A hidden messaging method based on DRM digital broadcasting

Abstract

A hidden signaling method based on DRM digital broadcasting, which collects DRM digital broadcasting signals, generates Barker codes, and assists the receiving end to achieve frame synchronization; splices the Barker codes with hidden information sample signals to generate hidden information prefabricated signals; performs direct sequence spread spectrum modulation on the hidden information prefabricated signals, performs weighted addition of the DRM digital broadcasting signals and the spread spectrum modulated signals to generate input signals, and transmits them to the channel; uses a Barker code identifier to identify the frame header, obtains a frame of information, and performs equalization compensation on the channel; performs sampling judgment after demodulating the DRM digital broadcasting signals, and obtains part of the DRM digital broadcasting signals using the judgment gain; reconstructs the DRM digital broadcasting signals and eliminates them from the received signals to obtain residual signals; and performs despread spectrum on the residual signals to obtain hidden signals. The present invention completes the hidden transmission of confidential information by improving the format of the signal without affecting the DRM digital broadcasting.

Description

Technical Field

[0001] The invention belongs to the technical field of covert communication, and in particular relates to a hidden signaling method based on DRM digital broadcasting. Background Art

[0002] Audio information hiding technology uses audio as a carrier, and utilizes the characteristics of the human auditory system and the redundancy of the audio signal itself to hide information in the carrier signal in an imperceptible way. In recent years, audio information hiding technology can be generally divided into two parts: the copyright protection of audio digital content and the covert communication problem in special scenarios. Both of these research issues belong to the research scope of audio information hiding, and the latter is the main research field of this patent. Covert communication is mostly used to transmit secret information. The secret information to be transmitted is embedded in the audio carrier and sent to the receiver. The receiver extracts the secret information from the received signal. This situation requires not only that the embedded information cannot be perceived, but also that the algorithm has good anti-interference and anti-attack capabilities.

[0003] DRM is a universal, open digital broadcasting system that is applicable to all broadcasting frequency bands, including long wave, medium wave, short wave and FM broadcasting. It can encode and modulate digital audio signals and various data signals to realize the digitization of the broadcasting system, and can support various types of broadcasting coverage, including local broadcasting, domestic broadcasting, and international shortwave broadcasting. At present, information hiding technology is involved in the fields of medical signals and satellite communications, but research in the special scenario of DRM digital broadcasting is relatively blank. Broadcasting signals have natural advantages such as all-weather and full coverage. If combined with information hiding technology, it can broaden the application scope and scenarios of covert communication, and is a research hotspot in the field of information security. Summary of the invention

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a hidden signaling method based on DRM digital broadcasting, which completes the hidden transmission of confidential information by improving the format of the signal without affecting the DRM digital broadcasting.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A hidden signaling method based on DRM digital broadcasting comprises the following steps:

[0007] Step 1, based on the DRM digital broadcast signal, transmit hidden information, including:

[0008] Collect DRM digital broadcast signals, generate Barker codes, and assist the receiving end in achieving frame synchronization;

[0009] splicing the Barker code with a hidden information sample signal to generate a hidden information prefabricated signal;

[0010] Direct sequence spread spectrum modulation is performed on the hidden information prefabricated signal, and a weighted addition is performed on the DRM digital broadcast signal and the spread spectrum modulated signal to generate an input signal, and the input signal is transmitted to the channel;

[0011] Step 2, recovering hidden information based on hierarchical iterative detection, including:

[0012] Use the Barker code identifier to identify the frame header, obtain a frame of information, and perform equalization compensation on the channel;

[0013] After demodulating the DRM digital broadcasting signal, sampling and decision are performed, and part of the DRM digital broadcasting signal is obtained by using the decision gain;

[0014] Reconstructing the DRM digital broadcast signal and eliminating it from the received signal to obtain a residual signal;

[0015] The residual signal is despread to obtain the hidden signal.

