System and method for positioning at least one mobile receiver

Abstract

The invention relates to a system (1) for positioning at least one mobile receiver (2), the system (1) comprising at least two stationary transmitter bases (4, 4A, 4B). Each transmitter base is configured to emit a sum (S1A, S1B) of at least two unmodulated pure-carrier signals having distinct frequencies; and the mobile receiver (2) comprises: • means for determining phases and amplitudes of signals in the frequency domain; and • computing means configured to: o apply an operation for converting the signal from the frequency domain to the time domain; o apply a probability metric extraction tool; o associate a potential direct-path probability with each pseudo-distance, the potential direct-path probability being associated using the extracted direct-path probability metric; o generate the set of possible positions for the mobile receiver (2); o associate, with each possible position generated for the mobile receiver (2), a signal path pseudo-distance; o associate a probability with each possible position generated for the mobile receiver (2); o determine the most probable position of the mobile receiver (2).

Description

DESCRIPTION TITLE: System and method for positioning at least one receiving mobile Technical field of the invention

[0001] The invention relates to a system and method for positioning at least one receiving mobile device. The technical field of the invention is the positioning of a receiving mobile device by the device itself, in both outdoor and indoor environments. The system comprises, in addition to the receiving mobile device, fixed transmitting bases or antennas configured to transmit radio frequency signals to the receiving mobile device. The calculation of pseudo-distances by the receiving mobile device during the transmission of these signals allows it to determine its distance from each base station, and thus deduce its position. Hereafter, "pseudo-distance" refers to an indirect distance measurement based on the transmission and reception times of a signal. Prior art

[0002] The location of mobile receivers in outdoor environments saw a significant 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 performs relatively poorly in urban environments. The two main limitations of indoor or urban environments are: - the penetration of buildings and various obstacles by signals of interest (which constitutes a limiting factor for the range of the positioning system); and - the existence of multipath impacts on 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 multipath signals are called rebounds.

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

[0004] As is well known, a location system for outdoor or indoor environments typically includes, in addition to the mobile device to be located, a set of at least three beacons. These beacons are unique in 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 calculating the difference between the transmission time and the reception time, allows the distance between the beacon and the mobile device to be determined. 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.

[0005] Radio-frequency identification (RFI) 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 it 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 meter or sub-meter accuracy. Furthermore, such RFI systems do not allow for dual-use operation in either outdoor or indoor environments.

[0006] Prior art is also known for object positioning systems that implement a phase interferometry method, utilizing amplitude and phase. US patent document 2020 / 0209337 A1 describes such a positioning system. The system comprises at least two fixed transmitting bases that emit radio frequency signals. The system also includes a receiving mobile device capable of determining the position of one of the fixed transmitting bases. To do this, the receiving mobile device acts as a master, emitting a signal that includes a sinusoidal portion. The transmitting base whose position is to be determined acts as a slave device, measuring the phase and amplitude of the received signal. It returns this information, along with a similar sinusoidal portion, to the master device, enabling it 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 to determine the distance, and thus the position, of the slave device. This determination is performed by time-of-flight measurement. However, such a positioning system does not allow the receiving mobile device to quickly and easily determine its own position. Indeed, the receiving mobile device is forced to successively determine the position of at least three fixed transmitting bases, and then cross-reference these measurements to deduce its position. Such a determination is lengthy, tedious, and therefore costly. Furthermore, to avoid measurement interference due to multipath propagation, the system described in this document implements super-resolution algorithms. However, the implementation of such a system introduces a relatively large noise band, which reduces the system's sensitivity.Indeed, the information transmission involved in this system (modulated signal transmission) requires a relatively large channel width, meaning the receiver must use the entire channel to retrieve the information. Consequently, the extensive use of the spectral band forces the manufacturer to use high carrier frequencies (typically above 1 GHz). However, such waves do not penetrate walls, and this type of system cannot be used interchangeably indoors and outdoors.

[0007] A positioning system for at least one receiving mobile device is also known from patent document EP 4323789 A1, enabling the mobile device itself to position itself precisely by discriminating line-of-sight signals from a transmitting base from various signal bounces (multipath). The system comprises, in addition to the mobile device, at least two fixed transmitting bases. Each transmitting base is configured to transmit radio frequency signals, more precisely to transmit a sum of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of a continuous unmodulated wave, preferably sinusoidal.The transmitting bases are synchronized to transmit their respective signals. The receiving mobile unit is configured to receive and process these radio frequency signals and to deduce its position by calculating the time-of-flight difference(s) between the receiving mobile unit and the transmitting bases. The receiving mobile unit includes means for storing position data from the fixed transmitting bases; means for measuring, for each given signal frequency and for each respective transmitting base, the phase of the signal composed of the different signals originating from that base and exhibiting said frequency; and computing means connected to the measurement and storage means.The receiving mobile's computing resources are configured to: apply, for each transmitting base station, a Fourier transform to a signal composed of the different measured phases of the radio frequency signals originating from that base station; determine, for each transmitting base station and from the Fourier transform, a time-of-flight (TOF) between the receiving mobile and the base station; calculate at least one time-of-flight difference between the mobile and two transmitting bases; and finally, determine the position of the receiving mobile, based on the calculated time-of-flight difference(s) and the position data of the transmitting bases. However, a drawback of such a positioning system is that it does not utilize all the information contained in the signals, such as silences in the signals and / or the presence of signal bounces in time.Therefore, because it does not exhaustively take into account all the information at its disposal, the reliability of position determination by such a positioning system can still be improved. Summary of the invention.

