A radar communication integrated signal generation method based on NLFM

Abstract

The present invention belongs to the field of radar communication integrated signal technology, and specifically relates to a radar communication integrated signal generation method based on NLFM. The method includes: generating a radar nonlinear frequency modulation signal; generating a binary unipolar code element, passing it through a serial / parallel conversion circuit and a 2 / 4 level conversion circuit, and then performing sixteenth-order quadrature amplitude modulation to generate a corresponding communication symbol; modulating the generated sixteenth-order quadrature amplitude modulation communication symbol on the radar nonlinear frequency modulation signal carrier to form a nonlinear frequency modulation sixteenth-order quadrature amplitude modulation radar communication integrated signal. The present invention performs 16QAM modulation communication information on the original NLFM radar signal. This method can improve the signal's frequency band utilization and thus achieve a higher communication rate. At the same time, it utilizes the characteristic that the NLFM signal has a low range sidelobe to reduce the range sidelobe level of the integrated signal, thereby improving the signal's autocorrelation performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar communication integrated signal, and in particular relates to a radar communication integrated signal generation method based on NLFM (Non-Linear Frequency Modulation). Background Art

[0002] Simply stacking critical equipment like radar and communication equipment on the same platform not only increases the platform's size but also creates electromagnetic interference between devices, impacting overall system performance. Radar and communication integration is a key solution to these problems. A radar and communication integration system combines radar and communication functions on a single hardware device, improving spectrum utilization, mitigating electromagnetic interference between devices, and significantly enhancing system reliability.

[0003] Designing a signal waveform that can achieve both target detection and information transmission is a key component of radar communication integrated systems. To date, many researchers both domestically and internationally have achieved remarkable results in exploring integrated radar communication signal design. Integrated radar communication signals can be categorized into two main types: those designed using resource reuse technology and those using the same waveform technology. Integrated signals designed using resource reuse technology can be categorized into four types: space-division multiplexing (SDM), time-division multiplexing (TDM), code-division multiplexing (CDM), and frequency-division multiplexing (FDM). While implementing integrated radar communication signal waveforms using this approach is simple, the resource utilization of the integrated system is relatively low.

[0004] The integrated signal designed with the same waveform technology boasts relatively high signal power and spectrum efficiency, enabling simultaneous radar detection and communication data transmission. As a single waveform signal, it can fundamentally mitigate interference between systems. Currently, two forms of integrated signals can be implemented using the same waveform technology: a communication-shared signal, which directly uses the communication signal or modifies it to provide radar functionality; and a radar-shared signal, which modulates communication information onto the original radar signal to ensure both radar functionality and information transmission. One approach to designing a communication-shared signal involves dividing each pulse of an Orthogonal Frequency-Division Multiplexing (OFDM) radar into sub-pulses composed of multiple OFDM symbols. Information is transmitted using the OFDM symbols within each pulse, enabling high-speed communication. However, the distortion caused by the transmitted OFDM signal significantly impacts information demodulation. For radar common signal design, the lower chirp signal (linear frequency modulation signal) used by the radar function is used to achieve synchronization during communication. The upper chirp signal is modulated using multi-phase shift keying (MPSK) to design an integrated radar communication system. This method can transmit communication information while ensuring communication spectrum efficiency and radar detection performance, but its implementation is relatively difficult. Another approach is to use a millimeter-wave frequency-modulated continuous wave radar to implement the communication function using a multi-slope keying modulation frequency-modulated continuous wave integrated system. This system uses the phase difference between adjacent pulses to estimate the target's velocity and simultaneously loads the communication information onto different slopes. At the receiving end, a matched filter-based method is used to demodulate the communication data. However, when the slope changes, the signal bandwidth of the system also changes, resulting in a loss of system bandwidth utilization. The third method is to propose an integrated waveform that combines 16-order Quadrature Amplitude Modulation (QAM) with the traditional radar linear frequency modulation (LFM) signal. The LFM (Linear Frequency Modulation) signal is modulated as a subcarrier of the 16QAM signal. This method can effectively improve the communication rate, but it has the problem of high autocorrelation sidelobes.

[0005] Therefore, we can design the radar communication integrated signal by comprehensively considering multiple aspects such as the difficulty of signal implementation, communication transmission rate and radar detection performance. Summary of the Invention

[0006] In order to overcome the problems in the prior art, the present invention proposes a radar communication integrated signal generation method based on NLFM.

