CN114070417B - Terahertz communication system based on periodic rough metal surface and communication method thereof - Google Patents
Terahertz communication system based on periodic rough metal surface and communication method thereof Download PDFInfo
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Abstract
The 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 comprises a sending end and a receiving end; the transmitting terminal transmits and propagates the signal; the receiving end captures and processes the signals; and the rough periodic metal surface is used for reflecting and scattering signals. The invention not only can generate more scattering paths, but also can determine the direction of the paths according to the requirement, and can lead the receiving end to carry out signal superposition through multi-direction and multi-path transmission, thereby obtaining more information and improving the accuracy of communication. In addition, the terahertz rough surface designed by the invention belongs to a light weight level, has high flexibility, is simple in structure and low in manufacturing cost, and can reduce electromagnetic pollution and energy waste.
Description
Technical Field
The invention belongs to the technical field of communication, and particularly relates to a terahertz communication system based on a periodic rough metal surface and a communication method thereof.
Background
With the continuous increase of network capacity, the requirement of wireless communication on data rate is increasing, which promotes the research of wireless channels at terahertz frequency. The coverage capability of the network is the most important and basic capability of the wireless communication system, and the terahertz communication has extremely high data rate and huge bandwidth, so that the terahertz has a position which is difficult to replace in the future wireless communication system. And it has unique advantages in a secure communication system due to its limited transmission distance and highly directional narrow beams. This is because it is more difficult to place the eavesdropping device in the narrow beam range 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 sensitivity of terahertz signals to blockage greatly influences the coverage and reliability of a high-mobility link.
The terahertz frequency band also has the characteristic of shorter wavelength, and the wavelength of the terahertz frequency band is equivalent to the roughness of the surface of a common object. In signal transmission, besides free space attenuation and molecular absorption, the signal transmission also undergoes reflection or scattering from the surface of a rough object. Multipath, multi-directional signals scattered by rough surfaces may make possible the construction of communication links other than transceiver links. This is a great challenge for terahertz secure communication, but is also an opportunity. The research on the scattered signal communication by using the rough surface is deficient in China, and no relevant patent is provided at present.
Millimeter waves in a low frequency band are commonly used for indoor or outdoor short-distance transmission communication, and Xu et al proposed in 2002 that a signal with a frequency of 60GHz is used for the research of the time domain and space domain characteristics of a multipath channel. They selected 8 different transmission environments, and used 54.7m long hallways, meeting rooms, parking lots and other places, and adopted the communication modes of line-of-sight transmission, non-line-of-sight transmission and penetration transmission respectively. It has been found that line-of-sight transmission and reflections from surrounding walls and objects (especially objects with smooth metal surfaces) occupy the major components of multipath transmission, whether indoors or outdoors. Moreover, in the transmission through a composite wall, the signal strength reflected by the metal nails inside the wall, which have surfaces with different roughness, is different, the smooth surface generates strong reflection, and the coarse periodic metal surface causes large scattering loss. Xu et al have shown that, when channel estimation is performed under low-frequency millimeter waves, multipath transmission to be considered mainly depends on point-to-point line-of-sight transmission and transmission of first-order reflected waves, and common metal objects in the environment can reflect, but a rough metal surface cannot effectively reflect low-frequency millimeter wave signals, so that the signal transmission efficiency is reduced.
The wavelength of low frequency millimeter waves is on the order of millimeters to meters, while the roughness of the surface of common objects is on the order of sub-millimeters to millimeters. This means that when transmission is performed using low-frequency millimeter waves, only point-to-point line-of-sight transmission and reflected signal transmission are possible, and the strength of the other signals is insufficient for effective decoding. This is a waste of spectrum and resources to some extent, which is not in line with the current green and low carbon communication concept. And the transmission path is less through the line-of-sight transmission and the reflection transmission, and when a shelter exists in the path, the signal can be blocked, so that the signal cannot be received timely or accurately.