[0016] In one embodiment, before step 1, a modeling analysis is first performed on the transmission system of the DRM digital broadcasting system carrying hidden information, and the method is as follows:

[0017] 1) DRM digital broadcast channel modeling

[0018] According to the transmission characteristics of DRM broadcast signals, a wide-sense stationary non-correlated scattering channel model is established;

[0019] 2) Determine the key performance indicators of the hidden information spread spectrum modulation system, including the spread spectrum gain G of the spread spectrum communication system p and interference tolerance M j ;

[0020] 3) Analyze the power domain multiplexing transmission system of DRM digital broadcasting signals and hidden information, and obtain the system channel capacity for covert messaging.

[0021] In one embodiment, the Barker code is an 11-bit bipolar Barker code, and the number of bits of the hidden information sample signal is 9989, which is converted into a bipolar non-return-to-zero code to generate a final hidden information sample signal; the Barker code is in front and the hidden information sample signal is in the back, and they are spliced ​​to generate a hidden information prefabricated signal with a bit number of 10,000.

[0022] In one embodiment, the spread spectrum modulation is implemented as follows:

[0023] Generate two sets of m-sequences with a period of 1023 bits, m0 and m1, generated by a 10-stage linear shift register;

[0024] The m-sequence is used to perform direct sequence spread spectrum modulation on the hidden information prefabricated signal, wherein the sequence m0 is used as the spread spectrum code of the binary code position -1 in the hidden signal, and the sequence m1 is used as the spread spectrum code of the binary code position 1 in the hidden signal.

[0025] In one embodiment, the layered iterative detection method:

[0026] For the received mixed signal composed of DRM digital broadcasting signal, hidden signal and noise signal, based on power judgment, the DRM digital broadcasting signal whose power is obviously greater than that of the hidden signal and the noise signal is removed to obtain a residual signal composed of the hidden signal and the noise signal; then a synchronization is performed, that is, spread spectrum codes m0 and m1 are used to perform cross-correlation with the residual signal to find the position of despreading; then the residual signal is despread; then a secondary synchronization is performed, that is, a local Barker code is used to perform cross-correlation on the despread signal to find the position of the Barker code frame header, and the hidden signal can be obtained according to the number of bits of the Barker code.

[0027] In one embodiment, for the mixed signal, the power of each signal is estimated, and the signals are arranged in descending order. The signal with the highest power, i.e., the DRM digital broadcasting signal, is detected first. The DRM digital broadcasting signal is reconstructed using the estimated amplitude and phase values ​​combined with the bit estimation of the judgment output, and then removed from the received mixed signal. The remaining signal with the highest power is the hidden signal, which is extracted for despreading.

[0028] In one embodiment, the equalization compensation method is a minimum mean square error (MMSE) algorithm.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] First, the information hiding scheme proposed in the present invention fills the gap in the field of information hidden communication based on the DRM digital broadcasting system, realizes the efficient transmission of hidden information in this special scenario, and broadens the application scope and adaptation scenarios of DRM digital broadcasting.

[0031] Secondly, the noise-hiding hidden information design scheme adopted by the present invention can reasonably balance the power relationship between the DRM digital broadcast signal and the hidden signal, perform spectrum spread and superposition at the signal level, and have differences in the frequency domain, which is conducive to demodulation.

[0032] Thirdly, the efficient hidden information recovery mechanism based on layered iterative detection adopted by the present invention can reduce the demodulation difficulty of the receiving end of the conforming signal composed of the DRM digital broadcast signal and the hidden signal, and realize layered cyclic detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of the method of the present invention.

[0034] Figure 2 It is a 10-bit linear shift register of the present invention.

[0035] Figure 3 A flow chart of the signal processing process is provided for hiding information in the present invention.

[0036] Figure 4 It is a flow chart of the direct sequence spread spectrum steganography scheme of the present invention.

[0037] Figure 5 This is a flow chart of the hidden information recovery process of the layered iterative detection of the present invention.

[0038] Figure 6 This is a flow chart of the hidden information extraction solution of the present invention.

[0039] Figure 7 The present invention is an algorithm design flow chart of an embodiment of the present invention.

[0040] Figure 8 This is a verification result of the spread spectrum code correlation of an embodiment of the present invention.

[0041] Fig. 9 This is a simulation diagram of the hierarchical iterative detection and demodulation effect of an embodiment of the present invention.

