CN103716128A - Communication digital watermark embedding method and communication digital watermark extracting method - Google Patents

Abstract

The invention discloses a digital watermarking method for communication modulation channel transmission. The method comprises three parts: watermark embedding, signal transmitting and watermark extracting. The method comprises the steps of adopting a communication digital watermark embedding method to embed watermark information into an original modulation signal, acquiring a watermark-embedded modulation signal through communication channel transmission, and adopting a communication digital watermark extracting method to extract a synchronization signal and to obtain original data and watermark information. According to the method, digital watermark information is embedded in a communication signal, and secret information can be transmitted in the communication signal by the use of digital watermarks without influencing normal communication. The methods of the invention can be used for correspondent identity verification and secret information transmission and provide a reliable guarantee for secret communication.

Description

A kind of embedding of the digital watermarking of communicating by letter and extracting method

Technical field

The present invention relates to digital watermark technology, relate in particular to a kind of digital watermark method towards the transmission of communication modulation channel.

Background technology

Digital watermark technology is at high speed development in recent years, and application has obtained expansion widely.The basic application of digital watermarking is copyright protection, hide sign, authentication is communicated by letter with safe and secret.Digital watermark technology has broad prospects for secure communication field, at present for it, in the research aspect secure communication, also start to increase gradually, but the maturation of being nowhere near, and current research all concentrates on the multimedia aspects such as graphics/audio, also few in the research in communication modulation signal field.

Summary of the invention

For the deficiencies in the prior art, the object of the invention is to propose a kind of embedding and extracting method of the digital watermarking of communicating by letter, embed digital watermark information in signal of communication, can, in the situation that not affecting proper communication, utilize digital watermarking to transmit hidden information.

For realizing above goal of the invention, the present invention by the following technical solutions:

A communication digital watermark method, comprises watermark embedding, signal transmission and three parts of watermark extracting, wherein,

Described watermark embeds and comprises the following steps:

Step 1.1, by modulation after primary signal segmentation in time domain, each is segmented into a frame, i frame original modulated signal is s (i, t);

Step 1.2, every frame original modulated signal of step 1.1 gained is carried out to frequency domain filtering, frequency components is specified in filtering, obtains time-domain signal s _n(i, t);

Step 1.3, by the be added to time-domain signal s of step 1.2 gained of watermark information _n(i, t), obtains watermarked each frame signal x (i, t), then before each frame, adds modulated synchronizing signal, obtains the modulation signal with synchronizing signal and watermark information;

Described signal transmission comprises the following steps:

The modulation signal that embeds synchronizing signal and watermark information is sent on channel, through traffic channel, at receiving terminal of communication system collection signal;

Described watermark extracting comprises the following steps:

Step 3.1, receive the modulation signal that embeds synchronizing signal and watermark information, utilize the synchronous demodulation method of correlation operation, demodulate the sequence of symhols that comprises synchronizing signal and primary signal;

Step 3.2, utilize frame synchronizing to catch synchronous code tuple, isolate primary signal sequence of symhols, thereby obtain primary signal;

Step 3.3, according to the speed ratio of primary signal code element and watermark signal, determine the start-stop position of each code element in watermark information section, by auto-correlation algorithm demodulation watermark signal code element, extract watermark information.

The invention also discloses a kind of communication data waterprint embedded method, comprise the following steps:

Step 1.1, by modulation after primary signal segmentation in time domain, each is segmented into a frame, i frame original modulated signal is s (i, t);

Step 1.2, every frame original modulated signal of step 1.1 gained is carried out to frequency domain filtering, frequency components is specified in filtering, obtains time-domain signal s _n(i, t);

Step 1.3, by the be added to time-domain signal s of step 1.2 gained of watermark information _n(i, t), obtains watermarked each frame signal x (i, t), then before each frame, adds modulated synchronizing signal, obtains the modulation signal with synchronizing signal and watermark information.

The present invention has following beneficial effect: not only can resist interchannel noise and disturb, can also resist common signal and process attack, and the error rate be lower.

