CN113098653B - Physical layer hidden transmission device and method based on constant envelope signal - Google Patents
Physical layer hidden transmission device and method based on constant envelope signal Download PDFInfo
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- CN113098653B CN113098653B CN202110338342.4A CN202110338342A CN113098653B CN 113098653 B CN113098653 B CN 113098653B CN 202110338342 A CN202110338342 A CN 202110338342A CN 113098653 B CN113098653 B CN 113098653B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
- H04K1/00—Secret communication
- H04K1/02—Secret communication by adding a second signal to make the desired signal unintelligible
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
- H04K1/00—Secret communication
- H04K1/10—Secret communication by using two signals transmitted simultaneously or successively
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- H04L27/00—Modulated-carrier systems
- H04L27/02—Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation
Abstract
The invention relates to a physical layer hidden transmission device and method based on constant envelope signals, and belongs to the field of wireless communication. The impedance switching device is embedded between the constant envelope signal generator and the transmitting antenna to realize the rapid switching of the antenna impedance, so that the envelope of an original signal is changed at a radio frequency transmitting end in an analog keying mode to achieve the aim of realizing the hidden transmission at a physical layer; meanwhile, the invention adds interference signals to the hidden information and encrypts the transmitted hidden information in a multi-antenna mode on the basis of not influencing the original signal demodulation. The invention uses envelope detection, channel estimation and corresponding hidden information decoder to obtain the hidden information after removing the interference signal at the receiving end, and uses constant envelope signal demodulator to obtain the original constant envelope information. The invention has the characteristics of low power consumption, low cost, high concealment and strong anti-interception capability.
Description
Technical Field
The invention relates to a physical layer hidden transmission device and method based on constant envelope signals, and belongs to the field of wireless communication.
Background
The wireless communication technology commonly used in the internet of things includes a Zigbee technology, a Wifi technology, a Bluetooth technology, a LoRa technology, and the like. Among them, the Zigbee technology, the Bluetooth technology, the Lora technology, and the like are all constant envelope signals, and all encode information by changing the phase or frequency of a transmission signal, and the relevant demodulation end demodulates information only by detecting the phase or frequency of the transmission signal. Therefore, these constant envelope signals lack the detection and utilization of the physical layer signal amplitude, and therefore, for these technologies, it is possible to establish a hidden channel by modulating the information of the physical layer signal amplitude, and accomplish the modulation and demodulation of the hidden information without affecting the original signal demodulation.
The existing anti-interception and anti-interference technologies for various constant envelope signals generally adopt a direct sequence spread spectrum technology, a frequency hopping technology and the like to realize low signal level perceptibility or encryption and decryption at a protocol layer, however, because the time of the technologies is relatively early, a plurality of effective countermeasure means exist for the encryption and hiding technologies, and related equipment of the technologies has relatively low concealment and is easy to identify, steal or interfere and destroy. Therefore, it is necessary to design a physical layer hidden transmission apparatus and method capable of realizing effective transmission of hidden information without affecting transmission of original envelope information.
Disclosure of Invention
The invention aims to provide a physical layer hidden transmission device and method based on constant envelope signals, which change the envelope value of the signals in a radio frequency end amplitude keying mode, thereby achieving the purpose of transmitting hidden information by taking the signal envelope as a carrier and realizing low consumption and high reliability of hidden transmission. Meanwhile, the invention adds interference signals to the hidden information and encrypts the transmitted hidden information in a multi-antenna mode on the basis of not influencing the original signal demodulation.
The purpose of the invention is realized by the following technical scheme.
A physical layer concealment transmission apparatus based on a constant envelope signal, comprising: the device comprises a constant envelope signal transmitting module, a hidden information acquiring and modulating module, a control module, an impedance switching module, a constant envelope signal demodulating module, an envelope detecting module, a hidden information extracting module and a hidden information demodulating module.
The device comprises a constant envelope signal transmitting module, a hidden information acquiring and modulating module, a control module, a first impedance switching module and a second impedance switching module, wherein the constant envelope signal transmitting module, the hidden information acquiring and modulating module, the control module, the first impedance switching module and the second impedance switching module form a physical layer hidden information transmitting end; the constant envelope signal demodulation module, the envelope detection module, the hidden information extraction module and the hidden information demodulation module form a physical layer hidden information receiving end.
