Communication method and device based on QAM-OFDM

Abstract

The invention discloses a QAM-OFDM (Quadrature Amplitude Modulation-Orthogonal Frequency Division Multiplexing)-based communication method and device, and relates to the technical field of ultrasonic communication, and the method comprises the following steps: using a convolutional code for an original signal to obtain an initial signal, converting the initial signal into a modulation signal by using a QAM modulation technology, and converting the modulation signal into an analog signal by using an OFDM modulation technology; performing a spread spectrum technology on the analog signal, and performing signal processing on the spread spectrum analog signal by using a power amplifier and a band-pass filter; receiving an analog signal which is transmitted by a steel rail channel and is subjected to signal processing; and performing signal conversion on the received signal by using an analog-to-digital converter, demodulating the converted signal by using an OFDM demodulation technology, and restoring the demodulated signal into an original signal by using a QAM demodulation technology. According to the invention, signal anti-interference capability can be enhanced, and high-efficiency signal transmission can be maintained.

Description

Technical Field

[0001] The present invention relates to the field of ultrasonic communication technology, and in particular to a communication method and device based on QAM-OFDM. Background Art

[0002] Ultrasonic guided waves, sound waves that propagate through solid materials, are widely used for health monitoring of metal structures such as rails, especially in railway track fault detection. Piezoelectric sensors effectively convert electrical signals into ultrasonic guided waves, enabling long-distance, real-time monitoring of rails and other targets. Existing digital modulation technologies include Orthogonal Frequency-Division Multiplexing (OFDM) and Quadrature Amplitude Modulation (QAM). OFDM decomposes high-speed data streams into multiple lower-rate subcarriers, each modulated independently, significantly improving spectrum efficiency. OFDM uses cyclic prefix (CP) technology to effectively mitigate multipath effects and enhance signal transmission reliability. Although OFDM combined with piezoelectric ultrasonic guided wave communication technology has achieved some progress in certain areas, its application in long-distance rail monitoring still faces numerous challenges, including difficulty maintaining stable and efficient communication in complex environments.

[0003] To sum up, how to enhance the signal's anti-interference capability while maintaining efficient signal transmission is an important issue that needs to be solved urgently. Summary of the Invention

[0004] The embodiments of the present invention provide a communication method and apparatus based on QAM-OFDM, which can enhance the anti-interference capability of a signal while maintaining efficient signal transmission.

[0005] An embodiment of the present invention provides a communication method based on QAM-OFDM, comprising the following steps: obtaining a signal to be sent as an original signal through a transmitting end, wherein the signal to be sent is an ultrasonic guided wave signal excited by a piezoelectric material; using a convolution code to obtain an initial signal from the original signal, converting the initial signal into a modulated signal using a QAM modulation technology, and converting the modulated signal into an analog signal using an OFDM modulation technology; using a spread spectrum technology to process the analog signal, and using a power amplifier and a bandpass filter to process the spread spectrum analog signal; communicating the processed analog signal through a rail channel; receiving the processed analog signal transmitted by the rail channel through a receiving end; performing signal conversion on the received signal using an analog-to-digital converter, demodulating the converted signal using an OFDM demodulation technology, and restoring the original signal from the demodulated signal using a QAM demodulation technology.

[0006] Furthermore, before performing signal conversion on the received signal using the analog-to-digital converter, the method further includes: performing signal processing again on the analog signal after signal processing using a power amplifier and a bandpass filter.

[0007] Furthermore, the use of OFDM modulation technology to convert the modulated signal into an analog signal specifically includes: mapping the modulated signal using subcarriers, and using inverse fast Fourier transform IFFT to generate multiple subcarrier signals; adding cyclic prefixes CP to the multiple subcarrier signals and converting them into analog signals.

[0008] Furthermore, the OFDM demodulation technology is used to demodulate the converted signal, and the specific steps include: removing the cyclic prefix CP in the converted signal; using fast Fourier transform FFT to convert the converted signal with the cyclic prefix CP removed from the time domain to the frequency domain, separating the subcarriers, and completing OFDM demodulation.

