Microwave photon BPSK direction modulation signal generation device and method

Abstract

The application discloses a microwave photon BPSK direction modulation signal generation device and method, which comprises a laser LD, a double parallel Mach-Zehnder modulator DPMZM, a 90-degree electric bridge, phase modulators PM1 and PM2, an optical beam splitter OS, an optical combiner OC and a photoelectric detector PD; laser signals generated by the laser PD are input into the double parallel Mach-Zehnder modulator DPMZM and the phase modulator PM1 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 electric bridge; the pseudo-random binary signal PRBS generated by the arbitrary waveform generator AWG is input into the phase modulator PM1 of the lower branch to generate a phase encoding signal; finally, the direction modulation signal carrying different phase information is obtained through the photoelectric detector PD after the upper branch and the lower branch are combined and beat. Compared with the traditional BPSK direction modulation scheme, the scheme can realize the direction modulation of multiple frequency bands alone, and the frequency can reach 40 GHz, and the bandwidth can reach 4 GHz.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology, specifically relating to a microwave photonic BPSK direction 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 diffusion characteristics of electromagnetic wave propagation, information leakage is extremely easy to occur, 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, research on physical layer security technology has begun to attract attention, among which directional modulation (DM) technology has aroused 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 radio frequency terminal components, and the other focuses on the algorithm design of baseband signals. In the proposed physical layer secure communication methods, 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 driving elements has been proven to be an effective and flexible directional modulation transmitter. However, traditional electrical domain phased array methods have disadvantages such as beam deflection and narrow bandwidth. Therefore, the combination of microwave photonic phase shifting technology and direction modulation technology has been proposed, which has advantages such as resistance to electromagnetic interference and a wide operating frequency range. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a microwave photonic BPSK directional modulation signal generation device and method, including a laser LD, a dual parallel MAZM 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 at equal power to the DPMZM and PM1 after passing through the optical beam splitter. The local oscillator (LO) signal of the upper branch is split into two paths after passing through the 90-degree bridge. The pseudo-random binary signal (PRBS) generated by the arbitrary waveform generator (AWG) of the lower branch is input to the phase modulator PM1 to generate a phase-coded signal. Finally, the upper and lower branches are combined and beat by the photodetector PD to obtain directional modulation signals carrying different phase information. Compared with traditional BPSK directional modulation schemes, the proposed scheme can independently achieve directional modulation in multiple frequency bands, with frequencies reaching up to 40 GHz and bandwidths up to 4 GHz.

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

[0005] A microwave photonic BPSK direction modulation signal generation device includes a laser LD, a dual parallel MAZM modulator, 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 at equal power to the dual parallel MAZM modulator and the phase modulator PM1 after passing through the optical beam splitter.

[0007] The microwave photonic BPSK directional modulation signal generation device includes two branches: an upper branch and a lower branch.

[0008] In the upper branch, the local oscillator (LO) signal is split into two paths after passing through a 90-degree bridge. One path is input to the sub-modulator MZM1 of the dual parallel MAZM modulator, and the other path is input to the sub-modulator MZM2 of the dual parallel MAZM modulator after a 90-degree phase shift. The sub-modulators MZM1 and MZM2 of the dual parallel MAZM modulator are biased at the minimum point, and the main modulator of the dual parallel MAZM modulator operates at the quadrature 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 adjusted by a cascaded phase modulator PM2.

[0010] Finally, after the upper and lower branches are combined, the signal passes through the photodetector PD beat frequency to obtain a directional modulation signal carrying different phase information.

[0011] A method for generating microwave photonic BPSK direction modulation signals includes the following steps:

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

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

[0014]

[0015] The output signal of MZM2 is represented as follows:

[0016]

[0017] In the formula, m is the modulation index, and J n (·) is the nth-order Bessel function of the first kind, where j represents the imaginary unit;

[0018] After passing through 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 represented as:

[0022]

[0023] In the formula, It is the modulation index of the coded signal, V C V represents the amplitude of the symbol. π This represents the half-wave voltage of the phase modulator;

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

[0025]

[0026] From equation (5), it can be seen that when the phase-encoded signal changes between different symbols, the phase of the output optical signal of PM1 changes between 0 and π.

