Bluetooth transmission from a satellite to a ground telecommunication terminal

Description

FIELD OF INVENTION

[0001] The present invention relates to satellites, and in particular to the direct transmission of information from a satellite to one or more telecommunication terminals.

[0002] It applies particularly to satellites equipped with information processing capabilities, thus enabling the transmission of information from this processing directly to the telecommunications terminal(s). The invention is especially applicable to mobile or smartphone-type terminals equipped with Bluetooth functionality. CONTEXT OF THE INVENTION

[0003] In critical situations such as natural disasters, it can be crucial to be able to directly inform residents living in an affected area as early as possible.

[0004] However, some regions of the world remain relatively underserved by telecommunications infrastructure, making the transmission of alert messages impossible in many areas or quickly overwhelming the existing infrastructure. This overload would not only prevent the entire affected population from being informed early enough, but would also hinder communications for emergency services.

[0005] Furthermore, in the event of natural disasters (floods, earthquakes, major fires, etc.), the telecommunications infrastructure may be impacted, cease to function, and thus no longer allow the communication of necessary information.

[0006] Furthermore, a constantly increasing number of satellites are continuously acquiring an extremely large volume of information. The number of satellites observing our planet is growing, and they are covering the Earth's surface with increasing precision.

[0007] Currently, this information is transmitted by observation satellites to ground stations, where it can be analyzed. The results of these analyses can then be transmitted to end users (or "consumers").

[0008] The volume of information to be processed has now reached such a scale that it is difficult to use and overwhelms ground stations. This results in a delay between the capture of information and its transmission to users, which can be detrimental and even render the information obsolete by the time it is received.

[0009] Studies show that only a small percentage of captured information is actually exploited and used, so useful information is drowned in the flood of useless information.

[0010] Advances in embedded systems allow for increasing processing capacity within satellites, particularly observation satellites, both in terms of onboard memory and digital processing resources (CPU, GPU, specialized circuits...).

[0011] However, today, these processing capabilities do not allow for improving the information transmission chain and quickly reaching end users, nor for effectively exploiting the large volume of available information.

[0012] Current mechanisms therefore do not allow the population concerned to be alerted quickly and directly enough, particularly in the absence of ground-based telecommunications infrastructure, even if an observation satellite had detected a critical situation or the imminence of such a situation.

[0013] This inadequacy of the state of technology makes it impossible to minimize the impact of a critical situation, for example by organizing an evacuation of the population or, at the very least, by preventing the population from unconsciously going towards a risk zone, by alerting in order to avoid panic effects, by providing instructions on how to behave, etc.

[0014] There is therefore a need to facilitate the transmission of relevant information to a population located on a site affected by a critical situation or by an imminent risk of a critical situation, particularly in the absence of ground communication infrastructure.

[0015] Document US2022 / 216896A1 relates to satellites, including cellular telecommunications means for disseminating information to at least one ground-based telecommunications terminal, relying on a terrestrial cellular network infrastructure. Document WO2022 / 076548A1 relates to a system and method for authenticating a mobile terminal by a space-based communication network comprising a constellation of satellites cooperating with ground stations, in order to perform terminal authentication at the satellite level in the absence of a connection to the terrestrial network. Document US2018 / 0239948A1 relates to a satellite imaging system comprising one or more imaging modalities and a wireless communication interface enabling the transmission of image data or information derived therefrom to a ground base station, capable of relaying messages or alerts to at least one telecommunications terminal.The document entitled "Understanding Bluetooth Range", published on the Internet at the URL: https: / / www.bluetooth.com / learn-about-bluetooth / key-attributes / range / , in 2022, describes a Bluetooth range simulator based on a propagation model used for terrestrial communications. SUMMARY OF THE INVENTION

[0016] The invention aims to provide a mechanism for broadcasting information directly from satellites to telecommunications terminals. The term "directly" here means that the information transmitted by a satellite is received by the terminals. In other words, no ground-based telecommunications infrastructure (base stations, cellular networks, etc.) is involved in this broadcast.

[0017] To this end, according to a first aspect, the present invention can be implemented by a device suitable for being carried on a satellite, comprising telecommunication means for disseminating information directly to at least one ground-based telecommunication terminal; said telecommunication means being adapted to disseminate said information via the Bluetooth Low Energy (BLE) communication protocol, in an "advertising" mode, in which no incoming connections are accepted, said at least one telecommunication terminal being compatible with said communication protocol and configured to receive said information without sending any connection request to the satellite's communication means, said telecommunication means comprising: a directional antenna adapted to transmit a signal carrying said information into a broadcast cone, with a transmission power greater than or equal to a few Watts in a frequency band between 2.4 and 2.8 GHz, a data rate of at least 125 kbits / s, said transmission power being determined so that a power of a signal received by at least one said terminal located in the broadcast cone is above a given reception sensitivity of said terminal for said "advertising" mode, depending on an elevation of the satellite relative to the ground, a directivity of the antenna, satellite pointing parameters and standard transmission losses related to a passage through the atmosphere.

