METHOD FOR TRANSMITTING A SIGNAL BY A TRANSMITTER DEVICE TO A NON-GEOSYNCHRONOUS SATELLITE

Abstract

A method for transmitting a signal by a transmitter device to a satellite moving in orbit around the Earth, the transmitter device and the satellite including wireless telecommunication means. The method includes the following steps: receiving, by the transmitter device, a signal transmitted by the satellite, referred to as a presence signal, analyzing a frequency shift caused by Doppler effect on a main frequency of the presence signal received by the device, evaluating a proximity criterion between the transmitter device and the satellite on the basis of the analysis of the frequency shift, and transmitting a signal by the transmitter device if the proximity criterion is met.

Claims

1. A method for transmitting a signal with an emitting device to a satellite moving in orbit about the Earth, said emitting device and the satellite comprising wireless telecommunication means, wherein said method comprises steps of: receiving with said emitting device a signal emitted by the satellite, called the presence signal; analyzing a frequency shift induced by Doppler effect in the presence signal received by said emitting device; evaluating a proximity criterion quantifying the proximity between said emitting device and said satellite, on the basis of the analysis of the frequency shift; and emitting a signal with said emitting device if the proximity criterion is met.

2. The method as claimed in claim 1, wherein the step of analyzing the frequency shift comprises a substep of measuring a main frequency of the presence signal and a substep of estimating the frequency shift induced by Doppler effect depending on the measured main frequency and on a theoretical main frequency of said presence signal.

3. The method as claimed in claim 2, wherein the step of evaluating the proximity criterion comprises a substep of comparing the estimated frequency shift with a threshold value.

4. The method as claimed in claim 1, wherein the step of analyzing the frequency shift comprises a substep of estimating a variation as a function of time in the frequency shift induced by Doppler effect on the basis of an evaluation of a variation as a function of time in the main frequency of the presence signal between at least two different respective times.

5. The method as claimed in claim 4, wherein the step of evaluating the proximity criterion comprises a substep of comparing the estimated variation as a function of time in the frequency shift with a threshold value.

6. The method as claimed in claim 1, wherein the presence signal emitted by the satellite comprises at least one modulated sub-carrier with a preset frequency difference with respect to a carrier frequency.

7. The method as claimed in claim 6, wherein the step of receiving the presence signal comprises a substep of detecting the presence signal depending on said frequency difference.

8. The method as claimed in claim 7, wherein the detecting substep is carried out by way of a super-regenerative receiver.

9. The method as claimed in claim 1, wherein the analysis of the frequency shift induced by Doppler effect in the presence signal comprises a step of measuring a main frequency of the presence signal or a variation as a function of time in said main frequency of said presence signal, carried out by way of a phase-locked loop.

10. The method as claimed in claim 1, wherein it furthermore comprises a step in which the proximity criterion is dynamically adjusted by the emitting device, depending on adjustment information received in a signal emitted by the satellite.

11. The method as claimed in claim 10, wherein the adjustment information is determined, by the satellite, depending on the number of signals received by said satellite in a preset period.

12. An emitting device of a wireless telecommunication system configured to implement the transmitting method as claimed in claim 1.

13. A wireless telecommunication system comprising at least one emitting device as claimed in claim 12, and at least one satellite moving in orbit about the Earth.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present disclosure will be better understood on reading the following description, which is given by way of completely nonlimiting example, with reference to the figures, which show:

[0041] FIG. 1: a schematic representation of an example of an embodiment of a telecommunication system,

[0042] FIG. 2: curves illustrating variations in the frequency shift as a function of the position of a satellite relative to an emitting device of the telecommunication system of FIG. 1,

[0043] FIG. 3: a flowchart illustrating an example of an implementation of a method for transmitting a signal with an emitting device to a satellite,

[0044] FIG. 4: two curves illustrating processing carried out to detect a presence signal emitted by the satellite,

[0045] FIG. 5: a curve illustrating an example of a frequency shift in a signal as a function of time.

[0046] In these figures, identical references have been used to reference elements that are identical or analogous. For the sake of clarity, the elements have not been drawn to scale unless otherwise indicated.

DETAILED DESCRIPTION

[0047] FIG. 1 schematically shows a wireless telecommunication system 100 comprising a plurality of emitting devices 110 and a satellite 120 of a constellation of nanosatellites previously placed in orbit around the Earth.

[0048] The emitting devices 110 and the satellite 120 exchange data in the form of electromagnetic signals. By electromagnetic signal, what is meant is an electromagnetic wave that propagates via non-wired means, and the frequencies of which are comprised in the conventional spectrum of electromagnetic waves (i.e. a few hertz to several hundred gigahertz).

[0049] The emitting devices 110 are, in the present nonlimiting example of the present disclosure, connected objects comprising telecommunication means 111 able to transmit signals to the satellite 120. It should be noted that the objects 110 may also, in particular embodiments, exchange signals between one another.

