FR3098304A1 - A method of determining at least one location for enhanced reception of a backscattered ambient signal - Google Patents

Abstract

Method for determining at least one location for improved reception of a backscattered ambient signal The invention relates to a method for determining at least one location for reception, by at least one receiving device (D_RX) associated with an area (Z_T), of an ambient radio signal backscattered by at least one transmitting device (D_TX), said transmitting device being associated with: - operating states, including at least one so-called “backscattering” state as well as one said state. of “non-backscattering”, - a frequency band called “working band”. In addition, said method is implemented by the receiving device when the transmitting device is in the non-backscattering state and comprises, for at least one sub-band of the working band: - a step (E10) of travel of the receiving device in at least part of said zone, - during the course of the receiving device, a step (E20) for acquiring electromagnetic power measurements in said sub-band and at respective locations, - a step (E30 ) comparing said measurements with a determined threshold, a location associated with a measurement being determined (E40) as being a reception location if said measurement is below said threshold. Figure for the abstract: Fig. 4.

Description

Method for determining at least one location for improved reception of a backscattered ambient signal

The present invention belongs to the general field of telecommunications. It relates more particularly to a method for determining at least one location for the reception, by at least one receiver device, of an ambient radio signal intended to be backscattered by at least one transmitter device. It also relates to a communication method between at least one transmitter device and at least one receiver device, by backscattering of an ambient radio signal. The invention finds a particularly advantageous application, although in no way limiting, for applications of the "Internet of Things" type ("Internet of Things" or IoT in the Anglo-Saxon literature).

Ambient backscatter technology is well known today. The technical principles on which this technology is based are described, in particular, in the document by N. Van Huynh et al. entitled “Ambient Backscatter Communications: A Contemporary Survey”, in IEEE Communications Surveys & Tutorials, vol. 20, no. 4, p. 2889-2922, Fourthquarter 2018.

Conventionally, the backscattering of an ambient signal takes place between at least one transmitting device and at least one receiving device. Furthermore, and as envisaged so far, said devices each occupy a fixed position.

The ambient signal concerned corresponds to a radio signal emitted, permanently or else recurrently, by a source in a given frequency band. For example, it can be a television signal, a mobile phone signal (3G, 4G, 5G), a Wi-Fi signal, a WiMax signal, etc.

To communicate with a receiver device, a transmitter device uses the ambient signal to send data to said receiver device. More particularly, the transmitter device reflects the ambient signal towards the receiver device, possibly by modulating it. The signal thus reflected is called a “backscattered signal”, and is intended to be decoded by the receiver device.

The fact that no additional radio wave (in the sense of a wave other than that resulting from the ambient signal) is emitted by the transmitting device makes the ambient backscatter technology particularly attractive. Indeed, the energy cost of a communication is thus optimized, which is particularly important in the current context of the IoT where each object of everyday life is intended to become a communicating object.

To implement this technology, the transmitter device is equipped with at least one antenna configured to receive the ambient signal but also to backscatter it to the receiver device.

The transmitting device is also associated with operating states, including at least one so-called "backscatter" state (the transmitting device backscatters the ambient signal) as well as an opposite state called "non-backscattering" (the transmitting device is transparent to the ambient signal). These states correspond to configurations in which said at least one antenna is connected to different impedances.

The receiver device, for its part, is configured to decode the backscattered signal. That said, and in practice, the implementation of this decoding can be deteriorated (decoding error, poor reception of the backscattered signal) due to the existence of interference at the level of the receiver device.

Indeed, the transmitter and receiver devices are generally positioned in a complex propagation environment comprising elements (walls, trees, ground, etc.) likely to generate reflections and diffractions of waves emitted by the source. Thus, and schematically, two types of signals reach the receiver device: the backscattered signal, the only carrier of data useful for the implementation of ambient backscattering, as well as a signal coming directly from the source called "interfering signal" and resulting from multiple reflections/diffractions of waves (by “directly”, reference is made here to waves not originating from the backscattered signal). Due to said reflections/diffractions, said interfering signal corresponds to a sum of waves which interfere with each other constructively or destructively. Consequently, the power distribution generated by this interfering signal is not uniform and presents areas where the power is locally maximum or, conversely, locally minimum. The areas where the power is locally maximum (respectively locally minimum) are areas where the level of interference is the highest (respectively the lowest).

FIG. 1 schematically represents an electromagnetic power distribution map radiated by a source. Such a map was generated in a manner known per se by digital simulation considering a wave propagation model corresponding to a Rayleigh distribution. The aspects related to the modeling of wave propagation are well known to those skilled in the art, and are therefore not recalled here.

In the example of Figure 1, said source corresponds to a television tower transmitting in a frequency band equal to [583 MHz, 590 MHz]. Said map corresponds to a square of side equal to 1m25. The radiated power levels are represented using level lines, it being understood that the more an area of the map has narrowing lines, the more this area corresponds to a local minimum of radiated power.

As illustrated by Figure 1, the power distribution has a plurality of local minima, and therefore ultimately also a plurality of local maxima. By way of example, zones Z_1, Z_2, Z_3 and Z_4, each comprising a local maximum of radiated power (power substantially equal to 5 dB), are indicated. Each zone Z_i, for i varying from 1 to 4, covers the portion of the map contained inside the dotted curve surrounding the acronym “Z_i”. Two other zones Z_5 and Z_6, each comprising a local radiated power minimum (power substantially equal to -6 dB), are also indicated, using arrows. Each zone Z_i, for i varying from 5 to 6, covers the portion of the map contained inside the dotted curve pointed by the arrow associated with said zone Z_i.

Ultimately, the existence of areas where the level of interference is high, in addition to the fact that the transmitter and transmitter devices occupy fixed positions, proves to be problematic to ensure good communication between these devices. Indeed, it is understood that if the receiver device occupies a position in a zone of locally maximum power (for example one of the zones Z_1, Z_2, Z_3 or Z_4), the level of interference can be high enough for the implementation decoding of the backscattered signal is compromised, thus causing communication between the devices to fail.

To circumvent this problem, solutions have been proposed implementing, at the level of the receiver device, signal processing techniques aimed at estimating, in a signal received by said receiver device, a component due to such interference. Once estimated, such a contribution is subtracted in order to retain only the signal useful for decoding, namely the backscattered signal. However, these techniques remain very complex to implement.

The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above, by proposing a solution which makes it possible to determine a location of at least one receiver device, so as to avoid that it cannot decode, due to interference, a signal backscattered by at least one transmitting device, and thus optimize the communication between these devices.

