Enhanced Non-Terrestrial Cellular Network

Abstract

Enhanced Non-Terrestrial Cellular Network This non-terrestrial cellular network (1), whose satellite component (10) consists of a constellation of satellites (21, 22, 23, 24) forming a satellite network (20), with at least one satellite (21) carrying a regenerative payload, is characterized in that it comprises first and second logical base stations, each logical base station being defined by a protocol stack combining lower and upper layers, the first logical base station (2) being entirely located within the payload of the satellite (21) and the second logical base station (4) being distributed so that its lower layers are located within the payload of the satellite (21) and its upper layers (G-CU) are located at a distance from the payload of the satellite (21), the lower layers (RU, DU) of the first and second logical base stations being common and shared. Figure for the abstract: Figure 2

Description

Title of the invention: Improved non-terrestrial cellular network

[0001] The invention relates to the field of non-terrestrial cellular networks - NTN ("Non-Terrestrial Networks") using cellular technology, as standardized by the 3GPP ("3rd Generation Partnership Project") standardization body, such as, for example, fourth generation - 4G, fifth generation - 5G or sixth generation - 6G cellular technology,

[0002] A non-terrestrial cellular network integrates a satellite component alone or in combination with a terrestrial component.

[0003] 3GPP produces standards defining requirements, architectures and operating procedures, such as protocols, for mobile communication.

[0004] Although the first normative elements relating to non-terrestrial cellular networks were defined in version 17 of the 3GPP standard (“Release 17”, completed in June 2022), normative work continues.

[0005] Thus, for example, the satellite component of a 5G network is studied more specifically in e.g. the technical specifications TS 23.501, TS 23.502, TS 38.401 and TS 38.300 as well as in the technical reports TR 23.700-28, TR 23.700-29, TR 23.737, TR 38.821 for the satellite component and TR 38.823, TR 38.816, TR 38.801 for the terrestrial component.

[0006] The latest findings of these studies, or recommendations, will be incorporated into version 19 of the 5G standard, which is expected to be published in June 2026.

[0007] These recommendations specify in particular a new satellite payload architecture called regenerative, in which the payload of a satellite of the satellite component is active in the processing of data packets, which makes it possible to offer new services, in particular terminal to terminal (i.e. "direct-to-device") without going through the ground component.

[0008] According to a first option proposed in these recommendations (in particular in technical report TR 23.700-29), the satellite payload comprises an entire base station, which is called a gNB (“next-Generation Node-B”) in the 5G standard. Thus, the satellite carries all the constituent layers of a gNB base station.

[0009] Such an architecture makes it possible, in particular, to provide space-based services such as terminal-to-terminal communication, through a constellation of satellites forming a mesh satellite network, without having to return via the ground. Thus, the output of the satellite's payload is connected, via an IP link, to the other satellites in the satellite network. Such space-based services are characterized by lower latency and very high communication security.

[0010] According to a second option proposed in these recommendations (in particular in technical specification TS 38.401 and technical report TR 38.823), the base station is divided into two parts, on either side of a standardized link "Fl": the lower layers of the gNB are carried on board the satellite, while the upper layers of the gNB are relocated to a ground installation.

[0011] The transport layer of the Fl link integrating a bidirectional "feederlink" communication link between the satellite component and the terrestrial component.

[0012] Given that the payload of a satellite remains constrained in terms of computing capacity, the first option is not suitable for the case where there is a large number of user devices seeking to access internet services, such as video streaming servers.

[0013] The second option has the advantage of reducing the computing requirements on board the satellite by offloading as much of it as possible to the ground. However, this second option introduces additional latency. Furthermore, it offers lower security, whereas some users require a high level of security, which is what the first option provides.

[0014] The aim of the invention is then to propose an architecture for the payload of a telecommunications satellite which meets the need to provide a user device with both a connectivity service for access to a satellite network and a connectivity service for access to a terrestrial network.

[0015] To this end, the invention relates to a non-terrestrial cellular network, the non-terrestrial cellular network comprising a satellite component, the satellite component comprising a constellation of satellites forming a satellite network, at least one satellite of the satellite constellation, referred to as the first satellite, carrying a regenerative payload, characterized in that the non-terrestrial cellular network comprises the first and second logical base stations, each logical base station being defined by a protocol stack associating lower and upper layers,The first logical base station is entirely located within the payload of the first satellite, and the second logical base station is distributed so that the lower layers of the second logical base station are located within the payload of the first satellite and the upper layers of the second logical base station are located at a distance from the payload of the first satellite, the lower layers of the first and second logical base stations being common and shared.

