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    • 专利摘要:
    A computer-implemented method for processing the signal transmitted by a distress beacon is disclosed, said signal being received by a plurality of satellites and retransmitted to at least one ground station, the method comprising the steps of determining a set of hypothetical positions of the distress beacon, and, for at least one of the hypothetical positions, for each satellite, shifting the received signal and retransmitted according to said hypothetical position; sum the off-set signals; and evaluating the validity of the sum of the shifted signals as a function of the presence in said sum of a predefined characteristic. Developments describe aspects of offset in time and / or frequency, construction of a digital replica of the signal emitted by the distress beacon, weight minimization weighted offsets. System aspects are described, including the calibration of an active antenna or an array of antennas. 150 words
    公开号:FR3023379A1
    申请号:FR1401510
    申请日:2014-07-04
    公开日:2016-01-08
    发明作者:Thibaud Pierre Jean Calmettes；Emanuela Ana Maria Petcu；Yoan Gregoire
    申请人:Centre National dEtudes Spatiales CNES；Thales SA；
    IPC主号:
    专利说明:

    [0001] FIELD OF THE DISCLOSURE The present invention relates to the field of satellite communications and in particular to the methods and methods for locating a distress beacon. STATE OF THE ART A distress beacon or "beacon" for the location of disasters is a transmitter that emits an emergency electromagnetic signal (in English "burst") to give the location of a ship, aircraft or aircraft. of a person in distress. This signal is received by one or more satellites of a network (for example Cospas-Sarsat or GEOSAR) which generally retransmit this signal to ground stations which determine the location of the beacon and transmit its coordinates to the research or research office. nearest rescue. The signal may contain GPS position information which makes locating easier. In other situations, no declared position information is transmitted. In most cases, the large number of tags marketed does not allow association with a unique identifier with each tag. As part of the development of the MEOSAR satellite distress network for search and rescue, commissioned in 2018, many 25 MEOLUT ground receiving stations are to be developed and deployed. One of the main technical problems of the transition to MEOSAR is the degradation of the link budget compared to the current LEOSAR version. If the LEOSAR system (Low Altitude) has been sized with sufficient margin to allow - despite this loss - a MEOSAR treatment, all of this margin should be absorbed by the modification of the satellite segment whereas it could or should normally cover also the most critical issue cases. In fact, a wrongly oriented antenna and / or lacking transmission power, or a partially immersed beacon may not be located in the future. To date, several actions have been put in place (or planned) to minimize the losses associated with the transition to MEOSAR: a) use of large receiving antennas to minimize the contribution of the downlink (knowing that with SAR payload P, there is only one rising path in LEOSAR context); b) overall visibility improvement: the geometrical diversity allowed by the continuous visibility of many simultaneous satellites (at least 8) leads to size mask and combination constraints of antennas gains on a more favorable case than in LEOSAR; c) improvement of the satellite antenna d) study of a new, more efficient modulation (confer EWG Cospas / Sarsat) Despite all these elements, the loss linked to the transition to MEOSAR leads to a degradation of 10 dB. In addition, a key problem is the cost of the antenna which leads to a very strong limitation on the number of satellites pursued at typically 4 or 5 (with a maximum of 8 on the most rich MEOLUT stations, but some on the contrary not have only two antennas) whereas 30 satellites are typically visible on all the constellations pursued. There is an industrial need for methods and systems for improved precision locations. The solution of the present invention overcomes the disadvantages of conventional approaches, at least in part.
