FR3049715B1 - DEVICE AND METHOD FOR LOCATING OBJECTS - Google Patents

Abstract

Device (1) for locating a plurality of objects (2) provided with a first wireless communication member (12) and at least one second infrared-signal receiving wireless communication member (22), comprising at least one communication beacon (3) comprising a first wireless communication member (13) and at least one second infrared signaling wireless communication member (23), each communication beacon (3) comprising a clock electronic device (33), each object (2) being configured to receive and process said localization infrared signal transmitted by the one or more beacons (3) via the second communication member (22), each object (2) also comprising a clock ( 32) and being configured to periodically remotely transmit a signal comprising identification information of the object (2) and location information received by the at least one tag (3), the objects (2), remotely over a radio frequency wave. ) and tags (3) are automatically switchable between a standby state and an active state and configured to periodically synchronize their active states upon transmission / reception of the infrared location signals transmitted by the one or more beacons (3) to the objects ( 2).

Description

The invention relates to a device and a method for locating objects. The invention more particularly relates to a device and a method for locating mobile objects in a volume or a specific area (building for example). The invention may relate in particular to a device comprising a plurality of moving objects, in particular pressurized fluid bottles, each object being provided with a first wireless communication element for transmitting and receiving radiofrequency waves and at least a second wireless communication element receiving infrared signals, the device further comprising at least one communication beacon comprising a first wireless communication member and at least one second wireless communication member transmitting infrared signals, each beacon communication device comprising an electronic clock and being configured to periodically broadcast an infrared signal containing information indicating its location, each object being configured to receive and process said infrared localization signal transmitted by the beacon or beacons via the second communication member, each object also including an electronic clock and a radio frequency signal being configured to remotely transmit a signal comprising object identification information and location information received by the one or more tags. The invention particularly relates to a device for locating a plurality of moving objects such as pressurized fluid bottles equipped with wireless communication systems.

Object location devices based on a radio signal (by signal level evaluation (RSSI) or by measuring the propagation time) are currently a problem of precision when it is necessary to detect the presence of an object in a space defined as a room for example. Either technology seamlessly traverses the partitions, it is difficult or impossible to dispel the doubt about the presence of the object in an adjacent room or room. Other technologies with very high frequency or ultrasound are more precise but pose a problem of cost and consumption. The invention relates in particular to a system for locating moving objects, for example gas cylinders, based on the cooperation of a radio link and an infrared link enriched with a synchronization system ensuring a very high low power consumption.

The documents US5917425 and WO9218956A disclose moving object positioning systems based on the cooperation of a radio link and an infrared link. These documents relate to badge detection systems.

In the case in particular where the moving objects comprise a source of energy (battery (s), such a localization system is generally very energy-consuming.The device described in the document US5917425 describes a periodic awakening of the receiver ( mobile object) to limit power consumption, but this solution still consumes too much power for some applications.

An object of the present invention is to overcome all or part of the disadvantages of the prior art noted above. For this purpose, the device according to the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the objects and tags are automatically switchable between a standby state and an active state. and configured to periodically synchronize their active states upon transmission / reception of the infrared location signals emitted by the one or more tags to the objects, i.e. the tags (3) and objects (2) synchronize to communicate in an active state and to remain in standby mode the rest of the time, to save their power consumption.

Thus, the synchronization and therefore the alarm (active mode more electrical consumer than the standby mode) is performed with both the receiver (object) and the infrared transmitter (beacon). This is obtained via a clock broadcast. This also reduces tag consumption.

The synchronization of the tags 3 and objects 2 which reduces the energy consumption of the two groups of objects. Indeed, the tag or tags 3 emit at a known moment of objects which limits the power supply period of infrared reception.

