Relaying of user equipment in non-terrestrial networks

Abstract

A method performed by a non-terrestrial communication network (NW) to relay a signal between a first user device (UE1) and a second user device (UE2), wherein the relay user device (UER) is mounted on a network access device (SAT) of the non-terrestrial communication network (NW), and the method is To obtain relay support information regarding the establishment of a sidelink communication mode between the relay user equipment (UER) and the first (UE1) and / or second user equipment (UE2), The relay support information is transmitted to the first user device (UE1) and the second user device (UE2). Based on the relay support information, establish first and second sidelink communication links between the relay user equipment (UER) and the first (UE1) and second user equipment (UE2), respectively. To relay signals between the first user equipment (UE1) and the second user equipment (UE2) via the first and second sidelink communication links using an established sidelink communication mode. Methods that include...

Description

Technical Field

[0001] The present disclosure relates to the field of communications using non-terrestrial networks, and more particularly to communications in a sidelink communication mode between user equipment in a non-terrestrial network. Priority is claimed based on European Patent Application No. 23306582.0 filed on September 22, 2023, the content of which is incorporated herein by reference.

Background Art

[0002] In non-terrestrial communication networks, such as satellite communication networks, connectivity may be provided to user equipment or terminals covered by such satellite communication networks based on the network architecture. Such a network architecture may include at least network access devices or payloads, such as satellites, that relay signals to one or more base stations via feeder links and satellite gateways. Such satellite gateways are typically located on Earth. For example, in wireless communication standards such as New Radio (i.e., NR), when user equipment connected to a satellite communication network wants to establish communication (e.g., when transmitting user equipment wants to send data packets from transmitting user equipment to receiving user equipment), a radio protocol is transmitted by the transmitting equipment to the satellite via a service link (e.g., via an air interface or Uu interface). Such a radio protocol can then be forwarded to a base station (e.g., a gNodeB or gNB) via a satellite gateway on Earth linked to the satellite by a feeder link. The base station can then connect to the user plane function (i.e., UPF) of the core network for the forwarding of application data (or data packets) that are looped back to the receiving user equipment via a network payload that provides services to such receiving user equipment. In particular, when user devices are serviced by the same network payload (typically when two communicating user devices are connected to the same satellite), the radio protocol is transmitted twice over the feeder link, so the data path between such two user devices includes a communication loop between the satellite and Earth.

[0003] Since the radio protocols exchanged between two user devices imply two transmissions over a feeder link, such a communication loop between the satellite and Earth causes latency and data rate problems. Such a communication loop can consume backhaul resources in particular and overload the feeder link bandwidth. Furthermore, communication between user devices is highly dependent on the availability of the feeder link, even if such user devices are connected to the same satellite or interconnected satellites (e.g., via an inter-satellite link i.e., ISL). Therefore, when the feeder link encounters bandwidth overload, interruption, or switching, communication between user devices connected to the satellite communication network will be interrupted or rendered inoperable.

[0004] To address such Earth-satellite loops, alternatives to existing communication protocols might involve, for example, implementing a full gNodeB and user-plan functional architecture on the satellite. However, such an architecture would involve complicating the satellite structure launched into orbit, thus significantly increasing computational complexity as well as implementation and maintenance costs. [Overview of the Initiative] [Means for solving the problem]

[0005] This disclosure will improve the situation.

[0006] In a first aspect of this disclosure, a method is provided by a non-terrestrial communication network for relaying a signal between at least a first user device and a second user device, wherein the relay user device is mounted on a network access device of the non-terrestrial communication network, and the method is To obtain at least relay support information regarding the establishment of a sidelink communication mode between the relay user equipment and at least one of the first and second user equipment, Transmit at least a portion of the relay support information to at least a first user device and a second user device. Based on the relay support information, establish at least a first sidelink communication link between the relay user equipment and the first user equipment, and a second sidelink communication link between the relay user equipment and the second user equipment. Using an established sidelink communication mode, signals are relayed between the first user device and the second user device via the first sidelink communication link and the second sidelink communication link. A method including this is proposed.

[0007] As a result, this disclosure proposes a method for enabling a direct communication mode between user devices connected to a non-terrestrial communication network.

[0008] In particular, the proposed method advantageously prevents communication loops and multiple transmissions between non-terrestrial access devices (e.g., satellites) and the Earth's surface during signal transmission between a first user device and a second user device connected to a non-terrestrial communication network. In fact, existing non-terrestrial networks provide connectivity between several end users (particularly user devices) by transmitting radio protocols between access devices located off the Earth's surface (such as satellites or high-altitude platform station access devices, i.e., HAPS access devices) and Earth-based structures such as gateways and terrestrial base stations. In particular, even when the first and second user devices are covered by the same satellite beam footprint projected by the same satellite beam, for example, the signal transmitted from the first user device to the second user device still requires two transmissions in the feeder link between the satellite and the Earth-based gateway. In fact, when the first user device transmits a data signal to the second user device, a typical communication path is as follows: - The uplink signal is transmitted from the first user equipment to the satellite via the service link. - The satellite transmits signals to an Earth-based gateway via a feeder link. - The signal is forwarded from the gateway through the base station to the core network, and then forwarded to one or more network functions so that a response signal containing the necessary data packets can be routed to a second user device. - The response signal is transmitted to the satellite via the feeder link. - The satellite transmits a response signal to a second user device via the service link using a downlink signal.

[0009] Therefore, the communication path between the first and second user equipment causes latency and efficiency problems because signal transmission requires two transmissions over the feeder link, even when the first and second user equipment are covered by the same satellite beam footprint. Furthermore, such a complex communication path is highly dependent on the feeder link bandwidth, and in the event of saturation due to a feeder link failure, it can lead to a disruption of communication between end users, thus affecting the reliability of the connectivity provided by the network.

[0010] As an alternative to such complex communication paths, network functions such as full base stations and user plane functions may be implemented and mounted on satellites to conserve significant signal loads in the Earth-satellite structure of the network by generating data network access and resource allocation at the access device level. However, implementing and mounting a full base station and user plane function structure on a satellite requires a considerable amount of computing and memory resources to be implemented and mounted on the satellite, and increases the amount of auxiliary hardware placed in orbit. Therefore, such alternatives present considerable drawbacks.

[0011] This disclosure addresses such problems by proposing a side-link communication mode between user devices, where transmissions between a first user device and a second user device can be freed from the complex communication paths involving communication loops and several Earth-satellite transmissions as described. As a result, communication between user devices can be optimized in terms of both latency and computational resource consumption without requiring costly adjustments to the satellite structure.

[0012] The Third Generation Partnership Project (3GPP) (registered trademark) 5G defines a direct (or sidelink) communication model in wireless communications in the context of proximity service (i.e., ProSe) applications, where terminals can communicate directly without involving network entities such as base stations. Such a direct communication mode allows terminals with geographical proximity to establish inter-device communication paths without sending packets to / from the core network via a base station. Such a direct communication mode may also be called “inter-device” or “D2D” communication mode. Such a direct communication mode may also be extended to specific use cases of devices acting as relay devices between two terminals or between a terminal and a network. Such specific direct communication modes may also be called “inter-device relay” and “device-to-network relay” (or “device-to-network relay service”), respectively. In inter-device relay (device-to-network relay, respectively), the relay device may, for example, communicate with an out-of-coverage terminal via a direct communication mode and relay such transmissions to another terminal via another direct communication mode (which may also be relayed to a network entity via a conventional network-to-device communication mode, respectively).

[0013] In both device-to-device communication and device-to-network relay, direct communication between terminals generally requires a discovery phase by such terminals. In fact, for each service (or application) provided by a terminal, the discovery phase allows the terminal to detect other nearby terminals and / or signal their presence to nearby terminals. For example, a terminal functioning as a relay terminal may transmit an announcement signal to indicate its relay capability. In another example, a terminal requiring relay services may transmit a request signal to indicate the type of service relay required. Thus, the discovery phase in direct communication mode typically involves multiple terminals transmitting multiple discovery signals (including announcement messages, request messages, and corresponding response messages in response to such announcement and request messages) over a wireless communication network. Therefore, a considerable amount of signaling occurs during such a discovery phase. However, in the context of short-range communication (i.e., terminal communication in D2D is geographically close), such a level of signaling may be acceptable because typically only a limited number of terminals are involved (for example, only a few terminals within a defined neighborhood may be able to perform D2D communication).

[0014] However, such existing direct communication models cannot be efficiently transferred directly to use cases of non-terrestrial communication networks, such as satellite communication networks.

[0015] In reality, in non-terrestrial communication networks, the context of proximity service (ProSE) applications does not apply because user equipment connected to the non-terrestrial communication network, and more generally, end users, are not necessarily geographically close. In fact, even if several user devices are connected to the non-terrestrial communication network via the same cell, such devices may still be geographically separated, for example, by hundreds of kilometers, depending on the size of the cell's coverage. Furthermore, such cells are projected by non-terrestrial access devices such as satellites, and the number of end users covered by such cells can be considerable. When considering mounting a specific user device on an access device to act as a relay device for all user devices covered by the same cell projected by such an access device, known direct communication models cannot be efficiently applied. Indeed, the discovery phase required in direct communication models involves a considerable amount of signaling within the non-terrestrial communication network. For example, if a mounted device attempts to function as a relay device for multiple terminals located on Earth, a large number of terminals may be involved in discovery, requiring a huge amount of signaling and therefore resources.

[0016] Furthermore, non-terrestrial contexts involve complex physical layer considerations that do not arise in terrestrial contexts. For example, when connectivity is provided by a non-terrestrial structure, signaling requires considering propagation delays between user equipment and network reference points that may be located between, for example, base stations, satellites, or two such network entities. Such propagation delays in non-terrestrial communication network signaling are considered by applying timing advances to the signals. However, existing direct communication models do not consider the timing advances that should be applied to signaling between terminals.

[0017] To address latency and computing resource consumption issues in non-terrestrial communication networks, this disclosure proposes including support-providing relay user equipment mounted on network entities of non-terrestrial communication networks, such non-terrestrial relay user equipment functioning as relay devices for establishing a sidelink communication mode and relaying signals between at least a first user device and a second user device based on provided relay support information. Based on the proposed method, a sidelink communication mode is established in which signals can be transmitted from a first user device to a second user device without a communication path involving base stations and a core network. In particular, such a communication path includes relaying signals via the relay user equipment. Thus, advantageously, the proposed disclosure enables optimization of the communication path when transmitting signals from a first user device to a second user device by saving transmit loops at the core network level and saving several transmissions performed between non-terrestrial network entities (e.g., satellites) and the ground via feeder links.

[0018] Advantageously, the proposed method provides a means for establishing such a sidelink communication mode. In fact, in existing non-terrestrial communication networks, signaling is performed on a network-device basis. In other words, control and / or data messages and packets are exchanged between the radio access network and the core network to provide connectivity to end users (e.g., to provide access for signal transmission between user devices). In particular, existing transmissions require that the radio protocol is transmitted to the core network and that core network functions and resources are allocated by base stations managing cells that provide services to end users. In the context of this disclosure, establishing sidelink communication provides an alternative mode of communication between user devices. To this end, this disclosure proposes relying on the non-terrestrial architecture of the network to establish the sidelink communication mode. In particular, the proposed establishment of the sidelink communication mode can be network-assisted. In other words, non-terrestrial network infrastructure can be used to assist non-terrestrial relay user devices, a first user device, and a second user device in establishing and using the sidelink communication mode.

[0019] In fact, existing direct communication models rely on the assumption of short distance (or proximity). Therefore, establishing sidelink communication modes in non-terrestrial communication networks involving ground-satellite communications requires consideration of specific configurations and limitations for different layers of network protocol architectures, such as 5G protocol architectures.

[0020] This disclosure proposes transmitting relay support information to at least a relay user device. In particular, such relay support can specifically assist the relay user device in establishing a sidelink communication mode. Such relay support information can provide the relay user device with information for configuring the sidelink communication mode, in particular with respect to, for example, radio interfaces, resource allocation, access rights, etc. Advantageously, such proposed relay support information enables the relay user device to function as a relay device for a first user device and a second user device without requiring a discovery phase or any equivalent step in which the relay user device must broadcast an announcement message. In other words, this disclosure makes it possible to generate a sidelink communication mode between terminals attempting to participate in sidelink communication without requiring an extended broadcast of an announcement message. The relay support information may include, for example, information about eligible user devices to which the relay user device can relay signals. Thus, by receiving the relay support information, the relay user device is relieved from performing the discovery phase and, therefore, can limit the amount of signaling in a non-terrestrial communication network. In fact, without relay support information, establishing sidelink communication between relay user equipment and end-user user equipment would require a discovery phase or any equivalent stage in which user equipment eligible to communicate via sidelink communication is identified. Because relay user equipment is mounted on (non-terrestrial) network entities and user equipment is on the ground or, more generally, at a lower altitude relative to the network entity (and therefore relative to the implemented relay user equipment), establishing sidelink communication between such mounted relay user equipment and user equipment would require a large amount of signaling between the relay user equipment and such user equipment.Therefore, as proposed in this method, the provided relay support information enables the establishment of a sidelink communication mode between user devices via relay user devices in a non-terrestrial communication network without requiring user devices and relay user devices to transmit multiple discovery messages, such as notification messages and / or request messages.

