Encrypted communication radar system based on noise phase coded modulation

Abstract

The invention provides an encryption communication and radar integrated system based on noise phase coded modulation. The system integrates noise phase modulation and photon frequency conversion technologies, and core devices comprise a laser, a tunable laser source, a Mach-Zehnder modulator, an optical amplifier, an optical coupler, a photoelectric detector, an envelope detector, a high-pass filter and the like. By using the random characteristic of Gaussian white noise and the self-correlation characteristic of a phase-coded signal, the system realizes noise phase modulation of a communication signal, and an integrated mixed signal fusing the noise characteristic and the phase modulation characteristic is generated. According to the system, the signal frequency can be flexibly tuned through the tunable laser source and the envelope detector, and meanwhile, phase noise and frequency deviation caused by introduction of millimeter waves generated by two free lasers are effectively avoided. According to the scheme, an efficient radar target detection function is realized, the communication security is improved, and the wide application potential and technical advantages in a future electronic warfare system are shown.

Description

Technical Field

[0001] The present invention relates to the field of communication and radar integration technology, and specifically to an encrypted communication radar system based on noise phase coding modulation. The system aims to utilize the unique characteristics of noise phase modulation signals to achieve encrypted transmission of communication signals through phase coding, while having target detection functions. The system is suitable for high-security communication and detection scenarios, including military communication radars, confidential communications, and other key application areas that need to counter interference and information theft. Background Art

[0002] With the rapid development of wireless technology, the number of connected devices worldwide is expected to reach 75 billion by 2025, and will further increase in the 6G era. However, this rapid expansion has exacerbated the problem of spectrum resource shortage. In order to alleviate this dilemma, the use of higher frequencies in the millimeter wave (MMW) and terahertz (THz) bands has become the key. At the same time, by integrating wireless devices with different functions such as navigation, communication and radar sensing, the shortage of spectrum resources can also be effectively alleviated. As one of the typical application scenarios of 6G, the integration of sensing and communication (ISAC) can not only share hardware platforms, reduce equipment size, and minimize interference, but also achieve mutual enhancement in functions. It is regarded as a key technology in the 6G era.

[0003] Photonic ISAC systems have attracted attention due to their many advantages over traditional electronic systems. Traditional systems require multiple levels of frequency doubling to generate MMW or THz signals, but the increase in frequency doubling will lead to performance degradation. Photonic systems use the large bandwidth of optical devices to directly generate high-frequency broadband signals and reduce electromagnetic interference, making it easier to integrate with fiber-optic wireless networks. However, in multi-target scene detection, nonlinear effects may cause target echo mixing and generate false targets, which still needs further optimization and resolution.

[0004] To address these challenges, we proposed an encrypted communication radar system based on noise phase coding modulation. By taking advantage of the good encryption properties of Gaussian white noise and the autocorrelation characteristics of the phase coded signal, we perform noise phase modulation on the communication signal to generate a hybrid noise-phase modulation integrated signal. The simulation results show that this signal not only has the radar's target detection and positioning function, but also has the function of encrypted communication, thus realizing the integrated function of signal encryption transmission and radar ranging.

[0005] This new system makes full use of the broadband characteristics of Gaussian white noise and the encryption ability of phase coding, making the communication signal have strong anti-eavesdropping and anti-interference capabilities. At the same time, the autocorrelation characteristics of phase coding are used to achieve high-precision target detection and positioning functions, ensuring the accuracy of radar ranging. Specifically, the system uses the randomness of noise and the autocorrelation of phase coding to encrypt the communication content during the transmission of the signal generated by the noise phase modulation technology, which makes the communication safe and reliable. By decoding the phase-coded signal, the receiving end can efficiently extract the communication data and use the autocorrelation characteristics to accurately detect and locate the target. Summary of the invention

[0006] In order to realize the synaesthesia integrated signal, the present invention provides an encrypted communication radar system based on noise phase coding modulation, which can effectively enhance the security of the communication system while realizing the radar ranging function.

