Method and apparatus for configuring a communication system with ambient backscatter

Description

Prior art

[0001] The present invention belongs to the general field of telecommunications. It relates more particularly to a method for configuring an ambient backscatter communication system, as well as an associated configuration device. It also relates to an ambient backscatter communication system duly configured according to said method. The invention finds a particularly advantageous, although in no way limiting, application for applications of the “Internet of Things” (IoT) type.

[0002] Ambient backscatter communication technology is now well known. The technical principles underlying this technology are described, among others, 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, pp. 2889-2922, Fourthquarter 2018.

[0003] Conventionally, backscattering of an ambient signal occurs between a transmitting device and a receiving device occupying respective fixed positions.

[0004] The ambient signal in question corresponds to a radio signal emitted, permanently or recurrently, by at least one source in a given frequency band. For example, it could be a television signal, a mobile phone signal (3G, 4G, 5G), a Wi-Fi signal, a WiMax signal, etc.

[0005] To communicate with a receiving device distinct from the source, a transmitting device uses the ambient signal to send data to said receiving device. More specifically, the transmitting device reflects the ambient signal towards the receiving device, possibly modulating it. The signal thus reflected is called a "backscattered signal", and is intended to be decoded by the receiving device (i.e. the receiving device extracts from the backscattered signal information transmitted by the transmitting device, for example in the form of bits).

[0006] The fact that no additional radio waves (in the sense of a wave other than that coming from the ambient signal) are emitted by the transmitting device makes ambient backscattering technology particularly attractive. Indeed, the energy cost of communication is thus optimized, which is particularly important in the current context of the IoT where every object in everyday life is intended to become a communicating object.

[0007] To implement ambient backscatter communication technology, the transmitting device is configured to receive the ambient signal, but also to backscatter it (so-called "backscatter" state) or not (so-called "non-backscatter" state) to the receiving device. The receiving device, in turn, is configured to decode the signal possibly backscattered by the transmitting device.

[0008] That being said, and in practice, this decoding can only be implemented if the difference in electromagnetic power received by the receiving device, between times when the transmitting device is in the non-backscattering and backscattering states respectively, and also called "the power difference", exceeds a determined threshold, called "power threshold". Indeed, if this power threshold is not reached, the receiving device is not able to detect that the transmitting device is in a backscattering state, and therefore does not implement any decoding (essentially for reasons of preserving its energy autonomy). In other words, reaching said power threshold is a limiting factor in ambient backscattering communication technology. Statement of the invention

[0009] 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 obtain a power difference greater, in absolute value, than said power threshold, so as to improve the efficiency of communication by ambient backscattering between a transmitting device and a receiving device.

[0010] To this end, and according to a first aspect, the invention relates to a method for parameterizing an ambient backscatter communication system comprising a transmitting source in a given frequency band, a transmitting device and a receiving device, said system also comprising a surface capable of reflecting signals coming from the source and / or the transmitting device towards the receiving device, said system being parameterized by: the respective positions of the source and the transmitting and receiving devices, the transmission frequency of the source in said frequency band, said method being implemented by a parameterization device and comprising a step of determining a value, called "calculated value", of at least one of said parameters so that a calculation function evaluating, as a function of said parameters and of the influence of the surface on the signals intended to be received by the receiving device, the difference in power received by the receiving device depending on whether the transmitting device is in a backscattering or non-backscattering state, is, in absolute value, greater than or equal to a threshold at from which the receiving device is able to decode a signal emitted by the source and backscattered by the transmitting device.

[0011] Thus, according to said parameterization method, it is proposed to control the value of the power difference by varying one or more parameters defining the ambient backscatter communication system. More particularly, the invention makes it possible to search for one or more values of said parameters so as to guarantee that the power difference is greater than or equal to the power threshold beyond which the decoding of a backscattered signal is ensured.

[0012] To ensure that said power threshold is achieved, at a minimum, the parameterization method advantageously relies, on the one hand, on the fact that the ambient backscatter communication system comprises said surface capable of reflecting signals from the source and / or the transmitting device towards the receiving device. Such a surface, due to its presence in the environment of the source and the transmitting and receiving devices, contributes to increasing the maximum power difference achievable on the receiving device side in comparison with a configuration where the surface would not be present.

[0013] Indeed, due to the presence of said surface, more signals are likely to be routed to the receiving device. These are signals coming from the source and / or the transmitting device and which, thanks to the surface, are reflected towards the receiving device, even though these signals would have followed a different path (i.e. a path not leading to the receiving device) if the surface had not been deliberately introduced into the environment of the source and the transmitting and receiving devices.

[0014] It is important to note that the invention covers not only the case where the surface forms an element introduced manually and voluntarily into the environment of the source and the transmitting and receiving devices, but also the case where the surface is already present fortuitously in this environment (e.g. street sign) and used deliberately, via the configuration of the ambient backscatter communication system, to ensure that the power threshold is reached. Thus, the invention can be advantageously adapted to any type of spatial configuration.

[0015] On the other hand, the parameterization method is advantageously based on said calculation function which translates, via an analytical expression that the inventors have succeeded in establishing, the influence of the aforementioned parameters for the ambient backscatter communication system but also of the surface in the evaluation of the power difference.

[0016] This analytical expression, described in detail later in a particular embodiment of the invention, is expressed in the form of a sum of several terms each involving all or part of the parameters of the ambient backscatter communication system. Furthermore, the expression of at least part of these terms is dependent on the presence of the surface, in particular via the presence of homogeneous quantities at distances and representative of the respective positions of the source and the transmitting and receiving devices relative to said surface.

[0017] From a mathematical point of view, said calculation function is therefore a function of several variables (i.e. said variables correspond to the parameters of the communication system). The invention is therefore remarkable in that it provides very precise access, via said calculation function, to variations in the power difference as a function of variations in each of the parameters of the communication system.

[0018] Ultimately, the invention makes it possible to efficiently take advantage, via said calculation function, of the surplus power transmitted to the receiving device due to the presence of the surface, by determining a parameterization of the communication system by which the achievement of said power threshold is guaranteed. As a result, the detectability of the transmitting device, when it is in a backscattering state, by the receiving device is improved, which ultimately leads to improving the efficiency of communication by ambient backscattering between these devices.

[0019] In particular embodiments, the parameterization method may further comprise one or more of the following characteristics, taken individually or in all technically possible combinations.

[0020] In particular embodiments, the method further comprises, before implementing the determination step, a step of obtaining said calculation function.

