EP4256729A1

EP4256729A1 - Method for controlling backscattering of an ambient signal, device for implementing said control method

Info

Publication number: EP4256729A1
Application number: EP21839240.5A
Authority: EP
Inventors: Dinh Thuy Phan Huy
Original assignee: Orange SA
Current assignee: Orange SA
Priority date: 2020-12-02
Filing date: 2021-11-30
Publication date: 2023-10-11
Also published as: US20240097805A1; WO2022117950A1; FR3116972A1

Abstract

The invention relates to a method for controlling the backscattering of an ambient signal emitted by an emitter device (SO). The method includes steps implemented by a transmitter device (D_TX) configured to backscatter the ambient signal: - acquiring (E20_1) a measurement (M_CUR) of power received from the emitter device; - evaluating (E20_3) a criterion (CRIT) consisting of at least checking whether a distance (D_COUV), counted from a position occupied by the transmitter device during the acquiring of the current measurement and in which a given reception quality value (VAL_C) is attained for a signal obtained by backscattering the ambient signal, is in a given interval (I_COUV), the distance of coverage being defined as a function of the measurement and the value; - if the criterion is met, ambient backscattering (E20_4) of the ambient signal; - if the criterion is not met, absence of ambient backscattering (E20_5) of the ambient signal.

Description

Title of the invention: Method for controlling the backscattering of an ambient signal, device for implementing said control method

Prior technique

The present invention belongs to the general field of telecommunications. It relates more particularly to a method for controlling the backscatter of an ambient signal transmitted by a transmitting source. It also relates to a transmitter device configured to implement said control method as well as an ambient backscatter communication system comprising said transmitter device. The invention finds a particularly advantageous application, although in no way limiting, for applications of the "Internet of Things" type ("Internet of Things" or loT in the Anglo-Saxon literature), in particular in the context of communications called " terminal to terminal” (“device-to-device communications” or even “D2D communications” in the Anglo-Saxon literature).

[0002] Ambient backscatter communication technology is well known today. The technical principles on which this technology is based are described, in particular, in the document: “Ambient Backscatter Communications: A Contemporary Survey”, N. Van Huynh, D. Thai Hoang, X. Lu, D. Niyato, P. Wang , D. In Kim, IEEE Communications Surveys & Tutorials, vol. 20, no. 4, p. 2889-2922, Fourthquarter 2018.

[0003] Conventionally, the backscattering of an ambient signal takes place between a transmitting device and a receiving device. The ambient signal concerned corresponds to a radio signal emitted, permanently or else recurrently, in a given frequency band by a source distinct from said transmitter and receiver devices. 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 the receiver device, the 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, optionally modulating it by selectively connecting an antenna which equips it to distinct impedances. The signal thus reflected is called a “backscattered signal”, and is intended to be decoded by the receiver device (i.e. the receiver device extracts from the backscattered signal information transmitted by the transmitter device, for example in the form of bits).

[0005] The fact that no additional radio wave (in the sense of a wave other than that coming from the ambient signal) is emitted by the transmitter device makes the backscattering technology particularly attractive environment. Indeed, the energy cost of a communication is thus reduced, which is particularly important in the current context of the IoT where each object of everyday life is intended to become a communicating object.

[0006] The fact remains that the conventional use of communication technology by ambient backscatter is carried out without checking the coverage that the transmitting device is able to provide (the source transmits independently of the coverage provided by the transmitting device). By “coverage”, reference is made here to the extent of the zone within which a quality of reception (“achievable received quality” in the Anglo-Saxon literature) of the backscattered signal is achieved, sufficient to guarantee correct decoding, for a possible receiver device positioned in said zone, of information transmitted by the transmitter device.

[0007] The fact that the coverage of the transmitter device cannot be controlled is problematic. Indeed, when the transmitter device is not sufficiently illuminated by the source (i.e. when the electromagnetic power received by the transmitter device from the source, via the ambient signal, is low), the coverage of the latter is restricted. This then results, for the transmitting device, in a useless expenditure of energy since the information that it can transmit by ambient backscatter can only be decoded with a very low probability.

Conversely, when the transmitter device is excessively illuminated by the source (i.e. when the electromagnetic power received by the transmitter device from the source, via the ambient signal, is very high), the coverage of the latter is high. . This has the effect of increasing the probability that the coverage of the transmitting device overlaps that of another transmitting device. However, such a superimposition is a source of mutual interference between the transmitting devices concerned. Consequently, the probability that the decoding of this information is compromised increases.

[0009] More recently, it has been proposed to extend the conventional scope of use of ambient backscatter communication technology by integrating it into the implementation of D2D communications. In more detail, it is a question of implementing, in addition to traditional modes of communication (up/down mode in which a terminal/a base station transmits data to a base station/a terminal ), another mode, called “backscatter mode”, in which two terminals communicate with each other by ambient backscatter. The addition of backscattering mode advantageously makes it possible to unload the network used for the traditional modes, and therefore to save frequency resources.

[0010] The transition from a traditional mode to said backscattering mode takes place conditionally. In particular, it is possible to assess, during a preliminary phase, a criterion consisting in checking, on the receiving device side, whether the quality of reception of a backscattered signal is sufficient to ensure correct decoding of information transmitted by the transmitting device. If the criterion is verified, the passage from the traditional mode to the said backscatter mode is validated (sending of a message from the receiver device to the transmitter device to signify this validation). It is therefore understood that the fact of authorizing the use of ambient backscattering only under conditions makes it possible to control the coverage of the transmitting device (absence of ambient backscattering if the quality of reception is insufficient). For more details concerning these aspects, those skilled in the art can refer to the document: "Wireless-Powered Device-to-Device Communications with ambient backscattering: performance modeling and analysis", X. Lu, H. Jiang, D. Niyato , DI Kim, Z. Han, IEEE Transactions on Wireless Communications, vol. 17, no. 3, p. 1528-1544, March 2018.

[0011] The fact remains that these recent developments (evaluation of a criterion on the receiver device side in the context of D2D communications) remain complex to implement. Indeed, exchanges of signals are necessary between the transmitter device and the receiver device to confirm that the backscatter mode can be implemented (the system formed by the transmitter and receiver devices is a closed loop control system given the transmission of a backscattered signal and the sending of the validation message relating to said backscattered signal).

[0012] Furthermore, the evaluation of the criterion requires the implementation, by the receiver device, of complex calculations aimed at decoding the backscattered ambient signal (extraction of information in the backscattered signal by implementing attenuation processing interference). These complex calculations are moreover carried out whatever the final decision, namely validation or not of a switch to the backscattering mode.

Disclosure of Invention

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 control the coverage of a transmitter device in a simpler way than the solutions of the prior art. Consequently, the solution proposed by the invention also makes it possible to more easily control the selective implementation of a communication by ambient backscatter.

