Microwave photon BPSK directional modulation signal generation device and method

Abstract

The invention discloses a microwave photon BPSK direction modulation signal generation device and method. The device comprises a laser LD, a double parallel Mach-Zehnder modulator DPMZM, a 90-degree bridge, phase modulators PM1 and PM2, a light beam splitter OS, a light beam combiner OC and a photoelectric detector PD. A laser signal generated by the laser PD passes through the light beam splitter and then is input into the double parallel Mach-Zehnder modulator DPMZM and the phase modulator PM1 at equal power. A local oscillator LO signal of the upper branch is divided into two paths after passing through a 90-degree bridge; in the lower branch, a pseudo-random binary signal PRBS generated by an arbitrary waveform generator AWG is input into a phase modulator PM1 to generate a phase coded signal; and finally, after beam combination of the upper branch and the lower branch, beat frequency is carried out through a photoelectric detector PD, so that direction modulation signals carrying different phase information are obtained. Compared with a traditional BPSK directional modulation scheme, the scheme provided by the invention can independently realize directional modulation of a plurality of frequency bands, the frequency can reach 40GHz, and the bandwidth can reach 4GHz.

Description

Technical Field

[0001] The invention belongs to the field of microwave technology, and in particular relates to a microwave photon BPSK directional modulation signal generating device and method. Background Art

[0002] With the rapid development of information technology and antenna technology, wireless communication is increasingly used in various fields, and the requirements for communication quality and speed are constantly increasing. However, in the process of signal transmission and reception, due to the diffusion characteristics of electromagnetic wave propagation, it is extremely easy to cause information leakage, endangering social and even national security. Traditional information security transmission methods mainly rely on upper-layer encryption technology, but these methods often affect transmission efficiency and have specific requirements for transmission channels. In order to improve information security, the research on physical layer security technology has begun to attract attention, among which directional modulation (DM) technology has attracted widespread research interest due to its effectiveness. At present, the implementation methods of directional modulation are mainly divided into two categories. One is to use the combination of RF end components to achieve it, and the other focuses on the algorithm design of baseband signals to achieve it. In the proposed physical layer security communication method, phase shifters are used as a means to change the array element weights. The advantage of this scheme is that if the angle of the eavesdropping direction is known, the phase weights of the antenna array source can be found only through theoretical derivation and mathematical calculation. This phased array with driven elements has been proven to be an effective and flexible directional modulation transmitter. However, the traditional electrical domain phased array method has disadvantages such as beam deflection and narrow bandwidth. To this end, a combination of microwave photon phase shifting technology and directional modulation technology was proposed, which has the advantages of anti-electromagnetic interference and a wide operating frequency range. Summary of the invention

[0003] In order to overcome the shortcomings of the prior art, the present invention provides a microwave photon BPSK directional modulation signal generation device and method, including a laser LD, a dual parallel Mahz modulator DPMZM, a 90-degree bridge, phase modulators PM1 and PM2, an optical beam splitter OS, an optical beam combiner OC and a photodetector PD; the laser signal generated by the laser PD is input into the dual parallel Mahz modulator DPMZM and the phase modulator PM1 with equal power after passing through the optical beam splitter; the local oscillator LO signal of the upper branch is divided into two paths after passing through the 90-degree bridge; the pseudo-random binary signal PRBS generated by the arbitrary waveform generator AWG in the lower branch is input into the phase modulator PM1 to generate a phase encoding signal; finally, after the upper branch and the lower branch are combined, they are beat by the photodetector PD, thereby obtaining a directional modulation signal carrying different phase information. Compared with the traditional BPSK directional modulation scheme, the proposed scheme can independently realize directional modulation of multiple frequency bands, and the frequency can reach 40GHz and the bandwidth can reach 4GHz.

