SYSTEM AND METHOD FOR POSITIONING AT LEAST ONE MOBILE RECEIVER

Description

Technical field

[0001] The invention relates to a system and method for positioning at least one receiving mobile. The technical field of the invention is that of positioning a receiving mobile, by the mobile itself, in an environment both outdoors and indoors. The system comprises, in addition to the receiving mobile, fixed transmitting bases or antennas which are configured to transmit radiofrequency signals to the receiving mobile. The calculation of the transmission time or flight time, by the receiving mobile during the transmission of these signals, allows it to determine the distance at which it is from each base, and therefore to deduce its position. Prior art

[0002] The location of mobile receivers in outdoor environments experienced a significant technological leap with the deployment of the GPS (Global Positioning System) system in the 1980s. However, GPS technology does not work indoors, typically inside buildings, and relatively poorly in urban environments. The two main constraints of indoor or urban environments are: the penetration of buildings and various obstacles by the signals of interest (which constitutes a limiting factor for the range of the positioning system); and the existence of multi-paths impacting the emitted wave, which results in numerous replicas of the original signal shifted in time and of variable amplitude arriving at the receiving mobile, such multi-path signals being called bounces.

[0003] There is therefore a need for mobile receiver positioning systems that have both a long range (typically greater than 10 km) and that operate in both outdoor and indoor environments.

[0004] As is known, a location system in an outdoor or indoor environment most often includes, in addition to the mobile to be positioned, a set of at least three beacons. These beacons are particularized in that their position is known. In addition, they are most often fixed. In such a system configuration, the beacons control the transmissions: a beacon transmits to a mobile, the mobile responds by retransmitting to the beacon. The measurement of the transmission time, by differential measurement of the date of transmission relative to the date of reception, makes it possible to determine the distance between the beacon and the mobile. However, such a system requires a retransmission of signals from the receiving mobile to the beacons, so that a remote server can deduce the position of the mobile, and therefore does not allow the mobile to perform its own positioning.

[0005] Also known, radiolocation systems use modulated radiofrequency signals, emitted by fixed beacons or antennas, to transmit, for example, positioning data or random data to a receiver. Such random data, for example known in advance to the receiver, are used to help the latter synchronize with the random data by performing signal correlations. However, such systems involve the use of a large frequency transmission bandwidth, typically a bandwidth of 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 dual operation, either in an outdoor or indoor environment.

[0006] Also known from the state of the art are systems for positioning an object, implementing a phase interferometry method, which uses amplitude and phase. Patent document US 2020 / 0209337 A1 describes such a positioning system. The system comprises at least two fixed transmitting bases which transmit radiofrequency signals. The system also comprises a receiving mobile, capable of determining the position of one of the fixed transmitting bases. To do this, the receiving mobile becomes a master device which transmits a signal comprising a sinusoidal portion. The transmitting base whose position is to be determined becomes a slave device which measures the phase and amplitude of the signal upon reception. It returns this information to the master device as well as a similar sinusoidal portion to allow the master device to detect the phase and amplitude of the received signal.The master device then applies a discrete Fourier transform to the measured signals, in the time domain, in order to determine the distance and thus the position of the slave device. Such a determination is carried out by time-of-flight measurement. However, such a positioning system does not allow the receiving mobile to quickly and easily determine its own position. Indeed, the receiving mobile is obliged in this case to successively determine the position of at least three fixed transmitting bases, then to cross-reference these measurements to deduce its position. Such a determination is long, tedious and therefore expensive. In addition, in order to avoid the disturbance of the measurements due to the presence of multi-paths, the system described in this document implements super-resolution algorithms. However, the implementation of such a system results in a relatively large noise band, which affects the sensitivity of the system.Indeed, the transmission of information caused by this system (transmission of modulated signals) implies having a relatively large channel width, and therefore the receiver is obliged to take into account the entire channel to find the information. The precision of the location can thus be affected.

[0007] Document US 2015 / 201309 A1 discloses the TDOA ("Time Difference of Arrival") technique. Summary of the invention

[0008] An aim of the present invention is to at least partially overcome the aforementioned drawbacks.