[0014] To this end, and according to a first aspect, the invention relates to a method for controlling the ambient backscattering of a signal, called “ambient signal”, emitted by a transmitter device. Said method comprises a so-called “current phase” phase implemented by a transmitter device configured to backscatter said ambient signal and comprising steps of: - acquisition of a measurement, called "current measurement", of electromagnetic power received from the transmitter device via the ambient signal received,

- evaluation of a criterion consisting of at least verifying whether a distance, called "coverage distance", counted from a position occupied by the transmitter device during the acquisition of the current measurement and in which a value is reached given, called “target value”, of reception quality of a signal obtained by ambient backscattering of the ambient signal, is included in a given interval, said coverage distance being defined according to said current measurement and said target value,

- if said criterion is satisfied, ambient backscattering of the ambient signal,

- if said criterion is not satisfied, absence of ambient backscattering of the ambient signal.

The method according to the invention therefore proposes that it be the transmitter device which alone controls its coverage via said evaluation step.

[0016] More specifically, the transmitter device carries out, on the basis of the current measurement acquired, calculations allowing it to assess whether the theoretical coverage distance in which the target value of the reception quality is reached ("achievable received quality in Anglo-Saxon literature) remains included in the given interval. In other words, the transmitter device thus performs a simulation of the coverage that it is able to provide when it is illuminated by the source under conditions which cause it to acquire said current measurement.

[0017] Thus, thanks to the method of the invention, the transmitter device is able to control its coverage on its own, without the assistance of another device, as is done in the state of the art. The transmitter device therefore does not require, from any other device, confirmation as to the possibility of implementing the backscatter of the ambient signal.

[0018] In particular modes of implementation, the control method may also comprise one or more of the following characteristics, taken in isolation or in all technically possible combinations.

In particular modes of implementation, said target value is a value of any one of the following quantities:

- a signal to noise ratio,

- a signal-to-noise plus interference ratio,

- a decoding error rate.

[0020] In particular modes of implementation, the ambient signal is characterized by:

- a first spectral density when the current measurement acquisition step is executed,

- a second spectral density, distinct from said first spectral density, when the step evaluation of the criterion is carried out.

Further, said coverage distance is also defined as a function of the ratio between said first and second power spectral densities.

[0021] Such provisions make it possible to take account of variations in the conditions of illumination of the transmitter device by the transmitter device. In this way, the transmitter device can achieve finer control over its coverage, and therefore a fortiori also over the possibility of backscattering of the ambient signal.

In particular embodiments, the transmitter device is configured to backscatter said ambient signal to at least one receiver device, said receiver device being configured to decode said backscattered ambient signal, said transmitter and receiver devices being respectively characterized by antenna gains G_TX and G_RX, said coverage distance also being defined as a function of said antenna gains G_TX and G_RX.

[0023] Knowing the values of such antenna gains allows the transmitter device to perform an evaluation of the criterion based on an analytical expression derived from the Friis equation.

In particular modes of implementation, said method comprises, before the implementation of said current phase, a preliminary experimental phase during which the transmitter device is fixed and comprising steps of acquisition, by the transmitter device , of a measurement, called "reference measurement", of electromagnetic power received from a transmitter device emitting a signal, called "experimental ambient signal",

- ambient backscattering of the experimental ambient signal by the transmitter device and towards a receiver device configured to decode said backscattered experimental ambient signal, said experimental preliminary phase further comprising, during the execution of said ambient backscattering step, a search for a location at which the backscattered experimental ambient signal is received by the receiver device with a reception quality reaching said target value, the distance separating the receiver device from the transmitter device when such a location has been found being called the "reference distance" and said coverage distance also being defined as a function of said reference measurement and said reference distance.

[0025] Such provisions allow the transmitter device to carry out an evaluation of the criterion from an alternative analytical expression with respect to that which can be used when the antenna gains G_TX, G_RX are given.

[0026] In particular modes of implementation, said current phase further comprises a step of determining the coverage distance, said at least one verification carried out during the evaluation of the criterion consisting of a direct verification of the belonging of the coverage distance determined to said interval.

[0027] In particular embodiments, the interval associated with the coverage distance comprises a lower limit and an upper limit, said current phase further comprising steps of:

- determination of an electromagnetic power, called "minimum power", which, if it is received by the transmitting device from the transmitting device, allows said target value to be reached at a distance counted from the position occupied by the device transmitter during the acquisition of the current measurement and equal to said lower limit,

- determination of an electromagnetic power, called "maximum power", which, if it is received by the transmitting device from the transmitting device, allows said target value to be reached at a distance counted from the position occupied by the device transmitter during acquisition of the current measurement and equal to said upper limit, said at least one verification performed during the evaluation of the criterion consisting in verifying whether the current measurement is between said minimum and maximum powers.

[0028] In particular modes of implementation, the transmitter device is mobile at a speed V between instants at which said steps of acquisition and evaluation of said current phase are executed, the evaluation of the criterion also consisting in verifying whether the duration separating said instants of execution is sufficiently small compared to the ratio λ/V, where λ corresponds to the wavelength of the carrier frequency of the ambient signal, so that the electromagnetic power received by the transmitting device from of the transmitting device via the ambient signal is substantially constant during said duration.

[0029] The fact of including carrying out such a verification (in addition to the verification relating to the belonging of the coverage distance to the given interval) makes it possible to ensure that the illumination conditions of the transmitter device remain stable over time despite the fact that the latter is in motion.

According to a second aspect, the invention relates to a computer program comprising instructions for the implementation of at least the steps of the current phase of a control method according to the invention when said program is executed. by a computer.

[0031] This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in no any other desirable shape. According to a third aspect, the invention relates to an information or recording medium readable by a computer on which is recorded a computer program according to the invention.

The information or recording medium can be any entity or device capable of storing the program. For example, the medium may comprise a storage means, such as a Flash type memory, for example a USB key or an SSD (“Solid State Drive”) disk, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or alternatively a magnetic recording medium, such as a hard disk, for example a hard disk HDD (“Hard Disk Drive”).

[0034] On the other hand, the information or recording medium can be a transmissible medium such as an electrical or optical signal, which can be conveyed via an electrical or optical cable, by radio or by other means. . The program according to the invention can in particular be downloaded from an Internet-type network.

Alternatively, the information or recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

According to a fourth aspect, the invention relates to a transmitter device for controlling the ambient backscatter of a signal, called “ambient signal”, emitted by a transmitter device. Said transmitter device is configured to backscatter said ambient signal and comprises:

- an acquisition module configured to acquire a measurement, called "current measurement", of electromagnetic power received from the transmitter device via the ambient signal received,

- an evaluation module configured to evaluate a criterion consisting of at least verifying whether a distance, called "coverage distance", counted from a position occupied by the transmitter device during the acquisition of the current measurement and which a given value, called "target value", of reception quality of a signal obtained by ambient backscattering of the ambient signal is reached, is included in a given interval, said coverage distance being defined as a function of said current measurement and said target value,

- a control module configured to implement the backscatter/not implement the backscatter of the ambient signal if said criterion is satisfied/not satisfied.

