Device and method for generating index modulation chirp signal

Abstract

The invention provides an index modulation linear frequency modulation signal generation device which is characterized by comprising a dual-wavelength laser source (1), a wavelength division demultiplexer (2), a dual-parallel Mach-Zehnder modulator (3), a 90-degree electric coupler (4), an intermediate frequency signal source (5), an optical coupler (6) and a photoelectric detector (7). The invention also provides an index modulation chirp signal generation method. According to the invention, multi-order slope modulation and cyclic shift modulation are combined, and a high-frequency-band ultra-wideband index modulation LFM signal is output through a photon up-conversion technology. The generated signal has good robustness under the condition of strong Doppler frequency shift, and the communication rate can be further expanded at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave photonics and microwave signal generation, and specifically relates to an index-modulated linear frequency modulation signal generation device and method for synaesthesia integrated application in a high-dynamic and low-signal-to-noise ratio environment. Background Art

[0002] Synaesthesia technology can make full use of spectrum, energy and hardware resources, and is expected to solve the spectrum shortage problem caused by the increasing types and number of frequency-using equipment, and promote the multi-function and integration of electronic equipment. Therefore, it has received widespread attention in recent years. Synaesthesia based on waveform sharing can realize the functional integration of communication and perception without dividing the hardware platform and transmission power, and has become one of the mainstream technologies of synaesthesia. Linear frequency modulation signals have been maturely applied in radar detection and spread spectrum communication due to their good pulse compression performance. Many researchers have designed synaesthesia signals of perception centers based on linear frequency modulation signals. However, with the large-scale deployment of low-orbit satellites, their high dynamic characteristics will bring serious Doppler frequency shift, which will cause the communication performance of synaesthesia signals to deteriorate sharply. In addition, high-precision perception and high-speed communication have prompted the development of synaesthesia platforms towards high-frequency broadband. Traditional signal generation technologies based on electronic devices such as frequency synthesizers and digital-to-analog converters are difficult to directly generate high-frequency broadband RF signals due to limitations in sampling clock rate, working bandwidth, etc. At the same time, mutual interference between electronic devices needs to be suppressed by electromagnetic shielding measures, which will further increase the system volume and power consumption, which is not conducive to the miniaturization of the system. Microwave photonic technology combines the advantages of optics and electricity to achieve direct generation, flexible processing and low-loss transmission of high-frequency broadband microwave signals, and has the ability to resist electromagnetic interference. Therefore, the use of microwave photonic technology to generate linear frequency modulation signals has developed rapidly in recent years. 1) Bai W, Li P, Zou X, et al. Millimeter-wave joint radar and communication system based on photonic frequency-multiplying constant envelope LFM-OFDM [J]. Optics Express, 2022, 30 (15): 26407-26425. Combining microwave photonic up-conversion technology and frequency doubling technology, the experiment achieved a detection resolution of 1.5 cm and a wireless communication rate of 8 Gbps. 2) Lyu Z, Zhang L, Zhang H, et al. Radar-centric photonic terahertz integrated sensing and communication system based on LFM-PSK waveform[J]. IEEE Transactions on Microwave Theory and Techniques, 2023. A pulse-coded BPSK-LFM optical generation scheme was proposed, and the ranging accuracy of 1.3 cm and the communication rate of 6 Gbps were experimentally verified. The influence of modulation index and bit rate on radar peak sidelobe ratio and communication bit error rate was analyzed.3) He J, Yin L, Li J, et al. NOMA-LFM Waveform and ANN Scheme for W-Band Integrated Sensing and Communication System[J]. IEEE Photonics Technology Letters, 2024, 36(8): 559-562. A NOMA-LFM integrated waveform generation scheme is proposed, combined with an ANN neural network to realize communication information recovery. Its detection resolution is 11.5 cm and the communication rate is 0.8 Gbps. 4) Li X, Zhou Y, Wang G, et al. Photonic joint radar and communication system using a chirp-polarity coded LFM waveform[J]. Optics Communications, 2024, 552: 130091. An optical generation scheme such as BOK-LFM integrated signal is designed, with detection resolution and communication rate reaching 1.875cm and 0.01Gbps. This scheme realizes binary coding by changing the positive and negative slopes of the LFM signal. It has strong Doppler tolerance in both target detection and communication functions, and can be applied to high dynamic scenarios.