[0021] In particular modes of implementation, the transmission frequency is a given fixed parameter and: the respective positions of the transmitting and receiving devices are given fixed parameters, the parameter whose calculated value is determined being the position of the source; or the respective positions of the source and the transmitting device are given fixed parameters, the parameter whose calculated value is determined being the position of the receiving device; or the respective positions of the source and the receiving device are given fixed parameters, the parameter whose calculated value is determined being the position of the transmitting device.

[0022] According to such arrangements, it is considered that three of the system parameters are given fixed parameters and that the fourth remaining parameter is variable. Thus, the calculated value that is determined is that of said parameter considered to be variable. Proceeding in this manner therefore amounts to considering that the value of the power difference can be adjusted according to a single degree of freedom, namely that defined by said variable remaining parameter. Such arrangements therefore make it possible to simplify the parameterization of the ambient backscatter communication system since the search for a calculated value now only concerns a single parameter.

[0023] In particular embodiments, the respective positions of the source and the transmitting and receiving devices are given fixed parameters, the parameter whose calculated value is determined being the transmission frequency.

[0024] Such an implementation constitutes a variant of that mentioned above, in which the transmission frequency as well as the respective positions of two elements (source, transmitting device, receiving device) of the communication system are fixed.

[0025] In particular modes of implementation, said calculated value is determined in said frequency band so as to maximize the calculation function.

[0026] In particular embodiments, said calculated value is determined by a dichotomy method.

[0027] In particular embodiments, the surface is configured to reflect signals from the source and / or transmitting device without a preferred direction.

[0028] In particular modes of implementation, the calculation function comprises three terms, including: a first term representative of the contribution, in terms of power, of signals backscattered by the transmitting device and reaching the receiving device without reflection on the surface, a second term representative of the contribution, in terms of power, of a coupling between signals backscattered by the transmitting device and reaching the receiving device without reflection on the surface and signals emitted by the source and reaching the receiving device without reflection on the surface, a third term representative of the contribution, in terms of power, of a coupling between signals backscattered by the transmitting device and reaching the receiving device without reflection on the surface and signals emitted by the source and reaching the receiving device after reflection on the surface.

[0029] According to a second aspect, the invention relates to a computer program comprising instructions for implementing the parameterization method according to the invention when said program is executed by a computer.

[0030] This program may use any programming language, and may be in the form of source code, object code, or code intermediate between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0031] According to a third aspect, the invention relates to a computer-readable information or recording medium on which a computer program according to the invention is recorded.

[0032] The information or recording medium may be any entity or device capable of storing the program. For example, the medium may include a storage medium, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording medium, for example a floppy disk or a hard disk.

[0033] On the other hand, the information or recording medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention may in particular be downloaded from a network such as the Internet.

[0034] Alternatively, the information or recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to carry out or to be used in carrying out the method in question.

[0035] According to a fourth aspect, the invention relates to a device for parameterizing an ambient backscatter communication system comprising a transmitting source in a given frequency band, a transmitting device and a receiving device, said system also comprising a surface capable of reflecting signals coming from the source and / or the transmitting device towards the receiving device, said system being parameterized by: the respective positions of the source and the transmitting and receiving devices, the transmission frequency of the source in said frequency band, said device comprising a determination module, configured to determine a value, called "calculated value", of at least one of said parameters so that a calculation function evaluating, as a function of said parameters and of the influence of the surface on the signals intended to be received by the receiving device, the difference in power received by the receiving device depending on whether the transmitting device is in a backscattering or non-backscattering state, is, in absolute value, greater than or equal to a threshold from which the receiving device is able to decode a signal emitted by the source and backscattered by the transmitting device.

[0036] In particular embodiments, the parameterization device may further comprise one or more of the following characteristics, taken individually or in all technically possible combinations.

[0037] In particular modes of implementation, said parameterization device also comprises an obtaining module configured to obtain said calculation function.

[0038] In particular embodiments, the parameterization device is included in the source, or in the transmitting device, or in the receiving device.

[0039] According to a fifth aspect, the invention relates to an ambient backscatter communication system comprising a transmitting source in a given frequency band, a transmitting device and a receiving device, said system also comprising a parameterization device according to the fourth aspect as well as a surface capable of reflecting signals coming from the source and / or the transmitting device towards the receiving device, said system being parameterized by: the respective positions of the source and the transmitting and receiving devices, the transmission frequency of the source in said frequency band, the value of at least one of said parameters being determined by said parameterization device. Brief description of the drawings

[0040] 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 without any limiting character. In the figures: [ Fig. 1 ] there figure 1 schematically represents, in its environment, a particular embodiment of an ambient backscatter communication system according to the invention; [ Fig. 2 ] there figure 2 corresponds to another representation of the system of the figure 1 , in which the respective positions of a transmitting device, a receiving device, a source and a surface belonging to said system are indicated; [ Fig. 3 ] there figure 3 schematically represents an example of hardware architecture of a parameterization device for implementing a parameterization method according to the invention; [ Fig. 4 ] there figure 4 represents, in the form of a flowchart, a particular mode of implementation of the parameterization method, said method comprising a step of determining a calculated value of at least one parameter of the ambient backscatter communication system; [ Fig. 5 ] there figure 5 schematically represents a particular mode of implementation of the step of determining the process of the figure 4 ; [ Fig. 6 ] there figure 6 schematically represents another particular mode of implementation of the step of determining the process of the figure 4 . Description of the embodiments

[0041] There figure 1 schematically represents, in its environment, a particular embodiment of a system 10 for communication by ambient backscattering according to the invention.

[0042] As illustrated by the figure 1 , the communication system 10 comprises a transmitting source SO configured to transmit, according to a transmission frequency F_E included in a given frequency band called “transmission band”, a radio signal called “ambient signal”. The transmission of the ambient signal is carried out for example permanently or recurrently.

[0043] For the remainder of the description, and as illustrated by the figure 1 , the case where the ambient signal is emitted by only a single source is considered in a non-limiting manner. The choice of 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 within the framework of the present invention, the following developments being in fact generalizable without difficulty by those skilled in the art to the case of a plurality of sources that are not coherent with each other.

[0044] By "radio signal" we mean an electromagnetic wave propagating by non-wireless means, whose frequencies are included in the traditional spectrum of radio waves (a few hertz to several hundred gigahertz).

