Bluetooth transmission from satellite to terrestrial telecommunications terminal

Abstract

An apparatus (10) mountable on a satellite (1) comprises telecommunication means (13) for broadcasting information directly to at least one telecommunication terminal (2) on the ground. The information is broadcast according to a Bluetooth Low Energy Protocol and in AD mode. The device is particularly useful in earth observation satellites.

Description

Technical Field

[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] In particular, the invention is applicable to satellites having on-board information processing equipment, enabling the information from this processing to be transmitted directly to the telecommunication terminal or terminals. The invention is particularly applicable to mobile terminals or smartphone terminals having Bluetooth functionality. Background Art

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

[0004] However, telecommunication infrastructure coverage is still relatively low in some parts of the world, making the transmission of warning messages impossible in many areas or quickly leading to the saturation of the existing infrastructure. Such saturation not only prevents all concerned from receiving information at the earliest opportunity, but also adversely affects the communications required by emergency services.

[0005] Furthermore, in the event of natural disasters (floods, earthquakes, fires, etc.), the telecommunications infrastructure may be affected and no longer function, thus making it impossible to communicate the necessary information.

[0006] Furthermore, an ever-increasing number of satellites are acquiring an enormous amount of information. More and more satellites are observing our planet, providing increasingly precise 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 to be processed has now reached levels that are unwieldy and have led to congestion at ground stations. The delay between capturing information and transmitting that information to the user can be detrimental or even render the information obsolete by the time it is received.

[0009] Research shows that only a small fraction of the captured information is actually developed and used, causing useful information to be drowned out by a large amount of useless information.

[0010] Advances in onboard systems mean that satellites (especially observation satellites) are increasingly capable of processing both onboard memory and digital processing resources (CPU, GPU, dedicated circuits, etc.).

[0011] Today, however, these processing capabilities do not allow us to improve the information transmission chain, reach end users quickly, or effectively utilize the large amounts of available information.

[0012] Therefore, even if observation satellites were able to detect a critical situation or the imminence of such a situation, current mechanisms would not be able to alert the relevant population quickly and directly enough, especially in the absence of terrestrial telecommunications infrastructure.

[0013] This inadequacy of the prior art means that it is not possible to minimize the impact of a critical situation, for example by organizing the evacuation of the population, or at least by preventing the population from unintentionally moving into the risk zone, by warning to avoid panic, by providing instructions on how to act, etc.

[0014] Therefore, there is a need to facilitate the transmission of relevant information to populations located in locations affected by critical situations or imminent risk of critical situations, particularly in the absence of terrestrial communications infrastructure.

[0015] Documents US2022 / 216896A1 and US2018 / 254825A1 relate to a satellite having a cellular telecommunication device 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 telecommunication terminal. The term "directly" here means that the information transmitted by the satellite is received by the terminal. In other words, the terrestrial telecommunication infrastructure (base stations, cellular networks, etc.) is not affected by the broadcast.

[0017] To this end, according to a first aspect, the present invention can be implemented by a device suitable for being placed on a satellite, the device comprising telecommunication means for broadcasting information directly to at least one telecommunication terminal on the ground; the telecommunication means being suitable for broadcasting the information via the Bluetooth Low Energy communication protocol BLE according to an "announcement" mode, according to which no incoming connections are accepted, the at least one telecommunication terminal being compatible with the communication protocol and configured to receive the information without sending any connection request to the communication means of the satellite, the telecommunication means comprising:

[0018] a directional antenna adapted to transmit a signal carrying said information in a broadcast cone in a frequency band between 2.4 GHz and 2.8 GHz at a bit rate of at least 125 kbits / s with a transmission power greater than or equal to a few Watts,

[0019] - said transmission power is determined so that the power of the signal received by at least one of said terminals located in the broadcast cone is higher than a given reception sensitivity of said terminal for said "announcement" mode, as a function of the altitude of the satellite relative to the ground, the antenna directivity, the satellite pointing parameters and the standard transmission losses related to passage through the atmosphere.

[0020] The satellite may be a communications satellite, an Earth observation satellite (especially a remote sensing satellite) or any other type of satellite.

[0021] This embodiment of the invention also enables to exploit the ever-increasing capabilities of observation satellites and avoids the processing (and non-processing) delays of conventional processing chains.

[0022] To achieve this, the device also includes:

[0023] - at least one sensor for acquiring primary information

[0024] - processing means for analyzing said primary information in order to detect within said primary information a situation corresponding to a criterion and to determine secondary information related to said situation; and

[0025] - said telecommunication means being provided for transmitting said secondary information within said message.

