Method for wirelessly synchronizing a communication system, including a master device and at least one slave device

Abstract

The present invention relates to a method (100) for wirelessly synchronizing a communication system, comprising transmitting bases configured to transmit radiofrequency signals, the transmitting bases comprising a master device and at least one slave device, the method (100) comprising the following steps: a step (110) of receiving and processing signals, in which the slave device receives radiofrequency signals from the master, then demodulates and identifies the master's internal reference frequency; a frequency synchronization step (120), in which the slave device modifies its internal reference frequency in order to align itself with the master's internal reference frequency; a calculation step (130), in which the slave device calculates an actual time of flight from the master, for comparison with a theoretical time of flight; and a temporal synchronization step (140), in which the slave device calculates and applies a coefficient by which its internal reference frequency should be slowed down or sped up along with a duration of application of this coefficient in order to obtain a corrected actual time of flight equal to the theoretical time of flight.

Description

[0001] A wireless synchronization method for a communication system, including a master device and at least one slave device.

[0002] [1] Technical field

[0003] [2] The present invention relates to a method for wirelessly synchronizing a communication system, comprising transmitting bases (gateways) configured to transmit radio frequency signals, the transmitting bases including a master device and at least one slave device. The invention also relates to a communication system configured to implement this method. The invention further relates to a system for positioning a receiving mobile device.

[0004] [3] The field of the invention is that of the wireless synchronization of transmitting bases within a communication system.

[0005] [4] Prior art

[0006] [5] The location of receiving mobile devices in outdoor environments has seen a major technological leap with the deployment of the GPS (Global Positioning System) in the 1980s. However, GPS technology does not work in indoor environments, typically inside buildings, and relatively poorly in urban environments.

[0007] [6] There is therefore a need for mobile receiver positioning systems that have both a long range (typically over 10 km) and that work well both outdoors and indoors.

[0008] [7] As is known, a location system in an outdoor or indoor environment most often includes, in addition to the mobile device to be positioned, a set of at least three beacons. These beacons are distinguished by the fact that their position is known. Furthermore, they are usually fixed. In such a system configuration, the beacons control the transmissions: a beacon transmits to a mobile device, and the mobile device responds by retransmitting to the beacon. Measuring the transmission time, by taking the difference between the transmission time and the reception time, makes it possible to determine the distance between the beacon and the mobile device. However, such a system requires the receiving mobile device to retransmit signals to the beacons so that a remote server can deduce the mobile device's position, and therefore does not allow the mobile device to perform its own positioning.

[0009] [8] Radiolocation systems also commonly use modulated radio frequency signals, emitted by fixed beacons or antennas, to transmit, for example, positioning data or random data to a receiver. Such random data, for example, data known in advance to the receiver, helps the receiver synchronize with the random data by performing signal correlations. However, such systems require a large frequency transmission bandwidth, typically several tens or hundreds of MHz for positioning systems with metric or sub-metric accuracy. Such operation is particularly expensive. Furthermore, such radiolocation systems do not allow for dual operation in either outdoor or indoor environments.

[0010] [9] WO2022219286A1 describes a system and method for positioning at least one receiving mobile, by the mobile itself, in both outdoor and indoor environments. By overcoming the drawbacks of the prior art, this technology constitutes a particularly advantageous solution, capable of further improvement.

[0011]

[0010] US2014241175, US2006034407 and US2024125883 describe different examples of synchronization methods, illustrating the general technological background of the invention.

[0012]

[0011] In the prior art, systems are known that achieve time synchronization between different beacons located several kilometers apart. However, a time synchronization of less than 10 ns implies that the clock references of these beacons have negligible drift over several hundred years (atomic clock) or drift compensated by a feedback loop. In the first case, it is necessary to use an atomic clock, which is cost-intensive and increases the system size, or to resort to the Global Navigation Satellite System (GNSS), which entails a dependence on the availability and reception of GNSS signals. In the second case, existing methods are limited by the inability of traditional systems to track a transmitted frequency without discriminating between the direct path and multiple paths.The presence of random bounces causes random micro-variations in frequency which prevent the receiver from receiving the exact frequency of the transmitter.

[0012] Description of the invention.

[0013]

[0013] The object of the present invention is to propose a synchronization solution for a communication system, comprising several transmitting bases.