    [0002] SUMMARY OF THE INVENTION There is disclosed a computer-implemented method for processing the signal transmitted by a distress beacon, said signal being received by a plurality of satellites and retransmitted to at least one ground station, the method comprising the steps of determining a set of hypothetical positions of the distress beacon; and, for at least one of the hypothetical positions, for each satellite, shifting the received signal and retransmitted according to said hypothetical position; summing the shifted signals and evaluating the validity of the sum of the shifted signals as a function of the presence in said sum of a predefined characteristic. The beacon has in physical reality a "true" (exact) position, the object of the present invention is precisely to determine the coordinates in the fastest and most accurate manner possible. On receipt of a signal transmitted by a beacon, as a first approximation, a first geographical area within which the beacon is located can be determined. By defining a certain resolution step (for example 5 km), a finite number of positions in the space can be defined: the search space is discretized. A set of "hypothetical" or "likely" or "possible" or "candidate" or "potential" positions is determined discretely and therefore approximated. In reality, the distress beacon can be between two discrete positions. The position of the beacon is specified iteratively, when the best point (s) of the grid is determined. This set of positions, according to different embodiments, corresponds to a "grid" or a "matrix" or a "table" or a "mesh". A logical or abstract view will indeed consider the list of possible positions as coordinate data, while a geometric view may correspond to a regular or irregular grid. For example, it is possible to have an irregular mesh on the positions (for example to take into account the tightening of the degrees of longitude when the latitude increases). In general, a set of hypothetical positions is determined, regardless of the underlying name of the coordinate representation thus established. The set of potential positions of the position grid beacon makes it possible to discretize the space of possibilities and to converge quickly to a precise position. Beyond the literal sense, in a particular embodiment, the position grid can be obtained by generating a finite set of geographic coordinates to which the beacon is likely to be located (for example as a first approximation). The "pivot" of the location is given by the list of positions in the grid. A grid of positions is for example a grid of 1 ° x 1 ° in latitude and longitude. Considering the entire planet, 180 x 360 or 64800 points can be obtained. By limiting itself to the points visible from the station, this number of positions can be divided by 5 (the exact number depends on the latitude), about 13000 points. According to one aspect of the invention a "coherent integration" of the satellite signals is performed at a hypothetical position (or point of the position grid). Borrowed from the technical field of GNSS signals, this "coherent integration" corresponds, in a particular embodiment, to the "sum of the shifted signals" of the satellites. The signals are shifted ("relatively"), i.e. relative to each other (according to the transmit position assumption). The relative offset between the signals is taken into account (and not the absolute offset). The "vector search" - which is then undertaken - refers to the operation of traversing this set of positions or position grids to obtain a valid coherent integration, instead of seeking in the set of offsets in time and frequency possible between all the satellites which would create a combinatorics too big. The evaluation of "validity" (or "quality" of the sum) can be carried out in different ways, the following developments giving different implementation solutions. In general, the validity of the summed signal (i.e. offset signals) can be quantified, hence the term evaluation involving association with different values. This evaluation or quantization can for example be performed according to the presence - or a contrario of the absence - of a predefined or known signal (i.e. presence of a certain characteristic in the summed signal). If a predefined and / or known characteristic is absent (eg under a certain predefined value threshold, possibly configurable), the position hypothesis (ie according to which a signal has been emitted from the hypothetical position of the position grid) is abandoned for the grid point considered and the process is iterated. If a predefined characteristic and / or is recognized or identified or detected or otherwise established as similar (eg by the use of criteria and / or thresholds), the position assumption is retained and other steps continue the validation tests of the hypothesis (eg demodulation, TOA / FOA measurements). Other subsequent rejection points may occur (for example the number of bit errors during the decoding of the BCH code especially for the demodulation in CospasSarsat). In cases where the presence or absence of a predefined and / or known characteristic is not established with certainty (eg interval or limit or insufficient confidence rate), the signal is compared with respect to white noise of to detect a useful signal (for example by means of thresholds and trade-offs between detection probability - eg ability to validate a signal received at low signal-to-noise ratio - and probability of false alarm - eg risk of performing test processing on noise.
    [0003] In a particular embodiment, there is disclosed a computer-implemented method for processing the signal transmitted by a distress beacon, said signal being received by a plurality of satellites and retransmitted to one or more ground stations, the method comprising the steps 5 of generating a grid of positions of the distress beacon, each point of the grid representing a position assumption of the beacon; summing the offset satellite signals at each point of said position grid; and determining the validity of each sum of the shifted signals as a function of the presence or absence of a predefined characteristic in the transmitted signal. Several stages are combined according to the method: a "vector" search is implemented on a "grid of positions" (ie potential or potential positions) of the distress beacon, this search being carried out on the so-called "coherent" integration ( ie by summation of the relative offset signals of the satellites), and "valid" (ie by means of searching for and identifying the presence of a predefined characteristic contained in the signal transmitted by the distress beacon), signals different satellites at each point in the set of hypothetical positions (eg the "position grid" as defined). In one development, the step of shifting the signal of a satellite comprising a step of temporally shifting the signal of said satellite by a time equal to the opposite of the beacon-satellite-station delay. The propagation time corresponds to the total travel time of the distress signal, that is to say to the travel time of the distance between the hypothetical position of the distress beacon and the satellite, added to the travel time of the distress signal. distance between the satellite and the receiving station. This path is performed at the transmission speed of an electromagnetic signal, or substantially at the speed of light in the vacuum.