[0009] In particular, an objective of the present invention is to provide a system for positioning at least one receiving mobile having both a long range (typically greater than 10 km) and operating in both outdoor and indoor environments, allowing the mobile itself to position itself precisely, and making it possible to limit spectral occupation while having increased sensitivity and a minimally reduced equivalent noise band.

[0010] Another objective of the present invention is to provide a system for positioning at least one receiving mobile allowing the mobile itself to position itself precisely, by discriminating between the direct line-of-sight signals coming from a transmitting base and the different signal bounces (multi-path).

[0011] For this purpose, the invention relates to a system for positioning at least one receiving mobile, the system comprising, in addition to the mobile, at least two fixed transmitting bases, each transmitting base being configured to transmit radiofrequency signals, the transmitting bases being synchronized with each other to transmit their respective signals, the receiving mobile being configured to receive and process said radiofrequency signals and to deduce its position therefrom by calculating the difference(s) in flight time between the receiving mobile and the transmitting bases, the receiving mobile comprising means for storing position data of the fixed transmitting bases, wherein 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, preferably sinusoidal, continuous wave; and the receiving mobile further comprises: means for measuring, for each given signal frequency and for each respective transmitting base, the phase of the signal consisting of the different signals originating from said base and having said frequency; and calculation means connected to the measuring means and to the storage means, and configured to: o apply, for each transmitting base, a Fourier transform on a signal consisting of the different measured phases of the radiofrequency signals originating from said base; o determine, for each transmitting base, from the Fourier transform calculated for said base, a time of flight between the receiving mobile and said base;o calculate at least one flight time difference between the mobile and two transmitting bases, said difference being calculated as the difference between the flight times determined for said bases; o determine the position of the receiving mobile, from the calculated flight time difference(s) and the position data of the transmitting bases.;

[0012] The system's use of pure carrier signals in the form of unmodulated continuous waves makes it possible to limit spectral occupancy, and therefore to ensure very good system sensitivity by minimizing the equivalent noise band. Such signals in fact have a spectral occupancy reduced to a minimum. This makes it possible to obtain a receiver mobile positioning system with a long range and low operating cost, operating both in outdoor and indoor environments, and allowing the mobile itself to position itself precisely.Such an approach by transmitting sums of unmodulated pure carrier signals is not used in prior art positioning and radiolocation systems, in particular because of multipaths (bounces of the transmitted signal which arrive at the receiving mobile with a time shift) which are difficult to dissociate from the original signal in direct line of sight, when such a signal is an unmodulated continuous wave. The use by the system according to the invention of a Fourier transform applied to a signal consisting of the different measured phases of the radiofrequency signals allows the receiving mobile to discriminate the bounces of the main signal, and thus to measure the flight times (between the mobile and the bases) not affected by errors due to multipath.Unlike some prior art positioning systems, which apply a Fourier transform to a time signal, the positioning system according to the invention applies a Fourier transform to a signal consisting of phases of signals of different frequencies. Such an approach allows the receiving mobile to be able to distinguish the bounces from the main signal, the latter being the first to arrive at the receiving mobile (the bounces arriving later). In addition, the transmitting bases of the positioning system according to the invention do not transmit any modulated data, unlike many prior art systems. This makes it possible to reduce the spectral occupation and therefore the cost and complexity of the system.

[0013] Advantageously, for each transmitting base, the frequency difference between the minimum frequency and the maximum frequency of the pure carrier signals transmitted by said base is greater than 50 MHz. This makes it possible to reduce the resolution of the Fourier transform, and therefore to obtain improved location accuracy, typically less than 1 m. The resolution of the Fourier transform thus reduced then makes it possible to improve the separation or discrimination between the direct line-of-sight signal coming from a transmitting base on the one hand, and the different bounces of the signal (multi-path) on the other hand. Indeed, such a separation or discrimination is possible provided that the resolution of the Fourier transform is sufficiently fine, more precisely provided that it is less than the time interval separating the main signal (in direct line of sight) from the bounce considered.The positioning system according to the invention makes it possible to obtain a location accuracy for the receiving mobile of less than 1 m, even inside buildings or in an urban environment, and this without resorting to GPS or GNSS (Global Navigation Satellite System) type signals.