[0008] One 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 positioning system for at least one receiving mobile that allows the mobile itself to position itself accurately, by discriminating between line-of-sight signals from a transmitting base and the various signal bounces (multipath), while improving the reliability and accuracy of the position determination it provides.

[0010] Another objective of the present invention is to provide a positioning system for at least one receiving mobile exhibiting both a large range (typically greater than 10 km) and operating equally well in outdoor and indoor environments, allowing the mobile itself to position itself accurately, and allowing to limit spectral occupancy while exhibiting increased sensitivity and an equivalent noise band reduced to the maximum.

[0011] To this end, the invention relates to a positioning system for 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 emit radio frequency signals, the transmitting bases being synchronized with each other to emit their respective signals, the receiving mobile being configured to receive and process said radio frequency signals and to deduce its position by calculating pseudo-distance(s) between the receiving mobile and the transmitting bases, each radio frequency signal being representative of a path between the receiving mobile and one of the transmitting bases which is either a direct path or a path resulting from one or more signal bounce(s), the receiving mobile comprising means for storing position data of the fixed transmitting bases,in which 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; and the receiving mobile further comprises: • means for determining, for each given signal frequency and for each respective transmitting base, the phase and amplitude of the signal consisting of the different signals originating from said base and exhibiting said frequency, said phase and said amplitude being represented in the frequency domain; and • computing resources connected to the determination resources and storage resources, and configured to: to apply, for each respective transmitting base, on the set of phases and amplitudes of signals represented in the frequency domain, a signal conversion operation from the frequency domain to the time domain, thus providing a set of data in the time domain and a set of pseudo-distances representing the different signal paths; o apply a probability metric extraction tool on said data in the time domain in order to extract, for each emitting base, a direct path probability metric; to associate, for each transmitting base and for each determined pseudo-distance, a potential direct path probability to said pseudo-distance, using the extracted direct path probability metric o generate all possible positions for the receiving mobile; o associate, for each transmitting base and for each possible position of the receiving mobile generated, a pseudo signal path distance to said possible position of the receiving mobile; o associate, for each transmitting base, a probability to each possible position of the receiving mobile generated, from the pseudo signal path distance associated with its potential direct path probability; o determine the most probable position of the receiving mobile, from the set of possible positions of the receiving mobile associated with their probabilities, as well as the position data of the transmitting bases.

[0012] By using a probabilistic method to determine the most probable position of the receiving mobile device, and by measuring both the phase and amplitude of the radio frequency signals from each transmitting base station (for a comb of distinct frequencies, representing this phase and amplitude in the frequency domain), the positioning system according to the invention makes it possible to obtain more information, and in particular all the information contained in the results, such as silences in the signals and / or the presence of signal bounces in time. Among this information, the system according to the invention thus makes it possible to determine the probability that a given radio frequency signal received by the receiving mobile device originates from a direct signal path or from a signal bounce. This is particularly advantageous for clearly distinguishing direct signal paths from signal bounces, and thus improving positioning accuracy.This approach allows the receiving device to distinguish the reflections of the main signal, the latter being the first to arrive at the receiving device (the reflections arriving subsequently). Furthermore, utilizing all available information contained in the time-space results ensures that no signal path is excluded, even if an initial error was made in the distinction. This significantly improves the robustness, reliability, and accuracy of the position determination performed by the system.

[0013] Furthermore, the system's use of pure carrier signals in the form of unmodulated sustained waves limits spectral occupancy, thus ensuring very high system sensitivity by minimizing the equivalent noise band. Such signals exhibit minimal spectral occupancy. This results in a mobile receiver positioning system with a long range, low operating cost, and good wave penetration, functioning equally well outdoors and indoors, and enabling the mobile device itself to position itself precisely. Moreover, unlike many prior art systems, the transmitting bases of the positioning system according to the invention do not transmit any modulated data. This reduces spectral occupancy and therefore the cost and complexity of the system.

[0014] Preferably, the operation of passing the signal from the frequency domain to the time domain is an operation selected from the group consisting of: an inverse Fourier transform and a Lasso method.

