Microwave photon QPSK direction modulation signal generation device and method

Abstract

The application provides a microwave photon QPSK direction modulation signal generation device and method, and belongs to the field of direction modulation and microwave photon; mainly solves the problems of narrow bandwidth and high-speed jumping of a phase shifter in the prior art based on a traditional electric domain phased array direction modulation method. The scheme of the application includes four identical direction modulation channels, each of which modulates a local oscillator electrical signal and an external input digital signal onto an optical carrier, simultaneously performs symbol-level phase shifting, finally obtains the direction modulation signal of each antenna, and then sends the direction modulation signal to a photodetector (PD) after passing through a polarization controller and a polarizer to obtain a final transmission signal; compared with the traditional QPSK direction modulation scheme, the application can realize direction modulation of multiple frequency bands alone, the bandwidth can reach 2GHz, and the program-controlled real-time high-speed jumping of the phase shifter is no longer needed.

Description

Technical Field

[0001] This invention belongs to the field of directional modulation and microwave photonics, and mainly relates to a microwave photonic QPSK directional modulation signal generation device and method. Background Technology

[0002] With the rapid development of information technology and antenna technology, wireless communication is increasingly widely used in various fields, and the requirements for communication quality and speed are constantly increasing. However, during signal transmission and reception, due to the broadcast characteristics of electromagnetic wave propagation, information leakage is extremely easy to occur, making communication links highly susceptible to eavesdropping and interference. Non-target receivers, as long as they are within the signal coverage area, may intercept information through highly sensitive receiving equipment, leading to data leakage, exposure of communication privacy, and even threats to system security. Traditional information security transmission methods mainly rely on upper-layer encryption technologies, but these methods often affect transmission efficiency and have specific requirements for the transmission channel. To improve information security, research on physical layer security technologies has begun to attract attention, among which Directional Modulation (DM) technology has aroused widespread research interest due to its effectiveness. Currently, the implementation methods of directional modulation are mainly divided into two categories: one is implemented using a combination of radio frequency components, and the other focuses on the algorithm design of baseband signals. In proposed physical layer secure communication methods, phase shifters are used as a means to change the weights of array elements. The advantage of this approach is that if the angle of the legitimate receiving direction is known, the phase weights of the antenna elements can be found simply through theoretical derivation and mathematical calculation. However, the directional modulation method based on traditional electric domain phased arrays has disadvantages such as narrow bandwidth and the need for phase shifters to switch at high speeds at the symbol rate. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies and solve the problems of narrow bandwidth and high-speed switching of phase shifters at symbol rates in traditional electric domain phased array-based directional modulation methods, this invention provides a microwave photonic QPSK directional modulation signal generation device and method.

[0004] A microwave photonic QPSK directional modulation signal generation device includes a laser, an external input digital signal, an optical beam splitter, a first directional modulation path, a second directional modulation path, a third directional modulation path, and a fourth directional modulation path; the laser generates an optical signal; No. The input to the directional modulation path includes the split signal output from the optical beam splitter and the externally input digital signal; The output of the directional modulation path is the first Directional modulation signal; The range is [1,4]; the structures of the first direction modulation path, the second direction modulation path, the third direction modulation path and the fourth direction modulation path are all the same; the first direction modulation path, the second direction modulation path, the third direction modulation path and the fourth direction modulation path modulate the local oscillator signal and the external input digital signal onto the optical carrier, and perform symbol-level phase shifting to finally obtain the directional modulation signal of each antenna.

[0005] Furthermore, the first The directional modulation path includes a radio frequency (RF) signal generator, an arbitrary signal generator (AWG), a 90-degree phase shifter, a modulation module, a polarization controller, a polarizer, and a photodetector. The RF signal generator (MSG) generates a local oscillator signal. An externally input digital signal is input to the arbitrary signal generator (AWG) to obtain an analog signal. ,analog signal Includes the phase shift values ​​of four phase shifters The range of k is [1,4]; the input of the modulation module includes the local oscillator signal, the output signal of the local oscillator signal after passing through a 90-degree phase shifter, and the analog signal. And the split signal; the output of the modulation module is the modulation module output signal; the modulation module output signal is sent to the photodetector PD after passing through the polarization controller PC and the polarizer Pol, and then obtains the first... Directional modulation signal; the modulation module is used to modulate the local oscillator RF signal onto the optical carrier, modulate the QPSK signal onto the optical carrier, and perform symbol-level phase shifting.

