CN106101047A - A kind of anonymous communication Waveform generation method based on OFDM - Google Patents

Abstract

The present invention provides a method for generating concealed communication waveforms based on OFDM, which includes the following steps: S1: define the total number of OFDM channels N and the number of channels n that actually transmit signals for digital signals, and perform the process according to the number of OFDM carriers and the QPSK signal pattern Serial-to-parallel conversion grouping; S2: Phase mapping is performed on the basis of digital symbols in the QPSK signal format; S3: Perform IFFT transformation on the generated DQPSK format complex symbol matrix, and modulate the digital signal to the corresponding carrier to form a digital multi-carrier symbol matrix , and add guard interval processing and noise processing to each frame matrix; S4: form a row matrix of transmitted digital symbols, and finally digital-to-analog conversion forms communication signals based on DQPSK and OFDM digital modulation methods. The present invention can achieve the hidden effect through the flexible selection of the channel, the communication is difficult to be cracked, and the internal signal modulation mode of the communication adopts the DQPSK modulation mode.

Description

A Waveform Generation Method for Covert Communication Based on OFDM

technical field

The invention relates to the technical field of communication, in particular to an OFDM-based concealed communication waveform generation method.

Background technique

In modern communication, traditional concealed communication methods such as frequency hopping communication technology and secret communication technology have revealed great disadvantages. On the one hand, because the frequency hopping communication technology requires a large signal-to-noise ratio at the receiving end, with the continuous improvement of the performance of the reconnaissance detection equipment, the frequency spectrum of the FM signal can be clearly seen on the reconnaissance detection equipment and related communication deciphering; On the one hand, secure communication technology equipment and algorithms are complex and costly. They have good use value in a few occasions where high-level information is transmitted, but they appear to be too cost-effective in occasions where the transmission level is not high but confidentiality requirements are required. The concealed communication technology based on OFDM can well hide the communication information in one or more carrier channels by using multi-carrier, making it difficult for reconnaissance equipment to detect and track, and the secrecy effect is very good. At the same time, the carriers of this technology are strictly orthogonal, which greatly increases the utilization rate of the carrier channel. And its implementation algorithm is relatively simple, and the hardware cost is moderate, so it is a cost-effective covert communication technology.

Contents of the invention

In order to solve the above-mentioned technical problems, the present invention provides a method for generating concealed communication waveforms based on OFDM, which includes the following steps:

S1: Define the total number of channels N of OFDM and the number of channels n of the actual transmission signal for the digital signal, and perform serial-to-parallel conversion grouping according to the number of OFDM carriers and the QPSK signal pattern to form a digital symbol matrix of I and Q dual-channel multi-channel data patterns;

S2: Perform phase mapping on the basis of digital symbols in the QPSK signal format, and then generate a signal digital symbol matrix in a DQPSK modulation style;

S3: Perform IFFT transformation on the generated complex symbol matrix in DQPSK format, modulate the digital signal onto the corresponding carrier to form a digital multi-carrier symbol matrix, and perform guard interval processing and noise processing on each frame matrix;

S4: Perform parallel-to-serial conversion on the digital symbol matrix processed by the guard interval to form a row matrix of transmitted digital symbols, and finally digital-to-analog conversion to form communication signals based on DQPSK and OFDM digital modulation methods.

Preferably, the digital symbol matrix forming the I, Q dual-channel multi-channel data pattern specifically includes the following two steps:

First, according to the dual-channel data pattern, two adjacent signal data bits are grouped into a group;

Then, according to the number of OFDM channels, the number of frames and the mode of sending and receiving, the data is serial-to-parallel converted to form a multi-channel digital symbol matrix.

Preferably, the step S2 specifically includes the following two steps:

First define the mapping relationship between the digital symbol and the phase of the QPSK signal format and calculate the phase difference between adjacent digital symbols: According to a symbol consisting of two bits, the phase of the defined symbol is 0, π, four;

Then set the initial phase and calculate the differential phase, and encode the differential phase according to the phase definition to form a digital symbol matrix in DQPSK format;

Finally, amplitude and two-channel encoding are performed to form an amplitude-normalized complex symbol matrix.