To this end, and according to a first aspect, the invention relates to a method for determining at least one location for the reception, by at least one receiver device, of an ambient signal emitted in a frequency band, called "d band". 'transmission', and intended to be backscattered by at least one transmitter device to the receiver device, said transmitter device being associated with:
- operating states, including at least one so-called "backscatter" state as well as a contrary state called "non-backscatter",
- a frequency band, called "working band", included in said emission band,
said receiver device being associated with a zone depending on said transmission band. Furthermore, said method is implemented by the receiver device when the transmitter device is in the non-backscattering state and comprises, for at least one sub-band of said working band:
- a step of traversing the receiver device in at least part of said zone,
- during the course of the receiver device, a step of acquiring electromagnetic power measurements received by said receiver device, the measurements being acquired in said sub-band and at respective locations of said part,
- a step of comparing said measurements with a determined threshold, a location associated with a measurement being determined as being a reception location if said measurement is below said threshold.

It should be noted that the expression "sub-band" is here defined in the broad sense, and thus refers to a frequency band of width less than or equal to the width of the working band. Consequently, nothing excludes, according to a particular example of implementation, to consider a sub-band equal to the working band B_T.

Thus, the determination method according to the invention makes it possible to envisage a path of the receiver device within at least part of said zone. In other words, and unlike the methods of the state of the art, the receiver device is not forced to remain fixed and can advantageously move with a view to detecting at least one location at which the electromagnetic power received in a sub -band of the working band is low enough for the associated level of interference to make it possible to envisage good communication by backscatter with the transmitting device.

It is also noted that insofar as the method is implemented when the ambient signal is not backscattered, said at least one location corresponds to a location in which the power generated by the interfering signal is lower than the threshold. In other words, the method according to the invention offers the possibility of optimizing the contribution of the backscattered signal, in terms of power received by the receiver device, when the transmitter device switches to a backscatter state.

The determination method according to the invention therefore offers the possibility, in the case where a location is actually determined, of avoiding the failure of a communication between the transmitting device and the receiving device. The invention thus advantageously overcomes the disadvantages presented by the solutions of the state of the art and which are linked to the stationarity of the transmitter and receiver devices.

In addition, the determination method according to the invention is particularly simple to implement in that it does not require the use of complex signal processing techniques, such as for example techniques which would aim to estimate and delete, in a signal received by said receiver device, a component due to interference.

In particular modes of implementation, the method for determining at least one location may also include one or more of the following characteristics, taken in isolation or in all technically possible combinations.

In particular modes of implementation, a plurality of sub-bands is considered, said sub-bands being distinct from each other, and at least the browsing and acquisition steps being iterated for each of said sub-bands.

The fact of considering sub-bands of the working band makes it possible to discretize the latter, thus offering the possibility of finely detecting in the vicinity of which frequencies the level of interference is low enough to consider effective communication between the devices, it being understood that this level of interference varies according to the frequency considered for the acquisition of measurements.

In particular embodiments, said method comprises, when several locations have been determined and the transmitter device is in the non-backscattering state, a step of selecting, among said locations, a location, called " optimal location”, of which an associated electromagnetic power measurement is minimum among the power measurements associated with said locations.

Said optimal location therefore designates a location in which the power received from the source is minimized, so that the level of interference will also be minimal when the receiver device occupies said optimal location to receive the backscattered signal in the sub-band associated with the extent for which the power is thus minimized. In this way, the communication between the transmitter and receiver devices will be optimized.

In particular modes of implementation, the route of the receiver device is carried out in the entire zone.

Proceeding in this way makes it possible to maximize the probability of finding a local power minimum during the course of the receiver device. Indeed, the more the path is carried out in a wide area, the greater the probability of finding a local power minimum.

In particular modes of implementation, the route of the receiver device is carried out in an autonomous manner or in an assisted manner.

In particular modes of implementation, the measurements are acquired according to a determined time step or a determined distance step between each location in said part of the zone.

In particular embodiments, the transmitter device is associated with a determined operating pattern over time corresponding to alternations between the non-backscatter state and said at least one backscatter state, the receiver device having knowledge of said flowsheet.

Such arrangements advantageously make it possible to facilitate the implementation of the determination method while the transmitting device is in the non-backscattering state, without it being necessary for an operator to intervene.

In particular embodiments, a plurality of transmitting devices is considered, the steps of said method being implemented when said transmitting devices are simultaneously in the non-backscatter state.

According to a second aspect, the invention relates to a method of communication between at least one transmitter device and at least one receiver device, by backscattering of an ambient radio signal emitted in a frequency band, called "emission band", said device transmitter being associated with:
- operating states, including at least one so-called "backscatter" state as well as a contrary state called "non-backscatter",
- a frequency band, called "working band", included in said emission band.
said receiver device being associated with a zone depending on said transmission band. Furthermore, said method comprises:
- a step of determining at least one location for reception according to a method according to the invention,
- when at least one location has been determined and the transmitter device is in the non-backscattering state, a step of moving the receiver device in the zone, so as to reach a fixed position depending on said at least one determined location ,
- a step of backscattering, by the transmitter device, of the ambient signal,
- a step of reception, by the receiver device and in the sub-band associated with a measurement from which said at least one location has been determined, of the backscattered ambient signal.

Thus, once at least one location has been determined, the receiver device can move to such a location in which it will occupy a fixed position, for example for a determined duration, to receive the ambient signal backscattered by the transmitter device .

In particular modes of implementation, the communication method may also include one or more of the following characteristics, taken in isolation or in all technically possible combinations.

In particular modes of implementation, when an optimal location is determined, said fixed position corresponds to the position of the receiver device when it has carried out the measurement of minimum electromagnetic power associated with said optimal location, reception taking place in the sub-band associated with said minimum power measurement.

In particular modes of implementation, the steps of determining at least one location, of moving the receiver device so as to reach a fixed position, of backscattering and of receiving are iterated in a recurring manner.

Such arrangements make it possible to take into account the variability of the environment in which the transmitter device and the receiver device are positioned.

Typically, elements likely to reflect and/or diffract the waves coming from the ambient signal can see their respective positions modified in the environment close to the transmitter and receiver devices. By way of purely illustrative example, if the transmitter and receiver devices are placed in an apartment room and furniture is moved, a location previously determined to be suitable for backscattering may no longer be suitable. By "no longer suitable", we refer here to the fact that the power level may no longer be below the threshold, the power distribution having been modified due to the movement of the cabinet.

Thus, the fact of considering a recurring implementation of the communication method according to the invention advantageously allows the receiver device to adapt to an environment liable to change.

According to a third aspect, the invention relates to a computer program comprising instructions for implementing a method for determining at least one location according to the invention or a communication method according to the invention when said program is executed by a computer.

According to a fourth aspect, the invention relates to a computer-readable recording medium on which a computer program according to the invention is recorded.

According to a fifth aspect, the invention relates to a receiver device for receiving an ambient radio signal emitted in a frequency band, called the "emission band", and intended to be backscattered by at least one transmitter device to said receiver device , said transmitter device being associated with:
- operating states, including at least one so-called "backscatter" state as well as a contrary state called "non-backscatter",
- a frequency band, called "working band", included in said emission band,
Furthermore, said receiver device is associated with a zone depending on said transmission band and comprises:
- means of movement in said zone,
- acquisition means, configured to acquire electromagnetic power measurements received by said receiver device, the measurements being acquired in at least one sub-band of said working band and at respective locations of said zone,
- a comparison module, configured to compare the measurements respectively associated with said locations with a determined threshold,
- a determination module, configured to determine, when one of said measurements is below said threshold, that the location associated with said measurement is a location for receiving the ambient signal intended to be backscattered.

