CN119383050A - Orthogonal frequency division multiplexing hydroacoustic communication system transmission method, device, equipment and product - Google Patents
Orthogonal frequency division multiplexing hydroacoustic communication system transmission method, device, equipment and product Download PDFInfo
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Abstract
The application discloses a transmission method, a device, equipment and a product of an orthogonal frequency division multiplexing underwater acoustic communication system, and relates to the technical field of underwater acoustic communication, wherein the method comprises the steps of carrying out phase modulation and linear conversion on transmitted information bits at a transmitting end to obtain a real number sequence, wherein the real number sequence has sparse characteristics; the method comprises the steps of carrying out inverse discrete Hartley transformation modulation on a real number sequence to obtain modulated information, sending the modulated information to a receiving end through an underwater sound channel, carrying out signal transformation and demodulation on the modulated information at the receiving end, and recovering original information bits. The underwater acoustic channel has the characteristic of being suitable for transmitting sparse signals, and complex signals are mapped into sparse real sequences suitable for an underwater acoustic system through phase modulation and linear conversion, so that the influence of noise on the signals is reduced. The high-order phase modulation symbol is effectively transmitted, so that 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 stability of underwater acoustic channel transmission is improved.
Description
Technical Field
The application relates to the technical field of underwater acoustic communication, in particular to a transmission method, a transmission device, a transmission equipment and a transmission product of an orthogonal frequency division multiplexing underwater acoustic communication system.
Background
In modern communication systems, orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) can effectively cope with the problems of multipath fading and frequency selective fading. However, the computational complexity of conventional OFDM systems is high, especially in the context of high data rate transmissions, where frequent complex operations lead to a burden on the processing power of the device. In certain specific environments, particularly in the particular propagation environment of the underwater acoustic channel, signal attenuation and multipath effects further exacerbate the stability problem of high data rate transmissions.
Therefore, how to achieve stable transmission with high data rate in the underwater acoustic channel is a problem to be solved.
Disclosure of Invention
The application mainly aims to provide a transmission method, a device, equipment and a product of an orthogonal frequency division multiplexing underwater acoustic communication system, which aim to solve the technical problem of unstable high data rate transmission in an underwater acoustic channel environment.
In order to achieve the above object, the present application provides a transmission method of an orthogonal frequency division multiplexing underwater acoustic communication system, the method comprising:
Carrying out phase modulation and linear conversion on the transmitted information bits at a transmitting end to obtain a real number sequence, wherein the real number sequence has sparse characteristics;
performing inverse discrete hartley transformation modulation on the real number sequence to obtain modulated information;
transmitting the modulated information to a receiving end through an underwater sound channel;
And carrying out signal conversion and demodulation on the modulated information at a receiving end, and recovering original information bits.
In an embodiment, the step of performing phase modulation and linear conversion on the transmission information bits at the transmitting end to obtain a real number sequence includes:
Performing high-order phase modulation on the transmitted information bits at a transmitting end to obtain a complex signal;
And performing sequence conversion on the complex signal through a real-complex conversion algorithm to obtain a real sequence.
In an embodiment, the step of performing inverse discrete hartley transform modulation on the real number sequence to obtain modulated information includes:
performing inverse discrete Hartley transformation modulation on the real number sequence to obtain a baseband signal;
up-sampling the baseband signal, and adding a cyclic prefix to obtain a preprocessed signal;
And carrying out carrier modulation on the preprocessed signals to obtain modulated information.
In an embodiment, the step of performing signal conversion and demodulation on the modulated information at the receiving end to recover the original information bits includes:
the modulated information is processed through demodulation and signal transformation, and a real number sequence is recovered;
the real sequence is converted into a complex signal and the original information bits are recovered by phase demodulation.
In one embodiment, the step of recovering the real number sequence by demodulating and signal converting the modulated information includes:
Carrying out carrier demodulation on the modulated information, removing the cyclic prefix and carrying out downsampling to obtain a downsampled signal;
carrying out equalization processing on the down-sampled signal by combining with channel estimation, and outputting an equalized time domain signal;
And performing discrete Hartley transform demodulation on the equalized time domain signal, and outputting a real number sequence.
