Method for pointing a SATCOM terminal towards a satellite of a non-terrestrial cellular communication network

Abstract

Method for pointing a SATCOM terminal towards a satellite of a non-terrestrial cellular communication network. This pointing method consists of: generating a beacon stream from a reference data shared with the terminal (10) by the satellite (20); transmitting a 5G NTN signal by the satellite, integrating the beacon stream into predefined physical radio beacon blocks; receiving the transmitted signal by the terminal; extracting binary data from the physical radio beacon blocks by the terminal; calculating an estimate of the reference data from said binary data; calculating an instantaneous quantity corresponding to the error between the estimate of the reference data and the reference data; and controlling the beam (61) of an antenna (60) of the terminal, taking into account said instantaneous quantity. Figure for the abstract: Figure 1

Description

Title of the invention: Method for pointing a SATCOM terminal towards a satellite of a non-terrestrial cellular communication network

[0001] The invention relates to the field of methods for pointing the beam of a mechanically or electronically scanned antenna of a SATCOM terminal towards a satellite moving in a non-terrestrial cellular telecommunications network - NTN ("Non-Terrestrial Network") using 5th generation technology - 5G, the moving satellite carrying a regenerative payload.

[0002] The 3GPP (“3rd Generation Partnership Project”) produces standards defining the requirements, architectures and operating procedures of cellular telecommunication networks.

[0003] Although the first normative elements relating to non-terrestrial networks were defined in version 17 of the 5G standard (“Release 17”, completed in June 2022), normative work continues.

[0004] The technical specifications 3GPP TS 38.300 and 3GPP TS 23.501, as well as the technical reports 3GPP TR 23.700-28, 3GPP TR 23.700-29, 3GPP TR 23.737, 3GPP TR 38.821, were thus published.

[0005] The latest findings from these studies will be incorporated into version 19 of the 5G standard, which is expected to be published in June 2026.

[0006] These studies propose, in particular, a 5G NTN network architecture in which all or part of a base station (also called a gNode-B or gNB) of a radio access network (RAN) is integrated into the payload of a satellite and participates in the processing of data packets. This is referred to as a regenerative architecture. The regenerative 5G NTN network can reduce the number of ground stations and also provide connectivity services with higher data rates than a 5G NTN network that uses satellites solely to transparently retransmit data packets.

[0007] The regenerative architecture uses the flexibility of the NG-RAN architecture, which allows for different disaggregation options for a gNB on either side of a standardized interface. For example, in a so-called "higher layer split" (HLS) of the gNB, as specified in 3GPP TS 38.401, a gNB consists of a high unit, gNB-CU, and a low unit, gNB-DU, and the interface between gNB-CU and gNB-DU is called the FL interface.

[0008] With such a separation of the gNB, the protocol layers associated with the low unit of the gNB are implemented by the payload on board a satellite and the protocol layers of the high unit of the gNB are in a ground station.

[0009] From the ground station, the upper unit of the gNB connects to a 5G - CN (“Core Network”) core network, comprising for example a gateway to a public network, such as the Internet.

[0010] A SATCOM terminal is a user device, as defined in 5G, equipped with a directional antenna, meaning that its beam can be oriented either mechanically or electronically, to track the movement of a satellite in a constellation of non-geostationary satellites in low Earth orbit (LEO) and / or medium Earth orbit (MEO). In the following, the term LEO satellite will be used to refer to a satellite in orbit within an LEO and / or MEO constellation.

[0011] Due to its high directivity and very narrow beam, a SATCOM terminal must be able to point very precisely at the satellite with which it is communicating. In the case of a LEO satellite, the terminal must continuously track the LEO satellite as it moves and adjust its antenna pointing accordingly. A mobile SATCOM terminal must also compensate for its movements in order to maintain the most precise possible aiming at the LEO satellite.

[0012] Furthermore, a LEO satellite can implement a coverage switching technique (“beam-hopping”). According to this technique, the LEO satellite covers a multitude of geographical areas on the ground (“spots”) according to a time cycle, such that a ground spot is served by the LEO satellite at least once per cycle.

