CN114070417B - Terahertz communication system based on periodic rough metal surface and communication method thereof - Google Patents

Abstract

The present invention relates to a terahertz communication system based on a periodic rough metal surface and a communication method thereof, the terahertz communication system and the rough periodic metal surface; the terahertz communication system includes a sending end and a receiving end; the sending end transmits signals, and Propagation; receiving end, capturing and processing the signal; rough periodic metal surface, used to reflect and scatter the signal. The present invention can not only generate more scattering paths, but also determine the direction of the paths according to needs, and can also transmit signals in multiple directions and paths, so that the receiving end can superimpose signals, obtain more information, and improve the accuracy of communication. Moreover, the terahertz-level rough surface designed by the present invention is lightweight and has high flexibility. It not only has a simple structure and low manufacturing cost, but also can reduce electromagnetic pollution and energy waste.

Description

Terahertz communication system and communication method based on periodic rough metal surface

technical field

The invention belongs to the technical field of communication, and in particular relates to a terahertz communication system based on a periodic rough metal surface and a communication method thereof.

Background technique

With the continuous growth of network capacity, the data rate requirements of wireless communication are increasing, which promotes the research of wireless channels at terahertz frequencies. Network coverage is the most important and basic capability of wireless communication systems. Terahertz communication has extremely high data rates and huge bandwidth, making terahertz irreplaceable in future wireless communication systems. And because of its limited transmission distance and highly directional narrow beam, it has unique advantages in secure communication systems. That's because it's harder to place bugs in the narrow beams of terahertz than at lower frequencies. Although this highly directional narrow-angle transmission is a very challenging environment for eavesdroppers, it also increases the risk of information transmission: the susceptibility of terahertz signals to jamming greatly affects the performance of high-mobility links. coverage and reliability.

The terahertz frequency band is also characterized by a shorter wavelength, which is comparable to the roughness of the surface of common objects. During signal transmission, in addition to experiencing free space attenuation and molecular absorption, it will also experience reflection or scattering on the surface of rough objects. Multi-path, multi-directional signals scattered by rough surfaces will enable the establishment of communication links other than transceiver links. This is a great challenge for terahertz secure communication, but it is also an opportunity. Domestic research on the use of rough surfaces for scattered signal communication is relatively scarce, and no relevant patents have been proposed so far.

The millimeter wave in the low frequency band is often used for indoor or outdoor short-distance transmission and communication. In 2002, Xu et al. proposed to use 60GHz frequency signals to study the time domain and air domain characteristics of multipath channels. They chose 8 different transmission environments, using 54.7m-long corridors, meeting rooms, and parking lots, and adopted line-of-sight transmission, non-line-of-sight transmission, and penetration transmission respectively. After research, it is found that whether it is indoor or outdoor, line-of-sight transmission and reflection from surrounding walls and objects (especially objects with smooth metal surfaces) occupy the main components of multipath transmission. Moreover, when performing penetrating transmission through composite walls, the signal intensity reflected by the metal nails on the inside of the wall and the surfaces with different roughnesses are different. Smooth surfaces will produce strong reflections, while rough periodic metal surfaces will cause scattering. Loss becomes large. Research by Xu et al. shows that when channel estimation is performed under low-frequency millimeter waves, the multipath transmission that needs to be considered mainly relies on point-to-point line-of-sight transmission and transmission of first-order reflected waves. Common metal objects in the environment will bring reflections, but rough Metal surfaces cannot effectively reflect low-frequency millimeter-wave signals, which will reduce signal transmission efficiency.

The wavelength of low-frequency millimeter waves is on the order of millimeters to meters, while the surface roughness of common objects is on the order of submillimeters to millimeters. This means that when using low-frequency mmWave for transmission, it can only be transmitted through point-to-point line-of-sight transmission and reflected signal transmission, and the strength of other signals is not enough for effective decoding. To a certain extent, there is a waste of frequency spectrum and resources, which is inconsistent with the current green and low-carbon communication concept. And only through line-of-sight transmission and reflection transmission, the transmission path is less. When there is an obstruction in the path, the signal will be blocked, resulting in the inability to receive the signal in time or accurately.

