Apparatus and system for receiving ADS-B messages from an orbiting satellite

Description

Technical field

[0001] The present invention belongs to the field of satellite telecommunications, and relates more particularly to the reception of ADS-B (“Automatic Dependent Surveillance-Broadcast”) messages from a satellite in orbit around the Earth. Prior art

[0002] Nowadays, most aircraft, especially airplanes, spontaneously transmit ADS-B messages.

[0003] Several physical layer protocols exist for ADS-B messages. The most common is known as "1090 MHz Extended Squitter" or 1090 ES and is an extension of Mode S radar transponders using frequencies around 1090 megahertz (MHz). Other physical layer protocols are also known, including the UAT (Universal Access Transponder) protocol, which uses frequencies around 978 MHz, and the VDL (VHF Data Link) Mode 4 protocol, which uses frequencies around 108-118 MHz.

[0004] ADS-B messages are transmitted in particular to avoid collisions between aircraft. Indeed, an aircraft equipped with an ADS-B transponder recurrently transmits ADS-B messages which include in particular the position of the aircraft (generally in the form of GPS coordinates - "Global Positioning System"), the direction of the aircraft, the speed of the aircraft, etc. These ADS-B messages can be received by any aircraft within range of the transmitting aircraft, and the receiving aircraft can then compare its own position, direction, speed, etc., with those indicated in the received ADS-B messages, and detect any risk of collision and, if necessary, inform the pilot crew.

[0005] Such ADS-B messages can also be received by ADS-B ground stations, thus enabling air traffic control authorities to know the positions, directions, speeds, etc., of aircraft within range of ADS-B ground stations, and to use this information to significantly improve air traffic awareness and control.

[0006] However, there are many geographical areas where it is not possible to install ADS-B ground stations. This is the case, for example, for oceans, mountains, deserts, etc. Thus, the geographical coverage of the Earth's surface, for collecting ADS-B messages by means of ADS-B ground stations, can only be partial.

[0007] In order to increase the geographical coverage for the collection of ADS-B messages, it has been proposed to embed ADS-B receiving devices in satellites, in order to supplement the geographical coverage provided by ADS-B ground stations, or even to replace said ADS-B ground stations. Thus, ADS-B messages transmitted by aircraft can be received by a satellite, which returns the information included in the received ADS-B messages to a ground station. Typically, the information included in the ADS-B messages is transmitted to the ground stations using a physical layer protocol different from the ADS-B protocol, for example using a frequency band reserved for satellite communications.

[0008] However, ADS-B protocols were not designed for ADS-B messages to be received from satellites. Therefore, receiving ADS-B messages from satellites, including those in low Earth orbit (LEO), poses certain difficulties.

[0009] In particular, due to its positioning at a high altitude and its field of view directed towards the Earth, a satellite is likely to receive ADS-B messages transmitted from geographical areas much larger than the maximum range of the ADS-B protocol in the case of terrestrial communication between two aircraft or between an aircraft and an ADS-B ground station. Thus, a satellite is likely to receive ADS-B messages from a much larger number of aircraft than in the case of terrestrial communication. As a result, the probability of collision between ADS-B messages at a satellite is significantly greater than in the case of terrestrial communication, and it is very difficult to detect ADS-B messages when the number of collisions between ADS-B messages is large.

[0010] In order to reduce the probability of collision, it is known to embed an antenna adapted to form a plurality of beams, each beam being narrower than the field of view of the satellite. Thus, the footprint of a beam, called a "spot", is reduced compared to the service area defined by the footprint of the satellite's field of view, consequently reducing the number of ADS-B messages likely to be received in a beam, and therefore also reducing the probability of collision in a beam. [Yu2020] also proposes adapting the size of the beams according to the density of aircraft.

[0011] However, to be able to collect the ADS-B messages transmitted from the entire service area, it is necessary to be able to simultaneously process the signals received in the different beams, which requires the satellite to carry a greater number of processing modules, possibly even carrying as many processing modules as beams formed (independently of redundancy issues for which additional processing modules could be carried to compensate for the failure of a processing module).

[0012] Thus, the greater the number of beams, the smaller the spots formed, which reduces the probability of collision in each beam. However, the greater the number of beams, the greater the number of processing modules that must be on board the satellite, which adversely increases the volume and mass of the satellite, as well as its power consumption. Summary

[0013] The present invention aims to overcome all or part of the limitations of the solutions of the prior art, in particular those set out above, by proposing a solution which makes it possible to collect ADS-B messages from a satellite while limiting the probability of collision between ADS-B messages and the number of processing modules which must be on board the satellite.

[0014] For this purpose, and according to a first aspect, there is proposed a device for receiving ADS-B messages for a satellite in orbit around the Earth, the receiving device comprising an array of sources and a beamforming module adapted to form beams within a field of vision of said array of sources, a footprint of said field of vision defining a service area of ​​said receiving device, different service areas being associated with different respective positions of the satellite on the orbit, a footprint of a beam defining a spot within the service area, said beamforming module being configured to form each beam by combining signals supplied by the array of sources by applying combination coefficients.Furthermore, said receiving device comprises a processing circuit configured to obtain information representative of a position of the satellite on the moving orbit and to modify a set of combination coefficients of the beam forming module to adapt the surface area and / or the shape of the spots of the beams formed to a geographical distribution of aircraft within the service area associated with the position of said satellite on the moving orbit.

[0015] Thus, the area and / or shape of the spots of the beams formed are dynamically adapted, as the satellite moves on its moving orbit, to the geographical distribution, known a priori, of the aircraft within the service area associated with the current position of said satellite on its moving orbit.

[0016] Indeed, it is possible to establish a priori an aircraft density map on the scale of all or part of the Earth, based on a priori knowledge of air traffic. Such an aircraft density map represents, for example, the average density or the maximum density of aircraft flying over each part of the Earth's surface. In practice, the probability of collision increases with the number of aircraft present in a beam spot. To limit the probability of collision, it is therefore advantageous, when defining the beam spots to be formed, to take into account a priori knowledge of the theoretical geographical distribution of aircraft in the service area considered.

