WO2017081417A1

WO2017081417A1 - Method and system for the geolocalisation of a beacon by means of time-stamping

Info

Publication number: WO2017081417A1
Application number: PCT/FR2016/052919
Authority: WO
Inventors: Yan MENNEKENS
Original assignee: Uwinloc
Priority date: 2015-11-11
Filing date: 2016-11-10
Publication date: 2017-05-18
Also published as: FR3043468A1; FR3043468B1

Abstract

The invention relates to a method for the geolocalisation of a beacon by a geolocalisation server on the basis of a plurality of time-stamping terminals, each of the terminals that has a position known by the server being identified by a unique identifier and able to communicate with the other time-stamping terminals of the plurality of time-stamping terminals over an ultra-wideband radio communication link. The method particularly comprises a step (E6) of calculation of clock differences between the terminals, by a geolocalisation server, on the basis of time-stamped reference pulses, a step (E8) of compensating the time-stamping instants of received time-stamped messages on the basis of the calculated differences, and a step (E9) of localisation of the beacon on the basis of the compensated time-stamping instants.

Description

METHOD AND SYSTEM FOR GEOLOCATING A BEACON

BY DAMPING

TECHNICAL AREA

The present invention relates to the field of localization and relates more particularly to a method and a geolocation system of a beacon. The invention is particularly applicable to the geolocation of objects stored in a warehouse.

STATE OF THE ART

Nowadays, there are several types of geolocation systems for objects or people. These systems use a mobile device which one wants to know the geographical location or "geolocation".

In the known solution called GPS (Global Positioning System), the system comprises a plurality of satellite-type transceivers, fixed with respect to the Earth, and the device is a mobile receiver which receives detection signals emitted, continuous or periodic, by the plurality of satellites. The mobile receiver compares the transmission delays of each received signal to determine its position by trilateration.

However, the signals sent by the satellites can not always be received inside a structure such as a warehouse or a building, which does not make it possible to precisely locate objects in a closed space and thus presents a disadvantage . In addition, the mobile receiver device must perform the trilateration calculations from the transmission delays of each received signal, which makes it complex and expensive and therefore has another disadvantage. Moreover, such a satellite geolocation system may have a low precision, of the order of 5 to 10 meters because of the distance between the satellites and the mobile receiver device and because of the Earth's atmosphere, which can be problematic when you want geolocate objects of small dimensions. In addition, the clock of each transceiver can naturally and in a known manner derive, which causes errors of geolocation. For example, a temperature controlled crystal oscillator has a precision of the order of 50 ppb and the signal travels about 15 cm in 500 ps. Also, a shift greater than 500 ps between the clocks of two transmitters may correspond to a geolocation error greater than 15 cm, which may result in the case of satellites, given the distance, into an error of several meters. To limit these errors, it is therefore necessary to synchronize the transmitters with each other so that the mobile receiver device can compare the transmission delays of each received signal and thus determine its position. Such synchronization is however complex and expensive, which has a major disadvantage. GENERAL PRESENTATION OF THE INVENTION

For this purpose, the invention firstly relates to a geolocation method of a beacon by a geolocation server from a plurality of timestamps, each of the terminals, whose position is known to said server , being identified by a unique identifier and being able to communicate with the other timestamps of the plurality of timestamps, said method comprising:

a step of transmitting, on an ultra wideband radio communication link, a reference pulse by each of the timestamp terminals to the other timestamp terminals, said reference pulse comprising the identifier of the terminal d 'program,

a step of reception by each of the timestamp terminals of the reference pulses emitted by the other timestamp terminals,

a time stamping step, on reception, by each of the timestamp terminals of the reference pulses received from the other terminals,

a step of sending, by each of the time stamping terminals, to the geolocation server, time-stamped reference pulses,

a step of reception by the geolocation server of the pulses of time-stamped reference sent by each of the timestamping terminals, a step of calculation by the geolocation server of the differences (or offsets) of clock between the terminals from the time-stamped reference pulses and the known position of the terminals,

a step of reception by the geolocation server of a plurality of time-stamped location messages, each received time-stamped location message corresponding to the same location message previously broadcast by the beacon on the ultra wideband radio communication link, and which has has been timestamped and sent by one (and only one) of the timestamps,

a compensation step, by the geolocation server, based on the calculated differences, the time stamp instants of the time stamped location messages received, and

a step of locating, by the geolocation server, the beacon from the compensated timestamp times.

By "ultra broadband" radio communication link, it is meant that a signal transmitted on such a communication link has an instantaneous frequency spectrum of width (at -10 dB relative to the maximum power of said instantaneous frequency spectrum) greater than 500 MHz.

In particular modes of implementation, the geolocation method may further comprise one or more of the following characteristics, taken in isolation or in any technically possible combination.

In particular modes of implementation, the ultra-wideband radio communication link on which the reference pulses are transmitted by the time stamp terminals and on which the location messages are broadcast by the beacon is of modulation type. radio pulses. The ultrahigh-band radio-pulse modulation technology (or IR-UWB for "Impulse Radio Ultra Wide Band" in the English literature), is based on the transmission of pulses of very short duration, that is to say less than two nanoseconds, or even less than one nanosecond. In particular modes of implementation, the ultra-wideband radio communication link on which the reference pulses are transmitted by the time stamp terminals and on which the location messages are broadcast by the beacon uses a radio pulse modulation. in all or nothing (known by the acronym OOK for "On-Off Keying" in the Anglo-Saxon literature).