[0026] The secondary information corresponds to the information (or is a part of the information) broadcast by the previously defined device. In one embodiment, when only the secondary information is broadcast, the two terms are equivalent.

[0027] According to the embodiment, the present invention includes one or several of the following features, which can be used alone or in combination with each other in part or in combination with each other in full:

[0028] The primary information is an image.

[0029] The telecommunication device is adapted to broadcast said information via the Bluetooth protocol, for example in BLE 125k S=8 mode.

[0030] The processing means are adapted to pre-compensate for frequency shifts related to the Doppler effect as a function of the position of the satellite, the position of the at least one telecommunication terminal and the speed of the satellite relative to the ground.

[0031] The secondary message indicates a warning.

[0032] According to a second aspect, the invention may also be implemented by a satellite comprising a device as previously defined, optionally with one or more of the described optional features.

[0033] According to another aspect, the invention is also implemented by a system comprising at least one such satellite and said at least one telecommunication terminal.

[0034] According to another aspect, the invention also relates to a method for broadcasting information from a satellite directly to at least one telecommunication terminal on the ground. The method implements the Bluetooth Low Energy protocol BLE in an "announcement" mode, according to which the satellite's telecommunication device is adapted to broadcast the information without accepting any incoming connection, and the at least one telecommunication terminal (2) is compatible with the protocol and is configured to receive the information without sending any connection request to the satellite's telecommunication device, the method comprising:

[0035] - transmitting in the broadcast cone a signal carrying said information, by means of a matched directional antenna, in a frequency band between 2.4 GHz and 2.8 GHz, at a data rate of at least 125 kbits / s, with a transmission power generated by a power amplifier that meets the requirements of the onboard system, said transmission power being greater than or equal to a few Watts, said transmission power being determined so that the power of the signal received by at least one of said terminals located in the broadcast cone is higher than the reception sensitivity of said terminal corresponding to said "announcement" mode, as a function of the altitude of the satellite relative to the ground, the antenna directivity, the satellite pointing parameters and the standard transmission losses associated with passing through the atmosphere.

[0036] Depending on the embodiment, the method is suitable for implementing one or more of the previously described features, mutatis mutandis, which features can be used alone or in part or completely in combination with one another.

[0037] According to another aspect, the present invention can be implemented by a computer program including instructions, and when the program is executed by a computer, the instructions cause the computer to implement the above contents.

[0038] 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 and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings illustrate the present invention:

[0040] Figure 1 An example of a functional architecture according to an embodiment of the present invention is schematically represented.

[0041] Figure 2 An example of a detailed functional architecture of a processing device according to an embodiment of the present invention is schematically depicted.

[0042] Figure 3 A simulation of the evolution of a satellite's received power relative to its transmitted power according to an embodiment of the invention is shown.

[0043] Figure 4A simulation of the evolution of a satellite's received power relative to its transmitted power according to another embodiment of the invention is shown. DETAILED DESCRIPTION

[0044] The invention relates to all types of satellites, in particular communication satellites and observation satellites.

[0045] According to an embodiment, the invention relates specifically to Earth observation satellites, in particular remote sensing satellites.

[0046] The invention may also relate to a constellation of low earth orbit communications satellites for relaying information back to earth from other satellites, in particular earth observation satellites.

[0047] The invention also relates to the transmission of information from a ground station via a communications satellite.

[0048] Earth observation satellites are artificial satellites used for geophysical and geographical observation of the Earth from Earth orbit. Such satellites are used for purposes such as meteorology, natural resource surveys, geodesy, climate research and modeling, natural disaster prevention and monitoring, military reconnaissance, etc.

[0049] Most Earth observation satellites belong to the category of remote sensing satellites, whose instruments analyze electromagnetic waves (visible light, but also ultraviolet, infrared, X-rays, etc.) emitted by the object being observed or by the wave trains emitted by the satellite. Usually, the instruments used are cameras, spectrometers, radars, radiometers, etc. For example, the Pleiades, Sentinel and METEOSAT satellites belong to this category of remote sensing satellites.

[0050] The 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, and they are not remote sensing satellites. They use instruments such as magnetometers, passive receivers like laser reflectors, GPS, accelerometers or ion or neutral atom detectors.

[0051] In general, an observation satellite includes equipment for managing the satellite's own onboard resources (power supply, positioning, etc.) and representing its payload, that is, onboard functions that are useful to third parties rather than to its own operation. Thus, this type of observation satellite equipment includes means for implementing its observation functions (that is, essentially observation means) and telecommunication means for transmitting the observed information to the ground.

