JP2010008876A - Device which extracts electronic watermark information from carrier signal, method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly search a section, in which electronic watermark information is embedded, in a carrier signal with a small quantity of computation to extract the electronic watermark information in the section concerned. <P>SOLUTION: An approximate synchronization searching part 272 of an extraction device 200 retrieves an approximate position of a section, in which a synchronization symbol line is embedded, in a carrier signal while shifting, in rough steps, evaluation sections to be evaluated on a mutual correlation between the carrier signal and a modulation signal corresponding to the synchronization symbol line. A detailed synchronization searching part 273 retrieves the detail position of the section, in which the synchronization symbol line is embedded, in the carrier signal while shifting, in fine steps, the evaluation sections with the approximate position as an initial value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for embedding and transmitting digital watermark information, and more particularly to an apparatus, method, and program suitable for extracting digital watermark information embedded in an acoustic signal propagating in the air.

Various techniques have been proposed in which an audio signal is used as a carrier signal that bears digital watermark information, and the digital watermark information is embedded in the audio signal itself. According to this embedding technique, for example, an audio signal in which digital watermark information is embedded is reproduced as sound, and the audio signal obtained by collecting the sound with a microphone is recorded and propagated in the process of being recorded and propagated. Digital watermark information can be kept in an audio signal. Therefore, this embedding technique can be used for a wider range of applications than the technique of embedding digital watermark information in compression-encoded data.
Japanese Patent No. 3953425 Japanese Patent No. 3659321 JP 2006-251676 A

  By the way, in order for a device that has received a carrier signal to extract digital watermark information from the carrier signal, it is necessary to specify a section in which the digital watermark information is embedded in the carrier signal. For this reason, for example, in a system in which a data symbol indicating digital watermark information is embedded in a carrier signal and a synchronization symbol sequence indicating an embedding interval is embedded in the carrier signal and transmitted, the digital watermark information extracting device that acquired the carrier signal is the carrier The signal was analyzed in small increments from the beginning to determine the location of the synchronization symbol. For this reason, there has been a problem that the amount of calculation of the entire digital watermark information extraction apparatus is large and the time required until the digital watermark information is extracted becomes long.

  The present invention has been made in view of the circumstances described above, and can quickly search for an embedded section of digital watermark information in a carrier signal and extract digital watermark information in the embedded section with a small amount of computation. The purpose is to provide technical means.

An apparatus for extracting digital watermark information according to the present invention is a carrier signal obtained by performing modulation processing on at least one series of symbol sequences including a symbol sequence indicating digital watermark information on a component of a part of a band of a part of a section. Band dividing means for receiving a signal and performing band division and outputting a plurality of band carrier signals belonging to different bands, and a band including a component subjected to modulation processing by at least one series of symbol sequences in the plurality of band carrier signals Correlation calculation for calculating a cross-correlation coefficient between a demodulation unit that performs demodulation processing on the carrier signal and outputs a demodulation result signal, and a demodulation result signal obtained by the demodulation processing and a reference signal indicating one or more predetermined symbols And evaluation of the carrier signal while sequentially shifting the evaluation section from the head position of the carrier signal by a predetermined step width. Control is performed to deliver a demodulation result signal corresponding to the inter-frequency signal to the correlation calculation means, and based on the cross-correlation coefficient history obtained from the correlation calculation means, the carrier signal is modulated by a symbol string. An approximate synchronization searching means for searching for an approximate position of the embedded section, an initial position of the evaluation section based on the approximate position obtained by the approximate synchronization searching means, and an evaluation section for the approximate synchronization searching means The demodulation result signal corresponding to the signal in the evaluation interval of the carrier signal is controlled to be transferred to the correlation calculation means while sequentially shifting with a step width finer than the step width used by the Detailed synchronization search means for searching for a detailed position of the embedded section based on a history of cross-correlation coefficients.
According to such an extraction device, after a rough position search of the embedded section is performed by the rough synchronization search means while the evaluation section is shifted in rough steps from the beginning of the carrier signal, based on this rough position. The initial setting of the position of the evaluation section is performed, and the detailed position of the embedded section is searched by the detailed synchronization search means while shifting the evaluation section in finer steps. Therefore, it is possible to quickly search for the embedded section of the digital watermark information in the carrier signal and extract the digital watermark information in the embedded section with a small amount of calculation.
Patent Documents 1 to 3 are related to techniques for searching for some information related to embedding of digital watermark information. However, Patent Document 1 relates to a technique for searching for a boundary between contents using digital watermark information in a carrier signal representing a plurality of contents, and is not related to the present invention. Patent Documents 2 and 3 relate to searching for an embedded section of digital watermark information, but as in the present invention, a two-stage search is performed, that is, a rough position search and a detailed position search of an embedded section. It is not a thing.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embedding device 100 that embeds digital watermark information in a carrier signal. FIG. 2 is a block diagram showing the configuration of the extraction apparatus 200 according to this embodiment for extracting digital watermark information from the carrier signal in which the digital watermark information is embedded. Note that each of the embedding device 100 and the extraction device 200 may be realized as dedicated hardware for executing processing for embedding digital watermark information in a carrier signal or processing for extracting digital watermark information from a carrier signal, or embedding processing. Or a computer program that causes a computer to execute extraction processing.