[0013] The pointing of the SATCOM terminal is generally ensured by an antenna control unit - ACU (“Antenna Control Unit”) which controls the pointing of the antenna to the reception of a reference signal, called a beacon, which is transmitted continuously by the LEO satellite.

[0014] After selecting a LEO satellite to point towards, a search phase for this LEO satellite is implemented, during which T ACU uses elementary information (such as the geographical position of the SATCOM terminal, the ephemerides of the satellites, etc.), to roughly estimate the expected position of the LEO satellite.

[0015] The ACU controls the pointing of the antenna beam towards the expected position and then searches for the LEO satellite by measuring the power level variations in reception of the beacon emitted by this LEO satellite for different pointing directions around the expected position of the LEO satellite.

[0016] Once the LEO satellite is found and confirmed through decoding the information contained in the beacon signal emitted by the LEO satellite, the terminal optimizes its pointing by maximizing the power level of this beacon signal.

[0017] The ACU then enters the tracking phase in order to maintain aiming towards the LEO satellite. This tracking phase implements, for example, a conical scan technique, which keeps the antenna beam centered on a pointing direction where the reception of the beacon emitted by the LEO satellite is optimized.

[0018] The beacon can take the form of a continuous narrowband signal (or an unmodulated carrier) allowing for a rapid and precise measurement of its power level by the terminal. The beacon must then have a frequency sufficiently far removed from the frequency band in which communications are taking place so that its reception does not disrupt communications, nor does it interfere with the beacon measurement.

[0019] Alternatively, the beacon drifts from the received traffic signal when the latter uses a modulated carrier with a quasi-constant power envelope. The terminal is equipped with a receiver that allows for an immediate and approximate estimation of the traffic signal power level in order to estimate, more precisely but more slowly, the quality of the received signal. This information is used to optimize satellite pointing and tracking.

[0020] However, using a narrowband beacon in a low-Earth orbit satellite constellation requires equipping each satellite in the constellation with a dedicated RF chain for transmitting the beacon, as well as a dedicated (large-aperture) antenna for broadcasting the beacon. This RF chain occupies space on board the satellite and consumes a fraction of the available power, which is then unavailable for transmissions.

[0021] Furthermore, each satellite must have a beacon characterized by a frequency distinct from that of neighboring satellites. Indeed, since the satellites are present in several orbital planes, satellites in disjoint planes may appear close together along the line of sight of the SATCOM terminal. A satellite must therefore have a unique frequency distinct from that of neighboring satellites. This characteristic results in a significant consumption of spectral resources just for the transmission of the beacons.

[0022] Furthermore, using the traffic signal on the downlink as a beacon requires a sufficiently stable power envelope, limiting the choice of waveforms. This is well suited to the Digital Video Broadcasting (DVB) standard or its equivalents, but not to the 5G telecommunications standard. However, the DVB standard (S2X downlink and RCS2 uplink) amount) is not optimized for use in a LEO and / or MEO moving constellation, unlike the 5G NTM standard which is therefore implemented.

[0023] Regardless of the nature of the beacon, these approaches based on a beacon signal received continuously by the terminal are not compatible with the implementation of a 5G NTN waveform which is discontinuous in nature.

[0024] This is even less so when a "beam hopping" technique is also implemented and a spot is only served intermittently.

[0025] Indeed, the SATCOM terminal on the ground would only receive the beacon during the short period of time when the spot within which it is located is illuminated by the beam of the LEO satellite. However, this period of time is too short for the terminal to receive enough energy to precisely locate the LEO satellite.

[0026] It would therefore be desirable to be able to eliminate the disadvantages of the prior art by freeing oneself from an RF chain, a dedicated satellite channel or an insufficiently flexible waveform, while being compatible with the waveform of the 5G NTN standard, while advantageously allowing the implementation of a beam-hopping technique.

[0027] The object of the present invention is to address this problem.