[0050] For example, the connected objects 110 furthermore comprise an electronic board 112 equipped with a microprocessor able to process data, or even a computer memory able to store data before they are transmitted via signals.

[0051] The signals transmitted by the emitting devices 110, and/or the signals transmitted by the satellite 120, are for example UNB (ultra-narrow band) signals.

[0052] The UNB signals exchanged within the telecommunication system 100 comprise a carrier the frequency of which is about 100 MHz, or even about 1 GHz. The bandwidth of the UNB signals is narrower than 2 kHz, or even narrower than 1 kHz.

[0053] The telecommunication means 111 connected to the electronic board 112 of said connected object 110 comprise in the present nonlimiting example of the present disclosure an antenna able to transmit and receive UNB signals, a phase-locked loop and a super-regenerative receiver.

[0054] The satellite 120 is, in the present example, a nanosatellite of the CubeSat type formed by a cubic structure of ten-centimeter side length. Two photovoltaic panels 121 deployed on either side of the cubic structure supply the satellite 120 with power. The mass of the satellite 120 is substantially equal to five kilos. An antenna 122 directed toward the Earth's surface allows UNB signals to be transmitted to or received from the connected objects 110. It should be noted that the satellite 120 is placed in an orbit at about five-hundred kilometers from the Earth. The satellite 120 thus moves around the Earth at a speed of about seven kilometers per second, and makes a complete orbit about the planet in a time of about ninety minutes. Generally, the satellite 120 is in a non-geosynchronous orbit, for example in an LEO (ow Earth orbit) or an MEO (medium Earth orbit).

[0055] The satellite 120 furthermore comprises a beacon 125 that continuously emits a UNB signal, called the presence signal below. The presence signal emitted by the beacon 125 for example comprises a carrier the frequency of which, at the moment of emission, is for example substantially constant over time.

[0056] In one variant of this particular embodiment of the present disclosure, the beacon 125 discontinuously emits presence signals, preferably at regular intervals. The emitted presence signals are for example of limited duration, for example comprised between a few hundred milliseconds and a few seconds.

[0057] It should be noted that, to save energy, the connected object 110 is generally in standby mode most of the time and that it exits from this standby mode at regular intervals in order to listen for and/or transmit signals.

[0058] FIG. 2 shows an example of curves 150 of the variation in the frequency shift in signals received by a connected object 110 from the satellite 120 as a function of the position of the satellite with respect to the connected object. FIG. 2 comprises five curves each of which corresponds to a different maximum angle of elevation of the satellite 120 seen by the connected object 110. By maximum angle of elevation, also referred to as cross-track angle, what is meant is the angle between the ground and the direction of the satellite 120, measured at the object when the satellite 120 is at its closest to the connected object 110. The x-axis of the curves 150 corresponds to the difference between the latitude of the satellite 110 and the latitude of the connected object 110. When the maximum angle of elevation is small, as in the case of the curve 150.sub.1, the satellite 120 is seen by the connected object 110 as being close to the horizon, whereas when the maximum angle of elevation is about ninety degrees, as in the case of the curve 150.sub.2, the connected object 110 is located substantially plumb with the trajectory of the satellite 120.

[0059] FIG. 3 shows in the form of a flowchart a method 200 for transmitting a signal between one of the connected objects 110 and the satellite 120 moving in orbit.

[0060] The method 200 comprises a step 210 in which the connected object 110 receives the presence signal emitted by the satellite 120.

[0061] In preferred implementations, the presence signal comprises a carrier of frequency f.sub.c_sat and at least one modulated sub-carrier having a preset frequency difference f.sub.s with respect to the frequency f.sub.c_sat in order to make it possible to differentiate between signals coming from the beacons and signals coming from the connected objects 110, which signals do not have this particular form or, in the contrary case, have a preset frequency different from the frequency difference f.sub.s of the presence signal.

[0062] In other words, the presence signal of the satellite 120 contains information allowing the origin of the presence signal to be identified, i.e. in the present case the beacon 125 of the satellite 120, via the presence of the modulated sub-carrier having a preset frequency difference f.sub.s with respect to the frequency f.sub.c_sat. More generally, the identification information of the presence signal may be coded into the presence signal emitted by the beacon 125 using any technique known to those skilled in the art.

[0063] It should be noted that such a presence signal comprising a carrier and at least one sub-carrier is of self-timed type. The recognition of the presence signals by virtue of the presence of a sub-carrier having a preset frequency difference with respect to the carrier is advantageously used in the case of a hybrid telecommunication network comprising a plurality of connected objects and a plurality of satellites, in which type of network a connected object may receive signals originating both from a satellite and from another connected object.

