BLUETOOTH transmission from satellite to ground telecommunications terminal

Abstract

A device (10) that can be installed on a satellite (1) and that comprises telecommunication means (13) for broadcasting information directly to at least one terrestrial telecommunication terminal (2). The information is broadcast in AD mode according to the Bluetooth low energy protocol. The device can be used in particular for Earth observation satellites.

Description

[Technical Field]

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

[0002] In particular, the invention applies to satellites equipped with information processing equipment, making it possible to transmit information from this processing directly to this or these telecommunications terminals, and in particular to Bluetooth®-enabled mobile or smartphone terminals. [Background technology]

[0003] In crisis situations such as natural disasters, it can be crucial to be able to provide information directly to people living in affected areas as quickly as possible.

[0004] However, some parts of the world still have a relatively poorly developed telecommunications infrastructure, and as a result, transmission of warning messages may be impossible in many areas or may quickly lead to saturation of the existing infrastructure, which not only prevents the entire concerned population from being notified quickly enough, but also disadvantages the communications required by emergency services.

[0005] Furthermore, in the event of a natural disaster (flood, earthquake, major fire, etc.), the telecommunications infrastructure may be affected and no longer function, thus making it impossible to communicate the necessary information.

[0006] Furthermore, ever-increasing numbers of satellites are constantly acquiring ever-increasing amounts of information. More and more satellites are observing the Earth, providing ever-more accurate coverage of the Earth's surface.

[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 passed on to end users (or "consumers").

[0008] The amount of information being processed is now reaching a scale that is difficult to utilize, causing congestion at ground stations, and the delay between capturing the information and transmitting it to the user can be detrimental or even cause the information to be outdated by the time it is received.

[0009] Studies have shown that only a small percentage of captured information is actually utilized and used, resulting in useful information being drowned out by a deluge of useless information.

[0010] Advances in onboard systems mean that satellites, especially observation satellites, will have increased processing power, both in terms of onboard memory and digital processing resources (CPUs, GPUs, dedicated circuits, etc.).

[0011] However, with this processing power it is not currently possible to improve the information transmission chain, to reach end users quickly, or to efficiently utilize the large amount of information available.

[0012] Therefore, current mechanisms, especially in the absence of terrestrial communication infrastructure, are unable to warn relevant people quickly and directly enough, even if observation satellites are able to detect a critical situation or an imminent danger.

[0013] This inadequacy of state-of-the-art technology means that it is not possible to minimize the consequences of a crisis situation, for example by organizing the evacuation of people, or at least by preventing them from unknowingly entering danger zones, warning them to avoid panic, and providing instructions on how to act.

[0014] There is therefore a need to facilitate the transmission of relevant information to people at the scene affected by a crisis situation or impending crisis situation, particularly in the absence of terrestrial communications infrastructure.

[0015] Documents US 2022 / 216896 A1 and US 2018 / 254825 A1 relate to a satellite having cellular communication means for broadcasting information to at least one telecommunication terminal on the ground based on a terrestrial cellular network infrastructure. Summary of the Invention

[0016] The object of the present invention is to provide a mechanism for broadcasting information directly from a satellite to a telecommunications terminal, where the term "directly" means that the information transmitted by the satellite is received by the terminal, in other words, the terrestrial communications infrastructure (base stations, cellular networks, etc.) is not affected by this broadcast.

[0017] To this end, according to a first aspect, the invention may be implemented by an apparatus suitable to be on board a satellite, the apparatus comprising telecommunication means adapted to broadcast information directly to at least one telecommunication terminal on the ground, said telecommunication means being adapted to broadcast said information via a Bluetooth® Low Energy communication protocol (BLE) according to an "advertisement" mode, according to which no incoming connections are accepted, said at least one telecommunication terminal being compatible with said communication protocol and adapted to receive said information without sending any connection request to the communication means of the satellite, said telecommunication means being - a directional antenna adapted to transmit a signal carrying said information in a broadcast cone, the transmission power being equal to or greater than several watts in the frequency band 2.4-2.8 GHz, and the bit rate being at least 125 kbit / s; The transmission power is determined so that the power of the signal received by at least one terminal located within the broadcast cone exceeds the given reception sensitivity of the terminal for the "advertise" mode as a function of the satellite's altitude relative to the ground, the antenna directivity, the satellite pointing parameters, and the standard transmission loss associated with passing through the atmosphere.