[0028] For this purpose, the invention relates to a method of pointing a SATCOM terminal towards a satellite carrying a regenerative payload, in a 5G NTN type cellular communication network, comprising the steps of: generating, by the payload, a beacon stream from a reference data shared with the SATCOM terminal; transmitting a signal in 5G NTN format, by the payload, by integrating the beacon stream into at least one physical radio block called a beacon of a subframe of the signal according to a predefined time-frequency pattern; reception of the signal by the SATCOM terminal; extraction, by the SATCOM terminal, of the physical radio beacon blocks contained in each subframe of the received signal; performing an instantaneous measurement from the physical radio beacon blocks; and, orienting a beam of an antenna of the SATCOM terminal taking into account the instantaneous measurement.

[0029] According to particular embodiments, the process comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0030] - each physical radio beacon block has a predefined position in frequency and in time in a subframe.

[0031] - the tag stream consists of a repetition of the reference data.

[0032] - the beacon stream is generated by a beacon generator on the satellite payload by applying a fountain code type algorithm to the reference data.

[0033] - The oced includes a step consisting of evaluating, by the SATCOM terminal, a signal level indicator from physical beacon radio blocks as an instantaneous measurement used for terminal antenna beam orientation.

[0034] - the process comprises the steps of: calculating an estimate of the data reference from binary data extracted from physical beacon radio blocks; calculate an error between the reference data estimate and the reference data as an instantaneous measurement used for terminal antenna beam orientation.

[0035] - the error is a signal-to-noise ratio.

[0036] - the error is used to verify the identity of the satellite.

[0037] The invention also relates to a 5G NTN format signal comprising a plurality of subframes, each subframe being composed of a time-frequency matrix of a plurality of physical radio blocks, characterized in that at least one physical radio block of a subframe, in a predefined position, is reserved for the transmission of a beacon stream.

[0038] The invention also relates to a regenerative payload of a satellite of a 5G NTN type cellular communication network, adapted to generate a signal in 5G NTN format conforming to the previous signal.

[0039] Preferably, the payload includes a beacon generator capable of generating a beacon stream from a reference data and applying the generated beacon stream as input to a MAC layer of the payload, the beacon generator indicating a modulation and a coding to be used for the emission of the beacon stream.

[0040] Preferably, the beacon stream is modulated and coded according to a robust coding.

[0041] The invention also relates to a SATCOM terminal, capable of operating on a 5G NTN type cellular communication network, characterized in that it is adapted to drive a SATCOM terminal antenna from a beacon stream contained in a 5G NTN format signal conforming to the previous signal.

[0042] Preferably, the SATCOM terminal includes a beacon receiver adapted to calculate an estimate of the reference data from the binary data extracted from the subframes of a frame of the signal and to calculate a second instantaneous measurement corresponding to the error between the estimate of the reference data and the reference data, and to apply said second instantaneous measurement to the input of a control unit of the antenna of the SATCOM terminal.

[0043] Preferably, a SATCOM terminal includes a physical layer adapted to perform a first instantaneous measurement corresponding to an instantaneous indicator of the level of the received signal and to apply said first measurement to the input of the antenna control unit.

[0044] Preferably, the beacon receiver executes a fountain code type algorithm to calculate an estimate of the reference data.

[0045] The invention ultimately relates to a method for planning an allocation of physical radio beacon blocks in a subframe of a 5G NTN format signal conforming to the previous signal, consisting of: calculating a target value of the instantaneous measurement, taking into account a maximum tolerated pointing error and a reception time by a terminal of the signal; calculating the number of physical radio beacon blocks required to reach the target value of the instantaneous quantity; and, pre-positioning the necessary number of physical radio beacon blocks in a time-frequency matrix corresponding to a subframe of the signal, and thus defining an allocation of physical radio beacon blocks.

[0046] Preferably, the planning method includes a step of distributing the allocation to SATCOM terminals and regenerative payloads of satellites of a 5G NTN type cellular communication network.

[0047] Preferably, the planning method in which the number of physical radio beacon blocks needed to achieve the target value of the first or second instantaneous measurement is calculated takes into account an estimated link budget between a satellite and a terminal and / or a choice of modulation and coding of the beacon stream.