The constant envelope signal transmitting module is used for generating constant envelope signals of different modulation systems and used as an embedded carrier of the hidden information.
The hidden information acquisition and modulation module acquires hidden information from the outside through other ways, codes and modulates the hidden information into binary bit stream data, and generates corresponding interference signals according to the codes.
The control module is used for converting the hidden information in the form of binary bit stream into an envelope keying signal and controlling the impedance switching module to carry out impedance transformation, thereby changing the envelope value in real time.
The first impedance switching module is used for switching the impedance value of the antenna in real time, so that the antenna sends radio frequency signals to the outside according to different impedances, the signal envelope is changed, and the purpose of modulating the hidden information in the envelope is achieved.
The second impedance switching module is used for switching the impedance value of the antenna in real time, so that the antenna sends radio frequency signals to the outside according to different impedances, the envelope of signals at a receiving end is further changed, interference signals are superposed in the hidden information, and a listener cannot identify the hidden information contained in the envelope.
The constant envelope signal demodulation module is used for demodulating the corresponding constant envelope signal, and the original information in the constant envelope signal can be obtained from the constant envelope signal demodulation module.
The envelope detection module is used for detecting the envelope value of the received signal and obtaining the signal envelope containing the hidden information and the interference signal.
The hidden information extraction module is used for distinguishing and extracting the hidden information from the signal envelope containing the hidden information and the interference signal.
The hidden information demodulation module is used for acquiring the content carried in the extracted hidden information.
Further, the constant envelope signal transmitting module includes: the device comprises a communication data storage and reading module, an information coding module, a protocol framing module and a constant envelope signal modulation module, wherein the modules are connected in an explanation sequence.
Further, the hidden information acquiring and modulating module comprises: the device comprises a hidden information acquisition and storage module, a hidden information coding module and an interference signal generation module, wherein the modules are connected in the description sequence.
Furthermore, the control module comprises a control part of the multi-pole multi-throw radio frequency switch, and the control module acquires a voltage control signal and a switch control signal from the hidden information acquisition and modulation module.
Furthermore, the first impedance switching module and the second impedance switching module both comprise a multi-pole multi-throw switch switching part and a multi-path system impedance, and the impedance value is selected according to the impedance characteristic of the antenna.
Furthermore, the constant envelope signal demodulation module comprises a frame header synchronization module, a demodulation module, a frame decoding module and a decoding module, and all the modules are connected in the order of description.
Further, the envelope detection module comprises an envelope detection module and an envelope extraction module.
Furthermore, the hidden information extraction module comprises an amplitude averaging and sampling module, a channel coefficient estimation module and a hidden signal extraction module, and all the modules are connected in the order of description.
Furthermore, the hidden information demodulation module comprises a threshold decision module and a decoding module.
A physical layer hidden transmission method based on constant envelope signals comprises the following steps:
step one, a hidden information acquisition and storage module continuously acquires hidden information to be transmitted from an environment or an upper computer and stores the hidden information in a register;
step two, the instruction sending computer transmits original information to a constant envelope signal transmitting module, a baseband polarization signal is obtained through information coding, framing and constant envelope modulation, and a constant envelope radio frequency output signal A is obtained through up-conversion;
step three, the instruction sending computer sends a wake-up instruction to the hidden information acquisition and modulation module, the hidden information storage module starts to read stored hidden information from the register, a serial single-bit hidden information data stream B is obtained through the encoding module, and an interference signal C is generated based on the hidden information data stream B;
specifically, when the constant envelope signal transmitting module starts to transmit, the instruction computer instructs the hidden information coding acquisition modulation module to generate an instruction. Upon receiving the instruction, the module reads and encodes the covert information into a frame consisting of a 01 sequence, a preamble, a frame header, the covert information, and redundant cyclic check bits in the order specified. And on the basis of the data structure of the hidden information, a 0 or 1 sequence is correspondingly and randomly generated in the parts of a preamble, a frame header, the hidden information, a redundant cyclic code check bit and the like to form an interference signal C for further carrying out encryption transmission on the hidden information.
And step four, the control module converts the hidden information data stream B into a level signal D1 and converts the interference signal C into a level signal D2. The D1 and D2 are used for controlling the switching of the radio frequency switch so as to realize the modulation of the envelope of the radio frequency end of the constant envelope transmission system signal.
