Mobile phone audio signal data communication method and system

Abstract

The application relates to the technical field of communication, and particularly discloses a mobile phone audio signal data communication method, which mainly comprises the following steps: a sending end generates a baseband signal containing a chirp signal preamble, collects environmental noise and receives feedback channel state information, dynamically selects optimal modulation and coding parameters and a frequency hopping pattern according to the baseband signal, and finally converts the signal to an ultrasonic frequency band and transmits the signal through a loudspeaker; a receiving end receives the signal through a special piezoelectric ceramic sensor, performs frequency conversion, uses the chirp signal to complete synchronization and channel estimation, compensates distortion by using a hybrid adaptive equalization algorithm, finally demodulates and decodes output data, and feeds back channel state information to the sending end to form a closed-loop adaptive control. By combining software and hardware and adopting a closed-loop adaptive mechanism, the application effectively overcomes the influences of multipath, noise and Doppler, realizes stable, reliable and manual configuration-free data communication in a complex environment, and provides excellent user experience.

Description

Technical Field

[0001] This invention relates to the field of communication technology, specifically to a method and system for mobile phone audio signal data communication. Background Technology

[0002] As smartphones become more powerful and cheaper, current short-range data communication based on smartphones mainly relies on technologies such as Bluetooth, Wi-Fi, NFC, or QR codes.

[0003] Currently, Chinese patent application number CN201610487156.6 discloses a real-time communication method for smartphones based on covert audio signals. This method involves eight steps: designing signals using orthogonal frequency division multiplexing (OFDM), determining subcarrier modulation methods, analyzing the original audio signal to determine suitable locations for embedding data packets, adaptively embedding data signals, packet header detection, channel estimation, signal extraction, and data correction. By utilizing the masking effect of human hearing and readily available audio signals in daily life, this method achieves real-time, non-obvious speaker-microphone covert communication while ensuring that the human ear's audio listening experience on the main channel is not affected.

[0004] However, existing communication methods operate in the audible frequency band, making it difficult to avoid interference from environmental speech and noise, and their performance depends on the characteristics of the main audio signal. In scenarios with strong multipath reflection, sudden noise, or equipment movement, communication reliability drops significantly. Furthermore, existing communication methods lack closed-loop adaptive mechanisms and dedicated hardware support for time-varying channels, making it difficult to guarantee stable communication quality in complex acoustic environments. Summary of the Invention

[0005] The purpose of this invention is to provide a mobile phone audio signal data communication method and system to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a mobile phone audio signal data communication method, comprising the following steps: S1. The transmitting device generates a baseband signal, which includes a chirped preamble for channel estimation and symbol synchronization, and an effective data payload. S2. The transmitting end collects the current ambient audio noise and analyzes its spectral characteristics. At the same time, it receives channel state information feedback from the receiving end based on the previous communication. The channel state information includes at least the signal-to-noise ratio (SNR) and frequency response. S3. Based on the spectrum of the ambient audio noise and the channel state information, dynamically select the optimal modulation constellation diagram, symbol rate and forward error correction (FEC) coding rate from the predefined modulation and coding scheme (MCS) lookup table, and use the selected parameters to modulate and code the baseband signal. S4. The modulated and encoded signal is upconverted to the 18kHz-24kHz ultrasonic frequency band that is insensitive to the human ear, and after digital-to-analog conversion and power amplification, it is transmitted as a sound wave signal through the mobile phone speaker; S5. The receiving device receives the acoustic signal through a wide-frequency response piezoelectric ceramic sensor, converts it into an electrical signal, and then performs down-conversion and adaptive equalization on the electrical signal; wherein, the high time-frequency resolution characteristics of the chirped signal preamble are used to perform accurate multipath delay and Doppler frequency offset estimation, and a time-domain equalizer is constructed. S6. Based on the modulation and coding scheme identifier carried by the transmitting end in the data frame, demodulate and decode the equalized signal, then output the decoded data, and extract the channel state information of this communication from the decoded data, encapsulate it into the feedback frame, and use it for adaptive adjustment in the next communication.

