Cross-medium wearable audio transmission system and transmission method thereof

Abstract

The invention discloses a cross-medium wearable audio transmission system and a transmission method thereof, which are suitable for audio communication scenes in an air and water body junction environment such as a natatorium. The system comprises a shore transmitting terminal and an underwater receiving earphone, and adopts a blue-green light wave band as a transmission carrier to realize cross-medium wireless transmission of audio signals. The transmitting terminal comprises an audio preprocessing module, a modulation and driving module and a coarse-fine composite light beam alignment module; the receiving earphone comprises an optical receiving module, a posture sensing and aligning module, a signal processing module and a bone conduction audio output unit. According to the system, through a dynamic attitude compensation and light beam alignment mechanism, the audio transmission rate greater than or equal to 1Mbps in a 10-meter range is realized, the error rate is less than or equal to 1 * 10 <-6 >, and the transmission delay is less than 50ms. The method has the advantages of high communication quality, strong anti-interference capability, good wearable performance and the like, and is suitable for scenes of underwater training, voice guidance, immersive audio playing and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of audio communication, in particular to a cross-medium wearable audio transmission system and a transmission method thereof, which is suitable for underwater audio transmission, wearable device communication and other application scenarios. BACKGROUND

[0002] Underwater audio communication is a key supporting technology in scenarios such as swimming training, underwater command transmission and entertainment audio playback. Currently, there are mainly three types of schemes for realizing this function: wired transmission, radio frequency wireless communication and traditional underwater optical communication.

[0003] The first type is a wired audio communication scheme, which usually directly connects the audio source and the underwater earphone through a waterproof earphone cable. This method can provide relatively stable signal quality, but has significant defects: on the one hand, the cable causes drag resistance in water, limiting the freedom of movement of swimmers; on the other hand, the connector sealing structure is prone to failure under long-term water pressure, causing water ingress and short circuit, resulting in a significant increase in the failure rate of the entire machine. Statistics show that the interface failure rate of this type of equipment can exceed 30%.

[0004] The second type is a radio frequency (RF) wireless communication scheme, typically such as a Bluetooth or WiFi audio module. However, due to the high dielectric constant and high electrical conductivity of water, electromagnetic waves are severely attenuated when propagating in water. Taking 2.4 GHz as an example, its attenuation per meter in pool water can exceed 100 dB, resulting in an effective communication distance of less than 0.3 meters, which is difficult to meet the requirements of coverage range and signal continuity in actual applications.

[0005] The third type is a traditional underwater visible light communication (VLC) scheme, which utilizes the low attenuation characteristics of blue-green light in water to achieve high-speed communication over a medium-short distance under certain conditions. However, existing implementation technologies usually have the following bottlenecks:

[0006] 1. Poor adaptability to dynamic attitude changes: During swimming, the swimmer's head undergoes significant yaw and pitch angle changes, resulting in frequent changes in the incident angle between the receiving end and the transmitted light beam, which significantly increases the light link interruption rate.

[0007] 2. Poor robustness to water body disturbances: In a swimming pool environment, the water body is often accompanied by complex disturbances such as bubbles, eddies, suspended particles, etc., which cause non-Gaussian signal distortion in the optical channel, and traditional equalizers cannot effectively compensate for it, resulting in audio stuttering and distortion.

[0008] 3. High requirements for terminal integration and existing solutions are bulky: Some existing systems propose a mechanism of "coarse-fine alignment + optical compensation", but use large servo motors or turntable mechanisms (diameter > 10 cm, power consumption > 5 W), which are difficult to integrate in ear-mounted wearable devices, and cannot meet the actual needs of lightweight, low power consumption and IP68 protection.

[0009] In addition, most of the existing systems lack efficient and low-latency audio processing links, making it difficult to meet the requirements of high-quality experiences such as synchronous voice instructions and immersive playback.

[0010] Therefore, the existing underwater audio transmission technology still has obvious deficiencies in the following aspects:

[0011] Lack of high-speed alignment mechanism suitable for dynamic posture scenarios;

[0012] Lack of hardware structure that balances low power consumption, miniaturization and robustness;

[0013] Insufficient real-time compensation capability for complex underwater channels, making it difficult to guarantee audio quality;

[0014] It is difficult to achieve a good balance between communication distance, bit error rate and delay;

[0015] Not suitable for swimming pools, which are closed, highly reflective and highly disturbed underwater scenarios.

[0016] To address the above problems, a new underwater audio transmission system is needed that can adapt to changes in user motion posture, has high alignment accuracy and channel adaptive capability, and meets the requirements of wearability and practicality, to achieve higher reliability and user experience for cross-media audio communication. SUMMARY

[0017] The purpose of the present application is to overcome the deficiencies of existing underwater audio communication methods in terms of poor posture change adaptability, weak anti-interference capability, and bulky system structure, and to propose a cross-media wearable audio transmission system and method suitable for closed and complex underwater environments such as swimming pools. The system integrates blue-green light communication, dynamic beam alignment mechanism, posture prediction compensation algorithm and low-power wearable structure, achieving stable and high-fidelity audio transmission within 10 meters, bit error rate as low as 1x10 -6 , and transmission delay less than 50ms.