[0014]

[0014] To this end, the invention relates to a method for wirelessly synchronizing a communication system, comprising transmitting bases configured to emit radio frequency signals, the position of each transmitting base being memorized by the other transmitting bases, the transmitting bases comprising a master device and at least one slave device, the master device emitting radio frequency signals with an internal reference frequency configured to remain fixed, the slave device emitting radio frequency signals with an adjustable internal reference frequency, the method comprising the following steps:

[0015] - a signal reception and processing stage, in which the slave device receives radio frequency signals from the master device, then demodulates and identifies the internal reference frequency of the master device;

[0016] - a frequency synchronization step, in which the slave device modifies its internal reference frequency to match the internal reference frequency of the master device;

[0017] - a calculation step, in which the slave device calculates an actual flight time between the master device and the slave device, for comparison with a theoretical flight time between the master device and the slave device;

[0018] - a time synchronization step, in which the slave device calculates and applies a deceleration or acceleration coefficient to its internal reference frequency, as well as a duration of application of this coefficient, to obtain a corrected actual flight time equal to the theoretical flight time.

[0019]

[0015] Thus, the invention makes it possible to synchronize a system comprising several remote beacons, without cables, with an accuracy of less than 10 ns. The slave device(s) synchronize with the master device. Time synchronization is performed by each of the slave devices, which receive the signals from the master device, demodulate them, and calculate a time of flight. Knowing their own position and the position of the master device, the slave devices can deduce the time correction to be applied.

[0020]

[0016] The invention applies to any system requiring synchronization of less than 10 ns between devices not connected by cable: geolocation, sensor networks and smart grids, ultra-precise wireless communication, high-frequency trading, etc.

[0021]

[0017] When the system includes several slave devices, each slave device must be synchronized with the master device:

[0022] emits radio frequency signals, with an adjustable internal reference frequency;

[0023] executes the steps of the synchronization method.

[0024]

[0018] For the slave device or for each slave device to be synchronized with the master device, the method comprises the following steps:

[0025] - a signal reception and processing stage, in which the slave device receives radio frequency signals from the master device, then demodulates and identifies the internal reference frequency of the master device;

[0026] - a frequency synchronization step, in which the slave device modifies its internal reference frequency to match the internal reference frequency of the master device;

[0027] - a calculation step, in which the slave device calculates an actual flight time between the master device and the slave device, for comparison with a theoretical flight time between the master device and the slave device;

[0028] - a time synchronization step, in which the slave device calculates and applies a deceleration or acceleration coefficient to its internal reference frequency, as well as a duration of application of this coefficient, to obtain a corrected actual flight time equal to the theoretical flight time.

[0029]

[0019] In the rest of the description, when reference is made to a slave device: either the communication system includes a single slave device to be synchronized with the master device; or the communication system includes several slave devices to be synchronized with the master device, and in this case the description refers to one of the slave devices to be synchronized with the master device.

[0030]

[0020] According to other advantageous features of the method according to the invention, taken individually or in combination:

[0021] In the calculation step, the slave device applies a direct path discrimination algorithm between the master device and the slave device.

[0031]

[0022] For the application of the direct path discrimination algorithm, the calculation step performed by the slave device includes:

[0032] - a sub-step of measuring, for each given signal frequency, the phase and amplitude of the signal made up of the different signals received from the master device and presenting said frequency;

[0033] - a substep of applying a high-resolution spectral analysis algorithm to a signal consisting of the different phases and measured amplitudes of the radio frequency signals received from the master device, in order to discriminate between the direct path and the various reflections undergone by the signal; and

[0034] - a sub-step of identifying the direct route among the multiple routes discriminated during the sub-step of applying the algorithm.

[0035]

[0023] Each transmitting base is configured to transmit a sum of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated continuous wave, preferably sinusoidal. In the calculation step, the slave device calculates the actual time of flight between the master device and the slave device using the pure carrier signals.

[0036]

[0024] The slave device performs the signal reception and processing step and the frequency synchronization step only once, at the start of the algorithm

[0037] self-synchronization.

[0038]

[0025] The slave device repeats the calculation step and the time synchronization step to continuously maintain the corrected actual flight time equal to the theoretical flight time.

[0039]

[0026] When the communication system includes several slave devices, each slave device performs the signal reception and processing step and the frequency synchronization step only once, at the start of the algorithm

[0040] self-synchronization.