[0004] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0005] A microwave photon BPSK directional modulation signal generating device comprises a laser LD, a dual parallel Magnetron modulator DPMZM, a 90-degree bridge, phase modulators PM1 and PM2, an optical beam splitter OS, an optical beam combiner OC and a photodetector PD;

[0006] The laser signal generated by the laser PD is input into the dual parallel MPZ modulator DPMZM and the phase modulator PM1 with equal power after passing through the optical beam splitter;

[0007] The microwave photon BPSK directional modulation signal generating device comprises two branches, an upper branch and a lower branch;

[0008] In the upper branch, the local oscillator LO signal is divided into two paths after passing through a 90-degree bridge. One path is input into the sub-modulator MZM1 of the dual parallel MPa modulator DPMZM, and the other path is input into the sub-modulator MZM2 of the dual parallel MPa modulator DPMZM after the signal is phase-shifted by 90 degrees. The sub-modulators MZM1 and MZM2 of the dual parallel MPa modulator DPMZM are biased at the minimum point, and the main modulator of the dual parallel MPa modulator DPMZM works at the orthogonal point to perform carrier suppressed single sideband modulation of the RF signal.

[0009] In the lower branch, the pseudo-random binary signal PRBS generated by the arbitrary waveform generator AWG is input into the phase modulator PM1 to generate a phase coded signal; then, the phase of the phase coded signal is regulated by a cascaded phase modulator PM2;

[0010] Finally, after the upper branch and the lower branch are combined, they are beat by the photodetector PD to obtain a directional modulation signal carrying different phase information.

[0011] A method for generating a microwave photon BPSK directional modulation signal comprises the following steps:

[0012] Step 1: Assume that the laser emits a laser represented by E in (t) = E0exp(jw c t), the generated RF signal is expressed as Vcos(Ωt); where w C is the angular frequency of the optical carrier, Ω is the angular frequency of the RF signal, E0 represents the amplitude of the laser signal, and V represents the amplitude of the RF signal;

[0013] Step 2: In the upper branch, the output signal of MZM1 is expressed as:

[0014]

[0015] The output signal of MZM2 is expressed as:

[0016]

[0017] Where m is the modulation index, J n (·) is the Bessel function of the first kind of order n, j represents the imaginary unit;

[0018] After the main modulator, the output signal of DPMZM is expressed as:

[0019]

[0020] Step 3: In the lower branch, the arbitrary waveform generator AWG generates a pseudo-random binary sequence PRBS, denoted as s(t);

[0021] After the phase modulator PM1 modulates the pseudo-random binary sequence PRBS, the output optical signal is expressed as:

[0022]

[0023] In the formula, is the modulation index of the coded signal, V C Indicates the amplitude of the code element, V π represents the half-wave voltage of the phase modulator;

[0024] Adjust the amplitude of the encoding signal so that V C =V π , formula (4) is expressed as:

[0025]

[0026] From equation (5), it can be obtained that when the phase coding signal changes between different code elements, the phase of the PM1 output optical signal changes between 0 and π;

[0027] The signal output from PM1 enters PM2 and is converted into a DC signal. DC PM2 is controlled to perform phase regulation, and the output optical signal is expressed as:

[0028]

[0029] Where m2 represents the modulation index of PM2;

[0030] Step 4: Send the combined optical signal to the PD for detection to obtain the photocurrent after the beat frequency:

[0031]

[0032] Where ξ is the responsivity of the photodetector, is the phase shift introduced by controlling PM2, J1(m) represents the first-order Bessel function of the first kind;

[0033] Formula (7) is the phase-shifted RF signal modulated by the phase-coded signal. Its carrier frequency is Ω / 2π, which is determined by the local oscillator. The phase of the signal is determined by the amplitude of the coded signal and the DC voltage V of PM2. DC The modulator's half-wave voltage V π The signal power is determined by the input optical power, the modulation efficiency of the modulator and the responsivity of the PD.

[0034] Step 5: The directional modulation signal output by the PD is transmitted using antenna 1 and antenna 2 respectively. Antenna 1 and antenna 2 are placed in parallel. It is assumed that the normal direction of the two antennas, i.e., 0 degrees, is the desired communication direction, and the eavesdropping direction is in the direction of α degrees to the right of the normal lines of the two antennas. The signal phase is adjusted so that the BPSK phase information can be correctly restored in the desired direction, but the BPSK phase information cannot be correctly restored in the eavesdropping direction.