[0017] For example, to limit the probability of collision in the beams, it is possible to form beam spots of different surface areas depending on the density of aircraft in the respective parts of the service area in which the spots are to be formed. For example, it is possible to form spots of small surface area in parts with a high density of aircraft, and conversely to form spots of large surface area in parts with a low density of aircraft. It is also possible, in certain examples, to determine the surface area and / or the shape of each spot so as to ensure that the number of aircraft, likely to be present in each spot according to the geographical distribution of the aircraft in the service area, remains below a predetermined threshold value. Said threshold value is for example of the order of 200 aircraft, or even of the order of 100 aircraft.

[0018] It is therefore understood that taking into account the theoretical geographical distribution of aircraft in the service area considered makes it possible to adapt the formed beams to the air traffic expected in this service area. This adaptation makes it possible in particular to optimize the number of formed beams, the surface area and / or shape of which can be determined, for example, to have substantially the same probability of collision in each formed beam. Such optimization of the number of formed beams therefore makes it possible to reduce the requirements in terms of processing modules to be carried in the satellite, since the maximum number of beams to be formed simultaneously determines the minimum number of processing modules to be carried in the satellite.

[0019] Indeed, in the prior art solutions, the formed beams were static (not dynamically modifiable). Their shapes and areas were determined once and for all and sized for the worst case. The beams thus formed were necessarily all sized to limit the maximum number of aircraft that could be in the corresponding spots, which required in particular having a small area for all the beam spots and, ultimately, a large number of beams to be formed. According to the invention, small area beam spots are formed only in the parts of the service area where this is necessary. Elsewhere, it is possible to increase the area of ​​the beam spots, which makes it possible to reduce the total number of beams to be formed to cover the entire service area.

[0020] It should be noted that the beams to be formed within a given service area are not necessarily all formed simultaneously. It is also possible to form all or some of the beams successively, during an observation period of the service area, of predetermined duration. Forming certain beams successively (known as "beam hopping" in the English literature) makes it possible to reduce the number of beams to be activated simultaneously, which also makes it possible to reduce the number of processing modules to be carried in the satellite.

[0021] Furthermore, the processing circuit is configured to control the respective activation durations of the spots of the beams formed within the service area associated with the position of the satellite as a function of the geographical distribution of the aircraft within said service area.

[0022] Such arrangements are advantageous in that they allow the respective activation durations of the beam spots, i.e. the durations during which said beam spots are actually formed, to be adapted to the expected air traffic conditions in the service area. Such an adaptation may make it possible to reduce the probability of collision and / or to resolve certain collisions. In particular, the transmission of ADS-B messages is pseudoperiodic in that the transmission period of the ADS-B messages comprises a fixed part and a random part. Due to this random part, two aircraft that transmit respective ADS-B messages at the same time will transmit their subsequent ADS-B messages at different times. Thus, prolonged listening (activation duration) of a spot makes it possible to resolve certain collisions.In addition, extended monitoring also improves collision resolution when implementing Multi-User Detection (MUD) techniques. More generally, the greater the number of aircraft present in a beam spot, the greater the time potentially required to extract each ADS-B message received in that beam spot.

[0023] Thus, it is advantageous, for example, to provide longer activation times for beam spots likely to include a large number of aircraft than for beam spots likely to include a smaller number of aircraft. Furthermore, such optimization of the activation times also makes it possible to optimize the processing over an observation period of predetermined duration. In particular, reducing the activation time when possible (a priori low number of aircraft in the beam concerned) makes it possible in certain cases to process sequentially, by the same processing module, beams whose sum of the activation times remains less than the duration of the observation period. The activation time of a beam must, however, be sufficient to allow each aircraft located in the associated spot to transmit at least one ADS-B message.

[0024] In particular embodiments, the receiving device may further comprise one or more of the following features, taken individually or in any technically possible combination.

[0025] In particular embodiments, the set of coefficients is modified to adapt the shape of at least one beam spot formed to a preferred trajectory of aircraft within the service area associated with the position of the satellite.

[0026] Indeed, air traffic is not random, and there are sometimes air corridors towards which many aircraft converge, for example to connect Europe to North America. Such air corridors correspond to preferred trajectories which can also be taken into account when defining the beam spots to be formed. For example, the shape of at least one beam spot can be chosen to be oblong following a preferred trajectory of the aircraft or even oblong transversely to said preferred trajectory.

[0027] In particular embodiments, the set of combining coefficients is configured to not form spots within a predetermined exclusion zone for the service area associated with the satellite position. For example, the exclusion zone may correspond to a geographic area provided with ADS-B ground stations and / or a geographic area in which the aircraft density is greater than a predetermined threshold value.

[0028] In particular embodiments, the reception device comprises a module for receiving a mission plan, said mission plan comprising a plurality of sets of combination coefficients for the beamforming module, each set of combination coefficients being associated with a respective position of the satellite on the moving orbit and making it possible to form beam spots whose surface area and / or shape is adapted to the theoretical geographical distribution of aircraft within the service area associated with said respective position of the satellite on said moving orbit.

[0029] According to a second aspect, there is provided a satellite comprising a receiving device according to any one of the embodiments of the invention.

[0030] According to a third aspect, there is provided a method for controlling, by a ground station, an ADS-B message reception device on board a satellite in orbit around the Earth, said reception device comprising an array of sources and a beamforming module adapted to form beams within a field of view of said array of sources, a footprint of said field of view defining a service area of ​​said reception device, different service areas being associated with different respective positions of the satellite on the orbit, a footprint of a beam defining a spot within the service area, said beamforming module being configured to form each beam by combining signals provided by the array of sources by applying combination coefficients.The control method comprises, for each of a plurality of predetermined positions of the satellite on said moving orbit, steps of: . obtaining an aircraft density map representative of the geographical distribution of aircraft within the service area associated with the considered position of the satellite on the moving orbit, determining a set of combination coefficients as a function of the aircraft density map, the set of combination coefficients being determined to adapt the surface area and / or the shape of the beam spots formed to the geographical distribution of aircraft within the service area associated with the considered position, determining an activation duration of each beam spot as a function of the geographical distribution of aircraft within the service area associated with the considered position. The control method further comprises a step of transmitting, to the reception device on board the satellite, a mission plan grouping together the sets of combination coefficients associated respectively with the plurality of positions of the satellite on the moving orbit.