In particular embodiments, said receiver device comprising a control module, configured to command, when at least one location for reception has been determined, a movement of the receiver device in the zone, so as to reach a fixed position according to said at least one determined location.

According to a sixth aspect, the invention relates to a communication system comprising at least one receiver device according to the invention and at least one transmitter device.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof which is devoid of any limiting character. In the figures:
FIG. 1 schematically represents an electromagnetic power distribution card radiated by a source corresponding to a television tower;
FIG. 2 schematically represents, in its environment and in a particular embodiment, a communication system 10 according to the invention;
FIG. 3 schematically represents a partial view of an exemplary embodiment of a transmitter device D_TX of the communication system according to the invention;
FIG. 4 represents, in the form of a flowchart, the main steps of a method for determining at least one location for the reception of a backscattered ambient signal according to the invention;
FIG. 5 schematically represents a preferred mode of implementation of the determination method of FIG. 4;
FIG. 6 represents, in the form of a flowchart, the main steps of a communication method according to the invention.

FIG. 2 schematically represents, in its environment and in a particular embodiment, a communication system 10 according to the invention.

The communication system 10 comprises a transmitter device D_TX which remains fixed, as well as a receiver device D_RX.

In the remainder of the description, and as illustrated by the embodiment of FIG. 2, it is considered in a non-limiting manner that the communication system 10 comprises a single transmitter device D_TX and a single receiver device D_RX. It should however be specified that the invention is also applicable to a communication system comprising a plurality of transmitting devices and/or a plurality of transmitting devices.

The operation of the communication system 10 is based on ambient backscatter technology. This technology consists, in a manner known per se, of the backscattering, by the transmitter device D_TX and towards the receiver device D_RX, of an ambient radio signal emitted in a determined frequency band, called the “emission band”. In other words, to communicate with the receiver device D_RX, the transmitter device D_TX uses said ambient signal to send data to said receiver device D_RX. More particularly, the transmitter device D_TX reflects the ambient signal towards the receiver device D_RX, possibly by modulating it. The signal thus reflected is called “backscattered signal”, and is intended to be decoded by the receiver device D_RX.

The aspects concerning the transmission of data by backscatter intended for the receiver device D_RX, as well as those concerning the decoding techniques implemented by the latter, are known to those skilled in the art and fall outside the scope of the present invention. Therefore, they are not detailed here further.

The ambient signal corresponds to a radioelectric signal emitted, permanently or else recurrently, by at least one source 20. For the rest of the description, and as illustrated by FIG. 2, we consider in no way limiting the case where the ambient signal is emitted by only one source. However, no limitation is attached to the number of sources that can be considered in the context of the present invention, since these sources emit in respective bands whose intersection is not empty and which also intersects an associated frequency band to the transmitter device D_TX, as described below in more detail.

By “radioelectric signal”, reference is made here to an electromagnetic wave propagating by non-wired means, the frequencies of which are included in the traditional spectrum of radioelectric waves (a few hertz to several hundred gigahertz).

The remainder of the description relates more specifically, but in no way limiting, to an ambient UHF signal (acronym of the expression “Ultra High Frequencies”) emitted by a television tower in the emission band [583 MHz, 590 MHz] .

It should however be specified that the invention remains applicable to any type of radioelectric signal, such as for example a mobile telephone signal (for example 3G, 4G, 5G), a Wi-Fi signal, a WiMax signal, a DVB- T, etc

Moreover, no limitation is attached to the structural forms that can be taken respectively by the source 20 and the receiver device D_RX. By way of non-limiting examples, the following configurations are possible (depending, of course, on the transmission band considered):
- the source 20 is a base station, and the D_RX receiver device is a smartphone,
- the source 20 is a smartphone, and the D_RX receiver device is a base station,
- the source 20 is a smartphone, and the receiver device D_RX is also a smartphone,
- the source 20 is a home gateway (also called "Internet box") emitting a Wi-Fi signal, and the receiver device D_RX is a smartphone.

The waves conveyed by the signals considered in the present invention are represented conceptually by wavy arrows in FIG. 2. More particularly, the arrows F_1 and F_2 represent waves of the ambient signal emitted by the source 20. The waves represented by the arrow F_1 are backscattered by the transmitter device D_TX, and the waves of the backscattered signal are here represented by the arrow F_3. The waves represented by the arrow F_2 are not backscattered and arrive directly at the receiver device D_RX. It is further noted that only the waves represented by the arrow F_3 transport the data that the receiver device D_RX is intended to decode.

It should be noted that Figure 2 is given for purely illustrative purposes. Thus, for example, it does not include any element likely to reflect or diffract the waves of the ambient signal. In this sense, Figure 2 is intended to be a simplified version of the environment in which the D_TX transmitter and D_RX receiver devices are located. It should nevertheless be kept in mind that this environment is generally of a complex configuration and includes, in practice, elements (walls, trees, ground, etc.) capable of generating such reflections and diffractions.

As mentioned before, the transmitter device D_TX and the receiver device D_RX are respectively configured in order to communicate with each other by ambient backscatter.

FIG. 3 schematically represents a partial view of an exemplary embodiment of the transmitter device D_TX of FIG. 2. The configuration of such a transmitter device D_TX is known to those skilled in the art.

As illustrated by FIG. 3, the transmitter device D_TX is equipped with an antenna 111 configured, in a manner known per se, to receive the ambient signal but also to backscatter it towards the receiver device D_RX. It should be noted that no limitation is attached to the number of antennas that can equip the D_TX transmitter device.

In the example of Figure 3, said antenna is constructed so as to have a larger dimension substantially equal to half the wavelength associated with a frequency F_C included in the transmission band. More specifically, the F_C frequency considered here is the central frequency of the transmission band [583 MHz, 590 MHz], i.e. 586.5 MHz. Thus, said largest dimension of the antenna 111 is substantially equal to 25 cm.

In practice, the transmitter device D_TX is associated with a frequency band, called "influence band", which corresponds to the frequency band in which the antenna 111 is able to receive/backscatter signals. Thus, in the example given above with reference to FIG. 3, said band of influence corresponds to a frequency interval centered on said frequency F_C, and whose amplitude is equal to a sampling frequency F_E applied by an analog/digital converter equipping the transmitter device D_TX to the signals likely to be received. In other words, said band of influence is equal to [F_C - F_E / 2, F_C + F_E/2].

For example, said sampling frequency is equal to 1 MHz, and the influence band is then equal to [585.5 MHz, 587.5 MHz]. It is then noted that the influence band is included in the emission band associated with the source 20. Because of this inclusion, said influence band is qualified as “working band” B_T. By “working band”, reference is made here to the fact that the transmitter device D_TX is compatible with the source 20, namely therefore that the backscattering can be performed for any frequency included in said working band B_T.