[0048] The invention and its advantages will be better understood upon reading the following detailed description of a particular embodiment, given solely by way of non-limiting example, this description being made with reference to the accompanying drawings in which:

[0049] [Fig-1] Fig. 1 is a schematic representation of one embodiment of a system for implementing the pointing method according to the invention; and,

[0050] [Fig.2] The [Fig.2] is a schematic representation of a frame emitted by a LEO satellite of the [Fig.1] system illuminating a particular spot on the ground;

[0051] [Fig.3] Fig.3 is a schematic block representation of an embodiment of a pointing method according to the invention; and,

[0052] [Fig.4] The [Fig.4] is a schematic block representation of an embodiment of a planning process according to the invention.

[0053] As illustrated in [Fig.1], system 1 comprises a SATCOM terminal 10 and a LEO satellite 20 of a LEO and / or MEO type drifting constellation.

[0054] The LEO 20 satellite carries a regenerative payload 22. In other words, the payload 22 comprises, in addition to antenna means 24, a low unit 26 of a disaggregated gNB base station, the high unit 32 of the disaggregated GNB base station being on the ground, for example in a ground station 30.

[0055] The constellation is connected to the ground station 30 by a feeder link 31, originating from the LEO 20 satellite or from another satellite in the constellation with which the LEO 20 satellite is connected.

[0056] The upper unit 32 is connected to a 5G core network - CN (“Core Network”) 34. The CN 34 is for example connected to a public network such as the internet 36.

[0057] According to the invention, the payload 22 of the LEO 20 satellite is modified to implement a specific transmission method.

[0058] The lower unit 26 of the payload 22 comprises, in a conventional manner, a physical layer 42, a MAC layer 44 and an RLC layer 46.

[0059] According to the invention, the lower unit 26 further comprises a beacon generator 48.

[0060] Advantageously, the LEO 30 satellite implements a beam-hopping technique. The beam 21 of the LEO 30 satellite covers a multitude of geographical areas on the ground (“spots”). These spots are referenced 50 to 56 in [Fig. 1].

[0061] The spots are served according to a plan repeated cyclically over time. For example, the spots are served successively during a cycle. A spot is served by the LEO satellite at least once per cycle.

[0062] Thus, in the signal emitted by the LEO 20 satellite during a cycle, at least one time slot is dedicated to a particular sport, for example spot 52 within which terminal 10 is located at the current time considered.

[0063] In a time slot dedicated to a particular spot, the signal emitted by the LEO 20 satellite transmits data streams to the terminals present inside the spot.

[0064] The payload 22 of the LEO 20 satellite generates a signal in 5G NTN format.

[0065] According to the 5G NTN format, the signal is generated from traffic streams, corresponding to user data and 5G signaling enabling network access for terminals present in the spot in question.

[0066] The signal consists of a succession of frames, each frame itself consisting of a succession of sub-frames.

[0067] For example, in [Fig.3], the first three subframes STI, ST2 and ST3 of a T frame are schematically represented.

[0068] Each subframe is a frequency-time matrix, subdivided into a plurality of cells called resource elements - RE ("resource element"). Each resource element is identified by a frequency index (corresponding to a subcarrier frequency) and a time index (corresponding to a symbol).

[0069] NxM neighboring resource elements - RE (i.e. according to N consecutive frequency indices and M consecutive time indices) are grouped together to form a physical radio block - PRB (“Physical Radio Block”).

[0070] Thus, a subframe is subdivided into a plurality of PRBs.

[0071] The MAC 44 layer conventionally allocates PRBs to each traffic flow. For example, in [Fig.2], the PRB_T_1, PRB_T_2, and PRB_T_3 of the second ST2 subframe contain traffic flow data, user data, and / or signaling data.

[0072] According to the invention, the MAC layer 44 is configured to allocate one or more PRBs to a beacon stream delivered by the beacon generator 48. These PRBs are referred to as beacon PRBs in the following. For example, in [Fig. 2], the PRB_B_1, PRB_B_2, PRB_B_3, and PRB_T_4 of the second subframe ST2 contain beacon stream data.