[0021] Furthermore, the proposed relay support information advantageously enables the establishment of sidelink communication modes to be adapted to the constraints of non-terrestrial communication networks. In fact, the relay support information can provide the relay user equipment with protocol information, radio interface information, configuration information, access information, resource allocation information, network information, and physical layer information to establish sidelink communication with the first and second user equipment. Therefore, by providing the relay support information to the relay user equipment, the proposed method, in the context of non-terrestrial networks, - Discovery (or identification) of user equipment eligible to communicate in sidelink communication mode. - To provide information for establishing a wireless interface between the relay user equipment and each of the first and second user equipment in order to communicate in sidelink communication mode. - To provide protocols and configuration information for establishing a first sidelink communication link and a second sidelink communication link with the first user equipment and the second user equipment, respectively. This will become possible.

[0022] A non-terrestrial communication network can be understood as a space and aerial communication network supported by a network infrastructure that includes non-terrestrial network entities. In particular, such a non-terrestrial communication network is supported by at least one network access device. The network access device can refer to a satellite constellation that includes one or several satellites. Such a satellite constellation can be a geostationary orbit (i.e., GEO), medium Earth orbit (i.e., MEO), or low Earth orbit (i.e., LEO) satellite. The network access device can also refer to, for example, a high-altitude platform system (i.e., HAPS) or a low-altitude platform system (LAPS).

[0023] A relay user device can be understood as a relay device configured to relay signals from and / or to another user device. Such a relay user device may, for example, be a network-to-device relay for relaying signals between another user device and a (non-terrestrial) network entity of a non-terrestrial communication network. Such a relay user device may also be an inter-device relay for relaying signals between at least one user device and a second user device. In particular, a relay user device is implemented and mounted on a network access device of a non-terrestrial communication network. Mounted on a network access device of a non-terrestrial communication network can be understood as the relay user device being located on a non-terrestrial network access device. Information received by the relay user device may be communicated to the relay user device when it is communicated to the network access device by the core network, with respect to the access network level. For example, the relay user device may receive information from the core network of a non-terrestrial communication network via a feeder link control channel linking a non-terrestrial network gateway and an access device (e.g., a satellite). In particular, the distance separating such relay user equipment from other user equipment located on or near the Earth's surface and connected to a non-terrestrial communication network is at least several hundred kilometers (e.g., in the case of LEO satellites) or several thousand kilometers (e.g., in the case of GEO satellites).

[0024] The first and second user devices can be understood as end-user terminals whose communications are supported by a non-terrestrial communication network. In other words, the first and second user devices are connected to the non-terrestrial communication network at least via a cell or coverage of the network's access device. Thus, the first and second user devices are located within the access device's coverage footprint (e.g., within a satellite beam cell) for at least a predetermined time. The first and second user devices may belong to the same or different coverage footprints deployed by the same or different access devices. Furthermore, being connected to the network can be understood as the first and second user devices having performed network access procedures, such as RACH procedures or handover procedures. Thus, the first and second user devices are considered to have been allocated radio resources (e.g., in a configured or semi-configured grant) for transmitting and / or receiving signals and / or messages supported by the non-terrestrial communication network. In particular, the first and second user devices are configured to transmit uplink signals to the access device (or each of their respective access devices) and to receive downlink signals from the access device (or each of their respective access devices). Such uplink and downlink signals may be transmitted to / by the first and second user devices via the Uu interface. In particular, the first and second user devices are considered to be on or near the ground. Near the ground can be understood as a maximum distance of about 10 kilometers separating the first or second user device from the ground. The first and second user devices may be, for example, mobile terminals, telephones, or aircraft.

[0025] Relaying a signal between the first user equipment and the second user equipment can be understood as the relay user equipment functioning as a relay device for communication between the first user equipment and the second user equipment. The signal relayed between the first user equipment and the second user equipment can be, for example, a signal including a data packet transmitted from the first user equipment to the second user equipment.

[0026] The sidelink communication mode can be understood as a direct communication mode between user equipments where signals are not handled by a base station. In particular, such a direct communication mode can be understood as being provided by a non-terrestrial communication network. In such a proposed sidelink communication mode, signals are relayed from one user equipment to another via a relay user equipment mounted on an access device of the non-terrestrial communication network. In particular, in such a sidelink communication mode, signals transmitted from and / or signals transmitted to a user equipment do not require a communication loop between the Earth and a non-terrestrial access device (e.g., a satellite).

[0027] Establishing the sidelink communication mode between the relay user equipment and the user equipment can be understood as both the relay user equipment and the user equipment receiving information and starting a protocol for functioning in the direct communication mode. For example, in the sidelink communication mode, the radio resources selected and used for transmitting a signal are specific resources allocated to the sidelink communication mode, the radio interface used for transmitting a signal is a PC5 interface distinct from the Uu interface, and the feederlink control channel may be interrupted or may not be used.

[0028] Establishing a sidelink communication link can be understood as a wireless link setup for establishing a wireless interface between a relay user device and a user device. The first and second sidelink communication links are used in sidelink communication modes for transmitting signals, in particular, between the relay user device and the first user device, and between the relay user device and the second user device. Establishing a sidelink communication link may require providing PC5 setup configuration information to both the relay user device and the user device. The establishment of a sidelink communication link can then be initiated by sending a sidelink communication request (which may also be called a sidelink establishment request). Such a sidelink establishment request may be initiated, for example, by the relay user device or by the first or second user device.

[0029] Relay support information can be understood as information for establishing a sidelink communication mode in a non-terrestrial communication network. Such relay support information may be provided, in particular, to relay user equipment, first user equipment, second user equipment, and / or any other user equipment within a non-terrestrial communication network that are eligible to communicate in sidelink communication mode. Such relay support information may be obtained based on knowledge, measurements, and calculations performed within the non-terrestrial communication network by one or more of its network entities, such as base stations, access devices, and core network entities. Relay support information may include control support information regarding the conditions for switching to sidelink communication mode. For example, such control support information may include timing conditions, power conditions, radio conditions, and network conditions that must be met to establish sidelink communication mode. Relay support information may also include access support information for actually establishing sidelink communication mode. Such access support information may include high-level support information, in particular, such as user equipment access rights, sidelink identifiers, cryptographic keys, and the quality of service (i.e., QoS) level required to access sidelink communication mode. Access assistance information may also include low-level assistance information such as information about the radio interface in sidelink communication mode (e.g., PC5 interface), PC5 setup configuration information, and information for establishing a sidelink communication link. In particular, relay assistance information is specific to non-terrestrial contexts. For example, as a difference from the existing context of direct communication in terrestrial networks, relay assistance information may provide user equipment with assistance information for calculating the timing advance used to transmit signals through relay user equipment in sidelink communication mode. Furthermore, resource allocation, signal transmission, and radio interfaces may also be specific to non-terrestrial contexts.

[0030] Acquiring relay support information can be understood as determining, receiving, and / or measuring relay support information. Such relay support information may be acquired sequentially or at regular intervals according to pre-configured timings managed by the network. Different parts of the relay support information may be acquired at different times and / or from different entities. Such relay support information may be acquired as cell-specific information or general system information.

[0031] Transmitting at least a portion of the relay support information to the first and second user equipment can be understood as providing at least a portion of the relay support information to the first and second user equipment. For example, the first and second user equipment may be provided with support information to identify the relay user equipment to be used as a repeater in sidelink communication mode. The first and second user equipment may also receive support information that provides the conditions for accessing the relay user equipment and establishing sidelink communication mode. The first and second user equipment may also receive configuration information regarding the physical resources allocated to communicate in sidelink communication mode via the relay user equipment. The first and second user equipment may also receive support information for calculating timing advance in sidelink communication mode. The relay support information may be transmitted to the first and second user equipment by the relay user equipment, the base station(s) managing the cell(s) covering the locations of the first and second user equipment, the core network entity, and / or any other network entity of the non-terrestrial communication network.

[0032] Relaying a signal over first and second sidelink communication links using an established sidelink communication mode can be understood as the relay user equipment being configured to relay signals between the first and second user equipment once the sidelink communication mode is established. In particular, radio resources, radio interfaces, and radio links based on relay support information are used to relay signals in sidelink communication mode. Signal relaying may be performed based on specific sidelink control information (i.e., SCI) associated with the signal, and therefore the sidelink communication mode is used for signal relaying.

[0033] According to one embodiment, the method or at least some steps of the method are performed by relay user equipment.

[0034] As a result, this method proposes including, and potentially relying on, a relay user device implemented in a network access device to establish a sidelink communication mode. In particular, when the proposed method or at least some steps of the method are performed by the relay user device, relay support information may be received by the relay user device from the rest of the communication network. Optionally, some of such relay support information may then be transmitted (or forwarded) to the first and second user devices as relayed support information. Network entities of a non-terrestrial communication network may provide support information to the relay user device so that the relay user device can manage the establishment of a sidelink communication mode with at least the first and second user devices, and more generally with user devices eligible to communicate in a sidelink communication mode.

[0035] According to one embodiment, this method is The system further includes initiating the last of the first and second sidelink communication links based on the relay support information.

[0036] As a result, a first sidelink communication link and / or a second sidelink communication may be established by a non-terrestrial communication network initiating such establishment. Advantageously, the first and / or second sidelink communication links may be initiated based on acquired relay support information. For example, based on received relay support information including the identifier of a first user device and / or a second user device, as well as the low-level setup configuration of a sidelink communication interface (e.g., a PC5 radio interface), a relay user device mounted on a non-terrestrial access device may initiate a sidelink communication link with the first and / or second user device.

[0037] Initiating a sidelink communication link can be understood as sending a sidelink communication request (also called a sidelink establishment request) to request the establishment of a first and / or second sidelink communication link, respectively. To initiate a sidelink communication request, the device initiating the sidelink communication link may be provided with, for example, identifiers of the first and / or second user equipment in relay support information (e.g., PC5 or sidelink identifier), as well as a PC5 configuration.

[0038] According to one embodiment, this method is The method further includes transmitting additional support information to at least one of the first and second user devices, wherein the additional support information relates to a non-terrestrial communication network.

[0039] According to such an embodiment, additional supporting information is - System Information Block (SIB) related to non-terrestrial communication networks, - Data on satellite ephemeris in non-terrestrial communication networks, -Reference signals for network communication interfaces used in network communication modes. -Data related to network communication mode, - Data regarding the termination of sidelink communication mode, - Wireless link failure (RLF), recovery data, and -Data projected by a network access device relating to at least one cell covering at least one user device It includes at least one of the following elements.

[0040] As a result, this method proposes providing user equipment with additional network-related support information so that user equipment can favorably maintain updated synchronization with the network even when in side-link communication mode. Such additional support information may enable user equipment to still maintain communication via a network radio interface (e.g., a Uu radio interface) in order to communicate with other devices that are not eligible to communicate in side-link communication mode (e.g., other user equipment not covered by the same network access device).

[0041] Advantageously, the transmission of additional support information enables user equipment to simultaneously use sidelink communication mode (via relay user equipment) and network communication mode (particularly via conventional network infrastructure including core network, base stations, uplink, and downlink transmissions). User equipment is provided with additional support information and therefore with up-to-date knowledge regarding non-terrestrial communication networks. In particular, the additional support information enables user equipment to receive such knowledge even when feeder links are unavailable.

[0042] Additional support information can be understood as support information provided to at least the first and second user equipment to provide updated knowledge about non-terrestrial communication networks. Such additional support may include, for example, information for maintaining synchronization with the network, information about network communication interfaces (e.g., Uu radio interfaces), information for switching between sidelink communication mode and network communication mode, information about network constellations (e.g., ephemeris of satellite constellations), and information for recovering network communication links (e.g., Uu links) or feeder links after radio link failure (i.e., RLF).

[0043] A network communication mode can be understood as a communication structure on a non-terrestrial communication network in which communication of user equipment is managed by a base station, uplink and downlink signals are exchanged between the user equipment and the access device, and the signals are then forwarded to the core network by the user plane function via the gateway and base station. In particular, in such a network communication mode, several communication loops occur between the non-terrestrial access device and the Earth because signaling is managed by the core network, base station, and / or other network entities. For example, in a network communication mode, the radio resources allocated to user equipment for transmitting signals are managed by a base station that manages the cell covering the location of such user equipment. In such a network communication mode, user equipment may receive broadcast messages from the non-terrestrial communication network, for example, using SIB broadcasts. Such broadcast messages may be cell-specific, for example.

[0044] Data relating to network communication modes can be understood as supporting information regarding the network infrastructure and radio conditions for transmitting signals in network communication mode via a network communication interface (e.g., a Uu radio interface).