According to a fifth aspect, the invention relates to an ambient backscatter communication system, said system comprising a transmitter device configured to transmit an ambient signal and a transmitter device according to the invention. Brief description of the drawings

Other characteristics and advantages of the present invention will become apparent from the description given below, with reference to the appended drawings which illustrate an example of embodiment devoid of any limiting character. In the figures:

[Fig. 1] FIG. 1 schematically represents, in its environment, a particular embodiment of a communication system by ambient backscatter according to the invention;

[Fig. 2] FIG. 2 schematically represents an example of hardware architecture of a transmitter device according to the invention belonging to the communication system of FIG. 1;

[Fig. 3] FIG. 3 represents, in the form of a flowchart, a particular mode of a control method according to the invention, as it is implemented by the transmitter device of FIG. 2;

[Fig. 4] FIG. 4 represents, in the form of a flowchart, another particular mode of the control method according to the invention;

[Fig. 5] FIG. 5, in the form of a flowchart, yet another particular mode of the control method according to the invention.

Description of embodiments

FIG. 1 schematically represents, in its environment, a particular embodiment of a system 10 for communication by ambient backscatter according to the invention.

As illustrated in Figure 1, the communication system 10 comprises a transmitter device, also called "source" SO, configured to transmit, according to a transmission frequency F_E included in a given frequency band called "band d 'emission', a radioelectric signal called an "ambient signal". The emission of the ambient signal is carried out for example permanently or else recurrently.

For the rest of the description, and as illustrated by Figure 1, we consider in no way limiting the case where the ambient signal is only emitted by a single source. The choice consisting in considering a single source is made here for the purpose of simplifying the description only. Also, no limitation is attached to the number of sources that can be considered in the context of the present invention, the developments that follow being in fact generalizable without difficulty by those skilled in the art in the case of a plurality of sources that are not consistent between they.

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). By way of non-limiting example, the ambient signal is a 4G mobile telephony signal transmitted in the transmission band [811 MHz, 821 MHz] by the source SO.

It should however be specified that the invention remains applicable to other types of radio signals, such as for example a mobile telephone signal other than 4G (for example 2G, 3G, 5G), a Wi-Fi signal, a WiMax signal, a DVB-T signal, etc. In general, no limitation is attached to the ambient radio signal that can be considered in the context of the present invention as long as the latter can be used to communicate by ambient backscatter.

The communication system 10 also comprises a transmitter device D_TX and a receiver device D_RX respectively configured in order to communicate with each other by ambient backscatter from the ambient signal emitted by the source SO. It should be noted that, in accordance with the invention, the transmitter D_TX and receiver D_RX devices are distinct from each other as well as from the source SO.

In the following description, and as illustrated by Figure 1, 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 developments necessary for such a generalization being able to be implemented without difficulty by man. of career.

[0047] In addition, and as is described in more detail later, nothing excludes considering the case where no receiver device is present, since the transmitter device D_TX is able to control the coverage. that it is able to provide in the context of an ambient backscatter communication.

In a manner known per se, communication by ambient backscatter consists of the exploitation of the ambient signal, by the transmitter device D_TX, to send information data to said receiver device D_RX, such as for example an identification data specific to said transmitter device D_TX.

In this embodiment, the D_TX transmitter device is equipped with an antenna (not shown in Figure 1) configured, in a manner known per se, to receive the ambient signal but also to backscatter it to the D_RX receiver device . It should however be noted that the invention remains applicable in the case where the transmitter device D_TX comprises a plurality of antennas.

The transmission of the backscattered signal by the transmitter device D_TX is carried out by variation of the backscattering of the ambient signal, this variation being based on the possibility that the transmitter device T to modify the impedance presented to the antenna which equips it, according to the information datum to be transmitted.

More particularly, the transmitter device D_TX can be associated with operating states depending on the impedance which is presented to the antenna with which it is fitted. For the rest of the description, it is considered in a non-limiting manner that these states are a so-called "backscatter" state (the transmitter device T can backscatter the ambient signal), as well as a contrary state called "non-backscatter" ( the transmitter device T cannot backscatter the ambient signal, or, in other words, is "transparent" to the ambient signal). The impedance associated with the backscatter state typically corresponds to zero or infinite impedance, whereas the impedance associated with the non-backscatter state typically corresponds to the complex conjugate of the characteristic impedance of the antenna in the medium considered propagation and at the considered frequency.

[0052] It is important to note that the invention is not limited to this ideal case in which only two states respectively perfectly backscattering using and perfectly non-backscattering would be considered. Indeed, the invention also remains applicable in the case where at least two states (first state and second state) are not perfectly backscattering/non-backscattering, since the variation of the used backscattering waves is perceptible by the receiver device D_RX when it is positioned at an appropriate distance from the transmitting device D_TX.

An information datum intended to be transmitted by the transmitter device D_TX, by means of the backscattered signal, is conventionally encoded by means of a set of symbols, comprising for example a so-called "high" symbol (bit of value " 1”), or else a so-called “low” symbol (bit with value “0”). The transmission of such information data can therefore be carried out, in a manner known per se, by alternating between said backscatter and non-backscatter states, each of said states being dedicated to the transmission of a symbol of a particular type (e.g. high symbol for backscatter state and low symbol for non-backscatter state, or vice versa). In other words, an information datum is transported to the receiver device D_RX by modulation of the waves of the ambient signal (i.e. by retromodulation).

In the present embodiment, the receiver device D_RX is also equipped with a reception antenna (not shown in the figures) configured to receive signals coming directly from the source SO as well as backscattered signals coming from the D_TX transmitter device. It should however be noted that the invention remains applicable in the case where the transmitter device D_TX comprises a plurality of antennas.

In general, no limitation is attached to the structural forms that can be taken respectively by the source SO, the transmitter device D_TX and the receiver device D_RX. By way of non-limiting examples, the following configurations are possible (depending on the emission frequency band considered):

the source SO is a base station, and the transmitter device D_TX (respectively the receiver device D_RX) is a cell phone, for example of the smartphone type, or a touch pad, or a personal digital assistant, or even a personal computer , etc.

the source SO (respectively the transmitter device D_TX) is a cell phone, for example of the smartphone type, or a touch pad, or a personal digital assistant, or even a personal computer, etc., and the receiver device D_RX is a base station,

- the source SO, the transmitter device D_TX and the receiver device D_RX are all three cellular telephones, for example of the smartphone type,

- the source SO is a home gateway (also called "Internet box") emitting a Wi-Fi signal, and the transmitter device D_TX (respectively the receiver device D_RX) is a cell phone, for example of the smartphone type, or a touch pad , or a personal digital assistant, or even a personal computer, etc., capable of communicating according to the Wi-Fi protocol.