[0018] The satellite may be a telecommunications satellite, an earth observation satellite (in particular 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 avoid the processing (and non-processing) delays of typical processing chains.

[0020] To achieve this, the device also at least one sensor for obtaining primary information, processing means for analyzing said primary information to detect situations in said primary information corresponding to criteria and for determining secondary information relating to said situations; said telecommunication means being provided for transmitting said secondary information within said information;

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

[0022] According to an embodiment, the present invention includes one or several of the following features, which can be used separately or in partial combination with each other or in full combination with each other: The primary information is an image. The telecommunication means are adapted to broadcast said information via the Bluetooth protocol, for example in BLE 125k S=8 mode. The processing means is adapted to pre-compensate for frequency shifts associated with the Doppler effect as a function of the position of the satellite, the position of the at least one telecommunications terminal, and the velocity of the satellite relative to the earth. The secondary information represents an alert.

[0023] According to a second aspect, the invention may also be implemented by a satellite comprising an apparatus as previously defined and optionally including one or more of the optional features described.

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

[0025] According to another aspect, the invention also relates to a method for broadcasting information directly from a satellite to at least one terrestrial telecommunication terminal, said method comprising: implementing the Bluetooth Low Energy protocol (BLE) in an "advertise" mode, according to which the satellite's telecommunication means are adapted to broadcast said information without accepting any incoming connection, said at least one telecommunication terminal (2) being compatible with said protocol and configured to receive said information without sending any connection request to the satellite's telecommunication means, said method comprising: - transmitting by a matched directional antenna a signal carrying said information in a broadcast cone area using a transmission power generated by a power amplifier compatible with the requirements of the onboard system, said transmission power being equal to or greater than several watts in the 2.4-2.8 GHz frequency band, and a data rate of at least 125 kbit / s, said transmission power being determined as a function of the satellite's altitude relative to the Earth, antenna directivity, satellite pointing parameters, and standard transmission losses associated with passing through the atmosphere, such that the power of the signal received by at least one said terminal located within the broadcast cone area exceeds the receiving sensitivity of said terminal corresponding to said "advertisement" mode.

[0026] According to an embodiment, the method is adapted to implement one or more of the features already described, which may be used separately or in part or in whole combination with one another, mutatis mutandis.

[0027] According to another aspect, the invention may be implemented by a computer program comprising instructions which, when the program is executed by a computer, cause the computer to perform the above-described operations.

[0028] Further features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention, given by way of example with reference to the accompanying drawings. [Brief explanation of the drawings]

[0029] The accompanying drawings illustrate the invention. [Figure 1] 1 illustrates a schematic representation of an example of a functional architecture according to an embodiment of the present invention. [Figure 2] 2 depicts schematically an example of a detailed functional architecture of a processing means according to an embodiment of the present invention; [Figure 3] 4 illustrates a simulation of the change in received power of a satellite with respect to transmitted power, according to one embodiment of the present invention. [Figure 4] 10 illustrates a simulation of the change in satellite received power versus satellite transmitted power in accordance with another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0031] According to an embodiment, the invention relates in particular to earth observation satellites, in particular remote sensing satellites.

[0032] The invention may also relate to constellations of low earth orbit telecommunications satellites used to relay information back to Earth from other satellites, particularly Earth observation satellites.

[0033] The invention may also relate to the transmission of information from a ground station by means of a telecommunications satellite.

[0034] Earth observation satellites are artificial satellites used to make geophysical and geographic observations of the Earth from Earth orbit. Satellites in this category are used for purposes such as meteorological surveys, natural resource inventories, geodetic surveys, climate research and modeling, natural disaster prevention and monitoring, and military reconnaissance.

[0035] The majority of Earth observation satellites fall into the category of remote sensing satellites, whose instruments analyze electromagnetic waves (not only visible light, but also ultraviolet, infrared, X-rays, etc.) emitted by the object being observed or by wave trains emitted by the satellite. Typically, the instruments used are cameras, spectrometers, radar, radiometers, etc. For example, Pleiades, Sentinel and METEOSAT satellites fall into this category of remote sensing satellites.

[0036] The second category of Earth observation satellites are those that only perform in situ measurements, such as GOCE, which measures the Earth's gravity field, or SWARM, which measures the Earth's magnetic field, and are not remote sensing satellites. These satellites use instruments such as magnetometers, passive receivers such as laser reflectors, GPS, accelerometers, or ion or neutral atom detectors.