[0035] Step 6: In order to avoid the influence of signal grating lobes, the relationship between wavelength and the distance between transmitting antennas is: d = λ / 2; since the eavesdropping direction is at α degrees of the normal of antenna 1 and antenna 2, the optical path difference is △d = d sinα; assuming that the transmitted signal is a single-frequency signal, at the eavesdropping position, the relative phase shift of the signal emitted by antenna 1 relative to the signal emitted by antenna 2 is

[0036] Let θ 1,0 and θ 1,1 Respectively represent the phase of the signal sent by antenna 1 when the code element is "0" and "1", θ 2,0 and θ 2,1 Respectively represent the phase of the signal sent by antenna 2 when the code element is "0" and "1", and the expression of the two code elements of the signal in the eavesdropping direction can be obtained as follows:

[0037]

[0038] Among them, w LO Indicates the angular frequency of the RF local oscillator signal used;

[0039] At the same time, the phase of the two code elements of the signal in the desired direction is:

[0040]

[0041] Using the sum-difference-product formula:

[0042]

[0043] Simplifying the phase of the signal in the eavesdropping direction and the desired direction, that is, simplifying formula (9) and formula (10), we get:

[0044]

[0045]

[0046] If the eavesdropping direction cannot identify the received "0" and "1" signals, while the expected direction can be demodulated normally, and it is different from the "null trap" method of the phased array, the following formula is satisfied:

[0047]

[0048] Therefore, as long as the phase between the "0" and "1" signals emitted by the two antennas meets the conditions in formula (13), the signal emitted by the system is a directional modulation signal, which can realize the directional modulation function in the far field.

[0049] A computer program, wherein the computer program enables a computer to execute the above-mentioned modulation signal generation method.

[0050] An electronic device comprises: a processor and a memory; the memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that the electronic device executes the above-mentioned modulation signal generation method.

[0051] A computer-readable storage medium stores a computer program, which implements the above-mentioned modulation signal generation method when executed by a processor.

[0052] A chip includes: a processor, which is used to call and run a computer program from a memory, so that a device equipped with the chip executes the above-mentioned modulation signal generation method.

[0053] A computer program product, the computer program product comprising a computer storage medium, the computer storage medium storing a computer program, the computer program comprising instructions executable by at least one processor, and the above-mentioned modulation signal generation method is implemented when the instructions are executed by the at least one processor.

[0054] The beneficial effects of the present invention are as follows:

[0055] Compared with the traditional BPSK directional modulation scheme, the proposed scheme can independently realize directional modulation of multiple frequency bands, and the frequency can reach 40GHz, and the bandwidth can reach 4GHz. Compared with the traditional QPSK directional modulation scheme, the proposed scheme no longer requires high-speed jumps of the phase shifter. After calculating the phase through the specific application scenario, the phase shifter only needs to be set once. In addition, the present invention can also perform long-distance transmission and control of signals by utilizing the characteristics of optical fiber transmission. The signal is modulated at the central station, transmitted to the base station through optical fiber for frequency beat, and finally sent to the desired receiver position through the antenna to realize the function of directional modulation. Compared with cable transmission, the use of optical fiber for long-distance transmission will greatly reduce signal loss and improve signal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a schematic diagram of a BPSK directional modulation signal generating device based on microwave photons of the present invention;

[0057] Figure 2 is the output spectrum of DPMZM;

[0058] Figure 3 is the output spectrum of PM;

[0059] Figure 4 Model for transmitting and receiving directional modulation signals for two-dimensional antennas;

[0060] Figure 5 The signal spectrum of the eavesdropping direction (left) and the signal spectrum of the desired direction (right);

[0061] Figure 6 The waveform diagram of the eavesdropping direction signal (above) and the expected direction signal waveform (below);

[0062] Figure 7 Phase information recovered for the eavesdropping direction;

[0063] Figure 8 The phase information recovered for the desired direction;

[0064] Fig. 9 PRBS signal generated by AWG;

[0065] Fig.10 The constellation diagram of the desired direction (left) and the constellation diagram of the eavesdropping direction (right);

[0066] Fig.11 The relationship between the bit error rate measured in different receiving directions and the communication bit error rate and the signal-to-noise ratio (1G)

[0067] Fig.12 The relationship between the bit error rate measured in different receiving directions and the communication bit error rate and the signal-to-noise ratio (10G)

[0068] Fig.13 The bit error rate measured in different receiving directions and the relationship between the communication bit error rate and the signal-to-noise ratio (40G); DETAILED DESCRIPTION

[0069] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0070] The present invention proposes a microwave photon directional modulation signal generation device based on a dual parallel Mach-Zehnder modulator (DPMZM) and a phase modulator (PM) for securely transmitting BPSK signals. Microwave photon phase shifting technology is used to solve the limitations of traditional technology, and long-distance signal transmission and control are achieved through optical fiber, reducing losses and system complexity, and improving application convenience.