[0003] The above schemes all have certain limitations: Scheme (1), Scheme (2) and Scheme (3) modulate the high-speed data stream on the ultra-wideband LFM carrier through intra-pulse phase or amplitude modulation, which can achieve high communication rate and detection accuracy under good signal-to-noise ratio conditions. However, in order to reduce the impact on detection performance, it is necessary to reduce the modulation index, which limits its communication reliability under low signal-to-noise ratio conditions. At the same time, in a high dynamic environment, Doppler frequency shift will have a greater impact on the recovery of communication information; Scheme (4) uses chirped polarity modulation, so that communication information can still be recovered under strong Doppler frequency shift. However, the communication symbol of this method only carries 1 bit on each pulse, which is difficult to be further expanded. Summary of the invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides an index modulated linear frequency modulation signal generating device, which comprises a dual-wavelength laser source 1, a demultiplexer 2, a dual parallel Mach-Zehnder modulator 3, a 90° electrical coupler 4, an intermediate frequency signal source 5, an optical coupler 6, and a photodetector 7;

[0005] A dual-wavelength laser source 1, which outputs dual-wavelength laser;

[0006] A wavelength division demultiplexer 2 receives the dual-wavelength laser output by the dual-wavelength laser source 1, performs wavelength separation on the dual-wavelength laser, and outputs separated optical wavelength signals from two output ports of the upper and lower branches respectively;

[0007] Intermediate frequency signal source 5, positive chirp linear frequency modulation signal and negative chirp linear frequency modulation signal are slope mapped and cyclically shifted according to corresponding communication symbols;

[0008] The 90° electric coupler 4 receives the intermediate frequency radiation, generates an intermediate frequency index modulated linear frequency modulation signal and outputs it through the intermediate frequency signal source 5; the intermediate frequency index modulated linear frequency modulation signal output by the intermediate frequency signal source 5 is subjected to a 90° phase shift, and outputs a phase-shifted intermediate frequency index modulated linear frequency modulation signal and an intermediate frequency index modulated linear frequency modulation signal that has not been phase-shifted;

[0009] A dual parallel Mach-Zehnder modulator 3 receives the optical wavelength signal output by the upper branch of the demultiplexer 2 and the phase-shifted intermediate frequency index modulated linear frequency modulation signal and the non-phase-shifted intermediate frequency index modulated linear frequency modulation signal output by the 90° electrical coupler 4, generates a positive first-order optical sideband of the intermediate frequency index modulated linear frequency modulation signal, suppresses even-order optical sidebands, and ignores higher-order odd-order optical sidebands;

[0010] An optical coupler 6 receives the positive first-order optical sideband output by the dual parallel Mach-Zehnder modulator 3 and the optical wavelength signal output by the lower branch of the demultiplexer 2, performs additive coupling processing on them, and outputs a coupled optical signal;

[0011] The photodetector 7 receives the coupled optical signal output by the optical coupler 6, and outputs an index-modulated linear frequency modulation electrical signal in a high frequency band after photoelectric conversion.

[0012] A method for generating an index modulated linear frequency modulation signal is also provided, which is based on the above-mentioned index modulated linear frequency modulation signal generating device, and the method is specifically as follows:

[0013] Step 1: The dual-wavelength continuous light at the output end of the dual-wavelength laser source 1 is input to the demultiplexer 2 for wavelength separation, and two optical wavelength signals with different frequencies are output from the two output ports of the upper and lower branches respectively;

[0014] Assume that the dual-wavelength continuous light E output by the dual-wavelength laser source 1 in (t) is:

[0015] E in (t) = E in [exp(2πf L t)+exp(2πf H t)] (1)

[0016] Among them, E in is the amplitude of the dual-wavelength continuous optical signal, f L and fH Respectively represent the optical frequencies of the lower frequency wavelength signal and the higher frequency wavelength signal in the dual-wavelength optical signal; these two wavelength signals E in [exp(2πf L t)+exp(2πf H t)] After entering the demultiplexer, the frequency is f L The wavelength of the optical signal and the frequency is f H The upper wavelength optical signal is separated into the lower branch and the upper branch respectively;

[0017] Step 2: In the intermediate frequency signal source 5, the positive chirp linear frequency modulation signal and the negative chirp linear frequency modulation signal are slope mapped and cyclic shift mapped according to the corresponding communication symbols to generate an intermediate frequency index modulated linear frequency modulation signal, which is input into the 90° electrical coupler 4 for 90° phase shift, generating a phase-shifted intermediate frequency index modulated linear frequency modulation signal and an unphase-shifted intermediate frequency index modulated linear frequency modulation signal, which are input into the dual parallel Mach-Zehnder modulator 3;