[0014] According to a preferred embodiment, each pure carrier signal emitted by a transmitting base has a frequency located in the very high frequency band, in other words has a frequency in the range from 30 MHz to 300 MHz. This makes it possible to obtain the best compromise between penetrability of the signals inside buildings, limitation of multi-path phenomena, and dimensions of the transmitting and receiving antennas. In addition, the use of such signals greatly limits the bandwidth used. The very high frequency band also offers a wide choice regarding the use of pure sinusoidal signals.

[0015] Preferably, the fixed transmitter bases are configured to transmit the same number of unmodulated pure carrier signals.

[0016] Advantageously, the fixed transmitting bases are configured so as to transmit their sums of unmodulated pure carrier signals in a frequency-shifted manner, with a predetermined frequency shift between two successive transmitting bases. This allows the receiving mobile to be able to distinguish the sums of unmodulated pure carrier signals from each of the transmitting bases.

[0017] Preferably, the frequency offset is in the range from 100 Hz to 1 kHz. Such a frequency offset value allows the sums of unmodulated pure carrier signals to be easily separated by the receiving mobile, while remaining in the same frequency channel (with a frequency width equal to 12.5 kHz, in the very high frequency band). This makes it possible to limit the number of occupied frequency channels, and consequently to reduce the cost of implementing the system.

[0018] According to a particular technical characteristic of the invention, the fixed transmitting bases are antennas, preferably antennas distributed such that the distance between two adjacent antennas is greater than or equal to 5 km.

[0019] According to another particular technical characteristic of the invention, the receiving mobile is a chip or an electronic card or even a mobile communication device such as a mobile telephone.

[0020] Preferably, each fixed transmitting base is configured to synchronize with each other the unmodulated pure carrier signals transmitted by the base.

[0021] According to a particular technical characteristic of the invention, each fixed transmitting base is configured to transmit a sum S1 of N unmodulated sinusoidal signals of distinct frequencies ω k, said sum S1 verifying the form of the following equation: S 1 = ∑ k = 1 N cos ω k t

[0022] The invention also relates to a method for positioning at least one receiving mobile, implemented by a positioning system comprising, in addition to the mobile, at least two fixed transmitting bases, each transmitting base being configured to transmit radiofrequency signals, the transmitting bases being synchronized with each other to transmit their respective signals, the receiving mobile comprising signal phase measurement means, data storage means, and calculation means connected to the measurement means and to the storage means, the method comprising an initial step of transmitting position data from the fixed transmitting bases to the storage means of the receiving mobile, in which the method further comprises the following steps: an emission, by each of the transmitting bases, of a sum of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated, preferably sinusoidal, continuous wave; a reception, by the receiving mobile, of the radiofrequency signals from the transmitting bases; a measurement, by the receiving mobile, for each given signal frequency and for each respective transmitting base, of the phase of the signal consisting of the different signals from said base and having said frequency; an application, by the receiving mobile and for each transmitting base, of a Fourier transform on a signal consisting of the different measured phases of the radiofrequency signals received from said base; a determination, by the receiving mobile and for each transmitting base, from the Fourier transform calculated for said base, of a time of flight between the receiving mobile and said base;a calculation, by the receiving mobile, of at least one flight time difference between the mobile and two transmitting bases, said difference being calculated as the difference between the flight times determined for said bases; a determination, by the receiving mobile, of its position from the calculated flight time difference(s) and the position data of the transmitting bases.;

[0023] According to a particular technical characteristic of the invention, during the step of applying a Fourier transform, the Fourier transform is a discrete Fourier transform.

