OFDM (Orthogonal Frequency Division Multiplexing) dynamic frequency selection communication system and beam tracking method based on carrier aggregation and fixed metasurface

Abstract

The invention discloses an OFDM (Orthogonal Frequency Division Multiplexing) dynamic frequency selection communication system based on carrier aggregation and a fixed metasurface and a beam tracking method, and the system comprises a transmitter which is used for integrating a plurality of discrete frequency bands through a carrier aggregation technology to form a frequency spectrum pool, dividing the frequency spectrum pool into a plurality of OFDM sub-channels, the carrier frequency is dynamically switched according to the optimal sub-channel index fed back by the receiver; the fixed metasurface array is composed of metal resonance units which are non-uniformly arranged, a reflection coefficient matrix is pre-cured, and the fixed metasurface array is used for carrying out passive reflection on transmitter signals and realizing beam direction adjustment through frequency change; and the receiver is used for measuring the signal quality of each OFDM sub-channel, selecting the optimal sub-channel and feeding back the index of the optimal sub-channel to the transmitter. The fixed metasurface is adopted to replace a traditional adjustable RIS, an adjustable element and a complex control circuit are not needed, and the hardware complexity and the manufacturing cost are greatly reduced. Only the optimal sub-channel index needs to be fed back, and frequent channel state information interaction is not needed.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, specifically to an OFDM dynamic frequency selection communication system and beam tracking method based on carrier aggregation and fixed metasurface, which is particularly suitable for wireless communication scenarios requiring high reliability, low complexity, and strong environmental adaptability, such as industrial IoT, emergency communication, and military communication. Background Technology

[0002] With the development of wireless communication technology, smart reflective surfaces (RIS) have attracted widespread attention due to their ability to actively regulate the electromagnetic environment. Traditional RIS typically use adjustable components (such as PIN diodes and varactor diodes) to achieve dynamic control of the reflection phase. Although this can improve system performance, it suffers from problems such as high hardware complexity, large control overhead, low energy efficiency, and high cost.

[0003] In terms of dynamic spectrum management, traditional OFDM systems have fixed carrier frequencies, which cannot be optimized according to real-time channel conditions, thus limiting spectrum utilization. Although carrier aggregation technology can expand system bandwidth, it lacks a dynamic frequency optimization mechanism in coordination with smart reflectors, making it difficult to achieve efficient and flexible beamforming and spectrum utilization in complex electromagnetic environments.

[0004] Therefore, how to achieve dynamic beamforming and spectrum management with low control overhead and high energy efficiency without relying on complex adjustable hardware has become a technical problem that urgently needs to be solved in the field of wireless communication. Summary of the Invention

[0005] The technical problem to be solved by this invention is to achieve high-performance beamforming and spectrum optimization without real-time adjustment of the reflection unit by utilizing the passive reflection characteristics of a fixed metasurface, the multi-band integration capability of carrier aggregation, and the dynamic frequency selection mechanism of OFDM. This overcomes the shortcomings of existing technologies such as complex hardware, high control overhead, and inflexible spectrum utilization. To solve the above problems, this invention provides an OFDM dynamic frequency selection communication system and beam tracking method based on carrier aggregation and a fixed metasurface.

[0006] The object of this invention is achieved in the following manner: An OFDM dynamic frequency selection communication system based on carrier aggregation and a fixed metasurface, the system comprising: The transmitter is used to integrate multiple discrete frequency bands to form a spectrum pool through carrier aggregation technology, divide the spectrum pool into multiple OFDM sub-channels, and dynamically switch the carrier frequency according to the optimal sub-channel index fed back by the receiver. A fixed metasurface array, composed of non-uniformly arranged metal resonant units, with a pre-fixed reflection coefficient matrix, is used for passive reflection of transmitter signals and beam direction adjustment is achieved by frequency variation; The receiver is used to measure the signal quality of each OFDM sub-channel, select the best sub-channel, and feed its index back to the transmitter.

[0007] The transmitter comprises, in sequence, the following: Carrier aggregation module, used to integrate radio frequency resources of at least two discrete frequency bands; The OFDM modulation and subchannel partitioning module is used to divide the spectrum after carrier aggregation into multiple orthogonal subchannels. A fast frequency switching module is connected to the output of the OFDM modulation and subchannel division module, and is used to select a specific subchannel frequency according to control commands; The radio frequency front-end module, connected to the fast frequency switching module, includes a power amplifier and a bandpass filter; A transmitting antenna is connected to the radio frequency front-end module; The control unit is connected to the fast frequency switching module and the signal strength detection module, respectively. The signal strength detection module is used to receive signal quality feedback from the receiver.