In one embodiment, the step of converting the real sequence into a complex signal and recovering the original information bits by phase demodulation includes:
performing real-to-complex conversion on the real sequence and outputting a frequency domain complex signal;
and performing high-order phase demodulation on the frequency domain complex signal to obtain original information bits.
In addition, to achieve the above object, the present application also provides an ofdm underwater acoustic communication system transmission apparatus, including:
the modulation conversion module is used for carrying out 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 sparse characteristics;
The inverse transformation modulation module is used for carrying out inverse discrete Hartley transformation modulation on the real number sequence to obtain modulated information;
The underwater sound channel transmission module is used for transmitting the modulated information to a receiving end through an underwater sound channel;
And the demodulation recovery module is used for carrying out signal conversion and demodulation on the modulated information at the receiving end and recovering original information bits.
In addition, in order to achieve the above object, the present application also proposes an apparatus for transmitting an orthogonal frequency division multiplexing underwater acoustic communication system, the apparatus 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 method for transmitting an orthogonal frequency division multiplexing underwater acoustic communication system as described above.
In addition, in order to achieve the above object, the present application also proposes a storage medium, which is a computer-readable storage medium, on which a computer program is stored, the computer program implementing the steps of the transmission method of the orthogonal frequency division multiplexing underwater acoustic communication system as described above when being executed by a processor.
Furthermore, to achieve the above object, the present application provides a computer program product comprising a computer program which, when executed by a processor, implements the steps of the method for transmitting an orthogonal frequency division multiplexing underwater acoustic communication system as described above.
One or more technical schemes provided by the application have at least the following technical effects:
the method comprises the steps of carrying out phase modulation and linear conversion on transmitted information bits at a transmitting end to obtain a real number sequence, carrying out inverse discrete Hartley transformation modulation on the real number sequence to obtain modulated information, transmitting the modulated information to a receiving end through an underwater sound channel, carrying out signal transformation and demodulation on the modulated information at the receiving end, and recovering original information bits. Because the underwater acoustic channel has the characteristic of being suitable for transmitting sparse signals, complex signals are mapped into sparse real sequences suitable for an underwater acoustic system through phase modulation and linear conversion, the influence of multipath interference and noise on the signals is reduced, and the transmission stability and the anti-interference capability of the system are improved. By utilizing the characteristics of the Inverse Discrete Hartley Transformation (IDHT) modulation and sparse signals, the modulation and demodulation calculation complexity of a transmitting end and a receiving end is simplified, and the processing requirement of equipment is reduced. By combining with the real-complex conversion algorithm, the efficient transmission of the high-order phase modulation symbols is realized, and the requirement of high-data-rate communication is met. The receiving end accurately restores original information bits by utilizing discrete Hartley transformation and complex number recovery technology through signal transformation and demodulation, and further improves the reliability and stability of communication in the underwater acoustic channel environment.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and together with the description, serve to explain the principles of the application.
In order to more clearly illustrate the embodiments of the application or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, and it will be obvious to a person skilled in the art that other drawings can be obtained from these drawings without inventive effort.
Fig. 1 is a schematic flow chart of a first embodiment of a transmission method of an ofdm underwater acoustic communication system according to the present application;
fig. 2 is a schematic flow chart of a second embodiment of a transmission method of an ofdm underwater acoustic communication system according to the present application;
fig. 3 is a schematic flow chart of a third embodiment of a transmission method of an ofdm underwater acoustic communication system according to the present application;
Fig. 4 is a schematic flow chart of a fourth embodiment of a transmission method of an ofdm underwater acoustic communication system according to the present application;
fig. 5 is a schematic block diagram of implementing DHT-OFDM system high-order symbol transmission based on real-complex conversion algorithm in the present application;
fig. 6 is a QPSK constellation according to the present application;
Fig. 7 is a QPSK constellation with C2RT added according to the present application;
Fig. 8 is a 16QAM constellation according to the present application;
fig. 9 is a 16QAM constellation with C2RT added according to the present application;
FIG. 10 is a simulation diagram of the C2RT of the present application in an OFDM system;
FIG. 11 is a graph showing transmission performance of the DHT-OFDM system with and without C2RT and the conventional OFDM system according to the present application;
fig. 12 is a schematic block diagram of a transmission device of an ofdm underwater acoustic communication system according to an embodiment of the present application;
fig. 13 is a schematic diagram of a device structure of a hardware operating environment related to a transmission method of an ofdm underwater acoustic communication system according to an embodiment of the present application.