[0024] Advantageously, during the step of applying a Fourier transform, the calculation means of the receiving mobile use the flight time as an independent variable for the applied Fourier transform. Brief description of the drawings

[0025] The invention will be better understood by reading the following description, given solely by way of example, and with reference to the appended figures in which: [ Fig. 1 ] shows a diagram of a system for positioning a receiving mobile according to the invention, [ Fig. 2 ] shows a flowchart representing a method of positioning a receiving mobile according to the invention, implemented by the system of the figure 1 , And [ Fig. 3 ] shows a graph representing two Fourier transforms as a function of the time of flight, each Fourier transform corresponding to a distinct transmitting base and having been applied by the receiving mobile to a signal consisting of the different measured phases of the radiofrequency signals coming from this base. Description of the embodiments

[0026] In the following, a system 1 is disclosed for positioning a receiving mobile 2. The system 1 comprises, in addition to the receiving mobile 2, at least two fixed transmitting bases 4. In the particular embodiment of the figure 1 , on which such a positioning system 1 is shown, the system 1 comprises two fixed transmitting bases 4A, 4B. However, the invention applies in the same way to any positioning system comprising a number of transmitting bases greater than or equal to two, and preferably greater than or equal to three. The fact of providing at least three transmitting bases in the positioning system makes it possible to ensure greater robustness for the system.

[0027] The receiving mobile 2 is configured to receive and process radiofrequency signals s dA , s dB , s rA , s rB from the fixed transmitting bases 4A, 4B, and to deduce its position therefrom by calculating the difference(s) in flight time between the receiving mobile 2 and the transmitting bases 4A, 4B (as will be described later). This calculation of differential flight time makes it possible to avoid any time synchronization constraint between the receiving mobile 2 and the transmitting bases 4A, 4B.

[0028] The receiving mobile 2 comprises storage means (not shown), configured to store position data of the fixed transmitting bases 4A, 4B. The storage means typically consist of a memory, typically a non-volatile memory. The receiving mobile 2 further comprises means for measuring phases of radiofrequency signals, these measuring means not being shown in the figures for reasons of clarity. The receiving mobile 2 also comprises calculation means (not shown) connected to the measuring means and to the storage means. The measuring and calculation means typically consist of a processing unit, for example formed of one or more processors, or integrated within an electronic chip.By way of non-limiting examples, the receiving mobile 2 is typically made up of a chip or an electronic card, for example integrated into a portable device; or a mobile communication device such as a mobile telephone. In the case where the receiving mobile 2 is made up of an electronic chip or a mobile communication device of the mobile telephone type, this or the latter is typically equipped with an analog-digital converter.

[0029] Each transmitting base 4A, 4B is typically an antenna for transmitting radiofrequency signals S1 A, S1 B, s dA, s dB, s rA, s rB. Preferably, when the transmitting bases 4A, 4B are antennas, the latter are distributed such that the distance between two adjacent antennas is greater than or equal to 5 km. The transmitting bases 4A, 4B of the positioning system 1 are synchronized with each other to transmit their respective signals. By "synchronized with each other" is meant that the phase shift between the signals transmitted by the different transmitting bases 4A, 4B is constant, this in order to avoid drifts in the signals, and thus to avoid distorting the measurement carried out by the receiving mobile 2 for its positioning.

[0030] Each transmitting base 4A, 4B is configured to transmit a sum S1 A , S1 B of at least two unmodulated pure carrier signals of distinct frequencies. Each pure carrier signal is in the form of an unmodulated, preferably sinusoidal, continuous wave. According to a preferred embodiment, each unmodulated pure carrier signal is a pure sinusoidal signal, and each fixed transmitting base 4A, 4B is configured to transmit a sum S1 A , S1 B of N unmodulated sinusoidal signals of distinct frequencies ω k. Each sum S1 A , S1 B of signals satisfies the form of the following general equation: S 1 A , B = ∑ k = 1 N cos ω k t

[0031] Preferably, the frequency difference between the minimum frequency and the maximum frequency among the frequencies ω k of the pure carrier signals emitted by each transmitting base 4A, 4B is greater than 50 MHz. More preferably, each pure carrier signal emitted by a transmitting base 4A, 4B has a frequency located in the very high frequency band, in other words has a frequency in the range from 30 MHz to 300 MHz. Frequency bands belonging to the very high frequencies VHF (from the English Very High Frequencies) are thus allocated to the fixed transmitting bases 4A, 4B of the positioning system 1.

