Transmission method, device, equipment and product of orthogonal frequency division multiplexing underwater acoustic communication system

Abstract

The invention discloses an orthogonal frequency division multiplexing underwater acoustic communication system transmission method, device, equipment and product, and relates to the technical field of underwater acoustic communication, and the method comprises the steps: carrying out the phase modulation and linear conversion of a sending information bit at a sending end, and obtaining a real number sequence which 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 through an underwater acoustic channel; and performing signal conversion and demodulation on the modulated information at a receiving end, and recovering original information bits. An underwater acoustic channel has the characteristic suitable for transmitting sparse signals, complex signals are mapped into a sparse real number sequence suitable for an underwater acoustic system through phase modulation and linear conversion, and the influence of noise on the signals is reduced. Through effective transmission of high-order phase modulation symbols, the requirement of high-data-rate communication is met, original information bits are accurately restored through signal conversion and demodulation at a receiving end, and the transmission stability of an underwater acoustic channel is improved.

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) can effectively deal with the problems of multipath fading and frequency selective fading. However, the computational complexity of traditional OFDM systems is high, especially in scenarios with high data rate transmission, where frequent complex number operations burden the processing power of the equipment. In certain specific environments, especially the special propagation environment of underwater acoustic channels, signal attenuation and multipath effects further exacerbate the stability problem of 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 the present 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 an orthogonal frequency division multiplexing water acoustic communication system transmission method, the method comprising: 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 through an underwater acoustic channel; The modulated information is subjected to signal conversion and demodulation at the receiving end to restore the original information bits.

[0006] 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: At the transmitting end, high-order phase modulation is performed on the transmitted information bits to obtain a complex signal; The complex signal is sequence-converted by a real-to-complex conversion algorithm to obtain a real number sequence.

[0007] In one embodiment, 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.

[0008] 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: Processing the modulated information by demodulation and signal transformation to restore the real number sequence; The real number sequence is converted into a complex number signal, and the original information bits are restored through phase demodulation.

[0009] In one embodiment, the step of processing the modulated information by demodulation and signal transformation to restore the real number sequence includes: Carrier demodulation is performed on the modulated information, a cyclic prefix is ​​removed, and down-sampling is performed to obtain a down-sampled 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.

[0010] In one embodiment, the step of converting the real number sequence into a complex number signal and restoring the original information bits by phase demodulation includes: Performing real-to-complex conversion on the real number sequence, and outputting a frequency domain complex signal; High-order phase demodulation is performed on the frequency-domain complex signal to obtain original information bits.

[0011] In addition, to achieve the above-mentioned purpose, the present application also proposes an orthogonal frequency division multiplexing water acoustic communication system transmission device, and the orthogonal frequency division multiplexing water acoustic communication system transmission device includes: A modulation conversion module, used for 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; An inverse transform modulation module, used for performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information; An underwater acoustic channel transmission module, used to send the modulated information to a receiving end through an underwater acoustic channel; The demodulation recovery module is used to perform signal conversion and demodulation on the modulated information at the receiving end to recover the original information bits.

[0012] In addition, to achieve the above-mentioned purpose, the present application also proposes an orthogonal frequency division multiplexing water acoustic communication system transmission device, the device comprising: a memory, a processor, and a computer program stored on the memory and executable on the processor, the computer program being configured to implement the steps of the orthogonal frequency division multiplexing water acoustic communication system transmission method as described above.

[0013] 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 a processor, the steps of the orthogonal frequency division multiplexing water acoustic communication system transmission method as described above are implemented.

[0014] 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, the steps of the orthogonal frequency division multiplexing water acoustic communication system transmission method as described above are implemented.

[0015] One or more technical solutions proposed in this application have at least the following technical effects: At the transmitting end, the transmitted information bits are phase modulated and linearly transformed to obtain a real number sequence, which has a sparse characteristic; the real number sequence is modulated by inverse discrete Hartley transform to obtain the modulated information; the modulated information is sent to the receiving end through the underwater acoustic channel; at the receiving end, the modulated information is signal transformed and demodulated to restore the original information bits. Since the underwater acoustic channel has the characteristics of being suitable for transmitting sparse signals, the complex signal is mapped into a sparse real number sequence suitable for the underwater acoustic system through phase modulation combined with linear transformation, reducing the impact of multipath interference and noise on the signal and improving the transmission stability and anti-interference ability of the system. By utilizing the characteristics of inverse discrete Hartley transform (IDHT) modulation and sparse signals, the modulation and demodulation calculation complexity of the transmitting and receiving ends is simplified, and the processing requirements of the equipment are reduced. By combining the real-complex conversion algorithm, the effective transmission of high-order phase modulation symbols is realized to meet the needs of high data rate communication. The receiving end accurately restores the original information bits through signal transformation and demodulation, using discrete Hartley transform and complex recovery technology, further improving the reliability and stability of communication in the underwater acoustic channel environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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.