[0006] Furthermore, the modulation module includes a radio frequency signal modulation submodule and a QPSK signal symbol modulation submodule; the radio frequency signal modulation module includes a first submodulator and a second submodulator; the input of the first submodulator is a split signal and a local oscillator signal; the input of the second submodulator is a split signal and a local oscillator signal after passing through a 90-degree phase shifter; the output of the first submodulator is a first radio frequency modulation output signal; the output of the second submodulator is a second radio frequency modulation output signal; the first radio frequency modulation output signal and the second radio frequency modulation output signal are combined to obtain a radio frequency modulation signal; The QPSK signal symbol modulation module includes a third sub-modulator and a fourth sub-modulator; the inputs of both the third and fourth sub-modulators include a split signal and an analog signal. The output of the third sub-modulator is a third symbol modulated signal; the output of the fourth sub-modulator is a fourth symbol modulated signal; the third symbol modulated signal and the fourth symbol modulated signal are combined to obtain a phase modulated signal; The radio frequency modulation signal and the phase modulation signal are combined to obtain the output signal of the modulation module.

[0007] Furthermore, both the first and second sub-modulators are biased at the minimum point, and the radio frequency signal modulation module operates at the orthogonal point.

[0008] Furthermore, the third sub-modulator is biased at the maximum point, the fourth sub-modulator is biased at the minimum point, and the QPSK signal symbol modulation module operates at the quadrature point.

[0009] Furthermore, the modulation module is a DP-QPSK modulator.

[0010] Furthermore, the obtained modulation module output signal The steps are as follows: Step S1: The arbitrary waveform generator (AWG) generates the phase shift value carrying the k-th phase shifter based on the externally input digital signal. analog signal ; Arbitrary waveform generator (AWG) based on the desired communication direction angle Calculate the phase shift value of the k-th phase shifter The process is as follows: Assuming a QPSK signal is transmitted using four antennas placed in parallel, with the center of the antenna array as the origin and the vertical direction as the normal, the angle between the far-field receiver and the horizontal plane is the azimuth angle. ,wavelength Spacing with transmitting antenna The relationship is: ; The far-field received signal is then represented as : ; In the formula, Indicates the first One received symbol, It is the azimuth angle of the receiver, and k represents the k-th element of the antenna. , It is the distance from the kth array element to the center of the array; It is the phase shift value of the kth phase shifter; the range of k is [1,4]; Directional modulation is achieved using a single-objective function, which is: ; It is the desired communication direction angle. It is the set of constellation points of the QPSK modulated signal. ; For a single-objective cost function, i.e., to find a single-objective function. At the minimum value , , and The possible values ​​of , where ; Step S2: Based on the analog signal The optical signal and local oscillator electrical signal generated by the laser source respectively generate radio frequency modulation signals. and phase modulation signal ; ; in, This is the first radio frequency modulation output signal; This is the second radio frequency modulation output signal; The imaginary unit; It is the modulation index. It is an nth-order Bessel function of the first kind; First radio frequency modulation output signal for: ; Second radio frequency modulation output signal for: ; The optical signal generated by the laser source; ; It is the amplitude of the light signal. It is the angular frequency of the optical carrier wave; For a specific moment; This is the local oscillator signal; It is the amplitude of the light signal. It is the angular frequency of the radio frequency signal; Phase modulation signal for: ; in, It is an analog signal The modulation index, It is an analog signal The range; It is a third-symbol modulated signal; It is a fourth symbol modulated signal; Step S3: Based on the radio frequency modulation signal and phase modulation signal Generate modulation module output signal : The modulation module outputs a signal for: ; in, It refers to the responsivity of the photodetector.