  First, the electronic watermark information embedding device 100 will be described. As shown in FIG. 1, the embedding device 100 includes a band dividing unit 110, a carrier separating unit 120, a data symbol embedding unit 130, a synchronization symbol embedding unit 140, a carrier combining unit 150, a band synthesizing unit 160, A modulation signal generation unit 170.

  FIG. 3 is a diagram showing processing contents of the embedding device 100. The embedding device 100 is a device that embeds a data symbol sequence indicating digital watermark information and a synchronization symbol sequence indicating a section where the data symbol sequence is present in the carrier signal in the carrier signal. The carrier signal is, for example, an audio sample string obtained by sampling an audio waveform at a constant sampling rate, a pixel signal string obtained by one-dimensionalizing two-dimensional image data in raster scan order, and the like. In the present embodiment, each data symbol constituting the data symbol sequence and each synchronization symbol constituting the synchronization symbol sequence have the same time length. Hereinafter, a section of a carrier signal in which one data symbol and one synchronization symbol are embedded is referred to as a symbol frame. One symbol frame is composed of N × Lm (N and Lm are predetermined integers) carrier signal samples.

  When embedding the data symbol sequence and the synchronization symbol sequence, the band dividing unit 110 divides the sample sequence of the carrier signal into symbol frames composed of N × Lm samples, and further, the symbol frame is Lm whose phase is shifted by N samples. Each block of the carrier signal is divided into a plurality of band carrier signals belonging to different M bands.

  In a preferred embodiment, the band dividing unit 110 includes a windowing unit and a band dividing filter bank (not shown). Here, the windowing unit divides the band by multiplying the sample sequence of the carrier signal into half blocks of N samples per half block, and multiplying the sample sequence of the latest 1 block = 2 half blocks up to the present by a window function The process of supplying to the filter bank is repeated.

Each of the band division filter banks includes M complex coefficients BPF (Band Pass Filter) whose passband center angular frequency is ω _i (i = 0 to M−1). Each complex coefficient BPF corresponding to each passband center angular frequency ω _i (i = 0 to M−1) is received every time a sequence of samples for one block multiplied by a window function is received from the windowing unit. By performing BPF processing using a complex coefficient corresponding to each passband center angular frequency ω _i on the sequence, a complex spectrum coefficient X () indicating a component of the passband center angular frequency ω _i included in the sample sequence ω _i ) is calculated and output as a band carrier signal.

In another preferred embodiment, the band dividing unit 110 performs an FFT (Fast Fourier Transform) on a windowing unit similar to the above and a sample sequence for one block obtained by multiplying the window function by the windowing unit. The FFT unit calculates complex spectrum coefficients X (ω _i ) respectively corresponding to the angular frequencies ω _i (i = 0 to M−1).

  Carrier separating section 120 separates the M band carrier signals output from band dividing section 110 into a data carrier to which data symbols are embedded and a pilot carrier to which synchronization symbols are embedded, and the data carrier is a data symbol embedding section. 130, the pilot carrier is supplied to the synchronization symbol embedding unit 140.

  When embedding one series of data symbol sequences indicating each symbol (bit in this example) of the digital watermark information in the carrier signal, the modulation signal generation unit 170 indicates the data symbol sequence and is in an opposite phase relationship to each other. Two-phase data symbol modulation signal is output. The two-phase data symbol modulation signal is a periodic signal composed of Lm samples per period, and represents one data symbol per period. In the example shown in FIG. 3, the data symbol modulation signal is a triangular wave signal. When the data symbol to be expressed is a bit “0” in the positive phase data symbol modulation signal of the two phases, the first half has a peak waveform and the second half has a valley waveform, and the data symbol to be expressed has a bit “1”. In some cases, the first half is a valley and the second half is a peak. The modulation signal for data symbols having a reverse phase is a signal having a reverse phase. Also, when the modulation signal generation unit 170 outputs a two-phase data symbol modulation signal, the modulation signal generation unit 170 outputs a two-phase synchronization symbol modulation signal that is synchronized with the two-phase data symbol modulation signal and that is in opposite phase relation to each other. This two-phase synchronization symbol modulation signal is also a periodic signal composed of Lm samples per period, and represents one synchronization symbol per period. In a preferred embodiment, the synchronization symbol sequence has a minimum necessary constant length, and the modulation signal generation unit 170 matches the start of the data symbol synchronization signal and the start of the synchronization symbol modulation signal to perform synchronization symbol modulation. Output a signal.