[0018] To achieve the above purpose, the present application provides a series of technical solutions, covering the structure and composition of the system, key functional modules and their cooperative relationship, and including complete audio modulation, posture sensing, beam tracking, signal restoration and other functional links. The following will describe the technical solutions of the present application through multiple possible embodiments.

[0019] In one embodiment of the present application, a cross-medium wearable audio transmission system is provided, including a shore transmitting terminal and an underwater receiving earphone, both of which realize wireless audio transmission in a swimming pool environment through a blue-green light carrier with a wavelength of 450 nm; the shore transmitting terminal includes an audio preprocessing unit, a modulation and driving unit, and a coarse-fine composite axis alignment unit; the underwater receiving earphone includes an optical receiving and alignment unit, a signal processing and audio output unit; the system realizes an audio transmission rate of ≥1 Mbps within a range of 10 meters, a bit error rate ≤1×10 -6 , and a transmission delay less than 50 ms.

[0020] Further, the coarse-fine composite axis alignment unit includes:

[0021] A coarse alignment module: a miniature stepping motor with a step angle of 0.9° is adopted, and the response time is not more than 50 ms, so as to realize preliminary alignment within a field of view of ±30°;

[0022] A fine alignment module: a MEMS mirror with a mirror size of 3 mm×3 mm and a resonant frequency of 1 kHz is integrated, and supports high-precision dynamic adjustment within a range of ±5° with a resolution of 0.01°;

[0023] A control algorithm: a PID algorithm is adopted, and a control quantity is output according to a feedback attitude error signal of the receiving end, and the formula is:

[0024]

[0025] wherein, K p =0.5, K i =0.1, and K d =0.05, so as to ensure that an adjustment overshoot is <5% and a steady-state error is <0.1°.

[0026] Preferably, the modulation and driving unit adopts a QAM-16 modulation mode, loads an audio signal to a 450 nm blue light carrier, and the modulation signal s(t) is expressed as:

[0027]

[0028] wherein, A is a light intensity amplitude (10–50 mW adjustable), s(k) is a modulation symbol sequence, T s =4μs is a symbol period, f0=6.67×10 14 Hz is a carrier frequency, rect(·) is a rectangular window function, t is a time variable, k is a symbol index, and N is a modulation symbol quantity.

[0029] In one embodiment of the present application, the optical receiving and alignment unit includes:

[0030] 4x4 avalanche photodiode (APD) array, single-element responsivity no less than 0.4 A / W, dark current no more than 1 nA;

[0031] Six-axis attitude sensor, sampling rate 1 kHz, range covering ±2000° / s angular velocity and ±16g acceleration;

[0032] Miniature piezoelectric deflection mirror, response time no more than 1 ms, deflection range no less than ±3°;

[0033] Dynamic alignment algorithm uses extended Kalman filter (EKF) for attitude prediction, state prediction and observation update equation are:

[0034]

[0035] Wherein: is the system state vector, defined as yaw angle, pitch angle and their first-order derivatives, respectively;

[0036] F k is the state transition matrix, H k is the measurement matrix; B is the control input matrix; u k-1 is the control input signal; ω k-1 ,v k are process noise and measurement noise, both are zero-mean Gaussian white noise, variances are 1x10 -4 , 1x10 -5 .

[0037] Further, the audio pre-processing unit includes: a PCM encoder with a sampling rate of 44.1 kHz and a quantization accuracy of 16 bits; using RS (255, 239) forward error correction coding, the encoding gain is not less than 3 dB.

[0038] Preferably, the signal processing and audio output unit includes:

[0039] Transimpedance amplifier (TIA), gain no less than 100 kΩ, bandwidth range covering 100 kHz to 1 MHz;

[0040] Coherent demodulator and LMS adaptive equalizer, equalizer coefficient update formula is:

[0041]

[0042] Wherein, w n is the equalizer coefficient of the nth iteration, μ=0.01 is the step size, e n is the error signal, For receiving the complex conjugate of the signal, n is a discrete time index; after coding and D / A conversion, the bone conduction speaker is driven, the frequency response range is 20Hz to 20kHz, and the total harmonic distortion is less than 1%.

[0043] In an embodiment of the present application, the structure parameters of the underwater receiving earphone include: a volume not greater than 30mm*20mm*15mm, a weight not more than 50g; the shell is made of polycarbonate material, and the waterproof level is IP68; a built-in 3.7V / 500mAh lithium battery is used, the average power consumption is not more than 30mW with the cooperation of the LDO voltage stabilizing circuit, and the endurance time is not less than 4 hours.

[0044] Optionally, the transmitting terminal uses a 12bit, 250MSPS digital-to-analog converter, drives a blue LED array with a peak wavelength of 450±5nm and a half-power angle not greater than ±5°, and the total light power is adjustable between 50-200mW.

[0045] Optionally, the system supports adaptive configuration of sampling rates of 22.05kHz to 48kHz, including AUX audio input, USB digital audio input and Bluetooth input.

