Watermark Generator Phase Rotation Encoding
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Solution Overview
Problem
Existing watermarking systems face challenges in robustness against host signal interference and amplitude scaling attacks, particularly in reverberant environments, and are limited by the sensitivity of quantization index modulation methods.
Innovation Solution
A differential encoding method is introduced where the phase of the current watermark coefficient is based on the phase of a previous spectral coefficient of the watermarked signal, combined with host interference rejection, to reduce distortion and improve decoding accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quantization index modulation is used for watermark embedding, then the watermark can be embedded in discrete valued data, but the system becomes sensitive to amplitude scaling attacks and host signal interference
Solution Approach 1:
The patent changes the embedding parameter from amplitude-based (quantization index) to phase-based (phase rotation). By rotating the phase of spectral coefficients rather than changing their amplitude through quantization, the system achieves robustness against amplitude scaling attacks while maintaining immunity to host signal interference, as phase rotations are not affected by additive host signal components.
Solution Approach 2:
The patent substitutes the mechanical quantization process with a phase rotation operation. Instead of quantizing amplitude values which introduces sensitivity to scaling and interference, the system applies phase rotations to spectral coefficients, replacing the vulnerable amplitude-based mechanism with a more robust phase-based approach that is invariant to amplitude scaling and additive interference.
2Reliability
If differential encoding is applied to the watermark signal, then robustness against phase rotation is improved, but the complexity of the encoding process increases
Solution Approach 1:
The patent merges the differential encoding operation with the phase rotation embedding operation into a single integrated process. Instead of separately applying differential encoding then phase rotation, the system combines these operations so that the phase rotation angle itself encodes the differential information, eliminating the need for separate encoding stages and reducing overall system complexity while maintaining robustness.
Solution Approach 2:
The phase rotation operation serves multiple functions simultaneously: it embeds the watermark information, performs differential encoding to provide robustness against phase rotation and frequency mismatch, and maintains imperceptibility of the watermarked signal. This multi-functionality reduces the need for separate processing stages, thereby reducing system complexity.
3Measurement precision
If the phase of the current watermark coefficient is based on the phase of a previous spectral coefficient, then decoding accuracy is improved, but the dependency on previous signal values increases
Solution Approach 1:
The patent implements feedback by using the phase of the previous spectral coefficient to determine the phase rotation angle for the current coefficient. This feedback mechanism ensures that the phase rotation is adapted to the local signal characteristics, improving decoding accuracy by compensating for phase variations and frequency shifts. The feedback loop operates naturally through the sequential processing of spectral coefficients, adding minimal complexity.
Data Source
AI summary
A watermark generator for providing a watermark signal as a sequence of subsequent watermark coefficients based on a stream of subsequent stream values representing discrete valued data includes a differential encoder. The differential encoder is configured to apply a phase rotation to a current stream value of the stream values representing the discrete valued data or to a current watermark symbol, the current watermark symbol corresponding to a current stream value of the stream values representing the discrete valued data, to obtain a current watermark coefficient of the watermark signal. The differential encoder is configured to derive a phase of a previous spectral coefficient of a watermarked signal which is a combination of the host signal and the watermark signal, and to provide the watermark signal such that a phase angle of the phase rotation applied to the current stream value or the current watermark symbol is dependent on the phase of the previous spectral coefficient of the watermarked signal.