[0009] An embodiment of the present invention provides a communication device based on QAM-OFDM, comprising: a QAM modulator, an OFDM modulation module, an analog-to-digital converter, an OFDM demodulation module, and a QAM demodulator, wherein the output end of the QAM modulator is communicatively connected to the input end of the OFDM modulation module, the input end of the analog-to-digital converter receives a signal from the output end of the OFDM modulation module transmitted through a rail channel, the output end of the analog-to-digital converter is communicatively connected to the input end of the OFDM demodulation module, and the output end of the OFDM demodulation module is communicatively connected to the input end of the QAM demodulator.

[0010] The embodiments of the present invention provide a communication method and apparatus based on QAM-OFDM. Compared with the prior art, the advantageous effects thereof are as follows: The original signal is converted into an initial signal using a convolutional code, and then converted into an analog signal using QAM modulation and OFDM modulation techniques. Spread spectrum technology is applied to the analog signal, and the spread spectrum analog signal is processed using a power amplifier and a bandpass filter. The processed analog signal is transmitted through a rail channel. The processed analog signal transmitted by the rail channel is received. The received signal is converted using an analog-to-digital converter, and OFDM demodulation and QAM demodulation techniques are used to restore the original signal. The combination of QAM modulation and OFDM modulation techniques enables efficient information transmission, and the power amplifier increases the signal's anti-interference ability, ultimately achieving enhanced anti-interference capabilities while maintaining efficient signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A block diagram of a QAM-OFDM system provided in an embodiment of the present invention; Figure 2Flowchart of the QAM-OFDM piezoelectric ultrasonic guided wave communication system provided by an embodiment of the present invention; Figure 3 QAM-OFDM constellation diagram provided by an embodiment of the present invention; Figure 4 A diagram showing the demodulation results of QAM-OFDM without convolutional coding and spread spectrum technology provided by an embodiment of the present invention; Figure 5 A diagram showing the optimized demodulation results of QAM-OFDM with the addition of convolutional coding and spread spectrum technology provided in an embodiment of the present invention; Figure 6 A comparison chart of bit error rates under different signal-to-noise ratios provided by an embodiment of the present invention; Figure 7 This is a flowchart provided for an embodiment of the present invention. DETAILED DESCRIPTION

[0012] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0013] See also Figure 1~Figure 2 , an embodiment of the present invention provides a communication method based on QAM-OFDM, comprising the following steps: Step 1: The transmitting end obtains the signal to be transmitted as the original signal, where the signal to be transmitted is an ultrasonic guided wave signal excited by the piezoelectric material.

[0014] Step 2: Use convolutional coding on the original signal to obtain the initial signal. This initial signal is converted into a modulated signal using QAM modulation technology. This modulated signal is then converted into an analog signal using OFDM modulation technology. Spread spectrum technology is applied to the analog signal. The spread spectrum analog signal is then processed using a power amplifier and a bandpass filter. The processed analog signal is then communicated through the rail channel.

[0015] OFDM modulation technology is used to convert the modulated signal into an analog signal, including: mapping the modulated signal to subcarriers and generating multiple subcarrier signals using an inverse fast Fourier transform (IFFT); adding a cyclic prefix (CP) to the multiple subcarrier signals and converting them into analog signals. OFDM demodulation technology is used to demodulate the converted signal, including: removing the cyclic prefix (CP) from the converted signal, converting it from the time domain to the frequency domain using a fast Fourier transform (FFT) to separate the subcarriers; and demodulating the QAM symbols on each subcarrier to recover the original signal (the original bit stream).

[0016] Step 3: Receive the processed analog signal transmitted by the rail channel through the receiving end; use the analog-to-digital converter to convert the received signal, and use OFDM demodulation technology to demodulate the converted signal, and use QAM demodulation technology to restore the original signal to the demodulated signal.

[0017] This invention uses piezoelectric ultrasonic guided waves as a communication medium, combined with OFDM technology to encode and transmit signals. OFDM effectively reduces the effects of multipath and frequency-selective fading by dividing broadband signals into multiple subcarriers for transmission. Piezoelectric transducers excite and receive ultrasonic guided wave signals, which are modulated and demodulated using OFDM, enabling long-distance signal transmission.