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0018] Figure 1 This is a flow chart of the first embodiment of the transmission method of the orthogonal frequency division multiplexing hydroacoustic communication system of the present application; Figure 2 This is a flow chart of a second embodiment of the transmission method of an orthogonal frequency division multiplexing hydroacoustic communication system of the present application; Figure 3 This is a flow chart of a third embodiment of the transmission method of an orthogonal frequency division multiplexing hydroacoustic communication system of the present application; Figure 4 This is a flowchart of a fourth embodiment of the transmission method of an orthogonal frequency division multiplexing hydroacoustic communication system of the present application; Figure 5 This is a block diagram of the principle of implementing high-order symbol transmission of the DHT-OFDM system based on the real-complex conversion algorithm of this application; Figure 6 QPSK constellation diagram for this application; Figure 7 Added QPSK constellation diagram of C2RT for this application; Figure 8 This is the 16QAM constellation diagram for this application; Fig. 9 Added 16QAM constellation diagram of C2RT for this application; Fig.10 This is the simulation diagram of C2RT in OFDM system of this application; Fig.11 A comparison chart of transmission performance of DHT-OFDM and traditional OFDM systems with and without C2RT is added for this application; Fig.12 This is a schematic diagram of the module structure of a transmission device of an orthogonal frequency division multiplexing hydroacoustic communication system according to an embodiment of the present application; Fig.13 Schematic diagram of the device structure of the hardware operating environment involved in the transmission method of the orthogonal frequency division multiplexing hydroacoustic communication system in the embodiment of the present application.

[0019] The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0020] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0021] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0022] Although the traditional OFDM system has good anti-interference ability, its computational complexity is high, especially in the scenario of high data rate transmission, frequent complex number operations lead to a burden on the processing power of the device. Therefore, as a solution based on real number operations, the Discrete Hartley Transform - Orthogonal Frequency Division Multiplexing (DHT-OFDM) system can significantly reduce the computational complexity by using discrete Hartley transform (DHT) instead of traditional discrete Fourier transform (DFT), thereby achieving low power consumption and efficient signal processing. However, the limitation of DHT-OFDM is that it only supports transmission in the real number domain, so it cannot directly support high-order phase modulation such as QAM (quadrature amplitude modulation). This limitation makes the system face challenges in high data rate transmission, especially in application scenarios with high transmission rate requirements, the bandwidth utilization of the communication system cannot be fully utilized, resulting in data transmission efficiency being restricted.

[0023] In certain specific environments, especially in the special propagation environment of underwater acoustic channels, signal attenuation and multipath effects further exacerbate the stability problem of high data rate transmission. Underwater acoustic channels have characteristics such as frequency selective fading and signal distortion, which can easily cause significant interference to the signal, resulting in the inability of the receiving end to effectively restore the original information, thus affecting the transmission stability and reliability of the system. Therefore, achieving stable transmission of high data rates in underwater acoustic channels has become a technical challenge.

[0024] The present application provides a solution, which performs 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; performs inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information; sends the modulated information to the receiving end through an underwater acoustic channel; performs signal conversion and demodulation on the modulated information at the receiving end to restore the original information bits. Since the underwater acoustic channel has the characteristics of being suitable for transmitting sparse signals, the complex signal is mapped into a sparse real number sequence suitable for the underwater acoustic system through phase modulation combined with linear conversion, reducing the impact of multipath interference and noise on the signal, and improving the transmission stability and anti-interference ability of the system. By utilizing the characteristics of inverse discrete Hartley transform modulation and sparse signals, the modulation and demodulation calculation complexity of the transmitting end and the receiving end is simplified, and the processing requirements of the equipment are reduced. By combining the real-complex conversion algorithm, the effective transmission of high-order phase modulation symbols is realized to meet the needs of high data rate communication. The receiving end accurately restores the original information bits through signal conversion and demodulation, using discrete Hartley transform and complex recovery technology, and further improves the reliability and stability of communication in the underwater acoustic channel environment.