And step five, selecting different types of switches by the impedance switching module according to the signal modulation depth so as to achieve the purpose of converting the signal modulation depth. And different types of switch switching modules are selected according to the requirements of different hidden information transmission rates;
step six, the radio frequency output signal A is subjected to impedance switching, and finally, a radio frequency signal E, F with variable envelope is output and is sent out by an antenna;
specifically, when the first impedance switching module switch is turned off, the branch is turned off, the signal is directly transmitted through the sky, and the power of the branch is 0. The transmission power of the rf signal E may be P1, and the transmission power of the rf signal F may be 0. When the first impedance switch is closed, the branch is closed, if the impedance of the branch is Z1 at this time and the inherent impedance of the antenna is Zc, the transmission power of the radio frequency signal E is (Zc) ^2/(Z1+ Zc) ^2 × P1, and at this time, when the second impedance switch is connected with the antenna, the transmission power of the radio frequency signal F is (Z1) ^2/(Z1+ Zc) ^2 × P1, and when the second impedance switch is grounded, the transmission power of the radio frequency signal F is 0.
Seventhly, receiving the signal E, F by the receiving antenna and dividing the signal into two paths by a splitter, wherein the split signal H1 obtains the sending information of the constant-envelope transmission system through a carrier synchronization module, a frame header synchronization module and a de-framing decoding module;
step eight, obtaining discrete envelope sampling points by the shunt signal H2 through modules of envelope detection and extraction, amplitude averaging, sampling and the like;
step nine, distinguishing and measuring channel coefficients in the transmission process of the concealed signals, and distinguishing and extracting the concealed signals based on the channel coefficients;
the calculation method comprises the following steps: the first transmitting antenna of the transmitting terminal transmits the hidden signal E, the second transmitting antenna transmits the interference signal F, and the order isxi(t) is the signal transmitted by the ith transmitting antenna, alphai、τiAnd thetaiRespectively, the channel gain, delay and angle of arrival of the i-th transmitting antenna transmitted to the receiving end, the values of which are related to the relative positions of the receiver antenna and the two antennas. Wherein, the angle of arrival refers to the angle between the incident path and the vertical direction of the antenna element. The received signal vector can be expressed as:
y(t)＝α1c(θ1)x1(t-τ1)+α2c(θ2)x2(t-τ2)+N(t)
wherein, c (θ)1) And c (theta)2) Is the steering vector of the antenna array, and n (t) is the channel noise during transmission. As can be seen from the above equation, α is the channel gain and the angle of arrival1c(θ1) And alpha2c(θ2) The value of (c) is different. Therefore, the energy of the signal received by the receiving end is different for the antenna 1 and the antenna 2. Therefore, the receiving end can calculate and distinguish the signal energy of the energy detection and the signal energy of the energy detection, and then extracts x from the received signals1(t-τ1) I.e. the concealment signal to be demodulated.
Step ten, according to the coding form of the hidden information, demodulating the hidden signal extracted in the step nine to obtain corresponding hidden information;
advantageous effects
1. The constant envelope signal has the characteristic of constant envelope, and a common receiving end does not demodulate the signal envelope of the constant envelope signal, so that possibility is provided for information hiding. According to the invention, extra signal hiding modulation is carried out on the envelope of the constant envelope transmission system of the common Internet of things at the radio frequency front end, the encryption transmission of the hidden information is completed, the amplitude-frequency orthogonal characteristic of the constant envelope signal is fully utilized, and the frequency band utilization rate is high.
2. Compared with the existing digital quadrature modulation technology, the invention is an analog modulation technology for additionally modulating the radio frequency front-end signal, the additional modulation does not influence the signal structure and the coding mode of the original transmission system, and the hidden information modulation and impedance switching module can be widely applied to the existing mature constant envelope transmission system.
3. Compared with the prior information encryption technology, the invention is a method for hiding the information of the physical layer of the constant envelope signal, the channel where the hidden information is located is orthogonal to the original channel, and the hidden information is not contained in the original information, so the hidden information can not be obtained by a common decoding mode, and the system confidentiality is strong.
4. The invention also adds interference signals aiming at the possible hidden information listeners, the interference signals can not influence the transmission of the original constant envelope signal, but can further modulate the envelope of the transmission signal, so that the hidden information can not be obtained even if a decoding mode aiming at the signal amplitude exists, and the confidentiality of the hidden information is further improved.
