JP2010147919A - Apparatus and program for embedding and extracting electronic watermark information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance robustness with respect to noise or echo in a propagation process, without generating any sense of incompatibility in hearing when propagating a carrier signal as sound, by eliminating the necessity of a source signal for extracting a symbol at a receiving side when transmitting the carrier signal while embedding the symbol therein. <P>SOLUTION: A subcarrier generating section 120 applies band division to a carrier signal and generates subcarriers of a plurality of bands. An embedding section 130 defines a subcarrier in at least a part of the sub carriers of the plurality of bands as a data carrier that is a destination to embed a data symbol sequence, and replacing the phase component of the data carrier with a data symbol modulation signal of a continuous waveform indicating the symbol sequence. A carrier combining section 140 applies band combination to the subcarrier after processing by the embedding section 130 and outputs the subcarrier as a carrier signal in which electronic watermark information has been embedded. <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 and program for embedding and extracting digital watermark information for an acoustic signal propagating in the air.

As techniques for embedding digital watermark information in a carrier signal such as an acoustic signal, there are embedding techniques such as an amplitude modulation method, a phase modulation method, an acoustic OFDM (Orthogonal Frequency Division Multiplexing) method, and an echo hiding method. The amplitude modulation method is a technique for embedding a symbol string in a carrier signal by performing amplitude modulation processing corresponding to a symbol string of digital watermark information to be embedded on subcarriers obtained by dividing a carrier signal into bands. (For example, refer to Patent Documents 1 and 2). The phase modulation method is a method in which a carrier signal is passed through an all-pass filter, and at that time, the frequency phase characteristics of the all-pass filter are changed in accordance with the symbol to be embedded (see, for example, Patent Document 3). The acoustic OFDM scheme is a plurality of subcarriers that belong to an audio band and are orthogonal to each other, that is, each subcarrier having a frequency interval corresponding to the reciprocal of the symbol frame length (see Non-Patent Document 1). This is a method of obtaining an acoustic signal in which a symbol sequence is embedded by adding modulation after performing modulation in accordance with the symbol sequence to be embedded, and adding the added signal and an acoustic signal such as a mask sound (for example, (See Patent Document 4). The echo hiding method is a method in which an echo sound signal having a delay time corresponding to a symbol is superimposed on the carrier signal by convolving two impulse responses having a time difference corresponding to the symbol to be embedded into the carrier signal. Yes (see, for example, Patent Document 5).
Japanese Patent No. 3659321 JP 2006-251676 A JP 2003-44067 A JP 2007-104598 A Japanese Patent No. 3554825 OFDM / OFDMA textbook, pp. 51-55, Impress R & D Co., Ltd., issued on September 21, 2008 Multirate Signal Processing and Filter Bank, Science and Technology Publishing, published March 10, 2002

  By the way, the amplitude modulation method embedding technique has a problem that the robustness against noise is weak, that is, when the carrier signal in which the symbol is embedded is exposed to the noise in the propagation process, the symbol from the carrier signal is received on the receiving side of the carrier signal. There was a problem that it was difficult to extract. Although the phase modulation method embedding technique is more robust against noise than the amplitude modulation method, a carrier accompanying symbol embedding is used for symbol extraction on the receiving side of the carrier signal in which the symbol is embedded. Since it is necessary to determine the amount of change in the phase of the signal, there is a problem that the original signal, that is, the carrier signal before symbol embedding is necessary. In addition, in the acoustic OFDM method embedding technique, when attention is paid to each subcarrier after modulation corresponding to a symbol, a discontinuity in the phase of the subcarrier occurs at a delimiter position between symbols in each subcarrier. There was a problem of causing discomfort. In addition, the echo hiding method, when an echo is generated in the process of propagation of the carrier signal in the air, and a carrier signal containing this echo component is received, the carrier signal and the echo component Depending on the phase relationship, it is difficult to extract symbols from the carrier signal.

  The present invention has been made in view of the circumstances described above. When extracting a symbol from a carrier signal in which a symbol is embedded, an original signal is unnecessary, and the carrier signal in which the symbol is embedded is propagated as sound. It is an object of the present invention to provide a technique for embedding and transmitting digital watermark information that hardly causes a sense of discomfort in the sense of hearing and that is excellent in robustness against noise and echo generated in the propagation process.

This invention divides a carrier signal into bands, generates subcarriers of a plurality of bands, and generates a modulated signal for data symbols having a continuous waveform indicating a data symbol string of digital watermark information to be embedded And a data symbol modulation signal generating means, and a subcarrier of at least a part of the plurality of subcarriers of the plurality of bands as a data carrier into which a data symbol sequence is embedded, and a phase component of the data carrier is modulated with the data symbol Phase modulation means for replacing with a signal; and carrier synthesis means for performing band synthesis on the subcarriers of the plurality of bands that have undergone the processing of the phase modulation means and outputting as a carrier signal in which digital watermark information is embedded. An electronic watermark information embedding device is provided.
According to this invention, since the phase component of the subcarrier signal constituting the carrier signal is replaced with the data waveform modulation signal having a continuous waveform indicating the data symbol sequence of the digital watermark information, and output, the carrier in which the symbol is embedded When extracting symbols from the signal, the original signal is unnecessary, and it is less likely to cause a sense of incongruity when propagating the carrier signal in which the symbol is embedded as sound, and against noise and echo generated in the propagation process. Can improve robustness.

