U.S. Philips Corporation

Geert F Depovere

Alphons A Bruekers

Markus T Tomesen

Petrus A Nuijten

Arnoldus W Oomen

Rene A Van Gils

Method of embedding watermarks in a signal encoded by an encoder having a feedback loop, for example, a sigma-delta modulator (21,22,23). A digital watermark pattern (w) is embedded in the signal (z) by modifying selected samples (for example, replacing every 100th bit) of the encoded signal (y) by samples of the watermark pattern. The circuit (24) for modifying the samples is located inside the loop of the encoder. The effect of watermarking is thus compensated in subsequent encoding steps and the signal-to-noise ratio is only slightly affected.

Embedding supplemental data in an encoded signal, such as audio / video

An optical heterodyne receiver converts a received modulated optical signal into an electrical IF signal by an IF converter which includes a local laser, a coupling element and an opto-electrical converter. The IF signal is converted into a demodulated signal by a demodulator having a quadratic transfer characteristic. To permit a relatively low intermediate frequency, the IF converter converts the received signal into two quadrature IF signals and in the demodulator two sub-demodulators recover therefrom two demodulated signals which are then combined. This eliminates unwanted quadratic components in the combined signal.

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Eindhoven, Netherlands

Geert F Depovere