A method and system for cascade modulation and demodulation transmission of unmanned aerial vehicles for low-altitude economy

Abstract

This invention relates to a cascaded modulation and demodulation transmission method and system for unmanned aerial vehicles (UAVs) geared towards low-altitude economics. The method includes cascaded modulation transmission at the transmitting end, comprising data classification and acquisition, telemetry and control data modulation, payload data modulation, cascaded fusion, and transmission; and cascaded demodulation reception at the receiving end, comprising signal reception and preprocessing, branching processing, telemetry and control data demodulation, payload data demodulation, and data output and processing. The system includes an airborne UAV transmission system, comprising a data acquisition module, a primary modulation module, a secondary modulation module, a cascaded fusion module, an RF transmission module, a channel quality detection module, and a modulation mode switching module; and a ground receiving and processing system, comprising an RF receiving module, a signal preprocessing module, a branching module, a primary demodulation module, a secondary demodulation module, a data verification module, a demodulation mode switching module, and a data output module. This invention achieves layered transmission of two types of data through cascaded modulation, balancing transmission reliability and speed.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) communication technology, specifically to a UAV cascaded modulation and demodulation transmission method and system for low-altitude economy. Background Technology

[0002] With the rapid development of the low-altitude economy, drones are increasingly being used in logistics delivery, agricultural plant protection, urban security, and power line inspection. In these low-altitude application scenarios, drones need to transmit two types of core data simultaneously: one type is the measurement and control data that ensures flight safety (including flight attitude, position information, control commands, equipment status, etc.). This type of data has the characteristics of high priority, small data volume, and extremely high requirements for transmission reliability. Once the transmission is interrupted or errors occur, it may cause the drone to lose control. The other type is the payload data for completing the task (including high-definition images, real-time video, and operational parameter acquisition data, etc.). This type of data has the characteristics of large data volume, high transmission rate requirements, and tolerance for a certain number of errors (which can be compensated for by subsequent error correction processing).

[0003] Existing drone data transmission technologies have the following main drawbacks: 1) Data transmission is not layered, and all data is transmitted using a single modulation method: If a low-rate, high-reliability modulation method (such as FSK) is used, although the security of measurement and control data transmission can be guaranteed, it cannot meet the high-speed transmission requirements of payload data; if a high-rate, high-spectral-efficiency modulation method (such as QPSK, 16QAM) is used, although the data transmission rate of payload data can be improved, the reliability of measurement and control data transmission is difficult to guarantee in complex low-altitude electromagnetic environments (such as multipath interference from urban buildings, co-channel interference from ground communication base stations, electromagnetic noise in plant protection scenarios, etc.), and packet loss and bit error problems are likely to occur; 2) Existing cascaded modulation technology is mostly used in military communications and satellite communications, and has not been adapted to the characteristics of UAVs in low-altitude economic scenarios: UAVs fly at low altitudes (usually below 1000 meters), have variable flight speeds, and their communication links are easily blocked and interfered with. In addition, UAV onboard equipment has strict limitations on power consumption, size, and weight. Existing technologies cannot meet the requirements of "low power consumption and miniaturization" and "reliable transmission of layered data". 3) Interference exists between payload data and telemetry and control data transmission: In the existing technology, the two types of data share the same transmission link, which can easily lead to a situation where the bandwidth of telemetry and control data transmission is squeezed when the payload data flow suddenly increases, resulting in delays or loss of control commands and affecting the flight safety of UAVs.

[0004] Therefore, given the unique characteristics of UAV data transmission in low-altitude economic scenarios, there is an urgent need for a modulation and demodulation technology that can achieve layered transmission of telemetry and control data and payload data, balance transmission reliability and speed, and adapt to complex low-altitude environments, so as to ensure the safety and efficiency of UAV operations. Summary of the Invention

[0005] The purpose of this invention is to provide a cascaded modulation and demodulation transmission method and system for unmanned aerial vehicles (UAVs) oriented towards low-altitude economy. By cascading modulation, the method achieves layered transmission of telemetry and control data and payload data, ensuring high-reliability transmission of telemetry and control data and high-speed transmission of payload data.

[0006] To achieve the above objectives, this invention provides a cascaded modulation and demodulation transmission method for unmanned aerial vehicles (UAVs) geared towards low-altitude economics, comprising a cascaded modulation and transmission step at the transmitting end and a cascaded demodulation and reception step at the receiving end. The cascaded modulation and transmission step at the transmitting end includes: S1, acquiring telemetry and control data and payload data; S2, modulating the telemetry and control data using a first modulation method to generate a primary modulation signal; S3, modulating the payload data using a second modulation method to generate a secondary modulation signal; S4, using the primary modulation signal as a subcarrier signal and performing amplitude-weighted fusion with the secondary modulation signal to generate a cascaded modulation signal; the cascaded modulation signal is amplified by radio frequency power and transmitted through an airborne antenna. The cascaded demodulation and reception step at the receiving end includes: R1, the receiving end... The system receives the cascaded modulated signal, amplifies it with low noise, down-converts it to an intermediate frequency (IF) signal, and then performs filtering preprocessing to remove stray interference signals in the low-altitude environment. R2 splits the preprocessed IF signal using two bandpass filters, resulting in two signals: one is a primary modulated signal containing telemetry and control (TT&C) data, and the other is a secondary modulated signal containing payload data. R3 demodulates the split primary modulated signal using a demodulation method corresponding to the primary modulation method to restore the TT&C data. R4 demodulates the split secondary modulated signal using a demodulation method corresponding to the secondary modulation method to restore the payload data. R5 transmits the demodulated TT&C data to the flight control center and the demodulated payload data to the data processing terminal.