[0041]

[0027] When the communication system includes several slave devices, each slave device repeats the calculation step and the time synchronization step to continuously maintain the corrected actual flight time equal to the theoretical flight time.

[0042]

[0028] In the frequency synchronization step, the modification of the internal reference frequency of the slave device is carried out by a clock generator equipping the slave device.

[0029] The invention also relates to a communication system, configured to implement the method presented above.

[0043]

[0030] According to one embodiment, the slave device includes an antenna, an analog-to-digital converter, a computing unit, a clock generator, and a digital-to-analog converter.

[0044]

[0031] According to one embodiment, the slave device includes a data bus between the processing unit and the digital-to-analog converter. When the sampling frequency of the digital-to-analog converter is changed, the data rate passing through the data bus is changed accordingly.

[0045]

[0032] The invention also relates to a positioning system for at least one receiving mobile relative to transmitting bases. The positioning system includes a communication system as described above. The receiving mobile is configured to receive and process radio frequency signals from the transmitting bases and to deduce its position by calculating the time-of-flight difference(s) between the receiving mobile and the transmitting bases. The receiving mobile includes means for storing position data of the fixed transmitting bases. Each transmitting base is configured to transmit a sum of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated continuous wave, preferably sinusoidal.

[0046]

[0033] The receiving mobile unit further comprises:

[0047] means for measuring, for each given signal frequency and for each respective transmitting base, the phase and amplitude of the signal consisting of the different radio frequency signals originating from said transmitting base and exhibiting said frequency; and

[0048] computing resources connected to measurement and storage resources, and configured for:

[0049] to apply, for each transmitting base, a high-resolution spectral analysis algorithm on a signal consisting of the different phases and measured amplitudes of the radio frequency signals from said transmitting base;

[0050] o determine, for each transmitting base, from the spectral analysis carried out previously, a time of flight between the receiving mobile and said transmitting base; o calculate at least one difference in time of flight between the receiving mobile and two transmitting bases, said difference being calculated as the difference between the times of flight determined for said transmitting bases;

[0051] o determine the position of the receiving mobile, from the calculated time-of-flight difference(s) and the position data of the transmitting bases.

[0052]

[0034] Description of the figures

[0053]

[0035] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and with reference to the accompanying drawings in which:

[0054]

[0036] Figure 1 is a schematic representation of a positioning system according to the invention, comprising a receiving mobile relative to transmitting bases, the positioning system integrating a communication system also according to the invention, consisting of transmitting bases including a master device and a slave device.

[0055]

[0037] Figure 2 is a graph representing two Fourier transforms as a function of time of flight, each Fourier transform corresponding to a distinct transmitting basis and having been applied by the receiving mobile to a signal consisting of the different measured phases of the radio frequency signals from that basis.

[0056]

[0038] Figure 3 is a schematic representation of the wireless synchronization method according to the invention, including its various stages.

[0057]

[0039] Figure 4 is a schematic representation of a communication system consisting of transmitting bases, including a master device and four slave devices.

[0058]

[0040] Figure 5 is a schematic representation of a slave device and its constituent elements.

[0059]

[0041] Detailed description of the invention

[0060]

[0042] Figure 1 illustrates a positioning system (1) according to the invention, configured for positioning at least one receiving mobile (2) relative to transmitting bases (20). The positioning system (1) incorporates a communication system (10) also according to the invention, consisting of the transmitting bases (20) including a master device (22) and a slave device (24), the operation of which will be detailed later.

[0061]

[0043] The receiving mobile (2) is configured to receive and process radio frequency signals from the transmitting bases (20) and to deduce its position by calculating the time-of-flight difference(s) between the receiving mobile (2) and the transmitting bases (20). The receiving mobile (2) includes means for storing position data from the fixed transmitting bases (20).

[0062]

[0044] Each transmitting base (20) is configured to emit a sum (SIA, SI B) of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated continuous wave, preferably sinusoidal.