[0064] Step 210 for example comprises a substep 211 of detecting the signal of the beacon 125 among a plurality of received signals. To this end, the super-regenerative receiver included in the connected object 110 allows the presence signal emitted by the beacon 125 to be detected by virtue of the presence of the sub-carrier in the presence signal, the frequency difference of which with respect to the carrier frequency of the presence signal is advantageously preset. It should be noted that the super-regenerative receiver advantageously has a very low power consumption of about one-hundred microwatts when actively receiving. The power consumption of the super-regenerative receiver may be decreased by employing cycles of recurrent non-contiguous detections. Increasing the latency between two consecutive detections in particular allows the power consumption of this receiver to be decreased.

[0065] Moreover, it should be noted that the super-regenerative receiver is advantageously insensitive to frequency variations if the carrier and the sub-carriers vary in a similar way, as is the case when the presence signal is affected by the Doppler effect.

[0066] An example of a result obtained via this detection mechanism is illustrated in FIG. 4, which comprises a curve 310 before detection and a curve 320 after detection. The curve 310 comprises a carrier 311 of frequency f.sub.c_sat and a modulated sub-carrier 312 of frequency f.sub.2. The frequency difference between the carrier and the subcarrier is equal to f.sub.s. The detection allows a signal 321 of frequency f.sub.s, a signal 322 of frequency 2f.sub.c_sat, a signal 323 of frequency f.sub.c_sat+f.sub.2 and a signal 324 of frequency 2f.sub.2 to be extracted.

[0067] The frequency shift induced by Doppler effect in the presence signal received by the connected object 110 is analyzed in a step 220 of the method 200.

[0068] In this analyzing step 220, the variation as a function of time in a main frequency of the presence signal is for example evaluated in a substep 221. The main frequency in question for example corresponds to the frequency of the carrier of the presence signal.

[0069] In order to evaluate the variation as a function of time in the main frequency, the presence signal is for example duplicated into two replicas one of which is delayed by a set time, for example of about a few seconds. Simultaneous analysis of these two replicas, for example of the correlation of said two replicas, allows the variation as a function of time in the main frequency of the presence signal to be evaluated.

[0070] In one variant of this particular implementation of the present disclosure, the variation as a function of time in the main frequency may be calculated on the basis of a measurement of the main frequency at at least two different respective times.

[0071] It should be noted that the variation as a function of time in the main frequency, which corresponds in the present example to the carrier frequency of the presence signal, is for example analyzed using a synchronous detection mechanism similar to that of a phase-locked loop or a lock-in amplifier. The phase-locked loop in particular allows measurements of frequency or of the phase shift between two signals to be carried out. During this analysis, the super-regenerative receiver may advantageously use its absolute local reference oscillator. The variation as a function of time in the frequency shift induced by Doppler effect is then estimated in a substep 222. Given that the presence signal is emitted with a main frequency that remains constant over time, the variation as a function of time in the frequency shift induced by Doppler effect is equal to the variation as a function of time in the main frequency.

[0072] In particular implementations of the analyzing step 220, which may be used as alternatives to or to complement the implementations described above, the frequency shift induced by Doppler effect may be estimated on the basis of a measurement of the main frequency of the presence signal. For example, the measured main frequency of the presence signal is compared to a theoretical main frequency of the present signal, which corresponds to the frequency of the carrier at the moment of emission of the presence signal by the beacon 125. The emission frequency of the carrier is in certain cases known beforehand, in which case the beacon 125 emits at a preset frequency for example corresponding to a previously established standard. When the emission frequency of the carrier is not known, the value of said emission frequency may for example be coded into the presence signal, and for example modulates the modulated subcarrier of said present signal.

[0073] The method 200 then comprises a third step 230 of evaluating a proximity criterion depending on the result of the analysis of the frequency shift carried out in the analyzing step 220.

[0074] Generally, the evaluation of the proximity criterion aims to determine the period propitious to the trigger of the emission of the signal by the connected object 110, and the choice of one particular proximity criterion is merely one variant of implementation of the present disclosure.

[0075] The evaluated proximity criterion depends on the type of analysis of the frequency shift induced by Doppler effect in the present signal. Thus, if the analysis carried out results in an estimate of the variation as a function of time in the frequency shift, then the evaluation of the proximity criterion uses the estimated variation as a function of time in said frequency shift; if the analysis carried out results in an estimate of the frequency shift, then the evaluation of the proximity criterion uses the estimated frequency shift, etc.

[0076] In the rest of the description, the case considered, nonlimitingly, is the case where the analyzing step 220 comprises both estimating the frequency shift and estimating the variation as a function of time in said frequency shift, and where the evaluation of the proximity criterion uses both the estimated frequency shift and the estimated variation as a function of time in said frequency shift. The proximity criterion is for example considered to be met if at least one among the following conditions is met: a first condition relating to the value of the frequency shift induced by Doppler effect in the main frequency of the present signal and a second condition relating to the variation as a function of time in this frequency shift. Alternatively, the proximity criterion may be considered to be met if both the first condition and the second condition are met.