    [0004] In one development, the step of shifting the signal of a satellite comprising a step of frequency shifting the satellite signal by a frequency equal to the opposite of the Doppler effect. The Doppler effect is associated with the relative displacement of the satellite relative to the hypothetical position of the distress beacon and relative to the relative movement of the satellite relative to the receiving station. In one development, the step of shifting the signal from a satellite comprising a step of shifting the signal power by a power equal to the opposite of the measured power attenuation for said satellite. The power attenuation is determined by (a) the link budget losses between the hypothetical position of the distress beacon and the satellite and (b) the link budget losses between the satellite and the receiving station; The link budget losses are essentially losses of free space, itself dependent on (i) the distance and depending on (ii) antenna gains on transmission and reception, said antenna gains depending in turn on the elevation and the azimuth of emission and reception. Since the orbit of the satellites can be sufficiently well determined, it is also conceivable to correct the arrival phase. This development remains entirely optional (the estimate of validity of the sum is made in a non-coherent way, that is to say assuming that the phases are different). In one development, a characteristic of the transmitted signal includes the presence of a pure carrier, and the validity of the sum of the signals shifted from the satellites is determined by the appearance of a line in the Fourier transform of the summed signal. In this particular case, for which the signal starts with the pure carrier, it is possible not to compensate the delay but only the Doppler since a peak of FFT (Fast Fourier Transform) occurs as soon as the Doppler is correctly corrected. In a development, the transmitted signal further comprises the presence of a synchronization signal, and the validity of the sum of the signals shifted from the satellites is determined by correlation between the summed signal and a replica of said synchronization signal. The signal transmitted by the distress beacon may comprise a synchronization "signal" (for example and in a particular case a "word" of synchronization). In an advantageous embodiment, the synchronization signal has the same properties as the following useful signal (same modulation, for example). Several modulations of the system "Search and Rescue" S.A.R. are possible. The current modulation provides for a carrier then the message, the message starting with a predefined sequence. The so-called "new generation" modulation provides the message directly but with a predefined sequence known at the beginning of the signal transmission and with a spreading code. Such a sequence is a useful and advantageous marker for the validity of the coherent integration step. In the case of pure carrier modulation, a composition is considered valid if the coherent summation causes a line in the frequency domain to graphically materialize. The signal transmitted by the distress beacon may include a predefined message portion marking the start of the broadcast. In the case where the transmitted signal comprises a predefined marker 25 (i.e. known a priori), a composition is considered valid if the correlation with the predefined message portion graphically materializes a line in the time / frequency domain. In other words, it may appear a "peak" during a synchronization search in the frequency and time domain.
    [0005] This development corresponds to the so-called "Search-And-Rescue" signals. It is first checked if there is a line and if there is a line it is searched for the synchronization word. This development provides the best operational performance. In particular, the correlation search makes it possible to eliminate the detections on interfering interference-related lines, and the search for the line before the correlation search makes it possible to reduce the frequency uncertainty and thus to maintain compatible computing complexities. a real-time implementation. In one development, the correlation is obtained for a particular time and frequency offset between said signal obtained by the sum of the signals shifted from the satellites and the replica of the synchronization word. The search for the particular time and frequency offset can be performed by calculating the correlation for each position of the set of hypothetical positions including a time shift and a frequency offset (ie without a direct link with the hypothetical position of the distress beacon The method includes defining a set of hypothetical positions of the distress beacon. By iteration, it is considered a particular hypothetical position. For this position, the signals of each satellite are shifted in time and frequency, as a function of the hypothetical position considered, as well as delays and Doppler shifts associated with the propagation of the signal. These modified signals are summed. For example, by naming s1, s2, s3, and s4 the signals on four satellites and f (s, p) the signal shift function s according to the hypothetical position p, the resulting summed signal S will be S (p) = f (s1, p) + f (s2, p) + f (s3, p) + f (s4, p). In this summed signal S, it is searched or tested or evaluated if S (p) contains an intelligible signal, e.g comprising a known signal. To do this, one method is to correlate S (p) with a replica of the synchronization word. If S (p) and the replica are well aligned in terms of frequency and time, the correlation will be strong and a high value of this one will be observed, which will make it possible to validate the hypothesis of position p. However, in the general case, S (p) and the replica will not be aligned because the date and the frequency of transmission of the signal are not known. To take into account the non-knowledge of the emission date and the transmission frequency, a grid ("regular") of offsets can be created (offset time of emission, offset frequency of emission), and by then it will be possible to calculate the correlation with the replica for each point of this grid. The sum S (p) will be valid if a point of this grid is identified, for which point the correlation with the replica is high. Incidentally, only knowledge and manipulation of S (p) is required (position information is no longer required). Iteratively so, the position of the distress beacon can be determined.