[0007] In order to achieve the above-mentioned purpose, the present invention establishes a communication link based on photon frequency conversion, and the devices in the link include a laser source, an arbitrary waveform generator, a tunable laser source, a Mach-Zehnder modulator, a polarization modulator, an optical coupler, an optical amplifier, an optical fiber, a photodetector, an envelope detector, a high-pass filter, an electrical amplifier, an analog-to-digital conversion module and a digital signal processing module.

[0008] The process of an encrypted communication radar system based on noise phase coding modulation described in the present invention is:

[0009] Step 1: The system first phase-modulates the QAM signal through the arbitrary waveform generator 3 combined with the Gaussian random sequence to generate a phase-modulated signal with noise characteristics.

[0010] The output signal of arbitrary waveform generator 3 can be expressed as:

[0011]

[0012] where s QAM (t) is the communication QAM signal, β is a random variable with uniform distribution on [-π,π], k u is the noise modulation coefficient, u(t) has a mean of 0 and a variance of is a stationary Gaussian white noise, and u(t) is statistically independent of α.

[0013] This signal is modulated onto an optical carrier through a Mach-Zehnder modulator 2, and its output is:

[0014]

[0015] Where P 1 is the optical signal power, ω 1is the angular frequency of the laser 1 optical signal, Δω 1 (t) and are the time-varying frequency drift and phase noise of the laser, m is the intensity modulation index, and s(t) is the noise phase modulation signal, thereby achieving an efficient and accurate photoelectric conversion process.

[0016] Step 2: The system uses a tunable laser source 5 to perform photon frequency conversion operation to achieve up-conversion processing of the noise phase signal and down-conversion reception of the echo signal. The processed optical signal is completed by the high-speed photodetector 7 to complete the photoelectric mixing and generate a millimeter wave signal, the output of which is:

[0017]

[0018] Where P 2 ,ω 2 , Δω 2 (t) and are the output power of the tunable laser source, the angular frequency of the optical carrier, the time-varying frequency drift, and the phase noise, respectively. α is a scaling factor representing the power loss caused by the optical fiber transmission link. In formula (3), the first two terms are the DC component and the low-frequency signal component, respectively, which can be effectively removed by an electronic bandpass filter or a high-pass filter, thereby retaining the desired millimeter-wave signal contained in the third term for transmission to the user receiving end. In the actual transmission process, the power of the millimeter-wave signal will attenuate due to the loss of the optical fiber link. This problem can be solved by introducing an optoelectronic amplifier in the optical fiber link for power compensation. In addition, the influence of the dispersion effect on the optically carried millimeter-wave signal cannot be ignored, which will cause the generated millimeter-wave signal to have a power attenuation problem introduced by dispersion in ED detection. The following two solutions can be considered: on the one hand, the bandwidth and center frequency of the QAM signal can be set so that it falls outside the notch point range; on the other hand, single-sideband modulation combined with a digital compensation algorithm can be used.

[0019] Step 3: The generated millimeter wave signal is transmitted to the receiving end via the optical fiber link and the wireless millimeter wave link. At the receiving end, the envelope detector 11 performs incoherent down-conversion on the received signal and restores it to an intermediate frequency noise phase modulated signal, and its output is:

[0020]

[0021] Wherein, γ is a scaling factor representing the signal power loss caused by the wireless link. The first two terms are the DC component and the desired signal, respectively. The third term is the unwanted high frequency component, which can be easily removed by the low-pass filter 12. As can be seen from formula (4), the envelope detector 11 is able to automatically suppress the unnecessary phase noise and frequency offset caused by the optical beat frequency. In addition, the deployment of the envelope detector 11 not only enables the user equipment receiving end to use an analog-to-digital converter that only operates within the transmission signal bandwidth, but also simplifies the digital signal processing receiver because no complex digital signal processing algorithm is required to correct the frequency offset and phase noise effects.

