In a sphere decoding process, P PPM symbols emitted simultaneously are represented by a point of the modulation product constellation in a space of signals transmitted of dimension MP decomposed into P layers, each layer representing M modulation positions. The signal received is transformed into a representative point. The point of the product constellation closest to the received point within a sphere of given quadratic radius is determined. For each layer of rank p, ZF-DFE equalization is carried out; sorting in a list of the M PPM symbols as a function of the contributions that they would make to the quadratic distance to the received point is then carried out, followed by selection of the PPM symbol making the lowest contribution. The contribution is added to those from previous layers to obtain a sum of contributions. These steps are repeated until the lowest layer is attained.