[0031] In particular embodiments, the control method may further comprise one or more of the following characteristics, taken individually or in all technically possible combinations.

[0032] In particular embodiments, each set of combination coefficients makes it possible to form a plurality of beams simultaneously and / or successively during an observation period of predetermined duration of the service area associated with the position associated with said set of combination coefficients.

[0033] In particular embodiments, the sets of combination coefficients are determined to form spots of smaller area in high aircraft density portions of the service area considered than in low aircraft density portions of the service area considered.

[0034] In particular embodiments, the sets of combination coefficients are determined to control the area and / or shape of each beam spot to have a number of aircraft within each beam spot less than a predetermined threshold value.

[0035] In particular embodiments, at least one set of combination coefficients is determined to adapt the shape of at least one beam spot to a preferred trajectory of the aircraft within the service area associated with the position considered.

[0036] In particular embodiments, the shape of the at least one beam spot is oblong following the preferred trajectory of the aircraft or oblong transversely to said preferred trajectory of the aircraft.

[0037] In particular embodiments, at least one set of combination coefficients is configured to not form spots within a predetermined exclusion zone within the service zone associated with the position in question.

[0038] According to a fourth aspect, a ground station is proposed comprising means configured to implement a control method according to any one of the embodiments of the invention.

[0039] According to a fifth aspect, there is proposed a system for receiving ADS-B messages transmitted by aircraft, said reception system comprising at least one ground station according to any one of the embodiments of the invention and at least one satellite in orbit around the Earth, said at least one satellite carrying a device for receiving ADS-B messages according to any one of the embodiments of the invention. Brief description of the drawings

[0040] The invention will be better understood by reading the following description, given as a non-limiting example, and made with reference to the figures which represent: Figure 1 : a schematic representation of a particular embodiment of a satellite reception system for ADS-B messages transmitted by aircraft, Figure 2: a schematic representation of a particular embodiment of an ADS-B message receiving device for satellite, Figure 3 : a schematic representation of a particular embodiment of a ground station for controlling a satellite carrying an ADS-B message reception device, Figure 4 : a diagram illustrating the main steps of a particular mode of implementation of a method for controlling a satellite carrying an ADS-B message reception device, Figure 5 : an example illustrating beamforming for the collection of ADS-B messages in a service area of ​​a satellite carrying an ADS-B message receiving device, Figure 6 : a diagram illustrating the main steps of a particular method of implementing the determination of a set of combination coefficients and beam activation durations.

[0041] In these figures, like references from one figure to another designate identical or similar elements. For reasons of clarity, the elements shown are not to scale, unless otherwise stated. Description of the embodiments

[0042] There figure 1 schematically represents an exemplary embodiment of a system 10 for receiving by satellite ADS-B messages transmitted by aircraft, such as airplanes 20.

[0043] As illustrated by the figure 1 , the reception system 10 comprises one or more satellites 11, each satellite 11 carrying a device 40 for receiving ADS-B messages which will be described below with reference to the figure 2 .

[0044] As previously indicated, several physical layer protocols exist for ADS-B messages, and the receiving device 40 supports at least one possible physical layer protocol for ADS-B messages, for example the 1090 ES protocol. The receiving device 40 may also support several physical layer protocols, and may in particular support both the 1090 ES, UAT and VDL Mode 4 protocols.

[0045] The ADS-B messages transmitted by the aircraft 20 are received by the reception device 40 of the satellite 11. The detected ADS-B messages and / or the information included in the detected ADS-B messages are retransmitted to the ground, to a collection ground station 13. The present invention mainly relates to the collection of the ADS-B messages by the satellite 11, and the processing carried out on the ADS-B messages received by the reception device 40, apart from those detailed below, is outside the scope of the present invention. Thus, the reception device 40 can be, for the ADS-B messages, a transparent or regenerative payload.Likewise, the downlink from the satellite 11 to the collection ground station 13 is outside the scope of the present invention, it being understood that the ADS-B messages detected by the satellite 11 and / or the information extracted therefrom must be able to be sent down to the ground, directly or indirectly (via another satellite), in order to be able to be used, for example by the air traffic authorities. Typically, the downlink from the satellite 11 to the collection ground station 13 uses a physical layer protocol different from the ADS-B protocol, for example using a frequency band reserved for satellite communications.

[0046] Satellite 11 is in a tracking orbit, meaning that its projection on the ground moves across the Earth's surface. The tracking orbit of satellite 11 is, for example, a low-altitude orbit (LEO) or a medium-altitude orbit (MEO). Preferably, the altitude of the tracking orbit is equal to or less than 2000 kilometers (km), or even equal to or less than 1000 km. The tracking orbit is, for example, an inclined orbit, such as a polar orbit.

[0047] As illustrated by the figure 1 , the ADS-B messages transmitted by the aircraft 20 can also be received by ADS-B ground stations 30. Unlike the ground collection stations 13, the ADS-B ground stations 30 directly receive the ADS-B messages transmitted by the aircraft, whereas the ground collection stations 13 aim to collect on the ground the ADS-B messages received by the satellite 11. Furthermore, in the non-limiting example illustrated by the figure 1, the ADS-B ground stations 30 and the ground collection stations 13 are connected to the same air traffic monitoring center 31, to which they send the information included in the received ADS-B messages. However, nothing precludes, according to other examples, having in particular a system 10 for receiving ADS-B messages by satellite without ADS-B ground stations 30, in which case the ADS-B messages are collected exclusively by satellites 11.

[0048] In the non-limiting example illustrated by the figure 1, the system 10 for receiving ADS-B messages by satellite also comprises at least one ground station 12 for controlling the at least one satellite 11. The ground control station 12 is used, in certain embodiments, to send to a satellite 11 configuration information for the device 40 for receiving said satellite 11. It should be noted that, in particular embodiments, the ground control station 12 may be confused with a ground collection station 13, in which case it transmits configuration information to the satellite 11 and receives from the satellite 11 the information included in the ADS-B messages received by said satellite 11. The configuration information is transmitted to the satellite 11 using a physical layer protocol different from the ADS-B protocol, for example using a frequency band reserved for satellite communications.