[0007] The above-mentioned UAV cascade modulation and demodulation transmission method for low-altitude economy, in which the telemetry and control data is first scrambled and CRC-32 encoded before being modulated by the first modulation method; the scrambling process uses LFSR to generate a scrambling sequence to scramble the bit distribution of the telemetry and control data.

[0008] The aforementioned UAV cascaded modulation and demodulation transmission method for low-altitude economy, wherein, before modulating the payload data using the second modulation method, the payload data is first subjected to frame segmentation, LDPC encoding, and interleaving; in step S3, the second modulation method adopts QPSK modulation or 16QAM modulation, and the modulation method is dynamically switched according to the real-time low-altitude channel quality, specifically: when the signal-to-noise ratio of the low-altitude channel is ≥18dB, it switches to 16QAM modulation; when 10dB≤SNR<18dB, it switches to QPSK modulation; when SNR<10dB, it maintains QPSK modulation and increases the LDPC encoding code rate.

[0009] The above-mentioned UAV cascaded modulation and demodulation transmission method for low-altitude economy, wherein in step S4, during cascaded fusion, the ratio of the amplitude of the primary modulation signal to the amplitude of the secondary modulation signal is controlled to be 1:3 to 1:5; the cascaded fusion adopts an adaptive amplitude-weighted fusion strategy: adjusting the ratio of the amplitude of the primary modulation signal to the amplitude of the secondary modulation signal based on the real-time low-altitude channel quality, specifically: when the signal-to-noise ratio of the low-altitude channel is <10dB, increasing the amplitude proportion of the primary modulation signal; when the signal-to-noise ratio is ≥10dB, decreasing the amplitude proportion of the primary modulation signal.

[0010] The aforementioned UAV cascaded modulation and demodulation transmission method for low-altitude economy, wherein in step R3, a digital frequency discriminator + bit synchronization algorithm is used in the demodulation process to achieve accurate demodulation of the primary modulation signal, and CRC-32 check ensures the integrity of the demodulated telemetry and control data; if the demodulated telemetry and control data fails the CRC-32 check, a retransmission mechanism is triggered, and the receiving end sends a retransmission command to the transmitting end, requesting the UAV to retransmit the telemetry and control data.

[0011] The aforementioned UAV cascaded modulation and demodulation transmission method for low-altitude economy includes step R4, in which a Costas ring is used for carrier recovery during demodulation, a soft-decision demodulation algorithm is used to improve demodulation accuracy, Gray code inverse mapping is used for QPSK modulation, and constellation diagram matching demodulation is used for 16QAM modulation. At the same time, LDPC decoding error correction processing is used to reduce the transmission bit error rate of payload data. If the bit error rate of payload data after LDPC decoding error correction processing exceeds a set threshold, only the current erroneous data packet is discarded, and no retransmission mechanism is triggered.

[0012] This invention also provides a UAV cascaded modulation and demodulation transmission system for low-altitude economy, used to implement the aforementioned UAV cascaded modulation and demodulation transmission method for low-altitude economy. The system includes an UAV airborne transmission system and a ground receiving and processing system. The UAV airborne transmission system includes a data acquisition module, a primary modulation module, a secondary modulation module, a cascaded fusion module, a radio frequency transmission module, a channel quality detection module, and a modulation mode switching module. The data acquisition module is used to acquire telemetry and control data and payload data, transmit the telemetry and control data to the primary modulation module, and transmit the payload data to the secondary modulation module. The primary modulation module is used to scramble, CRC-32 encode, and FSK modulate the telemetry and control data to generate a primary modulated signal. The channel quality detection module is used to detect the signal-to-noise ratio and bit error rate of the low-altitude channel in real time, and output the channel quality assessment result to the cascaded fusion module and the modulation mode switching module. The secondary modulation module is used to perform framing, LDPC encoding, interleaving, and... QPSK or 16QAM modulation is used to generate a secondary modulation signal. The modulation mode switching module is connected to the secondary modulation module and is used to dynamically switch the modulation mode of the secondary modulation module according to the real-time channel quality assessment results. The cascade fusion module is used to adaptively amplitude-weightedly fuse the primary and secondary modulation signals according to the channel quality assessment results to generate a cascaded modulation signal. The radio frequency transmission module is used to amplify the cascaded modulation signal before transmission. The ground receiving and processing system includes a radio frequency receiving module, a signal preprocessing module, a splitter module, a primary demodulation module, a secondary demodulation module, a data verification module, a demodulation mode switching module, and a data output module. The radio frequency receiving module is used to receive the cascaded modulation signal and perform preliminary amplification. The signal preprocessing module is used to downconvert the amplified cascaded modulation signal to an intermediate frequency signal and filter out spurious interference signals in the low-altitude environment. The splitter module includes two bandpass filters, which are used to extract the primary and secondary modulation signals, respectively. The primary demodulation module demodulates the primary modulation signal to restore the measurement and control data; the demodulation mode switching module dynamically switches the demodulation mode of the secondary demodulation module; the secondary demodulation module demodulates the secondary modulation signal to restore the payload data; the data verification module performs integrity verification on the measurement and control data and performs bit error rate statistics on the payload data; the data output module transmits the verified measurement and control data to the flight control center and transmits the demodulated payload data to the data processing terminal.