[0018] 1. System architecture

[0019] The system architecture of the present invention mainly consists of an ultrasonic sensor, an OFDM modulation and demodulation module, a signal processing unit and a receiving device (such as Figure 1 shown): Ultrasonic sensor: used to excite and receive piezoelectric ultrasonic guided wave signals in the rail.

[0020] OFDM modulation and demodulation module: At the transmitter, the OFDM module modulates the ultrasonic guided wave signal and transmits the modulated signal to the receiver. The receiver demodulates the received signal to recover the original data.

[0021] Signal processing unit: used to perform denoising, amplification and filtering on the received signal to improve the signal quality.

[0022] Receiving equipment: used to receive and demodulate ultrasonic guided wave signals, ultimately realizing long-distance data transmission.

[0023] 2. Key technologies.

[0024] Piezoelectric ultrasonic guided wave excitation and reception technology: Through the characteristics of piezoelectric materials, ultrasonic guided wave signals are excited and echo signals are received for rail condition monitoring.

[0025] OFDM signal modulation and demodulation technology: OFDM is used to efficiently encode signals, making the transmitted signals less susceptible to attenuation over long distances.

[0026] Signal attenuation compensation and enhancement technology: To address signal attenuation during long-distance transmission, a signal enhancement algorithm is used to compensate for received signals. This signal enhancement algorithm is a received signal compensation technology based on a mean square error (MSE) equalization algorithm combined with a turbo coding and decoding mechanism. This algorithm does not amplify the signal amplitude in the traditional sense, but rather enhances the reliability and recoverability of the received signal at a logical level to address the attenuation, distortion, and bit errors encountered in long-distance multipath transmission environments. Therefore, using a signal enhancement algorithm to compensate for received signals specifically involves using a frequency domain equalization algorithm based on the mean square error (MSE) criterion, combined with a turbo coding and decoding mechanism, to compensate for errors and enhance the quality of the received signal, improving the system's information recovery capabilities under complex channel conditions.

[0027] 3. The structural composition of the present invention is as follows: (1) Transmitter: Data input (DATA): The transmitted data is input to the QAM modulator.

[0028] QAM modulator: Converts input digital data into modulation symbols, which are then frequency-division multiplexed in an OFDM system.

[0029] S / P conversion: Convert serial data into parallel data for easy subsequent processing.

[0030] IFFT (Inverse Fast Fourier Transform): Converts the frequency domain signal back to the time domain signal and uses IFFT to generate multiple subcarrier signals.

[0031] Add cyclic prefix (Add CP): Add a cyclic prefix (CP) before the OFDM symbol to mitigate the impact of multipath propagation.

[0032] P / S conversion: Converts parallel data back to serial data for DAC to convert into analog signals.

[0033] DAC (Digital-to-Analog Converter): Converts digital signals into analog signals, amplifies the ultrasonic guided wave signals through signal amplifiers and sends them out to ensure that the signal strength is sufficient for long-distance transmission in the rails.

[0034] (2) Receiver: Received signal (rail channel): The receiver receives the signal passing through the rail channel. Due to the physical properties of the rails, the rail channel is affected by attenuation and noise during the transmission process.

[0035] ADC (Analog-to-Digital Converter): Converts the received analog signal into a digital signal for subsequent processing.

[0036] S / P conversion: Converts serial data into parallel data to facilitate FFT operations.

[0037] Remove CP: Removes the cyclic prefix from the received signal to facilitate subsequent signal recovery.

[0038] FFT (Fast Fourier Transform): Converts time domain signals into frequency domain signals for subcarrier separation.

[0039] P / S Conversion (P / S): Converts parallel data back to serial data in preparation for QAM demodulation.

[0040] QAM demodulator: Demodulates the frequency domain signal into the original data and recovers the transmitted digital data.