Contents of the invention

In view of the above technical problems, the present invention provides a terahertz communication system and method based on a periodic rough metal surface, which can increase signal utilization, expand signal coverage, and enhance communication accuracy, flexibility and security.

Specific technical solutions:

Terahertz communication system based on periodic rough metal surface, including two parts: Terahertz communication system and rough periodic metal surface;

Terahertz communication system, including sending end and receiving end;

Described sending end, uses Xilinx Vertix-7 FPGA to produce 16QAM modulation signal under intermediate frequency frequency; The digital signal that FPGA produces is converted into analog signal through DAC, then the signal is up-converted to RF frequency through second harmonic mixer; Finally, the transmitted signal propagates through the terahertz transmitting antenna;

At the receiving end, the low-noise amplifier amplifies the signal captured by the terahertz receiving antenna, and outputs it to the second harmonic mixer for down-conversion to obtain an intermediate frequency signal; the intermediate frequency signal is converted into a digital signal by ADC and Transfer to Xilinx XC7VX690T FPGA to complete subsequent synchronization and demodulation signal processing;

The rough periodic metal surface is a polished aluminum plate with periodic corrugations in the one-dimensional direction of the surface.

Based on the above system, the present invention provides a terahertz communication method based on a periodic rough metal surface, including the following steps:

At the sending end, a Xilinx Vertix-7 FPGA is used to generate a 16QAM modulation signal at an intermediate frequency; the digital signal generated by the FPGA is converted into an analog signal by a DAC, and then the signal is up-converted to an RF frequency by a second harmonic mixer; finally, The transmitted signal is propagated through the terahertz transmitting antenna;

The transmitted signal is radiated to the rough periodic metal surface at a certain angle through the terahertz transmitting antenna, and the rough periodic metal surface generates reflected waves and scattered waves, which are radiated at a certain angle and returned to the receiving end through the terahertz receiving antenna;

At the receiving end, the low-noise amplifier amplifies the signal captured by the terahertz receiving antenna, and outputs it to the second harmonic mixer for down-conversion to obtain an intermediate frequency signal; the intermediate frequency signal is converted into a digital signal by ADC and transmitted to The subsequent synchronization and demodulation signal processing is completed in Xilinx XC7VX690T FPGA.

Aiming at the disadvantages of fewer transmission paths, low frequency spectrum utilization, and easy blocking, the present invention proposes a signal transmission method using terahertz signals and rough periodic metal surfaces. The wavelength of the terahertz signal is relatively small, which is equivalent to the roughness of the surface of common objects. This makes the signal incident on the rough surface not only produce reflection, but also produce a scattering phenomenon with sufficient signal strength to be effectively decoded. Moreover, the rough surface provided by the present invention can not only generate more scattering paths, but also determine the direction of the paths as required. When one path is blocked, other paths can be used for information transmission. This not only increases the signal transmission efficiency and power utilization rate, which is in line with the green and low-carbon new era communication concept, but also allows the receiving end to superimpose signals through multi-directional and multi-path transmission to obtain more information and improve communication accuracy. Spend. Moreover, the terahertz-level rough surface designed by the present invention is lightweight, easy to install on the surface of walls, ceilings and other objects, and can even be combined with drones to adjust the position according to people's needs at any time, with high flexibility It has great prospects in indoor application scenarios such as airports and stadiums. Moreover, the beam of terahertz waves is very narrow and has strong directivity. The method of using rough surface scattering for communication can not only solve the problems of blocked transmission paths and short communication distances, but also determine the scattering angle and azimuth through calculation. The receiving end performs signal interference to further enhance the security and privacy of the wireless communication system. Moreover, the periodic surface is passive, which not only has a simple structure and low manufacturing cost, but also can reduce electromagnetic pollution and energy waste.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Figure 2 is a schematic diagram of the scattering and reflection phenomena of the rough periodic metal surface in the room;