However, nothing excludes considering other values for the frequencies F_C and F_E. It nevertheless clearly appears that for the transmitter device D_TX to be able to backscatter the ambient signal, said influence band should have a non-empty intersection with said emission band, the working band B_T corresponding as soon as at this intersection. Thus, if the transmitter device D_TX is configured so as to be associated with an influence band containing the transmission band, then the working band B_T of said transmitter device D_TX is defined as being equal to said transmission band.

The transmitter device D_TX is also associated with operating states, namely a state called "backscatter" (the transmitter device D_TX backscatters the ambient signal) as well as a contrary state called "non-backscatter" (the transmitter device D_TX is transparent to the ambient signal). These states correspond to configurations in which said antenna 111 is connected to distinct impedances. It is typically a positive or even zero impedance in the case of a backscattering state, and conversely a theoretically infinite impedance in the case of the non-backscattering state.

For example, and as illustrated by FIG. 3, the transmitter device comprises two switches 112, 113 configured so as to be able to connect to the antenna 111, according to their respective positions, an impedance I_1, for example equal to 0 Ohms, or even equal to R Ohms where R is a finite strictly positive value. When at least one of the switches 112, 113 is not connected to the impedance I_1, the antenna 111 is in a so-called "open circuit" configuration corresponding to said non-backscattering state.

In addition, the transmitter device D_TX is configured to perform, from the ambient signal received via its antenna 111 and when it is in the backscatter state, processing aimed at backscattering said ambient signal, by implementing a method of backscatter.

To this end, the transmitter device D_TX comprises for example one or more processors and storage means (magnetic hard disk, electronic memory, optical disk, etc.) in which are stored data and a computer program, in the form a set of program code instructions to be executed to implement the backscatter method.

Alternatively or in addition, the transmitter device D_TX also comprises one or more programmable logic circuits, of the FPGA, PLD, etc. type, and/or specialized integrated circuits (ASIC), and/or a set of discrete electronic components, etc. adapted to implement the backscattering method.

In other words, the transmitter device D_TX comprises a set of means configured in software (specific computer program) and/or hardware (FPGA, PLD, ASIC, etc.) to implement the backscatter method.

The aspects specifically related to the implementation of the backscattering method (processing of the ambient signal, modulation, etc.) are outside the scope of the present invention, and are also known to those skilled in the art. Therefore, they are not detailed here further.

The D_RX receiver device, on the other hand, is configured to:
- receive the ambient signal emitted by the source 20, including in particular any reflections and diffractions undergone by the waves of this signal due to elements placed in the environment in which the transmitter D_TX and receiver D_RX devices are located,
- receive the backscattered signal from the transmitter device D_TX.

To this end, said receiver device D_RX comprises at least one reception antenna. It should be noted that no limitation is attached to the number of antennas that can equip the D_RX receiver device.

The receiver device D_RX is also associated with a zone Z_T determined according to said transmission band. Such a zone Z_T corresponds to a geographical space within which the receiver device D_RX can move from an initial location that it occupies, to find a location in which the distribution of power radiated by the source 20 is locally minimal.

Said zone Z_T is for example defined at the time of design of the receiver device D_RX.

Alternatively, said zone Z_T is defined while the receiver device D_RX already occupies a position in situ, depending on a type of source from which it is desired to backscatter the ambient signal. For this purpose, a message comprising information defining said zone Z_T can be transmitted, for example by an operator, to the receiver device D_RX.

Preferably, said zone Z_T has at least one dimension substantially equal to half the wavelength associated with a frequency included in the emission band, preferably a frequency corresponding to the central frequency of said emission band. The fact of considering such a value for said at least one dimension results from the fact that the local minima of the distribution of power radiated by the source 20 (such as for example those associated with the zones Z_5 and Z_6 in FIG. 1) are on average two two separated by a distance equal to half the wavelength associated with the center frequency of the transmission band. It is therefore thus understood that the fact of considering a zone Z_T having at least such a dimension advantageously allows the receiver device D_RX to maximize the probability of finding a local minimum during a movement in said zone Z_T.

By way of non-limiting example, such a zone Z_T is illustrated in FIG. 1. In this example, the frequency considered in the transmission band is said frequency F_C, so that said at least one dimension of the zone Z_T is equal to 25 cm. More particularly, the zone Z_T here corresponds to a square whose side length is equal to 25 cm. Furthermore, the receiver device D_RX occupies an initial location corresponding to the center of this square. It is noted that this initial location is determined independently of any a priori knowledge of the power distribution radiated by the source 20.

Nothing excludes however, according to other examples not detailed here, to consider a zone of shape different from a square, as well as having one or several (or even all) dimensions lower or higher than half of the wavelength associated with a frequency included in the transmission band. Furthermore, no limitation is attached to the initial location occupied by the receiver device D_RX within the zone Z_T. For example, in the case where the zone Z_T is a square, said initial location may correspond to a corner of this square.

The D_RX receiver device further comprises displacement means (not shown in the figures) in said zone Z_T, and more broadly throughout the environment in which the D_TX transmitter and D_RX receiver devices are located.

For example, said displacement means comprise drive means, such as for example at least one electric motor, as well as guide means, such as wheels for example. However, nothing excludes considering other means of training, such as a heat engine, as well as other means of guidance, such as tracks.

Preferably, the receiver device D_RX takes the form of a robot comprising an electric motor and wheels. For example, such a robot is intended to evolve in a hangar in which goods are stored, these goods being likely to be extracted from the hangar, one by one, in order to be dispatched following orders from consumers. Said transmitter device D_TX, for example of the computer type, is capable of updating the inventory of the stock of goods in the hangar. Therefore, the data backscattered to the D_RX receiver device can be representative, at a given instant, of a part of said inventory, this part relating to a zone of the hangar in which the D_RX receiver device is moving.

The receiver device D_RX also comprises acquisition means configured to acquire, at at least one location of said zone Z_T, measurements of electromagnetic power received by said receiver device D_RX, said measurements being respectively acquired in at least one sub-band of said working band B_T.

It should be noted that the expression “sub-band” is defined here in the broad sense, and thus refers to a frequency band of width less than or equal to the width of the working band B_T. Consequently, nothing excludes considering a sub-band equal to the working band B_T.

Conventionally, said acquisition means comprise an acquisition chain connected to a sensitive element configured to supply an analog electrical signal representative of the measured electromagnetic power. In the present exemplary embodiment, said sensitive element corresponds to a reception antenna fitted to the receiver device D_RX.

Said acquisition chain comprises for example an acquisition card configured to condition said electrical signal. The conditioning implemented by the acquisition card comprises for example, in a manner known per se, an amplification and/or a filtering and/or a current-power conversion. In general, the configuration of such acquisition means is well known to those skilled in the art, and is therefore not detailed here further.

It should be noted that the acquisition means are configured to carry out the acquisition of power measurements both in the non-backscattering state and in the backscattering state of the transmitter device D_TX.