[0018] Assume that the unmodulated linear frequency modulation signal is expressed by formula (1):

[0019] S LFM (t) = A exp(jπ(2f0+kt 2 )),t∈[0,T] (2)

[0020] Among them, s LFM (t) represents the unmodulated linear frequency modulation signal, A, f0, k and T are the amplitude, carrier frequency, slope and period of the linear frequency modulation signal respectively; the communication symbol is mapped to the slope of the linear frequency modulation signal to realize slope modulation, and the obtained signal is expressed as:

[0021] c i (t) = A exp(jπ(2f0+k i t 2 )),t∈[0,T],i∈{1,2,…,K} (3)

[0022] Among them, c i (t) represents the slope modulated linear frequency modulation signal, k i is the slope of the slope modulated linear frequency modulation signal, the positive integer i is the slope index, and K is the number of slope indexes; k i Further expressed as:

[0023]

[0024] Among them, B minis the minimum bandwidth of the slope modulated linear frequency modulation signal, ΔB is the minimum bandwidth difference of the linear frequency modulation signal under different slopes; then the signal is cyclically shifted and modulated. Assuming that the shift amount is t0, the shifted linear frequency modulation signal is expressed as:

[0025]

[0026] Assume x i (n) is the slope modulated linear frequency modulation signal with sampling rate f s The discrete sequence obtained after sampling is the sampling sequence of the shifted linear frequency modulation signal, which is expressed by formula (5):

[0027]

[0028] Among them, the positive integers n and m represent the sequence number and the number of shifted points of the discrete sequence respectively, and satisfy n, m∈{1,2,3,...,f s T}, at the same time, m / f s = t0 holds; when the sampling rate f s is equal to the signal bandwidth and both are f s 、f s When T is even, formula (5) can be rewritten as:

[0029]

[0030] Cyclic shift modulation is equivalent to modulating the carrier frequency of the linear frequency modulation signal; positive integers p and j are defined as the minimum unit of cyclic shift and the cyclic shift index respectively, then the linear frequency modulation signal modulated by the intermediate frequency index is expressed as:

[0031] x i (n+jp),n∈[0,f s T],j∈{0,1,...,L-1} (8)

[0032] Where L represents the maximum number of cyclic shift indices, so the communication rate of the index modulated linear frequency modulation signal is expressed as:

[0033] R=PRF·log2(KL) (9)

[0034] Wherein, PRF is the repetition frequency of the linear frequency modulation signal; the intermediate frequency index modulated linear frequency modulation signal is generated by the intermediate frequency signal source 5 and then input into the dual parallel Mach-Zehnder modulator 3;

[0035] Step 3: The optical wavelength signal outputted from the upper branch of the demultiplexer 2 enters the dual parallel Mach-Zehnder modulator 3, and is subjected to single sideband modulation by the phase-shifted intermediate frequency index modulated linear frequency modulation signal and the non-phase-shifted intermediate frequency index modulated linear frequency modulation signal outputted by the 90° electrical coupler 4. The dual parallel Mach-Zehnder modulator 3 generates a positive first-order optical sideband, suppresses even-order optical sidebands, and ignores higher-order odd-order optical sidebands.

[0036] Assume that the complex continuous form of the intermediate frequency index modulated linear frequency modulation signal is s IND (t), the output signal of the intermediate frequency signal source 5 is Re{s IND (t)}; Re{·} represents the real part; after the phase shift of 90° coupler, it is input to the dual parallel Mach-Zehnder modulator 3, and the output positive first-order optical sideband signal E DPZMZM (t) is:

[0037] E DPZMZM (t) = E in (t)J1(α)exp(j2πf H )s IND (t) (10)

[0038] Where α is the modulation coefficient of the dual parallel Mach-Zehnder modulator 3, J n (·) is the Bessel function of the first kind of order n;

[0039] Step 4: The positive first-order optical sideband output by the dual parallel Mach-Zehnder modulator 3 and the downlink output optical wavelength signal of the de-wavelength division multiplexer 2 are input into the optical coupler 6 for coupling, and the coupled optical signal output by the optical coupler 6 is input into the photodetector 7, and after photoelectric conversion, an index modulated linear frequency modulation signal of a high frequency band is obtained;

[0040] The optical signal E coupled to the photodetector 7 by the optical coupler 6 is PD (t) is expressed as:

[0041] E PD (t) = E in (t)[exp(j2πf L t+J1(α)exp(j2πf H )s IND (t))] (11)

[0042] After photodetection, the output photocurrent of the photodetector 7 is:

[0043] i PD (t)∝Re{exp(j2π(f H -f L )t)·S IND (t)} (12)

[0044] Among them, Re{·} means taking the real part;

[0045] The high frequency band index modulation linear frequency modulation signal is generated; by tuning the frequency f of the output light wavelength of the dual wavelength laser source L and f H To change the working frequency band of the index modulated linear frequency modulation signal.