In particular modes of implementation, the reference pulses and the location messages are formed of information symbols, and the timestamps and the beacon are configured to modulate the same spreading sequence predefined by each symbol d. information so as to obtain, for each information symbol, a sequence of spreading symbols used for the modulation of radio pulses. Thus, the information symbols are subjected to a direct sequence spread spectrum (DSSS for "Direct Sequence Spread Spectrum" in the Anglo-Saxon literature) which makes it possible to introduce a gain of reception processing facilitating the detection of the signal and extracting the reference pulse or the location message. The spreading sequence is for example a pseudo-random sequence, such as an M-sequence which has particular correlation properties. However, according to other examples, nothing excludes having a spreading sequence of another type, such as a so-called "Gold" or "Barker" or "Hadamard-Walsh" sequence. etc. An ultra wide band signal with radio pulse modulation has several advantages, including good robustness to difficult environments (greater resistance to interference related to the multiple paths of the signal), simplicity of realization of the transmitter and receiver devices (and therefore a cost potentially low cost), low energy consumption (which is essential for an energetically passive beacon), and a high geolocation capability (the accuracy of the position measurements being directly related to the bandwidth and the sampling frequency of the device). reception system). On the other hand, in order to transmit the time stamping information (time-stamped location messages or time-stamped reference pulses) to the geolocation server, it is possible to use a wired or wireless communication link that is not ultra wideband, for example. example a communication link type 3G, 4G, Wifi, Ethernet, etc.

With the method according to the invention, it is not necessary to synchronize the clocks of the terminals to prevent them from drifting. Indeed, the method according to the invention makes it possible to compensate or correct the transmission delays of the signals between the beacon and the terminals from reference pulses exchanged between the terminals. Such compensation makes it possible to ensure that the clock differences between the clocks of the terminals remain low, preferably less than 500 ps in order to be able to geolocate a beacon with an accuracy of less than 15 cm. The method can thus advantageously be used in a closed space, for example such as a warehouse or a building. In addition, since the beacon merely broadcast a signal comprising a location message including its identifier and no location calculation is performed by the beacon, it is simple and inexpensive, which reduces the complexity and cost of the system.

In particular modes of implementation, the time stamping step further comprises inserting the identifier of the terminal performing the time stamp in each reference pulse timestamped (previously received from another terminal).

In particular modes of implementation, the step of calculating the clock differences is performed between the timestamp terminals two by two.

In particular modes of implementation, the clock difference between two terminals A and B is calculated according to the following equation:

or :

- is the instant of reception, by the terminal A, of a reference pulse by the terminal C,

- is the moment of reception, by the terminal B, of the reference pulse sent by the terminal C,

- is the signal transmission delay between terminal A and terminal C,

- is the signal transmission delay between terminal B and terminal C.

Advantageously, the clock difference between two terminals A and B can be determined at a time t3 between two calculations of clock differences by the server, at times t1 and t2, according to the following e uation:

or :

is the clock difference between the terminal A and the terminal B computed by the server at a time t1,

is the clock difference between terminal A and terminal B calculated by

the server at a time t2, later than the instant t1,

t3 is an instant between time t1 and time t2. In particular modes of implementation, the location is achieved by trilateration, which is an easy method of localization.

In particular modes of implementation, the transmission of a reference pulse by each of the terminals to the other terminals is carried out periodically, for example with a period of between one millisecond and one hour. Preferably, the period is of the order of a few hundreds of seconds in order to prevent the clocks of the terminals from drifting too much relative to each other while avoiding consuming too much energy with a too high transmission frequency .

The invention also relates to a time stamping terminal of a beacon geolocation system, said system comprising a plurality of terminals time stamp, said terminal being able to communicate with the other terminals of the system and comprising:

a reception module configured to receive, on an ultra wideband radio communication link, reference pulses emitted by the other timestamp terminals, and location messages broadcast by the beacon,

a timestamp module configured to timestamp reference pulses and location messages received by the reception module, and

a transmission module configured to transmit, on the one hand, periodically on an ultra wideband radio communication link, a reference pulse destined for the other terminals, and to transmit on the other hand, for example periodically, to a geolocation server a plurality of reference pulses and a plurality of location messages timestamped by the timestamp module.

In particular embodiments, the time stamp terminal may further comprise one or more of the following characteristics, taken separately or in any technically possible combination.

In particular embodiments, the ultra-wideband radio communication link on which are received the reference pulses emitted by the other terminals and the location messages broadcast by the beacon and on which the reference pulses are sent to the others. terminals is of type radio pulse modulation.

In particular embodiments, the ultra wideband communication link on which the reference pulses emitted by the other terminals and the location messages broadcast by the beacon and on which the reference pulses are sent to the other terminals are received. uses radio pulse modulation in all or nothing.

In particular embodiments, the signals that the module of receiver is configured to receive beacon or other terminals, and that the transmitting module is configured to transmit to the other terminals, have spreading symbols, each spreading symbol sequence corresponding to the same sequence of predefined spread modulated by an information symbol of the reference pulse or the location message.

