A secure communication system for encrypting OFDM signals

Abstract

A secure communication system for encrypting OFDM signals. The transmitting end includes n channels. Each channel generates intensity chaos through optical feedback, forms a complex symbol sequence through QAM modulation, and converts it into parallel symbols. The symbols in the frequency domain are converted to the time domain and modulated onto the chaotic carrier output by the laser. The optical signal output by the intensity modulator passes through two phase modulators and then enters the optoelectronic oscillator loop, where the phase change is converted into an intensity change and then into a radio frequency signal. After amplification, the two optical signals are phase-modulated respectively to generate phase-chaotic and intensity-chaotic optical signals. The n-channel signals are coupled into one channel and sent to the receiving end, and then divided into n channels. Each channel passes through two optoelectronic oscillator loops to generate an anti-phase phase shift to cancel the phase chaos. Then, the chaotic signal and the intensity chaos are converted into electrical signals and subtracted to separate the OFDM symbols. The symbols in the frequency domain are converted to the time domain, passed through a pilot cyclic prefixer, and then through a serial-parallel converter to convert the parallel symbols into serial symbols, and the original information is restored.

Description

Technical Field

[0001] The present invention belongs to the technical field of secure communication and information security in chaotic communication networks, and particularly relates to a secure communication system for encrypting OFDM signals. Background Art

[0002] Chaos is a random phenomenon of a deterministic system, sensitive to initial values, and is widely used in secure communication and image encryption. Orthogonal frequency division multiplexing technology (OFDM) makes full use of frequency band resources. It is a technology that uses mutually orthogonal multi-subcarriers. First, the information is modulated by quadrature amplitude modulation (M-QAM) or phase shift keying (M-PSK), and then modulated onto each subcarrier. The signal is mapped into complex symbols, and the inverse fast Fourier transform (IFFT) is used to convert the signal into a time-domain signal. After adding pilots and cyclic prefixes, through digital-to-analog conversion and up-conversion, using an intensity modulator, it is modulated onto the chaotic optical signal on the intensity modulator, and then transmitted through an optical fiber channel.

[0003] In the prior art, chaotic communication generally uses digital information to modulate the bias current to achieve information encryption, and the digital information itself carries noise, which will have a negative impact on the signal-to-noise ratio of the system, thereby increasing the bit error rate. Summary of the Invention

[0004] The existing OFDM-PON technology is not conducive to chaotic carrier communication. In chaotic communication, the modulated signal is a binary digital signal (that is, chaotic communication uses digital information to modulate the bias current to achieve information encryption, and the digital information itself carries noise, which will have a negative impact on the signal-to-noise ratio of the system, thereby increasing the bit error rate). In view of these deficiencies of the prior art, the present invention provides a secure communication system for encrypting OFDM signals.

[0005] In the QAM modulation module (QAM modulator: MAX5852 module) of the present invention, the digital signal is converted into in-phase and quadrature complex signals, and through a serial-to-parallel conversion circuit, it becomes a parallel signal and is output to the OFDM modulation module (the OFDM modulation chip is preferably the DSS7700 chip). The OFDM modulation module generates OFDM symbols, and through a parallel-to-serial conversion circuit, it becomes a serial signal, and using an intensity modulator, it is modulated onto the chaotic optical signal on the intensity modulator. Here, the bias current of the laser is set, so that the feedback laser generates intensity chaos, and then it is transmitted to the optoelectronic oscillation loop, so that the signal has the characteristics of both intensity chaos and phase chaos. The phase chaos generator composed of the optoelectronic oscillation loop is different from the existing oscillation loop. When converting the optical signal into an electrical signal, the optical signal is divided into two paths, one of which is delayed, and then the two signals are added. Its advantage is that it can hide the time delay signature.

[0006] The receiving end of the present invention is a synchronous optoelectronic oscillation loop that generates phase chaos opposite to that of the transmitting end, thereby canceling out the chaotic phase in the received signal. Then, it subtracts the chaos generated by the laser in the receiving end through optoelectronic conversion to demodulate the OFDM signal. The OFDM demodulation module (OFDM demodulation chip: DSS7700 chip) converts the received information into frequency-domain information through down-conversion, removing the pilot and cyclic prefix, and using the fast Fourier transform (FFT). Then, using coherent demodulation and the mapping relationship, the original information is demodulated by the QAM demodulation module.

[0007] To achieve the above invention objective, the present invention adopts the following technical solutions:

[0008] A secure communication system for encrypting OFDM signals includes a transmitting end and a receiving end, which are connected by an optical fiber. Its structure is as follows:

[0009] The transmitting end includes n paths with the same structure. The structure of the nth path is as follows: The nth mirror is connected to the nth semiconductor laser. The chaotic signal output by the nth semiconductor laser is injected into the nth intensity modulator through an optical fiber. The nth QAM modulation module is connected to the nth OFDM modulation module. The signal output by the nth OFDM modulation module is connected to the nth intensity modulator. The nth intensity modulator is connected to the (2n - 1)th phase modulator. The (2n - 1)th phase modulator is connected to the (2n - 1)th optical coupler. One port of the (2n - 1)th optical coupler is connected to the 2nth phase modulator. The 2nth phase modulator is connected to the (2n - 1)th Mach-Zehnder interferometer through a delay optical fiber. The (2n - 1)th Mach-Zehnder interferometer is connected to the 2nth optical coupler. One port of the 2nth optical coupler is connected to the 2nth photodetection module of the dual PD (photodetector). The 2nth photodetection module of the dual PD is connected to the 2nth radio frequency amplifier. The signal output by the 2nth radio frequency amplifier modulates the phase of the optical chaos signal in the 2nth phase modulator. One port of the 2nth optical coupler is connected to the 2nth Mach-Zehnder interferometer through a delay optical fiber. The 2nth Mach-Zehnder interferometer is connected to the (2n - 1)th photodetection module of the dual PD. The (2n - 1)th photodetection module is connected to the (2n - 1)th radio frequency amplifier. The signal output by the (2n - 1)th radio frequency amplifier modulates the phase of the optical chaos signal in the (2n - 1)th phase modulator. After the optical chaos signal in the (2n - 1)th phase modulator is input into the (2n - 1)th optical coupler, the other end of the (2n - 1)th optical coupler is connected to a multiplexer through an optical fiber. There are n paths of signals multiplexed into the multiplexer, and the signals are combined into one path and sent to the receiving end through an optical fiber.