[0037] Generally speaking, an observation satellite includes on-board resources for managing the satellite itself (power supply, positioning, etc.) and equipment representing the satellite's payload, i.e., on-board functions that are useful to third parties and not for the operation of the satellite itself. This type of observation satellite equipment therefore includes means for performing its observation functions, i.e., essentially observation means, and telecommunication means for transmitting the observed information to the ground.

[0038] The present invention primarily relates to such an arrangement for a satellite 1, referenced 10 in FIG.

[0039] In FIG. 1, a satellite 1 is positioned in orbit 30 around the Earth 40 .

[0040] In one embodiment of the present invention, the satellite is located in Low Earth Orbit (LEO). However, in other embodiments, it may be in other orbits, such as GEO (geostationary orbit, etc.). .

[0041] The apparatus 10 is suitable for installation on a satellite 1 and is shown in FIG. 1 as actually installed on the satellite.

[0042] According to the invention, the device 10 comprises telecommunication means 13 for broadcasting information directly to at least one telecommunication terminal 2 on the ground 40 .

[0043] The signals emitted by the telecommunication means 13 form a cone 50, the aperture (or solid angle) of which depends on the directivity of these means (antennas). A mobile terminal located in the center of this broadcast cone 50 will receive the signal in the best conditions.

[0044] If the satellite is an observation satellite, the device 10 one or more sensors 11 for obtaining primary information; processing means 12 for analysing the primary information to detect situations in the primary information that correspond to predefined criteria and for determining secondary information relating to said situations;

[0045] The telecommunication means 13 are then designed to transmit this secondary information (in other words, the secondary information represents the information indicated in the previous paragraph).

[0046] In the case of communications satellites, the information broadcast may be obtained by other means, such as being received by the satellite from a ground station or another satellite. For example, an observation satellite may transmit secondary information to a transmitting satellite, which then broadcasts it to ground terminals. This embodiment may free the observation satellite from this function and / or allow the observation satellite to reach other coverage areas, since each satellite may only broadcast to a defined geographic area (which may change over time in the case of mobile satellites).

[0047] The primary information acquired or "captured" by the sensor 11 corresponds to the various items of information observed by the observation satellites. As mentioned above, the observation satellites are very diverse and therefore the observation spectrum is vast: optical, radar, infrared, ultraviolet, radioelectric or electromagnetic signal reception, ionizing radiation, etc.

[0048] Examples of electromagnetic signals include AIS (Automatic Identification System) ship beacon signals, which are electronic messages between ships over VHF radio waves, allowing ships and ground-based traffic monitoring systems to learn the identity, status, characteristics, position, course, and speed of ships within a navigation zone. Mechanisms for detecting these signals by satellite have already been proposed. Another example is ADS-B (Automatic Dependent Surveillance-Broadcast), a cooperative surveillance system for air traffic control and related applications. ADS-B-equipped aircraft determine their position via a satellite positioning system (GNSS, which stands for "Geolocation and Navigation Satellite System") and periodically transmit this position and other information to ground stations and other ADS-B-equipped aircraft operating in the area.

[0049] Primary information can be extremely diverse.

[0050] In one embodiment, the primary information is images. These images may be two-dimensional representations of the observed portion of the Earth. Typically, observation satellites acquire a stream of images, each associated with the satellite's position relative to the Earth.

[0051] The image content (ie, the information associated with each point on the Earth's observed surface) depends on the type of sensor 11: optical (or "photographic"), radar, infrared, etc.

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

[0053] These processing means may be configured to perform this analysis according to a granularity specific to the structure of the primary information: for example, this analysis may be performed frame by frame.

[0054] This analysis step is represented by reference numeral 121 in FIG.

[0055] The results of this analysis may be processed 122 in a normal manner corresponding to normal operation of the satellite 1. For example, the results may be stored in on-board memory, transmitted to a ground station for further processing, etc. This step is optional and not relevant to the present invention.

[0056] A test step 123 is provided to detect situations in the primary information that correspond to the criteria.

[0057] The criteria can be varied. Generally speaking, the goal is to distinguish between normal and critical situations in the primary information. This is a traditional problem for classifying and processing digital data. Various solutions are available to those skilled in the art and need not be elaborated here.

[0058] However, the criterion can be either fixed or adaptive. The criterion can be single or multiple. The criterion can be formulated as a loss function, for example, when the analysis is performed by a multilayer neural network.