[0022] Step 4: At the receiving end, the system demodulates and processes the received intermediate frequency signal through the digital signal processing module. First, the de-phase modulation operation is performed to restore the original modulation information; then, the signal is frequency-domain equalized to correct the impact of the channel on the signal; finally, the signal is reconstructed to restore the encrypted original data to ensure the integrity and accuracy of the information.

[0023] Step 5: After receiving the echo signal, the system first filters the echo signal through a high-pass filter 17 to remove unnecessary low-frequency components. Then, the signal is photon down-converted using a Mach-Zehnder modulator 18. The processed optical signal is photoelectrically converted through a high-speed photodetector 20 and enters a data processing module 21 for signal analysis.

[0024] Through the autocorrelation characteristics of the noise phase modulation signal, the system can efficiently extract the distance and speed characteristics of the target. Assuming the distance of the target is R, the radial velocity is v, and the time delay of its return signal equivalent to the transmitted signal is:

[0025]

[0026] The Doppler shift is:

[0027]

[0028] The system uses a fuzzy function to describe the time-frequency composite autocorrelation function of the target signal, which is defined as:

[0029]

[0030] Where τ represents the delay and ξ represents the frequency offset. The modulus of the ambiguity function |χ(τ,ξ)| describes the system's ability to resolve the distance and speed of the target. When the frequency difference between the targets ξ=0, the ambiguity function degenerates into a time autocorrelation function:

[0031]

[0032] When the delay difference between the targets τ = 0, the ambiguity function degenerates into the frequency autocorrelation function:

[0033]

[0034] Through fuzzy function analysis, the system can achieve high-precision target detection and positioning while ensuring the security of the communication process. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of an encrypted communication radar system based on noise phase coding modulation according to the present invention;

[0036] Figure 2 This is a schematic diagram of an optical link of an encrypted communication radar system based on noise phase coding modulation proposed by the present invention;

[0037] Figure 3 A flow chart showing the modulation of a data signal; DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings:

[0039] Figure 1 This is a flow chart of the encrypted communication radar system based on noise phase coding modulation according to the present invention, which specifically includes the following steps:

[0040] Step 1: Figure 2 As shown, the system first phase modulates the input QAM signal through the arbitrary waveform generator 3 combined with the Gaussian random sequence, thereby generating a phase modulated signal with noise characteristics. In this process, the arbitrary waveform generator 3 dynamically modulates the signal using the Gaussian random sequence, so that the output signal has higher encryption characteristics and anti-interference capabilities. This modulation method not only ensures data security during signal transmission, but also lays the foundation for subsequent signal processing.

[0041] The output signal of the arbitrary waveform generator 3 can be mathematically expressed as:

[0042]

[0043] where s QAM (t) is the communication QAM signal, β is a random variable with uniform distribution on [-π,π], k u is the noise modulation coefficient, u(t) has a mean of 0 and a variance of is a stationary Gaussian white noise, and u(t) is statistically independent of α.

[0044] like Figure 3As shown, this signal is loaded onto an optical carrier through the Mach-Zehnder modulator 2 to complete the intensity modulation of the optical signal. The modulated signal is transmitted in the form of an optical domain and transmitted to the far end through the optical fiber 4, providing an efficient optical transmission channel for subsequent processing. Its output signal can be expressed as:

[0045]

[0046] Where P 1 is the optical signal power, ω 1 is the angular frequency of the laser 1 optical signal, Δω 1 (t) and are the time-varying frequency drift and phase noise of the laser, m is the intensity modulation index, and s(t) is the noise phase modulation signal, thereby achieving an efficient and accurate photoelectric conversion process.