Drawings
FIG. 1 is a block diagram of a physical layer hidden transmission apparatus based on a constant envelope signal according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a transmitting end structure of a physical layer concealed transmission device for constant envelope signals according to an embodiment of the present invention;
FIG. 3 is a timing diagram of the transmitting end of the physical layer hidden transmission apparatus for constant envelope signals according to the embodiment of the present invention;
FIG. 4 is a schematic diagram of a receiving end structure of a physical layer concealment transmission apparatus for constant envelope signals according to an embodiment of the present invention;
FIG. 5 is a flowchart of a method for hiding physical layer information of a constant envelope signal according to an embodiment of the present invention;
fig. 6 is a schematic diagram of waveforms of a receiving end in a time domain and a frequency domain according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of an indoor test scenario provided by an embodiment of the present invention;
fig. 8 is a schematic diagram of a bit error rate of a receiving end according to an embodiment of the present invention.
Detailed Description
The invention is further illustrated and described in detail below with reference to the figures and examples.
Example 1:
as shown in fig. 1, the physical layer hidden transmission apparatus based on a constant envelope signal disclosed in this embodiment includes a constant envelope signal transmitting module, a hidden information acquiring and modulating module, a control module, an impedance switching module, a constant envelope signal demodulating module, an envelope detecting module, a hidden information extracting module, and a hidden information decoding module.
The device comprises a physical layer hidden information transmitting end, a physical layer hidden information receiving end, a physical layer hidden information transmitting end, a physical layer hidden information receiving end and a physical layer hidden information receiving end, wherein the physical layer hidden information transmitting end is composed of a constant envelope signal transmitting module, a hidden information acquiring and modulating module, a control module and an impedance switching module, and the physical layer hidden information receiving end is composed of a constant envelope signal demodulating module, an envelope detecting and hidden information decoding module.
The constant envelope signal transmitting module is used for generating constant envelope signals of different modulation systems and used as an embedded carrier of the hidden information.
The hidden information acquisition and modulation module is used for acquiring hidden information from the outside through other ways and encoding and modulating the hidden information into binary bit stream data according to a certain mode.
The control module is used for converting the hidden information in the form of binary bit stream into an envelope keying signal and controlling the impedance switching module to carry out impedance transformation, thereby changing the envelope value in real time.
The first impedance switching module is used for switching the impedance value of the antenna in real time, so that the antenna sends a constant envelope radio frequency signal to the outside according to different impedances, the change of signal envelope is realized, and the aim of hiding the hidden information in the envelope is fulfilled.
The second impedance switching module is used for switching the impedance value of the antenna in real time, so that the antenna sends a constant envelope radio frequency signal to the outside according to different impedances, an interference signal is transmitted, the envelope of a signal at a receiving end is further changed, and the hidden information is further encrypted.
The constant envelope signal demodulation module is used for demodulating the corresponding constant envelope signal, and the original information in the constant envelope signal can be obtained from the constant envelope signal demodulation module.
The envelope detection is used for detecting the envelope value of the received signal and obtaining the signal envelope containing the hidden information and the interference signal.
And the hidden information extraction module is used for acquiring the information carried by the signal amplitude from the envelope value and extracting the hidden signal from the interference information.
And the hidden information demodulation module is used for decoding the extracted hidden signal to acquire corresponding hidden information.
Fig. 2 is a schematic structural diagram of a transmitting end of a hidden transmission apparatus for physical layer of constant envelope signal according to an embodiment of the present invention, and as can be seen from fig. 2, the transmitting end of the hidden transmission apparatus for physical layer of constant envelope signal includes: the device comprises a constant envelope signal transmitting module, a hidden information acquiring and modulating module, a control module and an impedance switching module.
The constant envelope signal transmitting module comprises a communication data storage and reading module, an information coding module, a protocol framing module and a constant envelope signal modulating module. The communication data is stored in a reading module, original sending information is read from an instruction sending computer, and a radio frequency signal with constant envelope characteristic is obtained after specific coding, protocol framing, modulation and up-conversion;
the hidden information acquisition and modulation module comprises a hidden information acquisition and storage module, a hidden information coding module and an interference signal generation module. The hidden information acquisition and storage module acquires hidden information from the outside, performs information coding and scrambling modulation after receiving a computer awakening instruction to obtain a digital bit stream of the hidden information, and correspondingly generates an interference signal at a specified position based on the hidden information;
the control module and the impedance switching module comprise a digital level conversion module, a radio frequency switch and impedances at different levels for switching, the digital level conversion module converts the hidden information in the form of binary bit streams into envelope keying level signals for driving and controlling the radio frequency switch to switch among different impedances, so that the impedance of the transmitting antenna is changed according to the modulation requirement, and the antenna sends a variable envelope signal containing the hidden information to the outside.