[0018] The satellite can be a telecommunications satellite, an Earth observation satellite (including a remote sensing satellite), or any other type of satellite.

[0019] This embodiment of the invention also makes it possible to take advantage of the increasing capabilities of observation satellites, and to avoid the processing delays (and non-processings) of the usual processing chain.

[0020] To achieve this, the system also includes: at least one sensor to acquire primary information, processing means to analyze said primary information to detect within said primary information a situation corresponding to a criterion, and to determine secondary information relating to said situation; and said telecommunication means are provided to transmit said secondary information within said information.

[0021] This secondary information corresponds to (or is part of) the information disseminated by the previously defined device. According to one embodiment, the two terms are therefore equivalent when only secondary information is disseminated.

[0022] According to embodiments, the invention comprises one or more of the following features which can be used separately or in partial combination with each other or in total combination with each other: The primary information consists of images. The telecommunications equipment is adapted to transmit this information via the Bluetooth protocol, for example, using a BLE 125k S=8 mode. The processing equipment is adapted to pre-compensate for a frequency shift related to the Doppler effect based on the position of the satellite, the position of at least one telecommunications terminal, and the satellite's speed relative to the ground. The secondary information represents an alert.

[0023] According to a second aspect, the invention can also be implemented by a satellite comprising a device as previously defined, possibly with one or more of the optional features described.

[0024] According to another aspect, the invention can also be implemented by a system comprising at least one such satellite and said at least one telecommunications terminal.

[0025] According to another aspect, the invention also relates to a method for disseminating information from a satellite directly to at least one ground-based telecommunications terminal. This method implements the Bluetooth Low Energy (BLE) protocol in an "Advertising" mode, whereby the satellite's telecommunications means are adapted to disseminate said information without accepting any incoming connections, and said at least one telecommunications terminal (2) is compatible with said protocol and configured to receive said information without sending any connection requests to the satellite's communications means. This method comprises: the transmission by a suitable directional antenna of a signal carrying said information in a broadcast cone, with a transmission power, produced by a power amplifier conforming to the requirements of an on-board system, said transmission power being greater than or equal to a few Watts, in a frequency band between 2.4 and 2.8 GHz, with a bit rate of 125 kbits / s, said transmission power being determined so that a power of a signal received by at least one said terminal located in the broadcast cone, is above a reception sensitivity of said terminal, corresponding to said "Advertising" mode, depending on an elevation of the satellite relative to the ground, a directivity of the antenna, pointing parameters of the satellite and standard transmission losses related to a passage through the atmosphere.

[0026] Depending on the embodiments, the process is adapted to implement one or more of the previously described characteristics, mutatis mutandis, which can be used separately or in partial combination with each other or in total combination with each other.

[0027] According to another aspect, the invention can be implemented by a computer program comprising instructions which, when the program is executed by a computer, cause the computer to implement the as previously defined.

[0028] Other features and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention, given by way of example and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE FIGURES

[0029] The attached drawings illustrate the invention: [ Fig. 1 [ ] schematically represents an example of a functional architecture according to one embodiment of the invention. ] Fig. 2 ] schematically illustrates an example of a detailed functional architecture of the processing means, according to an embodiment of the invention [Fig. 3] illustrates a simulation of the evolution of the reception power relative to the transmission power of the satellite, according to an embodiment of the invention [ Fig. 4 ] illustrates a simulation of the evolution of the reception power relative to the transmission power of the satellite, according to another embodiment of the invention DETAILED DESCRIPTION OF METHODS OF IMPLEMENTING THE INVENTION

[0030] The invention relates to all types of satellites, in particular telecommunications satellites and observation satellites.

[0031] Depending on the embodiment, it relates in particular to Earth observation satellites, and especially to remote sensing satellites.

[0032] It can also concern low-Earth orbit telecommunications satellites of the constellation type serving as relays to Earth of information that may come from other satellites, particularly Earth observation satellites.

[0033] It can also relate to the transmission by telecommunications satellites of information from ground stations.

[0034] An Earth observation satellite is an artificial satellite used to perform geophysical and geographic observations of the Earth from Earth orbit. This category of satellite is used for purposes such as meteorology, natural resource inventory, geodesy, climate study and modeling, natural disaster prevention and monitoring, military reconnaissance, and more.

[0035] The majority of Earth observation satellites fall into the category of remote sensing satellites, whose instruments analyze electromagnetic waves (visible light, but also ultraviolet, infrared, X-rays, etc.) emitted either by the observed object or by the reflection of a wave train emitted by the satellite. Typically, the instruments used are cameras, spectrometers, radars, radiometers, etc. For example, the Pleiades, Sentinel, and ME-TEOSAT satellites belong to this category of remote sensing satellites.

[0036] A second category of Earth observation satellites performs only in-situ measurements, such as GOCE, which measures the Earth's gravitational field, or SWARM, which measures the Earth's magnetic field; these are therefore not remote sensing satellites. They use instruments such as magnetometers, passive receivers like laser reflectors, GPS, and accelerometers, or detectors of ions or neutral atoms, etc.

