FR3112864A1 - Identification and localization of objects in a volume - Google Patents

Abstract

The invention relates to a method for locating a first device (200) in a predefined volume (V) associated with an orthogonal reference (x,y,z), - in which said volume is delimited by at least a first and a second side walls, - in which at least a second relay device (201, 202, 203, 204) and a third control device (205) are arranged in said volume (V), - in which said second and third devices are arranged in the same plane at a predetermined height (H0), - in which said second and third devices are separated by a predefined longitudinal distance (D0k) in a longitudinal direction (x) of said volume (V). No abstract figure

Description

Identification and localization of objects in a volume

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of systems and methods for the identification, location, counting of objects or people in a predefined volume.

The present invention has applications in the cabins of means of transport such as airplanes or the like.

TECHNICAL BACKGROUND

In order to determine the position of a point in a volume, it is possible to use the distances from this point to three reference points. The systems and processes exploiting this type of technique are grouped together under the name “ multilateration ”.

Multilateration is the process of determining the location of a target by measuring its distance from known points. Unlike triangulation, it is therefore not a matter of measuring angles, but a relative distance between the two devices.

More specifically, multilateration systems can calculate a position of a target device relative to source devices by exchanging sets of data carried by signals sent by the source devices. Multilateration uses the propagation time of the signal sent by a transmitter and received by a receiver to determine its relative distance.

For example, in air traffic management, the measurement of distances is carried out by different radar methods by devices installed at these known points.

However, in applications in restricted and congested spaces, the presence of several transmitters, as well as multiple obstacles makes the robustness of the relative distance information unreliable, due to the phenomenon of rebound which noisy the signal received by the transmitter.

Thus, there is a need to improve multilateration techniques. The present invention falls within this context.

A first aspect of the invention relates to a method for locating a first device in a predefined volume associated with an orthogonal marker,
- in which said volume is delimited by at least a first and a second side wall,
- in which at least a second relay device and a third control device are arranged in said volume,
- in which said second and third devices are arranged in the same plane at a predetermined height,
- in which said second and third devices are separated by a predefined longitudinal distance along a longitudinal direction of said volume,
the method comprising the following steps:
- transmission by the first device of a first signal in said volume,
- reception of said signal by said first device after rebound on said side walls of said volume,
- estimation of a longitudinal position of said first device relative to said walls from said first signal,
- transmission by said first device to the second device, of a second signal comprising at least said longitudinal position,
- estimation of a distance separating said first and second devices from said second signal and said predetermined height,
- transmission by said second device to said third device, of a third signal comprising at least said distance,
- Estimation by said third device of said location of said first device from said third signal and said predefined longitudinal distance.

According to embodiments, several second devices are arranged in said volume and
each second device receives said first signal,
each second device estimates a proper distance separating it from the first device and transmits a third proper signal comprising at least said proper distance,

According to embodiments, said estimation of said location includes the calculation of a weighted average of longitudinal distances estimated by each second device.

According to embodiments, said step of receiving said first signal comprises a first reception corresponding to a first detected bounce and a second reception corresponding to a second bounce in a direction opposite to the first bounce.

According to embodiments, said first and second signal includes an identification of their respective transmitter.

According to embodiments, the method further comprises a step of transmitting said estimate to a display device to display said location.

A second aspect of the invention relates to a system comprising:
- a first device in a predefined volume associated with an orthogonal marker, said volume being delimited by at least a first and a second side walls,
- at least a second relay device and a third control device arranged in said volume,
- in which said second and third devices are arranged in the same plane at a predetermined height,
- in which said second and third devices are separated by a predefined longitudinal distance along a longitudinal direction of said volume,
in which :
- the first device is configured to emit a first signal in said volume,
- said first device is configured to receive said signal by after rebound on said side walls of said volume,
- said first device is configured to estimate a longitudinal position of said first device relative to said walls from said first signal,
- said first device is configured to transmit to the second device a second signal comprising at least said longitudinal position,
- said second device is configured to estimate a distance separating said first and second devices from said second signal and said predetermined height,
- said second device is configured to transmit to said third device a third signal comprising at least said distance,
- said third device is configured to estimate said location of said first device from said third signal and said predefined longitudinal distance.

According to embodiments, several second devices are arranged in said volume and in which
each second device is configured to receive said first signal,
each second device is configured to estimate a proper distance separating it from the first device and transmits a third proper signal comprising at least said proper distance,

According to embodiments, said estimation of said location includes the calculation of a weighted average of longitudinal distances estimated by each second device.

