Method and system for handling asynchronous data exchange in a non-terrestrial communication network operating in store and forward mode

Abstract

A method and a system for handling asynchronous data exchange in a non-terrestrial communication system operating in Store and Forward (S&F) mode are provided. The method comprises detecting, by a user equipment (UE), a satellite within communication range; identifying, by the UE, that the satellite can handle asynchronous data exchange; transmitting, by the UE, user data in a first protected control message, comprising at least one S&F Information Element (IE), to the satellite; storing, by the satellite, the user data; triggering, by the satellite, at least one indication message or data management policy based on the at least one S&F IE; establishing a feeder link connection between the satellite and a ground station; and forwarding, by the satellite, the stored user data to the ground station.

Description

[0001] METHOD AND SYSTEM FOR HANDLING ASYNCHRONOUS DATA EXCHANGE IN A NON-TERRESTRIAL COMMUNICATION NETWORK OPERATING IN STORE AND FORWARD MODE

[0002] TECHNICAL FIELD

[0003] The present invention primarily relates to wireless communication systems, such as 3GPP communication systems. Particularly, it relates to a method and system for handling asynchronous data exchange in a non-terrestrial communication network operating in store and forward (S&F) mode.

[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 (NTN) systems, 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. In this context, WO2023094715, describes an asynchronous data communication method for a system comprising a satellite constellation, a ground network with at least one ground station, and User Equipment (UE). The method allows bidirectional data transmission even when the user equipment and ground station do not have simultaneous connectivity to the satellites. The user equipment sends data to the satellite constellation, which stores it until it can be forwarded to the ground network. The ground network can then transmit the data to the mobile network core. The satellite constellation can also receive data from the mobile network core and deliver it to the user equipment in an asynchronous manner, leveraging the S&F mechanism onboard the satellites to overcome the lack of continuous connectivity between the different system components.

[0008] [2] discloses a similar asynchronous data communication method but it furthers introduces a high-level view of the network’s architecture for implementing the S&F mechanism, illustrated in Fig. 1. The satellites, equipped with eNB / gNB and a Mobility Management Entity (MME), store and forward both data and signaling to compensate for the lack of constant connectivity with ground stations. Three proxy modules — Authentication Proxy, User Data Proxy, and UE Context Proxy — facilitate the storage and forwarding of authentication information, Mobile- Originated (MO) and Mobile-Terminated (MT) data traffic, and user context, respectively.

[0009] Fig. 2 describes the process for Mobile-Originated (MO) traffic transmission disclosed in [2], where a UE sends data to a ground network. Due to the lack of continuous feeder link, the satellite stores the data in the Satellite Data Proxy module until connectivity with the ground station is established.

[0010] Fig. 3, on the other hand, illustrates the process for Mobile-terminated (MT) traffic, where the ground network sends data to the UE. The ground station stores the data in the Ground Station Data Proxy module until the feeder link with a satellite is established. The satellite then stores the data until the loT device is within coverage range, at which point the data is transmitted to the device.

[0011] The 3GPP TS 23.401 [3] introduced an optimized Evolved Packet System (EPS) architecture for Cellular loT (CloT), incorporating a CloT Serving Gateway Node (C-SGN). As shown in Fig. 4, this architecture is a combined EPC node implementation designed to minimize the number of physical entities by collocating EPS entities in both the control and user planes, such as MME, Serving Gateway (S-GW), and Packet Data Network Gateway (P-GW), which may be more suitable for CloT deployments. Moreover, [3] describes CloT EPS optimizations, aimed at improving the support for the transfer of small data for loT devices. Two main optimizations are presented: the user plane CloT EPS optimization and the control plane CloT EPS optimization. The user plane optimization allows for the transfer of user plane data without the need to establish an Access Stratum (AS) context between the eNodeB and the serving UE, while the control plane optimization transmits user data or Short Message Service (SMS) messages through the MME by encapsulating them in Non-Access Stratum (NAS).

[0012] Fig. 5 illustrates the detailed procedures for MO data transport for the control plane CloT EPS optimization, including the signaling involved and handling scenarios like paging and downlink data notification.

[0013] The 3GPP TS 24.301 [4] provides further details on the messages’ functional definitions and contents. For example, it describes that the EPS Session Management (ESM) STATUS message is sent by the network or the UE to pass information on the status of the indicated EPS bearer context and report certain error conditions.