  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 illustrated in FIG. 1, the embedding device 100 includes a modulation signal generation unit 110, a subcarrier generation unit 120, an embedding unit 130, and a carrier synthesis unit 140.

Modulation signal generation section 110 is a data symbol modulation signal generation section 111 that generates a data symbol modulation signal indicating a data symbol string to be embedded, and a pilot symbol that indicates a pilot symbol string that is a synchronization signal of the data symbol string And a pilot symbol modulation signal generation unit 112 for generating a modulation signal. In the present embodiment, the data symbol modulation signal for one period indicating one data symbol is a sample string composed of Nb samples. In the present embodiment, the symbol is binary information (bit). The data symbol modulation signal indicating the bit “0” is composed of Nb sample strings G _pm0 (n) (n = 0 to Nb−1) represented by the following formula (1), and indicates the bit “1”. The data symbol modulation signal is composed of Nb sample strings G _pm1 (n) (n = 0 to Nb−1) represented by the following equation (2). However, in the following formulas (1) and (2), A _pm is a numerical value satisfying 0 <A _pm <π. The data symbol modulation signal generation unit 111 includes a data symbol modulation signal sample sequence G _pm0 (n) (n = 0 to Nb−1) corresponding to the data symbol “0” and data corresponding to the data symbol “1”. The symbol modulation signal sample string G _pm1 (n) (n = 0 to Nb−1) is stored in a built-in memory. When the data symbol to be embedded is “0”, the former sample sequence G _pm0 (n) (n = 0 to Nb−1) is used. When the data symbol to be embedded is “1”, the latter sample sequence is used. G _pm1 (n) (n = 0 to Nb−1) is read from the memory and supplied to the embedding unit 130.

The pilot symbol modulation signal is a signal having the same period (number of samples) as the data symbol modulation signal. For example, the sample string G _pm0 (n) (n = 0 to Nb−1) shown in the above equation (1) may be used as a pilot symbol modulation signal for one period. The pilot symbol modulation signal generation unit 112 stores in the embedding unit 130 Nb sample sequences of data symbol modulation signals corresponding to one data symbol “0” or “1”. When supplying, a sample string of pilot symbol modulation signals for one period is supplied to the embedding unit 130.

  In this embodiment, the data symbol modulation signal for one period indicating one data symbol has a continuous waveform without a jump within one period, as shown in the above formulas (1) and (2). . In addition, in both the data symbol “0” and the data symbol “1”, the sample value of the data symbol modulation signal is 0 at the timing of the data symbol boundary (timing of n = 0). Therefore, the waveform of the data symbol modulation signal does not jump even at the boundary between the data symbol modulation signal for one cycle indicating the preceding data symbol and the data symbol modulation signal for one cycle indicating the subsequent data symbol. It will be continuous. Therefore, the waveform of the modulation signal for data symbols representing the symbol string of the digital watermark information is a continuous waveform throughout the entire section. The same applies to the pilot symbol modulation signal. This is one feature of the present embodiment.

  The subcarrier generation unit 120 is a unit that divides a carrier signal such as an acoustic signal into a plurality of subcarriers with different bands from which data symbols and pilot symbol sequences are embedded. Each section obtained by dividing each of the plurality of subcarriers obtained from the subcarrier generation unit 120 into the length of one symbol frame is a data symbol or pilot symbol embedding destination for one symbol. Here, the carrier signal is divided into a plurality of subcarriers by increasing the number of signals (here, the number of subcarriers) into which data symbols or pilot symbols are embedded within the interval of one symbol frame, and the data rate. It is for improving.

The subcarrier generation unit 120 includes a band division unit 121, a band grouping unit 122, and a data / pilot carrier separation unit 123. As illustrated in FIG. 3A, the band dividing unit 121 according to the present embodiment selects 2M downsamplers 1211 _k (k = 0) that select and output input samples at a ratio of 1 to M samples. ~ M-1), 2M analysis filters 1212 _k (k = 0 to 2M-1) in the subsequent stage, and a matrix operation unit 1213. More specifically, the analysis filter bank which is the band dividing unit 121 is a complex exponential modulation filter bank, which is a cosine modulation filter bank (CMFB) and a sine modulation filter bank (SMFB). It is a functional configuration that has been parallelized.

Each of the analysis filters 1212 _k (k = 0 to 2M−1) in this complex exponential modulation filter bank represents a prototype filter p ₀ (n) satisfying the following expression (3) as an exponent as shown in the following expression (4). An analysis filter based on a polyphase expression modulated by a modulation function is realized. However, in following formula (3), it is n = 0-N and is N = 2 mM-1 (m is an integer greater than or equal to 1).