Accompanying drawing explanation

Explanation with reference to below, by reference to the accompanying drawings, can have best understanding to the present invention.In the accompanying drawings, identical part can be represented by identical label.

Fig. 1 is embodiments of the invention flow charts;

Fig. 2 is that communication digital watermarking of the present invention embeds flow chart;

Fig. 3 is hiding watermark information structural representation of the present invention;

Fig. 4 is modulation signal transmitting procedure schematic diagram of the present invention;

Fig. 5 is the digital watermark extracting flow chart of communication of the present invention.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearer, below in conjunction with accompanying drawing and exemplary embodiment, the present invention is further elaborated.Should be appreciated that exemplary embodiment described herein is only in order to explain the present invention, the scope of application being not intended to limit the present invention.

Communication digital watermark method provided by the invention comprises watermark embedding, signal transmission and three parts of watermark extracting, and its flow chart, referring to Fig. 1, is described respectively below.

Watermark embedding method as shown in Figure 2, is embedded into synchronizing signal and watermark information in primary signal.

The communication data waterprint embedded method of the present embodiment, comprises the following steps:

Step 1.1, by modulation after primary signal segmentation in time domain, each is segmented into a frame, i frame original modulated signal is s (i, t).

In the present embodiment, primary signal adopts BPSK modulation, and carrier signal is:

c(t)＝cos(2πf _ct) (1)

F wherein _cfor primary signal carrier frequency, in embodiment, be set as f _c=500Hz.If raw symbol sequence is d _n, chip rate R=500bit/s, the primary signal expression formula after modulation is:

$s\left(t\right)=\left\{\begin{array}{cc}c\left(t\right),& d_n=1;\\ -c\left(t\right),& d_n=-1.\end{array}\right.---\left(2\right)$

As shown in Figure 3, the primary signal s after modulation is carried out to segmentation.In the present embodiment, setting every section of primary signal time span is 60 seconds.

Step 1.2, every frame original modulated signal of step 1.1 gained is carried out to frequency domain filtering, frequency components is specified in filtering, obtains time-domain signal s _n(i, t).

Wherein, every frame original modulated signal s (i, t) is made to Fourier transform, obtain frequency-region signal S (i, f), filtering obtains:

F wherein _cwfor the carrier frequency of watermark information, R _wfor watermark information chip rate.In embodiment, set f _cw=900Hz, R _w=100bit/s.To S _n(i, f) makes Fourier inversion, obtains time-domain signal s _n(i, t).

Step 1.3, by the be added to time-domain signal s of step 1.2 gained of watermark information _n(i, t), obtains watermarked each frame signal x (i, t), then before each frame, adds modulated synchronizing signal, obtains the modulation signal with synchronizing signal and watermark information.

The present embodiment adopts BPSK to modulate watermark information, and carrier signal is:

c _w(t)＝cos(2πf _cwt) (4)

F wherein _cwfor the carrier frequency of watermark information, ditto described in, f _cw=900Hz.Watermark information expression formula after modulation is:

$s_w\left(t\right)=\left\{\begin{array}{cc}{c}_w\left(t\right),& d_w=1;\\ {-c}_w\left(t\right),& d_w=-1.\end{array}\right.---\left(5\right)$

D wherein _wfor watermark code metasequence.

For the ease of synchronously, in the present invention, by the watermark information embedding minute frame in time domain, frame length is consistent with modulation signal.If i frame watermark signal is s _w(i, t), is added to watermark information on the time-domain signal of step 1.2 gained, obtains watermarked each frame signal x (i, t):

x(i,t)＝s _n(i,t)+s _w(i,t) (6)

In the present embodiment, the concrete mode that synchronizing signal embeds is the synchronous method based on autocorrelation, Barker code technology is incorporated in frame synchornization method, using Barker code as synchronous code.Specific implementation is as follows:

Select the Barker code d of 13 _b=1,1,1,1,1,0,0,1,1,0,1,0,1} is as synchronizing signal mark, and Barker code also adopts BPSK modulation, and carrier signal is all c (t) mutually with the carrier wave of primary signal, and the synchronizing signal expression formula after modulation is:

$s_b\left(t\right)=\left\{\begin{array}{cc}c\left(t\right),& d_b=1;\\ -c\left(t\right),& d_b=-1.\end{array}\right.---\left(7\right)$

Subsequently, before each frame of embed watermark information, add modulated Barker code.