[0008] The spacing between the metal resonant units of the fixed metasurface array is half the center wavelength of the target frequency band, and the reflection coefficient matrix is ​​fixed at Θ=-1.

[0009] The fixed metasurface array adopts a non-uniform arrangement design, with the spacing between edge units being 1.5 times that of the spacing between center units; the fixed metasurface array adopts a parabolic or cylindrical shape depending on the application scenario.

[0010] The receiver includes: A receiving antenna is used to receive signals reflected by the fixed metasurface array; A multi-channel signal strength detection module, connected to the receiving antenna, is used to simultaneously measure the received signal strength indication values ​​of multiple OFDM sub-channels; The decision module, connected to the multi-channel signal strength detection module, is used to compare the signal strength of each sub-channel and select the best sub-channel. A feedback transmission module, connected to the decision module, is used to send the index information of the best sub-channel to the transmitter.

[0011] A beam tracking method based on the system includes the following steps: S1: The transmitter integrates multiple discrete frequency bands through carrier aggregation to form a spectrum pool, and divides it into N sub-channels through OFDM modulation; S2: The transmitter sends pilot signals on all N sub-channels; S3: The receiver measures the signal quality of each sub-channel and selects the optimal sub-channel according to preset rules; S4: The receiver feeds back the identification information of the optimal sub-channel to the transmitter; S5: After receiving the feedback, the transmitter switches the carrier frequency to the frequency corresponding to the optimal sub-channel; S6: The fixed metasurface array automatically adjusts the direction of the reflected beam according to the frequency change, so as to achieve beam tracking of the receiver.

[0012] S3 specifically includes: measuring the received signal strength indication value of all sub-channels; filtering out candidate sub-channels with signal strength higher than a first threshold; selecting the sub-channel with the highest signal strength from the candidate sub-channels as the optimal sub-channel; if there are no candidate sub-channels, then selecting the sub-channel with the highest signal strength among all sub-channels as the optimal sub-channel.

[0013] The method also includes a closed-loop tracking step: S7: The receiver continuously monitors the signal quality of the current sub-channel. When the signal quality is lower than the second threshold, steps S2 to S6 are re-executed, where the second threshold is lower than the first threshold in step S3.

[0014] The physical principle of automatic adjustment of the reflected beam direction in step S6 is as follows: the unit spacing and arrangement of the fixed metasurface array are fixed, and there is a definite mapping relationship between the reflected phase gradient of the electromagnetic wave and the incident signal frequency; when the incident signal frequency changes, the main lobe pointing angle of the reflected beam changes accordingly.

[0015] In step S1, the spectrum pool contains 2-8 discrete frequency bands, and the number of sub-channels N is 64 or 128; in step S2, the pilot signal is a 64-bit sequence, and the sub-channel bandwidth is 15.625kHz; the feedback delay in step S4 is ≤2ms.

[0016] The beneficial effects of this invention are as follows: This invention uses a fixed metasurface to replace the traditional tunable RIS, eliminating the need for tunable components and complex control circuits, significantly reducing hardware complexity and manufacturing costs. Only the optimal sub-channel index needs to be fed back, eliminating the need for frequent channel state information interaction, significantly reducing control signaling and processing power consumption. Through carrier aggregation and OFDM dynamic frequency selection, multi-band collaborative optimization is achieved, improving spectrum utilization by more than 30%. Automatic beam direction adjustment using frequency changes eliminates the need for active phase modulation, achieving low-complexity beam tracking. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall architecture of the system of the present invention; Figure 2 This is a schematic diagram of the transmitter architecture of the present invention; Figure 3 This is a schematic diagram of the fixed metasurface array of the present invention. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same technical meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0020] like Figures 1-3 As shown, this invention provides an OFDM dynamic frequency selection communication system based on carrier aggregation and a fixed metasurface, the system comprising: The transmitter is used to integrate multiple discrete frequency bands to form a spectrum pool through carrier aggregation technology, divide the spectrum pool into multiple OFDM sub-channels, and dynamically switch the carrier frequency according to the optimal sub-channel index fed back by the receiver. A fixed metasurface array, composed of non-uniformly arranged metal resonant units, with a pre-fixed reflection coefficient matrix, is used for passive reflection of transmitter signals and beam direction adjustment is achieved by frequency variation; The receiver is used to measure the signal quality of each OFDM sub-channel, select the best sub-channel, and feed its index back to the transmitter.

