Communication method and apparatus based on qam-ofdm

Abstract

The application discloses a communication method and device based on QAM-OFDM, relates to the technical field of ultrasonic communication, and comprises the following steps: using convolution code on an original signal to obtain an initial signal, using QAM modulation technology on the initial signal to convert the initial signal into a modulated signal, and using OFDM modulation technology to convert the modulated signal into an analog signal; using spread spectrum technology on the analog signal, and using a power amplifier and a band-pass filter to process the analog signal; receiving the analog signal processed by a steel rail channel; using an analog-digital converter to convert the received signal, using OFDM demodulation technology to demodulate the converted signal, and using QAM demodulation technology to restore the original signal from the demodulated signal. The application can enhance the anti-interference capability of the signal while maintaining efficient signal transmission.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultrasonic communication, in particular to a communication method and device based on QAM-OFDM. BACKGROUND

[0002] Ultrasonic guided waves are acoustic waves propagating through solid materials, which are widely used in health monitoring of metal structures such as steel rails, and have important application value in fault detection of railway tracks. Through a piezoelectric sensor, an electrical signal can be effectively converted into an ultrasonic guided wave, thereby realizing long-distance and real-time monitoring of targets such as steel rails. Existing digital modulation techniques such as OFDM (Orthogonal Frequency-Division Multiplexing) and QAM (Quadrature Amplitude Modulation) can significantly improve the spectral efficiency by decomposing a high-speed data stream into multiple low-speed subcarriers and independently modulating each subcarrier. OFDM uses the Cyclic Prefix (CP) technology to effectively resist multipath effects and improve the reliability of signal transmission. Although OFDM combined with piezoelectric ultrasonic guided wave communication technology has made some progress in certain fields, its application in long-distance steel rail monitoring still faces many challenges, and it is often difficult to maintain the stability and efficiency of communication in complex environments.

[0003] In summary, how to enhance the signal anti-interference ability while maintaining efficient signal transmission is an important problem to be solved. SUMMARY

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

[0005] The embodiments of the present application provide a communication method based on QAM-OFDM, which includes the following steps: obtaining a to-be-sent signal as an original signal through a transmitting end, the to-be-sent signal being an ultrasonic guided wave signal excited by a piezoelectric material; using convolution code on the original signal to obtain an initial signal, and using QAM modulation technology to convert the initial signal into a modulated signal, and using OFDM modulation technology to convert the modulated signal into an analog signal; using spread spectrum technology on the analog signal, and using a power amplifier and a band-pass filter to process the spread spectrum analog signal; communicating the processed analog signal through a steel rail channel; receiving the processed analog signal transmitted by the steel rail channel through a receiving end; using an analog-to-digital converter to convert the received signal, and using OFDM demodulation technology to demodulate the converted signal, and using QAM demodulation technology to restore the original signal from the demodulated signal.

[0006] Further, before the received signal is converted by the analog-digital converter, the signal is further processed by a power amplifier and a band-pass filter.

[0007] Further, the step of converting the modulated signal into an analog signal using the OFDM modulation technology comprises: mapping the modulated signal using a sub-carrier, and generating a plurality of sub-carrier signals using an inverse fast Fourier transform (IFFT); and adding a cyclic prefix (CP) to the plurality of sub-carrier signals and converting the plurality of sub-carrier signals into an analog signal.

[0008] Further, the step of demodulating the converted signal using the OFDM demodulation technology comprises: removing the CP from the converted signal; converting the converted signal from which the CP is removed from a time domain to a frequency domain using a fast Fourier transform (FFT) to separate the sub-carrier, and completing the OFDM demodulation.

[0009] The embodiment of the present application provides a QAM-OFDM-based communication device, which comprises a QAM modulator, an OFDM modulation module, an analog-digital converter, an OFDM demodulation module, and a QAM demodulator.

[0010] The embodiment of the present application provides a QAM-OFDM-based communication method and device, which has the following advantages compared with the prior art.

[0011] The original signal is converted into an initial signal using a convolution code, and the initial signal is converted into an analog signal using a QAM modulation technology and an OFDM modulation technology; the analog signal is processed using a power amplifier and a band-pass 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-digital converter, and the original signal is restored using an OFDM demodulation technology and a QAM demodulation technology. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 A QAM-OFDM system block diagram is provided for the embodiment of the present application.

[0013] Figure 2 A flow chart of a QAM-OFDM piezoelectric ultrasonic guided wave communication system provided by an embodiment of the present application is shown in FIG. 1.

[0014] Figure 3 A QAM-OFDM constellation provided by an embodiment of the present application is shown in FIG. 2.