[0052] The present invention relates primarily to such an arrangement for a satellite 1, in which Figure 1 Marked as 10.

[0053] exist Figure 1 In FIG. 4 , satellite 1 is located in orbit 30 around earth 40 .

[0054] In one embodiment of the invention, the satellite is located in a low earth orbit (LEO), but in other embodiments it may be located in other orbits such as GEO (geostationary earth orbit, etc.).

[0055] The device 10 is suitable for installation in a satellite 1 and Figure 1 is shown as actually installed in a satellite.

[0056] 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 .

[0057] The signals transmitted by the telecommunication devices 13 form a cone 50, the aperture (or solid angle) of which depends on the directivity of these devices (antennas). A mobile terminal located in the centre of this broadcast cone 50 receives the signals under the best possible conditions.

[0058] In the case where the satellite is an observation satellite, the device 10 may further include:

[0059] - one or more sensors 11 for acquiring primary information; and

[0060] - Processing means 12 for analyzing the primary information in order to detect situations within the primary information corresponding to predetermined criteria and to determine secondary information related to said situations.

[0061] The telecommunication device 13 is then designed to transmit this secondary information (in other words, it represents the information indicated in the previous paragraph).

[0062] In the case of a communication satellite, 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 transmission satellite, which then broadcasts the secondary information to ground terminals. This embodiment may relieve the observation satellites of this function and / or enable them to reach other coverage areas, since each satellite may only broadcast to a limited geographic area (which may change over time in the case of a mobile satellite).

[0063] The main information acquired or "captured" by the sensor 11 corresponds to the information observed by the observation satellites. As seen earlier, the observation satellites are of various types and therefore have a wide spectrum of observations: optical, radar, infrared, ultraviolet, listening to radio or electromagnetic signals, ionizing radiation, etc.

[0064] Examples of electromagnetic signals include AIS (Automatic Identification System) ship beacon signals, which are electronic messages transmitted between ships via VHF radio waves, enabling ships and land-based traffic monitoring systems to understand the identity, status, characteristics, position, heading and speed of ships in the navigation area. Mechanisms have been proposed for detecting these signals by satellite. Another example is ADS-B (Automatic Dependent Surveillance-Broadcast), a cooperative surveillance system for air traffic control and related applications. An aircraft equipped with ADS-B determines its position via a satellite positioning system ("Geolocation and Navigation Satellite System" GNSS) and periodically sends this position and other information to ground stations and other ADS-B equipped aircraft operating in the area.

[0065] The primary information can be extremely rich and varied.

[0066] In one embodiment, the primary information is images. These images can be two-dimensional representations of the observed portion of the Earth. Typically, an observation satellite acquires a stream of images, each associated with the position of the satellite relative to the Earth.

[0067] The image content (ie the information associated with each point on the Earth's surface observed) depends on the type of sensor 11: optical (or "photographic"), radar, infrared, etc.

[0068] The primary information is analyzed by processing means 12 of the device 10 on board the satellite 1 .

[0069] These processing means may be adapted to perform the analysis according to a granularity specific to the structure of the primary information. For example, the analysis may be performed frame by frame.

[0070] This analysis step consists of Figure 2 Indicated by reference numeral 121 in the figure.

[0071] The results of this analysis can be processed in a conventional manner, 122, corresponding to normal operation of the satellite 1. For example, the results may be stored in an onboard memory, they may be sent to a ground station for further processing, etc. This step is optional and outside the present invention.

[0072] A test step 123 is provided to detect a situation corresponding to a criterion within the main information.

[0073] The criteria discussed may vary. Generally speaking, the purpose is to distinguish between normal and critical situations within the main information. This is a conventional problem for classifying and processing digital data. Various solutions are available to those skilled in the art and do not need to be developed here.

[0074] However, the criterion can be fixed or adaptive. It can be single or multiple. For example, when the analysis is implemented by a multi-layer neural network, it can be formalized as a loss function.

[0075] Existing technologies include ground-based image analysis systems for measuring precipitation, river levels, lava or mudslides, fire detection, storm warnings, and more.