The processing aimed at backscattering the ambient signal (respectively at decoding the backscattered signal) are conventionally carried out by the transmitter device D_TX (respectively the receiver device D_RX), by implementing a backscattering method (respectively a decoding method) not shown in the figures.

To this end, the transmitter device D_TX (respectively 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 data are stored and a computer program, in the form of a set of program code instructions to be executed to implement the backscatter method (respectively the decoding method).

Alternatively or in addition, the transmitter device D_TX (respectively 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. adapted to implement the backscatter method (respectively the decoding method).

In other words, the transmitter device D_TX (respectively the receiver device D_RX) comprises a set of means configured in software (specific computer program) and/or hardware (FPGA, PLD, ASIC, etc.) to implement the backscatter method (respectively the decoding method). The specific aspects concerning the signal processing techniques for the transmission of data by ambient backscatter as well as the decoding of these data are known and for example detailed in the document by N. Van Huynh et al. already mentioned before.

As regards more specifically the decoding of the backscattered signal, it is known that this can only be implemented if the variation in electromagnetic power, called "power difference" E_P, received by the receiver device D_RX depending on whether the transmitter device D_TX is in a backscattering or non-backscattering state is, in absolute value, greater than a determined threshold, referred to as the “power threshold” S_P. In other words, said power threshold S_P determines the value of the power difference E_P from which the receiver device D_RX is able to decode a signal backscattered by the transmitter device D_TX. Consequently, it is understood that the power threshold S_P is representative of a desired reception quality for the backscattered signal.

[0062] It should however be noted that although the decoding can be theoretically implemented as soon as | E_P| > S_P, nothing prevents a more restrictive decoding condition from being imposed on the receiver device D_RX, such as | E_P| > N x S_P where N is a real number strictly greater than 1. Imposing a more restrictive condition makes it possible to increase the quality of communication between the transmitter D_TX and receiver D_RX devices, but it also limits the quantity of data likely to be exchanged between these devices. In general, those skilled in the art know what range of values can be considered for the absolute value of the power difference E_P so that the operation of the system 10 is not compromised.

The power threshold S_P can be defined in different ways. Thus, according to an exemplary embodiment, the power threshold S_P is defined from a value of a signal to noise ratio "SNR_RX" (acronym of the English expression "Signal to Noise Radio") on the receiver device side D_RX.

According to another example, the power threshold S_P is defined from a value of a signal-to-noise plus interference ratio "SINR_RX" (acronym of the English expression "Signal to Interference plus Radio Noise" ) on the D_RX receiving device side.

[0065] However, nothing excludes considering still other quantities to define said power threshold, such as for example a decoding error rate "BER_RX" (acronym of the English expression "Bit Error Rate") . Concerning these aspects, those skilled in the art can refer to the document: "Real-Time Ambient Backscatter Demonstration", K. Rachedi, DT Phan-Huy, N. Selmene, A. Ourir, M. Gautier, A. Gati, A Gal indo- Serra no, R. Fara, J. De Rosny, IEEE INFOCON 2019 Posters and Demos, 1 ^st May 2019, Paris, France. As mentioned before, the power threshold S_P is representative of a desired reception quality for the backscattered signal. Therefore, the quantities from which the power threshold S_P can be set (SNR_RX, SINR_RX, BER_RX, etc.) also inherit this characteristic. In other words, the fact of setting a value, called “target value” VAL_C, for such a quantity on the receiver device side D_RX makes it possible to define an expected quality of reception for the backscattered signal.

For the rest of the description, it is considered that the quantity chosen to evaluate the quality of reception of the backscattered signal is the signal-to-noise ratio SNR_RX. Thus, with regard to the foregoing, the target value VAL_C considered below corresponds to a value of said signal-to-noise ratio SNR_RX.

It should however be noted that it is possible to express a quantity among a signal to noise, a signal to noise plus interference, a decoding error rate as a function of another of said quantities. This is done conventionally by means of an analytical function specific to the quantities considered. In other words, the choice according to which said reception quality is evaluated by means of the signal to noise SNR_RX only constitutes an implementation variant of the invention, and it is completely equivalent to take into account a quantity other than the signal to noise ratio SNR_RX.

The signal-to-noise ratio SNR_RX is conventionally defined as follows: expression in which:

- P(D_RX) is the electromagnetic power received by the receiver device D_RX at its antenna and from the transmitter device D_TX,

- P_NOISE(D_RX) is a coefficient corresponding to the adaptation losses at the level of the transmitter device D_RX.

The target value VAL_C can itself be formulated analytically by means of the Friis equation. More specifically, we have that: expression and in which:

- P(D_TX) is the electromagnetic power received by the transmitter device D_TX at its antenna and from the source SO, - P_NOISE(D_TX) is a coefficient corresponding to the adaptation losses at the level of the transmitter device D_TX,

- À is the wavelength of the carrier frequency of the ambient signal,

- r is a power transmission coefficient (between 0 and 1) of the transmitter device D_TX. In particular, r is defined according to the impedance of the antenna equipping the transmitter device D_TX,

- G_RX is the gain of the antenna equipping the receiver device D_RX,

- G_TX is the gain of the antenna fitted to the transmitter device D_TX,

- d is the distance separating the transmitting device D_TX from the receiving device D_RX.

For information, it is noted that the coefficient P(D_TX)/P_NOISE(D_TX) corresponds to a value (denoted “VAL_M” below) of the signal-to-noise ratio on the transmitter device side D_TX. This signal-to-noise ratio is for its part denoted “SNR_TX” in the remainder of the description.

It is important to note that, for reasons of simplification of the description, the analytical expression given above for the target value VAL_C of the signal to noise ratio SNR_RX is an expression in which all the parameters which could theoretically be taken into account. Indeed, in this analytical expression, it is considered that the respective antennas of the transmitter D_TX and receiver D_RX devices are correctly aligned in terms of polarization of the electromagnetic field. It would nevertheless be possible to generalize this analytical expression by adding (in the rightmost member between square brackets) a multiplicative coefficient corresponding to the polarization efficiency. These aspects are known to those skilled in the art.

Also for reasons of simplification of the description, it is considered in the present embodiment and with regard to the analytical formulation of the target value VAL_C, that the spectral density (expressed in Watts per Hertz) of the ambient signal remains substantially constant over time.