Furthermore, embodiments of the invention may include one or more of the following features: the device comprises a central communication station comprising a first wireless communication element for transmitting and receiving radiofrequency waves, the first communication organs on the one hand objects and / or beacon (s) and on the other hand, the central station being configured to exchange data, in particular object identification data and location of the latter, - the objects are configured to switch their second communication element from a standby state to an active state on receipt of infrared signals periodically and in a given time window, the tag or beacons are configured to switch their second infrared communication device from a state of standby to an active state periodically and in a given time window, - the temp window orelle has a duration of between 5 milliseconds and a minute and preferably has a duration of one second, - the central communication station comprises an electronic clock and is configured to send simultaneously to the objects and / or to the at least one tag ( 3) a synchronization signal of the corresponding clocks, - the synchronization signal of the clocks of the objects and beacons (s) sent by the communication unit is a radiofrequency type signal, - the device comprises several distinct beacons, at least some of the beacons being configured to activate their second wireless communication device non-simultaneously or to broadcast periodically and in turn an infrared signal containing beacon location information, - at least a portion of the beacons comprises an infrared signal receiver , the synchronization signals of the clocks of the objects and beacon (s) being sent by the central unit communication device and / or by a reference beacon and is an infrared type signal, - the device comprises a reference beacon whose first wireless communication member is provided with a radio frequency receiver, the device comprising at least one other beacon comprising an infrared signal receiver, the reference beacon being configured to receive a synchronization signal from its radio frequency clock and to transmit, in response, an infrared signal for synchronizing the clocks of the other beacons so that the reference beacon and the other beacons transmit sequentially their periodic infrared signal containing location and possibly identification information, the beacons are configured to repeat several times the periodic diffusion of the infrared signal containing location information during the determined time window; duration of said window determined re time during which the second wireless communication member is switched from a standby state to an active state is equal to the time elapsed since the last reception of a synchronization signal, possibly multiplied by a drift factor understood by For example, between 5 ppm and 50 ppm, the second wireless communication member with infrared signal transmission of each communication beacon is configured to send modulated signals at a frequency of between 10 KHz and 500 KHz and preferably 32.768 KHz. the second infrared-signal wireless communication member of each communication beacon is configured to generate and send a signal comprising a main carrier wave at the determined frequency and digitally modulated via a standard serialization unit in the form of 8-bit words formed of four groups of "manchester" type bits, - the tags are in the re of N, N being an integer, the reference beacon being a first beacon called "beacon No. 1", the beacons being configured to sequence their respective periodic broadcasts of an infrared signal containing information indicating the location of the beacon , in which a determined duration P (in seconds) is provided between the emission of said signal by two consecutive tags in that the tag number "n", (n being an integer between 2 and N) is configured to activate its first wireless communication device, in particular its infrared receiver, in a period prior to the periodic diffusion of an infrared signal, said activation period being greater than or equal to nxP, and, in the event of reception in this prior period, of the beacon signal reference, use the instant of reception of this signal to synchronize its clock with the clock of the reference beacon and to deactivate er its first wireless communication device, in particular its infrared receiver, until the scheduled time for the periodic broadcast of an infrared signal, or, if the signal of the reference beacon is not received in this prior period, wait for the reception of the following tag n + 1 and repeat the operation to the tag n = N-1, - the duration of the determined time window during which the second wireless communication member is switched from a standby state to an active state is equal to the elapsed time of the preceding window multiplied by the product of the time elapsed since the last reception of a synchronization signal by a drift factor of, for example, between (1 + 5E-6) and (1 + 120E- 6). The invention also relates to a method for locating objects in a determined volume, using a device comprising a plurality of moving objects, in particular bottles of pressurized fluid, each object being provided with a first wireless communication member to transmission and reception of radiofrequency waves and at least one second infrared signal-receiving wireless communication element, the device further comprising at least one communication beacon comprising a first wireless communication member and at least one second organ wireless communication device with infrared signal transmission, each communication beacon comprising an electronic clock and being configured to periodically broadcast an infrared signal containing information indicating its location, each object being configured to receive and process said location signal transmitted by the or tags via the second common organ ication, each object also comprising an electronic clock and being configured to periodically remotely transmit by radio-frequency wave an infrared signal comprising object identification information and location information received by the one or more tags, objects and tags being automatically switchable between a standby state and an active state, the method comprising a step of periodically synchronizing their active states during the transmission / reception of the location signals transmitted by the one or more tags to the objects, that is, the tags and objects are synchronized to communicate in an active state and to remain in sleep mode the rest of the time to save their power consumption. The invention may also relate to any alternative device or method comprising any combination of the above or below features. Other features and advantages will appear on reading the following description, with reference to the figures in which: - Figure 1 shows a schematic and partial view illustrating an example of structure and operation of a locating device according to an exemplary embodiment of the invention, - Figures 2 to 4 show schematic and partial views illustrating examples of the structure and operation of elements of the device of Figure 1, respectively, an object, a beacon and a central station FIG. 5 represents a schematic and partial view of a detail of structure and operation of the locating device of FIG. 1, illustrating an example of signal transmission, in particular infrared transmission, - FIG. 6 represents a schematic view. and partial symbolizing an example of synchronization signals of electronic clocks of the localization device, FIG. 7 represents a schematic and partial view symbolizing a first example of emission of an infrared signal by a beacon of the location device with respect to a time window of observation; FIG. 8 represents a schematic and partial view symbolizing a second example of transmission of a signal by a beacon of the locating device with respect to a time window of observation.

