Improved non-terrestrial cellular network

Abstract

This non-terrestrial cellular network (1), the satellite component (10) of which consists of a constellation of satellites (21, 22, 23, 24) together forming a satellite network (20), 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 associating lower layers and higher layers with each other, the first logical base station (2) being located entirely in the payload of the satellite (21) and the second logical base station (4) being distributed such that its lower layers are located in the payload of the satellite (21) and its higher 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.

Description

[0001] DESCRIPTION

[0002] Enhanced Non-Terrestrial Cellular Network

[0003] The invention relates to the field of non-terrestrial cellular networks (NTNs) using cellular technology, as standardized by the 3GPP (3rd Generation Partnership Project) standardization body, such as fourth generation (4G), fifth generation (5G) or sixth generation (6G) cellular technology.

[0004] A non-terrestrial cellular network integrates a satellite component alone or in combination with a terrestrial component.

[0005] 3GPP produces standards defining the requirements, architectures and operating procedures, such as protocols, for mobile communication.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] According to a first option proposed in these recommendations (notably in technical report TR 23.700-29), the satellite payload includes 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.

[0011] This type of architecture makes it possible to provide space-based services such as terminal-to-terminal communication, through a constellation of satellites forming a mesh network, without having to return to the ground. The satellite's payload output is connected, via an IP link, to the other satellites in the network. Such space-based services are characterized by lower latency and very high communication security.

[0012] According to a second option proposed in these recommendations (notably 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 "F1" link: 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.

[0013] The F1 link transport layer incorporates a bidirectional "feederlink" communication link between the satellite component and the terrestrial component.

[0014] Given that the payload of a satellite remains constrained in terms of computing capacity, the first option is not suitable in the case where there is a large number of user devices seeking to access internet services, such as video streaming servers.

[0015] The second option has the advantage of reducing the computing power required on board the satellite by offloading as much 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.

[0016] The aim of the invention is therefore to propose an architecture for the payload of a telecommunications satellite that 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.

[0017] 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, called 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 such 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. According to other advantageous aspects of the invention, the network comprises one or more of the following features, taken individually or in any technically feasible combination:

[0018] - the upper and lower layers of the second logical base station are linked by a standardized "F1" link, the lower layers comprising a shared radio unit and a shared distributed unit, the upper layers of the first logical base station comprising a first centralized unit and the upper layers of the second logical base station comprising a second centralized unit;

[0019] - the satellite constellation includes a first onboard network core, with the upper layers of the first logical base station being connected to the first onboard network core;

[0020] - 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;

[0021] - a two-way communication link, or IP link, is established between an IP interface of the payload of the first satellite and an IP interface of the payload of the second satellite, with flows between the lower and upper layers of the second logical base station circulating along the IP link;

[0022] - 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;

[0023] - the non-terrestrial cellular network comprising, in addition, 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;

[0024] - the non-terrestrial cellular network comprising a two-way communication link, or feed link, between a satellite feed interface of the satellite component and a terrestrial feed interface of the terrestrial component, with flows between the lower and upper layers of the second logical base station circulating along the feed link (FeederLink);

[0025] - the payload of the first satellite includes: a first onboard network core to which the upper layers of the first logical base station are connected; an IP interface and a satellite power interface; a service separation module, connected at the output of the shared lower layers, to route 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 logical base station, or the upper layers of the second logical base station; an onboard "F1" routing module, to route flows between the satellite power interface, an IP routing module and the service separation module; and, the IP routing module, to route flows between the first onboard network core, the onboard "F1" routing module, and the IP interface;

[0026] - the ground installation includes a ground routing module "F1" for routing flows between a terrestrial power interface, on the one hand, and the upper layers of the second logical base station;

[0027] - a user device is adapted to issue an initial connection request, and the second logical base station is adapted to handle said initial connection request by default to attach said user device to the second logical base station and to a second associated core network, and wherein a user device, 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 device from the second logical base station and the second core network, to the first logical base station and a first associated core network;

[0028] - the predefined field is a quality of service flow identifier field;

[0029] - 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;

[0030] - the payload of the first satellite includes a module for controlling common and shared lower layers.