[0010] The receiving end routes the signals according to wavelengths through a demultiplexer, and divides the signals into n paths with the same structure. The structure of the nth path is as follows: the nth interface of the demultiplexer is connected to the 4n - 1 coupler; one port of the 4n - 1 coupler is connected to the 4n - 1 phase modulator; the 4n - 1 phase modulator is connected to the 4n coupler; one port of the 4n coupler is connected to the 4n - 1 Mach - Zehnder interferometer through a delay fiber; the 4n - 1 Mach - Zehnder interferometer is connected to the 4n - 1 photodetector; the 4n - 1 photodetector is connected to the 4n - 1 radio frequency amplifier; the 4n - 1 radio frequency amplifier is connected to the 4n - 1 phase modulator; the other port of the 4n coupler is connected to the 4n Mach - Zehnder interferometer through a delay fiber; the 4n Mach - Zehnder interferometer is connected to the 4n photodetection module; the 4n photodetection module is connected to the 4n radio frequency amplifier; the 4n radio frequency amplifier is connected to the 4n phase modulator; one port of the 4n - 1 coupler is connected to the left port of the 4n phase modulator; the signal output by the 4n radio frequency amplifier phase - modulates the optical signal from the 4n - 1 coupler in the 4n phase modulator. Due to the synchronization effect, the generated antiphase cancels the chaotic phase in the optical signal from the 4n - 1 coupler, so that the signal that is both intensity - chaotic and phase - chaotic becomes intensity - chaotic. In the signal recovery structure, the 4n phase modulator is connected to the nth beam splitter; one port of the nth beam splitter is connected to the nth circulator; the nth circulator is connected to the 2n laser; the 2n laser is connected to the 2n mirror; the other port of the nth beam splitter is connected to the 2n - 1 photodetector of the single PD; the 2n - 1 photodetector of the single PD is connected to the nth subtractor; the other end of the nth subtractor is connected to the 2n single - PD photodetector; the 2n single - PD photodetector is connected to the nth circulator. In this way, the OFDM signal is recovered through the subtractor. In the OFDM demodulation module (the OFDM demodulation chip preferably uses the DSS7700 chip), through down - conversion, removing the pilot and cyclic prefix, and using the fast Fourier transform (FFT), the received information is converted into frequency - domain information, and then using coherent demodulation and the mapping relationship, the original information is demodulated in the QAM demodulation module.

[0011] Aiming at the deficiencies of the prior art, in the present invention, when encrypting information, instead of modulating the bias current with digital information, the information is modulated by quadrature amplitude modulation (M - QAM) or phase - shift keying (M - PSK) in the electrical domain, and then modulated onto each sub - carrier, mapping the signal into complex symbols. Using the inverse fast Fourier transform (IFFT), the signal is converted into a time - domain signal, adding a pilot and a cyclic prefix, and then through digital - to - analog conversion and up - conversion, using an intensity modulator, it is modulated onto each path of chaotic optical signals on the intensity modulator, and then transmitted to an improved optoelectronic oscillation loop to generate phase and intensity chaos, thereby further increasing the complexity of encryption and improving the security of communication.

[0012] As a preferred solution, the splitting ratio of the optical coupler is 1:1.

[0013] As a preferred solution, the channel spacing between the multiplexer and the demultiplexer is 2 nm.

[0014] As a preferred solution, the corresponding chaotic semiconductor lasers are at the transmitting end and the receiving end, and the optoelectronic oscillation loop is in a synchronous state before the signal is transmitted.

[0015] As a preferred solution, at the transmitting end, the bias current of all lasers is 20 mA.

[0016] As a preferred solution, at the transmitting end, in the QAM modulation module, the formed complex symbol sequence is converted from a serial symbol sequence to a parallel symbol stream by the serial-to-parallel conversion circuit therein; then in the OFDM modulation module, the inverse fast Fourier transform is performed using the IFFT converter to transform the symbols in the frequency domain to the time domain.

[0017] As a preferred solution, at the transmitting end, the time-domain symbols output by the IFFT converter are converted into a serial signal in the OFDM modulation module through the parallel-to-serial conversion circuit, a cyclic prefix is added, and intensity modulation is applied to the chaotic carrier output by the semiconductor laser.

[0018] As a preferred solution, at the transmitting end, the optical signal output by the intensity modulator passes through two phase modulators and then enters the optoelectronic oscillation loop. The Mach-Zehnder interferometer converts the phase change into an intensity change, and then the optoelectronic detector module of the dual PD converts it into a radio frequency signal. After amplification, the optical signals in the two phase modulators are phase-modulated respectively, thereby generating phase-chaotic and intensity-chaotic optical signals.