[0027] The signal output from PM1 enters PM2, using DC V DC By controlling PM2 and performing phase modulation, the output optical signal is represented as follows:

[0028]

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

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

[0031]

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

[0033] Formula (7) is the phase-shiftable radio frequency signal modulated by the phase-encoded signal, whose carrier frequency is Ω / 2π, determined by the local oscillator; the phase of the signal is determined by the amplitude of the encoded signal and the DC voltage V controlling PM2. DC With the modulator's half-wave voltage V π The signal power is determined by the magnitude of 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. Assume that the normal direction of the two antennas, i.e., 0 degrees, is the desired communication direction, while the eavesdropping direction is α degrees to the right of the normal direction of the two antennas. Adjust the signal phase so that it can correctly recover the BPSK phase information in the desired direction, but cannot correctly recover the BPSK phase information in the eavesdropping direction.

[0035] Step 6: To avoid signal grating lobe interference, 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 to antennas 1 and 2, the resulting optical path difference is Δd = d sinα; Assuming the transmitted signal is a single-frequency signal, at the eavesdropping position, the relative phase shift of the signal received from antenna 1 relative to the signal received from antenna 2...

[0036] Let θ 1,0 and θ 1,1 θ represents the phase of the signal emitted by antenna 1 when the symbol is "0" and "1", respectively. 2,0 and θ 2,1 Let represent the phases of the signal emitted by antenna 2 when the code elements are "0" and "1" respectively. The expressions for the two code elements of the signal at the eavesdropping direction can be obtained as follows:

[0037]

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

[0039] At the same time, the phase of the two symbols of the signal at the desired direction is:

[0040]

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

[0042]

[0043] Simplifying the phases of the signals from the eavesdropping direction and the desired direction, i.e., simplifying formulas (9) and (10), we get:

[0044]

[0045]

[0046] To satisfy the condition that the received "0" and "1" signals cannot be identified in the direction of eavesdropping, while the desired direction can be demodulated normally, and this is different from the "null trap" method of phased arrays, the following equation must be satisfied:

[0047]

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

[0049] A computer program that causes a computer to perform the above-described modulation signal generation method.

[0050] An electronic device includes: 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 to cause the electronic device to perform the above-described modulation signal generation method.

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

[0052] A chip includes a processor for retrieving and running a computer program from a memory, causing a device on which the chip is mounted to perform the above-described modulation signal generation method.

[0053] A computer program product includes a computer storage medium storing a computer program, the computer program including instructions executable by at least one processor, which, when executed by the at least one processor, implement the above-described modulation signal generation method.

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

[0055] Compared to traditional BPSK directional modulation schemes, the proposed scheme can independently achieve directional modulation across multiple frequency bands, with a frequency range reaching 40 GHz and a bandwidth of 4 GHz. Compared to traditional QPSK directional modulation schemes, the proposed scheme eliminates the need for high-speed phase shifting; after calculating the phase according to the specific application scenario, the phase shifter only needs to be set once. Furthermore, this invention utilizes the characteristics of optical fiber transmission to enable long-distance signal transmission and control. The signal is modulated at the central station, transmitted via optical fiber to the base station for beat frequency adjustment, and finally sent to the desired receiver location via an antenna, achieving directional modulation. Compared to cable transmission, using optical fiber for long-distance transmission significantly reduces signal loss and improves signal quality. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the BPSK direction modulation signal generation device based on microwave photons of the present invention;

[0057] Figure 2 The output spectrum of DPMZM;

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

[0059] Figure 4 This is a two-dimensional antenna directional modulation signal transmission and reception model;

[0060] Figure 5 The image shows the spectrum of the signal from the direction of eavesdropping (left) and the spectrum of the signal from the desired direction (right).