[0076] References include: Jean- Lenat's book "Aléas et surveillance de l'activité volcanique 2: sismologie, déformation et télédétection", ISTEéditions, 2022, ISBN 9781789480450; or the article "Amélioration de la précision d'un" by Bonakdari, H., Zaji, AH, Soltani, K. and Gharabaghi, B. "It's the right thing to do if you don't know how to deal with it", published in Comptes Rendus Géosciences, 352, 73-86 (2020); or by Catry, T., Révillion, C., Mouquet, P. and Pennober, G. capteur", published in EchoGéo, (51), 2020.

[0077] As long as no situation corresponding to the criterion is detected, the mechanism may loop back to step 121 to analyze a new portion of the primary information (eg, a new image).

[0078] When a situation corresponding to the criterion is detected, a step 124 for determining secondary information related to the situation is triggered.

[0079] This secondary information may include the results of the analysis performed in step 121 .

[0080] The secondary information may also be enriched with other data, such as satellite identifiers, timestamps, satellite positions, etc.

[0081] Generally speaking, due to the applied processing, the secondary information corresponds to a semantically higher level than the primary information. It is also smaller in size.

[0082] A portion of the secondary information provided directly by analysis 121 may contain data of the same nature as the primary information.

[0083] For example, they may contain images representing geographical areas but representing semantic data derived from the processing: for example, segmentation may distinguish image points corresponding to detected critical situations, or different color levels may correspond to different severity levels of the situation or to the type of situation (flood, fire, destruction, etc.), labels may be associated with image points or with areas derived from the segmentation and represent terrain type or cloud cover, etc.

[0084] Additionally, other types of data may be derived from the analysis 121 that are not of the same nature as the primary information: for example, the type of emergency situation, the estimated severity level, the size of the area involved, the geographic location of the area involved, etc.

[0085] In one embodiment, the secondary information represents an alert. The ground terminal may have means for effectively alerting a user based on the secondary information.

[0086] As is known, there are various possible ways to determine secondary information which can be suitably utilized by a terrestrial telecommunication terminal equipped with a suitable software application.

[0087] The secondary information is then formatted, step 125, for broadcast by the onboard telecommunication means 13 of the satellite.

[0088] The purpose of formatting is to convert digital data into analog data, typically by modulating a carrier signal, in accordance with the specifications of the telecommunication protocol used by telecommunication device 13 to broadcast information to ground terminals.

[0089] Figure 2 The reference numerals 121-125 in the figure can be seen as steps in the process of implementing an embodiment of the present invention, but can also be seen as modules in the functional architecture. The processing device 12 can be implemented by components of electronic circuits and / or by software modules running on an information processing infrastructure.

[0090] According to one embodiment of the invention, the protocol used is the Bluetooth protocol.

[0091] According to the collaborative encyclopedia Wikipedia, "Bluetooth is a telecommunications standard for two-way data exchange over short distances using UHF radio waves in the 2.4 GHz band. Its purpose is to simplify the connection between nearby electronic devices by eliminating wired links. For example, it can replace cables between computers, tablets, speakers, cell phones, or printers, scanners, keyboards, mice, joysticks, cell 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)

[0092] One of the advantages of the Bluetooth protocol is that it is implemented on the vast majority of telecommunication terminals on the market.

[0093] Therefore, the proposed mechanism is operable on existing terminals and does not require hardware modifications. In particular, this mechanism contrasts with the use of specific terminals for satellite communications, such as those adapted for the Iridium network, which are less widespread and more expensive.

[0094] Furthermore, the reception of information by the terrestrial terminal is independent of the subscription to any type of service. This makes it possible to address all mobile phone users even without a subscription to an operator and even in areas not covered by the terrestrial network.

[0095] Broadcasting the secondary information via satellite using this telecommunication protocol means that the secondary information can be received by most terminals in the world and thus alert a large number of persons involved in, for example, a critical situation or a detected risk.

[0096] In the case where the telecommunication terminal may be a mobile terminal, in particular a mobile terminal of the "smart phone" type, the user may be promptly notified even when the user is on the move, and may be alerted very quickly whenever a critical situation or the risk of an imminent critical situation is detected by the satellite, regardless of network coverage.

[0097] In addition, there is a Bluetooth protocol for broadcasting information to a series of terminals. In telecommunications, broadcast is a technology used to transmit a signal one-way (or one-way) to a large number of customers. This is in contrast to multicast and unicast, which represent a direct, personalized or "connected" link between the sender and the receiver.

[0098] Thus, according to the invention, the telecommunication means 13 of the satellite 1 do not have to be individually aware of the ground terminals, but only have to transmit. When the ground terminals receive this information, they can recognize it as a broadcast signal and therefore consider themselves as receivers (without indicating their own address in this signal, such as in unicast or multicast mode).