The locating device illustrated in FIG. 1 can be used in a building (for example a hospital or a factory) to locate objects such as communicating bottles of fluid under pressure.

The device comprises moving objects 2, one or more communication beacons 3 and, preferably, a central communication station 4.

The objects 2 are equipped with a first wireless communication device 12 for transmitting and receiving radiofrequency type waves (radiofrequency transmitter / receiver in frequency ranges of preferably between 430 MHz and 960 MHz) and a second communication member 22 comprising one or more infrared receivers. The mobile object 2 (in particular its electronic communication devices) is powered autonomously from a battery 52 or a rechargeable battery or any other appropriate source of energy.

The beacons 3 are preferably equipped with a first radiofrequency wireless communication member (radiofrequency transmitter / receiver) and a second wireless communication member 23, namely an infrared emitter. The infrared transmitter 23 may consist of one or more infrared LEDs. Each tag 3 can also be powered independently from a battery 53, a rechargeable battery or any other suitable system. For example, if the installation allows, each tag 3 can also be powered by a wired electrical network.

The central station 4 is equipped for example with a first wireless communication member 14 such as a radiofrequency transmitter / receiver. The central station 4 is configured to be able to communicate, either directly or by means of relays, with the mobile objects 2 and the beacons 3. As previously, the station 4 is supplied with energy by an independent source or by a network.

Each beacon 3 is equipped with an internal clock 33 and is configured to broadcast periodically an encoded infrared signal indicating its location (for example a location code uniquely associated with the local area in the building).

Each mobile object 2 in view (within range of signal) of a beacon 3 receives the infrared signal, decodes it and deduces the value of the location code associated with the beacon in infrared visibility. As illustrated in FIG. 5, the signal can be received directly or via reflection / diffusion on the walls of the room delimiting the volume.

Each mobile object 2 is also equipped with an internal clock 32. Periodically, each object 2 transmits to the central station 4 a radiofrequency information including its identifier and the location code (received from the tag or tags 3). The central station 4 can then locate the mobile objects 2 on the basis of this information.

In order to minimize the energy consumption of both beacons 3 and moving objects 2, and thus to allow, for example, autonomous battery power, the device is preferably configured as described below.

The central station 4 synchronizes beacons 3 and mobile objects 2 during a radio transmission concerning it. The rate of resynchronization is chosen to ensure the proper operation of the device despite the inevitable slippage of different internal clocks.

Similarly, all mobile objects 2 in connection with a reference station 4 activate their infrared receiver 22 only in a predetermined and common observation time window. For example, at the second "zero" of each hour. Outside this time window, the consumption induced by the infrared reception is zero or almost zero (standby mode as opposed to an active mode).

Similarly, all the tags 3 in connection with a reference station 4 transmit their infrared localization code only in the common time window (for example substantially in the middle of this window). Outside this window, the tags 3 also remain in a rest mode (standby) in which only their internal clock 33 is active.

To treat the case of a large room (for example several tens of meters in length) that could not be covered by a single tag 3 (infrared transmitter), a particular device can use several tags for the same location, this without risk of interference between tags 3.

The common time window can be divided into several sub-windows of the same duration (for example 10 windows of 100 milliseconds if the main window is 1 second).

Each of the tags 3 may have a unique identification code or may share the same location code as the tags present in the same room. Each tag is for example assigned a number of "sub-window" of its own. Thus, if there are P tags in the same room, where P is an integer (and thus sharing the same location), the P tags will emit at a different time, which will not cause a collision between the infrared signals.

The location code transmitted by each beacon 3 and the window number can be introduced very simply during installation, for example by means of a coding wheel, or introduced using the radio link. For reasons of energy consumption, it will be advantageous to use short codes, (for example, and 66bit and in particular between 0 to 15 bit). In order to guarantee the relevance of the location indication transmitted by the mobile objects 2, they preferably automatically delete the location code received after a given period (for example 3 times the period of transmission of the locations by the tags 3). .

