Patent ID: 8599646

Claim:
A method of estimating a distance by ultrasonic telemetry, said method being implemented by a drone (D 1 ), in particular for measuring the altitude (h) of the drone, comprising: a) emitting, from a time origin, an ultrasound burst, said burst being repeated at a predetermined recurrence frequency; b) after the end of each emission and over the duration of a time frame (n−1, n, n+1, . . . ) separating two consecutive emissions, receiving a plurality of successive signal peaks appearing at respective times of arrival during the same frame, wherein said successive signal peaks include spurious peaks (E′ n−1 , E′ n , E′ n+1 , . . . ) and one useful peak (E n−1 , E n , E n+1 , . . . ) corresponding to the distance to be estimated; characterized in that: it is provided a preliminary step of adjusting said recurrence frequency to a predetermined value different from the corresponding recurrence frequency of another drone (D 2 ) intended to be used at the same time as the considered drone, the step b) includes the possible reception of spurious peaks due to the emission of ultrasound bursts from the other drone; and for the considered drone (D 1 ) implementing the method, said method further comprises: c) for two consecutive frames, comparing the times of arrival of the p signal peaks of the current frame with the times of arrival of the q signal peaks of the previous frame, and determining, for each of the p.q pairs of peaks, a corresponding relative time gap; d) applying to the p.q relative time gaps determined at step c) at least one criterion of selection making it possible to retain only one peak of the current frame, wherein the step d) includes, as another criterion of selection, a filtering by which are retained only the peaks of the current frame for which the relative time gap with the peaks of the previous frame is lower than a predetermined threshold; and e) estimating the distance based on the time of arrival of the peak retained at step d) with respect to the time of emission of the last burst, wherein the respective recurrence frequencies of the considered drone (D 1 ) and of the other drone (D 2 ) are adjusted so that the difference between these frequencies verifies the following relation: abs( F 1 −F 2 )/max( F 1 ,F 2 )>2 *V max /c+W *min( F 1 ,F 2 )/ F s wherein: F 1 is the recurrence frequency of said considered drone, F 2 is the recurrence frequency of said other drone, V max is the maximum velocity, in the direction of estimation of the distance, of said considered drone, c is the velocity of sound propagation, W is the time width of the burst, and F s is the sampling frequency of the received signal.