[0046] The present invention combines multi-order slope modulation and cyclic shift modulation, and outputs high-frequency ultra-wideband index modulation LFM signals through photon up-conversion technology. The generated signal has good robustness under strong Doppler frequency shift conditions, and the communication rate can be further expanded. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a structural schematic diagram of an index modulation linear frequency modulation signal generating device of the present invention;

[0048] Figure 2 The present invention generates a time domain waveform diagram and a time-frequency diagram of an index modulated linear frequency modulation signal, wherein Figure 2 (a) is the time domain waveform of the index modulated linear frequency modulation signal; Figure 2 (b) is a time-frequency diagram of the generated index modulated linear frequency modulation signal;

[0049] Figure 3 The present invention generates an index modulated linear frequency modulation signal to detect the target distance and obtain a one-dimensional distance image, wherein Figure 3 (a) shows the one-dimensional range image of a signal with a bandwidth of 0.5 GHz; Figure 3 (b) shows the one-dimensional range image of a signal with a bandwidth of 1 GHz; Figure 3 (c) shows the one-dimensional range image of a signal with a bandwidth of 1.5 GHz;

[0050] Figure 4 is the communication bit error rate curve of the present invention under different signal-to-noise ratios and different Doppler frequency shifts, where Figure 4 (a) shows the bit error rate curve under different signal-to-noise ratios; Figure 4 (b) shows the bit error rate curve under different Doppler frequency shifts. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings:

[0052] The present invention provides an index modulation linear frequency modulation signal generating device, such as Figure 1 As shown, it includes a dual-wavelength laser source 1, a wavelength division demultiplexer 2, a dual parallel Mach-Zehnder modulator 3, a 90° electrical coupler 4, an intermediate frequency signal source 5, an optical coupler 6, and a photodetector 7.

[0053] A dual-wavelength laser source 1, which outputs dual-wavelength laser;

[0054] A wavelength division demultiplexer 2 receives the dual-wavelength laser output by the dual-wavelength laser source 1, performs wavelength separation on the dual-wavelength laser, and outputs separated optical wavelength signals from two output ports of the upper and lower branches respectively;

[0055] The intermediate frequency signal source 5 performs slope mapping and cyclic shift mapping on the positive chirp linear frequency modulation signal and the negative chirp linear frequency modulation signal according to the corresponding communication symbol to generate an intermediate frequency index modulated linear frequency modulation signal and output it from the intermediate frequency signal source 5;

[0056] The 90° electric coupler 4 receives the intermediate frequency index modulated linear frequency modulation signal output by the intermediate frequency signal source 5, performs a 90° phase shift on the intermediate frequency index modulated linear frequency modulation signal, and outputs the intermediate frequency index modulated linear frequency modulation signal after the phase shift and the intermediate frequency index modulated linear frequency modulation signal without the phase shift;

[0057] A dual parallel Mach-Zehnder modulator 3 receives the optical wavelength signal output by the upper branch of the demultiplexer 2 and the phase-shifted intermediate frequency index modulated linear frequency modulation signal and the non-phase-shifted intermediate frequency index modulated linear frequency modulation signal output by the 90° electrical coupler 4, generates a positive first-order optical sideband of the intermediate frequency index modulated linear frequency modulation signal, and suppresses even-order optical sidebands. Higher-order odd-order optical sidebands can be ignored due to their low power.

[0058] An optical coupler 6 receives the positive first-order optical sideband output by the dual parallel Mach-Zehnder modulator 3 and the optical wavelength signal output by the lower branch of the demultiplexer 2, performs additive coupling processing on them, and outputs a coupled optical signal;

[0059] The photodetector 7 receives the coupled optical signal output by the optical coupler 6, and outputs an index-modulated linear frequency modulation electrical signal in a high frequency band after photoelectric conversion.