The fact remains that the variation of said spectral density could also be taken into account (this is however not the case in the remainder of the description). For example, if we assume that the ambient signal is characterized by:

- a first spectral density DSP1 in an instant, called "first instant", in which a measurement of the quantity P(D_TX) is acquired,

- a second spectral density DSP2 for any instant greater than said first instant, then, if the target value VAL_C is calculated later than said first instant, said analytical expression becomes:

The distance d considered in the analytical expression given above corresponds to the distance, counted from the transmitter device D_TX, at which said target value VAL_C of the signal-to-noise ratio SNR_RX is reached. In other words, said distance d represents the coverage of the transmitter device D_RX for a target value fixed at VAL_C. For the rest of the description, said distance d is therefore called “coverage distance”, as denoted “D_COUV”.

[0076] Given the writing elements considered above, it is possible to give the following analytical expression for the coverage distance D_COUV:

In the context of the present invention, the transmitter device D_TX is associated with a coverage constraint. This coverage constraint corresponds to an interval I_COUV in which the coverage distance D_COUV must be comprised so that the backscattering of the ambient signal, by said transmitter device D_TX, is implemented. It is therefore understood that the fact of imposing such a coverage constraint, in order to decide whether the ambient backscatter must be implemented or not, ultimately amounts to exercising control over said ambient backscatter.

To this end, the transmitter device D_TX is configured not only to backscatter the ambient signal, as has already been mentioned previously, but also to carry out processing aimed at controlling the implementation of said backscattering of the ambient signal, by implementing steps of a control method according to the invention.

No limitation is attached to the way in which the lower D_MIN and upper D_MAX bounds of the interval I_COUV associated with said coverage constraint are calculated. For example, once the upper limit D_MAX has been chosen, the lower limit D_MIN is deduced from the upper limit D_MAX by application of a tolerance coefficient. Such a tolerance coefficient can for example correspond to a multiplicative coefficient (eg: D_MAX×0.9). Of course, nothing excludes considering other types of coefficients, such as for example a subtractive coefficient applied to D_MAX. In practice, the D_MIN and D_MAX limits can be defined according to the context in which the invention is implemented.

For example, if provision is made for the control method of the invention to be implemented by a large number of transmitter devices, the upper limit D_MAX can be chosen to be substantially equal to one meter. Such a value makes it possible to ensure that a receiver device will decode the signal backscattered by a transmitter device only when it is close to the latter (i.e. at a distance between said lower D_MIN and upper D_MAX terminals). In this way, mutual interference between transmitting devices is minimized at the receiving device, which increases the probability of achieving correct decoding.

It is noted that the fact of considering that the upper limit D_MAX is substantially equal to one meter also applies advantageously when a large number of receiver devices are located in the environment of the transmitter device(s) implementing the control method according to the invention. Indeed, in this case, this makes it possible to limit the probability that a backscattered signal will be decoded by a receiver device not intended to receive said backscattered signal. The security of communications between two devices is therefore reinforced.

[0083] Moreover, for this type of context aimed at guaranteeing the security of communications, it is of course possible to envisage an upper limit D_MAX of less than one meter, such as ten centimeters for example. Being able to envisage such a small upper limit D_MAX proves to be particularly advantageous for applications in which the communications are intended to take place over very short distances, such as for example contactless purchases.

Conversely, and according to another example, if provision is made for the control method of the invention to be implemented by a small number of transmitter devices, the upper limit D_MAX can be increased with respect to the previous examples, and be for example chosen substantially equal to ten meters. In this way, the communication range (and therefore the coverage) of a transmitter device is advantageously increased.

In general, no limitation is attached to the values that can be taken by said lower D_MIN and upper D_MAX limits. A person skilled in the art knows in fact which values can be envisaged according to the context of application of the invention.

FIG. 2 schematically represents an example of hardware architecture of the transmitter device D_TX belonging to the system 10 of FIG. 1, for the implementation of said control method. As illustrated by FIG. 2, the transmitter device D_TX has the hardware architecture of a computer. Thus, the transmitter device D_TX comprises, in particular, a processor 1, a random access memory 2, a read only memory 3 and a non-volatile memory 4. It also comprises a communication module 5.

The read only memory 3 of the transmitter device D_TX constitutes a recording medium in accordance with the invention, readable by the processor 1 and on which is recorded a computer program PROG in accordance with the invention, comprising instructions for the execution of at least some of the steps of the control method according to the invention. The PROG program defines functional modules of the D_TX transmitter device, which relies on or controls the hardware elements 1 to 5 of the D_TX transmitter device mentioned above, and which include in particular:

- an acquisition module MOD_ACQ configured to acquire an electromagnetic power measurement received from the source SO via the ambient signal,

- a determination module MOD_DET configured to determine the coverage distance D_COUV in accordance with the analytical expression mentioned above (said coverage distance D_COUV being counted from a position occupied by the transmitter device D_TX during the acquisition of said measurement and at which the target value VAL_C is reached, the coefficient VAL_M being calculated according to said acquired measurement),

- an evaluation module MOD_EVAL configured to evaluate a CRIT criterion consisting of at least checking whether the coverage distance D_COUV is included in the interval I_COUV,

- a control module MOD_CONT configured to implement the backscatter/not to implement the backscatter of the ambient signal if said criterion CRIT is satisfied/not satisfied.

The communication module 5 notably allows the transmitter device D_TX to communicate with the receiver device D_RX, and for this purpose incorporates the antenna fitted to said transmitter device D_TX. Nothing however excludes considering, according to other examples not detailed here, that the communication module 5 is also configured to allow the transmitter device D_TX to communicate with devices other than the receiver device D_RX, such as for example with the SO source, following any technically conceivable communication protocol.

[0090] Conventionally, the acquisition module MOD_ACQ comprises an acquisition chain connected to a sensitive element configured to provide an analog electrical signal representative of the measured electromagnetic power. In the present exemplary embodiment, said sensitive element corresponds to the antenna fitted to the transmitter 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 an acquisition module MOD_ACQ is well known to those skilled in the art, and is therefore not detailed here further.

The CRIT criterion can comprise one or more conditions to be verified, including in particular the condition according to which the coverage distance D_COUV belongs to the interval I_COUV.

Thus, and according to a first example, the criterion CRIT includes a single condition to be verified (it is therefore the aforementioned condition relating to the coverage distance D_COUV). The implementation of such an example turns out to be preferred when the transmitter device D_TX is fixed. Indeed, it is understood that the fact of considering the transmitter device D_TX as being fixed makes it possible to guarantee that the conditions of illumination of the latter by the source SO do not vary over time (except in the event of modification of the spectral density of the ambient signal, this aspect being dealt with above).