[0045] As a non-limiting example, the ambient signal is a 4G mobile telephone signal in the transmission band [811 MHz, 821 MHz] by the SO source which takes the form of a relay antenna.

[0046] 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 within the scope of the present invention. Consequently, it should be noted that the number of antennas equipping the SO source does not constitute a limiting factor of the invention.

[0047] The communication system 10 also comprises a transmitter device D_TX and a receiver device D_RX respectively configured to communicate with each other by ambient backscattering from the ambient signal emitted by the source SO. It should be noted that, in accordance with the invention, the receiver device D_RX is distinct from the source SO.

[0048] In the following description, and as illustrated by the 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 transmitter devices and / or a plurality of transmitter devices, the developments necessary for such a generalization being able to be implemented without difficulty by those skilled in the art.

[0049] In a manner known per se, communication by ambient backscattering consists of the exploitation of the ambient signal, by the transmitter device D_TX, to send data to said receiver device D_RX. More particularly, the transmitter device D_TX (respectively the receiver device D_RX) is configured to carry out, from the ambient signal (respectively from the backscattered signal), processing aimed at backscattering said ambient signal (respectively aimed at decoding said backscattered signal), by implementing a backscattering method (respectively a decoding method).

[0050] For this purpose, 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 and a computer program are stored, in the form of a set of program code instructions to be executed to implement the backscattering method (respectively the decoding method).

[0051] 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 backscattering method (respectively the decoding method).

[0052] 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 backscattering method (respectively the decoding method).

[0053] The specific aspects concerning the transmission of data by backscattering to the receiving device D_RX, as well as those concerning the decoding techniques implemented by the latter, are known to those skilled in the art and are outside the scope of the present invention. Consequently, they are not detailed here further.

[0054] In the present embodiment, the transmitter device D_TX is equipped with an antenna (not shown in the figures) 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 transmitter device D_TX.

[0055] In practice, the transmitter device D_TX is associated with a frequency band, called the “influence band”, which corresponds to the frequency band in which the antenna is capable of receiving / backscattering signals. When said influence band is included in the transmission band associated with the SO source, it is referred to as the “working band”. By “working band”, we refer here to the fact that the transmitter device D_TX is compatible with the SO source, namely that backscattering can be carried out for any frequency included in said working band.

[0056] However, nothing excludes the consideration of an influence band that is not included in the transmission band. It is nevertheless implicit that for the transmitting device D_TX to be able to backscatter the ambient signal, said influence band and said transmission band must be of non-empty intersection, the working band therefore corresponding to this intersection.

[0057] The transmitter device D_TX is also associated with operating states, namely at least one so-called "backscatter" state (the transmitter device D_TX backscatters the ambient signal) as well as a contrary state called "non-backscatter" (the transmitter device D_TX does not backscatter the ambient signal, or, in other words, is "transparent" to the ambient signal). These states correspond to configurations in which said antenna is connected to distinct impedances. This is typically a positive, or even zero, impedance for a backscatter state, and conversely a theoretically infinite impedance for the non-backscatter state.

[0058] For the remainder of the description, it is considered in a non-limiting manner that the transmitter device D_TX is associated with a single backscattering state and a single non-backscattering state. The invention nevertheless remains applicable in the case where the transmitter device D_TX is associated with a plurality of backscattering states, these states being distinct from each other in that they are implemented thanks to respective impedances distinct from each other (the non-backscattering state itself remains unique). The following developments can be generalized without difficulty by those skilled in the art to the case where a plurality of backscattering states is considered.

[0059] In the present embodiment, the receiver device D_RX is equipped with a receiving antenna (not shown in the figures) configured to receive signals in said working band. For example, said receiver device D_RX is a smartphone-type cell phone.

[0060] It should be noted, however, that there is no limitation on the number of antennas that can be fitted to the D_RX receiving device.

[0061] Generally speaking, no limitation is attached to the structural forms that can be taken respectively by the source SO and the receiving device D_RX. As non-limiting examples, the following configurations are possible depending on the working frequency band considered: the source SO is a cell phone, for example a smartphone, and the receiver device D_RX is a base station, the source SO and the receiver device D_RX are both cell phones, for example a smartphone, the source SO is a home gateway (also called an “Internet box”) emitting a Wi-Fi signal, and the receiver device D_RX is a cell phone, for example a smartphone, etc.

[0062] According to the invention, the ambient backscatter communication system 10 also comprises a surface 11 capable of reflecting signals originating from the source SO and / or the transmitter device D_TX towards the receiver device D_RX. This surface 11 is for example configured to reflect the signals without a preferred direction. Such a surface 11 has at least one face (i.e. the face towards which the incident signal waves are directed) whose roughness is for example adapted so as to allow such reflection.

[0063] By way of non-limiting example, said surface 11 has a face whose roughness is defined by asperities distributed periodically in a direction in which the surface 11 extends. According to a more specific example, said asperities are identical to each other and take the form of circular half-cylinders whose respective axes are parallel to each other. For more information on the design of such a surface, a person skilled in the art may refer to chapter 2.3 of the document: “Recommendation ITU-R P.2040-1 (07 / 2015): Effects of building materials and structures on radiowave propagation above about 100 MHz-P Series-Radiowave”. A surface 11 thus produced makes it possible to reflect an incident signal directed towards said asperities without a preferred direction. In other words, such an incident signal is reflected, in the part of the environment positioned on the side of the asperities, in an omnidirectional manner.

[0064] However, nothing excludes having a surface having a face whose roughness is defined by asperities other than half cylinders parallel to each other. Nothing excludes either that said asperities are distributed non-periodically. Generally speaking, the person skilled in the art knows how to design a surface whose topology is capable of reflecting a radio signal towards the receiving device D_RX.

[0065] In the present embodiment, said surface 11 is positioned fixed, normally to the plane in which the figure 1 , to reflect signals coming from the source SO and the transmitter device D_TX towards the receiver device D_RX. Such a configuration of the surface 11 therefore implies, in particular, that the source SO and the transmitter devices D_TX and receiver D_RX are positioned on the same side of the surface 11, more particularly opposite a face whose roughness is adapted, as mentioned above.

[0066] It is of course understood that in order for signals coming from both the source SO and the transmitting device D_TX to be reflected towards the receiving device D_RX, the size of the surface 11 must be adapted accordingly.

[0067] For purely illustrative purposes, the surface 11 is flat and extends between two ends, denoted A and B, and separated by a distance of 1 meter. Furthermore, the distances between the source SO and the surface 11 on the one hand, and the source SO and the transmitting device D_TX on the other hand, are equal to 1 meter. The distance between the source SO and the receiving device D_RX is equal to 2 meters.