Preferably, step S2 specifically includes the following steps:

Define the mapping relationship between sign and phase:

The digital symbols of the QPSK modulation style include four types: 00, 01, 10, and 11. The current mapping relationship is defined as Perform phase mapping on the symbols according to the mapping relationship;

Perform differential change coding, specifically including the following steps:

First set an initial phase for the first group of phase symbols: now set the initial phase as That is, the differential reference phases of n channels in the first group are

Then, the phase of the symbol mapping is used as the differential phase for phase calculation: for example, the mapping phase of the first row and the first column is Then according to the difference principle, the phase of the first channel of the second group is In this way, a total of M+1 groups are obtained, and the phases of n signals in each group;

Then perform phase inverse encoding: the phase is inversely encoded into a two-bit code symbol style. According to the principle of I and Q channels, the mapping relationship of phase inverse encoding is: According to this mapping relationship, the phases of each group of n signals in the M+1 group are reverse-coded to form M+1 groups, and a symbol matrix of n two-digit symbols in each group;

Finally, the magnitude and quadrature dual-channel transformation of the generated digital symbols are performed: for normalization, the magnitude of the digital symbols is set to That is, each digit sign value is multiplied by At the same time, for each pair of digital symbols, the first one is used as the real part, and the latter one is used as the imaginary part to form a matrix of complex digital symbols.

Preferably, S3 specifically includes the following steps:

First, N-point I FFT transformation is performed on each group to generate M+1 groups of complex digital matrices. After the transformation, each symbol of each group is modulated onto the carrier channel from the 1st to the Nth carrier channel in order to form channel modulation. good digital signal matrix;

Secondly, the method of inserting a cyclic guard interval is used to eliminate the influence of ISI, and the guard interval is taken as Requirements, for each group of symbol matrix after IFFT transformation, the subsequent The data symbols of the group are copied to the front of the group to form M+1 groups, each group A symbol matrix with a guard interval;

Finally, add noise to the digital symbol matrix.

Preferably, S4 specifically includes the following steps:

First, the digital signal matrix of M+1 groups and each group of N symbols is converted from parallel to serial to form a serial data string comprising N*(M+1) signal symbols;

Next, according to the requirements of the carrier channel frequency, digital-to-analog conversion is performed at a certain digital-to-analog conversion frequency to form baseband DQPSK and orthogonal frequency division multiplexing multi-carrier modulated signals;

The relationship between the carrier channel frequency Δf and the channel number N and the digital-to-analog conversion frequency f is as follows:

f=N×Δf (1)

The baseband signal is up-converted at the _{f 0} frequency to form a DQPSK and positive Cross-frequency division multiplexing of multi-carrier modulated signals.

The present invention has the following beneficial effects:

The present invention can achieve the hidden effect through the flexible selection of the channel, the communication is difficult to be cracked, and the internal signal modulation mode of the communication adopts the DQPSK modulation mode.

Of course, any product implementing the present invention does not necessarily need to achieve all the above-mentioned advantages at the same time.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that are required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. Those of ordinary skill in the art can also obtain other drawings based on these drawings without any creative effort.

FIG. 1 is a schematic diagram of an OFDM-based concealed communication waveform generation method provided by an embodiment of the present invention;

FIG. 2 is a schematic diagram of a first mode of an OFDM modulation pattern provided by an embodiment of the present invention;

FIG. 3 is a schematic diagram of phase mapping of QPSK and DQPSK provided by an embodiment of the present invention;

4 is an equivalent effect diagram of DQPSK phase modulation information modulation provided by an embodiment of the present invention;

FIG. 5 is a waveform diagram of communication signals based on DQPSK and OFDM digital modulation methods provided by an embodiment of the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

As shown in Figure 1, the embodiment of the present invention provides a method for generating a concealed communication waveform based on OFDM, which includes the following steps:

S1: Define the total number of OFDM channels N and the number of channels n that actually transmit the signal for the digital signal, and perform serial-to-parallel conversion grouping according to the number of OFDM carriers and the QPSK signal style to form a digital symbol matrix of I, Q dual-channel multi-channel data style, It consists of the following two steps:

First, according to the dual-channel data pattern, two adjacent signal data bits are grouped into a group;

Then, according to the number of OFDM channels, the number of frames, and the transceiver mode, the data is serially converted into a multi-channel digital symbol matrix;

S2: Perform phase mapping on the basis of digital symbols in the QPSK signal format, and then generate a signal digital symbol matrix of a DQPSK modulation style, which includes the following two steps: as shown in Figure 3, the phase mapping of QPSK and DQPSK;