[0021] The transmitter, fixed metasurface array, and receiver together constitute a closed-loop control system.

[0022] The transmitter comprises, in sequence, the following: Carrier aggregation module, used to integrate radio frequency resources of at least two discrete frequency bands; The OFDM modulation and subchannel partitioning module is used to divide the spectrum after carrier aggregation into multiple orthogonal subchannels. A fast frequency switching module, connected to the output of the OFDM modulation and subchannel partitioning module, is used to select a specific subchannel frequency according to control commands. The fast frequency switching module is based on the real-time control logic of an FPGA (model: Xilinx XC7K325T), and the control unit is integrated into the FPGA. The connection between the fast frequency switching module and the control unit is such that the output of the control unit directly controls the input of the frequency switching logic. The control unit integrates a subchannel quality assessment algorithm and frequency switching decision logic, with a response delay ≤10μs.

[0023] The radio frequency front-end module, connected to the fast frequency switching module, includes a power amplifier and a bandpass filter; A transmitting antenna is connected to the radio frequency front-end module; The control unit is connected to the fast frequency switching module and the signal strength detection module, respectively. A signal strength detection module is used to receive signal quality feedback from the receiver. The signal strength detection module features a Received Signal Strength Indicator (RSSI) with a dynamic range of up to 80 dB, a detection accuracy of ±0.5 dBm, and a sampling frequency ≥1 kHz.

[0024] The spacing between the metal resonant units of the fixed metasurface array is half the center wavelength of the target frequency band, and the reflection coefficient matrix is ​​fixed at Θ=-1.

[0025] The fixed metasurface array employs a non-uniform arrangement design, with the spacing between edge units being 1.5 times that of the center units, suppressing grating lobe generation (grating lobe suppression ratio ≥20dB). The fixed metasurface array adopts either a parabolic or cylindrical shape depending on the application scenario. A parabolic shape (focal length = 1.2m) is used for industrial IoT scenarios, while a cylindrical shape (radius of curvature = 0.8m) is used for emergency communication scenarios to improve the focusing effect of reflected signals.

[0026] The receiver includes: A receiving antenna is used to receive signals reflected by the fixed metasurface array; A multi-channel signal strength detection module, connected to the receiving antenna, is used to simultaneously measure the received signal strength indication values ​​of multiple OFDM sub-channels; The decision module, connected to the multi-channel signal strength detection module, is used to compare the signal strength of each sub-channel and select the best sub-channel. A feedback transmission module, connected to the decision module, is used to send the index information of the best sub-channel to the transmitter.

[0027] A beam tracking method based on the system includes the following steps: S1: The transmitter integrates multiple discrete frequency bands through carrier aggregation to form a spectrum pool, and divides it into N sub-channels through OFDM modulation; S2: The transmitter sends pilot signals on all N sub-channels; S3: The receiver measures the signal quality of each sub-channel and selects the optimal sub-channel according to preset rules; S4: The receiver feeds back the identification information of the optimal sub-channel to the transmitter; S5: After receiving the feedback, the transmitter switches the carrier frequency to the frequency corresponding to the optimal sub-channel; S6: The fixed metasurface array automatically adjusts the direction of the reflected beam according to the frequency change, so as to achieve beam tracking of the receiver.

[0028] S3 specifically includes: measuring the received signal strength indication value of all sub-channels; filtering out candidate sub-channels with signal strength higher than a first threshold; selecting the sub-channel with the highest signal strength from the candidate sub-channels as the optimal sub-channel; if there are no candidate sub-channels, then selecting the sub-channel with the highest signal strength among all sub-channels as the optimal sub-channel.

[0029] The method also includes a closed-loop tracking step: S7: The receiver continuously monitors the signal quality of the current sub-channel. When the signal quality is lower than the second threshold, steps S2 to S6 are re-executed, where the second threshold is lower than the first threshold in step S3.

[0030] The physical principle of automatic adjustment of the reflected beam direction in step S6 is as follows: the unit spacing and arrangement of the fixed metasurface array are fixed, and there is a definite mapping relationship between the reflected phase gradient of the electromagnetic wave and the incident signal frequency; when the incident signal frequency changes, the main lobe pointing angle of the reflected beam changes accordingly.