[0015] Advantageously, the receiving mobile's computing resources are further configured to apply hidden-parameter Markov model filtering to the receiving mobile's position probabilities. This allows the results to be filtered, thus further improving the accuracy of the receiving mobile's positioning.

[0016] Advantageously, the receiving vehicle further comprises at least one device for measuring a parameter belonging to the group consisting of: a Doppler velocity measuring device and / or a tachometer and / or an accelerometer and / or a barometer and / or a magnetometer, and the computing means of the receiving vehicle are further configured to fuse position and / or distance and / or signal amplitude and / or time and / or velocity and / or acceleration and / or magnetic field direction and / or pressure data from said at least one measuring device and to apply, from said fused data, a further improvement in the reliability and accuracy of the positioning of the receiving vehicle.

[0017] Advantageously, the computing means of the receiving mobile are further configured to generate, for each transmitting base station and from the aforementioned potential direct path probabilities associated with a pseudo-distance, a four-dimensional temporal and spatial map representing the position probabilities of the receiving mobile. This allows for an intercorrelation of the probabilistic results between the fixed transmitting bases (probabilistic distributions represent the travel times for each transmitting base station), thus enabling trilateration between positions. By determining the maximum trilateration on this four-dimensional map, the system according to the invention can determine a position and a time, allowing it to reliably and rapidly determine the most probable position of the receiving mobile.

[0018] Advantageously, for each transmitting base station, the frequency difference between the minimum and maximum frequencies of the pure-carrier signals emitted by said base station is greater than 30 MHz. This reduces the resolution of the results in the time domain, thus improving localization accuracy, typically less than 1 m. This reduced time-domain resolution then improves the separation or discrimination between the line-of-sight signal from a transmitting base station and the various signal bounces (multipath) on the other. The positioning system according to the invention achieves a localization accuracy for the receiving mobile device of less than 1 m, even indoors or in urban environments, without resorting to GPS or GNSS (Global Navigation Satellite System) signals or the installation of additional indoor base stations.

[0019] In a preferred mode, each pure-carrier signal emitted by a transmitting base station has a frequency in the very high frequency band, specifically in the range of 30 MHz to 300 MHz. This provides the best compromise between signal penetration inside buildings, minimizing multipath propagation, and the size of the transmitting and receiving antennas. Furthermore, the use of such signals significantly reduces the bandwidth required. The very high frequency band also offers a wide range of options for using pure sinusoidal signals.

[0020] Preferably, fixed transmitting bases are configured to transmit the same number of unmodulated pure carrier signals.

[0021] Advantageously, the fixed transmitting bases are configured to transmit their sums of unmodulated pure carrier signals with a frequency shift, with a predetermined frequency shift between two successive transmitting bases. This allows the receiving mobile device to distinguish the sums of unmodulated pure carrier signals from each of the transmitting bases.

[0022] Preferably, the frequency offset is within the range of 100 Hz to 1 kHz. Such a frequency offset allows the signals generated by the different transmitting bases to be easily separated by the receiving mobile device, while remaining within the same frequency channel (with a frequency bandwidth of 6.25 kHz or 12.5 kHz, in the very high frequency band). This limits the number of frequency channels occupied and consequently reduces the system implementation cost.

[0023] According to a particular technical feature of the invention, the fixed transmitting bases are antennas, preferably antennas distributed in such a way that the distance between two adjacent antennas is greater than or equal to 300 m, typically on the order of 500 m.

[0024] According to another particular technical feature of the invention, the receiving mobile is a chip or an electronic card or even a mobile communication device such as a mobile phone.

[0025] Preferably, each fixed transmitting base is configured to synchronize the unmodulated pure carrier signals emitted by the base with each other.

[0026] According to a particular technical feature of the invention, each fixed transmitting base is configured to emit a sum Si of N unmodulated sinusoidal signals of distinct frequencies wk, said sum Si satisfying the form of the following equation (1):

