System, satellite and method for performing asynchronous communication in a non-terrestrial communication network

Abstract

A system, satellite and method for performing asynchronous communication in a non- terrestrial communication network are proposed. The system comprises at least one user equipment (UE); a constellation of satellites, with at least one satellite, and a ground network. Each satellite of the constellation comprises a base station configured to communicate with the at least one UE and an onboard core network (CN) element (C-SGN-SAT) to perform a first subset of CN functions, including the functions required by the satellite to handle an S1 interface with the base station and the functions to support Non-Access Stratum (NAS) protocol signaling with the at least one UE. The ground network comprises a ground-based CN element (C-SGN-GND) to perform a second subset of CN functions. The first subset of CN functions and the second subset of CN functions form a complete set of CN functions of a CIoT Serving Gateway Node (C-SGN).

Description

[0001] SYSTEM, SATELLITE AND METHOD FOR PERFORMING ASYNCHRONOUS COMMUNICATION IN A NON-TERRESTRIAL COMMUNICATION NETWORK

[0002] TECHNICAL FIELD

[0003] The present invention primarily relates to system architectures that support asynchronous communication in non-terrestrial communication networks. Particularly, it relates to multisatellite store and forward (S&F) operations in a non-terrestrial communication network.

[0004] BACKGROUND OF THE INVENTION

[0005] The 3GPP TS 23.401 [1] introduced an optimized Evolved Packet System (EPS) architecture for Cellular loT (CloT), incorporating a CloT Serving Gateway Node (C-SGN). As shown in Fig. 1 , 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 (i.e., MME, S-GW, and P-GW), which may be more suitable for CloT deployments.

[0006] NB-loT is a rapidly growing CloT technology, gaining popularity due to its ability to provide low-power, wide-area connectivity for massive loT applications. However, to fully harness the potential of new technologies in massive loT, achieving global connectivity is crucial. NonTerrestrial Networks (NTNs) that are based on satellites are essential in delivering the required connectivity. While existing global connectivity solutions are not cost-effective, efforts within the 3GPP have aimed to standardize cellular NTN based on established terrestrial cellular technologies, including NB-loT.

[0007] In this context, NB-loT delay-tolerant loT applications, such as smart agriculture, livestock monitoring, asset tracking, and environmental monitoring, can benefit from the deployment of low-density LEO satellite constellations. These constellations offer small complexity and regenerative payloads. This approach significantly reduces costs and enhances interoperability. However, it presents challenges, as using a low-density satellite constellation introduces service and feeder link discontinuities.

[0008] In NTN systems with limited feeder link capacity and scarce ground station availability, maintaining a continuous connection between the satellite constellation and a ground station may not always be possible. However, asynchronous bidirectional data communication can still be achieved through a Store and Forward (S&F) mechanism. By utilizing regenerative payloads in satellites and supporting S&F operations, these networks can continue functioning even when the satellite is temporarily disconnected from a ground station [2, 3],

[0009] In a 3GPP NTN system which uses an S&F mechanism, the core network is responsible for retaining temporary signaling information. In light of this, in [2], the architecture illustrated in Fig. 2 was developed. Each satellite is equipped with a regenerative payload and provides radio access via an onboard eNB / gNB. The payload contains core components necessary to complete UE interactions within the same visibility window, without requiring the satellite to be connected to the ground. In this architecture an MME entity is deployed on the satellite so that the NAS signaling procedures can be executed between the UE and the MME on the satellite even when there is no feeder-link connectivity to the ground station.

[0010] This architecture also includes proxy elements containing S&F entities for control plane as well as user data plane messaging. 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.

[0011] Moreover, enabling access via multi-satellite constellations is crucial for increasing the capacity of the NTN and reducing delays for end-to-end data transmission. To achieve this, the inventors of present invention previously proposed to extend the regenerative payload design to a multi-satellite scenario. This approach involves placing and distributing the MME entity functionality onboard each satellite of the constellation, as shown in Fig. 3, and implementing a context transfer mechanism between these multiple distributed MME entities. This distribution allows, for example, the sharing of the context between the satellites of the same constellation. As a result, the authentication procedure only needs to be performed with a single satellite and the resulting UE context is then distributed to the MME entities in the other satellites, avoiding the need to repeat the authentication procedure with each of the satellites, reducing the need for frequent re-authentication processes. This reduces signaling load and energy consumption on the UE side, prevents unnecessary latency and helps to avoid potential network overload.