[0014] Table 1: ESM STATUS message content

[0015] Similarly, [4] also describes that the ESM DATA TRANSPORT message is sent by the UE or the network in order to carry user data in an encapsulated format.

[0016] Table 2: ESM DATA TRANSPORT message content References:

[0017] [1] WO2023094715: “Method of asynchronous data communication and registration of a user equipment”, June 2023.

[0018] [2] 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.

[0019] [3] 3GPP TS 23.401 version 18.3.0, 3rd Generation Partnership Project, Technical Specification Group Services and System Aspects, General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access, Release 18, September 2023.

[0020] [4] 3GPP TS 24.301 version 18.4.0,3rd Generation Partnership Project, Technical Specification Group Core Network and Terminals, Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS), Stage 3, Release 18, September 2023.

[0021] DESCRIPTION OF THE INVENTION

[0022] An object of the present invention is to extend the 3GPP Control Plane CloT EPS Optimization to accommodate satellite cells capable of performing asynchronous bidirectional data communication. This is particularly achieved by providing a new solution for data transport during S&F operation, where specific Information Elements (lEs) can be defined to provide the network with key information to optimize resource utilization and improve the overall reliability of S&F satellite operations in loT NTN environments:

[0023] • lEs to indicate whether further data transmission is permitted.

[0024] • lEs to notify if quota limits have been reached.

[0025] • lEs to specify the priority level of S&F data (e.g., low, medium, high).

[0026] • lEs to provide the expected delivery time for buffered data (e.g., time remaining for data delivery to the ground network).

[0027] The addition of new lEs in the ESM DATA TRANSPORT messages and new causes in the ESM STATUS messages to manage S&F data quotas and service performance aspects enables addressing several technical challenges related to satellite-based loT networks. First, by incorporating lEs that provide notifications on data storage allowance or trigger status messages when data quotas are reached, the network can better manage limited satellite storage resources, ensuring smoother data flows and preventing dropped or delayed transmissions. This is particularly critical in S&F operations, where intermittent satelliteground connectivity requires efficient storage and transfer management. Secondly, the introduction of lEs for service performance management, such as delivery priority levels and data retention periods, would allow more granular control over data transmission based on the urgency and importance of the information. This would improve the Quality of Service (QoS) in scenarios where different types of data (e.g., critical vs. non-critical) compete for bandwidth and storage, ensuring that high-priority data is transferred first and that data with longer validity periods can be effectively retained and forwarded when satellite connectivity is restored.

[0028] According to a first aspect, the present inventio provides a method for handling asynchronous data exchange in an NTN communication system operating in S&F mode. The method comprises detecting, by a UE, a satellite within communication range; identifying, by the UE, that the satellite can handle asynchronous data exchange; transmitting, by the UE to the satellite, user data in a first protected control message, the latter comprising at least one S&F Information Element (IE); storing, by the satellite, the user data; triggering, by the satellite, at least one indication message or data management policy based on the at least one S&F IE; establishing a feeder link connection between the satellite and a ground station; and forwarding the stored user data to the ground station by the satellite.

[0029] According to a second aspect, the present invention provides NTN communication system for handling asynchronous data exchange in S&F mode. The system comprises at least one UE, at least one satellite, and at least one ground station.

[0030] In the proposed system, the UE is configured to detect the satellite within its communication range, identify that the satellite can handle asynchronous data exchange, and transmit to the satellite user data in a first protected control message comprising at least one S&F IE. The satellite is configured to store the user data therein, trigger at least one indication message or data management policy based on the at least one S&F IE, and forward the stored user data to the ground station when a feeder link is available.

[0031] In some embodiments, the first protected control message is an integrity-protected Non- Access Stratum (NAS) Protocol Data Unit (PDU).

[0032] In some embodiments, additional user data is further transmitted from the UE to the satellite through an EPS Session Management (ESM) data transport mechanism that includes at least one S&F IE.

[0033] According to the invention, the S&F IE can comprise any of a request for data storage allowance; an indication of an expected delivery time for the transmitted user data; and / or an indication of a priority level (e.g. low, medium, high) of the transmitted user data. In some embodiments, the request for data storage allowance triggers a status message indicating that a storage quota has been reached.