[0013] The aforementioned UAV cascaded modulation and demodulation transmission system for low-altitude economy includes a ground receiving and processing system that further includes a retransmission control module. This module is used to send a retransmission command to the UAV after data verification fails, requiring the UAV to retransmit the data.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are: (1) Achieve layered data transmission while balancing reliability and speed: FSK modulation is used to ensure highly reliable transmission of measurement and control data (bit error rate ≤ 10). -6 The system employs QPSK / 16QAM modulation to meet the high-speed transmission requirements of payload data (up to 1Mbps), solving the problem that a single modulation method in the existing technology cannot meet the needs of two types of data transmission, thus ensuring the flight safety and operational efficiency of UAVs in low-altitude operations. (2) Adapting to the complex environment of low-altitude economic scenarios: By optimizing modulation parameters (such as the low-rate and narrow-bandwidth design of FSK, and the adaptive switching of QPSK / 16QAM), adopting an adaptive cascade fusion strategy, and adding multiple error correction processing (CRC-32, LDPC coding), the system's anti-interference capability in complex environments such as low-altitude building multipath, electromagnetic interference, and signal blockage is improved, making it suitable for various low-altitude economic application scenarios such as logistics distribution, urban inspection, and plant protection operations. (3) Meets the requirements of low power consumption and miniaturization of UAV onboard equipment: The hardware architecture of FPGA + dedicated radio frequency chip is adopted, and the overall power consumption is controlled to be <5W and the PCB size is <10cm×10cm, which meets the strict limitations of UAV onboard equipment on size, weight and power consumption, and is easy to integrate on various small and medium-sized UAVs. (4) It has dynamic adaptation capability: It supports dynamic switching of secondary modulation mode and adaptive adjustment of cascade fusion ratio. It can optimize transmission strategy according to real-time changes in low-altitude channel quality, prioritize the transmission of measurement and control data when the channel quality is poor, and increase the data transmission rate of payload when the channel quality is good, thereby improving the flexibility and adaptability of the system. Attached Figure Description

[0015] The UAV cascaded modulation and demodulation transmission method and system for low-altitude economy of the present invention are given by the following embodiments and figures.

[0016] Figure 1 This is a flowchart of a UAV cascaded modulation and demodulation transmission method for low-altitude economy according to Embodiment 1 of the present invention.

[0017] Figure 2 This is a schematic diagram of the UAV airborne launch system in Embodiment 2 of the present invention.

[0018] Figure 3 This is a schematic diagram of the ground receiving and processing system in Embodiment 2 of the present invention. Detailed Implementation

[0019] The following will combine Figures 1-3 The present invention provides a further detailed description of the unmanned aerial vehicle cascaded modulation and demodulation transmission method and system for low-altitude economy.

[0020] The UAV cascaded modulation and demodulation transmission method for low-altitude economy of the present invention includes a cascaded modulation and transmission step at the transmitting end and a cascaded demodulation and reception step at the receiving end.

[0021] The cascaded modulation transmission steps at the transmitting end include: S1, Data Classification and Acquisition: The UAV airborne launch system collects two types of data—telemetry and control data and payload data; The measurement and control data includes at least one of flight attitude data, position coordinate data, flight control commands, airborne equipment status data, and battery power data; the payload data includes at least one of high-definition image data, real-time video stream data, environmental data collected from the work area, and plant protection parameter data. S2, Primary modulation (measurement and control data modulation): The measurement and control data is modulated using the first modulation method to generate a primary modulation signal; The first modulation method uses a low-rate, high-reliability, and strong anti-interference constant envelope modulation method, such as FSK (Frequency Shift Keying) modulation. The modulation parameters are configured as follows: subcarrier frequency range of 500kHz to 1MHz, frequency offset of ±5kHz to ±10kHz, and symbol rate of 1kbaud to 5kbaud, ensuring that the bit error rate of the measurement and control data transmission is ≤10 in the complex electromagnetic environment at low altitude. -6 ; Preferably, before modulating the measurement and control data using the first modulation method, the measurement and control data is first subjected to scrambling and CRC-32 encoding. The scrambling process uses an LFSR (Linear Feedback Shift Register) to generate a scrambling sequence, which disrupts the bit distribution of the measurement and control data and improves its anti-interception capability. The CRC-32 encoding process is used for integrity verification during subsequent demodulation to ensure that the measurement and control data has not been tampered with or transmitted incorrectly. S3, Secondary Modulation (Load Data Modulation): The load data is modulated using a second modulation method to generate a secondary modulation signal; The second modulation method uses a high-speed, high-spectral-efficiency modulation method, such as QPSK modulation or 16QAM modulation. The modulation method can be dynamically switched according to the low-altitude channel quality. The modulation parameters are configured as follows: the main carrier frequency range is 2.4GHz to 5.8GHz (adapted to the common communication frequency band of UAVs), the symbol rate is 100kbaud to 1Mbps, and raised cosine shaping filtering (roll-off factor α=0.35~0.5) is used to suppress spectrum spread and improve the payload data transmission rate. Preferably, before modulating the payload data using the second modulation method, the payload data is first subjected to frame segmentation, LDPC encoding, and interleaving. The frame segmentation divides the payload data into fixed-length data packets (frame length 1024 bytes to 4096 bytes) to facilitate frame synchronization during subsequent demodulation. The LDPC encoding (code rate 1 / 2 to 3 / 4) improves the anti-interference capability of the payload data and adapts to the time-varying characteristics of low-altitude channels. The interleaving disperses continuous bit errors into discrete bit errors, avoiding payload data loss caused by local bit errors. Preferably, the second modulation scheme can be dynamically switched according to the real-time low-altitude channel quality. Specifically, when the signal-to-noise ratio (SNR) of the low-altitude channel is ≥18dB, it switches to 16QAM modulation; when 10dB≤SNR<18dB, it switches to QPSK modulation; when SNR<10dB, it maintains QPSK modulation and increases the code rate of LDPC coding. S4, Cascaded Fusion and Transmission: The primary modulation signal is used as a subcarrier signal and fused with the secondary modulation signal by amplitude weighting to generate a cascaded modulation signal; the cascaded modulation signal is amplified by radio frequency power and then transmitted through an airborne antenna. During fusion, the ratio of the amplitude of the primary modulation signal to the amplitude of the secondary modulation signal is controlled to be 1:3 to 1:5 to avoid the subcarrier signal overwhelming the main carrier signal or the main carrier signal interfering with the subcarrier signal. Preferably, the cascaded fusion adopts an adaptive fusion strategy: the ratio of the amplitude of the primary modulation signal to the amplitude of the secondary modulation signal is adjusted based on the real-time low-altitude channel quality. Specifically, when the signal-to-noise ratio (SNR) of the low-altitude channel is <10dB, the amplitude ratio of the primary modulation signal is increased (e.g., adjusted to 1:3) to prioritize the transmission of telemetry and control data; when the SNR is ≥10dB, the amplitude ratio of the primary modulation signal is decreased (e.g., adjusted to 1:5) to improve the transmission rate of payload data.