[0042] Fig.10 This is a simulation diagram of the impact of hidden information embedding on the original communication effect according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0044] The present invention is based on the special scenario of DRM digital broadcasting system and proposes an information hiding design scheme. Under the premise of not affecting the civilian DRM broadcasting communication, the transmission signal in the channel is graded according to the transmission target, the high-power DRM signal executes the original broadcasting service, and the low-power signal transmits the hidden information. The latter is carried in the system of the former to realize the multiplexing of the same-band hidden signal and the public broadcasting signal in the power domain. The specific implementation process is: direct sequence spread spectrum technology is adopted at the transmitting end, and a pseudo-random sequence is generated by using a key to modulate the hidden information sequence to obtain an extended spectrum sequence. The secret information modulated by the carrier and the pseudo-random sequence is multiplied by the power factor and superimposed on the broadcast audio signal of each frame in the time domain; the key is also used at the receiving end for correlation decoding, and the signal waveform, coding, channel estimation and compensation research are carried out.

[0045] Please refer to the attached Figure 1 , the implementation steps of the method of the present invention are further described.

[0046] Step 1: Modeling the transmission system of DRM digital broadcasting system with hidden information

[0047] Step 1.1, DRM digital broadcast channel modeling. According to the transmission characteristics of DRM broadcast signals, a wide-sense stationary non-correlated scattering channel model is established. The expression of the system output signal is:

[0048]

[0049] Where s(t) and x(t) are the complex envelope curves of the output and input signals respectively; k represents the number of paths, with a maximum of n=4; ρ k Represents the relative attenuation after receiving through the channel; c k (t) Zero-mean complex stationary Gaussian random process, whose amplitude value |c k (t)| obeys Rayleigh distribution, while the phase Φ(t) is uniformly distributed, and its distribution is related to Doppler frequency deviation and Doppler spread; Δ k is the delay of each path. The Doppler envelope on each path is defined as:

[0050]

[0051] Where, the Doppler spread D sp Defined as:

[0052] D sp =2σ d

[0053] σ d represents the standard deviation of the Doppler envelope, D sh represents Doppler shift, and f represents frequency.

[0054] Step 1.2, key performance measurement indicators of the spread spectrum modulation system for hidden information. The broadband DRM broadcast signal is a broadband blocking interference to the communication in the covert channel. The cross-correlated interference signal in the present invention is the DRM broadcast service signal, which is a continuous coverage signal, and the service signal is not only powerful and has a large bandwidth, but also covers the entire spread spectrum signal band, drowning the spread spectrum signal. For communication in covert channels, spread spectrum modulation needs to have a certain anti-interference ability to ensure that the hidden information can be detected by the receiving node. The performance indicators of the spread spectrum communication system using pseudo-random code modulation are spread spectrum gain and interference tolerance. The spread spectrum gain G of the spread spectrum communication system p , defined as the output signal-to-noise ratio SNR of the receiver correlator out and input signal-to-noise ratio SNR in The ratio is used to measure the anti-interference performance of the spread spectrum system and can be expressed as:

[0055] G p =SNR out -SNR in

[0056] Under ideal carrier synchronization and spread spectrum sequence synchronization conditions, the spread spectrum gain can also be expressed as the expanded spectrum bandwidth B. c The information bandwidth B before spectrum expansion b Ratio:

[0057]

[0058] Interference tolerance M j It indicates the ability of the system to work normally under a certain interference intensity, which can be expressed as:

[0059]

[0060] Among them, G p is the spreading gain, L sys is the system loss, is the demodulation threshold.

[0061] Step 1.3: Analysis of the power domain multiplexing transmission system of DRM digital broadcasting signals and hidden information. Assume that the transmitter allocates power P1 to the hidden signal and power P2 to the broadcast user signal. The mixed signal carrying the hidden information is expressed as:

[0062]

[0063] P S Represents the total power of the transmitted signal, P i represents the power of the i-th signal, x1 represents the hidden signal, and x2 represents the DRM digital broadcast signal.