The prototype filter p ₀ (n) designs a prototype filter of a cosine modulation filter that is a real part of a complex exponential modulation filter, and uses the prototype filter of the cosine modulation filter. When designing a prototype filter for a cosine modulation filter, it is necessary to take care not to cause embedded symbol distortion due to aliasing that cannot be completely erased between adjacent subcarriers in the band when subcarrier modulation is performed. . Therefore, a pseudo-QMF (Quadrature Mirror Filter) bank design method that is effective in eliminating aliasing between adjacent subcarriers in a band during no modulation is employed. Specifically, as described in Section 8.2 of Chapter 8 of Non-Patent Document 2, a prototype filter p ₀ (n) that minimizes the evaluation function φ shown in the following equation (5) is obtained. However, 0 <α <1 in the following formula (5).

Here, φ ₁ and φ ₂ in the above equation (5) are given by the following equations (6) and (7). However, in the following formulas (6) and (7), ε> 0, P ₀ (e ^jω ) is the frequency response of the prototype filter p ₀ (n), and FFT (Fast Fourier Transform) is applied to p ₀ (n). Obtained by applying Fast Fourier Transform). That is, the content of the prototype filter p ₀ (n) is such that the frequency response P ₀ (e ^jω ), which is the result of applying the FFT to the prototype filter p ₀ (n), minimizes the evaluation function φ of the above equation (5). It is determined.

In FIG. 3A, X (z) is a z-transform of a sample x (n) of a carrier signal, z ⁻¹ is a one-sample delay, and X _k (z) (k = 0 to M−1) is a subcarrier. Sample z-transform. The matrix calculation unit 1213 analyzes the 2M × M complex value matrix {t _kn } (k = 0 to M−1, n = 0 to 2M−1) including the element t _kn shown in Expression (8) as an analysis filter. Multiply 2M output sample sequences of 1212 _k (k = 0 to 2M−1) to generate subcarrier samples Xk (z) (k = 0 to M−1) for M bands.

  In FIG. 1, the band grouping unit 122 divides the M-band subcarriers output from the band dividing unit 121 as described above into a plurality of groups that are groups of a plurality of subcarriers having close bands. . Each of the plurality of groups is a data carrier group into which data symbols are embedded or a pilot carrier group into which pilot symbols are embedded. It is preferable that a group of data carriers to be embedded with data symbols and a group of pilot carriers to be embedded with pilot symbols that serve as synchronization signals for the data symbols are adjacent on the frequency axis. The relationship between the data carrier group and the pilot carrier group may not be a one-to-one relationship. For example, one pilot carrier group is associated with two data carrier groups on both sides thereof on the frequency axis, and as a synchronization signal of each data symbol embedded in the data carrier groups on both sides of the pilot carrier group. A pilot symbol that plays the role of

  Here, the bandwidth of each of a plurality of groups (a group of data carriers or a group of pilot carriers) is a reverberation impulse response that is expected to occur in the process of transmitting an acoustic signal from the embedding device 100 to the extraction device 200. It is desirable to be determined by the length of time. Ideally, if the total bandwidth of the pair of data carriers and pilot carriers is sufficiently short compared to the reciprocal of the same response time length, the data carrier group and pilot It can be considered that the phase variation due to reverberation is the same in the entire band of the carrier group. The number of data carriers or pilot carriers that constitute one group is determined within a range that satisfies this condition. When the reciprocal of the reverberation impulse response time length is short, one group may be composed of only one data carrier or one pilot carrier.

  The data / pilot carrier separation unit 123 separates the plurality of groups divided by the band grouping unit 122 into a group of data carrier groups and a group of pilot carrier groups.

The embedding unit 130 includes an amplitude / phase separation unit 131, a phase modulation unit 132, and an amplitude / phase coupling unit 133. The amplitude / phase separation unit 131 separates the samples of the subcarriers in the data carrier group and the pilot carrier group into amplitude components and phase components. More specifically, when the real part of the sample at the time n of the subcarrier in the k-th band is X _kr (n) and the imaginary part is X _ki (n), the amplitude / phase separation unit 131 represents the following equation (9 ) To calculate the amplitude component A _k (n) of the sample, and calculate the phase component φ _k (n) of the sample by the following equation (10).

  Phase modulation section 132 replaces the phase component of the data carrier sample with the sample of the data symbol modulation signal, and replaces the phase component of the pilot carrier sample with the sample of the pilot symbol modulation signal. At that time, the phase modulation unit 132 has a high function value in the center band of each group of the plurality of data carrier groups and the plurality of pilot carrier groups, and the upper limit band and the lower limit of the group. Using a window function with a low function value in the band, the amplitude of the data symbol modulation signal or pilot symbol modulation signal replaced with the data carrier or pilot carrier phase component of each band in the group is limited by the function value of each band To do. Of course, when only one data carrier or pilot carrier is included in one group, this window function multiplication is not performed.

