Orthogonal frequency division multiplexing water acoustic communication system transmission method, device, equipment and product

Abstract

The present application discloses a transmission method, device, equipment and product for an orthogonal frequency division multiplexing (OFDM) underwater acoustic communication system, which relates to the field of underwater acoustic communication technology. The method comprises: performing phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence, which has a sparse characteristic; performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information; transmitting the modulated information to the receiving end through an underwater acoustic channel; performing signal conversion and demodulation on the modulated information at the receiving end to restore the original information bits. The underwater acoustic channel has the characteristic of being suitable for transmitting sparse signals. Through phase modulation and linear conversion, the complex signal is mapped into a sparse real number sequence suitable for the underwater acoustic system, reducing the impact of noise on the signal. Through the effective transmission of high-order phase modulation symbols, the needs of high data rate communication are met. At the receiving end, the original information bits are accurately restored through signal conversion and demodulation, thereby improving the transmission stability of the underwater acoustic channel.

Description

Technical Field

[0001] The present application relates to the field of underwater acoustic communication technology, and in particular to an orthogonal frequency division multiplexing underwater acoustic communication system transmission method, device, equipment and product. Background Art

[0002] In modern communication systems, Orthogonal Frequency Division Multiplexing (OFDM) effectively addresses multipath fading and frequency-selective fading. However, traditional OFDM systems suffer from high computational complexity, especially in high-data-rate transmission scenarios, where frequent complex number operations burden device processing capabilities. In certain environments, particularly underwater acoustic channels, signal attenuation and multipath effects further exacerbate stability issues during high-data-rate transmission.

[0003] Therefore, how to achieve stable transmission of high data rates in underwater acoustic channels is a problem that needs to be solved urgently. Summary of the Invention

[0004] The main purpose of this application is to provide a transmission method, device, equipment and product for an orthogonal frequency division multiplexing underwater acoustic communication system, aiming to solve the technical problem of unstable high data rate transmission in an underwater acoustic channel environment.

[0005] To achieve the above objectives, the present application proposes a transmission method for an orthogonal frequency division multiplexing (OFDM) water acoustic communication system, the method comprising:

[0006] Performing phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence, wherein the real number sequence has a sparse characteristic;

[0007] Performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information;

[0008] sending the modulated information to a receiving end via an underwater acoustic channel;

[0009] At the receiving end, the modulated information is subjected to signal conversion and demodulation to restore the original information bits.

[0010] In one embodiment, the step of performing phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence includes:

[0011] At the transmitting end, high-order phase modulation is performed on the transmitted information bits to obtain a complex signal;

[0012] The complex signal is sequence-converted using a real-to-complex conversion algorithm to obtain a real number sequence.

[0013] In one embodiment, the step of performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information includes:

[0014] Performing inverse discrete Hartley transform modulation on the real number sequence to obtain a baseband signal;

[0015] Upsampling the baseband signal and adding a cyclic prefix to obtain a preprocessed signal;

[0016] Carrier modulation is performed on the preprocessed signal to obtain modulated information.

[0017] In one embodiment, the step of performing signal conversion and demodulation on the modulated information at the receiving end to restore the original information bits includes:

[0018] Processing the modulated information through demodulation and signal transformation to restore the real number sequence;

[0019] The real number sequence is converted into a complex number signal, and the original information bits are restored through phase demodulation.

[0020] In one embodiment, the step of processing the modulated information by demodulation and signal transformation to restore the real number sequence includes:

[0021] Performing carrier demodulation on the modulated information, removing the cyclic prefix and performing downsampling to obtain a downsampled signal;

[0022] performing equalization processing on the downsampled signal in combination with channel estimation, and outputting an equalized time domain signal;

[0023] Discrete Hartley transform demodulation is performed on the equalized time domain signal to output a real number sequence.

[0024] In one embodiment, the step of converting the real number sequence into a complex number signal and recovering the original information bits through phase demodulation includes:

[0025] Performing real-to-complex conversion on the real number sequence to output a frequency domain complex signal;

[0026] High-order phase demodulation is performed on the frequency-domain complex signal to obtain original information bits.

[0027] In addition, to achieve the above-mentioned purpose, the present application also proposes an orthogonal frequency division multiplexing (OFDM) acoustic communication system transmission device, the OFDM acoustic communication system transmission device comprising:

[0028] A modulation conversion module is used to perform phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence, wherein the real number sequence has a sparse characteristic;

[0029] an inverse transform modulation module, configured to perform inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information;

[0030] An underwater acoustic channel transmission module, configured to transmit the modulated information to a receiving end via an underwater acoustic channel;

[0031] The demodulation and recovery module is used to perform signal conversion and demodulation on the modulated information at the receiving end to recover the original information bits.

[0032] In addition, to achieve the above-mentioned purpose, the present application also proposes an orthogonal frequency division multiplexing water acoustic communication system transmission device, which includes: a memory, a processor, and a computer program stored on the memory and runnable on the processor, and the computer program is configured to implement the steps of the orthogonal frequency division multiplexing water acoustic communication system transmission method as described above.

[0033] In addition, to achieve the above-mentioned purpose, the present application also proposes a storage medium, which is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by the processor, the steps of the orthogonal frequency division multiplexing water acoustic communication system transmission method as described above are implemented.