[0073] The beacon PRBs have predefined positions in a subframe. In [Fig.2], it can be seen that the PRB pattern in time and frequency is repeated from one subframe to another.

[0074] Thus, according to the invention, the beacon is directly integrated into the 5G NTN communication protocol. The beacon therefore becomes intermittent for each spot. This mechanism is compatible with the (optional) implementation of a beam-hopping technique using LEO satellites.

[0075] The tag generator 48 thus has the function of generating the tag stream.

[0076] The tag stream is developed from a predefined and unique reference data. For example, the reference data contains at least one piece of information from among a constellation identifier, a transmitting satellite identifier, and an identifier of the ground spot illuminated by the satellite at the current time.

[0077] It should be noted that when the reference data contains constellation identification information, the positioning of the beacon PRBs in the subframe can be identical from one constellation to another instead of being specific to each constellation. It should also be noted that when the reference data contains identification information for a satellite in the constellation, the positioning of the beacon PRBs in the subframe can be identical from one satellite to another in the constellation instead of being specific to each satellite in the constellation. Finally, it should be noted that when the reference data contains identification information for a ground spot, the positioning of the beacon PRBs in the subframe can be identical from one spot to another (or at least between a spot and a neighboring spot) instead of being specific to each ground spot.

[0078] In a first variant, the beacon flow consists of the reference data repeated from one beacon PCB to another.

[0079] However, preferably, the beacon stream is generated from the reference data but coded differently from one beacon PCB to another. The beacon generator 48 executes a stream generation algorithm for this purpose, implementing, for example, a fountain code. Such an algorithm constitutes the best method of implementation, but other types of flow generation from data are conceivable by a person skilled in the art.

[0080] The beacon generator 48 is seen as a traffic user by the 5G MAC layer 44. The beacon generator 18 must therefore specify the modulation and coding to be used for transmitting the beacon stream. For example, the beacon stream is modulated and coded with robust and preferably constant modulation and coding, typically QPSK^2. This coding is applied at the physical layer 42. It is applied to the beacon stream, i.e., in addition to the fountain code executed by the beacon generator 48 on the reference data.

[0081] The SATCOM 10 terminal includes:

[0082] - an antenna with positioner (electronic or mechanical) 60;

[0083] - an ACU 62, adapted to drive the antenna 60 so as to orient the direction of pointing D of the transmit / receive beam 61 of the antenna 60;

[0084] - a transmitting / receiving chain 64, connected to the antenna 60 for transmission of a data stream to a LEO satellite to which terminal 10 is connected, and the reception of a data stream from this LEO satellite;

[0085] - a satellite positioning unit 63, enabling the position to be determined instantaneous output from terminal 10 and deliver a clock signal; and,

[0086] - a software application 65 for generating and consuming data applications, connected to the transmission / reception chain 64.

[0087] More specifically, the transmission / reception chain 64 includes, in a conventional manner, a physical layer 72, a MAC layer 74 and an RLC layer 76, in order to implement the modem functions.

[0088] According to the invention, the transmission / reception chain 64 further comprises a beacon receiver 78.

[0089] Terminal 10 thus implements a symmetrical reception chain of the transmission chain of the payload of a satellite of the constellation.

[0090] In reception, the physical layer 72 processes the signal received from the LEO satellite and captured by the antenna 60, so as to extract the different PRBs and transmit them to the MAC layer 74.

[0091] The physical layer 72 is advantageously adapted to, in a first phase of searching for satellite 20, detect the portions of the received signal which correspond to the beacon PRBs, these being organized according to a regular pattern (in time and frequency) known in advance.

[0092] For this purpose, a signal level indicator – RSSI – is evaluated on the pattern of the beacon PRBs. This initial measurement of the energy level in the received signal is quick and easy to perform in order to identify the presence of beacon information in a received signal, without having to decode the content of the beacon PRBs.

[0093] This first measurement is advantageously time-stamped and transmitted to ACU 62.

[0094] The Media Access Control (MAC) layer 74 of terminal 10 identifies received PRBs according to whether they relate to a traffic flow or a reference flow. The identification of beacon PRBs is based on their (predefined) position in the time-frequency matrix of a subframe.