Disclosure of Invention
In order to solve the technical problems, the invention provides a terahertz communication system based on a periodic rough metal surface and a method thereof, which can increase the signal utilization rate, enlarge the signal coverage range and enhance the accuracy, flexibility and safety of communication.
The specific technical scheme is as follows:
the terahertz communication system based on the periodic rough metal surface comprises two parts: a terahertz communication system and a rough periodic metal surface;
the terahertz communication system comprises a sending end and a receiving end;
the transmitting end uses Xilinx Vertix-7 FPGA to generate a 16QAM modulation signal under the intermediate frequency; converting a digital signal generated by the FPGA into an analog signal through a DAC (digital-to-analog converter), and up-converting the signal to radio frequency through a second harmonic mixer; finally, transmitting signals are transmitted through the terahertz transmitting antenna;
at the receiving end, a low-noise amplifier amplifies a signal captured by the terahertz receiving antenna and outputs the signal to a second harmonic mixer for down-conversion to obtain a signal of an intermediate frequency; the intermediate frequency signal is converted into a digital signal through the ADC and is transmitted to the Xilinx XC7VX690T FPGA to complete the subsequent processes of synchronizing and demodulating the signal;
the rough periodic metal surface is a polished aluminum plate, and periodic ripples are arranged in the one-dimensional direction of the surface.
Based on the system, the invention provides a terahertz communication method based on a periodic rough metal surface, which comprises the following steps:
at a transmitting end, using Xilinx Vertix-7 FPGA to generate a 16QAM modulation signal under intermediate frequency; converting a digital signal generated by the FPGA into an analog signal through a DAC (digital-to-analog converter), and up-converting the signal to radio frequency through a second harmonic mixer; finally, transmitting signals are transmitted through the terahertz transmitting antenna;
the transmission signal is radiated to the rough periodic metal surface at a certain angle through the terahertz transmission antenna, the rough periodic metal surface generates reflected waves and scattered waves, the reflected waves and the scattered waves are radiated at a certain angle, and the radiation returns to the receiving end through the terahertz receiving antenna;
at a receiving end, a low-noise amplifier amplifies a signal captured by the terahertz receiving antenna and outputs the signal to a second harmonic mixer for down-conversion to obtain a signal of an intermediate frequency; the intermediate frequency signal is converted into a digital signal through the ADC and transmitted to the Xilinx XC7VX690T FPGA to complete the subsequent processes of synchronizing and demodulating signals.
Aiming at the defects of few transmission paths, low frequency spectrum utilization rate, easy blockage and the like, the invention provides a method for transmitting signals by using terahertz signals and a rough periodic metal surface. The wavelength of the terahertz signal is small and is equivalent to the roughness of the surface of a common object, so that when the signal is incident to a rough surface, not only reflection is generated, but also a scattering phenomenon that the signal intensity is enough to be effectively decoded is generated. In addition, the rough surface provided by the invention not only can generate more scattering paths, but also can determine the direction of the paths according to requirements. When a certain path is blocked, other paths can be used for information transmission. The signal transmission efficiency and the power utilization rate are increased, the novel era communication idea of green and low carbon is met, the receiving end can perform signal superposition through multi-direction and multi-path transmission, more information is acquired, and the communication accuracy is improved. In addition, the terahertz rough surface designed by the invention belongs to a lightweight class, is convenient to mount on the surfaces of objects such as walls, ceilings and the like, can be combined with an unmanned aerial vehicle even, can adjust the position according to the requirements of people at any time, has high flexibility, and has huge prospects in indoor application scenes such as airports, gymnasiums and the like. The terahertz wave has narrow wave beam and strong directivity, and the method for carrying out communication by using rough surface scattering can solve the problems of blocked transmission path, short communication distance and the like, and can also determine the scattering angle direction through calculation to carry out signal interference at an unexpected receiving end, thereby further enhancing the safety and the privacy of the wireless communication system. And the periodic surface is passive, so that the structure is simple, the manufacturing cost is low, and the electromagnetic pollution and the energy waste can be reduced.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic diagram of scattering and reflection phenomena of a rough periodic metal surface in a room;
fig. 3 is a scattering spectrum at frequency f =300GHz for rough periodic surfaces S2, S3 of the same period and different amplitudes, and for comparison a smooth surface S1;
fig. 4 is a scattering spectrum at frequency f =300GHz for rough periodic surfaces S3, S4 of the same amplitude and different periods, and for comparison smooth surface S1;
fig. 5 is a scattering spectrum of the rough periodic surface S4 at a frequency f =300 GHz;
fig. 6 is a scattering spectrum of the rough periodic surface S4 at a frequency f =300 GHz;
FIG. 7 is a schematic view of the installation of a roughened periodic metal surface on a glass surface;
fig. 8 is a schematic view of the installation of a coarse periodic metal surface on a drone surface.