[0012] However, the placement of a full MME entity and additional network functions onboard each satellite payload is not optimal, as only a minimal subset of C-SGN functions and 3GPP interfaces are required. The choice of which interfaces are terminated onboard the satellite versus those that remain on the ground is critical. This decision is essential for enabling signaling procedures during feeder link interruptions, supporting S&F mechanisms, and allowing signaling to initiate on one satellite and conclude on another in multi-satellite constellations, all while avoiding modifications to the ground interfaces connecting to the rest of the network.

[0013] New and improved solutions for performing asynchronous communication in non-terrestrial communication networks are therefore needed.

[0014] References:

[0015] [1] 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.

[0016] [2] 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.

[0017] [3] US2021 / 0297147 “Method and system for non-terrestrial cellular wireless communication networks”.

[0018] DESCRIPTION OF THE INVENTION

[0019] An object of the present invention is thus to provide a new solution for multi-satellite asynchronous communication (e.g. S&F operation) in non-terrestrial communication networks.

[0020] Particularly, the present invention provides novel implementations of architectures that distribute core functionalities between terrestrial and non-terrestrial infrastructures in a 3rd Generation Partnership Project (3GPP) wireless communication network capable of delivering S&F services in multi-satellite constellations.

[0021] The present invention proposes, according to a first aspect, a system for performing asynchronous communication in a non-terrestrial communication network. The system comprises at least one UE, a constellation of satellites with at least one satellite, and a ground network. Each satellite comprises an onboard base station to communicate with the at least one UE and an onboard CN element (C-SGN-SAT) to perform a first subset of CN functions. These first subset of functions includes functions required by the satellite to handle an S1 interface with the base station and functions to support NAS protocol signaling with the UE. The ground network comprises a ground-based CN element (C-SGN-GND) to perform a second subset of CN functions. In the proposed system, the first subset of CN functions and the second subset of CN functions form a complete set of CN functions of a CloT Serving Gateway Node (C-SGN).

[0022] The present invention also proposes, according to a second aspect, a satellite for performing asynchronous communication. The satellite comprises a base station configured to communicate with at least one UE and an onboard CN element (C-SGN-SAT), which is configured to perform a first subset of CN functions, comprising the functions required by the satellite to handle an S1 interface with the base station, and the functions to support NAS protocol signaling with the UE. Moreover, the C-SGN-SAT is also configured to enable asynchronous communication with a ground network comprising a ground-based CN element (C-SGN-GND) configured to perform a second subset of CN functions, wherein the first subset of CN functions and the second subset of CN functions form a complete set of CN functions of a CloT Serving Gateway Node (C-SGN).

[0023] The present invention also proposes, according to a third aspect, a method for performing asynchronous communication in a non-terrestrial communication network, the method comprising: receiving, on a base station onboard a satellite, data from at least one UE; forwarding the data to an onboard CN element (C-SGN-SAT) via a S1 interface, the C-SGN- SAT being configured to perform a first subset of CN functions comprising the functions required by the satellite to handle the S1 interface with the base station and the functions to support NAS protocol signaling with the UE; storing the data in the satellite when a feeder link between the satellite and a ground network is unavailable; and transmitting the data to the ground network via the feeder link when the feeder link becomes available, the ground network comprising a ground-based CN element (C-SGN-GND) configured to perform a second subset of CN functions, the first subset of CN functions and the second subset of CN functions forming a complete set of CN functions of a CloT Serving Gateway Node (C-SGN).

[0024] Therefore, the present invention efficiently splits the C-SGN functions into the C-SGN-SAT and the C-SGN-GND, without introducing additional complexity to the network.

[0025] In some embodiments, wherein the constellation comprises more than one satellite, and all the onboard CN elements (C-SGN-SAT) distributed across the different satellites of the constellation are configured to collectively operate as a single logical entity with the C-SGN- GND on the ground network. In some embodiments, the C-SGN-SAT and the C-SGN-GND are operably connected via a S&F interface.

[0026] In some embodiments, the first subset of CN functions is deployed on a regenerative payload of the satellite.

[0027] In some embodiments, the constellation of satellites comprises LEO satellites.

[0028] In some embodiments, the base station comprises an Evolved Node B or a Next Generation Node B.

[0029] In some embodiments, the C-SGN-GND is operably connected with a HSS on the ground network via a S6a interface. Complementarily or alternatively, in some embodiments, the C- SGN-GND and a P-GW on the ground network are operably connected via a S8 interface.

[0030] In some embodiments, the storing of the data on the satellite is enabled by S&F proxies.

