Image Number 3 for United States Patent #7529941.
A system and method of retrieving a watermark in a watermarked signal are disclosed. The watermarked signal comprises odd and even overlapped blocks where the watermark is contained in the even blocks. The method comprises, for each kth even block, subtracting the two adjacent odd numbered blocks from the kth even block of the watermarked signal to retrieve s*.sub.k(n), transforming s*.sub.k(n) into the frequency domain to generate S.sub.k(f), calculating a phase of S.sub.k(f) as .phi.(f) and a phase of S.sub.k(f) as .phi.(f), calculating the difference .PSI.(f) between .phi.(f) and .phi.(f), unwrapping .PSI.(f) to obtain the phase modulation {tilde over (.phi.)}.sub.k(f), and using a Viterbi search to retrieve the watermark embedded in {tilde over (.PHI.)}.sub.k(f).