According to embodiments, the system further comprises a display device and wherein said third device is configured to transmit said estimate to said display device to display said location.

FIGURES

FIG. 1 schematically illustrates the estimation of distances according to embodiments of the invention.
Figure 2 illustrates an application of embodiments in an aircraft cabin viewed from above.
FIG. 3 illustrates an application of embodiments in an aircraft cabin according to a longitudinal view.
Figure 4 is a step diagram of a method according to embodiments.
Figure 5 schematically illustrates network architectures for implementing embodiments of the invention.
Figure 6 schematically illustrates a weighting function for determining the location of an object according to embodiments of the invention.
Figure 7 schematically illustrates a device according to embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments make it possible to identify, locate and/or count objects connected (or sources or even sensors) to a network or people carrying such objects in a considered volume such as a compartment of a means of transport ( such as an aircraft).

As described in the following, the embodiments of the invention make it possible to carry out a more precise multilateration in particular by taking into account the bounces in the volume considered and to deduce therefrom in a precise manner the distances from the sources to the reference objects.

The embodiments are compatible with multiple network topologies existing and deployed in industrial applications. Such topologies are illustrated in figure 5 . Topology 500 is a “bus” network. Topology 501 is a ring network. Topology 50 2 is a star topology.

For example, the exchange of data and signals can be done using the LoRaWAN protocol.

• un dispositif source comportant émetteur-récepteur sur une fréquence (par exemple, une fréquence du protocole LoRaWAN),
• un ou plusieurs points d’accès (par exemple compatibles avec le protocole LoRaWAN),
• un serveur équipé de moyens de communication, d’un processeur et d’un espace de stockage,
• un programme d’ordinateur pour la gestion du procédé de localisation et le traitement de l’information.

For example, an architecture for implementing embodiments may include:

• a source device comprising a transceiver on a frequency (for example, a frequency of the LoRaWAN protocol),
• one or more access points (for example compatible with the LoRaWAN protocol),
• a server equipped with means of communication, a processor and a storage space,
• a computer program for managing the location process and processing information.

Generally speaking, the system according to such an architecture functions as follows.

Each property or person to be located is equipped with a source device. This source device can for example have its own energy source, which makes it portable.

To allow the identification of the source device (and possibly its carrier), the transmission frequency of the information sent by the transceiver can be configurable.

Optionally, in order to save energy, the information is sent at regular time intervals. These intervals can also be configurable.

Access points allow the reception of signals sent by the transceivers of the source devices. They are equipped with a processing unit allowing them to perform various functions. The processing unit calculates the distance between the source device and the access point and sends the distance information to the server.

For this purpose, the processing unit can operate a filter to take into account the rebounds of the signals on the obstacles present in the volume in which the localization is carried out. The processing unit can also measure the propagation time of the signals and the information exchanged.

The server receives all the relative distance information calculated by the access points and processes this information to deduce the location of the transceivers or their carriers in the volume considered (such as a passenger compartment).

For this, the server can perform a certain number of functionalities. For example, filtering makes it possible to reduce measurement errors or noise contained in the information provided by the access points. It can also carry out the counting of the number of transmitter-receiver sensors present in the volume considered through the information received.

Communication between the server and the multiple access points can be done using a wired connection. However, other network topologies are compatible with embodiments of the invention.

Embodiments of the invention are described in more detail in the following, in the context of implementation in a passenger cabin of an aircraft.

In this application, a tool is provided to on-board personnel for the purpose of identifying equipment and/or people in real time. For example, this can enable them to improve the services provided on board, to anticipate passenger needs, to optimize the movement of on-board staff in the cabin, to have a means of real-time monitoring for the purser or pilots or even other advantages.

In more specific examples, the on-board staff wishes to check the position of the medical kits or even the position of unaccompanied children. In these cases, it may be useful for them to have, on a digital display dedicated to them, the real-time position of the kits or children.

This position determination is described with reference to FIG .

A system according to embodiments of the invention comprises a device 100 carried by the person or the object A to be located in the volume V of the cabin. Device 100 includes a transceiver. This transceiver operates for example according to the LoRaWan protocol used to communicate with the other devices of the system. It may also comprise its own energy source (for example a source of the low consumption type). The device further comprises a processing unit for processing the information received by the transceiver.