[0099] Obviously, the Bluetooth protocol was designed for communication between devices at close range, so using it to broadcast information between a satellite and a ground terminal is completely destructive.

[0100] The inventors have performed simulations to demonstrate that in the context of the present invention, the Bluetooth protocol can be used over long distances under certain conditions defined by the inventors.

[0101] Another constraint on the conventional operation of the Bluetooth protocol is the initial pairing phase between two devices before exchanging information. In the context of the present invention, it is not possible to establish such a pairing between a satellite and a ground terminal, on the one hand because it would require a transmission power of the ground terminal that is incompatible with the specifications of the ground terminal, and also because it would involve a lot of weight and load on the satellites, which would potentially have to pair with thousands of ground terminals and if the satellites are moving, the operation would have to be repeated regularly.

[0102] The inventors have identified a specific operating mode of the Bluetooth protocol, called "advertising", which satisfies both constraints of avoiding pairing mechanisms and allowing broadcasting, and can therefore be used to implement the present invention.

[0103] 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 as of July 13, 2021.

[0104] The "Announce" mode allows several types of connections via the Generic Access Profile (GAP) mechanism described in Section 6.2. Specifically, there is a "Broadcaster" mode, in which a sender sends information without allowing (and therefore not waiting for) a return. This mode can generally be used to implement the present invention.

[0105] In one embodiment, the operating mode corresponds to the BLE protocol. In one embodiment, the BLE protocol is used.

[0106] Bluetooth Low Energy (BLE or BTLE) is a wireless transmission technology created by Nokia in 2006 as an open standard based on Bluetooth, which complements Bluetooth rather than replaces it. It has been integrated into the Bluetooth standard since version v4.0 released by the Bluetooth SIG in June 2010.

[0107] According to Wikipedia, "BLE offers data rates of the same order of magnitude (1Mbit / s) with 10 times lower energy consumption than Bluetooth. This enables the technology to be integrated into new types of equipment such as watches, medical monitoring devices or motion sensors. The technology enables devices to be connected within a radius of about 10 meters."

[0108] One of the advantages of the BLE protocol is its low energy consumption, which is an important consideration for satellite-mounted devices.

[0109] Bluetooth devices send packets to broadcast data in the advertising mode. These are 31-byte blocks that can contain information specific to the transmitter. They are also used to enable other devices to connect to them (pairing). There are several types of "advertising" packets, each one fulfilling a different function (for direct or indirect advertising, with or without the possibility of connection).

[0110] Bluetooth enables bidirectional or unidirectional data exchange using UHF radio waves and operates in the 2.4 GHz band. 40 physical channels are allocated for time and frequency reuse, each spaced 2 MHz apart (i.e., from 2.4 GHz to 2.8 GHz). Some channels are used for announcements, while other channels are used for unicast or multicast transmissions.

[0111] According to the BLE standard, an object can have up to 4 functions. They are as follows:

[0112] Broadcaster: can act as a server. Therefore, its purpose is to send data to devices periodically, but it does not accept any incoming connections;

[0113] Observer: The object can only listen and interpret the data sent by the broadcaster. In this case, the object cannot initiate connections to the server.

[0114] In this embodiment, the satellite may implement the "broadcaster" portion of the BLE protocol operating mode, while the ground telecommunication terminal implements the "observer" portion.

[0115] As mentioned before, secondary information (due to its high-level semantic content) can be low-volume. Therefore, the use of the BLE protocol is justified.

[0116] Depending on the standard, the BLE protocol can operate at different data rates.

[0117] In one embodiment of the invention, the data rate used is 125 kbits / s. In addition, the 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 greater sensitivity. This BLE protocol mode corresponds to a sensitivity of -103 dBm.

[0118] The BLE protocol is described and specified in the aforementioned normative document. Specifically, on page 218, there is a table summarizing the various possible BLE modes.

[0119] The signal strength received by a landline phone must be greater than the sensitivity of the receiver.

[0120] According to simulations performed by the inventors, this mode of operation of the BLE protocol (125k S=8) enables the use of low-orbit satellites to close the link budget using satellite directional antennas, where the transmit power is in phase with what commercial power amplifiers can generate from low-orbit satellites.

[0121] Antenna directivity may depend on a trade-off between satellite stability and maximum power consumption. In practice, the more directional the antenna, the more stable the satellite will need to be in pointing at the Earth, and the lower the required transmit power.