[0031] 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.

[0032] 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: Figure 1 is a representation of the protocol stacking of a 5G gNB base station defined by 3GPP for a terrestrial network; and Figure 2 is a schematic representation of a preferred embodiment of the architecture of a cellular network according to the invention.

[0033] Generalities 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 embedded on board the first satellite, while its upper layers are located away from the payload of the first satellite.

[0034] 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.

[0035] 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.

[0036] This hybrid architecture is hidden from user equipment connected to 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.

[0037] Advantageously, the division between lower and upper layers of the second logical base station follows the division proposed in the 5G standard, through the concept of F1 link.

[0038] 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 enables, in particular, user equipment to access a satellite network. The payload of the first satellite thus comprises the lower layers shared between the two logical base stations and the upper layers of the first logical base station.

[0039] 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 comprises the upper layers of the second logical base station. The G-gNB allows a user device to access a terrestrial network.

[0040] In this preferred embodiment, the hybrid architecture allows access to a terrestrial network, limiting the computing load required on board the first satellite and thus addressing the constraint imposed by the limited capacity of the satellite's payload. This hybrid architecture maintains the possibility of accessing the satellite network, for example, for terminal-to-terminal communications for certain user equipment.

[0041] F1 link positioning options

[0042] Figure 1 represents, according to the 5G standard initially defined for terrestrial networks, the different possible options for positioning an F1 link in the stack of protocol layers.

[0043] From bottom to top, this stack includes, for example:

[0044] - an RF layer;

[0045] - a low physical layer, "Low-PHY";

[0046] - a high physical layer, "High-PHY" or "Hi-PHY";

[0047] - a medium access control layer - low-MAC (“Medium Access Control”);

[0048] - a high MAC layer, “High-MAC” or “Hi-MAC”;

[0049] - a low-RLC radio link control layer;

[0050] - a high RLC layer, “High-RLC” or “Hi-RLC”;

[0051] - 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 (“User Plane Function” entity);

[0052] - a PDCP layer of the control plane, PDCP-C, associated with an RRC layer and an AMF entity (“Access & Mobility Management Function”);

[0053] 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.

[0054] The combination of the RF and Low-PHY physical layers constitutes a radio unit - RU ("Radio Unit"). They enable the establishment of a service link Uu with a user equipment - UE ("User Equipment").

[0055] The F1 link then delineates, within the stack of protocol layers of the gNB, outside of the physical layers, on the one hand, lower layers, located below the F1 link and together forming a distributed unit (DU), and, on the other hand, upper layers, located above the F1 link and together forming a centralized unit (Cil). The F1 link constitutes the interface between a DU and a CU.

[0056] Alternatively, several CUs can share the same DU, or several DUs can share the same CU.

[0057] The data actually transported along the F1 link depends on the protocol layers between which this link is placed, that is to say the option chosen for the positioning of the F1 link.

[0058] The F1 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.

[0059] According to the invention, the positioning option of link F1 corresponds to option 5, option 4, option 3 or option 2.

[0060] Since the physical layers are shared between the two logical base stations, there is only one cell, and data packets must be scheduled at the high MAC layer, "Hi-MAC". Therefore, the selected option must be option 5 or higher from among options 1 to 8.

[0061] Placing the F1 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 offer only a marginal gain in reducing the computing load on board the satellite.

[0062] Among the options 5 to 2, some are more advantageous than others depending on the embodiment envisaged. Thus, particularly 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.

[0063] For example, by selecting option 5, data packets 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.

[0064] Preferably, the F1 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.

[0065] In the remainder of this description, option 3 is presented in more detail, but another option, such as option 5, could also be used. 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 is important to note that the two centralized units do not operate in redundancy (in which case there would only be one logical base station), but rather in parallel. Therefore, there are indeed two logical base stations.

[0067] Methods for supporting a regenerative payload with an onboard gNB or the splitting 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] However, the invention requires the implementation of various additional functionalities to provide unified connectivity to terrestrial and non-terrestrial / satellite networks:

[0069] - 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 requires access to the terrestrial network or the satellite network;

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

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

[0073] Non-terrestrial cellular network

[0074] In more detail, as illustrated in Figure 2, network 1 is a non-terrestrial cellular network according to the invention.