[0049] There figure 2schematically represents an exemplary embodiment of a device 40 for receiving ADS-B messages. As illustrated by the figure 2 , the reception device 40 comprises a network 41 of sources, a beamforming module 42 and a processing circuit 43. It should be noted that the reception device 40 may also comprise other elements, in particular for the radio reception part (low noise amplifiers, analog filters, mixers, local oscillators, etc.), which are outside the scope of the present invention and are not shown for the sake of clarity of the figures.

[0050] The network 41 of sources of the reception device 40 is adapted to receive the ADS-B messages transmitted by the aircraft 20. Each source of the network 41 of sources can be of any type known to those skilled in the art, and the choice of a particular type of source constitutes only a variant of implementation of the reception device 40. For example, it is possible to use sources of the patch antenna, horn antenna, etc. type.

[0051] The network 41 of sources determines a field of view of the receiving device 40, within which the receiving device 40 can receive ADS-B messages transmitted by aircraft 20 on the surface of the Earth. The footprint of the field of view defines a service area of ​​the receiving device 40. It should be noted that the field of view of the network 41 of sources may also be limited by the roundness of the Earth, in which case the service area is limited to the part of the Earth which is actually visible from the satellite 11. Due to the moving nature of the orbit of the satellite 11, the service area is not fixed and moves with the satellite 11. Thus, different service areas are associated with different respective positions of the satellite 11 on its moving orbit.

[0052] The beamforming module 42 is adapted to form beams within the field of view of the source array 41. The footprint of a formed beam, within the service area, is referred to as a "spot".

[0053] In a manner known per se, the beamforming module 42 combines, for beamforming, signals provided by all or some of the sources of the source array 41 by means of combination coefficients. Each combination coefficient is a quantity defined by a gain and a phase. By appropriately controlling the combination coefficients, it is possible to control the radiation pattern of the beam. Thus, it is possible to dynamically control different parameters of the beam, such as for example the main radiation direction (and therefore the position of the spot in the service area), the width of the main radiation lobe in several dimensions (and therefore the shape and area of ​​the spot in the service area), etc.In the present invention, the combination coefficients are dynamically modifiable to enable the different beams formed to be adapted to the air traffic conditions expected in the service area.

[0054] As indicated above, several combination coefficients are required to form a beam. A "set of combination coefficients" refers to the set comprising all the combination coefficients of all the beams to be formed within a single service area. A set of combination coefficients therefore comprises several combination coefficients to be used to form a first beam, several combination coefficients to be used to form a second beam, etc.

[0055] The beamforming module 42 may, for example, be primarily analog, and may include controllable analog phase shifters and gains to apply variable combination coefficients. Where appropriate, the combination coefficients are modified by appropriately controlling the analog phase shifters and gains.

[0056] According to other examples, the beamforming module 42 may be entirely digital, in which case it may be integrated into the processing circuit 43 which is described below. In such a case, the beamforming coefficients are applied directly to digital signals obtained after analog / digital conversion of the signals supplied by the sources of the source network 41. The use of an entirely digital beamforming module 42 is advantageous in that it allows new combination coefficients to be applied more quickly, but also in that the combination coefficients can be determined and controlled more precisely, so that it is easier to form beams that are both precise and complex.

[0057] The processing circuit 43 comprises, for example, one or more processors and storage means (magnetic hard disk, electronic memory, optical disk, etc.) in which a computer program product is stored, in the form of a set of program code instructions to be executed to control the beamforming module 42. Alternatively or in addition, the processing circuit 43 may comprise one or more programmable logic circuits (FPGA, PLD, etc.), and / or one or more specialized integrated circuits (ASIC, etc.), and / or a set of discrete electronic components, etc., adapted to carry out all or part of the control of the beamforming module 42.

[0058] In practice, the processing circuit 43 is configured to obtain information representative of the position of the satellite 11 on the moving orbit. The information representative of the position of the satellite 11 may correspond, for example, directly to the current position of said satellite 11, for example in the form of GPS coordinates. According to another non-limiting example, the information representative of the position of the satellite 11 may correspond, for example, to a current date. Indeed, it is possible to predict in advance the date on which the satellite 11 will be at a predetermined position, so that any date is associated with a position of the satellite 11 on its moving orbit.Obtaining information representative of the position is carried out in a conventional manner, and the choice of a particular method for obtaining such information representative of the position of the satellite 11 in its moving orbit constitutes only a variant of implementation of the reception device 40.

[0059] The position of satellite 11 in its rotating orbit determines the associated service area within which beamforming module 42 is to form beam spots.

[0060] For each service area, it is possible to establish a priori, that is to say before satellite 11 flies over said service area in order to form beam spots there, an aircraft density map representative of a theoretical geographical distribution of aircraft within each service area. Indeed, air traffic is controlled according to certain well-established rules. For example, there are air corridors which represent preferred trajectories followed at least locally by aircraft. In addition, airports are convergence points for aircraft which determine the trajectories of aircraft, etc. It follows that air traffic is not random, and that the density of aircraft is not the same at all points on the Earth's surface, and varies during the day.Thus, it is possible to carry out a priori a statistical analysis of air traffic, in order to estimate a priori the aircraft density map on the scale of all or part of the Earth, representative of the geographical distribution of aircraft. The aircraft density map may include, for example, an average aircraft density, a maximum aircraft density, etc., for each part of each service area. The aircraft density map therefore makes it possible to know in particular which parts of a given service area are densely populated with aircraft, and which other parts of said service area are sparsely populated. Such an aircraft density map may be updated on a recurring basis, to take into account changes in air traffic. Such an update may take into account air traffic observations made on the basis of ADS-B messages received by satellite 11, during previous overflights of each service area.

[0061] It should be noted here that the aircraft density map does not concern all aircraft, but only aircraft that transmit ADS-B messages. Indeed, not all aircraft or planes are equipped with ADS-B transponders, and only those that transmit ADS-B messages are of interest to the receiving device 40. It is however possible, in certain implementation modes, to also take into account aircraft that transmit signals in the same frequency bands as those of the ADS-B messages considered. For example, Mode S radar transponders use the same frequency as the ADS-B messages of the 1090 ES protocol. The establishment of the aircraft density map can therefore also take into account aircraft that, although not transmitting 1090 ES ADS-B messages, are equipped with Mode S radar transponders.