Thus, advantageously, when it emits a reference pulse, each terminal behaves as a beacon from the point of view of the other terminals.

In particular embodiments, the terminal being identified by a unique identifier in the system, the timestamp module is configured to insert the identifier of the terminal in each timestamp reference pulse received from another terminal.

The invention also relates to a geolocation server of a beacon from a plurality of time stamping terminals as presented above, the position of each of the terminals being known from said server, said beacon being configured to broadcast a signal comprising a location message comprising an identifier of the tag, the server comprising:

a reception module configured, on the one hand, to receive a plurality of time-stamped location messages, each received time-stamped location message corresponding to the same location message previously broadcast by the beacon on an ultra wideband radio communication link, and which has been timestamped and sent by one (and only one) of the timestamps, and, on the other hand, to receive a plurality of sets of reference pulses, each set having been sent by the one (and only one) of the timestamps and comprising a plurality of reference pulses timestamped by said transmitting terminal,

a module for calculating the differences (or shifts) in clocking between the time stamp terminals from the plurality of received sets and the known position of the terminals,

a module for compensating the instant of time stamping of each message time-stamped location received from the calculated differences,

a module for locating the tag by trilateration from the compensated timestamp times. By using an ultra-wideband radio pulse modulation communication link for the location messages broadcast by the beacon and for the reference pulses emitted by the terminals, it is possible to achieve a very good accuracy for the measurements of their signals. instants of arrival, and thus obtain a geolocation accuracy of the beacon of the order of 15 to 30 cm.

On the other hand, in order to transmit the time stamping information (time-stamped location messages or time-stamped reference pulses) to the geolocation server, it is possible to use a wired or wireless communication link that is not ultra wideband, for example. example a communication link type 3G, 4G, Wifi, Ethernet, etc.

A set of clocked reference pulses comprises the reference pulses received and time stamped by the same terminal over a so-called "calibration" time interval, for example of the order of a few seconds, during which each terminal transmits a pulse at its destination. others. This calibration time interval is preferably periodic, for example every 1000 seconds, and may for example be triggered by the server via a control message sent to the terminals. The calibration time interval allows each terminal to receive the reference pulses sent by the other terminals, time stamp them and send them to the server so that it can periodically evaluate the drifts of the terminal clocks relative to each other. to others in order to compensate for the timestamps of the messages emitted by the beacon and to allow precise localization.

Preferably, the calculation module is configured to calculate the clock difference between two terminals A and B according to the following equation:

is the instant of emission of a reference pulse by the terminal A, is the moment of reception, by the terminal B, of the reference pulse

sent by terminal A,

is the delay of signal transmission between terminal A and terminal C, is the delay of signal transmission between terminal B and terminal C.

More preferably, the calculation module is configured to determine the clock difference between two terminals A and B at a time t3 between two calculations of clock differences by the server, at times t1 and t2, according to the equation next :

or :

is the clock difference between terminal A and terminal B calculated by

the server at a time t1,

- is the clock difference between terminal A and terminal B calculated by

the server at a time t2, later than the instant t1,

t3 is an instant between time t1 and time t2.

Advantageously, the geolocation server further comprises a transmission module configured to transmit or make available the geographical position of the beacon 10 determined by the location module, for example so that an operator can quickly find the object on which the tag is placed.

The invention also relates to a system comprising a plurality of time stamping terminals as presented above and at least one geolocation server as presented above. DESCRIPTION OF THE FIGURES

Figure 1 schematically illustrates an embodiment of the system according to the invention.

FIG. 2 schematically illustrates an embodiment of a time stamp terminal according to the invention.

FIG. 3 schematically illustrates an embodiment of a geolocation server according to the invention.

Figure 4 schematically illustrates a system of three terminals for the trilateration of a beacon and the compensation of differences in clocks.

FIG. 5 schematically illustrates a trilateration by the system of FIG. 4.

FIG. 6 schematically illustrates one embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Description of an embodiment of the system according to the invention The system according to the invention will be presented hereinafter with reference to FIGS. 1 to 5.

I. System 1 Firstly, with reference to FIG. 1, the system 1 according to the invention makes it possible to geolocate a beacon 10 placed on an object 3 placed in a space 5, preferably closed such as a room , a building, a warehouse, a factory etc. However, it goes without saying that the system 1 according to the invention could equally well be used in an open space, for example outdoors. In addition, note that the tag 10 could also be mounted or implemented in equipment, for example worn by a user.

The term "geolocation" means the determination of the position of object 3 in space 5. This position can be defined by coordinates, geographical or otherwise, defined in a frame linked to the space 5 or the Earth, for example in two dimensions or in three dimensions. In this illustrative non-limiting example of the scope of the invention, the system 1 comprises a geolocation beacon 10 fixed on the object 3 to be geolocated, four time stamp terminals 20-1, 20-2, 20-3, 20 -4 and a geolocation server 30. It goes without saying that in practice a plurality of tags 10 can be used simultaneously in space 5, for example to manage a stock in a warehouse.