The following equation (11) shows the contents of the arithmetic processing executed by the phase modulation unit 132 with respect to the phase component of the data carrier. As shown in this equation (11), when the data symbol b embedded in the band k is “0” with respect to the data carrier in each band k, the phase modulation unit 132 samples the data carrier in the band k. windows of the phase component phi _k a _(n), corresponding to the band k to the sample G _{pm0 (n)} of the corresponding data symbol modulation signal for the symbol "0" output from that time data symbol for modulation signal generator 111 Replace with the product of the function value w (k). On the other hand, when the data symbol b embedded in the band k is “1”, the phase component φ _k (n) of the sample of the data carrier in the band k is output by the data symbol modulation signal generation unit 111 at that time. The data symbol modulation signal sample G _pm1 (n) corresponding to the symbol “1” is multiplied by the window function value w (k) corresponding to the band k. The phase component of the pilot carrier sample is replaced with the pilot modulation signal sample multiplied by the window function value corresponding to the band.

  In this way, for each data carrier or pilot carrier group, the data symbol modulation signal or pilot symbol modulation signal in each band within the group is subjected to window function multiplication in the phase near the subcarrier in the band near the group boundary. This is because the amplitude of the data symbol modulation signal or pilot symbol modulation signal embedded as a component is reduced to suppress a sudden change in the phase between the bands and to prevent a sense of incongruity from occurring.

The amplitude / phase coupling unit 133 outputs each of the amplitude component of the data carrier and the amplitude component of the pilot carrier output from the amplitude / phase separation unit 131, the amplitude / phase separation unit 131, and the phase modulation unit 132. The phase component of the data carrier and the phase component of the pilot carrier that have undergone processing (replacement with the modulation signal for data symbol or pilot symbol modulation and windowing processing) and the phase component of the pilot carrier are combined, and the complex data carrier and pilot carrier are combined. Synthesize. More specifically, when the amplitude component of the data carrier or pilot carrier sample of the band k is A _k (n) and the phase component is φ _k (n), the amplitude / phase coupling unit 133 is expressed by the following formula (12). To calculate a sample X _k (n) of subcarriers in band k.

  FIG. 4 shows the processing contents of each part of the subcarrier generation unit 120 and the embedding unit 130 described above. As shown in FIG. 4, every time a carrier signal mM sample is given, subcarrier generation section 120 generates m samples of subcarriers for one M band per band using the latest 2 mM sample. The amplitude / phase separation unit 131 of the embedding unit 130 separates each sample of each subcarrier in the M band into an amplitude component and a phase component. When band grouping operation is performed in the phase modulation unit 132, the phase component of the data carrier sample in each group of data carriers is the symbol to be embedded for each symbol frame of the frame length Nb. b is replaced with a sample of the modulation signal for data symbol indicating b and a window function value w (k) corresponding to band k, and the phase component of the pilot carrier sample in each group of pilot carriers is the pilot symbol. This is replaced with a product of the modulation signal sample multiplied by the window function value w (k) corresponding to the band k. Then, the phase component of the data carrier sample and the phase component of the pilot carrier sample that have undergone the processing of the phase modulation unit 132, the amplitude component of the data carrier sample output from the amplitude / phase separation unit 131, and the sample of the pilot carrier Are combined with each other to obtain a complex data carrier sample and a pilot carrier sample.

  In FIG. 1, carrier combining section 140 includes data / pilot carrier combining section 141, band group separation section 142, and band combining section 143. Here, the data / pilot carrier combining unit 141 rearranges the data carrier group and the pilot carrier group obtained from the amplitude / phase coupling unit 133 in the order in which the data / pilot carrier separating unit 123 performs the processing. Band group separation section 142 rearranges the data carriers and pilot carriers that have undergone the processing of data / pilot carrier combining section 141 in the order in which the data carriers and pilot carriers have not been grouped by band grouping section 122. Band combining section 143 performs band combining of subcarriers (data carrier and pilot carrier) for M bands output from band group separation section 142, and converts them into a time domain carrier signal.

In the present embodiment, the band synthesis unit 143 is an M band synthesis filter bank. As shown in FIG. 3B, this synthesis filter bank includes a matrix operation unit 1431, 2M synthesis filters 1432 _k (k = 0 to 2M−1), and 2M up-samplers 1433 _{k in the} subsequent stage. (K = 0 to 2M-1). In FIG. 3B, X _k (z) (k = 0 to M−1) is the z-transform of the subcarrier sample, and X (z) is the band-synthesized carrier signal sample x (n). z conversion. Here, the matrix calculation unit 1431 multiplies the M-band subcarrier samples by the transpose matrix of the matrix used by the matrix calculation unit 1213 of the band division unit 121 to generate 2M samples to generate the synthesis filter 1432 _k ( k = 0 to 2M-1). The synthesis filter 1432 _k (k = 0 to 2M−1) performs the same filter processing as the analysis filter 1212 _k (k = 0 to 2M−1) of the band dividing unit 121 on each sample, and the upsampler 1433 _k (k = 0 to 2M−1). Up-sampler 1433 _k (k = 0 to 2M−1) inserts M−1 zero samples between each sample of subcarriers input thereto, and multiplies the subcarrier sampling frequency by M times. A band-combined carrier signal is obtained by adding the output samples of this upsampler 1433 _k (k = 0 to 2M−1) while shifting the phase one sample at a time.
The details of the embedding device 100 have been described above.