[0007] Preferably, the selection strategy for the predefined modulation and coding scheme (MCS) lookup table mentioned in step S3 is as follows: A lookup table is established with the estimated channel capacity as an index. The estimated channel capacity is calculated from the signal-to-noise ratio (SNR) fed back by the receiver and the ambient audio noise spectrum collected by the transmitter. For each channel capacity interval, it is mapped to an optimal modulation and coding combination that maximizes spectral efficiency at the target bit error rate.

[0008] Preferably, the calculation strategy for the combination is as follows: The estimated capacity C of the current channel is calculated using the formula: C = B log2(1 + SNR), where B is the available bandwidth and SNR is the signal-to-noise ratio estimate; The estimated capacity C is compared with the preset capacity range in the lookup table, and the modulation and coding combination with the highest spectral efficiency that meets the target frame error rate requirement within that range is selected.

[0009] Preferably, step S4 further includes: the transmitting end and the receiving end synchronously switch between multiple discontinuous ultrasonic frequency bands according to a preset frequency hopping pattern. The selection of the frequency hopping pattern depends on the ambient audio noise spectrum analyzed in step S2, and the frequency band with the lowest noise power is preferentially selected as the dwell frequency point.

[0010] Preferably, the adaptive equalization process in step S5 adopts a hybrid adaptive equalization algorithm that combines the decision-guided constant modulus algorithm with the recursive least squares algorithm. In the training sequence stage, the recursive least squares (RLS) algorithm is used to converge quickly, and in the data segment, the constant modulus (CMA) algorithm is switched to track the time-varying characteristics of the channel.

[0011] In addition, the present invention also provides a mobile phone audio signal data communication system for implementing the above method, which includes a transmitting terminal and a receiving terminal, wherein the transmitting terminal and the receiving terminal establish a bidirectional communication link through an acoustic channel for transmitting service data and the channel status information; The transmitting terminal includes: a signal generation and adaptive modulation module; an environmental noise acquisition module for acquiring ambient sound through a mobile phone microphone; and an ultrasonic transducer drive module. The receiving terminal includes a piezoelectric ceramic sensor, a signal conditioning and acquisition module, an adaptive equalization and demodulation decoding module, and a channel state information extraction and feedback generation module.

[0012] Preferably, the piezoelectric ceramic sensor includes: The outer shell is made of acoustic damping material and has an acoustic inlet. A multilayer composite piezoelectric sensing unit is disposed inside the housing and is used to generate a corresponding charge signal in response to an acoustic wave signal. The multilayer composite piezoelectric sensing unit is composed of at least two layers of piezoelectric ceramic sheets with different inherent resonant frequencies stacked together. The piezoelectric ceramic sheets of the multilayer composite piezoelectric sensing unit are connected in mechanical series and electrical parallel. An impedance matching circuit, which is electrically connected to the multilayer composite piezoelectric sensing unit, is used to convert a high-impedance charge signal into a low-impedance voltage signal. A signal output interface is used to transmit the voltage signal to the microphone input terminal of the mobile phone's audio interface.

[0013] Preferably, the impedance matching circuit is an active matching circuit with frequency selectivity, whose transfer function is opposite to the impedance frequency characteristic of the multilayer composite piezoelectric sensing unit, which is used to further flatten the overall frequency response curve and increase the output voltage of high-frequency signals.

[0014] Preferably, the interior of the outer shell is filled with sound-absorbing cotton to suppress sound resonance and cavity effect inside the outer shell, and to avoid interference with the frequency response of the received signal.

[0015] Preferably, the at least two layers of piezoelectric ceramic sheets with different inherent resonant frequencies include a high-frequency piezoelectric ceramic sheet and a low-frequency piezoelectric ceramic sheet. The resonant frequency of the high-frequency piezoelectric ceramic sheet is located at 15kHz-20kHz, and the resonant frequency of the low-frequency piezoelectric ceramic sheet is located at 8kHz-12kHz. The layers are superimposed to extend the flatness of the overall frequency response curve.

[0016] Preferably, the acoustic entrance of the housing is further provided with a waterproof and dustproof acoustic mesh cover, and a miniature acoustic damping tube is provided behind it to attenuate ambient noise below 8kHz and balance the sound pressure to protect the internal multilayer composite piezoelectric sensing unit.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention dynamically avoids interference and selects optimal transmission parameters by combining real-time spectrum sensing of environmental noise at the transmitting end, channel state information fed back by the receiving end, and intelligent frequency hopping technology. At the same time, it effectively overcomes signal distortion caused by multipath effect and Doppler frequency offset by using chirped signal preamble and hybrid adaptive equalization algorithm. Through the combination of hardware and software mechanism, the system can still maintain stable and reliable data transmission in complex indoor environments full of noise, reflections and dynamic changes.