[0064] At each receiving node, the received mixed signal is:

[0065]

[0066] h i is the channel fading coefficient from the transmitting station to the cooperative receiving node, and n0 is the channel additive white noise with variance N0.

[0067] After receiving the signal, the receiving node performs SIC detection. According to the power allocation factor, the strong broadcast signal is partially demodulated first, and then removed from the mixed signal. Based on this, the signal-to-noise ratio of the covert communication receiving end is:

[0068]

[0069] Among them, the signal fading coefficients of x1 and x2 at the covert communication receiving node are the same, P Lis the residual interference of the high-power broadcast signal, P1 is the power allocated by the transmitter to the hidden signal, and h1 is the channel fading coefficient from the transmitter to the hidden signal node. According to Shannon's theorem, the system channel capacity for covert messaging can be obtained as:

[0070]

[0071] Step 2: Design of hidden information transmission mechanism based on DRM digital broadcast signal

[0072] Step 2.1, DRM digital broadcast signal acquisition.

[0073] Step 2.2, generate a Barker code to assist the receiving end in achieving frame synchronization. In this embodiment, an 11-bit bipolar Barker code is used, and the 11-bit unipolar Barker code information is set to "1 1 1 0 0 0 1 0 0 1 0", which is converted into a bipolar non-return-to-zero encoding form of "1, 1, 1, -1, -1, -1, -1, -1, -1, to further improve the anti-interference ability.

[0074] Step 2.3, generate a hidden information sample signal. The hidden information setting has great autonomy. The preset hidden signal in the present invention is "101010...", that is, "10" is cycled in sequence, and the number of bits is 9989. The reason for selecting the hidden signal length of 9989 bits is that the length of the Barker code is 11 bits, and the total number after superposition is 10,000 bits. Then, the hidden signal is converted into a bipolar non-return-to-zero code to generate the final hidden information sample signal.

[0075] Step 2.4, splicing the Barker code with the hidden information sample signal to generate a hidden information prefabricated signal. In an embodiment of the present invention, the bipolar Barker code generated in step 2.2 is spliced ​​with the bipolar hidden information sample signal generated in step 2.3. The Barker code is in front and the hidden signal is in the back, and the total number of bits is exactly 10,000.

[0076] Step 2.5, generate two groups of m-sequences with a period of 1023 bits, which are generated by a 10th-order linear shift register, and are respectively m0 and m1. In spread spectrum communication, it is very important to select a coding sequence with good pseudo-random characteristics and correlation characteristics. The pseudo-random sequence used in spread spectrum should have the following characteristics: sharp autocorrelation characteristics, zero cross-correlation values ​​everywhere, balanced and equal numbers of different code elements, sufficient codes, poor cross-correlation between different code groups, and as high a complexity as possible. The binary pseudo-random m-sequence used in the embodiment of the present invention is generated by a 10th-order linear shift register. It is a code sequence generated by cyclic linear feedback of the register. The working principle is as shown in the attached figure. Figure 2 As shown in the figure, a0~a9 represent shift registers, C0~C 10 Indicates the feedback line.

[0077] Step 2.6, use the m sequence to perform direct sequence spread spectrum modulation on the hidden information prefabricated signal. The sequence m0 is used as the spread spectrum code for the binary code position -1 in the hidden signal, and the sequence m1 is used as the spread spectrum code for the binary code position 1 in the hidden signal. The spread spectrum preprocessing process for the hidden information is as shown in the attached figure. Figure 3 As shown, the specific process is as follows: first, the hidden information (i.e., the previously set [11-bit Barker code + 9989-bit 1010...bit information]) is parity-checked and error-corrected; secondly, the interleaving technology is used to discretize the bit errors (the interleaving technology used in the present invention is as follows: the hidden signal is composed of some 4-bit message groups, the first bit of the 4 consecutive groups is taken out, and the 4 first bits are made into a new 4-bit group, called the first frame, and the bits 2 to 4 in the 4 message groups are also processed in the same way.); then constellation mapping is performed, and QPSK is used in the present invention; then spread spectrum modulation is performed, using the m sequence generated in the previous text, where the key is the m sequence, the m0 sequence performs spread spectrum modulation on the information bit with a bit of -1, and the m1 sequence performs spread spectrum modulation on the information bit with a bit of 1; finally, the superposition operation is performed. The specific power allocation is shown in the following formula:

[0078]

[0079] The power attenuation factor assigned to the hidden signal x1 is The attenuation factor assigned to the DRM digital broadcast signal x2 is The DRM digital broadcast signal and the hidden information are superimposed in the time domain.

