New Geometric Analysis of Spread-Spectrum Data Hiding with Repetition Coding, with Implications for Side-Informed Schemes

In this paper we initially provide a new geometric interpretation of additive and multiplicative spread-spectrum (SS) watermarking with repetition coding and ML decoding. The interpretation gives an intuitive rationale on why the multiplicative scheme performs better in front of additive independent attacks, and it is also used to produce a novel quantitative performance analysis. Furthermore, the geometric considerations which explain the advantages of multiplicative SS with repetition afford the proposal of a novel side-informed STDM-like method, which we name Sphere-hardening Dither Modulation (SHDM). This method is the side-informed counterpart of multiplicative SS with repetition coding, in the same sense that STDM is the side-informed counterpart of additive SS with repetition coding.