[0063]

[0045] The receiving mobile (2) further comprises:

[0064] means for measuring, for each given signal frequency and for each respective transmitting base (20), the phase and amplitude of the signal consisting of the different radio frequency signals originating from said transmitting base (20) and exhibiting said frequency; and

[0065] computing resources connected to measurement and storage resources, and configured for:

[0066] to apply, for each transmitting base (20), a high-resolution spectral analysis algorithm on a signal consisting of the different phases and measured amplitudes of the radio frequency signals from said transmitting base (20);

[0067] to determine, for each transmitting base (20), from the spectral analysis carried out previously, a time of flight between the receiving mobile (2) and said transmitting base (20);

[0068] to calculate at least one difference in time of flight between the receiving mobile (2) and two transmitting bases (20), said difference being calculated as the difference between the times of flight determined for said transmitting bases (20);

[0069] to determine the position of the receiving mobile (2), from the calculated time-of-flight difference(s) and the position data of the transmitting bases (20).

[0070]

[0046] Advantageously, the positioning system (1) can be configured as follows: For each transmitting base (20), the frequency gap between the minimum frequency and the maximum frequency of the pure carrier signals emitted by said base (20) is greater than 50 MHz.

[0071] Each pure carrier signal emitted by a transmitting base station (20) has a frequency in the very high frequency band, that is, a frequency in the range from 30 MHz to 300 MHz. The transmitting bases (20) are configured to emit the same number of unmodulated pure carrier signals.

[0072] The transmitting bases (20) are configured so as to transmit their sums (SIA, SI B) of unmodulated pure carrier signals in a frequency-shifted manner, with a predetermined frequency shift between two successive transmitting bases (20).

[0073] The frequency offset is within the range of 100 Hz to 1 kHz.

[0074]

[0047] With reference to Figure 1, the following description assumes that the environment in which the receiving mobile (2) operates includes a first obstacle (01) and a second obstacle (02). The two obstacles (01, 02) are buildings, but could alternatively be any other type of structure without affecting the reasoning that follows. For each transmitting base station (20), the radio frequency signals received by the receiving mobile (2) and originating from that base station (20) are divided into two types: the first type consists of the SdA and SdB signals arriving along line of sight, and the second type consists of the SrA and SrB signals arriving at the receiving mobile (2) following a reflection off an obstacle (01, 02). The SdA and SrA signals, respectively sdB and srB, each correspond to the sum SIA and SI B, respectively, of unmodulated pure carrier signals, but they follow different paths.DA, and DB respectively, denote the line-of-sight distance between the receiving mobile (2) and the first transmitting base (22), and the second transmitting base (24) respectively, traveled by the SdA and SdB signals. DrA, and DrB respectively, denote the distance traveled by the SrA and SrB signals after bouncing off an obstacle (01) and an obstacle (02) respectively.

[0075]

[0048] For the sake of simplification, only the radio frequency signals originating from the first transmitting base (22) and bouncing off the obstacle (01) closest to it are considered hereafter. Indeed, the impact of the signals originating from this base (22) and bouncing off the other obstacle (02) is considered negligible. Similarly, only the radio frequency signals originating from the second transmitting base (24) and bouncing off the obstacle (02) closest to it are considered hereafter. Indeed, the impact of the signals originating from this base (24) and bouncing off the other obstacle (01) is considered negligible. Furthermore, for the sake of simplicity, it is assumed that the radio frequency signals bounce only once off one of the obstacles (01, 02).

[0076]

[0049] The positioning of the receiving mobile (2) by the positioning system (1) will now be described in detail, with reference in particular to Figure 1.

[0077]

[0050] The method includes an initial step of transmitting position data from the transmitting bases (20) to the storage means of the receiving mobile device (2). The transmission may, for example, consist of each transmitting base (20) transmitting its position coordinates to the receiving mobile device (2), or of pre-programming the position coordinates of the bases within the receiving mobile device (2) during its manufacture or configuration. Following this initial step, the storage means of the receiving mobile device (2) store the position data of the transmitting bases (20).

[0078]

[0051] The method includes a subsequent step in which each transmitting base (20) emits the sum (SIA, S1B) of unmodulated pure carrier signals of distinct frequencies œk. The phase shift between the signals (SIA, S1B) emitted by the different transmitting bases (22, 24) is constant. The sums (SIA, S1B) of pure carrier signals emitted by the bases (22, 24) are thus frequency-shifted by a frequency shift Aœ. The different frequencies œk used by the bases (22, 24), as well as the frequency shift Aœ, are known to the receiving mobile (2), being pre-implemented in or transmitted to it.