[0034] In addition, to achieve the above-mentioned purpose, the present application also provides a computer program product, which includes a computer program, and when the computer program is executed by a processor, it implements the steps of the orthogonal frequency division multiplexing water acoustic communication system transmission method as described above.

[0035] One or more technical solutions proposed in this application have at least the following technical effects:

[0036] At the transmitter, the transmitted information bits undergo phase modulation and linear transformation to obtain a sparse real number sequence. This real number sequence is then modulated using an inverse discrete Hartley transform (IDHT) to obtain the modulated information. This modulated information is then transmitted to the receiver via an underwater acoustic channel. At the receiver, the modulated information undergoes signal transformation and demodulation to recover the original information bits. Due to the underwater acoustic channel's suitability for transmitting sparse signals, phase modulation combined with linear transformation maps the complex signal into a sparse real number sequence suitable for underwater acoustic systems, minimizing the impact of multipath interference and noise on the signal and improving the system's transmission stability and anti-interference capabilities. Leveraging the characteristics of inverse discrete Hartley transform (IDHT) modulation and sparse signals, this approach simplifies the computational complexity of modulation and demodulation at both the transmitter and receiver, reducing device processing requirements. By combining a real-to-complex conversion algorithm, efficient transmission of high-order phase-modulated symbols is achieved, meeting the requirements of high-data-rate communications. At the receiver, signal transformation and demodulation, utilizing the discrete Hartley transform and complex recovery techniques, accurately restore the original information bits, further improving the reliability and stability of communications in underwater acoustic channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0039] Figure 1 This is a flowchart of the first embodiment of the transmission method of the orthogonal frequency division multiplexing hydroacoustic communication system of the present application;

[0040] Figure 2 This is a flow chart of a second embodiment of the transmission method of an orthogonal frequency division multiplexing (OFDM) hydroacoustic communication system of the present application;

[0041] Figure 3 This is a flowchart of a third embodiment of the transmission method of an orthogonal frequency division multiplexing (OFDM) hydroacoustic communication system of the present application;

[0042] Figure 4 This is a flowchart of a fourth embodiment of the transmission method of an orthogonal frequency division multiplexing (OFDM) hydroacoustic communication system of the present application;

[0043] Figure 5 This is a block diagram of the principle of implementing high-order symbol transmission in a DHT-OFDM system based on a real-to-complex conversion algorithm;

[0044] Figure 6QPSK constellation diagram for this application;

[0045] Figure 7 Added C2RT's QPSK constellation diagram for this application;

[0046] Figure 8 This is the 16QAM constellation diagram for this application;

[0047] Figure 9 Added C2RT's 16QAM constellation diagram for this application;

[0048] Figure 10 This is the simulation diagram of C2RT in OFDM system for this application;

[0049] Figure 11 Added a comparison chart of the transmission performance of DHT-OFDM and traditional OFDM systems with and without C2RT for this application;

[0050] Figure 12 This is a schematic diagram of the module structure of the transmission device of the orthogonal frequency division multiplexing water acoustic communication system according to an embodiment of the present application;

[0051] Figure 13 Schematic diagram of the device structure of the hardware operating environment involved in the transmission method of the orthogonal frequency division multiplexing water acoustic communication system in the embodiment of the present application.

[0052] The purpose, features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0053] It should be understood that the specific embodiments described herein are merely used to explain the technical solutions of the present application and are not intended to limit the present application.

[0054] In order to better understand the technical solution of this application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0055] While traditional OFDM systems offer good interference immunity, they suffer from high computational complexity, particularly in high-data-rate transmission scenarios, where frequent complex number operations burden device processing capabilities. Therefore, Discrete Hartley Transform - Orthogonal Frequency Division Multiplexing (DHT-OFDM), a real-number-based solution, significantly reduces computational complexity by replacing the traditional Discrete Fourier Transform (DFT) with the Discrete Hartley Transform (DHT), resulting in low power consumption and efficient signal processing. However, DHT-OFDM is limited in that it only supports transmission in the real domain and cannot directly support high-order phase modulation, such as QAM (Quadrature Amplitude Modulation). This limitation presents challenges for high-data-rate transmission, particularly in applications requiring high transmission rates. This prevents the system from fully utilizing the communication system's bandwidth, limiting data transmission efficiency.

[0056] In certain environments, particularly the unique propagation environment of underwater acoustic channels, signal attenuation and multipath effects further exacerbate the stability issues of high-data-rate transmission. Underwater acoustic channels exhibit characteristics such as frequency-selective fading and signal distortion, which can significantly interfere with signals, preventing the receiver from effectively recovering the original information, thus compromising the system's transmission stability and reliability. Therefore, achieving stable high-data-rate transmission in underwater acoustic channels has become a technical challenge.