The achievement of the objects, functional features and advantages of the present application will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the technical solution of the present application and are not intended to limit the present application.
For a better understanding of the technical solution of the present application, the following detailed description will be given with reference to the drawings and the specific embodiments.
Although the traditional OFDM system has better anti-interference capability, the traditional OFDM system has higher computation complexity, and particularly in a high data rate transmission scene, the frequent complex operation causes the burden of the processing capability of equipment. Therefore, the discrete hartley Transform orthogonal frequency division multiplexing system (DISCRETE HARTLEY Transform-Orthogonal Frequency Division Multiplexing, DHT-OFDM) as a real number operation-based scheme can significantly reduce the computational complexity by using the Discrete Hartley Transform (DHT) instead of the conventional Discrete Fourier Transform (DFT), thereby realizing low power consumption and efficient signal processing. However, DHT-OFDM is limited in that it supports only transmission in the real number domain, and thus cannot directly support high-order phase modulation such as QAM (quadrature amplitude modulation) or the like. This limitation makes the system challenging in high data rate transmission, especially in application scenarios with high requirements for transmission rate, the bandwidth utilization of the communication system cannot be fully exerted, resulting in limitation of data transmission efficiency.
In certain specific environments, particularly in the particular propagation environment of the underwater acoustic channel, signal attenuation and multipath effects further exacerbate the stability problem of high data rate transmissions. The underwater acoustic channel has the characteristics of frequency selective fading, signal distortion and the like, and is easy to cause larger interference on signals, so that a receiving end cannot effectively recover original information, and the transmission stability and reliability of a system are affected. Therefore, achieving stable transmission at high data rates in the underwater acoustic channel becomes a technical challenge.
The application provides a solution, which comprises the steps of carrying out phase modulation and linear conversion on transmitted information bits at a transmitting end to obtain a real number sequence, carrying out inverse discrete Hartley transformation modulation on the real number sequence to obtain modulated information, transmitting the modulated information to a receiving end through an underwater sound channel, carrying out signal transformation and demodulation on the modulated information at the receiving end, and recovering original information bits. Because the underwater acoustic channel has the characteristic of being suitable for transmitting sparse signals, complex signals are mapped into sparse real sequences suitable for an underwater acoustic system through phase modulation and linear conversion, the influence of multipath interference and noise on the signals is reduced, and the transmission stability and the anti-interference capability of the system are improved. By utilizing the characteristics of inverse discrete Hartley transformation modulation and sparse signals, the modulation and demodulation computation complexity of a transmitting end and a receiving end is simplified, and the processing requirement of equipment is reduced. By combining with the real-complex conversion algorithm, the efficient transmission of the high-order phase modulation symbols is realized, and the requirement of high-data-rate communication is met. The receiving end accurately restores original information bits by utilizing discrete Hartley transformation and complex number recovery technology through signal transformation and demodulation, and further improves the reliability and stability of communication in the underwater acoustic channel environment.
Based on this, an embodiment of the present application provides a transmission method of an ofdm underwater acoustic communication system, and referring to fig. 1, fig. 1 is a schematic flow chart of a first embodiment of the transmission method of an ofdm underwater acoustic communication system according to the present application.
In this embodiment, the transmission method of the orthogonal frequency division multiplexing underwater acoustic communication system includes steps S10 to S40:
Step S10, carrying out phase modulation and linear conversion on the transmitted information bits at a transmitting end to obtain a real number sequence, wherein the real number sequence has sparse characteristics.