[0025] 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 hydroacoustic communication system of the present application.

[0026] In this embodiment, the OFDM water acoustic communication system transmission method includes steps S10 to S40: Step S10, phase modulation and linear conversion are performed on the transmitted information bits at the transmitting end to obtain a real number sequence, which has a sparse characteristic.

[0027] It should be noted that the transmitted information bits can be understood as the raw data in the communication system, usually a bit stream in binary form. Phase modulation is a digital modulation method that represents different information bits by changing the phase of the carrier signal. Linear conversion can be understood as maintaining the linear structure of the data by converting a complex signal or data sequence into another form, that is, converting the phase modulated signal into a real sequence. The sparse characteristic can be understood as the characteristic that most elements in the signal are zero and only a few elements are non-zero. In the communication system, sparse signals can effectively reduce the complexity of data transmission, reduce the power consumption of the system, and improve the stability of the signal in a noisy environment.

[0028] Step S20, performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information.

[0029] It should be noted that the discrete Hartley transform (DHT) can be a transform similar to the Fourier transform, which is mainly used for the frequency domain representation of the signal. 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.

[0030] Step S30, sending the modulated information to the receiving end through the underwater acoustic channel.

[0031] It should be noted that the underwater acoustic channel can be understood as a sound wave propagation channel in an underwater environment. In underwater communications, sound wave signals propagate through water and are affected by factors such as multipath fading, noise, and signal attenuation.

[0032] Step S40: performing signal conversion and demodulation on the modulated information at the receiving end to restore the original information bits.

[0033] 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 frequency domain or time domain) into a format suitable for demodulation, which can include, for example, conversion from frequency domain to time domain or other forms. Demodulation can be understood as the receiver restoring the original transmitted information bits through an algorithm.

[0034] In this embodiment, since the underwater acoustic channel has the characteristics of being suitable for transmitting sparse signals, the complex signal is mapped into a sparse real number sequence suitable for the underwater acoustic system through phase modulation combined with linear conversion, thereby reducing the impact of multipath interference and noise on the signal and improving the transmission stability and anti-interference ability of the system. By utilizing the characteristics of inverse discrete Hartley transform modulation and sparse signals, the modulation and demodulation calculation 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 receiving end 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.

[0035] Reference Figure 2 , Figure 2 This is a flow chart of the second embodiment of the transmission method of the orthogonal frequency division multiplexing water acoustic communication system of the present application. 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.

[0036] In the second embodiment, the step S10 includes: Step S101: high-order phase modulation is performed on the transmitted information bits at the transmitting end to obtain a complex signal.

[0037] It should be noted that high-order phase modulation can encode information bits by changing the phase of the carrier signal. For example, the high-order phase modulation can be quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM). It can be 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.

[0038] Step S102, performing sequence conversion on the complex signal by using a real-to-complex conversion algorithm to obtain a real number sequence.

[0039] 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. It can be applied to the underwater acoustic DHT-OFDM communication system to realize the transmission of high-order phase symbols. It 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. Exemplarily, 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 length of the output real sequence is N , the range of values ​​in the sequence is ,in, Expressed as a complex result after phase modulation The corresponding real value, Expressed as a complex result after phase modulation The corresponding imaginary value.

[0040] 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):

[0041] 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):

[0042] In formula (2), Nis the IDHT / DHT point, for real number input sequence After IDHT operation, a bipolar time domain signal is obtained.

[0043] In this embodiment, by performing high-order phase modulation on the transmitted information bits at the transmitting end, multiple bits can be encoded in one symbol to achieve high data rate transmission, meeting different requirements for data rate and anti-interference capability. By carrying data simultaneously 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 to adapt it to the processing requirements of the discrete Hartley transform (DHT). The real sequence generated by the real-to-complex conversion usually has a sparse characteristic (most values ​​are close to zero), which can effectively reduce redundant information in data transmission and improve transmission efficiency.

[0044] Reference Figure 3 , Figure 3 This is a flow chart of the third embodiment of the transmission method of the orthogonal frequency division multiplexing water acoustic communication system of the present application. Figure 2 The second embodiment shown provides a third embodiment of the transmission method of the orthogonal frequency division multiplexing hydroacoustic communication system of the present application.

[0045] In the third embodiment, the step S20 includes: Step S201, performing inverse discrete Hartley transform modulation on the real number sequence to obtain a baseband signal.