[0037] An observation satellite generally comprises onboard systems for the satellite's operation (power supply, positioning, etc.) and a payload system, which carries the satellite's functions useful to third parties and not for its own operation. Such a system for an observation satellite therefore includes the means to fulfill its observation function, essentially observation instruments and telecommunications equipment to transmit the observed data back to the ground.

[0038] The invention relates primarily to such a device, referenced 10 on the FIGURE 1 , for a satellite 1.

[0039] On the figure 1 , satellite 1 is located in an orbit 30 around the earth 40.

[0040] According to one embodiment of the invention, the satellite is located in a low Earth orbit, LEO (for "Low Earth Orbit"), but, according to other embodiments, it can be in other orbits (GEO for "Geostationary Earth Orbit", etc.).

[0041] Device 10 is suitable for being carried on satellite 1 and, on the figure 1 , it is actually represented as being onboard in the satellite.

[0042] According to the invention, this device 10 includes in particular telecommunication means 13 for disseminating information directly to at least one ground-based telecommunication terminal 2 40.

[0043] The signal emitted by the telecommunications equipment 13 forms a cone 50 whose opening (or solid angle) depends on the directivity of this equipment (antenna). Mobile terminals located at the center of this broadcast cone 50 receive the signal under the best conditions.

[0044] In the case where the satellite is an observation satellite, device 10 may further include: one or more sensors 11 to acquire primary information and processing means 12 to analyze this primary information in order to detect within it a situation corresponding to a predefined criterion, and to determine secondary information relating to said situation.

[0045] Telecommunication means 13 are then intended to transmit this secondary information (in other words, it represents the information indicated in the previous paragraph)

[0046] In the case of a telecommunications satellite, the information broadcast can be acquired by other means, for example, received by the satellite from a ground station or another satellite. For instance, one can imagine an observation satellite transmitting secondary information to a transmission satellite, which is then responsible for broadcasting it to ground terminals. This implementation can relieve observation satellites of this function and / or allow them to reach other coverage areas, since each satellite can only broadcast to a defined geographic area (which varies over time in the case of Earth-orbiting satellites).

[0047] The primary information acquired, or "captured," by sensor(s) 11 corresponds to the various types of information observed by observation satellites. As seen previously, observation satellites are extremely varied, and therefore the observation spectrum is vast: optical, radar, infrared, ultraviolet, listening to radio or electromagnetic signals, ionic radiation, etc.

[0048] Among electromagnetic signals, one can cite, for example, AIS (Automatic Identification System) beacon signals, which are electronic messages between ships via VHF radio waves. These signals allow ships and land-based traffic monitoring systems to know the identity, status, characteristics, position, course, and speed of vessels within the navigation area. Mechanisms for detecting these signals using satellites are already available. Another example is ADS-B (Automatic Dependent Surveillance-Broadcast) signals, which represent a cooperative surveillance system for air traffic control and other related applications.An aircraft equipped with ADS-B determines its position using a satellite positioning system (GNSS for "Geolocation and Navigation by Satellite System") and periodically sends this position and other information to ground stations and other aircraft equipped with ADS-B operating in the area.

[0049] Primary information can be of an extremely varied nature.

[0050] In one embodiment, the primary information consists of images. These images can be two-dimensional representations of an observed portion of the Earth. Typically, observation satellites acquire image streams, each image being associated with a location of the satellite relative to the Earth.

[0051] The content of the image (i.e. the information associated with each point on the observed surface of the earth) depends on the type of sensor(s) 11: optical (or “photographic”) value, radar, infrared, etc.

[0052] The primary information is analyzed by the processing means 12 of the device 10 on board the satellite 1.

[0053] These processing methods can be adapted to perform this analysis at a level of granularity specific to the structure of the primary information. For example, this analysis can be performed image by image.

[0054] This analysis step is represented by reference 121 on the figure 2 .

[0055] The result of this analysis can undergo a standard processing procedure, 122, corresponding to the normal operation of satellite 1. For example, this result can be stored in onboard memory, it can be sent to a ground station for further processing, etc. This step is optional and outside the scope of the invention.

[0056] A test step 123 is planned to detect within the primary information a situation corresponding to a criterion.

[0057] The criterion in question can vary. Generally, it aims to distinguish between normal and critical situations within primary data. This is a classic problem in the classification and processing of digital data. Several solutions exist, accessible to those skilled in the art, and do not require further elaboration here.

[0058] It can be noted, however, that this criterion can be fixed or adaptive. It can be simple or multiple. For example, it can be formalized by a cost function (or "loss function") in the case where the analysis is implemented by a multilayer neural network.

[0059] The state of the art includes ground-based image analysis systems that allow for the measurement of precipitation volumes, the measurement of river levels, the measurement of lava or mudflows, fire detection, storm arrival detection, etc.