Fig. 3 is the scattering spectrum of the rough periodic surfaces S2 and S3 with the same period and different amplitudes, and the smooth surface S1 for comparison at the frequency f=300GHz;

Fig. 4 is the scattering spectrum of the rough periodic surfaces S3 and S4 with the same amplitude and different periods, and the smooth surface S1 for comparison, at a frequency f=300GHz;

Fig. 5 is the scattering spectrum of the rough periodic surface S4 at the frequency f=300GHz;

Fig. 6 is the scattering spectrum of the rough periodic surface S4 at the frequency f=300GHz;

Figure 7 is a schematic diagram of installing a rough periodic metal surface on a glass surface;

Figure 8 is a schematic diagram of installing a rough periodic metal surface on the surface of a drone.

Figure 9. Schematic diagram of a device for installing rough periodic surfaces around cars and roads.

Detailed ways

The specific technical solutions of the present invention are described in conjunction with the examples.

As shown in Figure 1, the terahertz communication system based on the periodic rough metal surface includes two parts: the terahertz communication system and the rough periodic metal surface 3;

A terahertz communication system, including a sending end 11 and a receiving end 12;

The transmitting end 11 uses a Xilinx Vertix-7 FPGA to generate a 16QAM modulation signal at an intermediate frequency; the digital signal generated by the FPGA is converted into an analog signal by a DAC, and then the signal is up-converted to a radio frequency by a second harmonic mixer; finally, The transmitting signal is propagated through the terahertz transmitting antenna 21;

At the receiving end 12, the low-noise amplifier amplifies the signal captured by the terahertz receiving antenna 22, and outputs it to the second harmonic mixer for down-conversion to obtain a signal at an intermediate frequency. The intermediate frequency signal is converted into a digital signal by ADC and transmitted to Xilinx XC7VX690T FPGA to complete subsequent signal processing processes such as synchronization and demodulation.

The rough periodic metal surface 3 is made of a polished aluminum plate, and the process design is carried out in the one-dimensional direction of the surface to produce periodic corrugations, which can adjust the height change in the vertical direction of the surface and the periodic change in the horizontal direction. The processing accuracy of the surface of the aluminum plate is on the order of tens to tens of microns, which can be regarded as a smooth and polished surface.

A terahertz communication method based on a periodically rough metal surface, comprising the following steps:

At the transmitting end 11, a Xilinx Vertix-7 FPGA is used to generate a 16QAM modulation signal at an intermediate frequency; the digital signal generated by the FPGA is converted into an analog signal by a DAC, and then the signal is up-converted to a radio frequency by a second harmonic mixer; finally , the transmit signal propagates through the terahertz transmit antenna 21;

The transmission signal is radiated to the rough periodic metal surface 3 at a certain angle through the terahertz transmitting antenna 21, the rough periodic metal surface 3 generates reflected waves and scattered waves, and radiates at a certain angle, and returns to the receiving end 12 through the terahertz receiving antenna 22 ;

At the receiving end 12, the low-noise amplifier amplifies the signal captured by the terahertz receiving antenna 22, and outputs it to the second harmonic mixer for down-conversion to obtain an intermediate frequency signal; the intermediate frequency signal is converted into a digital signal by ADC and It is transmitted to Xilinx XC7VX690T FPGA to complete subsequent synchronization and demodulation signal processing. And display the signal strength through the power meter.

As shown in FIG. 2 , it is a schematic diagram of scattering and reflection phenomena of the rough periodic metal surface 3 in the room. When using the rough periodic metal surface 3 for indoor short-distance signal transmission, the rough periodic metal surface 3 can be placed on the wall or ceiling. When the transmitter radiates the signal to the rough periodic metal surface 3, firstly, a reflected wave will be generated at a position equal to the incident angle of the beam; secondly, due to the periodic corrugation on the surface, it will be generated in other directions outside the angle of the reflected wave scattered beams. Through calculation, the radiation angle and direction of the scattered beam can be obtained, so that the receiving antenna or other rough periodic metal surface 3 can be placed at several specific positions reached by the scattering point. Moreover, the rough table can be combined with smart devices to rotate the rough periodic metal surface 3 in real time according to the needs, so that specific positions can avoid obstacles and continuously receive signals. Such a transmission method can reduce the obstruction of indoor walls and furniture to signals, thereby reducing coverage holes and blind areas; the constructive interference of multiple signals can increase signal strength and improve signal quality; the rotatability of the surface increases the flexibility of signal transmission . Moreover, both the terahertz communication system and the rough periodic metal surface 3 are lightweight, easy to install and remove, and easier to integrate into other devices for communication.