[0062] Since the (theoretical) geographical distribution of aircraft within each service area is known a priori, it is possible to adapt the formed beams to the expected air traffic conditions within the service area associated with the current position of satellite 11.

[0063] For this purpose, the processing circuit 43 is configured to modify a set of combination coefficients of the beam-forming module 42 to adapt the surface area and / or the shape of the spots of the beams formed to the geographical distribution of the aircraft within the service area associated with the position of the satellite 11 on its moving orbit, as a function of the information representative of said position of said satellite 11 on its moving orbit.

[0064] Preferably, the processing circuit 43 stores a mission plan comprising a plurality of sets of combination coefficients, each set of combination coefficients being associated with a respective position of the satellite 11 on the moving orbit and making it possible to form beam spots whose surface area and / or shape is adapted to the geographical distribution of aircraft within the service area associated with said respective position of the satellite 11 on said moving orbit. The mission plan therefore groups together the sets of combination coefficients which will be applied successively by the satellite 11, from one service area to another, as the satellite 11 moves from one position to another on its moving orbit.

[0065] The mission plan may be determined by the processing circuit 43, based on aircraft density maps associated with the different service areas, the aircraft density maps being able to be stored in the form of a single global aircraft density map representative of the geographical distribution of the aircraft in all the service areas. The aircraft density maps may be received for example from the ground control station 12.

[0066] In preferred embodiments, the mission plan is calculated on the ground, for example by the ground control station 12. Where appropriate, the receiving device 40 comprises, as illustrated by the figure 2, a module 44 for receiving the mission plan, transmitted by the ground control station 12 as configuration information. The mission plan stored by the ADS-B message reception device 40 can be updated recurrently by the ground control station 12, to take into account changes in air traffic.

[0067] Thus, from the information representative of the position of the satellite, the processing circuit 43 finds in the stored mission plan the set of combination coefficients associated with the corresponding position of the satellite 11, to be used for the service area flown over by the satellite 11, and uses this set of combination coefficients to control the beamforming module 42.

[0068] The set of combination coefficients is applied during an observation period of predetermined duration, which may vary from one service area to another. The set of combination coefficients comprises the combination coefficients of each beam to be formed. Each beam is formed for an activation duration which is equal to or less than the duration of the observation period, and which may vary from one beam to another. The beams may be formed simultaneously and / or successively according to a beam activation sequence, associated with the set of combination coefficients, which may also be included in the mission plan. The signal provided by a beam, which comprises the ADS-B messages received from the aircraft located in the associated spot, is processed by a processing module (not shown in the figures), which may be integrated into the processing circuit 43.The receiving device 40 preferably comprises several processing modules, and each processing module is for example configured to detect the ADS-B messages present in the beam signal, and possibly extract the information included in the detected ADS-B messages. The number of processing modules must make it possible to process the signals of all the beams formed during the observation period, and is for example equal to or greater than the maximum number of beams to be formed simultaneously for each service area. The detected ADS-B messages and / or the extracted information are then transmitted to a collection ground station 13, by means of a transmission module (not shown in the figures) of the receiving device 40.

[0069] In the remainder of the description, the case where the mission plan is calculated by the ground control station 12, and is received by the reception device 40 which applies it to control the beamforming module 42, for the reception of ADS-B messages, is considered in a non-limiting manner. The mission plan includes the sets of combination coefficients, and possibly the associated activation sequences, associated with a plurality of positions that the satellite 11 will occupy over a predetermined time horizon.

[0070] There figure 3 schematically represents an exemplary embodiment of a ground control station 12. In this example, the ground control station 12 comprises a transmission module 120 and a processing circuit 121.

[0071] The transmission module 120 is used to transmit configuration information to the reception module 44 of the satellite 11, where said configuration information can be used by the processing circuit 43. The configuration information can include the mission plan to be used, or an update of a mission plan stored by the reception device 40. The transmission module 120 corresponds to a radio circuit comprising equipment considered to be known to those skilled in the art.

[0072] The processing circuit 121 comprises, for example, one or more processors and storage means (magnetic hard disk, electronic memory, optical disk, etc.) in which a computer program product is stored, in the form of a set of program code instructions to be executed to implement with the transmission module 120 the different steps of a control method 50 described below. Alternatively or in addition, the processing circuit 121 may comprise one or more programmable logic circuits (FPGA, PLD, etc.), and / or one or more specialized integrated circuits (ASIC, etc.), and / or a set of discrete electronic components, etc., adapted to implement with the transmission module 120 all or part of the steps of the control method 50.

[0073] In other words, the processing circuit 121 and the transmission module 120 correspond to means configured in software (specific computer program product) and / or hardware (FPGA, PLD, ASIC, discrete electronic components, radio circuit, etc.) to carry out all or part of the steps of the control method 50 described below.

[0074] There figure 4 represents the main steps of an example of implementation of a method 50 for controlling the receiving device 40, the steps of which are implemented by the ground control station 12.

[0075] As illustrated by the figure 4 , the control method 50 comprises, for each position among a plurality of predetermined positions of the satellite 11 on its moving orbit, steps of: 51 obtaining an aircraft density map representative of the geographical distribution of aircraft within the service area associated with the considered position of satellite 11 on the moving orbit, 52 determining a set of combination coefficients as a function of the aircraft density map.

[0076] The aircraft density map obtained for a given service area corresponds, for example, to a portion of a global aircraft density map stored by the processing circuit 121. As indicated previously, the beams are formed during an observation period of predetermined duration. Consequently, the ground footprint of the field of view of the network 41 of sources will move during the observation period, due to the movement of the satellite 11 on its moving orbit. It is, for example, possible to consider that the movement of the service area is negligible during the duration of the observation period, or it is possible to consider a reference service area for the entire observation period, which corresponds, for example, to the service area associated with the initial position of the satellite 11 at the start of the observation period, or to the expected position of the satellite 11 in the middle of the observation period, etc.