[0057] This application provides a solution that involves performing phase modulation and linear transformation on transmitted information bits at the transmitter to obtain a sparse real number sequence. The real number sequence is then modulated using an inverse discrete Hartley transform to obtain modulated information. The modulated information is then transmitted to the receiver via an underwater acoustic channel. At the receiver, the modulated information is then subjected to signal transformation and demodulation to recover the original information bits. Because underwater acoustic channels are suitable for transmitting sparse signals, phase modulation combined with linear transformation maps complex signals into sparse real number sequences suitable for underwater acoustic systems, reducing the impact of multipath interference and noise on the signal and improving the system's transmission stability and anti-interference capabilities. Leveraging the inverse discrete Hartley transform modulation and the sparse signal properties, the computational complexity of modulation and demodulation at both the transmitter and receiver is simplified, reducing device processing requirements. By combining a real-to-complex conversion algorithm, efficient transmission of high-order phase modulated symbols is achieved, meeting the requirements of high-data-rate communications. At the receiver, signal transformation and demodulation, utilizing the discrete Hartley transform and complex number recovery techniques, accurately restore the original information bits, further improving the reliability and stability of communications in underwater acoustic channel environments.

[0058] Based on this, the embodiment of the present application provides an orthogonal frequency division multiplexing water acoustic communication system transmission method, referring to Figure 1 , Figure 1 This is a flow chart of a first embodiment of a transmission method of an orthogonal frequency division multiplexing (OFDM) hydroacoustic communication system of the present application.

[0059] In this embodiment, the OFDM acoustic communication system transmission method includes steps S10 to S40:

[0060] Step S10: performing phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence, which has a sparse characteristic.

[0061] It should be noted that the transmitted information bits can be understood as the raw data in a communication system, typically a binary bit stream. Phase modulation is a digital modulation method that represents different information bits by changing the phase of the carrier signal. Linear transformation can be understood as converting a complex signal or data sequence into another form while maintaining the linear structure of the data, that is, converting the phase-modulated signal into a real number sequence. Sparse characteristics can be understood as the characteristic that most elements in a signal are zero, with only a few non-zero elements. In communication systems, sparse signals can effectively reduce the complexity of data transmission, reduce system power consumption, and improve signal stability in noisy environments.

[0062] Step S20: performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information.

[0063] It should be noted that the discrete Hartley transform (DHT) can be a transform similar to the Fourier transform, which is mainly used for frequency domain representation of signals. The inverse discrete Hartley transform (IDHT) is the inverse transform of the DHT, which is used to recover the time domain signal from the frequency domain signal. The modulated information can be the signal after the inverse discrete Hartley transform.

[0064] Step S30: sending the modulated information to the receiving end through the underwater acoustic channel.

[0065] It should be noted that the underwater acoustic channel can be understood as the sound wave propagation channel in the underwater environment. In underwater communications, the acoustic wave signal propagates through water and is affected by factors such as multipath fading, noise, and signal attenuation.

[0066] Step S40: performing signal conversion and demodulation on the modulated information at the receiving end to restore the original information bits.

[0067] It should be noted that signal transformation can be understood as the receiver converting the received signal (modulated information) from the underwater acoustic channel transmission format (such as the frequency domain or time domain) into a format suitable for demodulation. Exemplary conversions may include frequency domain to time domain or other conversions. Demodulation can be understood as the receiver using an algorithm to recover the original transmitted information bits.

[0068] In this embodiment, since the underwater acoustic channel has the characteristics of being suitable for transmitting sparse signals, phase modulation is combined with linear conversion to map the complex signal into a sparse real number sequence suitable for the underwater acoustic system, thereby reducing the impact of multipath interference and noise on the signal and improving the transmission stability and anti-interference capability of the system. By utilizing the characteristics of inverse discrete Hartley transform modulation and sparse signals, the modulation and demodulation computational complexity of the transmitter and receiver is simplified, and the processing requirements of the equipment are reduced. By combining the real-to-complex conversion algorithm, the effective transmission of high-order phase modulation symbols is achieved to meet the needs of high data rate communication. Through signal conversion and demodulation, the receiver uses discrete Hartley transform and complex recovery technology to accurately restore the original information bits, further improving the reliability and stability of communications in the underwater acoustic channel environment.

[0069] Reference Figure 2 , Figure 2 This is a flow chart of the second embodiment of the OFDM acoustic communication system transmission method of the present application, based on the above Figure 1 The first embodiment shown provides a second embodiment of the transmission method of the orthogonal frequency division multiplexing water acoustic communication system of the present application.

[0070] In the second embodiment, step S10 includes:

[0071] Step S101: Perform high-order phase modulation on the transmitted information bits at the transmitting end to obtain a complex signal.

[0072] It should be noted that high-order phase modulation can encode information bits by changing the phase of the carrier signal. For example, high-order phase modulation can be Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM). It is understood that the result of high-order phase modulation is usually expressed in complex form. For example, the high-order phase modulation is performed on the transmitted information bit, and the output length is N / 2 complex sequence.

[0073] Step S102 : performing sequence conversion on the complex signal using a real-to-complex conversion algorithm to obtain a real sequence.

[0074] It should be noted that the Complex-to-Real Transform (C2RT) algorithm is a modulation method that converts complex modulation symbols into sparse real domain symbols through linear calculation. When applied to underwater acoustic DHT-OFDM communication systems, it can realize the transmission of high-order phase symbols and is used to convert complex signals (consisting of real and imaginary parts) into equivalent real signal sequences. The sequence containing only real numbers generated by real-to-complex conversion is a real sequence. For example, the real and imaginary parts of the complex signal generated by high-order phase modulation can be linearly combined to map the complex signal to the real domain, and the output real sequence length is N The range of values ​​in the sequence is ,in, Expressed as a complex result after phase modulation The corresponding real part value, Expressed as a complex result after phase modulation The corresponding imaginary part value.

