Patent ID: 7529941

Claim:
A computing device for 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 computing device comprising: a processor; a module configured to control the processor to subtract odd blocks from a k-th block of the watermarked signal to generate a first signal; a module configured to control the processor to apply a Fast Fourier Transform (FFT) to the first signal to generate a phase S k ( f ); a module configured to control the processor to calculate a phase of S k ( f ) as φ ( f ) and a phase of an original signal S k ( f ) as φ( f ); a module configured to control the processor to calculate the difference Ψ( f ) between φ ( f ) and φ( f ); and a module configured to control the processor to use 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 computing device further: unwraps 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 uses the Viterbi search to retrieve the watermark embedded in {tilde over (Φ)} k ( f ).