[0016] According to other advantageous aspects of the invention, the network comprises one or more of the following features, taken individually or in all technically possible combinations:

[0017] - the upper and lower layers of the second logical base station are linked by a standardized "Fl" link, the lower layers include a shared radio unit and a shared distributed unit, the upper layers of the first logical base station include a first centralized unit and the upper layers of the second logical base station include a second centralized unit;

[0018] - the satellite constellation includes a first onboard network core, the upper layers of the first logical base station being connected to the first embedded network core;

[0019] - the upper layers of the second logical base station are located in the payload of a second satellite in the satellite constellation, different from the first satellite;

[0020] - a two-way communication link, or IP link, is established between a IP interface of the first satellite's payload and an IP interface of the second satellite's payload, with flows between the lower and upper layers of the second logical base station circulating along the IP link;

[0021] - the satellite component includes a second embedded network core, the upper layers of the second logical base station being connected to the second embedded network core;

[0022] - the non-terrestrial cellular network further comprising a terrestrial component, the terrestrial component comprising a ground installation, the upper layers of the second logical base station being located in the ground installation, the terrestrial component comprising a second ground network core, the upper layers of the second logical base station being connected to the second ground network core;

[0023] - the non-terrestrial cellular network comprising a communication link bidirectional, or feed link, between a satellite feed interface of the satellite component and a terrestrial feed interface of the terrestrial component, flows between the lower and upper layers of the second logical base station circulating along the feed link (FeederLink);

[0024] - the payload of the first satellite comprises: a first onboard network core to which are connected the upper layers of the first logical base station; an IP interface and a satellite power interface; a service separation module, connected to the output of the shared lower layers, to route traffic between, on the one hand, a user device connected to one of the logical base stations, and, on the other hand, either the upper layers of the first logical base station or the upper layers of the second logical base station; an embedded "Fl" routing module, to route traffic between the satellite power interface, an IP routing module, and the service separation module; and the IP routing module, to route the flows between the first embedded network core, the embedded "Fl" routing module, and the IP interface;

[0025] - the ground installation includes a ground routing module "Fl" for routing flows between a terrestrial power interface, on the one hand, and the upper layers of the second logical base station;

[0026] - a user device is adapted to issue a connection request initial, and the second logical base station is adapted to handle by default said initial connection request to attach said user equipment to the second logical base station and to a second associated core network, and wherein a user equipment, attached to the second logical base station, is adapted to issue a connection request to the satellite network by incorporating in said request a specific value of a predefined field, and the second core network is adapted to recognize said value and trigger roaming of the user equipment from the second logical base station and the second core network, to the first logical base station and a first associated core network;

[0027] - the predefined field is a quality of service flow identifier field;

[0028] - the specific value of the predefined field is indicative of the parameters of a satellite service requested by the user equipment, the first logical base station and the first associated core network being adapted to allow roaming of the user equipment taking into account the parameters indicated;

[0029] - the payload of the first satellite includes a layer control module common and shared lower levels.

[0030] The invention also relates to a communication satellite, characterized in that it is adapted to be integrated, as a first satellite, into a non-terrestrial cellular network conforming to the previous network.

[0031] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0032] [Fig. 1] [Fig. 1] is a representation of the protocol stacking of a 5G gNB base station as defined by 3GPP for a terrestrial network; and,

[0033] [Fig.2] [Fig.2] is a schematic representation of a preferred embodiment of the architecture of a cellular network according to the invention. Generalities

[0034] In general, the non-terrestrial cellular network according to the invention adopts a hybrid architecture, in the sense that it comprises two logical base stations, the lower layers of which are implemented by the regenerative payload of a first satellite of the satellite component communication satellite constellation of the cellular network: - the first logical base station is fully embedded in the satellite component of the non-terrestrial cellular network; - the second logical base station is distributed on either side of a standardized link: its lower layers are carried on board the first satellite, while its upper layers are located away from the payload of the first satellite.

[0035] Furthermore, in the cellular network according to the invention, the lower layers of the two logical base stations are common and shared. Thus, the two logical base stations share the same physical interface on the service link side, this physical interface being onboard the first satellite.

[0036] Put another way, instead of implementing two sets of lower layers on board the first satellite, the cellular network according to the invention plans to share one set of lower layers between two sets of upper layers.

[0037] This hybrid architecture is hidden from user equipment in connection with the physical interface on board the first satellite. The user equipment sees only a single cell, served by the lower layers shared between the two logical base stations, although their upper layers are distinct.

[0038] Advantageously, the division between lower and upper layers of the second logical base station follows the division proposed in the 5G standard, through the Fl link concept.

[0039] In the preferred embodiment, which is the subject of the detailed description that follows: - The first logical base station, or spatial gNB, or S-gNB ("Spatial gNB"), is entirely located within the payload of the first satellite in the constellation. This first logical base station allows, in particular, user equipment to access a satellite network. The payload of the first satellite thus includes the lower layers shared between the two logical base stations and the upper layers of the first logical base station. The second logical base station, or ground gNB, or G-gNB ("Ground gNB"), is distributed between the payload of the first satellite in the satellite component and a ground station in the terrestrial component of the cellular network. The ground installation thus includes the upper layers of the second logical base station. The G-gNB allows user equipment to access a terrestrial network.

[0040] In this preferred embodiment, the hybrid architecture allows access to a terrestrial network, limiting the computing load required to do so on board the first satellite and thus meeting the constraint imposed by the limited capabilities of the satellite payload. This hybrid architecture allows for continued access to the satellite network, for example for terminal-to-terminal communications for certain user equipment. Fl connection positioning options

[0041] Fig. 1 represents, according to the 5G standard initially defined for terrestrial networks, the different possible options for positioning a Fl link in the stack of protocol layers.