[0059] State-of-the-art technology includes ground-based image analysis systems for measuring precipitation, river levels, lava or mud flows, fire detection, storm warnings, and the like.

[0060] References include the book "Aleas" by Jean-Francois Lenat. Bonakdari, H., Zaji, AH, Soltani, K., & Comptes Rendus Geosciences, 352, 73-86 (2020) Gharabaghi, B., ``Amelioration de la precision d'un systeme d'alerte de crue par teledetection a l'aide d'une methode de pretraitement multi-objectifs pour Catry, T., Revillion, C., Mouquet, P., & Pennober, G., “Apports de l'imagerie satellite pour le suivi de l'impact des evenements cycloniques a Madagascar.Complementarite des echelles et des "capteur" is mentioned.

[0061] As long as no conditions corresponding to the criteria are detected, the facility may loop back to step 121 to analyze a new piece of primary information (eg, a new image).

[0062] When a situation corresponding to the criteria is detected, step 124 is triggered for determining secondary information regarding this situation.

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

[0064] The secondary information can also be enriched with other data such as satellite identifiers, timestamps, satellite positions, etc.

[0065] Generally speaking, secondary information corresponds to a higher semantic level than primary information due to the processing applied to it. Secondary information is also smaller in size.

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

[0067] For example, they may include images that represent geographic areas but that represent semantic data derived from processing, e.g., segmentation may identify image points that correspond to detected crisis situations, or different color levels may correspond to different levels of severity of the situation or type of situation (flood, fire, destruction, etc.), and labels may be associated with image points or may be derived from segmentation and associated with areas that represent terrain types or cloud cover, etc.

[0068] In addition, other types of data may result from the analysis 121 that are not of the same nature as the primary information, such as the type of crisis situation, the estimated level of severity, the size of the area involved, the geographic location of the area involved, etc.

[0069] In one embodiment, this secondary information represents an alert, and the ground terminal may have means to effectively alert a user based on this secondary information.

[0070] It will be appreciated that there are a variety of possible ways of determining secondary information that may be suitably utilized by a terrestrial telecommunications terminal with a suitable software application.

[0071] This secondary information is then formatted for broadcast by the satellite's on-board telecommunications means 13 (step 125).

[0072] The purpose of formatting is to convert the digital data into analog data, typically by modulating a carrier signal, in accordance with the specifications of the telecommunications protocol used by the telecommunications means 13 to broadcast the information to the ground terminals.

[0073] 2 can be considered as steps in a process for implementing an embodiment of the present invention, but also as modules in a functional architecture. The processing means 12 can be implemented by an assembly of electronic circuits and / or by software modules running on an information processing infrastructure.

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

[0075] According to the collaborative encyclopedia Wikipedia, "Bluetooth is a 2. It is a telecommunications standard for bidirectional data exchange over short distances using UHF radio waves in the 4 GHz frequency band. Its purpose is to simplify connections between nearby electronic devices by eliminating wired links. For example, Bluetooth eliminates the need for cables between computers, tablets, speakers, and mobile phones, or between printers, scanners, keyboards, It can replace cables to mice, joysticks, mobile phones, PDAs, 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 the majority of telecommunications terminals on the market.

[0077] The proposed mechanism can therefore operate on existing terminals and does not require hardware modifications, in particular in contrast to the use of specific terminals for satellite communications, such as terminals adapted for the Iridium network, which are less widespread and more expensive.

[0078] Furthermore, the reception of information by terrestrial terminals is independent of subscription to any type of service, making it possible to address all handset owners, even those without operator subscriptions, in areas not covered by terrestrial networks.

[0079] Broadcasting secondary information via satellite using this telecommunications protocol means that the secondary information can be received by most terminals in the world and can therefore, for example, alert large numbers of people who are concerned about a critical situation or detected risk.

[0080] Insofar as the telecommunications terminal may be a mobile terminal, in particular a "smart phone" type mobile terminal which is likely to be accessible to the user at all times, the user can be alerted very quickly as soon as the satellite detects a crisis situation or an imminent risk of a crisis situation, even when the user is on the move and regardless of network coverage.

[0081] Additionally, there is a Bluetooth protocol for broadcasting information to a range of terminals. In telecommunications, broadcasting is a technique for the one-way (or unidirectional) transmission of a signal to multiple users. This contrasts with multicast and unicast, which represent a direct, personalized, or "connected" link between sender and receiver.

