Transmitter system based on time domain coding transmission-type metasurface and information modulation method

Abstract

The invention discloses a transmitter system based on a time domain coding transmission-type metasurface and an information modulation method, and belongs to the technical field of wireless communication. The system comprises a time domain coding metasurface and a control system of the time domain coding metasurface, and the amplitude and phase of electromagnetic waves can be accurately regulated and controlled through time domain coding. The method specifically comprises the following steps of: applying control signals with different time delays to each column of units of the metasurface, and realizing 2bit phase coding of first-order harmonics through Fourier transform; and in combination with QPSK modulation, mapping the information bit stream into a transmission coefficient time domain waveform, and generating a phase gradient by using time delay to complete baseband signal modulation. The method does not need to depend on a traditional radio frequency link and a frequency mixer, has the advantages of low power consumption and low cost, remarkably reduces hardware complexity, and is suitable for efficient wireless communication of the 5GHz frequency band.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and particularly to a transmitter system and an information modulation method based on a time-domain encoded transmissive metasurface, which are applicable to low-power signal modulation in high-frequency wireless communication. Background Art

[0002] In the information age, wireless communication technologies play a crucial role. With the development of wireless communication technologies, the requirements for their stability, high speed, and low latency are increasing day by day, which also significantly raises the cost and complexity of hardware implementation. For example, radio frequency (RF) modules and antennas, as the core components of most wireless communication systems, are responsible for converting digital signals into microwave signals to achieve long-distance information transmission. However, in 5G communication systems, due to the need to achieve a sampling rate and multiple RF links at the GHz level, hardware implementation faces huge challenges. Especially in the 5GHz frequency band, antenna coupling, power control, and electromagnetic compatibility limit the performance of the system. Therefore, the development of new wireless communication transmitter systems has always been a hot topic in the fields of communication and microwave research.

[0003] In this context, electromagnetic metasurfaces have attracted extensive attention. This technology has been extensively studied for controlling wavefront characteristics of electromagnetic waves such as amplitude, phase, polarization, frequency, etc., thus bringing a rich variety of applications. As an interdisciplinary research field, electromagnetic metasurfaces integrate multiple disciplines such as physics, chemistry, materials science, electronic engineering, and information technology, resulting in many amazing phenomena and devices, and achieving a series of important results internationally.

[0004] In summary, traditional RF transmitters rely on complex hardware (such as mixers and power amplifiers), resulting in high costs and large power consumption. Electromagnetic metasurface technology provides a new idea for simplifying the transmitter architecture by regulating the characteristics of electromagnetic waves. However, existing metasurface systems are mostly limited to static coding and are difficult to achieve dynamic modulation. The present invention solves the above problems by time-domain coding and achieving equivalent 2-bit precise phase modulation on a 1Bit metasurface. Summary of the Invention

[0005] The purpose of the present invention is to provide a transmitter system and an information modulation method based on a time-domain encoded transmissive metasurface, which directly complete baseband information modulation through time-domain encoded metasurfaces. This system has the advantages of not relying on complex devices such as RF links and mixers and having low power consumption.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A transmitter system based on a time-domain encoded transmissive metasurface, comprising:

[0008] The transmitting end is used to generate and encode an information bit stream;

[0009] The metasurface modulation end includes a time-domain encoder and a transmissive metasurface array. The metasurface array is composed of multiple units, and each unit controls the transmission phase through the switching state of a PIN diode;

[0010] The receiving end is used to receive and demodulate the transmitted harmonic signal;

[0011] The time-domain encoder encodes four phase states on the positive first-order harmonic by applying control signals with different time delays to each column of the metasurface, and combines QPSK modulation to complete the baseband signal modulation.

[0012] Preferably, the transmissive metasurface unit is composed of a transmission layer, a feeding layer, a receiving layer, and a dielectric layer. The transmission layer is loaded with at least two PIN diodes, and a 180° phase difference is achieved through the state switching between ON-OFF and OFF-ON.

[0013] Preferably, the time-domain coding algorithm adopted by the time-domain encoder includes:

[0014] Set the time delays of the square-wave control signals with a duty cycle of 0.5 to 0, 0.25T, 0.5T, and 0.75T (T is the message symbol duration). Generate 0°, 90°, 180°, and 270° phase compensations on the +1st-order harmonic through Fourier transform to form the phase gradient required for beamforming.