The data symbol embedding unit 130 sets 2 for data carriers for two bands among the data carriers supplied from the carrier separation unit 120 (in the example shown in FIG. 3, data carriers for each band of the angular frequencies ω ₂ and ω ₃ ). The data symbol sequence is embedded by performing amplitude modulation processing or phase modulation processing using the phase signal of the phase data symbol modulation signal. Here, the amplitude modulation processing, for example, separates a complex spectrum coefficient, which is a data carrier, into an absolute value component and a declination component, performs amplitude modulation on the absolute value component according to the data symbol modulation signal, It can be executed by the procedure of recombination. Further, the phase modulation processing, for example, separates a complex spectrum coefficient, which is a data carrier, into an absolute value component and a declination component, and performs phase modulation (phase shift operation) on the declination component according to a data symbol modulation signal. It can be executed by the procedure of recombining with the absolute value component. The synchronization symbol embedding unit 140 has 2 bands for the pilot carriers supplied from the carrier separation unit 120 (pilot carriers in the respective bands of the angular frequencies ω ₀ and ω _{1 in} the example shown in FIG. 3). The synchronization symbol string is embedded by performing amplitude modulation processing or phase modulation processing using the phase signal of the phase synchronization symbol modulation signal.

The carrier combining unit 150 returns the data carrier output from the data symbol embedding unit 130 and the pilot carrier output from the synchronization symbol embedding unit 140 in the order before separation by the carrier separation unit 120, and M band carriers obtained as a result The signal is output to band synthesizer 160. Then, the band synthesizing unit 160 combines the M band carrier signals (complex spectrum coefficients) back to the time domain signal, and outputs a carrier signal in which digital watermark information is embedded.
The details of the embedding device 100 have been described above.

  Next, the digital watermark extracting apparatus 200 will be described with reference to FIG. The operation of the extraction apparatus 200 according to the present embodiment can be broadly divided into a synchronous search phase and a data extraction phase. Here, the synchronization search phase is a phase in which a synchronization symbol embedding interval in a pilot carrier of a carrier signal, that is, a data symbol embedding interval in a data carrier of a carrier signal is searched. In addition, the data extraction phase is to identify an embedding section of a data symbol sequence from the embedding section of the synchronization symbol sequence searched by the synchronization search phase in the data carrier of the carrier signal, and to extract a data symbol sequence from the embedding section of the data symbol sequence. This is the extraction phase. Each unit described below may operate differently in the synchronous search phase and the data extraction phase.

  The buffer 210 is a device that stores a carrier signal in which digital watermark information is embedded. For example, when an audio signal is used as a carrier signal, the carrier signal (audio signal) in which digital watermark information is embedded by the embedding device 100 described above is emitted into the air as sound, for example, and collected by a sound collecting device (not shown). The carrier signal, which is a time-series sample of the speech waveform, is stored in the buffer 210. Further, in an aspect in which an image signal is used as a carrier signal, a carrier signal (image signal) in which digital watermark information is embedded by the above-described embedding device 100 is converted into a television signal, for example, via a wired or wireless transmission path. The data is received by the television receiver, and is one-dimensionalized in the raster scan order and stored in the buffer 210 in the television receiver. The read control unit 220 is a device that reads the carrier signal stored in the buffer 210.

  The band dividing unit 230 has the same configuration as the band dividing unit 110 of the embedding device 100. The band dividing unit 230 divides the sample sequence of the carrier signal read from the buffer 210 by the read control unit 220 into a plurality of blocks that overlap each other on the time axis, and performs windowing processing and band division for each block. Processing is performed, and band carrier signals for M bands, each of which is a complex spectrum coefficient sequence, are output.

  In the synchronization search phase, the carrier extraction unit 240 extracts pilot carriers for two bands in which synchronization symbols are embedded from the band carrier signals for M bands output from the band division unit 230, and sends them to the demodulation unit 250. Supply. Further, in the data extraction phase, the carrier extraction unit 240 extracts data carriers for two bands in which data symbols are embedded from the band carrier signals for M bands output from the band dividing unit 230, and the demodulation unit 250. To supply.