It should be noted that the transmission information bit may be understood as raw data in a communication system, typically a bit stream in binary form. The phase modulation is a digital modulation scheme in which different information bits are represented by varying the phase of a carrier signal. Linear conversion is understood to mean that the linear structure of the data, i.e. the conversion of a phase modulated signal into a real sequence, is maintained by converting a complex signal or a data sequence into another form. Sparse characteristics can be understood as characteristics where most elements in a signal are zero, with only a few elements being non-zero. In a 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 signals in a noise environment.
And step S20, performing inverse discrete Hartley transformation modulation on the real number sequence to obtain modulated information.
It should be noted that, the Discrete Hartley Transform (DHT) may be a transform similar to a fourier transform, mainly used for frequency domain representation of a signal, the Inverse Discrete Hartley Transform (IDHT) is an inverse transform of the DHT, used for recovering a time domain signal from a frequency domain signal, and the modulated information may be a signal after passing through the inverse discrete hartley transform.
And step S30, the modulated information is sent to a receiving end through an underwater sound channel.
It should be noted that the underwater acoustic channel is understood to be an acoustic wave propagation channel in an underwater environment. In underwater communications, acoustic signals propagate through water and are affected by factors such as multipath fading, noise, signal attenuation, and the like.
And step S40, the modulated information is subjected to signal conversion and demodulation at the receiving end, and original information bits are recovered.
It should be noted that, the signal transformation may be understood as converting the received signal (modulated information) from the underwater acoustic channel transmission format (such as frequency domain or time domain) to a format suitable for demodulation, and may include, for example, conversion from the frequency domain to the time domain or other forms. Demodulation can be understood as the recovery of the original transmitted information bits by the receiving end through an algorithm.
In this embodiment, because the underwater acoustic channel has a characteristic suitable for transmitting sparse signals, the complex signals are mapped into a sparse real number sequence suitable for the underwater acoustic system by combining phase modulation and linear conversion, so as to reduce the influence of multipath interference and noise on the signals and improve the transmission stability and anti-interference capability of the system. By utilizing the characteristics of inverse discrete Hartley transformation modulation and sparse signals, the modulation and demodulation computation complexity of a transmitting end and a receiving end is simplified, and the processing requirement of equipment is reduced. By combining with the real-complex conversion algorithm, the efficient transmission of the high-order phase modulation symbols is realized, and the requirement of high-data-rate communication is met. The receiving end accurately restores original information bits by utilizing discrete Hartley transformation and complex number recovery technology through signal transformation and demodulation, and further improves the reliability and stability of communication in the underwater acoustic channel environment.
Referring to fig. 2, fig. 2 is a flow chart of a second embodiment of the transmission method of the ofdm underwater acoustic communication system according to the present application, and based on the first embodiment shown in fig. 1, the second embodiment of the transmission method of the ofdm underwater acoustic communication system according to the present application is proposed.
In a second embodiment, the step S10 includes:
Step S101, high-order phase modulation is carried out on the transmitted information bit at the transmitting end, and a complex signal is obtained.
It should be noted that, the higher-order phase modulation may encode information bits by changing the phase of the carrier signal, and by way of example, the higher-order phase modulation may be Quadrature phase shift keying (Quadrature PHASE SHIFT KEYING, QPSK) or Quadrature amplitude modulation (Quadrature Amplitude Modulation, QAM), and it is understood that the result of the higher-order phase modulation is generally represented as complex. Illustratively, the transmitted information bits are subjected to high-order phase modulation, outputting a complex sequence of length N/2.
Step S102, performing sequence conversion on the complex signal through a real-complex conversion algorithm to obtain a real sequence.
It should be noted that, a Real-to-Real Transform (C2 RT) is a modulation method for implementing conversion of a Complex modulation symbol into a sparse Real-number domain symbol through linear computation, and is applied to an underwater acoustic DHT-OFDM communication system to implement transmission of a high-order phase symbol, so as to convert a Complex signal (composed of a Real part and an imaginary part) into an equivalent Real signal sequence, and a Real sequence is a Real sequence only including a Real number generated through Real-to-Real Transform. Exemplary, the real part and the imaginary part of the complex signal generated by the high-order phase modulation can be linearly combined, the complex signal is mapped to the real number domain, the length of the output real number sequence is N, and the value range of the value in the sequence isWherein, the method comprises the steps of, wherein,Represented as a phase modulated complex resultThe corresponding real part value of the real part,Represented as a phase modulated complex resultCorresponding imaginary values.