To increase the responsiveness of the system during the movement of the objects 2, the system can be configured to trigger a continuous transmission by the tags 3 of the location code which amounts to making two consecutive time windows. In addition, the infrared receiver 22 of the mobile object 2 can be activated before each of its radio frequency transmissions. This mode of operation (temporary or not), however, will constantly feed the beacons 3 via for example the power grid.

The period of transmission of the infrared signal can be chosen arbitrarily (if it is greater than the infrared transmission time of these N tags). But the power consumption will be inversely proportional to this period, which should be chosen wisely to maximize the life of the batteries.

The main modulation of the infrared signal preferably uses a frequency of a few tens of KHz and ideally 32,768 KHz. This makes it possible to ensure the operation of the transmitter from a very low consumption clock, the frequency of 32.768 KHz being that universally used for clock functions (digital watches, computer). The use of a particular bit rate in the infrared transmission (full fraction of the clock frequency of 32.768 KHz) further reduces the consumption of the infrared reception side (object 2).

The digital signal used to modulate (in all or nothing) the infrared subcarrier (at 1.213 KHz for example, which is close to the standard frequency of 1.200 KHz) can be directly produced by a standard serialization unit ("UART", such as found in all usual processors) in the form of 8-bit words consisting of 4 groups of "manchester" bits. This makes it possible to simplify the transmission and reception functions and to avoid activating the processor for receiving each bit of data. The impact is particularly interesting if a modern processor capable of receiving data while the heart is in idle mode is used ("Low Energy UART" Low Energy UART). More precisely, for sending an 8-bit word whose bits are B1 to B8, noting Bx * the inverse bit of Bx, we would have the following transmissions, which satisfy the Manchester criterion:

Octet 1:

To further reduce the power consumption of the system and increase the reliability of operation, the device can be configured to synchronize the emissions of several beacons 3 located in the same room or volume via infrared signals. This reduces the cost and the probability of malfunction (the infrared channel is assumed to be less easily disturbed than the radio channel).

Alternatively or in combination, the device may be configured to compensate for the effects of desynchronization of communicating elements (tag 3 or mobile objects 2) in the event of a temporary malfunction of the radio used for clock synchronization.

Example of synchronization of emissions via infrared signals.

In the case where a large room is covered by several tags 3, they must emit clocked (or sequential) to avoid the superposition of infrared signals. Indeed, in case of simultaneous transmission by several tags 3, there may be a data collision and therefore a loss of information.

The solution described above (synchronization by radio) requires radio equipment of all the tags 3. To reduce costs, an alternative solution of infrared synchronization is possible In this case or the tags 3 are equipped with a receiver 43 infrared in addition to the infrared transmitter 23.

Such an infrared synchronization makes it possible to reduce the costs of the device (for example by about 30%).

For simplicity, a reference tag (called for the sake of explanation "the tag # 1") is then arbitrarily considered as the master of the other tags 3 (# 2, 3 ... up to N integer) of " slaves "that will lock in relation to the reference tag. This timing can be achieved according to the process below.

If P is the nominal duration (in seconds) separating the emission of two consecutive tags 3, the tag number "n" (n integer between 2 and N) will open a period of observation prior to its emission and set to receive l transmitting beacon 1, ie a period of nxP, preferably increased by a safety margin determined according to the probable drift of the clocks since the last synchronization. If the signal of the beacon No. 1 is received, then on the one hand the reception time is used to reset the internal clock 33 of the beacon "n" and, on the other hand, the reception is stopped ( standby mode) until the expected time for the signal from the "n" beacon is reached. If the signal of the beacon n ° 1 is not received (which can be related to its distance in space), then the beacon n (if n is greater than 2), waits for a possible reception of the beacon n ° 2 . If there is no reception from beacon 2, the same process is performed until the number N-1.

This mechanism described above allows on the one hand to treat the case of large premises, thanks to the possibility of synchronization step by step, and on the other hand to cope with interference situations of the infrared signal leading to a temporary loss of synchronization.

In the latter case, the observation period of the beacons 3 can also be increased in order to immediately be able to operate the resynchronization after disappearance of the interference.

Since the radio communication channel is an open definition channel, the risk of communication failure is still to be considered. This break can make it impossible to synchronize the objects 2 on a common clock 44 for an indefinite duration that varies according to the source of the disturbance. So that this break in the synchronization mechanism does not cause application dysfunction (in this case the absence of location code reception) one or two particular configurations can be chosen according to the priority given to the respective consumptions.