[0042] From bottom to top, this stacking comprises, for example:

[0043] - an RF layer;

[0044] - a low physical layer, "Low-PHY";

[0045] - a high physical layer, "High-PHY" or "Hi-PHY";

[0046] - a medium access control layer - MAC ("Medium Access Control") bass, “Low-MAC”;

[0047] - a high MAC layer, “High-MAC” or “Hi-MAC”;

[0048] - a low-level radio link control layer - RLC ("Radio Link Control"), "Low- RLC »;

[0049] - a high RLC layer, “High-RLC” or “Hi-RLC”;

[0050] - a data packet convergence protocol layer - PDCP (Packet Data Convergence Protocol") of the user plane, PDCP-U, associated with an SDAP layer and a UPF entity ("User Plane Function");

[0051] - a PDCP layer of the control plane, PDCP-C, associated with an RRC layer and with an AMF entity (“Access & Mobility Management Function”);

[0052] The UPF and AMF entities are located in a core network - CN ("Core Network") and all other layers are located in a gNB and define a gNB.

[0053] The set formed by the RF and Low-PHY physical layers corresponds to a radio unit - RU (“Radio Unit”). They allow the establishment of a service link Uu with a user equipment - UE (“User Equipment”).

[0054] The Fl link then delimits, in the stacking of protocol layers of the gNB, outside of the physical layers, on the one hand, lower layers, located below the Fl link and together forming a distributed unit - DU ("Distributed Unit"), and, on the other hand, upper layers, located above the Fl link and together forming a centralized unit - CU ("Centralized Unit"). The Fl link constitutes the interface between a DU and a CU.

[0055] Alternatively, several CUs can share the same DU, or several DUs can share the same CU.

[0056] The data actually transported along the Fl link depends on the protocol layers between which this link is placed, that is to say, the option chosen for the positioning of the FL link

[0057] The Fl link supports both the user plane, which uses GTP, UDP and / or IP protocols, and the control plane, which uses SCTP and / or IP protocols.

[0058] According to the invention, the Fl link positioning option corresponds to option 5, option 4, option 3 or option 2.

[0059] Since the physical layers are shared between the two logical base stations, there is only one cell, and data packet scheduling must be performed at the high MAC layer, "Hi-MAC". Therefore, the selected option must be option 5 or higher from among options 1 to 8.

[0060] Placing the Fl link according to option 1 for a non-terrestrial network would cause the satellite payload to systematically process the majority of each data packet. The hybrid architecture would then provide only a marginal gain in reducing the computing load on board the satellite.

[0061] Among the options 5 to 2, some are more advantageous than others depending on the embodiment envisaged. Thus, in particular for the preferred embodiment, when taking into consideration the limiting characteristics of the satellite payload for the non-terrestrial network as well as the limitations of the on-board-to-ground communication link ("Feederlink") between the satellite payload and the ground installation.

[0062] For example, by selecting option 5, the data packets that are transmitted from the edge to the ground retain a long header, which increases the throughput on the edge-to-ground communication link and risks saturating it.

[0063] Preferably, the Fl link is thus positioned in option 3, between the low RLC layers, “Low-RLC”, and high RLC layers, “Hi-RLC”, or in option 2, between the high RLC layer, “Hi-RLC”, and the PDCP layers.

[0064] In the remainder of this description, option 3 is presented more particularly, but for example another option such as option 5 could also be used.

[0065] In the hybrid architecture of the non-terrestrial cellular network according to the invention, the RU unit and the DU unit are shared between the two centralized units, respectively the CU of the S-gNB, or S-CU, located on board the satellite, and the CU of the G-gNB, or G-CU, located on the ground.

[0066] It should be emphasized that the two centralized units do not operate in redundancy with respect to each other (there would then be only one logical base station), but rather in parallel with each other. Therefore, there are indeed two logical base stations.

[0067] Methods for supporting a regenerative payload with an onboard gNB or the cutting of a gNB between the edge and the ground are outside the scope of the present invention. These methods correspond to the prior art, as defined by the 5G standard for a terrestrial network.

[0068] On the other hand, the invention requires the implementation of various additional functionalities to provide unified connectivity to terrestrial and non-terrestrial / satellite networks:

[0069] - a routing of exchanges between the satellite component and the terrestrial component of the communication network;

[0070] - an access procedure for a given user device depending on whether it wants a access to the terrestrial or satellite network;

[0071] - a control of shared radio resources to coordinate the two stations of base.

[0072] The satellite payload and the ground installation must therefore include specific means to implement these processes. Non-terrestrial cellular network

[0073] In more detail, as illustrated in [Fig.2], network 1 is a non-terrestrial cellular network according to the invention.

[0074] It allows user equipment to access, via an air interface, remote services, such as communication with other user equipment or data servers.

[0075] In [Fig.2], a first user equipment 11, a second user equipment 12 and a third user equipment 13, as well as a server 14, have been shown.

[0076] Network 1 comprises a satellite component 10 and a ground component 40. Satellite component

[0077] Two embodiments of the satellite component are conceivable: according to the first embodiment, it comprises a constellation of satellites; according to the second embodiment, it comprises a plurality of flying platforms, such as high-altitude platforms (HAPS) or medium-altitude platforms (such as aerial drones). Hybridizations between these two embodiments are also conceivable.

[0078] The first variant will be presented in more detail in what follows.

[0079] The satellite component 10 comprises a constellation of satellites.