[0060] References can be made to the work "Hazards and monitoring of volcanic activity 2: seismology, deformation and remote sensing" by Jean-François Lenat, ISTE editions, 2022, ISBN 9781789480450, or the articles by Bonakdari, H., Zaji, AH, Soltani, K., & Gharabaghi, B., "Improvement of the accuracy of a flood warning system by remote sensing using a multi-objective preprocessing method for the detection and elimination of signal defects" in Comptes Rendus Géosciences, 352, 73-86 (2020), or by Catry, T., Révillion, C., Mouquet, P., & Pennober, G., "Contributions of satellite imagery for monitoring the impact of cyclonic events in Madagascar. Complementarity of scales and sensors”, in EchoGéo, (51), 2020.

[0061] As long as a situation corresponding to the criterion is not detected, the mechanism can loop back to step 121 of analyzing a new portion of the primary information (a new image, for example).

[0062] When a situation matching the criterion is detected, a step 124 for determining secondary information relating to that situation is triggered.

[0063] This secondary information may include the result of the analysis performed in step 121.

[0064] It is also possible to enrich the secondary information with other data, such as for example: a satellite identifier, a timestamp, a satellite location, etc.

[0065] In general, secondary information corresponds to a semantically higher level than primary information, due to the processing applied. It is also smaller in size.

[0066] The secondary information, provided directly by analysis 121, may contain data of the same nature as the primary information.

[0067] For example, they may contain an image representing a geographical area but representing semantic data from the processing: for example, a segmentation may discriminate the points of the image corresponding to a detected critical situation, or different color levels may correspond to different levels of severity of a situation, or to a type of situation (flood, fire, destruction, etc.), labels may be associated with the points of the image, or with areas resulting from a segmentation, and representing the type of terrain or cloud cover, etc.

[0068] Furthermore, other types of data may result from analysis 121 without being of the same nature as the primary information: for example, a type of critical situation, an estimated level of severity, a size of the area concerned, a geolocation of the area concerned, etc.

[0069] In one embodiment, this secondary information represents an alert. Ground terminals may have means to effectively alert users based on this secondary information.

[0070] It is clear that different implementation methods are possible to determine secondary information that can be properly used by ground-based telecommunications terminals equipped with a suitable software application.

[0071] This secondary information is then formatted, step 125, for dissemination by the telecommunications means 13 on board the satellite.

[0072] The shaping aims to format digital data in order to convert it into analog data, typically by modulating a carrier signal, according to the specifications of a telecommunications protocol used by telecommunications means 13 to broadcast information to ground terminals.

[0073] References 121-125 of the figure 2 These can be viewed as steps in a process implementing an embodiment of the invention, but also as modules of a functional architecture. The processing means 12 can be implemented by an assembly of electronic circuits and / or by software modules operating on an information processing infrastructure.

[0074] According to one embodiment of the invention, the protocol used is the Bluetooth protocol.

[0075] According to the collaborative encyclopedia Wikipedia, "Bluetooth is a telecommunications standard that enables bidirectional data exchange over short distances using UHF radio waves in the 2.4 GHz frequency band. Its purpose is to simplify connections between nearby electronic devices by eliminating wired connections. It can replace cables, for example, between computers, tablets, speakers, and mobile phones, or between computers, tablets, speakers, and mobile phones, or between computers, tablets, speakers, mobile phones, mobile mice, game controllers, personal digital assistants, hands-free systems for microphones or headphones, car radios, digital cameras, barcode scanners, and interactive advertising kiosks." (https: / / fr.wikipedia.org / wiki / Bluetooth)

[0076] One of the advantages of the Bluetooth protocol is that it is implemented on a very large majority of telecommunications terminals in circulation on the market.

[0077] The proposed mechanism can therefore operate on the existing fleet of terminals and requires no hardware modifications to these terminals. In particular, this mechanism precludes the use of terminals specifically designed for satellite telecommunications, such as those adapted for the Iridium network, which are far less widespread and more expensive.

[0078] Furthermore, the reception of information by ground terminals is independent of any type of subscription. This allows all terminal owners to be reached, even without a subscription to an operator and even in areas not covered by ground networks.

[0079] Also, the dissemination of secondary information by satellite via this telecommunication protocol allows its good reception by the majority of terminals existing in the world and therefore, for example, to alert a large part of the people concerned by a critical situation or by a detected risk.

[0080] Insofar as telecommunications terminals can be mobile terminals, particularly of the "smartphone" type, which can be constantly accessible to users even when they are on the move, they can be alerted extremely quickly, as soon as a satellite detects a critical situation, or an imminent risk of a critical situation, regardless of network coverage.

[0081] Furthermore, there is a Bluetooth protocol that allows the broadcasting of information to a group of devices. It's worth noting that in telecommunications, broadcasting (sometimes also called telecasting) is a technique for transmitting signals unidirectionally to a large number of clients. This contrasts with multicast and unicast, which represent direct, even individualized, or "connected," links between the sender and the receiver.