[0068] Generally speaking, the person skilled in the art knows how to determine the appropriate size for such signals to be reflected towards the receiver device D_RX. It should also be noted that he knows how to adapt this size in cases where only signals from the source SO or only signals from the transmitter device D_TX are reflected, via the surface 11, towards the receiver device D_RX.

[0069] Furthermore, nothing excludes considering a surface 11 which is not flat, such as for example a curved surface, since its position and its size are adapted to allow the reflection of signals from the source SO and / or signals from the transmitter device D_TX to the receiver device D_RX. Nothing also excludes considering a surface 11 which is not normal to the plane in which the figure 1 , in other words an inclined surface since, here again, it is capable of reflecting signals from the source SO and / or signals from the transmitting device D_TX towards the receiving device D_RX.

[0070] Moreover, it should also be noted that the invention covers not only the case where the surface 11 forms an element introduced manually and voluntarily into the environment of the source SO and the transmitter D_TX and receiver D_RX devices, but also the case where the surface 11 is already present (fortuitously) in this environment and used deliberately for the invention. In the latter case, and as already mentioned above, no limitation is attached to the nature of the surface 11 since it is configured to allow the reflection of signals from the source SO and / or signals from the transmitter D_TX device towards the receiver D_RX device. For example, it may be a plate fixed to a wall and indicating a street name or a street number.

[0071] The wave paths carried by the signals considered in the present invention are represented by dotted arrows in this figure 1 . More specifically: path P1 refers to a wave coming from the source SO and arriving directly (i.e. without being reflected by the diffusing surface 11) at the receiver device D_RX; path P2 (respectively path P3) refers to a wave coming from the source SO and a reflection of which at the end A (respectively at the end B) of the surface 11 reaches the receiver device D_RX; path P4 refers to a wave coming from the source SO, then backscattered by the transmitter device D_TX and arriving directly at the receiver device D_RX; path P5 refers to a wave coming from the source SO, then backscattered by the transmitter device D_TX and a reflection of which at the surface 11, between the ends A and B, reaches the receiver device D_RX.

[0072] It should be noted that in this figure 1 , only the waves associated with paths P4 and P5 carry data that the receiving device D_RX is intended to decode in the context of ambient backscatter communication. It is also important to note that said figure 1 is given for purely illustrative purposes. Thus, it does not include, for example, any element, other than the surface 11, capable of reflecting or diffracting the waves of the ambient signal emitted by the source SO. In this sense, the figure 1 is intended to be a simplified representation of the environment in which the ambient backscatter communication system 10 is positioned. It should nevertheless be borne in mind that this environment is generally of complex configuration and may, in practice, include various elements (walls, trees, ground, etc.).

[0073] As mentioned above, the receiver device D_RX is configured to decode the signal backscattered by the transmitter device D_TX. For this purpose, it is known that the decoding of the backscattered signal can only be implemented if the variation in electromagnetic power, called the “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, called 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 emitted by the source SO and backscattered by the transmitter device D_TX.

[0074] It should be noted, however, that although decoding can theoretically be implemented when |E_P| > S_P, nothing excludes that a more restrictive decoding condition is imposed on the receiver device D_RX, such as for example |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 amount of data that can be exchanged between these devices. Generally speaking, the person skilled in the art knows 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.

[0075] Said power threshold S_P is for example defined from a signal-to-noise ratio “SNR” (acronym for the English expression “Signal to Noise Radio”) on the receiver device D_RX side or, according to a variant, from a signal-to-noise plus interference ratio “SINR” (acronym for the English expression “Signal to Interference plus Noise Radio”) on the receiver device D_RX side. However, nothing excludes considering other metrics to define said power threshold, such as for example a decoding error rate “BER” (acronym for the English expression “Bit Error Rate”). Concerning these aspects, the person 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. Galindo-Serrano, R. Fara, J. De Rosny, IEEE INFOCOM 2019 Posters and Demos, 1st May 2019, Paris, France.

[0076] For reasons of simplification of writing (deletion of the absolute value), we adopt for the rest of the description the convention according to which the said power difference E_P is evaluated according to the following general formulation: E_P = P + R − P_NR .

[0077] In this formula, we have that: P_R corresponds to the power received by the receiving device D_RX when the transmitting device D_TX is in the backscatter state (referring to the figure 1 , the waves following paths P1 to P5 contribute to the value of P_R), P_NR corresponds to the power received by the receiving device D_RX when the transmitting device D_TX is in the non-backscattering state (with reference to the figure 1 , the waves following paths P1, P2 and P3 contribute to the value of P_NR).

[0078] It is of course understood that, following this writing convention, the power difference E_P is a positive number. If an opposite convention were to be adopted (i.e. E_P = P_NR - P_R), the comparison of the difference E_P with the power threshold S_P would require the use of the absolute value.

[0079] Remarkably, the inventors have succeeded in establishing a precise analytical expression of the power deviation E_P in the context of the present invention, namely when a surface such as the surface 11 mentioned above is present in the environment of the source SO and the transmitter D_TX and receiver D_RX devices. This analytical expression is expressed as a function of parameters of the ambient backscatter communication system 10. More precisely, the parameters in question are: the respective positions S, T, R of the source SO and the transmitter D_TX and receiver D_RX devices, the transmission frequency F_E of the source SO in the transmission frequency band.

[0080] In other words, the power difference E_P can be expressed in the form of a function which takes as arguments said parameters F_E, S, T and R. Said function also translates, as detailed below, the influence of the surface 11 on the signals intended to be received by the receiving device D_RX. This function is called “calculation function” for the remainder of the description.

[0081] Calculation elements are now described which make it possible to arrive at the expression taken by said calculation function in the context of the embodiment illustrated by the figure 1 . To this end, we introduce the figure 2 which corresponds to another representation of the system 10 of the figure 1 , in which the said positions S, T, R are indicated as well as the ends A and B of the surface 11. A straight line D1 and a straight line D2 are also represented in the figure 2 , the line D1 (respectively the line D2) corresponding to the line parallel to the segment [AB] and passing through the position S of the source SO (respectively passing through the position T of the transmitting device D_TX).