[0022] The cascaded demodulation receiving steps at the receiving end include: R1, Signal reception and preprocessing: The receiving end receives the cascaded modulated signal through the receiving antenna, and after low-noise amplification and down-conversion to intermediate frequency signal, it performs filtering preprocessing to filter out stray interference signals in the low-altitude environment. R2, Path splitting: The preprocessed intermediate frequency signal is split into two signals by a bandpass filter: one is a primary modulation signal containing measurement and control data (extracted by a bandpass filter with a center frequency of 500kHz to 1MHz and a bandwidth of 10kHz to 20kHz), and the other is a secondary modulation signal containing load data (extracted by a bandpass filter with a center frequency of 2.4GHz to 5.8GHz and a bandwidth of 200kHz to 2MHz). R3, First demodulation (measurement and control data demodulation): The first modulation signal after splitting is demodulated using a demodulation method corresponding to the first modulation method to restore the measurement and control data; The demodulation process employs a digital frequency discriminator and a bit synchronization algorithm to achieve accurate demodulation of the FSK signal, while CRC-32 verification ensures the integrity of the demodulated measurement and control data. Preferably, if the demodulated telemetry and control data fails the CRC-32 check, a retransmission mechanism is triggered, and a retransmission command is sent from the receiver to the transmitter, requesting the UAV to retransmit the telemetry and control data. R4, Secondary demodulation (load data demodulation): The secondary modulation signal after splitting is demodulated using a demodulation method corresponding to the secondary modulation method to restore the load data; Preferably, during demodulation, a Costas ring is used to achieve carrier recovery, a soft-decision demodulation algorithm is used to improve demodulation accuracy, Gray code inverse mapping is used for QPSK modulation, constellation matching demodulation is used for 16QAM modulation, and LDPC decoding error correction is used to reduce the transmission bit error rate of payload data. Preferably, if the bit error rate of the payload data after LDPC decoding and error correction exceeds a set threshold (10... -5 If the error occurs, only the current erroneous data packet is discarded, and the entire data is not retransmitted, thus avoiding impact on the real-time transmission of measurement and control data. R5, Data Output and Processing: The demodulated telemetry and control data is transmitted to the flight control center for UAV flight status monitoring and control command issuance; the demodulated payload data is transmitted to the data processing terminal for image display, video storage, and operational data analysis.

[0023] The UAV cascaded modulation and demodulation transmission system for low-altitude economy of the present invention includes an UAV airborne transmission system and a ground receiving and processing system.