[0045] Data regarding the termination of sidelink communication mode can be understood as information that enables user equipment to have knowledge of when and how sidelink communication mode terminates, and how the switch back to network communication mode may occur. For example, such data may be timing conditions and / or radio conditions for accessing sidelink communication mode. Such data may depend in particular on the orbits of the satellite ephemeris and network access equipment, as well as the radio characteristics of the relay user equipment.

[0046] Wireless link failure recovery data can be understood as support information provided to user equipment to recover a failed wireless link used in network communication modes. For example, side-link communication mode may be provided as an alternative communication solution to ensure communication continuity during a wireless link failure. During such a wireless link failure, user equipment may receive additional support information via side-link communication mode, enabling wireless link recovery.

[0047] The data projected by the network access device for at least one cell can be understood as cell-specific support information provided to user equipment covered by such cell. Such data may include wireless resource allocation information, wireless conditions within the cell, upcoming cell switching that requires user equipment to perform a handover or cell reselection procedure, and timing advance updates in the cell.

[0048] In particular, when the proposed method is implemented by a relay user device, additional support information can be provided to the user device via the established sidelink communication link. Thus, the relay user device may transmit such additional support information, including reference signals specific to the network communication mode, in the sidelink communication mode, for example, on behalf of the base station or core network. Consequently, via the relay user device, the user device can still receive system information such as ephemeris, complementary synchronization information, and information for radio link recovery, even if the network communication interface and / or feeder link are not in use or unavailable.

[0049] According to one embodiment, the relay support information includes control support information relating to instructions for switching between network communication mode and sidelink communication mode.

[0050] As a result, relay support information may provide timing and / or wireless conditions for adopting a specific communication mode. In particular, control support information may be binary information indicating that user equipment may switch from network communication mode to sidelink communication mode, or vice versa.

[0051] Switching to a communication mode can be understood as adopting specific radio resources, timing advances, and communication protocols, and adapting the radio signaling to transmit a signal. For example, when transmitting a signal in network communication mode, the radio resources to be used to transmit the signal may depend on base station resource management, the radio interface to be used is the network communication interface (typically a Uu radio interface), and the timing advance to be used depends on the relative positions of the access device, user equipment, base station, and reference points between the base station and the access device. When transmitting a signal in sidelink communication mode, the radio resources and timing advance to be used to transmit the signal depend, for example, on the content of the relay support information and the location of the relay user equipment. Furthermore, the transmission may include sidelink control information (i.e., SLI) that is specifically adapted to the non-terrestrial context, for example, by including the identifier of the relay user equipment in the SCI for signal transmission. Thus, switching to a communication mode means relying on specific support information provided by the non-terrestrial communication network to adapt the signaling of the user equipment.

[0052] According to one embodiment, the relay support information includes access support information relating to data that identifies user equipment that is connected to a non-terrestrial network and is eligible to communicate with relay user equipment via side-link communication mode.

[0053] As a result, relay assistance information can advantageously enable the identification of devices that can transmit and / or receive signals via sidelink communication mode. Therefore, when such access assistance information is obtained by a relay user device, such access assistance information may provide the relay user device with a list of eligible user devices. Thus, the relay user device will relay signals to user devices whose identifiers belong to such a list. When such access assistance information is provided to a given user device, that user device has knowledge of its opportunity to access sidelink communication mode and of other user devices that can communicate with the given user device in sidelink communication mode.

[0054] User equipment eligible to communicate with a relay user equipment via sidelink communication mode can be understood as user equipment whose coverage enables access to sidelink communication mode using the relay user equipment as a relay. For example, such eligible user equipment may refer to all equipment covered by the same access equipment that houses the relay user equipment. Such eligible user equipment may include equipment covered by different access equipment linked by an intersatellite link (i.e., ISL), one of which houses the relay user equipment. Such eligible user equipment may also include equipment that has radio capability, quality of service level, service priority level, or any other service or radio conditions for accessing sidelink communication mode.

[0055] Access assistance information can be understood as high-level and low-level assistance information for accessing sidelink communication mode. Therefore, such access assistance information may include identifiers of eligible user equipment and cryptographic keys for signaling in sidelink communication mode. Such access assistance information may also include radio information for establishing a sidelink communication link or sidelink communication interface, such as PC5 setup configuration information.

[0056] According to one embodiment, relay support information, for example, access support information, - Setup configuration information for establishing a sidelink communication interface in sidelink communication mode. -Data relating to timing advance to be applied by at least the first and second user devices in sidelink communication mode, and - Data regarding resource allocation for sidelink communication mode It includes at least one of the following elements.

[0057] According to one embodiment, before relaying the signal, Receiving a sidelink communication request from at least the first user device, Based on relay support information and the sidelink communication request, establish a first sidelink communication link. It also includes.

[0058] As a result, this method proposes establishing a sidelink communication mode initiated by the user equipment. Such an embodiment advantageously allows the network to remain passive and conserves computational resources related to establishing the first sidelink communication link. In particular, this method proposes providing the first user equipment with relay support information so that such a sidelink communication request can be initiated on the first user equipment side at a timing selected by that first user equipment. For example, by providing the first user equipment with an identifier of the relay user equipment and sidelink setup configuration information, the establishment of the first sidelink communication link can be initiated by the first user equipment.

[0059] In another aspect of this disclosure, a non-terrestrial communication network is proposed, which includes at least a network access device equipped with relay user equipment, and the network is configured to perform the proposed method.

[0060] In another aspect of the present disclosure, a relay user device mounted on a network access device of a non-terrestrial communication network is proposed, which is configured to perform the proposed method, and such method, when performed by the relay user device, is referred to as the relay method.

[0061] In another aspect of the present disclosure, a network access device, preferably a satellite, is proposed that is included in a non-terrestrial communication network and carries relay user equipment, the network access device includes at least network communications, Uu, interface and sidelink communications, PC5, interface, and the network access device is configured to perform the proposed method.

[0062] In another aspect of this disclosure, a computer-readable non-temporary recording medium is proposed, which is registered to implement the Method when the software is executed by a processor.

[0063] A second aspect of this disclosure relates to a communication method performed by a first user device to transmit a signal to at least a second user device in a non-terrestrial communication network, wherein the communication method is To receive user support information at least related to the establishment of a sidelink communication mode with relay user equipment, At least based on the user support information, establish a first sidelink communication link with the relay user equipment. To transmit a signal to a second user device via the established first sidelink communication link. A communication method including the following is proposed.

[0064] As a result, the proposed communication allows user equipment (referred to here as the first user equipment) to access a sidelink communication mode, in which signals can be transmitted in direct communication mode using relay user equipment as a relay. Such a sidelink communication mode makes it possible to avoid several communication loops between non-terrestrial access equipment covering the first user equipment, typically between satellites and Earth, thus shortening the round-trip time (i.e., RTT) of transmission and thus improving the service latency of the user equipment. Furthermore, such a communication method provides an advantageous alternative to conventional network communication modes involving signaling with base stations and the core network, where such communication loops occur. Such an alternative is also advantageously useful in cases of radio link failures (i.e., RLF), Uu link failures, feeder link saturation, etc., which lead to interruptions or delays in signal transmission on non-terrestrial communication links.

[0065] In particular, in a non-terrestrial context, the establishment of such a sidelink communication mode is made possible by providing user assistance information to the first user equipment (more generally, the user equipment accessing the sidelink communication mode). Such user assistance information may be provided, for example, by a network entity of the non-terrestrial communication network or by a relay user equipment. Such user assistance information enables the first user equipment to perform network assistance procedures for accessing such a sidelink communication mode. Advantageously, by relying on user assistance information as proposed, access to the sidelink communication mode becomes possible in the context of a non-terrestrial communication network, where the conventional discovery or resource detection phase present in terrestrial D2D communications can be time- and / or resource-intensive and / or may fail to meet the service requirements of most 5G applications serviced by user equipment, for example, particularly in terms of data throughput rate or latency.

[0066] User assistance information can be understood as assistance information provided to a first user device for accessing a sidelink communication mode. User assistance information may, for example, correspond to a portion of relay assistance information obtained by a network in a manner consistent with a first aspect of this disclosure. Such user assistance information may be received by the first user device from a relay user device, a base station, a core network entity, any other network entity, some of the aforementioned entities, or more generally from a non-terrestrial communication network. Such user assistance information may provide knowledge of the opportunity to access a sidelink communication mode, radio conditions and / or timing conditions for such access, link setup information for accessing the communication interface for such access, timing advances used to transmit signals in sidelink communication, identification information of the relay user device, and resource allocation procedures to be performed for such access.

[0067] Similarly, a second user device, more generally any user device eligible to access the sidelink communication mode, may receive such user assistance information or a portion of such user assistance information.

[0068] According to one embodiment, the communication method is: The system further includes initiating a first sidelink communication link with the relay user equipment by sending a sidelink communication request based at least on the user support information.

[0069] As a result, the communication method proposes providing user assistance information to a first user device so that such a first user device can initiate a first sidelink communication link to access sidelink communication mode. For example, by including the identifier of the relay user device and PC5 link setup configuration information in the user assistance information, the first user device can initiate a first sidelink communication link by sending a sidelink communication request to the relay user device. In particular, the timing of such an initiation may be selected by the user device according to its requirements and capabilities, provided that the timing conditions for accessing sidelink communication mode are met.

[0070] According to one embodiment, the communication method is: This further includes receiving additional support information regarding non-terrestrial communication networks.

[0071] As a result, while accessing sidelink communication mode and transmitting signals in such sidelink communication mode, the first user equipment can still update its knowledge of the non-terrestrial communication network and achieve synchronization with the Uu radio interface so that the network communication mode can still be used concurrently with the sidelink communication mode (or can remain up-to-date on the user equipment side).

[0072] According to one embodiment, the user support information includes at least data relating to the identification of the relay user equipment.

[0073] According to one embodiment, user support information is - Setup configuration information for establishing a sidelink communication interface in sidelink communication mode. - Data regarding the timing advance to be applied in side-link communication mode, - Data regarding resource allocation for sidelink communication mode It includes at least one of the following elements.

[0074] According to one embodiment, a portion of the user support information is received in side-link communication mode.

[0075] For example, such a portion of user support information may be received from the relay user device after the relay user device has initiated a first sidelink communication link by sending a sidelink communication request to the first user device.

[0076] Receiving information in sidelink communication mode can be understood as receiving information once sidelink communication mode is established. Such sidelink communication mode can be established after a first signal corresponding to a sidelink establishment request is transmitted from one end device of the sidelink communication link to the other end device of the sidelink communication link.

[0077] According to one embodiment, the communication method is: This further includes exchanging data with the relay user equipment regarding the establishment of a second sidelink communication link between the relay user equipment and the second user equipment, The transmission of signals to the second user device further depends on the second communication link.

[0078] Advantageously, the first user device may be involved in establishing a second sidelink communication link between the second user device and the relay user device. For example, data concerning the establishment of a sidelink communication link exchanged between the first device and the relay user device may be a message from the first user device to the relay user device requesting a sidelink communication mode with the second user device (and thus requesting the establishment of a second sidelink communication link). Such data may also be information provided to the first user device by the relay user device to inform the first user device that the second user device is a user device eligible for sidelink communication mode, and / or that a second sidelink communication link has been established and is valid for transmitting signals to the second user device via sidelink communication mode.

[0079] In another aspect of this disclosure, a first user device is proposed that is connected to a non-terrestrial communication network and configured to perform the proposed communication method.

[0080] In another aspect of this disclosure, a computer-readable non-temporary recording medium is proposed, which is registered to implement a communication method when the software is executed by a processor.

[0081] In another aspect of the present disclosure, a switching method performed by a network entity to establish a communication switching in a non-terrestrial communication network for signals between a first user device and a second user device, wherein the communication switching is performed between a network communication mode and a side-link communication mode, and the switching method is To relay signals between the first user device and the second user device, determine at least relay user devices associated with the first user device and the second user device. At a minimum, determine network support information regarding the establishment of side-link communication mode. Transmitting at least a portion of the network support information to the relay user equipment via network communication mode. At least based on the network support information, establish a communication switch between network communication mode and sidelink communication mode. A switching method is proposed, which includes [this].

[0082] As a result, the switching method makes it possible to determine the opportunity to establish a sidelink communication mode between user devices connected to a non-terrestrial communication network via relay user devices. Accordingly, the switching method proposes to determine or identify relay user devices that can relay signals between first and second user devices. The switching method also makes it possible to provide a procedure for enabling all involved user devices to switch to sidelink communication mode. Such a procedure is particularly specific to the non-terrestrial context. To that end, the switching method advantageously includes determining network support information to assist both the identified relay user devices and the user devices eligible to access sidelink communication mode when accessing sidelink communication mode.

[0083] A network entity can be understood as a non-terrestrial entity of a non-terrestrial communication network. Such a network entity may be, for example, an access device, a satellite, a base station, or a gNodeB (i.e., gNB), a core network entity, or a session management function (i.e., SMF) entity. Such a network entity is not a relay user device, a first user device, a second user device, or any user device connected to the network.