[0080] The satellite constellation includes non-geosynchronous satellites - NGSO (“Non-GeoSynchronous Orbit”), i.e., satellites in very low Earth Orbit - vLEO for “very Low Earth Orbit” and / or in low Earth Orbit - LEO for “Low Earth Orbit” and / or in intermediate Earth Orbit - MEO for “Medium Earth Orbit”; and / or geosynchronous satellites - GSO (“GeoSynchronous Orbit”), in particular geostationary - GEO for “Geosynchronous Earth Orbit” / “Geosynchronous Equatorial Orbit” / “Geostationary Earth Orbit”.

[0081] The constellation comprises at least one satellite according to the invention. For example, as illustrated in [Fig.2], the constellation comprises a first satellite 21, a second satellite 22, a third satellite 23, and a fourth satellite 24.

[0082] The satellites in the satellite constellation are connected to each other to form a satellite network 20 of the mesh type. Each satellite constitutes a node in this satellite network 20. The satellites in each pair of satellites in the constellation are linked by an inter-satellite data link, constituting an ISL (Inter Satellite Link). Preferably, communications on the satellite network 20, i.e., along the ISL data links, are carried out using an IP protocol.

[0083] Each satellite therefore includes an interface for accessing the satellite network. For example, the first satellite 21 includes an interface 280 for accessing the satellite network 20.

[0084] In what follows, the structure of satellite 21 will be presented in more detail as an example of a satellite according to the invention. If the network 1 comprises at least one satellite conforming to satellite 21, advantageously several or even all of the satellites in the constellation are similar to satellite 21.

[0085] Satellite 21 is a communications satellite. It carries a payload integrating the hardware and software necessary for the implementation of the various communication functionalities of satellite 21.

[0086] The satellite 21 includes antenna means 310 for defining a plurality of ground coverage areas, or cells. For example, the satellite 21 includes antenna means 310 for defining a first cell 31 and a second cell 32.

[0087] A ground user equipment, such as the first equipment 11 located in the first cell 31 and the second equipment 12 located in the second cell 32, can each establish a service link Uu with the satellite 21.

[0088] According to the breakdown of [Fig.1], the payload of satellite 21 comprises:

[0089] - a radio unit - RU, 220, shared between the S-gNB 2 and the G-gNB 4;

[0090] - a distributed unit - DU, 230, shared between the S-gNB 2 and the G-gNB 4; and,

[0091] - a centralized unit - CU, 240, or S-CU, onboard the satellite and dedicated at S-gNB 2.

[0092] Alternatively, the S-CU could be carried on board a satellite neighbouring 22, 23 or 24 of the satellite 21 carrying the shared DU.

[0093] The payload of satellite 21 comprises, in the particular embodiment shown in [Fig.2], a satellite core network - CN (“Core Network”), or S-CN, 250.

[0094] Alternatively, the core of the satellite network is on board another satellite of the constellation or distributed among several satellites of the constellation.

[0095] The payload of the satellite 21 further includes an interface 270 for accessing the on-board-to-ground communication link (“Feederlink”).

[0096] The payload of satellite 21 also includes:

[0097] - a service differentiation module, 260;

[0098] - a Fl, 265 routing module; and,

[0099] - an IP 210 routing module.

[0100] The payload of satellite 21 ultimately includes a controller, 290.

[0101] The various components of the satellite payload 21 are connected in the following manner, in the case of the Fl link positioning in option 3.

[0102] The shared RU unit, 220, comprises an RF layer, connected to the radio communication means 310, and a low-PHY physical layer, connected to the shared DU 230.

[0103] The shared DU unit 230 comprises a high physical layer, "Hi-PHY", a low MAC layer, "Low-MAC", a high MAC layer, "Hi-MAC" and generally as many low RLC layers, "Low-RLC" (or instantiation of the low RLC layer) as there is user equipment connected by a Uu service link to satellite 21.

[0104] The high physical layer, "Hi-PHY", is connected to the low physical layer, "Low-PHY", of the shared RU unit, 220, while each low RLC layer, "Low-RLC", is connected to the service differentiation module 260.

[0105] The service differentiation module 260 is connected, on one side, to the various low-RLC layers, "Low-RLC" of the shared DU unit, 230, and, on the other side, on one side to the S-CU 240 (for communications with the satellite network), and, on the other side, to the routing module Fl, 265 (for communications with the terrestrial network).

[0106] The S-CU integrates as many high RLC layers, "Hi-RLC", as low RLC layers, "Low-RLC", as well as a first stack of the user plane, consisting of a PDCP-U layer and an SD AP layer, and a second stack of the control plane, consisting of a PDCP-C layer and an RRC layer.

[0107] The S-CU is connected by its high RLC layers, “Hi-RLC”, to the service differentiation module 260.

[0108] The S-CU is connected to the S-CN, by its RRC layer and an N2 link to the AMF entity of the S-CN and by its SDAP layer and an N3 link to the UPF entity of the S-CN.

[0109] The S-CN is a lightweight 5G core network, in the sense that it only incorporates the essential functionalities of a 5G core network given the limited payload capabilities.

[0110] It includes in particular AMF (and / or SMS) and UPF entities, which are respectively connected to the on-board CU unit.