[0024] The UAV airborne launch system includes a data acquisition module, a primary modulation module, a secondary modulation module, a cascaded fusion module, a radio frequency transmission module, a channel quality detection module, and a modulation mode switching module. The data acquisition module is used to acquire measurement and control data and load data, transmit the measurement and control data to the primary modulation module, and transmit the load data to the secondary modulation module; The primary modulation module is used to scramble, encode CRC-32, and modulate the measurement and control data to generate a primary modulation signal. The channel quality detection module is used to detect parameters such as signal-to-noise ratio and bit error rate of the low-altitude channel in real time, and outputs the channel quality assessment results to the cascaded fusion module and the modulation mode switching module. The secondary modulation module is used to perform frame division, LDPC encoding, interleaving, and QPSK modulation or 16QAM modulation on the payload data to generate a secondary modulation signal. The modulation mode switching module is connected to the secondary modulation module and is used to dynamically switch the modulation mode of the secondary modulation module according to the real-time channel quality assessment results. Specifically, when the channel quality is good (i.e., SNR≥18dB), the modulation mode of the secondary modulation module is switched to 16QAM modulation; when the channel quality is average (i.e., 10dB≤SNR<18dB), the modulation mode of the secondary modulation module is switched to QPSK modulation; when the channel quality is poor (i.e., SNR<10dB), the payload data transmission rate is reduced, QPSK modulation is maintained, and the LDPC coding rate is increased to ensure the basic transmission requirements of the payload data. The cascaded fusion module is used to perform adaptive amplitude-weighted fusion of the primary modulation signal and the secondary modulation signal based on the channel quality assessment results to generate a cascaded modulation signal. The radio frequency transmission module is used to amplify the cascaded modulated signal before transmitting it.

[0025] The ground receiving and processing system includes a radio frequency receiving module, a signal preprocessing module, a splitting module, a primary demodulation module, a secondary demodulation module, a data verification module, a demodulation mode switching module, and a data output module; The radio frequency receiving module is used to receive cascaded modulated signals and perform preliminary amplification; The signal preprocessing module is used to downconvert the amplified cascaded modulation signal to an intermediate frequency signal and filter out stray interference signals in the low-altitude environment. The splitter module includes two bandpass filters, which are used to extract the primary modulation signal and the secondary modulation signal, respectively. The primary demodulation module is used to perform digital frequency discrimination, bit synchronization and demodulation on the primary modulation signal to restore the measurement and control data. The demodulation mode switching module is connected to the secondary demodulation module and is used to dynamically switch the demodulation mode of the secondary demodulation module. Specifically, when the secondary modulation signal is a 16QAM modulation signal, the demodulation mode of the secondary demodulation module is controlled to be 16QAM demodulation; when the secondary modulation signal is a QPSK modulation signal, the demodulation mode of the secondary demodulation module is controlled to be QPSK modulation. The secondary demodulation module is used to perform carrier recovery, soft decision demodulation, QPSK demodulation or 16QAM demodulation, and LDPC decoding on the secondary modulation signal to restore the payload data. The data verification module is used to verify the integrity of the measurement and control data and to perform bit error rate statistics on the load data. The data output module is used to transmit the verified telemetry and control data to the flight control center and the demodulated payload data to the data processing terminal.

[0026] This invention achieves layered transmission of telemetry and control data and payload data through cascaded modulation, ensuring high-reliability transmission of telemetry and control data and high-speed transmission of payload data, adapting to the low-power and miniaturization requirements of complex low-altitude electromagnetic environments and UAV airborne equipment.

[0027] Example 1: This embodiment takes an urban inspection drone as an example. The measurement and control data that the drone needs to transmit includes flight attitude (pitch angle, roll angle, heading angle), GPS position coordinates, inspection path adjustment instructions issued by the ground control center, onboard camera working status, and battery power data; the payload data includes high-definition images of the inspection area (resolution 1920×1080) and real-time video stream (frame rate 25fps).

[0028] like Figure 1 The UAV cascaded modulation and demodulation transmission method for low-altitude economy in this embodiment includes a cascaded modulation and transmission step at the transmitting end and a cascaded demodulation and reception step at the receiving end. The cascaded modulation transmission steps at the transmitting end specifically include: S1, Data Classification and Acquisition: Flight attitude and position coordinate data are collected through the UAV's onboard IMU sensor and GPS module; inspection path adjustment instructions are received from the ground control center via serial port; the working status and battery power data of the onboard high-definition camera are collected through the sensor to form measurement and control data; high-definition images and real-time video streams of the inspection area are collected through the onboard high-definition camera to form payload data. S2, First modulation (monitoring and control data modulation): The monitoring and control data undergoes LFSR scrambling processing (scrambling polynomial x). 8 +x 4 After processing with CRC-32 encoding (+x³+x²+1), the signal is modulated using FSK modulation to generate a primary modulation signal. The modulation parameters are configured as follows: subcarrier frequency 800kHz, frequency offset ±8kHz, symbol rate 3kbaud. S3, Secondary Modulation (Payload Data Modulation): After the payload data is processed by framing (frame length 2048 bytes), LDPC encoding (code rate 1 / 2), and interleaving, it is modulated using QPSK modulation to generate a secondary modulated signal; the modulation parameters are configured as follows: main carrier frequency 2.4GHz, symbol rate 500kbaud, raised cosine shaping filter roll-off factor α=0.4. S4, Cascaded Fusion and Transmission: The low-altitude channel signal-to-noise ratio (SNR) is detected in real time by the airborne channel quality detection module (currently detected SNR=15dB). An adaptive amplitude-weighted fusion strategy is adopted to control the ratio of the amplitude of the primary modulation signal to the amplitude of the secondary modulation signal to be 1:4. After fusion, a cascaded modulation signal is generated. The cascaded modulation signal is amplified by the RF power amplifier (output power 3W) and then transmitted through the airborne antenna. The cascaded demodulation receiving steps at the receiving end specifically include: R1, Signal reception and preprocessing: The ground receiver receives the cascaded modulated signal through the receiving antenna, amplifies it through a low-noise amplifier (noise figure <3dB), downconverts it to a 10MHz intermediate frequency signal, and filters out stray interference signals through a low-pass filter (cutoff frequency 2MHz). R2, splitting process: splitting is performed through two bandpass filters: the first bandpass filter (center frequency 800kHz, bandwidth 16kHz) extracts the primary modulation signal, and the second bandpass filter (center frequency 2.4GHz, bandwidth 1MHz) extracts the secondary modulation signal. R3, First demodulation (measurement and control data demodulation): The first modulation signal is processed by a digital frequency discriminator, and bit synchronization is achieved by Gardner synchronization algorithm. After demodulation, the measurement and control data is obtained, and the data integrity is confirmed by CRC-32 verification. R4, Secondary Demodulation (Payload Data Demodulation): A Costas ring is used to perform carrier recovery on the secondary modulated signal (frequency tracking range ±10kHz). The payload data is then restored using a soft-decision demodulation algorithm and Gray code inverse mapping. After LDPC decoding and error correction, the bit error rate is controlled at 10⁻. 5 within; R5, Data Output and Processing: Transmits the calibrated telemetry and control data to the city inspection flight control center for monitoring the UAV's flight status and adjusting the inspection path; transmits the demodulated high-definition images and real-time video streams to the inspection data processing terminal for urban facility fault detection and recording.

