Pseudo-random time modulation four-dimensional antenna array multi-target secret communication method and system

Abstract

The invention discloses a pseudo-random time modulation four-dimensional antenna array multi-target secret communication system which comprises a four-dimensional wave control module, a modulation time sequence generator, a baseband modulation module, a frequency mixer, a power divider, a radio frequency modulation switch, a filter, a power amplifier, an antenna unit, optical fibers and cables, wherein the optical fibers and the cables are used for connecting all the parts; according to the system, operation such as time modulation and filtering is executed before amplification of the power amplifier, so that power loss caused by time modulation or filtering is small and can be approximately ignored. The invention also discloses a pseudo-random time modulation four-dimensional antenna array multi-target secret communication method, which can perform digital-analog hybrid pseudo-random modulation on an original signal by combining a digital baseband and an analog time modulation degree of freedom, thereby transmitting different original undistorted signals in a plurality of expected directions. And signals in an unexpected direction are disturbed and distorted by pseudo-random, so that simultaneous multi-target secret communication transmission is realized.

Description

Technical Field

[0001] The present invention belongs to the field of antenna engineering technology and relates to the field of wireless communications. Specifically, a physical layer secure communication system and method for multi-target users are designed based on four-dimensional antenna array technology, which can be used for secure communication systems that require higher confidentiality performance and simultaneous multi-target transmission. Background Art

[0002] In 1963, American scholars Kummer and others proposed the concept of time-modulated antenna array: by changing the antenna state over time, the antenna's radiation aperture size can be controlled in the "time" dimension. Time-modulated antenna array is a type of four-dimensional antenna array. The four-dimensional antenna array uses high-speed RF switches, high-speed amplitude and phase modulators, mixers, etc. to control the working state of each unit according to a predetermined working sequence, so that the radiation state of the antenna array changes over time, that is, it has time modulation characteristics, thereby greatly increasing the design freedom of the antenna array. The four-dimensional antenna array has great advantages in directional modulation and shaped beams, and has achieved many results. In recent years, the engineering application research of the four-dimensional antenna array has received increasing attention. At present, there are literature reports on the application of four-dimensional antenna arrays in simultaneous multi-beam scanning, confidential communications, low probability of intercept radar, etc. As a new type of array antenna with strong design flexibility, the four-dimensional antenna has a very large application space and potential advantages in the field of radio frequency stealth radar and communications.

[0003] Different from the closed transmission of wired communication, in traditional wireless communication systems, antennas radiate signals in free space, and most of the signal characteristics of radiated signals in different directions are the same, making the signals extremely easy to be eavesdropped by illegal receivers. Therefore, in order to prevent eavesdropping, many scholars in related fields have proposed many methods to achieve confidential communication.

[0004] In the patent with publication number CN 105553641 A, a chaotic secure communication method and a secure communication system are proposed. The system adopts chaotic masking technology and selects a high-power chaotic masking signal to mask the chaotic keying signal. However, before working, the system needs to shake hands with the legal receiver to determine the working protocol, working mode and working mode selection strategy. If an illegal receiver steals the working protocol, mode, etc. of the system, the confidentiality of the system will be greatly reduced. In addition, due to the need to radiate additional high-power masking signals, the overall transmission efficiency of the system is not high.

[0005] In the patent with publication number CN 109996231 A, a confidential communication method in a multi-antenna system is proposed. This method combines spatial modulation technology and uses antennas that are not selected in spatial modulation technology to transmit interference signals. The legitimate receiver knows the serial number of the antenna that transmits useful information, so it can recover and demodulate the signal normally. However, since the illegal receiver does not know the serial number of the useful antenna in advance, it is difficult to separate the interference from the received signal, and therefore it is difficult to recover the correct information. However, this method requires the legitimate receiver to receive information about the useful antenna sequence in advance. If the illegal receiver steals the information of the useful antenna sequence, or guesses it through other algorithms, the confidentiality performance of this method will be sharply reduced.