[0075] For example, for the symbols output by QAM modulation , converted into a real number sequence through C2RT , the transformation process is expressed as formula (1):

[0076]

[0077] in, Expressed as The output sign of the bit, and They are The real and imaginary parts of It can be expressed as formula (2):

[0078]

[0079] In formula (2), N is the IDHT / DHT point, for real number input sequence After performing IDHT operation, a bipolar time domain signal is obtained.

[0080] In this embodiment, by performing high-order phase modulation on the transmitted information bits at the transmitting end, multiple bits can be encoded in a single symbol, achieving high data rate transmission and meeting different requirements for data rate and anti-interference capability. By simultaneously carrying data in the real and imaginary parts of the complex signal, the system can flexibly express the modulation information and provide complete data information for subsequent processing. The real-to-complex conversion converts the complex signal into a real-domain signal, making it compatible with the processing requirements of the discrete Hartley transform (DHT). The real number sequence generated by the real-to-complex conversion is typically sparse (most values ​​are close to zero), which can effectively reduce redundant information in data transmission and improve transmission efficiency.

[0081] Reference Figure 3 , Figure 3 This is a flow chart of the third embodiment of the OFDM water acoustic communication system transmission method of the present application, based on the above Figure 2 The second embodiment shown provides the third embodiment of the transmission method of the orthogonal frequency division multiplexing water acoustic communication system of the present application.

[0082] In the third embodiment, step S20 includes:

[0083] Step S201 : performing inverse discrete Hartley transform modulation on a real number sequence to obtain a baseband signal.

[0084] It should be noted that the Inverse Discrete Hartley Transform (IDHT) and the Discrete Hartley Transform (DHT) are inverse operations of each other, converting the real number sequence in the frequency domain into a time domain signal to generate a baseband signal.

[0085] Step S202 : up-sample the baseband signal and add a cyclic prefix to obtain a pre-processed signal.

[0086] It should be noted that upsampling is the process of increasing the signal's sampling rate to a higher frequency to accommodate subsequent signal processing or transmission requirements. For example, zero values ​​can be inserted between the original sampling points to expand the number of sampling points and improve signal resolution. A cyclic prefix is ​​a portion of tail data copied before each signal frame. The preprocessed signal is the signal after upsampling and the addition of a cyclic prefix.

[0087] Step S203: Carrier modulate the preprocessed signal to obtain modulated information.

[0088] It should be noted that carrier modulation can be the process of shifting a baseband signal to a target frequency range by mixing it with a high-frequency carrier signal. The modulated information can be understood as the output signal of the carrier modulation, which is adapted to the transmission format of the underwater acoustic channel.

[0089] For example, the DHT and IDHT transformation can be expressed as formula (3):

[0090]

[0091] In formula (3), Indicates the initial sending signal, It is expressed as DHT modulation signal. It should be noted that the kernel function of DHT can be expressed as formula (4):

[0092]

[0093] According to the DHT transformation formula, DHT and IDHT have the same form and satisfy formula (5):

[0094]

[0095] In formula (5), represents the index of the DHT transformation input, k It is expressed as the index of the DHT transform output. When the two are equal, the two sets of kernel functions satisfy the orthogonal relationship. For the real number sequence after real-complex conversion , after IDHT, the output sequence is formula (6):

[0096]

[0097] In formula (6), It is represented as the output sequence after IDHT. In the above formula, , The final transmitted DHT-OFDM signal is expressed as formula (7):

[0098]

[0099] In formula (7), Represented as the final transmitted DHT-OFDM signal, Indicates the initial sending signal, is represented as the fundamental frequency, Expressed as time, Represents the guard interval, Expressed as symbol period. Transmitting the transmitted signal in the underwater acoustic channel, only considering the multipath transmission characteristics, the underwater acoustic channel can be described by the tap delay model as formula (8):

[0100]

[0101] In formula (8), It is expressed as the amplitude relationship of the channel at different times, For the The gain of the path, is the corresponding relative delay, is the number of multipaths.

[0102] In this embodiment, by using the inverse discrete Hartley transform, complex number operations are avoided and only real signals need to be processed, which simplifies the hardware implementation and reduces computational complexity and power consumption. The real number sequence in the frequency domain is converted into a baseband signal in the time domain, providing a basic signal adapted to the characteristics of the underwater acoustic channel for subsequent transmission. The introduction of the cyclic prefix and upsampling reduce the quantization error, improve the anti-interference and accuracy of the signal, and provide periodic characteristics for subsequent modulation and demodulation, avoiding signal distortion caused by boundary effects during the transformation process. Carrier modulation enables the signal to effectively utilize the spectrum resources of the underwater acoustic channel, improves the stability and efficiency of the transmission, and meets the requirements of high data rate transmission.

[0103] Reference Figure 4 , Figure 4 This is a flow chart of the fourth embodiment of the OFDM acoustic communication system transmission method of the present application, based on the above Figure 3 The third embodiment shown provides the fourth embodiment of the transmission method of the orthogonal frequency division multiplexing water acoustic communication system of the present application.