[0080] Step 2.7, set the power factor, add the DRM digital broadcast signal and the spread spectrum modulated hidden signal prefabricated signal generated in step 2.6 by weighted addition, and generate the input signal. The power factor here is related to the power ratio of the above two signals, which in turn affects the signal-to-noise ratio. The working principle diagram is as follows Figure 4 As shown, the random number generator is used to generate the m sequence, as shown in the attached Figure 2As shown. Since the present invention is to generate two m sequences, namely, the m1 sequence and the m2 sequence. For the m0 sequence, the random number generated by the Key is 591, and the corresponding binary is 1 0 0 1 0 0 1 1 1 1, then C0 = 1, C1 = 0, C2 = 0, C3 = 1, C4 = 0, C5 = 0, C6 = 1, C7 = 1, C8 = 1, C9 = 1, and the input information of these feedback lines can obtain 1023 bits of m0 sequence information; similarly, for the m1 sequence, the random number generated by the Key is 111, and the corresponding binary is 0 0 0 1 1 0 1 11 1, then C0 = 0, C1 = 0, C2 = 0, C3 = 1, C4 = 1, C5 = 0, C6 = 1, C7 = 1, C8 = 1, C9 = 1, and the input information of these feedback lines can obtain 1023 bits of m1 sequence information different from the m0 sequence. According to the m0 and m1 sequences, spread spectrum modulation can be performed. The hidden signal with a bit of -1 is modulated with m0, and the hidden signal with a bit of 1 is modulated with m1 (the spread spectrum modulation here means: the -1 bit in the hidden information is replaced by the 1023-bit m0 sequence, and the 1 bit in the hidden information is replaced by the 1023-bit m1 sequence, so the 10,000-bit hidden information will be modulated into 10,000*1023=10,230,000-bit hidden spread spectrum information). Then follow the attached Figure 3 The attenuation factors shown continue to add up.

[0081] In step 2.8, the input signal is transmitted into the channel using the software platform USRPX310.

[0082] Step 3: Design of hidden information recovery mechanism based on hierarchical iterative detection

[0083] Step 3.1, theoretical analysis of hierarchical iterative detection in hidden channels. Assume that the received mixed signal is r(t) (i.e., the signal received from the receiver in the hierarchical iterative algorithm), perform matched filtering on it to obtain synchronization information, frequency offset estimation, channel estimation and channel equalization, perform constellation judgment, and then reconstruct the estimated value of the signal based on the judgment result. The amplitude is estimated by correlating it with the local spreading code of the hidden signal, and then the estimated value of the DRM signal is subtracted from the mixed signal to obtain a new received signal r1(t). This process is to demodulate and judge the signal x1(t) with the highest power in the mixed signal and eliminate the co-band interference of this signal to the hidden node signal. This process can be iterated until the re-judgment condition is no longer met.

[0084] Step 3.2: Perform layered iterative detection on the received signal. The working principle diagram is shown in the attached figure. Figure 5 As shown, the process is as follows:

[0085] Step 3.2.1, DRM digital broadcast signal capture and tracking. The mixed signal received by the receiver contains DRM digital broadcast signal, hidden information and noise signal. According to the priority of hierarchical iterative detection, the high-power signal - DRM digital broadcast signal - needs to be detected first.

[0086] Step 3.2.2, synchronization and equalization. Use the Barker code identifier to identify the frame header, obtain a frame of information, and perform equalization compensation on the channel. For example, the equalization compensation method is the minimum mean square error algorithm MMSE.

[0087] Step 3.2.3, demodulation decision: demodulate the mixed signal obtained from the receiver, sample and decide, and use the decision gain to obtain the DRM digital broadcast signal.