According to a second example, the criterion CRIT comprises two conditions to be verified. A first relating to said coverage distance D_COUV (this first condition is identical to that mentioned in the preceding example), and a second aimed at taking account of a mobility of the transmitter device D_TX. More particularly, in this other exemplary embodiment, it is considered that the transmitter device D_TX is mobile at a speed V between instants at which the acquisition module MOD_ACQ acquires a measurement of electromagnetic power coming from the source SO and the module d The MOD_EVAL evaluation evaluates the CRIT criterion. Therefore, said second condition of the CRIT criterion consists in verifying whether the duration separating said instants is sufficiently low compared to the λ/V ratio, so that the electromagnetic power received by the transmitter device D_TX from the source SO via the ambient signal is substantially constant during said duration. In other words, it is a question of guaranteeing that the conditions of illumination of the transmitter device D_TX remain stable over time, at the very least during said duration.

It is noted that said speed V can for example correspond to a speed defined in a telecommunications standard. According to another example, said speed V corresponds to a typical speed of movement for the transmitter device D_TX (example: a speed of the order of 3 km/h for a smartphone in the possession of a walking user).

In these examples (speed defined by a standard or typical speed), said speed V corresponds to data that can be stored in the storage means of the transmitter device D_TX during its design, such as for example in its non-volatile memory. 4. Alternatively, said speed V is data that can be stored by an ancillary device, such as for example a server storing a database, the transmitting device D_TX having access to this parameter thus stored by exchanging messages with said auxiliary device.

[0097] However, nothing excludes considering that the transmitter device D_TX is equipped with means configured to carry out measurements of its displacement speed V. Such means comprise for example an accelerometer.

For the rest of the description, and for the purpose of simplifying it, it is now considered that the transmitter device D_TX remains fixed over time. It is also considered that the criterion CRIT comprises a single condition to be checked, namely the condition according to which the distance of coverage D_COUV belongs to the interval I_COUV.

[0099] It is also noted that the evaluation of the criterion CRIT requires, in the present embodiment, to calculate the coverage distance D_COUV in accordance with the analytical expression given previously. This analytical expression notably involves the coefficients λ, r, G_TX and G_RX which may, in whole or in part, be defined in a telecommunications standard or even be measured in the factory. In other words, the transmitter device D_TX is aware of these coefficients when it evaluates the criterion CRIT by means of its module MOD_EVAL.

According to considerations similar to those mentioned above concerning the speed V, all or part of said coefficients λ, r, G_TX and G_RX can be stored in storage means of the transmitter device D_TX during its design, or else in an ancillary device.

In general, no limitation is attached to the manner in which the transmitter device D_TX obtains knowledge of said coefficients λ, r, G_TX and G_RX.

FIG. 3 represents, in the form of a flowchart, a particular mode of the control method according to the invention, as it is implemented by the transmitter device D_TX of FIG. 2.

The particular mode of FIG. 3 relates to a so-called “current phase” phase E20 of the control method. This current phase E20 comprises a plurality of steps, and may optionally be preceded, according to other modes of implementation and as described later, by a preliminary phase during which various quantities can be determined so that the evaluation of the distance of coverage D_COUV is carried out according to an analytical expression different from that given above. In any event, with regard to the description of Figure 3, it is considered that the coverage distance D_COUV is defined according to the expression considered so far, namely:

For the description of FIG. 3, it is also considered, in no way limiting, that the transmitter device D_TX is in the non-backscattering state when the control method is implemented.

As illustrated by FIG. 3, said current phase E20 includes a step E20_1 of acquiring a measurement, called “current measurement” M_CUR, of electromagnetic power received from the source SO via the ambient signal. Said step E20_1 is implemented by the acquisition module MOD_ACQ equipping the transmitter device D_TX.

Said current phase E20 also includes a step E20_2 for determining the coverage distance D_COUV. Said step E20_2 is implemented by the determination module MOD_DET equipping the transmitter device D_TX.

In the mode of implementation of Figure 3, said step 30 more particularly comprises:

- a sub-step E20_2_l of determining the value VAL_M of the signal-to-noise ratio on the transmitter device side D_TX from the current measurement M_CUR (this involves dividing M_CUR by P_NOISE(D_TX)). Said determination of the value VAL_M is implemented by a determination sub-module (not shown in the figures) of the determination module MOD_DET,

- A sub-step E20_2_2 for calculating the coverage distance D_COUV from the value VAL_M thus determined. Said calculation of D_COUV is implemented by a calculation sub-module (not shown in the figures) of the determination module MOD_DET.

Once the distance D_COUV has been determined, said current phase E20 includes a step E20_3 for evaluating the criterion CRIT. Said step E20_3 is implemented by the evaluation module MOD_EVAL equipping the transmitter device D_TX.

In the present mode of implementation, said step E20_3 consists in verifying that the coverage distance D_COUV determined in step E20_2 belongs to the interval I_COUV, that is to say is between the limits D_MIN and D_MAX.

Therefore, if the CRIT criterion is satisfied (i.e. the coverage distance D_COUV belongs to the interval I_COUV), said current phase E20 comprises a step E20_4 of backscattering of the ambient signal. Said step E20_4 is implemented by the control module MOD_CONT equipping the transmitter device D_TX.

[YES] Thus, if the criterion CRIT is verified, the step E20_4 consists in implementing the backscattering of the ambient signal by the transmitter device D_TX. Therefore, the module of control makes it possible to cause the transmitter device D_TX to pass selectively from the non-backscatter state to the backscatter state (and vice versa) as a function of an information datum that said transmitter device D_TX wishes to communicate to the receiver device D_RX.

Nothing, however, excludes considering that said implementation of the backscattering consists in passing the transmitter device D_TX from the non-backscattering state to the backscattering state, so that the said transmitting device D_TX remains in said backscatter state.

Conversely, if the CRIT criterion is not satisfied, said current phase E20 comprises a step E20_5 of absence of ambient backscattering of the ambient signal. Here again, said step E20_5 is implemented by the control module MOD_CONT equipping the transmitter device D_TX.

Insofar as the transmitter device D_TX is in the non-backscattering state when the current phase E20 of the control method begins, it is understood that said step E20_5 consists in maintaining the transmitter device D_TX in this non-backscattering state. backscatter.

The control method has been described so far considering that the transmitter device D_TX is in the non-backscattering state when the implementation of the steps of the current phase E20 begins. However, nothing excludes considering that the steps of the current phase E20 are implemented while the transmitter device D_TX is in the backscatter state. Consequently, if the criterion CRIT is satisfied following the execution of step E20_4, one can have, according to considerations similar to those described above, selective alternation between said states of non-backscatter and backscatter, or else further maintaining the transmitter device D_TX in said backscatter state. Conversely, if the criterion CRIT is not satisfied, the transmitter device D_TX passes from the backscattering state to the non-backscattering state by means of its control module MOD_CONT.