[0075] It allows user equipment to access, via an air interface, remote services, such as communication with other user equipment or data servers.

[0076] Figure 2 shows a first user equipment 11, a second user equipment 12 and a third user equipment 13, as well as a server 14.

[0077] Network 1 comprises a satellite component 10 and a ground component 40.

[0078] Satellite component

[0079] Two possible configurations for the satellite component are conceivable: the first involves a constellation of satellites; the second involves multiple flying platforms, such as high-altitude platform stations (HAPS) or medium-altitude platforms (like aerial drones). Hybrid configurations combining these two configurations are also possible.

[0080] The first variant will be presented in more detail below.

[0081] Satellite component 10 comprises a constellation of satellites.

[0082] The satellite constellation includes non-geosynchronous satellites - NGSO ("Non-GeoSynchronous Orbit"), i.e., satellites orbiting 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"), including geostationary satellites - GEO for "Geosynchronous Earth Orbit" I "Geosynchronous Equatorial Orbit" I "Geostationary Earth Orbit".

[0083] The constellation comprises at least one satellite according to the invention. For example, as illustrated in Figure 2, the constellation comprises a first satellite 21, a second satellite 22, a third satellite 23, and a fourth satellite 24.

[0084] The satellites in the constellation are interconnected to form a mesh-type satellite network. Each satellite constitutes a node in this satellite network. The satellites in each pair of satellites in the constellation are linked by an inter-satellite data link, forming an ISL (Inter-Satellite Link). Preferably, communications on the satellite network, i.e., along the ISL data links, are conducted using an IP protocol.

[0085] Each satellite therefore has an interface for accessing the satellite network. For example, the first satellite 21 has an interface 280 for accessing the satellite network 20.

[0086] The following will describe in detail the structure of satellite 21 as an example of a satellite according to the invention. If the network 1 includes at least one satellite conforming to satellite 21, advantageously several or even all of the satellites in the constellation are similar to satellite 21.

[0087] Satellite 21 is a communications satellite. It carries a payload integrating the hardware and software necessary to implement the various communication functionalities of Satellite 21.

[0088] Satellite 21 has antenna means 310 that allow it to define a plurality of ground coverage areas, or cells. For example, satellite 21 has antenna means 310 that allow it to define a first cell 31 and a second cell 32. A user device on the ground, such as the first device 11 located in the first cell 31 and the second device 12 located in the second cell 32, can each establish a service link Uu with satellite 21.

[0089] According to the breakdown in Figure 1, the payload of satellite 21 comprises:

[0090] - a radio unit - RU, 220, shared between the S-gNB 2 and the G-gNB 4;

[0091] - a distributed unit - DU, 230, shared between the S-gNB 2 and the G-gNB 4; and,

[0092] - a centralized unit - CU, 240, or S-CU, on board the satellite and dedicated to the S-gNB 2.

[0093] Alternatively, the S-CU could be carried on board a satellite near satellite 22, 23 or 24 of satellite 21 carrying the shared DU.

[0094] The payload of satellite 21 includes, in the particular embodiment shown in Figure 2, a satellite core network - CN (“Core Network”), or S-CN, 250.

[0095] Alternatively, the core of the satellite network is on board another satellite in the constellation or distributed between several satellites in the constellation.

[0096] The payload of satellite 21 also includes a 270 interface for accessing the on-board-to-ground communication link (“Feederlink”).

[0097] The payload of satellite 21 also includes:

[0098] - a service differentiation module, 260;

[0099] - a routing module F1, 265; and,

[0100] - an IP 210 routing module.

[0101] The payload of satellite 21 ultimately includes a controller, 290.

[0102] The various components of the satellite payload 21 are connected in the following way, in the case of positioning the F1 link in option 3.

[0103] The shared RU unit, 220, includes an RF layer, connected to the radio communication means 310, and a low physical layer, "Low-PHY", connected to the shared DU 230.