  The demodulation unit 250 is a device that performs demodulation processing on the pilot carrier or data carrier supplied from the carrier extraction unit 240. The contents of the demodulation process correspond to the contents of the modulation processes of the synchronization symbol embedding unit 140 and the data symbol embedding unit 130 of the embedding device 100. When the synchronization symbol embedding unit 140 performs amplitude modulation on the pilot carriers for two bands using a modulation signal corresponding to the synchronization symbol, the demodulation unit 250, for example, selects one of the pilot carriers for two bands supplied from the carrier extraction unit 240. The absolute value (amplitude component) is divided by the other absolute value (amplitude component). Then, a DC offset removal process and a normalization process are performed on the division result and output as a demodulation result signal. Here, in the DC offset removal processing, an average value (that is, a moving average value) of the division results obtained within a certain past period is obtained, and this average value is subtracted from the current division result. Also, in the normalization process, the maximum value of the absolute value of the division result after the DC offset removal within the past fixed period is obtained, and the division result after the current DC offset removal is divided by this maximum value. Further, when the synchronization symbol embedding unit 140 of the embedding device 100 performs phase modulation on the pilot carrier for two bands by using the modulation signal corresponding to the synchronization symbol, the demodulation unit 250, for example, for two bands supplied from the carrier extraction unit 240 The other declination angle (phase component) is subtracted from one declination angle (phase component) of the pilot carrier, and the DC offset process and normalization process similar to those described above are performed on the subtraction result and output as a demodulation result signal. When the demodulator 250 performs a demodulation process in a section in which a modulation process using a synchronization symbol is performed on a pilot carrier, a demodulation result signal output from the demodulator 250 is a signal having a waveform approximate to the modulation signal used for the modulation process. Become. Similarly to the above, the content of the demodulation processing for the data carrier also corresponds to the content of the modulation processing of the data symbol embedding unit 130.

  The reference signal generation unit 260 is a device that supplies a reference signal to the correlation calculation unit 280 under the control of the synchronization control unit 270. More specifically, in the synchronization search phase, the reference signal generation unit 260 repeats the operation of outputting the modulation signal indicating the synchronization symbol string as the reference signal while shifting the phase in small increments. Various means for generating the reference signal by shifting the phase in this way are conceivable. For example, a sample sequence of the reference signal for one period is stored in the memory in advance, and the reading start point is shifted. It may be configured to repeat an operation of reading a sample sequence for one cycle. In the data extraction phase, reference signal generation section 260 repeats the operation of alternately outputting the modulation signal corresponding to data symbol “0” and the modulation signal corresponding to data symbol “1”.

  In the synchronization search phase, correlation calculation section 280 performs a correlation between the demodulation result signal output from demodulation section 250 and each reference signal supplied from reference signal generation section 260 (in this case, a modulation signal indicating a synchronization symbol sequence). Each correlation coefficient is calculated. Further, in the data extraction phase, correlation calculation section 280 delimits the signal in the section corresponding to the data carrier embedding section of the demodulation result signal output from demodulation section 250 by dividing it into a length corresponding to one symbol. For each signal corresponding to the symbol, the cross-correlation coefficient between the modulation signal corresponding to the data symbol “0” and the modulation signal corresponding to the data symbol “1” is calculated.

  The synchronization control unit 270 is a device that performs control for searching for an embedded section of a synchronization symbol sequence in a carrier signal, and includes a correlation history storage unit 271, an approximate synchronization search unit 272, and a detailed synchronization search unit 273. . The correlation history accumulating unit 271 is an apparatus that accumulates the cross-correlation coefficients for a certain past period calculated by the correlation calculating unit 280. The approximate synchronization search unit 272 and the detailed synchronization search unit 273 are devices that control each unit of the extraction device 200 in the synchronization search phase. Specifically, the approximate synchronization searching unit 272 sequentially shifts the evaluation section from the head position of the carrier signal with a rough step width, and outputs the demodulation result signal corresponding to the signal in the evaluation section of the carrier signal to the correlation calculation section 280. Control each part to deliver. Then, based on the cross-correlation coefficient history obtained from the correlation calculation unit 280, the approximate synchronization search unit 272 searches for an approximate position of the embedded section that is modulated by the synchronization symbol sequence in the carrier signal. Further, the detailed synchronization search unit 273 initializes the position of the evaluation interval based on the approximate position obtained by the approximate synchronization search unit 272, and the evaluation interval is smaller than the step width used by the approximate synchronization search unit 272. Control is performed so that the demodulation result signal corresponding to the signal in the evaluation interval of the carrier signal is transferred to the correlation calculation unit 280 while sequentially shifting by the width. Then, the detailed synchronization search unit 273 searches the detailed position of the embedded section based on the history of the cross correlation coefficient obtained from the correlation calculation unit 280. The processing contents of the approximate synchronization search unit 272 and the detailed synchronization search unit 273 will be described in detail later with a specific example.

