m sub windows this statistical value is for example the average of the rssi level over said sub window the maximum value of the rssi level over this sub window the standard deviation of the rssi level of the response signals of the tag over said sub window or the difference between the maximum value and the minimum value of the rssi level of the response signals of the tag over said sub window other characteristic values not related to the rssi level can be used such as the phase difference between the interrogation signals and the response signals received this phase difference varies when the tag is moving for the learning tags this step of calculating a characteristic value is advantageously carried out during the learning phase according to a second substep a distance is calculated between the statistical values of the response signals of the current tag and the statistical values of the response signals of the n learning tags this distance is for example a euclidean distance a minkowski distance or a mahalanobis distance let us consider the example of a time window comprising 5 sub windows a i designates the characteristic value of the response signals received for the current tag during the i th time sub window with i u03b5 1 2 3 4 5 b i designates the statistical.