[0095] The PRBs of the traffic flow are transmitted to the RLC layer 76 which extracts the user data and transmits it to the recipient application 68.

[0096] The PRBs of the beacon stream are transmitted to the beacon receiver 78.

[0097] The binary data extracted from a tag PRB can contain a high number of errors. This number of errors on the extracted binary data is estimated at any given time by the beacon receiver 78 from the reference data which it knows by prior configuration of terminal 10.

[0098] Advantageously, by implementing the fountain code algorithm, the reception of the beacon stream in the different beacon PRBs and its decoding by the beacon receiver 78, makes it possible to reduce the number of bit errors on the extracted binary data.

[0099] When all the beacon PRBs of a frame have been received, the beacon receiver 78 is able to define an estimate of the signal-to-noise ratio - SNR ("Signal Noise Ratio") of the beacon from the residual errors.

[0100] Advantageously, a low SNR level (for example below a predefined threshold) makes it possible to confirm the identity of the satellite whose beacon streams are captured (correlation between the characteristic reference data of the satellite in the selected constellation and the extracted binary data).

[0101] This beacon signal-to-noise ratio is then time-stamped, for example with the date supplied by unit 36, and transmitted to the ACU 62 piloting antenna 60, as a second measurement.

[0102] The ACU 62 is adapted to take into account the feedback quantity provided by the first or second measurement to control the antenna beam orientation. The first RSSI measurement is used, for example, when searching for a target satellite. This measurement is quick to obtain but lacks precision. It can cause confusion between satellites. The second SNR measurement is used, for example, for satellite tracking to maintain the pointing under dynamic satellite and / or terminal conditions. Pointing optimization before establishing a communication link with the target satellite can use one or both of the first and second measurements.

[0103] Fig. 3 presents a possible embodiment of a method for automatically controlling the antenna of a SATCOM terminal during its use.

[0104] The method 100 begins with a step of selecting, by the terminal 10, a satellite of the constellation, from for example an ephemeris file of the satellites of the constellation. For example satellite 20 is selected.

[0105] In the next phase of searching for satellite 20, the ACU 62 estimates (step 120), in accordance with the state of the art, the approximate position and time of appearance of satellite 20.

[0106] A few seconds before the appearance of satellite 20 above the horizon, the ACU 62 points (step 130) the antenna beam 61 towards the expected position.

[0107] In the next step 140, terminal 10 searches for satellite 30.

[0108] When the satellite 30 transmits in the spot in which the terminal 10 is located, the receiving chain 64 of the terminal 10 receives the signal transmitted by the satellite with sufficient energy to be able to perform a first measurement of the type Received Signal Strength Indicator - RSSI ("Received Signal Strength Indicator") during the satellite's transmission time slot.

[0109] In this step, it is not necessary to have a precise measurement of the RSSI. This first measurement can be done by digital filtering (averaging) of the signal received in the beacon channel, i.e. the beacon PCBs associated with the reference data.

[0110] This first RSSI measure, once dated, is transmitted to ACU 62.

[0111] In the absence of the LEO satellite, the RSSI is normally zero (RSSI=0). Any The antenna orientation that gives a positive variation in RSSI is then considered as a possible direction where the target satellite is located.

[0112] By small displacements of the antenna pointing direction, the ACU 62 tries to maximize the first RSSI measurement.

[0113] Once satellite 20 is locked on, in a step 140, the receiver 78 of terminal 10 confirms whether the received signal actually belongs to the target satellite.

[0114] If not, the satellite search procedure must be restarted.

[0115] If so, a classic procedure for establishing a bidirectional communication channel between the satellite and the cellular telecommunication network is carried out to establish a Uu link according to the 5G standard.

[0116] The process 100 then passes into a step 150 of tracking the satellite 20.

[0117] In this step, the receiver 78 of terminal 10 decodes the reference data and estimates a second measurement of the type signal-to-noise ratio - beacon SNR.

[0118] It is possible that the modulation, coding and transmission of the reference data in a single beacon PRB may not allow the receiving terminal to reliably estimate the SNR correctly.