[0071] The device uses a laser diode (LD), a dual parallel magnetostrictive modulator (DPMZM), a 90-degree bridge, a phase modulator (PM), an optical splitter (OS), an optical combiner (OC), and a photodetector (PD) to generate a BPSK directional modulation signal.

[0072] The technical solution adopted by the present invention is:

[0073] The laser signal generated by the laser passes through the optical beam splitter and is input into DPMZM and PM1 with equal power. In the upper branch, the local oscillator (LO) signal is divided into two paths after passing through a 90-degree bridge. One signal is input into the sub-modulator MZM1 of the DPMZM, and the other signal is input into the sub-modulator MZM2 of the DPMZM after the signal is phase-shifted by 90 degrees. The sub-modulators MZM1 and MZM2 of the DPMZM are biased at the minimum point, and the main modulator works at the orthogonal point to perform carrier suppressed single-sideband modulation of the RF signal. In the lower branch, the pseudo-random binary signal (PRBS) generated by the AWG is input into PM1 to generate a phase-encoded signal. After that, the phase of the phase-encoded signal is adjusted through a cascaded phase modulator (PM2). Finally, after the upper and lower beams are combined, they are beat by the photodetector (PD) to obtain a direction modulated signal carrying different phase information.

[0074] Assume that the laser emits laser light represented by E in (t) = E0exp(jw c t), the generated RF signal is expressed as Vcos(Ωt).C is the angular frequency of the optical carrier, and Ω is the angular frequency of the RF signal. In the upper branch, the output signal of MZM1 is expressed as:

[0075]

[0076] The output signal of MZM2 is expressed as:

[0077]

[0078] Where m is the modulation index, J n (·) is the Bessel function of the first kind of order n.

[0079] After the main modulator, the output signal of DPMZM is expressed as:

[0080]

[0081] In formula (3), when m < < 1, that is, when small signal modulation is performed, the properties of the Bessel function show that the value of the high-order Bessel function is very small compared to the value of the low-order Bessel function and can be ignored. Here, only the first-order optical sideband is considered. It can be seen that the output optical signal of DPMZM contains only the negative first-order optical variable band, realizing the carrier suppressed single sideband modulation of the RF signal.

[0082] In the lower branch, an arbitrary waveform generator (AWG) generates a pseudo-random binary sequence (PRBS), denoted as s(t).

[0083] After the phase modulator PM1 modulates the pseudo-random binary sequence (PRBS), the output optical signal is expressed as:

[0084]

[0085] In the formula, is the modulation index of the coded signal, V C is the amplitude of the code element. If the amplitude of the coded signal is properly adjusted, V C =V π , formula (4) can be expressed as:

[0086]

[0087] From equation (5), it can be obtained that when the phase coding signal changes between different code elements, the phase of the PM1 output optical signal changes between 0 and π.

[0088] The signal after PM1 output enters PM2 and is converted into a DC voltage DC PM2 is controlled to perform phase regulation, and the output optical signal is expressed as:

[0089]

[0090] By analyzing the expression, we can know that by properly regulating V DC , the phase of the output optical signal can be effectively controlled.

[0091] The combined optical signal is sent to the PD for detection to obtain the photocurrent after the beat frequency:

[0092]

[0093] Where ξ is the responsivity of the photodetector, It is the phase shift introduced by controlling PM2.

[0094] Formula (7) is the phase-shifted RF signal modulated by the phase-coded signal. Its carrier frequency is Ω / 2π, which is determined by the local oscillator. The phase of the signal is determined by the amplitude of the coded signal and the DC voltage V of PM2. DC The modulator's half-wave voltage V π The signal power is determined by the input optical power, the modulation efficiency of the modulator and the responsivity of the PD.