  Next, the digital watermark information extraction 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 pilot symbol embedded section in a pilot carrier of a carrier signal, that is, a data symbol embedded section in a data carrier of a carrier signal is roughly searched. The data extraction phase is a phase in which a data symbol sequence is extracted from the embedded section of the data symbol sequence searched in the synchronous search 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 acoustic signal is used as a carrier signal, the carrier signal (acoustic signal) in which digital watermark information is embedded by the embedding device 100 described above is emitted into the air as sound and collected by a sound collecting device (not shown), A carrier signal that is a time-series sample of the speech waveform is stored in the buffer 210.

Reference signal generation section 220 includes data symbol reference signal generation section 221 and pilot symbol reference signal generation section 222. The data symbol reference signal generation unit 221 generates a sample string G _pm0 (n) (n) for one period (Nb) of data symbol reference signals having the same waveform as the data symbol modulation signal indicating the data symbol “0”. = 0 to Nb-1) and one period (Nb) of the sample string G _pm1 (n) of the data symbol reference signal having the same waveform as the data symbol modulation signal indicating the data symbol “1”. It has a function of outputting (n = 0 to Nb-1). Pilot symbol reference signal generation section 222 is equivalent to one period (Nb) of pilot symbol reference signals having the same waveform as the pilot symbol modulation signal output from pilot symbol modulation signal generation section 112 of embedding apparatus 100. Has a function of outputting a sample sequence.

  The subcarrier generation unit 230 includes a band division unit 231, a band grouping unit 232, and a data / pilot carrier separation unit 233 similar to those of the subcarrier generation unit 120 of the embedding device 100. The subcarrier generation unit 230 divides the carrier signal read from the buffer 210 into M-band subcarriers, and outputs the subcarriers divided into a data carrier group and a pilot carrier group.

  The demodulation processing unit 240 includes an amplitude / phase separation unit 241 and a phase demodulation unit 242. Here, similarly to the amplitude / phase separation unit 241 and the amplitude / phase separation unit 131 of the embedding apparatus 100, each sample of the data carrier and the pilot carrier which are complex values is separated into an amplitude component and a phase component. The phase demodulator 242 controls the data carrier in the embedded section in preparation for signal processing and data symbol sequence extraction for searching for the embedded section of the data symbol sequence in the data carrier under the control of the frame synchronization search section 250 described later. Signal processing for correcting the phase component is performed.

  The frame synchronization search unit 250 is a device that performs read control of the carrier signal stored in the buffer 210 and performs timing control of each unit of the extraction device 200. When the carrier signal is accumulated in the buffer 210, the frame synchronization search unit 250 controls each unit for executing the synchronization search phase, and thereafter controls each unit for executing the data extraction phase.

  In the synchronization search phase, the frame synchronization search unit 250 executes an approximate synchronization search process for obtaining an approximate position of the start point of the embedded section of the pilot symbol sequence based on the phase component of each pilot carrier. Specifically, the process shown in FIG. 5 is performed for each pilot carrier in each band.

  In the example shown in FIG. 5, a stripe indicating one pilot carrier is shown. The solid line that divides the stripes in the vertical direction exemplifies the boundary of the evaluation interval for checking whether or not the pilot symbol is embedded. A sine wave with a broken line in the stripe exemplifies a modulation signal waveform for a pilot symbol inherent in the phase component of the pilot carrier, and a broken line in the vertical direction exemplifies a boundary between pilot symbols.

First, an interval of one symbol frame (interval including 2 mM L samples) starting from the leading position B ₀ of the carrier signal is used as an evaluation interval, and the carrier signal in this evaluation interval is read from the buffer 210, and the subcarrier generation unit 230 and The amplitude / phase separation unit 241 performs processing. The phase component of the sample sequence (Nb samples) for one symbol frame of one pilot carrier in the carrier signal in the information output from the amplitude / phase separation unit 241 and the pilot symbol reference signal generation unit 222 output The phase demodulator 242 calculates the cross-correlation coefficient with the sample sequence (Nb samples) of the pilot symbol reference signal to be stored, and accumulates the cross-correlation coefficient.

  More specifically, at this time, the pilot symbol reference signal generation unit 222 performs, for example, a cyclic shift operation of moving the last sample to the beginning of the sample sequence with respect to the sample sequence of the pilot symbol reference signal for one period. By repeatedly applying, pilot symbol reference signals for each period with the initial phase shifted by one sample are sequentially output. The phase demodulating unit 242 mutually outputs a phase component of a sample sequence of one pilot carrier generated from the carrier signal in the evaluation interval and each pilot symbol reference signal sequentially output by the pilot symbol reference signal generating unit 222. Each correlation coefficient is calculated, and the frame synchronization search unit 250 accumulates each cross-correlation coefficient.

The frame synchronization search unit 250 determines whether there is any cross-correlation coefficient accumulated in this way that exceeds a predetermined threshold. If there is no cross-correlation coefficient exceeding a predetermined threshold, the frame synchronization search unit 250 considers that the pilot symbol is not embedded in the current evaluation interval of the carrier signal, and sets the start of the evaluation interval to the current position B. Shift from ₀ to the rear delimiter 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.

While the evaluation interval is completely outside the pilot symbol sequence embedding interval, the cross-correlation coefficient output from the phase demodulator 242 is substantially 0 (that is, no correlation). 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.

