Signal modulation and demodulation method based on electromagnetic metasurface

Abstract

The invention discloses a signal modulation and demodulation method based on an electromagnetic metasurface, and relates to the technical field of wireless communication, and the method comprises the following steps: S1, electromagnetic metasurface design: a programmable electromagnetic metasurface is designed, the electromagnetic metasurface is composed of a plurality of unit structures, and each unit structure is independently controlled; according to the signal modulation and demodulation method based on the electromagnetic metasurface, through a series of complete operation processes of encoding, modulation, transmission, demodulation, recovery and the like on digital information, the requirements for the transmission rate, stability and accuracy of the digital information in different application scenes are met, the signal modulation and demodulation strategy is improved, and the signal modulation and demodulation efficiency is improved. The continuity and accuracy of digital information transmission are ensured, and the situations of jamming, disconnection or data errors are avoided.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a signal modulation and demodulation method based on electromagnetic metasurface. Background Art

[0002] With the continuous development of science and technology, the application of wireless communication in various fields is becoming more and more extensive, and people's demand for wireless communication is also growing. In high-speed mobile scenarios, passengers inside high-speed trains use wireless networks based on electromagnetic metasurface technology to transmit digital information. Especially during video calls and large file downloads, due to the Doppler frequency shift and rapid signal switching caused by rapid movement, how to improve signal modulation and demodulation strategies to ensure the continuity and accuracy of digital information transmission and avoid freezes, disconnections or data errors is a problem that needs to be solved urgently. Summary of the invention

[0003] In order to solve the above technical problems, the present invention is implemented through the following technical solutions: a signal modulation and demodulation method based on electromagnetic metasurface, comprising the following steps: S1. Electromagnetic metasurface design: Design a programmable electromagnetic metasurface, which consists of multiple unit structures, each of which is independently controlled to control the amplitude, phase, frequency and polarization of electromagnetic waves; S2. Digital signal encoding: Encode the digital information to be transmitted into a digital signal, and further process it to form an in-phase branch I and an orthogonal branch Q signal; S3. Modulation strategy: adopt the modulation scheme of binary frequency shift keying BFSK or quadrature phase shift keying QPSK, and obtain the modulated electromagnetic wave signal by changing the time coding sequence of the electromagnetic metasurface unit to realize the modulation of digital signal; S4. Space-time coding: A far-field phase modulation communication method is proposed using space-time coding metasurfaces. By modulating the radiation phase of the main beam, the digital signal is transmitted within the main beam. S5. Signal reception and processing: At the receiving end, the electromagnetic wave signal modulated by the electromagnetic metasurface is received; then the received signal is demodulated and the in-phase branch I and the orthogonal branch Q signals are extracted; S6. Signal recovery: Convert the demodulated I / Q signal back to the original digital information, which includes video and pictures.

[0004] Preferably, the process of designing a programmable electromagnetic metasurface is as follows: According to the needs of the electromagnetic wave control function, a unit structure is selected; including: performing electromagnetic simulation analysis on the selected unit structure, analyzing its amplitude, phase, frequency response and polarization conversion characteristics under different electromagnetic wave frequencies by changing the length, width and spacing parameters of the unit structure, establishing a database between the parameters of the unit structure and the electromagnetic response characteristics, and obtaining the unit structure type and unit structure characteristics; wherein the electromagnetic wave control function includes amplitude, phase, frequency and polarization control; the basic unit structure forms include metal patches, gap structures, resonant rings and their combinations; according to the expected application scenarios and performance requirements, combined with the electromagnetic wave propagation characteristics and the uniformity of the field distribution, a uniform array, a non-uniform array or a specific periodic layout is used to plan the arrangement of the unit structure on the electromagnetic metasurface and determine the overall size and shape of the electromagnetic metasurface; at the same time, the spacing between the unit structures is determined within an acceptable range to meet the electromagnetic coupling effect, so as to ensure that each unit structure can be relatively independent The electromagnetic waves can be regulated and controlled while avoiding the over-sizing of the overall metasurface or the deterioration of the electromagnetic wave propagation characteristics due to excessive spacing; a unit structure layout plan is obtained based on the spacing between the unit structures and the overall size and shape of the electromagnetic metasurface; based on the unit structure layout plan, an independent programmable control circuit is designed for the unit structure to obtain an independent control circuit; the designed unit structure and the corresponding independent control circuit are integrated and packaged; then the performance of the packaged electromagnetic metasurface is tested to obtain the test results, and a vector network analyzer is used to measure the actual control effect of the electromagnetic metasurface on the amplitude, phase, frequency and polarization of the electromagnetic wave under different control signals, and the control effect is compared and analyzed with the design goals; according to the test results, the unit structure parameters, control circuit parameters or layout methods are optimized and adjusted to obtain the adjusted electromagnetic metasurface, so as to improve the performance indicators of the electromagnetic metasurface, such as control accuracy, response speed and bandwidth, to ensure that it meets the application requirements in digital information transmission systems.

[0005] Preferably, the process of encoding the digital information to be transmitted into a digital signal and further processing it to form an in-phase branch I and an orthogonal branch Q signal is as follows: Determine the original information to be transmitted and preprocess it to obtain digital information; use Huffman coding to compress and encode the digital information to obtain a coding sequence; use a suitable source coding algorithm to compress and encode the preprocessed digital information, which can reduce the amount of digital information and improve transmission efficiency without losing or minimizing information loss; then perform channel coding on the coding sequence to obtain a digital signal by adding redundant information to the coding sequence; channel coding realizes error correction and error detection functions by adding redundant information to the coding sequence; Mapping the digital signal into in-phase branch I and quadrature branch Q signals according to the requirements of the modulation scheme; the modulation scheme includes binary frequency shift keying BFSK modulation and quadrature phase shift keying QPSK modulation; For binary frequency shift keying BFSK modulation, the digital signal is mapped to carrier signals of different frequencies according to the 0 and 1 states of the digital signal, where one frequency corresponds to the I signal and the other frequency corresponds to the Q signal; For quadrature phase shift keying (QPSK) modulation, every two consecutive coded bits are combined into four possible states: 00, 01, 10, and 11. Each state corresponds to a specific phase value, and then the phase value is mapped to the amplitude of the I and Q signals. By changing the amplitude of I and Q signals to represent different phase states, the conversion of digital signals to I / Q signals is achieved; Preferably, the process of the modulation strategy in step S3 is as follows: determine the modulation scheme according to the design requirements and application scenarios of the wireless communication system of the electromagnetic metasurface; input the encoded in-phase branch I and orthogonal branch Q signals into the determined modulation scheme to obtain a selected carrier signal; produce an electromagnetic metasurface unit control signal according to the selected carrier signal and modulation scheme, that is, generate a time code sequence for controlling the electromagnetic metasurface unit; send the generated time code sequence to the programmable control circuit of each unit structure of the electromagnetic metasurface; the control circuit adjusts the capacitance and inductance parameters of the unit structure according to the received time code sequence, changes the response characteristics of the unit structure to the electromagnetic wave, and forms a modulated electromagnetic wave signal; Preferably, the process of determining the modulation scheme is as follows: adopting a binary frequency shift keying BFSK or quadrature phase shift keying QPSK modulation scheme; if BFSK is selected, determining two carrier frequencies f for representing digital information 0 and 1 1 and f 2 If QPSK is selected, determine the I and Q signal amplitude combinations corresponding to the four phase states 0°, 90°, 180°, and 270° and the corresponding carrier frequency f c ; At the same time, the time coding sequence of the electromagnetic metasurface unit is initialized to the default state or the preset starting state; For BFSK modulation, if the input digital signal is 0, the frequency is selected as f 1 If it is 1, the frequency is selected as f 2 The carrier signal; when selecting f 1 When, the time code sequence T is generated 1 , time coding sequence T 1 Control the electromagnetic properties of the electromagnetic metasurface unit so that energy is transferred from the carrier frequency to a specific harmonic frequency associated with the corresponding phase state; when f is selected 2 When, the time code sequence T is generated 2 ; For QPSK modulation, the corresponding phase state is determined according to the input I and Q signal amplitude combination, and the corresponding carrier signal is selected; the corresponding time code sequence is generated according to the four different phase states: T00 、T 01 、T 10 、T 11 , time coding sequence: T 00 、T 01 、T 10 、T 11 The energy of the electromagnetic metasurface unit is guided to the specific harmonic frequency associated with the corresponding phase state; in BFSK, when sending a time coding sequence, the electromagnetic metasurface unit transfers energy to the relevant harmonic frequency to form a modulated electromagnetic wave signal; in QPSK, according to different time coding sequences, the energy is transferred to the harmonic frequency corresponding to different phase states to realize the modulation of the digital signal.