[0018] This invention transmits signals by modulating them in the ultrasonic frequency band, which is insensitive to the human ear. This avoids auditory interference with users and improves comfort. It also cleverly utilizes the existing speaker and microphone of the mobile phone as the transceiver. The receiving end does not require users to manually pair or connect to the network, realizing "plug and play" automated operation, which greatly simplifies the interaction process and provides users with a convenient and discreet information acquisition experience.

[0019] This invention establishes an ultrasonic feedback channel from the receiver to the transmitter, using the evaluation of the effect of each communication as the basis for decision-making for the next transmission, forming a complete closed-loop control. Furthermore, it can continuously and autonomously optimize its modulation, coding, and frequency band selection strategies based on the latest channel conditions and environmental information, thereby enabling continuous improvement in communication performance in constantly changing real-world application scenarios, and possessing strong self-learning and adaptive capabilities. Attached Figure Description

[0020] Figure 1 This is a flowchart of the communication method of the present invention; Figure 2 This is a schematic diagram of the structure of the piezoelectric ceramic sensor of the present invention; Figure 3 This is a flowchart illustrating the workflow of the receiving end of the present invention. Figure 4 This is a flowchart illustrating the workflow of the transmitting end of the present invention. Figure 5 This is a schematic diagram illustrating the implementation process of an embodiment of the present invention.

[0021] In the diagram: housing-1, multilayer composite piezoelectric sensing unit-2, impedance matching circuit-3, signal output interface-4, acoustic inlet-11. Detailed Implementation

[0022] To further explain the technical solution of the present invention, a detailed description is provided below through specific embodiments.

[0023] Please see Figure 1 This invention provides a method for mobile phone audio signal data communication, comprising the following steps: First, the transmitting device generates a baseband signal, which includes a chirped preamble for channel estimation and symbol synchronization, as well as an effective data payload. A linear frequency modulated chirped signal is used as the preamble, which utilizes its excellent autocorrelation characteristics to achieve fast and robust symbol timing synchronization in acoustic channels with significant multipath effects, and provides a foundation for subsequent high-precision channel estimation.

[0024] Second, the transmitting end collects the current ambient audio noise and analyzes its spectral characteristics. At the same time, it receives channel state information feedback from the receiving end based on the previous communication. The channel state information includes at least the signal-to-noise ratio (SNR) and frequency response. By collecting noise through the local microphone, the transmitting end realizes the perception of the transmission environment, and by receiving feedback, the transmitting end realizes the perception of the transmission channel state, providing real-time and comprehensive input basis for the next step of intelligent decision-making.

[0025] Third, based on the spectrum and channel state information of ambient audio noise, the optimal modulation constellation diagram, symbol rate, and forward error correction (FEC) coding rate are dynamically selected from the predefined modulation and coding scheme (MCS) lookup table. The selected parameters are then used to modulate and code the baseband signal. When the signal-to-noise ratio (SNR) is high, higher-order modulation and higher code rate are selected to increase the rate; when the SNR is low, lower-order modulation and strong error correction coding are selected to ensure reliability. This ensures that communication performance is always optimized in complex and ever-changing sound environments. The predefined modulation and coding scheme (MCS) lookup table includes a selection strategy as follows: A lookup table indexed by the estimated channel capacity is established. The estimated channel capacity is calculated from the signal-to-noise ratio (SNR) fed back from the receiver and the ambient audio noise spectrum collected by the transmitter. For each channel capacity interval, an optimal modulation and coding combination is mapped to maximize the spectral efficiency at the target bit error rate. The calculation strategy for this combination is as follows: (1) Calculate the estimated capacity C of the current channel (unit: bps). The calculation formula is: C = B log2(1 + SNR), where B is the available channel bandwidth (unit: Hz) obtained from the ambient audio noise spectrum analysis, and SNR is the signal-to-noise ratio (linear value, not decibel value) fed back by the receiver. (2) Compare the calculated real-time capacity C with the preset capacity range in the lookup table, and select the modulation and coding combination with the highest spectral efficiency that meets the target frame error rate requirement within the range, so as to approximate the maximum transmission capacity under the current channel conditions to the greatest extent.