[0011] The advantages of this invention are that, compared to traditional QPSK directional modulation schemes, the proposed scheme can independently achieve directional modulation across multiple frequency bands, with a bandwidth of up to 2GHz. Compared to traditional QPSK directional modulation schemes, the proposed scheme eliminates the need for programmable, real-time, high-speed phase shifting via a phase shifter; instead, it achieves this through a single pre-coding of the transmitted signal. Furthermore, each antenna uses only one integrated modulator for modulation processing, ensuring system stability. In addition, the system utilizes the characteristics of fiber optic transmission for long-distance signal transmission and control. The signal is modulated at the central station, transmitted via fiber optic cable to the base station for beat frequency, and finally transmitted to the desired receiver location via an antenna, achieving directional modulation. Compared to cable transmission, using fiber optic cable for long-distance transmission significantly reduces signal loss and improves signal quality. Attached Figure Description

[0012] Figure 1 This is a flowchart of the QPSK directional modulation signal generation design method based on microwave photonics according to the present invention; Figure 2 These are schematic diagrams and enlarged views of the device structure of the present invention; Figure 3 The output spectrum of DPMZM1; Figure 4 The output spectrum of DPMZM2; Figure 5 This is a model for transmitting and receiving directional modulation signals. Figure 6 A constellation diagram for receiving signals in the desired and eavesdropping directions; wherein, Figure 6 (a) is a constellation diagram at 60 degrees to the desired direction; Figure 6 (b) Constellation diagram at 45 degrees to the direction of eavesdropping; Figure 6 (c) Constellation diagram showing the direction of eavesdropping at 90 degrees; Figure 7 The bit error rate is measured for different receiving directions. Detailed Implementation

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0014] A microwave photonic QPSK directional modulation signal generation device includes a laser diode (LD), an external input digital signal, an optical splitter (OS), a first directional modulation path, a second directional modulation path, a third directional modulation path, and a fourth directional modulation path; the laser diode (LD) generates an optical signal. No. The input to the directional modulation path includes the split signal output from the optical beam splitter (OS) after the optical signal passes through it, and the externally input digital signal; The output of the directional modulation path is the first Directional modulation signal; The range is [1,4]; the structures of the first direction modulation path, the second direction modulation path, the third direction modulation path, and the fourth direction modulation path are all the same; The first The directional modulation path includes a microwave signal generator (MSG), an arbitrary waveform generator (AWG), a 90-degree phase shifter (PS), a modulation module, a polarization controller (PC), a polarizer (Pol), and a photodetector (PD). The MSG generates a local oscillator signal. An externally input digital signal is input to the AWG to obtain an analog signal. ,analog signal Including the phase shift value information of the k-th phase shifter The range of k is [1,4]. The modulation module includes a radio frequency signal modulation submodule and a QPSK signal symbol modulation submodule; The radio frequency signal modulation submodule is used for modulation of the local oscillator electrical signal, modulating the local oscillator radio frequency signal onto the optical carrier. The QPSK signal symbol modulation submodule is used for QPSK signal modulation, modulating the QPSK signal onto the optical carrier, and performing symbol-level phase shifting; The radio frequency signal modulation module includes a first sub-modulator and a second sub-modulator; the inputs of the first sub-modulator are a split signal and a local oscillator signal; the inputs of the second sub-modulator are a split signal and a local oscillator signal after passing through a 90-degree phase shifter; the output of the first sub-modulator is a first radio frequency modulation output signal; the output of the second sub-modulator is a second radio frequency modulation output signal. The first RF modulation output signal and the second RF modulation output signal are combined to obtain the RF modulation signal; The QPSK signal symbol modulation module includes a third sub-modulator and a fourth sub-modulator; the inputs of both the third and fourth sub-modulators include a split signal and an analog signal. ; The output of the third sub-modulator is a third symbol modulated signal; the output of the fourth sub-modulator is a fourth symbol modulated signal. The third-symbol modulated signal and the fourth-symbol modulated signal are combined to obtain the phase-modulated signal; The RF modulation signal and the phase modulation signal are combined to obtain the output signal of the modulation module. The output signal of the modulation module is then fed into the photodetector PD after passing through the polarization controller PC and the polarizer Pol to obtain the beat frequency. Directional modulation signal, antenna receives the first Directional modulation signals transmit electromagnetic wave signals to the far field.