[0019] As a preferred solution, at the transmitting end, n optical signals with phase chaos and intensity chaos are coupled into the multiplexer, synthesized into one path and then sent to the receiving end.

[0020] As a preferred solution, at the receiving end, the demultiplexer routes the signal into n paths according to the wavelength and sends them to two optoelectronic oscillation loops symmetric to the transmitting end respectively, generating an anti-phase phase shift to cancel the phase chaos.

[0021] As a preferred solution, at the receiving end, the chaotic signal from the local chaotic semiconductor laser and the intensity chaos with dephased chaos from the phase modulator are converted into an electrical signal by the PD, and subtracted using a subtractor to separate the OFDM symbols.

[0022] As a preferred solution, at the receiving end, in the OFDM demodulation module, the inverse fast Fourier transform is performed using the FFT converter to transform the symbols in the frequency domain to the time domain. After removing the pilot cyclic prefix, the parallel-to-serial converter converts the parallel symbols into serial symbols.

[0023] As a preferred solution, at the receiving end, in the QAM demodulation module, the serial symbols are restored to the original information according to the mapping rule.

[0024] The principle and process of a secure communication system for encrypting OFDM signals of the present invention are as follows: At the transmitting end, it includes n paths with the same structure. In each path, a mirror is connected to a semiconductor laser to realize optical feedback on the semiconductor laser and generate intensity chaos. At the transmitting end, the complex symbol sequence formed by the QAM modulation module is converted into a parallel symbol stream by the serial-to-parallel conversion circuit therein; then in the OFDM modulation module, using the IFFT transformer, an inverse fast Fourier transform is performed to transform the symbols in the frequency domain to the time domain. Through the parallel-to-serial conversion circuit, it is converted into a serial signal, a cyclic prefix is added, and intensity modulation is performed on the chaotic carrier output by the semiconductor laser. The optical signal output by the intensity modulator passes through two phase modulators and then enters the optoelectronic oscillator loop. The Mach-Zehnder interferometer converts the phase change into an intensity change, and then it is converted into a radio frequency signal by the optoelectronic detector module of the dual PD. After amplification, the optical signals in the two phase modulators are phase-modulated respectively, thereby generating phase-chaotic and intensity-chaotic optical signals. Its advantage is that it can hide the delay information, making it impossible for attackers to synchronize the chaotic system. In this way, the n paths of phase-chaotic and intensity-chaotic optical signals are coupled into a multiplexer, synthesized into one path and then sent to the receiving end.

[0025] At the receiving end, the signal is divided into n paths by the demultiplexer according to the wavelength routing and sent to two optoelectronic oscillator loops symmetric to the transmitting end respectively to generate an anti-phase phase shift and cancel the phase chaos. Then, the chaotic signal from the local chaotic semiconductor laser and the intensity chaos of the de-phased chaos from the phase modulator are converted into an electrical signal by the PD, and subtracted by the subtractor to separate the OFDM symbol. In the OFDM demodulation module, using the FFT transformer, an inverse fast Fourier transform is performed to transform the symbols in the frequency domain to the time domain. After removing the pilot cyclic prefix, the parallel-to-serial converter converts the parallel symbols into serial symbols. Transmitted to the QAM demodulation module, the original information can be restored according to the mapping rule for the serial symbols.

[0026] The present invention constructs a phase chaos generator composed of an optoelectronic oscillation loop. Different from the existing oscillation loops, when converting an optical signal into an electrical signal, the optical signal is divided into two paths, one of which is delayed, and then the two signals are added. Its advantage is that it can hide the time delay signature. Here, the generated OFDM symbol is modulated onto the chaotic optical signal of the intensity modulator by using the intensity modulator, and at the same time, the feedback laser generates intensity chaos and then transmits it to the optoelectronic oscillation loop. In this way, the signal has both the characteristics of intensity chaos and phase chaos. At the receiving end, the synchronized optoelectronic oscillation loop generates phase chaos that is opposite to the phase at the transmitting end, so as to cancel the chaotic phase in the received signal, and then subtract it from the chaos generated by the laser at the receiving end through optoelectronic conversion to demodulate the OFDM signal. Then, through down-conversion, removing the pilot and cyclic prefix, and using the fast Fourier transform (FFT), the received information is converted into frequency-domain information, and then the original information is demodulated by using coherent demodulation and the mapping relationship.

[0027] It is also an innovation of the present invention to modulate the optical signal output by the laser at the transmitting end by using the OFDM signal intensity. The technology of the present invention has a wide range of applications, such as secure access to the Internet of Things, secure transmission of broadcast images and videos, etc.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The present invention realizes the secure communication of encrypted OFDM signals. Its security lies in: using a chaotic laser to generate a chaotic signal, hiding the OFDM information in the chaotic carrier. Further, using an optoelectronic oscillation loop to generate phase chaos, further enabling the signal to be well hidden in the carrier, and the chaotic system can hide the delay information, making it impossible for attackers to synchronize the chaotic system. In this way, eavesdroppers cannot separate the transmitted signal. Therefore, the encryption technology of the present invention has strong security. Description of the Drawings

[0030] Figure 1 It is the architecture diagram of a secure communication system for encrypting OFDM signals according to an embodiment of the present invention.

[0031] Figure 2 (a) is the constellation diagram before encryption according to an embodiment of the present invention, Figure 2 (b) is the constellation diagram after encryption according to an embodiment of the present invention. As shown in the figure, the transmitted information cannot be recovered from the encrypted constellation diagram.

[0032] Figure 3 It is the constellation diagram recovered at the receiving end after the OFDM encryption communication system according to an embodiment of the present invention passes through the Rayleigh channel.