[0077] Then, during step 52, the set of combination coefficients is determined to adapt the surface area and / or the shape of the beam spots formed to the geographical distribution of the aircraft within the service area associated with the position considered. Thus, step 52 of determining a set of combination coefficients for a given position comprises the definition, within the service area associated with the position considered, of beam spots whose surface areas and / or shapes are adapted to the geographical distribution of the aircraft within said service area.Once the areas and / or shapes of said spots have been defined, as well as the positions of said spots within said service zone, the set of combination coefficients making it possible to form these spots can be calculated according to any method known to those skilled in the art, the choice of a particular calculation method constituting only a variant of implementation of the invention.

[0078] As indicated above, the adaptation of the beam spots to the expected air traffic conditions aims, for example, to form spots of smaller surface area in parts with a high density of aircraft than in parts with a low density of aircraft. Alternatively or in addition, the adaptation of the beam spots aims, for example, to control the surface area and / or the shape of each beam spot to have a number of aircraft inside said beam spot lower than a predetermined threshold value. Alternatively or in addition, the adaptation of the beam spots aims, for example, to adapt the shape of at least one beam spot to a preferred trajectory of the aircraft inside the service area associated with the position considered.

[0079] As illustrated by the figure 4, the control method 50 comprises, for each position considered, a step 53 of determining the activation duration of each beam spot as a function of the geographical distribution of the aircraft within the service area considered. The activation durations of the beam spots can be determined jointly with the determination of the areas and / or shapes of said beam spots. For example, it is possible to provide longer activation durations for beam spots likely to include a large number of aircraft than for beam spots likely to include a smaller number of aircraft. However, nothing precludes, according to other examples, considering the same activation duration for all the beam spots, equal to or less than the duration of the observation period for the service area considered.

[0080] The determination of the sets of combination coefficients for forming the beams and the activation durations of said beams is for example carried out by simulation, according to an iterative process which takes into account the geographical distribution of the aircraft in the service area considered, a maximum number of aircraft in each beam, the duration of the observation period, a maximum number of beams which can be formed, etc. Such an iterative process aims for example to maximize the number of ADS-B messages which can be detected during the observation period, or to maximize the probability of detecting at least one ADS-B message per aircraft located in the service area considered, etc.

[0081] Preferably, the beam spots to be formed are determined so as to have a spot formed in any part of the service area considered for at least part of the observation period. Preferably, the beam spots to be formed may also be determined to have a partial overlap between adjacent spots, for example to avoid missing ADS-B messages transmitted by aircraft located at the edge of adjacent spots.

[0082] It should be noted that it is also possible not to seek to cover the entire service area with beam spots. In particular, it is possible, in particular modes of implementation, to provide an exclusion zone within a service area. Thus, the set of combination coefficients is configured not to form spots within this predetermined exclusion zone within the service area associated with the position considered.

[0083] Such an exclusion zone is predetermined, and corresponds for example to a geographical area in which there are other means of receiving ADS-B messages transmitted by aircraft, for example due to the presence of ADS-B ground stations 30 in this geographical area. Such an exclusion zone may also correspond to a geographical area which cannot be correctly observed from a satellite 11, for example if the density of aircraft in this geographical area is too high (airports, etc.). This possibility of excluding certain geographical areas during beam formation, in particular geographical areas well covered by other means, also makes it possible to reduce the total number of beams to be formed.

[0084] As illustrated by the figure 4, the control method 50 further comprises a step 54 of transmitting, to the reception device 40 on board the satellite 11, the mission plan grouping together the sets of combination coefficients associated respectively with the plurality of positions considered of the satellite 11 on its moving orbit.

[0085] There Figure 5 schematically represents an example of implementation of the control method 50.

[0086] More specifically, part (a) of the Figure 5schematically represents an example of an aircraft density map showing the geographical distribution of aircraft in Europe and North Africa. The service area ZS is shown in solid lines. Aircraft are represented by black dots in this aircraft density map, and we can see in particular that the density of aircraft in the European zone is very high. We also see the presence of air corridors, particularly in the North-West part of Europe towards North America or in the South-West part of Europe towards South America.

[0087] As illustrated by part (b) of the Figure 5, it is decided that Europe should not be covered (for example, due to the high density planned there and / or due to satisfactory coverage by ADS-B 30 ground stations), and an exclusion zone ZE is planned for Europe. Therefore, there is no need to form spots in this exclusion zone ZE.

[0088] Part c) of the Figure 5 schematically represents examples of beam spots that can be formed in the service area ZS, excluding the exclusion zone ZE, by adapting the area and / or shape of the beam spots to the geographical distribution of the aircraft. In this example, 10 (ten) beam spots are formed, respectively designated S1 to S10 and represented by broken lines. For the sake of clarity of part c) of the Figure 5 , the aircraft present in the ZS service area, visible in part a), are not shown in part c) of the Figure 5 .

[0089] As illustrated by part (c) of the Figure 5 , the S1-S10 spots are of various shapes and surfaces.

[0090] For example, spot S5 is substantially circular and has the largest area, and covers a low-density portion of aircraft 20. Spots S3, S4, S6, S8, S9, and S10 are also substantially circular in shape, with respective areas smaller than that of spot S5.

[0091] The spots S2 and S7 are positioned on the air corridors, and said air corridors define preferred trajectories for the aircraft 20. In the example illustrated, the spots S2 and S7 are oblong in shape following the preferred trajectory of the aircraft 20. In the example illustrated by part c) of the Figure 5, each preferred trajectory is served by a single oblong-shaped spot following the preferred trajectory considered. It is also possible, in particular if the preferred trajectory extends over a significant portion of the service area ZS, to provide at least two oblong-shaped spots arranged in the extension of one another following said preferred trajectory. However, nothing excludes other examples from covering the preferred trajectories of the aircraft 20 in a different manner. For example, it is possible to form spots of oblong-shaped beams, but arranged transversely to said preferred trajectory of the aircraft 20. It is also possible, according to other examples, to form spots of substantially circular shape, arranged along the preferred trajectory. Such circular spots are for example of small surface area, taking into account the fact that the density of aircraft in an air corridor is generally high.

[0092] Spot S1 is also oblong in shape, arranged to cover most of the northern part of the ZS service area. In this northern part of the ZS service area, the aircraft density is low, so that the surface area of ​​spot S1 is larger than, in particular, those of spots S2 and S7.

[0093] As previously indicated, the activation times of the beam spots are adapted to the distribution of aircraft 20 in the service area ZS considered.