[0029] Example 2: like Figure 2 and Figure 3 The UAV cascaded modulation and demodulation transmission system for low-altitude economy in this embodiment is used to implement the transmission method in embodiment 1, including UAV airborne transmission system 1 and ground receiving and processing system 2; The UAV airborne launch system 1 includes a data acquisition module 11, a primary modulation module 12, a secondary modulation module 13, a cascaded fusion module 14, a radio frequency transmission module 15, a channel quality detection module 16, and a modulation mode switching module 17. The data acquisition module 11 includes an IMU sensor, a GPS module, a serial communication unit, and a camera, which are used to acquire flight attitude data, position coordinate data, control command data, and image and video data, respectively. The primary modulation module 12 is implemented using the internal logic of a Xilinx Artix-7 FPGA, including an LFSR scrambling unit, a CRC-32 encoding unit, and an FSK modulator, which are used to perform LFSR scrambling, CRC-32 encoding, and FSK modulation on the measurement and control data to generate a primary modulation signal; The secondary modulation module 13 is implemented using the internal logic of a Xilinx Artix-7 FPGA, including a frame processing unit, an LDPC encoding unit, an interleaving unit, a QPSK modulator, and a 16QAM modulator. It is used to perform frame division, LDPC encoding, interleaving, and QPSK modulation or 16QAM modulation on the payload data to generate a secondary modulation signal. The channel quality detection module 16 uses a dedicated channel evaluation chip to detect the signal-to-noise ratio and bit error rate of the low-altitude channel in real time, and outputs the channel quality evaluation results to the cascaded fusion module 14 and the modulation mode switching module 17. The modulation mode switching module 17 is connected to the secondary modulation module 13 and dynamically switches the modulation mode of the secondary modulation module 13 according to the channel quality assessment results: when the low-altitude channel signal-to-noise ratio is detected to be ≥18dB, it switches to 16QAM modulation; when 10dB≤SNR<18dB, it switches to QPSK modulation; when SNR<10dB, it reduces the payload data transmission rate, maintains QPSK modulation and increases the LDPC coding rate to ensure the basic transmission requirements of the payload data. The cascaded fusion module 14 uses multipliers and adders inside the FPGA to implement an adaptive amplitude-weighted fusion strategy, adjusting the fusion ratio of the primary modulation signal and the secondary modulation signal according to the channel quality assessment results to generate a cascaded modulation signal. The radio frequency transmission module 15 includes an ADI AD8345 power amplifier and a 2.4GHz airborne antenna, used to amplify the cascaded modulated signal (output power 3W) before transmission; The ground receiving and processing system 2 includes a radio frequency receiving module 21, a signal preprocessing module 22, a splitting module 23, a primary demodulation module 24, a secondary demodulation module 25, a data verification module 26, a data output module 27, and a retransmission control module 28. The radio frequency receiving module 21 includes a 2.4 GHz receiving antenna and a low-noise amplifier, used to receive cascaded modulated signals and perform preliminary amplification; The signal preprocessing module 22 includes an ADI AD9361 downconverter and a SAW filter, used to downconvert the amplified cascaded modulation signal to a 10MHz intermediate frequency signal and filter out spurious interference. The splitter module 23 includes two custom LC bandpass filters: a bandpass filter with a center frequency of 800 kHz and a bandwidth of 16 kHz, and a bandpass filter with a center frequency of 2.4 GHz and a bandwidth of 1 MHz, used to extract the primary modulation signal and the secondary modulation signal. The primary demodulation module 24 is implemented using FPGA internal logic, including a digital frequency discriminator, a bit synchronization unit, and an FSK demodulator, used to demodulate the primary modulation signal and restore the measurement and control data. The demodulation mode switching module 29 is connected to the secondary demodulation module 25 and is used to dynamically switch the demodulation mode of the secondary demodulation module 25; The secondary demodulation module 25 is implemented using FPGA internal logic and includes a Costas ring carrier recovery unit, a soft decision demodulation unit, an LDPC decoding unit, a QPSK demodulator, and a 16QAM demodulator, which are used to demodulate the secondary modulation signal and restore the load data. The data verification module 26 includes a CRC-32 verification unit and a bit error rate statistics unit, which are used to perform integrity verification on the demodulated measurement and control data and to perform bit error rate statistics on the load data. The retransmission control module 28 is used to send a retransmission command to the drone after data verification fails, requiring the drone to retransmit the data. The data output module 27 includes an Ethernet interface and a serial port interface, which are used to transmit payload data to the data processing terminal and transmit telemetry and control data to the city inspection flight control center, respectively.