[0033] Figure 4 (a) The original signal transmitted by the first path, Figure 4 (b) is the demodulated signal.

[0034] Wherein:

[0035] The first mirror 1-1, …, the nth mirror 1-n, the first chaotic laser 2-1, …, the nth chaotic laser 2-n, the first QAM modulation module 3-1, …, the nth QAM modulation module 3-n, the first OFDM modulation module 4-1, …, the nth OFDM modulation module 4-n, the first intensity modulator 12-1, …, the nth intensity modulator 12-n, the first phase modulator 5-1, …, the 2nth phase modulator 5-2n, the first Mach-Zehnder interferometer 7-1, …, the 2nth Mach-Zehnder interferometer 7-2n, the first optical coupler 6-1, …, the 2nth optical coupler 6-2n, the first dual-PD photodetector module 8-1, …, the 2nth dual-PD photodetector module 8-2n, the first RF amplifier 9-1, …, the 2nth RF amplifier 9-2n, and a multiplexer 10; n is a positive integer (n≥1).

[0036] A demultiplexer 11, the (n + 1)th mirror 1-(n + 1), …, the 2nth mirror 1-2n, the (n + 1)th chaotic laser 2-(n + 1), …, the 2nth chaotic laser 2-2n, the (2n + 1)th phase modulator 5-(2n + 1), …, the 4nth phase modulator 5-4n, the (2n + 1)th Mach-Zehnder interferometer 7-(2n + 1), …, the 4nth Mach-Zehnder interferometer 7-4n, the (2n + 1)th optical coupler 6-(2n + 1), …, the 4nth optical coupler 6-4n, the (2n + 1)th dual-PD photodetector module 8-(2n + 1), …, the 4nth dual-PD photodetector module 8-4n, the (2n + 1)th RF amplifier 9-(2n + 1), …, the 4nth RF amplifier 9-4n, the first single-PD photodetector 13-1, …, the 2nth single-PD photodetector 13-2n, the first subtractor 14-1, …, the nth subtractor 14-n, the first OFDM demodulation module 15-1, …, the nth OFDM demodulation module 15-n, the first QAM demodulation module 16-1, …, the nth QAM demodulation module 16-n, the first beam splitter 17-1, …, the nth beam splitter 17-n, the first circulator 18-1, …, the nth circulator 18-n. Detailed implementation manners

[0037] To more clearly illustrate the embodiments of the present invention, the following will describe the specific implementation manners of the present invention with reference to the accompanying drawings. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings, and other implementation manners can also be obtained.

[0038] In a preferred embodiment of the present invention, a secure communication system for encrypted OFDM signals of multiple users (modulating different information onto different chaotic carriers and then synthesizing them into one path) includes a transmitting end and a receiving end, and the transmitting end and the receiving end communicate through an optical fiber channel.

[0039] Specifically, the transmitting end includes a first mirror, …, an nth mirror, a first chaotic laser, …, an nth chaotic laser, a first QAM modulation module, …, an nth QAM modulation module, a first OFDM modulation module, …, an nth OFDM modulation module, a first intensity modulator, …, an nth intensity modulator, a first phase modulator, …, a 2nth phase modulator, a first Mach-Zehnder interferometer, …, a 2nth Mach-Zehnder interferometer, a first optical coupler, …, a 2nth optical coupler, a first dual-PD photodetector module, …, a 2nth dual-PD photodetector module, a first radio frequency amplifier, …, a 2nth radio frequency amplifier, and a combiner.

[0040] The receiving end includes a demultiplexer, an (n + 1)th mirror, …, a 2nth mirror, an (n + 1)th chaotic laser, …, a 2nth chaotic laser, a (2n + 1)th phase modulator, …, a 4nth phase modulator, a (2n + 1)th Mach-Zehnder interferometer, …, a 4nth Mach-Zehnder interferometer, a (2n + 1)th optical coupler, …, a 4nth optical coupler, a (2n + 1)th dual-PD photodetector module, …, a 4nth dual-PD photodetector module, a (2n + 1)th radio frequency amplifier, …, a 4nth radio frequency amplifier, a first single-PD photodetector, …, a 2nth single-PD photodetector, a first subtractor, …, an nth subtractor, a first OFDM demodulation module, …, an nth OFDM demodulation module, a first QAM demodulation module, …, an nth QAM demodulation module, a first beam splitter, …, an nth beam splitter.

[0041] The receiving end and the transmitting end are connected through two optical fiber channels.

[0042] A secure communication system for encrypted OFDM signals of multiple users according to the present invention is specifically as follows:

[0043] The transmitting end includes n paths with the same structure. Taking the first path as an example, the first mirror is connected to the first semiconductor laser to achieve optical feedback to the semiconductor laser, generating intensity chaos. At the transmitting end, the complex symbol sequence formed by the first QAM modulation module is converted from a serial symbol sequence to a parallel symbol stream through the serial-to-parallel conversion circuit therein; then in the first OFDM modulation module, using the IFFT transformer, an inverse fast Fourier transform is performed to transform the symbols in the frequency domain to the time domain. Through the parallel-to-serial conversion circuit, it is converted into a serial signal, a cyclic prefix is added, and intensity modulation is performed on the chaotic carrier output by the semiconductor laser. The optical signal output by the first intensity modulator passes through the first and second phase modulators and then enters two optoelectronic oscillation loops through the second optical coupler. The phase change is converted into an intensity change by the first and second Mach-Zehnder interferometers, and then converted into a radio frequency signal by the first and second dual-PD optoelectronic detector modules. After amplification, the optical signals in the first and second phase modulators are respectively phase-modulated, thereby generating phase-chaotic and intensity-chaotic optical signals. Its advantage is that it can hide delay information, making it impossible for attackers to synchronize the chaotic system. In this way, n paths of phase-chaotic and intensity-chaotic optical signals are coupled into a multiplexer, synthesized into one path and then sent to the receiving end.