[0006] Preferably, in step S4, the process of performing space-time coding is as follows: Design the space-time coding metasurface structure by determining the layout and electromagnetic characteristics of the space-time coding metasurface unit structure; analyze the response characteristics of the space-time coding metasurface to electromagnetic waves at different time and space positions, obtain the layout and electromagnetic characteristics of the space-time coding metasurface unit structure, establish a relationship model between the unit structure and the main beam radiation phase change under different coding states, and obtain the scattering parameter matrix of the space-time coding metasurface through electromagnetic simulation software or experimental measurement to form the space-time coding metasurface structure; the scattering parameter matrix describes the relationship between the input electromagnetic wave and the output electromagnetic wave at different time and space points, providing basic data for subsequent coding design; The digital signal to be transmitted is mapped according to a preset space-time coding rule to obtain a mapping relationship between the digital signal and the code; the preset space-time coding rule includes the coding capability of the space-time coding metasurface and the adjustable range of the main beam radiation phase; according to the mapping relationship between the digital signal and the code, a space-time coding sequence is generated; the space-time coding sequence includes control instructions for the space-time coding metasurface unit structure at multiple time steps and spatial positions; the generated space-time coding sequence is loaded into the programmable control circuit of the space-time coding metasurface to ensure that each unit structure receives the corresponding control signal at the correct time to achieve accurate modulation of the main beam radiation phase; Main beam radiation phase modulation: when the space-time coding metasurface loaded with the space-time coding sequence receives an input electromagnetic wave signal (such as the electromagnetic wave signal from the modulation step S3), the radiation phase of the main beam is modulated according to a preset space-time coding rule by controlling the change of the electromagnetic characteristics of the cell structure in time and space according to the space-time coding sequence; including: according to the space-time coding sequence, the cell structure in a specific area changes its phase response, so that the radiation phase of the main beam in this direction changes, and in this way, digital information is encoded into the radiation phase change of the main beam; The electromagnetic wave signal after the main beam radiation phase modulation propagates in the far field space; at the receiving end, an antenna array or a receiving device is set to receive the electromagnetic wave signal transmitted by the main beam, and the information of the main beam radiation phase is obtained by measuring the phase difference or amplitude change of the signal received by different antenna units; The receiving end decodes the main beam radiation phase information according to the inverse process of the space-time coding rule; converts the received main beam radiation phase change sequence back to the original digital signal; It includes: through a decoding algorithm corresponding to the coding mapping relationship of the transmitter, the change of the main beam radiation phase is restored to bits or symbols in the digital information unit, and finally the complete original digital information, including video and picture content, is restored.

[0007] Preferably, the process of demodulating the received signal is as follows: select a receiving antenna according to the operating frequency range, transmission distance and signal polarization mode of the wireless communication system of the electromagnetic metasurface; if the operating frequency is high and high gain and directivity are required, select a parabolic antenna; if omnidirectionality is required, select a dipole antenna or a microstrip antenna; construct a receiving system, including an antenna matching network, a low noise amplifier LNA and a filter component; when the receiving antenna receives the electromagnetic wave signal modulated by the electromagnetic metasurface, the signal is first transmitted to the LNA through the antenna matching network for amplification, and then filtered through the filter to obtain a preliminary processed signal, which is still in the form of a modulated electromagnetic wave signal, but after filtering and amplification, its signal quality is improved, which is more convenient for subsequent demodulation operations.

[0008] Preferably, the process of demodulating the received signal and extracting the in-phase branch I and the orthogonal branch Q signals is as follows: first, using an automatic gain control AGC circuit to adjust the amplitude of the signal after preliminary processing at the receiving end to complete the preprocessing of the received signal; then selecting and initializing a demodulator according to a preset modulation scheme, including: if a BFSK demodulator is selected, then setting two matched filters corresponding to the frequencies of 0 and 1 respectively; if a QPSK demodulator is selected, then configuring a demodulation structure for processing orthogonal signals, including a local carrier recovery circuit and an integral decision circuit; For BFSK demodulation: the pre-processed received signal is passed through two matched filters respectively. The frequency responses of the two filters are matched with the sum of the two carrier frequencies used in modulation. The function of the matched filter is to enhance the signal component that matches its own frequency and suppress other frequency components, thereby improving the signal-to-noise ratio of the signal. Envelope detection is performed on the two signals after matched filtering to obtain the envelopes of the two signals; the envelope detection is realized through rectification and low-pass filtering operations, and it can extract the amplitude change information of the signal; then, the sizes of the two envelopes are compared, and the received digital signal is determined to be 0 or 1 according to the preset decision threshold to obtain a digital signal sequence; after BFSK demodulation, according to the digital signal sequence obtained by the decision, according to the mapping rule between the digital signal and the I / Q signal during modulation, it is determined in the modulation step, and the digital signal sequence is converted into the corresponding in-phase branch I and orthogonal branch Q signals; For QPSK demodulation: First, the local carrier signal with the same frequency and phase as the transmitter must be restored, which can be achieved by using a Costas loop or a carrier recovery algorithm based on digital signal processing (DSP). Taking the Costas loop as an example, the orthogonal characteristics of the received signal are used to synchronize the local carrier signal output by the VCO with the carrier signal in the received signal in frequency and phase through a phase detector, a loop filter and a voltage-controlled oscillator VCO, so as to restore the local carrier signal with the same frequency and phase as the transmitter; the pre-processed received signal is multiplied with the recovered local carrier signal to achieve orthogonal demodulation; specifically, the received signal is multiplied with the in-phase component and the orthogonal component of the local carrier respectively to obtain two product signals; after low-pass filtering, the two product signals are subjected to baseband signals of the in-phase branch I and the orthogonal branch Q signals; According to the constellation diagram and decision area of ​​the QPSK signal, by comparing the sampling value with the preset decision threshold, the symbol point corresponding to each sampling moment is determined and the digital signal sequence is restored.