The digital watermark information extraction unit 290 is a device that performs processing in the data extraction phase. When the detailed synchronization search unit 273 specifies the detailed position of the start point of the embedded period of the synchronization symbol sequence, the synchronization control unit 270 causes the read control unit 220 to read the signal of the embedded period in the carrier signal, The band division unit 230 divides the carrier signal into band carrier signals. Also, the carrier extraction unit 240 extracts the data carrier in which the data symbol is embedded from the band carrier signal obtained from the band division unit 230, and causes the demodulation unit 250 to perform demodulation thereof. Correlation calculation section 280 divides the demodulation result signal obtained from demodulation section 250 at this time into sections corresponding to one symbol frame, and the cross-correlation coefficient and data symbol “" with the modulation signal corresponding to data symbol “0” for each section. The cross-correlation coefficient with the modulation signal corresponding to 1 ″ is calculated. The digital watermark information extraction unit 290 performs a cross-correlation coefficient with a modulation signal corresponding to the data symbol “0” and a modulation corresponding to the data symbol “1” for each section corresponding to one symbol frame obtained by dividing the demodulation result signal. It is determined which of the cross-correlation coefficients with the signal is larger. If the former is larger, the data symbol embedded in the section is “0”, and if the latter is larger, the data symbol embedded in the section is “0”. It is determined that it is 1 ″.
The above is the details of the extraction apparatus 200 according to the present embodiment.

  The feature of this embodiment lies in the operations of the approximate synchronization search and the detailed synchronization search that are performed under the control of the synchronization control unit 270 in the extraction device 200. FIG. 4 illustrates the operation of the former general synchronous search, and FIG. 5 illustrates the operation of the latter detailed synchronous search.

  In the example shown in FIG. 4, a stripe indicating a carrier signal is shown. The solid line dividing the stripes in the vertical direction exemplifies the boundary of the evaluation section. A triangular wave with a broken line in the stripe exemplifies a modulation signal waveform corresponding to a synchronization symbol present in the carrier signal, and a broken line in the vertical direction exemplifies a boundary of the synchronization symbol.

First, the approximate synchronization search unit 272 uses a section having the same length as the length of the synchronization symbol sequence starting from the head position B ₀ of the carrier signal as an evaluation section, and performs read control to read out the carrier signal in the evaluation section from the buffer 210. To the unit 220. Also, the carrier signal in the evaluation section read from the buffer 210 is processed by the band dividing unit 230, the carrier extracting unit 240, and the demodulating unit 250. Then, at this time, the correlation calculation unit 280 calculates a cross-correlation coefficient between the decoding result signal obtained from the demodulation unit 250 and the reference signal output from the reference signal generation unit 260 (a modulation signal corresponding to the synchronization symbol sequence). The data is accumulated in the history accumulation unit 271.

  More specifically, at this time, the reference signal generator 260 moves the last sample to the beginning of the sample sequence with respect to the sample sequence of the reference signal (modulation signal corresponding to the synchronization symbol sequence), for example. By repeatedly performing the above, reference signals whose initial phases are shifted by one sample are sequentially output. Instead of performing such a cyclic shift, a plurality of reference signals whose phases are slightly shifted by repeating the operation of shifting backward while adding “0” to the sample sequence of the reference signal. May be output sequentially. The correlation calculation unit 280 calculates the cross-correlation coefficient between the demodulation result signal generated from the carrier signal in the evaluation section by the demodulation unit 250 and each reference signal sequentially output by the reference signal generation unit 260, and The cross-correlation coefficient is stored in the correlation history storage unit 271.

The approximate synchronization search unit 272 determines whether any of the cross-correlation coefficients stored in the correlation history storage unit 271 exceeds a predetermined threshold value. If there is no cross-correlation coefficient exceeding a predetermined threshold, the approximate synchronization search unit 272 considers that a synchronization symbol string is not embedded in the current evaluation interval of the carrier signal, and sets the beginning of the evaluation interval to the current position. Shift from B ₀ to a rearward separation position B ₁ by a length corresponding to one symbol frame. Then, it is to repeat the same processing as described above for a new evaluation period beginning with break position B _1.

Since the cross-correlation coefficient output from the correlation calculation unit 280 is substantially 0 (that is, no correlation) while the evaluation interval is completely out of the embedded interval of the synchronization symbol sequence, the approximate synchronization search unit 272 performs the evaluation. the head position of the section from the head position B ₀ to the break position B _1, from the break position B ₁ to the separated position B _2, ... slide into sequentially shifted to the rear so on.