[0079]

[0052] In a subsequent step, the receiving mobile (2) receives the radio frequency signals SdA, SdB, SrA, SrB from the transmitting bases (22, 24). These signals SdA, SrA, and SdB, respectively, each correspond to the sum S1A and S1B, respectively, of unmodulated pure carrier signals, but they follow different paths. Because the sums S1A and S1B of signals are frequency-shifted by a predetermined frequency shift, known to the receiving mobile (2), the receiving mobile (2) can distinguish the SdA and SrA signals from the first transmitting base (22) from the SdB and SrB signals from the second transmitting base (24).

[0053] In a subsequent step, the receiving mobile (2) determines, via its measuring means, for each given signal frequency œk and for each transmitting base (22, 24), the phase of the signal consisting of the different signals SdA, SrA; respectively SdB, SrB, originating from that base (22, 24) and exhibiting the frequency œk. Indeed, for example, for the first base (22) and for a given frequency œk, the two signals SdA(œk) and SrA(œk) are received by the receiving mobile (2) as a mixture. The phase measured by the receiving mobile (2) for the frequency œk then corresponds to the phase of the signal consisting of the sum of the direct signal SdA and the reflected signal SrA. The same reasoning applies to the signals SdB, SrB originating from the second base (24).

[0080]

[0054] In a subsequent step, the receiving mobile (2) applies, via its computing means and for each of the transmitting bases (22, 24), a Fourier transform to a signal consisting of the different phases and measured amplitudes of the radio frequency signals received from that base. Indeed, the principle used by the invention is that for a given time delay, the phase shift undergone by a signal with a pure, unmodulated carrier depends on the frequency of that signal. The Fourier transform is typically a discrete Fourier transform, and in particular a discrete Fourier transform with complex coefficients.

[0081]

[0055] For each transmitting base (22, 24), the Fourier transform FT applied to the measured phases and amplitudes of the signals from this base is then expressed mathematically via the following function:

[0082] [Math 1] T

[0083]

[0084] F(d n ) = XLi Kœfc ). e~^

[0085]

[0056] In this way, by graphically representing, for each emitting base (22, 24), the result of the applied Fourier transform, the computing means can in a subsequent step isolate different peaks corresponding to each SdA, SrA or SdB, SrB signal, and deduce the time of flight of each of these signals.

[0086]

[0057] This is illustrated in the graph in Figure 2, on which two graphical functions 3OA, 30B are represented. These two functions 3OA, 30B correspond respectively to the calculation of the Fourier transform for the first transmitting base (22), and for the second transmitting base (24), represented as a function of the time of flight (which is therefore read on the x-axis). During this step, the computing means of the receiving mobile (2) determine the time of flight between the receiving mobile (2) and each of the bases (22, 24). To do this, the computing means isolate the peak P1A, PIB having the shortest time of flight. This peak P1A, PIB corresponds to the SdA, SdB signal in line of sight. In the embodiment shown, for the first base (22), the peak P1A corresponding to the SdA signal has a time of flight TV1A approximately equal to 230 ns. The time of flight TV1 A between the receiving mobile (2) and the first base (22) is therefore approximately 230 ns.For the second base (24), the PIB peak corresponding to the SdB signal has a TV1B time of flight approximately equal to 310 ns. The TV1B time of flight between the receiving mobile (2) and the second base (24) is therefore approximately 310 ns. For each of the bases (22, 24), the second peak P2A, P2B, which has a lower amplitude than the first peak P2A, P2B and a longer time of flight, corresponds to the SrA, SrB signal having been reflected off an obstacle (01, 02). This P2A, P2B peak can therefore be advantageously isolated from the first peak P2A, PIB and not taken into account in the subsequent calculations.

[0087]

[0058] In a subsequent step, the receiving mobile (2) calculates at least one time-of-flight difference TVdiff between the mobile (2) and two transmitting bases (22, 24). The time-of-flight difference TVdiff is calculated as the difference between the time-of-flight values ​​TV1A and TV1B determined for the transmitting bases (22, 24). In the embodiment shown in Figure 2, the time-of-flight difference TVdiff is approximately equal to 80 ns (310 ns - 230 ns).

[0088]

[0059] In the case where the positioning system (1) has a number of transmitting bases (20) greater than or equal to three, the receiving mobile (2) calculates several differences in time of flight, between the mobile (2) and transmitting bases (20) taken two by two, each difference in time of flight being calculated between the mobile (2) and two distinct transmitting bases (20).