[0104] The shared DU unit 230 has 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.

[0105] 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.

[0106] The service differentiation module 260 is connected, on one side, to the various low-RLC layers of the shared DU unit, 230, and, on the other side, on one side to the S-Cil 240 (for communications with the satellite network), and, on the other side, to the routing module F1, 265 (for communications with the terrestrial network).

[0107] The S-Cil 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-11 layer and an SDAP layer, and a second stack of the control plane, consisting of a PDCP-C layer and an RRC layer.

[0108] The S-CU is connected via its high RLC layers, "Hi-RLC", to the service differentiation module 260.

[0109] The S-CU is connected to the S-CN, via its RRC layer and an N2 link to the AMF entity of the S-CN and via its SDAP layer and an N3 link to the UPF entity of the S-CN.

[0110] The S-CN is a lightweight 5G core network, in the sense that it only includes the essential functionalities of a 5G core network given the limited payload capabilities.

[0111] It includes AMF (and / or SMS) and UPF entities, which are respectively connected to the onboard CU unit.

[0112] The S-CN 250 is connected to the IP 210 routing module.

[0113] The F1 265 routing module is connected to the 260 differentiation module, the 270 communication interface, and the 210 IP routing module.

[0114] The IP routing module 210 is connected to the S-CN 250, the ISL interface 280 and the F1 265 routing module.

[0115] The 290 control module drives the shared DU 230 of the satellite payload.

[0116] Earth component

[0117] The land component 40 comprises:

[0118] - a ground installation, 42, connected to the satellite component 10 by one or more edge-to-ground communication links "Feederlink";

[0119] - the core network - terrestrial CN, or G-CN, 45; and,

[0120] - a terrestrial network 46, like the internet.

[0121] The ground installation 40 includes:

[0122] - a 420 interface for access to the or each ground-to-surface 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 Figure 2);

[0123] - one or more centralized ground control units (GCUs), each GCU being associated with a payload from a single satellite in the constellation, i.e., with a single shared DU. For example, installation 40 comprises 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,

[0124] - a routing module "F1", 470, between, on the one hand, interface 420 and, on the other hand, each G-CU, 440, 442.

[0125] The G-CU 440 unit has 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 user plane stack, consisting of a PDCP-U layer and an SDAP layer, and a second control plane stack, consisting of a PDCP-C layer and an RRC layer.

[0126] 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.

[0127] Alternatively, the solution may include 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 solution may include several G-CNs (e.g., if multiple operators are involved).

[0128] G-CN on the ground 45 includes all the services of a 5G core network.

[0129] It is connected to the terrestrial network 46.

[0130] The latter allows access to various services, notably those provided by servers, such as server 14 connected to the terrestrial network 46.

[0131] We can see that we do indeed have a complete first 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.

[0132] We observe 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.

[0133] Routing

[0134] Within the payload of satellite 21, the following routing means are planned.

[0135] The 260 service differentiation module is responsible for routing the flows:

[0136] - in the upstream direction (from a user device), from the shared DU, to the correct processing entity, i.e., either the G-CU (via the onboard-to-ground communication link) or the S-CU; and,

[0137] - in the downward direction (towards a user device), towards the correct RLC layer (or RLC layer instantiation) of the shared DU.

[0138] To direct the flows, module 260 makes advantageous use of 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.

[0139] If a data packet needs 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 needs to be exchanged between the shared DU and the G-CU 440, the 260 module transmits it, modifying the format according to the protocol chosen for the F1 link, preferably IP. The 260 module encapsulates an upstream stream and decapsulates a downstream stream. The 260 module can also perform stream filtering.

[0140] The F1 265 routing module is responsible for routing the following flows:

[0141] - between the access interface 270 and the service differentiation module 260, for exchanges between associated G-CU and DU, to serve a user equipment connected to satellite 21;

[0142] - between the access interface 270 and the IP routing module 210, when using the satellite 21's edge-to-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,

[0143] - between module 260 and IP routing module 210, when using the edge-to-ground communication link of another satellite to route flows between the ground and satellite 21, for example when the edge-to-ground communication link of satellite 21 is too busy.