[0047] Step 2: At the remote end, the system uses a tunable laser source 5 to perform photon frequency conversion. Figure 3 As shown in the spectrum diagram, by adjusting the optical carrier frequency of the tunable laser source 5, the up-conversion processing of the noise phase modulation signal and the down-conversion reception of the echo signal are realized. The optical signal after frequency conversion carries the distance and speed information of the target. The processed optical signal is completed by the high-speed photodetector 7 to complete the photoelectric mixing and generate a millimeter wave signal, and its output can be expressed as:

[0048]

[0049] Where P 2 ,ω 2 , Δω 2 (t) and are the output power of the tunable laser source, the angular frequency of the optical carrier, the time-varying frequency drift, and the phase noise, respectively. α is a scaling factor representing the power loss caused by the optical fiber transmission link. In formula (3), the first two items are the DC component and the low-frequency signal component, respectively, which can be removed by an electronic bandpass filter or a high-pass filter, thereby retaining the third item, i.e., the desired millimeter-wave signal, for transmission to the user receiving end to ensure the effectiveness and integrity of signal transmission.

[0050] Step 3: The generated millimeter wave signal is transmitted to the receiving end through the optical fiber link and the wireless millimeter wave link. The receiving end uses the envelope detector 11 to perform incoherent down-conversion on the received millimeter wave signal, convert the signal from the millimeter wave frequency band to the intermediate frequency, and recover the noise phase modulation signal. The intermediate frequency signal output by the envelope detector 11 can be expressed as:

[0051]

[0052] Where γ is a scaling factor representing the signal power loss caused by the wireless link. The first two terms are the DC component and the desired signal, respectively. The third term is the unwanted high frequency component, which can be easily filtered out by a low pass filter 12.

[0053] Step 4: At the receiving end, the system demodulates and processes the received intermediate frequency signal through the digital signal processing module. First, the de-phase modulation operation is performed to restore the original modulation information; then, the influence of the channel on the signal is corrected through frequency domain equalization processing, and the amplitude and phase distortion caused by the channel is compensated; finally, the signal reconstruction is completed, and the encrypted original data is successfully restored to ensure the integrity and accuracy of data transmission.

[0054] Combining formula (4) and Figure 3 It can be observed from the spectrum diagram and constellation diagram displayed by the low-pass filter 12 that the signal constellation diagram after processing by the low-pass filter is clear and stable, which verifies the effectiveness of the envelope detector 11 in signal processing. Specifically, the envelope detector 11 can automatically suppress the additional phase noise and frequency offset caused by the optical beat frequency, thereby improving the quality and stability of the signal. In addition, the use of the envelope detector 11 not only allows the user equipment receiving end to adopt an analog-to-digital converter that only covers the bandwidth range of the transmission signal, greatly reducing the hardware complexity, but also simplifies the design of the digital signal processing receiver. Because the envelope detector 11 can effectively handle frequency offset and phase noise problems, the system no longer needs to rely on complex digital signal processing algorithms for correction, thereby significantly improving the processing efficiency and reliability of the receiving end.

[0055] Step 5. After receiving the echo signal, the system first filters the signal through a high-pass filter 17 to remove low-frequency noise and unnecessary signal components and retain valid frequency band information. Then, the signal is photon down-converted using a Mach-Zehnder modulator 18 to convert the frequency of the echo signal to a frequency band suitable for subsequent photoelectric detection. The down-converted optical signal is converted into an electrical signal by a high-speed photodetector 20 to achieve efficient photoelectric conversion. Subsequently, the signal is transmitted to a data processing module 21 for echo signal processing. Figure 3 As shown in the figure, the echo signal processed by the system shows a clear spectrum distribution in the spectrum diagram, and also shows good autocorrelation characteristics in the autocorrelation function diagram. This characteristic shows that the system can effectively identify the distance information of the target and has good radar ranging capability.

[0056] Through the autocorrelation characteristics of the noise phase modulation signal, the system can efficiently extract the distance and speed characteristics of the target. Assuming the distance of the target is R, the radial velocity is v, and the time delay of its return signal equivalent to the transmitted signal is:

[0057]

[0058] The Doppler shift is:

[0059]

[0060] The system uses a fuzzy function to describe the time-frequency composite autocorrelation function of the target signal, which is defined as:

[0061]

[0062] Where τ represents the delay and ξ represents the frequency offset. The modulus of the ambiguity function |χ(τ,ξ)| describes the system's ability to resolve the distance and speed of the target. When the frequency difference between the targets ξ=0, the ambiguity function degenerates into a time autocorrelation function:

[0063]

[0064] When the delay difference between the targets τ = 0, the ambiguity function degenerates into the frequency autocorrelation function:

[0065]

[0066] Through fuzzy function analysis, the system can achieve high-precision target detection and positioning while ensuring the security of the communication process.