1) Beacon 10 of geolocation

The geolocation tag 10 may for example be in the form of a self-adhesive label tag. The tag 10 is associated with a unique identifier (at least within the system 1), making it possible to associate an object 3 with a position and thus to geolocate the object 3 on which the tag 10 is fixed. This identifier may for example be in the form of a sequence of bits or alphanumeric characters.

The beacon 10 is configured to broadcast recurrently, for example periodically or whenever it has produced and stored sufficient energy, on an ultra-wideband radio communication link K1, to the timestamp terminals 20 -1, 20-2, 20-3, 20-5 4, a signal in which is coded a message called "location" including the identifier of the tag 10. Note that this location message may include, in addition to identifier, other information, preferably of small digital size in order to keep sending the message energy-saving, such as, for example, an external status (open door, alarm triggered ...), a temperature measurement, etc.

The broadcast period of the location message is preferably low, for example of the order of a few tenths of a second or a few seconds. This period can be variable by being determined by reaching a level sufficient energy from the beacon 10 to transmit the signal.

The radio communication link is advantageously ultra-wideband type with radio pulse modulation in order to benefit from the advantages inherent in such a type of signal, ie it requires little energy to be emitted by the beacon 10, it allows a high accuracy in estimating the arrival time of a location message by a timestamp terminal, and the transmission module of such a signal is relatively simple and inexpensive to achieve. In a preferred embodiment, the beacon 10 is configured to produce and store electrical energy from an electromagnetic field generated for example by the time stamp terminals 20-1, 20-2, 20-3, 20-2. -4. In another embodiment, the beacon 10 could produce and store electrical energy from solar energy, received via a solar collector, or kinetic energy generated by the vibrations or displacements of the beacon 10. note that any suitable form of energy collection or production

electric could be considered. It will also be noted that, in another embodiment, the beacon 10 could comprise a battery for supplying electrical energy.

2) Time stamp terminal 20-1, 20-2. 20-3, 20-4

Each time stamp terminal 20-1, 20-2, 20-3, 20-4 is identified by a unique identifier in the system 1, for example a series of alphanumeric characters.

The number of four timestamps of this example is not limiting to the scope of the present invention which could include more or fewer than four depending on the configuration of the closed space 5 or the desired degree of accuracy of the location. . The use of four timestamps makes it possible to locate an object in space, that is to say in three dimensions. The use of three timestamps makes it possible to locate an object on a surface, that is to say in two dimensions. The use of two timestamps makes it possible to locate an object along an axis, that is to say according to one dimension.

In the example of FIG. 1, the use of four timestamping terminals 20-1, 20-2, 20-3, 20-4 advantageously makes it possible to locate the beacon 10 in the three-dimensional space. Such a configuration may for example be used when the tag 10 is associated with an object stored on a shelf in a warehouse. The time stamp terminals 20-1, 20-2, 20-3, 20-4 may for example be arranged in each corner of a warehouse. A number greater than the necessary minimum number of timestamping terminals enables the geolocation server 30 to obtain more time stamped messages and thus to improve the accuracy of the geolocation of the object 3.

With reference to FIG. 2, each time stamp terminal 20-1, 20-2, 20-3, 20-4 comprises a reception module 210, a time stamp module 220 and a transmission module 230.

The reception module 210 is configured to receive the signals transmitted periodically by the geolocation beacon 10 on the ultra-wideband radio pulse modulation communication link K1 and which comprise a location message comprising an identifier of said beacon 10. The receiving module 210 is also configured to receive reference pulses transmitted by the other terminals 20-1, 20-2, 20-3, 20-4. By the term "reference pulse" is meant a signal transmitted to the other terminals on the ultra-wideband radio pulse communication link comprising at least the identifier of the terminal 20-1, 20-2, 20-3 , 20-4 who issued it.

The timestamp module 220 is configured to time stamp the location messages and the reference pulses received by the reception module 210. By timestamping is meant the indication of at least one temporal information, for example with a precision of order of the nanosecond or tenth of a nanosecond, relative to a temporal reference predetermined date, the date being only optional information. This time information is used to indicate the time at which the reference message or pulse was received by the time stamp terminal 20-1, 20-2, 20-3, 20-4. To do this, each timestamp terminal 20-1, 20-2, 20-3, 20-4 comprises its own clock, made from an oscillator, which delivers a time indication that the timestamp module 220 is going to insert in each message received from the tag 10.

The transmission module 230 is firstly configured to transmit or broadcast periodically a signal comprising a reference pulse to the other terminals 20-1, 20-2, 20-3, 20-4 of the system 1. Thus, in the example of FIG. 1, the transmission module 230 of the terminal 20-1 is configured to periodically transmit a reference pulse to the other three time stamp terminals 20-2, 20-3 , 20-4 and so on. The signal comprising the reference pulse emitted by each terminal 20-2, 20-3, 20-4 is preferably of the same type as the signal diffused by the beacon 10 so that the terminal 20-2, 20-3, 20 -4 behaves like a beacon 10 vis-a-vis the other terminals 20-2, 20-3, 20-4 when it emits reference pulses. The transmission period may advantageously be adapted to enable correction of the time stamping instants by the geolocation server 30 on a regular basis in order to maintain the accuracy of the system 1 without using too many resources of the time stamping terminals 20-1, 20- 2, 20-3, 20-4. For example, the transmission period can be set to 1000 seconds. Preferably, the terminals 20-1, 20-2, 20-3, 20-4 of the system 1 transmit on a so-called "calibration" time interval a reference pulse destined for the other terminals 20-1, 20-2. , 20-3, 20-4.

