Method for encoding contactless communication data from a transponder to a reader via charge modulation, in the form of a set of patterns and device for implementing same

A method for encoding contactless communication data from a transponder to a reader by load modulation, in the form of a set of modulation patterns, said method comprising associating, with each symbol from a data encoding alphabet, a modulation pattern, thereby defining a list of elements, each element of said list having a symbol and a modulation pattern selected from said set of modulation patterns, causing said transponder to select each pattern in said set of modulation patterns to be a succession of load levels of a predefined length used for physical encoding and to have a duration equal to the product of a carrier period and a number of carrier steps, to comprise a succession of at least two load levels, to have a minimum pulse width corresponding to a shortest duration in terms of number of carrier steps of a same load level in the pattern, and to have a retromodulation rate corresponding to a ratio between the retromodulation time and the duration of a pattern, wherein the number of patterns is greater than four, the minimum pulse widths of at least two patterns are different, and the retromodulation rates of at least two patterns are different, said method further comprising identifying a symbol representing information to be transmitted, using said list, identifying a modulation pattern corresponding to said symbol, and transmitting a signal that encodes said modulation pattern.