Signal transmission as shown in Figure 4.The Hybrid-modulated Signal that embeds synchronizing signal and watermark information is sent on channel, through traffic channel, at receiving terminal of communication system collection signal.

Watermark extracting method as shown in Figure 5.Adopt the digital watermark extracting method of communication, extract the watermark information and the original transmission message that receive in signal.

In the present embodiment, the digital watermark extracting method of communicating by letter, comprises the following steps:

Step 3.1, receive the modulation signal that embeds synchronizing signal and watermark information, utilize the synchronous demodulation method of correlation operation, demodulate the sequence of symhols that comprises synchronizing signal and primary signal.

In the present embodiment, use to have received sampled point as one group of sequence for related operation, because the carrier frequency of synchronizing signal and primary signal is all f _c, by frequency, be f _ccarrier wave and above-mentioned sample sequence make related operation, correlation function is as follows:

$R_s\left(i\right)=\underset{j=1}{\overset{T}{\mathrm{\Σ}}}c\left(j\right)*A(i+j)---\left(8\right)$

Wherein, T=f _s/ R is the Baud Length of primary signal, wherein f _sfor the sample rate of receiving terminal, R is raw symbol speed.In the present embodiment, get f _s=2000Hz, T=4.The Hybrid-modulated Signal sampled point that embed synchronous and watermark information of A (i) for receiving, c (j) is j sampled value in carrier signal c (t) sampling.Utilize correlation operation to obtain coefficient R _s(i), set correlation coefficient threshold Th _slocate the judgement position of each code element, demodulate the sequence of symhols of synchronizing signal and primary signal

$\hat{d}\left(k\right)=\left\{\begin{array}{c}0,R_s\left(k\right)\≥{\mathrm{Th}}_s\\ 1,R_s\left(k\right)\≤-{\mathrm{Th}}_s\end{array}\right.---\left(9\right)$

Wherein k is natural number.Location coefficient correlation is not less than Th _sand apart from the determination point that is not less than Baud Length T, according to the positive-negative polarity judgement code element of phase relation numerical value, be 0 or 1 with last determination point.In the present embodiment, threshold value is made as Th _s=8.

Step 3.2, utilize frame synchronizing to catch synchronous code tuple, isolate primary signal sequence of symhols, thereby obtain primary signal.

The sequence of symhols that comprises synchronizing signal and primary signal demodulating based on step 3.1, utilizes frame synchronizing, catches sync symbols position, defines a relevance function R _b(i) as follows:

$R_b\left(i\right)=\underset{j=1}{\overset{13}{\mathrm{\Σ}}}{d}_b\left(j\right)*\hat{d}(i+j)---\left(10\right)$

D wherein _b(j) represent the j position of original Barker code synchronizing sequence, the i position of the sequence of symhols obtaining for demodulation in step 3.1.Set synchronizing signal location threshold value coefficient T h _b.If R _b(i)>=Th _b, location relevance function R _b(i)>=Th _b, and be not less than the synchronous code tuple of frame length with last synchronous point distance.In the present embodiment, set Th _b=13.

After positioning synchronous set of symbols, according to synchronous code tuple position, the sequence of symhols that comprises synchronizing signal and primary signal demodulating is carried out to segmentation, isolate and in every segment signal, remove the primary signal code element after sync symbols, thereby obtain primary signal.

Step 3.3, according to the speed ratio of primary signal code element and watermark signal, determine the start-stop position of each code element in watermark information section, by auto-correlation algorithm demodulation watermark signal code element, extract watermark information.