[0082] Thus, according to the invention, the telecommunication means 13 of the satellite 1 do not need to know the terrestrial terminals individually, but simply transmit, and when the terrestrial terminals receive the information, they can recognize it as a broadcast signal and therefore consider themselves receivers (for example, their own address is not indicated in the signal, as is the case in unicast or multicast mode).

[0083] It is clear that the Bluetooth protocol was designed for communication between devices in close proximity, so using it to broadcast information between satellites and ground terminals would be a completely disruptive change.

[0084] The inventors have performed simulations to demonstrate that the Bluetooth protocol can be used over long distances in connection with the present invention under certain conditions defined by the inventors.

[0085] A further constraint on the normal operation of the Bluetooth protocol is the initial pairing stage between two devices before any information is exchanged. Setting up such pairings between satellites is not possible because, on the one hand, it would require the transmission power of the ground terminals which would not match the specifications of the ground terminals, but also because it would involve a great deal of weight and load on the satellite which would have to pair with potentially thousands of ground terminals, and this operation would have to be repeated periodically if the satellite were moving.

[0086] The inventors have identified a particular mode of operation of the Bluetooth protocol known as "advertisement" that meets the two constraints of avoiding the pairing mechanism and allowing broadcasting, and therefore can be used to implement the present 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.bluetoothe.com. This document is currently available in version 5.3, dated July 13, 2021.

[0088] The "advertise" mode allows several types of connections via the Generic Access Profile (GAP) mechanism described in Section 6.2. In particular, there is a "broadcaster" mode, in which the sender sends information without allowing (and therefore without waiting for) a reply. This mode may typically be used to implement the present invention.

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

[0090] Bluetooth Low Energy (BLE or BTLE) is a wireless transmission technology developed by Nokia in 2006 as an open standard based on Bluetooth; this technology complements, but does not replace, Bluetooth. Bluetooth Low Energy has been incorporated into the Bluetooth standard since version v4.0, published by the Bluetooth SIG in June 2010.

[0091] According to Wikipedia, "Compared to Bluetooth, BLE offers a similar data rate (1 Mbit / s) with one-tenth the energy consumption. This makes it possible to integrate the technology into new types of devices such as watches, medical monitoring devices, or sports sensors. The technology allows devices to connect within a radius of about 10 meters."

[0092] One advantage of the BLE protocol is that it consumes less energy, which is an important consideration for space-borne devices.

[0093] Bluetooth devices send packets to broadcast data in advertisement mode. These packets are 31-byte blocks that can contain information specific to the sender. These packets are also used to allow other devices to connect to the Bluetooth device (pairing). There are several types of "advertisement" packets, each of which allows different functionality (used for direct or indirect advertisements, with or without the possibility of connection).

[0094] Bluetooth allows two-way or one-way data exchange using UHF radio waves and operates in the 2.4 GHz band. 40 physical channels are allocated for time and frequency multiplexing, each spaced 2 MHz apart (i.e., 2.4 GHz to 2.8 GHz). Some channels are used for advertising, others for unicast transmission or is used for multicast transmission.

[0095] According to the BLE standard, an object can have up to four functions. In particular: A broadcaster can act as a server: its purpose is therefore to periodically send data to devices, but not to accept incoming connections. Observer: The object can only listen and interpret data sent by the broadcaster. In this situation, the object cannot send connections to the server.

[0096] In this embodiment, the satellite may implement the "broadcaster" portion of this BLE protocol operating mode, and the terrestrial telecommunications terminal implements the "observer" portion.

[0097] As mentioned earlier, secondary information can be low volume (due to its high level of semantic content), thus justifying the use of the BLE protocol.

[0098] Depending on the standard, the BLE protocol can operate at different data rates.

[0099] In one embodiment of the present invention, a data rate of 125 kbit / s is used. Additionally, an S=8 mode can be used. This mode indicates that 8 symbols per data item are used for transmission during modulation, which reduces the useful data rate but provides greater robustness and therefore sensitivity. This BLE protocol mode corresponds to a sensitivity of -103 dBm.

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

[0101] The signal strength received by the landline telephone must be higher than the sensitivity of the receiver.

[0102] Simulations performed by the inventors show that this mode of operation of the BLE protocol (125k S=8) allows closing the link budget using satellite-pointed antennas with transmit power in phase with the power that a commercial power amplifier can generate from a low-Earth orbit satellite.

[0103] Antenna directivity may depend on a compromise between satellite stability and maximum power consumption: indeed, the more directional the antenna, the more stable the satellite needs to be in pointing towards the Earth, and the lower the required transmit power.