Exemplary, symbols for QAM modulated outputConversion to real sequence via C2RTThe conversion process is expressed as formula (1):
Wherein, Denoted as the firstThe output sign of the bit(s),AndRespectively isReal and imaginary parts of (i.e.)Can be expressed as formula (2):
in the formula (2), N is IDHT/DHT points, and the real number is input into the sequence And carrying out IDHT operation to obtain a bipolar time domain signal.
In this embodiment, by performing high-order phase modulation on the transmission information bits at the transmitting end, a plurality of bits can be encoded in one symbol, so as to realize high-data-rate transmission, and meet different requirements on data rate and anti-interference capability. The real part and the imaginary part of the complex signal simultaneously bear data, so that the system can flexibly express modulation information and provide complete data information for subsequent processing. The real-complex conversion converts the complex signal into a real-number domain signal, so that the real-number domain signal is suitable for the processing requirement of Discrete Hartley Transform (DHT), and a real number sequence generated by the real-complex conversion generally has sparse characteristics (most of values are close to zero), so that redundant information in data transmission can be effectively reduced, and the transmission efficiency is improved.
Referring to fig. 3, fig. 3 is a schematic flow chart of a third embodiment of the transmission method of the ofdm underwater acoustic communication system according to the present application, and based on the second embodiment shown in fig. 2, the third embodiment of the transmission method of the ofdm underwater acoustic communication system according to the present application is proposed.
In a third embodiment, the step S20 includes:
in step S201, inverse discrete hartley transform modulation is performed on the real number sequence to obtain a baseband signal.
The inverse discrete hartley Transform (INVERSE DISCRETE HARTLEY Transform, IDHT) and the Discrete Hartley Transform (DHT) are inverse operations, and convert the real number sequence of the frequency domain into a time domain signal, so as to generate a baseband signal.
Step S202, up-sampling the baseband signal and adding a cyclic prefix to obtain a preprocessed signal.
It should be noted that up-sampling is to increase the sampling rate of a signal to a higher frequency to adapt to subsequent signal processing or transmission requirements. Illustratively, the number of sample points of the signal may be expanded by inserting zero values between the original sample points, improving the resolution of the signal. The cyclic prefix may be to add a portion of replicated tail data before each signal frame. The pre-processed signal is an up-sampled and cyclic prefix added signal.
Step S203, carrier modulation is performed on the preprocessed signal, so as to obtain modulated information.
The carrier modulation may be a process of transferring the baseband signal to the target frequency range by mixing with the high-frequency carrier signal. The modulated information can be understood as an output signal modulated by a carrier wave, adapting the transmission format of the hydro-acoustic channel.
Illustratively, the DHT and IDHT transform can be expressed as formula (3):
in the formula (3), Represented as an initial transmission signal,Represented as DHT modulated signals. Note that, the kernel function of DHT may be expressed as formula (4):
As can be seen from the formula of DHT transformation, DHT has the same form as IDHT and satisfies formula (5):
In the formula (5) of the present invention, The index is expressed as the index of DHT transformation input, the index k is expressed as the index of DHT transformation output, when the index and the index are equal, two groups of kernel functions meet the orthogonal relation, and the real number sequence after real number and complex number transformationThe output sequence after IDHT is equation (6):
In the formula (6) of the present invention, Represented as the output sequence after IDHT passes,. In the above-mentioned formula(s),,. The final transmitted DHT-OFDM signal is expressed as formula (7):
In the formula (7) of the present invention, Represented as the final transmitted DHT-OFDM signal,Indicating that the signal was initially transmitted and,Represented as the fundamental frequency,Represented by the time period in which the time period,Denoted as a guard interval,Represented as symbol periods. Transmitting the transmitted signal on the underwater acoustic channel, considering only the multipath transmission characteristics, the underwater acoustic channel can be described as formula (8) using a tap delay model:
In the formula (8), the expression "a", Represented as amplitude relationships corresponding to different times of the channel,Is the firstThe gain of the path of the strip,For a corresponding relative time delay,Is the number of multipaths.