    [0006] This particular embodiment is advantageous for the methods of developing the validity of the coherent integration (e.g. sum of the shifted signals). The time / frequency grid corresponds to the two unknowns, the "date of transmission of the message" and the "transmission frequency of the message". The uncertainty on these elements does not prevent the coherent reconstruction by the process of pre-compensation delay and Doppler shift according to the grid of position, on the other hand if they are not correctly estimated / known, they can disrupt the processes Validity search. In one development, a characteristic of the transmitted signal is obtained by the combination of an initial message and a spreading code, and the validity of the sum of the signals shifted from the satellites is determined by correlation between the summed signal and a replica of the spreading code. In one development, the correlation is determined for a particular time and frequency offset between the summed signal and the replication of the spreading code. In one development, the method further comprises, for each satellite, a step consisting of determining a time offset and a frequency offset maximizing the correlation between the signal received from this satellite and the summed signal corresponding to the sum of the signals shifted from the satellites determined. as valid. In this development, it is advantageous to be able to evaluate the measurements of time and frequency offsets without having demodulated and reconstructed the replica. This is less precise (because the replica is made without noise, while the coherent integration always has a noise residue), but it also works, and this can notably make it possible to make a localization even if the binary content does not exist. could not be demodulated. According to this development, for each satellite is therefore determined a pair comprising a time offset and a frequency offset. In one development, the method further comprises, for each sum of satellite offset signals determined to be valid, a step of determining the binary content of the beacon signal relayed by the satellites and received by the station. Demodulation is not strictly part of coherent satellite integration. In one development, the method further comprises, for each sum of satellite offset signals determined to be valid, after the step of determining the binary content of the beacon signal, a step of constructing a digital replica baseband of the signal transmitted by the distress beacon. For the reconstitution of the signal emitted by the distress beacon, it is not necessary to know the propagation medium to remake the latter "upside down" and determine the distortions. This is a "baseband" reconstruction. It's about building a modulated signal without carrier offset.
    [0007] In one development, the method further comprises for each satellite a step of determining a time offset and a frequency offset maximizing the correlation between the signal received from that satellite and the digital replica after a step of demodulating the coherent composition.
    [0008] The "digital replica" corresponds to the signal emitted by the beacon as reconstituted after the coherent integration. The expression "from this satellite" means "relayed by the satellite in question and sent to the ground station". In the MEOSAR system, the signal is not processed in the satellite before being returned to the station.
    [0009] By simplifying, ground-based comparisons are made between the reconstructed transmitted signal (from the signal from the multisatellite coherent integration), with successively each of the individual real signals received by each individual satellite. For each satellite, therefore, a pair is determined (time offset, frequency shift). The time and frequency offsets evaluated here correspond to residuals with respect to those considered when creating the valid sum of the shifted signals. For the "true" position of the beacon, for a given satellite, the offset (in time and / or frequency) is denoted D. For the point of the position grid closest to the true position of the beacon, a Dl shift was used. By taking a small grid step, the difference between D1 and D has been small enough that the coherent integration, the search for validity thereon, and the demodulation, have acceptable losses. However, the most demanding processing step with respect to the measurement of D is the precise location step of the transmitter. It may therefore happen that this difference between D1 and D is too great to accurately estimate the location (process most dependent on measurement accuracy), and then there will be a need for a more accurate measurement of D. When builds the sum by pre-compensating for the offset, the satellite signal has been shifted by D1, so that the reference signal (that directly derived from the sum of the shifted signals or the replica signal) used for the measurement of "offset time, Frequency offset "is already shifted by Dl. Thus, the search for correlation between the satellite signal and the reference signal will give a residual offset value D2, and what will be used for the location as best estimated of D will be equal to the sum of D1 and D2. In a particular embodiment, the time and / or frequency measurements can be initialized from the preliminary measurements carried out previously described (eg time offset of the satellite signal by a time equal to the opposite of the beaconsatellite-station delay and / or frequency shift of the satellite signal by a frequency equal to the opposite of the Doppler effect). In one development, the method further comprises a step of determining the location of the distress beacon, said location minimizing the weighted time offset residue, or the weighted frequency shift residual, or the combined weighted time shift and frequency shift residual. frequency offsets between satellites. The minimization of weighted residuals can be determined using the Gauss-Newton algorithm. Time and frequency measurements are combined. Depending on the waveform (in particular), one or the other of the time or frequency will be associated with a higher confidence interval. Some satellites may have more or less good measurements.