[0046] In an embodiment of the present application, an audio transmission method based on the above-mentioned system is provided, comprising the following steps:

[0047] S1. The shore terminal encodes the audio signal by PCM, FEC and QAM-16 modulation, and loads it into the blue-green light carrier;

[0048] S2. The coarse-fine composite axis alignment module dynamically adjusts the direction of the light beam to track the position of the underwater earphone;

[0049] S3. The receiving earphone receives the light signal through the APD array, combines the EKF algorithm with the piezoelectric deflection mirror to predict and compensate the attitude change, and realizes the light axis alignment;

[0050] S4. The receiving end completes coherent demodulation, LMS equalization and FEC decoding, and drives the bone conduction speaker to output audio.

[0051] Based on the above technical solution, the cross-medium wearable audio transmission system of the present application has the following significant technical advantages and application values:

[0052] Firstly, in terms of transmission medium, the present application selects blue-green light with a wavelength of 450nm as the information carrier, fully utilizes its low absorption characteristics in water, overcomes the problem of rapid attenuation of traditional radio frequency communication in water, enables the audio signal to still achieve a reliable data rate of ≥1Mbps in a high-reflectivity and high-humidity environment such as a swimming pool, the transmission distance can reach 10 meters, and greatly improves the communication stability and practicality.

[0053] Secondly, in terms of dynamic optical alignment, the coarse-fine compound axis beam alignment mechanism proposed by the application combines a micro stepping motor with a MEMS galvanometer, covers a large field of view of ±30° and a high-precision adjustment capability of ±5° through multi-stage control, introduces a PID feedback closed-loop mechanism in the control algorithm, responds to the attitude change of the receiving end in real time, makes the light beam accurately point to the position of the receiving earphone at all times, effectively avoids the interruption of the optical link, and ensures that the link alignment rate is greater than 99.9%.

[0054] Thirdly, in terms of attitude change compensation, the system integrates a six-axis inertial sensor and a micro piezoelectric deflection mirror at the receiving end, predicts the head attitude by introducing an extended Kalman filter (EKF) algorithm, adjusts the APD receiving angle by driving the deflection mirror combined with the filter output, realizes active correction of the receiving path, and enables the system to have stable light receiving capability under ±30° attitude swing, which can adapt to dynamic actions such as swimming, looking up and rolling.

[0055] Fourthly, in terms of channel compensation and audio quality, the application dynamically compensates for signal distortion caused by underwater scattering and turbulence by designing an LMS adaptive equalizer, cooperates with forward error correction (FEC) encoding and a high-precision transimpedance amplifier, and controls the bit error rate to be less than 1×10 -6 Hereinafter, the subjective sound quality reaches the CD level (44.1kHz / 16bit); the whole system transmission delay is less than 50ms, which meets the requirements of voice command synchronization and high-fidelity playback.

[0056] Fifthly, in terms of system integration and wearability, the underwater earphone has a size of 30mm×20mm×15mm, is integrally formed by using polycarbonate material, meets the IP68 waterproof level, is built-in with a 500mAh lithium battery and a low-power control circuit, can be used continuously for more than 4 hours after a single charging, and is suitable for professional swimming training, recreational diving, rehabilitation guidance and other scenes; its unbound and lightweight design is obviously superior to existing wired or radio frequency solutions.

[0057] In summary, the application provides a complete system solution combining the low attenuation characteristics of blue and green light, the accurate attitude tracking mechanism and the efficient signal processing link, which significantly improves the practicality, reliability and intelligent level of underwater audio communication, and has a wide application and promotion prospect. BRIEF DESCRIPTION OF DRAWINGS

[0058] In order to more clearly illustrate the technical solutions of the application, the embodiments of the application are described below with reference to the drawings, which are used to illustrate but not limit the application.

[0059] Figure 1The core architecture schematic diagram of the underwater audio transmission system of the swimming pool based on the blue-green light wireless optical link of the application;

[0060] Figure 2 The specific implementation flowchart of the audio transmission method of the application;

[0061] Figure 3 The structure schematic diagram of the shore transmitting terminal of the application;

[0062] Figure 4 The left drawing is the overall mechanical structure schematic diagram of the underwater receiving earphone of the application, and the right drawing is the partial enlarged view of the earphone side light sensor structure. DETAILED DESCRIPTION

[0063] In order to more clearly understand the technical solutions of the application, the embodiments of the application will be described in detail below with reference to the drawings. The structural components, parameter selection, control logic and system functions involved in the embodiments of the application are only preferred examples of the application, which are used to illustrate the feasibility and implementation path of the application, and are not a limitation on the protection scope of the application.

[0064] The technical core of the application is that in the cross-medium environment of water and air, an audio transmission system with high-speed modulation capability, dynamic light beam alignment mechanism and real-time signal compensation capability is constructed, so that the blue-green light can realize stable communication with high fidelity and low delay in underwater dynamic scenes such as swimming pools.

[0065] The application specifically includes two main parts: a shore transmitting terminal and an underwater receiving earphone, and the structural design, working process and signal path thereof will be described in the following subsections. In addition, the audio processing flowchart ( Figure 2 ) and the equipment structure ( Figure 3 , Figure 4 ) will be described in the description to enhance the understanding and implementability of the application.

[0066] The specific embodiments of the application will be further described below with reference to the drawings.

[0067] In a preferred embodiment of the application, as shown in Figure 1 , the system includes a shore transmitting terminal and an underwater receiving earphone. The two are connected through a 450nm blue-green light optical link for audio data transmission, and the system is suitable for indoor swimming pools, training pools and other closed water environments, and realizes cross-medium high-fidelity wireless audio communication.