[0006] In the patent with publication number CN 110890908 B, a secure communication system and method based on a pre-modulated four-dimensional antenna array is disclosed. This method combines directional modulation technology with beamforming technology to effectively regulate the average radiation power within the sidelobe range while ensuring directional modulation performance, thereby reducing the probability of the radiation signal being intercepted by an illegal receiver. However, this method can only generate a single beam to serve a single desired communication target, and it is difficult to cope with the more common multi-target communication scenario.

[0007] In the patent with publication number CN 113114321 B, a space-time joint modulation secure communication system and method based on a four-dimensional antenna array is disclosed. By making full use of the space-time degrees of freedom of the antenna system, the modulation of the communication signal is divided into two parts, one part is baseband modulation, which is completed at the baseband digital end; the other part is antenna modulation, which has direction-dependent characteristics and is achieved by modulating the antenna unit. In this way, a distortion-free joint modulation signal can be transmitted in the desired direction, and a distorted joint modulation signal can be transmitted in the undesired direction. However, this method can also only generate a single beam to serve a target in a single desired direction, and is difficult to use in multi-target scenarios.

[0008] In the patent with publication number CN 110493777 B, a multi-target secure communication system based on a four-dimensional antenna array is disclosed. By optimizing the control timing of the system antenna unit, different harmonic patterns radiated by the antenna array are directed to different target users, thereby achieving multi-target secure communication. However, the system uses a highly complex three-state time modulation switch, whose harmonic patterns are at different frequencies and whose beam control freedom is relatively low, making it difficult to cope with scenarios with a large number of targets.

[0009] In response to the above application requirements, the present invention discloses a pseudo-random time modulated four-dimensional antenna array multi-target secure communication method and system, which combines the digital baseband and analog time modulation degrees of freedom to perform digital-analog hybrid pseudo-random modulation on the original signal, thereby transmitting different original undistorted signals in multiple desired directions, while the signals in undesired directions are distorted by pseudo-random disturbance, thereby achieving simultaneous multi-target secure communication transmission. This method fully exploits the digital baseband and analog time modulation degrees of freedom of the four-dimensional antenna array, and achieves simultaneous multi-target secure communication transmission at a lower hardware complexity. Summary of the invention

[0010] The present invention is achieved in view of the above background, overcomes the shortcomings of the prior art, and proposes a pseudo-random time modulated four-dimensional antenna array multi-target secure communication method and system, which effectively improves the simultaneous multi-target secure transmission capability of the physical layer secure communication system.

[0011] To achieve the above-mentioned purpose, the present invention adopts the following technical solution. Consider a four-dimensional antenna array with N units, whose time domain radiation field can be expressed as

[0012]

[0013] Where f0 is the carrier frequency, N is the number of antenna units, and U k (t) represents the modulation function of the kth unit, β represents the wave number of free space (usually β=2π / λ can be set, λ represents the wavelength of free space), d represents the distance between two adjacent units, θ represents the angular direction, t represents time, e represents the natural base, and j represents the imaginary unit.

[0014] When U k When (t) is considered as a periodic function, the radiation field of the four-dimensional antenna array can be expanded in the frequency domain as follows:

[0015]

[0016] in,

[0017]

[0018] Where a mk represents the equivalent complex excitation of the kth unit at the mth-order sideband, including amplitude and phase terms, f s Represents the modulation frequency of the timing signal, T s Represents the modulation period of the timing signal, t k Indicates the conduction start time, τ k In particular, when m = 0, a 0k =τ k , which is equal to the duty cycle of the timing. At this time, the center frequency radiation can be expressed as:

[0019]

[0020] From the above formula, it can be found that the center frequency radiation pattern has nothing to do with the time modulation frequency / period, but is mainly related to the on-duty cycle of the modulation timing. The duty cycle is also the equivalent weighting coefficient of the center frequency beam.