[0031] Therefore, the present invention provides a distribution of C-SGN functions between the satellites and ground for supporting asynchronous communication, such as S&F operations, based on the Optimized EPS architecture option for CloT from 3GPP TS 23.401 , where the functions onboard the satellites regenerative payloads particularly work as a single logic entity with the rest of core network functions on the ground.

[0032] The present invention offers the advantage of using a reduced number of 3GPP interfaces onboard the satellite and preserving existing interfaces on ground, enabling seamless adoption by minimizing implementation complexity.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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:

[0035] Fig. 1 schematically illustrates an optimized EPS architecture option for CloT.

[0036] Fig. 2 shows a regenerative satellite payload comprising an onboard eNB / gNB and MME.

[0037] Fig. 3 schematically illustrates a multi-satellite distributed MME architecture. Fig. 4 schematically illustrates the proposed distribution of the C-SGN functions between the satellite and the ground for asynchronous communication, according to an embodiment.

[0038] Fig. 5 schematically illustrates the proposed distribution of the C-SGN functions between the satellites and the ground for asynchronous communication in a multi-satellite deployment scenario, according to an embodiment.

[0039] Fig. 6 illustrates a logical view of the proposed C-SGN distribution, showing that all the C- SGN-SAT instances collectively operate with the C-SGN-GND as a single entity to other network nodes.

[0040] DETAILED DESCRIPTION OF THE INVENTION AND OF PREFERRED EMBODIMENTS

[0041] The present invention builds on the Optimized EPS architecture option for CloT from 3GPP TS 23.401 , by enabling asynchronous communication (e.g. S&F operations) in 3GPP nonterrestrial communication networks. The present invention proposes to divide the Cellular loT Serving Gateway Node (C-SGN) functions 300 into first subset CN functions, which are deployed / implemented on the onboard core network (CN) element (C-SGN-SAT) 310 of each of the satellites 200, and second subset functions, which are deployed / implemented on the ground-based core network elements (C-SGN-GND) 320, facilitating seamless communication across satellite networks even with intermittent connectivity.

[0042] Particularly, the present invention introduces concrete implementations of subsets of the C- SGN functions 300 onboard the satellite 200. These implementations enable the termination of essential signaling onboard the satellite 200, particularly when continuous connectivity between the satellite 200, the UE 100, and / or the ground network is not possible. This capability allows signaling processes to initiate on one satellite and conclude on another, effectively supporting multi-satellite constellations.

[0043] Additionally, in the proposed approach, there is a single instance of the second subset functions which interacts with all the first subset functions deployed in the satellites 200 through the corresponding feeder links, using S&F interfaces.

[0044] With regard to Fig. 4, therein a first embodiment of the present invention is shown. In this embodiment, the minimum set of functions that are part of the C-SGN-SAT 310, i.e. the first subset of CN functions, are the subset of the MME functions needed to handle the S1 interface with the onboard base station (e.g. eNB or gNB) 250, and the subset needed to support NAS protocol signaling with UEs 100. Particularly, the first subset of CN functions of the C-SGN-SAT 310 is deployed / embarked on the satellite regenerative payload, which interacts with the onboard base station 250 through the S1 interface. The C-SGN-GND 320 refers to the rest of the core network functions deployed on the ground network, which interacts with the rest of the 3GPP core network elements (i.e. S / P-GW402, SCEF 403, HSS 404, etc.) using standardized 3GPP interfaces.

[0045] Additionally, in this embodiment, the S6a and S8 interfaces are particularly placed on ground, avoiding additional complexity to interface the proposed architecture with the 3GPP network.

[0046] With regard to Fig. 5, in this second embodiment, the proposed architecture is further enhanced by introducing S&F satellite operations that support delay-tolerant services in multisatellite loT NTN deployments. Each satellite of the constellation 200#1 ... 200#N includes an instance of the C-SGN-SAT 310#1 ... 310#N with the functions needed to handle the S1 interface and to support NAS protocol signaling with UEs 100.

[0047] Particularly, all the C-SGN-SAT instances 310 distributed across the different satellites 200 of the same constellation work as a single logical entity with the C-SGN-GND 320 on the ground network, as shown in Fig. 6.

[0048] 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.

[0049] Those skilled in the art will recognize that the present teachings are amenable to a variety of modifications and / or enhancements. For example, although the implementation of various components described herein may be embodied in a hardware device, it may also be implemented as a software only solution — e.g., an installation on an existing server.