[0041] In the rail channel environment, the OFDM system can effectively combat the effects of multipath propagation and attenuation by introducing cyclic prefix and frequency domain processing, while using FFT and QAM demodulation technology to recover the transmitted data ( Figure 4 ), ensuring efficient and reliable data transmission.

[0042] Key technical parameters of the structure: OFDM parameters: Number of subcarriers: Based on rail communication requirements, 64, 128, or 256 subcarriers are typically selected. Modulation: 4-QAM, 16-QAM, or 64-QAM, dynamically adjusted based on channel conditions. Bandwidth: Based on the ultrasonic guided wave propagation characteristics of rails, an appropriate frequency band (e.g., 34 kHz to 35 kHz) is selected.

[0043] Ultrasonic guided wave parameters: Frequency range: 34 kHz to 35 kHz, ensuring low attenuation in rails. Transmission distance: Single transmission can reach several kilometers, further extended through relay nodes. Piezoelectric transducer sensitivity: Ensures conversion efficiency of transmitted and received signals.

[0044] The effect of this structure is as follows: (1) Efficient transmission: OFDM technology uses multiple orthogonal subcarriers to transmit data, which improves spectrum utilization and enables data transmission in rails.

[0045] (2) Strong anti-interference ability: When ultrasonic guided waves propagate in the rails, they are less susceptible to external electromagnetic interference, ensuring the stability of communication.

[0046] Long-distance transmission: Through the combination of signal amplifier and OFDM technology, ultrasonic guided wave signals can be transmitted for several kilometers in the rail without significant attenuation. Figures 3 to 5 Shown are the results using QAM-OFDM.

[0047] To further improve the performance of QAM-OFDM systems, spread spectrum technology and convolutional codes can be introduced. Spread spectrum increases the signal bandwidth, distributing information energy across a wider spectrum, thereby improving interference immunity and mitigating the effects of narrowband interference and multipath fading. Convolutional codes, as forward error correction (FEC) codes, add redundant bits, enabling the receiver to accurately recover data even in low signal-to-noise ratio (SNR) environments, effectively reducing the bit error rate (BER). The combination of these two technologies not only improves noise immunity and data reliability, but also enhances system robustness, making QAM-OFDM more suitable for complex wireless environments (such as 5G, satellite communications, and military communications).

[0048] from Figure 6 As can be seen, spreading reduces the BER, but its effect is limited at high SNRs. At low SNRs (0-4dB), the red curve decreases more rapidly, indicating that spreading enhances signal robustness. However, the BER decreases more slowly when the SNR exceeds 4dB, indicating that spreading alone offers limited improvement at high SNRs. However, convolutional coding combined with spreading outperforms spreading alone across the entire SNR range (the blue curve is consistently lower than the red curve), and the BER is significantly reduced when the SNR exceeds 4dB. This demonstrates that convolutional coding remains effective in low bit error rate scenarios and can further reduce the BER. Therefore, combining the two can minimize the bit error rate and improve QAM-OFDM transmission quality.

[0049] Fourth, the key points of the present invention are: (1) Orthogonal frequency division multiplexing (OFDM) technology is used to modulate and demodulate ultrasonic guided wave signals. The frequency multiplexing characteristics of OFDM can effectively reduce multipath effects and signal attenuation, and improve the transmission quality and stability of ultrasonic guided wave signals in long-distance rails.

[0050] (2) By utilizing the piezoelectric effect of piezoelectric materials, ultrasonic guided wave sensors are used to excite and receive ultrasonic guided wave signals in the rails, ensuring signal accuracy and efficiency. This method effectively solves the attenuation and noise problems of traditional ultrasonic guided wave technology in long-distance rail monitoring.

[0051] (3) To address the problem of signal attenuation during long-distance transmission, the present invention introduces a signal enhancement algorithm based on OFDM and combines it with a signal processing unit to perform denoising and amplification processing on the received signal, thereby further improving the signal transmission effect.

[0052] (4) The present invention combines the advantages of OFDM technology and ultrasonic guided wave transmission, significantly improving the reliability of long-distance rail monitoring, with lower power consumption and longer transmission distance, and is suitable for railway fault detection and long-term monitoring.