[0044] At the receiving end, the demultiplexer divides the signal into n paths according to wavelength routing. Taking the first path as an example, the first interface of the demultiplexer is connected to the third coupler. A part of the optical signal is input into the third phase modulator, and the other part is input into the third Mach-Zehnder interferometer through the delay fiber, converting the phase change into an intensity change, and then injected into the third dual-PD photodetector, which is converted into an electrical signal and amplified by the third RF amplifier to perform phase modulation on the signal in the third phase modulator; one port of the fourth coupler inputs the signal into the fourth Mach-Zehnder interferometer through the delay fiber, converting the phase change into an intensity change, input into the fourth dual-PD photodetection module, amplified by the fourth RF amplifier, and modulating the optical signal in the fourth phase modulator; the other port of the fourth coupler outputs the signal to the fourth phase modulator, and the signal output by the fourth RF amplifier performs phase modulation on the optical signal from the third coupler in the fourth phase modulator. Due to the synchronization effect, the generated anti-phase phase cancels the chaotic phase in the optical signal from the third coupler, so that the signal that is both intensity chaotic and phase chaotic becomes intensity chaotic. During the signal recovery process, the signal output by the fourth phase modulator is transmitted to the first beam splitter. A part of the optical signal of the first beam splitter is transmitted to the second laser through the first circulator, and the second laser is fed back through the second mirror to generate chaos. Another part of the first beam splitter is converted into an electrical signal by the first photodetector of the single PD and transmitted to the first subtractor; the chaotic signal generated by the second laser at the local receiving end is transmitted to the second single-PD photodetector through the first circulator, converting the optical signal into an electrical signal. In this way, through the subtractor, the OFDM signal is recovered. In the OFDM demodulation module (OFDM demodulation chip: DSS7700 chip), through down-conversion, removing the pilot and cyclic prefix, using the fast Fourier transform (FFT), the received information is converted into frequency-domain information, and then using coherent demodulation and the mapping relationship, the original information is demodulated in the QAM demodulation module. At the receiving end, after the optical signal passes through the demultiplexer, it is transmitted to two optoelectronic oscillation loops symmetric to the transmitting end, generating an anti-phase phase shift to cancel the phase chaos. Then, the chaotic signal from the local chaotic semiconductor laser and the intensity chaos of the dephased chaos from the phase modulator are converted into electrical signals by the PD, and subtracted using the subtractor to separate the OFDM symbol. In the OFDM demodulation module, using the FFT converter, the inverse fast Fourier transform is performed to transform the symbol in the frequency domain to the time domain. After removing the pilot cyclic prefixer, the serial-parallel converter converts the parallel symbol into a serial symbol. Transmitted to the QAM demodulation module, the original information can be recovered according to the mapping rule for the serial symbol.

[0045] The above completes the secure communication process of the encrypted OFDM signal for multiple users.

[0046] Such as Figure 1As shown in the figure, a secure communication system for multi-user encrypted OFDM signals in this embodiment includes a receiving end and a transmitting end, and the receiving end and the transmitting end are connected by an optical fiber. The specific structural relationship of the secure communication system in this embodiment is as follows.

[0047] The transmitting end includes the 1st mirror 1-1, …, the nth mirror 1-n, the 1st chaotic laser 2-1, …, the nth chaotic laser 2-n, the 1st QAM modulation module 3-1, …, the nth QAM modulation module 3-n, the 1st OFDM modulation module 4-1, …, the nth OFDM modulation module 4-n, the 1st intensity modulator 12-1, …, the nth intensity modulator 12-n, the 1st phase modulator 5-1, …, the 2nth phase modulator 5-2n, the 1st Mach-Zehnder interferometer 7-1, …, the 2nth Mach-Zehnder interferometer 7-2n, the 1st optical coupler 6-1, …, the 2nth optical coupler 6-2n, the 1st dual-PD photodetector module 8-1, …, the 2nth dual-PD photodetector module 8-2n, the 1st RF amplifier 9-1, …, the 2nth RF amplifier 9-2n, and a multiplexer 10.

[0048] The transmitting end includes n paths with the same structure. Taking the first path as an example to illustrate the connection relationship, the structure of the first path is as follows: The first mirror 1 is connected to the left end of the first semiconductor laser 2-1. The chaotic signal output from the right end of the first semiconductor laser 2-1 is injected into the first intensity modulator 12-1 through an optical fiber. The first QAM modulation module 3-1 is connected to the first OFDM modulation module 4-1. The output signal of the first OFDM modulation module 4-1 is input to the first intensity modulator 12-1. The first intensity modulator 12-1 is connected to the first phase modulator 5-1. The first phase modulator 5-1 is connected to the first optical coupler 6-1. One port of the first optical coupler 6-1 is connected to the second phase modulator 5-2. The second phase modulator 5-2 is connected to the second Mach-Zehnder interferometer 7-1 through a delay optical fiber and is connected to the second optical coupler 6-2. One port of the second optical coupler 6-2 is connected to the second photodetector module 8-2 of the dual PD (photodetector). The second photodetector module 8-2 of the dual PD is connected to the second radio frequency amplifier 9-2. The output signal of the second radio frequency amplifier 9-2 phase-modulates the optical chaotic signal in the second phase modulator 5-2. The other port of the second optical coupler 6-2 is connected to the second Mach-Zehnder interferometer 7-2 through a delay optical fiber. The second Mach-Zehnder interferometer 7-2 is connected to the first photodetector module 8-1 of the dual PD. The first photodetector module 8-1 is connected to the first radio frequency amplifier 9-1. The output signal of the first radio frequency amplifier 9-1 phase-modulates the optical chaotic signal in the first phase modulator 5-1. After the optical chaotic signal in the first phase modulator 5-1 is input to the first optical coupler 6-1, the other end of the first optical coupler 6-1 is connected to the multiplexer 1 through an optical fiber. There are n such paths of signals multiplexed into the multiplexer 10, and the signals are combined into one path and sent to the receiving end through an optical fiber.