[0030] In this embodiment, the UAV cascaded modulation and demodulation transmission system for low-altitude economy adopts a hardware architecture of FPGA + dedicated radio frequency chip. The FPGA is a low-power model (such as Xilinx Artix-7) used to realize digital signal processing functions such as primary modulation, secondary modulation, cascade fusion, and data preprocessing. The dedicated radio frequency chip is a highly integrated transceiver chip (such as ADI AD9361) used to realize radio frequency signal transmission and reception.

[0031] In this embodiment, the overall power consumption of the UAV-borne launch system 1 is approximately 3.5W, which meets the requirements of airborne equipment for urban inspection UAVs; in low-altitude environments, the bit error rate of telemetry and control data transmission is ≤10. -6 The payload data transmission rate can reach 500kbps, which can meet the operational needs of urban inspection.

[0032] The present invention provides a UAV cascaded modulation and demodulation transmission method and system for low-altitude economy, which is applicable to UAV data transmission in low-altitude economic scenarios such as low-altitude logistics, plant protection operations, urban inspection, and emergency rescue.

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of the present invention, and all such modifications and modifications shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for cascaded modulation and demodulation transmission of unmanned aerial vehicles (UAVs) for low-altitude economy, characterized in that, This includes the cascaded modulation and transmission steps at the transmitting end and the cascaded demodulation and reception steps at the receiving end. The cascaded modulation transmission steps at the transmitting end include: S1, collects measurement and control data and load data; S2, the measurement and control data is modulated using the first modulation method to generate a primary modulation signal; S3, the load data is modulated using the second modulation method to generate a secondary modulation signal; S4 uses the primary modulation signal as a subcarrier signal and performs amplitude-weighted fusion with the secondary modulation signal to generate a cascaded modulation signal; the cascaded modulation signal is then amplified by radio frequency power and transmitted through an airborne antenna. The cascaded demodulation receiving steps at the receiving end include: R1, the receiving end receives the cascaded modulation signal, which is then amplified by low noise, down-converted to an intermediate frequency signal, and then filtered and pre-processed to remove stray interference signals in the low-altitude environment. R2 splits the preprocessed intermediate frequency signal through two bandpass filters to obtain two signals: one is a primary modulation signal containing measurement and control data, and the other is a secondary modulation signal containing load data. R3 uses a demodulation method corresponding to the primary modulation method to demodulate the split primary modulation signal and restore the measurement and control data. R4 uses a demodulation method corresponding to the secondary modulation method to demodulate the split secondary modulation signal and restore the load data; R5 transmits the demodulated telemetry and control data to the flight control center and the demodulated payload data to the data processing terminal.

2. The UAV cascaded modulation and demodulation transmission method for low-altitude economy as described in claim 1, characterized in that, Before modulating the measurement and control data using the first modulation method, the measurement and control data is first scrambled and encoded using CRC-32. The scrambling process uses LFSR to generate a scrambling sequence, which disrupts the bit distribution of the measurement and control data.

3. The UAV cascaded modulation and demodulation transmission method for low-altitude economy as described in claim 1, characterized in that, Before modulating the payload data using the second modulation method, the payload data is first processed by framing, LDPC coding, and interleaving. In step S3, the second modulation method uses either QPSK modulation or 16QAM modulation, and the modulation method is dynamically switched according to the real-time low-altitude channel quality. Specifically, when the signal-to-noise ratio (SNR) of the low-altitude channel is ≥18dB, it is switched to 16QAM modulation; when 10dB≤SNR<18dB, it is switched to QPSK modulation; when the SNR<10dB, QPSK modulation is maintained and the LDPC coding rate is increased.

4. The UAV cascaded modulation and demodulation transmission method for low-altitude economy as described in claim 1, characterized in that, In step S4, the ratio of the amplitude of the primary modulation signal to the amplitude of the secondary modulation signal is controlled to be 1:3 to 1:5 during cascade fusion. The cascade fusion adopts an adaptive amplitude-weighted fusion strategy: the ratio of the amplitude of the primary modulation signal to the amplitude of the secondary modulation signal is adjusted based on the real-time low-altitude channel quality. Specifically, when the signal-to-noise ratio of the low-altitude channel is <10dB, the amplitude proportion of the primary modulation signal is increased; when the signal-to-noise ratio is ≥10dB, the amplitude proportion of the primary modulation signal is decreased.

5. The UAV cascaded modulation and demodulation transmission method for low-altitude economy as described in claim 2, characterized in that, In step R3, a digital frequency discriminator and bit synchronization algorithm are used in the demodulation process to achieve accurate demodulation of the primary modulation signal. At the same time, CRC-32 verification is used to ensure the integrity of the demodulated telemetry and control data. If the demodulated telemetry and control data fails the CRC-32 verification, a retransmission mechanism is triggered. The receiver sends a retransmission command to the transmitter, requesting the UAV to retransmit the telemetry and control data.