[0082] In addition, we designate by: P the emission power of the source SO, A', B' and R' the points resulting from the orthogonal projections (symbolized by dotted lines on the figure 2 ), on the line D1, points A, B and R respectively, A", B" and R" the points resulting from the orthogonal projections (symbolized by dotted lines on the figure 2 ), on the line D2, from points A, B and R respectively, GS< , GT< and GR< the respective gains of the source SO, the transmitting device D_TX and the receiving device D_RX, i.e. the gains of the antennas equipping the source SO, the transmitting device D_TX and the receiving device D_RX respectively, G d< a diffusion coefficient of the surface 11 (this is a dimensionless coefficient, analogous, for example, to the coefficient “R ν” indicated in formula (51) in the document “Recommendation ITU-R P.2040-1 (07 / 2015) [...]” already cited previously), c the speed of light, λ = c / F _ E the wavelength associated with the emission frequency F_E of the SO source, k = 2 π / λ the wave vector associated with the wavelength λ, K SR = G S × G R × λ 2 / 4 π , K SAR = G S × G d × G R × λ 4 / 16 π 2 , K TR = G T × G R × λ 2 / 16 π 2 , K STR = G S × G T 2 × G R × λ 4 / 64 π 2 , α = 0 or 1 if the transmitting device is in the non-backscattering or backscattering state respectively, β = AB × SA ′ / SA + SA ′ − SR ′ / AR , γ = AB × TA " / TA + TA " − TR " / AR .

[0083] In order to obtain the analytical expression of the calculation function, we consider that a signal S_RX received by the receiving device D_RX is written: S _ RX = S SO , DIR + S SO , DIFF + S D _ TX , DIR , expression which must be understood as being a vector relation on the body of complex numbers, and in which: S(SO, DIR) corresponds to the signal coming directly from the source SO (path P1 in reference to the figure 1 ) and has the expression: S SO DIR = K SR P SR 2 e iωt e − ikSR ; S(SO, DIFF) corresponds to the signal coming from the source SO after a reflection on the surface 11 (paths P2 and P3 with reference to the figure 1 ) and has the expression: S SO , DIFF = K SR K SAR SA 2 AR 2 P e iωt e − ik SA + AR ∫ u = 0 u = β e − iku du ; S(D_TX, DIR) corresponds to the backscattered signal coming directly from the transmitting device D_TX (path P4 with reference to the figure 1 ) and has the expression:

[0084] It should be noted that this vector relationship is based on the assumption that the power of a backscattered signal S(D_TX, DIFF) reaching the receiving device D_RX after reflection on surface 11 (path P5 with reference to the figure 1 ) is negligible in comparison with the powers respectively associated with the signals S(SO, DIR), S(SO, DIFF) and S(D_TX, DIR). It is understood that such a signal S(D_TX, DIFF) has undergone, throughout its path, two reflections: a first reflection at the level of the transmitting device D_TX due to backscattering, as well as a second reflection at the level of the surface 11. This plurality of reflections implies that the distance traveled by the signal S(D_TX, DIFF) is greater than those traveled respectively by S(SO, DIR), S(SO, DIFF) and S(D_TX, DIR), so that its amplitude is lower in comparison with the respective amplitudes of the latter. In other words, each reflection induces a weakening of the corresponding signal. It should be noted that this modeling hypothesis on which the formulation of the signal S_RX is based has been validated by numerical simulations by the inventors.

[0085] Finally, we also introduce the following series of notations: P(D_TX): P D _ TX = A 2 D _ TX Or A D_TX = α × K STR / ST 2 × TR 2 × P 1 / 2 , P(D_TX, DIR): P D _ TX , DIR = 2 A DIR A D _ TX cos k ST + TR − SR Or A DIR = K SR / SR 2 × P 1 / 2 , P(D_TX, DIFF): P D _ TX , DIFF = 4 k A DIFF A D _ TX sin kβ 2 cos k AS + AR − TS − TR + β 2 Or A DIFF = K SAR / AS 2 × AR 2 × P 1 / 2 , P(DIR): P DIR = A 2 DIR P(DIFF): P(DIR, DIFF): P DIR DIFF = 4 k A DIR A DIFF sin kβ 2 cos k SA + AR − SR + β 2 .

[0086] From this series of notations, we have that: P_R = P(DIR) + P(DIFF) + P(DIR, DIFF) + P(D_TX, DIFF | α = 1) + P(D_TX | α = 1) + P(D_TX, DIR | α = 1), expression in which the values of the terms P(D_TX, DIFF), P(D_TX), P(D_TX, DIR), as described above, are considered for α equal to 1 (i.e. the values of these terms are obtained for A(D_TX) = [K STR< / (ST 2< x TR 2< ) x P] 1 / 2< ); P_NR = P(DIR) + P(DIFF) + P(DIR, DIFF) + P(D_TX, DIFF | α = 0) + P(D_TX | α = 0) + P(D_TX, DIR | α = 0), expression in which the values of the terms P(D_TX, DIFF), P(D_TX), P(D_TX, DIR), as described above, are considered for α equal to 0 (i.e. the values of these terms are obtained for A(D_TX) = 0).

[0087] Ultimately, the calculation function for evaluating the power difference E_P, as a function of said parameters and the influence of the surface 11 on the signals intended to be received by the receiving device D_RX, is written:

[0088] According to this expression, the calculation function involves three terms which add up to each other, including: a first term representative of the contribution, in terms of power, of signals backscattered by the transmitter device D_TX and reaching the receiver device D_RX without reflection on the surface 11 (term without trigonometric function), a second term representative of the contribution, in terms of power, of a coupling between signals backscattered by the transmitter device D_TX and reaching the receiver device D_RX without reflection on the surface 11 and signals emitted by the source SO and reaching the receiver device D_RX without reflection on the surface 11 (term involving only the trigonometric function cos), a third term representative of the contribution, in terms of power,of a coupling between signals backscattered by the transmitter device D_TX and reaching the receiver device D_RX without reflection on the surface 11 and signals emitted by the source SO and reaching the receiver device D_RX after reflection on the surface 11 (term involving a product of trigonometric functions sin and cos).

[0089] It is then important to note that the third term (i.e. the term involving a product of trigonometric functions sin and cos) is the one which is representative of the influence (i.e. the contribution) of the surface 11 in the evaluation of the power difference E_P. It is therefore understood, in view of the analytical expression of the calculation function, that the voluntary use of the surface 11 in the environment of the source SO and the transmitter D_TX and receiver D_RX devices advantageously makes it possible to increase the maximum achievable power difference (due to the presence of said third term) in comparison with a configuration where the surface 11 would not be present.In other words, the invention is remarkable not only in that the expression of the calculation function was determined by the inventors, but also above all because the ambient backscatter communication system 10 deliberately comprises said surface 11, so that it is possible, via a parameterization method detailed below, to determine a value of at least one of the parameters of the system 10 so that said calculation function is greater than or equal to the threshold S_P.