[0122] Figure 3 A simulation of the evolution of the received power PR of the satellite (by a terrestrial telecommunication terminal) relative to the transmitted power PT is shown. The simulation is obtained by considering a transmitting antenna with a directivity defined by a -3dB aperture angle of 20° and a gain of 18dBi and a receiver located at the nadir of the satellite (i.e. the point on the ground vertically positioned between the satellite and the center of the Earth).

[0123] The curve shows that for low transmit power PT, the received power increases very fast. Therefore, from only a few watts of power transmitted by the satellite, the required sensitivity of the receiver (i.e., -103DB) is achieved. Figure 3 In the exemplary curve for , 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.

[0124] Figure 4 Another simulation is shown of the evolution of the satellite's received power PR (via a terrestrial telecommunication terminal) compared to the transmitted power PT, based on different assumptions, in particular a lower antenna gain and taking into account that the receiver may be located somewhere other than at the lowest point, and in particular at the edge of the coverage area.

[0125] The following is an example of a link budget calculation based on Figure 4 The simulation assumptions in Figure 2 are used and actual error tolerances are applied to the link budget.

[0126] The following parameters were considered:

[0127] - BLE mode 125k S=8,

[0128] - Satellite altitude H equals 550km,

[0129] -BLE receiver sensitivity: S = -103dBm,

[0130] - Link budget margin: margin = 4dB,

[0131] -Atmospheric loss at 2.4GHz: L atm =0.5dB,

[0132] -Polarization loss: L pol =3dB,

[0133] - Insertion loss: L i =2dB,

[0134] - Directivity of the antenna defined by an aperture angle at -3dB of 20°, which corresponds to a maximum communication distance of H = 550km (at the edge of the coverage): D max =560km,

[0135] - Maximum path loss: PL = 155 dB (e.g., as in https: / / en.wikipedia.org / wiki / Path_ loss as indicated on the website),

[0136] - Transmitting antenna gain: G tx =15dBi, and

[0137] -Average receive antenna gain: G rx =0.5dBi.

[0138] Satellite nadir loss is defined as follows:

[0139] PL+L atm +L pol +L I =160.5dB, and

[0140] The loss at -3dB is as follows:

[0141] Loss at 3dB = PL + L atm +L pol +L I =163.5dB

[0142] In order for a telecommunication terminal to be able to demodulate the signal broadcast by the satellite in BLE 125k S=8 mode, a minimum received power Min(Prx) is required:

[0143] Min(P rx )=S+Margin=-103+4=-99dBm

[0144] Using the telecommunications equation, the transmit power Ptx can be written as:

[0145] Ptx = Min(Prx) + Loss at 3dB - (G tx +G rx ).

[0146] Substituting the above values ​​gives:

[0147] Ptx = -99 + 163.5 - 15.5 = 49 dBm, which corresponds to about 79.5W.

[0148] Therefore, the satellite EIRP is: Ptx+Gtx=64dBm.

[0149] It can be seen that, using the practical assumptions of the calculations detailed above, the required sensitivity S is achieved at a power of several tens of Watts, which corresponds to fairly conventional transmission power values ​​of the communication device 13 .

[0150] Of course, other curves, and therefore other minimum transmit powers, are possible, depending on the telecommunication protocol used to broadcast the information. In particular, the "BLE 125k s=0" protocol (one example of which is described herein) may undergo standardization changes in the future, which may have an impact on the performance curve. In addition, other modes of the BLE protocol associated with higher data rates (e.g., 250kbits / s, 500kbits / s; 1M or even 2M) may also be used.

[0151] In any case, it is clear that the use of this Bluetooth standard operating mode enables the broadcasting of information from the satellite to ground-based terminals 2 having capabilities customary for telecommunication devices 13 and complying with the requirements of on-board systems.

[0152] Of course, other implementation modes are possible, particularly depending on the future evolution of various telecommunication standards or the emergence of new standards.

[0153] In the case of a mobile satellite (in low earth orbit or other orbit), the movement of the satellite relative to the ground terminal distorts the transmitted signal through the Doppler effect (frequency shift).

[0154] Since the Bluetooth protocol is designed for communication between nearby objects at zero or low relative speeds, it does not provide a facility for naturally recovering from these signal distortions.

[0155] Simulations performed by the inventors have demonstrated a sensitivity loss of approximately 4 dB and a packet loss rate of approximately 10-2.

[0156] According to one embodiment of the invention, the processing means 12 is adapted to pre-compensate for the frequency shift associated with the Doppler effect as a function of the satellite position, the telecommunication terminal position and the satellite's speed relative to the ground. The pre-compensation is designed to eliminate or at least significantly reduce the loss of sensitivity and the increase in the packet loss rate.