[0009] Preferably, during the preprocessing of the received signal, if the signal undergoes frequency deviation during transmission, a frequency locked loop (FLL) technique is used to correct the frequency deviation of the signal; wherein the FLL compares the frequency of the received signal with a local reference frequency, generates a control signal to adjust the frequency of the local oscillator, and matches the frequency of the received signal with the operating frequency of the demodulator.

[0010] Preferably, the process of converting the demodulated I / Q signal back to the original digital information, including video and picture, is as follows: First, the starting position of each frame of data is determined by detecting the synchronization header or synchronization sequence in the demodulated I / Q signal; then, the time synchronization calibration of each frame of data is performed on the time axis according to the system clock and frame synchronization information; then, the amplitude and phase relationship of the I / Q signal is checked and calibrated; using the known calibration signal, the actual received I / Q signal is compared, and the amplitude of the I / Q signal is corrected by adjusting the gain control circuit to make it conform to the standard proportional relationship; for phase deviation, a phase compensation algorithm is used to adjust the phase of the I / Q signal according to the detected phase difference to ensure the accuracy of the signal and facilitate the subsequent accurate recovery of digital information; If the QPSK modulation scheme is used in the modulation process, an inverse transformation is performed based on the mapping rule between the digital signal and the I / Q signal during QPSK modulation; the amplitude and phase states of the I / Q signals corresponding to each digital bit combination during modulation: 00, 01, 10, 11 are reviewed, and the corresponding digital bit combination is determined according to the amplitude and phase of the I / Q signal obtained after the current demodulation, and the I / Q signal is restored to a digital signal sequence symbol by symbol; If it is a BFSK modulation scheme, based on the mapping rule between the digital signal and the I / Q signal during BFSK modulation, the extracted I / Q signal is used to determine whether the corresponding state represents a digital 0 or 1, and the digital signal sequence is restored; the restored digital signal sequence is channel-decoded to determine the format of the original digital information, including H.264 for video and JPEG for pictures, and then the corresponding source decoding algorithm is used to decode the digital signal after channel decoding to restore the original video frame data or picture pixel data; For H.264 video decoding, the header information in the bitstream is parsed according to the syntax specification of H.264, and the compressed and encoded video data is gradually restored to the original pixel data frame by frame through entropy decoding, inverse quantization, inverse transformation and motion compensation to reconstruct the video image sequence; the header information includes the sequence header and the image header; for JPEG picture decoding, the pixel matrix of the picture is restored through Huffman decoding, inverse quantization and inverse discrete cosine transformation, and finally the original picture information is restored; and it is integrated in the correct order to restore the original digital information to be complete and accurate.

[0011] The present invention provides a signal modulation and demodulation method based on electromagnetic metasurface, which has the following beneficial effects: 1. The signal modulation and demodulation method based on electromagnetic metasurface, by designing a programmable electromagnetic metasurface, controls the amplitude, phase, frequency and polarization of the electromagnetic wave, and can better adapt to different application scenarios and signal transmission requirements; and based on the application of binary frequency shift keying BFSK or quadrature phase shift keying QPSK modulation schemes, combined with the time coding sequence control of the electromagnetic metasurface unit, it can effectively convert digital signals into modulated electromagnetic wave signals, thereby improving the flexibility and efficiency of signal modulation.

[0012] 2. The signal modulation and demodulation method based on electromagnetic metasurface meets the requirements of rate, stability and accuracy of digital information transmission in different application scenarios through a series of complete operation processes such as encoding, modulation, transmission, demodulation and recovery of digital information, improves the signal modulation and demodulation strategy, ensures the continuity and accuracy of digital information transmission, and avoids the occurrence of freezes, disconnections or data errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1This is a flowchart of a signal modulation and demodulation method based on an electromagnetic metasurface of the present invention. DETAILED DESCRIPTION

[0014] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for the purpose of illustration and description, and are not intended to be exhaustive or to limit the present invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0015] like Figure 1 As shown, the present invention provides a technical solution: a signal modulation and demodulation method based on an electromagnetic metasurface, comprising the following steps: S1. Electromagnetic metasurface design: Design a programmable electromagnetic metasurface, which consists of multiple unit structures, each of which is independently controlled to control the amplitude, phase, frequency and polarization of electromagnetic waves; S2. Digital signal encoding: Encode the digital information to be transmitted into a digital signal, and further process it to form an in-phase branch I and an orthogonal branch Q signal; S3. Modulation strategy: adopt the modulation scheme of binary frequency shift keying BFSK or quadrature phase shift keying QPSK, and obtain the modulated electromagnetic wave signal by changing the time coding sequence of the electromagnetic metasurface unit to realize the modulation of digital signal; S4. Space-time coding: A far-field phase modulation communication method is proposed using space-time coding metasurfaces. By modulating the radiation phase of the main beam, the digital signal is transmitted within the main beam. S5. Signal reception and processing: At the receiving end, the electromagnetic wave signal modulated by the electromagnetic metasurface is received; then the received signal is demodulated and the in-phase branch I and the orthogonal branch Q signals are extracted; S6. Signal recovery: Convert the demodulated I / Q signal back to the original digital information, which includes video and pictures.

[0016] The process of designing a programmable electromagnetic metasurface is as follows: According to the needs of the electromagnetic wave control function, the unit structure is selected; including: performing electromagnetic simulation analysis on the selected unit structure, analyzing its amplitude, phase, frequency response and polarization conversion characteristics under different electromagnetic wave frequencies by changing the length, width and spacing parameters of the unit structure, establishing a database between the parameters of the unit structure and the electromagnetic response characteristics, and obtaining the unit structure type and unit structure characteristics; wherein the electromagnetic wave control function includes amplitude, phase, frequency and polarization control; the basic unit structure forms include metal patches, gap structures, resonant rings and their combinations; according to the expected application scenarios and performance requirements, combined with the electromagnetic wave propagation characteristics and field distribution uniformity, uniform arrays, non-uniform arrays and so on are used. A uniform array or a specific periodic layout is used to plan the arrangement of the unit structures on the electromagnetic metasurface, and determine the overall size and shape of the electromagnetic metasurface; at the same time, the spacing between the unit structures is determined within an acceptable range to meet the electromagnetic coupling effect, so as to ensure that each unit structure can regulate the electromagnetic waves relatively independently, while avoiding the overall metasurface size being too large or the electromagnetic wave propagation characteristics being deteriorated due to excessive spacing; a unit structure layout plan is obtained based on the spacing between the unit structures and the overall size and shape of the electromagnetic metasurface; based on the unit structure layout plan, an independent programmable control circuit is designed for the unit structure to obtain an independent control circuit; it should be further explained that in the specific implementation process, The control circuit has the ability to receive external control signals and convert them into the ability to regulate the electromagnetic characteristics of the unit structure; including: in the case of regulating the resonant frequency of the unit structure by changing the capacitance or inductance, the control circuit is designed to include a digital-to-analog converter DAC, which outputs a corresponding voltage or current according to the received digital control signal, thereby changing the value of the capacitance or inductance. The control circuit also has an interface for communicating with an external control system: a signal processing unit or a control unit to receive control instructions and feedback status information of the unit structure; the designed unit structure is integrated and packaged with the corresponding independent control circuit; ensuring that the electrical connection between the control circuit and the unit structure is reliable and the electrical characteristics of the unit structure are controlled The magnetic properties are minimally affected; during the integration process, it is necessary to consider the wiring layout and electromagnetic shielding issues to reduce signal interference and electromagnetic leakage; after the integration is completed, the electromagnetic metasurface is packaged to protect the internal circuit and unit structure from the influence of humidity, dust, and mechanical impact in the environment, while ensuring that the permeability or reflectivity of the packaging material to electromagnetic waves meets the design requirements and does not affect the overall electromagnetic control performance of the electromagnetic metasurface; then the performance test of the packaged electromagnetic metasurface is carried out to obtain the test results, and the actual control effect of the electromagnetic metasurface on the amplitude, phase, frequency and polarization of the electromagnetic wave under different control signals is measured using a vector network analyzer, and compared with the design goals for analysis;According to the test results, the unit structure parameters, control circuit parameters or layout methods are optimized and adjusted to obtain the adjusted electromagnetic metasurface to improve the performance indicators of the electromagnetic metasurface, such as control accuracy, response speed, and bandwidth, to ensure that it meets the application requirements in digital information transmission systems. ;