The constant envelope signal transmitting module, the constant envelope signal demodulating module and the envelope detecting module adopt a software radio platform of ETTUS company USRP B210.
The hidden information acquisition and modulation module adopts an MSP430G2553 microprocessor chip of TEXAS INSTRUMENT company.
The control module and the impedance switching module adopt an ANALOG DEVICES family HMC radio frequency switch, and different types of radio frequency switches are selected according to different modulation modes and modulation rates of the hidden information, and the control module and the impedance switching module are specifically divided into an SPST radio frequency switch HMC1055, an SPDT radio frequency switch HMC284, an SP4T radio frequency switch HMC241, an SP8T radio frequency switch HMC253 and the like.
FIG. 3 is a timing diagram of the transmitting end of the constant envelope signal physical layer concealment transmission apparatus according to the embodiment of the present invention. When the instruction computer captures the emission of the constant envelope signal, the signal is transmitted to the hidden information acquisition and storage module to read the hidden information. After reading, the hidden information coding module performs coding framing on the hidden information, and meanwhile, the interference signal generating module synchronously generates a random 01 sequence as an interference signal aiming at a lead code, a frame header, hidden information, a cyclic check code and the like of the coding framing.
Fig. 4 is a schematic structural diagram of a receiving end of a hidden transmission apparatus for physical layer of constant envelope signal according to an embodiment of the present invention, and as can be seen from fig. 4, the receiving end of the hidden transmission apparatus for physical layer of constant envelope signal includes: the device comprises a constant envelope signal demodulation module, an envelope detection module and a hidden information decoding module.
The constant envelope signal demodulation module comprises a frame header synchronization module, a demodulation module, a de-framing module and a decoding module, wherein one path of shunt signal received from an antenna is converted into an intermediate frequency signal through down-conversion, and then is subjected to coherent demodulation, de-framing and decoding to obtain original bit information, and original sending information can be obtained from the original bit information;
the envelope detection module comprises an envelope detection module and an envelope extraction module, and the envelope detection module and the envelope extraction module are used for obtaining a signal envelope level containing hidden information and interference signals after the other branch signal received from the antenna passes through the envelope detection module and the envelope extraction module;
the hidden information extraction module comprises an amplitude averaging and sampling module, a channel coefficient estimation module and a hidden signal extraction module, wherein after signal envelope is subjected to amplitude averaging and sampling, channel coefficient estimation is carried out based on the envelope, and then a hidden signal is extracted based on the estimated channel coefficient.
The hidden information demodulation module comprises a threshold decision module and a decoding module, and is used for carrying out environment threshold self-adaptive decision on the extracted hidden information to obtain a corresponding 01 sequence, and correspondingly decoding the 01 sequence to obtain the transmitted hidden information.
The constant envelope signal receiving module employs the software radio platform of ETTUS corporation USRP B210.
Example 2:
the specific implementation process of the present invention is described by taking a standard bluetooth transmission system and a two-path impedance-switched constant envelope signal physical layer hidden transmission device as an example.
The working frequency band of the standard Bluetooth transmission protocol is the ISM frequency band of 2.4GHz, and because more radios work in the frequency band, the Bluetooth transmission system usually adopts a frequency hopping mode to resist interference in the transmission process. The Bluetooth transmission system has 79 frequency points, the carrier frequency is (2402+ k) MHz, and the frequency hopping rate is 1600 hops per second. In the baseband, the Bluetooth transmission system adopts GFSK constant envelope modulation as the modulation mode of the original information, and the information transmission rate is 1 Mb/s.
The system uses a standard Bluetooth transmission system as a constant envelope signal transmitting module, an SPST radio frequency switch HMC1055 and two paths of impedances as impedance switching modules, m sequences are adopted for hidden information modulation, when the Bluetooth transmission system transmits data, the hidden information is framed according to a flow chart shown in figure 3, and the information rate is 1 kHz.