According to a first configuration, the mobile objects 2 (infrared receivers 22) can increase their observation time window (active mode) of the time error value induced by the absence of synchronization. This value of the temporal error is for example equal to the value of their natural clock drift (evaluated in relative, typically in ppm) multiplied by the time elapsed since the last synchronization. The object 2 is naturally able to measure the elapsed time, as long as it has an internal clock 32, the maximum value of the drift being determined by design, typically between zero and the value of the maximum drift in a second possible configuration, the beacons 3 may repeat several times the emission of their signal (infrared code) in order to guarantee that at least one emission will be completely received during the time window of the clock. 'observation. This is preferably done taking into account the cumulative offsets of the transmissions and the reception windows with respect to the nominal position. In order to satisfy the criterion, the infrared transmitter 23 must perform, symmetrically with respect to its nominal emission, several emissions.

Thus the number Ne (Ne integer) of emissions can be calculated according to the various parameters including among: - the absolute value of the maximum relative drift of the transmitting clock (beacon) number without dimensions, generally of the order of 20 ppm (ie 10'6), - the absolute value Dr of the maximum drift of the receiving clock (moving object) also dimensionless and of the same order of magnitude. - the duration of the observation window Fon nominal of the moving object for example 0.1 seconds), - the nominal synchronization period tsn, expressed in the same units as Fon (for example 60 seconds) - the duration ts elapsed since the last synchronization; according to the formula Ne = 2 * (Ent (2 * (De + Dr) * ts) / Fon) +1 with Ent being the integer function.

The infrared emissions are obviously arranged preferably symmetrically with respect to the nominal emission.

Similarly, the nominal observation window Fon can itself be calculated to compensate for clock drifts Fon> 2 (De + Dr) * Tsn.

FIG. 7 represents, by a square signal, the emission period E infrared and the observation window Fon in the nominal case.

FIG. 8 represents the positioning of several infrared emission periods E to take into account the relative drifts of the transmitter and the receiver, the observation window Fon of the object 2 and the window Fd corresponding to a maximum forward drift.

For placement of the device in semi-open areas (volumes), an area may be delimited by a corner in a room and a barrier. To set up the system, it is then possible to place transparent plastic curtains for the visible range but reflecting for the infrared waves.

It will be understood that the device and method above makes it possible to propose a simple, reliable and energy-saving system for automatic inventories of objects, in particular gas cylinders.

As a variant or combination of infrared communications, the device can use light-emitting diode ("led" or equivalent) transmissions transmitting data invisible to the eye but detectable by appropriate receivers. This could provide some or all of the following functions: illumination of the object store 2, presence detection of object (s) (to determine movements, because there is always a doubt about rarely emitting objects), location coding .

Claims (12)