[0082] Thus, according to the invention, the telecommunication means 13 of satellite 1 do not need to know the ground terminals individually, but simply transmit. When they receive the information, the ground terminals can recognize that it is a broadcast signal and, consequently, consider themselves as receivers (without their own address being indicated in the signal as in unicast or multicast mode, for example).

[0083] It is clear that the Bluetooth protocol was designed for communication between nearby devices. Its use for information dissemination between a satellite and ground terminals is therefore completely disruptive.

[0084] The inventors conducted simulations to demonstrate that the Bluetooth protocol is usable over long distances in the context of the invention, under certain conditions defined by the inventors.

[0085] Furthermore, another constraint of the usual operation of the Bluetooth protocol is the initial pairing phase between two devices before the exchange of information. Within the framework of the invention, it is impossible to implement such pairing between the satellite and ground terminals, firstly because it would require a transmission power from the ground terminals incompatible with their specifications, but also because it would imply a significant burden and load on the satellites, which would potentially have to pair with thousands of ground terminals and, if the satellite is orbiting, would have to repeat this operation regularly.

[0086] The inventors have determined a particular operating mode of the Bluetooth protocol, called Advertising, which makes it possible to meet the two constraints: avoiding the pairing mechanism, and allowing broadcasting, and can thus make it possible to implement the invention.

[0087] These aspects of the Bluetooth protocol are described and specified in the "Core Specification" normative document, available on the official website http: / / www.bluetooth.com. This document is currently available in version 5.3, dated July 13, 2021.

[0088] The "Advertising" mode allows several types of connection via the "Generic Access Profile" (GAP) mechanism, described in section 6.2. In particular, there is a "Broadcaster" mode, in which the sender transmits information without allowing (and therefore without waiting for) a response. This mode can typically be used to implement the invention.

[0089] In one embodiment, this mode of operation corresponds to the BLE protocol. In another embodiment, the BLE protocol is used.

[0090] Bluetooth Low Energy (BLE or BTLE) is a wireless transmission technology created by Nokia in 2006 as an open standard based on Bluetooth, which it complements but does not replace. It has been integrated into the Bluetooth standards since version 4.0, published in June 2010 by the Bluetooth SIG.

[0091] According to Wikipedia, "compared to Bluetooth, BLE offers a data rate of the same order of magnitude (1 Mbit / s) with 10 times less energy consumption. This allows the technology to be integrated into new types of equipment such as watches, medical monitoring devices, or sensors for athletes. The technology allows devices to connect within a range of approximately 10 meters."

[0092] One of the advantages of the BLE protocol is its lower energy consumption, which is an important point for a device embedded on a satellite.

[0093] Bluetooth devices send packets to broadcast data in advertising mode. These packets are 31-byte blocks that can contain information specific to the sender. They are also used to allow other devices to connect to them (pairing). There are several types of advertising packets, each enabling different functionalities (used for direct or indirect advertising, with or without connection capabilities).

[0094] Bluetooth enables bidirectional or unidirectional data exchange using UHF radio waves and operates in the 2.4 GHz band. Forty physical channels are allocated for time and frequency multiplexing, each spaced 2 MHz apart (i.e., from 2.4 GHz to 2.8 GHz). Some channels are used for advertising, while others are used for connection-oriented transmissions (unicast or multicast).

[0095] According to the BLE standard, an object can have up to 4 functions. Specifically: The broadcaster: it can act as a server. Its purpose is to regularly transmit data to a device, but it does not accept any incoming connections. The observer: this device can only listen to and interpret the data sent by a broadcaster. In this case, the device cannot send connections to the server.

[0096] According to this embodiment, the satellite can implement the "broadcaster" part of this operating mode of the BLE protocol, while the ground-based telecommunications terminals implement the "observer" part.

[0097] As previously discussed, secondary information can (due to its high-level semantic content) be of small volume. Therefore, the use of the BLE protocol is justified.

[0098] According to the standard, the BLE protocol can operate at different data rates.

[0099] According to one embodiment of the invention, a data rate of 125 kbit / s is used. Furthermore, the S=8 mode can be used. This mode indicates that 8 symbols per data point are used for transmission during modulation, which reduces the effective data rate but allows for greater robustness and therefore sensitivity. This mode of using the BLE protocol corresponds to a sensitivity of -103 dBm.

[0100] This BLE protocol is described and specified in the aforementioned normative document. On page 218, in particular, there is a table summarizing the different possible BLE modes.

[0101] It is necessary that the signal strength received by the ground-based telecommunications telephone be above the receiver's sensitivity.

[0102] According to simulations carried out by the inventors, this mode of operation of the BLE protocol (125k S=8) makes it possible, by using a satellite in low orbit, to close the link budget using directional antennas on the satellite, with a transmission power in phase with what a commercial power amplifier can generate from a satellite in low orbit.

[0103] The antenna's directivity may depend on a compromise between satellite stability and maximum power consumption. Indeed, the more directional the antenna, the more stable the satellite must be in terms of its pointing towards Earth, and the lower the transmission power requirement.