Since the GFSK constant-envelope modulated signal is frequency-conversion modulated, no extra requirements are imposed on the amplitude and phase of the signal. In addition, because the amplitude and the frequency of the GFSK constant envelope modulation signal are in an orthogonal relation, the modulation on the signal frequency does not affect the signal amplitude, and conversely, the modulation on the signal amplitude also does not affect the signal frequency. Therefore, on the premise that the signal transmitting power and the receiving sensitivity meet the normal transmission requirement of the signal, the establishment of the hidden channel in the GFSK signal envelope has feasibility.
As shown in fig. 5, the present embodiment discloses a physical layer hidden transmission method based on a constant envelope signal, which includes the following specific steps:
step one, a GFSK modulation and transmission module generates a Gaussian frequency modulation signal with constant envelope and outputs the Gaussian frequency modulation signal to a radio frequency front end;
and step two, reading the hidden information in the register, generating the hidden information according to the graph shown in fig. 3, obtaining high and low level signals through a level conversion module, and controlling the switch to switch the impedance through the level signals. If the hidden information sequence is 1, the radio frequency switch is in an interruption state, and the alternating current signal I completely passes through the impedance Z1Signal amplitude V1 ═ I × Z1; if the hidden information sequence is 0, the radio frequency switch is in a closed state, part of the alternating current signal I' passes through the impedance Z2 by the branch circuit, and the signal amplitude of the main circuit is changed into V2＝(I-I`)×Z1Causing the signal envelope to fluctuate, such that the hidden information is hidden in the original signal envelope;
step three, the transmitting end synchronously generates interference information according to the diagram shown in fig. 3, and the signals of the branches in the step two are further utilized and modulated through the on-off of the switch, so that the fluctuation of the signal envelope of the receiving end is further caused, and the original information cannot be demodulated even if the change of the signal envelope is detected.
Step three, as shown in fig. 6, a signal time domain waveform received by a receiving end is divided into two paths of signals with the same power and phase by a splitter after receiving a radio frequency transmission signal, wherein one path of signal is subjected to down-conversion, GFSK demodulation and other processes to extract frequency information therein, and original information can be obtained through synchronization, filtering and judgment;
and step four, the other path is specially used for extracting envelope information, and different signal amplitude values before and after switching can be obtained from discrete envelope value sampling points. Due to the existence of the interference signal, the receiving end signal can be represented by the following formula:
y(t)＝h1x1(t-τ1)+h2x2(t-τ2)+N(t)
wherein x1(t-τ1) For the transmitting end of the hidden information, x2(t-τ1) To send outWhen the receiving end and the transmitting end are fixed, the channel coefficients of the receiving end and the transmitting end are both constant. Thus, let h1For transmitting channel coefficients, h, corresponding to antennas for the hidden information2The channel coefficient corresponding to the antenna for transmitting the interference information.
From the above equation, h can be obtained by using the 01 sequence to which no interference information is added in fig. 31Corresponding value, and then through the received signal, find h2The corresponding value.
Step five, based on h1And h2The corresponding value can extract the hidden signal, and the 01 sequence corresponding to the hidden information can be obtained through threshold self-adaptive judgment, and the hidden information can be correspondingly solved according to the coding form of the hidden information, namely the m sequence
Specifically, the present embodiment was tested in an indoor scenario as shown in fig. 7. The power of the transmitting device Tx is set to 10dBm, the receiving power of the receiving device A, B, C, D, E, F, G, H, I is set to 60dB, the modulation depths are set to 0.5, the placing positions are shown in fig. 6, and the corresponding test result hidden information error rate curve is shown in fig. 8. For the bluetooth signal and the hidden information, the A, B, C, D, F, J device can complete demodulation without error, i.e. the error rate is 0. The error rate of the E equipment for the hidden information is 0.52 percent; the bit error rate of the G equipment for the hidden information is 0.032%; the error rate of the device I for the hidden information is 0.81 percent; the bit error rate of the H equipment for the hidden information is 0.91 percent;
under the experimental conditions, the maximum transmission distance of the sending device for sending the hidden information is greater than or equal to 15.44 m. It should be emphasized that, in specific implementation, the transmission distance may be further increased by increasing the received power and increasing the modulation depth, and the security of the transmission of the hidden information may also be ensured by further encrypting the hidden information in the encryption manners such as link encryption, node encryption, end-to-end encryption, and the like.