[0061] Figure 6 The waveform diagrams for the direction of eavesdropping (top) and the desired direction of eavesdropping (bottom) are shown.

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

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

[0064] Figure 9 PRBS signal generated for AWG;

[0065] Figure 10 The constellation diagrams for the desired direction (left) and the direction of eavesdropping (right);

[0066] Figure 11 Relationship between bit error rate and communication bit error rate measured from different receiving directions and signal-to-noise ratio (1G)

[0067] Figure 12 Relationship between bit error rate and communication bit error rate measured from different receiving directions and signal-to-noise ratio (10G)

[0068] Figure 13 Relationship between bit error rate and communication bit error rate measured from different receiving directions and signal-to-noise ratio (40G); Detailed Implementation

[0069] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0070] This invention proposes a microwave photonic direction modulation signal generation device based on a dual parallel-Mach-Zehnder modulator (DPMZM) and a phase modulator (PM) for secure transmission of BPSK signals. It utilizes microwave photonic phase-shifting technology to overcome the limitations of traditional techniques and achieves long-distance signal transmission and control via optical fiber, reducing losses and system complexity, and improving application convenience.

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

[0072] The technical solution adopted in this invention is:

[0073] The laser signal generated by the laser is input to DPMZM and PM1 at equal power after passing through an optical beam splitter. In the upper branch, the local oscillator (LO) signal is split into two paths after passing through a 90-degree bridge. One path is input to the sub-modulator MZM1 of DPMZM, and the other path is phase-shifted by 90 degrees and input to the sub-modulator MZM2 of DPMZM. The sub-modulators MZM1 and MZM2 of DPMZM are biased at their minimum points, and the main modulator operates at the quadrature 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 to PM1 to generate a phase-coded signal. Then, the phase of the phase-coded signal is modulated by a cascaded phase modulator (PM2). Finally, the two beams are combined and beat by a photodetector (PD) to obtain a directional modulation signal carrying different phase information.

[0074] Assume the laser emitted by the laser is represented by E. in (t)=E0exp(jw c The generated radio frequency signal is represented as Vcos(Ωt). Where wC Ω is the angular frequency of the optical carrier wave, and Ω is the angular frequency of the radio frequency signal. In the upper branch, the output signal of MZM1 is expressed as:

[0075]

[0076] The output signal of MZM2 is represented as follows:

[0077]

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

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

[0080]

[0081] In formula (3), when m << 1, i.e., when small-signal modulation is performed, the higher-order Bessel function value is very small relative to the lower-order Bessel function value, and can be ignored, according to the properties of the Bessel function. 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 modulation band, realizing carrier-suppressed single-sideband modulation of the radio frequency signal.

[0082] In the lower branch, the 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 represented as:

[0084]

[0085] In the formula, It is the modulation index of the coded signal, V C It refers to the amplitude of the symbol. If the amplitude of the encoded signal is appropriately adjusted so that V... C =V π Formula (4) can then be expressed as:

[0086]

[0087] From equation (5), it can be seen that when the phase-encoded signal changes between different symbols, the phase of the output optical signal of PM1 changes between 0 and π.

[0088] The signal output from PM1 enters PM2 and is processed by DC V. DC By controlling PM2 and performing phase modulation, the output optical signal is represented as follows:

[0089]

[0090] Analysis of the expression shows that by reasonably adjusting V DC It can effectively control the phase of the output optical signal.

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

[0092]

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

[0094] Formula (7) is the phase-shiftable radio frequency signal modulated by the phase-encoded signal, whose carrier frequency is Ω / 2π, determined by the local oscillator; the phase of the signal is determined by the amplitude of the encoded signal and the DC voltage V controlling PM2. DC With the modulator's half-wave voltage V π The signal power is determined by the magnitude of 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 antennas 1 and 2, which are placed parallel to each other. Assume the normal direction of the two antennas (0 degrees) is the desired communication direction, while the eavesdropping direction is α degrees to the right of the antenna normals. To achieve directional modulation, the signal phase needs to be adjusted so that the BPSK phase information can be correctly recovered in the desired direction, but not in the eavesdropping direction.