[0095] The directional modulation signal output by the PD is transmitted using antenna 1 and antenna 2 respectively. Antenna 1 and antenna 2 are placed in parallel. It is assumed that the normal direction of the two antennas (i.e., 0 degrees) is the desired communication direction, and the eavesdropping direction is in the α degree direction to the right of the normal lines of the two antennas. In order to achieve directional modulation, the signal phase needs to be adjusted so that the BPSK phase information can be correctly restored in the desired direction, but the BPSK phase information cannot be correctly restored in the eavesdropping direction.

[0096] In order to avoid the influence of signal grating lobes, the relationship between wavelength and the distance between transmitting antennas is: d = λ / 2. Since the eavesdropping direction is at α degrees of the normal of antenna 1 and antenna 2, the optical path difference is △d = dsinα. Assuming that the transmitted signal is a single-frequency signal, at the eavesdropping position, the relative phase shift of the signal emitted by antenna 1 relative to the signal emitted by antenna 2 is

[0097] Let θ 1,0 and θ 1,1 Respectively represent the phase of the signal sent by antenna 1 when the code element is "0" and "1", θ 2,0 and θ 2,1 They represent the phase of the signal sent by antenna 2 when the code element is "0" and "1" respectively. According to the established far-field reception model, the phase of the two code elements of the signal in the eavesdropping direction can be obtained as:

[0098]

[0099] At the same time, the phase of the two code elements of the signal in the desired direction is:

[0100]

[0101] Using the sum-difference-product formula:

[0102]

[0103] By simplifying the phase of the signal in the eavesdropping direction and the desired direction, that is, simplifying formula (9) and formula (10), we can obtain:

[0104]

[0105]

[0106] After analysis, if the eavesdropping direction cannot identify the received "0" and "1" signals, while the expected direction can be demodulated normally, and it is different from the "null trap" method of the phased array, the following formula needs to be satisfied:

[0107]

[0108] Therefore, as long as the phase between the "0" and "1" signals transmitted by the two antennas meets the conditions in formula (13), the signal transmitted by the system is a directional modulation signal, which can realize the directional modulation function in the far field. Let's take the eavesdropping direction of 30° as an example. Assuming that the phase when antenna 1 transmits the "0" code is 60°, as long as the phase when the binary array antenna transmits the signal meets the conditions shown in Table 1:

[0109] Table 1 Phase table of antenna sending 0,1 code (eavesdropping direction 30°)

[0110] Antenna 1 Antenna 2 "0" code 60 315 "1" code 225 150

[0111] According to formula (7), the phase part of the signal emitted by the antenna is in, After analysis, it can be found that in the first antenna, the coding amplitude of the phase coding signal needs to meet V C =0.916×V π , PM2 needs to shift the signal by 60 degrees; in the second antenna, the encoding amplitude of the phase-coded signal needs to meet V C =1.083×V π , PM2 needs to shift the phase of the signal by 315 degrees. When the signals generated by the two antennas are coupled in space, the directional modulation function can be realized in the far field.

[0112] Example:

[0113] In this example, the device includes: a laser, a RF signal source, an AWG signal source, a DPMZM, PM1, PM2, an optical beam splitter, an optical beam combiner, a 90-degree bridge, a PD, and an antenna.

[0114] Step 1: Device connection, such as Figure 1 As shown. The output port of the laser is connected to the input port of the optical beam splitter, and the two output ports of the optical beam splitter are connected to the input ports of DPMZM1 and PM1 respectively. In the upper branch, the local oscillator signal is divided into two paths after passing through a 90-degree bridge. One signal is input into the sub-modulator MZM1 of the DPMZM, and the other signal is phase-shifted 90 degrees and input into the sub-modulator MZM2 of the DPMZM. In the lower branch, the pseudo-random binary signal generated by the AWG is input into PM1 to generate a phase-coded signal. After that, the phase of the phase-coded signal is adjusted through a cascaded phase modulator (PM2). After the upper and lower beams are combined, they are beat by the photodetector (PD) to obtain a direction modulated signal carrying different phase information. Finally, the electrical signal output by the photodetector enters the transmitting antenna.