In a particular embodiment, the transmitter device D_TX is associated with a determined operating pattern over time corresponding to alternations between the non-backscatter state and the backscatter state. For example, determined durations are allocated respectively to the non-backscattering state and to the backscattering state, the transmitter device D_TX operating according to said states according to said allocated durations. It should be noted that such an operating scheme is for example defined in a telecommunications standard.

Furthermore, in this particular embodiment, the receiver device D_RX is aware of said operating diagram. This knowledge comes for example from one or more data representative of said operating diagram and stored by the receiver device D_RX. These data are for example transmitted to the receiver device D_RX by an operator or even by the transmitter device D_TX itself.

However, nothing excludes considering that the transmitter device D_TX is not associated with any determined operating scheme. For example, switching from the backscatter state to the non-backscatter state (and vice versa) is achieved in an operator-assisted manner, depending on specific communication needs between the devices. Again, the knowledge of the state (backscatter or non-backscatter) of said transmitting device D_TX, by the receiving device D_RX, can come from a message transmitted to said receiving device D_RX, this message comprising data representative of the state. For example, this message is transmitted by an operator or else by the transmitter device D_TX itself.

In any event, and according to the invention, the receiver device D_RX is able to perform processing (for example a determination method as described later) when the transmitter device D_TX is in the non-backscatter state. In other words, the receiving device D_RX can perform such processing by synchronizing with periods during which the transmitting device D_TX is in the non-backscatter state.

The receiver device D_RX is also configured to perform, on the basis of power measurements acquired at at least one location, processing aimed at determining at least one location for the reception of the backscattered signal, by implementing all or part of the steps of a method for determining said at least one location.

For this purpose, the receiver device D_RX comprises for example one or more processors and storage means (magnetic hard disk, electronic memory, optical disk, etc.) in which are stored data and a computer program, in the form a set of program code instructions to be executed to implement at least some of the steps of the determination method.

Alternatively or in addition, the receiver device D_RX also comprises one or more programmable logic circuits, of the FPGA, PLD, etc. type, and/or specialized integrated circuits (ASIC), and/or a set of discrete electronic components, etc. suitable for implementing all or part of the steps of the determination method.

In other words, the D_RX receiver device comprises a set of means configured in software (specific computer program) and/or hardware (FPGA, PLD, ASIC, etc.) to implement all or part of the steps of the determination process.

In addition to allowing the determination of at least one location for reception, said means configured in software and/or hardware also make it possible to control the movement of the receiver device D_RX.

For this purpose, these means comprise for example a control module (not shown in the figures) configured to generate movement commands for the receiver device D_RX. Such commands can be generated regardless of the state (backscatter or non-backscatter) of the D_TX transmitting device.

For example, said commands are generated unattended. In other words, the receiver device D_RX is able to move in the zone Z_T autonomously, that is to say without the intervention of an operator.

Alternatively, the control of the receiver device D_RX is carried out in an assisted manner by an operator who remotely generates control signals, these control signals then being transmitted to said receiver device D_RX which moves according to the data conveyed in these signals. To this end, the receiver device D_RX comprises for example communication means for receiving said control signals, said signals then being processed by the piloting module. These means of communication are based, in a manner known per se, on a communication interface capable of exchanging data between said operator and said receiver device D_RX. No limitation is attached to the nature of this communication interface, which can be wired or wireless, so as to allow the exchange of data according to any protocol known to those skilled in the art (Ethernet, Wifi, Bluetooth , 3G, 4G, 5G, etc). There is also nothing to exclude considering, according to another example, that said control signals are received by a reception antenna of the receiver device D_RX.

For the remainder of the description, it is considered in no way limiting that the operation of the receiver device D_RX is ensured by electrical energy that the latter is able to store.

For example, said electrical energy is contained in an electric battery integrated in said D_RX receiver device, and which can be recharged for example by means of solar panels fitted to said D_RX receiver device, or else by capacitive effect, so that the D_RX receiver device is energetically autonomous. Alternatively, said battery is recharged via a connection to the domestic electrical network.

However, nothing excludes considering other types of energy, such as fossil energy, in particular in the case where the D_RX receiver device is equipped with a heat engine. Finally, nothing excludes considering an energy mix (electrical and thermal).

In other words, and in general, no limitation is attached to the energy considered for the operation of the receiver device D_RX, nor even to the way in which this energy is obtained by the latter.

In addition, and as mentioned above, the receiver device D_RX is configured to perform processing aimed at decoding the backscattered signal, by implementing a decoding method.

To this end, and according to characteristics identical to those described above in the case of the means for implementing the determination method, the receiver device D_RX also comprises a set of means configured in software (specific computer program) and/or hardware (FPGA, PLD, ASIC, etc.) to implement said decoding method.

The aspects specifically related to the implementation of the decoding method are outside the scope of the present invention, and are also known to those skilled in the art. Therefore, they are not detailed here further.

FIG. 4 represents, in the form of a flowchart, the main steps of the method for determining at least one location according to the invention.

Said determination method is implemented by the receiver device D_RX when the transmitter device D_TX is in the non-backscatter state.

It is recalled here that the non-backscattering state corresponds to a configuration in which the antenna 111 of the transmitter device D_TX is in the open circuit configuration. Also, for the implementation of the determination method, no limitation is attached to the fact that the transmitter device D_TX is in operation or not (i.e. the energy necessary for the operation of the transmitter device D_TX is in use or no), as long as it is in the non-backscatter state.

Said determination method comprises several steps. In its general principle, it consists in carrying out, for at least one sub-band of the working band B_T, measurements of electromagnetic power at locations in the zone Z_T when the receiver device D_RX makes a journey, in order to be able to locate a location in which the electromagnetic power generated by the source 20 is sufficiently low, thus limiting the presence of interference liable to cause the decoding of a signal backscattered by the transmitter device D_TX to fail.

For the remainder of the description, and purely by way of illustration, it is considered that the distribution of power radiated by the source 20 at the time when the determination method is implemented conforms to the distribution represented by FIG. that the zone Z_T associated with the receiver device D_RX corresponds to that indicated in figure 1.

It is further considered that the receiver device D_RX occupies, before the implementation of said determination method, an initial location corresponding to the center of the square forming the zone Z_T. It should however be noted that no limitation is attached to the location of said initial location within, or indeed along the border, of said zone Z_T.

The method will now be described by placing oneself in the configuration in which several sub-bands SB_1, SB_2, etc. are considered within the working band B_T to carry out acquisitions of electromagnetic power measurements.

However, no limitation is attached to the number of sub-bands that can be considered. Thus, the invention remains applicable in the case where a single sub-band is considered, this sub-band also being able to be equal to the working band B_T.

Said sub-bands SB_1, SB_2…are distinct from each other. Preferably, said sub-bands SB_1, SB_2, etc. form a partition of the working band B_T. Such arrangements make it possible to optimize the discrimination of the measurements between them, with a view to determining a reception location, as described later.