[0119] In order for the receiving terminal to be able to receive the reference data with sufficient energy, satellite 20 advantageously uses a fountain code for transform the reference data into a binary information stream, transmitted over several beacon PRBs.

[0120] The duration of the beacon stream then makes it possible to increase the level of redundancy on the transmitted information and consequently to increase the energy of the transmitted information (notion of energy per bit or "Energy per bit").

[0121] With this new approach, terminal 10 is able to estimate a beacon SNR value with high accuracy at each satellite illumination period.

[0122] The dated beacon SNR is communicated to ACU 62 to control the beam orientation of antenna 61 towards satellite 20.

[0123] Step 150 is iterated as long as terminal 10 is in contact with satellite 20 and ends when satellite 20 is no longer visible to terminal 10 or when terminal 10 decides to establish a link with another satellite in the constellation, in particular a satellite offering better quality of service.

[0124] Advantageously, the number of beacon PRBs to be placed in a subframe is dynamically defined by the satellite, based on the minimum energy that a SATCOM terminal located within a given spot in the geographical area illuminated by the satellite must receive in order for that terminal to be able to extract the reference data in a predefined time.

[0125] This minimum energy increases almost linearly with the number of PRBs.

[0126] The number of beacon PRBs to be transmitted to achieve a target beacon SNR value in the time slot during which a terminal receives the satellite beam is representative of the expected pointing performance.

[0127] A typical pointing accuracy value is given by an antenna pointing error of less than 0.5°. It is a function of the antenna size.

[0128] The planning process 200 is executed on a planning computer, offline, in mission configuration. The process 200 comprises the following steps, for each spot in the satellite coverage:

[0129] In a step 210, the target beacon SNR value is calculated, taking into account the maximum permissible pointing error, the PRB pattern repetition periodicity, optionally the beam-hopping cycle and advantageously other factors, such as the antenna gain (or more properly the G / T figure of merit).

[0130] In a step 220, the number of beacon PRBs required to achieve the target SNR value is calculated, for example by taking into account the estimated link budget between the satellite and a nominal terminal located in the spot under consideration, and the choice of modulation and coding performed by the physical layer of the satellite payload.

[0131] This link budget is taken in the least favorable configuration, i.e. when the satellite's elevation above the horizon is low: the attenuation through the atmospheric layer is then at its largest and the distance between the satellite and a potential terminal is at its maximum.

[0132] Once the number of PRBs required has been determined, in a step 230, the beacon PRBs are pre-positioned in the time-frequency matrix so that the MAC layer PRB allocator does not use them for the traffic flow.

[0133] Preferably, these beacon PRBs are positioned regularly along the time direction so that terminals can smooth their computational load related to the demodulation of the beacon stream by executing the fountain code algorithm.

[0134] Preferably, the beacon PRBs are distributed over different subcarriers, so as not to introduce bias if one or more frequencies have their propagation degraded compared to the average.

[0135] In a step 240, the allocation of beacon PRBs is broadcast to SATCOM terminals, via an external medium or via a terrestrial network, if these terminals can connect to it.

[0136] This same allocation of beacon PRBs is transmitted to the satellites of the constellation, with an effective start date for the use of this allocation of beacon PRBs by the payloads.

[0137] The present invention consists of integrating a beacon in the form of a set of PRBs directly into the 5G NTN transmission protocol.

[0138] The use of a fountain code increases the signal energy of this beacon and consequently the accuracy of the pointing.

[0139] The beacon can be transmitted and received intermittently, which may allow for the transparent implementation of beam-hopping operation of terminals / satellites.

Claims

Demands

1. A method for pointing (100) a SATCOM terminal (10) towards a satellite (20) carrying a regenerative payload (22), in a 5G NTN type cellular communication network, comprising the steps of: - generating, by the payload (22), a beacon stream from a reference data shared with the SATCOM terminal (10); - transmitting a signal in 5G NTN format, by the payload (22), integrating the beacon stream into at least one physical radio block called a beacon of a subframe of the signal according to a predefined time-frequency pattern; - receiving the signal by the SATCOM terminal (10); - extracting, by the SATCOM terminal, the physical radio beacon blocks contained in each subframe of the received signal; - performing an instantaneous measurement from the physical radio beacon blocks; and, - orienting a beam from an antenna of the SATCOM terminal taking into account the instantaneous measurement.