[0017] The process of encoding the digital information to be transmitted into a digital signal and further processing it to form the in-phase branch I and the orthogonal branch Q signal is as follows: Determine the original information to be transmitted and preprocess it to obtain digital information; the original information includes video files, picture files from the computer file system and digital data collected from the sensor; the preprocessing content includes: based on the source of the original information, the video files and picture files from the computer file system are converted into H.264 video coding and JPEG picture coding respectively to reduce data redundancy and facilitate subsequent processing; for the digital data collected by the sensor, that is, sensor data, data calibration and filtering are performed to remove noise and outliers; the digital information is compressed and encoded using Huffman coding to obtain a coding sequence; it should be further explained that in the specific implementation process, it includes: Huffman coding constructs an optimal binary tree according to the probability of occurrence of different characters or symbols in the digital information, represents the characters with high frequency of occurrence with short codes, and represents the characters with low frequency of occurrence with long codes, so as to achieve data compression; after source coding, the digital information is converted into a more compact coding sequence; Adopting appropriate source coding algorithm to compress and encode the pre-processed digital information can reduce the data volume of digital information and improve transmission efficiency without losing or minimizing the information loss. Then, the coding sequence is channel-coded, and a digital signal is obtained by adding redundant information to the coding sequence. It should be further explained that, in the specific implementation process, the channel coding realizes error correction and error detection functions by adding redundant information to the coding sequence. It includes: using convolution coding and cyclic redundancy check CRC coding. Among them, convolution coding is a linear block code, which generates a coding output with error correction capability by performing shift register operations and specific logical operations on the input coding sequence. Cyclic redundancy check CRC coding calculates a check value according to the data polynomial and appends the check value to the data. The receiving end determines whether an error occurs in the data during transmission by performing the same calculation on the received data and comparing the check value. By performing channel coding on the signal after source coding, the anti-interference ability of digital signals during transmission can be improved; Mapping the digital signal into an in-phase branch I and an orthogonal branch Q signal according to the requirements of the modulation scheme; the modulation scheme includes binary frequency shift keying BFSK modulation and orthogonal phase shift keying QPSK modulation; for binary frequency shift keying BFSK modulation, according to the 0 and 1 states of the digital signal, the digital signal is mapped to carrier signals of different frequencies respectively, wherein one frequency corresponds to the I signal and the other frequency corresponds to the Q signal; For quadrature phase shift keying (QPSK) modulation, every two consecutive coded bits are combined into four possible states: 00, 01, 10, and 11. Each state corresponds to a specific phase value, and then the phase value is mapped to the amplitude of the I and Q signals. By changing the amplitude of the I and Q signals to represent different phase states, the conversion of digital signals to I / Q signals is achieved. The generated in-phase branch I and orthogonal branch Q signals are adjusted and filtered for signal amplitude to meet the signal characteristic requirements for electromagnetic metasurface modulation; including: adjusting the signal amplitude to the effective response range of the electromagnetic metasurface unit structure, removing high-frequency noise and harmonic components through a low-pass filter to ensure signal purity and stability; the conditioned I / Q signal can be ready to be input into the electromagnetic metasurface for subsequent modulation operations, thereby realizing the transmission of digital information in the electromagnetic metasurface wireless communication system.

[0018] The process of modulation strategy in step S3 is as follows: Determine the modulation scheme based on the design requirements and application scenarios of the electromagnetic metasurface wireless communication system; Inputting the encoded in-phase branch I and quadrature branch Q signals into a determined modulation scheme to obtain a selected carrier signal; According to the selected carrier signal and modulation scheme, an electromagnetic metasurface unit control signal is produced, i.e., a time-coded sequence for controlling the electromagnetic metasurface unit is generated; The generated time code sequence is sent to the programmable control circuit of each unit structure of the electromagnetic metasurface; the control circuit adjusts the capacitance and inductance parameters of the unit structure according to the received time code sequence, changes the response characteristics of the unit structure to the electromagnetic wave, and forms a modulated electromagnetic wave signal; Monitoring and optimization of electromagnetic wave signals after modulation: Use a spectrum analyzer to monitor the electromagnetic wave signals obtained after modulation to check whether the frequency characteristics, amplitude characteristics and harmonic components of the signals meet the expected modulation requirements; if deviations or unsatisfactory conditions are found in the signals, including insufficient harmonic suppression and unstable amplitude, optimize the signals by adjusting the parameters of the time coding sequence, the electromagnetic parameters of the electromagnetic metasurface unit structure or by optimizing the modulation algorithm to ensure that the modulated electromagnetic wave signals can accurately carry digital information and have good transmission performance and anti-interference capabilities; Through the above steps, the modulation scheme of binary frequency shift keying BFSK or orthogonal phase shift keying QPSK can be effectively utilized, combined with the time coding sequence control of the electromagnetic metasurface unit, to realize the conversion of digital signals into modulated electromagnetic wave signals, thus preparing for the wireless transmission of digital information in the wireless communication system of the electromagnetic metasurface.