[0104] Figure 3 illustrates a simulation of the evolution of the reception power PR (by a ground-based telecommunications terminal) with respect to the transmission power of the satellite PT. This simulation was obtained by considering a transmitting antenna with a directivity defined by a beamwidth of 20° at -3dB and a gain of 18 dBi, and a receiver located at the nadir of the satellite (i.e., at the point on the ground located vertically between the satellite and the center of the Earth).

[0105] This curve shows that for low transmit power (TP), the receive power increases very rapidly. Thus, starting from just a few watts of transmitted power from the satellite, the sensitivity required by the receiver (i.e., -103 dB) is reached. In the example of the curve in Figure 3, this sensitivity is reached for approximately 1.5 W of transmitted power. Satellite elevation, cloud cover, and the satellite's pointing parameters towards the ground are factors that can influence this figure.

[0106] There Figure 4 illustrates another simulation of the evolution of the reception power PR (by a ground-based telecommunications terminal) relative to the transmission power of the satellite PT, based on different assumptions, including lower antenna gain and taking into account that the receiver may be located elsewhere than at the nadir and especially at the edge of coverage.

[0107] Below is a detailed example of how to calculate a liaison budget, based on the assumptions of the simulation. Figure 4 and by realistically applying a margin of error to the linkage balance.

[0108] We therefore consider the following parameters: BLE mode 125k S=8, Satellite elevation H = 550 km, BLE receiver sensitivity: S = -103dBm, Link budget margin = 4dB, Atmospheric losses at 2.4GHz: L atm = 0.5dB, Polarization losses: L pol = 3dB, Insertion losses L i = 2dB, Antenna directivity defined by a -3dB beamwidth of 20°, which corresponds to a maximum communication distance (at the edge of coverage) for H = 550 km: D max = 560km, Maximum path loss: PL = 155dB (as indicated, for example, on the webpage) https: / / en.wikipedia.org / wiki / Path loss), Transmitting antenna gain: G tx = 15dBi, and average receiving antenna gain: G rx = 0.5dBi.

[0109] The nadir losses of the satellite are defined as follows: PL + L atm + L pol + L l = 160.5 dB , and the losses at -3dB as follows: Pertes@ 3 dB = PL + L atm + L pol + L l = 163.5 dB

[0110] For the telecommunications terminal to be able to demodulate the signal broadcast in BLE 125k S=8 mode by the satellite, a minimum reception power Min(Prx) is required: Min P rx = S + Marge = − 103 + 4 = − 99 dBm

[0111] The telecommunications equation allows us to write that the transmission power Ptx is equal to: Ptx = Min Prx + Pertes@ 3 dB − G tx + G rx .

[0112] Substituting the numerical values ​​above, we obtain: Ptx = -99 + 163.5 - 15.5 = 49dBm, which corresponds to approximately 79.5W.

[0113] The PIRE satellite is therefore: Ptx + Gtx = 64dBm.

[0114] We can see that with the realistic assumptions of the detailed calculation above, the required sensitivity S is reached for a power of a few tens of Watts, which corresponds to quite classic transmission power values ​​for means of communication 13.

[0115] Of course, other curves, and therefore other minimum transmission powers, are possible depending on the telecommunications protocol used to disseminate the information. In particular, the "BLE 125k s=0" protocol, for which an implementation is described, may be subject to future standardization changes that could potentially impact this performance curve. Furthermore, other modes of the BLE protocol, associated with higher data rates, for example 250 kbps, 500 kbps, 1 Mbps, or even 2 Mbps, could also be used.

[0116] It appears in any case clearly that the use of this mode of operation of the Bluetooth standard allows the dissemination of information from a satellite to terminals 2 on the ground, with capacities usual for means of telecommunication 13 and conforming to the requirements of an embedded system.

[0117] Other implementation methods are obviously possible, particularly depending on the evolution of different telecommunication standards in the future, or the emergence of new standards.

[0118] In the case of a satellite in low Earth orbit (or other), the movement of the satellite relative to the ground terminals implies a distortion of the transmitted signal by the Doppler effect (frequency shift).

[0119] Since the Bluetooth protocol is designed for communication between nearby objects with relative speeds of zero or low, it does not allow for a device to natively recover these signal distortions.

[0120] Simulations carried out by the inventors demonstrated a loss of sensitivity on the order of 4dB and a packet loss rate on the order of 10-2.

[0121] According to one embodiment of the invention, the processing means 12 are adapted to pre-compensate for the frequency shift related to the Doppler effect as a function of the satellite's position, the position of the telecommunications terminals, and the satellite's velocity relative to the ground. This pre-compensation aims to eliminate, or at least significantly reduce, the loss of sensitivity and the increase in the packet loss rate.

[0122] This pre-compensation is indeed possible insofar as the telecommunications means 13 are aware of the position of the mobile terminals 2 to which the information is broadcast since these means are directional (that is to say on the ground footprint of the diffusion cone 50).