[0084] Network-assisted information can be understood as information determined by a network entity regarding the establishment of a sidelink communication mode. Such network-assisted information may refer to any information measured, determined, calculated, or estimated by a network entity based on signaling in a non-terrestrial communication network, core network knowledge, and pre-configured network information. Such network-assisted information may include, for example, knowledge of access associations between base stations and access devices, cell coverage, satellite ephemeris, dynamic or quasi-static mapping between base stations and the access types provided by such base stations, and configuration information from operational and maintenance functions (OAM). Network-assisted information may also be determined by different entities in the non-terrestrial communication network. Some of the network-assisted information transmitted to relay user equipment may correspond to relay-assisted information obtained in the manner of the first aspect of this disclosure.

[0085] Determining a relay user device associated with at least a first user device and a second user device can be understood as identifying a relay user device implemented in a network access device that is qualified to function as a relay between the first and second user devices. Such a determination may depend on the location, capabilities, and requirements of the first user device, the second user device, and the relay user device, respectively. A relay user device may be identified by a relay user device identifier, such an identifier enabling a device to communicate with such a relay user device by including that identifier in the transmitted signal (e.g., after a potential identification protocol such as the exchange of cryptographic keys).

[0086] Establishing a communication switch between network communication mode and sidelink communication mode can be understood as a network entity registering a switch between the two communication modes. Thus, the network has knowledge that the involved user equipment, including relay user equipment, first user equipment, and second user equipment, will switch to resource allocation procedures and signaling properties specific to sidelink or network communication mode. In particular, establishing such a communication switch makes it possible to update the non-terrestrial communication network's knowledge of the network's radio conditions, such as congestion levels on different access channels, saturation levels on feeder links, and bandwidth saturation levels, thereby improving the management of the non-terrestrial communication network's radio resources and capabilities. Such knowledge can also enable the network entity to manage the use of sidelink communication mode, network communication mode, or both, depending on requirements, capabilities, and the overall radio conditions within the network.

[0087] According to one embodiment, the switching method is: The method further includes transmitting user assistance information to at least a first user device and a second user device via a network communication mode. In such embodiments, the communication switching of the switching method can be established based on the network assistance information and / or user assistance information.

[0088] As a result, the network entity may provide the first and second user devices with user assistance information relating to the establishment of at least a sidelink communication mode, as proposed in a second aspect of this disclosure. Such user assistance information may be transmitted to the first and second user devices, in particular, using a network communication interface such as a Uu radio interface.

[0089] According to one embodiment, the switching method is: The further includes transmitting additional support information to at least one of relay user equipment, first user equipment, and second user equipment, wherein the additional support information relates to a non-terrestrial communication network.

[0090] As a result, simultaneously with the establishment of the sidelink communication mode, the switching method can provide additional support information to the user equipment, enabling the user equipment to maintain up-to-date information regarding the non-terrestrial communication network.

[0091] According to one embodiment, the relay user equipment is mounted on a first network access device of a non-terrestrial communication network, and the relay user equipment comprises at least, - Coverage zones for the first user equipment and the second user equipment by the first network access device, - An intersatellite link (ISL) between at least the first network access device and a second network access device of a non-terrestrial communication network covering at least one of the first and second user devices. It will be determined accordingly.

[0092] As a result, the relay user equipment is advantageously determined in accordance with the coverage conditions of the first and second user equipment, as well as the propagation conditions and characteristics between the first and second user equipment and the relay user equipment.

[0093] In another aspect of this disclosure, a network entity of a non-terrestrial communications network is proposed that is configured to perform a switching method as proposed.

[0094] In another aspect of this disclosure, a computer-readable non-temporary recording medium is proposed, in which the software is registered to perform a switching method when the software is executed by a processor. [Brief explanation of the drawing]

[0095] Other features, details, and benefits are shown in the detailed description and drawings below.

[0096] [Figure 1] This is an example of a satellite communication network using prior art.

[0097] [Figure 2] This is another example of a satellite communication network using prior art.

[0098] [Figure 3] This is another example of a satellite communication network using prior art.

[0099] [Figure 4] This is another example of a satellite communication network using prior art.

[0100] [Figure 5] This is part of a satellite communication network using a side-link communication mode according to one embodiment.

[0101] [Figure 6] This flowchart shows the steps of a relay method according to one embodiment.

[0102] [Figure 7] This flowchart shows the steps of a communication method according to one embodiment.

[0103] [Figure 8] This flowchart shows the steps of a method for relaying a signal according to one embodiment.

[0104] [Figure 9] The following steps outline a method for relaying a signal according to one embodiment. [Modes for carrying out the invention]

[0105] Next, refer to Figures 1, 2, and 3. Figures 1-3 represent some embodiments of non-terrestrial communication networks. This disclosure is not limited to any specific standard used in such networks, but for simplicity, this disclosure is described in the context of fifth-generation new radio (i.e., 5G NR) standards. In particular, such non-terrestrial communication networks may be satellite communication networks (NW).

[0106] Referring to Figures 1 to 3, such a non-terrestrial communication network NW may include at least one network entity. Such a network entity may be, for example, an access device. Such an access device may be, for example, a satellite SAT. Such a satellite SAT may be deployed in a non-geostationary orbit (i.e., NGSO), such as low Earth orbit (LEO) or medium Earth orbit (MEO). Thus, the satellite SAT has an altitude of 300 to 30,000 kilometers above the Earth's surface. In another embodiment, the satellite communication network NW may include several satellite SAT1, SAT2, as shown in Figure 4. In particular, several satellite SAT1, SAT2 may be linked via an inter-satellite link (i.e., ISL), as shown in Figure 4. In another embodiment (not shown), the access device of the non-terrestrial communication network NW may include a high-altitude platform station access device or a high-altitude pseudo-satellite, i.e., a HAPS access device. The network entity may also refer to other network devices such as gateways, base stations, and core network entities, as will be further detailed, for example. The term "network entity" may be understood as an entity of a non-terrestrial communications network NW and not as an end-user device (e.g., user equipment). This disclosure details embodiments based on a non-terrestrial communications network NW corresponding to a satellite communications network and access devices for a non-terrestrial communications network NW corresponding to a satellite SAT. In other embodiments, other access devices providing connectivity (e.g., HAPS) may be considered.

[0107] A satellite SAT deploys at least one satellite beam that projects its respective beam footprint onto the Earth's surface, and such a beam footprint forms one or more cells. For example, referring to Figures 1 to 4, each satellite SAT, SAT1, and SAT2 deploys one satellite beam. The satellite beam is configured in a specific frequency band so that data can be sent and received through the satellite beam according to radio resources allocated to the frequency band configured for the satellite beam by the satellite SAT. These radio resources may be shared according to frequency division multiplexing (e.g., frequency division multiplexing (FDM) or orthogonal frequency division multiplexing (OFDM)), time division multiplexing (e.g., time division multiplexing (TDM)), code division multiplexing (code division multiplexing (CDM)), polarization multiplexing, or a combination thereof.

[0108] The allocation of radio resources for satellite beams is achieved by at least one base station BS, also known as gNodeB or gNB. Each base station BS manages radio resources for one or more satellite beams. In particular, in the context of the 5G NR communication standard, a base station BS may include two distinct entities: a centralized unit (also known as CU or gNB-CU) and a distributed unit (also known as DU or gNB-DU). The centralized unit of the base station BS may be configured to support the protocol layers of the network NW, such as the Radio Resource Control (i.e., RRC) layer, the Service Data Adaptive Protocol (i.e., SDAP), and the Packet Data Convergence Protocol (i.e., PDCP). Such RRC, SDAP, and PDCP protocol layers are referred to as the upper protocol layers (or higher protocol layers) over lower layer protocols such as Radio Link Control (i.e., RLC), Medium Access Control (i.e., MAC), and the Physical Layer (PHY). Such lower layer protocols may be supported by the distributed unit of the base station BS. A distributed unit of a base station BS may manage one or more satellite beams, and a control unit of a base station BS may support multiple distributed units of the base station BS.

[0109] In one embodiment, the full base station BS (i.e., both the gNB-CU and gNB-DU) may be physically separate from and at a distance from the satellite SAT. For example, such a base station BS may be located on the Earth's surface, as shown in Figure 1. In such an embodiment, the satellite SAT may be said to have a transparent payload (or sometimes called a vented pipe structure). In other words, the satellite SAT may not have any substantial processing capacity and simply relays radio protocols between the satellite beam and the Earth-based base station BS.

[0110] The base station BS may also be implemented and deployed on a satellite SAT. In one embodiment, as shown in Figure 2, a full base station BS (i.e., both gNB-CU and gNB-DU) may be mounted on the satellite SAT. In another embodiment, as shown in Figure 3, distributed units of the base station BS may be mounted on the satellite SAT, while the control unit of the base station BS may be on the ground. In such embodiments where the satellite SAT carries some or all of the base station BS, the satellite SAT may be said to have a regenerative payload.

[0111] The satellite SAT may also be linked via feeder link FL1 to at least one ground station, also called a gateway node or gateway GW. Such a gateway GW may be located on the ground, as shown in Figures 1-3. The gateway GW, acting as the feeder link FL1 interface, may interface the radio access network (i.e., RAN) with the 5G core network (i.e., CN) when the base station BS is implemented on the satellite SAT, as shown in Figure 2. The gateway GW may also interface the physical layer of user equipment UE1, UE2 when the base station BS is located on Earth. The gateway GW may interface the satellite SAT, more generally the satellite access network, with 5G network functions located on Earth. Network functions may include, in particular, user plane functions UPF, as shown in Figures 1-3. In particular, user plane functions UPF may be configured to interconnect the radio access network with the data network (i.e., DN) to route packets and forward data packets, depending on pre-configured parameters and measurements such as available capacity, network NW policies, link performance, and / or the type of end-user profile using such packets.

[0112] A satellite communications network (NW) may provide connectivity to multiple devices, including user devices UE1 and UE2. User devices UE1 and UE2 may be covered by one or more satellite beam footprints. For example, referring to Figures 1-3, user devices UE1 and UE2 are covered by the same cell projected by satellite SAT. In another example, referring to Figure 4, user device UE1 is covered by a first cell projected by satellite SAT1, and user device UE2 is covered by a second cell projected by satellite SAT2. The cell covering user devices UE1 and UE2 may be called a serving cell. When user devices UE1 and UE2 are connected to a serving cell, they may be allocated radio resources by the corresponding base station (BS) that manages the serving cell's radio resources. User devices UE1 and UE2 may be in a state of being connected via a serving cell (RRC_CONNECTED). To this end, user devices UE1 and UE2 may access the satellite communications network NW via initial access, for example, through a random access (i.e., RACH) procedure to a serving cell of the satellite communications network NW. User devices UE1 and UE2 may also access the satellite communications network NW via a handover procedure, for example, when user devices UE1 and UE2 are connected to another cell and switch to a serving cell. User devices UE1 and UE2 may remain connected to the satellite communications network NW by accessing several consecutive cells of the satellite communications network, particularly due to the non-geostationary orbit characteristics of the satellite SAT, which result in a moving satellite beam footprint on the ground and / or the movement of user devices UE1 and UE2.

[0113] While connected, user devices UE1 and UE2 may transmit control signaling and / or traffic data to the base station BS. For example, user devices UE1 and UE2 may perform data transmission, send scheduling requests (i.e., SRs) and / or send buffer status reports (or BSRs) to the base station BS. User devices UE1 and UE2 may also perform uplink transmissions.

[0114] Transmissions performed between user devices UE1 and UE2 and the satellite SAT (or more generally, using network access devices) are carried out over the service link, in particular via a network communication interface, also known as the network communication interface Ni. Such a network communication interface Ni may specifically refer to the Uu interface.

[0115] The traffic data and signaling transmitted by user devices UE1 and UE2 may be intended to provide a variety of services, particularly in the context of use cases such as enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), or ultra-high reliability low-latency communications (URLLC). Such services provided by user devices UE1 and UE2 have quality of service (i.e., QoS) requirements, particularly regarding reliability and latency. Before transmitting the traffic data, user devices UE1 and UE2 may transmit buffered traffic data to the base station BS, and / or various signals (such as SR and BSR signals). The services provided by user devices UE1 and UE2 may also involve user devices UE1 and UE2 communicating with each other.

[0116] When connected, user devices UE1 and UE2 may also receive signals from at least the base station BS, the core network CN, and / or any other network entities. As previously mentioned, such network entities may refer to base stations, satellites, or any other entities on the network side. For example, user devices UE may receive system information (i.e., SI), control information, network commands, and / or data signals. For example, user devices UE1 and UE2 may receive system information blocks (i.e., SIBs) from various network entities via the cell covering the location of user devices UE1 and UE2. User devices UE1 and UE2 may receive network information, epoch time, radio resource configuration information, and cell-related information regarding satellite ephemeris. User devices UE1 and UE2 may receive downlink transmissions. User devices UE1 and UE2 may also receive commands (or orders) and coordination information from network entities. In particular, the user device UE may receive timing advance commands (i.e., TACs) via the media access control (i.e., MAC) layer, also known as MAC-CE TACs (i.e., MAC control element timing advance commands).