[0049] The receiving end includes: a demultiplexer 11, an (n + 1)th mirror 1-(n + 1), …, a 2nth mirror 1-2n, an (n + 1)th chaotic laser 2-(n + 1), …, a 2nth chaotic laser 2-2n, a (2n + 1)th phase modulator 5-(2n + 1), …, a 4nth phase modulator 5-4n, a (2n + 1)th Mach-Zehnder interferometer 7-(2n + 1), …, a 4nth Mach-Zehnder interferometer 7-4n, a (2n + 1)th optical coupler 6-(2n + 1), …, a 4nth optical coupler 6-4n, a (2n + 1)th dual-PD photodetector module 8-(2n + 1), …, a 4nth dual-PD photodetector module 8-4n, a (2n + 1)th RF amplifier 9-(2n + 1), …, a 4nth RF amplifier 9-4n, a first single-PD photodetector 13-1, …, a 2nth single-PD photodetector 13-2n, a first subtractor 14-1, …, an nth subtractor 14-n, a first OFDM demodulation module 15-1, …, an nth OFDM demodulation module 15-n, a first QAM demodulation module 16-1, …, an nth QAM demodulation module 16-n, a first beam splitter 17-1, …, an nth beam splitter 17-n, a first circulator 18-1, …, an nth circulator 18-n.

[0050] The receiving end includes n paths with the same structure. Taking the first path as an example to illustrate the connection relationship, the receiving end routes the signals according to wavelengths through a demultiplexer 11 and divides the signals into n paths with the same structure for transmission. Taking the first path as an example to illustrate the connection relationship, the structure of the first path is as follows: The first interface of the demultiplexer 11 is connected to the third optical coupler 6-3. One port of the third coupler 6-3 is connected to the third phase modulator 5-3. The third phase modulator 5-3 is connected to the fourth coupler 6-4. One port of the fourth coupler 6-4 is connected to the third Mach-Zehnder interferometer 7-3 through a delay fiber. The third Mach-Zehnder interferometer 7-3 is connected to the third photoelectric detection module 8-3 of the dual PD. The third photoelectric detection module 8-3 of the dual PD is connected to the third radio frequency amplifier 9-3. The third radio frequency amplifier 9-3 is connected to the third phase modulator 5-3. The other port of the fourth coupler 6-4 is connected to the fourth Mach-Zehnder interferometer 7-4 through a delay fiber. The fourth Mach-Zehnder interferometer 7-4 is connected to the fourth photoelectric detection module 8-4 of the dual PD. The fourth photoelectric detection module 8-4 of the dual PD is connected to the fourth radio frequency amplifier 9-4. The fourth radio frequency amplifier 9-4 is connected to the fourth phase modulator 5-4. The other port of the third coupler 6-3 is connected to the left port of the fourth phase modulator 5-4. The signal output by the fourth radio frequency amplifier 9-4 phase-modulates the optical signal from the third coupler in the fourth phase modulator 5-4. Due to the synchronization effect, the generated antiphase cancels the chaotic phase in the optical signal from the third coupler 6-3, thus changing the signal that is both intensity-chaotic and phase-chaotic into intensity-chaotic. In the signal recovery structure, the fourth phase modulator 5-4 is connected to the first beam splitter 17-1. One port of the first beam splitter 17-1 is connected to the first circulator 18-1. The first circulator 18-1 is connected to the second laser 2-2. The second laser 2-2 is connected to the second mirror 1-2. The other port of the first beam splitter 17-1 is connected to the first photodetector 13-1 of the single PD. The first photodetector 13-1 of the single PD is connected to the first subtractor 14-1. The other end of the first subtractor 14-1 is connected to the second single-PD photodetector 13-2. The second single-PD photodetector 13-2 is connected to the first circulator 18-1. In this way, the OFDM signal is recovered through the subtractor 14-1. The subtractor 14-1 is connected to the OFDM demodulation module 15-1. The OFDM demodulation module 15-1 is connected to the QAM demodulation module 16-1. In the OFDM demodulation module 15-1 (OFDM demodulation chip: DSS7700 chip), through down-conversion, removing the pilot and cyclic prefix, using the fast Fourier transform (FFT), the received information is converted into frequency-domain information, and then through coherent demodulation and the mapping relationship, the original information is demodulated in the QAM demodulation module 16-1.

[0051] The principle of the secure communication system of this embodiment will be described below in conjunction with the above system structure.