For example, the width of an SB_i sub-band is equal to 100 kHz. No limitation is attached to the width that can be considered for a sub-band SB_i. Further, such a width may be prescribed by a telecommunications standard.

It should be noted that the choice consisting in considering sub-bands forming a partition of the working band B_T constitutes however only one implementation variant of the invention. Thus, nothing excludes considering sub-bands which partially overlap.

As illustrated by FIG. 4, said determination method comprises, for a band SB_i considered among the sub-bands SB_1, SB_2, etc., several steps including a step E10 of traversing the receiver device D_RX in at least part of the Z_T area.

Such a path of the D_RX receiver device allows the latter to scan at least part of the Z_T zone with the aim of discovering there at least one location at which the power radiated by the source 20 is low enough for the D_RX receiver device can decode the signal that will be backscattered.

By "journey", reference is made here to an exploration phase, this phase possibly comprising a continuous movement (that is to say without stopping within said part) between respectively initial and final locations in which the device receiver D_RX is fixed, or even can be made in a split manner (that is to say with one or more intermediate stops within said part before reaching a final location).

In a particular mode of implementation, the route of the receiver device D_RX is carried out autonomously, that is to say without external assistance. For example, said receiver device D_RX is configured to analyze the environment in which it is located, in order to detect possible obstacles which it can then circumvent. Such detection is typically implemented through imaging means (for example a camera) fitted to the D_RX receiver device, as well as through processing implemented by said D_RX receiver and aimed at analyzing images obtained with said means. of imagery. Such treatments are well known to those skilled in the art, and are therefore not detailed here further.

In another particular mode of implementation, the course of the receiver device D_RX is carried out in an assisted manner, for example by an operator able to remotely control the movements of the receiver device D_RX.

Whatever the mode of implementation considered (autonomous or assisted), the course of the receiver device D_RX can be carried out according to a determined trajectory, such as for example a spiral, a line, in slots, etc.

Alternatively, the movement of the receiver device D_RX can be performed in a non-deterministic manner.

In general, no limitation is attached to the trajectory followed by the receiver device D_RX.

Furthermore, said part of the zone Z_T is for example configured so as to include the initial location of the receiver device D_RX.

By way of illustration, and with reference to FIG. 1, said part corresponds to one half (for example the right half) of the square formed by the zone Z_T. Thus, the initial location belongs to the border of said part.

Alternatively, said part does not include the initial location, so that the receiver device D_RX performs a preliminary movement in order to reach said part which is then traversed.

In general, no limitation is attached to the shape presented by said part of the Z_T zone. In addition, the course of the receiver device D_RX can be carried out for a determined duration which can be parameterized, so that the shape of said part can depend on this determined duration.

In a particular mode of implementation, the displacement of the receiver device D_RX is carried out throughout the zone Z_T. Proceeding in this way makes it possible to maximize the probability of finding a local power minimum during the course of the receiver device D_RX.

The determination method also comprises, for said sub-band SB_i, during the course of the receiver device D_RX, a step E20 of acquisition of measurements of electromagnetic power Pi_1, Pi_2,... received by said receiver device D_RX. Said measurements P1_i, P2_i,… are acquired in said sub-band SB_i and at respective locations E1_i, E2_i,… of said part of zone Z_T.

In other words, for a location Ej_i (j being an integer index greater than or equal to 1) considered, a measurement Pj_i is acquired in the sub-band SB_i. A map, called “acquisition map”, is thus obtained, grouping together the measurements carried out in said part of the zone Z_T for said sub-band SB_i.

Acquisitions are preferably made when stopped (split exploration phase). In other words, during its course, the receiver device D_RX marks stops when it wishes to acquire, at a location Ej_i, measurements of electromagnetic power.

However, there is nothing to exclude considering that said measurements P1_i, P2_i, etc. are acquired while the receiver device D_RX is in motion.

In a particular example of implementation, if a plurality of locations is considered during the acquisition step E20, the measurements are acquired according to a determined time step, for example configurable, between each location in said part of the Z_T area. To do this, the receiver device D_RX moves for example at constant speed.

According to another example, or in addition to the previous one in which a determined time step is considered, and when several locations are considered during step E20, the measurements are acquired according to a determined distance step, for example configurable, between each location in said part of the Z_T zone.

The number of slots Ej_i considered for the sub-band SB_i corresponds for example to a determined number which can be parameterized for example. It should however be noted that no limitation is attached to the number of locations Ej_i that can be considered. Thus, the invention remains applicable in the situation where a single location is considered for said sub-band SB_i.

Furthermore, nothing excludes considering that one of said power measurements Pj_i is acquired in the sub-band SB_i and at the initial location when the receiver device D_RX is stopped.

The determination method also includes, for said sub-band SB_i, a step E30 of comparing the measurements Pj_i respectively associated with said locations with a determined threshold S_D.

This comparison step E30 is here implemented by a comparison module equipping the receiver device D_RX. It should be noted that although this step E30 is here described as being implemented when said transmitter device D_TX is in the non-backscattering state, nothing excludes considering, according to a particular embodiment, that said module comparison is also able to perform such a comparison during a backscatter state.

The threshold S_D considered here for the comparison is typically determined as a function of a determined decoding error rate as well as a reception noise considered acceptable on the receiver device D_RX side. In general, those skilled in the art know how to set a threshold S_D from which a location can be considered for reception.

Thus, by setting such a threshold S_D, the objective is to avoid that a location in which there is a lot of interference, at least enough for the decoding error rate to exceed a given threshold, from being considered as a location valid for backscatter signal reception.

For example, said threshold S_D is chosen to be sufficiently low, for example in the interval [-6 dB, -2 dB], more particularly in the interval [-6 dB, -4 dB].

The comparison performed during step E30 is for example implemented each time a power measurement is acquired in the sub-band SB_i.

Alternatively, said comparison is implemented once a determined journey time has elapsed and/or when a determined number of locations Ej_i has been reached during the journey (for example when all the measurements P1_i, P2_i,…respectively associated with said locations Ej_i have been acquired), said measurements being in this case stored by the receiver device D_RX during its journey.

According to yet another alternative, or indeed in addition to the preceding alternatives, said comparison is implemented once the entire part of the zone Z_T, or even all of said zone Z_T if applicable, has been traversed.

Consequently, for said sub-band SB_i, and during a step E40 of the determination method, a location Ej_i associated with a measurement Pj_i acquired is determined as being a reception location, said measurement Pj_i is lower than said threshold S_D.

This determination step E40 is here implemented by a determination module equipping the receiver device D_RX. It should be noted that although this step E40 is here described as being implemented when said transmitter device D_TX is in the non-backscattering state, nothing excludes considering, according to a particular embodiment, that said module determining is also capable of making such a determination during a backscatter state.

It is therefore a question here of carrying out a sorting among the locations E1_i, E2_i,… at which power measurements have been acquired.

According to an example of implementation, when the comparison of the measurements P1_i, P2_i,... with the threshold S_D is performed each time a power measurement is acquired, the determination step E40 is stopped as soon as a measurement acquired is determined below the threshold S_D.