[0094] In the example illustrated by part c) of the Figure 5, it is possible to have an activation duration of 100% of the duration of the observation period for spots S2 and S7 only, which have the highest aircraft density. In the case of ADS-B messages of type 1090 ES, the duration of the observation period is greater than 1.2 seconds (s), and is for example between 5 s and 10 s. For other spots, it is possible to provide for shorter activation durations. For example, it is possible to provide for activation durations equal to 50% of the duration of the observation period for spots S1, S4, S5, and S10, and equal to 25% of the duration of the observation period for spots S3, S6, S8 and S9.Due to these different activation durations, it is possible to activate certain beam spots successively during the observation period, so that only 5 (five) processing modules are necessary to process the signals of the 10 (ten) formed beams, for example by applying the following activation sequence: . a first processing module and a second processing module process in parallel the signals of the beams of spots S2 and S7, throughout the duration of the observation period a third processing module successively processes the signals of the beams of spots S1 and S4, which are formed successively during the observation period, a fourth processing module successively processes the signals of the beams of spots S5 and S10, which are formed successively during the observation period, a fifth processing module successively processes the signals of the beams of spots S3, S6, S8 and S9, which are formed successively during the observation period.

[0095] There figure 6schematically represents the main steps of a particular mode of implementation of step 52 of determining a set of combination coefficients for beam formation for a considered position of the satellite 11 on its moving orbit, and of step 53 of determining the activation durations of said beams. The steps illustrated in the figure 6 are repeated for each considered position of satellite 11 on its moving orbit.

[0096] As illustrated by the figure 6, step 52 firstly comprises a step 520 of geographical segmentation of the service area associated with the considered position of the satellite 11. The step 520 of geographical segmentation consists for example in segmenting the service area according to a regular grid so as to obtain a plurality of segments all having substantially the same shape and substantially the same surface area. The surface area of ​​each segment is for example equal to or less than the minimum surface area that a spot formed by the satellite 11 can have.

[0097] Step 52 then comprises, for example, a step 521 of assigning a traffic density class to each segment constituting the service area. Thus, several traffic density classes are previously defined (for example low, medium and high density, etc.), and each segment is attached to a traffic density class according to the number of aircraft expected, according to the aircraft density map, within the segment considered.

[0098] Step 52 then comprises, for example, a step 522 of excluding segments in which the number of expected aircraft is greater than a predetermined maximum number. The segments thus excluded correspond to an exclusion zone in which no beam spot will be formed.

[0099] Step 52 then comprises, for example, a step 523 of configuring the beam spots by grouping adjacent segments belonging to the same traffic density class or to close traffic density classes. Each grouping of adjacent segments defines a spot to be formed, and the grouping is preferably carried out under the constraint of a predetermined maximum spot size for the traffic density class considered. Indeed, the number of adjacent segments that can be grouped is advantageously limited to avoid having too large a number of aircraft likely to be present in the spot thus defined.The maximum number of adjacent segments that can be grouped together for a high traffic density class is smaller than the maximum number of adjacent segments that can be grouped together for a low traffic density class, and such segment grouping ensures that the number of aircraft within each spot remains below a predetermined threshold value. The configuration of the spots is, for example, carried out iteratively in order to optimize the segment groupings, i.e., in order to identify segment groupings that make it possible to minimize the number of beams to be formed for the service area in question. The set of combination coefficients for forming the beam spots thus defined are, for example, calculated during step 523.

[0100] Step 52 then includes, for example, a step 524 for calculating an average density of aircraft in each spot defined during step 523 for configuring spots. As previously for the segments, each spot is, for example, attached to a traffic density class based on the average density calculated for the spot in question.

[0101] Step 53 comprises for example a step 530 of allocating the respective activation durations of the spots defined during step 523 of configuring spots, according to the traffic density classes assigned to said spots. The activation durations are equal to or less than the duration of the observation period. It is for example possible to provide reference activation durations associated respectively with the different traffic density classes. Thus, the activation duration of a spot is for example chosen to be equal to the reference activation duration associated with the traffic density class assigned to this spot. For example, the reference activation duration for a high traffic density class may be equal to 100% of the duration of the observation period. The reference activation duration for a medium traffic density class may be equal to 50% of the duration of the observation period.The reference activation duration for a low traffic density class may be equal to 25% of the duration of the observation period, etc.

[0102] Once the respective activation durations of the different spots have been allocated during step 530, step 52 comprises, for example, a step 531 for verifying compatibility with the processing capabilities of the receiving device 40. Indeed, the defined spots and their activation durations must preferably be able to be processed by the different processing modules during the duration of the observation period. In other words, it is verified during step 531 whether there is a sequence of successive and / or simultaneous activation of the different beam spots, verifying the allocated activation durations, making it possible to process the signals of the beams of the defined spots during the duration of the observation period. In the case where such an activation sequence exists (reference 531a on the figure 6 ), then step 52 includes a step 532 of storing the activation sequence and the set of combination coefficients making it possible to form the beam spots defined during step 523. In the case where the defined spots and their respective activation durations are not compatible with the processing capacities of the reception device 40 (reference 531b on the figure 6), then step 52 comprises for example a step 533 of reducing all or part of the respective activation durations of the different spots, until an activation sequence compatible with the processing capabilities of the receiving device 40 is obtained. The reductions applied are for example proportional to the activation durations, and the proportional coefficients applied depend for example on the traffic density class assigned to each spot. For example, the reduction applied (for example 5% reduction) to the activation duration of a spot associated with a low traffic density class may be proportionally higher than the reduction applied (for example 2% reduction) to a spot associated with a high traffic density class.

[0103] As indicated above, the steps illustrated by the figure 6are repeated for each considered position of the satellite 11 on its traveling orbit. The sets of combination coefficients thus calculated (and, where applicable, the associated activation sequences) are then incorporated into the mission plan which is transmitted to the satellite 11. The mission plan is further configured to allow the receiving device 40 to apply each set of combination coefficients (and, where applicable, the associated activation sequence) when the satellite 11 is in the correct position on its traveling orbit. For example, each set of combination coefficients is associated, in the mission plan, with information representative of the associated position of the satellite 11 on its traveling orbit.Thus, when the processing circuit 43 obtains information representative of the current position of the satellite 11 in its moving orbit, it can extract from the stored mission plan the set of combination coefficients associated with this position, and use it to form spots adapted to the distribution of aircraft in the service area associated with this position.