2. A method according to claim 1, wherein the beacon stream consists of a repetition of the reference data.

3. Method according to claim 1, wherein the beacon stream is generated by a beacon generator (48) of the satellite payload (22) by applying a fountain code type algorithm to the reference data.

4. A method according to any one of claims 1 to 3, comprising a step of evaluating, by the SATCOM terminal, a signal level indicator from the physical beacon radio blocks as an instantaneous measurement used for beam steering of the terminal antenna.

5. A method according to any one of claims 1 to 4, comprising the steps of: - calculating an estimate of the reference data from the binary data extracted from the physical radio beacon blocks; - calculate an error between the reference data estimate and the reference data as an instantaneous measurement used for the terminal antenna beam orientation.

6. Method according to claim 5, wherein the error is a signal-to-noise ratio.

7. A method according to claim 5 or claim 6, wherein the error is used to verify an identity of the satellite (20).

8. A 5G NTN format signal comprising a plurality of subframes, each subframe being composed of a time-frequency pattern of a plurality of physical radio blocks, characterized in that at least one physical radio block of a subframe, in a predefined position, is reserved for the transmission of a beacon stream.

9. Regenerative payload (22) of a satellite of a 5G NTN type cellular communication network, adapted to generate a signal in 5G NTN format according to claim 8.

10. Payload according to claim 9, comprising a beacon generator (48) suitable for generating a beacon stream from a reference data and for applying the generated beacon stream as input to an access control layer to the medium (44) of the payload, the beacon generator indicating a modulation and a coding to be used for the emission of the beacon stream.

11. Payload according to claim 10, wherein the beacon stream is modulated and coded according to a robust coding.

12. SATCOM terminal (10), capable of operating on a 5G NTN type cellular communication network, characterized in that it is adapted to drive an antenna (60) of the SATCOM terminal from a beacon stream contained in a signal in 5G NTN format according to claim 8.

13. SATCOM terminal according to claim 12, comprising a beacon receiver (78) adapted to calculate an estimate of the reference data from the binary data extracted from the physical radio beacon blocks carrying the beacon stream and to calculate an error between the estimate of the reference data and the reference data as a second instantaneous measurement, and to apply said second instantaneous measurement as input to an antenna (62) driver unit (60) of the SATCOM terminal (10).

14. SATCOM terminal according to claim 13, wherein the beacon receiver (78) executes a fountain code type algorithm to calculate an estimate of the reference data.

15. SATCOM terminal according to any one of claims 12 to 14, comprising a physical layer (72) adapted to evaluate an instantaneous signal level indicator from the physical radio blocks carrying the beacon stream as a first instantaneous measurement and to apply said first instantaneous measurement to the input of the antenna (60) driving unit (62).

16. A method for planning (200) an allocation of physical beacon radio blocks in a subframe of a 5G NTN format signal according to claim 8, consisting of: - calculating (210) a target value of an instantaneous measurement made by a SATCOM terminal, taking into account a maximum tolerated pointing error and a reception time by a terminal of the signal; - calculating (220) the number of physical beacon radio blocks required to reach the target value of the instantaneous quantity; and, - pre-positioning (230) the required number of physical beacon radio blocks in a time-frequency pattern corresponding to a subframe of the signal, and thus defining an allocation of physical beacon radio blocks.

17. A planning method (200) according to claim 16 comprising a step (240) of distributing the allocation to SATCOM terminals and to the regenerative payloads of satellites of a 5G NTN type cellular communication network.

18. A planning method according to claim 16 or claim 17, wherein calculating the number of physical radio beacon blocks required to achieve the target value of the instantaneous measurement takes into account an estimated link budget between a satellite and a terminal and / or a choice of beacon stream modulation and coding.

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