[0117] In particular, referring to the embodiments shown in Figures 1 to 3, we can consider a first user device UE1 and a second user device UE2 connected to a satellite communication network NW via a cell projected by a satellite SAT. Specifically, when the first user device UE1 and the second user device UE2 attempt to establish a communication protocol, for example, when the first user device UE1 attempts to transmit a communication signal such as a data signal to the second user device UE2, a typical communication path is represented by several thick arrows in each of Figures 1 to 3. Such a communication path is, - Uplink signal from the first user device UE1 to satellite SAT1 via network communication interface Ni, -Transmission from satellite SAT to ground gateway GW via feeder link FL1, - Relay transmission from the gateway to the core network CN, particularly to core network functions including the user plane function UPF. - The reverse communication path from the core network NW and core network functions to the gateway GW, and further back to the satellite SAT via feeder link FL1, as well as - Downlink signals (e.g., data packets) from the satellite SAT to the second user device UE2 via the network communication interface Ni. It contains a series of them.

[0118] Such a communication path includes a communication loop on the core network side, particularly because the communication path involves a round-trip path between the Earth's surface and the satellite (SAT). Such a communication path actually involves two transmissions via feeder link FL1.

[0119] In particular, as shown in Figures 2 and 3, even when a base station BS or a part of a base station BS is implemented and mounted on a satellite SAT, the communication path for establishing communication between the first user equipment UE1 and the second user equipment UE2 via the satellite communication network NW still involves two transmissions via the communication loop and feeder link FL1 on the core network side.

[0120] If a first user device UE1 is covered by a satellite beam footprint projected by satellite SAT1 and attempts to transmit a communication signal to a second user device UE2, which is covered by another satellite beam footprint projected by another satellite SAT2, and satellites SAT1 and SAT2 are interconnected via an intersatellite link ISL, then a communication loop on the core network side still occurs. In fact, as shown in Figure 4, two transmissions occur via feeder link FL2. In another embodiment (not shown in Figure 4), satellite SAT1 may have its own feeder link FL1 with a gateway GW or another gateway, but even in such an embodiment, two transmissions still occur between satellites SAT1 and SAT2 and the ground (i.e., one transmission via feeder link FL1 and one transmission via feeder link FL2).

[0121] Such communication loops and dual transmissions over feeder link FL1 result in transmission delays, feeder link overload, and / or even feeder link failures. These adverse conditions still occur, in particular, when user equipment UE1 and UE2 are covered by the same satellite or by satellites linked via the inter-satellite link ISL, as shown in the architectures of Figures 1-4.

[0122] To avoid such communication loops in the communication path between two user equipment UE1 and UE2 under the same satellite coverage, or under the coverage of satellites linked by an inter-satellite link (ISL), a local user plane function (UPF) and a full base station (BS) can be implemented and mounted on the satellite SAT. However, a satellite SAT equipped with a full user plane function (UPF) and base station (BS) incurs considerable additional costs (particularly computational costs) for launching into orbit.

[0123] To address these shortcomings, the Disclosure proposes a satellite communication network system as shown in Figure 5. The Disclosure also proposes method steps for enabling the transmission of at least one signal between a first user equipment UE1 and a second user equipment UE2, as shown in Figures 6, 7, 8, and / or 9. In particular, the proposed system and method consider the transmission of at least one signal between a first user equipment UE1 and a second user equipment UE2 that share similar coverage properties. Sharing similar coverage properties means, - The first user equipment UE1 and the second user equipment UE2 are covered by one or more satellite beam footprints projected by the same satellite SAT, as shown in Figures 1-3 and 5, or -As shown in Figure 4, the first user equipment UE1 and the second user equipment UE2 are covered by one or more satellite beam footprints projected by several satellites SAT1, SAT2, and such satellites SAT1, SAT2 are linked by an inter-satellite link ISL. It can be understood that this is the case.

[0124] Referring to Figure 5, a portion of the non-terrestrial communications network NW proposed in this disclosure is shown. Similar to the portion of the satellite communications network NW shown in Figures 1 to 4, the proposed satellite communications network NW shown in Figure 5 may include a radio access network (or RAN) and a core network side. More specifically, the satellite communications network NW may include access devices that provide connectivity to end users (e.g., user equipment UE1, UE2). Such access devices may be satellite SATs that project one or more satellite beam footprints, such as satellite beam footprints covering the locations of user equipment UE1, UE2. The non-terrestrial communications network NW may also include a gateway GW, at least one base station BS that manages the radio resources of the cell(s) formed by the satellite beam footprints, a core network CN, and one or more core network functions, such as a user plane function UPF. In another embodiment, end-user connectivity may be provided by another network entity other than the satellite SAT, in particular by another access device, such as a HAPS. In another embodiment, part of the non-terrestrial communication network NW may include several satellites SAT1, SAT2, and these satellites SAT1, SAT2 are interconnected by an inter-satellite link ISL, as shown in Figure 4.

[0125] At least the first user equipment UE1 and the second user equipment UE2 may be connected to a satellite communications network NW. The first user equipment UE1 and the second user equipment UE2 are considered to share similar coverage properties. In particular, in the context of this disclosure, the first user equipment UE1 and the second user equipment UE2 have an established network communication mode with the radio access network provided by the satellite communications network NW, at least in the initial stages (or initial steps) of this disclosure. In other words, the first user equipment UE1 and the second user equipment UE2 transmit uplink and downlink signals via a base station BS that allocates radio resources to the user equipment UE1 and UE2 in receiving and transmitting control information and / or data traffic. Such network communication (or network communication mode), also called network-to-device communication, is illustrated, for example, in Figures 1 to 4. As shown in Figures 1 to 4, such network communication mode between user equipment UE1 and UE2 and an access device of the satellite communications network NW (e.g., satellite SAT) depends on a network communication interface Ni. Such a network communication interface Ni may also be a Uu wireless interface.

[0126] In network communication mode, the first user device UE1 and the second user device UE2 may receive network information from different network entities (e.g., core network entities, base stations providing services to cells covering user devices UE1 and UE2, satellite SAT, etc.). Such network information may include, for example, broadcast system information (i.e., SI), synchronization information, satellite ephemeris information, Uu reference signals, epoch time, radio resource configuration information, and cell-related information. Such network information may be received specifically by user devices UE1 and UE2, for example, as unicast signals transmitted from base station BS to user devices UE1 and UE2 via dedicated downlink signaling. Such network information may also be common information transmitted to several devices, including user devices UE1 and UE2, via broadcast or groupcast channels, for example, as groupcast or broadcast signals. For example, intra-cell network information may be received by all devices covered by the same cell. User devices UE1 and UE2 may also receive network commands and coordination information from network entities. In particular, user devices UE1 and UE2 may receive timing advance commands (i.e., TACs) via the media access control (i.e., MAC) layer, also known as MAC-CE TACs (i.e., MAC control element timing advance commands).

[0127] In one embodiment, the disclosure proposes a switching method for switching from a network communication mode as shown in Figures 1 to 4 to a sidelink communication mode as shown in Figure 5. In one embodiment, the disclosure proposes a relay method for performing transmission relay between separate user devices in sidelink communication mode without requiring several round-trip transmissions between the access device and the ground. In one embodiment, the disclosure proposes a communication method for user devices UE1 and UE2 to exchange signals via sidelink communication mode.

[0128] The sidelink communication mode can be understood as a mode in which user equipment UE1 and UE2 can communicate with each other without transmitting signals via base station BS. In particular, in the proposed sidelink communication mode, the communication path between the first user equipment UE1 and the second user equipment UE2 for transmitting signals from the first user equipment UE1 and the second user equipment UE2 does not require any of the loops at the user plane function UPF breakout point and any of the transmissions between the satellite SAT and the ground via feeder link FL1.

[0129] To configure such a sidelink communication mode in the context of a non-terrestrial communication network NW, Figure 5 details the schematic architecture of user equipment UE1, UE2, core network entity CN, and relay user equipment UER in such a non-terrestrial communication network NW.

[0130] The core network entity CN may be configured to transmit network information relating to a non-terrestrial network NW to other network entities and / or user devices UE1, UE2. The core network entity CN may also be configured to perform a switching method for switching the communication mode of user devices UE1, UE2 from network communication mode to side-link communication mode. Such a switching method is further detailed in Figure 8. To this end, the core network entity CN may comprise at least a core network computing circuit comprising a processing unit PROC-N, a memory unit MEM-N, and a communication unit COM-N.

[0131] User devices UE1 and UE2 may be configured to perform a communication method in order to communicate with other user devices. A schematic architecture of the first user device UE1 is detailed in Figure 5, but such an architecture may also be applied to other user devices, such as the second user device UE2. Such a switching method is further detailed in Figure 8. To perform the communication method, user devices UE1 and UE2 may include at least a user device computing circuit comprising a processing unit PROC-1, a memory unit MEM-1, and a communication unit COM-1.

[0132] A relay user equipment UER can be understood as a relay device for relaying signals transmitted between a first user equipment UE1 and a second user equipment UE2 in sidelink communication mode. Such a relay user equipment UER may be installed in a network entity corresponding to an access device of a non-terrestrial communication network NW, in particular. A relay user equipment UER may be installed in a satellite that projects a satellite beam footprint covering the first user equipment UE1 and the second user equipment UE2, as shown in Figure 5. A common relay user equipment UER can relay signals between multiple user equipment UE1, UE2 that share similar coverage properties. For example, user equipment UE1 and UE2 covered by the same satellite beam footprint may share the same relay user equipment UER. A relay user equipment UER may be configured to perform a relay method for relaying signals at least between the first user equipment UE1 and the second user equipment UE2. Such a relay method is further detailed in Figure 6. To this end, the relay user equipment may include at least a relay computing circuit comprising a processing unit PROC-R, a memory unit MEM-R, and a communication unit COM-R.

[0133] Next, refer to Figure 6. Figure 6 is a flowchart illustrating the steps of a relay method performed by a relay user device UER to relay a signal between at least a first user device UE1 and a second user device UE2.

[0134] In the context of this disclosure, when the relay method is executed, the first user device UE1 and the second user device UE2 first communicate via network communication mode.

[0135] In step 610, the relay user equipment UER, mounted on the satellite SAT (or more generally, on an access device of a non-terrestrial communications network NW), receives relay support information. Such relay support information may be received by the relay user equipment UER via feeder link FL1. Such relay support information may be transmitted to the relay user equipment UER by one or more network entities. For example, the relay support information may be transmitted by the core network entity CN and forwarded to the relay user equipment UER. The relay support information may also be transmitted to the relay user equipment UER by another network entity, such as a base station BS, or by another access device or another satellite SAT, for example, via the inter-satellite link ISL.

[0136] Relay support information may be provided to the relay user equipment UER to enable the establishment of a sidelink communication link between the relay user equipment UER and eligible user equipment UE1 and UE2. Eligible user equipment UE1 and UE2 can be understood as user equipment UE1 and UE2 connected to a non-terrestrial communication network NW, which is coverage that enables communication with the relay user equipment UER in sidelink communication mode. In particular, by receiving the relay support information in step 610, the relay user equipment UER performs the network support discovery phase. In other words, the relay user equipment UER can identify eligible user equipment UE1 and UE2 from which a sidelink communication link can be established based on the received relay support information.

[0137] The relay support information received by the relay user equipment (UER) may include relay control support information, more simply called control support information.

[0138] Control support information may indicate switching between network communication mode and sidelink communication mode. Such control support information may include, for example, binary values ​​indicating that user devices UE1 and UE2 can switch to another communication mode (base station or sidelink). Such control support information may also include data regarding the conditions for switching to sidelink and / or network communication mode, such as timers, timing conditions, and signal quality conditions (e.g., the required level of the reference signal received power, i.e., RSRP, on the user device side).

[0139] The relay support information received by the relay user device UER may also include relay access support information, more simply called access support information. This access support information may correspond to data that enables user devices UE1 and UE2 to access sidelink communication mode. In particular, such access support information may include high-level and low-level access support information.

[0140] High-level access assistance information may include data identifying user devices that are qualified to communicate with a relay user device UER in sidelink communication mode by establishing a sidelink communication link with each qualified user device UE1, UE2. Qualified user devices UE1, UE2 for a given relay user device UER may refer to user devices covered by the satellite beam footprint projected by the satellite SAT carrying the relay user device UER. Such qualified user devices UE1, UE2 may be listed in the high-level access assistance information as having the right to communicate in sidelink communication mode via the relay user device UER. Therefore, such high-level access assistance information may correspond to user device access rights to sidelink communication mode, sidelink identifiers, cryptographic keys, and required levels of quality of service (or QoS) parameters. Thus, high-level access assistance information may include a list of user device identifiers, a list of services, a list of priorities, and / or required levels of quality of service (or QoS) parameters for accessing sidelink communication mode.