[0104] In the fourth embodiment, step S40 includes:

[0105] Step S401 : Process the modulated information through demodulation and signal transformation to restore the real number sequence.

[0106] It should be noted that demodulation extracts the original baseband signal from the carrier signal, removes the high-frequency components of the carrier, and restores the signal to the low-frequency domain. Signal transformation uses the Discrete Hartley Transform (DHT) to restore the received baseband signal from the time domain to the frequency domain, reconstructing the original real number sequence.

[0107] Step S402: convert the real number sequence into a complex number signal, and restore the original information bits through phase demodulation.

[0108] It should be noted that phase demodulation can be the process of restoring a complex signal to its original bit information by analyzing the phase changes of the complex signal to extract the encoded data. Exemplary phase demodulation methods include QAM, PSK, etc., matching the received phase value to the original bit sequence.

[0109] In this embodiment, demodulation extracts the modulated baseband signal, and combined with signal transformation to restore the real sequence, accurately restores the sparse signal transmitted by the transmitter. This effectively eliminates interference introduced by the underwater acoustic channel (such as noise and multipath), improving the system's stability in harsh environments. By converting the real sequence into a complex signal, accurately reconstructing the complex signal while fully preserving the transmitter's phase and amplitude information, and processing the complex signal through phase demodulation, the information bits in high-order modulation symbols (such as QAM) can be accurately restored, meeting the requirements of high data rate transmission, eliminating phase offset and distortion in channel transmission, and ensuring the accuracy of information bit restoration.

[0110] In one embodiment, based on the above-mentioned fourth embodiment, step S401 includes: performing carrier demodulation on the modulated information, removing the cyclic prefix and downsampling to obtain a downsampled signal; performing equalization processing on the downsampled signal in combination with channel estimation to output an equalized time domain signal; performing discrete Hartley transform demodulation on the equalized time domain signal to output a real number sequence.

[0111] It should be noted that the modulated information can be transmitted by the transmitter after carrier modulation. Carrier demodulation can convert the received modulated signal into a baseband signal by removing the high-frequency carrier component from the signal. At the receiver, the cyclic prefix is ​​removed to restore the original signal's time domain content. Downsampling can be performed by lowering the signal's sampling rate to reduce redundant data points. Channel estimation involves inferring the channel's transmission characteristics based on the characteristics of the received signal. The original characteristics of the signal can be restored by inversely compensating for the effects of the channel, resulting in an equalized time domain signal. This equalized time domain signal is then demodulated using a discrete Hartley transform to output a real number sequence.

[0112] For example, after the modulated signal passes through the channel, the received analog signal can be expressed as formula (9):

[0113]

[0114] In formula (9), is additive white Gaussian noise, and its power spectral density is The meanings of the remaining characters are given in formulas (7) and (8) and will not be repeated here. When the received signal is synchronized and the cyclic prefix length is greater than the maximum delay, the received signal can be expressed as formula (10).

[0115]

[0116] In formula (10), It can be expressed as the received signal synchronization, and the received signal with a cyclic prefix length greater than the maximum delay. It can be expressed as the received signal The components related to the subcarriers, It can be expressed as the received signal The components related to the subcarriers, Specifically, it can be expressed as formula (11):

[0117]

[0118] For the The subcarrier in the The phase offset related to an OFDM symbol period can be expressed as formula (12):

[0119]

[0120] is the time delay caused by the signal phase shift, which can be expressed as formula (13):

[0121]

[0122] After downsampling and DHT demodulation, the baseband signal is expressed as formula (14):

[0123]

[0124] In formula (14), Expressed as The baseband data symbols corresponding to the subcarriers are Expressed as the subcarriers, data symbols, Expressed as The noise on the subcarriers, and Expressed as The modulation coefficient corresponding to the subcarrier is and They are respectively expressed as formula (15) and formula (16):

[0125]

[0126] In the DHT-OFDM system, the time domain equalization method is used, and the equalization result of the received signal can be expressed as formula (17):

[0127]

[0128] In formula (17), Expressed as The equalization coefficients associated with each data symbol are Expressed as The equalization coefficients associated with each data symbol are Expressed as bit estimated value of the received signal, Expressed as bit estimated value of the received signal, and They are expressed as formula (18) and formula (19) respectively.

[0129]

[0130] In the above formula, Represents the phase offset. The communication rate of the system using real-complex conversion is expressed as formula (20):

[0131]

[0132] In formula (20), is the number of subcarriers, is the phase modulation parameter, which represents the number of digital bits per modulation symbol. is the channel coding rate, is the subcarrier spacing, = represents the number of subcarriers. The communication rate indicates the rate at which effective information bits are transmitted per unit time. Because complex conversion halves the communication rate, while QPSK modulation doubles it, the communication rate of a BPSK-modulated DHT-OFDM system without complex conversion is equal to that of a QPSK system with complex conversion, while the communication rate of a 16QAM system with complex conversion is twice that of these systems.

