Patent ID: 7131007

Claim:
A computer-implemented method of retrieving a watermark in a watermarked signal, the watermarked signal comprising odd and even overlapped blocks where the watermark is contained in even blocks, the method comprising, for each k-th block: subtracting odd blocks from a k-th block of the watermarked signal to generate {overscore (s)}* k (n); applying an FFT to {overscore (s)}* k (n) to generate a phase {overscore (S)} k (f); calculating a phase of {overscore (S)} k (f) as {overscore (φ)}(f) and a phase of an original signal S k (f) as φ(f); calculating the difference Ψ(f) between {overscore (φ)}(f) and φ(f); and using a Viterbi search to retrieve the watermark embedded in Ψ(f), wherein if during a phase-modulation stage of generating the watermarked signal, the result of adding a phase-modulation to the phase of the original signal has an absolute value greater than π, then the method further comprises: unwrapping Ψ(f) to obtain a correct phase modulation {tilde over (Φ)} k (f) only when φ(f)>π/2 and Ψ(f) is greater than a dynamic range of the phase modulation; and using the Viterbi search to retrieve the watermark embedded in {tilde over (Φ)} k (f).