[0096] To avoid signal grating lobe interference, the wavelength is related to the distance between the transmitting antennas as d = λ / 2. Since the eavesdropping direction is at α degrees of the normals to antennas 1 and 2, the resulting optical path difference is Δd = dsinα. Assuming the transmitted signal is a single-frequency signal, at the eavesdropping location, the relative phase shift of the received signal from antenna 1 relative to the signal from antenna 2...

[0097] Let θ 1,0 and θ 1,1 θ represents the phase of the signal emitted by antenna 1 when the symbol is "0" and "1", respectively. 2,0 and θ 2,1 These represent the phases of the signal emitted by antenna 2 when the symbol is "0" and "1", respectively. Based on the established far-field reception model, the phases of the two symbols of the signal at the eavesdropping direction can be obtained as follows:

[0098]

[0099] At the same time, the phase of the two symbols of the signal at the desired direction is:

[0100]

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

[0102]

[0103] Simplifying the phases of the signals from the eavesdropping direction and the desired direction, i.e., simplifying formulas (9) and (10), we can obtain:

[0104]

[0105]

[0106] Analysis shows that to satisfy the condition that the received "0" and "1" signals cannot be identified in the direction of eavesdropping, while the desired direction can be demodulated normally, and to differ from the "null trap" method of phased arrays, the following formula must be satisfied:

[0107]

[0108] Therefore, as long as the phase between the "0" and "1" signals transmitted by the two antennas satisfies the condition in formula (13), the signal transmitted by the system is a directional modulation signal, which can realize the function of directional modulation in the far field. Taking the eavesdropping direction as 30° as an example, assuming that the phase of antenna 1 when transmitting the "0" code is 60°, then as long as the phase of the two-element array antenna when transmitting the signal satisfies the conditions shown in Table 1:

[0109] Table 1. Phase table of 0 and 1 codes transmitted by the antenna (eavesdropping direction 30°)

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

[0111] According to formula (7), the phase component of the signal emitted by the antenna is: in, Analysis reveals that in the first antenna, the encoding amplitude of the phase-coded signal needs to satisfy V. C =0.916×V π PM2 requires a 60-degree phase shift of the signal; in the second antenna, the encoding amplitude of the phase-coded signal needs to satisfy V. C =1.083×V π PM2 requires a 315-degree phase shift of the signal. When the signals generated by the two antennas are spatially coupled, directional modulation can be achieved in the far field.

[0112] Example:

[0113] In this example, the device includes: a laser, a radio frequency 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: 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 two output ports of the beamsplitter connect to the input ports of DPMZM1 and PM1, respectively. In the upper branch, the local oscillator signal is split into two paths after passing through a 90-degree bridge. One path is input to the sub-modulator MZM1 of the DPMZM, and the other path, after being phase-shifted by 90 degrees, is input to the sub-modulator MZM2 of the DPMZM. In the lower branch, the pseudo-random binary signal generated by the AWG is input to PM1 to generate a phase-coded signal. Then, the phase of the phase-coded signal is modulated by a cascaded phase modulator (PM2). After the upper and lower beams are combined, they beat through a photodetector (PD) to obtain directional modulation signals carrying different phase information. Finally, the electrical signal output from the photodetector enters the transmitting antenna.

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

[0116] Step 3: Set the sub-modulators MZM1 and MZM2 in the DPMZM to operate at their minimum points, and the main modulator to operate at its quadrature point, to perform carrier suppression of the RF signal in single-sideband mode. Taking a carrier frequency of 1 GHz as an example, the output spectrum of the DPMZM is as follows: Figure 2 As shown. The bias voltages of PM1 and PM2 are set according to calculations to control the phase of the output signal. Taking a carrier frequency of 1 GHz and a symbol rate of 100 MHz as an example, the modulated spectrum is shown below. Figure 3 As shown.