[0089]

[0060] In a final step, the computing means of the receiving mobile (2) determine the position of the receiving mobile (2) from the calculated time-of-flight difference(s) TVdiff and the position data of the transmitting bases (22, 24), previously stored in the storage means. From the known position data of the transmitting bases (22, 24), the absolute position of the receiving mobile (2) is easily given by the classical relationship between wave speed and time-of-flight difference.

[0090]

[0061] In the case where the positioning system (1) comprises three or more transmitting bases (20), the computing means of the receiving mobile (2) combine the different time-of-flight difference measurements to determine the position of the receiving mobile (2).

[0062] Since the order of magnitude of the time-of-flight difference(s) thus determined is around the nanosecond, it is clear from the above that the positioning system (1) advantageously allows for sub-meter accuracy (less than 1 m) for positioning the mobile (2), even indoors or in urban environments. Furthermore, the receiving mobile (2) performs its own positioning autonomously.Finally, the positioning system (1) has both a large range (typically greater than 10 km), works well in both outdoor and indoor environments, and has limited spectral occupancy, increased sensitivity and a minimal equivalent noise band.

[0091]

[0063] In this context, we are now interested in the communication system (10) integrated into the positioning system (1) and comprising the transmitting bases (20). The signals sent by the transmitting bases (20) are received by the receiving mobile (2), but can also be received by the transmitting bases (20) themselves. In particular, the signals sent by the master device (22) can be received by the slave device (24), so that the slave device (24) synchronizes with the master device (24).

[0092]

[0064] Figure 3 shows the wireless synchronization method (100) of the communication system (10) of Figure 1, including a master device (22) and a slave device (24). The master device (22) has a fixed internal master reference frequency (F22), while the slave device (24) has an adjustable internal slave reference frequency (F24). The position of each transmitting base (20) is pre-memorized by the other transmitting base (20). The method (100) includes several steps (110, 120, 130, 140), detailed below.

[0093]

[0065] In a signal reception and processing step (110), the slave device (24) receives radio frequency signals from the master device (22), then demodulates and identifies the master reference frequency (F22).

[0094]

[0066] In a frequency synchronization step (120), the slave device (24) modifies its internal slave reference frequency (F24) to match the internal master reference frequency (F22). This modification of the internal slave reference frequency (F24) can be performed by a clock generator integrated into the slave device (24).

[0067] In a calculation step (130), the slave device (24) calculates an actual flight time between the master device (22) and the slave device (24), for comparison with a theoretical flight time between the master device (22) and the slave device (24). In this context, the slave device (24) applies a direct path discrimination algorithm between the master device (22) and the slave device (24).

[0095]

[0068] For the application of the direct path discrimination algorithm, the calculation step (130) performed by the slave device (24) may include:

[0096] - a measurement substep (131), for each given signal frequency, of the phase and amplitude of the signal consisting of the different signals received from the master device (22) and presenting said frequency;

[0097] - a substep of application (132) of a high-resolution spectral analysis algorithm on a signal consisting of the different phases and measured amplitudes of the radio frequency signals received from the master device (22), in order to discriminate the direct path and different bounces undergone by the signal;

[0098] - a substep of identification (133) of the direct path among the multiple paths discriminated during the substep of application (132) of the algorithm.

[0099]

[0069] In a time synchronization step (140), the slave device (24) calculates and applies a deceleration or acceleration coefficient to its internal reference frequency, as well as a duration of application of this coefficient, to obtain a corrected actual flight time equal to the theoretical flight time.

[0100]

[0070] In practice, the slave device (24) performs steps (110, 120) only once, at the launch of the self-synchronization algorithm, then repeats steps (130, 140) to continuously maintain the corrected actual flight time equal to the theoretical flight time.

[0101]

[0071] Thus, the invention makes it possible to synchronize a system (10) comprising several remote beacons (20), without cables, with an accuracy of less than 10 ns. The slave devices synchronize with the master device. Time synchronization is performed by each of the slave devices, which receive the signals from the master device, demodulate them, and calculate a time of flight. Knowing their position and the position of the master device, the slave devices can deduce the time correction to be applied.

[0102]

[0072] Figure 4 shows a communication system (10) consisting of five transmitting bases (20), including a master device (22) and four slave devices (24).