[0104] Figure 3 shows a simulation of the variation of the received power PR (by a terrestrial telecommunications terminal) with respect to the transmitted power PT of the satellite. This simulation was obtained by considering a transmitting antenna with a directivity defined by a -3 dB aperture angle of 20° and a gain of 18 dBi, and a receiver located at the satellite nadir (i.e., a point on the ground located perpendicularly between the satellite and the center of the Earth).

[0105] This curve shows that for low transmit powers, Pt, the received power increases very rapidly. Thus, the required sensitivity (i.e., -103 dB) is achieved by the receiver from only a few watts of power transmitted by the satellite. In the example curve of Figure 3, this sensitivity is achieved at a transmit power of about 1.5 W. Satellite altitude, cloud cover, and satellite pointing parameters can all affect this number.

[0106] Figure 4 shows the difference between the two cases, based on different assumptions, specifically a lower antenna gain and a receiver above nadir. Another simulation of the variation of the received power PR (by the terrestrial telecommunications terminal) compared to the transmitted power PT of the satellite is shown, taking into account the fact that the satellite may be located somewhere outside, especially at the edge of coverage.

[0107] Below is an example link budget calculation based on the simulation assumptions of Figure 4 and applying realistic tolerances to the link budget.

[0108] The following parameters are considered: -BLE mode 125k S=8, the satellite altitude H equal to -550 km, -BLE receiver sensitivity: S=-103dBm, -Link budget margin: margin = 4dB, -Atmospheric loss at 2.4Ghz: L atm =0.5dB, -Polarization loss:L pol =3dB, - Insertion loss: L i =2dB, The directivity of the antenna is defined by an aperture angle of 20° at -3 dB, which corresponds to a maximum communication distance (at the edge of coverage) of H=550 ​​km: D max =560km, - Maximum path loss: PL=155dB (for example, as shown on the https: / / en.wikipedia.org / wiki / Path_loss web page), -Transmitting antenna gain: G tx =15dBi, and -Average receiving antenna gain: G rx =0.5dBi.

[0109] The satellite nadir loss is defined as follows: PL+L atm +L pol +L I =160.5dB, and The loss at -3dB is: Loss@3dB=PL+L atm +L pol +L I =163.5dB.

[0110] In order for a telecommunication terminal to be able to demodulate a signal broadcast by a satellite in BLE 125k S=8 mode, a minimum received power of Min(Prx) is required. Minimum(P rx )=S+Margin=-103+4=-99dBm

[0111] Using telecommunications equations, the transmit power Ptx can be written as: Ptx=Min(Prx)+Loss@3dB-(G tx +G rx ).

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

[0113] Therefore, the satellite EIRP is Ptx+Gtx=64dBm.

[0114] With the realistic assumptions of the calculations detailed above, it turns out that the required sensitivity S is achieved for a power of a few tens of watts, which corresponds to very conventional transmission power values ​​of the telecommunication means 13 .

[0115] Of course, other curves, and therefore other minimum transmit powers, are possible depending on the telecommunications protocol used to broadcast the information. In particular, the "BLE 125k s=0" protocol (an example of which is described herein) may be subject to future standardization changes that may affect this performance curve. Furthermore, other modes of the BLE protocol may support higher data rates, e.g., 250 kbit / s, 500 kbit / s, etc. It is related to kbits / sec. 1M or even 2M can also be used.

[0116] In any case, it is clear that using this Bluetooth standard mode of operation makes it possible to broadcast information from the satellite to the ground-based terminal 2 in the capacity normally used for telecommunication means 13 and in accordance with the requirements of the on-board system.

[0117] Of course, other implementation modes are possible, especially as various telecommunications standards evolve in the future or new standards emerge.

[0118] In the case of a mobile satellite (such as in low Earth orbit), the movement of the satellite relative to the ground terminal distorts the transmitted signal due to the Doppler effect (frequency shift).

[0119] The Bluetooth protocol is designed for communication between nearby objects at zero or low relative velocity, and therefore does not provide a device to natively recover from these signal distortions.

[0120] Simulations performed by the inventors have demonstrated sensitivity losses on the order of 4 dB and packet loss rates on the order of 10-2.

[0121] According to one embodiment of the present invention, the processing means 12 is adapted to pre-compensate for frequency shifts related to the Doppler effect as a function of the satellite position, the telecommunication terminal position and the satellite's velocity relative to the earth, this pre-compensation being designed to eliminate or at least significantly reduce the loss of sensitivity and the increase in packet loss rate.