The variation curve of the rough periodic metal surface 3 of the technical solution follows the sine function equation, as shown below:

Wherein, A represents the amplitude, that is, the change of the height of the rough periodic metal surface 3 in the vertical direction, and X _p represents the period, that is, the change of the period of the rough periodic metal surface 3 in the horizontal direction.

When the signal is incident on the rough periodic metal surface 3, a reflected signal will be generated in the same direction as the incident angle, that is, the direction of the signal follows Snell's law; while the direction of scattering follows the Bragg diffraction theory, and the determination equation of the direction angle is as follows:

Among them, n=0, ±1, ±2, ±3..., represents the harmonic order, λ represents the signal wavelength, and θ _i represents the signal incident angle. θ _s represents the scattering angle. When the periodic surface is incident by a signal of a certain frequency in a certain direction, the angle of each scattering angle can be calculated to determine the receiving azimuth and place the receiver.

By changing the height and period of the surface or the transmission frequency of the signal, scattered waves in different directions can be generated. The following experiments are performed at different frequencies using four surfaces with different amplitudes and/or periods. Among them, S1 represents the aluminum plate with smooth surface, S2 represents the rough periodic surface with amplitude A=0.35mm, period _Xp =2mm, S3 represents the rough periodic surface with amplitude A=0.7mm, period _Xp =2mm, S4 represents the amplitude A = 0.7mm, period _Xp = 6mm rough periodic surface, the obtained scattering spectrum is as follows:

(1) Figure 3 shows the scattering spectrum of the rough periodic surfaces S2 and S3 with the same period and different amplitudes, and the smooth surface S1 for comparison, at the frequency f=300GHz, and the incident angle of the signal at this time θ _i =45 °. It can be found that the surfaces S1, S2, and S3 can all receive strong signals at the position of θ _s =45°, which shows that both the periodic surface and the smooth surface will follow the Snell reflection law and generate reflected beams. Secondly, the rough periodic surfaces S2 and S3 also have peak signals in the range of θ _s =0° to θ _s =10°, while S1 has no signal at this position, which shows that the rough periodic surface will cause scattering, and the scattering intensity Comparable to the strength of the reflected signal.

(2) Figure 4 shows the scattering spectrum of the rough periodic surfaces S3 and S4 with the same amplitude and different periods, and the smooth surface S1 for comparison, at the frequency f=300GHz, and the incident angle of the signal at this time θ _i =45 °. It can be seen that each rough periodic surface will generate reflected waves and scattered waves, and as the surface period increases, the peak value of the scattered signal will increase, and the signal strength is equivalent to that of one reflection, which is sufficient for decoding. This shows that the period of the rough periodic metal surface 3 has a strong influence on scattering.

(3) FIG. 5 is the scattering spectrum of the rough periodic surface S4 at the frequency f=300 GHz, and the incident angle θ _i of the signal at this time is 45°. It can be found that as the frequency increases, the angular position of the scattering component will move, that is, the movement of the power peak in the figure; the distance between each peak also decreases with the increase of frequency, and the distance between each two peaks The gaps are about the same, and the variation of the spacing between peaks has a periodic law.