[0115] Step 2: The laser generates an optical carrier with an operating wavelength of 1552.52nm and an optical power of 15dBm; the RF signal source generates an RF signal with a frequency of 1GHz and a power of 10dBm; the half-wave voltage of DPMZM is 3.5V, and the extinction ratio is 35dB; a pseudo-random code (PBRS) is used to simulate binary information code elements, the PBRS signal voltage is -3.5V, and the AWG outputs a PBRS signal; the PD's responsivity is 0.7A / W.

[0116] Step 3: Set the sub-modulators MZM1 and MZM2 in DPMZM to work at the minimum point, and the main modulator to work at the orthogonal point to perform carrier suppression of the RF signal. Taking the carrier frequency 1G as an example, the output spectrum of DPMZM is as follows: Figure 2 As shown. According to the calculation, the bias voltages of PM1 and PM2 are set to control the phase of the output signal. Taking the carrier frequency 1G and the symbol rate 100M as an example, the spectrum after modulation is as follows Figure 3 shown.

[0117] Step 4: PD performs photoelectric detection, recovers the directional modulation signal, and inputs it into the transmitting antenna.

[0118] Step 5: Use two identical devices to generate the signals required by transmitting antenna 1 and transmitting antenna 2 after synchronization operation, such as Figure 4 shown.

[0119] Step 5: The signal data of transmitting antenna 1 and transmitting antenna 2 are processed by MATLAB. According to the free space transmission model, the antenna propagation is simulated, the communication information is received in the desired direction and the eavesdropping direction respectively, the various characteristics of the information are tested, and the directional modulation function is verified.

[0120] Step 6: Observe and analyze the spectrum information of the signals received in two directions, such as Figure 5 As shown. Although the received signal power at 1GHz is significantly higher than the noise value in both the eavesdropping direction and the desired direction, indicating that there is a signal at 1GHz, the power spectrum in the eavesdropping direction shows that only a single-tone signal is received and does not carry useful information; while in the desired direction, the power spectrum is obviously the spectrum of the modulated signal, which belongs to the spectrum diagram of the phase-coded signal, indicating that the signal carries useful information. In addition, the power in the desired direction is slightly higher than that in the eavesdropping direction by 5dB, which is also consistent with the results of theoretical derivation. By analyzing the power spectrum diagram, it is shown that the system realizes the basic function of directional modulation. At the same time, it also explains the difference between the proposed method and the phased array "zero line" method. In the method of beam control using phased array, there is generally no signal power or very small signal power in the eavesdropping direction. The difference between directional modulation and eavesdropping direction is that the signal can be received in the eavesdropping direction, but useful information cannot be correctly demodulated.

[0121] Observe and analyze the waveform information of the signals received in two directions, such as Figure 6 As shown, it can be seen that the signal power in the eavesdropping direction is low and the waveform is messy. Before and after the symbol jump point 583ns, it can be seen that the phase of the signal in 578-579ns and 586-587ns is consistent, which means that although the signal has passed the symbol jump point, there is no obvious phase change, and useful information cannot be demodulated from it. However, the signal power in the desired direction is not only stable with a clear envelope relative to the eavesdropping receiver, but also has a stable frequency within the symbol period, and the phase information is clear and regular. Observing the waveform before and after the symbol jump point 583ns, it can be found that the phase of the signal in 578-579ns and 586-587ns is opposite. After the symbol jump point, the phase flip is obvious, indicating that the signal carries useful information.

[0122] Observe and analyze the phase information of the signals received in two directions, such as Figure 7 and Figure 8 As shown in Figure 1, the phase waveform recovered from the information received in the eavesdropping direction oscillates in a small range, which is different from the waveform of the input binary information code element ( Fig. 9 The phase waveforms (as shown) do not correspond to each other, while the phase waveform recovered from the information received in the desired direction is completely consistent with the input waveform.

[0123] Observe and analyze the constellation diagram of the signals received in two directions, such as Fig.10As shown in the figure, the constellation diagram of the signal received in the desired direction is concentrated at two points (-1,0) and (1,0), and the constellation points are relatively concentrated, with an EVM value of 6%, which is consistent with the standard constellation diagram of BPSK signals. In the eavesdropping direction, the constellation points are concentrated at one point, and the EVM value is as high as 99%.