[0019] The process of determining the modulation scheme is as follows: Adopt binary frequency shift keying BFSK or quadrature phase shift keying QPSK modulation scheme; If BFSK is selected, determine the two carrier frequencies f used to represent digital information 0 and 1 1 and f 2 ; If QPSK is selected, determine the I and Q signal amplitude combinations corresponding to the four phase states 0°, 90°, 180°, and 270° and the corresponding carrier frequency f c ; At the same time, the time coding sequence of the electromagnetic metasurface unit is initialized to a default state or a preset starting state; For BFSK modulation, if the input digital signal is 0, the frequency is selected as f 1 If it is 1, the frequency is selected as f 2 The carrier signal; when selecting f 1 When, the time code sequence T is generated 1 , time coding sequence T 1 Control the electromagnetic properties of the electromagnetic metasurface unit so that energy is transferred from the carrier frequency to a specific harmonic frequency associated with the corresponding phase state; when f is selected 2 When, the time code sequence T is generated 2 ; For QPSK modulation, the corresponding phase state is determined according to the input I and Q signal amplitude combination, and the corresponding carrier signal is selected; the corresponding time code sequence is generated according to the four different phase states: T 00 、T 01 、T 10 、T 11 , time coding sequence: T 00 、T 01 、T 10 、T 11 directing energy of electromagnetic metasurface units to specific harmonic frequencies associated with corresponding phase states; In BFSK, when sending a time-coded sequence, the electromagnetic metasurface unit transfers energy to the harmonic frequency associated with it, forming a modulated electromagnetic wave signal; In QPSK, the digital signal is modulated by transferring energy to harmonic frequencies corresponding to different phase states according to different time coding sequences; It should be further explained that, in the specific implementation process, the carrier frequency is assumed to be f d , then the carrier frequency f d The harmonic frequency is n×f d , n=1,2,3...; For BFSK, the harmonic frequency is an integer multiple of the carrier frequency, let f 1 =f d , f 2 =f d +Δf, where Δf is the frequency shift; except for f 1 and f 2 , their low-order harmonics 2f 1 , 2f 2 It may also appear during signal transmission, and the specific choice of harmonic frequency for transmission depends on the design characteristics and modulation requirements of the electromagnetic metasurface. 1 The amplitude and phase control performance of electromagnetic waves is better at low frequencies, and interference can be effectively avoided. Therefore, energy can be transmitted to 2f 1 This harmonic frequency carries the information related to the number 0; similarly, for the information related to the number 1, a suitable f can be selected 2 Harmonic frequencies, such as 3f 2 ; For QPSK modulation, the main carrier frequency is f c , the signal is expressed by changing the amplitude of the in-phase I and orthogonal Q branch signals to represent different phase states; similarly, the harmonic frequency can be an integer multiple of the carrier frequency. In this modulation mode, since the phase modulation of the signal is more complicated, in addition to considering the carrier frequency f c In addition to the harmonic frequencies, the sideband frequencies caused by phase changes must also be considered; according to modulation theory, the spectrum of the QPSK signal includes the carrier frequency f c And multiple sideband frequencies around the carrier frequency; these sideband frequencies can be regarded as a generalized harmonic frequency, and their frequency expression is f c ±k×f s , k=1,2,3...; f s is the frequency interval related to the signal bandwidth and depends on the baud rate of the digital signal; in practical applications, the electromagnetic metasurface may transfer energy to the carrier frequency f c and the main sideband frequencies near it, such as f c +f s and f c -f s, by finely controlling the amplitude and phase of the electromagnetic waves at these frequencies, the effective transmission of the QPSK modulated signal can be achieved; the frequency selection of the specific harmonics, i.e., the sidebands, needs to comprehensively consider the frequency response characteristics, signal bandwidth, and anti-interference capabilities of the electromagnetic metasurface to ensure that the digital signal can be transmitted accurately and stably; in this way, the process of transferring the energy of the input carrier signal from the carrier frequency to a specific harmonic frequency is achieved.

[0020] In step S4, the process of space-time coding is as follows: by determining the layout and electromagnetic characteristics of the space-time coding metasurface unit structure, the space-time coding metasurface structure is designed; the response characteristics of the space-time coding metasurface to electromagnetic waves at different time and space positions are analyzed to obtain the layout and electromagnetic characteristics of the space-time coding metasurface unit structure, and a relationship model between the unit structure and the main beam radiation phase change under different coding states is established, and the scattering parameter matrix of the space-time coding metasurface is obtained through electromagnetic simulation software or experimental measurement to form a space-time coding metasurface structure; the scattering parameter matrix describes the relationship between the input electromagnetic wave and the output electromagnetic wave at different time and space points, and provides basic data for subsequent coding design; The digital signal to be transmitted is mapped according to a preset space-time coding rule to obtain a mapping relationship between the digital signal and the code; the preset space-time coding rule includes the coding capability of the space-time coding metasurface and the adjustable range of the main beam radiation phase; it should be further explained that, in the specific implementation process, the space-time coding sequence corresponding to the bit or symbol in each digital information unit of the digital signal is determined according to the coding capability of the space-time coding metasurface and the adjustable range of the main beam radiation phase; including: for a simple binary digital signal, two different space-time coding sequences are designed, corresponding to the numbers 0 and 1, respectively, to determine the state change of the unit structure of the space-time coding metasurface at different time and space positions, thereby affecting the radiation phase of the main beam; Generate a space-time coding sequence according to the mapping relationship between the digital signal and the coding; the space-time coding sequence includes control instructions for the space-time coding metasurface unit structure at multiple time steps and spatial positions; The generated space-time coding sequence is loaded into the programmable control circuit of the space-time coding metasurface to ensure that each unit structure receives the corresponding control signal at the right time to achieve accurate modulation of the main beam radiation phase; Main beam radiation phase modulation: when the space-time coding metasurface loaded with the space-time coding sequence receives an input electromagnetic wave signal (such as the electromagnetic wave signal from the modulation step S3), the radiation phase of the main beam is modulated according to a preset space-time coding rule by controlling the change of the electromagnetic characteristics of the cell structure in time and space according to the space-time coding sequence; including: according to the space-time coding sequence, the cell structure in a specific area changes its phase response, so that the radiation phase of the main beam in this direction changes, and in this way, digital information is encoded into the radiation phase change of the main beam; The electromagnetic wave signal after the main beam radiation phase modulation propagates in the far field space; at the receiving end, an antenna array or a receiving device is set to receive the electromagnetic wave signal transmitted by the main beam, and the information of the main beam radiation phase is obtained by measuring the phase difference or amplitude change of the signal received by different antenna units; The receiving end decodes the main beam radiation phase information according to the inverse process of the space-time coding rule; converts the received main beam radiation phase change sequence back to the original digital signal; Including: through a decoding algorithm corresponding to the coding mapping relationship of the transmitter, the change of the main beam radiation phase is restored to bits or symbols in the digital information unit, and finally the complete original digital information, including video and picture content, is restored; Through the above steps, a far-field phase modulation communication method is realized using the space-time coding metasurface, which effectively transmits the digital signal within the main beam by modulating the radiation phase of the main beam, and successfully recovers the original digital information at the receiving end.