[0007] The technical solution of the present invention to solve the above technical problems is as follows:

[0008] The present invention provides a radar communication integrated signal generation method based on NLFM, comprising the following steps:

[0009] Step 1. Generate radar nonlinear frequency modulation signal;

[0010] Step 2. Generate binary unipolar code elements, pass them through a serial / parallel conversion circuit and a 2 / 4 level conversion circuit, and then perform sixteenth-order quadrature amplitude modulation to produce the corresponding communication symbol;

[0011] Step 3. Modulate the generated sixteenth-order quadrature amplitude modulation communication symbol on the radar nonlinear frequency modulation signal carrier to form a nonlinear frequency modulation sixteenth-order quadrature amplitude modulation radar communication integrated signal.

[0012] Furthermore, the specific process of step 1 is as follows:

[0013] Generate radar nonlinear frequency modulation signal SNLFM(t):

[0014]

[0015] Where A is the amplitude of the nonlinear frequency modulation signal, t is the time, T p is the time width of the nonlinear frequency modulation signal, j is the imaginary unit, fc is the carrier frequency of the nonlinear frequency modulation signal, is the phase function of the nonlinear frequency modulation signal.

[0016] Furthermore, the phase function of the nonlinear FM signal The generation method is:

[0017] Determine the group delay of the nonlinear FM signal as:

[0018]

[0019] Among them, T p is the signal time width; B is the signal bandwidth; K is the frequency modulation index, which is a constant and its value directly affects the nonlinearity of the frequency modulation;

[0020] The nonlinear frequency modulation signal is generated by digital method, and the frequency modulation function of the signal is obtained by interpolation method:

[0021] f(t)=t -1 (f)

[0022] Finally, by integrating the frequency modulation function, the phase function of the nonlinear frequency modulation signal can be obtained as:

[0023]

[0024] Furthermore, the specific process of step 2 is:

[0025] Generate binary unipolar code elements, pass through the serial / parallel conversion circuit and the 2 / 4 level conversion circuit, and then perform sixteenth-order orthogonal amplitude modulation to generate the corresponding communication symbol S 16QAM(t) :

[0026] S 16QΑΜ (t) = A m (t)g(t)exp[j(2πf c t+θ m (t))]

[0027] Among them, Am(t) represents the amplitude of the sixteenth-order quadrature amplitude modulation signal, g(t) represents the signal pulse, θ m(t) Represents the signal phase.

[0028] Furthermore, the specific process of step 3 is as follows:

[0029] The generated sixteenth-order quadrature amplitude modulation communication symbol is modulated on the radar nonlinear frequency modulation signal carrier to form a nonlinear frequency modulation sixteenth-order quadrature amplitude modulation radar communication integrated signal S(t):

[0030]

[0031] Where t is time, T p A is the time width of the radar communication integrated signal of the nonlinear frequency modulation sixteenth-order orthogonal amplitude modulation, m(t) is the amplitude of the radar communication integrated signal with nonlinear frequency modulation and sixteenth-order orthogonal amplitude modulation, j is the imaginary unit, fc is the carrier frequency of the radar communication integrated signal with nonlinear frequency modulation and sixteenth-order orthogonal amplitude modulation, is the phase function of the nonlinear frequency modulation signal, θ m(t) is the phase information after modulating the sixteenth-order quadrature amplitude modulation baseband signal.

[0032] Compared with the prior art, the present invention has the following technical effects:

[0033] (1) The nonlinear frequency modulation signal used in the present invention modifies the spectrum of the linear frequency modulation signal so that the signal has lower side lobes after passing through the matched filter without performing a windowing operation, and can effectively avoid the problem of signal-to-noise ratio loss caused by the linear frequency modulation signal.

[0034] (2) The sixteenth-order quadrature amplitude modulation adopted in the present invention is a sixteenth-order amplitude and phase joint keying, which has the characteristics of large noise tolerance, high communication transmission rate, and is suitable for use in occasions with limited frequency band resources. It is a high-order digital modulation with high spectrum utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 It is a structural schematic diagram of the present invention;

[0037] Figure 2 is a three-dimensional fuzzy function diagram of the present invention;

[0038] Figure 3 This is a comparison diagram of the autocorrelation performance of the simulation of the present invention. DETAILED DESCRIPTION

[0039] To further illustrate the technical means and effects employed by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the specific implementations, structures, features, and effects of the technical solutions proposed by the present invention. Specific features, structures, or characteristics in one or more embodiments may be combined in any suitable manner. Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention pertains.