FIG. 9 is a schematic view of an apparatus for mounting a rough periodic surface around a vehicle and road.
Detailed Description
The specific technical scheme of the invention is described by combining the embodiment.
As shown in fig. 1, the terahertz communication system based on the periodic rough metal surface includes two parts: a terahertz communication system and a rough periodic metal surface 3;
the terahertz communication system comprises a sending end 11 and a receiving end 12;
a sending terminal 11, which uses Xilinx Vertix-7 FPGA to generate 16QAM modulation signals under the intermediate frequency; converting a digital signal generated by the FPGA into an analog signal through a DAC (digital-to-analog converter), and up-converting the signal to radio frequency through a second harmonic mixer; finally, the transmission signal is propagated through the terahertz transmission antenna 21;
at the receiving end 12, the low noise amplifier amplifies the signal captured by the terahertz receiving antenna 22, and outputs the signal to the second harmonic mixer for down-conversion, so as to obtain a signal of an intermediate frequency. The intermediate frequency signal is converted into a digital signal through the ADC and is transmitted to the 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 is subjected to process design in the one-dimensional direction of the surface to manufacture periodic ripples, so that the height change of the surface in the vertical direction and the periodic change of the surface in the horizontal direction can be adjusted. The processing precision of the surface of the aluminum plate is in the order of tens of microns to tens of microns, and the aluminum plate can be regarded as a smooth polished surface.
The terahertz communication method based on the periodic rough metal surface comprises the following steps:
at a sending end 11, using a Xilinx Vertix-7 FPGA to generate a 16QAM modulation signal under an intermediate frequency; converting a digital signal generated by the FPGA into an analog signal through a DAC (digital-to-analog converter), and up-converting the signal to a radio frequency through a second harmonic mixer; finally, the transmission signal is propagated through the terahertz transmission antenna 21;
the transmitted signal is radiated to the coarse periodic metal surface 3 at a certain angle through the terahertz transmitting antenna 21, the coarse periodic metal surface 3 generates reflected waves and scattered waves, the reflected waves and the scattered waves are radiated at a certain angle, and the radiated waves return 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 the signal to the second harmonic mixer for down-conversion to obtain a signal of an intermediate frequency; the intermediate frequency signal is converted into a digital signal through the ADC and transmitted to the Xilinx XC7VX690T FPGA to complete the subsequent processes of synchronizing and demodulating signals. And the signal strength is displayed by a power meter.
Fig. 2 is a schematic diagram showing scattering and reflection phenomena of the rough periodic metal surface 3 in a room. When the coarse-period metal surface 3 is used for indoor short-distance signal transmission, the coarse-period metal surface 3 can be installed on a wall or a ceiling. When the transmitter radiates a signal to the coarse periodic metal surface 3, firstly, a beam of reflected wave is generated at a position equal to the beam incident angle; secondly, due to the periodic corrugations of the surface, scattered beams are generated in other directions than the angle of the reflected waves. By calculation, the radiation angle and direction of the scattered beam can be obtained, so that the receiving antenna or other coarse periodic metal surface 3 can be placed at several specific positions where the scattering points arrive. Moreover, the rough surface can be combined with intelligent equipment, and the rough periodic metal surface 3 is rotated in real time according to requirements, so that a specific position avoids blocking, and signals are continuously received. The transmission mode can reduce the blocking of indoor walls and furniture to signals, thereby reducing coverage holes and blind areas; constructive interference of multiple signals can increase signal strength and improve signal quality; the rotatability of the surface increases the flexibility of signal transmission. And the terahertz communication system and the rough periodic metal surface 3 belong to light-weight, are convenient to install and dismantle, and are easier to integrate into other equipment for communication.