[0124] Finally, observe the bit error rate of the system in different directions when the signal-to-noise ratio is 20dB. The experimental results with a carrier frequency of 1GHz and a bandwidth of 100MHz are shown in the figure below. Fig.11 The experimental results with a carrier frequency of 10 GHz and a bandwidth of 2 GHz are shown in Fig.12 The experimental results with a carrier frequency of 40 GHz and a bandwidth of 4 GHz are shown in Fig.13 As shown in Figure 1, it can be found that only the bit error rate near the desired direction of 0 degrees is below 10 -6 Below 0.05, the communication bit error rate in the remaining directions is very high and cannot meet the communication requirements, which achieves the established goal of directional modulation. In addition, compared with the traditional phased array beam steering method, this scheme can transmit low bit error rate in a narrower area than traditional transmitters. When the deviation on both sides of the desired direction is more than 6 degrees, the communication bit error rate increases to 10 -3 Left and right, achieving good signal directionality.

[0125] In summary, the present invention can generate a BPSK directional modulation signal with a carrier frequency of 1-40 GHz and a maximum symbol rate of 4 GHz, a low bit error transmission angle of up to 8 degrees, and a bit error rate as low as 10 -6 . Compared with traditional solutions, this system has fewer antennas, the phase shifter only needs to be set once, and it no longer needs to jump at a high speed at the symbol rate, which has lower loss and complexity. In addition, the system can make full use of the technical advantages of the optical radio frequency link. The modulation, mixing and other signal processing methods are all completed in the central station, and the low-loss and low-distortion long-distance transmission of the radio frequency signal is achieved through optical fiber. The use of components such as mixers and filters in the base station is avoided, which effectively simplifies the complexity of the base station. This is crucial in 5G and 6G mobile communication systems. This will greatly reduce the number of base stations and construction costs, while achieving higher network coverage and capacity. Finally, the scheme can obtain high-performance and large-bandwidth modulated signals, which is easy to implement and flexible to operate. It has great inspiration and potential application value in the directional modulation of today's radar, electronic warfare and wireless communication systems.

Claims

1. A microwave photon BPSK directional modulation signal generating device, characterized in that: It includes laser LD, dual parallel Magnetron modulator DPMZM, 90 degree bridge, phase modulators PM1 and PM2, optical beam splitter OS, optical beam combiner OC and photodetector PD; The laser signal generated by the laser PD is input into the dual parallel MPZ modulator DPMZM and the phase modulator PM1 with equal power after passing through the optical beam splitter; The microwave photon BPSK directional modulation signal generating device comprises two branches, an upper branch and a lower branch; In the upper branch, the local oscillator LO signal is divided into two paths after passing through a 90-degree bridge. One path is input into the sub-modulator MZM1 of the dual parallel MPa modulator DPMZM, and the other path is input into the sub-modulator MZM2 of the dual parallel MPa modulator DPMZM after the signal is phase-shifted by 90 degrees. The sub-modulators MZM1 and MZM2 of the dual parallel MPa modulator DPMZM are biased at the minimum point, and the main modulator of the dual parallel MPa modulator DPMZM works at the orthogonal point to perform carrier suppressed single sideband modulation of the RF signal. In the lower branch, the pseudo-random binary signal PRBS generated by the arbitrary waveform generator AWG is input into the phase modulator PM1 to generate a phase coded signal; then, the phase of the phase coded signal is regulated by a cascaded phase modulator PM2; Finally, after the upper branch and the lower branch are combined, they are beat by the photodetector PD to obtain a directional modulation signal carrying different phase information.