[0122] This pre-compensation is indeed possible as long as the telecommunication means 13 are aware of the location of the mobile terminal 2 to which the information is broadcast, since these means are directional (i.e. on the footprint of the broadcast cone 50).

[0123] If the solid angle of this scattering cone is small enough, the difference due to the Doppler effect between different positions of this footprint can be considered negligible.

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

[0125] If x(n) describes the signal to be broadcast (and therefore actually broadcast if Doppler effects are not taken into account), then according to one embodiment, the precompensated signal y(n) is formed as defined by the following equation:

[0126]

number

[0127] In this formula,

[0128]

number

[0129] Therefore, the received signal, which is naturally perturbed by the Doppler effect

[0130]

number

[0131]

number

[0132] The quantity w(n) represents the thermal noise of the receiver.

[0133] Using the expression for the precompensated signal y(n), this equation can be written as:

[0134]

number

[0135]

number

[0136]

number

[0137] Instantaneous phase fluctuations caused by the Doppler effect

[0138]

number

[0139] This estimation aims to minimize the estimation error.

[0140]

number

[0141] The instantaneous phase can be estimated using physical equations to calculate the Doppler effect. Various methods for performing these calculations are well documented in the technical literature. One example is the paper "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.

[0142] A telecommunications terminal 2 within the reception zone (footprint of the broadcast cone area) can therefore receive the information broadcast by the satellite with sufficient power to enable it to be processed correctly (demodulation with a sufficiently low error rate to enable the reconstruction of the secondary information determined by the processing means 12).

[0143] As already mentioned, the terminal can be a state-of-the-art terminal, in particular, conventional telecommunication means are sufficient to enable the terminal to receive the secondary information broadcast by the satellite, thereby eliminating the need for special antennas, demodulation circuits, etc.

[0144] As already mentioned, one embodiment of the present invention uses the Bluetooth protocol, in particular the BLE 125k s=8 operating mode of this protocol, the vast majority of telecommunications terminals being natively adapted to receive information broadcast using this protocol.

[0145] The telecommunication terminal may be of different types: it may be a fixed terminal (computer, TV set, etc.) or a mobile terminal (laptop, tablet, mobile phone, etc.).

[0146] The telecommunications terminal includes a software application 20 adapted to continuously receive a data stream on a predefined channel.

[0147] As explained above, this channel may correspond to the Bluetooth telecommunications protocol, and more specifically to the broadcast mode of this protocol, such as "BLE 125k S=8".

[0148] The software application is also adapted to analyze the content of this data stream to detect said secondary information and, if necessary, to determine within the secondary information data that makes it possible to trigger an action on the man-machine interface of the telecommunications terminal.

[0149] These data may include geolocation and / or situation type.

[0150] The software application may be adapted to compare this geographic location with the geographic location of the terminal and trigger an action only if these two geographic locations are sufficiently close. This notion of proximity may be fixed, configurable or adaptive, for example according to the type of situation or severity.

[0151] The software application may be adapted to compare this type of situation with a parameter set by the user of the telecommunications terminal, which indicates the type of service to which the user of the telecommunications terminal wishes to subscribe.

[0152] These parameters can be set by the application itself, so that several versions of the application can exist, each corresponding to, for example, a different type of user (general public, security experts, etc.) or a different application field.

[0153] An example of an application could be informing concerned people of critical situations (fires, floods, earthquakes, deluges, etc.) Critical situations can be detected by observation satellites using primary information acquired and analyzed as described above. This can also be done by other mechanisms and broadcast by telecommunication satellites.

[0154] Terminal 2 receives the Bluetooth broadcast stream when it is within the satellite's broadcast zone (footprint of broadcast cone area 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 (display of a signal or message on a screen, an audible alarm, a vibration, etc.).

[0155] Other applications are possible where a user may wish to be alerted to certain conditions as determined by satellite or other systems.

[0156] This determination may involve, for example, verifying that the terminal's location is actually within an area affected by a crisis situation (in a more precise manner than a satellite broadcast facility can do), or checking whether the user actually subscribes to an alert service.