[0068] I. Shore transmitting terminal structure

[0069] As shown in Figure 3 , the shore transmitting terminal is the core module of the audio sending side, which is compact in structure and complete in function, and is mainly composed of five functional subsystems:

[0070] (1) Audio input and pre-processing subsystem

[0071] This module is used to receive and pre-process audio signals, supporting multiple audio source access methods, including:

[0072] AUX analog audio input interface;

[0073] USB digital audio input;

[0074] Bluetooth audio input (supports SBC / AAC decoding).

[0075] Preferably, the audio input signal is a stereo audio with a sampling rate of 44.1 kHz and a quantization precision of 16 bits. After signal input, it is sent to the FPGA module through the digital audio interface chip for:

[0076] PCM encoding;

[0077] RS(255, 239) forward error correction encoding (can correct continuous errors within 8 bits);

[0078] Parallel to serial reconstruction of data frames.

[0079] The encoded audio symbol sequence output by this module is sent to the modulation subsystem.

[0080] (2) Modulation and drive subsystem

[0081] This module is used to modulate audio signals onto a blue light carrier, including:

[0082] QAM-16 modulator: based on FPGA, modulation rate up to 10 MBaud, output complex symbol pair;

[0083] Digital-to-analog converter (DAC): with 12-bit resolution, sampling rate of 250 MSPS, used to convert the modulated digital signal to an analog signal;

[0084] Carrier modulation: load the analog signal into a 450 nm blue-green light carrier, and the modulation model is as follows:

[0085]

[0086] Where:

[0087] A is the light intensity modulation amplitude (10-50 mW adjustable);

[0088] s(k) is the modulation symbol sequence;

[0089] f0 = 6.67 x 10 14 Hz, corresponding to a 450 nm center wavelength;

[0090] T s = 4μs is a symbol period.

[0091] Alternatively, to simplify the system, the modulation signal can also adopt a BPSK / QPSK scheme as a variant.

[0092] (3) Coarse-fine compound optical axis alignment subsystem

[0093] The subsystem realizes automatic tracking and locking of the light beam to the underwater receiving earphone, and includes:

[0094] Coarse alignment module: the reference angle of the LED array is controlled by a micro-step motor with a step angle of 0.9°, to realize initial search and coverage within a range of ±30°;

[0095] Fine alignment module: a high-frequency resonant MEMS mirror (mirror size 3mm x 3mm, resonant frequency 1kHz) is used to realize fine adjustment of the light beam within a range of ±5° with a resolution of 0.01°;

[0096] Control algorithm: the controller calculates the PID control quantity according to the attitude error signal fed back by the underwater receiving earphone:

[0097]

[0098] Wherein, K p = 0.5, K i = 0.1, K d = 0.05, to ensure that the adjustment overshoot is <5% and the steady-state error is <0.1°.

[0099] The subsystem ensures that the light beam is stably incident on the receiving surface of the underwater earphone, effectively reducing the link interruption rate.

[0100] (4) Light source and optical output system

[0101] The module is used for physical light emission and light beam shaping, and includes:

[0102] Blue LED array: 24 high-power LEDs (such as Nichia NCSB119E) of 450nm are used to form an array output, with a total optical power of 50mW-200mW, and the driving current of each LED is adjustable (0-500mA);

[0103] Constant current driving module: a MOS constant current source structure is used for stable power supply;

[0104] Optical collimation assembly: a collimation lens (half-power angle ≤±5°) is arranged at the front end of the LED to enhance directionality and improve receiving efficiency;

[0105] Light source fixing structure: LED array is installed on an aluminum alloy heat dissipation base plate with a thickness of 3 mm, attached with heat-conducting silica gel and connected with the shell heat dissipation fins to realize continuous work at high temperature.

[0106] (5) Whole machine control and interface system 15

[0107] The whole machine of the transmitting end is uniformly scheduled by a main control chip (ARM Cortex-M7 or FPGA SoC can be selected):

[0108] Control the audio stream path;

[0109] Manage the modulation and alignment process;

[0110] Process the earphone feedback information and make angle correction;

[0111] Provide system state output and OTA upgrade interface.

[0112] The terminal supports multiple control methods, including touch screen, Bluetooth remote control or mobile App interface, to realize power adjustment, input switching, alignment starting and other functions.

[0113] Structure packaging and installation instructions

[0114] The transmitting terminal as a whole adopts a 6061-T6 aluminum alloy shell with a size of 120mm x 90mm x 55mm and an IP65 protection level. The internal layout structure is reasonable, and the light source area, power supply area and control area are arranged separately, equipped with airtight optical window, suitable for onshore wall hanging, tripod fixing or hoisting on the top of the swimming pool, convenient for forming a downward angle of light.

[0115] II. Structure of underwater receiving earphone

[0116] As shown in Figure 4 , the underwater receiving earphone as a whole adopts an ear hanging design, with compact appearance and structure divided into front optical cavity and rear signal / power cavity. The earphone shell is integrally formed by polycarbonate (PC) material with a thickness of about 2.5mm, and O-ring sealing structure is arranged inside, achieving an IP68 protection level. The whole machine weighs less than 50g, with a size of not more than 30mm x 20mm x 15mm, ensuring comfort and safety of long-term underwater use.