The reference pulse comprises the identifier of the transmitting terminal 20-1, 20-2, 20-3, 20-4. Note that the terminals 20-1, 20-2, 20-3, 20-4 may be programmed to transmit a reference pulse periodically or may simultaneously receive an instruction from the location server 30 requesting them to transmit a reference pulse to other terminals 20-1, 20-2, 20-3, 20-4. The transmission module 230 is also configured to transmit to the geolocation server 30 a location message or a reference pulse that has been time stamped by the time stamp module 220 and to which it adds the identifier of the time stamp terminal. 20-1, 20-2, 20-3, 20-4 so that the geolocation server 30 can both determine the transmitter of a reference message or pulse and the terminal 20-2, 20-3, 20-4 having timestamped it.

For this purpose, with reference to FIG. 1, each time stamp terminal 20-1, 20-2, 20-3, 20-4 is connected to the geolocation server 30 on a communication link respectively L1, L2, L3, L4 to communicate location messages and reference pulses timestamped. These communications links L1, L2, L3, L4 can be wired or wireless communications links, for example 3G, 4G, Wifi, Ethernet etc.

3) Geolocation server 30

The geolocation server 30 may be located in the space 5 or outside the space 5 and is connected to the time stamp terminals 20-1, 20-2, 20-3, 20-4, for example via the Internet network. or any suitable communication link, as mentioned above.

With reference to FIG. 3, the geolocation server 30 comprises a reception module 310, a calculation module 320, a compensation module 330 and a location module 340.

The reception module 310 is configured to receive, from each timestamp terminal 20-1, 20-2, 20-3, 20-4, the location messages timestamped by said terminal 20-1, 20-2, 20- 3, 20-4 and the reference pulses (previously received from other terminals 20-1, 20-2, 20-3, 20-4) timestamped by said terminal 20-1, 20-2, 20-3, 20- 4 to which the identifier of said terminal 20-1, 20-2, 20-3, 20-4 has been added. A location message received by the geolocation server 30 therefore comprises the identifier of the tag 10 as well as the identifier and the time stamp of the terminal 20-1, 20-2, 20-3, 20-4 which has timestamped and sent to the server 30. Similarly, a reference pulse received by the server geolocation 30 includes the identifier of the terminal 20-1, 20-2, 20-3, 20-4 which issued it as well as the identifier and the time stamp of the terminal 20-1, 20 -2, 20-3, 20-4 which has timestamped and sent to the server 30. Note that, each terminal 20-1, 20-2, 20-3, 20-4 receiving and timestamp reference pulses sent by the other terminals 20-1, 20-2, 20-3, 20-4, the server 30 therefore receives from each terminal 20-1, 20-2, 20-3, 20-4 and periodically a set of reference pulses (received from other terminals) timestamped.

The calculation module 320 is configured to calculate the clock differences between the terminals 20-1, 20-2, 20-3, 20-4 two by two from the timestamped reference pulse sets received from each terminal 20. -1, 20-2, 20-3, 20-4 as will be detailed hereinafter.

The compensation module 330 is configured to compensate for the instant of time stamping of each location message transmitted by the beacon 10 and time stamped by each of the time stamp terminals 20-1, 20-2, 20-3, 20-4, from the differences calculated by the calculation module 320.

The locating module 340 of the beacon 10 is configured to determine the location of the beacon 10 by trilateration from the timestamp times compensated by the compensation module 330.

To perform this trilateration, the geolocation server 30 knows the predetermined fixed position, in the closed space 5, of each of the four timestamping terminals 20-1, 20-2, 20-3, 20-4. The trilateration is performed from a group of time-stamped messages corresponding to the same message transmitted by the beacon 10 and from the predetermined fixed position in the closed space 5 of each of the four timestamping terminals 20-1, 20-2. , 20-3, 20-4. For a given time stamp terminal 20-1, 20-2, 20-3, 20-4, the propagation delay of a radio signal is linearly dependent on the distance traveled according to the following equation:

where T is the delay of propagation of the signal between the beacon 10 and the time stamp terminal 20-1, 20-2, 20-3, 20-4 (transmission delay), S is the distance between the beacon 10 and the beacon time stamp terminal 20-1, 20-2, 20-3, 20-4 and c is the speed of light. The transmission delay τ thus makes it possible to determine the distance separating the beacon 10 from the time stamp terminal 20-1, 20-2, 20-3, 20-4. In order to avoid the use of an absolute reference time to determine this delay, especially at the level of the beacon 10, the arrival time differences, from a message transmitted by the beacon 10, are used to each of the time stamp terminals 20-1, 20-2, 20-3, 20-4. Indeed, management of an absolute reference time by the beacon 10 would require a constant power supply of the beacon 10 in electrical energy, which could therefore not operate at low consumption, a clock internal to the beacon 10 and a resynchronization method which would make the beacon 10 complex, bulky and expensive.