[0021] Assuming s(t) is the baseband modulated signal to be transmitted, the radiation field of the four-dimensional antenna array carrying the baseband signal can be expressed as

[0022]

[0023] Assumptions p (t) is the value that needs to be transmitted to θ p The original signal of the pth path in the direction of s p The baseband premodulation signal of (t) is expressed as h p (t), the total baseband modulation signal to be transmitted s(t) is formed by combining the pre-modulated signals of each channel, which can be further expressed as:

[0024]

[0025] Where Q represents the number of signal paths required to be transmitted. In order to achieve multi-target secure communication transmission, h p (t) can be expressed as:

[0026]

[0027] In this way, the radiation field of the four-dimensional antenna array carrying the baseband signal s(t) can be expressed as:

[0028]

[0029] Substituting formula (1) into the above formula, it can be written as:

[0030]

[0031] From the above formula, we can see that in θ p direction, the numerator and denominator of the right half of the formula are the same and cancel each other, making θ p Direction signals p The influence of baseband pre-modulation and time modulation on (t) cancels each other out. p (t) is transmitted to θ without distortion p In this way, by designing the timing, the signals in the non-desired directions except the desired direction can be modulated with maximum randomness while maintaining low sidelobe radiation, thereby achieving simultaneous multi-target secure communication transmission.

[0032] Assuming that the desired targets are scattered throughout the airspace, if "1" indicates that the modulation switch is on and "0" indicates that the modulation switch is off, then the timing of simultaneous multi-target confidential transmission needs to be pseudo-randomly generated after satisfying the following constraints:

[0033]

[0034] The most significant feature of its timing is that at any time only one unit is in the on-state, which means that the radiation energy can be distributed throughout the entire airspace and cover all desired targets. At this time, the radiation field represented by equation (9) can be written as:

[0035]

[0036] From the above formula, we can find that different signals s p (t) is directed by a p The beam radiates out in the direction of U k (t) is a pseudo-random time modulation, so the transmission s p The pth beam of (t) is written separately as:

[0037]

[0038] At this time, in the desired direction θ p Above, formula (12) can be further simplified as:

[0039]

[0040] It can be found that the signal is not time modulated at this time and can be demodulated correctly, while in the undesired direction, the signal is modulated by U k (t) Pseudo-random time modulation makes the energy pseudo-randomly dispersed on the spectrum, which makes it difficult for the signal in the undesired direction to be eavesdropped by the eavesdropping machine, ensuring good confidentiality transmission performance. On the other hand, although the energy in the undesired direction is dispersed on the spectrum through pseudo-random modulation, its center frequency radiation energy still carries a lot of original information, so the center frequency radiation also needs to be specially suppressed.

[0041] By observing equation (4), it can be found that no matter how the modulation frequency changes, the beam equivalent amplitude weighting of the center frequency is always equal to its timing duty cycle. Therefore, by controlling the timing duty cycle, the sidelobe levels of multiple radiation beams located at the center frequency can be effectively suppressed at the same time. At this time, the pseudo-random timing function can be split into multiple pulse shift timings. When the pseudo-random timing is generated, in addition to satisfying the relationship shown in equation (10), the following conditions must also be met:

[0042]

[0043] Where T w represents the wth observation period split by the pseudo-random time sequence, τ k,w represents the timing conduction duty cycle of the kth unit in the wth observation period, which is also the equivalent weighting coefficient of the center frequency beam. In this way, by controlling the conditions for pseudo-random timing generation, the radiation energy of the center frequency pattern in the undesired direction can be effectively suppressed, and aliasing interference can be generated pseudo-randomly, effectively hiding multiple real transmission information, and realizing simultaneous multi-target confidential communication transmission.