[0090] In the present embodiment, the implementation of said parameterization method is carried out by a parameterization device D_PAR which is included in said receiving device D_RX.

[0091] Furthermore, within the meaning of the present invention, and to implement said parameterization method, said calculation function typically corresponds to a set of code instructions. For example, said code instructions are written in the MATLAB language, so that said calculation function corresponds to a MATLAB script. The software environment of the D_PAR parameterization device is therefore adapted, in a manner known per se, to the execution of such a MATLAB script.

[0092] Generally, there is no limitation on the programming language in which the code instructions for said computational function are written, which may 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 any other desirable form.

[0093] There figure 3 schematically represents an example of hardware architecture of the D_PAR parameterization device for implementing the parameterization method according to the invention.

[0094] For this purpose, the D_PAR parameterization device has the hardware architecture of a computer. As illustrated by the figure 3 , the D_PAR parameterization device comprises, in particular, a processor 1, a random access memory 2, a read only memory 3 and a non-volatile memory 4.

[0095] The read-only memory 3 of the parameterization device D_PAR 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 executing the steps of the parameterization method according to the invention. The program PROG defines functional modules of the parameterization device D_PAR, which rely on or control the hardware elements 2 to 4 of the parameterization device D_PAR cited above, and which notably comprise a determination module MOD_DET, configured to determine a value, called “calculated value”, of at least one of said parameters so that said calculation function is greater than or equal to the threshold S_P.

[0096] It should be noted that said hardware architecture of the D_PAR parameterization device also integrates the means already described previously and configured to implement the method of decoding the backscattered signal (these means are however not shown on the figure 3 ).

[0097] For the remainder of the description, it is considered in a non-limiting manner that the code instructions defining the calculation function are initially stored in a memory equipping an entity other than the parameterization device D_PAR, for example a memory equipping the transmitter device D_TX, or the source SO, or even an entity external to the system 10 and capable of storing the instructions of said calculation function (e.g.: database server). Therefore, in the example of hardware architecture considered here, the parameterization device D_PAR also comprises an obtaining module MOD_OBT configured to obtain said calculation function.In other words, obtaining the code instructions of the calculation function, by the parameterization device D_PAR, is carried out via a data exchange (transmission / reception) controlled by the obtaining module MOD_OBT and implemented by communication means respectively equipping said parameterization device D_PAR (communication means 5 on the . figure 3 and which notably integrate the antenna of the receiving device D_RX) and said entity.

[0098] Generally speaking, the means of communication considered for such an exchange of data are based on a communication interface. No limitation is attached to the nature of this communication interface, which may be wired or wireless, and may implement any protocol known to those skilled in the art (Ethernet, Wifi, Bluetooth, 3G, 4G, 5G, etc.).

[0099] There figure 4 represents, in the form of a flowchart, a particular mode of implementation, by the D_PAR parameterization device, of the parameterization process.

[0100] As illustrated by the figure 4 , the parameterization process first involves a étape E10 of obtaining said calculation function evaluating, as a function of said parameters, the power difference E_P. This step E10 is implemented by said obtaining module MOD_OBT equipping the parameterization device D_PAR.

[0101] Once the obtaining step E10 has been executed, the parameterization device D_PAR has the calculation function making it possible to evaluate the difference E_P as a function of the parameters defining the ambient backscatter communication system 10. The parameterization device D_PAR is therefore able to calculate values of said difference E_P by assigning values to said parameters.

[0102] After obtaining the calculation function, the parameterization process includes a étape E20 determining a value, called “calculated value” V_CALC, of at least one of said parameters so that said calculation function is greater than or equal to the threshold S_P.

[0103] Determining such a calculated value V_CALC for at least one of said parameters amounts to seeking to optimize the parameterization of the ambient backscatter communication system 10 so as to improve the efficiency of the communication between the transmitter device D_TX and the receiver device D_RX.

[0104] The remainder of the description aims to detail particular modes of implementation of said determination step E20. In each of these modes of implementation of step E20, it is considered that three of the parameters of the system 10 are given fixed parameters and that the fourth remaining parameter is variable. Thus, the calculated value V_CALC which is determined is that of said parameter considered to be variable.

[0105] Proceeding in this way therefore amounts to considering that the value of the power difference E_P can be adjusted according to a single degree of freedom, namely that defined by the said variable remaining parameter.

[0106] By way of non-limiting example, and common to all said modes of implementation of the determination step E20, said calculated value V_CALC is determined by a dichotomy method.

[0107] Such a dichotomy method is classically implemented to iteratively test possible values of the variable parameter in a given range of values, thus making it possible to determine for which value of this range a target threshold is reached (i.e. the value for which the target threshold is reached therefore corresponds to said calculated value V_CALC).

[0108] This target threshold may correspond to a given threshold, such as for example said power threshold S_P, or, as mentioned above, a threshold higher than said power threshold S_P.

[0109] In yet another example, the target threshold may correspond to the maximum achievable by the calculation function when the variable parameter covers a given range of values. In this way, the power deviation E_P is maximized for the considered range of values. It should be noted that the theoretical global maximum of the calculation function is achievable when the variable parameter covers a range of values whose size is adapted, this point being detailed below.

[0110] Nothing precludes considering other methods for determining the calculated value V_CALC, the choice of the dichotomy method constituting only a variant of implementation of the invention. For example, the method implemented may be a Newton method, a fixed point method, a Lagrange method, a golden section method, etc.

[0111] Even more generally, it is possible to consider, during the determination step E20, a cost function corresponding to the calculation function from which said target threshold is subtracted. Therefore, the minimization of such a cost function can be implemented according to any optimization method known to those skilled in the art.

[0112] There figure 5 schematically represents a particular mode of implementation of the determination step E20 in which the transmission frequency F_E of the source SO as well as the respective positions S, T of the source SO and of the transmitting device D_TX are given fixed parameters. In other words, said given fixed parameters correspond to constant values, here denoted F_E_FIX, S_FIX and T_FIX.

[0113] Furthermore, in the mode illustrated by the figure 5 , the parameter of the system 10 whose calculated value V_CALC is determined during said determination step E20 is the position R of the receiving device D_RX.