[0060] The present invention also provides a method for generating an index modulated linear frequency modulation signal, which is specifically as follows:

[0061] Step 1: The dual-wavelength continuous light at the output end of the dual-wavelength laser source 1 is input to the demultiplexer 2 for wavelength separation, and two optical wavelength signals with different frequencies are output from the two output ports of the upper and lower branches respectively.

[0062] Assume that the dual-wavelength continuous light E output by the dual-wavelength laser source 1 in (t) is:

[0063] E in (t) = E in [exp(2πf L t)+exp(2πf H t)] (1)

[0064] Among them, E inis the amplitude of the dual-wavelength continuous optical signal, f L and f H They represent the optical frequencies of the lower frequency wavelength signal and the higher frequency wavelength signal in the dual-wavelength optical signal. in [exp(2πf L t)+exp(2πf H t)] After entering the demultiplexer, the frequency is f L The wavelength of the optical signal and the frequency is f H The upper wavelength optical signal is separated into the lower branch and the upper branch respectively.

[0065] Step 2: In the intermediate frequency signal source 5, the positive chirp linear frequency modulation signal and the negative chirp linear frequency modulation signal are slope mapped and cyclic shift mapped according to the corresponding communication symbols to generate an intermediate frequency index modulated linear frequency modulation signal, which is input into the 90° electrical coupler 4 for a 90° phase shift to generate a phase-shifted intermediate frequency index modulated linear frequency modulation signal and an unphase-shifted intermediate frequency index modulated linear frequency modulation signal, which are input into the dual parallel Mach-Zehnder modulator 3.

[0066] Assume that the unmodulated linear frequency modulation signal can be expressed by formula (1):

[0067] s LFM (t) = A exp(jπ(2f0+kt 2 )),t∈[0,T] (2)

[0068] Among them, s LFM (t) represents the unmodulated linear frequency modulation signal, A, f0, k and T are the amplitude, carrier frequency, slope and period of the linear frequency modulation signal respectively. The communication symbol is mapped to the slope of the linear frequency modulation signal to realize slope modulation, and the obtained signal can be expressed as:

[0069] c i (t) = A exp(jπ(2f0+k i t 2 )),t∈[0,T],i∈{1,2,…,K} (3)

[0070] Among them, c i (t) represents the slope modulated linear frequency modulation signal, k i is the slope of the slope modulated linear frequency modulation signal, the positive integer i is the slope index, and K is the number of slope indexes. i It can be further expressed as:

[0071]

[0072] Among them, B minis the minimum bandwidth of the slope modulated linear frequency modulation signal, and ΔB is the minimum bandwidth difference of the linear frequency modulation signal under different slopes. The signal is then cyclically shifted and modulated. Assuming the shift amount is t0, the shifted linear frequency modulation signal can be expressed as:

[0073]

[0074] Assume x i (n) is the slope modulated linear frequency modulation signal with sampling rate f s The discrete sequence obtained after sampling, the sampling sequence of the shifted linear frequency modulation signal can be expressed by formula (5):

[0075]

[0076] Among them, the positive integers n and m represent the sequence number and the number of shifted points of the discrete sequence respectively, and satisfy n, m∈{1,2,3,...,f s T}, at the same time, m / f s = t0 holds. When the sampling rate f s is equal to the signal bandwidth and both are f s 、f s When T is even, formula (5) can be rewritten as:

[0077]

[0078] It can be seen that cyclic shift modulation is equivalent to modulating the carrier frequency of the linear frequency modulation signal. Define the positive integers p and j as the minimum unit of cyclic shift and the cyclic shift index respectively, then the linear frequency modulation signal modulated by the intermediate frequency index can be expressed as:

[0079] x i (n+jp),n∈[0,f s T],j∈{0,1,...,L-1} (8)

[0080] Where L represents the maximum number of cyclic shift indices, so the communication rate of the index modulated linear frequency modulation signal can be expressed as:

[0081] R=PRF·log2(KL) (9)

[0082] Where PRF is the repetition frequency of the linear frequency modulation signal. The intermediate frequency index modulated linear frequency modulation signal is generated by an intermediate frequency signal source 5 and then input into a dual parallel Mach-Zehnder modulator 3.

[0083] Step 3: The optical wavelength signal output from the upper branch of the demultiplexer 2 enters the dual parallel Mach-Zehnder modulator 3, and is subjected to single sideband modulation by the phase-shifted intermediate frequency index modulated linear frequency modulation signal and the non-phase-shifted intermediate frequency index modulated linear frequency modulation signal output by the 90° electrical coupler 4. The dual parallel Mach-Zehnder modulator 3 generates a positive first-order optical sideband and suppresses even-order optical sidebands. Higher-order odd-order optical sidebands can be ignored due to their low power.