[0117] (1) Optical receiving and alignment subsystem

[0118] As shown in Figure 4 , the earphone front optical cavity is built-in 4x4 avalanche photodiode (APD) array. The specific structure is as follows:

[0119] APD array: Binson S1336-5BQ device is selected, single array element response ≥ 0.4A / W, dark current ≤ 1nA, reverse bias voltage about 200V. The array is packaged on a ceramic substrate and fixed by a brass block to improve mechanical stability.

[0120] Optical window: The front end uses a laser-welded quartz glass window, which has good light transmission and pressure resistance, effectively preventing water vapor from entering.

[0121] Piezoelectric deflection mirror: The APD array is integrated with a miniature piezoelectric deflection mirror, with a response time ≤ 1ms and a deflection angle range of ±3°, used for fast compensation when the receiving beam shifts.

[0122] In the attitude sensing part, the headset integrates a six-axis inertial measurement unit (IMU), such as MPU6050, with a sampling rate of 1kHz, a gyroscope range of ±2000° / s, and an accelerometer range of ±16g, used to obtain the yaw and pitch angle information of the wearer's head in real time.

[0123] The headset receiving end uses an extended Kalman filter (EKF) algorithm to predict the user's head posture changes and outputs a deviation correction amount to drive the piezoelectric deflection mirror, ensuring that the APD array always receives the best light intensity. The state and observation equations of EKF are:

[0124]

[0125] Where: the state vector represents the yaw angle, pitch angle and their first derivatives, respectively;

[0126] F k is the state transition matrix, H k is the observation matrix;

[0127] Bu k-1 is the control input;

[0128] ω k-1 , v k are the process noise and observation noise, respectively, with variances of 1×10 -4 , 1×10 -5 .

[0129] This structure can ensure that the optical link remains aligned when the user's head undergoes ±30° dynamic swings, with a link interruption rate below 0.1%.

[0130] (2) Signal processing and audio output subsystem

[0131] As Figure 4 shown in the left figure, the main control circuit board is installed in the signal / power cavity at the back of the headset. The main functions are as follows:

[0132] Trans-impedance amplifier (TIA): used to convert the photoelectric current output by the APD into a voltage signal, gain ≥ 100 kΩ, working bandwidth 100 kHz-1 MHz;

[0133] Low noise amplifier: AD8605 is used, noise factor ≤ 2 dB, signal is amplified to 1-5 V amplitude;

[0134] Demodulation and equalization: the host MCU (such as STM32H743, main frequency 400 MHz) runs the coherent demodulation and LMS adaptive equalization algorithm, and the equalizer update formula is:

[0135]

[0136] where w n is the equalization coefficient of the nth iteration, e n is the error signal, is the complex conjugate of the received signal, and n is the discrete time index.

[0137] Decoding and audio restoration: the signal is decoded by RS (255, 239) error correction, and then D / A conversion (16 bit, 44.1 kHz) is completed through the PCM5102 chip, and the bone conduction speaker is driven to output audio. The bone conduction speaker has a frequency response range of 20 Hz-20 kHz, and the total harmonic distortion is <1%, ensuring high fidelity.

[0138] (3) Power management and endurance subsystem

[0139] This earphone uses a 3.7V / 500mAh lithium polymer battery as the energy source, combined with a low-dropout LDO power management chip, to provide stable power supply for the APD array, signal processing unit and driving circuit.

[0140] Average power consumption: <30 mW;

[0141] Endurance time: ≥4 hours;

[0142] Charging method: 1 hour of fast charging is realized through a magnetic waterproof interface.

[0143] A separate cabin is set between the battery compartment and the signal circuit compartment, and epoxy resin is used for potting, improving electrical safety and waterproof ability.

[0144] (4) Mechanical structure and wearing method

[0145] Shell material: polycarbonate (PC) + silicone lining, with good anti-impact and corrosion resistance;

[0146] Wearing method: ear-hanging type, in line with the ergonomic curve, stable wearing;

[0147] Protection performance: overall waterproof level is IP68, can withstand water depth > 2m environment under continuous use.

[0148] The structural design of the earphone ensures that it will not slip off when swimming, and the weight is ≤50g, and there is no obvious fatigue feeling after long time wearing.

[0149] Through the above-mentioned optical receiving, attitude prediction, signal processing and mechanical structure, the underwater receiving earphone of the application realizes high sensitivity, strong anti-interference and high fidelity audio output while maintaining miniaturization, which is significantly better than traditional underwater audio equipment.

[0150] III. Audio transmission process

[0151] As shown in Figure 2 The audio transmission method of the application includes the whole process of the shore transmitting end and the underwater receiving end, mainly divided into four core steps, covering audio preprocessing, optical link modulation and tracking, attitude compensation receiving, and signal restoration and output, to ensure the real-time and robustness of audio transmission in underwater environment.