[0123] If the solid angle of this diffusion cone is sufficiently small, the differences related to the Doppler effect between the different positions of this footprint on the ground can be considered negligible.

[0124] This pre-compensation can be performed by device 10 by pre-processing the complex envelope of the signal before broadcast.

[0125] If we denote x(n) the signal to be broadcast (which would therefore be effectively broadcast if we did not take the Doppler effect into account), according to one embodiment, we form a pre-compensated signal y(n) defined by: y n = x n . e − j θ ^ D , S n

[0126] In this expression, θ̂ D,s ( n ) represents the estimated instantaneous phase representing the Doppler variation to be compensated on the surface S, which represents the footprint on the ground of the diffusion cone 50.

[0127] Thus, the received signal is naturally disturbed by the Doppler effect. θ D,S ( n ) will be written: z n = y n . e − j θ ^ D , S n + w n

[0128] The quantity w(n) represents the thermal noise of the receiver.

[0129] Using the pre-compensated signal expression y(n), this expression can be written as: z n = x n . e − j θ ^ D , S n . e j θ ^ D , S n + w n

[0130] Either : z n = x n . e ε D , S n + w n

[0131] ε D,S ( n ) represents the estimation error of the Doppler effect, expressed as: ε D , S n = θ D , S n − θ ^ D , S n

[0132] The variation of the instantaneous phase θ̂ D,S ( n The effect caused by the Doppler effect can be estimated deterministically by knowing: the position of the satellite, the position of the ground area to which the information is to be broadcast (corresponding to the ground footprint of the broadcast cone 50), the carrier frequency, the relative speed of the satellite with respect to the ground (or to the telecommunications terminal, if it is moving, knowing that given the speed of the satellite with respect to that of the terminal, the latter can be neglected).

[0133] This estimate aims to minimize the estimation error. ε D,S ( n )

[0134] The instantaneous phase can be estimated using the physics equations that allow for the calculation of the Doppler effect. Various methods for implementing these computational aspects are well described in the technical literature. For example, see the article "Doppler Characterization for LEO Satellites" by Irfan Ali, Naofal Al-Dhahir, and John E. Hershey in IEEE Transactions on Communications, vol. 46, no. 3, March 1998.

[0135] Telecommunications terminals 2 which are in the reception area (ground footprint of the diffusion cone) can therefore receive the information broadcast by the satellite with sufficient power to allow its proper processing (demodulation with a sufficiently low error rate to allow the reconstruction of secondary information determined by the processing means 12).

[0136] As previously discussed, the terminals can be state-of-the-art. In particular, standard telecommunications equipment is sufficient to enable them to receive secondary information transmitted by the satellite. Therefore, there is no need for special antennas, demodulation circuits, etc.

[0137] As we have seen, one embodiment of the invention uses the Bluetooth protocol, in particular the BLE 125k s=8 operating mode of this protocol. The vast majority of telecommunications terminals are natively adapted to receive information transmitted according to this protocol.

[0138] Telecommunications terminals can be of different types. They can be fixed (computer, television set, etc.) or mobile (laptop, tablet, mobile phone, etc.).

[0139] The telecommunications terminal includes a software application 20 adapted to continuously receive a data stream in a predefined channel. As explained above, this channel may correspond to the Bluetooth telecommunications protocol, and more specifically a broadcast mode of this protocol such as "BLE 125k S=8".

[0140] The software application is also adapted to analyze the content of this data stream in order to detect said secondary information, determine within it data enabling the triggering, where appropriate, of an action on the human-machine interface of the telecommunications terminal.

[0141] This data may include geolocation and / or the type of situation.

[0142] The software application can be adapted to compare this geolocation to the terminal's geolocation and only trigger an action if the two geolocations are sufficiently close. This proximity threshold can be fixed, configurable, or adaptable, for example, based on the type of situation or its severity.

[0143] The software application can be adapted to also compare this type of situation to parameters set by the user of the telecommunications terminal indicating the type of services to which he / she wishes to subscribe.

[0144] These parameters can be set by the application itself, so that several versions of the application can exist, each corresponding for example to a type of user (general public, security professionals, etc.), or to different application fields.

[0145] An example of an application is the notification of a critical situation (fire, flood, earthquake, major flooding, etc.) to the affected population. The detection of the critical situation can be carried out by an observation satellite using primary data acquired and analyzed as explained above. It can also be carried out by other mechanisms and disseminated via a telecommunications satellite.

[0146] Terminals 2 receive Bluetooth broadcast streams when they are within the satellite's broadcast area (ground footprint of the broadcast cone 50). If application 20 is properly configured, it can analyze this incoming stream and determine whether an alarm should be triggered via the human-machine interface (displaying a signal or message on a screen, audible alarm, vibrations, etc.).

[0147] Other applications are possible, in which users wish to be alerted to a particular situation determined by a satellite or other systems.

[0148] This determination may include verifying that the terminal's location is indeed in an area affected by the critical situation (in a more precise way than the satellite's broadcasting mechanism could do) or whether the user has actually subscribed to the alert service, for example.