[0157] This pre-compensation is actually possible as long as the telecommunication devices 13 know the positions of the mobile terminals 2 to which the information is broadcast, since these devices are directional (ie over the coverage area of ​​the broadcast cone 50).

[0158] If the solid angle of the scattering cone is small enough, the differences between different locations in the coverage area due to the Doppler effect can be considered negligible.

[0159] This pre-compensation may be performed by apparatus 10 by pre-processing the complex envelope of the signal prior to broadcast.

[0160] If the signal to be broadcast is denoted x(n) (and thus the signal that would actually be broadcast if the Doppler effect were not taken into account), then according to one embodiment, a pre-compensated signal y(n) is formed defined by:

[0161] [Mathematical formula 1]

[0162]

[0163] In this expression, denoting the estimated instantaneous phase, which represents the Doppler variation to be compensated on the surface S representing the footprint of the diffusion cone 50 .

[0164] Therefore, the Doppler effect θ D，S (n) The naturally perturbed received signal will be written as:

[0165] [Mathematical formula 2]

[0166]

[0167] The quantity w(n) represents the thermal noise of the receiver.

[0168] Using the expression for the pre-compensated signal y(n), this expression can be written as:

[0169] [Mathematical formula 3]

[0170]

[0171] or:

[0172]

[0173] ε D，S(n) represents the estimation error of the Doppler effect and is expressed as:

[0174] [Formula 4]

[0175]

[0176] The instantaneous phase due to the Doppler effect can be estimated deterministically by knowing Changes:

[0177] Satellite position;

[0178] the location of the area on the ground to which the information will be broadcast (corresponding to the terrestrial footprint of the broadcast cone 50);

[0179] Carrier frequency;

[0180] The relative speed of the satellite with respect to the ground (or the telecommunication terminal if it is in motion; remember that the latter can be neglected given the speed of the satellite with respect to the terminal).

[0181] The estimation aims to make the estimation error ε D,S (n) Minimization.

[0182] The instantaneous phase can be estimated using the physical equations used to calculate the Doppler effect. Various ways of implementing these computational aspects are well described in the technical literature. One example is the article "Doppler Characterization for LEO Satellites" by Irfan Ali, Naofal Al-Dhahir, and John E. Hershey, published in IEEE Transactions on Communications, Vol. 46, No. 3, March 1998.

[0183] Thus, telecommunication terminals 2 in the reception zone (coverage area of ​​the broadcast cone) are able to receive the information broadcast by the satellite with sufficient power to enable it to be processed correctly (demodulated with a sufficiently low error rate to enable reconstruction of the secondary information determined by the processing means 12).

[0184] As already seen, the terminals can be terminals of the prior art. In particular, conventional telecommunication means are sufficient to enable them to receive the secondary information broadcast by the satellite. Thus, the need for special antennas, demodulation circuits, etc. is eliminated.

[0185] As has been seen, one embodiment of the present invention uses the Bluetooth protocol, in particular the BLE125k s=8 operating mode of the protocol. The vast majority of telecommunication terminals are inherently adapted to receive information broadcast using this protocol.

[0186] The telecommunication terminal may be of different types. This may be a fixed terminal (computer, television, etc.) or a mobile terminal (laptop, tablet, cellular phone, etc.).

[0187] The telecommunication terminal comprises a software application 20 adapted to continuously receive a data stream in a predetermined channel.

[0188] As explained above, this channel may correspond to the Bluetooth telecommunication protocol, and more specifically to a broadcast mode of this protocol, such as "BLE 125k S=8".

[0189] The software application is also suitable for analyzing the content of this data stream in order to detect said secondary information and, if necessary, to determine within this secondary information data enabling the triggering of an action on the man-machine interface of the telecommunication terminal.

[0190] Such data may include geographic location and / or type of situation.

[0191] The software application may be adapted to compare this geographical location with the geographical location of the terminal and trigger an action only if the two geographical locations are close enough. This concept of proximity may be fixed, configurable or adaptable, for example depending on the type or severity of the situation.

[0192] The software application may also be adapted to compare this type of situation with parameters set by the user of the telecommunication terminal, which parameters indicate the type of service to which the user wishes to subscribe.

[0193] These parameters may be set by the application itself, so that there may be several versions of the application, each version corresponding, for example, to a different type of user (general public, security professionals, etc.), or to a different application domain.