[0032] Preferably, the fixed transmitting bases 4 are configured to transmit the same number N of unmodulated pure carrier signals. According to a preferred embodiment, the transmitting bases 4 are configured so as to transmit their sums S1 of unmodulated pure carrier signals in a frequency-shifted manner, with a predetermined frequency shift Δω between two successive transmitting bases 4. Thus, in the exemplary embodiment illustrated in the figure 1 , a first transmitting base 4A, respectively a second transmitting base 4B, is configured to transmit a sum S1 A , respectively S1 B , of unmodulated sinusoidal signals verifying the following equation: S 1 A = ∑ k = 1 N cos ω k t S 1 B = ∑ k = 1 N cos ω k + Δω t

[0033] The sums S1 A and S1 B of sinusoidal signals are thus shifted in frequency, by a frequency shift Δω (expressed for example in rad / s). The frequency shift Δω is preferably in the range from 100 Hz to 1 kHz. Each transmitting base 4A, 4B is advantageously configured to synchronize the sinusoidal signals that it transmits with each other.

[0034] In reference to the figure 1, it is assumed in the remainder of the description that the environment in which the receiving mobile 2 operates comprises a first obstacle O1 and a second obstacle O2. The two obstacles O1 and O2 are here buildings, but could alternatively be formed of any other type of structure without affecting the reasoning which follows. For each transmitting base 4A, 4B, the radiofrequency signals received by the receiving mobile 2 and originating from this base 4A, 4B are divided into two types: a first type consists of the signals s dA , s dB arriving in direct line of sight, and a second type consists of the signals s rA , s rB arriving on the receiving mobile 2 following a rebound on an obstacle O1, O2. The signals s dA , s rA , respectively s dB , s rB , each correspond to the sum S1 A , respectively S1 B , of unmodulated pure carrier signals, but take different paths.We call DA, respectively DB, the direct line-of-sight distance between the receiving mobile 2 and the first transmitting base 4A, respectively the second transmitting base 4B, traveled by the signals s dA, respectively s dB. We call D rA, respectively D rB, the distance traveled by the signals s rA, respectively s rB after bouncing off an obstacle O1, respectively O2. For the purposes of simplification, we subsequently only take into account, for the first transmitting base 4A, the radiofrequency signals coming from this base and having bounced off the obstacle O1 closest to this base 4A (the impact of the signals coming from this base and having bounced off the other obstacle O2 being considered negligible).Similarly, for the second transmitting base 4B, only the radiofrequency signals coming from this base and having bounced off the obstacle O2 closest to this base 4B are taken into account (the impact of the signals coming from this base and having bounced off the other obstacle O1 being considered negligible). For simplicity, it is also assumed that the radiofrequency signals only bounce off one of the obstacles O1, O2.

[0035] The method of positioning the receiving mobile 2, implemented by the positioning system 1, will now be described in detail, with particular reference to the figure 2 .

[0036] The method comprises an initial step 10 of transmitting position data from the fixed transmitting bases 4A, 4B to the storage means of the receiving mobile 2. The transmission 10 may for example consist of a transmission by each transmitting base 4A, 4B of its position coordinates to the receiving mobile 2, or even of a prior implantation of the position coordinates of the bases within the receiving mobile 2, at the time of its manufacture or its configuration. At the end of this initial step 10, the storage means of the receiving mobile 2 store the position data of the transmitting bases 4A, 4B.

[0037] The method comprises a following step 12 during which each transmitting base 4A, 4B transmits the sum S1 A , S1 B of unmodulated pure carrier signals of distinct frequencies ω k. The phase shift between the signals S1 A , S1 B transmitted by the different transmitting bases 4A, 4B is constant. The sums S1 A and S1 B of pure carrier signals transmitted by the bases 4A, 4B are thus shifted in frequency, by a frequency shift Δω. The different frequencies ω k used by the bases 4A, 4B, as well as the frequency shift Δω, are known by the receiving mobile 2 (pre-installed in or transmitted to the latter).

[0038] During a following step 14, the receiving mobile 2 receives the radiofrequency signals s dA , s dB , s rA , s rB coming from the transmitting bases 4A, 4B. These signals s dA , s rA , respectively s dB , s rB , each correspond to the sum S1 A , respectively S1 B , of unmodulated pure carrier signals, but take different paths. Thanks to the fact that the sums S1 A , S1 B of signals are frequency-shifted with a predetermined frequency shift (known to the receiving mobile 2), the receiving mobile 2 can distinguish the signals s dA , s rA coming from the first base 4A on the one hand, from the signals s dB , s rB coming from the second transmitting base 4B on the other hand.