Then, as illustrated in FIG. 5, it interval starting at break position B _k is the evaluation section, when the head portion of the pilot symbol becomes the phase relation as to be located within the evaluation interval, obtained from the phase demodulation section 242 Cross correlation coefficient increases. Therefore, the frame synchronization search unit 250 monitors the history of the cross-correlation coefficient obtained from the phase demodulation unit 242 in this state, and determines the phase delay amount of the pilot symbol reference signal when the cross-correlation coefficient reaches a peak. determined, the position after the phase delay by the start position of the buried section of the pilot symbol sequence from the separated position B _k.

In the approximate synchronization search process, the above process is performed for the pilot carrier of each band, and the start position of the embedded section is obtained for each band of the pilot carrier. FIG. 6 shows the waveform of the phase component of the data carrier Dk (k = 1, 2,...) And the phase component of the pilot carrier Pk (k = 1, 2,...) Among the subcarrier phase components obtained by dividing the carrier signal. This is an example of the waveform. As illustrated in FIG. 6, the phase of each subcarrier obtained by dividing the carrier signal into bands on the extraction device 200 side changes depending on the band. This is because each analysis filter constituting the analysis filter bank in the band dividing unit 121 and each synthesis filter constituting the synthesis filter bank in the band synthesis unit 143 do not have linear phase characteristics (8 of Non-Patent Document 2). (See Section 1.4). Therefore, in this embodiment, as illustrated in FIG. 6, in the approximate synchronization search process, the start positions of the embedded sections obtained for the pilot carriers of each band are averaged, and the result is the start point of the embedded sections for all bands. , And each section F _s0 , F _s1 , F _s2 ,... Of one symbol frame length starting from this position is determined as an embedded section of each symbol. The start point position averaged in this way is used as a rough start point position when the start point position obtained from one pilot carrier is used as the start point of the embedded section for the entire band. This is because symbol extraction from a data carrier having a start point at a position greatly deviated from the start point becomes inaccurate.

  Next, in the data extraction phase, the frame synchronization search unit 250 sequentially reads the sample of the carrier signal in the buffer 210 from the approximate position of the start point of the embedded section of the data symbol sequence obtained in the synchronization search phase. The carrier generator 230 and the amplitude / phase separator 131 are processed. Then, under the control of the frame synchronization search unit 250, the phase demodulation unit 242 executes the following processing. First, the same window function value w (k) used by the phase modulation unit 132 of the embedding device 100 is used for each phase component of each pilot carrier in the pilot carrier group obtained from the amplitude / phase separation unit 131 as necessary. Multiply. Then, using each phase component after multiplication of the window function value at each position arranged at the frame synchronization position, that is, at the position of one symbol frame length starting from the approximate position of the start point of the embedding interval of the data symbol sequence described above. A shift of the phase component of the obtained pilot carrier group is obtained, and this shift is set as a phase fluctuation due to reverberation or the like during signal transmission. The phase fluctuation obtained in this way is regarded as being equal to the phase fluctuation of the corresponding data carrier group, and the phase fluctuation of the corresponding data carrier group is corrected. Then, the phase component of the corrected data carrier is output to the symbol extraction unit 260.

A data symbol reference signal indicating a data symbol “0” and a data symbol reference signal indicating a data symbol “1” are supplied from the data symbol reference signal generation unit 221 to the symbol extraction unit 260. Each time the symbol extraction unit 260 receives the phase component of the corrected data carrier for one symbol frame from the phase demodulation unit 242, the data symbol reference signal indicating the phase component for one symbol frame and the data symbol “0”. And the cross-correlation coefficient corr1 between the phase component for one symbol frame and the data symbol reference signal indicating the data symbol “1”. If corr0> corr1, the data symbol embedded in the data carrier is determined to be “0”, and if corr0 <corr1, the data symbol embedded in the data carrier is determined to be “1”. Based on this, the embedded digital watermark information symbol is output.
The above is the details of the extraction apparatus 200 according to the present embodiment.

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

(1) According to the present embodiment, since the phase component of the data carrier in the carrier signal is replaced with the modulated signal having a continuous waveform indicating the data symbol sequence and transmitted, the original signal is extracted when extracting the data symbol from the carrier signal. It is unnecessary. In addition, since the modulation signal indicating the data symbol sequence is embedded in the carrier signal as the phase component of the data carrier, the robustness of the embedded symbol against noise and echo generated in the carrier signal propagation process can be improved. In addition, since the modulation signal embedded as a phase component in the data carrier of the carrier signal is a signal having a continuous waveform throughout the entire data symbol sequence, a sense of incongruity is generated when propagating the carrier signal embedded with the data symbol as sound There is little to let you.