[0046] It should be noted that the Inverse Discrete Hartley Transform (IDHT) and the Discrete Hartley Transform (DHT) are inverse operations of each other, which convert the real number sequence in the frequency domain into a time domain signal to generate a baseband signal.

[0047] Step S202: upsample the baseband signal and add a cyclic prefix to obtain a preprocessed signal.

[0048] It should be noted that upsampling is to increase the sampling rate of the signal to a higher frequency to adapt to the subsequent signal processing or transmission requirements. Exemplarily, the number of sampling points of the signal can be expanded by inserting zero values ​​between the original sampling points to improve the resolution of the signal. The cyclic prefix can be a portion of the copied tail data added before each signal frame. The preprocessed signal is the signal after upsampling and adding the cyclic prefix.

[0049] Step S203, performing carrier modulation on the preprocessed signal to obtain modulated information.

[0050] It should be noted that carrier modulation can be a process of transferring a baseband signal to a target frequency range by mixing it with a high-frequency carrier signal. The modulated information can be understood as an output signal of carrier modulation, which is adapted to the transmission format of the underwater acoustic channel.

[0051] For example, the transformation between DHT and IDHT can be expressed as formula (3):

[0052] In formula (3), Represents the initial sending signal, It is represented as DHT modulation signal. It should be noted that the kernel function of DHT can be expressed as formula (4):

[0053] According to the DHT transformation formula, DHT and IDHT have the same form and satisfy formula (5):

[0054] In formula (5), represents the index of the DHT transformation input, k It is represented 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):

[0055] 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):

[0056] 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, It is expressed as symbol period. When the transmitted signal is transmitted in the underwater acoustic channel, only the multipath transmission characteristics are considered. The underwater acoustic channel can be described by the tap delay model as formula (8):

[0057] 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.

[0058] 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 the computational complexity and power consumption. The real number sequence in the frequency domain is converted into a baseband signal in the time domain to provide 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.

[0059] Reference Figure 4 , Figure 4 This is a flow chart of the fourth embodiment of the transmission method of the orthogonal frequency division multiplexing hydroacoustic communication system of the present application. Figure 3 The third embodiment shown is a fourth embodiment of the transmission method of the orthogonal frequency division multiplexing hydroacoustic communication system of the present application.

[0060] In the fourth embodiment, the step S40 includes: Step S401, processing the modulated information by demodulation and signal transformation to restore the real number sequence.

[0061] It should be noted that demodulation can extract the original baseband signal from the carrier signal, remove the high-frequency components of the carrier, and restore the signal to the low-frequency domain. Signal transformation restores the received baseband signal from the time domain to the frequency domain through the discrete Hartley transform (DHT) to reconstruct the original real number sequence.

[0062] Step S402: convert the real number sequence into a complex number signal, and restore the original information bits through phase demodulation.

[0063] It should be noted that phase demodulation can be a process of restoring a complex signal to the original bit information, and extracting the encoded data by analyzing the phase change of the complex signal. Exemplary phase demodulation methods may include QAM, PSK, etc., matching the original bit sequence according to the received phase value.

[0064] In this embodiment, the modulated baseband signal is extracted by demodulation, and the real sequence is restored in combination with signal transformation to accurately restore the sparse signal transmitted by the transmitter, which can effectively eliminate the interference (such as noise and multipath effect) introduced by the underwater acoustic channel and improve the stability of the system in harsh environments. By converting the real sequence into a complex signal, accurately reconstructing the complex signal, and completely retaining the phase and amplitude information of the transmitter, the complex signal is processed by phase demodulation, and the information bits in the high-order modulation (such as QAM) symbols can be accurately restored to meet the needs of high data rate transmission, eliminate phase offset and distortion in channel transmission, and ensure the restoration accuracy of the information bits.

[0065] In one embodiment, based on the above-mentioned fourth embodiment, the 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.

[0066] It should be noted that the modulated information can be transmitted by the transmitter after carrier modulation, and carrier demodulation can convert the received modulated signal into a baseband signal by removing the high-frequency carrier component in the signal. The cyclic prefix is ​​removed at the receiving end to restore the time domain content of the original signal, and downsampling can be to reduce the sampling rate of the signal to reduce redundant data points in the signal. Channel estimation means to infer the transmission characteristics of the channel based on the characteristics of the received signal. The original characteristics of the signal can be restored by inversely compensating the influence of the channel to obtain the equalized time domain signal, and the equalized time domain signal is demodulated by discrete Hartley transform to output a real number sequence.