The invention has also been described so far considering that the condition relating to the coverage distance D_COUV (belonging or not to the interval I_COUV) is verified directly during the evaluation of the criterion CRIT. By “directly verified”, reference is made here to the fact that it is explicitly verified whether the coverage distance D_COUV determined during step E20_2 is between the limits D_MIN and D_MAX of the interval I_COUV.

However, the invention also remains applicable when such verification is carried out indirectly. By "indirectly verified", reference is made here to the fact that another condition relating to a distinct quantity of said coverage distance D_COUV is verified, the result of the verification of said other condition providing a result similar to that which would be obtained if the condition relating to the coverage distance D_COUV were verified. To illustrate the principle of an indirect verification of the condition relating to the coverage distance D_COUV, we consider, with reference to FIG. 4, an alternative mode of implementation of the control method of the invention in which the criterion CRIT now consists in verifying a condition relating to the electromagnetic power received by the transmitter device D_TX coming from the source SO. More particularly, and as illustrated by FIG. 4, said current phase E20 comprises, in this alternative mode of implementation and replacing step E20_2 of FIG. 3:

- a step E20_MIN for determining an electromagnetic power, called "minimum power" P_MIN, which, if it is received by the transmitter device D_TX from the source SO, allows said target value VAL_C to be reached at a distance equal to said lower limit D_MIN,

- a step E20_MAX of determining an electromagnetic power, called "maximum power" P_MAX, which, if it is received by the transmitter device D_TX from the source SO, allows said target value VAL_C to be reached at a distance equal to said upper limit D_MAX.

In addition, the verification carried out during the evaluation of the criterion CRIT (step E20_3) consists, in this alternative mode of implementation, in verifying whether the current measurement M_CUR is between said minimum powers P_MIN and maximum P_MAX. In other words, in this alternative mode of implementation, the transmitter device D_TX is associated with a coverage constraint corresponding to an interval whose limits are P_MIN and P_MAX, and in which the power received from the source SO must be included for ambient signal backscatter to be implemented.

The values P_MIN and P_MAX are deduced from the analytical expression given above for the coverage distance D_COUV, considering that they are respectively associated with said lower D_MIN and upper D_MAX limits. Thus, we have that: and : Ultimately, in said alternative mode of implementation, the fact of verifying that the current measurement M_CUR is between P_MIN and P_MAX is completely equivalent to verifying that the coverage distance D_COUV is between D_MIN and D_MAX.

It is important to note that the implementation of the method according to the invention is not limited to the modes of FIGS. 3 and 4. In particular, for these modes, it was considered that the coverage distance D_COUV could be determined by means of the analytical expression described above. However, other modes remain possible, in which said analytical expression is not used.

FIG. 5 represents, in the form of a flowchart, another particular mode of implementation of the control method according to the invention.

In the mode of FIG. 5, the control method comprises a preliminary experimental phase E10, for example carried out in the factory, during which the transmitter device D_TX is fixed and comprising a plurality of steps.

Also, said preliminary phase E10 initially comprises a step E10_1 of transmitting an ambient signal, called “experimental ambient signal” S_AMB_EXP, by a transmitter device D_EMI.

Said transmitter device D_EMI can for example correspond to the source SO considered previously, or even to a device distinct from said source SO.

The preliminary phase E10 also includes a step E10_2 of acquisition, by the transmitter device D_TX, of a measurement, called "reference measurement" M_REF, of electromagnetic power received from the transmitter device D_EMI via the experimental ambient signal S_AMB_EXP. The implementation of said step E10_2 is similar to that of step E20_1 described previously.

It is also noted that said reference measurement M_REF can for example be used for the determination, by the transmitter device D_TX, of a value VAL_REF of a signal-to-noise ratio on the transmitter device side D_TX.

The preliminary phase E10 also includes a step E10_3 of ambient backscattering of the experimental ambient signal S_AMB_EXP by the transmitter device D_TX and to a receiver device D_REC configured to decode said backscattered experimental ambient signal. It should be noted that the receiver device D_REC can for example correspond to the receiver device D_RX mentioned above.

Said preliminary phase E10 further comprises, during the execution of said ambient backscattering step E10_3, a search for a location LOC at which the backscattered experimental ambient signal S_AMB_EXP is received by the receiver device D_REC with a quality of reception reaching said target value VAL_C. This search for the location LOC is for example implemented thanks to an operator in charge of moving the receiver device D_REC, so that once moved, said receiver device D_REC can carry out an acquisition of a measurement of electromagnetic power received from the transmitter device D_TX and determining, on the basis of this power measurement, the signal-to-noise ratio at its level. Consequently, when the target value VAL_C is reached after a displacement, the receiver device D_REC can for example transmit a message intended for the transmitter device D_TX to inform it thereof.

According to another example, the receiver device D_REC corresponds to a mechatronic device (for example a robot) comprising drive means (such as for example an electric or thermal motor, etc.) as well as displacement means (such as for example wheels, caterpillars, etc.) allowing it to move autonomously or even remotely.

The distance separating the receiver device D_REC from the transmitter device D_TX when such a location LOC has been found is called the “reference distance” D_REF. The transmitter device D_TX then becomes aware of this reference distance D_REF, no limitation being attached to the way in which this awareness is carried out (examples: reference distance D_REF noted by the operator then stored in memory means of the transmitter device D_TX; receiver device D_REC equipped with means for measuring distance, the reference distance D_REF then being measured by said receiver device D_REC which communicates it to the transmitter device D_TX).

Ultimately, in the mode of implementation of Figure 5, said coverage distance D_COUV is defined as follows:

Such an expression of D_COUV translates that D_COUV is, in this mode of implementation, defined according to:

- the reference distance D_REF,

- the reference measurement M_REF, given the presence of the term VAL_REF,

- the current measurement M_CUR, given the presence of the term VAL_M,

- the target value VAL_C, given the presence of the term D_REF.

Therefore, once the experimental phase has been completed, the control method again comprises, in the mode of implementation of FIG. 5, a current phase E20. This current phase E20 is similar to those described above with reference to FIGS. 3 and 4, except that the expression used to determine the coverage distance D_COUV or expressing the power received by the transmitter device D_TX coming from the source SO is the expression given above in which the quantities D_REF and VAL_REF intervene.

As a complement, it can again be noted that the last expression of D_COUV given above implicitly takes into account the fact that the power spectral density of the experimental ambient signal S_AMB_EXP is substantially identical during the respective executions of said acquisition steps E10_l of the reference measurement M_REF and ambient backscatter E10_3 of the experimental ambient signal S_AMB_EXP. The fact remains that in the case where said spectral density varies between these instants, it is possible to take account of this variation in the expression of D_COUV according to technical characteristics similar to those described previously.