[0044] Based on the above principle, the present invention discloses a pseudo-random time modulation four-dimensional antenna array multi-target secure communication system, which includes a four-dimensional wave control module, a modulation timing generator, a baseband modulation module, a mixer, a power divider, a radio frequency modulation switch, a filter, a power amplifier, an antenna unit, and optical fibers and cables connecting the various parts; the four-dimensional wave control module is connected to the modulation timing generator and the baseband modulation module, the baseband modulation module is connected to the mixer, the power divider is connected to each radio frequency modulation switch, each radio frequency switch is respectively connected to the filter, and then each filter is connected to the power amplifier, the power amplifier is connected to each antenna unit, and each antenna unit radiates the final signal; wherein the four-dimensional wave control module is composed of a timing generation module and a pre-modulation signal generation module; the timing generation module is used to generate a corresponding pseudo-random timing output to the modulation unit according to a predetermined beam requirement. The timing generator is used to generate a pseudo-random modulation timing signal for controlling the RF modulation switch, which is sent to the RF modulation switch. The pre-modulation signal generation module is used to generate the specified pre-modulation signal information according to the timing information and the expected target direction information and transmit it to the baseband modulation module; the baseband modulation module performs baseband modulation according to the received pre-modulation signal information and the original signal information, and then sends the signal to the mixer; the mixer is used to up-convert the baseband modulated signal and then transmit it to the power divider; the power divider is used to divide the input signal and then send it to the RF switch of each channel; the RF switch is used to time-modulate the input RF signal according to the received timing; the filter is used to filter out the useless radiation signal out of the band to reduce the probability of the signal being eavesdropped; the power amplifier is used to amplify the filtered RF signal and then transmit it to the antenna unit, and finally the antenna unit radiates the signal.

[0045] Based on the above principle, the present invention also discloses a pseudo-random time modulated four-dimensional antenna array multi-target secure communication method, which includes the following steps:

[0046] (1) The four-dimensional wave control module generates modulation timing information and pre-modulation signal information according to the desired target direction and sends them to the modulation timing generator and baseband modulation module respectively;

[0047] (2) The baseband modulation module performs baseband modulation based on the received pre-modulated signal information and the original signal information to be sent, and then sends the modulated signal to the mixer;

[0048] (3) The mixer up-converts the baseband modulated signal into an RF signal and sends it to the power divider, which divides the RF signal into each RF modulation switch;

[0049] (4) The RF modulation switch performs pseudo-random time modulation on the incoming RF signal according to the pseudo-random timing control signal generated by the modulation timing generator;

[0050] (5) The time-modulated signal passes through filters to remove useless out-of-band radiation, and then is amplified by a power amplifier and radiated out by each antenna unit.

[0051] By combining the baseband modulation freedom and the time modulation freedom, multiple original information signals are pre-modulated by the baseband and modulated by the time of the switch, and then mapped to different units for radiation according to the predetermined transmission direction, and finally different original information signals are transmitted in different desired directions, thus realizing simultaneous multi-target confidential communication transmission. Since time modulation, filtering and other operations are performed before the power amplifier amplifies, the power loss caused by time modulation or filtering is small and can be approximately ignored. On the other hand, because pseudo-random time modulation is used to maximize the randomness of the timing, it is difficult for illegal receivers to demodulate the original signal information by deciphering the timing information. In addition, since the useful signals transmitted to different directions after baseband modulation and time modulation are at the same center frequency, the useless signals outside the band can be filtered out by filters to further ensure the confidentiality of the transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1The schematic diagram of the structure of the pseudo-random time modulated four-dimensional antenna array multi-target secure communication system. The system includes a four-dimensional wave control module, a modulation timing generator, a baseband modulation module, a mixer, a power divider, a radio frequency modulation switch, a filter, a power amplifier, an antenna unit, and optical fibers and cables connecting the various parts; the four-dimensional wave control module is connected to the modulation timing generator and the baseband modulation module, the baseband modulation module is connected to the mixer, the power divider is connected to each radio frequency modulation switch, each radio frequency switch is connected to a filter, and then each filter is connected to a power amplifier, and the power amplifier is connected to each antenna unit, and each antenna unit radiates the final signal; wherein, the four-dimensional wave control module is composed of a timing generation module and a pre-modulation signal generation module; the timing generation module is used to generate the corresponding timing output to the modulation timing generator according to the established beam requirements, and the modulation timing generator ... The signal generated for controlling the RF modulation switch is sent to the RF modulation switch. The pre-modulation signal generation module is used to generate the specified pre-modulation signal information according to the timing information and the expected target direction information and transmit it to the baseband modulation module; the baseband modulation module performs baseband modulation according to the received pre-modulation signal information and the original signal information, and then sends the signal to the mixer; the mixer is used to up-convert the baseband modulated signal and then transmit it to the power divider; the power divider is used to divide the input signal and then send it to the RF switch of each channel; the RF switch is used to time-modulate the input RF signal according to the received timing; the filter is used to filter out the useless radiation signal out of the band to reduce the probability of the signal being eavesdropped; the power amplifier is used to amplify the filtered RF signal and then transmit it to the antenna unit, and finally the antenna unit radiates the signal. ;