The trilateration calculations making it possible to determine the position of the beacon 10 in the space 5 will be described with reference to FIGS. 4 and 5. For the sake of clarity, FIG. 4 illustrates a reference beacon T of spatial coordinates (x, y , z) in the three-dimensional coordinate system (X, Y, Z) and only three time stamping terminals referenced A, B, C, in particular in order to present the calculations in a clear manner, these calculations being able to be transposed to four timestamping terminals 20 -1, 20-2, 20-3, 20-4.

In the absence of an absolute time reference, the transmission delay of a message transmitted by the tag T to each of the terminals A, B, C can be determined only in a relative way. In addition, the determination of this transmission delay for each of the terminals A, B, C will be accurate only if the delays due to the fact that the terminals A, B, C are not synchronized and drifting their clocks are not corrected.

To do this, we define:

as being the delay of transmission between the beacon T and the terminal A, as being the delay of transmission between the beacon T and the terminal B, as being the delay of transmission between the beacon T and the terminal C, as being the delay of transmission between terminal A and terminal B, as being the transmission delay between terminal B and terminal C, as being the transmission delay between terminal A and terminal C,

pos _A = (x _A , y _A , z _A ), the spatial coordinates indicating the position of the terminal A,

pos _B = (x _B , y _B , z _B ), the spatial coordinates indicating the position of the terminal B,

pos _c = (x _c , y _c , z _c ), the spatial coordinates indicating the position of the terminal C,

-

the distance separating terminal A from terminal B,

- the distance separating terminal B from

the terminal C,

the distance between terminal A and terminal C.

In the trilateration localization method, as illustrated in FIG. 5, the spatial coordinates tag T (x, y, z) is at the intersection of three circles CA, CB, CC each centered on one of the terminals A, B, C. We then have the distance separating the tag T from the

terminal A,

the distance separating the tag T from the

terminal B,

the distance separating the tag T from the

terminal C,

For a two-dimensional location along the X and Y axes (no coordinates along the Z axis), the system of equations to solve is as follows:

In order to integrate the differences between the distances traveled by the signal of the tag T at each of the terminals A, B, C in these equations, a reference terminal is defined, for example the terminal A, and:

which represents the difference between the distance between the beacon T and the terminal A and the distance between the beacon T and the terminal B,

- which represents the difference between the distance between the

tag T and terminal A and the distance between tag T and terminal C.

This definition makes it possible to reduce the system of equations [1] to the following system of equations [2] of three equations with three unknowns and y:

In order to solve such a system [2], it is reduced first to the system [3] next :

That we combine in the only equation:

This system is a system of three equations with three unknowns that can be solved analytically in a known manner.

For a three-dimensional location, the system of equations to solve is as follows:

that is to say a system of four equations with four unknowns x, y and z.

This system can be solved numerically in known manner, for example using a so-called least square method or any other suitable method.

In this preferred example, the geolocation server 30 further comprises a transmission module 350 configured to transmit or make available the geographical position of the beacon 10 determined by the location module 340, for example so that an operator can find quickly the object 3 on which the tag 10 is placed. The invention will now be described for a preferred mode of implementation with reference to Figures 4 to 6, this mode is in no way limiting the scope of the present invention. I. Implementation of the invention

Still for the sake of clarity, the implementation of the invention will be described with reference to FIGS. 4 to 6 for a system with three timestamp terminals A, B and C but may be transposed to a system comprising more or less three terminals.

The method according to the invention makes it possible to compensate for the differences between the time stamp clocks of the terminals A, B, C due in particular to the drift of their respective clocks.

First we define:

the delay of signal transmission between terminal A and terminal B, the delay of signal transmission between terminal B and terminal C, the delay of signal transmission between terminal A and terminal C,

the local error of the oscillator of the terminal A,

the local error of the oscillator of the terminal B,

the local error of the oscillator of the terminal C,

- the clock difference between terminal A and terminal B,

- the clock difference between terminal B and terminal C,

- the clock difference between terminal A and terminal C,

First, in a step E1, each terminal A, B, C diffuses in a radio signal, in the form of a reference pulse, to the two other terminals (respectively B, C; A, C; A). , B), its identifier periodically, for example every 1000 seconds. Each terminal A, B, C receives, in a step E2, the reference pulses emitted by the other terminals A, B, C. In other words, the terminal A receives the reference pulse sent by the terminal B and the reference pulse sent by the terminal C, the terminal B receives the reference pulse sent by the terminal A and the reference pulse sent by the terminal C and the terminal C receives the reference pulse sent by the terminal A and the impulse

reference sent by terminal B.

Each time a reference pulse is received, the time stamp module 220 of each terminal A, B, C time stamp, in a step E3, the two reference pulses that it receives from the two other terminals (respectively B, C; A, C; A, B) and inserts its identifier and then transmits this information in a step E4 to the geolocation server 30 which receives them in a step E5. The geolocation server 30 calculates, in a step E6, the clock differences between the terminals A, B, C from the received time-stamped reference pulses.