The system further comprises a device 101 arranged in an element B of the cabin and which corresponds to an access point of the system. This device comprises a transceiver. For example, this transceiver operates according to the LoRaWan protocol. The device further comprises a processing unit for processing the information received by the receiver. The transceiver allows communication with the device 100 . The device 101 also includes a unit for communicating to a server 102 to provide it with the information received and processed. Several elements B each comprising a device 101 can be used in the system depending on the application considered.

The server 102 is placed in an element C of the cabin. This server includes a communication unit to the access point (the device 101 ) to recover the information processed by the latter. The server further comprises a storage space enabling it to store the relative position information of the device 100 . The server 102 also comprises a processor for processing the information received by the access point(s) (the device(s) 10 1 ).

An orthonormal reference (xyz) is considered with the abscissa axis x the longitudinal axis of the car and the dimension axis z the height of the car (counted positively with respect to the ground – the z axis is oriented in the opposite direction gravity). The y-axis is the axis orthogonal to the previous axes.

The arrow 103 represents the height H0 between the device 100 and the cabin ceiling. In the example illustrated, the devices 101 and 102 are also located at the level of the cabin ceiling. The height H0 is therefore also the height between these devices and the device 100 .

The arrow 104 represents the distance D0 between the device 101 and the device 102 . It is considered here that these two devices are aligned parallel to the x axis of the marker. In case of plurality of devices 101 . Their respective distances from the device 102 are denoted D0k , with k being an index representing each device 101 .

Other distances are shown in Figure 1 and are discussed later in the description.

The steps of a location method are described herein in the context of Figure 2 and with reference to the step diagram of Figure 4 .

FIG. 2 illustrates a device 200 identical to the device 100 carried by the person or the object A located in, for example, an aircraft cabin having two side walls E and D oriented along the longitudinal axis of the cabin (the horizontal axis). In the cabin, are arranged devices 201 , 20 2 , 203 , 204 identical to the device 102 of Figure 1 and arranged in elements B1 , B2 , B3 , B4 of the cabin. A server 205 is also placed in the cabin identical to the server 103 of FIG. 1 and placed in an element C of the cabin. Figure 2 is a top view of the cabin (in the x,y plane).

In a step 401 , the device 200 emits a signal S1 . This signal S1 makes it possible to identify the device 100 . For example, the device 200 transmits a signal according to a specific modulation frequency. For example again, the signal S1 carries a certain number of device identification bits 200 . In addition, the signal S1 includes a timestamp tS1 making it possible to determine an instant of transmission of the signal. For example, this timestamp is expressed according to a clock common to the devices of the system (for example in hour, minute, second or other).

In a step 402 , the device 200 receives the signal S1 previously transmitted, following a bounce on a first element of the cabin. In particular, the device 200 receives the signal S1 after a rebound against a first side wall E of the cabin. The side walls of the cabin are those oriented along the longitudinal axis of the cabin (that is to say the axis of the abscissas of the reference).

In a step 403 , the device 200 receives the signal S1 previously transmitted, following a bounce on a second element of the cabin. In particular, the device 200 receives the signal S1 after a rebound against a second side wall D of the cabin opposite the first side wall. The side walls of the cabin are those oriented along the longitudinal axis of the cabin (that is to say the axis of the abscissas of the reference).

For example, the signal S1 is transmitted in all directions. The signal received during step 402 corresponds to the fastest reception corresponding to the rebound against the nearest wall. The signal received during step 403 is that resulting from the rebound in the opposite direction to that of the signal received in the previous step and therefore the opposite wall.

In a step 404 , the device 200 estimates its transverse position with respect to the first and second elements (in the present example, the walls E and D ). The device 200 first identifies the signals, for example by means of identification bits or the transmission frequency. The device 200 also estimates the propagation time of the signal in the cabin between its instant of transmission tS1 and its reception times tD and tE after rebound. This estimate is made using the propagation speed v of the signal in the cabin. For example, this is the speed of propagation of radiofrequency waves in the air, which is approximately 3x10^8 m/s.

From signal preparation timesS1, the device200can determine its position relative to the first and second elements (i.e. here the side wallsDandE) according to the following formulas. This position is expressed according to the distancestheandIDof the device200to the elements along the y-axis (i.e. the width of the cabin): ID = vx(tD-tS1)/2 andthe =v x (tE-tS1)/2 .