[0114] According to an example of implementation of the mode of the figure 5 , said calculated value V_CALC is determined (for example by dichotomy) so that the quantity homogeneous at a distance and present as argument of the cosine function of the second term of the calculation function (i.e. the quantity ST + TR - SR) varies in a range of values of length greater than or equal to half the wavelength λ associated with the emission frequency F_E The fact of considering a search for the calculated value V_CALC so that said quantity can vary in such a range of values results directly from the analytical expression of the calculation function. It is possible in fact to note, on reading this analytical expression, that the theoretical global maximum of the calculation function is necessarily reached when said quantity sweeps the range of values considered here.

[0115] It is important to note that it is possible to consider implementation examples similar to the previous example, in which the calculated value V_CALC is always associated with the position R of the receiving device D_RX, and in which the homogeneous quantity at a distance which is considered is: the quantity in argument of the cosine function of the third term of the calculation function (i.e. AB x [SA' / SA + (SA' - SR') / AR]), or the quantity in argument of the sine function of the third term of the calculation function (i.e. AS + AR - TS - TR + 1 / 2x AB x [SA' / SA + (SA' - SR') / AR]).

[0116] Furthermore, other modes of implementation, similar to that of the figure 5 , can also be considered. These other modes of implementation correspond to configurations in which the transmission frequency F_E is again a given fixed parameter, and where: the respective positions T, R of the transmitter D_TX and receiver D_RX devices are given fixed parameters, the parameter whose calculated value V_CALC is determined being the position S of the source SO; or the respective positions S, R of the source SO and the receiver D_RX device are given fixed parameters, the parameter whose calculated value V_CALC is determined being the position T of the transmitter D_TX device.

[0117] The implementation examples detailed above for the particular mode of the figure 5 , in which the calculated value V_CALC is associated with the position R of the receiving device D_RX, can of course be adapted to these other modes of implementation. Thus: if the calculated value V_CALC is associated with the position S of the source SO, the homogeneous quantities at a distance which can be considered are those in the argument of the cosine function of the second term of the calculation function, or of the cosine function of the third term of the calculation function or of the sine function of the third term of the calculation function; if the calculated value V_CALC is associated with the position T of the transmitting device D_TX, the homogeneous quantities at a distance which can be considered are those in the argument of the cosine function of the second term of the calculation function, or of the sine function of the third term of the calculation function.

[0118] There figure 6 schematically represents a particular mode of implementation of the determination step E20 in which the respective positions S, T, R of the source SO and of the transmitter D_TX and receiver D_RX devices are given fixed parameters. In other words, said given fixed parameters correspond to constant values, here denoted S_FIX, T_FIX and R_FIX.

[0119] Furthermore, in the mode illustrated by the figure 6 , the parameter of the system 10 whose calculated value V_CALC is determined during said determination step E20 is the emission frequency F_E of the source SO.

[0120] According to an example of implementation of the mode of the figure 6 , said calculated value V_CALC is determined (for example by dichotomy) in the emission band of the source SO so as to maximize the calculation function, and therefore ultimately maximize the power difference E_P for said emission band.

[0121] For reasons similar to those mentioned above in the context of the method of figure 5 and relating to the analytical expression of the calculation function, it should be noted that the calculation function will necessarily admit its theoretical global maximum when the emission band of the SO source includes at least one pair of frequencies, one of which is double the other.

[0122] The localization method has been described up to considering that a signal S_RX received by the receiving device D_RX is written: S_RX = S SO , DIR + S SO , DIFF + S D_TX , DIR . As mentioned, this vector relationship is based on the assumption that the power of a backscattered signal S(D_TX, DIFF) reaching the receiver device D_RX after reflection on the surface 11 is negligible in comparison with the powers respectively associated with the signals S(SO, DIR), S(SO, DIFF) and S(D_TX, DIR). The invention nevertheless remains applicable in the case where such a signal S(D_TX, DIFF) would be taken into account in the expression of the signal S_RX. To this end, the inventors were able to establish that the signal S(D_TX, DIFF) has the expression: S D _ TX , DIFF = α K SR K STR P TA 2 AR 2 TS 2 e iωt e − ik TS + TA + AR ∫ u = 0 u = γ e − iku du Or K STR = G S × G T 2 × G R × λ 4 / 64 π 2 .

[0123] From the expression of S(D_TX, DIFF), the person skilled in the art knows how to update the expression of the power P_R (respectively of the power P_NR) received by the receiver device D_RX when the transmitter device D_TX is in the backscattering state (respectively in the non-backscattering state). Correlatively, he also knows how to update the analytical expression of the calculation function, and determine the candidate positions T_i solutions of this updated calculation function.

[0124] The invention has been described so far by considering that the code instructions defining the calculation function are initially stored in a memory equipping an entity other than the parameterization device D_PAR. That being said, the invention of course remains applicable in the case where said code instructions are implemented in the parameterization device D_PAR from its design, thus making it optional for the parameterization device D_PAR to include an obtaining module and for the parameterization method to include an obtaining step E10.

[0125] For example, the code instructions of the calculation function are implemented in the read-only memory 3 of the parameterization device D_PAR so as to be integrated into the program PROG. However, nothing prevents the code instructions of the calculation function from being implemented, during design, in another memory of the parameterization device D_PAR, the program PROG then comprising instructions allowing access to the calculation function.

[0126] Furthermore, the invention also remains applicable when the parameterization method is implemented by a parameterization device not included in the receiver device D_RX. For example, it may be a parameterization device included in the source SO or included in the transmitter device D_TX.

[0127] According to another example, it may also be a device external to the ambient backscatter communication system 10. No limitation is attached to the nature of said external device, provided that it is configured in hardware and software to implement said parameterization method. For example, it may be a PC type computer.

[0128] Finally, the invention has also been described up to now by considering modes of implementation of the determination step E20 in which three of the parameters of the system 10 are given fixed parameters, the fourth remaining parameter being variable. However, the invention remains applicable, at the cost of more complex calculations during the step E20 (and therefore more consuming in computing resources), in cases where several parameters of the system 10 (for example two, three or even four parameters) are considered as variables. Indeed, and as detailed above, reaching a given threshold by the calculation function can always be reduced to solving a problem of optimizing a cost function. Any method of optimizing a cost function depending on several variables can be implemented, the choice of a particular method constituting only a variant of implementation of the invention.For example, it is always possible to use a dichotomy method when several parameters are considered as variables.