[0015] The modulation module is a DP-QPSK modulator.

[0016] Both the first and second sub-modulators are biased at the minimum point, and the radio frequency signal modulation module operates at the orthogonal point.

[0017] The third sub-modulator is biased at the maximum point, the fourth sub-modulator is biased at the minimum point, and the QPSK signal symbol modulation module operates at the quadrature point.

[0018] The obtained modulation module output signal The steps are as follows: Step S1: The arbitrary waveform generator (AWG) generates the phase shift value carrying the k-th phase shifter based on the externally input digital signal. analog signal ; Arbitrary waveform generator (AWG) based on the desired communication direction angle Calculate the phase shift value of the k-th phase shifter The process is as follows: Assuming a QPSK signal is transmitted using four antennas placed in parallel, with the center of the antenna array as the origin and the vertical direction as the normal, the angle between the far-field receiver and the horizontal plane is the azimuth angle. ,wavelength Spacing with transmitting antenna The relationship is: ; The far-field received signal is then represented as : ; In the formula, Indicates the first One received symbol, It is the azimuth angle of the receiver, and k represents the k-th element of the antenna. , It is the distance from the kth array element to the center of the array; It is the phase shift value of the kth phase shifter; the range of k is [1,4]; Directional modulation is achieved using a single-objective function, which is: ; It is the desired communication direction angle. It is the set of constellation points of the QPSK modulated signal. ; For a single-objective cost function, i.e., to find a single-objective function. At the minimum value , , and The possible values ​​of , where ; Step S2: Based on the analog signal The optical signal and local oscillator electrical signal generated by the laser source respectively generate radio frequency modulation signals. and phase modulation signal ; ; in, This is the first radio frequency modulation output signal; This is the second radio frequency modulation output signal; The imaginary unit; It is the modulation index. It is an nth-order Bessel function of the first kind; First radio frequency modulation output signal for: ; Second radio frequency modulation output signal for: ; The optical signal generated by the laser source; ; It is the amplitude of the light signal. It is the angular frequency of the optical carrier wave; For a specific moment; This is the local oscillator signal; It is the amplitude of the light signal. It is the angular frequency of the radio frequency signal; Phase modulation signal for: ; in, It is an analog signal The modulation index, It is an analog signal The range; It is a third-symbol modulated signal; It is a fourth symbol modulated signal; Step S3: Based on the radio frequency modulation signal and phase modulation signal Generate modulation module output signal : The modulation module outputs a signal for: ; in, It refers to the responsivity of the photodetector.

[0019] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings: In this example, the apparatus includes: a laser (LD), a radio frequency signal source (MSG), an AWG signal source, a DP-QPSK modulator, an optical beam splitter, a 90-degree phase shifter, a polarization controller, a polarizer, a photodetector, and an antenna.

[0020] Step 1: Connect the device, such as Figure 1 As shown. The laser's output port connects to the input port of the optical beamsplitter, and the four output ports of the beamsplitter connect to four DP-QPSK modulators respectively. In each modulator, in the upper branch, the local oscillator signal is split into two paths after passing through a 90-degree phase shifter. One path is input to sub-modulator MZM1 of DP-QPSK, and the other path is input to sub-modulator MZM2 after being phase-shifted by 90 degrees. In the lower branch, the analog signal generated by the AWG... The input is fed into the DPMZM2 to generate a directional modulation phase-coded signal. After the upper and lower beams are combined, they pass through a polarization controller, a polarizer, and a photodetector (PD) to beat, thus obtaining directional modulation signals carrying different phase information. Finally, the electrical signal output from the photodetector enters the transmitting antenna.