[0067] For example, after the modulated signal passes through the channel, the received analog signal can be expressed as formula (9):

[0068] In formula (9), is additive Gaussian white noise, and its power spectral density is The meanings of the remaining characters are given in formula (7) and formula (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).

[0069]

[0070] 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 components related to the subcarriers are It can be expressed as The components related to the subcarriers are It can be specifically expressed as formula (11):

[0071] For the The subcarrier is The phase offset related to an OFDM symbol period can be expressed as formula (12):

[0072] is the time delay caused by the signal phase shift, which can be expressed as formula (13):

[0073] After downsampling and DHT demodulation, the baseband signal is expressed as formula (14):

[0074] In formula (14), Expressed as The baseband data symbol corresponding to the subcarriers is Expressed as the subcarriers, 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):

[0075] 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):

[0076] 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 received signal estimate, Expressed as bit received signal estimate, and They are expressed as formula (18) and formula (19) respectively.

[0077]

[0078] In the above formula, Represents the phase offset. The communication rate of the system using real-complex conversion is expressed as formula (20):

[0079] In formula (20), is the number of subcarriers, is the phase modulation parameter, which indicates the number of digital bits per modulation symbol. is the channel coding rate, is the subcarrier spacing, Indicates the number of subcarriers. The communication rate indicates the rate at which effective information bits are transmitted per unit time. Since complex conversion will halve the communication rate, and QPSK modulation can double the communication rate, the communication rate of the BPSK modulation DHT-OFDM system without complex conversion is equal to the communication rate of the QPSK system after complex conversion, and the communication rate of the 16QAM system after complex conversion is twice that of the above systems.

[0080] In this embodiment, the high-frequency modulated signal is restored to the baseband signal through carrier demodulation, and the cyclic prefix is ​​removed to remove the redundant part in the transmission process, while retaining the integrity of the original signal, effectively reducing the inter-symbol interference. The redundant sampling points in the signal are reduced by downsampling, the amount of data is reduced, and the calculation efficiency for subsequent signal processing is improved. Using the results of channel estimation, the signal is equalized to inversely compensate for the noise, multipath effect and frequency selective fading in the channel to restore the original characteristics of the signal. Through signal equalization, the signal is made closer to the baseband signal of the transmitter, the bit error rate is reduced, and the accuracy and reliability of data transmission are improved.

[0081] 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.

[0082] It should be noted that the real-to-complex transform (R2CT) can be a process of converting a real sequence into a complex signal in the frequency domain, and restoring the complex signal at the transmitter by combining the real part and the imaginary part. The complex signal in the frequency domain can be represented by a complex number form, including amplitude and phase information. High-order phase demodulation can restore the original bit stream from the complex signal in the frequency domain, completing the restoration from the modulated signal to the data bit.

[0083] Exemplarily, 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):

[0084] In formula (21), and They are The real and imaginary parts of Expressed as The output sign of the bit.

[0085] In this implementation, by performing real-to-complex conversion on the real number 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.

[0086] In order to make the embodiments and implementation methods of the present 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 operation of execution length N, the required computational complexity is ; For discrete Fourier transform, we need / 2 complex operations, or Therefore, under the same calculation length, the computational complexity of DHT is reduced by 50% compared with FFT. As a linear operation, C2RT does not increase the computational complexity of the system. Therefore, the DHT-OFDM system with C2RT can reduce the computational complexity of the system by 50% under the same communication rate.

[0087] In one implementation, 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 Fig. 9 They are the original constellation diagram of 16QAM phase modulation and the constellation diagram after C2RT. Figures 6 to 9In 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 number domain, and 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 interference between subcarriers 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. Fig.10 is the bit error rate performance of the C2RT algorithm in the OFDM system. Fig.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. Fig.11 The transmission performance of DHT-OFDM with and without C2RT and traditional OFDM system under different orders of high-order phase modulation. Fig.11 The DHT-BPSK and DHT-QPSK systems with C2RT added have the same transmission data rate. The error rate deviation of DHT-QPSK with C2RT added relative to DHT-BPSK system is due to the closer distance between constellation points in high-order phase modulation. The DHT-16QAM modulation system with C2RT added has the same transmission rate relative to OFDM-QPSK system and achieves a gain of about 2.5dB, indicating that the DHT-OFDM system with C2RT added has better communication performance than the traditional FFT-OFDM system at the same transmission data rate.