[0026] Fourth, the modulated and encoded signal is upconverted to the 18kHz-24kHz ultrasonic frequency band, which is insensitive to the human ear. After digital-to-analog conversion (DAC) and power amplification (PA), it is transmitted as a sound wave signal through the mobile phone speaker. This avoids the rich environmental noise and voice interference in the audible frequency band (20Hz-20kHz), greatly improves the signal-to-noise ratio, and avoids the annoyance of audible sound, resulting in a better user experience. Furthermore, the transmitting and receiving ends synchronously switch between multiple discontinuous ultrasonic frequency bands according to the preset frequency hopping pattern. The selection of the frequency hopping pattern depends on the ambient audio noise spectrum analyzed in step S2. The frequency band with the lowest noise power is selected as the dwell frequency point. The "clean" frequency band is intelligently selected through spectrum sensing. Combined with pseudo-random switching, it can effectively avoid sudden narrowband interference (such as keyboard sounds and ringtones) and frequency selective fading, which greatly enhances the stability and robustness of the system.

[0027] Fifth, the receiving device receives the acoustic signal through a wide-frequency response piezoelectric ceramic sensor, converts it into an electrical signal, and then performs down-conversion and adaptive equalization on the electrical signal. It utilizes the high time-frequency resolution characteristics of the chirped signal preamble to accurately estimate the multipath delay and Doppler frequency offset, and constructs a time-domain equalizer. Among them, due to the severe multipath effect in acoustic channels and the Doppler frequency shift caused by slight movement of equipment, these parameters can be accurately estimated using chirped signals, providing accurate prior information for the equalizer, thereby constructing an inverse filter that can effectively compensate for channel distortion. The adaptive equalization process employs a hybrid adaptive equalization algorithm that combines the decision-guided constant modulus algorithm (CMA) with the recursive least squares algorithm (RLS). The RLS algorithm is used for fast convergence during the training sequence (preamble) stage, and the CMA algorithm is switched to the data segment to track the time-varying characteristics of the channel. RLS utilizes known training sequences to quickly converge the equalizer coefficients to an optimal state. Subsequently, CMA can continue to track slow channel changes caused by environmental changes (such as equipment movement) even without training sequences, ensuring continuous high-performance equalization throughout the entire data packet transmission.

[0028] Sixth, based on the modulation and coding scheme identifier carried by the transmitter in the data frame, the equalized signal is demodulated and decoded, and then the decoded data is output. The channel state information of this communication (such as the bit error rate of this transmission and the re-estimated channel response) is extracted from the decoded data and encapsulated into a feedback frame for adaptive adjustment in the next communication. This allows the effect evaluation of this communication to be fed back to the transmitter, enabling it to make better decisions for the next transmission based on the latest channel information, thus forming a continuously self-optimizing intelligent communication system.

[0029] Please see Figures 1-3 The present invention provides a mobile phone audio signal data communication system for implementing the above method and materializing the above method process. It includes a transmitting terminal and a receiving terminal. The transmitting terminal and the receiving terminal establish a bidirectional communication link through an acoustic channel for transmitting service data and channel status information. The transmitting terminal includes: a signal generation and adaptive modulation module; an environmental noise acquisition module for acquiring ambient sound via a mobile phone microphone; and an ultrasonic transducer drive module. The receiving terminal includes a piezoelectric ceramic sensor, a signal conditioning and acquisition module, an adaptive equalization and demodulation decoding module, and a channel state information extraction and feedback generation module.