[0111] The S-CN 250 is connected to the IP routing module 210.

[0112] The Fl 265 routing module is connected to the 260 differentiation module, at the communication interface 270 and the IP routing module 210.

[0113] The IP routing module 210 is connected to the S-CN 250, the ISL interface 280 and the Fl 265 routing module.

[0114] The control module 290 drives the shared DU or each DU 230 of the satellite payload. Earth component

[0115] The terrestrial component 40 comprises:

[0116] - a ground installation, 42, connected to the satellite component 10 by one or several "Feederlink" on-board-to-ground communication links;

[0117] - the core network - terrestrial CN, or G-CN, 45; and,

[0118] - a terrestrial network 46, like the internet.

[0119] The ground installation 40 comprises:

[0120] - a 420 interface for accessing the or each ship-to-ground communication link, for bidirectional communication with either of the satellites in the constellation presenting a conjugate 270 interface (for example satellite 21 and satellite 24 as shown in [Fig.2]);

[0121] - one or more centralized units - ground-based CU, or G-CU, each G-CU being associated with a payload from a single satellite in the constellation, i.e., a single shared DU. For example, installation 40 includes a first G-CU 440 associated with the DU of the first satellite 21 and a second G-CU 442 associated with the DU of the fourth satellite 24; and,

[0122] - a routing module "Fl", 470, between, on the one hand, interface 420 and, on the other hand, each G-CU, 440, 442.

[0123] The G-CU 440 unit includes as many high RLC layers, "Hi-RLC", as low RLC layers, "Low-RLC", associated with user equipment accessing the terrestrial network via satellite 21, as well as a first stack of the user plane, consisting of a PDCP-U layer and an SD AP layer, and a second stack of the control plane, consisting of a PDCP-C layer and an RRC layer.

[0124] The G-CU is connected to the G-CN, 45, by its RRC layer and an N2 link to the AMF entity of the G-CN and by its SDAP layer and an N3 link to the UPF entity of the G-CN.

[0125] Alternatively, the solution may comprise several G-CUs connected to the same shared DU, with different characteristic latencies (e.g., Feederlink connection, ISL connection plus Feederlink connection, etc.). Alternatively or in combination, the The solution may include several G-CNs (for example, if several operators are involved).

[0126] The G-CN on the ground 45 includes all the services of a 5G core network.

[0127] It is connected to the terrestrial network 46.

[0128] The latter allows access to various services, notably those provided by servers, such as server 14 connected to the terrestrial network 46.

[0129] It can be seen that there is indeed a first complete base station on board the satellite, for communications on the satellite network, via the onboard CN. This S-gNB 2 consists of the shared RU, the shared DU and the onboard CU.

[0130] It is noted that there is also a second base station, partly located on board the satellite and partly on the ground. On board the satellite, G-gNB 4 consists of the shared RU and the shared DU. On the ground, G-gNB 4 consists of the ground CU. Routing

[0131] Within the payload of satellite 21, the following routing means are provided.

[0132] The service differentiation module 260 has the function of routing the flows:

[0133] - in the upward direction (from a user device), from the shared DU, towards the good processing unit, that is to say either the G-CU (via the ground-to-shore communication link), or the S-CU; and,

[0134] - in the downward direction (towards a user device), towards the correct RLC layer (or instantiation of the RLC layer) of the shared DU.

[0135] To direct the flows, module 260 advantageously uses identifiers already present in the standard, such as the RNTI (“Radio Network Temporary Identifier”), for the user number, the DRB_ID (“Data Radio Bearer Identifier”), for the support number, and the TEID (“Tunnel End Point Identifier”), for the tunnel number.

[0136] If a data packet is to be exchanged between the shared DU and the S-CU 240, the 260 module simply transmits it without modifying its format. However, if a data packet is to be exchanged between the shared DU and the G-CU 440, the 260 module transmits it, modifying its format according to the protocol chosen for the Fl link, preferably the IP format. The 260 module encapsulates an upstream stream and decapsulates a downstream stream. The 260 module can also perform a stream filtering function.

[0137] The Fl 265 routing module is designed to route the flows:

[0138] - between the access interface 270 and the service differentiation module 260, for the exchanges between associated G-CU and DU, to serve a user equipment connected to satellite 21;

[0139] - between the access interface 270 and the IP routing module 210, when using of the satellite 21's on-ground communication link to route flows between the ground and another satellite in the constellation, for example to serve user equipment connected to that other satellite via the satellite network; and,

[0140] - between module 260 and IP routing module 210, when using the link of edge-to-ground communication from another satellite to carry flows between the ground and satellite 21, for example when the edge-to-ground communication link of satellite 21 is too busy.

[0141] The user flows to be routed to the terrestrial network correspond to a significant throughput along the edge-to-ground communication link, because of the nature of the services accessed by the users and the large number of these users.

[0142] In addition, other streams can also use this same communication link, such as those from other satellites in the constellation.

[0143] However, the capacity of an edge-to-ground communication link is necessarily limited to a limit capacity.

[0144] To meet this constraint, the Fl routing module advantageously implements a buffer mechanism to temporarily hold the flows when the limit capacity of the communication link is reached, and to release them as soon as there is, again, sufficient capacity on this link.