First define the mapping relationship between the digital symbol and the phase of the QPSK signal format and calculate the phase difference between adjacent digital symbols: According to a symbol consisting of two bits, the phase of the defined symbol is 0, π, four;

Then set the initial phase and calculate the differential phase, and encode the differential phase according to the phase definition to form a digital symbol matrix in DQPSK format;

Finally, amplitude and dual-channel encoding are performed to form a complex symbol matrix with normalized amplitude;

S3: Perform IFFT transformation on the generated complex symbol matrix in DQPSK format, modulate the digital signal onto the corresponding carrier to form a digital multi-carrier symbol matrix, and perform guard interval processing and noise processing on each frame matrix;

S4: Perform parallel-to-serial conversion on the digital symbol matrix processed by the guard interval to form a row matrix of transmitted digital symbols. Finally, the digital-to-analog conversion forms a communication signal based on DQPSK and OFDM digital modulation methods, as shown in Figure 5, which is a communication signal waveform diagram;

The specific process of S1 includes:

First, determine the total number of OFDM carriers N and the number of actual communication carriers n and frequency f ₀ +k×Δf,k=0,1,2,...,N-2,N-1, and the data sending and receiving pattern ( That is, the order in which data is sent and received). According to the characteristics of DQPSK and OFDM, data transmission and reception usually have two styles;

When the symbols of the OFDM modulation pattern are sent, N carrier symbols are sent at the same time. As shown in Figure 2, it is the first way, that is, the symbols carried by the first N carriers are sent first according to the symbol sequence of the signal, and then The N carriers carrying symbols are then sent, and the grouping algorithm is more complicated when sending in this style, but the decoding is simpler when receiving;

The second method is that the symbols are arranged in sequence according to the first carrier channel, the second carrier channel, ..., and the Nth carrier channel. The grouping algorithm of this pattern is relatively simple when sending, but the decoding is more complicated when receiving;

Mode 1 is now used as an example. According to the characteristics of QPSK and the actual number N of OFDM channels, a matrix with N rows and M columns is first generated, and an n×M communication channel matrix is determined in this matrix according to the number n of communication channels actually used. The channels other than the communication channel form an idle channel matrix for the idle channel, and the value of the idle channel matrix can be set to a pseudo code or set to be empty to achieve the purpose of concealment. Next, symbols are written into the actually used communication channel matrix. Firstly, divide the serial communication data into one group every n×2, and divide them into M groups in total. Then carry out the serial-to-parallel conversion and convert the signal symbols of a row into the 2×j-1 and the 2×j (j =1,2,3,...,N-1,N) symbols are placed in the unit of the jth row of the i-th column (here every two adjacent symbol bits occupy a unit), forming the QPSK symbol modulation pattern A two-dimensional matrix with n rows and M columns.

Preferably, the process of S2 specifically includes:

First, define the mapping relationship between symbols and phases: the digital symbols of the QPSK modulation style include four types: 00, 01, 10, and 11. The current mapping relationship is defined as follows: Then phase-map the symbols according to the mapping relationship;

Next, perform differential change encoding: the first step is to set an initial phase for the first group of phase symbols, and now set the initial phase as That is, the differential reference phases of n channels in the first group are In the second step, the phase of the symbol mapping is calculated as the differential phase, for example, the mapping phase of the first row and the first column is Then according to the difference principle, the phase of the first channel of the second group is In this way, a total of M+1 groups are obtained, and the phases of n signals in each group are obtained. The third step is phase inverse encoding, that is, the phase is inversely coded into a two-bit code symbol style. According to the principle of I and Q channels, the mapping relationship of phase inverse encoding yes: According to this mapping relationship, M+1 groups, each group of n signal phases are reverse-coded to form M+1 groups, each group of n two-digit symbol symbol matrices, and the unused channel matrix does not participate in the phase during this process. Mapping and coding can be filled in with the same symbols as the communication symbols;

Finally, the magnitude and quadrature two-channel transformations of the generated digital symbols are performed, and for normalization, the magnitude of the digital symbols is set to That is, each digit sign value is multiplied by At the same time, for each pair of digital symbols, the first one is used as the real part, and the latter one is used as the imaginary part to form a matrix of complex digital symbols. Taking a pair of digital symbols (1,-1) as an example, after magnitude and two-channel transformation, it becomes (i is an imaginary factor, ie i ² =-1).