[0034] In some embodiments, the satellite further determines whether to store the user data based on an ability to meet the expected delivery time.

[0035] In some embodiments, the priority level is categorized to enable differentiated handling.

[0036] In some embodiments, the forwarding of the user data to the ground station is performed based on the priority level.

[0037] In some embodiments, additional user data is also transmitted from the satellite to the UE using an ESM mechanism that includes at least one S&F IE. In this case, the latter may comprise an indication of whether further data transmissions are allowed; an indication of the expected delivery time for the stored user data; and / or an indication of whether storage quota limitations have been reached.

[0038] In some embodiments, upon receiving any of the above indications, the UE further initiates the release of the data exchange.

[0039] Consequently, the present invention augments existing Control Plane CloT Optimization protocol for enabling efficient data transfer between UE and satellite cells operating in S&F mode by introducing the following elements:

[0040] • New lEs in the ESM DATA TRANSPORT messages to manage S&F data quotas (e.g., notifications regarding data storage allowances or status messages that trigger the release of the data transfer procedure when the quota limit is reached). Alternatively, information for management of S&F data quotas can be introduced in new causes in the ESM STATUS messages.

[0041] • New lEs in the ESM DATA TRANSPORT used to manage service performance aspects (e.g., delivery priority level, retention / validity periods).

[0042] In view of the above, the present invention introduces new lEs to handle S&F data transfer. These lEs can provide the UE with information on whether further data transmission is permitted or if quota limitations have been reached. Alternatively, an IE may be used to indicate the priority level of S&F data (e.g., low, medium, or high), and another IE could allow the network to communicate the expected delivery time for buffered data, possibly upon request, such as the time remaining before the data is delivered to the ground network. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] 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:

[0044] Fig. 1 schematically illustrates a high-level view of a network’s architecture implementing a S&F mechanism.

[0045] Fig. 2 schematically illustrates Mobile-originated (MO) traffic via satellite transmitted in two steps with S&F mechanism in User Data Proxy module.

[0046] Fig. 3 schematically illustrates Mobile-terminated (MT) traffic via satellite transmitted in three steps with S&F mechanism in both ground and satellite.

[0047] Fig. 4 illustrates an Optimized Evolved Packet System (EPS) architecture option for Cellular loT (CloT).

[0048] Fig. 5 is a flow diagram showing MO data transport for the control plane CloT EPS optimization .

[0049] Fig. 6 schematically illustrates a distribution of Control Network (CN) functions between the satellites and the ground for S&F Satellite operation in a multi-satellite deployment scenario, according to some embodiments of the present invention.

[0050] Fig. 7 is a flow diagram illustrating the proposed MO user data transfer method, according to an embodiment.

[0051] Fig. 8 is a flow diagram illustrating another embodiment of the proposed method for handling asynchronous data exchange.

[0052] DETAILED DESCRIPTION OF THE INVENTION AND OF PREFERRED EMBODIMENTS

[0053] The present invention provides a method that enables bidirectional data transmission between user equipment (UE), a satellite constellation, and a ground station connected to the core of a mobile communication network based on 3GPP standards. The invention addresses scenarios where the UE and / or the ground station are not simultaneously visible to at least one satellite of the constellation. The present invention considers the use of Control Plane CloT EPS Optimization, introduced by [3], as the baseline protocol for data transfer between the UE and satellite cells. As illustrated in Fig. 6, the invention can establish a "Control Plane CloT EPS Optimization with S&F extensions". According to this embodiment, the operation in S&F Satellite mode is enabled based on an enhancement of the Control Plane CloT EPS Optimization by distributing the C-SGN functionalities between satellite-based components (C-SGN-SAT) and ground-based core network components (C-SGN-GND). A single instance of C-SGN-GND interacts with multiple C-SGN-SAT instances deployed across the satellite constellation via feeder links, utilizing predefined S&F interfaces. This design enables all C-SGN-SAT instances across the satellite constellation to function as a unified logical entity in conjunction with the C-SGN-GND on the ground.

[0054] After successful registration with a satellite Public Land Mobile Network (PLMN) and establishment of a valid LIE / MME context across the satellite constellation, data transfer can take place between the UE and any satellite of this constellation in reach of the UE. For data transfer, the Control Plane CloT EPS Optimization relies on an exchange of ESM DATA TRANSPORT messages between the UE and the MME, encapsulating user data within the User Data Container IE, as defined in [4], Furthermore, the protocol allows for the exchange of ESM STATUS messages between the UE and MME to report specific error conditions upon the reception of ESM protocol data.