[0157] Thus, according to the present invention, information is broadcast directly from the satellite to the communication terminals, without passing through any other device. Thus, in the event of a crisis situation such as a natural disaster, the mechanism of the present invention prevents damage or even destruction of the terrestrial telecommunications infrastructure, the existence of a terrestrial network in the area concerned; Joining the operator, This makes it possible to be immune to congestion of this same infrastructure due to the large number of communications initiated by people during this type of event, and the possible partial destruction of telecommunications infrastructure equipment.

[0158] The present invention therefore allows communication channels to potentially affected parties to remain unaffected.

[0159] Furthermore, some regions are poorly served by telecommunications infrastructure (wired, cellular, WiFi, etc.). This is especially true in remote rural areas. In this case, the present invention allows sending alerts, or more generally secondary information, to mobile terminals in the absence of a telecommunications infrastructure.

[0160] Additionally, some embodiments of the present invention allow for the utilization of the increasing capacity of observation satellites by transmitting analytical results directly to end-user mobile communication terminals.

[0161] This allows end users to get these results as quickly as possible without requiring ground stations to process or possibly retransmit the information, which no longer form a bottleneck that lengthens the information transmission chain and slows down the receipt of relevant information by users.

[0162] This ability to transmit directly from satellite to user opens the door to new applications and services, especially in developing countries or in areas where terrestrial telecommunications coverage is poor (forested areas, deserts, etc.).

[0163] Naturally, the invention is not limited to the examples and embodiments described and shown, but is defined by the claims, in particular because of the large number of variants available to those skilled in the art.

Claims

1. A device (10) suitable for being mounted on a satellite (1), said device (10) comprising telecommunication means (13) for broadcasting information directly to at least one terrestrial telecommunication terminal (2), said telecommunication means being adapted to broadcast said information via a Bluetooth Low Energy communication protocol (BLE) according to an "advertise" mode, according to which no incoming connections are accepted, said at least one telecommunication terminal (2) being compatible with said communication protocol and adapted 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 signals carrying said information in a broadcast cone area, the transmission power being equal to or greater than several watts in the frequency band of 2.4-2.8 GHz, the data rate being at least 125 kbit / s, the transmission power being determined so that the power of the signal received by at least one of said terminals located within said broadcast cone area exceeds a given reception sensitivity of said terminal for said "advertise" mode as a function of the altitude of said satellite relative to the earth, the directivity of said antenna, the pointing parameters of said satellite and the standard transmission loss associated with passing through the atmosphere.

2. For observation satellites, at least one sensor (11) for obtaining primary information, - processing means (12) for analyzing said primary information to detect situations in said primary information corresponding to criteria and for determining secondary information relating to said situations, - Device according to claim 1, characterized in that said telecommunication means (13) are arranged to transmit said secondary information within said information.

3. The apparatus of claim 2 , wherein the primary information is an image.

4. 4. The device according to claim 1, wherein the telecommunication means are adapted to broadcast the information via the Bluetooth Low Energy protocol (BLE) at 125 kbit / s with S=8 symbols per information bit, and wherein the sensitivity of the telecommunication terminal is in the order of −103 dBm.

5. 5. The device according to claim 2, wherein the processing means is adapted to pre-compensate for frequency shifts associated with the Doppler effect as a function of the position of the satellite, the position of the at least one telecommunication terminal and the velocity of the satellite relative to the ground.

6. The device according to any one of claims 2 to 5, wherein the secondary information represents an alarm.

7. A satellite comprising a device according to any one of claims 1 to 6.

8. A system comprising at least one satellite (1) according to claim 7 and said at least one telecommunication terminal (2).

9. A method for broadcasting information directly from a satellite (1) to at least one telecommunication terminal (2) on the ground, said method implementing the Bluetooth Low Energy protocol (BLE) in an "advertise" mode, according to which said telecommunication means of the satellite are adapted to broadcast said information without accepting any incoming connections, said at least one telecommunication terminal (2) being compatible with said protocol and sending any connection request to said communication means of said satellite. and configured to receive the information without transmitting the information to the server, the method comprising: - transmitting by means of a matched directional antenna a signal carrying said information in a broadcast cone area, with a transmission power of at least several watts in the frequency band 2.4-2.8 GHz and a data rate of at least 125 kbit / s, said transmission power being determined so that the power of the signal received by at least one of said terminals located within said broadcast cone area exceeds the reception sensitivity of said terminal corresponding to said "advertise" mode as a function of the altitude of said satellite relative to the earth, the directivity of said antenna, satellite pointing parameters and standard transmission losses associated with passing through the atmosphere.

10. A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the method of claim 9.

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