[0053] Figure 2 According to a multi-beam timing diagram, the white part indicates that the unit is turned on, and the black part indicates that it is turned off;

[0054] Figure 3 After demodulating the signals received by the user receivers in different directions, the original signals in the corresponding directions are compared with the demodulated signals, and it can be found that the corresponding original signals to be sent can be demodulated normally in each desired direction;

[0055] Figure 4 The bit error rate curves of the demodulated signals received in each direction to the original signals show that the original signals to be sent can only be correctly demodulated in their corresponding desired directions, but it is difficult to demodulate and identify the original signal information in the undesired directions.

[0056] Figure 5 The angle-frequency radiation power diagram of the four-dimensional antenna array using the conventional multi-harmonic beamforming method to generate five beams is shown. It can be seen that the conventional multi-harmonic beams of the conventional four-dimensional antenna array are not only at different sideband frequencies, but also have a relatively regular spectrum distribution, which is easy to be eavesdropped by illegal receivers.

[0057] Figure 6 This is a schematic diagram of the angle-frequency radiation power of the five beams radiated by the system proposed in the present invention. It is easy to find that the multiple beams emitted by the four-dimensional antenna array system proposed in the present invention are located at the same center frequency, and the spectrum distribution at different angles is relatively random, making it difficult to be eavesdropped by illegal receivers;

[0058] Figure 7 The schematic diagram of the radiation power in the angle-frequency dimension when the system proposed in the present invention transmits 5 different QPSK signals. It can be seen from the figure that the overall radiation power distribution of the system after loading the QPSK signal to be transmitted is highly random, which can effectively resist eavesdropping by illegal receivers in all directions; Specific implementation plan

[0059] The embodiment consists of 16 evenly arranged antenna units, and the unit spacing is half a wavelength. Figure 1 The schematic diagram of the structure of the pseudo-random time modulated four-dimensional antenna array multi-target secure communication system is given. The system includes a four-dimensional wave control module, a modulation timing generator, a baseband modulation module, a mixer, a power divider, a radio frequency modulation switch, a filter, a power amplifier, an antenna unit, and optical fibers and cables connecting the various parts; the four-dimensional wave control module is connected to the modulation timing generator and the baseband modulation module, the baseband modulation module is connected to the mixer, the power divider is connected to each radio frequency modulation switch, each radio frequency switch is connected to the filter, and then each filter is connected to the power amplifier, the power amplifier is connected to each antenna unit, and each antenna unit radiates the final signal; wherein, the four-dimensional wave control module is composed of a timing generation module and a pre-modulation signal generation module; the timing generation module is used to generate the corresponding timing output to the modulation timing generator according to the established beam requirements, and the modulation timing generator ... The signal generated for controlling the RF modulation switch is sent to the RF modulation switch. The pre-modulation signal generation module is used to generate the specified pre-modulation signal information according to the timing information and the expected target direction information and transmit it to the baseband modulation module; the baseband modulation module performs baseband modulation according to the received pre-modulation signal information and the original signal information, and then sends the signal to the mixer; the mixer is used to up-convert the baseband modulated signal and then transmit it to the power divider; the power divider is used to divide the input signal power and then send it to the RF switch of each channel; the RF switch is used to time-modulate the input RF signal according to the received timing; the filter is used to filter out the useless radiation signal out of the band to reduce the probability of the signal being eavesdropped; the power amplifier is used to amplify the filtered RF signal and then transmit it to the antenna unit, and finally the antenna unit radiates the signal.