    [0010] In one development, the method further comprises a step of calibrating an active antenna or an array of antennas based on the location of the distress beacon. In one development, the method further comprises a step of creating a warning bulletin comprising the demodulated content of the signal transmitted by the beacon and / or the determined location of the distress beacon. In one embodiment, the alert bulletin may include the demodulated content of the transmitted signal and / or the location (if determined, for example). In other words, it is also possible to create an alert bulletin comprising only the demodulated content (for subsequent processing or third parties for example), ie without the determination of the location of the tag (which remains a optional feature at this stage of the process). In a fully optional development, the method comprises in advance a step of removing the contribution of the downlink between the satellite and the ground station (s). The operation to "shift the signal received from a satellite" consists of compensating for the so-called rising channel (from the position of the beacon to the satellite) and the so-called descending channel (from the satellite to the ground station). Since the descending path does not depend on the position of the beacon, it is possible to pool the calculation of its contribution on all the hypothetical positions. This embodiment is advantageous for calculations. In particular, this downlink contribution retraction can be performed before the search is applied to the points of the hypothetical position grid of the distress beacon. This development (optional) corresponds to an optimization of calculations. In a simple embodiment, delays and Doppler shift values are removed from the entire path (from the beacon to the satellite, then from the satellite to the station). In practice, for all points of the grid, the path from the satellite to the station may be substantially the same, so many calculations may be superfluous. The present development proposes to remove contributions from the satellite signal path to the station once and for all, then to concentrate the computing resources on what depends solely on the position of the beacon. In a development, the set of hypothetical positions of the distress beacon is reduced to visible positions from the visible satellites 10 from the receiving station. In particular, the step of the grid of positions expected of the distress beacon can be optimized (reduction of the search space) The determination of the location of the distress beacon makes it possible, among other things, to anticipate or monitor a new issue of the distress beacon. A computer program product is disclosed, said computer program comprising code instructions for performing one or more steps of the method, when said program is run on a computer. A system for locating a distress beacon is disclosed, the system comprising means for carrying out one or more steps of the method. In a development, the system comprises at least one active antenna or an array of antennas. According to one aspect of the invention, an antenna array (optional) is used in combination with parallel multi-satellite processing. In particular, a "loopback" of the processing results is performed on the calibration of the antenna array.
    [0011] Among other advantages, the method allows the simultaneous processing of all visible satellites, without significant cost impact on the changes made to the antennas. Conversely, the signal processing chain is improved. The calibration of the antenna network can be optimized. In general, each segment where stages of the processing chain thus contributes to the optimization and improvement of others. The benefits of the disclosed method and system include improvements in performance and cost optimizations. The method makes it possible to envisage a theoretical gain of 10 * log (N) where N is the number of visible satellites. For N = 30, the gain reaches 14 dB. An objective at 10 dB included losses can therefore be legitimately considered. The implementation of the method can be carried out at reduced cost for the adaptation of the MEOLUT station (antenna network, and software adaptations).
    [0012] The software complexity (and also hardware for the RF antenna network) are indeed easily surmountable. Matlab experiments on single-core processors indicate that a processing (without particular optimization) is less than a factor of 10 real time. An implementation in C ++ on computing servers will be advantageous. In terms of antennas, the target number of satellites (of the order of fifty) remains feasible for an industrialist (the current systems have up to 200 elements). This disclosure presents a number of related interests. According to one aspect, the steps described can be combined together, "forward", so as to progressively enrich the estimate of the position, or "backward", so as to use the final position of the tag to true true network. In fact, an integrated quality management mechanism for measurements is also becoming possible. The method also allows the tracking of the deviations to the expected. It also allows the detection of jammers formed. Finally, the method allows re-calculations on accumulated data (ease of return in the past). DESCRIPTION OF THE FIGURES Various aspects and advantages of the invention will appear in support of the description of a preferred embodiment of the invention, but not limiting, with reference to the figures below: FIG. 1 illustrates the general operation of the existing methods for locating a distress beacon; FIG. 2 schematizes the multipath optimization according to the invention and presents various associated optimizations. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates the general operation of the existing methods for locating a distress beacon. A beacon 100 emits an electromagnetic signal, which is received by four satellites 111, 112, 113 and 114, from a constellation of satellites. These four satellites retransmit the distress signal to the ground stations. The MEOLUT 122 ground station is composed of LEOLUT 121 stations.
    [0013] Today, about ten MEOLUT 122 stations are deployed around the world. A LEOLUT 121 is associated with an antenna and sees only one satellite. Each LEOLUT station performs four successive measurements of FOA (time of arrival, frequency of arrival), with a Doppler measurement (which is strong at low altitudes). With four LEOLUT stations forming a MEOLUT, the beacon is located (the position of the satellites is known at every moment), with a single "burst".