In this embodiment, the process of S3 specifically includes:

First, N-point IFFT transformation is performed on each group to generate M+1 groups of complex digital matrices. When doing IFFT transformation, all channels of the communication channel matrix and the idle signal matrix are included. After the transformation, each symbol of each group can be considered Modulate in order from the 1st to the Nth carrier channel to form a channel-modulated digital signal matrix;

Secondly, the method of inserting a cyclic guard interval is adopted to eliminate the influence of ISI. According to the usual guard interval requirements (taken here ), for each group of symbol matrices after IFFT transformation, the subsequent The data symbols of the group are copied to the front of the group to form M+1 groups, each group A symbol matrix with a guard interval;

Finally, add noise to the digital symbol matrix.

The process of S4 in this embodiment specifically includes:

First, the digital signal matrix of M+1 groups and each group of N symbols is converted from parallel to serial to form a serial data string comprising N*(M+1) signal symbols;

Next, digital-to-analog conversion is performed at a certain digital-to-analog conversion frequency according to the requirements of the carrier channel frequency to form baseband DQPSK and orthogonal frequency division multiplexing multi-carrier modulated signals;

The relationship between the carrier channel frequency Δf and the channel number N and the digital-to-analog conversion frequency f is as follows:

f=N×Δf (1)

Finally, the baseband signal is up-converted at f ₀ frequency to form a DQPSK with carrier frequency of f ₀ +k×Δf (k=0,1,2,...,N-2,N-1) and OFDM multicarrier modulated signals.

The process of generating baseband DQPSK and OFDM multi-carrier modulated signals is demonstrated as follows:

Take the second group of digital symbols after DQPSK modulation and coding as an example (the first group is the reference phase symbol, which has little reference significance), the second group of digital symbol matrix after DQPSK modulation and coding is a column containing N As a column matrix of digital symbols, according to the definition of complex numbers, digital symbols can be expressed as ( or or or ).

Perform N-point IFFT transformation on the {X _k } sequence, and according to the principle of IFFT transformation, obtain the N-point sequence {x _n } (n=0,1,2,...,N-1) after IFFT transformation

$<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; N</span>}}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In formula (2) is the scaling factor.

It is not difficult to see from the formula that the sequence {x _n }(n=0,1,2,...,N-1) can be regarded as having N sample values of carrier signal x(t), where x(t) is

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; N</span>}}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In formula (3), T is the duration of the symbol. It can be seen that the subcarrier frequency f _k =k/T, k=0,1,2,...,N-1.

In formula (3) Formula (3) can be written as:

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; N</span>}}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formula (4) that the DQPSK phase modulation information has been successfully modulated onto each subcarrier, and the equivalent effect of the modulation is shown in FIG. 4 .

The frequency of D/A transformation is f, then the duration of each point The duration of a set of symbolic N points is So the subcarrier frequency can be obtained as:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

The above process successfully demonstrates the feasibility of the method.

The preferred embodiments of the invention disclosed above are only to help illustrate the invention. The preferred embodiments are not exhaustive in all detail, nor are the inventions limited to specific embodiments described. Obviously, many modifications and variations can be made based on the contents of this specification. This description selects and specifically describes these embodiments in order to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention. The invention is to be limited only by the claims, along with their full scope and equivalents.

Claims (7)

