The invention relates to a space-time coding method for a UWB transmission system comprising a plurality of radiative elements, said method coding a block of information symbols S=(σ1, σ2, . . . , σP) belonging to a PPM modulation alphabet, into a sequence of vectors, the components of a vector being intended to position-modulate a UWB pulse signal for a given radiative element of said system and a given transmission channel use, each component corresponding to a PPM modulation position, in which said vectors are obtained from the elements of the matrix: C = ( σ 1 σ 2 … σ P Ω ⁢ ⁢ σ P σ 1 ⋱ ⋮ ⋮ ⋱ ⋱ σ 2 Ω ⁢ ⁢ σ 2 … Ω ⁢ ⁢ σ P σ 1 ) a row of the matrix corresponding to a use of the transmission channel and a column of the matrix corresponding to a radiative element, the matrix C being defined to within a permutation of its rows and/or its columns and Ω carrying out a permutation operation on the PPM modulation positions.