[0145] Some flows are sensitive to delay. This is particularly true for control flows between the shared DU and the associated G-CU. Excessive latency can lead to disconnection of the user equipment or a decrease in service quality. Therefore, prioritization of flows is necessary. The Fl routing module advantageously implements a flow scheduling mechanism based on a priority level.

[0146] In the embodiment shown in [Fig. 2], it is not necessary to implement a buffer mechanism and / or a scheduling mechanism between the shared DU and the S-GU, since these two units are instantiated in the same payload. However, such mechanisms must be implemented in an alternative embodiment where the S-CU is onboard another satellite in the constellation, and an Fl interface must then be introduced, supported by a transport channel integrating an inter-satellite data link between the DU of one satellite and the S-CU of another satellite.

[0147] The IP routing module 210 is designed to route flows, preferably in IP format:

[0148] - between interface 280 for accessing an ISL link and S-CN 250, in order to another satellite can access the functionalities of the satellite network core hosted by the satellite;

[0149] - between interface 280 and the Fl 265 routing module, for use of the link ground-to-surface communication of satellite 21 via another satellite in the constellation to serve, for example, user equipment connected to that other satellite via the satellite network; and,

[0150] - between the Fl 265 routing module and the S-CN 250, in order to use the link of ground-based communication from the first satellite to allow G-CN 45 to access functionalities of S-CN 250 and vice versa, for example to allow terminal roaming.

[0151] It should be noted that flow routing is performed using three different components, namely modules 260, 265, and 210. This allows for flow segregation and thus increases network operational security. Alternatively, Fl and IP routing functionalities can be integrated directly into interfaces 270 and 280, respectively.

[0152] Within ground installation 42, the following routing means are provided.

[0153] The Fl 470 routing module allows routing flows between the 420 access interface to an edge-to-ground communication link and either of the G-CUs.

[0154] The flows can thus be routed along several routes:

[0155] - a first route between two user devices of different cells served by the antenna means of the first satellite's payload 21. For example, between user equipment 11 and 12, this first route follows the service link Uu between equipment 11 and antenna means 310, then the shared RU, the shared DU, module 260, the S-CU, and the S-CN. Once the latter has identified in which cell equipment 12 is located, the S-CN, via the S-CU, module 260, the shared DU, the shared RU, and the service link Uu between antenna means 310 and user equipment 12.

[0156] - a second route between a user device of a cell of the first satellite and the satellite network, specifically another satellite in the constellation, to access user equipment located in a cell served by that other satellite. For example, between user equipment 11 and 13, this second route follows the service link Uu between equipment 11 and the antenna means 310, then the shared RU, the shared DU, module 260, the S-CU, and the S-CN. Once the latter has identified which cell equipment 13 is located in, the S-CN, via the IP routing module 210, uses the satellite network access interface 280 to route the signal across this satellite network to reach the fourth satellite 24, to which equipment 13 is connected by a service link Uu.

[0157] - a third route between a user device of a cell of the first satellite 21 and the terrestrial network, to access, for example, an internet service offered by a server. For example, between user equipment 11 and server 14, this third route follows the service link Uu between equipment 11 and the antenna means 310, then the shared RU, the shared DU, the module 260 (which encapsulates the data packets according to the transport protocol chosen for the Fl link), the Fl routing module, the 270 edge-to-ground link access interface, the 420 edge-to-ground link access interface, the Fl 470 router, the data decapsulation module (which routes the flows to the associated G-CU), the G-CU, the G-CN, and then through the terrestrial network 46, to the server 14.

[0158] - a fourth route between the satellite network and the terrestrial network, to carry flows between a user equipment in a cell served by another satellite and the terrestrial network, in order to access, for example, an internet service offered by a ground server, using the edge-to-ground communication link of the first satellite 21. For example, between user equipment 13 and server 14, this fourth route follows the service link Uu between equipment 13 and the fourth satellite 24, then the inter-satellite data link between satellites 24 and 21, the ISL interface, the IP routing module, the Fl routing module, the edge-to-ground communication link, then the Fl 470 router, the G-CU associated with the DU of the fourth satellite serving terminal 13, the G-CN 45, then, through the terrestrial network 46, to server 14. Connection procedure

[0159] For connection, a user device, such as device 11, initiates the following connection procedure.

[0160] The user equipment uses standardized procedures to connect to the shared RU. It detects the SSB, the MIB, and then makes a random access attempt - RA ("Random Access").

[0161] The user equipment sends a connection request.

[0162] According to the invention, connection request messages issued by a user device are processed, by default, by the G-gNB, because the 5G core network associated with this base station is the G-CN which has the complete and extended functionalities of a 5G core network, in particular relating to the identification of user profiles.

[0163] Once the connection phase is completed, the user equipment can instantiate tunnels with the G-CN UPF entity and transmit data.

[0164] If the user equipment wishes, at a later stage, to access the satellite network for a particular service, a new procedure is defined.

[0165] According to a first embodiment of this procedure, the user equipment first issues a request of the type "PDU Session Modification REQUEST 5QI", as defined in document 3GPP TS 29 502 - V19.0.0 - 5G.

[0166] This request includes a QFI field (“QoS Flow Identifier”).