[0050] The present disclosure and / or some other examples have been described in the above. According to descriptions above, various alterations may be achieved. The topic of the present disclosure may be achieved in various forms and embodiments, and the present disclosure may be further used in a variety of practical implementations..

[0051] The scope of the present invention is defined in the following set of claims.

Claims

CLAIMS1. A system for performing asynchronous communication in a non-terrestrial communication network, comprising: at least one user equipment (UE); a constellation of satellites, with at least one satellite, each satellite comprising: a base station configured to communicate with the at least one UE; an onboard core network (CN) element (C-SGN-SAT) configured to perform a first subset of CN functions, the first subset of CN functions comprising: functions required by the satellite to handle an S1 interface with the base station; and functions to support Non-Access Stratum (NAS) protocol signaling with the at least one UE; and a ground network comprising a ground-based CN element (C-SGN-GND) configured to perform a second subset of CN functions, the first subset of CN functions and the second subset of CN functions forming a complete set of CN functions of a CloT Serving Gateway Node (C-SGN).

2. The system of claim 1 , wherein all the onboard CN elements (C-SGN-SAT) distributed across the different satellites within the constellation are configured to collectively operate as a single logical entity with the ground-based CN element (C-SGN-GND) on the ground network.

3. The system of claim 1 , wherein the onboard CN element (C-SGN-SAT) and the ground- based CN element (C-SGN-GND) are operably connected via a Store and Forward (S&F) interface.

4. The system of claim 1 , wherein the first subset of CN functions is deployed on a regenerative payload of the satellite.

5. The system of claim 1 , wherein the constellation of satellites comprises low earth orbit (LEO) satellites.

6. The system of claim 1 , wherein the base station comprises an Evolved Node B (eNB) or a Next Generation Node B (gNB).

7. The system of claim 1 , wherein the ground-based CN element (C-SGN-GND) and a Home Subscriber Server (HSS) are operably connected via a S6a interface.

8. The system of claim 1 , wherein the ground-based CN element (C-SGN-GND) and a Packet Data Network Gateway (P-GW) are operably connected via a S8 interface.

9. A satellite configured to perform asynchronous communication, comprising: a base station configured to communicate with at least one user equipment (UE); an onboard core network (CN) element (C-SGN-SAT) configured to: perform a first subset of CN functions, the first subset of CN functions comprising functions required by the satellite to handle an S1 interface with the base station and functions to support Non-Access Stratum (NAS) protocol signaling with the at least one UE; and enable asynchronous communication with a ground network comprising a ground-based CN element (C-SGN-GND) configured to perform a second subset of CN functions, the first subset of CN functions and the second subset of CN functions forming a complete set of CN functions of a CloT Serving Gateway Node (C-SGN).

10. The satellite of claim 9, wherein the onboard CN element (C-SGN-SAT) is configured to enable asynchronous communication with the ground-based CN element (C-SGN-GND) via a Store and Forward (S&F) interface.

11. The satellite of claim 9, wherein the satellite is a low earth orbit (LEO) satellite.

12. The satellite of claim 9, wherein the first subset of CN functions is deployed on a regenerative payload of the satellite.

13. A method for performing asynchronous communication in a non-terrestrial communication network, the method comprising: receiving, on a base station onboard a satellite, data from at least one user equipment (UE); forwarding the data to an onboard core network (CN) element (C-SGN-SAT) via a S1 interface, the onboard CN element (C-SGN-SAT) being configured to perform a first subset of CN functions comprising: functions required by the satellite to handle the S1 interface with the onboard base station; and functions to support Non-Access Stratum (NAS) protocol signaling with the at least one UE; storing the data in the satellite when a feeder link between the satellite and a ground network is unavailable; andtransmitting the data to the ground network via the feeder link when the feeder link becomes available, the ground network comprising a ground-based CN element (C-SGN- GND) configured to perform a second subset of CN functions, the first subset of CN functions and the second subset of CN functions forming a complete set of CN functions of a CloT Serving Gateway Node (C-SGN).

14. The method of claim 13, wherein communication between the onboard CN element (C- SGN-SAT) and the ground-based CN element (C-SGN-GND) occurs via a Store and Forward (S&F) interface.

15. The method of claim 13, wherein the storing of the data on the satellite is enabled by S&F proxies.

16. The method of claim 13, further comprising the step of communicating the ground-based CN element (C-SGN-GND) and a Home Subscriber Server (HSS) via a S6a interface.

17. The method of claim 13, further comprising the step of communicating the ground-based CN element (C-SGN-GND) with a Packet Data Network Gateway (P-GW) via a S8 interface.

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