[0129] Furthermore, and as already mentioned previously, the invention is also applicable in the case where the ambient backscatter communication system comprises a plurality of mutually incoherent sources. The fact that the sources are mutually incoherent implies in particular that the power differences induced by each source at the receiver device D_RX are added together. In other words, it is possible to determine an overall power difference at the receiver device D_RX by adding said power differences respectively associated with the sources (i.e. by adding calculation functions determined appropriately for each of the subsystems composed of a source, the transmitter device and the receiver device).

[0130] Ultimately, once the parameterization method has been executed, a calculated value V_CALC is available for at least one of the parameters of the ambient backscatter communication system 10. According to said at least one parameter considered during the determination step E20, it is then possible to obtain a duly parameterized system by adjusting the transmission frequency F_E of the source SO and / or the position S of the source SO and / or the position T of the transmitting device D_TX and / or the position R of the receiving device D_RX in accordance with the calculated value V_CALC determined for said at least one parameter.

[0131] With regard to the calculated value of one of the positions S, T, R, it is for example possible to materialize it in the environment of the system 10 using signaling means, such as for example a sign indicating that the position corresponding to said calculated value constitutes a position to be favored to improve communication by ambient backscattering.

Claims

1. Method for parametrizing a system (10) for communicating via ambient backscatter, comprising a source (SO) emitting in a given frequency band, a transmitter device (D_TX) and a receiver device (D_RX), said system also comprising a surface (11) capable of reflecting signals originating from the source and / or transmitter device towards the receiver device, said system being parametrized by: - the respective positions (S, T, R) of the source and of the transmitter and receiver devices, - the frequency (F_E) of emission of the source in said frequency band, said method being implemented by a parametrizing device (D_PAR) and comprising a step (E20) of determining a value, called the "calculated value" (V_CALC), of at least one of said parameters so that a calculation function, evaluating, depending on said parameters and on the influence of the surface (11) on the signals intended to be received by the receiver device (D_RX), the difference (E_P) in the power received by the receiver device when the transmitter device is in a backscattering state and in a non-backscattering state, is, in absolute value, greater than or equal to a threshold (S_P) from which the receiver device is capable of decoding a signal emitted by the source and backscattered by the transmitter device.

2. Method according to Claim 1, said method further comprising, before implementation of the determining step (E20), a step (E10) of obtaining said calculation function.

3. Method according to either of Claims 1 and 2, wherein the emission frequency (F_E) is a given set parameter and: - the respective positions (T, R) of the transmitter (D_TX) and receiver (D_RX) devices are given set parameters, the parameter whose calculated value (V_CALC) is determined being the position (S) of the source (SO); or - the respective positions (S, T) of the source (SO) and of the transmitter device (D_TX) are given set parameters, the parameter whose calculated value (V_CALC) is determined being the position (R) of the receiver device (D_RX); or - the respective positions (S, R) of the source (SO) and of the receiver device (D_RX) are given set parameters, the parameter whose calculated value (V_CALC) is determined being the position (T) of the transmitter device (D_TX).

4. Method according to either of Claims 1 and 2, wherein the respective positions (S, T, R) of the source (SO) and of the transmitter (D_TX) and receiver (D_RX) devices are given set parameters, the parameter whose calculated value (V_CALC) is determined being the emission frequency (F_E).

5. Method according to Claim 4, wherein said calculated value (V_CALC) is determined in said frequency band so as to maximize the calculation function.

6. Method according to any of Claims 1 to 5, wherein said calculated value (V_CALC) is determined by a bisection method.

7. Method according to any of Claims 1 to 6, wherein the surface (11) is configured to reflect signals originating from the source and / or transmitter device without privileged direction.

8. Method according to any of Claims 1 to 7, wherein the calculation function comprises three terms, namely: - a first term representative of the contribution, in terms of power, of signals backscattered by the transmitter device (D_TX) and that reach the receiver device (D_RX) without reflection from the surface (11), - a second term representative of the contribution, in terms of power, of coupling between signals backscattered by the transmitter device and that reach the receiver device without reflection from the surface and signals emitted by the source (SO) and that reach the receiver device without reflection from the surface, - a third term representative of the contribution, in terms of power, of coupling between signals backscattered by the transmitter device and that reach the receiver device without reflection from the surface and signals emitted by the source and that reach the receiver device after reflection from the surface.

9. Computer program comprising instructions for implementing a parametrizing method according to any of Claims 1 to 8 when said program is executed by a computer.

10. Computer-readable storage medium on which a computer program according to Claim 9 is stored.

11. Device (D_PAR) for parametrizing a system (10) for communicating via ambient backscatter, comprising a source (SO) emitting in a given frequency band, a transmitter device (D_TX) and a receiver device (D_RX), said system also comprising a surface (11), capable of reflecting signals originating from the source and / or transmitter device towards the receiver device, said system being parametrized by: - the respective positions (S, T, R) of the source and of the transmitter and receiver devices, - the frequency (F_E) of emission of the source in said frequency band, said parametrizing device (D_PAR) comprising a determining module (MOD_DET), configured to determine a value, called the "calculated value" (V_CALC), of at least one of said parameters so that a calculation function, evaluating, depending on said parameters and on the influence of the surface (11) on the signals intended to be received by the receiver device (D_RX), the difference (E_P) in the power received by the receiver device when the transmitter device is in a backscattering state and in a non-backscattering state, is, in absolute value, greater than or equal to a threshold (S_P) from which the receiver device is capable of decoding a signal emitted by the source and backscattered by the transmitter device.

12. Parametrizing device according to Claim 11, said parametrizing device also comprising an obtaining module (MOD_OBT) configured to obtain said calculation function.

13. Parametrizing device according to either of Claims 11 and 12, said parametrizing device being included in the source (SO), or in the transmitter device (D_TX), or in the receiver device (D_RX).

14. System (10) for communicating via ambient backscatter, comprising a source (SO) emitting in a given frequency band, a transmitter device (D_TX) and a receiver device (D_RX), said system also comprising a parametrizing device (D_PAR) according to any of Claims 11 to 13 and a surface (11) capable of reflecting signals originating from the source and / or transmitter device towards the receiver device, said system being parametrized by: - the respective positions (S, T, R) of the source and of the transmitter and receiver devices, - the frequency (F_E) of emission of the source in said frequency band, the value of at least one of said parameters being determined by said parametrizing device (D_PAR).