The transmission of the hidden information can be realized by the physical layer hidden transmission method based on the GFSK modulation signal. Because the information is hidden and demodulated in the transmission process without influencing the modulation and demodulation of the original transmission system, the possibility that the hidden transmission system is discovered is greatly reduced; because the interference signal is added in the transmission process, the possibility that the hidden information is demodulated by the monitoring end is greatly reduced even if a hidden transmission system is found.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention. Variations and modifications in other variations will occur to those skilled in the art upon reading the foregoing description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed, and obviously, many modifications and variations are possible in light of the above teaching.
Claims (5)
1. A physical layer hidden transmission device based on constant envelope signals is characterized in that: the method comprises the following steps: the device comprises a constant envelope signal transmitting module, a hidden information acquiring and modulating module, a control module, an impedance switching module, a constant envelope signal demodulating module, an envelope detecting module, a hidden information extracting module and a hidden information demodulating module;
the constant envelope signal transmitting module, the hidden information acquiring and modulating module, the control module, the first impedance switching module and the second impedance switching module form a physical layer hidden information transmitting end;
the constant envelope signal demodulation module, the envelope detection module, the hidden information extraction module and the hidden information demodulation module form a physical layer hidden information receiving end;
the constant envelope signal transmitting module is used for generating constant envelope signals of different modulation systems and used as an embedded carrier of the hidden information;
the hidden information acquisition and modulation module acquires hidden information from the outside through other ways, codes and modulates the hidden information into binary bit stream data and generates corresponding interference signals according to the codes;
the control module is used for converting the hidden information in the form of binary bit stream into an envelope keying signal and controlling the impedance switching module to carry out impedance transformation so as to change an envelope value in real time;
the first impedance switching module is used for switching the impedance value of the antenna in real time, so that the antenna sends radio frequency signals to the outside according to different impedances, thereby changing and realizing the change of signal envelopes and achieving the purpose of modulating hidden information in the envelopes;
the second impedance switching module is used for switching the impedance value of the antenna in real time, so that the antenna sends radio frequency signals to the outside according to different impedances, the envelope of signals at a receiving end is further changed, and the purposes that interference signals are superposed in hidden information and a listener cannot identify the hidden information contained in the envelope are achieved;
the constant envelope signal demodulation module is used for demodulating a corresponding constant envelope signal, and original information in the constant envelope signal can be obtained from the constant envelope signal demodulation module;
the envelope detection module is used for detecting an envelope value of a received signal and obtaining a signal envelope containing hidden information and an interference signal;
the hidden information extraction module is used for distinguishing and extracting hidden information from a signal envelope containing the hidden information and an interference signal;
the hidden information demodulation module is used for acquiring the content carried in the extracted hidden information.
2. A constant envelope signal based physical layer concealment transmission apparatus as claimed in claim 1, wherein: the constant envelope signal transmitting module includes: the device comprises a communication data storage and reading module, an information coding module, a protocol framing module and a constant envelope signal modulation module, wherein the modules are connected in sequence according to a description;
the hidden information acquisition and modulation module comprises: the device comprises a hidden information acquisition and storage module, a hidden information coding module and an interference signal generation module, wherein all the modules are connected in an explanation sequence;
the control module comprises a control part of the multi-pole multi-throw radio frequency switch, and acquires a voltage control signal and a switch control signal from the hidden information acquisition and modulation module;
the two impedance switching modules comprise a multi-pole multi-throw switch switching part and multi-path system impedance, and the impedance value is selected according to the impedance characteristic of the antenna;
the constant envelope signal demodulation module comprises a frame header synchronization module, a demodulation module, a frame decoding module and a decoding module, and all the modules are connected in the order of description;
the envelope detection module comprises an envelope detection module and an envelope extraction module;
the hidden information extraction module comprises an amplitude averaging and sampling module, a channel coefficient estimation module and a hidden signal extraction module which are connected in sequence according to the description;
the hidden information demodulation module comprises a threshold decision module and a decoding module.