[0030] Among them, piezoelectric ceramic sensors include: The housing 1 is made of acoustic damping material and is filled with sound-absorbing cotton to suppress sound resonance and cavity effect inside the housing 1, so as to avoid interference with the frequency response of the received signal. The housing 1 is provided with an acoustic inlet 11. The acoustic damping material and sound-absorbing cotton can effectively absorb the sound waves reflected inside the housing 1, prevent the formation of standing waves and resonance cavities, thereby avoiding these mechanical resonance points from distorting the frequency response curve of the sensor and ensuring the authenticity of the received signal. The multilayer composite piezoelectric sensing unit 2 is disposed inside the housing 1 and is used to generate a corresponding charge signal in response to the sound wave signal. The multilayer composite piezoelectric sensing unit 2 is composed of at least two layers of piezoelectric ceramic sheets with different inherent resonant frequencies, which broadens the overall operating frequency band. Moreover, the piezoelectric ceramic sheets of the multilayer composite piezoelectric sensing unit 2 are connected in mechanical series and electrical parallel, which ensures the consistency of vibration, and the output current is superimposed through electrical parallel connection to improve the overall sensitivity. Impedance matching circuit 3, which is electrically connected to multilayer composite piezoelectric sensing unit 2, is used to convert high-impedance charge signals into low-impedance voltage signals to facilitate transmission and acquisition and reduce signal loss. Signal output interface 4 is used to transmit voltage signals to the microphone input terminal of the mobile phone audio interface.

[0031] Among them, the impedance matching circuit 3 is an active matching circuit with frequency selectivity. Its transfer function is opposite to the impedance frequency characteristic of the multilayer composite piezoelectric sensing unit 2. It is used to further flatten the overall frequency response curve and increase the output voltage of the high-frequency signal. In order to make the final output voltage signal have a highly flat response in the entire working frequency band through the "peak shaving and valley filling" method, it provides a high-quality premise for subsequent signal processing. At least two layers of piezoelectric ceramic sheets with different inherent resonant frequencies include a high-frequency piezoelectric ceramic sheet and a low-frequency piezoelectric ceramic sheet. The resonant frequency of the high-frequency piezoelectric ceramic sheet is located at 19kHz±1kHz, and the resonant frequency of the low-frequency piezoelectric ceramic sheet is located at 10kHz±1kHz. By superimposing them, the flatness of the overall frequency response curve is extended, ensuring the best and flat sensitivity performance in the target frequency band. A waterproof and dustproof acoustic mesh is also provided at the acoustic inlet 11 of the outer casing 1. Behind it is a miniature acoustic damping tube, which is used to attenuate ambient noise below 8kHz and balance the sound pressure to protect the internal multilayer composite piezoelectric sensing unit 2. The miniature acoustic damping tube performs a pre-filter at the physical level, which significantly reduces the possibility of strong low-frequency noise interfering with the subsequent circuit and the risk of overload, playing a dual role in protecting the sensor and improving the signal-to-noise ratio.

[0032] Example: Scenario Description: A shopping mall is holding a promotional event, and the merchant wants to push electronic coupon information to the mobile phones of nearby customers. Traditional Bluetooth or Wi-Fi connections require users to manually pair or connect to the network, which is a cumbersome process. However, using this invention, the merchant can use one mobile phone as the sending terminal, and customers only need to use another mobile phone with a specific receiving application installed and connected to the piezoelectric ceramic sensor described in this invention as the receiving terminal to automatically complete the data transmission.

[0033] Implementation process: 1. Initialization and Signal Generation: The merchant's mobile phone (sender) launches the application, preparing to send coupon data. First, the sender's signal and adaptive modulation module generate a baseband signal frame. This frame uses a linear frequency chirped signal as a preamble, followed by a frame header containing a data packet type identifier, an identifier of the modulation and coding scheme used for subsequent data, and the final coupon information payload. 2. Environmental Awareness and Decision-Making: The environmental noise acquisition module at the transmitting end collects ambient audio (such as human voices and background music) in the mall in real time through the phone's built-in microphone. Simultaneously, the transmitting end continuously monitors the channel, waiting to receive feedback signals from any receiving phone. Assuming a customer's phone (receiving end) enters the range and attempts to receive for the first time, the transmitting end has not yet received feedback and will therefore use a conservative default modulation and coding scheme (MCS). At the same time, the transmitting end analyzes the current ambient noise spectrum to prepare for possible frequency-hopping communication.

[0034] 3. Signal Processing and Transmission: The ultrasonic transducer drive module at the transmitting end up-converts the encoded and modulated baseband signal to an ultrasonic frequency band insensitive to human hearing. After digital-to-analog conversion and power amplification, it is continuously broadcast through the mobile phone speaker. Because there are certain fixed narrowband noise sources in the shopping mall's environmental noise spectrum, the transmitting end periodically switches between multiple ultrasonic subbands according to a preset frequency hopping pattern, and intelligently selects to reside longer on the subband with the lowest noise power as shown in the analysis results, in order to maximize signal transmission quality.