6. The UAV cascaded modulation and demodulation transmission method for low-altitude economy as described in claim 3, characterized in that, In step R4, the carrier recovery is achieved using a Costas ring during demodulation, and a soft-decision demodulation algorithm is used to improve demodulation accuracy. Gray code inverse mapping is used for QPSK modulation, and constellation matching demodulation is used for 16QAM modulation. At the same time, LDPC decoding error correction processing is used to reduce the transmission bit error rate of the payload data. If the bit error rate of the payload data after LDPC decoding error correction processing exceeds a set threshold, only the current erroneous data packet is discarded, and the retransmission mechanism is not triggered.

7. The UAV cascaded modulation and demodulation transmission method for low-altitude economy as described in claim 1, characterized in that, The telemetry and control data includes at least one of flight attitude data, position coordinate data, flight control commands, airborne equipment status data, and battery power data; the payload data includes at least one of high-definition image data, real-time video stream data, environmental data collected from the work area, and plant protection parameter data; the first modulation method adopts FSK modulation, and the modulation parameters are configured as follows: subcarrier frequency range of 500kHz to 1MHz, frequency offset of ±5kHz to ±10kHz, and symbol rate of 1kbaud to 5kbaud, ensuring that the bit error rate of telemetry and control data transmission is ≤10% in the complex electromagnetic environment at low altitude. -6 The second modulation method adopts QPSK modulation or 16QAM modulation, and the modulation parameters are configured as follows: the main carrier frequency range is 2.4GHz to 5.8GHz, the symbol rate is 100kbaud to 1Mbps, the raised cosine shaping filter is used to suppress spectral spread and improve the data transmission rate of the payload, and the roll-off factor α = 0.35 to 0.5; in step R2, the primary modulation signal is extracted by a bandpass filter with a center frequency of 500kHz to 1MHz and a bandwidth of 10kHz to 20kHz, and the secondary modulation signal is extracted by a bandpass filter with a center frequency of 2.4GHz to 5.8GHz and a bandwidth of 200kHz to 2MHz.

8. A cascaded modulation and demodulation transmission system for unmanned aerial vehicles (UAVs) geared towards low-altitude economy, characterized in that, For implementing the UAV cascaded modulation and demodulation transmission method for low-altitude economy according to any one of claims 1 to 7, the system includes an UAV airborne transmission system and a ground receiving and processing system; The UAV airborne launch system includes a data acquisition module, a primary modulation module, a secondary modulation module, a cascaded fusion module, a radio frequency transmission module, a channel quality detection module, and a modulation mode switching module. The data acquisition module is used to acquire measurement and control data and load data, transmit the measurement and control data to the primary modulation module, and transmit the load data to the secondary modulation module; The primary modulation module is used to scramble, encode CRC-32, and modulate the measurement and control data to generate a primary modulation signal. The channel quality detection module is used to detect the signal-to-noise ratio and bit error rate of the low-altitude channel in real time, and output the channel quality assessment results to the cascaded fusion module and the modulation mode switching module. The secondary modulation module is used to perform frame division, LDPC encoding, interleaving, and QPSK modulation or 16QAM modulation on the payload data to generate a secondary modulation signal. The modulation mode switching module is connected to the secondary modulation module and is used to dynamically switch the modulation mode of the secondary modulation module according to the real-time channel quality assessment results. The cascaded fusion module is used to perform adaptive amplitude-weighted fusion of the primary modulation signal and the secondary modulation signal based on the channel quality assessment results to generate a cascaded modulation signal. The radio frequency transmission module is used to amplify the cascaded modulated signal before transmitting it. The ground receiving and processing system includes a radio frequency receiving module, a signal preprocessing module, a splitting module, a primary demodulation module, a secondary demodulation module, a data verification module, a demodulation mode switching module, and a data output module; The radio frequency receiving module is used to receive cascaded modulated signals and perform preliminary amplification; The signal preprocessing module is used to downconvert the amplified cascaded modulation signal to an intermediate frequency signal and filter out stray interference signals in the low-altitude environment. The splitter module includes two bandpass filters, which are used to extract the primary modulation signal and the secondary modulation signal, respectively. The primary demodulation module is used to demodulate the primary modulation signal and restore the measurement and control data. The demodulation mode switching module is used to dynamically switch the demodulation mode of the secondary demodulation module; The secondary demodulation module is used to demodulate the secondary modulation signal and restore the load data. The data verification module is used to verify the integrity of the measurement and control data and to perform bit error rate statistics on the load data. The data output module is used to transmit the verified telemetry and control data to the flight control center and the demodulated payload data to the data processing terminal.

9. A UAV cascaded modulation and demodulation transmission system for low-altitude economy as described in claim 8, characterized in that, The ground receiving and processing system also includes a retransmission control module, which sends a retransmission command to the UAV after a data verification failure, requiring the UAV to retransmit the data.

10. A UAV cascaded modulation and demodulation transmission system for low-altitude economy as described in claim 8, characterized in that, The UAV cascaded modulation and demodulation transmission system for low-altitude economy adopts a hardware architecture of FPGA + dedicated radio frequency chip. The FPGA realizes the functions of primary modulation, secondary modulation, cascade fusion, data preprocessing and digital signal processing. The dedicated radio frequency chip is a highly integrated transceiver chip to realize radio frequency signal transmission and reception.

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