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

[0118] Step 5: Using two identical devices, perform synchronization to generate the signals required for transmitting antenna 1 and transmitting antenna 2, such as... Figure 4 As shown.

[0119] Step 5: The signal data from transmitting antenna 1 and transmitting antenna 2 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.

[0120] Step Six: Observe and analyze the spectral information of the signals received from both directions, such as... Figure 5 As shown, although the received signal power at 1 GHz is significantly higher than the noise level in both the eavesdropping and desired directions, indicating the presence of a signal at 1 GHz, the power spectrum in the eavesdropping direction shows that only a single-tone signal is received, carrying no useful information. In contrast, the power spectrum in the desired direction is clearly the spectrum of a modulated signal, belonging to the spectrum of a phase-coded signal, indicating that the signal carries useful information. Furthermore, the power in the desired direction is slightly higher by 5 dB than in the eavesdropping direction, consistent with theoretical derivation. Analysis of the power spectrum demonstrates that the system achieves the basic function of directional modulation. It also elucidates the difference between the proposed method and the phased array "zero-line" method. In beam control using a phased array, there is generally no signal power or extremely low signal power in the eavesdropping direction. Directional modulation differs in that while a signal can be received in the eavesdropping direction, useful information cannot be correctly demodulated.

[0121] Observe and analyze the waveform information of the signals received from both directions, such as Figure 6 As shown, the signal power in the eavesdropping direction is low and the waveform is cluttered. Around the symbol transition point of 583ns, the phase of the signal remains consistent between 578-579ns and 586-587ns, indicating that although the signal passes the symbol transition point, no significant phase change occurs, making it impossible to demodulate useful information. However, the signal power in the desired direction is not only stable relative to the eavesdropping receiver and has a clear envelope, but also has a stable frequency within the symbol period, with clear and regular phase information. Observing the waveforms before and after the symbol transition point of 583ns, it can be found that the phases of the signal are opposite between 578-579ns and 586-587ns. After the symbol transition point, the phase reversal is obvious, indicating that the signal carries useful information.

[0122] Observe and analyze the phase information of the signals received from both directions, such as Figure 7 and Figure 8 As shown, the phase waveform recovered from the information received in the eavesdropping direction oscillates within a small range, which is different from the waveform of the input binary information code. Figure 9 The waveforms shown do not correspond to each other, but 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 diagrams of the signals received from both directions, such as Figure 10As shown, 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 conforms to the standard constellation diagram of BPSK signals. However, the constellation diagram in the eavesdropping direction shows the constellation points concentrated at a single point, with an EVM value as high as 99%.

[0124] Finally, the bit error rate of the system in different directions was observed at a signal-to-noise ratio of 20dB. The experimental results for a carrier frequency of 1GHz and a bandwidth of 100MHz are shown below. Figure 11 As shown; the experimental results with a carrier frequency of 10GHz and a bandwidth of 2GHz are as follows. Figure 12 As shown; the experimental results with a carrier frequency of 40GHz and a bandwidth of 4GHz are as follows. Figure 13 As shown, it can be observed that the bit error rate is only around 10 degrees near the desired direction of 0 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 on either side of the desired direction exceeds 6 degrees, the communication bit error rate increases to 10%. -3 Left and right, achieving good signal directionality.

[0125] In summary, this invention can generate BPSK directional modulation signals with carrier frequencies of 1-40 GHz and a maximum symbol rate of 4 GHz, achieving a low bit error rate transmission angle of up to 8 degrees and a bit error rate as low as 10%. -6 Compared to traditional solutions, this system requires fewer antennas, the phase shifter only needs to be set once, eliminating the need for high-speed symbol-rate switching, resulting in lower loss and complexity. Furthermore, this system fully leverages the technological advantages of optical-based radio frequency links, with modulation, mixing, and other signal processing all completed 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. It will significantly reduce 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 application value for directional modulation in today's radar, electronic warfare, and wireless communication systems.