2. A method for generating a microwave photon BPSK directional modulation signal using the modulation signal generating device as claimed in claim 1, characterized in that: The steps include: Step 1: Assume that the laser emits a laser represented by E in (t) = E0 exp(jw c t), the generated RF signal is expressed as Vcos(Ωt); where w C is the angular frequency of the optical carrier, Ω is the angular frequency of the RF signal, E0 represents the amplitude of the laser signal, and V represents the amplitude of the RF signal; Step 2: In the upper branch, the output signal of MZM1 is expressed as: The output signal of MZM2 is expressed as: Where m is the modulation index, J n (·) is the Bessel function of the first kind of order n, j represents the imaginary unit; After the main modulator, the output signal of DPMZM is expressed as: Step 3: In the lower branch, the arbitrary waveform generator AWG generates a pseudo-random binary sequence PRBS, denoted as s(t); After the phase modulator PM1 modulates the pseudo-random binary sequence PRBS, the output optical signal is expressed as: In the formula, is the modulation index of the coded signal, V C Indicates the amplitude of the code element, V π represents the half-wave voltage of the phase modulator; Adjust the amplitude of the encoding signal so that V C =V π , formula (4) is expressed as: From equation (5), it can be obtained that when the phase coding signal changes between different code elements, the phase of the PM1 output optical signal changes between 0 and π; The signal output from PM1 enters PM2 and is converted into a DC signal. DC PM2 is controlled to perform phase regulation, and the output optical signal is expressed as: Where m2 represents the modulation index of PM2; Step 4: Send the combined optical signal to the PD for detection to obtain the photocurrent after the beat frequency: Where ξ is the responsivity of the photodetector, is the phase shift introduced by controlling PM2, J1(m) represents the first-order Bessel function of the first kind; Formula (7) is the phase-shifted RF signal modulated by the phase-coded signal. Its carrier frequency is Ω / 2π, which is determined by the local oscillator. The phase of the signal is determined by the amplitude of the coded signal and the DC voltage V of PM2. DC The modulator half-wave voltage V π The signal power is determined by the input optical power, the modulation efficiency of the modulator and the responsivity of the PD. Step 5: The directional modulation signal output by the PD is transmitted using antenna 1 and antenna 2 respectively. Antenna 1 and antenna 2 are placed in parallel. It is assumed that the normal direction of the two antennas, i.e., 0 degrees, is the desired communication direction, and the eavesdropping direction is in the direction of α degrees to the right of the normal lines of the two antennas. The signal phase is adjusted so that the BPSK phase information can be correctly restored in the desired direction, but the BPSK phase information cannot be correctly restored in the eavesdropping direction. Step 6: In order to avoid the influence of signal grating lobes, the relationship between wavelength and the distance between transmitting antennas is: d = λ / 2; since the eavesdropping direction is at α degrees of the normal of antenna 1 and antenna 2, the optical path difference is △d = dsinα; assuming that the transmitted signal is a single-frequency signal, at the eavesdropping position, the relative phase shift of the signal emitted by antenna 1 relative to the signal emitted by antenna 2 is Let θ 1,0 and θ 1,1 Respectively represent the phase of the signal sent by antenna 1 when the code element is "0" and "1", θ 2,0 and θ 2,1 They represent the phase of the signal sent by antenna 2 when the code element is "0" and "1" respectively. The expression of the two code elements of the signal in the eavesdropping direction can be obtained as follows: Among them, w LO Indicates the angular frequency of the RF local oscillator signal used; At the same time, the phase of the two code elements of the signal in the desired direction is: Using the sum-difference-product formula: Simplifying the phase of the signal in the eavesdropping direction and the desired direction, that is, simplifying formula (9) and formula (10), we get: If the eavesdropping direction cannot identify the received "0" or "1" signal, but the desired direction can be demodulated normally, and it is different from the "nulling" method of the phased array, the following formula is satisfied: Therefore, as long as the phase between the "0" and "1" signals emitted by the two antennas meets the conditions in formula (13), the signal emitted by the system is a directional modulation signal, which can realize the directional modulation function in the far field.

3. A computer program, characterized in that The computer program enables a computer to execute the method according to any one of claims 1 to 2.

4. An electronic device, characterized in that: include: Processor and memory; The memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that the electronic device executes the method as claimed in any one of claims 1 to 2.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 2 is implemented.

6. A chip, characterized in that: include: A processor, configured to call and run a computer program from a memory, so that a device equipped with the chip executes a method as claimed in any one of claims 1 to 2.

7. A computer program product, characterized in that The computer program product comprises a computer storage medium storing a computer program, wherein the computer program comprises instructions executable by at least one processor, and when the instructions are executed by the at least one processor, the method according to any one of claims 1 to 2 is implemented.

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