After step 3.2 positioning synchronous signal, can determine the original position of watermark section, watermark signal is to be embedded in original signal sequence, consistent with primary signal original position, all after synchronous code tuple.Then, according to the speed ratio of primary signal code element and watermark signal, can determine the start-stop position of each code element in watermark information section, then by auto-correlation algorithm demodulation watermark signal code element.Specific implementation is:

The modulating frequency of watermark signal is f _cw=900Hz, known primary signal chip rate and watermark signal transmission rate ratio R/R _w.In the present embodiment, value is R/R _w=5.Chip rate ratio shows, every transmission R/R _windividual primary signal code element sends a watermark signal code element.Thus, utilize primary signal code element can judge the position of each watermark signal code element.Often demodulate R/R _windividual raw symbol, locates 1 hybrid modulation waveform sampling point A (i+j) receiving that watermark signal code element is corresponding, by this section of sampled point and frequency, is f _cwcarrier wave carry out related calculation:

$R_w\left(i\right)=\underset{j=1}{\overset{T_w}{\mathrm{\Σ}}}{c}_w\left(j\right)*A(i+j)---\left(11\right)$

Wherein, c _w(j) be carrier signal c _w(t) j sampled value in, T _wfor watermark information Baud Length.According to the positive-negative polarity of phase relation numerical value, judgement watermark information code element is 0 or 1, extracts watermark information.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., within all should being included in protection scope of the present invention.

Claims (10)

1. a communication digital watermark method, comprises watermark embedding, signal transmission and three parts of watermark extracting, wherein,

Described watermark embeds and comprises the following steps:

Step 1.1, by modulation after primary signal s (t) segmentation in time domain, each is segmented into a frame, i frame original modulated signal is s (i, t);

Step 1.2, every frame original modulated signal of step 1.1 gained is carried out to frequency domain filtering, frequency components is specified in filtering, obtains time-domain signal s _n(i, t);

Step 1.3, by the be added to time-domain signal s of step 1.2 gained of watermark information _n(i, t), obtains watermarked each frame signal x (i, t), then before each frame, adds modulated synchronizing signal, obtains the modulation signal with synchronizing signal and watermark information;

Described signal transmission comprises the following steps:

The modulation signal that embeds synchronizing signal and watermark information is sent on channel, through traffic channel, at receiving terminal of communication system collection signal;

Described watermark extracting comprises the following steps:

Step 3.1, receive the modulation signal that embeds synchronizing signal and watermark information, utilize the synchronous demodulation method of correlation operation, demodulate the sequence of symhols that comprises synchronizing signal and primary signal;

Step 3.2, utilize frame synchronizing to catch synchronous code tuple, isolate primary signal sequence of symhols, thereby obtain primary signal;

Step 3.3, according to the speed ratio of primary signal code element and watermark signal, determine the start-stop position of each code element in watermark information section, by auto-correlation algorithm demodulation watermark signal code element, extract watermark information.

Communication a data waterprint embedded method, comprise the following steps:

Step 1.1, by modulation after primary signal s (t) segmentation in time domain, each is segmented into a frame, i frame original modulated signal is s (i, t);

Step 1.2, every frame original modulated signal of step 1.1 gained is carried out to frequency domain filtering, frequency components is specified in filtering, obtains time-domain signal s _n(i, t);

Step 1.3, by the be added to time-domain signal s of step 1.2 gained of watermark information _n(i, t), obtains watermarked each frame signal x (i, t), then before each frame, adds modulated synchronizing signal, obtains the modulation signal with synchronizing signal and watermark information.

3. watermark embedding method according to claim 2, wherein, in step 1.1, primary signal adopts BPSK modulation, and the primary signal expression formula after modulation is:

$s\left(t\right)=\left\{\begin{array}{cc}c\left(t\right),& d_n=1;\\ -c\left(t\right),& d_n=-1.\end{array}\right.$

Wherein c (t) is carrier signal, d _nfor raw symbol sequence.