Claims

1. A method for generating microwave photonic BPSK direction modulation signals, characterized in that, Includes the following steps: Step 1: Assume the laser emitted by the laser is represented by E. in (t)=E0 exp(jw c The generated radio frequency signal is represented as Vcos(Ωt); where w C Ω is the angular frequency of the optical carrier, E0 is the angular frequency of the radio frequency signal, and V is the amplitude of the laser signal. Step 2: In the upper branch, the output signal of MZM1 is represented as: The output signal of MZM2 is represented as follows: In the formula, m is the modulation index, and J n (·) is the nth-order Bessel function of the first kind, where j represents the imaginary unit; After passing through 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 represented as: In the formula, It is the modulation index of the coded signal, V C V represents the amplitude of the symbol. π This represents the half-wave voltage of the phase modulator; Adjust the amplitude of the encoded signal so that V C =V π Formula (4) is expressed as: From equation (5), it can be seen that when the phase-encoded signal changes between different symbols, the phase of the output optical signal of PM1 changes between 0 and π. The signal output from PM1 enters PM2, using DC V DC By controlling PM2 and performing phase modulation, the output optical signal is represented as follows: Where m2 represents the modulation index of PM2; Step 4: Send the combined optical signal into the PD for detection to obtain the photocurrent after beat frequency: Where ξ is the responsivity of the photodetector. The phase shift is introduced by controlling PM2, and J1(m) represents the first-order Bessel function of the first kind; Formula (7) is the phase-shiftable radio frequency signal modulated by the phase-encoded signal, whose carrier frequency is Ω / 2π, determined by the local oscillator; the phase of the signal is determined by the amplitude of the encoded signal and the DC voltage V controlling PM2. DC With the modulator's half-wave voltage V π The signal power is determined by the magnitude of 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. Assume that the normal direction of the two antennas, i.e., 0 degrees, is the desired communication direction, while the eavesdropping direction is α degrees to the right of the normal direction of the two antennas. Adjust the signal phase so that it can correctly recover the BPSK phase information in the desired direction, but cannot correctly recover the BPSK phase information in the eavesdropping direction. Step 6: To avoid signal grating lobe interference, 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 to antennas 1 and 2, the resulting optical path difference is Δd = dsinα; Assuming the transmitted signal is a single-frequency signal, at the eavesdropping position, the relative phase shift of the signal received from antenna 1 relative to the signal received from antenna 2... Let θ 1,0 and θ 1,1 θ represents the phase of the signal emitted by antenna 1 when the symbol is "0" and "1", respectively. 2,0 and θ 2,1 Let "0" and "1" represent the phases of the signal emitted by antenna 2 when the code elements are "0" and "1" respectively. The expressions for the two code elements of the signal at the eavesdropping direction can then be obtained as follows: Among them, w LO Indicates the angular frequency of the radio frequency local oscillator signal used; At the same time, the phase of the two symbols of the signal at the desired direction is: Using the sum-to-product formula: Simplifying the phases of the signals from the eavesdropping direction and the desired direction, i.e., simplifying formulas (9) and (10), we get: To satisfy the condition that the received "0" and "1" signals cannot be identified in the direction of eavesdropping, while the desired direction can be demodulated normally, and this is different from the "null trap" method of phased arrays, the following formula must be satisfied: Therefore, as long as the phase between the "0" and "1" signals transmitted by the two antennas satisfies the condition in formula (13), the signal transmitted by the system is a directional modulation signal, which can realize the function of directional modulation in the far field.

2. 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 to cause the electronic device to perform the method as described in claim 1.

3. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in claim 1.

4. A chip, characterized in that, include: A processor for retrieving and running a computer program from memory, causing a device on which the chip is mounted to perform the method as described in claim 1.

5. A computer program product, characterized in that, The computer program product includes a computer storage medium storing a computer program, the computer program including instructions executable by at least one processor, which, when executed by the at least one processor, implement the method as described in claim 1.

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