[0152] Step S1: audio signal encoding and optical modulation

[0153] The shore transmitting terminal first preprocesses the input audio signal as follows:

[0154] The input source can be a mobile phone, an audio player, a smart coach, etc., supporting AUX, USB or Bluetooth input;

[0155] After PCM encoding, the audio data is converted into a digital pulse code stream (sampling rate 44.1kHz, quantization precision 16bit);

[0156] Then, RS(255,239) forward error correction encoding is performed, adding redundant code, supporting 8bit continuous error correction, and improving error code robustness;

[0157] Then, QAM-16 modulation is performed, which maps the audio digital signal into a complex modulation symbol pair;

[0158] Digital-to-analog conversion is performed by a 12bit DAC to generate an analog modulation signal;

[0159] Finally, the analog signal is loaded to the blue-green light LED array through a constant current driving module, outputting a high directivity light beam with a center wavelength of 450nm and a half-power angle of ±5°.

[0160] This step forms a blue-green light modulation signal carrier, laying the foundation for underwater communication.

[0161] Step S2: coarse and fine alignment and dynamic tracking of light beam

[0162] To ensure that the underwater earphone can stably receive the optical signal during exercise, the transmitting end dynamically adjusts the LED array emission direction through a coarse-fine composite optical axis alignment system:

[0163] Coarse alignment stage: The LED array base is rotated within ±30° by a stepper motor to achieve large field of view scanning and target search;

[0164] Fine alignment stage: Fine adjustment within ±5° by MEMS galvanometer to achieve high-frequency jitter compensation and real-time locking;

[0165] The adjustment control logic is based on a PID controller, which calculates the light beam correction amount in real time according to the attitude deviation e(t) returned by the underwater earphone:

[0166]

[0167] The controller output drives the MEMS galvanometer to keep the light beam aligned with the earphone receiving surface, greatly improving the link stability.

[0168] Step S3: underwater earphone receiving and attitude compensation alignment

[0169] When the underwater earphone receives the blue-green light modulation signal, it needs to be processed by multiple modules to achieve accurate reception:

[0170] Receiving component: The APD array at the front end receives the optical signal and converts it into a weak current signal;

[0171] Attitude sensing: The six-axis IMU detects the head yaw angle and pitch angle in real time at a frequency of 1 kHz;

[0172] Attitude prediction: The extended Kalman filter (EKF) algorithm runs inside the earphone to build a dynamic attitude state model and predict the angle change at the next moment:

[0173]

[0174] Optical axis correction: According to the EKF output result, control the miniature piezoelectric deflection mirror to adjust the receiving angle (±3° range) to ensure that the optical signal is stably landed in the APD sensitive area;

[0175] This process has a response capability of <1ms, so that the earphone can still maintain optical link reception during the dynamic swinging of the user's head, and the optical alignment maintenance rate is >99.9%.

[0176] Step S4: signal demodulation, equalization, decoding and audio output

[0177] The earphone signal processing link restores the received electrical signal completely:

[0178] TIA module: amplifies the APD current signal to a voltage signal;

[0179] Low noise amplifier: amplify the signal to 1-5V;

[0180] Coherent demodulator: restore the original QAM-16 modulation symbol;

[0181] LMS adaptive equalizer: compensate for channel distortion caused by underwater disturbance, coefficient update formula as follows:

[0182]

[0183] Error correction decoding: use RS(255,239) algorithm to remove possible error code;

[0184] D / A converter: restore the audio signal to analog waveform;

[0185] Bone conduction speaker: final drive output audio, frequency response range is 20Hz-20kHz, total harmonic distortion is less than 1%, users can clearly hear audio content or instructions underwater.

[0186] Overall effect and advantage

[0187] The whole process ensures:

[0188] 10m underwater high-quality audio transmission;

[0189] Data rate ≥1Mbps, error rate ≤1×10 -6 , delay <50ms;

[0190] Link retention rate >99.9%, strong anti-dynamic disturbance ability;

[0191] Support bone conduction playback, compatible with training instructions and entertainment audio dual requirements.

[0192] Four, test and application verification

[0193] In order to verify the practicability, stability and comprehensive performance of the cross-medium wearable audio transmission system, the inventor designs and completes the construction of system-level physical prototype, and carries out comprehensive function test and comparison verification in real swimming pool scene. Test environment and index are as follows:

[0194] (1) Test environment configuration

[0195] Site: standard indoor swimming pool, swimming lane length 25m, water depth 1.5m;

[0196] Water quality parameters: water temperature 25℃, water turbidity about 5NTU (moderate clear);

[0197] Background interference: LED lighting lamp (color temperature 5500K) at the top, test under the open state;

[0198] Swimmer state: wearing receiving earphone to do different postures (freestyle, backstroke, turn);

[0199] Test distance: the transmitter is installed on one side of the swimming pool, and the earphone is 10m away from the transmitter in a straight line.

[0200] (2) Link alignment capability test

[0201] The purpose of the test is to verify whether the coarse-fine composite shaft alignment system and the posture prediction mechanism described in the application can realize stable link maintenance in a dynamic scene.

[0202] Test method: the swimmer wearing the earphone moves at an average speed of 1.5m / s, and does free swing (including yaw, pitch) within ±30° range of the head. Measure whether the optical link is interrupted.

[0203] Test results: in the entire swimming path, the APD receiving end photocurrent has no significant drop, and the link maintenance rate is >99.9%; the response time of the galvanometer + piezoelectric deflection mirror is less than 1ms, and there is no perceptible delay in compensation.