[0035] 4. Signal reception and processing: The customer's mobile phone runs a receiving application and is connected to the piezoelectric ceramic sensor of the present invention through an audio interface; the sensor effectively captures the ultrasonic signal from the merchant's mobile phone and converts it into a high-quality electrical signal, thanks to its wide frequency response, high sensitivity and flat amplitude-frequency characteristics. The signal conditioning and acquisition module at the receiving end amplifies, filters, and down-converts the signal to recover the baseband signal. Subsequently, the adaptive equalization and demodulation / decoding module begins operation: first, it uses a unique chirped preamble to achieve precise symbol synchronization and estimates the signal delay spread caused by indoor multipath reflections and the Doppler frequency offset that may be caused by slight movement of the mobile phone; then, it employs a hybrid adaptive equalization algorithm (RLS+CMA) to quickly construct and dynamically adjust the equalizer, effectively compensating for channel distortion and providing a clear and stable signal for subsequent demodulation.

[0036] 5. Decoding and Feedback: The receiving end determines the modulation and coding format used by the sending end based on the identifier in the data frame header, and then correctly demodulates and decodes the signal to successfully restore the coupon information and display it on the customer's mobile phone screen. Meanwhile, the channel state information extraction and feedback generation module at the receiving end extracts key performance information (such as estimated channel frequency response, signal-to-noise ratio, etc.) from the successfully received data packet and encapsulates it into a short feedback frame. Subsequently, the receiving application transmits this feedback information back to the merchant's phone in the form of an ultrasonic signal through the phone's own speaker.

[0037] 6. Closed-loop adaptive formation: After receiving the feedback frame from the customer's mobile phone, the merchant's mobile phone (sender) parses the channel state information in it. Combined with the latest collected ambient audio noise spectrum, the sender queries its MCS lookup table to select a better set of transmission parameters for the next data transmission to the customer's mobile phone (or to other mobile phones under similar channel conditions). For example, if the channel quality is good enough, a higher-order modulation method and a higher coding rate can be selected to improve data transmission efficiency.

[0038] Results: This embodiment demonstrates the application of the present invention in a real, complex environment. Throughout the process, neither party needs to perform any manual configuration, achieving an "instant access" experience. The system ensures reliable data transmission in high-noise, multipath-prone indoor environments by intelligently sensing environmental noise, utilizing ultrasonic frequency band anti-interference, and employing advanced channel estimation and equalization techniques. This enables non-contact, convenient, and stable data communication via sound waves.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for mobile phone audio signal data communication, characterized in that, Includes the following steps: S1. The transmitting device generates a baseband signal, which includes a chirped preamble for channel estimation and symbol synchronization, and an effective data payload. S2. The transmitting end collects the current ambient audio noise and analyzes its spectral characteristics. At the same time, it receives channel state information feedback from the receiving end based on the previous communication. The channel state information includes at least the signal-to-noise ratio (SNR) and frequency response. S3. Based on the spectrum of the ambient audio noise and the channel state information, dynamically select the optimal modulation constellation diagram, symbol rate and forward error correction (FEC) coding rate from the predefined modulation and coding scheme (MCS) lookup table, and use the selected parameters to modulate and code the baseband signal. S4. The modulated and encoded signal is upconverted to the 18kHz-24kHz ultrasonic frequency band, which is insensitive to the human ear. After digital-to-analog conversion and power amplification, it is transmitted as a sound wave signal through the mobile phone speaker. S5. The receiving device receives the acoustic signal through a wide-frequency response piezoelectric ceramic sensor, converts it into an electrical signal, and then performs down-conversion and adaptive equalization on the electrical signal; wherein, the high time-frequency resolution characteristics of the chirped signal preamble are used to perform accurate multipath delay and Doppler frequency offset estimation, and a time-domain equalizer is constructed. S6. Based on the modulation and coding scheme identifier carried by the transmitting end in the data frame, demodulate and decode the equalized signal, then output the decoded data, and extract the channel state information of this communication from the decoded data, encapsulate it into the feedback frame, and use it for adaptive adjustment in the next communication.