[0194] An example of application could be to inform the population of a critical situation (fire, flood, earthquake, major flood, etc.). The critical situation can be detected by an observation satellite using the primary information acquired and analyzed as described above. It can also be performed by other mechanisms and broadcasted by a communication satellite.

[0195] When the terminal 2 is within the broadcast area of ​​the satellite (coverage area of ​​the broadcast cone 50), the terminal receives the Bluetooth broadcast stream. If the application 20 is appropriately configured, it can analyze the incoming stream and determine whether an alarm should be triggered via the human-machine interface (display of a signal or message on the screen, audible alarm, vibration, etc.).

[0196] Other applications are possible where a user wishes to be alerted to specific conditions as determined by satellite or other systems.

[0197] For example, the determination may include checking that the terminal's location is actually within an area affected by the emergency situation (in a more precise manner than a satellite broadcast mechanism could do), or whether the user has actually subscribed to an alert service.

[0198] Thus, according to the invention, the information is broadcast directly from the satellite to the telecommunication terminals. They are not transmitted through other devices. Thus, in critical situations such as natural disasters, the mechanism of the invention makes it possible to be immune to: damage or even destruction of the terrestrial telecommunication infrastructure;

[0199] The existence of terrestrial networks in the area involved;

[0200] Subscriptions to operators;

[0201] Congestion of telecommunication infrastructure due to the large number of communications initiated by the crowd during this type of event and possible partial destruction of this same infrastructure equipment.

[0202] Thus, the present invention enables resilient maintenance of a communication channel with involved persons who may have been affected.

[0203] In addition, some areas have low coverage of telecommunication infrastructure (wired, cellular, WiFi, etc.). This is especially true for remote rural areas. In this case, the present invention enables sending alerts or more generally sending secondary information to mobile terminals in the absence of telecommunication infrastructure.

[0204] Additionally, according to some of the embodiments of the present invention, the ever-increasing capabilities of observation satellites can be exploited by transmitting analysis results directly to the end user's mobile telecommunication terminal.

[0205] This allows them to obtain these results as quickly as possible without the need for ground stations to process the information or even retransmit it. These no longer form bottlenecks, lengthening the information transmission chain and slowing down the reception of relevant information by users.

[0206] This ability to transmit directly from satellites to users opens the way to new applications and services, especially in developing countries or in areas with insufficient terrestrial telecommunication coverage (forested areas, deserts, etc.).

[0207] Of course, the invention is not limited to the examples and embodiments described and shown, but is defined by the claims. In particular, the invention is susceptible to numerous variants that may be obtained by a person skilled in the art.

Claims

1. A device (10) suitable for installation on 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 device is suitable for broadcasting the information via the Bluetooth Low Energy communication protocol BLE according to an "announcement" mode, according to which no incoming connections are accepted, the at least one telecommunication terminal (2) being compatible with the communication protocol and configured to receive the information without sending any connection request to the communication device of the satellite, the telecommunication device comprising: - a directional antenna suitable for transmitting in a broadcast cone a signal carrying said information in a frequency band between 2.4 GHz and 2.8 GHz at a data rate of at least 125 kbits / s with a transmission power greater than or equal to a few Watts, said transmission power being determined so that the power of the signal received by at least one of said terminals located in said broadcast cone is higher than a given reception sensitivity of said terminal for said "announcement" mode, said given reception sensitivity being a function of the altitude of said satellite relative to the Earth's surface, the directivity of said antenna, the pointing parameters of said satellite and standard transmission losses related to passage through the atmosphere.

2. The device for observing a satellite according to claim 1, further comprising: - at least one sensor (11), the at least one sensor being used to acquire primary information - processing means (12) for analyzing the primary information in order to detect situations corresponding to a criterion within the primary information and to determine secondary information related to the situations; and - said telecommunication means (13) being provided for transmitting said secondary information within said message. The device according to claim 2 , wherein the primary information is an image.

4. Apparatus according to one of the preceding claims, wherein the telecommunication device is adapted to broadcast the information via the Bluetooth Low Energy protocol BLE at 125 kbits / s with S=8 symbols per bit of information, the sensitivity of the telecommunication terminal being approximately -103 dBm.

5. Apparatus according to one of claims 2 to 4, wherein the processing means are adapted to pre-compensate for frequency shifts related to the Doppler effect as a function of the position of the satellite, the position of the at least one telecommunication terminal and the speed of the satellite relative to the ground.

6. Device according to one of claims 2 to 5, wherein the secondary information represents a warning.

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

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

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

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

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