1. A concealed communication waveform generation method based on OFDM, characterized in that, comprising the following steps: S1: Define the total number of channels N of OFDM and the number of channels n of the actual transmission signal for the digital signal, and perform serial-to-parallel conversion grouping according to the number of OFDM carriers and the QPSK signal pattern to form a digital symbol matrix of I and Q dual-channel multi-channel data patterns; S2: Perform phase mapping on the basis of digital symbols in the QPSK signal format, and then generate a signal digital symbol matrix in a DQPSK modulation style; S3: Perform IFFT transformation on the generated complex symbol matrix in DQPSK format, modulate the digital signal onto the corresponding carrier to form a digital multi-carrier symbol matrix, and perform guard interval processing and noise processing on each frame matrix; S4: Perform parallel-to-serial conversion on the digital symbol matrix processed by the guard interval to form a row matrix of transmitted digital symbols, and finally digital-to-analog conversion to form communication signals based on DQPSK and OFDM digital modulation methods. 2. the concealed communication waveform generation method based on OFDM as claimed in claim 1, is characterized in that, the digital symbol matrix of described formation I, Q dual-channel multi-channel data pattern specifically comprises the following two steps: First, according to the dual-channel data pattern, two adjacent signal data bits are grouped into a group; Then, according to the number of OFDM channels, the number of frames and the mode of sending and receiving, the data is serial-to-parallel converted to form a multi-channel digital symbol matrix. 3. the hidden communication waveform generation method based on OFDM as claimed in claim 1, is characterized in that, the specific process of S1 comprises: Determine the total number of OFDM carriers N and the number of actual communication carriers n and frequency f ₀ +k×Δf,k=0,1,2,...,N-2,N-1, and the data sending and receiving style, according to The characteristics of DQPSK and OFDM, data transmission and reception are divided into two styles: The first method is specifically to send the symbols carried by the first N carriers first according to the symbol sequence of the signal, and then send the symbols carried by the next N carriers, and proceed sequentially; The second manner is specifically that the symbols are arranged sequentially according to the first carrier channel, the second carrier channel, . . . , the Nth carrier channel. 4. the concealed communication waveform generation method based on OFDM as claimed in claim 1, is characterized in that, described step S2 specifically comprises the following two steps: First define the mapping relationship between the digital symbol and the phase of the QPSK signal format and calculate the phase difference between adjacent digital symbols: According to a symbol consisting of two bits, the phase of the defined symbol is 0, π, four; Then set the initial phase and calculate the differential phase, and encode the differential phase according to the phase definition to form a digital symbol matrix in DQPSK format; Finally, amplitude and two-channel encoding are performed to form an amplitude-normalized complex symbol matrix. 5. the hidden communication waveform generation method based on OFDM as claimed in claim 1, is characterized in that, step S2 specifically comprises the following steps: Define the mapping relationship between sign and phase: The digital symbols of the QPSK modulation style include four types: 00, 01, 10, and 11. The current mapping relationship is defined as Perform phase mapping on the symbols according to the mapping relationship; Perform differential change coding, specifically including the following steps: First set an initial phase for the first group of phase symbols: now set the initial phase as That is, the differential reference phases of n channels in the first group are Then, the phase of the symbol mapping is used as the differential phase for phase calculation: for example, the mapping phase of the first row and the first column is Then according to the difference principle, the phase of the first channel of the second group is In this way, a total of M+1 groups are obtained, and the phases of n signals in each group; Then perform phase inverse encoding: the phase is inversely encoded into a two-bit code symbol style. According to the principle of I and Q channels, the mapping relationship of phase inverse encoding is: According to this mapping relationship, the phases of each group of n signals in the M+1 group are reverse-coded to form M+1 groups, and a symbol matrix of n two-digit symbols in each group; Finally, the magnitude and quadrature dual-channel transformation of the generated digital symbols are performed: for normalization, the magnitude of the digital symbols is set to That is, each digit sign value is multiplied by At the same time, for each pair of digital symbols, the first one is used as the real part, and the latter one is used as the imaginary part to form a matrix of complex digital symbols. 6. the hidden communication waveform generation method based on OFDM as claimed in claim 1, is characterized in that, S3 specifically comprises the following steps: First, N-point IFFT transformation is performed on the generated M+1 groups of complex digital matrices in units of each group. After the transformation, each symbol of each group is modulated onto the carrier channel from the 1st to the Nth carrier channel in order to form a channel modulation. digital signal matrix; Secondly, the method of inserting a cyclic guard interval is used to eliminate the influence of ISI, and the guard interval is taken as Requirements, for each group of symbol matrix after IFFT transformation, the subsequent The data symbols of the group are copied to the front of the group to form M+1 groups, each group A symbol matrix with a guard interval; Finally, add noise to the digital symbol matrix. 7. the hidden communication waveform generation method based on OFDM as claimed in claim 1, is characterized in that, S4 specifically comprises the following steps: First, the digital signal matrix of M+1 groups and each group of N symbols is converted from parallel to serial to form a serial data string comprising N*(M+1) signal symbols; Next, according to the requirements of the carrier channel frequency, digital-to-analog conversion is performed at a certain digital-to-analog conversion frequency to form baseband DQPSK and orthogonal frequency division multiplexing multi-carrier modulated signals; The relationship between the carrier channel frequency Δf and the channel number N and the digital-to-analog conversion frequency f is as follows: f=N×Δf (1) The baseband signal is up-converted at the _{f 0} frequency to form a DQPSK and positive Cross-frequency division multiplexing of multi-carrier modulated signals.