[0040] This invention addresses the problem of low autocorrelation performance after modulating communication information within radar signal pulses. By designing an integrated NLFM-16QAM radar communication signal, the core concept is to modulate the radar NLFM signal as the carrier of a 16QAM communication signal, enabling simultaneous data transmission and target detection.

[0041] The present invention provides a radar communication integrated signal generation method based on NLFM. Figure 1 , the implementation steps of the present invention are as follows:

[0042] Step 1. Generate radar nonlinear frequency modulation signal S NLFM (t):

[0043]

[0044] Where A is the amplitude of the nonlinear frequency modulation signal, t is the time, Tp is the time width of the nonlinear frequency modulation signal, j is the imaginary unit, fc is the carrier frequency of the nonlinear frequency modulation signal, is the phase function of the nonlinear frequency modulation signal.

[0045] Phase function of nonlinear frequency modulation signal in the real-time embodiment of the present invention The generation method is:

[0046] First, the group delay of the nonlinear FM signal can be determined as:

[0047]

[0048] Where, T p is the signal time width; B is the signal bandwidth; K is the frequency modulation index, which is a constant and its size directly affects the degree of nonlinearity of the frequency modulation.

[0049] Since the nonlinear frequency modulation signal is generated by digital methods, the frequency modulation function of the signal can be obtained by interpolation method:

[0050] f(t)=t -1 (f)

[0051] Finally, by integrating the frequency modulation function, the phase function of the nonlinear frequency modulation signal can be obtained as:

[0052]

[0053] Step 2. Generate binary unipolar code elements, pass through the serial / parallel conversion circuit and the 2 / 4 level conversion circuit, and then perform sixteenth-order orthogonal amplitude modulation to generate the corresponding communication symbol S 16QΑΜ (t):

[0054] S 16QΑΜ (t) = A m (t)g(t)exp[j(2πf c t+θ m (t))]

[0055] Among them, A m (t) represents the 16QAM signal amplitude, g(t) represents the signal pulse, θ m (t) represents the signal phase.

[0056] Step 3. Modulate the generated 16QAM communication symbol onto the NLFM signal carrier to form the NLFM-16QAM radar communication integrated signal S(t):

[0057]

[0058] Where t is time, T pA is the time width of the radar communication integrated signal of the nonlinear frequency modulation sixteenth-order orthogonal amplitude modulation, m(t) is the amplitude of the radar communication integrated signal with nonlinear frequency modulation and sixteenth-order orthogonal amplitude modulation, j is the imaginary unit, fc is the carrier frequency of the radar communication integrated signal with nonlinear frequency modulation and sixteenth-order orthogonal amplitude modulation, is the phase function of the nonlinear frequency modulation signal, θ m(t) is the phase information after modulating the sixteenth-order quadrature amplitude modulation baseband signal.

[0059] The effects of the present invention can be further illustrated by the following simulations.

[0060] 1. Simulation conditions:

[0061] The simulation sets the channel of the radar communication integrated system as a Gaussian white noise channel, with a pulse width of 10μs, a modulation bandwidth of 70MHz, a carrier frequency of 10MHz, a sampling rate of 320MHz, and a symbol rate of 5MS / s.

[0062] 2. Simulation content:

[0063] Simulation 1. Under the above simulation parameters, the method of the present invention is used to simulate the fuzzy function of the integrated signal of NLFM-16QAM radar communication. The results are as follows: Figure 2 shown.

[0064] Depend on Figure 2 It can be seen that the ambiguity function of the NLFM-16QAM radar communication integrated signal presents an ideal thumbtack-shaped feature, indicating that it has unambiguous resolution of both distance and Doppler.

[0065] Simulation 2. Under the above simulation parameters, the method of the present invention is used to simulate the autocorrelation performance of the NLFM-16QAM integrated signal and the LFM-16QAM (Linear Frequency Modulation-16Quadrature Amplitude Modulation) integrated signal. The results are as follows: Figure 3 shown.

[0066] Depend on Figure 3 As can be seen, the autocorrelation performance of NLFM-16QAM is significantly improved compared to the LFM-16QAM integrated signal. The integrated sidelobe ratio of the LFM-16QAM signal is -15.66dB, and the peak sidelobe ratio is -21.84dB. The integrated sidelobe ratio of the NLFM-16QAM signal designed in this paper is -38.73dB, and the peak sidelobe ratio is -47.92dB, which are 23.07dB and 26.08dB better than the LFM-16QAM integrated signal, respectively.