[0015] Figure 4 A QAM-OFDM demodulation result diagram without convolution code and spread spectrum technology provided by an embodiment of the present application is shown in FIG. 3.

[0016] Figure 5 A QAM-OFDM optimized demodulation result diagram with convolution code and spread spectrum technology provided by an embodiment of the present application is shown in FIG. 4.

[0017] Figure 6 A bit error rate comparison diagram under different signal-to-noise ratios provided by an embodiment of the present application is shown in FIG. 5.

[0018] Figure 7 A flow chart provided by an embodiment of the present application is shown in FIG. 6. DETAILED DESCRIPTION

[0019] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a number of ways other than those specifically described herein, and it is to be understood that the present application is not limited to the specific embodiments disclosed, but is open to equivalents.

[0020] Reference is made to Figures 1-2 An embodiment of the present application provides a QAM-OFDM-based communication method, including the following steps:

[0021] Step one: obtaining a to-be-sent signal as an original signal through a transmitting end, the to-be-sent signal being an ultrasonic guided wave signal excited by a piezoelectric material.

[0022] Step two: obtaining an initial signal by using convolution code on the original signal, converting the initial signal into a modulated signal by using QAM modulation technology, converting the modulated signal into an analog signal by using OFDM modulation technology, and processing the analog signal by using a spread spectrum technology; and processing the spread spectrum analog signal by using a power amplifier and a band-pass filter.

[0023] Wherein, using OFDM modulation technology to convert the modulated signal into analog signal, including: using sub-carrier mapping to convert the modulated signal, and using inverse fast Fourier transform IFFT to generate a plurality of sub-carrier signals; adding cyclic prefix CP to the plurality of sub-carrier signals and converting them into analog signals. The converted signals are demodulated using OFDM demodulation technology, including: removing the cyclic prefix CP in the converted signals, converting them from time domain to frequency domain through fast Fourier transform FFT, completing the separation of sub-carriers; demodulating the QAM symbols on each sub-carrier to recover the original signal (original bit stream).

[0024] Step three: receiving the processed analog signal transmitted by the steel rail channel through the receiving end; converting the received signal using an analog-to-digital converter, and demodulating the converted signal using OFDM demodulation technology, and restoring the original signal using QAM demodulation technology.

[0025] The application uses piezoelectric ultrasonic guided waves as a communication medium and combines OFDM technology to encode and transmit signals. OFDM technology divides the wideband signal into multiple sub-carriers for transmission, effectively reducing the influence of multipath effect and frequency selective fading on the signal. By exciting and receiving ultrasonic guided wave signals through piezoelectric sensors and using OFDM technology for modulation and demodulation, long-distance signal transmission is achieved.

[0026] I. System architecture.

[0027] The system architecture of the application mainly consists of an ultrasonic sensor, an OFDM modulation and demodulation module, a signal processing unit and a receiving device (as shown in Figure 1

[0028] Ultrasonic sensor: used for exciting and receiving piezoelectric ultrasonic guided wave signals in the steel rail.

[0029] OFDM modulation and demodulation module: in the transmitting end, the OFDM module modulates the ultrasonic guided wave signal, and the modulated signal is transmitted to the receiving end. The receiving end demodulates the received signal to recover the original data.

[0030] Signal processing unit: used for denoising, amplifying and filtering the received signal to improve the quality of the signal.

[0031] Receiving device: used for receiving and demodulating ultrasonic guided wave signals to finally realize long-distance transmission of data.

[0032] II. Key technologies.

[0033] 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 steel rail state monitoring. ​

[0034] OFDM signal modulation and demodulation technology: OFDM is used for efficient coding of signals, making it difficult for transmission signals to be attenuated in long distances.

[0035] Signal attenuation compensation and enhancement technology: In view of the problem of signal attenuation in long-distance transmission, a signal enhancement algorithm is used to compensate the received signal. Among them, the signal enhancement algorithm refers to a received signal compensation technology based on the combination of mean square error (MSE) equalization algorithm and Turbo coding and decoding mechanism. The algorithm is not to amplify the signal amplitude in the traditional sense, but to enhance the reliability and recoverability of the received signal at the logic level to cope with the attenuation, distortion and error problems in long-distance multipath transmission environment. Therefore, the signal enhancement algorithm for compensating the received signal specifically refers to: using the frequency domain equalization algorithm based on the mean square error (MSE) criterion, combining the Turbo coding and decoding mechanism, compensating the error and enhancing the quality of the received signal, and improving the information recovery ability of the system in complex channel conditions.