[0021] The process of demodulating the received signal is as follows: According to the operating frequency range, transmission distance and signal polarization mode of the wireless communication system of the electromagnetic metasurface, a receiving antenna is selected; if the operating frequency is high and high gain and directivity are required, a parabolic antenna is selected; if omnidirectionality is required, a dipole antenna or a microstrip antenna is selected; a receiving system is constructed, including an antenna matching network, a low-noise amplifier LNA and a filter component; the antenna matching network is used to ensure impedance matching between the receiving antenna and the subsequent circuit, so that the antenna can transmit the received electromagnetic wave energy to the subsequent circuit to the greatest extent and reduce reflection loss; the LNA is used to amplify the weak received signal without introducing too much noise, thereby improving the signal strength and signal-to-noise ratio; the filter is used to filter out interference signals outside the frequency band of the received signal; It should be further explained that, in a specific implementation, the bandpass filter can only allow signals within the operating frequency range of the wireless communication system of the electromagnetic metasurface to pass through, suppressing interference signals from nearby wireless devices; When the receiving antenna receives the electromagnetic wave signal modulated by the electromagnetic metasurface, the signal is first transmitted to the LNA through the antenna matching network for amplification, and then filtered through the filter to obtain a preliminarily processed signal. This signal is still in the form of a modulated electromagnetic wave signal, but after filtering and amplification, its signal quality is improved, which is more convenient for subsequent demodulation operations; During this process, you can also use signal monitoring equipment: oscilloscope or spectrum analyzer to monitor the signal after preliminary processing, observe the amplitude and frequency characteristics of the signal, and ensure that the signal reception and preliminary processing process are normal; Signal frequency band adjustment: The frequency band of the received signal is adjusted according to the system design and the requirements of subsequent demodulation; if the frequency of the received signal does not match the operating frequency of the demodulation device, or in order to facilitate signal processing, the frequency of the received signal is transformed through a mixer to obtain an intermediate frequency signal; the mixer mixes the received signal with the signal generated by the local oscillator to generate a new intermediate frequency signal; Through the above steps, the reception and preliminary processing of the electromagnetic wave signal modulated by the electromagnetic metasurface are completed at the receiving end, laying the foundation for the subsequent signal demodulation and restoration of the original digital information.

[0022] The process of demodulating the received signal and extracting the in-phase branch I and the orthogonal branch Q signals is as follows: First, the automatic gain control AGC circuit is used to adjust the amplitude of the signal after preliminary processing at the receiving end to complete the preprocessing of the received signal; then the demodulator is selected and initialized according to the preset modulation scheme, including: if the BFSK demodulator is selected, then two matched filters are set, corresponding to the frequencies of 0 and 1 respectively; if the QPSK demodulator is selected, then a demodulation structure for processing orthogonal signals is configured, including a local carrier recovery circuit and an integral decision circuit; For BFSK demodulation: the pre-processed received signal is passed through two matched filters respectively, and the frequency responses of the two filters are matched with the two carrier frequencies and used in modulation respectively. The function of the matched filter is to enhance the signal component that matches its own frequency and suppress other frequency components, thereby improving the signal-to-noise ratio of the signal; the two signals after matched filtering are subjected to envelope detection to obtain the envelopes of the two signals; the envelope detection is realized by rectification and low-pass filtering operations, and it can extract the amplitude change information of the signal; then, the sizes of the two envelopes are compared, and the received digital signal is determined to be 0 or 1 according to the preset decision threshold to obtain a digital signal sequence; wherein, if the envelope corresponding to is greater than the envelope corresponding to, and the difference exceeds the decision threshold, it is determined to be a digital signal 0, otherwise it is determined to be 1; in this way, the received BFSK modulated signal is demodulated into a digital signal sequence; after BFSK demodulation, according to the digital signal sequence obtained by the decision, according to the mapping rule between the digital signal and the I / Q signal during modulation, it is determined in the modulation step, and the digital signal sequence is converted into the corresponding in-phase branch I and orthogonal branch Q signals; For QPSK demodulation: First, the local carrier signal with the same frequency and phase as the transmitter must be restored, which can be achieved by using a Costas loop or a carrier recovery algorithm based on digital signal processing (DSP). Taking the Costas loop as an example, the orthogonal characteristics of the received signal are used to synchronize the local carrier signal output by the VCO with the carrier signal in the received signal in frequency and phase through a phase detector, a loop filter and a voltage-controlled oscillator VCO, so as to restore the local carrier signal with the same frequency and phase as the transmitter; the pre-processed received signal is multiplied with the recovered local carrier signal to achieve orthogonal demodulation; specifically, the received signal is multiplied with the in-phase component and the orthogonal component of the local carrier respectively to obtain two product signals; these two product signals are low-pass filtered to obtain the baseband signals of the in-phase branch I and the orthogonal branch Q signal; according to the constellation diagram and decision area of ​​the QPSK signal, the symbol point corresponding to each sampling moment is determined by comparing the sampling value with the preset decision threshold, and the digital signal sequence is restored; It should be further explained that, in the specific implementation process, in the standard QPSK constellation diagram, the symbol point is determined to be one of the four states 00, 01, 10, and 11 according to the amplitude and positive and negative of the I and Q signals; then, according to the mapping rule between the digital signal and the I / Q signal during modulation, the restored digital signal sequence is converted into the corresponding in-phase branch I and orthogonal branch Q signals; Through the above steps, the received signal can be effectively demodulated and the in-phase branch I and the orthogonal branch Q signals can be extracted, thus preparing for the subsequent restoration of the original digital information.

[0023] During the preprocessing of the received signal, if the signal has a frequency offset during transmission, the frequency locked loop FLL technology is used to correct the frequency offset of the signal; wherein, the FLL compares the frequency of the received signal with the local reference frequency, generates a control signal to adjust the frequency of the local oscillator, and matches the frequency of the received signal with the operating frequency of the demodulator.