In reality, the transmission of the signals induces a delay translated by measurements of the propagation timestDandyouerroneous. These delays also induce distance estimation errors.IDandtheratedelDandshe .Estimates ID ~ and I E ~ of these distances are expressed as follows:ID ~= I d + elDandI E ~= the + he E .

In order to ensure the validity of the estimates made, a control formula is used. This formula consists of expressing the fact that the sum of the estimated lengths lD ~ and l E ~ must correspond to the width La of the car: lD ~ + l E ~ = La .

During step 405 , the device 200 transmits its position as it has estimated it to the various devices 201 , 202 , 203 , 204 (or system access points).

This transmission is done by sending a signal S2 . This signal S2 can be identified by the access points. For example, the signal S2 includes identification bits for this purpose. It also makes it possible to determine its instant of emission. As for the signal S1 , this instant of transmission can be expressed with respect to a timestamp common to the devices of the system. The position of the device 200 is expressed by sending the estimates lD ~ and l E ~ .

The reception of the signal S2 by the access points is illustrated by FIG. 3 which is a side view of the cabin (in the x,z plane).

Each of the access points then estimates in steps 406 , 407 the longitudinal position of the device 200 . The signal S2 is first of all identified (for example by means of the identification bits). Then, the timestamp is used to estimate the longitudinal position of the device 200 with respect to the access point Bk considered, that is to say its position along the abscissa axis). As already explained above for the estimation of the transverse position of the device 200 , the knowledge of the instant of reception tBk of the signal S2 and its instant of transmission tS2 , as well as the speed of propagation v of the signal makes it possible to know the distance DBk between the device 200 and the access point Bk considered ( 201 , 202 , 203 , 204 ) along the abscissa axis x according to the formula: DBk =vx (tBk-tS2) .

As also already explained above, the transmission of the signal S 2 induces a delay reflected in the measurement of the instant tBk . This delay is expressed by an estimation error eS2k of the distance DB k . The estimated distances are expressed according to the formula: DBk ~ = DBk + eS2k .

The measurement of the relative longitudinal position LBk between the device 200 and the access point Bk can be estimated from the estimates lD ~ , lE ~ and the height H0 using the Pythagorean theorem according to one of the following formulas: LBk ~ = (DBk ~²-H0²- lD ~²)^(1/2) or LBk ~ = (DBk~²-H0²- lE ~ ²)^(1/2) .

The formula uses the estimates lD ~ or lE ~ depending on the position of the access point in the cabin. The access points are in fact arranged at the level of the side walls, either at the level of the side wall E or either of the side wall D. Thus, if the access point is on a wall E the estimate lE ~ is used, if the access point is on a wall D the estimate lD ~ is used.

Returning to FIG. 1 , the length LBk is represented by the arrow 105 . The length DBk is represented by the arrow 106 . Length 1D is represented by arrow 107 . The distance d between the access point 101 and the device 100 in the plane (y,z) is represented by the arrow 108 .

As can be seen, the Pythagorean theorem makes it possible to write d² = H0² + lD² because in this illustration, the access point 101 is located at the level of the wall D . In the same way, when the access point is at the level of the wall E, it is possible to write d² = H0² + l E ² and DBk² = d² + LBk² .

This same theorem also allows us to write DBk² = d² + LBk² . By writing the equality of writing of d² we can find the formula given above for LBk .

Returning to FIG. 4 , during steps 408 , 409 , each access point Bk transmits the estimate that it makes of the longitudinal position and of the lateral position of the device 200 . A signal S3k is transmitted from the access point Bk to the server 205 . This signal makes it possible to identify the source access point (for example with identification bis). It also makes it possible to identify the device 200 (for example with other identification bis). The signal also includes the estimates lD ~ , lE ~ and LBk .

Then, during the steps410,411, for each batch of information transmitted by the elementsBK, a position a longitudinal position of the device200relative to the server205is determined using the following formulalk ~= LBk ~ + D0k (on thefigure 1, this longitudinal distancelkis represented by the arrow109).

Finally, during step 412 , a final position of the device 200 in the cabin is determined from the different positions of the device 200 with respect to the different access points Bk . The purpose of this step is to accurately estimate the relative position L between the device 200 and the server 205 from the multiple estimates Lk ~ made in the previous steps.

As for the distances mentioned previously, each estimate Lk ~ presents uncertainties induced by the propagation of the signals S1 and S2 in the air.

