Insertion of a Secondary Binary Information Stream into a Main Symbol Stream of a Digital Modulation

• US 20080043871A1
• Filed: 09/12/2005
• Published: 02/21/2008
• Est. Priority Date: 09/15/2004
• Status: Active Grant

• Current Assignee: Airbus DS GMBH
• Original Assignee: EADS Secure Networks
• Inventors: Latouche, Gilles, Rousseau, Frederic
• Granted Patent: US 8,873,670 B2
• Time in Patent Office: Days
• US Class Current: 375/261
• CPC Class Codes: G06T 1/0021 Image watermarking
• CPC Class Codes: G06T 1/005 Robust watermarking, e.g. average attack or collusion attack resistant
• CPC Class Codes: G06T 1/0071 using multiple or alternating watermarks
• CPC Class Codes: H04L 27/186 in which the information is carried by both the individual signal points and the subset to which the individual signal points belong, e.g. coset coding or related schemes

Abstract

There is disclosed a method of inserting a secondary stream of binary information into a main symbol stream of at least one standard digital modulation. The stream to be transmitted resulting from the insertion of the secondary stream in the main stream is a symbol stream of a modified digital modulation. The stream to be transmitted has the same symbol rate as the main stream. The sequence of symbols of the stream to be transmitted is encoded according, cumulatively, to a first condition over at least two consecutive symbols of the main stream, on the one hand; and to a second condition on a current bit or a plurality of current bits of the secondary stream, on the other hand.

Claims

1. Method of inserting a secondary stream of binary information into a main symbol stream of at least one standard digital modulation, hereinafter called standard symbols,

wherein the stream to be transmitted resulting from the insertion of the secondary stream in the main stream is a symbol stream of a modified digital modulation, hereinafter called modified symbols, said stream to be transmitted having the same symbol rate as the main stream;

and,

wherein encoding of the sequence of symbols of the stream to be transmitted includes substituting modified symbols for respective standard symbols according, cumulatively;

to a first condition on at least two consecutive symbols of the main stream, on the one hand; and

,

to a second condition on a current bit or a plurality of current bits of the secondary stream, on the other hand.

2. Method of insertion according to claim 1, wherein said modified symbols are derived from said respective standard symbols by an additional shift in the Fresnel plane

3. Method of insertion according to claim 2, wherein the additional shift in the Fresnel plane is a phase shift only.

4. Method of insertion according to any one of claims 1 to 3, wherein the first condition is satisfied in case of a change of the sign of the phase transitions respectively associated with each symbol of a pair of consecutive symbols of the main stream.

5. Method of insertion according to claim 4, wherein, when the first condition is satisfied and when the current bit of the secondary stream is in a predefined one of the logical states TRUE or FALSE:

a first modified symbol is substituted for the first standard symbol of a pair of consecutive standard symbols of the main stream, said first modified symbol being derived from said first standard symbol by an additional phase shift corresponding to a negative angle −

α

where α

is less as an absolute value than the minimum phase transition of the standard modulation, the negative sign being defined as opposite to the sign of the phase transition associated with said first standard symbol; and

a second modified symbol is substituted for the second symbol of said pair of standard symbols, said second modified symbol being derived from said second standard symbol by an additional phase shift of a positive angle +α

, the positive sign being defined as identical to the sign of the phase transition associated with said first standard symbol

6. Method of insertion according to any one of claims 1 to 3, wherein the first condition is satisfied when, at one and the same time, the phase transitions associated with the pair of consecutive standard symbols have opposite signs, on the one hand, and neither one nor the other of these phase transitions is equal to the maximum phase transition of the standard modulation, on the other hand.

7. Method of insertion according to claim 6, wherein, when the first condition is satisfied:

a first modified symbol is substituted for the first standard symbol of a pair of consecutive standard symbols of the main stream, said first modified symbol being derived from said first standard symbol by a first additional phase shift corresponding to a negative angle −

α

/2 if the current bit of the second stream is in one of the predetermined logical states TRUE or FALSE, or to a positive angle +α

/2 if the current bit of the second stream is in the other of said logical states where α

is less as an absolute value than the minimum phase transition of the standard modulation, the negative sign and the positive sign being defined respectively as opposite and identical to the sign of the phase transition associated with said first standard symbol; and

a second modified symbol is substituted for the second symbol of said pail of standard symbols, said second modified symbol being derived from said second standard symbol by a second additional phase shift, of modulus that is the same as but of opposite sign to, respectively, the modulus and the sign of said first additional phase shift

8. Method of insertion according to any one of claims 5 and 7, wherein α

is close to and within the peak phase error specified for the standard digital modulation

9. Method of insertion according to one of the preceding claims, wherein the first condition is satisfied for a pair of standard symbols only if the cumulative phase state prior to said pair concerned is the zero or initial cumulative phase state

10. Method of insertion according to any one of the preceding claims, wherein the first condition is satisfied for a pair of standard symbols only if the phase transition associated with the first symbol of said pair has a predetermined sign, positive or negative.

11. Method of insertion according to any one of the preceding claims, wherein the first condition is satisfied for a pair of standard symbols only if these standard symbols belong to certain parts of one burst only, defined by distinguishing the training sequences from the payload sequences.

13. Method of insertion according to any one of claims 4 to 12, wherein the first condition is satisfied for a pair of standard symbols only if a phase turn-around concerning this pair of standard symbols involves a non-minimum amplitude

14. Method of insertion according to any one of claims 4 to 13, wherein the first condition is assessed successively on non-overlapping pairs of consecutive symbols of the main stream.

15. Method of extraction, from a stream of symbols transmitted in particular in radiofrequency form, of a secondary stream of binary information inserted using a method of insertion according to any one of claims 1 to 14, including, for the detection of the presence of said secondary stream, the observation of the satisfying of the first condition to deduct from it at least one current bit of the secondary stream.

16. Method of extraction according to claim 15, including, for the detection, in a stream of symbols transmitted in particular in radiofrequency form, of the existence of secondary information inserted using a method according to any one of claims 4 to 14, the observation of phase turn-arounds, followed by the statistical estimation of the phase states of standard symbols concerning these phase turn-arounds, then the detection of the presence of modified symbols in case of detection of significant phase shifts relative to said phase states

17. Method of extraction according to claim 16 in which, for the extraction of a secondary information bit from a transmitted symbol stream, which has been constructed using a method according to claim 5, said bit is set to said predetermined logical state in case of detection of the presence of modified symbols if and only if, there is a change of the sign of the phase transitions respectively associated with a pair of successive modified symbols of said transmitted symbol stream

18. Method of extraction according to claim 16 in which, for the extraction of a secondary information bit from a transmitted symbol stream, which has been constructed using a method according to claim 7, said bit is set to a predetermined one of said logical states in case of detection of the presence of modified symbols of a secondary information bit, according to the sign of the phase shifts detected.

19. Method of extraction according to any one of claims 15 to 18, in which, for the demodulation of the main stream, modified symbols, inserted in place of standard symbols, are compared to the most likely standard symbols.

20. Modulator for constructing a symbol stream to be transmitted from a main symbol stream of a standard digital modulation and a secondary stream of binary information, characterized in that it comprises means for implementing a method of insertion according to any one of claims 1 to 14

21. Demodulator for extracting a secondary stream of binary information from a symbol stream to be transmitted, constructed using an insertion method according to any one of claims 1 to 13, characterized in that it comprises means for implementing an extraction method according to any one of claims 1 to 14

22. Transmission device containing a modulator according to claim 20 and/or a demodulator according to claim 21, or a plurality of them.

12. Method of insertion according to any one of the preceeding claims, wherein it is implemented only intermittently.