[0133] In this implementation, carrier demodulation is used to restore the high-frequency modulated signal to a baseband signal. Removing the cyclic prefix eliminates redundancy during transmission while preserving the integrity of the original signal and effectively reducing inter-symbol interference. Downsampling reduces redundant sampling points in the signal, reducing the amount of data and improving computational efficiency for subsequent signal processing. Using the results of channel estimation, the signal is equalized to inversely compensate for channel noise, multipath effects, and frequency-selective fading, restoring the signal's original characteristics. Signal equalization brings the signal closer to the baseband signal at the transmitter, reducing the bit error rate and improving the accuracy and reliability of data transmission.

[0134] In one implementation, based on the fourth embodiment, step S402 includes: performing real-to-complex conversion on the real sequence to output a frequency-domain complex signal; and performing high-order phase demodulation on the frequency-domain complex signal to obtain original information bits.

[0135] It should be noted that real-to-complex transform (R2CT) is the process of converting a real number sequence into a complex signal in the frequency domain. By combining the real and imaginary parts, the complex signal at the transmitter is restored. A complex signal in the frequency domain can be represented in complex form, containing both amplitude and phase information. High-order phase demodulation can recover the original bit stream from the frequency domain complex signal, completing the process of restoring the modulated signal to data bits.

[0136] For example, after the receiving end obtains the detected time domain signal through channel estimation and equalization processing, the transmission sequence is restored through the FHT signal , after real-to-complex transform (R2CT), the frequency domain transmission sequence is restored , the definition of R2CT is expressed as formula (21):

[0137]

[0138] In formula (21), and They are The real and imaginary parts of Expressed as Output sign of the bit.

[0139] In this embodiment, by performing real-to-complex conversion on the real sequence, the original information bits of the transmitter are extracted from the amplitude and phase of the complex signal, thereby ensuring the integrity and accuracy of the frequency domain complex signal. By performing high-order phase demodulation on the frequency domain complex signal, it can adapt to high data rate transmission requirements and provide technical support for high data rate and high bandwidth efficiency communications, while reducing the system operation complexity and improving demodulation efficiency.

[0140] In order to make the embodiments and implementation methods of this application clearer, a principle block diagram of implementing high-order symbol transmission of a DHT-OFDM system based on a real-complex conversion algorithm is provided as follows: Figure 5 In addition, it should be noted that for the discrete Hartley transform, considering the execution length N, the required computational complexity is ; For discrete Fourier transform, / 2 complex operations, or Therefore, at the same computation length, the computational complexity of DHT is reduced by 50% compared to FFT. C2RT, as a linear operation, does not increase the system computational complexity. Therefore, a DHT-OFDM system with C2RT can reduce the system computational complexity by 50% at the same communication rate.

[0141] In one embodiment, when C2RT is applied in the system, it is added as a separate module after phase modulation and before IDHT modulation at the transmitting end, and after DHT demodulation and before phase modulation at the receiving end. Figure 6 and Figure 7 They are the original constellation diagram of QPSK phase modulation and the constellation diagram after C2RT. Figure 8 and Figure 9 They are the original constellation diagram of 16QAM phase modulation and the constellation diagram after C2RT. Figures 6 to 9 In the equation, the horizontal axis means the in-phase component of the modulation signal, that is, the real part of the signal, which can be expressed as Re(x), and the vertical axis means the orthogonal component of the modulation signal, that is, the imaginary part of the signal, which can be expressed as Im(x). Figures 6 to 9 It can be seen that C2RT uniformly converts the complex symbols on the high-order modulation constellation diagram into symbols in the real domain. Moreover, since each high-order real-to-complex conversion contains the mapping result at the zero constellation point, and this part of the data will not cause inter-subcarrier interference during DHT-OFDM modulation and system transmission, it increases the sparsity of the transmitted signal on the basis of the original phase modulation result, reduces the impact of underwater acoustic channel interference, and increases transmission reliability. Figure 10 is the bit error rate performance of the C2RT algorithm in the OFDM system. Figure 10 It can be seen that at the same transmission data rate, the bit error rate performance of the system with C2RT is slightly better than that of the traditional OFDM system. This is due to the sparsity of the transmitted data after adding C2RT. Figure 11 To compare the transmission performance of DHT-OFDM with and without C2RT and traditional OFDM systems under different orders of high-order phase modulation. Figure 11 The DHT-BPSK and DHT-QPSK systems with C2RT have the same transmission data rate. The bit error rate deviation of the DHT-QPSK system with C2RT compared to the DHT-BPSK system is due to the closer distance between the constellation points in the high-order phase modulation. The DHT-16QAM modulation system with C2RT has the same transmission rate as the OFDM-QPSK system and achieves a gain of about 2.5dB. This shows that the DHT-OFDM system with C2RT has better communication performance than the traditional FFT-OFDM system at the same transmission data rate.

[0142] It should be noted that the above examples are only used to understand the present application and do not constitute a limitation on the transmission method of the orthogonal frequency division multiplexing water acoustic communication system of the present application. More simple transformations based on this technical concept are all within the scope of protection of the present application.

[0143] This application also provides an orthogonal frequency division multiplexing water acoustic communication system transmission device, please refer to Figure 12, the transmission device of the orthogonal frequency division multiplexing water acoustic communication system includes:

[0144] The modulation conversion module 10 is used to perform phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence, wherein the real number sequence has a sparse characteristic;

[0145] an inverse transform modulation module 20, configured to perform inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information;

[0146] An underwater acoustic channel transmission module 30, configured to transmit the modulated information to a receiving end via an underwater acoustic channel;

[0147] The demodulation and recovery module 40 is used to perform signal conversion and demodulation on the modulated information at the receiving end to recover the original information bits.