[0144] The user flows to be routed to the terrestrial network correspond to a significant throughput along the edge-to-ground communication link, due to the nature of the services accessed by users and the large number of these users.

[0145] In addition, other streams can also use this same communication link, such as those from other satellites in the constellation.

[0146] However, the capacity of an air-to-ground communication link is necessarily limited to a maximum capacity.

[0147] To meet this constraint, the F1 routing module advantageously implements a buffer mechanism to temporarily hold 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.

[0148] Some flows are sensitive to delay. This is particularly true for control flows between the shared DU and the associated GCU. Excessive latency can lead to disconnection of the user equipment or a decrease in service quality. Therefore, prioritization of flows is necessary. The F1 routing module advantageously implements a flow scheduling mechanism based on a priority level. In the embodiment shown in Figure 2, it is not necessary to implement a buffer and / or scheduling mechanism between the shared DU and the SGU, since these two units are instantiated in the same payload.However, such mechanisms are to be implemented in an alternative embodiment where the S-CU is carried on board another satellite in the constellation and an F1 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.

[0149] The IP 210 routing module's function is to route traffic, preferably in IP format:

[0150] - between the 280 interface for accessing an ISL link and S-CN 250, so that another satellite can access the functionalities of the satellite core network hosted by the satellite;

[0151] - between interface 280 and routing module F1 265, for the use of the ground-to-surface communication link of satellite 21 by another satellite in the constellation, to serve, for example, user equipment connected to that other satellite via the satellite network; and,

[0152] - between the F1 265 routing module and the S-CN 250, in order to use the ground-side communication link of the first satellite to allow the G-CN 45 to access functionalities of the S-CN 250 and vice versa, for example to allow terminal roaming.

[0153] Note that traffic routing is performed using three different components: modules 260, 265, and 210. This allows for traffic segregation and thus increases network operational security. Alternatively, F1 and IP routing functionalities can be integrated directly into interfaces 270 and 280, respectively.

[0154] Within ground installation 42, the following routing means are planned.

[0155] The F1 470 routing module allows routing of flows between the 420 interface for accessing an edge-to-ground communication link and either of the G-CUs.

[0156] The flows can therefore be routed along several routes:

[0157] - A first route between two user devices in different cells served by the antenna means of the first satellite's payload. For example, between user devices 11 and 12, this first route follows the service link Uu between device 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 which cell device 12 is in, 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 device 12.

[0158] - A second route between a user device in a cell of the first satellite and the satellite network, specifically another satellite in the constellation, to access a user device located in a cell served by that other satellite. For example, between user devices 11 and 13, this second route follows the service link llu between device 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 device 13 is located in, the S-CN, via the IP routing module 210, uses the satellite network access interface 280 to route the device across this satellite network to reach the fourth satellite 24, to which device 13 is connected by a service link Uu.

[0159] - 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 device 11 and server 14, this third route follows the service link Uu between device 11 and the antenna means 310, then the shared RU, the shared DU, module 260 (which encapsulates the data packets according to the transport protocol chosen for the link F1), the routing module F1, the interface 270 accessing the edge-to-ground link, the interface 420 accessing the edge-to-ground link, the router F1 470, the data decapsulation module (which routes the flows to the associated G-CU), the G-CU, the G-CN, then through the terrestrial network 46, to server 14.

[0160] - 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 F1 routing module, the edge-to-ground communication link, then the F1 router 470, 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.

[0161] Connection procedure

[0162] For the connection, a user device, such as device 11, initiates the following connection procedure.

[0163] The user equipment uses standardized procedures to connect to the shared RU. It detects the SSB, the Ml B, and then makes a random access attempt - RA ("Random Access").

[0164] The user's equipment sends a connection request.

[0165] 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 full and extended functionalities of a 5G core network, in particular relating to the identification of user profiles.

[0166] Once the connection phase is complete, the user equipment can instantiate tunnels with the U PF entity of the G-CN and transmit data.

[0167] If the user equipment subsequently wishes to access the satellite network for a particular service, a new procedure is defined.