[0141] Low-level access assistance information may correspond to information about the sidelink communication radio interface, such as information for the PC5 setup configuration. In other words, low-level access assistance information may correspond to interface setup configuration information for establishing a sidelink communication interface, such as the PC5 radio interface. Therefore, low-level access assistance information may include PC5 setup configuration information. Low-level access assistance information may also provide information for eligible user equipment UE1, UE2 to access the sidelink communication interface. To this end, low-level access assistance information may also include data regarding switching to sidelink communication mode and / or resource allocation for communication in sidelink communication mode. For example, access assistance information may include information about the resource pool used to transmit signals in sidelink communication mode. Access assistance information may include information about one or more resource allocation modes for eligible user equipment UE1, UE2 to which radio resources for signal transmission in sidelink communication mode are allocated. For example, access assistance information may include information about resource allocation procedures (e.g., scheduled resource allocation by base station BS, or resource sensing mechanisms for autonomous resource allocation). Low-level access support information may also include data regarding timing advances to be applied by qualified user devices UE1 and UE2 to transmit signals in side-link communication mode.

[0142] In step 620, the relay service of the access device SAT of the non-terrestrial communication network NW is initiated. In other words, the access device, such as the satellite SAT, no longer functions as a bent pipe structure that relays signals to the ground via feeder link FL1. Based on the received relay support information, the relay user equipment UER can establish a sidelink communication interface, such as the PC5 wireless interface, on the relay user equipment UER side, and therefore on the access device SAT side.

[0143] In particular, in step 620, the relay user equipment UER may be allocated resources to send signals relating to the sidelink communication mode, such as a sidelink establishment request or a sidelink setup request, to user equipment UE1 and UE2, as described in the next step 630. Furthermore, during such step 620, the relay user equipment UER may broadcast information about the relay user equipment UER to user equipment UE1 and UE2, such as the relay user equipment UER identifier or the relay service proposed by the relay user equipment UER.

[0144] In step 630, a first sidelink communication link is established between the relay user equipment UER and the first user equipment UE1. In one embodiment, such a first sidelink communication link may be initiated by the relay user equipment UER, for example, by initiating a sidelink communication radio interface (i.e., the PC5 radio interface) with the first user equipment UE1. Such a first sidelink communication link may also be initiated by the relay user equipment UER based on received relay support information. In particular, such a first sidelink communication link may be initiated by the relay user equipment UER based on data relating to the identification of the first user equipment UE1 contained in the access support information. The relay user equipment UER may initiate the first sidelink communication link by sending a sidelink establishment request to the first user equipment UE1. In another embodiment, which will be described in further detail, the first sidelink communication link may be initiated by the first user equipment UE1. For example, as will be described in further detail, the relay user equipment UER may receive a sidelink communication link request from the first user equipment UE1. Next, in step 630, if the relay user equipment UER determines that the first user equipment UE1 is a qualified user equipment based on the access assistance information received, the first sidelink communication link may be established.

[0145] In step 640, a second sidelink communication link is established between the relay user equipment UER and the second user equipment UE2. Similar to the first sidelink communication link, in one embodiment, such a second sidelink communication link may be initiated by the relay user equipment UER by sending an establishment request signal to the second user equipment UE2, for example, via a sidelink communication radio interface (i.e., the PC5 radio interface), indicating that the second sidelink communication link can be established. Such a second sidelink communication link may also be initiated by the relay user equipment UER based on received relay support information. In particular, such a second sidelink communication link may be initiated by the relay user equipment UER based on data relating to the identification of the second user equipment UE2 contained in the access support information. In another embodiment, the second sidelink communication link may be initiated by the second user equipment UE2. For example, the relay user equipment UER may receive a sidelink communication link request from the second user equipment UE2. Next, in step 640, if the relay user device UER determines that the second user device UE2 is a qualified user device based on the access assistance information received, a second sidelink communication link may be established.

[0146] In the context of this disclosure, in steps 630 and 640 respectively, sidelink communication links are established between the first user equipment UE1 and the second user equipment UE2, with the relay user equipment UER relaying signals between the first user equipment UE1 and the second user equipment UE2. Such steps can be extended to the case of multiple eligible user equipment whose transmissions can be relayed by the relay user equipment UER. There may be as many sidelink communication links established with the relay user equipment UER as there are user equipment accessing the sidelink communication mode through such relay user equipment UER.

[0147] In the optional step 650, the relay user equipment UER may transmit a portion of the received relay support information, also called relayed support information, to user equipment UE1 and UE2. Such relayed support information may, for example, be a portion of the access support information received by the relay user equipment UER in step 610. In particular, such relayed support information may include, for example, data relating to timing advances to be applied by user equipment UE1 and UE2 to transmit signals via sidelink communication mode. Such relayed support information may also be low-level PC5 setup configuration information to help user equipment UE1 and UE2 establish their sidelink communication interfaces. Relayed support information may also include data relating to resource allocation procedures applied to user equipment UE1 and UE2 to allocate radio resources for performing transmissions in sidelink communication mode. Relayed support information may include information to user equipment UE1 and UE2 for accessing the sidelink radio interface. Relayed support information may be transmitted to user equipment UE1 and UE2 via the sidelink communication link established in steps 630 and 640. For example, relayed support information may be transmitted by the relay user equipment UER to user equipment UE1 and UE2 along with the sidelink establishment or setup request sent by the relay user equipment UER in steps 630 and 640 to initiate the first and second sidelink communication links.

[0148] In step 660, the relay user equipment UER can relay signals from at least the first user equipment UE1 to the second user equipment UE2 in sidelink communication mode. In other words, the relay user equipment UER, as well as each of the first user equipment UE1 and the second user equipment UE2, can communicate via a sidelink communication radio interface (in particular, an established PC5 radio interface). The relay user equipment UER may, for example, receive a signal from the first user equipment UE1 and relay such a signal to the second user equipment UE2 using sidelink communication mode. For this purpose, radio resources allocated for sidelink transmission may be used by the relay user equipment UER. More generally, the relay user equipment UER may relay signals between multiple eligible user equipment UE1, UE2.

[0149] In the optional step 670, the relay user equipment UER may provide additional support information to the eligible user equipment UE1, UE2. In particular, such additional support information may include some network information. Such additional support information may include, for example, information about reference signals transmitted, for example, by a base station via the Uu radio interface, information about satellite ephemeris, and / or system information about the non-terrestrial communication network NW. Such additional support information may also include, for example, information about the termination of relay services to indicate when and / or how to switch back from sidelink communication mode to network communication mode. Such additional support information may also include information for user equipment UE1, UE2 to restore their link to the non-terrestrial communication network NW in the event of a radio link failure. Such additional support information may be provided to the relay user equipment UER by a network entity for transmission to user equipment UE1, UE2. For example, the relay user equipment UER may acquire such additional support information in the support information it receives during step 610. Such additional support information may also be provided to and / or updated by other satellite SATs (e.g., via the inter-satellite link ISL) or via the feeder link FL1, even if the side-link communication mode is established and functional.

[0150] Next, refer to Figure 7. Figure 7 is a flowchart showing the steps for executing a communication method by user devices UE1 and UE2. Such a communication method may be executed, for example, by the first user device UE1 or the second user device UE2. More generally, the communication method may be executed by any qualified user devices UE1 and UE2 that have access rights to communicate via sidelink communication mode using relay user device UER.

[0151] In step 700, also called the initial step or initial stage, user devices UE1 and UE2 are connected to a non-terrestrial network NW via a cell managed by a base station BS. User devices UE1 and UE2 communicate via network communication mode. In other words, user devices UE1 and UE2 can transmit signals to other devices, such as a second user device UE2, UE1, via the network communication interface Ni. User devices UE1 and UE2 can also receive signals from other devices and / or network entities via the network communication interface Ni.

[0152] In step 710, user devices UE1 and UE2 may receive user assistance information. In particular, such user assistance information may include information for user devices UE1 and UE2 to switch from network communication mode to sidelink communication mode.

[0153] Such user assistance information may be received from a network entity such as a base station BS or a core network entity CN. More generally, such user assistance information may be received from one or more entities of a non-terrestrial communication network NW. Such user assistance information may be received via the network communication interface Ni of user equipment UE1, UE2. For example, such user assistance information may be received via non-access layer (NAS) signaling. Alternatively, such user assistance information may be received as radio resource control (RRC) signaling. In such cases, the user assistance information may be transmitted from the core network entity CN to the base station BS using, for example, access network level signaling, and the base station BS may forward such user assistance information to an access device (e.g., satellite SAT) as part of the feeder link FL1 control channel.

[0154] Such user support information may include cell-specific support information such as system information block (i.e., SIB) signals and / or user device-specific support information such as radio resource control (i.e., RRC) configuration information or dynamic control information.

[0155] In particular, user assistance information received by user devices UE1 and UE2 enables user devices UE1 and UE2 to switch from network communication mode to sidelink communication mode.

[0156] To this end, user assistance information may include identification data relating to the relay user equipment UER. Thus, such identification data included in the user assistance information enables a network assistance discovery phase for user equipment UE1 and UE2, allowing user equipment UE1 and UE2 to identify the relay user equipment UER as a relay device for establishing a sidelink communication link.

[0157] User support information may also include data relating to the conditions for accessing such relay user equipment UER and establishing a sidelink communication link with such relay user equipment UER. Such conditions may be, for example, timing conditions, radio capability conditions, and / or geographical conditions. For example, data relating to the conditions for accessing such relay user equipment UER may depend on pre-configured time windows, timers, power levels recognized by user equipment UE1, UE2 such as reference signal received power (i.e., RSRP), or the location of the user equipment. Thus, such conditions for accessing relay user equipment UER may be user equipment specific and / or relay user equipment specific.

[0158] User support information may also include information for the physical resource configuration for user devices UE1 and UE2 to communicate in sidelink communication mode. Such information for the physical resource configuration may, in particular, enable user devices UE1 and UE2 to be allocated radio resources for transmitting signals to relay user device UER. Such information for the physical resource configuration may also include information about the type of sidelink resource allocation. For example, such information about the type of sidelink resource allocation may describe resource discovery mechanisms, resource allocation procedures, and autonomous or network-assisted resource selection procedures performed by user devices UE1 and UE2. Examples of resource selection procedures are detailed, for example, in the new radio C-V2X radio resource allocation modes 1 and 2. Such information for the physical resource configuration may include, for example, data about resource pools, subsets of frames, subsets of slots, and subsets of symbols allocated to sidelink communication mode at the cell level. The information for the physical resource configuration may also correspond to a specific frame configuration via a mapping between the configured resource frame or slot structure used for the network communication interface Ni and the configured resource frame or slot structure used for the sidelink communication interface SLi.

[0159] Such user assistance information may also include information about timing advances that should be calculated by user devices UE1 and UE2 in order to access and / or maintain communication via a sidelink communication link with relay user device UER. For example, such information about timing advances may be the current value of the timing advance applied by user devices UE1 and UE2 in the initial network communication mode in step 700, plus a timing advance shift value applied by user devices UE1 and UE2 (e.g., a timing advance shift value to be applied to the current timing advance value applied when performing uplink transmission via the Uu radio interface). In such cases, the information about timing advances may also be common information disseminated to all user devices UE1 and UE2 within the cell, for example. The information about timing advances may also be a timing advance shift value applied to the recognized timing of frames received by each user device UE1 and UE2 from relay user device UER. Such information regarding timing advance may also be a value specific to each user device UE1, UE2, based, for example, on the core network CN's knowledge of the propagation delay between each user device UE1, UE2 and the access device SAT in network communication mode.

[0160] In step 720, a sidelink communication link is established between each user device UE1, UE2 and the relay user device UER. In the context of this disclosure, at least a first sidelink communication link may be established between the relay user device UER and the first user device UE1, and a second sidelink communication link may be established between the relay user device UER and the second user device UE2. In particular, such a sidelink communication link may be initiated by the relay user device UER or by either the first and / or second user devices UE1, UE2.

[0161] In fact, in one embodiment detailed in steps 630 and 640 of Figure 6, such a sidelink communication link may be initiated by a relay user device UER. In such an embodiment, in step 720, user devices UE1 and UE2 may receive a sidelink establishment request or a sidelink setup request from the communication network NW, for example, from the relay user device UER. Such received request may include an instruction that the relay user device UER can relay transmissions from the first and second user devices UE1 and UE2 in sidelink communication mode. In such an embodiment, during step 710, the first and second user devices UE1 and UE2 may receive at least an identifier of the relay user device UER, for example, the PC5 identifier of the relay user device UER, as part of user assistance information. Therefore, based on such received user support information and received sidelink establishment requests, the first and second user devices UE1 and UE2 can identify the relay user device UER and access the first and second sidelink communication links, respectively, when initiated by the relay user device UER, thus establishing the first and second sidelink communication links.