3. A physical layer hidden transmission method based on constant envelope signals is characterized in that: the method comprises the following steps:
step one, a hidden information acquisition and storage module continuously acquires hidden information to be transmitted from an environment or an upper computer and stores the hidden information in a register;
step two, the instruction sending computer transmits original information to a constant envelope signal transmitting module, a baseband polarization signal is obtained through information coding, framing and constant envelope modulation, and a constant envelope radio frequency output signal A is obtained through up-conversion;
step three, the instruction sending computer sends a wake-up instruction to the hidden information acquisition and modulation module, the hidden information storage module starts to read stored hidden information from the register, serial single-bit hidden information B is obtained through the encoding module, and an interference signal C is generated based on the hidden information B;
step four, the first control module converts the hidden information B into a level signal D1; the second control module converts the interference signal C into a level signal D2; the D1 and the D2 are used for controlling the switching of the radio frequency switch so as to realize the modulation of the envelope of the radio frequency end of the constant envelope transmission system signal;
fifthly, selecting different types of radio frequency switches by the impedance switching module according to the signal modulation depth so as to achieve the purpose of converting the signal modulation depth;
step six, the radio frequency output signal A is subjected to impedance switching, and finally, a radio frequency signal E, F with variable envelope is output and is sent out by an antenna;
seventhly, receiving the signal E, F by the receiving antenna and dividing the signal into two paths by a splitter, wherein the split signal H1 obtains the sending information of the constant-envelope transmission system through a carrier synchronization module, a frame header synchronization module and a de-framing decoding module;
step eight, obtaining discrete envelope sampling points by the shunt signal H2 through an envelope detection and extraction module, an amplitude averaging module and a sampling module;
step nine, measuring the discrete envelope sampling points obtained in the step eight, measuring channel coefficients in the transmission process of the concealed signals, and distinguishing and extracting the concealed signals based on the channel coefficients;
the calculation method comprises the following steps: the first transmitting terminal antenna is made to transmit the hidden signal E, the second transmitting antenna is made to transmit the interference signal F, and x is madei(t) is the signal transmitted by the ith antenna, αi、τiAnd thetaiRespectively representing the gain, delay and angle of arrival of the channel transmitted by the ith antenna to the receiving end, alphai、τiAnd thetaiThe value of (c) is related to the relative positions of the receiver antenna and the two antennas; the received signal vector is then expressed as:
y(t)＝α1c(θ1)x1(t-τ1)+α2c(θ2)x2(t-τ2)+N(t)
wherein, c (θ)1) And c (theta)2) Is a steering vector of the antenna array; n (t) is channel noise in the transmission process; due to the difference in channel gain and angle of arrival, α1c(θ1) And alpha2c(θ2) Are different in value; therefore, the energy of the signal received by the receiving end is different for the first antenna and the second antenna; the receiving end calculates and distinguishes signal energy of the first antenna and the second antenna through energy detection, and then extracts x from the received signals1(t-τ1) I.e. the concealment signal to be demodulated;
step ten, according to the coding form of the hidden information, demodulating the hidden signal extracted in the step nine to obtain the corresponding hidden information.
4. A constant envelope signal based physical layer blind transmission method as claimed in claim 3, characterized in that: the concrete implementation method of the third step is as follows: when the constant envelope signal transmitting module starts to transmit, the instruction computer generates an instruction for the hidden information acquiring and modulating module; after receiving the instruction, the module reads and encodes the hidden information into a frame consisting of a 01 sequence, a lead code, a frame header, the hidden information and a redundant cyclic check bit in a description sequence; and on the basis of the data structure of the hidden information, a 0 or 1 sequence is correspondingly and randomly generated in the preamble, the frame header, the hidden information and the redundant cyclic code check bit part to form an interference signal C for further carrying out encryption transmission on the hidden information.
5. A constant envelope signal based physical layer blind transmission method as claimed in claim 3, characterized in that: the concrete implementation method of the sixth step is as follows: when the first impedance switching module switch is switched off, the branch is switched off, the signal is directly transmitted through the antenna, and the power of the branch is 0; let the transmission power of the rf signal E be P1 and the transmission power of the rf signal F be 0; when the first impedance switch is closed, the branch is closed, if the impedance of the branch is Z1 at this time and the inherent impedance of the antenna is Zc, the transmission power of the radio frequency signal E is (Zc) ^2/(Z1+ Zc) ^2 × P1, and at this time, when the second impedance switch is connected with the antenna, the transmission power of the radio frequency signal F is (Z1) ^2/(Z1+ Zc) ^2 × P1, and when the second impedance switch is grounded, the transmission power of the radio frequency signal F is 0.
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