[0103] The master device (22) has a master internal reference frequency (F22) configured to remain fixed. Each slave device (24A, 24B, 24C, 24D) has its own internal slave reference frequency (F24A, F24B, F24C, F24D) which is adjustable.

[0104]

[0073] The position of each transmitting base (20) is stored by the other transmitting bases (20). The bases (20) can be fixed or mobile.

[0105]

[0074] When the bases (20) are located on board satellites, the transmission of position data functions as with GPS. A GPS receiver knows in advance the orbits of each satellite and can calculate their position to within a few meters every second. To achieve this accuracy, the orbital parameters must be regularly transmitted to the receiver (typically at least once an hour); otherwise, the drift is too significant.

[0106]

[0075] When the bases (20) are terrestrial, when we speak of a mobile system (10), we are generally referring to a system (10) that can be rapidly deployed anywhere. However, once the system (10) is deployed and operational, the bases (20) remain fixed. The positions of the bases (20) are therefore communicated to each other within the system (10), once they are in position, prior to the execution of method (100).

[0107]

[0076] The communication system (10) can be synchronized using the wireless synchronization method (100) described above.

[0108]

[0077] In a signal reception and processing step (110), each slave device (24) receives radio frequency signals from the master device (22), then demodulates and identifies the master internal reference frequency (F22).

[0109]

[0078] In a frequency synchronization step (120), each slave device (24) modifies its internal slave reference frequency (F24) to match the internal master reference frequency (F22). The modification of the internal slave reference frequency (F24) can be performed by a clock generator equipping the slave device (24).

[0110]

[0079] In a calculation step (130), each slave device (24) calculates an actual flight time between the master device (22) and the slave device (24), for comparison with a theoretical flight time between the master device (22) and the slave device (24). In this context, each slave device (24) applies a direct path discrimination algorithm between the master device (22) and the slave device (24).

[0111]

[0080] For the application of the direct path discrimination algorithm, the calculation step (130) carried out by each slave device (24) may include:- a measurement substep (131), for each given signal frequency, of the phase and amplitude of the signal made up of the different signals received from the master device (22) and having said frequency;

[0112] - a substep of application (132) of a high-resolution spectral analysis algorithm on a signal consisting of the different phases and measured amplitudes of the radio frequency signals received from the master device (22), in order to discriminate the direct path and different bounces undergone by the signal;

[0113] - a substep of identification (133) of the direct path among the multiple paths discriminated during the substep of application (132) of the algorithm.

[0114]

[0081] In a time synchronization step (140), each slave device (24) calculates and applies a deceleration or acceleration coefficient to its internal reference frequency (F24), as well as a duration of application of this coefficient, to obtain a corrected actual flight time equal to the theoretical flight time.

[0115]

[0082] In practice, each slave device (24) performs steps (110, 120) only once, at the start of the self-synchronization algorithm, then repeats steps (130, 140) to continuously maintain the corrected actual flight time equal to the theoretical flight time.

[0116]

[0083] Figure 4 shows a slave device (24) and its constituent elements (31, 32, 33, 34, 35, 36). The slave device (24) comprises an antenna (31), an analog-to-digital converter (32), a processing unit (33), a clock generator (34), a digital-to-analog converter (35), and a data bus (36) between the processing unit (33) and the digital-to-analog converter (35). When the sampling frequency of the digital-to-analog converter (35) is changed, the data rate through the data bus (36) is changed accordingly.

[0117]

[0084] Furthermore, the systems (1, 10) and the method (100) can be configured differently from Figures 1 to 5 without departing from the scope of the invention, which is defined by the claims. In addition, the technical characteristics of the various embodiments and variants mentioned above can be combined, in whole or in part. Thus, the systems (1, 2) and the method (100) can be adapted in terms of cost, functionality, and performance.