[0084] Assume that the complex continuous form of the intermediate frequency index modulated linear frequency modulation signal is s IND (t), the output signal of the intermediate frequency signal source 5 is Re{s IND (t)}. Re{·} represents the real part. After the phase shift of 90° coupler, it is input to the dual parallel Mach-Zehnder modulator 3, and the output positive first-order optical sideband signal E DPZMZM (t) is:

[0085] E DPZMZM (t) = E in (t)J1(α)exp(j2πf H )s IND (t) (10)

[0086] Where α is the modulation coefficient of the dual parallel Mach-Zehnder modulator 3, J n (·) is the nth-order Bessel function of the first kind.

[0087] Step 4: The positive first-order optical sideband output by the dual parallel Mach-Zehnder modulator 3 and the downlink output optical wavelength signal of the de-wavelength division multiplexer 2 are input into the optical coupler 6 for coupling, and the coupled optical signal output by the optical coupler 6 is input into the photodetector 7. After photoelectric conversion, an index-modulated linear frequency modulation signal in the high frequency band can be obtained.

[0088] The optical signal E coupled to the photodetector 7 by the optical coupler 6 is PD (t) can be expressed as:

[0089] E PD (t) = E in (t)[exp(j2πf L t+J1(α)exp(j2πf H )s IND (t))] (11)

[0090] After photodetection, the output photocurrent of the photodetector 7 is:

[0091] i PD (t)∝Re{exp(j2π(f H -f L )t)·s IND (t)} (12)

[0092] Here, Re{·} indicates taking the real part.

[0093] Finally, the high-frequency index-modulated linear frequency modulation signal is successfully generated. At the same time, the frequency f of the output light wavelength of the dual-wavelength laser source can be tuned L and f H To change the working frequency band of the index modulated linear frequency modulation signal.

[0094] In order to verify the feasibility and effectiveness of the present invention, the signal generation function and the performance of the generated signal of the device were verified using the optisystem optical simulation platform.

[0095] Set the output optical carrier frequency of the dual-wavelength laser source 1 to 193.1THz and 193.11THz, and the output optical power to 16dBm; set the half-wave voltage of the dual parallel Mach-Zehnder modulator 3 to 4V; set the intermediate frequency of the intermediate frequency signal source to 0.5GHz, the minimum bandwidth of the intermediate frequency index modulated linear frequency modulation signal to 0.512GHz, the maximum bandwidth to 1.536GHz, the repetition frequency to 1MHz, and the total number of slope index and frequency shift index to 128. Then the communication rate is 28Mbps;

[0096] First, the signal generation function of the invention is verified. The output signal of the photodetector 7 is collected, and the time domain waveform and time-frequency diagram of the generated signal are respectively Figure 2 (a) and (b). It can be seen that the index modulation signal has a flat envelope, which has low requirements on the amplifier and is conducive to long-distance transmission in free space. Figure 2 As can be seen in (b), the starting frequency of the generated signal is 10.5 GHz, the maximum bandwidth can reach 1.5 GHz, and both slope modulation and cyclic shift modulation have been achieved, which is consistent with the principle analysis and experimental settings.

[0097] In order to verify the target detection capability of the invention, the device is used to generate signals for target detection simulation. The target is set to have two scattering points, and the distances relative to the transmitting end of the device are 40m and 40.3m respectively. The generated signal is delayed to simulate the echo signal. Then the echo signal is de-slanted to obtain a one-dimensional range image. Figure 3 (a), (b), and (c) show the target ranging results for signals with bandwidths of 0.5 GHz, 1 GHz, and 1.5 GHz, respectively. As can be seen from the figure, both scattering points can be resolved, but with the increase of bandwidth, the ranging effect is significantly improved. In actual applications, the bandwidth of the transmitted signal can be changed according to specific needs.