[0027] [Math.Eq(l)] N SI = cos(cû k t) k=l

[0028] 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 emit radio frequency signals, the transmitting bases being synchronized with each other to emit their respective signals, the receiving mobile comprising means for determining the phases and amplitudes of signals in the frequency domain, data storage means, and computing means connected to the determination means and 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, wherein 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 sustained wave, preferably sinusoidal; • a reception, by the receiving mobile, of radio frequency signals from the transmitting bases, said radio frequency signals being received in an undifferentiated manner, each radio frequency signal being representative of a path between the receiving mobile and one of the transmitting bases which is either a direct path or a path resulting from one or more signal bounce(s); • a determination, by the receiving mobile, for each given signal frequency and for each respective transmitting base, of the phase and amplitude of the signal made up of the different signals from said base and presenting said frequency, said phase and said amplitude being represented in the frequency domain; • an application, by the receiving mobile, for each respective transmitting base, on all the phases and amplitudes of signals represented in the frequency domain, of a signal conversion operation from the frequency domain to the time domain, thus providing a set of data in the time domain and a set of pseudo-distances representing the different signal paths; • an application, by the receiving mobile, of a probability metric extraction tool on said data in the time domain in order to extract, for each sending base, a direct path probability metric; • an association, by the receiving mobile, for each transmitting base and for each determined pseudo-distance, of a potential direct path probability at said pseudo-distance, using the extracted direct path probability metric; • a generation, by the receiving mobile, of the set of possible positions for the receiving mobile; • an association, by the receiving mobile, for each transmitting base and for each possible position of the receiving mobile generated, of a pseudo signal path distance to said possible position of the receiving mobile; • an association, by the receiving mobile, for each transmitting base, of a probability at each possible position of the receiving mobile generated, from the pseudo signal path distance associated with its potential direct path probability; • a determination, by the receiving mobile, of its most probable position, from the set of possible positions of the receiving mobile associated with their probabilities, as well as the position data of the transmitting bases.

[0029] Preferably, during the step of applying a signal conversion operation from the frequency domain to the time domain, the operation is selected from the group consisting of: an inverse Fourier transform and a Lasso method.

[0030] Advantageously, during the application step of a probability metric extraction tool, said probability metric extraction tool consists of a convolution that is applied to the shape and / or amplitude and / or silences of the signal in the time domain. Brief description of the figures

[0031] Other features and advantages of the invention will become apparent from the detailed description below and the accompanying figures, in which:

[0032] [Fig. 1] shows a diagram of a positioning system for a receiving mobile according to the invention, and

[0033] [Fig. 2] shows a flowchart representing a method of positioning a receiving mobile according to the invention, implemented by the system of figure 1. Detailed description of the invention

[0034] In the following, a positioning system 1 for a receiving mobile 2 is disclosed. The system 1 comprises, in addition to the receiving mobile 2, at least two fixed transmitting bases 4. In the particular embodiment shown in Figure 1, which depicts such a positioning system 1, the system 1 comprises two fixed transmitting bases 4A, 4B. However, the invention applies equally to any positioning system comprising two or more transmitting bases, and preferably three or more. Providing at least three transmitting bases in the positioning system ensures greater robustness for the system.

[0035] The receiving mobile unit 2 is configured to receive and process radio frequency signals scLA, sdB, srA, and srB from the fixed transmitting bases 4A and 4B, and to deduce its position by calculating pseudo-distances between the receiving mobile unit 2 and the transmitting bases 4A and 4B (as will be described later). This pseudo-distance calculation avoids any time synchronization constraints between the receiving mobile unit 2 and the transmitting bases 4A and 4B.

[0036] The receiving unit 2 includes storage means (not shown) configured to store position data from the fixed transmitting bases 4A and 4B. The storage means typically consist of memory, typically non-volatile memory. The receiving unit 2 further includes means for determining the phases and amplitudes of radio frequency signals in the frequency domain. These means are not shown in the figures for clarity. Such means include, in particular, means for measuring the phases and amplitudes of radio frequency signals in the frequency domain, and means for converting these phases and amplitudes measured in the time domain to the frequency domain. The receiving unit 2 also includes computing means (not shown) connected to the determination and storage means.The means for determining and calculating values ​​typically consist of a processing unit, for example, one or more processors, or integrated within an electronic chip. Preferably, the receiving mobile 2 also includes at least one parameter measurement device (not shown). The parameter measurement device is, for example, a Doppler velocity measuring device and / or a tachometer and / or an accelerometer and / or a barometer and / or a magnetometer.

[0037] By way of non-limiting examples, the receiving mobile 2 typically consists of a chip or an electronic card, for example integrated into a portable device; or a mobile communication device such as a mobile phone. In the case where the receiving mobile 2 consists of an electronic chip or a mobile communication device such as a mobile phone, it is typically equipped with an analog-to-digital converter.

[0038] Each transmitting base 4A, 4B is typically an antenna for transmitting SIA, S1B, scLA, sdB, srA, and srB radio frequency signals. Preferably, when the transmitting bases 4A, 4B are antennas, they are distributed such that the distance between two adjacent antennas is greater than or equal to 300 m, typically (and without limitation) on the order of 500 m. 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," we mean that the phase difference between the signals emitted by the different transmitting bases 4A, 4B is constant, in order to avoid drift in the signals and thus prevent distortion of the measurement performed by the receiving mobile unit 2 for its positioning.