[0067] Table 1 compares the frequency band utilization of three radar communication integrated signals: NLFM-16QAM, NLFM-QPSK (Non-Linear Frequency Modulation-Quadrature Phase Shift Keying), and NLFM-PAM (Non-Linear Frequency Modulation-Pulse Amplitude Modulation).

[0068]

[0069] As shown in Table 1, the frequency band utilization of NLFM-16QAM signal is significantly higher than that of NLFM-PAM signal and NLFM-QPSK signal, which are radar communication integrated signals using low-order modulation.

[0070] In summary, the method of this embodiment performs 16QAM modulation communication information on the original NLFM radar signal. This method can improve the signal's frequency band utilization, thereby achieving a higher communication rate. At the same time, it utilizes the low range sidelobe characteristic of the NLFM signal to reduce the range sidelobe level of the integrated signal, thereby improving the signal's autocorrelation performance.

[0071] It should be understood that, although the various steps in the flowcharts involved in the various embodiments described above are displayed in sequence according to the instructions of the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified in the present invention, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the flowcharts involved in the various embodiments described above may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a portion of steps or stages in other steps.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A radar communication integrated signal generation method based on NLFM, characterized in that: The following steps are involved: Step 1. Generate radar nonlinear frequency modulation signal; Step 2. Generate binary unipolar code elements, pass them through a serial / parallel conversion circuit and a 2 / 4 level conversion circuit, and then perform sixteenth-order quadrature amplitude modulation to produce the corresponding communication symbol; Step 3. Modulate the generated sixteenth-order quadrature amplitude modulation communication symbol on the radar nonlinear frequency modulation signal carrier to form a nonlinear frequency modulation sixteenth-order quadrature amplitude modulation radar communication integrated signal.

2. The radar communication integrated signal generation method based on NLFM according to claim 1, characterized in that: The specific process of step 1 is: Generate radar nonlinear frequency modulation signal S NLFM(t) : Where A is the amplitude of the nonlinear frequency modulation signal, t is the time, T p is the time width of the nonlinear frequency modulation signal, j is the imaginary unit, fc is the carrier frequency of the nonlinear frequency modulation signal, is the phase function of the nonlinear frequency modulation signal.

3. The radar communication integrated signal generation method based on NLFM according to claim 2, characterized in that: Phase function of nonlinear frequency modulation signal The generation methods include: Determine the group delay t(f) of the nonlinear frequency modulation signal as: Among them, T p is the signal time width; B is the signal bandwidth; K is the frequency modulation index, which is a constant and its value directly affects the nonlinearity of the frequency modulation; The nonlinear frequency modulation signal is generated by digital method, and the frequency modulation function of the signal is obtained by interpolation method: f(t)=t -1 (f) Integrating the frequency modulation function, the phase function of the nonlinear frequency modulation signal is obtained as:

4. The radar communication integrated signal generation method based on NLFM according to claim 3, characterized in that: The specific process of step 2 is: Generate binary unipolar code elements, pass through the serial / parallel conversion circuit and the 2 / 4 level conversion circuit, and then perform sixteenth-order orthogonal amplitude modulation to generate the corresponding communication symbol S 16QAM(t) : S 16QΑΜ (t)=A m (t)g(t)exp[j(2πf c t+θ m (t))] Among them, A m(t) represents the amplitude of the sixteenth-order quadrature amplitude modulation signal, g(t) represents the signal pulse, θ m(t) Represents the signal phase.

5. The radar communication integrated signal generation method based on NLFM according to claim 4, characterized in that: The specific process of step 3 is: The generated sixteenth-order quadrature amplitude modulation communication symbol is modulated on the radar nonlinear frequency modulation signal carrier to form a nonlinear frequency modulation sixteenth-order quadrature amplitude modulation radar communication integrated signal S(t): Where t is time, T p A is the time width of the radar communication integrated signal of the nonlinear frequency modulation sixteenth-order orthogonal amplitude modulation, m(t) is the amplitude of the radar communication integrated signal with nonlinear frequency modulation and sixteenth-order orthogonal amplitude modulation, j is the imaginary unit, fc is the carrier frequency of the radar communication integrated signal with nonlinear frequency modulation and sixteenth-order orthogonal amplitude modulation, is the phase function of the nonlinear frequency modulation signal, θ m(t) is the phase information after modulating the sixteenth-order quadrature amplitude modulation baseband signal.

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