[0088] 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 protection scope of the present application.

[0089] The present application also provides an orthogonal frequency division multiplexing water acoustic communication system transmission device, please refer to Fig.12 , the transmission device of the orthogonal frequency division multiplexing water acoustic communication system comprises: 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; An inverse transform modulation module 20, used for performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information; An underwater acoustic channel transmission module 30, used to send the modulated information to a receiving end through an underwater acoustic channel; The demodulation 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.

[0090] The orthogonal frequency division multiplexing water acoustic communication system transmission device provided by the present application adopts the orthogonal frequency division multiplexing water acoustic communication system transmission method in the above embodiment, which can solve the technical problem of unstable high data rate transmission in the water acoustic channel environment. Compared with the prior art, the beneficial effects of the orthogonal frequency division multiplexing water acoustic communication system transmission device provided by the present application are the same as the beneficial effects of the orthogonal frequency division multiplexing water acoustic communication system transmission method provided by the above embodiment, and the other technical features in the orthogonal frequency division multiplexing water acoustic communication system transmission device are the same as the features disclosed in the above embodiment method, which will not be repeated here.

[0091] The present application provides an orthogonal frequency division multiplexing 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 orthogonal frequency division multiplexing water acoustic communication system transmission method in the above-mentioned embodiment 1.

[0092] Reference below Fig.13 , which shows a schematic diagram of the structure of an orthogonal frequency division multiplexing water acoustic communication system transmission device suitable for implementing the embodiment of the present application. The orthogonal frequency division multiplexing water acoustic communication system transmission device in the embodiment 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), vehicle-mounted terminals (such as vehicle-mounted navigation terminals), etc., and fixed terminals such as digital TVs, desktop computers, etc. Fig.13 The OFDM water acoustic communication system transmission device shown is only an example and should not bring any limitation to the functions and scope of use of the embodiments of the present application.

[0093] like Fig.13As shown, the transmission device of the OFDM water acoustic communication system may include a processing device 1001 (such as a central processing unit, a graphics processor, etc.), which can perform various appropriate actions and processes according to the program stored in the read-only memory (ROM: Read Only Memory) 1002 or the program loaded from the storage device 1003 to the random access memory (RAM: Random Access Memory) 1004. Various programs and data required for the operation of the OFDM water acoustic communication system transmission device are also stored in the RAM 1004. The processing device 1001, the ROM 1002 and the RAM 1004 are connected to each other through a bus 1005. The 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, a touchpad, a keyboard, a mouse, an image sensor, a microphone, an accelerometer, a gyroscope, etc.; output devices 1008 including, for example, a liquid crystal display (LCD), a speaker, a vibrator, etc.; storage devices 1003 including, for example, a magnetic tape, a hard disk, etc.; and communication devices 1009. The communication device 1009 can allow an orthogonal frequency division multiplexing hydroacoustic communication system transmission device to communicate with other devices wirelessly or by wire to exchange data. Although Fig.13 The OFDM hydroacoustic 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.

[0094] In particular, according to the embodiments disclosed in the present application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in the present application include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a 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 through 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.

[0095] The orthogonal frequency division multiplexing water acoustic communication system transmission device provided by the present application adopts the orthogonal frequency division multiplexing water acoustic communication system transmission method in the above embodiment, which can solve the technical problem of unstable high data rate transmission in the water acoustic channel environment. Compared with the prior art, the beneficial effects of the orthogonal frequency division multiplexing water acoustic communication system transmission device provided by the present application are the same as the beneficial effects of the orthogonal frequency division multiplexing water acoustic communication system transmission method provided by the above embodiment, and the other technical features in the orthogonal frequency division multiplexing water acoustic communication system transmission device are the same as the features disclosed in the method of the previous embodiment, which will not be repeated here.

[0096] It should be understood that the various parts disclosed in this application can be implemented by 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.

[0097] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0098] The present application provides a computer-readable storage medium having computer-readable program instructions (ie, computer programs) stored thereon, and the computer-readable program instructions are used to execute the transmission method of the orthogonal frequency division multiplexing hydroacoustic communication system in the above-mentioned embodiment.