[0021] Step 2: The laser generates an optical carrier with a working wavelength of 1552.52nm and an optical power of 15dBm; the RF signal source generates an RF signal with a frequency of 20GHz and a power of 10dBm; the half-wave voltage of the DP-QPSK modulator is 3.5V, and the extinction ratio is 35dB; the analog signal is calculated according to the desired receiving direction. Output by AWG; PD response is 0.7A / W.

[0022] Step 3: Set the sub-modulators MZM1 and MZM2 of DPMZM1 to operate at their minimum points, and the main modulator to operate at its quadrature point, to perform carrier suppression of the RF signal's single-sideband signal. Taking a carrier frequency of 20 GHz as an example, the output spectrum is as follows: Figure 2 As shown. The DPMZM2's MZM3 is set to operate at its maximum point, the MZM4 at its minimum point, and the main modulator at its quadrature point. Taking a 20 GHz carrier frequency and a 2 GHz symbol rate as an example, the modulated spectrum is shown below. Figure 3 As shown.

[0023] Step 4: The PD performs photoelectric detection, recovers the directional modulation electrical signal, and inputs it into the transmitting antenna.

[0024] Step 5: Using four identical sets of devices, generate the signals required for antennas 1 to 4, such as... Figure 4 The model shown.

[0025] Step 5: The signal data from the four transmitting antennas are processed by MATLAB. Based on the free space transmission model, the antenna propagation is simulated. Communication information is received in the desired direction and the eavesdropping direction, and the various characteristics of the information are tested to verify the directional modulation function.

[0026] Step Six: Observe and analyze the constellation diagram of the signals received from the expected and eavesdropping directions, such as... Figure 5 As shown, the constellation diagram of the signal received in the desired direction is a standard QPSK constellation, with all four phases clearly defined and 90° out of phase, indicating that the receiver in the desired direction can correctly receive and demodulate the signal. The constellation received by the receiver in the eavesdropping direction, however, is distorted, with no discernible pattern in amplitude and phase. The farther away from the desired direction, the more disordered the received constellation becomes.

[0027] Finally, the bit error rate of the system in different directions was observed at a signal-to-noise ratio of 20 dB. Experimental results with a carrier frequency of 20 GHz and a bandwidth of 2 GHz are shown below. Figure 6 As shown, it can be observed that the bit error rate is only around 10% near the expected direction of 60 degrees. -6 Below this, the communication bit error rate in other directions is very high, failing to meet communication requirements, thus achieving the intended goal of directional modulation. Furthermore, compared to traditional phased array beam control methods, this scheme can transmit with a lower bit error rate over a narrower area than traditional transmitters. When the deviation from the desired direction exceeds 8 degrees, the communication bit error rate increases to 10%. -3 Left and right, achieving good signal directionality.

[0028] The signal generation process is as follows: Step 1: The laser source generates an optical signal. The laser emitted by the laser is represented as... .in, It is the amplitude of the light signal. It is the angular frequency of the optical carrier wave.

[0029] Step 2: The local oscillator source generates a local oscillator signal. The generated local oscillator signal is represented as follows: .in, It is the amplitude of the light signal. It is the angular frequency of the radio frequency signal.

[0030] Step 3: Using a directional modulation algorithm, calculate the phase shift value of each array element when transmitting each symbol of the QPSK signal, so as to control the amplitude and phase in the electro-optic modulation module.

[0031] Assuming the directional modulation system uses 4 antennas for transmission, such as Figure 5 As shown, four antennas are placed in parallel, with the center of the antenna array as the origin, the vertical direction as the normal, and the angle between the far-field receiver and the horizontal plane as the azimuth angle. To avoid signal grating lobes from interfering with the signal, the relationship between wavelength and the distance between transmitting antennas is as follows: .