4. watermark embedding method according to claim 2, wherein, step 1.2 is specially:

Every frame original modulated signal s (i, t) is made to Fourier transform, obtain frequency-region signal S (i, f), filtering obtains:

F wherein _cwfor the carrier frequency of watermark information, R _wfor watermark information chip rate, to S _n(i, f) makes Fourier inversion, obtains time-domain signal s _n(i, t).

5. watermark embedding method according to claim 2 wherein, using Barker code as synchronous code, adds modulated Barker code in step 1.3 before each frame of embed watermark information.

Communication a digital watermark extracting method, comprise the following steps:

Step 3.1, receive the modulation signal that embeds synchronizing signal and watermark information, utilize the synchronous demodulation method of correlation operation, demodulate the sequence of symhols that comprises synchronizing signal and primary signal;

Step 3.2, utilize frame synchronizing to catch synchronous code tuple, isolate primary signal sequence of symhols, thereby obtain primary signal;

Step 3.3, according to the speed ratio of primary signal code element and watermark signal, determine the start-stop position of each code element in watermark information section, by auto-correlation algorithm demodulation watermark signal code element, extract watermark information.

7. watermark extracting method according to claim 6, wherein, the coefficient correlation of correlation operation described in step 3.1 is:

$R_s\left(i\right)=\underset{j=1}{\overset{T}{\mathrm{\Σ}}}c\left(j\right)*A(i+j)$

T=f wherein _s/ R is the Baud Length of primary signal, f _sfor the sample rate of receiving terminal, R is raw symbol speed, the Hybrid-modulated Signal sampled point that embed synchronous and watermark information of A (i) for receiving, and c (j) is j sampled value in carrier signal c (t) sampling.

8. watermark extracting method according to claim 7, wherein, in step 3.1, the described synchronous demodulation method of utilizing correlation operation, demodulates the sequence of symhols that comprises synchronizing signal and primary signal and comprises:

Set correlation coefficient threshold Th _s, location coefficient correlation is not less than Th _sand apart from the determination point that is not less than Baud Length T, be 0 or 1 according to the positive-negative polarity judgement code element of phase relation numerical value with last determination point, thereby the sequence of symhols of the synchronizing signal of demodulating and primary signal

$\hat{d}\left(k\right)=\left\{\begin{array}{c}0,R_s\left(k\right)\≥{\mathrm{Th}}_s\\ 1,R_s\left(k\right)\≤-{\mathrm{Th}}_s\end{array}\right.$

Wherein k is natural number.

9. watermark extracting method according to claim 6, wherein, step 3.2 is specially:

Define a relevance function R _b(i):

$R_b\left(i\right)=\underset{j=1}{\overset{13}{\mathrm{\Σ}}}{d}_b\left(j\right)*\hat{d}(i+j)$

D wherein _b(j) represent the j position of original (Barker code) synchronizing sequence,

the i position of the sequence of symhols obtaining for demodulation in step 3.1;

Set synchronizing signal location threshold value coefficient T h _b, location relevance function R _b(i)>=Th _b, and be not less than the synchronous code tuple of frame length with last synchronous point distance;

According to synchronous code tuple position, the sequence of symhols that comprises synchronizing signal and primary signal demodulating is carried out to segmentation, isolate in every segment signal and remove the primary signal code element after sync symbols, obtain primary signal.

10. watermark extracting method according to claim 6, wherein, in step 3.3, often demodulates R/R _windividual raw symbol, locates 1 hybrid modulation waveform sampling point A (i+j) receiving that watermark signal code element is corresponding, and wherein R is primary signal chip rate, R _wfor watermark information chip rate, this section of sampled point and carrier wave are carried out related calculation:

$R_w\left(i\right)=\underset{j=1}{\overset{T_w}{\mathrm{\Σ}}}{c}_w\left(j\right)*A(i+j)$

Wherein, c _w(j) be carrier signal c _w(t) j sampled value in, T _wfor watermark information Baud Length,

According to phase relation numerical value R _w(i) positive-negative polarity, judgement watermark information code element is 0 or 1, extracts watermark information.

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