1. Device (1) for locating objects (2) in a determined volume, comprising a plurality of moving objects (2), in particular bottles of fluid under pressure, each object (2) being provided with a first member Wireless communication device (12) for transmitting and receiving radiofrequency waves and at least one second infrared signal receiving wireless communication member (22), the device (1) further comprising at least one beacon (3). ) comprising a first wireless communication member (13) and at least one second infrared signal wireless communication member (23), each communication tag (3) comprising an electronic clock (33) and being configured for periodically broadcasting an infrared signal containing information indicating its location, each object (2) being configured to receive and process said infrared localization signal transmitted by the beacon (s) (3) via the second o communication member (22), each object (2) also comprising an electronic clock (32) and being configured to periodically remotely transmit a signal comprising object identification information (2) and a signal location information received by the one or more tags (3), characterized in that the objects (2) and tags (3) are automatically switchable between a sleep state and an active state and configured to periodically synchronize their active states when the transmitting / receiving infrared location signals transmitted by the one or more beacons (3) to the objects (2), i.e. the beacons (3) and objects (2) synchronize to communicate in a state active and to remain in standby mode the rest of the time, to save their power consumption, in that the device comprises several separate tags (3) and in that at least some of the tags (3) are configured for activating their second non-simultaneous wireless communication member (23) or for periodically and alternately broadcasting an infrared signal containing location information of the beacon (3), and comprising a beacon ( 3) of which the first wireless communication member (13) is provided with a radio frequency receiver, the device comprising at least one other beacon (3) comprising a receiver (43) of infrared signals and in that the beacon ( 3) is configured to receive a synchronization signal from its radio-frequency clock (32) and to transmit, in response, an infrared clock synchronization signal (32) from the other beacons (3) so that the beacon ( 3) and the other beacons (3) sequentially emit their periodic infrared signal containing location and possibly identification information. 2. Device according to claim 1, characterized in that it comprises a station (4) central communication comprising a first member (14) wireless communication transmission and reception of radiofrequency waves, the first members (12, 13 , 14) of communication on the one hand objects (2) and / or tag (s) (3) and on the other hand, the central station (4) being configured to exchange data, including data from identifying the objects (2) and locating them. 3. Device according to any one of claims 1 to 2, characterized in that the objects (2) are configured to switch their second member (22) of communication from a standby state to an active state receiving infrared signals periodically and within a specified time window. 4. Device according to any one of claims 1 to 3, characterized in that the one or more beacons (3) are configured to switch their second infrared communication member (23) from a standby state to a periodically active state and in a given time window. 5. Device according to any one of claims 3 or 4, characterized in that the time window has a duration between 5 milliseconds and a minute and preferably has a duration equal to one second. 6. Device according to any one of claims 1 to 5, characterized in that the station (4) communication center comprises an electronic clock (44) and is configured to send simultaneously to the objects (2) and / or to the least one beacon (3) a synchronization signal of the corresponding clocks (44, 32, 33). 7. Device according to claim 6, characterized in that the synchronization signal clocks (32, 33) objects (2) and beacons (3) sent by the central (4) communication is a signal of radio frequency type. 8. Device according to any one of claims 1 to 7, characterized in that at least a portion of the beacons (3) comprises a receiver (42) of infrared signals and in that the clock synchronization signals (32, 33) objects (2) and beacon (s) (3) is sent by the communication unit (4) and / or a reference beacon (3) and is an infrared type signal. 9. Device according to claim 3, characterized in that the beacons (3) are configured to repeat several times the periodic broadcast of the infrared signal containing location information during the determined time window. 10. Device according to any one of claims 3 or 9, characterized in that the duration of said determined time window during which the second member (22) wireless communication is switched from a standby state to an active state is equal to the time elapsed since the last reception of a synchronization signal, possibly multiplied by a drift factor of, for example, between 5 ppm and 50 ppm. 11. Device according to any one of claims 1 to 10, characterized in that the second infrared signal-transmitting wireless communication element (23) of each communication beacon (3) is configured to send modulated signals to a signal. frequency between 10 KHz and 500 KHz and preferably 32.768 KHz. 12. A method for locating objects (2) in a determined volume, using a device comprising a plurality of moving objects (2), in particular bottles of pressurized fluid, each object (2) being provided with a first member Wireless communication device (12) for transmitting and receiving radiofrequency waves and at least one second infrared signal receiving wireless communication member (22), the device further comprising at least one communication beacon (3). having a first wireless communication member (13) and at least one second infrared signal transmitting wireless communication member (23), each communication tag (3) comprising an electronic clock (33) and being configured to periodically broadcast an infrared signal containing information indicating its location, each object (2) being configured to receive and process said localization signal transmitted by the beacon (s) (3) via the sec communication member (22), each object (2) also comprising an electronic clock (32) and being configured to periodically remotely transmit an infrared signal comprising an identification information of the object (2) by radio frequency and location information received by the one or more beacons (3), characterized in that the objects (2) and beacons are automatically switchable between a sleep state and an active state, the method comprising a periodically synchronizing step of active state during the transmission / reception of the location signals transmitted by the one or more tags (3) to the objects (2), that is to say that the tags (3) and objects (2) are synchronized to communicate in an active state and to remain in the standby mode the rest of the time to save their power consumption, and in that the device comprises several separate tags (3) and in that at least some of the ba lises (3) are configured to activate their second wireless communication member (23) non-simultaneously or to periodically broadcast, in turn, an infrared signal containing beacon location information (3), and that it comprises a reference beacon (3) whose first wireless communication member (13) is provided with a radio frequency receiver, the device comprising at least one other beacon (3) comprising a receiver (43) of infrared signals and in that the reference beacon (3) is configured to receive a synchronization signal from its radio frequency clock (32) and to transmit, in response, an infrared clock synchronization signal (32) from the other beacons (3) in such a way that the reference beacon (3) and the other beacons (3) sequentially emit their periodic infrared signal containing location and possibly identification information.