[0015] Preferably, the QPSK mapping method includes:

[0016] Map every two-bit information bit stream to constellation points 00, 01, 10, and 11, and respectively correspond to four-way time-delay control signals (time delays are 0, 0.25T, 0.5T, and 0.75T);

[0017] Load the time-delay control signals to each column of the transmissive metasurface array through the time-domain encoder, so that each column of units generates corresponding 0°, 90°, 180°, or 270° phase compensations on the +1st-order harmonic;

[0018] Based on the superposition effect of the phase compensations, realize the QPSK modulation and beamforming of the baseband signal.

[0019] Preferably, the metasurface array is an 8×8 unit, the operating frequency band is 4.75 GHz - 5.65 GHz, the unit size is 27 mm × 27 mm × 5.632 mm, and the dielectric layer includes two layers of RO4350B and RO4450F.

[0020] The present invention also provides an information modulation method based on time-domain coding transmissive metasurface, including the following steps:

[0021] Modulate the information bit stream into four delay control signals by QPSK;

[0022] Load the corresponding delay signals to each column of the metasurface through a time-domain encoder to generate a transmitted wave with a phase gradient;

[0023] Utilize the phase distribution of the positive first-order harmonic to achieve baseband information modulation and signal transmission.

[0024] Preferably, the duty cycle of the delay control signal is 0.5, and the delay interval is 0.25T, where T is the message symbol duration.

[0025] Beneficial effects: The present invention proposes a transmitter system based on a time-domain encoded transmissive metasurface. By controlling the phase response of the information metasurface, when the carrier signal transmits through the metasurface, it can achieve QPSK modulation of the baseband signal in the time domain. By carefully designing the parameters of the control signal, a specific transmission coefficient is generated to achieve independent phase-amplitude modulation. This time-domain encoded transmissive metasurface directly realizes the functions of baseband signal modulation and signal transmission by regulating the transmission coefficient, and has the advantage of not relying on complex devices such as radio frequency links and mixers compared with traditional communication systems. In summary, the time-domain encoded transmissive metasurface technology is expected to provide new ideas and directions for the innovative development of future wireless communication systems. Description of the Drawings

[0026] Figure 1 : Working mechanism diagram and unit structure diagram of a 1-bit transmissive unit, where (a) is the unit working mechanism diagram, (b) is the front view, (c) is the top view, and (d) is the side view.

[0027] Figure 2 : Simulation results of electromagnetic parameters of a 1-bit transmissive metasurface unit, where (a) is the transmission amplitude response; (b) is the transmission phase response.

[0028] Figure 3 : Low-loss 1-bit transmissive intelligent metasurface sample.

[0029] Figure 4 : Measured results of electromagnetic parameters of a 1-bit transmissive metasurface unit, where (a) is the transmission amplitude response; (b) is the transmission phase response.

[0030] Figure 5 : QPSK message mapping method, where (a) shows the relationship between the time delay of the harmonic and the output waveform with the harmonic amplitude remaining unchanged, and (b) shows the relationship between the phase of the harmonic and the time delay t0 with a duty cycle of 0.5. Detailed Embodiments

[0031] The present invention will be further described below in conjunction with embodiments and drawings.

[0032] Example 1

[0033] In this example, a 1-bit transmissive metasurface with a 180° phase modulation function in the frequency band of 4.75 GHz to 5.65 GHz is designed. The three views of its unit structure are shown in Figure 1 (b)-(d) in the figure. The unit adopts a multi-layer stacked structure, which is composed of alternating metal layers and dielectric layers. The metal layers are, in the negative Z-axis direction, the receiving layer, the first ground layer, the feeding layer, the second ground layer, and the emitting layer in sequence, and the thickness of each metal layer is 0.036 mm. Vertically, the receiving layer and the emitting layer are connected through a cylindrical feeding post with a diameter of 0.98 mm, and at the same time, the receiving layer and the feeding layer are connected through a cylindrical feeding post with a diameter of 0.4 mm. The feeding layer adopts a fan-shaped capacitive feeding patch design, and through reasonable arrangement of the feeding lines and via structures, effective isolation of AC and DC signals is achieved. The geometric parameters of the unit have been optimized by CST Microwave Studio, and the specific dimensions are:

[0034] l1 = 27.00 mm, l2 = 15.17 mm, l3 = 13.04 mm, l4 = 1.77 mm, l5 = 8.90 mm, p1 = 27.00 mm, p2 = 4.55 mm, p3 = 1.28 mm, p4 = 7.1 mm, h = 5.56 mm. The above structural parameters are the optimal dimensions determined through multi-parameter optimization, ensuring the best electromagnetic performance of the unit within the target frequency band.