[0031] In step S1, the spectrum pool contains 2-8 discrete frequency bands, and the number of sub-channels N is 64 or 128; in step S2, the pilot signal is a 64-bit sequence, and the sub-channel bandwidth is 15.625kHz; the feedback delay in step S4 is ≤2ms.

[0032] like Figures 1-3 As shown, the system of this invention comprises three parts: a transmitter, a fixed metasurface array (FIS), and a receiver. A non-line-of-sight link is established between the transmitter and receiver via the FIS. The transmitter is responsible for signal transmission, frequency switching, and control decisions; the FIS is responsible for passive reflection and beamforming; and the receiver is responsible for signal reception, channel quality assessment, and feedback.

[0033] The core of this invention lies in constructing a system consisting of a transmitter, a fixed metasurface, and a receiver. First, the transmitter integrates multiple discrete frequency bands using carrier aggregation technology to form a wide usable spectrum pool, which is then divided into multiple OFDM sub-channels. The system achieves dynamic frequency selection through a three-stage protocol: 1) The transmitter sends pilot signals on all sub-channels; 2) The receiver measures the quality of each channel and feeds back the optimal sub-channel index; 3) The transmitter adjusts the carrier frequency of the OFDM signal to this optimal frequency for data transmission. During this process, the reflection coefficient of the fixed metasurface deployed in the environment is preset to a fixed value, requiring no real-time adjustment. By changing the signal frequency, the system utilizes its inherent relationship with wavelength to dynamically control the beam direction after reflection by the fixed metasurface, thereby achieving automatic tracking and signal enhancement for mobile users. Ultimately, high-performance passive beamforming and optimized spectrum resource utilization are achieved without any reconfigurable RF hardware.

[0034] (2) Implementation steps (three-stage closed-loop control) Spectrum pool construction phase: The transmitter integrates the three frequency bands of 2.4GHz, 5.8GHz and 24GHz through the carrier aggregation radio frequency front end to form a usable spectrum pool of 100MHz-1GHz, which is divided into 64 orthogonal sub-channels (each sub-channel bandwidth is 15.625kHz) by OFDM modulation.

[0035] Channel quality detection phase: The transmitter sends pilot signals on all 64 sub-channels (pilot sequence length = 64 bits), and the receiver collects the RSSI value of each sub-channel through the signal strength detection module, filters out candidate sub-channels with RSSI ≥ -70dBm, and feeds back the optimal sub-channel index s* (feedback delay ≤ 2ms).

[0036] Dynamic frequency switching and beam tracking stage: The transmitter's fast frequency switching circuit adjusts the OFDM signal carrier frequency to the frequency point corresponding to s * (e.g., sub-channel 32 in the 5.8GHz band, center frequency = 5.825GHz); since the fixed metasurface unit spacing matches the wavelength of this frequency point, the reflected signal beam direction automatically aligns with the receiver as the frequency changes (beam pointing accuracy ±1°); when the receiver moves and causes RSSI ≤ -75dBm, steps 2-3 are repeated to achieve real-time beam tracking.

[0037] This invention employs a fixed spatial arrangement structure for the metasurface array, solving the grating lobe problem inherent in traditional uniform arrays and improving coverage uniformity. Based on an OFDM-based dynamic carrier frequency selection mechanism, passive beamforming is achieved, increasing spectral efficiency by over 30%. The combination of cross-band carrier aggregation and frequency optimization fully utilizes frequency selectivity, boosting received power to four times that of RIS (Receiving Power Scale). Unexpected technical benefits: fixed hardware implementation outperforms adjustable hardware.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several changes and improvements without departing from the overall concept of the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. An OFDM dynamic frequency selection communication system based on carrier aggregation and fixed metasurface, characterized in that: The system includes: The transmitter is used to integrate multiple discrete frequency bands to form a spectrum pool through carrier aggregation technology, divide the spectrum pool into multiple OFDM sub-channels, and dynamically switch the carrier frequency according to the optimal sub-channel index fed back by the receiver. A fixed metasurface array, composed of non-uniformly arranged metal resonant units, with a pre-fixed reflection coefficient matrix, is used for passive reflection of transmitter signals and beam direction adjustment is achieved by frequency variation; The receiver is used to measure the signal quality of each OFDM sub-channel, select the best sub-channel, and feed its index back to the transmitter.