[0039] Each transmitting base 4A, 4B is configured to transmit a sum Si A, S1B of at least two unmodulated pure carrier signals of distinct frequencies. Each pure carrier signal is in the form of an unmodulated continuous wave, preferably sinusoidal. In 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 Si A, S1B of N unmodulated sinusoidal signals of distinct frequencies wk. Each sum Si A, S1B of signals satisfies the form of the following general equation (2):

[0040] [Math.Eq(2)] N S1 A,B = COS (œ k t) k=l

[0041] Preferably, the frequency difference between the minimum and maximum frequencies among the wk frequencies of the pure carrier signals emitted by each transmitting base 4A, 4B is greater than 30 MHz. Even more preferably, each pure carrier signal emitted by a transmitting base 4A, 4B has a frequency in the very high frequency band, that is, a frequency in the range from 30 MHz to 300 MHz. Frequency bands belonging to the very high frequencies (VHF) are thus allocated to the fixed transmitting bases 4A, 4B of the positioning system 1.

[0042] Preferably, the fixed transmitting bases 4 are configured to emit the same number N of unmodulated pure carrier signals. According to a preferred embodiment, the transmitting bases 4 are configured to emit their sums Si of unmodulated pure carrier signals with a frequency shift, by a predetermined frequency shift Aw between two successive transmitting bases 4. Thus, in the embodiment illustrated in Figure 1, a first transmitting base 4A, and respectively a second transmitting base 4B, is configured to emit a sum Si A, and respectively S1B, of unmodulated sinusoidal signals satisfying the following equation (3), and respectively the following equation (4):

[0043] [Math.Eq(3)] N 51^ = cos (œ k t) k=l

[0044] [Math.Eq(4)] N S1 B = cos((co k + A(jû)t) k=l

[0045] The sums SIA and S1B of sinusoidal signals are thus frequency-shifted by a frequency shift Aw (expressed, for example, in rad / s). The frequency shift Aw is preferably in the range of 100 Hz to 1 kHz. Each transmitting base 4A, 4B is advantageously configured to synchronize the sinusoidal signals it transmits.

[0046] Referring 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 and 02 are buildings here, but could alternatively be any other type of structure without affecting the reasoning that follows. For each transmitting base 4A, 4B, the radio frequency signals received by the receiving mobile 2 and originating from this base 4A, 4B are divided into two types: the first type consists of SdA and SdB signals arriving via direct line of sight, and the second type consists of s signals r A, SrB arriving at the receiving mobile 2 following a bounce off an obstacle 01, 02. The SdA signals, s r A, respectively SdB, s rB, each correspond to the sum S1A, respectively S1B, of unmodulated pure carrier signals, but they follow different paths. DA, respectively DB, is the line-of-sight distance between the receiving mobile 2 and the first transmitting base 4A, respectively the second transmitting base 4B, traversed by the signals SdA, respectively SdB. D r A, respectively D r B, the distance traveled by the signals s r A, respectively s r B after bouncing off an obstacle 01, respectively 02. For the sake of simplification, we will subsequently consider, for the first transmitting base 4A, only the radio frequency signals from this base and having bounced off the obstacle 01 closest to this base 4A (the impact of the signals from this base and having bounced off the other obstacle 02 being considered negligible).

[0047] Similarly, for the second transmitting base 4B, only the radio frequency signals originating from this base and having bounced off the obstacle 02 closest to this base 4B are considered (the impact of signals originating from this base and having bounced off the other obstacle 01 being considered negligible). Furthermore, for simplicity, it is assumed that the radio frequency signals only bounce once off one of the obstacles 01, 02.

[0048] The positioning process of the receiving mobile 2, implemented by the positioning system 1, will now be described in detail, with reference in particular to Figure 2.

[0049] The process includes an initial step 10 of transmitting position data from the fixed transmitting bases 4A, 4B to the storage means of the receiving mobile unit 2. This transmission 10 may, for example, consist of each transmitting base 4A, 4B transmitting its position coordinates to the receiving mobile unit 2, or of pre-programming the position coordinates of the bases within the receiving mobile unit 2 during its manufacture or configuration. Following this initial step 10, the storage means of the receiving mobile unit 2 store the position data of the transmitting bases 4A, 4B.

[0050] The process includes a subsequent step 12 in which each transmitting base 4A, 4B emits the sum S1A, S1B of unmodulated pure carrier signals of distinct frequencies wk. The phase shift between the signals S1A, S1B emitted by the different transmitting bases 4A, 4B is constant. The sums S1A and S1B of pure carrier signals emitted by the bases 4A, 4B are thus frequency-shifted by a frequency shift Aw. The different frequencies wk used by the bases 4A, 4B, as well as the frequency shift Aw, are known by the receiving mobile 2 (pre-implanted in or transmitted to it).