    [0014] According to the state of the art, these different stations 121 do not act in concert. The treatment routes are independent. The architecture is separate or compartmentalized, with a detection and processing chain specific to each antenna, the processing chains being separated not only in software terms but also most often in hardware terms. The existing architecture is mainly sized on the number of antennas (due to the significant cost of the antennas). In addition, of the thirty or so potentially addressable satellites, only four can currently be used simultaneously. According to a first aspect of the invention, the antenna part is improved (because of the use of an antenna array), this characteristic remaining nevertheless optional. This solution makes it possible to address all or a much larger number of satellites belonging to the constellation. In practice, this network of antennas can see the thirty satellites of the constellation. According to a second aspect of the invention, in combination with the use of the antenna array (optional), signal processing is the subject of cooperation between the various LEOLUT 121. In other words, an aspect of the invention provides multichannel optimization. FIG. 2 schematizes the multipath optimization according to the invention. The method generally describes a multi-antenna correlation for tracking GNSS satellites. by means of an array of optional antennas, a vector search is performed. In step 220 is implemented a vectorized search according to a grid of expected positions (not typical of 2 ° x 2 °) to check the presence of a SAR emission by recombination of the signals obtained on the different visible satellites. from the point of the grid and the MEOLUT. In step 230, the vectorized search is used as the entry point for implementing a coherent multi-satellite integration. In step 232, the integrated signal is processed. An ideal replica is deduced, and TONFOA measurements are built from a new iteration of correlations on this ideal replica. At step 238, a warning bulletin is produced. In step 240, the finally obtained location (and possibly to the vectorized search function to anticipate the presence of the next transmission of the same beacon) is retransmitted to the antenna calibration chain. In other words, the results of the locations on the processed beacons are looped together in order to recalibrate the network continuously. An "active antenna" or "antenna array" 210 is a set of separate antennas fed synchronously (the phase difference of the current between two pairs of antennas is fixed). The electromagnetic field produced by an array of antennas is the vectorial sum of the fields produced by each of the elements. By appropriately choosing the spacing between the elements and the phase of the current flowing in each, the directivity of the network can be modified by constructive interference in certain directions and destructive interference in other directions. The advantage of this type of network is that it is possible to change the direction in which the antenna "pulls" in microseconds (instead of seconds or tenths of seconds, which would be necessary to orient a dish mechanically). "Several targets can be simultaneously monitored Another advantage associated with this type of antenna is that these systems operate at a relatively reduced power.In a step 220, a" vector "search is carried out on a grid. positions, then to a coherent integration step 230. In order to determine the location of the beacon, it is in fact done by iteration on a grid, according to a so-called "vector" search mode 220.
    [0015] The pitch of the grid can be optimized in different ways (the search space can be restricted knowing the visible satellites of the beacon and the station, for example by excluding the areas of the terrestrial poles). Only the possible domain is covered. All possible combinations are tested (frequency and time offsets). It is therefore searched on a grid of positions. There are still two unknowns: the date and the frequency of the burst. By using hypotheses, via several satellites, the signals are recombined by coherent multi-satellite integration.
    [0016] In a first step, a position grid and traveled. For each point of the grid, the dopplers and the differential delays are calculated (for each satellite), and a corresponding composition (time / frequency) is created. If we find the presence - at a certain frequency and on a certain date - of a composition, we validate it.
    [0017] In a second step, for each valid composition, the signal is demodulated and then a digital replica of the burst is created (i.e. without additional noise). In a third step, for each satellite, the time offset and the frequency offset are sought which maximize the correlation with the replica. These offsets make it possible to find the precise location of the beacon. In other words, a coherent recombinant signal is reconstituted and this recombined signal is varied in time and frequency. These variations are compared with the actual signals, so as to improve the accuracy of the location of the beacon.