[0060] Assume that there are 5 different original signals to be sent, which are Quadrature Phase Shift Keying (QPSK) signals, with a baud rate of 10Mbps and a carrier frequency f0 = 3GHz. Among them, the 5 different signals are transmitted in five different directions (-30°, -20°, 0°, 20°, 40°).

[0061] First, the four-dimensional wave control module generates timing information and pre-modulation signal information according to the desired target direction and quantity, and transmits them to the modulation timing generator and baseband modulation module respectively. The modulation timing generator generates the corresponding modulation timing according to the received timing information to control each RF modulation switch to perform time modulation. The generated timing signal is as follows: Figure 2 As shown. The baseband modulation module pre-modulates the original information signal to be sent according to the received pre-modulated signal information and the signal to be sent, and then transmits the modulated baseband signal to the mixer for up-conversion, and then sends the obtained RF signal to the power divider for power division operation; after the power divider divides the signal, it is transmitted to the RF modulation switch for time modulation; the RF modulation switch transmits the time-modulated signal to the filter, and the filter filters out the invalid sideband signal and then transmits the signal to the power amplifier for amplification; the power amplifier amplifies the signal and then transmits it to each antenna unit, which is radiated by each antenna unit. User receivers in different directions receive the signal and then demodulate it. The comparison results of the original signal and the demodulated signal in the corresponding direction are shown as follows. Figure 3 As shown in the figure, it can be found that the corresponding original to-be-sent signal can be demodulated normally in each desired direction. Figure 4 The bit error rate curves of the demodulated signals received in each direction to the original signals are given. It can be seen that the original signals to be sent can only be correctly demodulated in their corresponding desired directions, but it is difficult to demodulate and identify the original signal information in the undesired directions.

[0062] also, Figure 5 A schematic diagram of the angle-frequency radiation power of a four-dimensional antenna array using conventional multi-harmonic beamforming methods to generate five beams is drawn. Figure 6 A schematic diagram of the angle-frequency radiation power of the five beams radiated by the system proposed in the present invention is given. Comparing the above two figures, it can be seen that the traditional multi-harmonic beams of the traditional four-dimensional antenna array are not only at different sideband frequencies, but also have a relatively regular spectrum distribution, which is easy to be eavesdropped by illegal receivers; on the contrary, the multiple beams emitted by the four-dimensional antenna array system proposed in the present invention are located at the same center frequency, and the spectrum distribution at different angles is relatively random, which is difficult to be eavesdropped by illegal receivers. Figure 7The schematic diagram of the radiation power in the angle-frequency dimension when the system proposed in the present invention transmits 5 different QPSK signals is shown. As can be seen from the figure, the overall radiation power distribution of the system after loading the QPSK signal to be transmitted is highly random, which can effectively resist eavesdropping by illegal receivers in all directions. It is worth mentioning that since the proposed system can handle multiple target communication users, it has a wider application prospect in actual wireless communication applications.

[0063] A specific embodiment of the present invention has been described above, and it should be understood that this is only presented in an exemplary form and is not restrictive. Therefore, various changes in form and details can be made without departing from the spirit and scope of the present invention, which is obvious to those skilled in the art and does not require creative work. All of the above should be regarded as the scope of the present invention.

