Apparatus and methods for watermarking using starting phase modulation

1. A watermark decoding apparatus comprising:

an instantaneous phase calculator to:

calculate a first instantaneous phase value for a first watermark component of a watermarked media signal at a first time;

calculate a second instantaneous phase value for a second watermark component of the watermarked media signal at the first time;

a phase comparator to:

determine a first sum of differences for the first and second instantaneous phase values relative to a first possible starting phase value;

determine a second sum of differences for the first and second instantaneous phase values relative to a second possible starting phase value;

a starting phase bit determiner to, in response to one of the first sum of differences or the second sum of differences satisfying a difference threshold:

select a corresponding one of the first possible starting phase value or the second possible starting phase value to be a starting phase value; and

decode a bit value corresponding to the starting phase value; and

a payload determiner to determine a payload based on the bit value and a symbol represented by watermark components including the first watermark component and the second watermark component.

2. The watermark decoding apparatus of claim 1 , wherein the instantaneous phase calculator is to:

in response to the first sum of differences and the second sum of differences not satisfying the difference threshold:

calculate a third instantaneous phase value of the first component at a second time, the second time prior to the first time; and

calculate a fourth instantaneous phase value of the second component at the second time.

3. The watermark decoding apparatus of claim 2 , wherein the phase comparator is to:

determine a third sum of differences for the third and fourth instantaneous phase values relative to the first possible starting phase value; and

determine a fourth sum of differences for the third and fourth instantaneous phase values relative to the second possible starting phase value.

4. The watermark decoding apparatus of claim 3 , wherein the starting phase bit determiner is to in response to one of the third sum of differences or the fourth sum of differences satisfying the difference threshold:

select a corresponding one of the first possible starting phase value or the second possible starting phase value to be the starting phase value; and

decode the bit value corresponding to the starting phase value.

5. The watermark decoding apparatus of claim 3 , wherein the second time differs from the first time by a time step size.

6. The watermark decoding apparatus of claim 5 , wherein (1) the instantaneous phase calculator is to iteratively calculate additional instantaneous phase values of the first watermark component and the second watermark component and (2) the phase comparator is to iteratively calculate additional sums of differences of the additional instantaneous phase values relative to the first possible starting phase value and the second possible starting phase value until one of the additional sums of differences satisfies the difference threshold.

7. The watermark decoding apparatus of claim 5 , wherein (1) the instantaneous phase calculator is to iteratively calculate additional instantaneous phase values of the first watermark component and the second watermark component and (2) the phase comparator is to iteratively calculate additional sums of differences of the additional instantaneous phase values relative to the first possible starting phase value and the second possible starting phase value until a symbol duration is reached.

8. The watermark decoding apparatus of claim 1 , further including a watermark component detector to select the first watermark component and the second watermark component for analysis based a first signal strength of the first watermark component and a second signal strength of the second watermark component.

9. The watermark decoding apparatus of claim 1 , wherein to determine the first sum of differences the phase comparator is to account for phase wrapping.

10. A non-transitory computer readable storage medium comprising computer readable instructions that, when executed, cause a processor to:

calculate a first instantaneous phase value for a first watermark component of a watermarked media signal at a first time;

calculate a second instantaneous phase value for a second watermark component of the watermarked media signal at the first time;

determine a first sum of differences for the first and second instantaneous phase values relative to a first possible starting phase value;

determine a second sum of differences for the first and second instantaneous phase values relative to a second possible starting phase value;

in response to one of the first sum of differences or the second sum of differences satisfying a difference threshold:

select a corresponding one of the first possible starting phase value or the second possible starting phase value to be a starting phase value;

decode a bit value corresponding to the starting phase value; and

determine a payload based on the bit value and a symbol represented by watermark components including the first watermark component and the second watermark component.

11. The non-transitory computer readable storage medium of claim 10 , wherein the instructions, when executed, cause the processor to:

in response to the first sum of differences and the second sum of differences not satisfying the difference threshold:

calculate a third instantaneous phase value of the first component at a second time, the second time prior to the first time; and

calculate a fourth instantaneous phase value of the second component at the second time.

12. The non-transitory computer readable storage medium of claim 11 , wherein the instructions, when executed, cause the processor to:

determine a third sum of differences for the third and fourth instantaneous phase values relative to the first possible starting phase value; and

determine a fourth sum of differences for the third and fourth instantaneous phase values relative to the second possible starting phase value.

13. The non-transitory computer readable storage medium of claim 12 , wherein the instructions, when executed, cause the processor to, in response to one of the third sum of differences or the fourth sum of differences satisfying the difference threshold:

select a corresponding one of the first possible starting phase value or the second possible starting phase value to be the starting phase value; and

decode the bit value corresponding to the starting phase value.

14. The non-transitory computer readable storage medium of claim 12 , wherein the second time differs from the first time by a time step size.

15. The non-transitory computer readable storage medium of claim 14 , wherein the instructions, when executed, cause the processor to:

iteratively calculate additional instantaneous phase values of the first watermark component and the second watermark component; and

iteratively calculate additional sums of differences of the additional instantaneous phase values relative to the first possible starting phase value and the second possible starting phase value until one of the additional sums of differences satisfies the difference threshold.

16. The non-transitory computer readable storage medium of claim 14 , wherein the instructions, when executed, cause the processor to:

iteratively calculate additional instantaneous phase values of the first watermark component; and

iteratively calculate additional sums of differences of the additional instantaneous phase values relative to the first possible starting phase value and the second possible starting phase value until a symbol duration is reached.

17. The non-transitory computer readable storage medium of claim 10 , wherein the instructions, when executed, cause the processor to select the first watermark component and the second watermark component for analysis based a first signal strength of the first watermark component and a second signal strength of the second watermark component.

18. The non-transitory computer readable storage medium of claim 10 , wherein to determine the first sum of differences, the instructions, when executed, cause the processor to account for phase wrapping.

19. A watermark decoding method comprising:

calculating a first instantaneous phase value for a first watermark component of a watermarked media signal at a first time;

calculating a second instantaneous phase value for a second watermark component of the watermarked media signal at the first time;

determining a first sum of differences for the first and second instantaneous phase values relative to a first possible starting phase value;

determining a second sum of differences for the first and second instantaneous phase values relative to a second possible starting phase value;

in response to one of the first sum of differences or the second sum of differences satisfying a difference threshold:

selecting a corresponding one of the first possible starting phase value or the second possible starting phase value to be a starting phase value;

decoding a bit value corresponding to the starting phase value; and

determining a payload based on the bit value and a symbol represented by watermark components including the first watermark component and the second watermark component.

20. The method of claim 19 , further including:

in response to the first sum of differences and the second sum of differences not satisfying the difference threshold:

calculating a third instantaneous phase value of the first component at a second time, the second time prior to the first time; and

calculating a fourth instantaneous phase value of the second component at the second time.