    [0018] The information from the plurality of satellites reduces the accuracy of the location of the beacon and a step of iterative calculation of travel on the grid makes it possible to locate the beacon more precisely. If the fineness of the grid is not sufficient, "bursts" can be missed. 302 3 3 7 9 21 Each satellite receives the same signal from the beacon. Assuming that the position of the distress beacon is known, all the dopplers are known, and it is therefore possible to sum the signals coherently and the balance is improved (the signal is 4 times stronger). Combine the signals on all the satellites to improve the signal. This operation can be advantageously performed on all the addressable satellites or on the largest possible part of them (which is achieved when an antenna array is used). An optional calibration step 240 makes it possible to optimize the calibration of the antenna array continuously. A satellite corresponds to an antennal element. If there are phase shifts for an antennal element, it will be possible to recalibrate this element (for example the phase will be modified by a few degrees, in a software way). All the antennas are generally disturbed as time goes by. Each beacon detection therefore provides the opportunity to recalibrate the antennal elements. The different steps of the method can be combined together, i.e. implemented synergistically. The steps of vector detection 220, coherent combination 230, final location 237 and antenna calibration 240 are related to the location of the beacon. During the vector detection, coherent combination and then final location steps, the position and the transmission characteristics (time, frequency) of the beacon are evaluated more and more finely, which will reduce the uncertainty, ambiguities, false alarms and calculation time for the successive steps. Conversely, the precise location of the beacon should be used for the a posteriori calibration of the antenna array (highlighting the law of correspondence between the phase shifts observed by the multi-antenna correlation and the geometric origin of the signal) .
    [0019] The method makes it possible to develop an integrated mechanism for managing the quality of the measurements, which can in particular result in a reduction in false alarms (and therefore an improvement in performance by reducing the associated thresholds on each stage of the treatment) and the 5 possibility of introducing a quality index. For example, if the final locating step leads to a beacon position outside the uncertainty domain of the coherent integration (i.e., if the beacon was actually where it is ultimately located, then coherent integration could not have worked and the signal could not be processed), the message may be rejected, or at least transmitted with low confidence. Another advantage of the method lies in the tracking of deviations from the expected. For example, if in a given situation, according to the vector search, five given satellites were to allow optimal visibility of the beacon (given their position and the position of the beacon in the grid), if proved that one of these 5 satellites did not contribute absolutely to the measurement, it could mean either that there is a common interference between the beacon and only this satellite (to check on other satellites and other beacons ), either a calibration error of the antenna on this satellite (to be checked on other beacons), or finally a problem at the satellite. In the case (in particular) where one would observe a degradation of the contribution of a satellite to the correlation during the vector search, a specific recalibration on this one would be advantageously carried out (for example by returning to an earlier calibration which then worked well and correcting it or not - the variation of position known by the orbit of the satellite). Until the coherent integration steps, the processing is generally the same whether in the context of a useful signal or a jammer formed. Most of the scrambler locating and detecting function is already natively included in the MEOLUT. The disclosed methods can identify relatively weak jammers (which can not be detected by an existing MEOLUT with its single channel processing). The vector approach effectively allows a return to the past. As an illustration, if a burst was detected on a given date, it is possible to return to the previous emission (50 seconds earlier, for example) and to reduce very strongly the areas of vector search and coherent integration. given the knowledge of the position of the tag to see if it is possible this time to extract the previous burst that could be missed (or confirm that it was missed). In the case of a satellite calibration fault, the signals can also be stored. If necessary, a next reliable detection on this satellite (on a strong orbitography tag message for example) makes it possible to recalibrate the antenna path (and for example to retreat the intermediate signal at that time). There is disclosed a method and system for integrating vector processing (antenna, detection, processing) into a single serialized MEOLUT chain. Also disclosed are various implementations of actions and feedbacks of the processing blocks on each other. Interference and false alarms can be managed. The present invention can be implemented from hardware and / or software elements. It may be available as a computer program product on a computer readable medium. The support can be electronic, magnetic, optical, electromagnetic or be an infrared type of diffusion medium.
    权利要求:
    Claims (21)
    [0001]
    REVENDICATIONS1. A computer-implemented method for processing the signal transmitted by a distress beacon, said signal being received by a plurality of satellites and retransmitted to at least one ground station, the method comprising the steps of: determining a set of positions hypothetical beacon; and for at least one of the hypothetical positions: for each satellite, shift the received signal and retransmitted according to said hypothetical position; sum the off-set signals; and evaluating the validity of the sum of the shifted signals as a function of the presence in said sum of a predefined characteristic.
    [0002]
    The method of claim 1, the step of shifting the signal from a satellite comprising a step of temporally shifting the signal of said satellite by a time equal to the opposite of the beacon-satellite-station delay.
    [0003]
    The method of claim 1 or 2, wherein the step of shifting the signal of a satellite comprising a step of frequency shifting the satellite signal by a frequency equal to the opposite of the Doppler effect.
    [0004]
    4. A method according to any one of claims 1 to 3, the step of shifting the signal of a satellite comprising a step of shifting the signal power by a power equal to the opposite of the attenuation of measured power for said satellite.
    [0005]
    A method according to any one of the preceding claims, wherein a characteristic of the transmitted signal comprises the presence of a pure carrier, and wherein the validity of the sum of the signals shifted from the satellites is determined by the appearance of a line. in the Fourier transform of the summed signal.