The invention has also been described so far considering that, as regards the current phase of the control method, a receiver device D_RX belongs to the system 10 for communication by ambient backscatter. It is then understood that the fact of considering the presence of such a receiver device D_RX makes it possible to envisage a particularly advantageous application of the invention in the context of D2D communications, the transmitter device D_TX now being able to control its coverage, at the difference from what is practiced in the state of the art.

The invention nevertheless remains applicable to the case where said system 10 does not include a receiver device D_RX during the implementation of said current phase, the transmitter device D_TX therefore contenting itself, for example, with backscatter the ambient signal without specifically seeking to transmit an information datum that is specific to it.

Claims

26 Claims

[Claim 1] Method for controlling the ambient backscattering of a signal, called "ambient signal", emitted by a transmitter device (SO), said method comprising a phase called "current phase" (E20) implemented by a device transmitter (D_TX) configured to backscatter said ambient signal and comprising steps of:

- acquisition (E20_l) of a measurement, called "current measurement" (M_CUR), of electromagnetic power received from the transmitter device via the ambient signal,

- evaluation (E20_3) of a criterion (CRIT) consisting of at least checking whether a distance, called

"coverage distance" (D_COUV), counted from a position occupied by the transmitter device during acquisition of the current measurement and at which a given value, called "target value" (VAL_C), of quality reception of a signal obtained by ambient backscattering of the ambient signal, is included in a given interval (I_COUV), said coverage distance being defined according to said current measurement and said target value,

- if said criterion is satisfied, ambient backscatter (E20_4) of the ambient signal,

- if said criterion is not satisfied, absence of ambient backscatter (E20_5) of the ambient signal.

[Claim 2] A method according to claim 1, wherein said target value (VAL_C) is a value of any one of the following quantities:

- a signal to noise ratio,

- a signal-to-noise plus interference ratio,

- a decoding error rate.

[Claim 3] A method according to any of claims 1 to 2, wherein the ambient signal is characterized by:

- a first spectral density when the acquisition step (E20_l) of the current measurement (M_CUR) is executed,

- a second spectral density, distinct from said first spectral density, when the step of evaluating (E20_3) the criterion (CRIT) is executed, said coverage distance (D_COUV) also being defined as a function of the ratio between said first and second power spectral densities.

[Claim 4] A method according to any one of claims 1 to 3, wherein the transmitter device (D_TX) is configured to backscatter said ambient signal to at least one receiver device (D_RX), said receiver device being configured to decode said signal backscattered ambient, said transmitter and receiver devices being respectively characterized by antenna gains G_TX and G_RX, said coverage distance also being defined as a function of said antenna gains G_TX and G_RX.

[Claim 5] Method according to any one of Claims 1 to 3, the said method comprising, before the implementation of the said current phase (E20), a preliminary experimental phase (E10) during which the transmitter device (D_TX) is fixed and includes steps of:

- acquisition (E10_2), by the transmitter device, of a measurement, called "reference measurement" (M_REF), of electromagnetic power received from a transmitter device (D_EMI) emitting a signal, called "experimental ambient signal" (S_AMB_EXP),

- ambient backscattering (E10_3) of the experimental ambient signal by the transmitter device and to a receiver device (D_REC) configured to decode said backscattered experimental ambient signal, said experimental preliminary phase further comprising, during the execution of said ambient backscattering step , a search for a location (LOC) at which the backscattered experimental ambient signal is received by the receiver device with a reception quality reaching said target value (VAL_C), the distance separating the receiver device from the transmitter device when such a location has been found being called “reference distance” (D_REF), and said coverage distance (D_COUV) also being defined according to said reference measurement and said reference distance.

[Claim 6] Method according to any one of Claims 1 to 5, in which the said current phase (E20) further comprises a step of determining (E20_2) the distance of coverage (D_COUV), the said at least one verification carried out during of the evaluation (E20_3) of the criterion (CRIT) consisting of a direct verification of whether the coverage distance determined belongs to said interval (I_COUV).

[Claim 7] Method according to any one of Claims 1 to 5, in which the interval (I_COUV) associated with the coverage distance (D_COUV) comprises a lower limit (D_MIN) and an upper limit (D_MAX), said phase current (E20) further comprising steps of:

- determination (E20J IN) of an electromagnetic power, called "minimum power" (P_MIN), which, if it is received by the transmitter device (D_TX) from the transmitter device (SO), allows said target value (VAL_C ) or reached at a distance counted from the position occupied by the transmitter device during acquisition of the current measurement (M_CUR) and equal to said lower limit,

- determination (E20_MAX) of an electromagnetic power, called "maximum power" (P_MAX), which, if it is received by the transmitter device from the transmitter device, allows said target value to be reached at a distance counted from the position occupied by the transmitter device during the acquisition of the current measurement and equal to said terminal higher, said at least one verification performed during the evaluation (E20_3) of the criterion (CRIT) consisting in verifying whether the current measurement is between said minimum and maximum powers.

[Claim 8] Method according to any one of Claims 1 to 7, in which the transmitter device (D_TX) is mobile at a speed V between instants at which said acquisition (E20_l) and evaluation ( E20_3) of said current phase (E20), the evaluation of the criterion (CRIT) also consisting in checking whether the duration separating said instants of execution is sufficiently short compared to the ratio λ/V, where λ corresponds to the wavelength of the carrier frequency of the ambient signal, so that the electromagnetic power received by the transmitter device from the transmitter device (SO) via the ambient signal is substantially constant during said duration.

[Claim 9] Computer program comprising instructions for implementing at least the steps of the current phase (E20) of a control method according to any one of Claims 1 to 8 when said program is executed by a computer.

[Claim 10] A computer-readable recording medium on which a computer program according to claim 9 is recorded.

[Claim 11] Transmitter device (D_TX) for controlling the ambient backscatter of a signal, called "ambient signal", emitted by a transmitter device (SO), said transmitter device being configured to backscatter said ambient signal and comprising:

- an acquisition module (MOD_ACQ) configured to acquire a measurement, called "current measurement" (M_CUR), of electromagnetic power received from the transmitter device via the ambient signal,

- an evaluation module (MOD_EVAL) configured to evaluate a criterion (CRIT) consisting of at least verifying whether a distance, called "coverage distance" (D_COUV), counted from a position occupied by the transmitter device during the acquisition of the current measurement and in which a given value, called "target value" (VAL_C), of reception quality of a signal obtained by ambient backscattering of the ambient signal is reached, is included in a given interval (I_COUV) , said coverage distance being defined as a function of said current measurement and said target value,

- a control module (MOD_CONT) configured for:

• implement the backscatter of the ambient signal if the criterion is satisfied,

• do not implement backscatter of the ambient signal if said criterion is not satisfied. 29

[Claim 12] An ambient backscatter communication system (10), said system comprising a transmitter device (SO) configured to transmit an ambient signal and a transmitter device (D_TX) according to claim 11.