[0088] Step 3.2.4, residual signal acquisition. After the high-power DRM digital broadcast signal in step 3.2.3 is eliminated, the remaining signal is the residual signal.

[0089] Step 3.2.5, locate the hidden information. Find the location of the hidden information in the residual signal obtained in step 3.2.4. First, use the m sequence to perform a cross-correlation operation with the received mixed signal to find the location of the despread spectrum; then use the Barker code identifier to identify the frame header, obtain the location of the Barker code, and then get the location of the hidden information.

[0090] Step 3.3, acquisition of hidden signal. Despread the residual signal obtained in step 3.2.5 to obtain the hidden signal. The working principle diagram is as follows Figure 6 shown.

[0091] That is, in the present invention, for a received mixed signal consisting of a DRM digital broadcasting signal, a hidden signal and a noise signal, based on power judgment, the DRM digital broadcasting signal whose power is obviously greater than that of the hidden signal and the noise signal is first eliminated to obtain a residual signal consisting of the hidden signal and the noise signal; then a cross-correlation operation is performed, that is, spread spectrum codes m0 and m1 are used to perform cross-correlation with the residual signal to find the position of despreading; then a despreading operation is performed on the residual signal; then a Barker code synchronization is performed, that is, a local Barker code is used to perform cross-correlation on the despread signal to find the position of the Barker code frame header, and the hidden signal can be obtained according to the number of bits of the Barker code.

[0092] Step 4: bit error rate statistics and demodulation performance evaluation.

[0093] The effect of the present invention can be further demonstrated through the following signal modulation and demodulation experiments.

[0094] Experimental conditions: MATLAB software environment, USRPX310, GNUradio simulation platform and HF shortwave loop antenna are used. The USRP hardware simulation platform is used to implement the transmission test of hidden information. MATLAB performs digital signal processing on the RF signal before and after up and down conversion to achieve the loading and detection of hidden information, test the detection threshold of hidden information, and observe the received signal spectrum. The specific process is as follows Figure 7 shown.

[0095] The OFDM parameter settings in the simulation are shown in the following table:

[0096]

[0097]

[0098] The spread spectrum concealed signal parameter settings in the simulation are shown in the following table:

[0099] Spread Spectrum Gain 30dB Spreading code period 1024 Signal bandwidth 10KHz Information Rate 1bps Modulation BPSK / CPM Embedding method Baseband time domain

[0100] Step 1, generate 11-bit Barker code information as "1 1 1 0 0 0 1 0 0 1 0", and convert it into bipolar non-return-to-zero encoding form "1, 1, 1, -1, -1, -1, -1, -1, -1, 1, -1".

[0101] Step 2, generate a hidden information sample signal of "101010..." with a number of 9989 bits.

[0102] Step 3, generate two m-sequences with a period of 1023 bits, defined as sequence m0 and sequence m1. The simulation results of their correlation are shown in the attached figure. Figure 8 shown.

[0103] Step 4: Concatenate the Barker code with the hidden information sample signal to generate a hidden information prefabricated signal. The number of bits is 10,000.

[0104] Step 5: Perform a spread spectrum operation on the signal in step 4, and use sequence m0 and sequence m1 as spread spectrum codes for the binary code bits -1 and 1 in the hidden signal, respectively.

[0105] Step 6, setting the power factor α=22, that is, DRM signal power / hidden signal power=22. According to this ratio, the DRM digital broadcast signal in step 3 and the hidden information prefabricated signal are superimposed in the time domain.

[0106] Step 7: Transmit the signal according to the signal parameter settings given in the above table.

[0107] Step 8: Perform hierarchical iterative detection and demodulation on the received signal.

[0108] Step 9: Use a Barker code identifier to identify the frame header, obtain a frame of information, and perform equalization compensation on the channel.

[0109] Step 10: Perform layered iterative detection and demodulation to separate the hidden signal. The demodulation effect simulation diagram is shown in the attached figure. Fig. 9 shown.

[0110] Step 11, despreading the hidden signal, sequence m0 and sequence m1 are used as despreading codes for binary code bits -1 and 1 in the hidden signal, respectively. The influence of the hidden signal on the constellation diagram of the DRM digital broadcasting signal is shown in the attached figure. Fig.10 shown.