[0204] Comparison with traditional system: the fixed beam system without dynamic alignment is frequently interrupted above ±10°, and the link maintenance rate is less than 80%.

[0205] Verification conclusion: the system has excellent optical link stability and fully adapts to the dynamic posture changes of users in the swimming scene.

[0206] (3) Audio transmission performance test

[0207] Test indicators include data rate, bit error rate, audio delay and subjective sound quality score.

[0208] Data rate: the actual data transmission rate is stable at more than 1.2Mbps;

[0209] Bit error rate: by comparing the audio bit streams of the sending end and the receiving end, the actual bit error rate is less than 1×10 -6 ;

[0210] Transmission delay: the total delay of encoding, modulation, link, demodulation, equalization, decoding and D / A is less than 42ms;

[0211] Sound quality subjective score: invite 5 professional swimming coaches to score the sound quality subjective MOS (Mean Opinion Score), the average score is 4.5 (full score 5, evaluation as "excellent");

[0212] Playing content: the test includes voice instructions ("change swimming posture", "speed up") and high dynamic music segments (drum + voice), which are all clear and have no lag.

[0213] Verification Conclusion: This system can realize real-time audio communication of CD sound quality level, and is suitable for training guidance, voice interaction and other scenarios.

[0214] (4) Anti-interference and environmental adaptability test

[0215] To verify the robustness of the system in a typical pool interference environment, the following working conditions are set:

[0216] Interference scenario one: turn on the strong LED ceiling light;

[0217] Interference scenario two: water agitation, bubble interference;

[0218] Interference scenario three: multiple people swimming at the same time, causing a large amount of water wave and scattering.

[0219] Test findings:

[0220] Background light interference suppression: with the help of APD front-end band-pass filter (100kHz-1MHz) and narrow-angle field of view, environmental LED noise interference <3dB;

[0221] Signal jitter compensation: LMS equalizer can quickly compensate for signal amplitude fluctuations (jitter standard deviation >20%), signal-to-noise ratio maintained at 28dB or more;

[0222] Multi-user interference suppression: the system has high single-link tracking performance, even if there are other swimmers nearby causing reflections and obstructions, it can still quickly recover the alignment.

[0223] Verification Conclusion: The system has good water disturbance, scattering, and background light adaptability, and its anti-interference performance is better than that of traditional Bluetooth or optical communication solutions.

[0224] (5) Power supply and endurance test

[0225] To verify the continuous use of wearable devices, a continuous work test is conducted:

[0226] Test conditions: continuous working time counting under full power, intermittent audio playback (including silent segments);

[0227] Test results: after continuous playback for 4 hours, the remaining battery capacity is about 23%, and the device does not overheat or fail;

[0228] Charging time: about 1 hour to fully charge through a 5V magnetic charging interface.

[0229] Verification Conclusion: The device meets the continuous use requirements of daily training period (2-3 hours), and has fast charging and long-term stability performance.

[0230] (6) Actual application feedback

[0231] The system is actually used in a youth swimming training center in a city for a week, and the user feedback is as follows:

[0232] Coach feedback: clear voice guidance can be heard, no need to approach the shore, rhythm and speed training efficiency is obviously improved;

[0233] Student feedback: no foreign body sensation when wearing earphones, clean and stable sound quality, suitable for music swimming and immersive training;

[0234] Operation and maintenance feedback: the equipment is easy to charge and manage, and there is no obvious maintenance burden.

[0235] Summary

[0236] The system of the present application completes a plurality of key performance verifications in the actual use environment, including:

[0237] Test item Achievement index Data rate ≥ 1 Mbps Error rate ≤ 1 x 10 -6 ]] Audio delay < 50 ms Link retention rate > 99.9% (within ± 30° attitude range) Signal-to-noise ratio ≥ 25 dB (against LED light and water wave disturbance) Headset endurance ≥ 4 hours Subjective sound quality score MOS score 4.5 / 5

[0238] The system of the present application verifies its excellent performance in underwater audio transmission applications such as swimming training and recreational entertainment, has high stability, high fidelity and actual wearability, is mature in technology, and has significant promotion value.

[0239] The above is a specific embodiment of the present application, and the structure, composition, working principle and application process of the present application are described in more detail in conjunction with the drawings. It should be understood that for those skilled in the art, without departing from the core concept of the present application, some modules, parameter selection, control logic or signal processing methods in the embodiments can be equivalently replaced, adjusted or combined, and these equivalent modifications or functional replacements shall be included in the protection scope of the present application.

[0240] In particular, the technical solution of the present application is not only suitable for underwater audio communication scenes in swimming pools, but also can be popularized to closed training pools, underwater teaching systems, diving communication equipment, underwater voice interaction platforms and other close-range optical communication occasions, and has good universality and industrialization basis.

[0241] It should be noted that the specific embodiments and drawings described in the present application are only used to help understand the technical concept and core content of the present application, and do not constitute a limitation on the protection scope of the present application. The protection scope of the present application should be based on the technical solution defined in the claims.