Thus, in this example, if the first measurement P1_i acquired by the receiver device D_RX in the sub-band SB_i is performed at its initial location, and this measurement P1_i is less than the threshold S_D, said receiver device remains immobile.

Doing so not only helps to determine a location so that the backscattered signal can be decoded by the D_RX receiver device, but also optimizes the power consumption of the D_RX receiver device.

The steps of the method have been described so far by considering a single sub-band SB_i among the sub-bands SB_1, SB_2,… of the working band B_T.

Also, in the present mode of implementation of the determination method, once the steps of travel E10, acquisition E20, comparison E30 as well as the determination E40 of at least one location have been executed for one of said sub -bands, they are iterated for each of the remaining sub-bands. In other words, said sub-steps are iterated as many times as the number of sub-bands.

The choice consisting in iterating all the steps of the method when several sub-bands are considered, however, only constitutes a variant implementation of the invention. For example, the comparison steps E30 and/or determination E40 can be executed once all the routes have been performed (iterations of step E10) and all the measurements have been acquired during these routes (iterations of the step E20).

In general, carrying out such iterations makes it possible in particular to obtain acquisition maps for each of the sub-bands of the working band B_T. The fact of considering several sub-bands advantageously makes it possible to finely discriminate the frequencies of the working band B_T according to the interference levels respectively associated with each of them. Indeed, it is known that the power level received at a location, and therefore ultimately the level of interference at this location, varies according to the frequency considered to acquire measurements.

It is important to note that the locations considered during the different iterations can for example coincide with each other. In other words, according to this example, the acquisition cards include measurements acquired at identical locations from one iteration to the next. However, nothing excludes considering separate locations, in whole or in part, from one iteration to another.

By way of illustrative example, and with reference to FIG. 1, ten sub-bands, all of the same width equal to 200 kHz so as to form a partition of the interval [585.5 MHz, 587.5 MHz], are considered. According to this example, the receiver device D_RX traverses, for each sub-band, the entire part corresponding to the right half of the square formed by the zone Z_T, and carries out acquisitions according to a distance step equal to 2 cm between each location. Furthermore, in this example, the comparison of the measurements acquired is carried out once the ten paths of the receiver device D_RX have been carried out. At the end of the process, the receiver device D_RX has determined two reception locations located respectively inside the zones Z_5 and Z_6.

FIG. 5 schematically represents a preferred mode of implementation of the determination method of FIG. 4.

In this preferred mode of implementation, and as illustrated by FIG. 5, said determination method comprises, when several locations have been determined as being locations for reception, a step E50 of selecting, among said reception locations , of a location, called “optimal location” E_OPT, whose associated power measurement is the minimum among the power measurements associated with said reception locations.

Said optimal location E_OPT therefore designates a location at which the power received from the source 20 is minimized, so that the probability of interference being generated there is also minimal there when the receiver device D_RX occupies said optimal location E_OPT to receive the backscattered signal . In this way, the communication between the devices D_TX, D_RX is optimized.

Returning to the illustrative example mentioned above, and in which two locations have been determined in the zones Z_5 and Z_6, the optimal location E_OPT selected corresponds for example finally to the location associated with the zone Z_5.

The invention also relates to a communication method between the transmitter device D_TX and the receiver device D_RX.

FIG. 6 represents, in the form of a flowchart, the main steps of said communication method.

As illustrated by FIG. 6, said backscattering method firstly comprises a step F10 of determining at least one location for reception.

Such a determination step F10 is carried out in accordance with the determination method described above.

Subsequently, and when at least one reception location has been determined and the transmitter device D_TX is in the non-backscattering state, said backscattering method comprises a step F20 of moving the receiver device D_RX into the zone Z_T , so as to reach a fixed position POS_F depending on said at least one determined location.

For example, said fixed position POS_F corresponds to a position identical to that occupied by the receiver device D_RX when it has carried out the measurement associated with said at least one determined location. By "identical position", it should be understood that, if the receiver device D_RX is equipped with several antennas, the relative positions (in terms of geographical coordinates) of said antennas, when the receiver device D_RX reaches said fixed position POS_F, correspond exactly to the positions relative antennas at the time when the measurement associated with said at least one location was acquired.

The choice of such a fixed position POS_F only constitutes one implementation variant of the invention. For example, the receiver device D_RX can occupy a fixed position POS_F according to which the position (in terms of geographical coordinates) of its center of gravity is identical to the position of its center of gravity at the moment when the measurement associated with said at least one location has been acquired. Although there is a correspondence concerning the position of the center of gravity, the relative positions of the antennas for said fixed position can nevertheless differ from the relative positions of the antennas at the time when the measurement associated with said at least one location was acquired.

It should be noted that if several locations are determined, the fixed position POS_F is for example a function of the position of the receiver device D_RX when it has carried out the electromagnetic power measurements associated with any one of said determined locations.

Preferably, when an optimal location E_OPT is selected, said fixed position POS_F is identical to the position of the transmitter device D_TX when it has carried out the electromagnetic power measurement associated with said optimal location E_OPT.

Once the receiver device D_RX has reached said fixed position POS_F, the communication method comprises a step F30 of backscattering, by the transmitter device D_TX, of the ambient signal. To do this, said device D_TX switches from the non-backscatter state to the backscatter state.

Furthermore, the communication method also includes a step F40 of reception, by the receiver device D_RX and in the sub-band associated with a measurement from which said at least one location has been determined, of the backscattered ambient signal.

Continuing with the preferred example described earlier, in which an optimal E_OPT location is selected, reception occurs in the sub-band associated with the minimum power measurement.

Preferably, backscattering steps F30 and receiving steps F40 are implemented simultaneously. However, there is nothing to exclude considering a time lag between said backscattering steps F30 and receiving steps F40. It is nevertheless implicit that the transmitter devices D_TX and receiver D_RX communicate with each other as soon as the periods during which the backscattering steps F30 and receiving steps F40 are respectively implemented overlap at least partially.

In a particular mode of implementation, the steps of determination F10 of at least one location, of displacement F20 of the transmitting device so as to reach a fixed position POS_F, of backscatter F30 and of reception F40 are iterated in a recurring manner.

The fact of carrying out these steps in a recurring manner makes it possible to take into account the variability of the environment in which the transmitter device D_TX and the receiver device D_RX are positioned.

For example, said steps are iterated periodically, for example once a day in an environment in which the power distribution is stable, or even more, for example once every hour if the power distribution is likely to change substantially every hour.

The invention has been described so far considering that the transmitter device D_TX was associated with a single backscatter state as well as a single non-backscatter state. The invention nevertheless remains applicable in the case where the transmitter device D_TX is associated with a plurality of backscatter states, these states being distinct from one another in that they are implemented thanks to respective impedances that are distinct from each other. It will of course be understood that the non-backscattering state itself remains unique.