    [0006]
    6. Method according to any one of the preceding claims, wherein the transmitted signal further comprises the presence of a synchronization signal, and for which the validity of the sum of the signals shifted from the satellites is determined by correlation between the summed signal. and a replica of said synchronization signal.
    [0007]
    The method of claim 6, wherein the correlation is obtained for a particular time and frequency offset between said signal obtained by the sum of the signals shifted from the satellites and said replica of the synchronization word.
    [0008]
    A method according to any one of the preceding claims, wherein a characteristic of the transmitted signal is obtained by the combination of an initial message and a spreading code, and the validity of the sum of the signals shifted from the satellites being determined. by correlation between the summed signal and a replica of the spreading code.
    [0009]
    The method of claim 8, wherein the correlation is determined for a particular time and frequency offset between the summed signal and the replica of the spreading code.
    [0010]
    The method according to one of the preceding claims, further comprising, for each satellite, a step of determining a time offset and a frequency offset maximizing the correlation between the signal received from said satellite and the summed signal corresponding to the sum signals shifted from the satellites determined to be valid.
    [0011]
    The method according to any one of claims 1 to 10, further comprising, for each sum of desatellite offset signals determined to be valid, a step of determining the binary content of the signal transmitted by the beacon, relayed by the satellites and received by the station.
    [0012]
    The method according to the preceding claim, further comprising, for each sum of signals shifted from the satellites determined to be valid, after the step of determining the binary content of the signal transmitted by the beacon, a step of building a replica. digital baseband of the signal transmitted by the distress beacon.
    [0013]
    13. The method according to the preceding claim, further comprising for each satellite a step of determining a time offset and a frequency offset maximizing the correlation between the signal received from this satellite and the digital replica after a step of demodulating the coherent composition.
    [0014]
    14. The method as claimed in the preceding claim, further comprising a step of determining the location of the distress beacon, said location minimizing the weighted residue of the time offsets, or the weighted residual of the frequency offsets, or the combined weighted residual of the time offsets. and frequency offsets between the satellites.
    [0015]
    The method of claim 14, further comprising a step of calibrating an active antenna or an array of antennas based on the location of the distress beacon.
    [0016]
    The method of claim 11 or 14, further comprising a step of creating a warning bulletin comprising the demodulated content of the beacon signal and / or the determined location of the distress beacon.
    [0017]
    17. The method of claim 1, comprising firstly a stepconsistent to remove the contribution of the downlink between the satellite and the ground station or stations.
    [0018]
    18. The method of claim 1, the set of hypothetical positions of the distress beacon being reduced to the visible positions from the satellites visible from the ground receiving station.
    [0019]
    19. A computer program product, said computer program comprising code instructions for performing the steps of the method of any one of claims 1 to 18 when said program is run on a computer. 10
    [0020]
    20. A system for locating a distress beacon, the system comprising means for implementing the steps of the method according to any one of claims 1 to 18.
    [0021]
    21. System according to claim 20, comprising at least one active antenna or an array of antennas. 15
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    同族专利:
    公开号 | 公开日
    US20160003933A1|2016-01-07|
    CA2896204A1|2016-01-04|
    FR3023379B1|2019-03-22|
    EP2963438A1|2016-01-06|
    ES2808085T3|2021-02-25|
    EP2963438B1|2020-05-20|
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    法律状态:
    2015-06-29| PLFP| Fee payment|Year of fee payment: 2 |
    2016-01-08| PLSC| Search report ready|Effective date: 20160108 |
    2016-06-28| PLFP| Fee payment|Year of fee payment: 3 |
    2017-06-28| PLFP| Fee payment|Year of fee payment: 4 |
    2018-06-28| PLFP| Fee payment|Year of fee payment: 5 |
    2020-06-25| PLFP| Fee payment|Year of fee payment: 7 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1401510A|FR3023379B1|2014-07-04|2014-07-04|LOCATION OF A DISTRESS BEACON|
    FR1401510|2014-07-04|FR1401510A| FR3023379B1|2014-07-04|2014-07-04|LOCATION OF A DISTRESS BEACON|
    ES15174861T| ES2808085T3|2014-07-04|2015-07-01|Locating an emergency beacon|
    EP15174861.3A| EP2963438B1|2014-07-04|2015-07-01|Location of an emergency beacon|
    US14/789,767| US20160003933A1|2014-07-04|2015-07-01|Location of a distress beacon|
    CA2896204A| CA2896204A1|2014-07-04|2015-07-03|Location of a distress beacon|
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