[0053] The present invention applies OFDM modulation technology to the communication process of piezoelectric ultrasonic guided waves, and proposes a new signal transmission method, which can effectively solve the signal attenuation problem existing in traditional ultrasonic guided wave technology in long-distance rail detection.

[0054] 5. The effects of the present invention are: (1) Significantly improve long-distance transmission effects.

[0055] This invention utilizes an OFDM-based ultrasonic guided wave signal transmission method, effectively overcoming the signal attenuation issues faced by traditional ultrasonic guided wave technology in long-distance rail monitoring. By using OFDM technology to split the signal into multiple subcarriers for transmission, it reduces multipath interference and significantly improves signal transmission stability and distance, enabling reliable transmission of ultrasonic guided wave signals over long rails.

[0056] (2) Enhance anti-interference and anti-attenuation capabilities.

[0057] Traditional ultrasonic guided wave signals are susceptible to noise and attenuation during long-distance transmission. This invention effectively enhances the system's anti-interference capabilities by introducing OFDM technology. OFDM's frequency reuse and diversity reception mechanism make the signal more robust in complex environments (such as multipath propagation and frequency-selective fading), ensuring accurate data transmission.

[0058] (3) Improve the reliability of signal transmission.

[0059] By adopting OFDM modulation and demodulation technology, the signal can maintain high reliability even in adverse transmission environments. Especially during long-distance rail monitoring, the system can effectively reduce transmission errors through precise signal modulation and demodulation algorithms, ensuring high fidelity and low bit error rate of ultrasonic guided wave signals, thereby improving the overall reliability of the system.

[0060] (4) Effectively solve the power consumption problem in rail monitoring.

[0061] The OFDM technology in the present invention enables signals to have higher transmission efficiency during long-distance transmission. Compared with traditional single-carrier communication methods, it can achieve long-distance communication with lower power consumption, thereby greatly extending the service life of the equipment and reducing the energy consumption of the system. It is particularly suitable for railway equipment that requires long-term monitoring.

[0062] (5) Strong adaptability, suitable for complex railway environments.

[0063] This invention can operate efficiently in complex railway environments, including monitoring different rail locations and detecting different types of rail defects. Due to the flexibility and adaptability of OFDM technology, it can achieve high signal transmission quality in different rail structures and transmission environments, thereby enhancing the diversity and applicability of railway inspection systems.

[0064] (6) Improve the accuracy of rail fault detection.

[0065] The ultrasonic guided wave communication method of this invention utilizes OFDM technology, enabling higher-quality transmission of ultrasonic guided wave signals to the receiving end, thereby improving the accuracy of rail fault detection. Through the efficient transmission of ultrasonic guided waves, the condition of rails can be monitored in real time, allowing for the timely detection of potential faults or hidden dangers, reducing maintenance costs and time, and improving rail transportation safety.

[0066] (7) Reduce system costs.

[0067] Because this invention directly integrates OFDM and piezoelectric ultrasonic guided wave sensors into existing rail monitoring systems, it reduces the need for additional equipment and complex system architecture. Compared to traditional technologies, this invention not only improves performance but also reduces hardware investment and maintenance costs, thereby improving the overall cost-effectiveness of the system.

[0068] An embodiment of the present invention provides a communication device based on QAM-OFDM, including: A QAM modulator, an OFDM modulation module, an analog-to-digital converter, an OFDM demodulation module, and a QAM demodulator, wherein the output end of the QAM modulator is communicatively connected to the input end of the OFDM modulation module, the input end of the analog-to-digital converter receives a signal from the output end of the OFDM modulation module transmitted through a rail channel, the output end of the analog-to-digital converter is communicatively connected to the input end of the OFDM demodulation module, and the output end of the OFDM demodulation module is communicatively connected to the input end of the QAM demodulator.

[0069] A specific embodiment is as follows: This embodiment discloses a communication method based on QAM-OFDM, and the specific steps are as follows: S1. Obtain the original signal.