[0036] Third, the structure of the present application is as follows:

[0037] (1) Transmitter:

[0038] Data input (DATA): The transmitted data is input to the QAM modulator.

[0039] QAM modulator: Convert the input digital data into modulation symbols, which will be frequency division multiplexed in the OFDM system.

[0040] S / P conversion: Convert serial data to parallel data for subsequent processing.

[0041] IFFT (Inverse Fast Fourier Transform): Convert the frequency domain signal back to the time domain signal, and use IFFT to generate multiple subcarrier signals.

[0042] Add CP: Add a cyclic prefix (CP) before the OFDM symbol to mitigate the effects of multipath propagation.

[0043] P / S conversion: Convert parallel data back to serial data for DAC conversion to analog signals.

[0044] DAC (Digital-to-Analog Converter): Convert digital signals to analog signals, amplify the ultrasonic guided wave signal through a signal amplifier, and ensure that the signal strength is sufficient for long-distance transmission in the rail.

[0045] (2) Receiver:

[0046] Received signal (rail channel): The receiving end receives the signal transmitted through the rail channel. As the rail channel serves as the propagation medium, the signal will be affected by attenuation and noise during transmission due to the physical characteristics of the rail.

[0047] ADC (Analog-to-Digital Converter): Converts the received analog signal into a digital signal for subsequent processing.

[0048] S / P conversion: Converts serial data into parallel data to facilitate FFT operation.

[0049] Remove CP (Remove Cyclic Prefix): Removes the cyclic prefix in the received signal to facilitate subsequent signal recovery.

[0050] FFT (Fast Fourier Transform): Converts time-domain signals into frequency-domain signals for subcarrier separation.

[0051] P / S conversion (P / S): Converts parallel data back to serial data to prepare for QAM demodulation.

[0052] QAM demodulator (QAM demodulator): Demodulates frequency-domain signals into original data to recover transmitted digital data.

[0053] In the environment of the rail channel, the OFDM system can effectively combat the effects of multipath propagation and attenuation by introducing a cyclic prefix and frequency-domain processing, while using FFT and QAM demodulation techniques to recover transmitted data Figure 4 ), ensuring efficient and reliable data transmission.

[0054] Key technical parameters of the structure:

[0055] OFDM parameters: Number of subcarriers: Typically choose 64, 128, or 256 subcarriers according to rail communication requirements. Modulation method: 4-QAM, 16-QAM, or 64-QAM, dynamically adjusted according to channel conditions. Bandwidth: Choose an appropriate frequency band (such as 34 kHz to 35 kHz) according to the ultrasonic guided wave propagation characteristics of the rail.

[0056] Ultrasonic guided wave parameters: Frequency range: 34 kHz to 35 kHz, ensuring low attenuation characteristics during transmission in the rail. Propagation distance: Single transmission can reach several kilometers, and can be further extended through relay nodes. Piezoelectric transducer sensitivity: Ensures the conversion efficiency of transmitted and received signals.

[0057] The effects of this structure are as follows:

[0058] (1) Efficient transmission: OFDM technology uses multiple orthogonal subcarriers to transmit data, improving spectral efficiency and enabling data transmission in the rail.

[0059] (2) Strong anti-interference capability: When ultrasonic guided waves propagate in the steel rail, they are less affected by external electromagnetic interference, ensuring the stability of communication.

[0060] Long-distance transmission: By combining signal amplifiers and OFDM technology, ultrasonic guided wave signals can be transmitted several kilometers in the steel rail without significant attenuation. As shown in Figures 3-5 , the relevant results using QAM-OFDM.

[0061] To further improve the performance of the QAM-OFDM system, spread spectrum technology and convolutional codes can be introduced. Spread spectrum disperses information energy over a wider frequency spectrum by increasing signal bandwidth, thereby improving anti-interference capability and reducing the impact of narrowband interference and multipath fading. Convolutional codes, as forward error correction coding (FEC), enable the receiving end to correctly recover data in a low signal-to-noise ratio (SNR) environment by adding redundant bits, effectively reducing the bit error rate (BER). The combination of the two not only improves the anti-noise capability and data reliability, but also enhances the robustness of the system, making QAM-OFDM more suitable for complex wireless environments (such as 5G, satellite communication, military communication, etc.).

[0062] From Figure 6 , it can be seen that spread spectrum reduces BER, but the effect is limited at high SNR. At low SNR (0~4dB), the red curve drops faster, indicating that spread spectrum enhances the robustness of the signal. However, after SNR>4dB, the BER of the red curve slows down, indicating that the use of spread spectrum alone has limited improvement at high SNR. However, convolutional code + spread spectrum is better than spread spectrum alone (blue curve is always lower than red curve) throughout the entire SNR range, especially when SNR>4dB, the BER is significantly reduced. This shows that convolutional codes are still effective in low error rate scenarios and can further reduce BER. Therefore, the combination of the two can maximize the reduction of error rate and improve the transmission quality of QAM-OFDM.