The variation curve of the metal surface 3 with the rough period of the technical scheme follows a sine function equation, and is as follows:
wherein A represents the amplitude, i.e., the change in height of the metal surface 3 in the vertical direction, X p Representing the period, i.e. the variation of the period of the roughened periodic metal surface 3 in the horizontal direction.
When a signal is incident on the rough periodic metal surface 3, a reflected signal is generated in the same direction as the incident angle, namely the direction of the signal follows Snell's law; while the direction of scattering follows bragg diffraction theory, the equation for determining the direction angle is as follows:
where n =0, + -1, + -2, + -3 \ 8230denotes harmonic order, λ denotes signal wavelength and θ denotes i Representative signalThe angle of incidence. Theta s Representing the scattering angle. When the periodic surface is incident in a determined direction by a signal of a certain frequency, the receiver can be placed by calculating the angle of each scattering angle to determine the receiving direction.
Scattered waves of different orientations can be generated by varying the height and period of the surface or the frequency of transmission of the signal, and experiments are performed below using 4 surfaces of different amplitudes and/or periods at different frequencies. Wherein S1 represents an aluminum plate having a smooth surface, S2 represents an amplitude A =0.35mm, and a period X p =2mm rough periodic surface, S3 stands for amplitude a =0.7mm, period X p =2mm rough periodic surface, S4 stands for amplitude a =0.7mm, period X p A rough periodic surface of =6mm, the resulting scattering spectrum being as follows:
(1) FIG. 3 shows the scattering spectrum of a rough periodic surface S2, S3 with the same period and different amplitudes, and a smooth surface S1 for comparison, at a frequency f =300GHz, when the angle of incidence θ of the signal is i =45 °. It can be found that the surfaces S1, S2, S3 are at θ s The position of =45 ° receives a strong signal, which means that both periodic and smooth surfaces follow snell's law of reflection, resulting in a reflected beam. Second, the rough periodic surfaces S2 and S3, at θ s =0 ° to θ s A peak signal also exists for the range of 10 °, but S1 has no signal at this position, which means that a rough periodic surface causes scattering, and the scattering intensity is comparable to the intensity of the reflected signal.
(2) FIG. 4 shows the scattering spectrum of a rough periodic surface S3, S4 of the same amplitude and different periods, and a smooth surface S1 for comparison, at a frequency f =300GHz, when the angle of incidence θ of the signal is i =45 °. It can be seen that each rough periodic surface generates reflected waves and scattered waves, and as the period of the surface increases, the peak value of the scattered signal increases, and the signal intensity is equivalent to the signal intensity of the primary reflection, which is enough for decoding. This shows that the period of the roughened periodic metal surface 3 has a strong influence on scattering.
(3) FIG. 5 shows the rough periodic surface S4 at a frequency f =300GHScattering spectrum at z, when angle of incidence θ of signal i =45 °. It can be seen that as the frequency increases, the angular position of the scattered component moves, i.e. the power peaks in the graph move; the distance between every two peaks is reduced along with the increase of the frequency, the difference between every two peaks is approximately the same, and the change of the distance between the peaks has a periodic rule.
(4) Fig. 6 shows the scattering spectrum of the rough periodic surface S4 at f =300GHz, where the angle and position of the transmitting end and the receiving end 12 of the signal are kept constant, θ i ＝θ s =45 °, power values for different angles are obtained by rotating the rough periodic surface only, from 0 ° (surface not rotated) to 35 °. It can be seen from the figure that there are 4 power peaks on the surface beyond the 0 position and that the signal strength is sufficient for decoding. This shows that the invention can arrange the receiving end 12 at different positions to receive signals, or change the signal radiation direction by intelligently regulating and controlling the rotating surface; the positions of the scattering peaks can be obtained through calculation, so that a communication path is planned, and an eavesdropper is avoided to prevent interference and eavesdropping.