In a detailed manner, starting from the terminal A, it is considered that the terminal A sends a reference pulse at the instant τ _Α which is received by the terminal B at the instant and by the terminal C at the instant

The time stamp depends on both the distance between terminal A and terminal B and the clock difference between terminal A and terminal B:

Similarly, the time stamp depends both on the distance between terminal A and terminal C and the clock difference between terminal A and terminal B:

Subtracting these two equations [6] and [7], we obtain:

is :

In the same way, we can define:

and

Since the trilateration calculations require subtracting the differences between the reception times, the addition of these equations [9], [1 0] and [1 1] will eliminate the clock differences between the terminals A, B, vs.

As mentioned above, the clock oscillators of terminals A, B, C drift with time or even with temperature, thus causing a drift of the time offs between the clocks.

We notice :

p _{AB t1} , the clock difference between the terminal A and the terminal B computed by the server at a time t1,

- P kB, ί 2 ' ^the clock difference between terminal A and terminal B calculated by the server at a time t2, later than time t1,

t3 is an instant between time t1 and time t2. Using terminal A as a reference, the clock difference between the

terminal A and terminal B at time t3 is given by the following equation:

This clock difference can be similarly calculated between the terminal A and the terminal C and between the terminal B and the terminal C by the geolocation server 30. It will be noted that the equation [12] is a linear interpolation. However, if the drifts of the clocks of the terminals A, B, C follow another curve, it is preferable to use an interpolation of a higher order, for example quadratic, or even by increasing the frequency of emission of the pulses. reference, to improve the correction of these clock differences.

Thus, when the geolocation server 30 receives, in a step E7, three time-stamped location messages following the transmission of a message by the beacon 10 (each of the three messages having been time-stamped and sent by one of the terminals A , B, C), it compensates, in a step E8, the timestamp times of the messages received from the time differences calculated between the clocks of the terminals A, B and C, and then locates the beacon 10 in a step E9 using the corrected moments to improve the accuracy of the location.

Each time-stamped location message received from a terminal is compensated with the time difference, positive or negative, calculated for the associated terminal.

All the time-stamped location messages received by the server 30, for example every 10 seconds, are compensated using the differences thus calculated until new time-stamped reference pulses are received by the server 30 which will then calculate new differences. (eg every 1000 seconds) and use them to compensate for later timestamp location messages and so on. The method according to the invention therefore advantageously makes it possible to correct the time drifts of the clocks of the terminals A, B, C between them in order to improve the accuracy of the trilateration and therefore of the geolocation of the beacon 10.

It should be noted that the present invention is not limited to the examples described above and is capable of numerous variants accessible to those skilled in the art. In particular, the shapes and dimensions of the object 3, the space 5, the beacon 10, the time stamp terminals 20-1, 20-2, 20-3, 20-4, A, B, C such that shown in the figures so as to illustrate an embodiment and implementation of the invention, can not be interpreted as limiting.

Claims

CLAIMS 1 - Method of geolocation of a beacon (10) by a geolocation server (30) from a plurality of time stamp terminals (20-1, 20-2, 20-3, 20-4; , B, C), each of the terminals (20), whose position is known from said server (30), being identified by a single identifier and being able to communicate with the other time stamp terminals (20-1, 20-2 , 20-3, 20-4; A, B, C) of the plurality of timestamps (20-1, 20-2, 20-3, 20-4; A, B, C), said method comprising :

a transmission step (E1), on an ultra wideband radio communication link, of a reference pulse by each of the time stamp terminals (20-1, 20-2, 20-3, 20-4; A, B, C) to the other time stamp terminals (20-1, 20-2, 20-3, 20-4; A, B, C), said reference pulse comprising the terminal identifier ( 20-1, 20-2, 20-3, 20-4, A, B, C) emission,

a step (E2) of reception by each of the timestamp terminals (20-

1, 20-2, 20-3, 20-4; A, B, C) reference pulses emitted by the other timestamps (20-1, 20-2, 20-3, 20-4; A, B, C),

a step (E3) of time stamping, on reception, by each of the time stamp terminals (20-1, 20-2, 20-3, 20-4, A, B, C) of the reference pulses received from the others terminals (20-1, 20-2, 20-3, 20-4, A, B, C),

a step (E4) of sending, by each of the timestamping terminals (20-1, 20-

2, 20-3, 20-4; A, B, C), to the geolocation server (30), time-stamped reference pulses,

a step (E5) of reception by the geolocation server (30) of the timestamped reference pulses sent by each of the timestamp terminals (20-1, 20-2, 20-3,20-4; A, B, VS),

a step (E6) of calculation by the geolocation server (30) of the clock differences between the terminals (20-1, 20-2, 20-3, 20-4, A, B, C) from the time-stamped reference pulses and the known position of the terminals (20-1, 20-2, 20-3, 20-4; A, B, C),

a step (E7) of reception by the geolocation server (30) of a plurality of time-stamped location messages, each message of received time-stamped location corresponding to the same location message previously broadcast by the beacon (10) on the ultra wide band radio communication link, and which has been time stamped and sent by one of the time stamp terminals (20-1, 20). -2, 20-3, 20-4; A, B, C),

a step (E8) of compensation, by the geolocation server, based on the calculated differences, the timestamp times of the received time-stamped location messages, and