[0051] In a subsequent step 14, the receiving mobile 2 indiscriminately receives the radio frequency signals scLA, sdB, srA, srB from the transmitting bases 4A and 4B. These signals scLA, srA, sdB, and srB, 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 these signals are frequency-shifted by a predetermined frequency shift (known to the receiving mobile 2), the receiving mobile 2 can distinguish the scLA and srA signals from the first base 4A from the sdB and srB signals from the second transmitting base 4B.

[0052] In a subsequent step 16, the receiving mobile 2 determines, using its determination means, for each given signal frequency wk and for each transmitting base 4A, 4B, the phase and amplitude of the signal consisting of the different signals sdA, srA; respectively sdB, srB, originating from this base 4A, 4B and exhibiting the frequency wk. Indeed, for example, for the first base 4A and for a given frequency wk, the two signals sdA(wk) and srA(wk) are received by the receiving mobile 2 in a mixed state. The phase determined (in other words, measured in the time domain) by the receiving mobile 2 for the frequency wk then corresponds to the phase of the signal consisting of the sum of the direct signal sdA and the reflected signal srA. Similarly, the amplitude determined (in other words, measured in the time domain) by the receiving mobile 2 for the frequency wk corresponds to the amplitude of the signal consisting of the sum of the direct signal sdA and the bounce signal srA.The same reasoning applies to the sdB and srB signals from the second base 4B. In one particular implementation, phase determination can be achieved by applying a multiplication factor eiwk to each signal composed of the different signals sdA and srA, respectively sdB and srB, from the first base 4A and second base 4B. This allows the phase and amplitude of each unmodulated pure carrier signal to be isolated for each frequency. Following this step, the determination means for the receiving mobile device represent, in the frequency domain, the phases and amplitudes of the signals initially measured in the time domain.

[0053] In a subsequent step 18, the receiving mobile 2 applies, via its computing resources and for each of the transmitting bases 4A, 4B, a signal conversion operation from the frequency domain to the time domain on all the phases and amplitudes of signals represented in the frequency domain for that base 4A, 4B. At the end of this application step 18, a set of data in the time domain and a set of pseudo-distances representing the different signal paths are obtained. Preferably, the signal conversion operation from the frequency domain to the time domain is an inverse Fourier transform or a Lasso method. The Lasso method is particularly preferred when the distinct frequencies wk are not uniformly distributed.

[0054] In a subsequent step 20, the receiving mobile device 2 applies, via its computing resources, a probability metric extraction tool to the time-domain data obtained at the end of step 18. This allows the extraction, for each transmitting base station 4A, 4B, of a direct path probability metric (which will then allow the direct path to be distinguished from the bounce paths of the signals originating from this base station 4A, 4B). Preferably, the probability metric extraction tool used for the calculation in step 20 consists of a convolution applied to the results in the time domain (typically the shape and / or peaks and / or silences of the signal). Applying such a convolution notably highlights the line-of-sight path relative to the location of the gap (silence, direct path, then bounce tail) and the profile of the signal bounces.To achieve this, the computing means of the receiving mobile 2 have an ideal profile of the temporal response of a line-of-sight signal followed by one or more bounces caused by obstacles. They also have information indicating that the ideal temporal response profile of a line-of-sight signal is silence, the signal bounce profile exhibits increasingly thin bounce tails, and the position of a line-of-sight signal is prior to the position of a signal bounce.

[0055] In a subsequent step 22, for each transmitting base 4A, 4B and for each pseudo-distance determined in step 18, the computing means of the receiving mobile 2 associate a potential direct path probability with this pseudo-distance. This is done using, in particular, the direct path probability metric extracted in the previous step 20.

[0056] In a subsequent step 24, the receiving mobile 2 generates, via its computing means, the set of possible positions for the receiving mobile 2.

[0057] In a subsequent step 26, for each transmitting base 4A, 4B and for each possible position of the receiving mobile 2 generated during step 24, the computing means of the receiving mobile 2 associate a pseudo signal path distance with this possible position of the receiving mobile 2.

[0058] In a subsequent step 28, for each transmitting base 4A, 4B, the computing means of the receiving mobile 2 associate a probability with each possible position of the receiving mobile 2 generated during step 24. This association is carried out, for each transmitting base 4A, 4B and for each possible position of the receiving mobile 2, by means of the corresponding pseudo signal path distance which was associated with it during step 26 (as well as its potential direct path probability associated with it during step 22).

[0059] Preferably, at the end of step 28, the computing resources of the receiving mobile 2 generate, for each transmitting base 4A, 4B, a four-dimensional temporal and spatial map representing the position probabilities of the receiving mobile 2 determined during step 28. This map is generated from the potential direct path probabilities associated with a pseudo-distance (with probabilistic distributions overlaid on the map to represent the travel times for each transmitting base 4A, 4B). On such a map, direct paths can potentially be confused with signal bounce paths and aberrations. Therefore, the latter are not eliminated from the map but are represented by a nominally lower probability.