[0055] Fig. 7 and Fig. 8 present different embodiments of the proposed method for handling asynchronous data exchange. In these embodiments, the UE is assumed to be already registered in the satellite network and to have previously acquired Long-Term Ephemeris (TLEs) during past satellite contacts (e.g., from SIB32). It is also assumed that new data from the application layer is ready for transfer and that the UE is capable of estimating the timing of its next contact with an upcoming satellite (SAT#i), which has a valid UE / MME context. Moreover, in these embodiments, the satellites include an onboard base station, and the C- SGN functionalities previously described with reference to Fig. 6, are distributed between satellite components (C-SGN-SAT) and the ground component (C-SGN-GND).

[0056] In the embodiment illustrated in Fig. 7, at step 101 , a UE detects a satellite within communication range and, in step 102, identifies that the satellite supports asynchronous data exchange. Then, at step 103, the UE transmits user data within a protected control message (e.g. a NAS PDU) containing one or more S&F lEs to the satellite. At step 104, the satellite's base station forwards the message to the C-SGN-SAT instance via the S1 interface. In step 105, the user data is stored in the satellite, and more specifically in the C-SGN-SAT component. Subsequently, in steps 106 and 107, it generates and sends an indication message or data management policy to the UE based on the S&F lEs. Finally, in step 109, the satellite transmits the stored user data to a ground station via an established feeder link connection, which is set up in step 108 when the satellite has visibility to a ground station.

[0057] In the embodiment illustrated in Fig. 8, in step 201 , a satellite comes within the communication range of a UE. The UE detects the satellite cell and verifies that S&F Satellite mode is supported. In step 202, the UE either establishes a Radio Resource Control (RRC) connection or sends an RRCEarlyDataRequest message, which includes an integrity- protected NAS PDU. The NAS PDU carries the EPS Bearer ID and encrypted Uplink Data. The UE may also indicate in a NAS Release Assistance Information in the NAS PDU whether no further Uplink or Downlink Data transmissions are expected, or only a single Downlink data transmission (e.g. Acknowledgement or response to uplink data) subsequent to this Uplink Data transmission is expected. The UE may also include in the NAS PDU any needed S&F lEs (e.g. a new IE to ask for data storage allowance). Next, the satellite's base station (e.g. eNB), based on configuration, may retrieve (step 202b) the EPS negotiated QoS profile from the MME, if not previously retrieved. It may also retrieve additional parameters (e.g. UE Radio Capabilities).

[0058] In step 203, the NAS PDU previously sent is relayed to the MME by the base station using a S1-AP Initial UE message. If the RRCEarlyDataRequest message was received, the base station includes the "EDT Session" indication in the S1-AP Initial UE message. Then, in step 204, the C-GCN-SAT instance checks the integrity of the incoming NAS PDU, decrypts the encapsulated data and stores it.

[0059] In step 205, additional user data may be exchanged using the ESM data transport mechanism. Data is stored in the satellite. The ESM data transport messages now may include specific S&F lEs to manage S&F data quotas (e.g. notification on data storage allowance or status messages forcing the release of the data transfer procedure when the quota is reached) or inform about expected S&F delivery time.

[0060] In step 206, to complete the data transfer, RRC connection and S1 release is triggered. Alternatively, RRC Early Data Complete is sent if the data transfer procedure was initiated using an RRCEarlyDataRequest message. Then, the satellite gets connected to the ground network via an available feeder link. The satellite forwards (step 207) the stored user data to the C-SGN-GND. Downloaded user data is forwarded to the destination via proper interfaces (step 208).

[0061] The same embodiment depicted in Fig. 8 for MO traffic is equally applicable to MT traffic, with a few key differences. In the case of MT traffic, the data will initially be received by the C- SGN-GND element, then uploaded to the satellite and stored in the C-SGN-SAT component at the beginning of the process. Once the satellite enters the UE’s communication range (step 201), the C-SGN-GND initiates a paging procedure, prompting the UE to activate the proposed “Control Plane CloT EPS Optimization with S&F extensions” procedure.