[0148] The OFDM acoustic communication system transmission device provided in this application utilizes the OFDM acoustic communication system transmission method described in the aforementioned embodiments, resolving the technical issue of unstable high-data-rate transmission in underwater acoustic channel environments. Compared to the prior art, the OFDM acoustic communication system transmission device provided in this application achieves the same beneficial effects as the OFDM acoustic communication system transmission method described in the aforementioned embodiments. Other technical features of the OFDM acoustic communication system transmission device are the same as those disclosed in the aforementioned embodiments and are not further detailed here.

[0149] The present application provides an orthogonal frequency division multiplexing (OFDM) water acoustic communication system transmission device, which includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the OFDM water acoustic communication system transmission method in the above-mentioned embodiment 1.

[0150] Reference below Figure 13 , which shows a schematic diagram of the structure of an orthogonal frequency division multiplexing (OFDM) acoustic communication system transmission device suitable for implementing the embodiments of the present application. The OFDM acoustic communication system transmission device in the embodiments of the present application may include, but is not limited to, mobile terminals such as mobile phones, laptop computers, digital broadcast receivers, PDAs (Personal Digital Assistants), PADs (Portable Application Descriptions), PMPs (Portable Media Players), in-vehicle terminals (e.g., in-vehicle navigation terminals), and fixed terminals such as digital TVs and desktop computers. Figure 13The OFDM acoustic communication system transmission device shown is merely an example and should not limit the functions and scope of use of the embodiments of the present application.

[0151] like Figure 13 As shown, the OFDM acoustic communication system transmission device may include a processing device 1001 (e.g., a central processing unit, a graphics processing unit, etc.), which can perform various appropriate actions and processes based on programs stored in a read-only memory (ROM) 1002 or programs loaded from a storage device 1003 into a random access memory (RAM) 1004. RAM 1004 also stores various programs and data required for the operation of the OFDM acoustic communication system transmission device. Processing device 1001, ROM 1002, and RAM 1004 are interconnected via a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Typically, the following systems can be connected to the I / O interface 1006: input devices 1007 including, for example, a touch screen, touchpad, keyboard, mouse, image sensor, microphone, accelerometer, gyroscope, etc.; output devices 1008 including, for example, a liquid crystal display (LCD), speaker, vibrator, etc.; storage devices 1003 including, for example, a magnetic tape, hard disk, etc.; and communication devices 1009. The communication device 1009 can allow the OFDM water acoustic communication system transmission device to communicate with other devices wirelessly or by wire to exchange data. Although Figure 13 The OFDM water acoustic communication system transmission device with various systems is shown, but it should be understood that it is not required to implement or have all the systems shown. More or fewer systems may be implemented or have instead.

[0152] In particular, according to the embodiments disclosed in the present application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, the embodiments disclosed in the present application include a computer program product comprising a computer program carried on a computer-readable medium, the computer program comprising program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network via a communication device, or installed from a storage device 1003, or installed from a ROM 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the method of the embodiment disclosed in the present application are executed.

[0153] The OFDM-based acoustic communication system transmission device provided in this application utilizes the OFDM-based acoustic communication system transmission method described in the aforementioned embodiment, resolving the technical issue of unstable high-data-rate transmission in underwater acoustic channel environments. Compared to the prior art, the OFDM-based acoustic communication system transmission device provided in this application achieves the same beneficial effects as the OFDM-based acoustic communication system transmission method described in the aforementioned embodiment. Other technical features of the OFDM-based acoustic communication system transmission device are the same as those disclosed in the aforementioned embodiment and are not further detailed here.

[0154] It should be understood that the various parts disclosed in this application can be implemented using hardware, software, firmware, or a combination thereof. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0155] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

[0156] The present application provides a computer-readable storage medium having computer-readable program instructions (ie, computer program) stored thereon, wherein the computer-readable program instructions are used to execute the transmission method of the orthogonal frequency division multiplexing water acoustic communication system in the above-mentioned embodiment.

[0157] The computer-readable storage medium provided herein may be, for example, a USB flash drive, but is not limited to electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, systems, or devices, or any combination thereof. More specific examples of computer-readable storage media may include, but are not limited to, an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In this embodiment, the computer-readable storage medium may be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, system, or device. The program code contained on the computer-readable storage medium may be transmitted using any suitable medium, including, but not limited to, wires, optical cables, RF (Radio Frequency), etc., or any suitable combination thereof.

[0158] The computer-readable storage medium may be included in the transmission device of the OFDM hydroacoustic communication system; or may exist independently without being assembled into the OFDM hydroacoustic communication system transmission device.

[0159] The above-mentioned computer-readable storage medium carries one or more programs. When the above-mentioned one or more programs are executed by the orthogonal frequency division multiplexing water acoustic communication system transmission equipment, the orthogonal frequency division multiplexing water acoustic communication system transmission equipment performs phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence, and the real number sequence has a sparse characteristic; performs inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information; sends the modulated information to the receiving end through the water acoustic channel; and performs signal conversion and demodulation on the modulated information at the receiving end to restore the original information bits.