[0099] The computer-readable storage medium provided in the present application 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 of the above. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM: Random Access Memory), a read-only memory (ROM: Read Only Memory), an erasable programmable read-only memory (EPROM: Erasable Programmable Read Only Memory or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM: CD-Read Only Memory), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program, which may be used by or in combination with an instruction execution system, system or device. The program code contained on the computer-readable storage medium may be transmitted using any appropriate medium, including but not limited to: wires, optical cables, RF (Radio Frequency: Radio Frequency), etc., or any suitable combination of the above.

[0100] The computer-readable storage medium may be included in the OFDM hydroacoustic communication system transmission device; or may exist independently without being assembled into the OFDM hydroacoustic communication system transmission device.

[0101] 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.

[0102] 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 separate 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 through 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).

[0103] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present application. In this regard, each square box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the 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 square box can also occur in a sequence different from that marked in the accompanying drawings. For example, two square 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 square box in the block diagram and / or flow chart, and the combination of the square boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0104] The modules involved in the embodiments described in this application may be implemented by software or hardware, wherein the name of the module does not constitute a limitation on the unit itself in some cases.

[0105] The readable storage medium provided in the present application is a computer-readable storage medium, which stores computer-readable program instructions (i.e., computer programs) for executing the above-mentioned orthogonal frequency division multiplexing water acoustic communication system transmission method, and can solve the technical problem of unstable high data rate transmission in the water acoustic channel environment. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided in the present application are the same as the beneficial effects of the orthogonal frequency division multiplexing water acoustic communication system transmission method provided in the above-mentioned embodiment, and will not be repeated here.

[0106] 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.

[0107] The computer program product provided by the present application can solve the technical problem of unstable high data rate transmission in an underwater acoustic channel environment. Compared with the prior art, the beneficial effects of the computer program product provided by the present application are the same as the beneficial effects of the transmission method of the orthogonal frequency division multiplexing underwater acoustic communication system provided by the above embodiment, and will not be repeated here.

[0108] The above descriptions are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A transmission method of an orthogonal frequency division multiplexing hydroacoustic 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 through an underwater acoustic channel; The modulated information is subjected to signal conversion and demodulation at the receiving end to restore the original information bits.

2. The method according to claim 1, characterized in that The step of performing phase modulation and linear conversion on the transmitted information bits at the transmitting end to obtain a real number sequence comprises: At the transmitting end, high-order phase modulation is performed on the transmitted information bits to obtain a complex signal; The complex signal is sequence-converted by a real-to-complex conversion algorithm to obtain a real number sequence.

3. The method according to claim 2, characterized in that The step of performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information comprises: 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.

4. The method according to any one of claims 1 to 3, characterized in that The step of performing signal conversion and demodulation on the modulated information at the receiving end to restore the original information bits includes: Processing the modulated information by demodulation and signal transformation to restore the real number sequence; The real number sequence is converted into a complex number signal, and the original information bits are restored through phase demodulation.

5. The method according to claim 4, characterized in that The step of processing the modulated information by demodulation and signal transformation to restore the real number sequence comprises: Carrier demodulation is performed on the modulated information, a cyclic prefix is ​​removed, and down-sampling is performed to obtain a down-sampled 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.

6. The method according to claim 5, characterized in that The step of converting the real number sequence into a complex number signal and restoring the original information bits by phase demodulation comprises: Performing real-to-complex conversion on the real number sequence, and outputting a frequency domain complex signal; High-order phase demodulation is performed on the frequency domain complex signal to obtain original information bits.

7. A transmission device for an orthogonal frequency division multiplexing hydroacoustic communication system, characterized in that: The device comprises: A modulation conversion module, used for 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; An inverse transform modulation module, used for performing inverse discrete Hartley transform modulation on the real number sequence to obtain modulated information; An underwater acoustic channel transmission module, used to send the modulated information to a receiving end through an underwater acoustic channel; The demodulation recovery module is used to perform signal conversion and demodulation on the modulated information at the receiving end to recover the original information bits.

8. An orthogonal frequency division multiplexing hydroacoustic communication system transmission device, characterized in that: The device comprises: 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 transmission method of an orthogonal frequency division multiplexing water acoustic communication system according to any one of claims 1 to 6.

9. 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 an orthogonal frequency division multiplexing water acoustic communication system according to any one of claims 1 to 6 are implemented.

10. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the steps of the transmission method of an orthogonal frequency division multiplexing hydroacoustic communication system according to any one of claims 1 to 6 are implemented.

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