[0024] The process of converting the demodulated I / Q signal back to the original digital information, including video and pictures, is as follows: First, the starting position of each frame of data is determined by detecting the synchronization header or synchronization sequence in the demodulated I / Q signal; then, the time synchronization calibration of each frame of data is performed on the time axis according to the system clock and frame synchronization information; then, the amplitude and phase relationship of the I / Q signal are checked and calibrated; it should be further explained that, in the specific implementation process, the known calibration signal is used to compare the actually received I / Q signal, and the amplitude of the I / Q signal is corrected by adjusting the gain control circuit to make it conform to the standard proportional relationship; for the phase deviation, the phase compensation algorithm is used to adjust the phase of the I / Q signal according to the detected phase difference to ensure the accuracy of the signal, so as to facilitate the subsequent accurate recovery of digital information; If the QPSK modulation scheme is used in the modulation process, an inverse transformation is performed based on the mapping rule between the digital signal and the I / Q signal during QPSK modulation; the amplitude and phase states of the I / Q signals corresponding to each digital bit combination during modulation: 00, 01, 10, 11 are reviewed, and the corresponding digital bit combination is determined according to the amplitude and phase of the I / Q signal obtained after the current demodulation, and the I / Q signal is restored to a digital signal sequence symbol by symbol; It should be further explained that, in the specific implementation process, if the amplitude and phase corresponding to the I / Q signal at a certain moment falls in the area representing "01" in the QPSK constellation diagram, the symbol is restored to the binary digital signal corresponding to "01"; If it is a BFSK modulation scheme, based on the mapping rules of digital signals and I / Q signals during BFSK modulation, the extracted I / Q signals are used to determine whether the corresponding state represents a digital 0 or 1, and the digital signal sequence is restored; for example, if according to the mapping rules, when the I signal is a certain value and the Q signal is 0, it represents a digital 0, then the corresponding determination and restoration are performed based on the actual I / Q situation after demodulation; Channel decoding is performed on the restored digital signal sequence. It should be further explained that, in the specific implementation process, if the transmitting end adopts convolutional coding for channel coding, then the receiving end uses the Viterbi decoding algorithm for decoding, and by calculating the metrics of different paths, the most likely correct path is selected to restore the original digital signal sequence before encoding, thereby reducing the bit error rate and improving the accuracy of signal recovery; Determine the format of the original digital information, including H.264 for video and JPEG for pictures, and then use the corresponding source decoding algorithm to decode the digital signal after channel decoding to restore the original video frame data or picture pixel data; For H.264 video decoding, according to the syntax specification of H.264, the header information in the bitstream is parsed, and the compressed and encoded video data is gradually restored to the original pixel data frame by frame through entropy decoding, inverse quantization, inverse transformation and motion compensation, and the video image sequence is reconstructed; the header information includes the sequence header and the image header; For JPEG image decoding, Huffman decoding, inverse quantization, and inverse discrete cosine transform are performed to restore the pixel matrix of the image and finally restore the original image information. And integrate them in the correct order, including: for video, ensure that each frame of the image is accurately arranged in chronological order, and check whether there is frame loss or frame error, and verify it by checking the frame sequence number and timestamp information; for pictures, check the integrity of pixel data to verify whether all pixels are accurately restored; if data is missing or wrong, use the error correction mechanism to repair it by using redundant data and checksum, or in a wireless communication system that supports feedback retransmission, request to retransmit part of the data to ensure that the original digital information is finally restored complete and accurate; through the above steps, the demodulated I / Q signal can be gradually converted back to the original digital information containing video and pictures, so as to realize the effective transmission and accurate recovery of digital information in the wireless communication system based on electromagnetic metasurface.

[0025] It should be further explained that in the specific implementation process, a far-field phase modulation communication method was proposed using space-time coding metasurface, which further expanded the mode and capability of signal transmission. The transmission of digital signals in the main beam was achieved by modulating the radiation phase of the main beam, which increased the dimension and controllability of signal transmission. At the receiving end, the receiving antenna can be reasonably selected according to the operating frequency range, transmission distance, signal polarization mode and other factors of the wireless communication system of the electromagnetic metasurface, and a receiving system including antenna matching network, low-noise amplifier and filter components can be constructed, which effectively improves the quality and stability of signal reception; According to different modulation schemes, corresponding demodulation methods are used to accurately extract the in-phase branch I and orthogonal branch Q signals. Through a series of signal processing steps, the accuracy and reliability of demodulation are ensured; It can accurately convert the demodulated I / Q signal back to the original digital information. Through frame synchronization processing, signal amplitude and phase calibration, channel decoding, and decoding of sources of different formats, it ensures the integrity and accuracy of digital information recovery, effectively reduces the bit error rate, and improves the reliability of signal transmission. During the design process of the electromagnetic metasurface, this method takes into account different unit structures, layout methods and control circuit designs, so that it can adapt to different electromagnetic wave frequency ranges, amplitude and phase control requirements, and can be applied to a variety of wireless communication scenarios, including short-distance or long-distance communications indoors and outdoors, communications in high-speed mobile scenarios, as well as smart homes and video transmission.

[0026] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without creative work should fall within the scope of protection of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention are implemented according to the conventional means in the field unless otherwise specified and limited.

Claims

1. A signal modulation and demodulation method based on electromagnetic metasurface, characterized in that: The following steps are involved: S1. Electromagnetic metasurface design: Design a programmable electromagnetic metasurface, which consists of multiple unit structures, each of which is independently controlled to control the amplitude, phase, frequency and polarization of electromagnetic waves; S2. Digital signal encoding: Encode the digital information to be transmitted into a digital signal, and further process it to form an in-phase branch I and a quadrature branch Q signal; S3. Modulation strategy: adopt the modulation scheme of binary frequency shift keying BFSK or quadrature phase shift keying QPSK, and obtain the modulated electromagnetic wave signal by changing the time coding sequence of the electromagnetic metasurface unit; S4. Space-time coding: A far-field phase modulation communication method is proposed using space-time coding metasurfaces. By modulating the radiation phase of the main beam, the digital signal is transmitted within the main beam. S5. Signal reception and processing: At the receiving end, the electromagnetic wave signal modulated by the electromagnetic metasurface is received; then the received signal is demodulated and the in-phase branch I and the orthogonal branch Q signals are extracted; S6. Signal recovery: Convert the demodulated I / Q signal back to the original digital information, which includes video and pictures.

2. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 1, characterized in that: The process of designing a programmable electromagnetic metasurface is as follows: According to the needs of the electromagnetic wave control function, a unit structure is selected; including: performing electromagnetic simulation analysis on the selected unit structure, analyzing its amplitude, phase, frequency response and polarization conversion characteristics at different electromagnetic wave frequencies by changing the length, width and spacing parameters of the unit structure, establishing a database between the parameters of the unit structure and the electromagnetic response characteristics, and obtaining the unit structure type and unit structure characteristics; according to the expected application scenarios and performance requirements, combined with the electromagnetic wave propagation characteristics and the uniformity of the field distribution, using uniform arrays and non-uniform arrays, planning the arrangement of the unit structure on the electromagnetic metasurface, and determining the overall size and shape of the electromagnetic metasurface; at the same time, determining the spacing between the unit structures within an acceptable range that satisfies the electromagnetic coupling effect; obtaining a unit structure layout plan based on the spacing between the unit structures and the overall size and shape of the electromagnetic metasurface; based on the unit structure layout plan, designing a programmable control circuit for the unit structure to obtain an independent control circuit; integrating and packaging the designed unit structure with the corresponding independent control circuit; then performing a performance test to obtain the test results, and optimizing and adjusting the unit structure parameters, control circuit parameters or layout methods according to the test results to obtain the adjusted electromagnetic metasurface.

3. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 2, characterized in that: The process of encoding the digital information to be transmitted into a digital signal and further processing it to form the in-phase branch I and the orthogonal branch Q signal is as follows: Determine the original information to be transmitted and perform preprocessing to obtain digital information; use Huffman coding to compress and encode the digital information to obtain a coding sequence; then perform channel coding on the coding sequence to obtain a digital signal by adding redundant information to the coding sequence; map the digital signal into an in-phase branch I and an orthogonal branch Q signal according to the requirements of the modulation scheme; Modulation schemes include binary frequency shift keying BFSK modulation and quadrature phase shift keying QPSK modulation; For binary frequency shift keying BFSK modulation, the digital signal is mapped to carrier signals of different frequencies according to the 0 and 1 states of the digital signal, where one frequency corresponds to the I signal and the other frequency corresponds to the Q signal; for orthogonal phase shift keying QPSK modulation, every two consecutive coded bits are combined into four possible states: 00, 01, 10, 11, each state corresponds to a phase value, and then the phase value is mapped to the amplitude of the I and Q signals.

4. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 3 is characterized in that: The process of modulation strategy in step S3 is as follows: According to the design requirements and application scenarios of the wireless communication system of the electromagnetic metasurface, a modulation scheme is determined; the encoded in-phase branch I and orthogonal branch Q signals are input into the determined modulation scheme to obtain a selected carrier signal; according to the selected carrier signal and modulation scheme, a time code sequence for controlling the electromagnetic metasurface unit is generated; the generated time code sequence is sent to the programmable control circuit of each unit structure of the electromagnetic metasurface; the control circuit adjusts the capacitance and inductance parameters of the unit structure according to the received time code sequence, changes the response characteristics of the unit structure to the electromagnetic wave, and forms a modulated electromagnetic wave signal.

5. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 4, characterized in that: The process of determining the modulation scheme is as follows: Use binary frequency shift keying BFSK or quadrature phase shift keying QPSK modulation scheme; if BFSK is selected, determine two carrier frequencies f1 and f2 for representing digital information 0 and 1; if QPSK is selected, determine the I and Q signal amplitude combinations and carrier frequencies f corresponding to the four phase states 0°, 90°, 180°, and 270° c ; For BFSK modulation, if the input digital signal is 0, a carrier signal with a frequency of f1 is selected; if it is 1, a carrier signal with a frequency of f2 is selected; when f1 is selected, a time code sequence T1 is generated, and when f2 is selected, a time code sequence T2 is generated; for QPSK modulation, the corresponding phase state is determined according to the input I and Q signal amplitude combination, and the corresponding carrier signal is selected; the corresponding time code sequences are generated according to the four different phase states: T 00 , T 01 , T 10 , T 11 ; In BFSK, when a time-coded sequence is sent, the electromagnetic metasurface unit transfers energy to the harmonic frequencies associated with it, forming a modulated electromagnetic wave signal; in QPSK, energy is transferred to harmonic frequencies corresponding to different phase states according to different time-coded sequences.

6. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 5, characterized in that: In step S4, the process of space-time coding is as follows: Design a space-time coding metasurface structure by determining the layout and electromagnetic characteristics of the space-time coding metasurface unit structure; analyze the response characteristics of the space-time coding metasurface to electromagnetic waves at different times and spatial positions, obtain the layout and electromagnetic characteristics of the space-time coding metasurface unit structure, establish a relationship model between the unit structure and the phase change of the main beam radiation under different coding states, and obtain the scattering parameter matrix of the space-time coding metasurface through electromagnetic simulation software or experimental measurement to form a space-time coding metasurface structure; Mapping the digital signal to be transmitted according to a preset space-time coding rule to obtain a mapping relationship between the digital signal and the code; generating a space-time coding sequence according to the mapping relationship between the digital signal and the code; and loading the generated space-time coding sequence into a programmable control circuit of the space-time coding metasurface; When the space-time coding metasurface loaded with the space-time coding sequence receives an input electromagnetic wave signal, the radiation phase of the main beam is modulated according to the preset space-time coding rule according to the changes in the electromagnetic characteristics of the space-time coding sequence control unit structure in time and space; The electromagnetic wave signal after the phase modulation of the main beam radiation propagates in the far field space; at the receiving end, an antenna array or a receiving device is set to receive the electromagnetic wave signal transmitted by the main beam; The receiving end decodes the main beam radiation phase information according to the inverse process of the space-time coding rule; The received sequence of main beam radiation phase changes is converted back into the original digital signal.

7. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 6, characterized in that: The process of demodulating the received signal is as follows: selecting a receiving antenna according to the operating frequency range, transmission distance and signal polarization mode of the wireless communication system of the electromagnetic metasurface; constructing a receiving system, including an antenna matching network, a low-noise amplifier LNA and a filter component; when the receiving antenna receives the electromagnetic wave signal modulated by the electromagnetic metasurface, the signal is first transmitted to the LNA through the antenna matching network for amplification, and then filtered through the filter to obtain a preliminarily processed signal.

8. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 7, characterized in that: The process of demodulating the received signal and extracting the in-phase branch I and the orthogonal branch Q signals is as follows: First, the automatic gain control AGC circuit is used to adjust the amplitude of the signal after preliminary processing at the receiving end to complete the preprocessing of the received signal; then the demodulator is selected and initialized according to the preset modulation scheme, including: if the BFSK demodulator is selected, then two matched filters are set, corresponding to the frequencies of 0 and 1 respectively; if the QPSK demodulator is selected, then a demodulation structure for processing orthogonal signals is configured, including a local carrier recovery circuit and an integral decision circuit; For BFSK demodulation: the pre-processed received signal is passed through two matched filters respectively, and the envelope detection is performed on the two signals after matched filtering to obtain the envelopes of the two signals; then, the sizes of the two envelopes are compared, and the received digital signal is determined to be 0 or 1 according to the preset decision threshold to obtain a digital signal sequence; after BFSK demodulation, according to the digital signal sequence obtained by the decision, according to the mapping rule between the digital signal and the I / Q signal during modulation, the digital signal sequence is converted into the corresponding in-phase branch I and orthogonal branch Q signals; For QPSK demodulation: a Costas loop is used to utilize the orthogonal characteristics of the received signal. Through a phase detector, a loop filter and a voltage-controlled oscillator VCO, the local carrier signal output by the VCO is synchronized with the carrier signal in the received signal in frequency and phase, and the local carrier signal with the same frequency and phase as the transmitting end is restored; the preprocessed received signal is multiplied by the restored local carrier signal to achieve orthogonal demodulation; the baseband signals of the in-phase branch I and the orthogonal branch Q signals are obtained; according to the constellation diagram and decision area of ​​the QPSK signal, the symbol point corresponding to each sampling moment is determined by comparing the sampling value with the preset decision threshold, and the digital signal sequence is restored.

9. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 8, characterized in that: During the preprocessing of the received signal, if the signal has a frequency offset during transmission, the frequency locked loop FLL technology is used to correct the frequency offset of the signal; wherein, the FLL compares the frequency of the received signal with the local reference frequency, generates a control signal to adjust the frequency of the local oscillator, and matches the frequency of the received signal with the operating frequency of the demodulator.

10. The signal modulation and demodulation method based on electromagnetic metasurface according to claim 9, characterized in that: The process of converting the demodulated I / Q signal back to the original digital information, including video and pictures, is as follows: First, the starting position of each frame of data is determined by detecting the synchronization header or synchronization sequence in the demodulated I / Q signal; then, the time synchronization calibration of each frame of data is performed on the time axis according to the system clock and frame synchronization information; If the QPSK modulation scheme is used in the modulation process, an inverse transformation is performed based on the mapping rule between the digital signal and the I / Q signal during QPSK modulation; The I / Q signal is restored symbol by symbol to a digital signal sequence; if it is a BFSK modulation scheme, based on the mapping rule between the digital signal and the I / Q signal during BFSK modulation, the extracted I / Q signal is judged to correspond to the state representing the digital 0 or 1, and the digital signal sequence is restored; the restored digital signal sequence is channel-decoded to determine the format of the original digital information, including H.264 for video and JPEG for pictures, and then the corresponding source decoding algorithm is used to decode the digital signal after channel decoding to restore the original video frame data or picture pixel data.

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