2. The mobile phone audio signal data communication method according to claim 1, characterized in that, The selection strategy for the predefined modulation and coding scheme (MCS) lookup table mentioned in step S3 is as follows: A lookup table is established with the estimated channel capacity as an index. The estimated channel capacity is calculated from the signal-to-noise ratio (SNR) fed back by the receiver and the ambient audio noise spectrum collected by the transmitter. For each channel capacity interval, it is mapped to an optimal modulation and coding combination that maximizes spectral efficiency at the target bit error rate.

3. The mobile phone audio signal data communication method according to claim 1, characterized in that, Step S4 also includes: the transmitting end and the receiving end synchronously switch between multiple discontinuous ultrasonic frequency bands according to a preset frequency hopping pattern. The selection of the frequency hopping pattern depends on the ambient audio noise spectrum analyzed in step S2, and the frequency band with the lowest noise power is preferentially selected as the dwell frequency point.

4. The mobile phone audio signal data communication method according to claim 1, characterized in that, The adaptive equalization process described in step S5 adopts a hybrid adaptive equalization algorithm that combines the decision-guided constant modulus algorithm with the recursive least squares algorithm. In the training sequence stage, the recursive least squares (RLS) algorithm is used to converge quickly, and in the data segment, the constant modulus (CMA) algorithm is switched to track the time-varying characteristics of the channel.

5. A mobile phone audio signal data communication system for implementing the method of any one of claims 1-4, characterized in that, It includes a transmitting terminal and a receiving terminal, wherein the transmitting terminal and the receiving terminal establish a two-way communication link through an acoustic channel for transmitting service data and the channel status information; The transmitting terminal includes: a signal generation and adaptive modulation module; an environmental noise acquisition module for acquiring ambient sound through a mobile phone microphone; and an ultrasonic transducer drive module. The receiving terminal includes a piezoelectric ceramic sensor, a signal conditioning and acquisition module, an adaptive equalization and demodulation decoding module, and a channel state information extraction and feedback generation module.

6. The mobile phone audio signal data communication system according to claim 5, characterized in that, The piezoelectric ceramic sensor includes: The outer shell (1) has an acoustic inlet (11) on it; A multilayer composite piezoelectric sensing unit (2) is disposed inside the housing (1) and is used to generate a corresponding charge signal in response to an acoustic signal. The multilayer composite piezoelectric sensing unit (2) is composed of at least two layers of piezoelectric ceramic sheets with different inherent resonant frequencies stacked together. The piezoelectric ceramic sheets of the multilayer composite piezoelectric sensing unit (2) are connected in a mechanical series and an electrical parallel manner. Impedance matching circuit (3), which is electrically connected to the multilayer composite piezoelectric sensing unit (2), is used to convert high-impedance charge signals into low-impedance voltage signals. The signal output interface (4) is used to transmit the voltage signal to the microphone input terminal of the mobile phone audio interface.

7. The mobile phone audio signal data communication system according to claim 6, characterized in that, The impedance matching circuit (3) is an active matching circuit with frequency selectivity. Its transfer function is opposite to the impedance frequency characteristic of the multilayer composite piezoelectric sensing unit (2). It is used to further flatten the overall frequency response curve and increase the output voltage of high-frequency signals.

8. A mobile phone audio signal data communication system according to claim 6, characterized in that: The shell (1) is filled with sound-absorbing cotton to suppress sound resonance and cavity effect inside the shell (1) and avoid interference with the frequency response of the received signal.

9. A mobile phone audio signal data communication system according to claim 6, characterized in that: The at least two layers of piezoelectric ceramic sheets with different inherent resonant frequencies include a high-frequency piezoelectric ceramic sheet and a low-frequency piezoelectric ceramic sheet. The resonant frequency of the high-frequency piezoelectric ceramic sheet is located at 15kHz-20kHz, and the resonant frequency of the low-frequency piezoelectric ceramic sheet is located at 8kHz-12kHz. They are superimposed to expand the flatness of the overall frequency response curve.

10. A mobile phone audio signal data communication system according to claim 6, characterized in that: The acoustic inlet (11) of the outer shell (1) is also provided with a waterproof and dustproof acoustic mesh cover, and a miniature acoustic damping tube is provided behind it to attenuate environmental noise below 8kHz and balance the sound pressure to protect the internal multilayer composite piezoelectric sensing unit (2).

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