[0149] Thus, according to the invention, information is transmitted directly from a satellite to telecommunications terminals. It does not pass through any other devices. Therefore, in the event of a critical situation, particularly a natural disaster, the mechanism of the invention makes it possible to bypass damage to, or even destruction of, ground-based telecommunications infrastructure, the presence of a ground network in the areas concerned, subscription to an operator, the congestion of this same infrastructure due to both the numerous communications initiated by the population during this type of event, and a possible partial destruction of the telecommunications infrastructure devices.

[0150] The invention therefore makes it possible to maintain a communication channel to the people concerned, possibly affected by disasters, in a resilient manner.

[0151] Furthermore, some regions have limited telecommunications infrastructure (wired, cellular, Wi-Fi, etc.). This is particularly true of remote rural areas. In such cases, the invention enables alerts or, more generally, the transmission of secondary information to mobile devices in the absence of telecommunications infrastructure.

[0152] Furthermore, according to embodiments of the invention, it makes it possible to take advantage of the growing capabilities of observation satellites by directly transmitting an analysis result to the mobile telecommunications terminals of end users.

[0153] This allows them to obtain these results as quickly as possible, without the need for ground stations to process or retransmit information. These stations thus eliminate the bottlenecks that lengthen the information transmission chain and slow down users' access to relevant information.

[0154] This ability to transmit directly from satellites to users opens the way to new applications and services, particularly in developing countries or in regions where ground-based telecommunications coverage is insufficient (forest areas, deserts, etc.).

[0155] Of course, the present invention is not limited to the examples and embodiment described and illustrated, but is defined by the claims. In particular, it is susceptible of numerous variations accessible to those skilled in the art.

Claims

1. A device (10) suitable for being placed on board a satellite (1), comprising telecommunication means (13) for broadcasting information directly to at least one telecommunication terminal (2) on the ground, characterized in that the telecommunication means are suitable for broadcasting said information via the Bluetooth Low Energy communication protocol, BLE, according to an "advertising" mode, according to which no incoming connection is accepted, said at least one telecommunication terminal (2) being compatible with said communication protocol and configured to receive said information without sending any connection request to the communication means of the satellite, said telecommunication means comprising: - a directional antenna suitable for transmitting a signal carrying said information in a broadcast cone, with a transmission power greater than or equal to a few watts in a frequency band between 2.4 and 2.8 GHz, a data rate of at least 125 kbits / s, said transmission power being determined so that power of a signal received by at least one said terminal located in the broadcast cone is above a given sensitivity of reception of said terminal for said "advertising" mode, depending on an elevation of the satellite with respect to the ground, a directivity of the antenna, pointing parameters of the satellite and standard transmission losses related to passing through the atmosphere.

2. The device according to claim 1, for an observation satellite, further comprising: - at least one sensor (11) for acquiring primary information - processing means (12) for analyzing said primary information to detect within said primary information a situation corresponding to a criterion, and determining secondary information relating to said situation; and - said telecommunication means (13) being provided to transmit said secondary information within said information.

3. The device according to claim 2, wherein said primary information is images.

4. The device according to any of the preceding claims, wherein the telecommunication means are suitable for broadcasting said information via the Bluetooth Low Energy protocol, BLE, at 125 kbits / s with S=8 symbols per bit of information, said sensitivity of the telecommunication terminal being in the order of -103 dBm.

5. The device according to any of claims 2 to 4, wherein said processing means are suitable for pre-compensating for a frequency shift related to the Doppler effect depending on a position of said satellite, a position of said at least one telecommunication terminal, and the speed of said satellite relative to the ground.

6. The device according to any of claims 2 to 5, wherein said secondary information is representative of an alert.

7. A satellite comprising a device according to any of the preceding claims.

8. A system comprising at least one satellite (1) according to the preceding claim and said at least one telecommunication terminal (2).

9. A method for broadcasting information from a satellite (1) directly to at least one telecommunication terminal (2) on the ground, characterized in that said method implements the Bluetooth Low Energy protocol, BLE, in "Advertising" mode, according to which telecommunication means of the satellite are suitable for broadcasting said information without accepting any incoming connection and said at least one telecommunication terminal (2) is compatible with said protocol and configured to receive said information without sending any connection request to the communication means of the satellite, said method comprising: - transmission by a suitable directional antenna of a signal carrying said information in a broadcast cone, with a transmission power greater than or equal to a few watts, in a frequency band between 2.4 and 2.8 GHz, with a data rate of at least 125 kbits / s, said transmission power being determined so that power of a signal received by at least one said terminal located in the broadcast cone is above a reception sensitivity of said terminal, corresponding to said "Advertising" mode, depending on an elevation of the satellite with respect to the ground, a directivity of the antenna, pointing parameters of the satellite and standard transmission losses related to passing through the atmosphere.

10. A computer program product comprising instructions which, when the program is executed by a computer, cause said computer to implement the method according to the preceding claim.