A dynamic weighted average is used, the principle of which is as follows. The weight wk associated with each relative longitudinal position Lk ~ follows a deterministic law f depending on the errors on the relative longitudinal distance estimates DBk ~ and lateral lD ~ (or lE ~ ): wk = f( eS 1D, eS2k) or wk = f(eS1E,eS2k) . This empirically determined function is characterizable according to the configuration of the system in the volume in which the localization is carried out (according to the configuration of the system in the aircraft cabin in the present example).

Figure 6 gives an example of an empirical law which links a weight P to a distance D. This law has the characteristic of being monotonically decreasing with a limit which tends towards 0 at infinity.

To determine such a law, a characterization of the measurement system used can be done according to the following iterative process. The system is placed at a calibrated distance, known and verified by another more precise measuring device (for example a laser measure or other). A certain number of measurements, for example three measurements, are carried out by the system. An average is then calculated. The relative difference between this average and the true distance is then determined. This process is then repeated for different distances.

The estimate of the relative position is thus determined by the following formula:L= [ (w0 x L 0 ~) + (w1 x L1~) + (…) + (wk-1 x Lk-1~) + ( wk x lk ~)]/(w0 + (…) + xk ).

In the case where it is a question of determining the number of devices 200 in the cabin, it is possible to determine this number from the information received by the server 205 in addition to their relative position determined as described previously.

Once all the position information (and the number of devices 200) are transmitted during a step 413 to a display device available to the aircrew. This information is then displayed on this display device during a step 414 .

In the foregoing, with reference to FIG . 1 , the calculations were made considering that the server 102 and the device 101 are aligned on a longitudinal axis of the cabin (they are aligned on a parallel to the abscissa axis x). However, in other cases, where they would not be aligned on a longitudinal axis, the calculation can be done using the value D 0 k as the projection on the x axis of the distance between the server 102 and the device 101 .

Figure 7 is a block diagram of a device 700 for implementing one or more embodiments of the invention. The devices or servers described above may have the same structure.

The device 700 comprises a communication bus to which are connected:

- A processing unit 701 , such as a microprocessor, called CPU;

- a random access memory unit 7 02 , called RAM, for storing executable code of a method according to one embodiment of the invention as well as registers suitable for recording the variables and parameters necessary for the implementation of a method according to embodiments, the memory capacity of which can be extended by an optional RAM connected to an extension port for example;

- A memory unit 703 , called ROM, for storing computer programs intended to implement the embodiments of the invention;

- A network interface unit 704 connected to a communication network on which the digital data to be processed is transmitted or received. The network interface 704 can be a single network interface, or composed of a set of different network interfaces (eg wired and wireless interfaces, or different types of wired or wireless interfaces). Data is written to the network interface for transmission or is read from the network interface for reception under the control of the software application running in the CPU 701 ;

- a graphical user interface unit 705 for receiving input from a user or displaying information to a user;

- a 7 06 HD rated hard drive

- an I/O input/output module 7 07 to receive/send data from/to external devices such as a video source or a screen.

The executable code can be stored either in read-only memory 703 , or on the hard disk 706 , or on a removable digital medium such as a disk, for example. According to a variant, the executable code of the programs can be received by means of a communication network, via the network interface 7 04 , in order to be stored in one of the storage means of the communication device 7 00 , as the hard disk 7 06, before being executed.

The central processing unit 7 01 is suitable for controlling and directing the execution of the instructions or parts of software code of the program or programs according to the embodiments of the invention, these instructions being stored in one of the aforementioned storage means. . After power-up, the processing unit 701 is capable of executing the instructions of the main random access memory 702 relating to a software application after these instructions have been loaded from the ROM program 703 or from the hard disk. (HD) 7 06 for example. Such a software application, when it is executed by the central unit 7 01 , leads to the execution of the steps of a method according to incarnations.

The present invention has been described and illustrated in this detailed description with reference to the accompanying figures. However, the present invention is not limited to the embodiments presented. Other variants, embodiments and combinations of characteristics can be deduced and implemented by those skilled in the art on reading this description and the appended figures.

To meet specific needs, a person competent in the field of the invention may apply modifications or adaptations.

In the claims, the word "include" does not exclude other elements or other steps. The indefinite article "one" does not exclude the plural. The various characteristics presented and/or claimed can be advantageously combined. Their presence in the description or in different dependent claims does not in fact exclude the possibility of combining them. The reference signs cannot be understood as limiting the scope of the invention.