[0063] Four, the key point of the present application is:

[0064] (1) Adopting orthogonal frequency division multiplexing (OFDM) technology to modulate and demodulate ultrasonic guided wave signals. Through the frequency multiplexing characteristics of OFDM, the multipath effect and signal attenuation can be effectively reduced, and the transmission quality and stability of ultrasonic guided wave signals in long-distance steel rails can be improved.

[0065] (2) Utilizing the piezoelectric effect of piezoelectric materials, ultrasonic guided wave sensors are used to excite and receive ultrasonic guided wave signals in the steel rail, ensuring the accuracy and efficiency of the signals. This method effectively solves the attenuation and noise problems of traditional ultrasonic guided wave technology in long-distance monitoring of steel rails.

[0066] (3) For the problem of signal attenuation in long-distance transmission, the application introduces a signal enhancement algorithm based on OFDM, and combines the signal processing unit to perform denoising and amplification processing on the received signal, further improving the transmission effect of the signal.

[0067] (4) The application combines the advantages of OFDM technology and ultrasonic guided wave transmission, significantly improves the reliability of long-distance rail monitoring, has low power consumption and long transmission distance, and is suitable for railway fault detection and long-term monitoring.

[0068] The application 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 of traditional ultrasonic guided wave technology in long-distance rail detection.

[0069] The effect of the application is:

[0070] (1) Significantly improve the long-distance transmission effect.

[0071] The application adopts an ultrasonic guided wave signal transmission method based on OFDM, which effectively overcomes the signal attenuation problem faced by traditional ultrasonic guided wave technology in long-distance rail monitoring. Through OFDM technology, the signal is divided into multiple subcarriers for transmission, reducing the interference of multipath effect, significantly improving the transmission stability and distance of the signal, so that the ultrasonic guided wave signal can be reliably transmitted on a longer rail.

[0072] (2) Enhance anti-interference and anti-attenuation.

[0073] Traditional ultrasonic guided wave signals are easily affected by noise and attenuation in long-distance transmission. The application effectively enhances the anti-interference ability of the system by introducing OFDM technology. The frequency multiplexing characteristics and diversity receiver mechanism of OFDM technology make the signal have stronger robustness in complex environments (such as multipath propagation and frequency selective fading), ensuring accurate transmission of data.

[0074] (3) Improve the reliability of signal transmission.

[0075] After adopting OFDM modulation and demodulation technology, the signal can still maintain high reliability in poor transmission environment. Especially in the process of long-distance rail monitoring, the system can effectively reduce transmission errors through accurate signal modulation and demodulation algorithms, ensuring high fidelity and low error rate of ultrasonic guided wave signals, thereby improving the overall reliability of the system.

[0076] (4) Effectively solve the power consumption problem in rail monitoring.

[0077] The OFDM technology in the application enables higher transmission efficiency of signals during long-distance transmission, and compared with the traditional single-carrier communication mode, it can realize long-distance communication under lower power consumption, thereby greatly prolonging the service life of the device and reducing the energy consumption of the system, and is particularly suitable for railway equipment that needs long-term monitoring.

[0078] (5) Strong adaptability, suitable for complex railway environment.

[0079] The application can work efficiently in a complex railway environment, including monitoring different positions on the rail and detecting different types of rail defects. Due to the flexibility and adaptability of the OFDM technology, it can achieve higher signal transmission quality in different rail structures and transmission environments, thereby improving the diversity and applicability of the railway detection system.

[0080] (6) Improve the accuracy of rail fault detection.

[0081] The ultrasonic guided wave communication method of the application introduces OFDM technology, so that the ultrasonic guided wave signal can be transmitted to the receiving end with higher quality, thereby improving the accuracy of rail fault detection. Through efficient transmission of ultrasonic guided waves, the state of the rail can be monitored in real time, potential faults or hidden dangers can be found in time, and maintenance cost and time are reduced, thereby improving the safety of railway transportation.

[0082] (7) Reduce system cost.

[0083] Since the application can directly integrate OFDM and piezoelectric ultrasonic guided wave sensors in the existing rail monitoring system, the need for additional equipment and complex system architecture is reduced. Compared with the traditional technology, the application not only improves the performance, but also reduces the hardware investment and maintenance cost, thereby improving the overall system performance.