(4) Figure 6 shows the scattering spectrum of the rough periodic surface S4 at f=300GHz. At this time, the angle and position between the transmitting end of the signal and the receiving end 12 remain unchanged, θ _i =θ _s =45°, only by rotating the rough Periodic surface, from 0° (surface not rotated) to 35°, to obtain power values at different angles. It can be seen from the figure that there are 4 power peaks on the surface outside the position of 0°, and the signal strength is sufficient for decoding. This shows that the present invention can set the receiving end 12 at different positions to receive signals, or change the direction of signal radiation by intelligently adjusting the rotating surface; it can also obtain the positions of these scattering peaks through calculation, so as to plan communication paths and avoid Eavesdropper to prevent interference and eavesdropping.

As shown in Figure 7, the rough periodic metal surface is installed on the glass surface, which can effectively reflect the signal of the transmitter to the room, and realize the communication project that the outdoor base station covers the room. Moreover, more information can be obtained through multiple reflections, thereby improving signal quality.

As shown in Figure 8, due to the lightness of the rough surface, they can be installed on the surface of the UAV. The UAV has high maneuverability and is easy to deploy to the target area. Other rough surfaces can also be placed on the roof, wall and suitable ground to establish a reliable communication link. The use of drones enhances the flexibility of communication and reduces coverage blind spots.

As shown in Figure 9, the rough periodic surface is installed on the equipment around the vehicle and the road, which can realize the communication between the vehicle and the traffic facilities, and the communication between the vehicles. Each vehicle can share data to provide information for other vehicles, which can predict road conditions in advance, facilitate route planning, and reduce traffic accidents.

Claims (4)

1. A terahertz communication system based on a periodic rough metal surface, comprising two parts: a terahertz communication system and a rough periodic metal surface; Terahertz communication system, including sending end and receiving end; The sending end transmits a signal and propagates it; The receiving end captures the signal and processes it; The rough periodic metal surface is used to reflect and scatter signals; The rough periodic metal surface is a polished aluminum plate with periodic corrugations in the one-dimensional direction of the surface; The change curve of the rough periodic metal surface follows the sinusoidal function equation, as shown below:

(1) Among them, A represents the amplitude, that is, the change of the height of the rough periodic metal surface in the vertical direction, and X _p represents the period, that is, the change of the period of the rough periodic metal surface in the horizontal direction. 2. The terahertz communication system based on the periodic rough metal surface according to claim 1, wherein the transmitting end uses a Xilinx Vertix-7 FPGA to generate a 16QAM modulation signal at an intermediate frequency; the digital signal produced by the FPGA The signal is converted to an analog signal by a DAC, and then the signal is up-converted to a radio frequency by a second harmonic mixer; finally, the transmitted signal is propagated through a terahertz transmitting antenna. 3. The terahertz communication system based on a periodic rough metal surface according to claim 1, wherein at the receiving end, the low noise amplifier amplifies the signal captured by the terahertz receiving antenna and outputs it to two The sub-harmonic mixer performs down-conversion to obtain an intermediate frequency signal; the intermediate frequency signal is converted into a digital signal by ADC and transmitted to Xilinx XC7VX690T FPGA to complete subsequent synchronization and demodulation signal processing. 4. The communication method of the terahertz communication system based on the periodic rough metal surface according to any one of claims 1 to 3, characterized in that it comprises the following steps: At the sending end, a Xilinx Vertix-7 FPGA is used to generate a 16QAM modulation signal at an intermediate frequency; the digital signal generated by the FPGA is converted into an analog signal by a DAC, and then the signal is up-converted to an RF frequency by a second harmonic mixer; finally, The transmitted signal is propagated through the terahertz transmitting antenna; The transmitted signal is radiated to the rough periodic metal surface at a certain angle through the terahertz transmitting antenna, and the rough periodic metal surface generates reflected waves and scattered waves, which are radiated at a certain angle and returned to the receiving end through the terahertz receiving antenna; At the receiving end, the low-noise amplifier amplifies the signal captured by the terahertz receiving antenna, and outputs it to the second harmonic mixer for down-conversion to obtain an intermediate frequency signal; the intermediate frequency signal is converted into a digital signal by ADC and transmitted to The subsequent synchronization and demodulation signal processing is completed in Xilinx XC7VX690T FPGA.

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