[0111] The above experimental results analysis proves the correctness and effectiveness of the method proposed in the present invention.

Claims

1. A hidden signaling method based on DRM digital broadcasting, characterized in that: The steps include: Step 1, based on the DRM digital broadcast signal, transmit hidden information, including: Collect DRM digital broadcast signals, generate Barker codes, and assist the receiving end in achieving frame synchronization; splicing the Barker code with a hidden information sample signal to generate a hidden information prefabricated signal; Direct sequence spread spectrum modulation is performed on the hidden information prefabricated signal, and a weighted addition is performed on the DRM digital broadcast signal and the spread spectrum modulated signal to generate an input signal, and the input signal is transmitted to the channel; Step 2, recovering hidden information based on hierarchical iterative detection, including: Use the Barker code identifier to identify the frame header, obtain a frame of information, and perform equalization compensation on the channel; After demodulating the DRM digital broadcasting signal, sampling and decision are performed, and part of the DRM digital broadcasting signal is obtained by using the decision gain; Reconstructing the DRM digital broadcast signal and eliminating it from the received signal to obtain a residual signal; Despread the residual signal to obtain the hidden signal; Before step 1, a modeling analysis is first performed on the transmission system of the DRM digital broadcasting system carrying hidden information, and the method is as follows: 1) DRM digital broadcast channel modeling According to the transmission characteristics of DRM broadcast signals, a wide-sense stationary non-correlated scattering channel model is established; 2) Determine the key performance indicators of the hidden information spread spectrum modulation system, including the spread spectrum gain G of the spread spectrum communication system p and interference tolerance M j ; 3) Analyze the power domain multiplexing transmission system of DRM digital broadcasting signals and hidden information, and obtain the system channel capacity of covert messaging; The method of layered iterative detection: For the received mixed signal composed of DRM digital broadcasting signal, hidden signal and noise signal, based on power judgment, the DRM digital broadcasting signal whose power is obviously greater than that of the hidden signal and the noise signal is removed to obtain a residual signal composed of the hidden signal and the noise signal; then a synchronization is performed, that is, spread spectrum codes m0 and m1 are used to perform cross-correlation with the residual signal to find the position of despreading; then the residual signal is despread; then a secondary synchronization is performed, that is, a local Barker code is used to perform cross-correlation on the despread signal to find the position of the Barker code frame header, and the hidden signal can be obtained according to the number of bits of the Barker code.

2. The hidden signaling method based on DRM digital broadcasting according to claim 1, characterized in that: The Barker code is an 11-bit bipolar Barker code, and the number of bits of the hidden information sample signal is 9989, which is converted into a bipolar non-return-to-zero code to generate a final hidden information sample signal; the Barker code is in front and the hidden information sample signal is in the back, and they are spliced ​​to generate a hidden information prefabricated signal with a bit number of 10000.

3. The hidden signaling method based on DRM digital broadcasting according to claim 1, characterized in that: The implementation method of the spread spectrum modulation is: Generate two sets of m-sequences with a period of 1023 bits, m0 and m1, generated by a 10-stage linear shift register; The m-sequence is used to perform direct sequence spread spectrum modulation on the hidden information prefabricated signal, wherein the sequence m0 is used as the spread spectrum code of the binary code position -1 in the hidden signal, and the sequence m1 is used as the spread spectrum code of the binary code position 1 in the hidden signal.

4. The hidden signaling method based on DRM digital broadcasting according to claim 1, characterized in that: For the mixed signal, the power of each signal is estimated and arranged in descending order. The signal with the largest power, i.e., the DRM digital broadcasting signal, is detected first. The DRM digital broadcasting signal is reconstructed using the estimated amplitude and phase values ​​combined with the bit estimation of the judgment output, and then removed from the received mixed signal. The signal with the largest power among the remaining signals is the hidden signal, which is extracted for despreading.

5. The hidden signaling method based on DRM digital broadcasting according to claim 1, characterized in that: The equalization compensation method is a minimum mean square error algorithm MMSE.

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