[0098] In order to verify the communication performance of the signal generated by the invention under noise conditions and strong Doppler frequency shift conditions, a bit error rate test was performed on the generated signal with a communication rate of 13.67Mbps. Figure 4 (a) is the bit error rate curve under the Gaussian white noise channel with a signal-to-noise ratio ranging from -20dB to 5dB. It can be seen that when the signal-to-noise ratio is higher than -10dB, the communication bit error rate of the index-modulated linear frequency modulation signal can be lower than 10 -3 This indicates that the generated signal has strong anti-noise performance. Figure 4 (b) is the bit error rate curve when the Doppler frequency shift is from 0 to 100kHz when the signal-to-noise ratio is 5dB. When the Doppler frequency shift is 100kHz, the communication bit error rate of the signal can still be maintained at nearly 10 -3 Therefore, the signal can still have good communication reliability in a high dynamic environment without relying on Doppler compensation.

Claims

1. An index modulated linear frequency modulation signal generating device, characterized in that: The device comprises a dual-wavelength laser source (1), a wavelength division multiplexer (2), a dual parallel Mach-Zehnder modulator (3), a 90° electrical coupler (4), an intermediate frequency signal source (5), an optical coupler (6), and a photodetector (7); A dual-wavelength laser source (1) which outputs dual-wavelength laser light; A wavelength division demultiplexer (2) receives the dual-wavelength laser light output by the dual-wavelength laser source (1), performs wavelength separation on the dual-wavelength laser light, and outputs separated optical wavelength signals from two output ports of the upper and lower branches respectively; An intermediate frequency signal source (5) performs slope mapping and cyclic shift mapping on the positive chirp linear frequency modulation signal and the negative chirp linear frequency modulation signal according to corresponding communication symbols; A 90° electric coupler (4) receives the intermediate frequency radiation, generates an intermediate frequency index modulated linear frequency modulation signal and outputs the signal from the intermediate frequency signal source (5); Performing a 90° phase shift on the intermediate frequency index modulated linear frequency modulation signal output by the intermediate frequency signal source (5), and outputting a phase-shifted intermediate frequency index modulated linear frequency modulation signal and an intermediate frequency index modulated linear frequency modulation signal without phase shift; A dual parallel Mach-Zehnder modulator (3) receives the optical wavelength signal output by the upper branch of the de-wavelength division multiplexer (2) and the phase-shifted intermediate frequency index modulated linear frequency modulation signal and the non-phase-shifted intermediate frequency index modulated linear frequency modulation signal output by the 90° electrical coupler (4), generates a positive first-order optical sideband of the intermediate frequency index modulated linear frequency modulation signal, suppresses even-order optical sidebands, and ignores higher-order odd-order optical sidebands; An optical coupler (6) receives the positive first-order optical sideband output by the dual parallel Mach-Zehnder modulator (3) and the optical wavelength signal output by the lower branch of the demultiplexer (2), performs additive coupling processing on them, and outputs a coupled optical signal; The photodetector (7) receives the coupled optical signal output by the optical coupler (6), and outputs an index-modulated linear frequency-modulated electrical signal in a high-frequency band after undergoing photoelectric conversion.

