , wherein at least one of the first attach request and the second attach request further comprise a flag indicating that the UE supports asynchronous operations.

3. The method according to claim 1 , wherein if the UE does not support asynchronous operations, the attach reject message sent by the satellite is a definitive reject cause forcing the UE to retry in a next satellite pass.

4. The method according to claim 1 , wherein the attach reject message further comprises a list of satellites identifiers to indicate to the UE which satellites to consider for subsequent attempts.

5. The method according to claim 1 , wherein the second satellite is the same as the first satellite.

6. The method according to claim 1 , wherein the confirmation message comprises a second backoff timer to indicate when the UE can begin user data exchange with satellites operating in a same Public Land Mobile Network (PLMN).

7. The method according to claim 1 , wherein the confirmation message further comprises a list of satellites identifiers to indicate to the UE which satellites to consider for data exchange.

8. The method according to claim 1 , wherein before the sending of the first attach request, the UE receives a PLMN and Two-Line Elements (TLEs) of multiple satellites within the same constellation through system information broadcasted by the mobile communication network.

9. The method according to claim 8, wherein the system information is broadcasted via a System Information Block (SIB) 32.

10. The method according to claim 1 , wherein before the sending of the fist attach request, the UE detects or learns that the first satellite is configured for asynchronous operation based on system information broadcasted by the mobile communication network.11 . The method according to claim 10, wherein the system information is broadcasted by the mobile communication network via a SIB31 or SIB32.

12. A multi-satellite non-terrestrial communication system configured to execute asynchronous registration of a user equipment (UE) in a mobile communication network, comprising: a first satellite, comprising: a communication unit configured to receive a first attach request from a UE, the first attach request comprising identification information associated with the UE; a storage unit configured to store the identification information associated with the UE; a processing unit configured to generate a first attach reject message, the attach reject message comprising a first backoff timer to indicate when the UE can reattempt an attach request; the communication unit being further configured to send the attach reject message to the UE and to send an authentication information request, generated with the stored information associated with the UE, to a ground network; and a second satellite, comprising:a communication unit configured to receive UE subscription information, including Authentication Vectors (AVs) of the UE, from the ground network upon successful authentication by a Home Subscriber Server (HSS); a storage unit configured to store the UE subscription information; the communication unit being further configured to receive a second attach request from the UE after expiration of the first backoff timer, the second attach request comprising identification information associated with the UE; a processing unit configured to generate a confirmation message indicating successful completion of the registration procedure; and the communication unit being further configured to send the confirmation message to the UE.

13. The satellite system according to claim 12, wherein at least one of the first attach request and the second attach request further comprise a flag indicating that the UE supports asynchronous operations.

14. The satellite system according to claim 12, wherein if the UE does not support asynchronous operations, the attach reject message is a definitive reject cause forcing the UE to retry in a next satellite pass.

15. The satellite system according to claim 12, wherein the attach reject message further comprises a list of satellites identifiers to indicate to the UE which satellites to consider for subsequent attempts.

16. The satellite system according to claim 12, wherein the second satellite is the same as the first satellite.

17. The satellite system according to claim 12, wherein the confirmation message comprises a second backoff timer to indicate when the UE can begin user data exchange with satellites operating in a same Public Land Mobile Network (PLMN).

18. The satellite system according to claim 12, wherein the confirmation message further comprises a list of satellites identifiers to indicate to the UE which satellites to consider for data exchange.

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