[0062] 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.

[0063] The scope of the present invention is defined in the following set of claims.

Claims

CLAIMS1. A method for handling asynchronous data exchange in a non-terrestrial communication system operating in Store and Forward (S&F) mode, the method comprising: detecting, by a user equipment (UE), a satellite within communication range; identifying, by the UE, that the satellite can handle asynchronous data exchange; transmitting, by the UE, user data in a first protected control message, comprising at least one S&F Information Element (IE), to the satellite; storing, by the satellite, the user data; triggering, by the satellite, at least one indication message or data management policy based on the at least one S&F IE; establishing a feeder link connection between the satellite and a ground station; and forwarding, by the satellite, the stored user data to the ground station.

2. The method of claim 1 , wherein the first protected control message is an integrity-protected Non-Access Stratum (NAS) Protocol Data Unit (PDU).

3. The method of claim 1 , further comprising transmitting additional user data through an EPS Session Management (ESM) data transport mechanism, including at least one S&F IE, from the UE to the satellite.

4. The method according to any one of claims 1-3, wherein the S&F IE comprises at least one of: a request for data storage allowance; an indication of an expected delivery time for the transmitted user data; an indication of a priority level of the transmitted user data.

5. The method according to claim 4, wherein the request for data storage allowance triggers a status message indicating that a storage quota has been reached.

6. The method according to claim 4, further comprising determining, by the satellite, whether to store the user data based on an ability to meet the expected delivery time.

7. The method according to claim 4, wherein the priority level is categorized to enable differentiated handling.

8. The method according to claim 4, wherein the forwarding of the user data to the ground station is performed based on the priority level.

9. The method according to any one of the previous claims, further comprising transmitting additional user data through an ESM data transport mechanism, including at least one S&F IE, from the satellite to the UE.

10. The method according to claim 9, wherein the S&F IE comprises at least one of: an indication of whether further data transmissions are allowed; an indication of the expected delivery time for the stored user data; an indication of whether storage quota limitations have been reached.

11. The method according to claim 10, further comprising initiating the release of the data exchange by the UE upon receiving at least one of the indications.

12. A non-terrestrial communication system for handling asynchronous data exchange in Store and Forward (S&F) mode, comprising: at least one ground station; at least one user equipment (UE); at least one satellite; the UE being configured to: detect the at least one satellite within its communication range, identify that the satellite can handle asynchronous data exchange, and transmit to the satellite user data in a first protected control message comprising at least one S&F Information Element (IE); and the satellite being configured to: store the user data on the satellite, trigger at least one indication message or data management policy based on the at least one S&F IE, and forward the stored user data to the ground station using an available feeder link.

13. The system according to claim 12, wherein the first protected control message is an integrity-protected Non-Access Stratum (NAS) Protocol Data Unit (PDU).

14. The system according to claim 13, wherein the UE is further configured to transmit additional user data to the satellite through an EPS Session Management (ESM) data transport mechanism, including at least one S&F IE.

15. The system according to any one of previous claims 12-14, wherein the S&F IE comprises at least one of: a request for data storage allowance; an indication of an expected delivery time for the stored user data; an indication of a priority level of the transmitted user data.

16. The system according to claim 15, wherein the satellite is further configured to transmit a status message indicating to the UE that a storage quota has been reached in response to the request for data storage allowance.

17. The system according to claim 15, wherein the satellite is further configured to determine whether to store the user data based on an ability to meet the expected delivery time.

18. The system according to claim 15, wherein the priority level is categorized to enable differentiated handling.

19. The system according to claim 15, wherein the satellite is further configured to forward the user data to the ground station based on the priority level.

20. The system according to any one of claims 12-19, wherein the satellite is further configured to transmit to the UE a second protected control message comprising at least one S&F IE.

21. The system according to any one of claims 14-20, wherein the satellite is further configured to transmit additional user data to the UE through an ESM data transport mechanism, including at least one S&F IE.

22. The system according to any one of claims 20-21 , wherein the S&F IE comprises at least one of: an indication of whether further data transmissions are allowed; an indication of the expected delivery time for the stored user data; an indication of whether storage quota limitations have been reached.

23. The system according to claim 22, wherein the UE is further configured to initiate the release of the data exchange upon receiving at least one of the indications.

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