[0052] The receiving end and the sending end are connected by an optical fiber. The sending end includes n paths with the same structure. Taking the first path as an example, the first mirror 1-1 is connected to the first semiconductor laser 2-1 to realize optical feedback on the semiconductor laser 2-1, generating intensity chaos. After the signal is input into the first QAM modulation module 3-1, the formed complex symbol sequence is converted from a serial symbol sequence to a parallel symbol stream through the serial-to-parallel conversion circuit therein, and then passes through the first OFDM modulation module 4-1. Using the IFFT converter, the inverse fast Fourier transform is performed, and a cyclic prefix and a pilot signal are added to transform the symbols in the frequency domain into the time domain. Then, through the parallel-to-serial conversion circuit, it is converted into a serial signal and intensity-modulated onto the chaotic carrier output by the semiconductor laser. The optical signal output by the first intensity modulator 12-1 passes through the first phase modulator 5-1 and the second phase modulator 5-2, and then enters two optoelectronic oscillation loops through the two output ports of the second optical coupler 6-2. The first Mach-Zehnder interferometer 7-1 and the second Mach-Zehnder interferometer 7-2 convert the phase change into an intensity change, and then the optoelectronic detector modules 8-1 of the first dual-PD and 8-2 of the second dual-PD convert it into a radio frequency signal. After amplification, the optical signals in the first phase modulator 5-1 and the second phase modulator 5-2 are respectively phase-modulated, thereby generating phase-chaotic and intensity-chaotic optical signals. Its advantage is that it can hide delay information, making it impossible for attackers to synchronize the chaotic system. In this way, the n paths with phase-chaotic and intensity-chaotic optical signals are coupled into the multiplexer 10, synthesized into one path and then sent to the receiving end.

[0053] At the receiving end, the demultiplexer 11 routes the signal into n paths according to the wavelength. Taking the first path as an example, the first interface of the demultiplexer is connected to the third coupler 6-3, and a part of the optical signal is input to the third phase modulator 5-3. Another part is input to the third Mach-Zehnder interferometer 7-3 through the delay fiber, where the phase change is converted into an intensity change, and then injected into the third photodetector 8-3 of the dual PD, converted into an electrical signal, and amplified by the third RF amplifier 9-3 to modulate the signal in the third phase modulator 5-3. Another port of the fourth coupler 6-4 inputs the signal into the fourth Mach-Zehnder interferometer 7-4 through the delay fiber, converts the phase change into an intensity change, inputs it into the fourth photodetection module 8-4 of the dual PD, and is amplified by the fourth RF amplifier 9-4 to modulate the optical signal of the fourth phase modulator 5-4. A port of the third coupler 6-3 outputs the signal to the fourth phase modulator 5-4, and the signal output by the fourth RF amplifier 9-4 modulates the optical signal from the third coupler 6-3 in the fourth phase modulator 5-4. Due to the synchronization effect, the generated anti-phase phase cancels the chaotic phase in the optical signal from the third coupler 6-3, so that the signal that is both intensity-chaotic and phase-chaotic becomes intensity-chaotic. In the process of signal recovery, the output signal of the fourth phase modulator 5-4 is transmitted to the first beam splitter 17-1. A part of the optical signal of the first beam splitter 17-1 is transmitted to the second laser 2-2 through the first circulator 18-1, and the second laser 2-2 is fed back through the second mirror 1-2 to generate chaos. Another part of the first beam splitter 17-1 converts the optical signal into an electrical signal through the second photodetector 13-1 of the single PD and transmits it to the first subtractor 14-1. The chaotic signal generated by the second laser 2-2 at the local receiving end is transmitted to the second single PD photodetector 13-2 through the first circulator 18-1 to convert the optical signal into an electrical signal. In this way, through the subtractor, the OFDM signal is recovered. In the OFDM demodulation module 15-1 (OFDM demodulation chip: DSS7700 chip), through down-conversion, removing the pilot and cyclic prefix, using the fast Fourier transform (FFT), the received information is converted into frequency-domain information, and then using coherent demodulation and the mapping relationship, the original information is demodulated in the QAM demodulation module 16-1. At the receiving end, after the optical signal passes through the demultiplexer, it is transmitted to two optoelectronic oscillation loops symmetric to the transmitting end, generating an anti-phase phase shift to cancel the phase chaos. Then, the chaotic signal from the local chaotic semiconductor laser and the intensity chaos of the dephased chaos from the phase modulator are converted into electrical signals through the PD, and subtracted using the subtractor to separate the OFDM symbol. In the OFDM demodulation module, using the FFT converter, the inverse fast Fourier transform is performed to transform the symbol in the frequency domain to the time domain. After removing the pilot cyclic prefixer, the serial-parallel converter converts the parallel symbol into a serial symbol. It is transmitted to the QAM demodulation module, and the original information is recovered from the serial symbol according to the mapping rule.

[0054] In the present invention, information is hidden in a chaotic carrier through chaotic masking and chaotic modulation. Since the delay information is hidden, an attacker cannot synchronize the chaotic signal of the laser, and the original information cannot be decrypted, thus achieving secure communication.

[0055] The process of realizing communication in the present invention is briefly summarized as follows:

[0056] 1. Synchronize the chaotic lasers and optoelectronic oscillation loops at the transmitting end and the receiving end.

[0057] 2. Perform QAM modulation and OFDM modulation on the information.

[0058] 3. Modulate the OFDM signal onto the chaotic carrier.

[0059] 4. Convert the signal with phase chaos removed and the local chaotic signal of the laser at the receiving end into electrical signals.

[0060] 5. Use a subtractor to subtract the two signals in step 4 to demodulate the OFDM signal.

[0061] 6. Demodulate the QAM symbols in the OFDM demodulation module.

[0062] 7. Demodulate the original information in the QAM demodulation module.