[0039] During a following step 16, the receiving mobile 2 determines via its measuring means, for each given signal frequency ω k and for each transmitting base 4A, 4B, the phase of the signal consisting of the different signals s dA , s rA ; respectively s dB , s rB , coming from this base 4A, 4B and having the frequency ω k . Indeed, for example for the first base 4A and for a given frequency ω k , the two signals s dA (ω k ) and s rA (ω k ) are received by the receiving mobile 2 while being mixed. The phase measured by the receiving mobile 2 for the frequency ω k then corresponds to the phase of the signal consisting of the sum of the direct signal s dA and the rebound signal s rA . The same reasoning applies for the signals s dB , s rB coming from the second base 4B.According to a particular embodiment, this phase measurement may consist in the measurement means applying, for each frequency ω k , a multiplier coefficient e iωk< on each signal consisting of the different signals s dA , s rA ; respectively s dB , s rB , coming from the first base 4A, respectively from the second base 4B. This makes it possible to isolate the phase of each unmodulated pure carrier signal forming part of the signals s dA , s rA , respectively s dB , s rB .

[0040] During a following step 18, the receiving mobile 2 applies, via its calculation means and for each of the transmitting bases 4A, 4B, a Fourier transform to a signal consisting of the different measured phases of the radiofrequency signals received from this base. Indeed, the principle used by the invention is that for a given time delay, the phase shift undergone by a signal with an unmodulated pure carrier depends on the frequency of this signal. The Fourier transform applied during step 18 is typically a discrete Fourier transform, and in particular a discrete Fourier transform with complex coefficients.

[0041] For each transmitting base 4A, 4B, the Fourier transform TF applied to the measured phases of the signals coming from this base is then expressed mathematically via the following function: TF d n = ∑ k = 1 N r ω k . e − iω k d n c where r(ω k ) is the phase of the signals coming from the base and having frequency ω k , as measured during the previous step 16; and d n c represents the time of flight of a signal from the transmitting base 4A, 4B in question and received by the receiving mobile 2. The complex coefficients of the Fourier transform TF are then: e − iω k d n c The independent variable of the Fourier transform TF thus expressed is then the time of flight d n c .

[0042] In this way, by graphically representing, for each emitting base 4A, 4B, the result of the Fourier transform applied during step 18, the calculation means can during a following step 20 isolate different peaks corresponding to each signal s dA , s rA or s dB , s rB , and deduce therefrom the time of flight of each of these signals. This is illustrated on the graph of the figure 3, on which two graphical functions 30A, 30B have been represented. These two functions 30A, 30B correspond respectively to the calculation of the Fourier transform for the first transmitting base 4A, and for the second transmitting base 4B, represented as a function of the flight time (which is therefore read on the abscissa axis). During this step 20, the calculation means of the receiving mobile 2 determine the flight time between the receiving mobile 2 and each of the bases 4A, 4B. To do this, the calculation means isolate the peak P1A, P1B having the shortest flight time. This peak P1A, P1B corresponds to the signal s dA, s dB in direct line of sight. In the exemplary embodiment represented, for the first base 4A, the peak P1A corresponding to the signal s dA has a flight time TV1A substantially equal to 230 ns. The flight time TV1A between the receiving mobile 2 and the first base 4A is therefore approximately 230 ns.For the second base 4B, the peak P1B corresponding to the signal s dB has a flight time TV1B substantially equal to 310 ns. The flight time TV1B between the receiving mobile 2 and the second base 4B is therefore substantially 310 ns. For each of the bases 4A, 4B, the second peak P2A, P2B, which has a lower amplitude than that of the first peak P2A, P2B and a longer flight time, corresponds to the signal s rA , s rB having undergone a rebound on an obstacle O1, O2. This peak P2A, P2B can therefore be advantageously isolated from the first peak P1A, P1B, and not be taken into account in the rest of the calculations.