[0032] The far-field received signal is represented as: (1) In the formula, Indicates the first One received symbol, It is the azimuth angle of the receiver, and k represents the k-th element of the antenna. , It is the distance from the k-th array element to the center of the array. It is the phase shift value of the k-th phase shifter.

[0033] To achieve the directional modulation function, a single objective function for directional modulation is given: (2) It is the desired communication direction angle. It is the set of constellation points of the QPSK modulated signal.

[0034] When the desired communication direction is 60 degrees ( When the phase shift value of each antenna is obtained by using a genetic algorithm, as shown in Table 1.

[0035] Table 1. Phase table corresponding to directional modulation antennas (desired direction 60°)

[0036] Step 4: The electro-optic modulation module receives the optical signal emitted by the laser, the local oscillator electrical signal input from the local oscillator source, and the analog signal input from the direction modulation algorithm. It performs electro-optic modulation and outputs the modulated optical signal.

[0037] In the electro-optic modulation module, in the upper branch, the local oscillator (LO) signal is split into two paths after passing through a 90-degree phase shifter. One path is input to sub-modulator MZM1 of DPMZM1, and the other path is input to sub-modulator MZM2 of DPMZM1 after a 90-degree phase shift. Sub-modulators MZM1 and MZM2 of DPMZM1 are biased at their minimum points, and the main modulator operates at its quadrature point, performing carrier-suppressed single-sideband modulation of the RF signal.

[0038] In the upper branch, the output signal of MZM1 is represented as: (3) The output signal of MZM2 is represented as follows: (4) In the formula, It is the modulation index. It is an nth-order Bessel function of the first kind.

[0039] After passing through the main modulator, the output signal of DPMZM1 is expressed as: (5) In formula (5), when m At step 1, i.e., when performing small-signal modulation, the properties of Bessel functions indicate that the values ​​of higher-order Bessel functions are very small relative to those of lower-order Bessel functions and can be ignored. Here, only the first-order optical sideband is considered. It can be seen that the output optical signal of the DPMZM1 contains only the negative first-order optical modulation band, achieving carrier-suppressed single-sideband modulation of the RF signal.

[0040] In the lower branch, the analog signal generated by the AWG The input is fed into the sub-modulators MZM3 and MZM4 of DPMZM2. MZM3 is biased at its maximum point, and MZM4 is biased at its minimum point. The main modulator operates at the quadrature point to generate the QPSK signal. This is achieved by processing the analog signal... The level amplitude is pre-encoded to achieve symbol-level phase modulation of the generated QPSK signal.

[0041] After the DPMZM2 modulated phase-coded signal, the output optical signal is represented as: (6) in, It is the modulation index of the coded signal. It refers to the amplitude of the code element.

[0042] The modulator has a built-in PBC at the output terminal. The optical signals output by DPMZM1 and DPMZM2 are polarized and combined by the PBC to output a polarization multiplexed optical signal. The two polarization states of this signal are orthogonal to each other, namely the first-order optical sideband carrying radio frequency signal information and the optical carrier carrying phase-coded signal.

[0043] Step 5: The photodetector module receives the polarization-multiplexed optical signal output from the electro-optic modulation module. After passing through the polarization controller and polarizer, it is beat-detected by the photodetector (PD) to output a QPSK directional modulation signal carrying phase information at different symbol levels. To maximize the utilization of the output optical signal, the principal axis of the polarizer and the principal axis of the PBC are at a 45-degree angle, ultimately obtaining the beat-detected photocurrent: (7) in, It refers to the responsivity of the photodetector. It is the modulation index of the coded signal. It is the amplitude of the symbol. Formula (7) is the analog signal. The modulated radio frequency signal has a carrier frequency of The phase of the signal is determined by the local oscillator; the phase of the signal is determined by the analog signal. The amplitude and half-wave voltage of the modulator The signal power is jointly determined by the input optical power, the modulation efficiency of the modulator, and the responsivity of the PD. Since the antenna used in the directional modulation system has bandpass filtering characteristics, the DC component has no effect on the microwave signal and can be ignored. If the amplitude of the coded signal is appropriately adjusted, so that... Formula (7) can then be expressed as: (8) From equation (8), we can obtain that when the analog signal When varying between different amplitudes, the phase of the DP-QPSK output electrical signal is at 0, / 2、 and 3 The value varies between / 2.