(2) In a situation where the frequency interval between subcarriers is short, one phase component of two data carriers in adjacent bands is replaced with a sine wave corresponding to symbol “0”, and the other phase component is symbol “1”. When a sine wave corresponding to "" is replaced, a sudden phase change occurs between adjacent data carriers in the band, causing a sense of incongruity in hearing. However, in the present embodiment, a plurality of subcarriers adjacent to each other in the band are grouped, and the phase components of the plurality of subcarriers in the group are replaced with modulated signals having the same waveform corresponding to the same symbol. Therefore, a sudden change in phase component between adjacent subcarriers is avoided in the same group. On the other hand, for example, two data carrier groups are adjacent to each other, and the symbol “0” is embedded in the high band group, and the symbol “1” is embedded in the low band group. In this case, if no measures are taken, there is a sudden phase change between the phase component of the data carrier in the lower band of the high band group and the phase component of the data carrier in the upper band of the low band group. Is not preferable. Therefore, in this embodiment, for each group, the modulation function that replaces the phase component of each subcarrier with a window function that spans a plurality of subcarriers in the group is multiplied, and the change in the phase component between the subcarriers in the group is calculated. While making it gentle, the change of the phase component between subcarriers near the boundary between groups is suppressed. Therefore, in a situation where the frequency interval between the subcarriers is narrow, it is possible to prevent a sense of incongruity from occurring when the carrier signal is output as sound.

(3) When a carrier signal is emitted as a sound from a speaker (not shown) of the embedding device 100, or when a carrier signal that is a sound is reflected by a wall, or when the carrier signal is a microphone (not shown) of the extraction device 200 When receiving the signal, the subcarriers constituting the carrier signal have a phase shift corresponding to the phase characteristic of the transfer function from the speaker to the microphone for each band. However, in embedding device 100 in the present embodiment, a subcarrier in a band adjacent to the data carrier is used as a pilot carrier, and the phase component of this pilot carrier is replaced with a sine wave modulation signal representing a pilot symbol. Further, in the extraction apparatus 200 according to the present embodiment, in the received carrier signal, the phase shift occurring in the data carrier is considered to be the same as the phase shift occurring in the pilot carrier in the band adjacent to the data carrier, and the pilot The phase component of the data carrier is corrected based on the phase component of the carrier. Therefore, even in a situation where a phase shift depending on the band occurs in the subcarrier in the carrier signal transmission process, the symbols embedded in the phase component of the data carrier can be stably extracted.

<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 band grouping unit 232, the band group separation unit 142 of the embedding device 100, and the band grouping unit 232 of the extraction device 200 are omitted, and subcarriers are not grouped, and one system data symbol string is stored as one data. One pilot symbol sequence may be embedded in one pilot carrier and transmitted.

(2) When the sampling frequency of the carrier signal is high, the number of low-frequency subcarriers available for symbol embedding decreases. Therefore, it is necessary to increase the number M of band divisions to increase the number of low-frequency subcarriers that can be used for symbol embedding. However, in order to increase the number M of band divisions, it is necessary to make the pass band of the prototype filter very narrow, which makes it difficult to design the prototype filter. Therefore, in order to avoid such inconvenience, the carrier signal may be resampled as necessary, and the sampling frequency may be lowered to embed symbols. FIG. 7 shows an example of the configuration. In this configuration example, a carrier signal having a sampling frequency of 44.1 kHz is divided into a high frequency component of 8 k to 22.05 kHz and a low frequency component of 0 to 8 kHz by the HPF 311 and the LPF 301. The low-frequency component that has passed through the LPF 301 is down-sampled by the down-sampler 302 and supplied to the above-described embedding device 100. The embedding device 100 embeds a symbol in a subcarrier in a band of, for example, 4 k to 8 kHz of a carrier signal given via the down sampler 302, synthesizes the band, and outputs a carrier signal. The upsampler 303 returns the sampling frequency of this carrier signal to the original sampling frequency of 44.1 kHz. The LPF 304 removes high-frequency noise generated by upsampling of the upsampler 303 from the carrier signal. Then, the adder 320 adds the carrier signal (0 to 8 kHz) that has passed through the LPF 304 and the high frequency component (8 k to 22.05 kHz) of the carrier signal that has passed through the HPF 311 and outputs the result as, for example, a sound from a speaker. . According to this configuration, since the sampling frequency of the carrier signal given to the embedding device 100 is low, when the carrier signal is band-divided to generate subcarriers in the embedding device 100, even if the number of band divisions M is small, Since the number of low-frequency subcarriers available for symbol embedding increases, the design of the prototype filter is facilitated.

1 is a block diagram showing a configuration of a digital watermark information embedding device 100 according to an embodiment of the present invention. FIG. It is a block diagram which shows the structure of the electronic watermark information extraction apparatus 200 by the embodiment. 3 is a block diagram illustrating a configuration example of an analysis filter bank and a synthesis filter bank used in the embedding device 100. FIG. FIG. 4 is a diagram illustrating processing contents of a subcarrier generation unit 120 and an embedding unit 130 in the embedding device 100. It is a figure which shows the content of the outline synchronous search process performed in the same extracting device 200. 4 is a diagram illustrating a phase waveform of each subcarrier obtained by band division in the extraction apparatus 200. FIG. It is a block diagram which shows the structure of the embedding apparatus of the digital watermark information by other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Embedding device, 200 ... Extraction device, 110 ... Modulation signal generation unit, 111 ... Data symbol modulation signal generation unit, 112 ... Pilot symbol modulation signal generation unit, 120, 230 ... Subcarrier generation , 121, 231... Band dividing unit, 122, 232 ... band grouping unit, 123, 233 ... data / pilot carrier separating unit, 130 ... embedding unit, 131 ... amplitude / phase separating unit, 132 ... ... Phase modulation section, 133 ... Amplitude / phase coupling section, 140 ... Carrier combining section, 141 ... Data / pilot carrier combining section, 142 ... Band group separating section, 143 ... Band combining section, 210 ... Buffer , 220... Reference signal generator, 221... Data symbol reference signal generator, 222... Pilot symbol reference signal generator , 240... Demodulation processing unit 241... Amplitude / phase separation unit 242... Phase demodulation unit 250... Frame synchronization search unit 260... Symbol extraction unit 301, 304. , 302 ... down sampler, 303 ... up sampler, 320 ... adder.