As a result, the rear part of the evaluation interval eventually overlaps the front part of the embedded section of the synchronization symbol sequence in the carrier signal. As a result, the maximum value of the cross-correlation coefficient output by the correlation calculation unit 280 increases as compared with the case where the evaluation interval and the embedded interval of the synchronization symbol sequence are completely separated. When the evaluation interval further moves backward and the length of the overlap portion between the evaluation interval and the synchronization symbol sequence embedding interval becomes longer, the maximum value of the cross-correlation coefficient output by the correlation calculation unit 280 further increases. To do. And, ideally, the section becomes an evaluation period beginning with the delimiter position B _k illustrated in FIG. 4, the phase relation as the top portion is positioned in the synchronization symbol sequence in a symbol frame corresponds in the interval of the beginning of the evaluation interval The maximum value of the cross-correlation coefficient obtained from the correlation calculation unit 280 reaches the peak. Therefore, the approximate synchronization search unit 272 monitors the history of the cross-correlation coefficient accumulated in the correlation history accumulation unit 271 and, for example, sets the evaluation interval when the cross-correlation coefficient reaches a peak as the approximate position of the embedding interval. It is judged.

The detailed synchronization search unit 273 initially sets the position of the evaluation section based on the approximate position of the embedded section (position B _{k in} the examples of FIGS. 4 and 5) obtained by the general synchronization search unit 272 as described above. In addition, while shifting the evaluation section backward by a step Δt corresponding to one sampling period of the carrier signal, specifically, a step having a time length shorter than one symbol frame, the carrier signal in the evaluation section is read from the buffer 210. The reading control unit 220 performs reading, and the band division unit 230, the carrier extraction unit 240, and the demodulation unit 250 process the carrier signal in the read evaluation section. Then, the cross-correlation coefficient between the decoding result signal obtained from the demodulator 250 and the reference tone signal output from the reference signal generator 260 is calculated by the correlation calculator 280 and stored in the correlation history storage unit 271. Details of operations of the reference signal generation unit 260 and the correlation calculation unit 280 in this case are the same as those performed in the approximate synchronization search.

  In the detailed synchronization search, various methods for determining the range for shifting the position of the evaluation interval can be considered. In this embodiment, the half block is determined from the approximate position of the embedding interval obtained by the approximate synchronization search unit 272. The position returned by the size N is set as the initial position of the evaluation section, and the position rearward by the size N of one half block from the approximate position is set as the final position of the evaluation section. The detailed synchronization search unit 273 monitors the history of the cross-correlation coefficient written in the correlation history storage unit 271 from the correlation calculation unit 280 while shifting the evaluation interval in small increments from the initial position to the final position. Find the evaluation interval where the cross-correlation coefficient peaks. Then, this evaluation interval is determined to be a synchronization symbol sequence embedding interval. In the data extraction phase, the signal in the embedded section obtained in this way is read out from the carrier signal in the buffer 210, and data symbols are extracted. Note that the step size Δt is desirably one sampling period, but if it is desired to shorten the synchronization search time, a step size slightly larger than that (preferably a divisor of the size N of one half block) is preferable. Good.

  According to this embodiment described above, the following effects can be obtained.

(1) The extraction apparatus 200 outlines a synchronization symbol sequence embedding interval in a carrier signal while shifting an evaluation interval to be evaluated for cross-correlation with a modulation signal corresponding to the synchronization symbol sequence in the carrier signal in coarse steps. Using this approximate position as an initial value, a detailed position search of the embedded section of the synchronization symbol sequence in the carrier signal is performed while shifting the evaluation section in fine steps. Therefore, compared with the case where the embedded section is searched while shifting the evaluation section from the beginning of the carrier signal in fine steps, the detailed position of the embedded section of the synchronization symbol sequence, that is, the embedded section of the data symbol is reduced with a small amount of calculation. Can be sought.

(2) The approximate synchronization search unit 272 of the extraction device 200 searches for the approximate position of the embedded section of the synchronization symbol sequence while shifting the start position of the evaluation section by one symbol frame from the start of the carrier signal in the buffer 210. I do. Here, among the evaluation sections sequentially set by the shift operation, there is an evaluation section having a long overlap with the embedded section of the synchronization symbol sequence. However, even in such an evaluation interval, the phase is generally shifted from the embedded interval of the synchronization symbol string. However, in this embodiment, a plurality of reference signals whose phases are shifted in small increments are generated, and the respective cross-correlation coefficients between the demodulation result signal in the evaluation section and each of these reference signals are calculated. For this reason, even if the evaluation section and the embedded section of the synchronization symbol sequence do not exactly match, if the overlap portion between the evaluation section and the embedded section is long to some extent, the cross-correlation coefficient calculated by the correlation calculation unit 280 The maximum value is increased, and the approximate position of the embedded section can be obtained stably.