2. A method for generating an index modulated linear frequency modulation signal, based on the index modulated linear frequency modulation signal generating device as claimed in claim 1, characterized in that: The details are as follows: Step 1: The dual-wavelength continuous light at the output end of the dual-wavelength laser source (1) is input to the wavelength division multiplexer (2) for wavelength separation, and two optical wavelength signals with different frequencies are output from the two output ports of the upper and lower branches respectively; Assume that the dual-wavelength continuous light E output by the dual-wavelength laser source (1) in (t) is: E in (t)=E in [exp(2πf L t)+exp(2πf H t)] (1) Among them, E in is the amplitude of the dual-wavelength continuous optical signal, f L and f H Respectively represent the optical frequencies of the lower frequency wavelength signal and the higher frequency wavelength signal in the dual-wavelength optical signal; these two wavelength signals E in [exp(2πf L t)+exp(2πf H t)] After entering the demultiplexer, the frequency is f L The wavelength of the optical signal and the frequency is f H The upper wavelength optical signal is separated into the lower branch and the upper branch respectively; Step 2: In the intermediate frequency signal source (5), the positive chirp linear frequency modulation signal and the negative chirp linear frequency modulation signal are slope mapped and cyclic shift mapped according to the corresponding communication symbols to generate an intermediate frequency index modulated linear frequency modulation signal, which is input into the 90° electrical coupler (4) for 90° phase shift, generating a phase-shifted intermediate frequency index modulated linear frequency modulation signal and an unphase-shifted intermediate frequency index modulated linear frequency modulation signal, which are input into the dual parallel Mach-Zehnder modulator (3); Assume that the unmodulated linear frequency modulation signal is expressed by formula (1): s LFM (t)=A exp(jπ(2f0+kt 2 )),t∈[0,T] (2) Among them, s LFM (t) represents the unmodulated linear frequency modulation signal, A, f0, k and T are the amplitude, carrier frequency, slope and period of the linear frequency modulation signal respectively; the communication symbol is mapped to the slope of the linear frequency modulation signal to realize slope modulation, and the obtained signal is expressed as: c i (t)=Aexp(jπ(2f0+k i t 2 )),t∈[0,T],i∈{1,2,…,K} (3) Among them, c i (t) represents the slope modulated linear frequency modulation signal, k i is the slope of the slope modulated linear frequency modulation signal, the positive integer i is the slope index, and K is the number of slope indexes; k i Further expressed as: Among them, B min is the minimum bandwidth of the slope modulated linear frequency modulation signal, ΔB is the minimum bandwidth difference of the linear frequency modulation signal under different slopes; then the signal is cyclically shifted and modulated. Assuming that the shift amount is t0, the shifted linear frequency modulation signal is expressed as: Assume x i (n) is the slope modulated linear frequency modulation signal with sampling rate f s The discrete sequence obtained after sampling is the sampling sequence of the shifted linear frequency modulation signal, which is expressed by formula (5): Among them, the positive integers n and m represent the sequence number and the number of shifted points of the discrete sequence respectively, and satisfy n, m∈{1,2,3,...,f s T}, at the same time, m / f s = t0 holds; when the sampling rate f s is equal to the signal bandwidth and both are f s 、f s When T is even, formula (5) can be rewritten as: Cyclic shift modulation is equivalent to modulating the carrier frequency of the linear frequency modulation signal; positive integers p and j are defined as the minimum unit of cyclic shift and the cyclic shift index respectively, then the linear frequency modulation signal modulated by the intermediate frequency index is expressed as: x i (n+jp),n∈[0,f s T],j∈{0,1,...,L-1} (8) Where L represents the maximum number of cyclic shift indices, so the communication rate of the index modulated linear frequency modulation signal is expressed as: R=PRF·log2(KL) (9) Wherein, PRF is the repetition frequency of the linear frequency modulation signal; the intermediate frequency index modulated linear frequency modulation signal is generated by an intermediate frequency signal source (5) and then input into a dual parallel Mach-Zehnder modulator (3); Step 3: The optical wavelength signal outputted from the upper branch of the de-wavelength division multiplexer (2) enters the dual parallel Mach-Zehnder modulator (3), and is subjected to single sideband modulation by the phase-shifted intermediate frequency index modulated linear frequency modulation signal and the non-phase-shifted intermediate frequency index modulated linear frequency modulation signal outputted by the 90° electrical coupler (4). The dual parallel Mach-Zehnder modulator (3) generates a positive first-order optical sideband, suppresses even-order optical sidebands, and ignores higher-order odd-order optical sidebands. Assume that the complex continuous form of the intermediate frequency index modulated linear frequency modulation signal is s IND (t), then the output signal of the intermediate frequency signal source (5) is Re{s IND (t)}; Re{·} represents the real part; after the phase shift of 90° coupler, it is input into the dual parallel Mach-Zehnder modulator (3), and the output positive first-order optical sideband signal E DPZMZM (t) is: E DPZMZM (t)=E in (t)J1(α)exp(j2πf H )s IND (t) (10) Where α is the modulation coefficient of the dual parallel Mach-Zehnder modulator (3), J n (·) is the Bessel function of the first kind of order n; Step 4: The positive first-order optical sideband output by the dual parallel Mach-Zehnder modulator (3) and the downlink optical wavelength signal output by the de-wavelength division multiplexer (2) are input into the optical coupler (6) for coupling, and the coupled optical signal output by the optical coupler (6) is input into the photodetector (7), and after photoelectric conversion, a high-frequency index modulated linear frequency modulation signal is obtained; The optical signal E coupled to the photodetector (7) through the optical coupler (6) is PD (t) is expressed as: E PD (t)=E in (t)[exp(j2πf L t+J1(α)exp(j2πf H )s IND (t))] (11) After photodetection, the output photocurrent of the photodetector (7) is: i PD (t)∝Re{exp(j2π(f H -f L )t)·s IND (t)} (12) Among them, Re{·} means taking the real part; The high frequency band index modulation linear frequency modulation signal is generated; by tuning the frequency f of the output light wavelength of the dual wavelength laser source L and f H To change the working frequency band of the index modulated linear frequency modulation signal.

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