In the embodiment, complex operation is avoided by using the inverse discrete hartley transformation, only real signals need to be processed, hardware implementation is simplified, and computational complexity and power consumption are reduced. The real sequence of the frequency domain is converted into a baseband signal of the time domain, providing a base signal adapted to the characteristics of the underwater acoustic channel for subsequent transmission. The introduction and up-sampling of the cyclic prefix reduces quantization errors, improves the anti-interference performance and precision of signals, provides periodic characteristics for subsequent modulation and demodulation, and avoids signal distortion caused by boundary effects in the conversion process. The carrier modulation enables signals to effectively utilize the frequency spectrum resources of the underwater acoustic channel, improves the stability and efficiency of transmission, and meets the transmission requirement of high data rate.
Referring to fig. 4, fig. 4 is a schematic flow chart of a fourth embodiment of the transmission method of the ofdm underwater acoustic communication system according to the present application, and based on the third embodiment shown in fig. 3, the fourth embodiment of the transmission method of the ofdm underwater acoustic communication system according to the present application is proposed.
In a fourth embodiment, the step S40 includes:
In step S401, the modulated information is processed by demodulation and signal conversion to recover the real number sequence.
The demodulation may extract the original baseband signal from the carrier signal, remove the high frequency component 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 by Discrete Hartley Transformation (DHT), reconstructing the original real sequence.
Step S402, converting the real number sequence into complex number signal, and recovering the original information bit through phase demodulation.
It should be noted that, the phase demodulation may be a process of recovering the complex signal into the original bit information, and the encoded data may be extracted by analyzing the phase change of the complex signal. Illustratively, the method of phase demodulation may include QAM, PSK, etc. matching the original bit sequence based on the received phase value.
In this embodiment, the modulated baseband signal is demodulated and extracted, and the real number sequence is recovered by combining signal transformation, so that the sparse signal transmitted by the transmitting end is accurately recovered, interference (such as noise and multipath effect) introduced by the underwater acoustic channel can be effectively eliminated, and the stability of the system in a severe environment is improved. The real number sequence is converted into the complex number signal, the complex number signal is accurately reconstructed, the phase and amplitude information of the transmitting end is completely reserved, the complex number signal is processed through phase demodulation, information bits in high-order modulation (such as QAM) symbols can be accurately recovered, the high-data rate transmission requirement is met, phase offset and distortion in channel transmission are eliminated, and the recovery precision of the information bits is ensured.
In one implementation, based on the fourth embodiment, the step S401 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, outputting an equalized time domain signal, performing discrete hartley transform demodulation on the equalized time domain signal, and outputting a real number sequence.
The modulated information may be transmitted by the transmitting end after being modulated by a carrier, and the carrier demodulation may convert the received modulated signal into a baseband signal by removing a high-frequency carrier component in the signal. The cyclic prefix is removed at the receiving end for recovering the original signal time domain content, and downsampling may be to reduce the sampling rate of the signal for reducing redundant data points in the signal. The channel estimation indicates that the transmission characteristics of the channel are estimated from the characteristics of the received signal. The original characteristics of the signals can be restored through the influence of the inverse compensation channel, the time domain signals after equalization are obtained, discrete Hartley transformation demodulation is carried out on the time domain signals after equalization, and a real number sequence is output.
Illustratively, after passing the modulated signal through the channel, the received analog signal may be expressed as equation (9):
in the formula (9) of the present invention, Is additive white Gaussian noise with a power spectral density ofThe meaning of the other characters is given in the formula (7) and the formula (8), and will not be described here. The received signal may be expressed as equation (10) in case the received signal is synchronized and the cyclic prefix length is greater than the maximum delay.