[0162] In another embodiment, such a sidelink communication link may be initiated by the first user device UE1 when a user device transmits a signal, for example, by a first or second user device UE1, UE2. In such an embodiment, in step 720, the first user device UE1 may initiate the first sidelink communication link by transmitting a first access signal via the first sidelink communication interface SLi to be received by a relay user device UER. Such a first access signal received by the relay user device UER may be a sidelink request signal from the first user device UE1 requesting relaying of the relay user device UER to the second user device UE2 in sidelink communication mode. In such an embodiment, during step 710, the first user device UE1 may receive, as part of user assistance information, at least an identifier of the relay user device UER, for example, the PC5 identifier of the relay user device UER, and information for initiating the first sidelink communication link. For example, such received information may correspond to part of low-level access assistance information, as detailed in step 610 of Figure 6. Therefore, based on such received user assistance information, the first user device UE1 may identify the relay user device UER and send a first access signal to the relay user device UER to initiate the first sidelink communication link, thereby establishing the first sidelink communication link. Then, in such an embodiment, the second user device UE2 may receive a first access signal from the relay user device UER to access the second sidelink communication link following the initiated sidelink request from the first user device UE1.

[0163] In an optional step 730, user devices UE1 and UE2 may receive relayed support information. Such relayed support information may be received by user devices UE1 and UE2 from relay user device UER. In particular, such relayed support information may be received via a sidelink communication link established between them in step 720. Thus, such an optional step 730 may occur after or concurrently with step 720, for example, when the relayed support information is transmitted to user devices UE1 and UE2 along with a sidelink establishment request sent by relay user device UER to initiate the sidelink communication link during step 720.

[0164] Such relayed support information may provide user equipment UE1, UE2 with support information for accessing sidelink communication mode, establishing a sidelink communication interface SLi, and / or more generally for performing transmissions over the sidelink communication link. For example, the relayed support information may include low-level sidelink setup configuration information, data on timing advances applied when transmitting signals over the sidelink communication link, and information for physical resource configuration.

[0165] In such embodiments, the relayed support information may be a complementary source of support information for user devices UE1 and UE2 with respect to user support information such as that received in step 720. In fact, some of the aforementioned user support information may be received from the relay user device UER via the relayed support information. Advantageously, such relayed support information can be combined with the user support information to provide user devices UE1 and UE2 with comprehensive support information for switching from network communication mode to sidelink communication mode. In particular, the provision of some of the user support information via the relayed support information reduces the signaling and / or computing resources required in the network communication mode in step 710 for transmitting user support information, and therefore reduces the bandwidth requirements of the feeder link FL1. In another embodiment described above, all support information provided to user devices UE1 and UE2 may consist only of user support information transmitted by, for example, a non-terrestrial communication network NW.

[0166] In step 740, user devices UE1 and UE2 may transmit and / or receive communication signals in sidelink communication mode. Based on the received user assistance information and / or the received relayed assistance information, user devices UE1 and UE2 may rely on allocated radio resources and / or select radio resources allocated to sidelink communication mode to transmit communication signals using relay user device UER as a relay. Furthermore, user devices UE1 and UE2 may use data related to timing advance in sidelink communication mode to apply timing advance to the communication signals transmitted in step 740.

[0167] In an optional embodiment, user devices UE1 and UE2 may also exchange data at this stage regarding the establishment of a sidelink communication link(s) between a relay user device UER and other user devices. For example, such exchanged data may be a message sent by user devices UE1 to relay user device UER requesting a sidelink communication mode with such other user devices. Such exchanged data may also be information provided by relay user device UER to user devices UE1 and UE2 to inform them that a particular user device is eligible for a sidelink communication mode and / or that another sidelink communication link(s) has been established and is valid for transmitting signals to such eligible user device via the sidelink communication mode. Thus, such an embodiment allows user devices UE1 and UE2 to further target a particular eligible user device for transmitting signals in sidelink communication mode.

[0168] Once a sidelink communication link is established between user devices UE1 and UE2 and relay user device UER, a communication step may be performed in step 740. With the network access device SAT functioning as a relay device via the mounted relay user device UER, signals can be transmitted and received by user devices UE1 and UE2.

[0169] Advantageously, once the sidelink communication mode is established in step 740, user devices UE1 and UE2 can transmit signals using the sidelink communication mode even without the feeder link FL1 and without using the network communication interface Ni. In one embodiment, the feeder link FL1 and the network communication interface Ni may be maintained during the sidelink communication mode. For example, the first user device UE1 may communicate with the second user device UE2 using the sidelink communication mode via the sidelink communication interface SLi, and in particular, if such another user device is not a qualified user device UE1 or UE2 to communicate in sidelink communication mode, it may communicate in parallel with the other user device using the network communication mode via the network communication interface Ni.

[0170] Once the sidelink communication mode is established in step 740, user devices UE1 and UE2 may perform direct communication operations using the received user support information, and possibly relayed support information.

[0171] For example, in sidelink communication mode, user devices UE1 and UE2 calculate timing advance values ​​for transmitting signals over the sidelink communication link based on the received user assistance information and / or relayed assistance information (no longer MAC-CE TAC signals).

[0172] Another example of direct communication operation is that user devices UE1, UE2 may select resources based on a sidelink resource selection procedure according to information received for physical resource configuration. In one embodiment, once the sidelink communication mode is established in step 740, user devices UE1, UE2 may be provided with a limited set of resources specific to the sidelink communication mode via a configured grant. User devices UE1, UE2 may then send a resource release request or control signal to the relay user device UER indicating the amount of radio resources needed to be allocated to the sidelink communication link to send a signal. In one embodiment, each eligible user device UE1, UE2 may, after establishing a sidelink communication link with the relay user device UER, select resources in the resource pool based on the respective identification information of such user devices UE1, UE2 and / or the combined identification information of the transmitting and receiving user devices UE1, UE2 when the signal was sent. Such resource selection by user devices UE1, UE2 may, in particular, be performed after excluding resources reserved for the relay user device UER.

[0173] Another example of direct communication operation is that user devices UE1 and UE2 may include sidelink control information (or SCI) in their transmissions in sidelink communication mode. In particular, such sidelink control information takes into account a relay user device UER for transmission. For example, when a first user device UE1 transmits a signal to a second user device UE2 in sidelink communication mode, the first user device UE1 may set the relay user device UER as the target (or destination) user device for the signal and include the identifier of the second user device UE2 in the sidelink control information. In another embodiment, when a first user device UE1 transmits a signal to a second user device UE2 in sidelink communication mode, the first user device UE1 may set the second user device UE2 as the target (or destination) user device for the signal, and the relay user device UER may be configured with a set of identifiers for all eligible user devices UE1 and UE2 for communication in sidelink communication mode.

[0174] In the optional step 750, user devices UE1 and UE2 may receive additional support information. Such additional support information may be received by user devices UE1 and UE2 before, during, or after the establishment of the sidelink communication mode in step 740. For example, such additional support information may be updated to user devices UE1 and UE2 after the sidelink communication mode has been established in step 740. Alternatively, such additional support information may also be provided to user devices UE1 and UE2 simultaneously with the user support information received in step 710, or simultaneously with the support information relayed in the optional step 730.

[0175] In one embodiment, such additional support information may be transmitted to user devices UE1, UE2 by a network entity such as a core network CN or base station BS, for example via non-access layer signaling, in parallel with the sidelink signal transmitted via relay user device UER. In another embodiment, such additional support information may be transmitted to user devices UE1, UE2 by relay user device UER via the sidelink communication link established in step 720.

[0176] Such additional support information may enable user devices UE1 and UE2 to obtain updated network information regarding a portion of the non-terrestrial communication network NW, synchronization information regarding the cells covering such user devices UE1 and UE2, and information for recovering from wireless link failures.

[0177] To this end, additional support information may include, in particular, system information and network information such as satellite ephemeris. In particular, when such additional support information is provided to user equipment UE1, UE2 by relay user equipment UER via sidelink communication link, the proposed step 750 advantageously enables user equipment UE1, UE2 to acquire network information even when there is no network communication mode, and as a result, user equipment UE1, UE2 can still update its synchronization data and knowledge of the non-terrestrial communication network NW while communicating in sidelink communication mode. Advantageously, such step 750 also enables user equipment UE1, UE2 to update its synchronization data and knowledge of the non-terrestrial communication network NW even when feeder link FL1 is absent in the event of a radio link failure (RLF) or when user equipment UE1, UE2 is out of coverage of some cells in the non-terrestrial communication network NW and cannot receive the corresponding system information block (SIB) from the core network entity CN.

[0178] In step 760, user devices UE1 and UE2 may switch back to network communication mode. Such a switch back to network communication mode may be based on the condition of deactivating or terminating sidelink communication mode. Such conditions may be timing conditions, such as the termination of service or timer expiration of a relay service performed by relay user device UER. Such conditions may also be the recovery of a wireless link failure.

[0179] Information for switching back to network communication mode may be provided to user devices UE1 and UE2 in steps 710, 730, and 750, simultaneously with user assistance information, relayed assistance information, and / or additional assistance information. User devices UE1 and UE2 may receive data regarding the termination of sidelink communication mode, for example, included in the conditions for accessing relay user device UER in the user assistance information. Data regarding the termination of sidelink communication mode may also be provided to user devices UE1 and UE2 by relay user device UER in the relayed assistance information, or via another signal during sidelink communication mode. In the event of a wireless link failure, user devices UE1 and UE2 may also receive data regarding link recovery for switching back to network communication.

[0180] Next, refer to Figure 8. Figure 8 is a flowchart showing the steps of a method performed by a non-terrestrial communication network NW to relay signals between a first user device UE1 and a second user device UE2. In particular, such a non-terrestrial communication network NW may correspond to the satellite communication network NW shown in Figure 5.

[0181] In step 800, also called the initial step, the non-terrestrial communication network NW provides services to user equipment UE1 and UE2 in network communication mode. In other words, transmissions from user equipment UE1 and UE2 connected to the non-terrestrial communication network NW are performed by user equipment UE1 and UE2 communicating via the base station BS and / or any other network entities of the core network CN, based on the satellite vent pipe structure. The network entities may execute radio protocols from the radio access network and route data packets to user equipment UE1 and UE2 via feeder link FL1, through core network functions (e.g., user plane function UPF), base station BS, and / or satellite SAT. In step 800, the non-terrestrial communication network NW may transmit network information to user equipment UE1 and UE2, for example, via a System Information Block (SIB). Such network information may include, for example, configuration data, satellite ephemeris, data on resource allocation, data on timing advances applied to transmit signals to base station BS in network communication mode, information on handover procedures, and / or information on cell coverage. Such network information may be broadcast or groupcast, for example, to multiple user devices UE1, UE2 covered by the same cell. Network information may also be unicast to specific user devices UE1, UE2. The network information sent to user devices UE1, UE2 in step 800 may be sent at specific times and / or according to specific periods, depending on the network entity sending such network information.

[0182] In step 800, the non-terrestrial communication network NW operates in network communication mode. The non-terrestrial communication network NW has knowledge that, in particular, the network access device SAT that provides services to user equipment UE1 and UE2 in the initial step 800 operates in network communication mode. For example, the non-terrestrial communication network NW may have knowledge that the network access device SAT relays transmissions from user equipment UE1 and UE2 to the terrestrial-based base station BS at the physical layer via feeder link FL1 using a network communication interface Ni such as a vent pipe module and a Uu radio interface.

[0183] During step 800, the non-terrestrial communication network NW may determine that several user devices UE1, UE2 share similar coverage and are eligible to communicate in sidelink communication mode via a common relay user device UER. Referring to Figure 5, the non-terrestrial communication network NW may also identify that a first user device UE1 and a second user device UE2 are covered by the same satellite beam footprint and may communicate in sidelink communication mode via the same relay user device UER implemented and mounted on a satellite SAT. In one embodiment, the non-terrestrial communication network NW may store a correspondence between each satellite beam footprint (e.g., each satellite cell) and the associated relay user device UER. Such storage may be, for example, at the core network CN level. Such associated relay user device UER may be, for example, a relay user device UER implemented and mounted on a satellite SAT projecting such a satellite beam footprint. In another embodiment, for example, when several such satellites SAT1, SAT2 are linked by an interstellar link ISL, several satellite beam footprints projected by several satellites SAT1, SAT2 may be associated with the same relay user equipment UER mounted on any one of those satellites SAT1, SAT2. In such an embodiment, the interstellar link ISL may be configured to function as a vent pipe satellite link for transmitting signals between the relay user equipment UER mounted on satellite SAT1 and user equipment covered by the other satellite SAT2. In a particular embodiment, the satellites SAT1, SAT2 linked by the interstellar link ISL may include their respective relay user equipment UERs, which appear as unique relay interfaces to the core network CN, more generally to the non-terrestrial communications network NW. Thus, the interstellar link ISL between satellites SAT1, SAT2 may be able to extend to relay coverage of user equipment covered by different satellites SAT1, SAT2.