[0035] In terms of the selection of dielectric layer materials, F4B materials are used between the receiving layer and the first ground layer, and between the second ground layer and the transmission layer. Its dielectric constant is 2.65, the loss tangent is 0.0015, and the thickness is 2.50 mm. Rogers RO4450F material is used between the first ground layer and the feeding layer. Its dielectric constant is 3.7, the loss tangent is 0.004, and the thickness is 0.16 mm. Between the feeding layer and the second ground layer, it is composed of a composite of Rogers RO4450F material (dielectric constant 3.7, loss tangent 0.004, thickness 0.16 mm) and Rogers RO4350B material (dielectric constant 3.66, loss tangent 0.0037, thickness 0.168 mm).

[0036] In the rectangular metal slit of the receiving layer, two PIN diodes (MADP-000907-14020) are integrated, with their anodes connected to the inner patch and cathodes connected to the outer patch. By regulating the switching states of the PIN diodes, dynamic adjustment of the transmission phase of electromagnetic waves can be achieved. Specifically, when the pins of the two PIN diodes are in the OFF-ON state (encoding "0") and ON-OFF state (encoding "1") respectively, the transmitted electromagnetic waves will generate a phase difference of 180°, thus realizing the switching function of digital encoding states.

[0037] Based on the above structural design, in this embodiment, the full-wave simulation of the unit is carried out using the CST Microwave Studio simulation software. Figure 5 The amplitude and phase response results of the unit are shown. The simulation results show that in the frequency range of 4.75 GHz to 5.65 GHz, the transmission amplitude of the unit is better than -3 dB, and the phase difference is stable at about 180°, with the fluctuation range controlled within ±5%, fully verifying that the designed unit has 1-bit phase characteristics. In addition, in the frequency range of 4.82 GHz to 5.31 GHz, the transmission coefficient of the unit is always higher than -1 dB, and the lowest loss of -0.54 dB is achieved at the 5 GHz frequency point. The simulation results confirm that the unit realizes efficient regulation of the transmission phase in a relatively wide frequency band, and at the same time achieves the design goal of low loss of the transmission coefficient, fully meeting the research requirements of this article.

[0038] Based on the simulation optimization results, in this embodiment, a low-loss 1-bit transmissive time-domain coded metasurface sample composed of 8×8 units is fabricated, as Figure 3 shown. The sample adopts column control design, and each column of units shares the control voltage through the bias line, enabling 8-column independent control. To verify the actual performance of this low-loss 1-bit transmissive intelligent metasurface, we tested the electromagnetic parameters of the sample in an actual communication environment, and the test results are as Figure 4 shown.

[0039] The test results show that the sample exhibits good phase regulation performance in the operating frequency band of 4.75 GHz to 5.65 GHz: the transmission amplitude is better than -3 dB, and the phase difference between the two states is close to 180°, maintaining stable transmission amplitude and phase characteristics in a relatively wide frequency band. By comparing the full-wave simulation and the measured results, it can be found that the measured transmission amplitude loss is slightly higher than the simulation value, which may be the combined result of factors such as the array surface error during the processing, the unit consistency deviation caused by process limitations, the edge effect of the metasurface, and the coupling effect with the surrounding environment. It should be emphasized that this small difference will not have a great impact on the construction and experiment of the wireless communication system based on this metasurface.