[0043] During a following step 22, the receiving mobile 2 calculates at least one flight time difference TV diff between the mobile 2 and two transmitting bases 4A, 4B. The flight time difference TV diff is calculated as the difference between the flight times TV1A, TV1B determined for the transmitting bases 4A, 4B during step 20. In the exemplary embodiment shown in the figure 3 , the time difference in flight time TV diff is substantially equal to 80 ns (310 ns - 230 ns). In the case where the positioning system comprises a number of transmitting bases greater than or equal to three, the receiving mobile 2 calculates several flight time differences, between the mobile and transmitting bases taken two by two, each flight time difference being calculated between the mobile 2 and two distinct transmitting bases.

[0044] During a final step 24, the calculation means of the receiving mobile 2 determine the position of the receiving mobile 2 from the calculated flight time difference(s) TV diff and the position data of the transmitting bases 4A, 4B, previously stored in the storage means. From the known position data of the transmitting bases 4A, 4B, the absolute position of the receiving mobile is easily given by the conventional relationship between wave speed and flight time difference. In the case where the positioning system comprises a number of transmitting bases greater than or equal to three, the calculation means of the receiving mobile 2 cross-reference the different flight time difference measurements in order to determine the position of the receiving mobile 2.

[0045] Because the order of magnitude of the flight time difference(s) thus determined is around the nanosecond, it is understood from reading the above that the system 1 according to the invention advantageously makes it possible to achieve sub-metric precision (less than 1 m) for the positioning of the mobile 2, even inside buildings or in an urban environment. In addition, the receiving mobile 2 carries out its own positioning autonomously. Finally, the positioning system 1 has a long range (typically greater than 10 km), operates both in an outdoor and indoor environment, and has limited spectral occupation, increased sensitivity and a minimally reduced equivalent noise band. All these characteristics, obtained together in the same system, are novel and particularly advantageous compared to the various positioning systems of the prior art.

Claims

1. A system (1) for positioning at least one mobile receiver (2), the system (1) comprising, in addition to the mobile (2), at least two stationary transmitter bases (4, 4A, 4B), each transmitter base (4, 4A, 4B) being configured to transmit radio frequency signals (S1A, S1B, sdA, sdB, srA, srB), the transmitter bases (4, 4A, 4B) being synchronized to each other to transmit their respective signals, the mobile receiver (2) being configured to receive and process said radio frequency signals (sdA, sdB, srA, srB) and to deduce therefrom its position by calculating the time-of-flight difference(s) between the mobile receiver (2) and the transmitter bases (4, 4A, 4B), the mobile receiver (2) comprising means for storing position data of the stationary transmitter bases (4, 4A, 4B), characterized in that each transmitter base (4, 4A, 4B) is configured to transmit a sum (S1A, S1B) of at least two unmodulated pure carrier signals of different frequencies, each pure carrier signal being in the form of an unmodulated continuous wave, which is preferably sinusoidal; and in that the mobile receiver (2) further comprises: • means for measuring, for each given signal frequency and for each respective transmitter base (4A, 4B), the phase of the signal consisting of the various signals (sdA, srA, sdB, srB) coming from said base and having said frequency; and • computing means connected to the measuring means and to the storage means, and configured to: o apply, for each transmitter base (4A, 4B), a Fourier transform to a signal consisting of the various measured phases of the radio frequency signals coming from said base (4A, 4B); o determine, for each transmitter base (4A, 4B), from the Fourier transform computed for said base, a time-of-flight between the mobile receiver (2) and said base (4A, 4B); o calculate at least one time-of-flight difference between the mobile (2) and two transmitter bases (4A, 4B), said difference being calculated as the difference between the determined times-of-flight for said bases (4A, 4B); o determine the position of the mobile receiver (2), from the calculated time-of-flight difference(s) and position data of the transmitter bases (4A, 4B).

2. The system (1) according to the preceding claim, characterized in that, for each transmitter base (4, 4A, 4B), the frequency difference between the minimum frequency and the maximum frequency of the pure carrier signals transmitted by said base (4, 4A, 4B) is greater than 50 MHz.