[0077] The frequency shift estimated in step 220 is compared, in a substep 231, with a preset threshold value, called the proximity threshold.

[0078] An example of a curve 510 of the variation in the estimated frequency shift Af is shown in FIG. 5. Thus, if the estimated frequency shift is lower in absolute value than the proximity threshold ( in FIG. 5), the satellite 120 is considered to be within range of the connected object 110 and the first condition is met.

[0079] It should be noted that if the maximum angle of elevation of the satellite 120 is small, i.e. when the satellite 120 is seen by the connected object 110 as being on the horizon, the curve of the frequency shift may most of the time be below the threshold value. In this case, it is possible that the signal received from the connected object 110 by the satellite 120 will be of low power.

[0080] Therefore, in order to improve the transmission of signals from the connected objects 110 to the satellite 120, the second proximity-criterion condition may advantageously be used alone or in combination with the first condition evaluated in substep 231. The second condition is for example considered to be met when the estimated variation as a function of time in the measured carrier frequency of the present signal is greater than a second preset threshold value. In other words, the second condition is met when the estimated variation as a function of time in the frequency shift induced by Doppler effect is greater than the second threshold value. The second proximity-criterion condition thus relates to the slope of the curve of the carrier frequency of the present signal, or to the curve of the frequency shift, which is similar.

[0081] To this end, the variation as a function of time in the frequency shift is compared with the second threshold value in a substep 232. When the slope of the curve is in absolute value greater than a threshold value, the second condition is considered to be met. Such a proximity-criterion condition is advantageous in that it furthermore allows emission of a signal by the connected object to be limited to a range, about 90, of particular values of the maximum angle of elevation.

[0082] Such as indicated above, the proximity criterion is for example considered to be met if the first condition and/or second condition are/is met. When the proximity criterion is met, the connected object 110 may transmit a signal to the satellite 120 in step 240 in which the connected object 110 emits the signal. In the contrary case, i.e. when the proximity criterion is not met, the connected object 110 does not transmit any signal to the satellite 120.

[0083] More generally, and such as indicated above, the choice of one particular proximity criterion, and therefore of one or more conditions that must be met in order for the proximity criterion to be considered to have been met, is merely one variant of implementation of the present disclosure. For example, it is possible to require one or more of the following conditions to be met for the proximity criterion to be considered to have been met: [0084] the estimated frequency shift or the absolute value of the estimated frequency shift must be lower than a threshold; [0085] the estimated frequency shift must be lower in absolute value than one threshold and higher in absolute value than a second threshold; [0086] the estimated frequency shift must be lower than one threshold and higher than a second threshold; [0087] the estimated frequency shift or the absolute value of the estimated frequency shift must be higher than a threshold; [0088] the estimated variation as a function of time in the frequency shift or the absolute value of the estimated variation as a function of time in the frequency shift must be higher than a threshold; [0089] the estimated variation as a function of time in the frequency shift must be higher in absolute value than one threshold and lower in absolute value than a second threshold; [0090] the estimated variation as a function of time in the frequency shift must be higher than one threshold and lower than a second threshold; [0091] the estimated variation as a function of time in the frequency shift or the absolute value of the estimated variation as a function of time in the frequency shift must be lower than a threshold, etc.

[0092] Advantageously, the method 200 may also comprise a step 250 in which the connected object 110 dynamically adjusts the proximity criterion depending on adjustment information received in a signal emitted by the satellite 120. The adjustment information allows the value of the proximity threshold, of the first and/or second condition(s) allowing the proximity criterion to be evaluated by the connected object 110 to be adjusted.

[0093] It should be noted that the proximity criterion may be adjusted dynamically depending on the number of signals received by the satellite 120 in a preset period, or depending on the number of connected objects 110 having the satellite 120 in range. Moreover, the range of the satellite 120, corresponding to the maximum distance at which signals emitted by the satellite 120 may be received by a connected object 110, is generally different from the range of the connected object, corresponding to the maximum distance at which signals emitted by the connected object 110 may be received by the satellite 120. The range of the satellite 120, also called the down-link range, may be different from the range of the object, also called the up-link range.

[0094] In the present example, the power of the presence signals emitted by the beacon 125 is higher than the power of the signals emitted by the connected objects 110. Therefore, the range of the satellite is in principle greater than the range of the connected object 110.

[0095] In other words, adjustment of the proximity criterion allows the size of the coverage of the satellite 120, also called the swath of the satellite 120, to be adjusted by determining the number of connected objects 110 in range of the satellite 120 and able to transmit a signal to the satellite 120.