[0167] According to the invention, the set of possible QFI values ​​is extended by defining at least one additional value, or spatial QFI, indicative of a request for access to the satellite network.

[0168] For example, three values ​​of the QFI field are newly defined as corresponding to a spatial QFI in the set of possible QFI values: - "Voice-over-satellite" ("Voice over satellite"), for communication terminal-to-terminal telephone via satellite network; - “Critical mission over satellite”, for access to a critical service via the satellite network; and, - “Low latency satellite services” (“Low latency satellite services”), for accessing a service via the satellite network with low latency.

[0169] On the ground, the QFI modification request is routed to the G-CN's Session Management Function (SMF). Finding that the QFI value of the request corresponds to a spatial QFI, the ground-based SMF sends a "QoS not supported" message to the G-CN's Access and Mobility Management Function (AMF) via the standard Nil interface.

[0170] The G-CN's AMF then proceeds to a re-selection of the AMF towards the S-GN's AMF. This re-selection of the AMF in turn triggers an inter-gNB transfer ("handover") of the user equipment.

[0171] In a second embodiment, the cell is subdivided into a plurality of slices, as defined in document 3GPP TS 28.630 V18.0.0, each slice being associated with an identifier. A particular slice can then be associated with satellite access, the other slices being associated with terrestrial access.

[0172] In accordance with the standard, an admission check is generally performed by the S-gNB based on its load factor and that of the satellite network. Communication must then take place between a satellite network controller and the S-gNB to determine whether the admission of this new user equipment can be authorized. The admission constraints can advantageously vary according to the spatial QFI value indicated in the user equipment application: "Voice-over-Satellite" requires limited data rate and constant latency; "Critical mission over satellite" requires low latency at a low data rate; and "Low latency satellite services" is the most expensive, as it requires low latency and a higher data rate.

[0173] Once the user equipment is admitted, it performs an RRC reconfiguration, in accordance with the 5G standard. Synchronization is immediate since it is the same cell.

[0174] The RLC instances and buffers that were associated with the user equipment during its initial connection to the G-gNB do not need to be reallocated to the user equipment. It is sufficient to change the identifiers of these instances to associate them with the S-gNB and to modify the routing table used by module 260.

[0175] The user equipment is then connected to the satellite network via the S-gNB and the S-CN, and can no longer interact with the terrestrial network. All DRB radio data carriers associated with the terrestrial network are then terminated for this user equipment. Control

[0176] The control module 290 has the function of controlling the shared DU(s).

[0177] Its role is to mask from the centralized units, respectively onboard S-CU and ground-based G-CU, in particular for the control plan, the fact that a cell is shared.

[0178] Each centralized unit behaves as if it were managing a dedicated cell, characterized by a physical cell identifier - PCI (“Physical Cell ID”).

[0179] The DU transmits this identifier to the S-CU and the G-CU (the PCI identifier actually transmitted may be different for the S-CU and for the G-CU, while designating the same cell).

[0180] PCI identifier configurations and other cell-related information are configured at the DU level and reported to the S-CU and G-CU via standardized Fl AP messages (as defined in TS 138 473 - V15.3.0 - 5G / NG-RAN).

[0181] The DU operates in such a way that a CU cannot modify the cell configurations. Radio resource management is performed only by the DU, which implies that the DU must reject all requests related to radio resource management received from a CU.

[0182] With regard to procedures related to user equipment, the procedures are not altered since a terminal can only be linked to one logical gNB at a time. Variants and Advantages

[0183] The proposed architecture offers a user device the possibility of accessing a satellite network for space services (terminal-to-terminal communication, low latency, etc.) or a terrestrial network for Internet connection services.

[0184] Alternatively, the division between lower and upper layers of the second base station can follow the division proposed in the O-RAN standard.

[0185] Alternatively, with regard to the first logical base station: - while the lower layers of the first logical base station are hosted by the payload of a satellite (or first satellite), the layers The upper layers of the first logical base station are hosted on another satellite (or second satellite) in the constellation. In this case, an Fl link is established between the lower and upper layers, this Fl link relying on a transport layer integrating an IP link (direct or indirect via the satellite network) between the first and second satellites. - while the upper layers of the first logical base station are hosted by the payload of a satellite, the core network associated with this first base station, or first core network, can be located in the payload of that same satellite or in the payload of another satellite (using in this case an IP link through the satellite network);

[0186] Alternatively, independently of the preceding variant or in combination with it, with regard to the second logical base station: While the lower layers of the second logical base station are hosted by the payload of a satellite (or first satellite), the upper layers of the second logical base station are hosted not by a ground station, but by the payload of another satellite (or second satellite) in the constellation. In this case, an Fl link is established between the lower and upper layers. This Fl link relies on a transport layer that integrates not the feeder link, but an IP link (direct or indirect via the satellite network) between the first and second satellites. - while the upper layers of the second logical base station are hosted by the payload of a satellite, the associated core network, or second core network, can be located in the payload of that same satellite or in a ground base station, a feed link between the satellite component and the terrestrial component being used as a medium for the communication of flows between the second logical base station and the second ground core network.

[0187] The invention applies to the different modes of operation: "unicast", "multicast" and "broadcast".