[0044] According to formula (7), the phase component of the signal emitted by the antenna is: ,in, Through the analysis of By precoding and inputting different amplitudes, we can obtain the required QPSK directional modulation signals carrying phase information at different symbol levels. When the signals generated by each antenna are spatially coupled, the directional modulation function can be realized in the far field.

[0045] Step 6: The antenna receives the electrical signal generated by the photoelectric detection module and sends electromagnetic wave signals to the far field.

[0046] In summary, this invention can generate QPSK directional modulation signals with a carrier frequency of 20 GHz and a symbol rate of 2 GHz, achieving a low bit error rate transmission angle of up to 8 degrees and a bit error rate as low as 10%. -6Compared to traditional solutions, the pre-coded level approach eliminates the need for phase shifters that jump at high symbol rates, resulting in lower loss and complexity. Furthermore, this system fully leverages the advantages of optical radio frequency links, completing modulation, mixing, and other signal processing entirely at the central station, achieving low-loss, low-distortion long-distance transmission of radio frequency signals via optical fiber. This avoids the use of mixers, filters, and other components in base stations, effectively simplifying base station complexity. This is crucial in 5G and 6G mobile communication systems, significantly reducing the number of base stations and construction costs while achieving higher network coverage and capacity. Finally, this solution yields high-performance, high-bandwidth modulated signals, is easy to implement, and offers flexible operation, providing significant inspiration and potential applications for directional modulation in modern radar, electronic warfare, and wireless communication systems.

Claims

1. A microwave photonic QPSK directional modulation signal generation device, characterized in that: Includes a laser, an external input digital signal, an optical beam splitter, a first-direction modulation path, a second-direction modulation path, a third-direction modulation path, and a fourth-direction modulation path; the laser generates an optical signal; the... The input to the directional modulation path includes the split signal output from the optical beam splitter and the externally input digital signal; The output of the directional modulation path is the first Directional modulation signal; The range is [1,4]; the structures of the first direction modulation path, the second direction modulation path, the third direction modulation path and the fourth direction modulation path are all the same; the first direction modulation path, the second direction modulation path, the third direction modulation path and the fourth direction modulation path modulate the local oscillator signal and the external input digital signal onto the optical carrier, and perform symbol-level phase shifting to finally obtain the directional modulation signal of each antenna.

2. The microwave photonic QPSK directional modulation signal generation device according to claim 1, characterized in that, The first The directional modulation path includes a radio frequency (RF) signal generator, an arbitrary signal generator (AWG), a 90-degree phase shifter, a modulation module, a polarization controller, a polarizer, and a photodetector. The RF signal generator (MSG) generates a local oscillator signal. An externally input digital signal is input to the arbitrary signal generator (AWG) to obtain an analog signal. ,analog signal Includes the phase shift values ​​of four phase shifters The range of k is [1, 4]. The inputs to the modulation module include the local oscillator signal, the output signal of the local oscillator signal after passing through a 90-degree phase shifter, and the analog signal. And the split signal; the output of the modulation module is the modulation module output signal; The output signal of the modulation module is fed into the photodetector PD after passing through the polarization controller PC and the polarizer Pol to obtain the beat frequency, thus obtaining the first... Directional modulation signal; the modulation module is used to modulate the local oscillator RF signal onto the optical carrier, modulate the QPSK signal onto the optical carrier, and perform symbol-level phase shifting.