Claims

1. A pseudo-random time modulation four-dimensional antenna array multi-target secure communication system, comprising a four-dimensional wave control module, a modulation timing generator, a baseband modulation module, a mixer, a power divider, a radio frequency modulation switch, a filter, a power amplifier, an antenna unit, and optical fibers and cables connecting the various parts; the four-dimensional wave control module is connected to the modulation timing generator and the baseband modulation module, the baseband modulation module is connected to the mixer, the power divider is connected to each radio frequency modulation switch, each radio frequency switch is respectively connected to the filter, and then each filter is connected to the power amplifier, the power amplifier is connected to each antenna unit, and each antenna unit radiates the final signal; wherein, The four-dimensional beam control module consists of a timing generation module and a pre-modulation signal generation module; the timing generation module is used to generate a corresponding pseudo-random timing according to the established beam requirements and output it to the modulation timing generator, and the modulation timing generator generates a pseudo-random modulation timing signal for controlling the RF modulation switch and sends it to the RF modulation switch. The pre-modulation signal generation module is used to generate specified pre-modulation signal information according to the timing information and the expected target direction information and transmit it to the baseband modulation module; The baseband modulation module performs baseband modulation according to the received pre-modulated signal information and the original signal information, and then sends the signal to the mixer; The mixer is used to up-convert the baseband modulated signal and then transmit it to the power divider; The power divider is used to divide the input signal power and send it to the RF switch of each channel; The RF switch is used to time-modulate the input RF signal according to the received timing; The filter is used to filter out useless out-of-band radiation signals to reduce the probability of the signal being eavesdropped; the power amplifier is used to amplify the filtered RF signal and transmit it to the antenna unit, which finally radiates the signal.

2. A pseudo-random time modulated four-dimensional antenna array multi-target secure communication method, characterized in that The steps include: S1, the four-dimensional wave control module generates modulation timing information and pre-modulation signal information according to the desired target direction and sends them to the modulation timing generator and baseband modulation module respectively; S2, the baseband modulation module performs baseband modulation according to the received pre-modulated signal information and the original signal information to be sent, and then sends the modulated signal to the mixer; S3, the mixer up-converts the baseband modulated signal into a radio frequency signal and sends it to the power divider, which divides the radio frequency signal into each radio frequency modulation switch; S4, the RF modulation switch performs pseudo-random time modulation on the incoming RF signal according to the pseudo-random timing control signal generated by the modulation timing generator; S5. The time-modulated signal is filtered out by filters to remove useless radiation out of the band, and the power amplifier amplifies the signal and then radiates it out from each antenna unit.

3. The pseudo-random time modulated four-dimensional antenna array multi-target secure communication method according to claim 2, further characterized by: The pseudo-random timing can be split into multiple pulse shift timings. By controlling the conditions for generating the pseudo-random timing, the radiation energy of the center frequency pattern in the undesired direction can be effectively suppressed, and aliasing interference can be generated pseudo-randomly to effectively hide multiple real transmission information. When the pseudo-random timing is generated, the following two conditions must be met at the same time: Among them U k (t) represents the modulation function of the kth unit, T w represents the wth observation period split by the pseudo-random time sequence, τ k,w It represents the sequential conduction duty cycle of the kth unit in the wth observation period, which is also the equivalent weighting coefficient of the center frequency beam.

4. The pseudo-random time modulation four-dimensional antenna array multi-target secure communication method according to claim 2, further characterized by: Since operations such as time modulation and filtering are performed before amplification by the power amplifier, the power loss caused by time modulation or filtering is relatively small and can be approximately ignored.

5. The pseudo-random time modulated four-dimensional antenna array multi-target secure communication method according to claim 2, further characterized by: Because pseudo-random time modulation is used to maximize the randomness of the timing, it is difficult for illegal receivers to demodulate the original signal information by deciphering the timing information.

6. The pseudo-random time modulated four-dimensional antenna array multi-target secure communication method according to claim 2, further characterized by: Since the useful signals transmitted in different directions after baseband modulation and time modulation are at the same center frequency, filters can be used to filter out useless signals out of the band to further ensure transmission confidentiality performance.

Images