Selection method for optimizing communications by ambient backscattering, and associated system

1. A method implemented by an ambient backscatter communication system including an emitting source as well as a transmitting device and a receiving device, the source being associated with a focusing precoder P including a first and a second component for focusing signals towards respectively the transmitting device and the receiving device,

said method including, for a value Φ_i comprised in the interval [0, 2π]:

phase-shifting, by the source, one of the components of the precoder P according to said value Φ_i, so as to obtain a precoder Q_i,

emission, by the source, using said precoder Q_i,

acquiring, by the receiving device, a first measurement and a second measurement of electromagnetic power when the transmitting device is respectively in a non-backscattering state and in a backscattering state,

determining, by the receiving device, a value D1_i representative of a power deviation, in absolute value, between said first and second measurements,

said phase-shift, emission, acquisition and determination being iterated for a plurality of values Φ_1, . . . , Φ_N distinct from each other,

the method further including selecting, by the receiving device, a maximum value, called intermediate optimum value, among the determined values D1_1, . . . , D1_N.

2. The method according to claim 1 , wherein said phase-shift, emission, acquisition and determination steps are iterated as long as the value D1_i determined during a determination step for a value Φ_i is lower than a predetermined threshold.

3. The method according to claim 1 , wherein said phase-shift, emission, acquisition and determination are iterated a determined number of times.

4. The method according to claim 1 , wherein the values Φ_1, . . . , Φ_N are sampled on a logarithmic scale or alternatively on a linear scale.

5. The method according to claim 1 , wherein the precoder P is of a zero forcing type or of a Minimum Mean Square Error type.

6. The method according to claim 1 , said method further including, before the implementation of the phase-shift, emission, acquisition and determination, at least one act of updating, by the source, the precoder P, the updated precoder P corresponding to the precoder P whose first and second components are weighted respectively by strictly positive first coefficient and second coefficient forming a pair of coefficients, and the phase-shift being applied to said updated precoder P.

7. The method according to claim 6 , comprising performing a plurality of the update acts, the pairs of first and second coefficients considered during said update acts being distinct from each other, wherein:

the iterations of the phase-shift, emission, acquisition and determination for the values Φ_1, . . . , Φ_N, and

the selecting an intermediate optimum value,

are iterated for each of the update acts, so that each update act corresponds to an intermediate optimum value,

said method further including selecting, by the receiving device, a maximum value, called final optimum value, among said intermediate optimum values.

8. The method according to claim 6 , wherein, for a given update, the first coefficient is equal to a value δ, where δ is chosen from the interval]0,1[, and the second coefficient is equal to √{square root over (1−δ 2 )}.

9. The method according to claim 1 , said method including, after the of selecting said intermediate optimum value, transmitting, by the receiving device and towards the source, information identifying the precoder, called intermediate optimum precoder Q, based on which said intermediate optimum value was determined,

said method further including, for a pair of first and second strictly positive coefficients:

updating, by the source, the precoder Q, the updated precoder Q corresponding to the precoder Q whose first and second components are weighted by said first and second coefficients respectively,

emission, by the source, using said updated precoder Q,

acquiring, by the receiving device, a first measurement and a second measurement of electromagnetic power when the transmitting device is respectively in a non-backscattering state and in a backscattering state, and

determining, by the receiving device, a value D2_m representative of a power deviation, in absolute value, between said measurements,

said update, emission, acquisition and determination performed for a pair of coefficients being iterated for a plurality of pairs of coefficients distinct from each other, the method further including selecting, by the receiving device, a maximum value, called final optimum value, among the determined values D2_1, . . . , D2_M.

10. The method according to claim 9 , including:

obtaining the intermediate optimum value selected among the determined values D1_1, . . . , D1_N, or the final optimum value selected, among the determined values D2_1, . . . , D2_M,

transmitting, by the receiving device and towards the source, information identifying the precoder, called optimized precoder, based on which said intermediate optimum value or said final optimum value was obtained,

emitting, by the source, an ambient signal using said optimized precoder,

backscattering, by the transmitting device, said ambient signal,

receiving, by the receiving device, the backscattered ambient signal.

11. A non-transitory computer readable medium having stored thereon instructions which, when executed by a processor, cause the processor to implement of at least part of a selection method according to claim 1 .

12. An ambient backscatter communication system including:

an emitting source;

a transmitting device; and

a receiving device,

the source being associated with a focusing precoder P including a first and a second component for focusing signals towards respectively the transmitting device and the receiving device, said source including:

at least one first processor; and

at least one first non-transitory computer-readable medium comprising instructions stored thereon which when executed by the at least one first processor configure the source to:

phase-shift, for a value Φ_i comprised in the interval [0, 2π], one of the components of the precoder P according to said value Φ_i, so as to obtain a precoder Q_i,

emit using said precoder Q_i,

and said receiving device including:

at least one second processor; and

at least one second non-transitory computer-readable medium comprising instructions stored thereon which when executed by the at least one second processor configure the receiving to:

acquire electromagnetic power measurements when the transmitting device is respectively in a non-backscattering state and in a backscattering state,

determine, from two acquired measurements, a value representative of a power deviation between said two acquired measurements,

select, when several values have been determined, a maximum value among said determined values.

13. The system according to claim 12 , the receiving device further including a transmitter, configured to transmit towards the source information identifying a precoder based on which said maximum value was determined.