Claims

Demands 1) Method (100) of wireless synchronization of a communication system (10), comprising transmitting bases (20) configured to transmit radio frequency signals, the position of each transmitting base (20) being memorized by the other transmitting bases (20), the transmitting bases (20) comprising a master device (22) and at least one slave device (24), the master device (22) transmitting radio frequency signals with an internal reference frequency (F22) configured to remain fixed, the slave device (24) transmitting radio frequency signals with an adjustable internal reference frequency (F24), Method (100) comprises the following steps: - a signal reception and processing stage (110), in which the slave device (24) receives radio frequency signals from the master device (22), then demodulates and identifies the internal reference frequency (F22) of the master device (22); - a frequency synchronization step (120), in which the slave device (24) modifies its internal reference frequency (F24) to match the internal reference frequency (F22) of the master device (22); - a calculation step (130), in which the slave device (24) calculates an actual flight time between the master device (22) and the slave device (24), for comparison with a theoretical flight time between the master device (22) and the slave device (24); - a time synchronization step (140), in which the slave device (24) calculates and applies a deceleration or acceleration coefficient to its internal reference frequency (F24), as well as a duration of application of this coefficient, to obtain a corrected actual flight time equal to the theoretical flight time. 2) Method (100) according to claim 1, characterized in that in the calculation step (130), the slave device (24) applies a direct path discrimination algorithm between the master device (22) and the slave device (24). 3) Method (100) according to claim 2, characterized in that for the application of the direct path discrimination algorithm, the calculation step (130) performed by the slave device (24) comprises: - a measurement substep (131), for each given signal frequency, of the phase and amplitude of the signal consisting of the different signals received from the master device (22) and presenting said frequency; - a substep of application (132) of a high-resolution spectral analysis algorithm on a signal consisting of the different phases and measured amplitudes of the radio frequency signals received from the master device (22), in order to discriminate the direct path and different bounces undergone by the signal; - a substep of identification (133) of the direct path among the multiple paths discriminated during the substep of application (132) of the algorithm. 4) Method (100) according to any one of the preceding claims, characterized in that each transmitting base (20) is configured to emit a sum (SIA, S1B) of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated continuous wave, preferably sinusoidal; and in that in the calculation step (130), the slave device (24) calculates the actual time of flight between the master device (22) and the slave device (24) using the pure carrier signals. 5) Method (100) according to any one of the preceding claims, characterized in that the slave device (24) repeats the calculation step (130) and the time synchronization step (140) to continuously maintain the corrected actual flight time equal to the theoretical flight time. 6) Method (100) according to any one of the preceding claims, characterized in that in the frequency synchronization step (120), the modification of the internal reference frequency (F24) of the slave device is carried out by a clock generator equipping the slave device (24). 7) Communication system (10), configured to implement method (100) according to any one of claims 1 to 6.8) System (10) according to claim 7, characterized in that the slave device (24) comprises an antenna (31), an analog-to-digital converter (32), a computing unit (33), a clock generator (34), and a digital-to-analog converter (35). 9) System (10) according to claim 8, characterized in that the slave device (24) comprises a data bus (36) between the computing unit (33) and the digital-to-analog converter (35), and in that when the sampling frequency of the digital-to-analog converter (35) is changed, the data rate through the data bus (36) is changed accordingly. 10) Positioning system (1) of at least one receiving mobile (2) relative to transmitting bases (20), characterized in that the positioning system (1) includes a communication system (10) according to any one of claims 7 to 9, in that the receiving mobile (2) is configured to receive and process radio frequency signals from the transmitting bases (20) and to deduce its position by calculating the difference(s) in time of flight between the receiving mobile (2) and the transmitting bases (20), the receiving mobile (2) comprising means for storing position data of the fixed transmitting bases (20), in that each transmitting base (20) is configured to transmit a sum (SIA, S1B) of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated continuous wave, preferably sinusoidal; and in that the receiving mobile (2) further comprises: • means for measuring, for each given signal frequency and for each respective transmitting base (20), the phase and amplitude of the signal consisting of the different radio frequency signals originating from said transmitting base (20) and exhibiting said frequency; and • computing resources connected to measurement and storage resources, and configured to: to apply, for each transmitting base (20), a high-resolution spectral analysis algorithm on a signal consisting of the different phases and measured amplitudes of the radio frequency signals from said transmitting base (20); determine, for each transmitting base (20), from the spectral analysis carried out previously, a time of flight between the receiving mobile (2) and said transmitting base (20); calculate at least one difference in time of flight between the receiving mobile (2) and two transmitting bases (20), said difference being calculated as the difference between the times of flight determined for said transmitting bases (20); determine the position of the receiving mobile (2), from the calculated time difference(s) and the position data of the transmitting bases (20).

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