Claims

1. A cross-media wearable audio transmission system, characterized by, The system comprises a shore-based transmitting terminal and an underwater receiving earphone, and the two achieve wireless audio transmission in a swimming pool environment through a blue-green light carrier with a wavelength of 450 nm. The shore-based transmitting terminal comprises an audio preprocessing unit, a modulation and driving unit, and a coarse-fine composite axis alignment unit. The underwater receiving earphone comprises an optical receiving and alignment unit, a signal processing and audio output unit. The system achieves audio transmission rate ≥ 1 Mbps in a range of 10 meters, bit error rate ≤ 1 x 10 -6 , transmission delay less than 50 ms.

2. The system of claim 1, wherein, The coarse-fine composite axis alignment unit comprises: A coarse alignment module: a miniature stepping motor with a step angle of 0.9° is adopted, and the response time is not more than 50 ms, so as to realize preliminary alignment within a field of view of ±30°. A fine alignment module: a MEMS mirror with a mirror size of 3 mm×3 mm and a resonance frequency of 1 kHz is integrated, and the module supports high-precision dynamic adjustment within a range of ±5° with a resolution of 0.01°. A control algorithm: a PID algorithm is adopted, and a control quantity u(t) is output according to an attitude error signal e(t) fed back by the receiving end, and the formula is: Where, K p = 0.5, K i = 0.1, K d = 0.05, to ensure that the adjustment overshoot <5%, steady-state error <0.1°.

3. The system of claim 1, wherein, The modulation and driving unit adopts a QAM-16 modulation mode, loads the audio signal to the 450 nm blue light carrier, and the modulated signal s(t) is expressed as: Wherein: A is the light intensity amplitude, and is adjustable between 10-50 mW; S(k) is a modulation symbol sequence; T s = 4μs is the symbol period; f0 = 6.67 x 10 14 Hz, corresponding wavelength 450 nm; t is a time variable, k is a symbol index, and N is the number of modulation symbols; rect(·) is a rectangular window function.

4. The system of claim 1, wherein, The optical receiving and alignment unit comprises: A 4×4 avalanche photodiode (APD) array, the single-element responsivity is not less than 0.4 A / W, and the dark current is not more than 1 nA; A six-axis attitude sensor, the sampling rate is 1 kHz, and the range covers an angular velocity of ±2000° / s and an acceleration of ±16g; A miniature piezoelectric deflection mirror, the response time is not more than 1 ms, and the deflection range is not less than ±3°; A dynamic alignment algorithm adopts an extended Kalman filter (EKF) for attitude prediction, and the state prediction and observation update equations are: where: is the system state vector, defined as denote the yaw angle, the pitch angle and their first derivatives, respectively; F k is the state transition matrix, H k is the measurement matrix; B is the control input matrix; u k-1 is the control input signal; ω k-1 , v k are the process noise and measurement noise, respectively, both are zero-mean Gaussian white noise with variances 1 x 10 -4 , 1 x 10 -5 , respectively.

5. The system of claim 1, wherein, The audio preprocessing unit comprises: A PCM encoder with a sampling rate of 44.1 kHz and a quantization accuracy of 16 bits; An RS (255, 239) forward error correction coding is adopted, and the coding gain is not less than 3 dB.

6. The system of claim 1, wherein, The signal processing and audio output unit comprises: A transimpedance amplifier (TIA), the gain is not less than 100 kΩ, and the bandwidth range covers 100 kHz to 1 MHz; A coherent demodulator and an LMS adaptive equalizer, and the equalizer coefficient update formula is: wherein: w n is the equalizer coefficient for the nth iteration; μ = 0.01 is the step size; e n is the error signal; is the complex conjugate of the received signal; n is the discrete-time index; the equalized signal, after being decoded and D / A converted, drives the bone conduction speaker with a frequency response range of 20 Hz to 20 kHz and a total harmonic distortion less than 1%.

7. The system of claim 1, wherein, The structural parameters of the underwater receiving earphone comprise: The volume is not more than 30 mm×20 mm×15 mm, and the weight is not more than 50 g; The shell is made of polycarbonate material, and the waterproof level is IP68; A built-in 3.7 V / 500 mAh lithium battery is used, the average power consumption is not more than 30 mW in cooperation with an LDO voltage stabilizing circuit, and the endurance time is not less than 4 hours.

8. The system of claim 1, wherein, The transmitting terminal adopts a digital-to-analog converter with 12 bits and 250 MSPS, drives a blue light LED array with a peak wavelength of 450±5 nm and a half-power angle not greater than ±5°, and the total light power is adjustable between 50-200 mW.

9. The system of claim 1, wherein, The system supports AUX audio input, USB digital audio input and Bluetooth input, and supports adaptive configuration of sampling rates of 22.05 kHz to 48 kHz.

10. An audio transmission method based on the system of any one of claims 1 to 9, characterized in that, The method comprises the following steps: S1. The shore terminal encodes the audio signal by PCM, FEC and QAM-16 modulation, and loads it to the blue-green light carrier; S2. The coarse-fine composite axis alignment module dynamically adjusts the light beam direction to track the position of the underwater earphone; S3. The earphone receives the light signal through the APD array, combines the EKF algorithm and the piezoelectric deflection mirror to predict and compensate the attitude change, and realizes the light axis alignment; S4. The receiving end completes coherent demodulation, LMS equalization and FEC decoding, and drives the bone conduction loudspeaker to output audio.

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