As shown in fig. 7, the rough periodic metal surface is mounted on the glass surface, so that the signal of the transmitting end can be effectively reflected indoors, and the communication engineering of covering the indoor space by the outdoor base station is realized. And more information can be acquired through multiple reflections, thereby improving the signal quality.
As shown in fig. 8, the rough surface is light, so that they can be installed on the surface of the unmanned aerial vehicle, the unmanned aerial vehicle has high mobility and is convenient to deploy to a target area, and other rough surfaces can be arranged on the roof, the wall and the appropriate ground, so as to establish reliable communication connection. The use of unmanned aerial vehicle has strengthened the flexibility of communication for the coverage blind area reduces.
The installation of a coarse periodic surface on vehicles and equipment around the road, as shown in fig. 9, enables communication between vehicles and transportation facilities as well as between vehicles. Each vehicle can share data, so that information is provided for other vehicles, road conditions can be predicted in advance, path planning is facilitated, traffic accidents are reduced, and the like.
Claims (4)
1. Terahertz communication system based on periodic rough metal surface is characterized in that includes two parts: a terahertz communication system and a rough periodic metal surface;
the terahertz communication system comprises a sending end and a receiving end;
the sending end transmits and propagates signals;
the receiving end captures and processes the signals;
the rough periodic metal surface is used for reflecting and scattering signals;
the rough periodic metal surface is a polished aluminum plate, and periodic ripples are arranged in the one-dimensional direction of the surface;
the variation curve of the rough periodic metal surface follows a sine function equation as follows:
wherein A represents amplitude, i.e., variation in height of the metal surface in the vertical direction, X p Representing the period, namely the periodic change of the rough periodic metal surface in the horizontal direction.
2. The terahertz communication system based on the periodic rough metal surface as claimed in claim 1, wherein the sending end uses Xilinx Vertix-7 FPGA to generate 16QAM modulation signal at intermediate frequency; converting a digital signal generated by the FPGA into an analog signal through a DAC (digital-to-analog converter), and up-converting the signal to radio frequency through a second harmonic mixer; finally, the transmission signal is propagated through the terahertz transmission antenna.
3. The terahertz communication system based on the periodic rough metal surface as claimed in claim 1, wherein at the receiving end, the low noise amplifier amplifies the signal captured by the terahertz receiving antenna and outputs the amplified signal to the second harmonic mixer for down-conversion to obtain a signal of an intermediate frequency; the intermediate frequency signal is converted into a digital signal through the ADC and transmitted to the Xilinx XC7VX690T FPGA to complete the subsequent processes of synchronizing and demodulating signals.
4. The communication method of the terahertz communication system based on the periodic rough metal surface as claimed in any one of claims 1 to 3, comprising the following steps:
at a transmitting end, using Xilinx Vertix-7 FPGA to generate a 16QAM modulation signal under intermediate frequency; converting a digital signal generated by the FPGA into an analog signal through a DAC (digital-to-analog converter), and up-converting the signal to radio frequency through a second harmonic mixer; finally, transmitting signals are transmitted through the terahertz transmitting antenna;
the transmission signal is radiated to the rough periodic metal surface at a certain angle through the terahertz transmission antenna, the rough periodic metal surface generates reflected waves and scattered waves, the reflected waves and the scattered waves are radiated at a certain angle, and the radiation returns to the receiving end through the terahertz receiving antenna;
at a receiving end, a low-noise amplifier amplifies a signal captured by a terahertz receiving antenna and outputs the signal to a second harmonic mixer for down-conversion to obtain a signal of an intermediate frequency; the intermediate frequency signal is converted into a digital signal through the ADC and is transmitted to the Xilinx XC7VX690T FPGA to complete the subsequent processes of synchronizing and demodulating the signal.
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