[0060] Preferably, at the end of this step 28, the computing means of the receiving mobile 2 apply a filtering with a hidden parameter Markov model on the position probabilities of the receiving mobile 2 determined during step 28.

[0061] Preferably, at the end of this step 28, the computing means of the receiving mobile 2 apply a weighting to the probabilities of the position of the receiving mobile 2 determined during step 28. The application of a weighting is for example carried out from fused data of position and / or distance and / or signal amplitude and / or time and / or speed and / or acceleration and / or direction of magnetic field and / or pressure from the device measuring a parameter.

[0062] In a final step 30, the computing means of the receiving mobile 2 determine the most probable position of the receiving mobile 2, based on the set of possible positions of the receiving mobile associated with their probabilities (obtained in step 28), as well as the position data of the transmitting bases 4A, 4B, previously stored in the storage means. To do this, using the detailed map previously, the computing means of the receiving mobile 2 can apply a maximum function (or alternatively an average function) to extract from the map a most probable position of the receiving mobile 2 (and an associated time).

[0063] By combining phase and amplitude determinations (in the frequency domain) of radio frequency signals from each transmitting base station with the use of a probabilistic method to determine the most probable position of the receiving mobile 2, as well as the calculation of pseudo-distances, it is clear from the foregoing that the system 1 according to the invention advantageously discriminates between line-of-sight signals from a transmitting base station and various signal bounces (multipath), while simultaneously improving the reliability, accuracy, and robustness of its position determination. Furthermore, the receiving mobile 2 performs its own positioning autonomously.Finally, positioning system 1 offers both a long range (typically exceeding 10 km), operates equally well outdoors and indoors, and features limited spectral occupancy, increased sensitivity, and a minimal equivalent noise band. All these characteristics, combined in a single system, are particularly advantageous compared to the various positioning systems of the prior art.

Claims

DEMANDS:

1. A positioning system (1) for at least one receiving mobile (2), the system (1) comprising, in addition to the mobile (2), at least two fixed transmitting bases (4, 4A, 4B), each transmitting base (4, 4A, 4B) being configured to transmit radio frequency signals (S1A, S1B, SdA, SdB, s r A, SÆ), the transmitting bases (4, 4A, 4B) being synchronized with each other to transmit their respective signals, the receiving mobile (2) being configured to receive and process said radio frequency signals (sdA, SdB, s rA, SÆ) and to deduce its position by calculating pseudo-distance(s) between the receiving mobile (2) and the transmitting bases (4, 4A, 4B), each radio frequency signal being representative of a path between the receiving mobile and one of the transmitting bases which is either a direct path or a path resulting from one or more signal bounce(s), the receiving mobile (2) comprising means for storing position data of the fixed transmitting bases (4, 4A, 4B), characterized in that each transmitting base (4, 4A, 4B) is configured to emit a sum (S 1A, S 1B) of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated sustained wave, preferably sinusoidal; and in that the receiving mobile (2) further comprises: • means of determining, for each given signal frequency and for each respective transmitting base (4, 4A, 4B), the phase and amplitude of the signal consisting of the different signals (sdA, srA; sdB, srB) originating from said base and exhibiting said frequency, said phase and said amplitude being represented in the frequency domain; and • computing resources connected to the determination resources and storage resources, and configured to: o apply, for each respective transmitting base (4, 4A, 4B), on the set of phases and amplitudes of signals represented in the frequency domain, a signal conversion operation from the frequency domain to the time domain, thus providing a data set in the time domain and a set of pseudodistances representing the different signal paths; o apply a probability metric extraction tool to said data in the time domain in order to extract, for each transmitting base (4, 4A, 4B), a direct path probability metric; o associate, for each transmitting base (4, 4A, 4B) and for each determined pseudodistance, a potential direct path probability to said pseudodistance, using the extracted direct path probability metric; o generate all possible positions for the receiving mobile (2); to associate, for each transmitting base (4, 4A, 4B) and for each possible position of the receiving mobile (2) generated, a pseudo-distance of signal path to said possible position of the receiving mobile (2); to associate, for each transmitting base (4, 4A, 4B), a probability to each possible position of the receiving mobile (2) generated from the pseudo signal path distance associated with its potential direct path probability; to determine the most probable position of the receiving mobile (2), from the set of possible positions of the receiving mobile (2) associated with their probabilities, as well as the position data of the transmitting bases (4, 4A, 4B).

2. System (1) according to the preceding claim, characterized in that the operation of passing the signal from the frequency domain to the time domain is an operation selected from the group consisting of: an inverse Fourier transform and a Lasso method.

3. System (1) according to claim 1 or 2, characterized in that the computing means of the receiving mobile (2) are further configured to apply hidden parameter Markov model filtering on the position probabilities of the receiving mobile (2).