Claims (10)

Method for locating a first device (200) in a predefined volume (V) associated with an orthogonal marker (x,y,z),
- in which said volume is delimited by at least a first and a second side wall,
- in which at least a second relay device (201, 202, 203, 204) and a third control device (205) are arranged in said volume (V),
- in which said second and third devices are arranged in the same plane at a predetermined height (H0),
- in which said second and third devices are separated by a predefined longitudinal distance (D0k) along a longitudinal direction (x) of said volume (V),
The process comprising the following steps:
- emission (401) by the first device (200) of a first signal (S1) in said volume (V),
- reception (402, 403) of said signal by said first device (200) after rebound on said side walls of said volume (V),
- estimation (404) of a longitudinal position (lD, lE) of said first device (200) relative to said walls from said first signal (S1),
- transmission (405) by said first device (200) to the second device (201, 202, 203, 204), of a second signal (S2) comprising at least said longitudinal position,
- estimation (406, 407) of a distance (DBk) separating said first (200) and second (201, 202, 203, 204) devices from said second signal (S2) and said predetermined height (H0),
- transmission (408, 409) by said second device (201, 202, 203, 204) to said third device (205), of a third signal (S3k) comprising at least said distance (DBk),
- estimation (408, 409) by said third device of said location of said first device (200) from said third signal and said predefined longitudinal distance (D0k). Method according to claim 1, in which several second devices (201, 202, 203, 204) are arranged in said volume (V) and in which

• each second device (201, 202, 203, 204) receives said first signal (S1),
• each second device (201, 202, 203, 204) estimates (406, 407) a proper distance (DBk) separating it from the first device (200) and transmits (408, 409) a third proper signal (S3k) comprising at least said proper distance (DBk),

A method according to claim 2, wherein said estimating said location includes calculating a weighted average (L) of longitudinal distances estimated (Lk) by each second device (201, 202, 203, 204). A method according to claim 3, according to any preceding claim, wherein said step of receiving (402, 403) said first signal comprises a first reception (402) corresponding to a first detected bounce and a second reception (403) corresponding to a second bounce in a direction opposite to the first bounce. A method according to any preceding claim, wherein said first and second signals include an identification of their respective transmitter. A method according to any preceding claim, further comprising the step of transmitting (413) said estimate to a display device to display (414) said location. System comprising:
- a first device (200) in a predefined volume (V) associated with an orthogonal reference (x,y,z), said volume being delimited by at least a first and a second side wall,
- at least a second relay device (201, 202, 203, 204) and a third control device (205) arranged in said volume (V),
- in which said second and third devices are arranged in the same plane at a predetermined height (H0),
- in which said second and third devices are separated by a predefined longitudinal distance (D0k) along a longitudinal direction (x) of said volume (V),
in which :
- the first device (200) is configured to emit (401) a first signal (S1) in said volume (V),
- said first device (200) is configured to receive (402, 403) said signal by after rebound on said side walls of said volume (V),
- said first device (200) is configured to estimate (404) a longitudinal position (lD, lE) of said first device (200) relative to said walls from said first signal (S1),
- said first device (200) is configured to transmit (405) to the second device (201, 202, 203, 204), a second signal (S2) comprising at least said longitudinal position,
- said second device (201, 202, 203, 204) is configured to estimate (406, 407) a distance (DBk) separating said first (200) and second (201, 202, 203, 204) devices from said second signal (S2) and said predetermined height (H0),
- said second device (201, 202, 203, 204) is configured to transmit (408, 409) to said third device (205), a third signal (S3k) comprising at least said distance (DBk),
- said third device (205) is configured to estimate (408, 409) said location of said first device (200) from said third signal and said predefined longitudinal distance (D0k). System according to claim 7, in which several second devices (201, 202, 203, 204) are arranged in said volume (V) and in which

• each second device (201, 202, 203, 204) is configured to receive said first signal (S1),
• each second device (201, 202, 203, 204) is configured to estimate (406, 407) a proper distance (DBk) separating it from the first device (200) and transmits (408, 409) a third proper signal (S3k) comprising at least said proper distance (DBk),

A system according to claim 8, wherein said estimating said location includes calculating a weighted average (L) of longitudinal distances estimated (Lk) by each second device (201, 202, 203, 204). A system according to any of claims 6 to 8, further comprising a display device and wherein said third device is configured to transmit said estimate to said display device to display said location.