[0168] 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 the document 3GPP TS 29 502 - V19.0.0 - 5G.

[0169] This request includes a QFI field (“QoS Flow Identifier”).

[0170] 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.

[0171] For example, three values ​​of the QFI field are newly defined as corresponding to a spatial QFI within the set of possible QFI values:

[0172] “Voice-over-satellite” (“Voice over satellite”), for terminal-to-terminal telephone communication via the satellite network;

[0173] "Critical mission over satellite" ("Critical mission over satellite"), for access to a critical service via the satellite network; and,

[0174] "Low latency satellite services" ("Low latency satellite services"), for access to a service via the satellite network with low latency.

[0175] On the ground, the QFI modification request is routed to the G-CN's Session Management Function (SMF). Detecting that the QFI value in 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 N11 interface.

[0176] The G-CN's AMF then performs an AMF re-selection towards the S-GN's AMF. This AMF re-selection in turn triggers an inter-gNB transfer ("handover") of the user equipment.

[0177] In a second embodiment, the cell is subdivided into a plurality of slices, as defined in the 3GPP TS 28.630 V18.0.0 document, 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.

[0178] 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 higher data rates.

[0179] Once the user equipment is accepted, it performs an RRC reconfiguration, in accordance with the 5G standard. Synchronization is immediate since it is the same cell.

[0180] 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.

[0181] The user equipment is then connected to the satellite network via the S-gNB and 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.

[0182] Control

[0183] The 290 control module is used to control the shared DU(s).

[0184] Its role is to mask from the centralized units, respectively onboard S-CU and ground-based G-CU, particularly for the control plan, the fact that a cell is shared.

[0185] Each centralized unit behaves as if it were managing a dedicated cell, characterized by a physical cell identifier - PCI (“Physical Cell ID”).

[0186] 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).

[0187] 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 F1AP messages (as defined in TS 138 473 - V15.3.0 - 5G / NG-RAN).

[0188] The DU operates in such a way that a CU cannot modify cell configurations. Radio resource management is performed exclusively by the DU, which means the DU must reject all radio resource management requests received from a CU.

[0189] Regarding procedures related to user equipment, these procedures remain unchanged since a terminal can only be linked to one logical gNB at a time. Variants and Advantages

[0190] The proposed architecture offers user equipment 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.

[0191] Alternatively, the division between lower and upper layers of the second base station can follow the division proposed in the O-RAN standard.

[0192] Alternatively, regarding the first logical base station: while the lower layers of the first logical base station are hosted by the payload of one satellite (or first satellite), the upper layers of the first logical base station are hosted on another satellite (or second satellite) in the constellation. In this case, an F1 link is established between the lower and upper layers, this F1 link relying on a transport layer incorporating an IP link (direct or indirect via the satellite network) between the first and second satellites. Alternatively, while the upper layers of the first logical base station are hosted by the payload of one 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 an IP link across the satellite network in this case).

[0193] Alternatively, independently of or in combination with the previous variant, regarding 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 F1 link is established between the lower and upper layers. This F1 link relies on a transport layer that integrates, instead of the feeder link, 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 a satellite payload, the associated core network, or second core network, can be located within the payload of that same satellite or in a ground base station. A feed link between the satellite and ground components is used to carry the data streams between the second logical base station and the second ground core network. The invention applies to the different operating modes: unicast, multicast, and broadcast.

[0194] 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 previous 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, called 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-Cll) 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 logical base station (4) are linked by a standardized link "F1", the lower layers comprising a shared radio unit (RU) and a shared distributed unit (DU), the upper layers of the first logical base station (2) comprising a first centralized unit (S-CU) and the upper layers of the second logical 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-Cll) 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 embedded 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, to route the flows between, on the one hand, a user equipment connected to one of the logical base stations, and, on the other hand, either the upper layers of the first logical base station (2), or the upper layers of the second logical base station (4); - an onboard "F1" routing module (265), for routing 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 embedded network core, the embedded "F1" 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 “F1” (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 manage 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 (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 equipment 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 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.

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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