(3) In this embodiment, the embedding apparatus 100 is a two-phase modulation signal having a pair of two band carrier signals as one symbol embedding destination and having a waveform corresponding to the symbol, and having a phase relationship with each other. The symbol is embedded in the carrier signal by subjecting the two band carrier signals to amplitude modulation or phase modulation using the two-phase modulation signal in FIG. Therefore, the extraction device 200 can detect the modulation signal used for the modulation of the band carrier signal by dividing the amplitude component or subtracting the phase component of the two band carrier signals in which the symbols are embedded. In addition, at that time, a modulated signal having a waveform used for modulation can be obtained with a large amplitude.

<Other embodiments>
Although one embodiment of the present invention has been described above, various other embodiments are conceivable for the present invention. For example:

(1) The length of the synchronization symbol string may be at least the step width when shifting the evaluation interval in the approximate synchronization search. Further, the ratio between the length of the synchronization symbol string and the length of the search step of the approximate synchronization search may not be an integer ratio.

(2) The symbol frame lengths of the synchronization symbol and the data symbol may be different.

(3) A mode in which no synchronization symbol is used is also conceivable. In this aspect, the embedding device 100 performs a modulation process using a data symbol sequence indicating digital watermark information in an arbitrary section of a carrier signal. In the synchronization search phase, the reference signal generation unit 260 of the extraction device 200 includes a plurality of reference signals indicating, for example, one symbol “0” while shifting the initial phase in small increments every time one evaluation interval is set. Output once. The approximate synchronization search unit 272 controls each unit to divide the carrier signal into evaluation periods each having a length of one symbol frame and to deliver a demodulation result signal corresponding to the carrier signal in each evaluation section to the correlation calculation unit 280. In the meantime, the history of the cross-correlation coefficient with the reference signal obtained for each evaluation interval is accumulated in the correlation history accumulating unit 271 in parallel with the switching of the evaluation interval. Based on the monitoring result of the cross-correlation function history, the approximate synchronization search unit 272 performs the modulation process using the evaluation interval considered to be “0” -based data symbol and the data symbol “1”. Estimate the evaluation interval considered to be Based on this estimation result, the approximate position of the embedded section of the data symbol sequence in the carrier signal is obtained. The detailed synchronous search operation is the same as the general synchronous search operation except that the step width when shifting the evaluation interval is small.

(4) In the above-described embodiment, the position of the evaluation section where the maximum value of the cross-correlation coefficient peaks in the approximate synchronization search is determined to be the approximate position of the embedded section of the synchronization symbol sequence. The position slightly before the position of the evaluation section where the maximum value of the cross-correlation coefficient reaches a peak may be set as a rough position.

It is a block diagram which shows the structure of the embedding apparatus 100 of the digital watermark information used in one Embodiment of this invention. It is a block diagram which shows the structure of the electronic watermark information extraction apparatus 200 by the embodiment. It is a figure which shows the processing content of the embedding apparatus 100. FIG. It is a figure which shows the processing content of the general | schematic synchronous search part 272 of the extraction apparatus 200. FIG. It is a figure which shows the processing content of the detailed synchronous search part 273 of the extraction apparatus 200. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Embedding device, 200 ... Extraction device, 110, 230 ... Band division unit, 120 ... Carrier separation unit, 130 ... Data symbol embedding unit, 140 ... Synchronization symbol embedding unit, 150 ... Carrier combination unit , 160 ... band synthesis unit, 170 ... modulation signal generation unit, 210 ... buffer, 220 ... read control unit, 240 ... carrier extraction unit, 250 ... demodulation unit, 260 ... reference signal generation unit, 270 ... Synchronization control unit, 280... Correlation calculation unit, 290... Digital watermark information extraction unit, 271... Correlation history storage unit, 272.

Claims (6)