[0040] Embodiment 2

[0041] The wireless communication system designed in this embodiment consists of two core parts: a transmitter and a receiver. At the transmitter, the system is composed of a control host, a signal source, a feed antenna, and the transmissive metasurface designed above. Among them, the control host undertakes functions such as information modulation and signal generation, encodes the information to be transmitted into a binary bit stream, and generates corresponding control signals to be output to the metasurface; the signal source is responsible for generating a carrier signal of 5 GHz, and the feed antenna realizes the radiation transmission of the carrier signal. When the encoded control signal is loaded onto the metasurface, the carrier signal radiated by the feed antenna is vertically incident from one side, and after passing through the metasurface for phase modulation, it vertically exits from the other side. The receiver consists of a receiving antenna and a software radio platform (USRP-2974). Among them, the receiving antenna is responsible for capturing the modulated radio frequency signal and transmitting it to the USRP-2974 for subsequent processing; the USRP-2974 extracts the signal spectrum characteristics by performing down-conversion and Fourier transform processing on the received signal, and demodulates and restores the original information. This architecture design realizes a complete communication link from signal transmission, modulation to reception and demodulation, providing a reliable experimental platform for subsequent system performance testing.

[0042] The information modulation process adopted in this embodiment is as follows: first, every two bits of the information bit stream to be transmitted are mapped to the time-domain waveform of the transmission coefficient within a time slot T, and then each mapped time slot is spliced into the entire time-domain waveform of the transmission coefficient. The entire time-domain waveform of the transmission coefficient is respectively delayed by T / 4 as a whole to form four control signals. According to time-domain coding, each column of the metasurface is connected to the corresponding control signal, that is, the spatio-temporal joint information modulation of the metasurface is completed.

Claims

1. A transmitter system based on a time-domain encoded transmissive metasurface, characterized in that Including: A transmitting end, which is used to generate and encode an information bit stream; A metasurface modulation end, including a time-domain encoder and a transmissive metasurface array, the transmissive metasurface array is composed of a plurality of transmissive metasurface units, and each transmissive unit regulates the transmission phase through different switching states of PIN diodes; A time-domain encoder, which is used to apply control signals with different time delays to each column of the transmissive metasurface array to achieve at least two-bit phase modulation on the +1st harmonic, and complete baseband signal modulation and beamforming in combination with QPSK mapping; A receiving end, which is used to receive and demodulate the transmitted harmonic signal.

2. The transmitter system according to claim 1, wherein The transmissive metasurface unit includes: A receiving layer, a feeding layer, a transmitting layer and a dielectric layer. Among them, the receiving layer is loaded with at least two PIN diodes, and realizes a 180° phase difference in adjacent states through ON-OFF and OFF-ON state switching.

3. The transmitter system according to claim 1, characterized in that, The time-domain coding algorithm adopted by the time-domain encoder includes: Set the time delays of square wave control signals with a duty cycle of 0.5 to 0, 0.25T, 0.5T, 0.75T, where T is the message symbol duration, and generate 0°, 90°, 180°, 270° phase compensations on the +1st harmonic through Fourier transform to form the phase gradient required for beamforming.

4. The transmitter system according to claim 3, characterized in that, The QPSK mapping method includes: Map every two-bit information bit stream to constellation points 00, 01, 10, 11, and respectively correspond to four-way time delay control signals with time delays of 0, 0.25T, 0.5T, 0.75T; Load the time delay control signals to each column of the transmissive metasurface array through the time-domain encoder, so that each column of units generates corresponding 0°, 90°, 180° or 270° phase compensations on the +1st harmonic; Based on the superposition effect of phase compensation, realize QPSK modulation and beamforming of the baseband signal.

5. The transmitter system according to claim 1, wherein, The transmissive metasurface array has the following parameters: The array scale is 8×8 units, and the operating frequency band is 4.75GHz - 5.65GHz; The unit size is 27mm×27mm×5.56mm; The dielectric layer includes two layers of RO4350B and RO4450F.

6. An information modulation method based on a time-domain encoded transmissive metasurface, characterized in that, Including the following steps: Map the information bit stream to four-way time delay control signals according to QPSK; Load the corresponding time delay signals to each column of the metasurface through the time-domain encoder to generate a transmitted wave with a phase gradient; Utilize the phase distribution of the +1st harmonic to realize baseband information modulation and signal transmission.

7. The information modulation method according to claim 6, characterized in that, The parameters of the time delay control signal include: The duty cycle is 0.5, and the time delay interval is 0.25T, where T is the message symbol duration.

8. The information modulation method according to claim 6, characterized in that, The phase compensation calculation formula of the transmitted wave is as follows: where d x and d y are the periods of the metasurface unit in the x - direction and y - direction respectively, θ, are the azimuth angle and elevation angle of the beam respectively, m and n are the rows and columns of the metasurface unit respectively, and k is the harmonic order.

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