4. System (1) according to any one of the preceding claims, characterized in that the receiving mobile (2) further comprises at least one parameter measurement device belonging to the group consisting of: a Doppler velocity measurement device and / or a tachometer and / or an accelerometer and / or a barometer and / or a magnetometer, and in that the computing means of the receiving mobile (2) are further configured to fuse position and / or distance and / or signal amplitude and / or time and / or velocity and / or acceleration and / or magnetic field direction and / or pressure data from said at least one measurement device and to apply, from said fused data, a weighting to said position probabilities of the receiving mobile (2).

5. System (1) according to any one of the preceding claims, characterized in that the computing means of the receiving mobile (2) are further configured to generate, for each transmitting base (4, 4A, 4B) and from said potential direct path probabilities associated with a pseudo-distance, a four-dimensional temporal and spatial map representing the position probabilities of the receiving mobile (2).

6. System (1) according to any one of the preceding claims, characterized in that, for each transmitting base (4, 4A, 4B), the frequency difference between the minimum frequency and the maximum frequency of the pure carrier signals emitted by said base (4, 4A, 4B) is greater than 30 MHz.

7. System (1) according to any one of the preceding claims, characterized in that each pure carrier signal emitted by a transmitting base (4, 4A, 4B) has a frequency in the very high frequency band, in other words has a frequency in the range from 30 MHz to 300 MHz.

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

9. Method for positioning at least one receiving mobile (2), implemented by a positioning system (1) comprising, in addition to the mobile (2), at least two fixed transmitting bases (4, 4A, 4B), each transmitting base (4, 4A, 4B) being configured to transmit radio frequency signals (Si A, S1B, scLA, sdB, srA, srB), the transmitting bases (4, 4A, 4B) being synchronized with each other to transmit their respective signals, the receiving mobile (2) comprising means for determining the phases and amplitudes of signals in the frequency domain, means for storing data, and computing means connected to the determination means and the storage means, the method comprising an initial step (10) of transmitting position data from the fixed transmitting bases (4A, 4B) to the storage means of the receiving mobile (2), characterized in that it further comprises the following steps: • an emission (12), by each of the transmitting bases (4A, 4B), of a sum (Si A, S1B) of at least two unmodulated pure carrier signals of distinct frequencies, each pure carrier signal being in the form of an unmodulated sustained wave, preferably sinusoidal; • a reception (14), by the receiving mobile (2), of radio frequency signals (scLA, sdB, srA, srB) from the transmitting bases (4A, 4B), said radio frequency signals being received in an undifferentiated manner, each radio frequency signal being representative of a path between the receiving mobile and one of the transmitting bases which is either a direct path or a path resulting from one or more signal bounce(s); • a determination (16), by the receiving mobile (2), for each given signal frequency and for each respective transmitting base (4A, 4B), of the phase and amplitude of the signal consisting of the different signals (sdA, srA; sdB, srB) from said base and presenting said frequency, said phase and said amplitude being represented in the frequency domain; • an application (18), by the receiving mobile (2), for each respective transmitting base (4A, 4B), on the set of phases and amplitudes of signals represented in the frequency domain, of a signal transition operation from the frequency domain to the time domain, thus providing a set of data in the time domain and a set of pseudo-distances representing the different signal paths; • an application (20), by the receiving mobile (2), of a probability metric extraction tool on said data in the time domain in order to extract, for each transmitting base (4A, 4B), a direct path probability metric; • an association (22), by the receiving mobile (2), for each transmitting base (4A, 4B) and for each determined pseudo-distance, of a potential direct path probability at said pseudo-distance, using the extracted direct path probability metric; • a generation (24), by the receiving mobile (2), of the set of possible positions for the receiving mobile (2); • an association (26), by the receiving mobile (2), for each transmitting base (4, 4A, 4B) and for each possible position of the receiving mobile (2) generated, of a pseudo signal path distance to said possible position of the receiving mobile (2); • an association (28), by the receiving mobile (2), for each transmitting base (4, 4A, 4B), of a probability at each possible position of the receiving mobile (2) generated, from the pseudo signal path distance associated with its potential direct path probability; • a determination (30), by the receiving mobile (2), of its most probable position, from the set of possible positions of the receiving mobile (2) associated with their probabilities, as well as the position data of the transmitting bases (4A, 4B).

10. Method according to claim 9, characterized in that, during the step (18) of applying a signal conversion operation from the frequency domain to the time domain, the operation is selected from the group consisting of: an inverse Fourier transform and a Lasso method.

11. Method according to claim 9 or 10, characterized in that, during step (20) of applying a probability metric extraction tool, said probability metric extraction tool consists of a convolution which is applied to the shape and / or amplitude and / or silences of the signal in the time domain.

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