Different band components are received by receiving carrier signals that have been subjected to modulation processing using at least one series of symbol sequences including a data symbol sequence indicating digital watermark information with respect to some band components of some sections, and are different from each other. Band dividing means for outputting a plurality of band carrier signals belonging to the band;
Demodulation means for performing demodulation processing on a band carrier signal including a component subjected to modulation processing by at least one series of symbol sequences in the plurality of band carrier signals and outputting a demodulation result signal;
Correlation calculating means for calculating a cross-correlation coefficient between a demodulation result signal obtained by the demodulation processing and a reference signal indicating one or more predetermined symbols;
While sequentially shifting the evaluation interval from the head position of the carrier signal by a predetermined step width, control is performed to deliver a demodulation result signal corresponding to the signal in the evaluation interval of the carrier signal to the correlation calculating unit, thereby Based on the history of the cross-correlation coefficient obtained from the calculating means, searching for the approximate position of the embedded section of the carrier signal that has been modulated by the symbol sequence;
Based on the approximate position obtained by the approximate synchronization search means, the position of the evaluation interval is initially set, and the carrier is transferred while sequentially shifting the evaluation interval by a step width smaller than the step width used by the approximate synchronization search means. A control is performed to deliver a demodulation result signal corresponding to a signal in an evaluation interval of the signal to the correlation calculation unit, and based on a history of cross-correlation coefficients obtained from the correlation calculation unit, a detailed position of the embedded interval And a detailed synchronization search means for searching for digital watermark information. The carrier signal belongs to mutually different bands, and includes a component subjected to modulation processing by a data symbol sequence indicating digital watermark information and a component subjected to modulation processing by a synchronization symbol sequence synchronized with the data symbol sequence,
While the approximate synchronization search means and the detailed synchronization search means search the embedded section, the demodulation means performs demodulation processing on the band carrier signal including the component subjected to the modulation processing by the synchronization symbol sequence. 2. The digital watermark information extracting apparatus according to claim 1, wherein a result signal is output.   The correlation calculating means calculates each cross-correlation coefficient between each of a plurality of reference signals whose phases are sequentially shifted with respect to a demodulation result signal corresponding to a carrier signal in the evaluation section. The electronic watermark information extracting device according to claim 1 or 2. The carrier signal is subjected to modulation processing using a two-phase modulation signal indicating a symbol and having a reverse phase relationship with respect to the components of two bands forming a pair,
The demodulation means generates a demodulation result signal indicating a waveform of a modulation signal used for the modulation processing from each band carrier signal including each of the two band components forming the pair. The electronic watermark information extracting device according to any one of claims 3 to 4. Different band components are received by receiving carrier signals that have been subjected to modulation processing using at least one series of symbol sequences including a data symbol sequence indicating digital watermark information with respect to some band components of some sections, and are different from each other. A band division process for outputting a plurality of band carrier signals belonging to a band; and
A demodulation process of performing demodulation processing on a band carrier signal including a component subjected to modulation processing by a symbol sequence of a part of at least one sequence of symbol sequences in the plurality of band carrier signals and outputting a demodulation result signal;
A correlation calculation step of calculating a cross-correlation coefficient between a demodulation result signal obtained by the demodulation process and a reference signal indicating one or more predetermined symbols;
While sequentially shifting the evaluation interval from the head position of the carrier signal by a predetermined step width, control is performed to deliver a demodulation result signal corresponding to the signal in the evaluation interval of the carrier signal to the correlation calculation process, and thereby the correlation Based on a history of cross-correlation coefficients obtained in the calculation process, an approximate synchronization search process for searching for an approximate position of an embedded section modulated by a symbol sequence in the carrier signal;
While initially setting the position of the evaluation interval based on the approximate position obtained in the approximate synchronization search process, while sequentially shifting the evaluation interval with a step width smaller than the step width used in the approximate synchronization search process, Control is performed to deliver a demodulation result signal corresponding to the signal in the evaluation interval of the carrier signal to the correlation calculation process, and based on the history of the cross-correlation coefficient obtained in the correlation calculation process, the details of the embedded interval are determined. A detailed synchronous search process for searching for a position. A method for extracting digital watermark information, comprising: On the computer,
Different band components are received by receiving carrier signals that have been subjected to modulation processing using at least one series of symbol sequences including a data symbol sequence indicating digital watermark information with respect to some band components of some sections, and are different from each other. A band division process for outputting a plurality of band carrier signals belonging to a band; and
A demodulation process of performing demodulation processing on a band carrier signal including a component subjected to modulation processing by at least one series of symbol sequences in the plurality of band carrier signals and outputting a demodulation result signal;
A correlation calculation step of calculating a cross-correlation coefficient between a demodulation result signal obtained by the demodulation process and a reference signal indicating one or more predetermined symbols;
While sequentially shifting the evaluation interval from the head position of the carrier signal by a predetermined step width, control is performed to deliver a demodulation result signal corresponding to the signal in the evaluation interval of the carrier signal to the correlation calculation process, and thereby the correlation Based on a history of cross-correlation coefficients obtained in the calculation process, an approximate synchronization search process for searching for an approximate position of an embedded section modulated by a symbol sequence in the carrier signal;
While initially setting the position of the evaluation interval based on the approximate position obtained in the approximate synchronization search process, while sequentially shifting the evaluation interval with a step width smaller than the step width used in the approximate synchronization search process, Control is performed to deliver a demodulation result signal corresponding to the signal in the evaluation interval of the carrier signal to the correlation calculation process, and based on the history of the cross-correlation coefficient obtained in the correlation calculation process, the details of the embedded interval are determined. A detailed synchronous search process for searching for a position is executed.

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