[0184] To determine that several user devices UE1, UE2 share similar coverage, a non-terrestrial telecommunications network (NW) may use information stored in the core network (CN) of the NW. In fact, the core network may have knowledge about each base station (BS) associated with a cell that provides services to each end user. In particular, in conventional implementations of non-terrestrial telecommunications networks (NW), each base station (BS) may provide the core network (CN) with information about the satellite access of such base station (BS). Alternatively, the core network (NW) may consist of operational and maintenance functions (i.e., OAM) with dynamic or static mappings between base station identifiers and the type of access provided by each base station (e.g., terrestrial access or satellite access). Alternatively, the core network (CN) may also associate base station (BS) with access devices (SAT) for specific services. More generally, the core network (CN) has knowledge about the coverage of user devices UE1, UE2 and the correspondence between them and the associated access devices (SAT) that provide services to such user devices UE1, UE2.

[0185] In step 810, the non-terrestrial communication network NW may determine relay support information. Such relay support information may correspond, for example, to the relay support information detailed in step 610 of Figure 6. Such relay support information may be determined by the core network CN, base stations BS, and / or any other network entities of the non-terrestrial communication network NW. Such relay support information may be determined based on the coverage of user equipment UE1, UE2, associated access devices SAT that provide services to such user equipment UE1, UE2, and the non-terrestrial communication network NW's knowledge of measurements performed in the non-terrestrial communication network NW.

[0186] In step 810a, the non-terrestrial communication network NW may determine and transmit relay support information to the relay user equipment UER. The relay support information transmitted to the relay user equipment UER may correspond to the relay support information described in step 610 of Figure 6. In particular, such relay support information may also include information specific to the cell or satellite beam footprint associated with the relay user equipment UER.

[0187] In step 810b, the network entity may determine user assistance information and transmit it to eligible user devices UE1, UE2. Such eligible user devices UE1, UE2 may include, for example, at least a first user device UE1 and a second user device UE2. Such user assistance information may be spread, broadcast, or groupcast, for example, entirely or partially, to all user devices UE1, UE2 that the network entity has determined to have similar coverage properties. For example, the network entity may spread common user assistance information to user devices belonging to the same cell, user devices covered by the same satellite beam footprint, or user devices covered by satellite beam footprints projected by interconnected satellites. The user assistance information may also include both a portion of user assistance information common to multiple user devices and a portion of user assistance information specific to a particular user device. The user assistance information may correspond to the user assistance information described in step 710 of Figure 7.

[0188] When steps 810a and 810b are performed, the non-terrestrial communication network NW encounters a communication switch from network communication mode to sidelink communication mode. When the switch between sidelink communication modes is performed, the network entity may stop sending messages to the relay user equipment UER or to either user equipment UE1 or UE2. For example, the network communication mode may be paused after steps 810a and 810b. For example, after steps 810a and 810b, feeder link FL1 may remain unused without interrupting signal transmission between the first user equipment UE1 and the second user equipment UE2 via the relay user equipment UER in sidelink communication mode. In another embodiment, both network communication mode and sidelink communication mode may be activated simultaneously.

[0189] In the optional step 820, the network entity may transmit additional support information. Such additional support information may be transmitted to the relay user equipment UER. Such additional support information may also be transmitted to user equipment UE1, UE2, for example, when the network communication mode and the sidelink communication mode are used simultaneously by user equipment UE1, UE2. Such additional support information may also be network information such as satellite ephemeris, synchronization information, and / or system information block (SIB). Such additional support information may also include information for switching back from sidelink communication mode to network communication mode. Such additional support information may correspond to the additional support information of step 750 received by user equipment UE1, UE2, or the additional support information of step 670 relayed by the relay user equipment UER. Such additional support information may be transmitted by the network entity simultaneously with the relay support information transmitted to the relay user equipment in step 810a and / or simultaneously with the user support information transmitted to user equipment UE1, UE2 in step 810b.

[0190] In step 830, a network entity may command a communication back switch to network communication mode. Such a back switch may be triggered, for example, by the expiration of a timer indicating the termination of service in sidelink communication mode. Such a back switch may also occur after a radio link recovery performed by user equipment UE1, UE2 following a radio link failure (i.e., RLF), thereby re-establishing network communication mode.

[0191] Next, refer to Figure 9. Figure 9 shows steps outlining a proposed method for relaying signals between a first user device UE1 and a second user device UE2 in a non-terrestrial communication network NW. In particular, Figure 9 shows signaling performed between the first user device UE1, the second user device UE2, the relay user device UER, and at least one non-terrestrial network entity N of the non-terrestrial communication network NW. Such a network entity N could be, for example, a core network CN or a base station BS. Signaling is represented by arrows, and dotted arrows represent optional or alternative signaling.

[0192] In step 100, network entity N transmits at least a portion of network support information to relay user equipment UER. Such portions of network support information correspond, in particular, to relay support information relating to the establishment of a sidelink communication mode between relay user equipment UER and at least one of the user equipment, the first user equipment UE1 and the second user equipment UE2. Such portions of network support information are determined by one or more non-terrestrial network entities N of the network NW and may be transmitted to relay user equipment UER implemented in access device SAT, for example, via a feeder link control channel.

[0193] In steps 101 and 102, network entity N may also transmit another portion of network support information to the first user equipment UE1 and / or the second user equipment UE2. Such another portion of network support information may, in particular, correspond to at least a portion of user support information relating to the establishment of a sidelink communication mode with the relay user equipment (UER). Such another portion of network support information may at least partially coincide with the portion of network support information transmitted to the relay user equipment UER in step 100.

[0194] In steps 201 and 202, the relay user device UER may send messages to the first user device UE1 and the second user device UE2. In one embodiment, such messages may correspond to sidelink communication requests to initiate a sidelink communication interface (or PC5 interface) with the first user device UE1 and the second user device UE2, respectively.

[0195] In steps 301 and 302, in one embodiment, the relay user equipment UER may also relay a portion of the relay support information, also called relayed support information, to the first user equipment UE1 and / or the second user equipment UE2. Thus, from the perspective of the first and second user equipment UE1 and UE2, the user support information received by the first user equipment UE1 and the second user equipment UE2 may be transmitted by the network entity N and / or the relay user equipment UER. The relay user equipment UER may transmit such portions of the relay support information to the first and / or second user equipment UE1 and UE2 after or while the sidelink communication interface has been initiated in steps 201 and 202.

[0196] In steps 311 and 312, as an alternative step to steps 201 and 202, the first user device UE1 and the second user device UE2 may send a message to the relay user device UER. Such a message may correspond to a sidelink communication request to initiate a sidelink communication interface (or PC5 interface) with the relay user device UER. In particular, such a sidelink communication request initiated on the user devices UE1 and UE2 may depend on user assistance information provided to the first and second user devices UE1 and UE2 in steps 101, 102 and / or 301, 302.

[0197] In steps 401 and 402, a sidelink communication interface (or PC5 interface) is established between the first user device UE1 and the relay user device UER, and between the second user device UE2 and the relay user device UER, respectively. Thus, a sidelink communication mode is established for the first and second user devices UE1 and UE2, and the relay user device UER functions as a repeater. In steps 401 and 402, signals may be transmitted between the first user device UE1 and the second user device UE2 via the relay user device UER.

[0198] In steps 501 and 502, the relay user equipment UER may transmit additional support information to the first and second user equipment UE1 and UE2, respectively. In particular, such additional support information may be transmitted to the user equipment UE1 and UE2 by the relay user equipment UER via the sidelink communication interface in sidelink communication mode.

[0199] Instead of, or in addition to, steps 501 and 502, network entity N (or several network entities of the non-terrestrial communication network NW) may transmit such additional support information to the first and second user equipment UE1, UE2 in steps 511 and 512, respectively. In particular, such additional support information may be transmitted by network entity N to user equipment UE1, UE2 via the Uu interface, especially in the case of an active feeder link maintained during sidelink communication mode.

Claims

1. A method performed by a non-terrestrial communication network (NW) to relay a signal between at least a first user device (UE1) and a second user device (UE2), wherein the relay user device (UER) is mounted on a network access device (SAT) of the non-terrestrial communication network (NW), and the method is To obtain at least relay support information relating to the establishment of a sidelink communication mode between the relay user equipment (UER) and at least one of the first user equipment (UE1) and the second user equipment (UE2), Transmit at least a portion of the relay support information to at least the first user device (UE1) and the second user device (UE2), Based on the relay support information, establish at least a first sidelink communication link between the relay user equipment (UER) and the first user equipment (UE1), and a second sidelink communication link between the relay user equipment (UER) and the second user equipment (UE2). Using the established sidelink communication mode, the signal is relayed between the first user device (UE1) and the second user device (UE2) via the first sidelink communication link and the second sidelink communication link. Methods that include...

2. Based on the relay support information, the last of the first and second sidelink communication links is initiated. The method according to claim 1, further comprising:

3. The method according to claim 1 or 2, wherein the relay support information includes control support information relating to an instruction to switch between the network communication mode and the sidelink communication mode.

4. The method according to any one of claims 1 to 3, wherein the relay support information includes access support information relating to data identifying user equipment that is connected to the non-terrestrial communication network (NW) and is qualified to communicate with the relay user equipment (UER) via the side-link communication mode.

5. The aforementioned relay support information, - Setup configuration information for establishing the sidelink communication interface (SLi) in the aforementioned sidelink communication mode, - Data relating to timing advance to be applied by at least the first user device (UE1) and the second user device (UE2) in the sidelink communication mode, and - Data relating to resource allocation for the side-link communication mode The method according to any one of claims 1 to 4, comprising at least one of the elements.

6. The further includes transmitting additional support information to at least one of the first user equipment (UE1) and the second user equipment (UE2), wherein the additional support information relates to the non-terrestrial communication network (NW). The method according to any one of claims 1 to 5.

7. The aforementioned additional support information is, - System information block SIB relating to the aforementioned non-terrestrial communication network (NW), - Data relating to satellite ephemeris in the aforementioned non-terrestrial communication network (NW), - Reference signals for the network communication interface (Ni) used in network communication mode. - Data relating to the aforementioned network communication mode, - Data regarding the termination of the side link communication mode, - Data on wireless link failure (RLF), recovery, and - Data relating to at least one cell projected by the network access device (SAT) and covering at least one user device. The method according to claim 6, comprising at least one of the elements.

8. Before relaying the aforementioned signal, Receiving a sidelink communication request from at least the first user device (UE1), Based on the relay support information and the sidelink communication request, the first sidelink communication link is established. The method according to any one of claims 1 to 7, further comprising:

9. A communication method performed by a first user device (UE1) to transmit a signal to at least a second user device (UE2) in a non-terrestrial communication network (NW), wherein the communication method is To receive user assistance information relating to at least the establishment of a sidelink communication mode with a relay user device (UER), To establish a first sidelink communication link with the relay user equipment (UER) based at least on the user support information, Transmitting the signal to the second user equipment (UE2) via the established first sidelink communication link. A communication method that includes this.

10. At least based on the user support information, the first sidelink communication link with the relay user equipment (UER) is initiated by sending a sidelink communication request. The communication method according to claim 9, further comprising:

11. The communication method according to claim 9 or 10, wherein the user support information includes at least data relating to the identification of the relay user equipment (UER).

12. The aforementioned user support information is - Setup configuration information for establishing the sidelink communication interface (SLi) in the aforementioned sidelink communication mode, - Data relating to the timing advance to be applied in the aforementioned side-link communication mode, - Data relating to resource allocation for the side-link communication mode A communication method according to any one of claims 9 to 11, comprising at least one of the elements.

13. A switching method performed by a network entity (N) to establish a communication switch in a non-terrestrial communication network (NW) for a signal between a first user device (UE1) and a second user device (UE2), wherein the communication switch is performed between a network communication mode and a side-link communication mode, and the switching method is To determine relay user equipment (UER) associated with at least the first user equipment (UE1) and the second user equipment (UE2) in order to relay signals between the first user equipment (UE1) and the second user equipment (UE2), To determine at least network support information regarding the establishment of the side-link communication mode, Transmitting at least a portion of the network support information to the relay user equipment (UER) via the aforementioned network communication mode, At least based on the network support information, establish a communication switch between the network communication mode and the side-link communication mode. Switching methods, including those mentioned above.

14. The relay user equipment (UER) is mounted on the first network access device (SAT) of the non-terrestrial communication network (NW), and the relay user equipment (UER) is at least, - Coverage zones of the first user equipment (UE1) and the second user equipment (UE2) by at least the first network access device (SAT1), - Intersatellite link ISL between at least the first network access device (SAT1) and the second network access device (SAT2) of the non-terrestrial communication network (NW) covering at least one of the first user equipment (UE1) and the second user equipment (UE2). A switching method according to claim 13, which is determined accordingly.

15. When the software is executed by the processor, the software is as follows: - The method according to any one of claims 1 to 8, - A communication method according to any one of claims 9 to 12, and - Switching method according to claim 13 or 14 A computer-readable non-temporary recording medium registered to perform one of the following actions.

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