[0084] The embodiment of the application provides a communication device based on QAM-OFDM, which comprises:

[0085] The QAM modulator, the OFDM modulation module, the analog-to-digital converter, the OFDM demodulation module, and the QAM demodulator are connected in communication. The output end of the QAM modulator is connected to the input end of the OFDM modulation module. The input end of the analog-to-digital converter receives signals from the output end of the OFDM modulation module transmitted through the rail channel. The output end of the analog-to-digital converter is connected to the input end of the OFDM demodulation module. The output end of the OFDM demodulation module is connected to the input end of the QAM demodulator.

[0086] One specific embodiment is as follows:

[0087] The embodiment discloses a communication method based on QAM-OFDM, and the specific steps are as follows:

[0088] S1, obtaining an original signal.

[0089] S2, obtaining an initial signal using a convolution code on the original signal, converting the initial signal into a modulated signal using a QAM modulation technique, and converting the modulated signal into an analog signal using an OFDM modulation technique; processing the analog signal using a spread spectrum technique, and processing the spread spectrum analog signal using a power amplifier and a bandpass filter.

[0090] S3, receiving the signal-processed analog signal transmitted by the rail channel; converting the received signal using an analog-to-digital converter, demodulating the converted signal using an OFDM demodulation technique, and restoring the original signal using a QAM demodulation technique, as shown in the flowchart. Figure 7

[0091] The application scenarios of the present application are extended:

[0092] (1) Railway safety monitoring: using the present application to monitor the rail state (such as cracks, stress, temperature) in real time, and transmitting data to the control center to realize railway safety warning.

[0093] (2) Train positioning and communication: in environments with weak GPRS signals such as tunnels and mountainous areas, precise positioning and communication of trains are realized through rail communication.

[0094] (3) Intelligent railway system: applying the present application to the intelligent railway system to realize efficient data interaction between trains and the ground control center, supporting automatic driving and intelligent scheduling.

[0095] The following contents need to be paid attention to in the technical implementation:

[0096] (1) Installation of piezoelectric transducer: ensure the close contact of the piezoelectric transducer with the rail to avoid signal loss.

[0097] (2) Signal interference suppression: other ultrasonic signals (such as train wheel-rail noise) may exist in the rail, and a filter needs to be designed to suppress interference.

[0098] (3) Environmental adaptability: consider the ultrasonic guided wave propagation characteristics of the rail in different environments (such as high temperature, low temperature, and humidity) to optimize system design.

[0099] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.​

Claims

1. A method of QAM-OFDM based communication, characterized in that, The method comprises the following steps: An original signal is obtained by a transmitting end as a to-be-sent signal, which is an ultrasonic guided wave signal excited by piezoelectric material; An initial signal is obtained by using convolution code on the original signal, and the initial signal is converted into a modulated signal by using QAM modulation technology, and the modulated signal is converted into an analog signal by using OFDM modulation technology; the analog signal is processed by using a power amplifier and a band-pass filter; The modulated signal is converted into an analog signal by using OFDM modulation technology, and the specific steps include: The modulated signal is mapped by using a sub-carrier, and a plurality of sub-carrier signals are generated by using inverse fast Fourier transform (IFFT); The plurality of sub-carrier signals are added with a cyclic prefix (CP) and converted into an analog signal; The processed analog signal is transmitted through a rail channel; The processed analog signal transmitted by the rail channel is received by a receiving end; the received signal is converted by using an analog-to-digital converter, and the converted signal is demodulated by using OFDM demodulation technology; and the demodulated signal is restored into an original signal by using QAM demodulation technology; The converted signal is demodulated by using OFDM demodulation technology, and the specific steps include: The cyclic prefix (CP) in the converted signal is removed; The converted signal from which the cyclic prefix (CP) is removed is converted from a time domain to a frequency domain by using fast Fourier transform (FFT), and a sub-carrier is separated, thereby completing OFDM demodulation.

2. The QAM-OFDM based communication method of claim 1, wherein, Before the received signal is converted by using an analog-to-digital converter, the following step is further included: The analog signal processed by using a power amplifier and a band-pass filter is processed again.

3. A communication apparatus for performing the QAM-OFDM based communication method according to claim 1, characterized in that, The method comprises the following steps: A QAM modulator, an OFDM modulation module, an analog-to-digital converter, an OFDM demodulation module, and a QAM demodulator are provided, the output end of the QAM modulator is in communication connection with 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 in communication connection with the input end of the OFDM demodulation module, and the output end of the OFDM demodulation module is in communication connection with the input end of the QAM demodulator.

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