A person skilled in the art knows how to adapt the configuration of the transmitter device D_TX as shown in FIG. 3 to take several backscatter states into consideration. For example, with reference to FIG. 3, several mutually distinct impedances can be arranged in parallel between switches 112, 113.

Furthermore, the invention has also been described hitherto by considering a single transmitter device D_TX. The invention nevertheless remains applicable in the case where a plurality of transmitter devices D_TX is considered. For example, when a plurality of D_TX transmitter devices are considered, the steps of the method for determining at least one location (step E10 of course, step E20 of acquisition, step E30 of comparison, step E40 of determination, and step E50 selection if applicable) are implemented by the receiver device D_RX when said transmitter devices D_TX are simultaneously in the non-backscatter state. To ensure such simultaneity, said D_TX transmitting devices are for example synchronized with each other by GPS (acronym of the Anglo-Saxon expression "Global Positioning System") and each observe the same non-backscattering duration according to a period which is also theirs. common, such a duration and such a period being for example defined in a telecommunications standard. Preferably, said transmitter devices D_TX simultaneously backscatter the ambient signal (step F30).

It is clear to those skilled in the art that the provisions described above in the case where several synchronized D_TX transmitting devices are considered apply independently of the number of D_RX receiving devices considered. Preferably, when several D_RX receiver devices are considered, the reception step F40 is executed for each of said D_RX receiver devices simultaneously with the backscatter step F30.

Claims (16)

Method for determining at least one location for the reception, by at least one receiver device (D_RX), of an ambient signal emitted in a frequency band, called "emission band", and intended to be backscattered by at least a transmitter device (D_TX) to the receiver device (D_RX), said transmitter device (D_TX) being associated with:
- operating states, including at least one so-called "backscatter" state as well as a contrary state called "non-backscatter",
- a frequency band, called "working band", included in said emission band,
said receiver device (D_RX) being associated with a zone (Z_T) depending on said transmission band,
said method being implemented by the receiver device (D_RX) when the transmitter device (D_TX) is in the non-backscattering state and comprising, for at least one sub-band (SB_i) of said working band:
- a step (E10) of traversing the receiver device (D_RX) in at least part of said zone (Z_T),
- during the course of the receiver device (D_RX), a step (E20) of acquiring electromagnetic power measurements (Pj_i) received by said receiver device (D_RX), the measurements being acquired in said sub-band (SB_i) and at respective locations (Ei_j) of said part,
- a step (E30) of comparing said measurements with a determined threshold (S_D), a location associated with a measurement being determined (E40) as being a reception location if said measurement is below said threshold. Method according to claim 1, in which a plurality of sub-bands is considered, said sub-bands being distinct from one another, and at least the traversing (E10) and acquisition (E20) steps being iterated for each of said sub-bands. bands. Method according to any one of Claims 1 to 2, the said method comprising, when several locations have been determined and the transmitting device (D_TX) is in the non-backscattering state, a step (E50) of selecting, among the said locations, of a location, called “optimal location” (E_OPT), for which an associated electromagnetic power measurement is minimum among the power measurements associated with said locations. Method according to any one of Claims 1 to 3, in which the path of the receiver device (D_RX) is carried out in the entire zone (Z_T). Method according to any one of Claims 1 to 4, in which the path of the receiver device (D_RX) is carried out autonomously or in an assisted manner. Method according to any one of Claims 1 to 5, in which the measurements are acquired according to a determined time step or a determined distance step between each location in the said part of the zone (Z_T). Method according to any one of Claims 1 to 6, in which the transmitter device (D_TX) is associated with a determined pattern of operation over time corresponding to alternations between the "non-backscatter" state and the said at least one “backscatter” state, the receiver device (D_RX) having knowledge of said operating diagram. Method according to any one of Claims 1 to 7, in which a plurality of transmitting devices (D_TX) is considered, the steps (E10, E20, E30, E40, E50) of the method being implemented when said transmitting devices (D_TX ) are simultaneously in the non-backscatter state. Communication method between at least one transmitter device (D_TX) and at least one receiver device (D_RX), by backscattering of an ambient radio signal transmitted in a frequency band, called "transmission band", said transmitter device (D_TX) being associated with:
- operating states, including at least one so-called "backscatter" state as well as a contrary state called "non-backscatter",
- a frequency band, called "working band", included in said emission band,
said receiver device (D_RX) being associated with a zone (Z_T) depending on said transmission band, and said method comprising:
- a step (F10) of determining at least one location for reception according to a method in accordance with any one of claims 1 to 8,
- when at least one location has been determined and the transmitter device (D_TX) is in the non-backscattering state, a step (F20) of moving the receiver device (D_RX) in the zone (Z_T), so to reach a fixed position (POS_F) function of said at least one determined location,
- a step (F30) of backscattering, by the transmitter device (D_TX), of the ambient signal,
- a step (F40) of reception, by the receiver device (D_RX) and in the sub-band associated with a measurement from which said at least one location has been determined, of the backscattered ambient signal. Method according to claim 9, in which, when an optimal location (E_OPT) is determined, said fixed position corresponds to the position of the receiver device (D_RX) when it has carried out the measurement of minimum electromagnetic power associated with said optimal location (E_OPT ), reception taking place in the sub-band associated with said minimum power measurement. Method according to any one of Claims 9 to 10, in which the steps of determining (F10) at least one location, of moving (F20) the receiver device (D_RX) so as to reach a fixed position (POS_F), backscatter (F30) and receive (F40) are iterated recursively. Computer program comprising instructions for implementing a method for determining at least one location according to any one of claims 1 to 8 or a communication method according to any one of claims 9 to 11 when said program is executed by a computer. A computer-readable recording medium on which a computer program according to claim 12 is recorded. Receiver device (D_RX) for receiving an ambient radio signal emitted in a frequency band, called the "emission band", and intended to be backscattered by at least one transmitter device (D_TX) to said receiver device (D_RX), said transmitter device (D_TX) being associated with:
- operating states, including at least one so-called "backscatter" state as well as a contrary state called "non-backscatter",
- a frequency band, called "working band", included in said emission band,
said receiver device (D_RX) being associated with a zone (Z_T) depending on said transmission band and comprising:
- means of movement in said zone (Z_T),
- acquisition means, configured to acquire electromagnetic power measurements received by said receiver device (D_RX), the measurements being acquired in at least one sub-band of said working band and at respective locations of said zone (Z_T ),
- a comparison module, configured to compare the measurements respectively associated with said locations with a determined threshold,
- a determination module, configured to determine, when one of said measurements is below said threshold, that the location associated with said measurement is a location for receiving the ambient signal intended to be backscattered. Receiver device (D_RX) according to claim 14, said receiver device (D_RX) comprising a piloting module, configured to command, when at least one location for reception has been determined, a movement of the receiver device (D_RX) in the area (Z_T), so as to reach a fixed position (POS_F) depending on said at least one determined location. Communication system comprising at least one receiver device (D_RX) according to any one of Claims 14 to 15 and at least one transmitter device (D_TX).