[0104] More generally, it should be noted that the methods of implementation and embodiment considered above have been described as non-limiting examples, and that other variants are consequently conceivable. References

[0105] [Yu2020] Sunquan Yu et al. : “Integrated antenna and receiver system with self-calibrating digital beamforming for space-based ADS-B”, ACTA ASTRONAUTICA, PERGAMON PRESS, ELMSFORD, GB, Volume 170, pages 480-486, February 5, 2020

Claims

1. Device (40) for the reception of ADS-B messages for a satellite (11) in non-geostationary orbit around the Earth, said reception device (40) comprising an array (41) of sources and a beamforming module (42) capable of forming beams within a field of view of said array (41) of sources, a ground footprint of said field of view defining a service area of said reception device, different service areas being associated with different respective positions of the satellite (11) on the non-geostationary orbit, a ground footprint of a beam defining a spot within the service area, said beamforming module being configured to form each beam by combining signals provided by the array of sources by applying combination coefficients, said reception device comprising a processing circuit (43) configured to obtain information representative of a position of the satellite (11) on the non-geostationary orbit and to modify a set of combination coefficients of the beamforming module (42) so as to adapt the surface area and / or the shape of the spots of the formed beams to a geographical distribution of the aircrafts within the service area associated with the position of said satellite on the non-geostationary orbit, the processing circuit (43) being further configured to control respective activation durations of the spots of the beams formed within the service area associated with the position of the satellite (11) according to the geographical distribution of aircrafts within said service area.

2. Reception device (40) according to claim 1, wherein the set of combination coefficients is determined so as to form spots of smaller surface area in portions of high aircraft density of the service area than in portions of low aircraft density of the service area.

3. Reception device (40) according to any one of claims 1 to 2, wherein the set of combination coefficients is modified so as to control the surface area and / or the shape of each beam spot formed within the service area associated with the position of the satellite (11) in order to have a number of aircrafts, within each beam spot, that is lower than a predetermined threshold value.

4. Reception device (40) according to any one of claims 1 to 3, wherein the set of coefficients is modified so as to adapt the shape of at least one formed beam spot to a preferred trajectory of the aircrafts within the service area associated with the position of the satellite (11).

5. Reception device (40) according to claim 4, wherein the shape of the at least one beam spot is oblong along the preferred trajectory of aircrafts or oblong transversely to said preferred trajectory of aircrafts.

6. Reception device (40) according to any one of claims 1 to 5, wherein the set of combination coefficients is configured so as not to form spots within a predetermined exclusion region for the service area associated with the position of the satellite (11).

7. Reception device (40) according to any one of claims 1 to 6, comprising a module (44) for the reception of a mission plan, said mission plan comprising a plurality of sets of combination coefficients for the beamforming module (42), each set of combination coefficients being associated with a respective position of the satellite (11) on the non-geostationary orbit and making it possible to form beam spots whose surface area and / or shape is adapted to the geographical distribution of aircrafts within the service area associated with said respective position of the satellite (11) on said non-geostationary orbit.

8. Method (50) for controlling, by a ground station (12), a device (40) for the reception of ADS-B messages which is carried onboard a satellite (11) in non-geostationary orbit around the Earth, said reception device (40) comprising an array (41) of sources and a beamforming module (42) capable of forming beams within a field of view of said array (41) of sources, a ground footprint of said field of view defining a service area of said reception device, different service areas being associated with different respective positions of the satellite (11) on the non-geostationary orbit, a ground footprint of a beam defining a spot within the service area, said beamforming module being configured to form each beam by combining signals supplied by the array of sources by applying combination coefficients, said control method (50) comprising, for each among a plurality of predetermined positions of the satellite (11) in said non-geostationary orbit, the steps of: - (51) obtaining an aircraft density map representative of the geographical distribution of aircrafts within the service area associated with the considered position of the satellite (11) on the non-geostationary orbit, - (52) determining a set of combination coefficients on the basis of the aircraft density map, the set of combination coefficients being determined so as to adapt the surface area and / or the shape of the formed beam spots to the geographical distribution of aircrafts within the service area associated with the position considered, - (53) determining an activation duration of each beam spot on the basis of the geographical distribution of aircrafts within the service area associated with the position considered, said control method (50) further comprising a step (54) of transmitting, to the reception device (40) onboard the satellite (11), a mission plan which groups together the sets of combination coefficients respectively associated with the plurality of positions of the satellite (11) on the non-geostationary orbit.

9. Control method (50) according to claim 8, wherein each set of combination coefficients makes it possible to form a plurality of beams simultaneously and / or successively during an observation period of predetermined duration for observing the service area associated with the position associated with said set of combination coefficients.

10. Control method (50) according to any one of claims 8 to 9, wherein the sets of combination coefficients are determined so as to form spots of smaller surface area in portions of high aircraft density of the service area considered than in portions of low aircraft density of the service area considered.

11. Control method (50) according to any one of claims 8 to 10, wherein the sets of combination coefficients are determined so as to control the surface area and / or the shape of each beam spot in order to have a number of aircrafts, within each beam spot, that is below a predetermined threshold value.

12. Control method (50) according to any one of claims 8 to 11, wherein at least one set of combination coefficients is determined so as to adapt the shape of at least one beam spot to a preferred trajectory of aircrafts within the service area associated with the position considered.

13. Control method (50) according to claim 12, wherein the shape of the at least one beam spot is oblong along the preferred trajectory of aircrafts or is oblong transversely to said preferred trajectory of aircrafts.

14. Control method (50) according to any one of claims 8 to 13, wherein at least one set of combination coefficients is configured so as not to form spots within a predetermined exclusion region within the service area associated with the position considered.

15. Ground station (12) comprising means configured for implementing a control method (50) according to any one of claims 8 to 14.

16. System (10) for the reception of ADS-B messages transmitted by aircrafts (20), said reception system comprising at least one ground station (12) according to claim 15 and at least one satellite (11) in non-geostationary orbit around the Earth, said at least one satellite (11) carrying onboard a device (40) for the reception of ADS-B messages according to claim 7.