Claims (6)

Subcarrier generation means for performing band division on the carrier signal and generating subcarriers of a plurality of bands;
Data symbol modulation signal generating means for generating a data waveform modulation signal having a continuous waveform indicating a data symbol sequence of digital watermark information to be embedded;
Phase modulation means for substituting at least a part of the subcarriers of the plurality of bands as a data carrier into which a data symbol sequence is embedded, and replacing the phase component of the data carrier with the modulation signal for data symbols;
A digital watermark information embedding apparatus, comprising: carrier combining means for performing band synthesis on the subcarriers of the plurality of bands that have undergone the processing of the phase modulation means, and outputting the resultant as a carrier signal in which digital watermark information is embedded. . Further comprising pilot symbol modulation signal generating means for generating a pilot symbol modulation signal having a continuous waveform indicating a pilot symbol sequence which is a synchronization signal of the data symbol sequence;
The phase modulation means is a subcarrier of at least a part of the subcarriers of the plurality of bands, and other than the data carrier is a pilot carrier into which a pilot symbol string is embedded, and the phase component of the pilot carrier The digital watermark information embedding apparatus according to claim 1, wherein: is replaced by the pilot symbol modulation signal.   The phase modulation means divides the sub-carriers of the plurality of bands into a plurality of data carrier groups and a plurality of pilot carrier groups each composed of a group having a close band, and all of the sub-carriers in the plurality of data carrier groups The phase component of the data carrier is replaced with the data symbol modulation signal, and the phase components of all pilot carriers in the plurality of pilot carrier groups are replaced with the pilot symbol modulation signal. A window function having a high function value in the center band of the group and a low function value in the upper limit band and the lower limit band of each group of the data carrier group and the plurality of pilot carrier groups is used. Within the group 3. The digital watermark information embedding according to claim 2, wherein the amplitude of the data symbol modulation signal or pilot symbol modulation signal to be replaced with the phase component of the band data carrier or pilot carrier is limited by a function value of each band. apparatus. Band dividing means for receiving a carrier signal, performing band division, and outputting subcarriers of a plurality of bands;
A data carrier that is an embedding destination of a data symbol sequence of digital watermark information and a pilot carrier that is an embedding destination of a pilot symbol sequence that is a synchronization signal are identified from the subcarriers of the plurality of bands, and the phase component of the data carrier Demodulation processing means for extracting the phase component of the pilot carrier, correcting the phase component of the data carrier with the phase component of the pilot carrier, and outputting the corrected phase component;
A cross-correlation coefficient between the phase component of the corrected data carrier output from the demodulation processing unit and a reference signal indicating a predetermined symbol is calculated, and the data carrier is used as a phase component based on the calculated cross-correlation coefficient An apparatus for extracting digital watermark information, comprising: symbol extraction means for determining a symbol of embedded digital watermark information. Computer
Subcarrier generation means for performing band division on the carrier signal and generating subcarriers of a plurality of bands;
Data symbol modulation signal generating means for generating a data waveform modulation signal having a continuous waveform indicating a data symbol sequence of digital watermark information to be embedded;
Phase modulation means for substituting at least a part of the subcarriers of the plurality of bands as a data carrier into which a data symbol sequence is embedded, and replacing the phase component of the data carrier with the modulation signal for data symbols;
A computer program that performs band synthesis on the subcarriers of the plurality of bands that have undergone the processing of the phase modulation unit, and functions as carrier synthesis unit that outputs a carrier signal in which digital watermark information is embedded. Computer
Band dividing means for receiving a carrier signal, performing band division, and outputting subcarriers of a plurality of bands;
A data carrier that is an embedding destination of a data symbol sequence of digital watermark information and a pilot carrier that is an embedding destination of a pilot symbol sequence that is a synchronization signal are identified from among the plurality of subcarriers, and the phase component of the data carrier and the A demodulation processing means for extracting a phase component of the pilot carrier, correcting the phase component of the data carrier by the phase component of the pilot carrier, and outputting the corrected phase component;
A cross-correlation coefficient between the phase component of the corrected data carrier output from the demodulation processing unit and a reference signal indicating a predetermined symbol is calculated, and the data carrier is used as a phase component based on the calculated cross-correlation coefficient A computer program that functions as symbol extraction means for determining a symbol of embedded digital watermark information.

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