In the formula (10) of the present invention,Which may be expressed as a received signal synchronization, and a cyclic prefix length greater than the received signal with maximum delay,Can be expressed as the received signal and the firstThe component parts of the sub-carrier correlation,Can be expressed as the received signal and the firstThe component parts of the sub-carrier correlation,Specifically, the expression (11) can be expressed as:
Is the first The sub-carrier is at the firstThe relative phase offset over the OFDM symbol period can be expressed as equation (12):
Is the delay caused by the phase shift of the signal, and can be expressed as formula (13):
After downsampling and DHT demodulation, the resulting baseband signal is expressed as equation (14):
In the formula (14) of the present invention, Denoted as the firstThe baseband data symbols corresponding to the sub-carriers,Represented as representing the firstThe data symbols of the sub-carriers are transmitted,Denoted as the firstNoise on the individual sub-carriers is transmitted,AndDenoted as and NoThe modulation factor corresponding to the subcarrier is used,AndExpressed as formula (15) and formula (16), respectively:
the method of time domain equalization is adopted in the DHT-OFDM system, and the equalization result of the received signal can be expressed as a formula (17):
in the formula (17) of the present invention, Denoted as and NoThe equalization coefficients associated with the data symbols are,Denoted as and NoThe equalization coefficients associated with the data symbols are,Denoted as the firstAn estimate of the bit-received signal,Denoted as the firstAn estimate of the bit-received signal,AndExpressed as equation (18) and equation (19), respectively.
In the above formula, the water content of the water-soluble polymer,Representing the amount of phase offset. The communication rate of a system employing real-time complex conversion is expressed as formula (20):
in the formula (20) of the present invention, As the number of sub-carriers,For the phase modulation parameter, the number of digital bits representing a unit modulation symbol,For the channel coding rate,For the subcarrier spacing to be a function of the subcarrier spacing,Representing the number of subcarriers. The communication rate represents the rate at which valid information bits are transmitted per unit time, and because the communication rate is halved by the multiplexing conversion, and the communication rate can be doubled by the QPSK modulation, the communication rate of the BPSK modulation DHT-OFDM system without the multiplexing conversion is equal to that of the QPSK system after the multiplexing conversion, and the communication rate of the 16QAM system after the multiplexing conversion is twice that of the system.
In this embodiment, the high-frequency modulation 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, so that the integrity of the original signal is maintained, and the inter-symbol interference is effectively reduced. Redundant sampling points in the signal are reduced through downsampling, the data size is reduced, and the calculation efficiency is improved for subsequent signal processing. And carrying out equalization processing on the signal by utilizing the result of channel estimation, and inversely compensating noise, multipath effect and frequency selective fading in the channel to restore the original characteristics of the signal. Through signal equalization, the signal is more similar to the baseband signal of the transmitting end, the error rate is reduced, and the accuracy and reliability of data transmission are improved.
In one embodiment, based on the fourth embodiment, the 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 an original information bit.
It should be noted that Real-to-Complex Transform, R2CT may be a process of converting a Real sequence into a complex signal in the frequency domain and restoring the complex signal at the transmitting end through a combination of the Real part and the imaginary part. The frequency domain complex signal may be represented in complex form, containing amplitude and phase information. The high-order phase demodulation can recover the original bit stream from the frequency domain complex signal, and the recovery from the modulated signal to the data bit is completed.
Exemplary, after the receiving end obtains the detected time domain signal through channel estimation and equalization processing, the transmitting sequence is recovered through FHT signalRecovery of frequency domain transmit sequences via real-to-complex transform, R2CTThe definition of R2CT is expressed as formula (21):
in the formula (21), the expression "a", AndRespectively isIs used for the real and imaginary parts of (a),Denoted as the firstThe output sign of the bit.
In the embodiment, the real number and complex number conversion is performed on the real number sequence, the original information bit of the transmitting end is extracted from the amplitude and the phase of the complex number signal, the integrity and the accuracy of the frequency domain complex number signal are guaranteed, the high-data rate transmission requirement can be adapted by performing high-order phase demodulation on the frequency domain complex number signal, technical support is provided for communication with high data rate and high bandwidth efficiency, meanwhile, the operation complexity of the system is reduced, and the demodulation efficiency is improved.