[0067] In summary of the above description, the present invention exhibits the following characteristics: 1) Simple and efficient structure: The present invention adopts an encrypted communication radar system based on noise phase coding modulation, and the structural design is simple and efficient. By loading the noise phase modulation signal into the optical domain and the electrical domain, the combination of encrypted transmission of the communication signal and the radar detection function is realized. While supporting high-precision target detection, the system ensures the security of communication data, effectively prevents information from being cracked and tampered with, and meets the application requirements of high-security communication and detection. 2) High robustness and anti-interference ability: The present invention significantly improves the anti-interference performance and communication stability of the system by utilizing the autocorrelation characteristics of the noise phase modulation signal. In a complex electromagnetic environment, the system can automatically correct the frequency drift and phase noise caused by the channel effect, thereby realizing accurate decoding of the encrypted communication signal. At the same time, the application of the fuzzy function ensures high-precision measurement of target distance and speed, providing reliable technical support for multi-target scenarios.

Claims

1. An encrypted communication radar system based on noise phase coding modulation is characterized by: The following steps are involved: Step 1: The system first uses a Gaussian random sequence to phase modulate the communication signal to generate a phase modulated signal with noise characteristics. This signal is modulated onto an optical carrier through a Mach-Zehnder modulator, laying the foundation for subsequent signal processing. Step 2: At the remote end, the system uses a tunable laser source to perform photon frequency conversion operations to achieve up-conversion processing of the noise phase signal and down-conversion reception of the echo signal. The processed optical signal is completed by photoelectric mixing through a high-speed photodetector to generate a millimeter wave signal. Step 3: The generated millimeter wave signal is transmitted to the receiving end via the optical fiber link and the wireless millimeter wave link. At the receiving end, the envelope detector (ED) performs incoherent down-conversion on the received signal and restores it to an intermediate frequency noise phase modulated signal, preparing for subsequent signal decryption. Step 4: At the receiving end, the system demodulates and processes the received intermediate frequency signal through the digital signal processing module. First, the phase removal operation is performed to restore the original modulation information, and then the frequency domain equalization processing is performed to correct the channel influence, and finally the signal reconstruction is completed to restore the encrypted original data. Step 5: After receiving the echo signal, the system uses the digital signal processing module to perform high-precision analysis on the echo signal. With the help of the autocorrelation characteristics of the noise phase modulation signal, the system can efficiently extract target features and achieve accurate target detection while ensuring the security of communication.

2. According to claim 1, the encrypted communication radar system based on noise phase coding modulation is unique in that the system can realize the integration of encrypted communication and radar detection functions based on the characteristics of noise phase coding modulation signals. In terms of communication functions, by performing phase coding processing on the signal, high-security transmission of data can be achieved, effectively preventing information from being illegally stolen or tampered with. In terms of radar functions, by utilizing the autocorrelation characteristics of the phase-coded signal, the system can accurately extract target echo information and provide reliable detection capabilities. This design of the system meets the needs of modern communication and radar integration, and is suitable for diversified application scenarios such as electronic warfare, multi-functional detection and encrypted communications.

3. According to claim 2, an encrypted communication radar system based on noise phase coding modulation is characterized in that: The system is designed with a high dynamic range. The system has a superior dynamic range in design, which can effectively deal with problems such as phase noise and frequency offset in complex environments, ensuring the stability and anti-interference ability of the signal during transmission. The improvement of dynamic range not only enhances the robustness of the signal, but also supports a variety of high-precision radar detection and high-security communication functions. In a complex electromagnetic environment, the system can maintain stable working performance and is suitable for demanding application scenarios that require high reliability and high efficiency, providing solid technical support for the coordination of encrypted communications and radar functions.

Images