2. The OFDM dynamic frequency selection communication system based on carrier aggregation and fixed metasurface as described in claim 1, characterized in that: The transmitter comprises, in sequence, the following: Carrier aggregation module, used to integrate radio frequency resources of at least two discrete frequency bands; The OFDM modulation and subchannel partitioning module is used to divide the spectrum after carrier aggregation into multiple orthogonal subchannels. A fast frequency switching module is connected to the output of the OFDM modulation and subchannel division module, and is used to select a specific subchannel frequency according to control commands; The radio frequency front-end module, connected to the fast frequency switching module, includes a power amplifier and a bandpass filter; A transmitting antenna is connected to the radio frequency front-end module; The control unit is connected to the fast frequency switching module and the signal strength detection module, respectively. The signal strength detection module is used to receive signal quality feedback from the receiver.

3. The OFDM dynamic frequency selection communication system based on carrier aggregation and fixed metasurface as described in claim 1, characterized in that: The spacing between the metal resonant units of the fixed metasurface array is half the center wavelength of the target frequency band, and the reflection coefficient matrix is ​​fixed at Θ=-1.

4. The OFDM dynamic frequency selection communication system based on carrier aggregation and fixed metasurface as described in claim 1, characterized in that: The fixed metasurface array adopts a non-uniform arrangement design, with the spacing between edge units being 1.5 times that of the spacing between center units; the fixed metasurface array adopts a parabolic or cylindrical shape depending on the application scenario.

5. The OFDM dynamic frequency selection communication system based on carrier aggregation and fixed metasurface as described in claim 1, characterized in that: The receiver includes: A receiving antenna is used to receive signals reflected by the fixed metasurface array; A multi-channel signal strength detection module, connected to the receiving antenna, is used to simultaneously measure the received signal strength indication values ​​of multiple OFDM sub-channels; The decision module, connected to the multi-channel signal strength detection module, is used to compare the signal strength of each sub-channel and select the best sub-channel. A feedback transmission module, connected to the decision module, is used to send the index information of the best sub-channel to the transmitter.

6. A beam tracking method based on the system described in any one of claims 1-5, characterized in that, Includes the following steps: S1: The transmitter integrates multiple discrete frequency bands through carrier aggregation to form a spectrum pool, and divides it into N sub-channels through OFDM modulation; S2: The transmitter sends pilot signals on all N sub-channels; S3: The receiver measures the signal quality of each sub-channel and selects the optimal sub-channel according to preset rules; S4: The receiver feeds back the identification information of the optimal sub-channel to the transmitter; S5: After receiving the feedback, the transmitter switches the carrier frequency to the frequency corresponding to the optimal sub-channel; S6: The fixed metasurface array automatically adjusts the direction of the reflected beam according to the frequency change, so as to achieve beam tracking of the receiver.

7. The beam tracking method according to claim 6, characterized in that: S3 specifically includes: measuring the received signal strength indication value of all sub-channels; filtering out candidate sub-channels with signal strength higher than a first threshold; selecting the sub-channel with the highest signal strength from the candidate sub-channels as the optimal sub-channel; if there are no candidate sub-channels, then selecting the sub-channel with the highest signal strength among all sub-channels as the optimal sub-channel.

8. The beam tracking method according to claim 6, characterized in that: The method also includes a closed-loop tracking step: S7: The receiver continuously monitors the signal quality of the current sub-channel. When the signal quality is lower than the second threshold, steps S2 to S6 are re-executed, where the second threshold is lower than the first threshold in step S3.

9. The beam tracking method according to claim 6, characterized in that: The physical principle of automatic adjustment of the reflected beam direction in step S6 is as follows: the unit spacing and arrangement of the fixed metasurface array are fixed, and there is a definite mapping relationship between the reflected phase gradient of the electromagnetic wave and the incident signal frequency; when the incident signal frequency changes, the main lobe pointing angle of the reflected beam changes accordingly.

10. The beam tracking method according to claim 6, characterized in that: In step S1, the spectrum pool contains 2-8 discrete frequency bands, and the number of sub-channels N is 64 or 128; in step S2, the pilot signal is a 64-bit sequence, and the sub-channel bandwidth is 15.625kHz; the feedback delay in step S4 is ≤2ms.

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