[0188] Although the invention was presented in the specific context of 5G cellular technology, more generally it is also applicable to networks / communications using 4G technologies and future non-terrestrial 6G technologies. For example, for a 4G architecture, a person skilled in the art will consider the entities equivalent to those presented in the preceding embodiment, typically the Mobility Management Entity (MME) instead of the AMF, and the Serving Gateway / Packet Data Network Gateway (S-GW / P-GW) instead of the SMF / UPF.

Claims

Demands

1. Non-terrestrial cellular network (1), the non-terrestrial cellular network comprising a satellite component (10), the satellite component comprising a constellation of satellites (21, 22, 23, 24) forming a satellite network (20), at least one satellite of the satellite constellation, referred to as the first satellite (21), carrying a regenerative payload, characterized in that the non-terrestrial cellular network (1) comprises the first and second logical base stations, each logical base station being defined by a protocol stack associating lower and upper layers,the first logical base station (2) being entirely located within the payload of the first satellite (21) and the second logical base station (4) being distributed such that the lower layers of the second logical base station are located within the payload of the first satellite (21) and the upper layers (G-CU) of the second logical base station are located at a distance from the payload of the first satellite (21), the lower layers (RU,DU) of the first and second logical base stations being common and shared.

2. Non-terrestrial cellular network according to claim 1, wherein the upper and lower layers of the second logic base station (4) are linked by a standardized link "Fl", the lower layers comprising a shared radio unit (RU) and a shared distributed unit (DU), the upper layers of the first logic base station (2) comprising a first centralized unit (S-CU) and the upper layers of the second logic base station (4) comprising a second centralized unit (G-CU).

3. Non-terrestrial cellular network according to any one of claims 1 to 2, wherein the satellite constellation comprises a first onboard network core (S-CN), the upper layers of the first logical base station (2) being connected to the first onboard network core.

4. Non-terrestrial cellular network according to any one of claims 1 to 3, wherein the upper layers of the second logical base station are located in the payload of a second satellite (24) of the satellite constellation, different from the first satellite.

5. Non-terrestrial cellular network according to claim 4, wherein a two-way communication link, or IP link, is established between an IP interface of the payload of the first satellite (21) and an IP interface of the payload of the second satellite (24), with flows between the lower and upper layers of the second logical base station circulating along the IP link.

6. Non-terrestrial cellular network according to any one of claims 4 and 5, wherein the satellite component includes a second onboard network core, the upper layers of the second logical base station being connected to the second onboard network core.

7. Non-terrestrial cellular network according to any one of claims 1 to 3, the non-terrestrial cellular network further comprising a terrestrial component (40), the terrestrial component comprising a ground installation (42), the upper layers (G-CU) of the second logical base station (4) being located in the ground installation, the terrestrial component comprising a second ground network core (G-CN), the upper layers of the second logical base station (4) being connected to the second ground network core.

8. Non-terrestrial cellular network according to claim 7, the non-terrestrial cellular network comprising a two-way communication link, or feed link, between a satellite feed interface (270) of the satellite component (10) and a terrestrial feed interface (420) of the terrestrial component (40), with flows between the lower and upper layers of the second logical base station (4) flowing along the feed link (FeederLink).

9. Non-terrestrial cellular network according to claim 8, wherein the payload of the first satellite (21) comprises: - a first onboard network core (S-CN) to which the upper layers of the first logical base station (2) are connected; - an IP interface (280) and a satellite power interface (270); - a service separation module (260), connected at the output of the shared lower layers, for routing flows between, on the one hand, a user device connected to one of the logical base stations, and, on the other hand, either the upper layers of the first base station logic (2), i.e. the upper layers of the second logical base station (4); - an onboard "Fl" routing module (265), to route flows between the satellite power interface, an IP routing module and the service separation module; and, - the IP routing module (210), to route flows between the first onboard network core, the onboard "Fl" routing module, and the IP interface.

10. Cellular network according to claim 8 or claim 9, wherein the ground installation (42) comprises a ground routing module “Fl” (470) for routing flows between a terrestrial power interface (420), on the one hand, and the upper layers of the second logical base station (4).

11. Non-terrestrial cellular network according to any one of the preceding claims, wherein, a user device (11) is adapted to issue an initial connection request, and the second logical base station (4) is adapted to handle by default said initial connection request to attach said user device to the second logical base station and to a second associated core network, and wherein a user device (11), attached to the second logical base station (4), is adapted to issue a connection request to the satellite network by incorporating in said request a specific value of a predefined field, and the second core network is adapted to recognize said value and trigger roaming of the user device from the second logical base station (4) and the second core network, to the first logical base station (2) and a first associated core network.

12. Non-terrestrial cellular network according to claim 11, wherein the predefined field is a quality of service flow identifier field.

13. Non-terrestrial cellular network according to either claim 11 or claim 12, wherein the particular value of the predefined field is indicative of the parameters of a satellite service requested by the user equipment (11), the first logical base station (12) and the first associated core network being adapted to allow roaming of the user equipment taking into account the indicated parameters. 22

14. Non-terrestrial cellular network according to any one of claims 1 to 13, wherein the payload of the first satellite (21) comprises a control module (290) for the common and shared lower layers.

15. Communication satellite, characterized in that it is adapted to be integrated, as a first satellite (21), into a non-terrestrial cellular network (1) according to any one of the preceding claims.

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