a step (E9) of locating, by the geolocation server, the beacon (10) from the compensated timestamp times. The method according to claim 1, wherein the ultra wideband radio communication link on which the reference pulses are transmitted by the time stamp terminals (20-1, 20-2, 20-3, 20-4; A, B). , C) and on which the location messages are broadcast by the beacon (10) is of the radio pulse modulation type. The method of claim 2 wherein the ultra wideband radio communication link on which the reference pulses are transmitted by the time stamp terminals (20-1, 20-2, 20-3, 20-4; A, B). , C) and on which the location messages are broadcast by the beacon (10) uses a radio pulse modulation in all or nothing. 4 Method according to one of claims 2 to 3 wherein the reference pulses and location messages are formed of information symbols, and said timestamps and said beacon are configured to modulate a same predefined spreading sequence by each information symbol so as to obtain, for each information symbol, a sequence of spreading symbols used for the modulation of radio pulses. Method according to one of claims 1 to 4, wherein the step of time stamping (E3) further comprises inserting the identifier of the terminal (20-1, 20-2, 20-3, 20-4, A, B, C) performing the time stamping in each time-stamped reference pulse.

6 - Method according to one of claims 1 to 5, wherein the step (E6) for calculating the clock differences is performed between the timestamps

(20-1, 20-2, 20-3, 20-4, A, B, C) two by two.

7 - Process according to claim 6, wherein the clock difference between two terminals (A, B) is calculated according to the following equation: where:

is the moment of reception, by the terminal A, of a pulse of

reference by terminal C,

is the moment of reception, by the terminal B, of the reference pulse

sent by terminal C,

8 - Process according to one of claims 1 to 7, wherein the location is carried out by trilateration.

9 - Process according to one of claims 1 to 8, wherein the emission of a reference pulse by each of the terminals (20-1, 20-2, 20-3, 20-4; A, B, C ) to the other terminals (20-1, 20-2, 20-3, 20-4, A, B, C) is carried out periodically.

10 - Process according to claim 9, wherein the period is of the order of a few hundred seconds. 1 1 - Time stamp (20-1, 20-2, 20-3, 20-4, A, B, C) comprising a receiver module (210) configured to receive reference pulses transmitted by other terminals (20-1, 20-2, 20-3, 20-4, A) on an ultra wideband radio communication link; , B, C), and location messages broadcast by a beacon (10),

a time stamping module (220) configured to timestamp reference pulses and location messages received by the reception module (210), and

a transmission module (230) configured to transmit periodically on the ultra wideband radio communication link a reference pulse to other terminals (20-1, 20-2, 20-3); , 20-4; A, B, C), and for transmitting to another geolocation server (30) a plurality of reference pulses and a plurality of location messages timestamped by the module timestamp (220). The time-stamping terminal (20-1, 20-2, 20-3, 20-4, A, B, C) according to claim 11, wherein the ultra wideband radio communication link on which are received the reference pulses emitted by the other terminals and the location messages broadcast by the beacon and on which the reference pulses are sent to the other terminals is of the radio pulse modulation type. The timestamp (20-1, 20-2, 20-3, 20-4, A, B, C) of claim 12 wherein the ultra wideband radio communication link on which the pulses of reference transmitted by the other terminals and location messages broadcast by the beacon and on which are sent the reference pulses to the other terminals uses a radio pulse modulation in all or nothing. The timestamp (20-1, 20-2, 20-3, 20-4, A, B, C) according to one of claims 12 to 13 wherein the signals that the receiving module is configured for receive beacon or other terminals, and that the transmission module is configured to transmit to the other terminals, comprise spreading symbols, each sequence of spreading symbols corresponding to the same predefined spreading sequence modulated by an information symbol of the pulse of reference or location message. A server (30) for locating a beacon (10) from a plurality of timestamps (20-1, 20-2, 20-3, 20-4; A, B, C) according to one of the claims 1 to 14, the position of each of the terminals (20-1, 20-2, 20-3, 20-4; A, B, C) being known from said server (30), said beacon ( 10) being configured to broadcast a signal including a location message comprising an identifier of the beacon (10), the server (30) comprising:

a reception module (310) configured, on the one hand, to receive a plurality of time-stamped location messages, each received time-stamped location message corresponding to the same location message previously broadcast by the tag (10) which has been time stamped and sent by one of the time stamp terminals (20-1, 20-2, 20-3, 20-4; A, B, C), and, on the other hand, to receive a plurality of sets of reference pulses, each set having been sent by one of the timestamps (20-1, 20-2, 20-3, 20-4; A, B, C) and comprising a plurality of time stamped by said transmitting terminal (20-1, 20-2, 20-3, 20-4, A, B, C),

a module (320) for calculating the clock differences between the time stamp terminals (20-1, 20-2, 20-3, 20-4, A, B, C) from the plurality of sets received and the known position of the terminals (20-1, 20-2, 20-3, 20-4, A, B, C),

a module (330) for compensating the time stamp of each timestamp location message received from the calculated differences,

a module (340) for locating the beacon (10) by trilateration from the compensated timestamp times. 16 - System (1) comprising a plurality of time stamping terminals (20-1, 20-2, 20-3, 20-4, A, B, C) according to one of claims 1 1 to 14 and at least a geolocation server (30) according to claim 15.