3. The microwave photonic QPSK directional modulation signal generation device according to claim 2, characterized in that, The modulation module includes a radio frequency (RF) signal modulation submodule and a QPSK signal symbol modulation submodule; the RF signal modulation module includes a first submodulator and a second submodulator; the inputs of the first submodulator are a split signal and a local oscillator signal; the inputs of the second submodulator are a split signal and a local oscillator signal after passing through a 90-degree phase shifter; the output of the first submodulator is a first RF modulation output signal; the output of the second submodulator is a second RF modulation output signal; the first RF modulation output signal and the second RF modulation output signal are combined to obtain an RF modulation signal; The QPSK signal symbol modulation module includes a third sub-modulator and a fourth sub-modulator; the inputs of both the third and fourth sub-modulators include a split signal and an analog signal. The output of the third sub-modulator is a third symbol modulation signal; the output of the fourth sub-modulator is a fourth symbol modulation signal; the third symbol modulation signal and the fourth symbol modulation signal are combined to obtain a phase modulation signal; the radio frequency modulation signal and the phase modulation signal are combined to obtain the output signal of the modulation module.

4. The microwave photonic QPSK directional modulation signal generation device according to claim 3, characterized in that, Both the first and second sub-modulators are biased at the minimum point, and the radio frequency signal modulation module operates at the orthogonal point.

5. The microwave photonic QPSK directional modulation signal generation device according to claim 3, characterized in that, The third sub-modulator is biased at the maximum point, the fourth sub-modulator is biased at the minimum point, and the QPSK signal symbol modulation module operates at the quadrature point.

6. The microwave photonic QPSK directional modulation signal generation device according to claim 2, characterized in that, The modulation module is a DP-QPSK modulator.

7. The method for generating the output signal of the modulation module of a microwave photonic QPSK directional modulation signal generation device according to claim 2, characterized in that, The obtained modulation module output signal The steps are as follows: Step S1: The arbitrary waveform generator (AWG) generates the phase shift value carrying the k-th phase shifter based on the externally input digital signal. analog signal ; Arbitrary waveform generator (AWG) based on the desired communication direction angle Calculate the phase shift value of the k-th phase shifter The process is as follows: Assuming a QPSK signal is transmitted using four antennas placed in parallel, with the center of the antenna array as the origin and the vertical direction as the normal, the angle between the far-field receiver and the horizontal plane is the azimuth angle. ,wavelength Spacing with transmitting antenna The relationship is: ; The far-field received signal is then represented as : ； In the formula, Indicates the first One received symbol, It is the azimuth angle of the receiver, and k represents the k-th element of the antenna. , It is the distance from the kth array element to the center of the array; It is the phase shift value of the kth phase shifter; the range of k is [1,4]; Directional modulation is achieved using a single objective function, which is: ； It is the desired communication direction angle. It is the set of constellation points of the QPSK modulated signal. ; For a single-objective cost function, i.e., to find a single-objective function. At the minimum value , , and The possible values ​​of , where ; Step S2: Based on the analog signal The optical signal and local oscillator electrical signal generated by the laser source respectively generate radio frequency modulation signals. and phase modulation signal ; ； in, This is the first radio frequency modulation output signal; This is the second radio frequency modulation output signal; The imaginary unit; It is the modulation index. It is an nth-order Bessel function of the first kind; First radio frequency modulation output signal for: ； Second radio frequency modulation output signal for: ； The optical signal generated by the laser source; ; It is the amplitude of the light signal. It is the angular frequency of the optical carrier wave; For a specific moment; This is the local oscillator signal; It is the amplitude of the light signal. It is the angular frequency of the radio frequency signal; Phase modulation signal for: ； in, It is an analog signal The modulation index, It is an analog signal The range; It is a third-symbol modulated signal; It is a fourth symbol modulated signal; Step S3: Based on the radio frequency modulation signal and phase modulation signal Generate modulation module output signal : The modulation module outputs a signal for: ； in, It refers to the responsivity of the photodetector.

8. A terminal device, comprising a signal modulation and generation module and a transmitting antenna, characterized in that, The signal modulation generation module generates a signal according to any one of claims 1-7 of the microwave photonic QPSK directional modulation signal generation device, and the signal is transmitted through a transmitting antenna.

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