[0063] The preferred embodiments and principles of the present invention have been described in detail above. For those of ordinary skill in the art, according to the idea provided by the present invention, there will be changes in the specific implementation manners, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A secure communication system for encrypting OFDM signals, including a transmitting end and a receiving end, with the transmitting end and the receiving end connected by an optical fiber; characterized in that: The transmitting end includes n paths with the same structure. The structure of the nth path is as follows: The nth mirror is connected to the nth intensity modulator through the nth semiconductor laser; the nth QAM modulation module is connected to the nth intensity modulator through the nth OFDM modulation module; the nth intensity modulator is connected to the (2n - 1)th phase modulator, and the (2n - 1)th phase modulator is connected to the (2n - 1)th optical coupler. Two ports of the (2n - 1)th optical coupler are respectively connected to the 2nth phase modulator and the combiner; the 2nth phase modulator is connected to the 2nth optical coupler through the (2n - 1)th Mach-Zehnder interferometer. One port of the 2nth optical coupler is connected to the 2nth photoelectric detection module, the 2nth photoelectric detection module is connected to the 2nth radio frequency amplifier, and the output signal of the 2nth radio frequency amplifier performs phase modulation on the optical chaos signal in the 2nth phase modulator; the other port of the 2nth optical coupler is connected to the (2n - 1)th radio frequency amplifier through the 2nth Mach-Zehnder interferometer and the (2n - 1)th photoelectric detection module, and the output signal of the (2n - 1)th radio frequency amplifier performs phase modulation on the optical chaos signal in the (2n - 1)th phase modulator; The receiving end receives the signal sent by the combiner and transmits the signal divided into n paths with the same structure through a demultiplexer. The structure of the nth path is as follows: The nth interface of the demultiplexer is connected to the (4n - 1)th optical coupler. Two ports of the (4n - 1)th optical coupler are respectively connected to the (4n - 1)th phase modulator and the 4nth phase modulator; the (4n - 1)th phase modulator is connected to the 4nth coupler. Two ports of the 4nth coupler are respectively connected to the (4n - 1)th Mach-Zehnder interferometer and the 4nth Mach-Zehnder interferometer. The (4n - 1)th Mach-Zehnder interferometer is connected to the (4n - 1)th radio frequency amplifier through the (4n - 1)th photoelectric detector, and the (4n - 1)th radio frequency amplifier is connected to the (4n - 1)th phase modulator; the 4nth Mach-Zehnder interferometer is connected to the 4nth radio frequency amplifier through the 4nth photoelectric detection module, and the 4nth radio frequency amplifier is connected to the 4nth phase modulator; the 4nth phase modulator is connected to the nth beam splitter. One port of the nth beam splitter is connected to the nth circulator, the nth circulator is connected to the 2nth laser, and the 2nth laser is connected to the 2nth mirror; the other port of the nth beam splitter is connected to the (2n - 1)th photoelectric detector, the (2n - 1)th photoelectric detector is connected to the first end of the nth subtractor, the second end of the nth subtractor is connected to the 2nth photoelectric detector, and the 2nth photoelectric detector is connected to the nth circulator; the third end of the nth subtractor is connected to the nth QAM demodulation module through the nth OFDM demodulation module.

2. The secure communication system for encrypting OFDM signals according to claim 1, characterized in that, The splitting ratio of the optical coupler is 1:

1.

3. A secure communication system for encrypting OFDM signals according to claim 1, characterized in that At the transmitting end, the bias current of the chaotic laser is 20 mA.

4. A secure communication system for encrypting OFDM signals according to claim 1, characterized in that, At the transmitting end, in the QAM modulation module, a complex symbol sequence is formed. The serial symbol sequence is converted into a parallel symbol stream through a serial-to-parallel conversion circuit. Then, in the OFDM modulation module, using an IFFT transformer, an inverse fast Fourier transform is performed to transform the symbols in the frequency domain to the time domain.

5. A secure communication system for encrypting OFDM signals according to claim 1, characterized in that, At the transmitting end, the time-domain symbols output by the IFFT transformer are converted into a serial signal through a parallel-to-serial conversion circuit in the OFDM modulation module, a cyclic prefix is added, and the signal is intensity-modulated onto the chaotic carrier output by the chaotic laser.

6. A secure communication system for encrypting OFDM signals according to any one of claims 1-5, characterized in that, At the transmitting end, the optical signal output by the intensity modulator passes through two phase modulators and then enters the optoelectronic oscillation loop. The Mach-Zehnder interferometer converts the phase change into an intensity change, and then the optoelectronic detector module converts it into a radio frequency signal. After amplification, the radio frequency signal is used to phase-modulate the optical signals in the two phase modulators respectively, thereby generating phase-chaotic and intensity-chaotic optical signals.

7. A secure communication system for encrypting OFDM signals according to claim 6, characterized in that, The described optoelectronic detector module is a dual-PD optoelectronic detector module.

8. The secure communication system for encrypting OFDM signals according to claim 1, characterized in that, At the receiving end, the chaotic signal from the local chaotic laser and the intensity-chaotic signal with dephased chaos from the phase modulator are converted into electrical signals through a PD, and a subtractor is used for subtraction to separate the OFDM symbols.

9. The secure communication system for encrypting OFDM signals according to claim 1, characterized in that, At the receiving end, in the OFDM demodulation module, using an FFT transformer, an inverse fast Fourier transform is performed to transform the symbols in the frequency domain to the time domain. After removing the pilot cyclic prefix, a serial-to-parallel converter is used to convert the parallel symbols into serial symbols.

10. A secure communication system for encrypting OFDM signals according to any one of claims 1-5, 8, and 9, characterized in that, At the receiving end, in the QAM demodulation module, the serial symbols are restored to the original information according to the mapping rule.

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