[0070] S2. Use convolution code to obtain the initial signal from the original signal, convert the initial signal into a modulated signal using QAM modulation technology, and convert the modulated signal into an analog signal using OFDM modulation technology; use spread spectrum technology on the analog signal, and use a power amplifier and a bandpass filter to process the spread spectrum analog signal.

[0071] S3, receiving the analog signal after signal processing transmitted by the rail channel; converting the received signal using an analog-to-digital converter, demodulating the converted signal using OFDM demodulation technology, and restoring the original signal using QAM demodulation technology. The flow chart is as follows Figure 7 shown.

[0072] The application scenarios of the present invention are extended as follows: (1) Railway safety monitoring: The technology of the present invention is used to monitor the rail status (such as cracks, stress, and temperature) in real time and transmit the data to the control center to achieve railway safety early warning.

[0073] (2) Train positioning and communication: In environments with weak GPRS signals such as tunnels and mountainous areas, accurate train positioning and communication can be achieved through rail communication.

[0074] (3) Intelligent railway system: The technology of the present invention is applied to the intelligent railway system to achieve efficient data interaction between trains and ground control centers, and support automatic driving and intelligent scheduling.

[0075] The following should be noted during technical implementation: (1) Installation of piezoelectric transducer: Ensure close contact between the piezoelectric transducer and the rail to avoid signal loss.

[0076] (2) Signal interference suppression: There may be other ultrasonic signals (such as train wheel-rail noise) in the rails, and a filter needs to be designed to suppress the interference.

[0077] (3) Environmental adaptability: Considering the ultrasonic guided wave propagation characteristics of rails in different environments (such as high temperature, low temperature, and humidity), optimize the system design.

[0078] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A communication method based on QAM-OFDM, characterized in that: The following steps are involved: Acquire a signal to be transmitted as an original signal through a transmitting end, wherein the signal to be transmitted is an ultrasonic guided wave signal excited by a piezoelectric material; The original signal is converted into an initial signal using a convolutional code, and the initial signal is converted into a modulated signal using QAM modulation technology, and the modulated signal is converted into an analog signal using OFDM modulation technology; the analog signal is processed using spread spectrum technology, and the spread spectrum analog signal is processed using a power amplifier and a bandpass filter; Communicate the processed analog signal through the rail channel; The processed analog signal transmitted by the rail channel is received by the receiving end; the received signal is converted by an analog-to-digital converter, and the converted signal is demodulated using OFDM demodulation technology, and the demodulated signal is restored to the original signal using QAM demodulation technology.

2. The communication method based on QAM-OFDM according to claim 1, wherein: Before performing signal conversion on the received signal using the analog-to-digital converter, the method further comprises: The analog signal that has undergone signal processing is further processed using a power amplifier and a bandpass filter.

3. The communication method based on QAM-OFDM according to claim 1, wherein: The OFDM modulation technology is used to convert the modulated signal into an analog signal, and the specific steps include: The modulated signal is mapped to a subcarrier, and an inverse fast Fourier transform (IFFT) is used to generate multiple subcarrier signals. A cyclic prefix (CP) is added to the multiple subcarrier signals and converted into analog signals.

4. The communication method based on QAM-OFDM according to claim 1, wherein: The converted signal is demodulated using OFDM demodulation technology, and the specific steps include: Removing the cyclic prefix CP from the converted signal; The fast Fourier transform (FFT) is used to convert the converted signal with the cyclic prefix (CP) removed from the time domain to the frequency domain, separate the subcarriers, and complete the OFDM demodulation.

5. A communication device based on QAM-OFDM, characterized in that: include: A QAM modulator, an OFDM modulation module, an analog-to-digital converter, an OFDM demodulation module, and a QAM demodulator, wherein the output end of the QAM modulator is communicatively connected to the input end of the OFDM modulation module, the input end of the analog-to-digital converter receives a signal from the output end of the OFDM modulation module transmitted through a rail channel, the output end of the analog-to-digital converter is communicatively connected to the input end of the OFDM demodulation module, and the output end of the OFDM demodulation module is communicatively connected to the input end of the QAM demodulator.

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