[0160] Computer program code for performing the operations of the present application may be written in one or more programming languages, or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0161] The flow charts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, program segment or a part of code, and the module, program segment or a part of code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order than that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented by a dedicated hardware-based system that performs the specified function or operation, or can be implemented by a combination of dedicated hardware and computer instructions.

[0162] The modules described in the embodiments of the present application may be implemented in software or hardware, wherein the name of a module does not necessarily limit the unit itself.

[0163] The computer-readable storage medium provided in this application stores computer-readable program instructions (i.e., a computer program) for executing the aforementioned OFDM-based acoustic communication system transmission method. This computer-readable storage medium can address the technical issue of unstable high-data-rate transmission in underwater acoustic channel environments. Compared to the prior art, the computer-readable storage medium provided in this application offers the same beneficial effects as the OFDM-based acoustic communication system transmission method provided in the aforementioned embodiments, and will not be further elaborated upon here.

[0164] The present application also provides a computer program product, including a computer program, which implements the steps of the above-mentioned orthogonal frequency division multiplexing water acoustic communication system transmission method when executed by a processor.

[0165] The computer program product provided in this application can address the technical issue of unstable high-data-rate transmission in underwater acoustic channel environments. Compared to existing technologies, the computer program product provided in this application offers the same beneficial effects as the OFDM-based underwater acoustic communication system transmission method described in the aforementioned embodiments, and will not be further elaborated here.

[0166] The above description is only part of the embodiments of the present application and does not limit the patent scope of the present application. All equivalent structural transformations made by using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect application in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A transmission method for an orthogonal frequency division multiplexing water acoustic communication system, characterized in that: The method includes: Performing phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence, wherein the real number sequence has a sparse characteristic; Performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information; sending the modulated information to a receiving end via an underwater acoustic channel; Processing the modulated information through demodulation and signal transformation to restore the real number sequence; Converting the real number sequence into a complex number signal and recovering the original information bits through phase demodulation; The step of performing phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence includes: At the transmitting end, high-order phase modulation is performed on the transmitted information bits to obtain a complex signal; Performing sequence conversion on the complex signal using a real-to-complex conversion algorithm to obtain a real number sequence; The step of performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information includes: Performing inverse discrete Hartley transform modulation on the real number sequence to obtain a baseband signal; Upsampling the baseband signal and adding a cyclic prefix to obtain a preprocessed signal; Carrier modulation is performed on the preprocessed signal to obtain modulated information.

2. The method according to claim 1, wherein The step of processing the modulated information by demodulation and signal conversion to restore the real number sequence includes: Performing carrier demodulation on the modulated information, removing the cyclic prefix and performing downsampling to obtain a downsampled signal; performing equalization processing on the downsampled signal in combination with channel estimation, and outputting an equalized time domain signal; Discrete Hartley transform demodulation is performed on the equalized time domain signal to output a real number sequence.

3. The method according to claim 1, wherein The step of converting the real number sequence into a complex number signal and restoring the original information bits through phase demodulation comprises: Performing real-to-complex conversion on the real number sequence to output a frequency domain complex signal; High-order phase demodulation is performed on the frequency-domain complex signal to obtain original information bits.

4. The method according to claim 1, wherein The step of sending the modulated information to the receiving end through the underwater acoustic channel includes: Establishing a tap delay model based on the amplitude relationship corresponding to different moments of the channel, wherein the tap delay model is used to simulate the underwater acoustic channel; Based on the tap delay model, the modulated information is sent to a receiving end.

5. A transmission device for an orthogonal frequency division multiplexing water acoustic communication system, characterized in that: The device comprises: A modulation conversion module is used to perform phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence, wherein the real number sequence has a sparse characteristic; an inverse transform modulation module, configured to perform inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information; An underwater acoustic channel transmission module, configured to transmit the modulated information to a receiving end via an underwater acoustic channel; A demodulation recovery module is used to process the modulated information through demodulation and signal conversion to recover the real number sequence; convert the real number sequence into a complex signal, and recover the original information bits through phase demodulation; The modulation conversion module is further configured to perform high-order phase modulation on the transmitted information bits at the transmitting end to obtain a complex signal; and perform sequence conversion on the complex signal using a real-to-complex conversion algorithm to obtain a real sequence; The underwater acoustic channel transmission module is also used to perform inverse discrete Hartley transform modulation on the real number sequence to obtain a baseband signal; upsample the baseband signal and add a cyclic prefix to obtain a preprocessed signal; and perform carrier modulation on the preprocessed signal to obtain modulated information.

6. An orthogonal frequency division multiplexing water acoustic communication system transmission device, characterized in that: The device includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the orthogonal frequency division multiplexing water acoustic communication system transmission method according to any one of claims 1 to 4.

7. A storage medium, characterized in that: The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the transmission method of the orthogonal frequency division multiplexing water acoustic communication system according to any one of claims 1 to 4 are implemented.

8. A computer program product, characterized in that The computer program product includes a computer program, and when the computer program is executed by a processor, the steps of the orthogonal frequency division multiplexing water acoustic communication system transmission method according to any one of claims 1 to 4 are implemented.

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