3. The system (1) according to claim 1 or 2, characterized in that each pure carrier signal transmitted by a transmitter base (4, 4A, 4B) has a frequency located in the band of very high frequencies, in other words has a frequency in the range from 30 MHz to 300 MHz.

4. The system (1) according to any one of the preceding claims, characterized in that the stationary transmitter bases (4, 4A, 4B) are configured to transmit the same number of unmodulated pure carrier signals.

5. The system (1) according to the preceding claim, characterized in that the stationary transmitter bases (4, 4A, 4B) are configured so as to transmit their sums (S1A, S1B) of unmodulated pure carrier signals in a frequency-shifted manner, with a predetermined frequency shift between two successive transmitter bases (4).

6. The system (1) according to the preceding claim, characterized in that the frequency shift is in the range from 100 Hz to 1 kHz.

7. The system (1) according to any one of the preceding claims, characterized in that the stationary transmitter bases (4, 4A, 4B) are antennas, preferably antennas distributed such that the distance between two adjacent antennas is greater than or equal to 5 km.

8. The system (1) according to any one of the preceding claims, characterized in that the mobile receiver (2) is a chip or an electronic card or else a mobile communication device such as a cell phone.

9. The system (1) according to any one of the preceding claims, characterized in that each stationary transmitter base (4, 4A, 4B) is configured to synchronize between them the unmodulated pure carrier signals transmitted by the base (4, 4A, 4B).

10. The system (1) according to any one of the preceding claims, characterized in that each stationary transmitter base (4, 4A, 4B) is configured to transmit a sum S1 of N unmodulated sinusoidal signals of different frequencies ωk, said sum S1 satisfying the following equation: S 1 = ∑ k = 1 N cos ω k t 11. A method for positioning at least one mobile receiver (2), implemented by a positioning system (1) comprising, in addition to the mobile (2), at least two stationary transmitter bases (4, 4A, 4B), each transmitter base (4, 4A, 4B) being configured to transmit radio frequency signals (S1A, S1B, sdA, sdB, srA, srB), the transmitter bases (4, 4A, 4B) being synchronized to each other to transmit their respective signals, the mobile receiver (2) comprising means for measuring signal phases, data storage means, and computing means connected to the measuring means and to the storage means, the method comprising an initial step (10) of transmitting position data from the stationary transmitter bases (4A, 4B) to the storage means of the mobile receiver (2), characterized in that it further comprises the following steps: • an emission (12), by each of the transmitter bases (4A, 4B), of a sum (S1A, S1B) of at least two unmodulated pure carrier signals of different frequencies, each pure carrier signal being in the form of an unmodulated continuous wave, which is preferably sinusoidal; • a reception (14), by the mobile receiver (2), of the radio frequency signals (sdA, sdB, srA, srB) coming from the transmitter bases (4A, 4B); • a measurement (16), by the mobile receiver (2), for each given signal frequency and for each respective transmitter base (4A, 4B), of the phase of the signal consisting of the various signals (sDA, srA; sdB, srB) coming from said base and having said frequency; • an application (18), by the mobile receiver (2) and for each transmitter base (4A, 4B), of a Fourier transform to a signal consisting of the different measured phases of the radio frequency signals received from said base (4A, 4B); • a determination (20), by the mobile receiver (2) and for each transmitter base (4A, 4B), from the Fourier transform computed for said base (4A, 4B), of a time-of-flight (TV1A, TV1B) between the mobile receiver (2) and said base (4A, 4B); • a calculation (22), by the mobile receiver (2), of at least one time-of-flight difference (TVdiff) between the mobile (2) and two transmitter bases (4A, 4B), said difference (TVdiff) being calculated as the difference between the determined times-of-flight (TV1A, TV1B) for said bases (4A, 4B); • a determination (24), by the mobile receiver (2), of its position from the calculated time-of-flight difference(s) (TVdiff) and from the position data of the transmitter bases (4A, 4B).

12. The method according to claim 11, characterized in that, during the step (18) of applying a Fourier transform, the Fourier transform is a discrete Fourier transform.

13. The method according to claim 11 or 12, characterized in that, during the step (18) of applying a Fourier transform, the computing means of the mobile receiver (2) use the time-of-flight as an independent variable for the applied Fourier transform.