In order to make the embodiments and implementations of the present application clearer, a schematic block diagram for implementing high-order symbol transmission of a DHT-OFDM system based on a real-complex conversion algorithm is provided as shown in fig. 5. In addition, for the discrete hartley transform, the calculation complexity required to perform the operation of length N is considered to beAnd for discrete Fourier transform/2 Complex operations, orThe real number operation is performed, so that the calculation complexity of the DHT is reduced by 50% relative to the FFT under the same calculation length. The C2RT is used as a linear operation mode, so that the system calculation complexity is not increased, and the DHT-OFDM system added with the C2RT can be reduced by 50% under the condition of the same communication rate.
In one embodiment, the C2RT is added as a separate module to the phase modulation at the transmitting end and before IDHT modulation when applied in the system, and after the receiving end is added to the DHT demodulation and before phase modulation. Fig. 6 and 7 are the original constellation of QPSK phase modulation and the constellation over C2RT, respectively. Fig. 8 and 9 are the original constellation of 16QAM phase modulation and the constellation over C2RT, respectively. In fig. 6 to 9, the abscissa means an in-phase component of the modulated signal, i.e., a real part of the signal, may be denoted as Re (x), and the ordinate means a quadrature component of the modulated signal, i.e., an imaginary part of the signal, may be denoted as Im (x). As can be seen from fig. 6 to fig. 9, the C2RT uniformly converts the complex symbols on the high-order modulation constellation diagram into symbols on the real number domain, and since each high-order real complex conversion includes the mapping result of the sporadic base points, the data will not cause inter-subcarrier interference during DHT-OFDM modulation and system transmission, so that the sparsity of the transmission signal is increased on the basis of the original phase modulation result, the influence of the underwater acoustic channel interference is reduced, and the transmission reliability is increased. Fig. 10 shows the bit error rate performance of the C2RT algorithm in an OFDM system. As can be seen from fig. 10, the bit error rate performance of the system with the added C2RT is slightly better than that of the conventional OFDM system at the same transmission data rate, which is caused by the sparseness of the transmission data after the added C2 RT. Fig. 11 shows transmission performance of DHT-OFDM with and without C2RT added and conventional OFDM systems under higher order phase modulation of different orders. The DHT-BPSK and the DHT-QPSK system added with C2RT in fig. 11 have the same transmission data rate, wherein the error rate deviation of the DHT-QPSK added with C2RT relative to the DHT-BPSK system is caused by the closer distance between constellation points in the higher-order phase modulation, the DHT-16QAM modulation system added with C2RT has the same transmission rate relative to the OFDM-QPSK system, and the gain of about 2.5dB is achieved, which indicates that the DHT-OFDM system added with C2RT has better communication performance at the same transmission data rate relative to the conventional FFT-OFDM system.
It should be noted that the foregoing examples are only for understanding the present application, and do not constitute limitation of the transmission method of the ofdm underwater acoustic communication system of the present application, and it is within the scope of the present application to perform more simple transformation based on the technical idea.
The present application also provides a transmission device of an ofdm underwater acoustic communication system, referring to fig. 12, the transmission device of an ofdm underwater acoustic communication system includes:
the modulation conversion module 10 is configured to perform phase modulation and linear conversion on the transmission information bits at the transmitting end, so as to obtain a real number sequence, where the real number sequence has sparse characteristics;
The inverse transformation modulation module 20 is configured to perform inverse discrete hartley transformation modulation on the real number sequence to obtain modulated information;
The underwater acoustic channel transmission module 30 is configured to send the modulated information to a receiving end through an underwater acoustic channel;
and the demodulation recovery module 40 is configured to perform signal conversion and demodulation on the modulated information at the receiving end, and recover the original information bits.
The transmission device of the OFDM underwater acoustic communication system provided by the application can solve the technical problem of unstable high data rate transmission in the underwater acoustic channel environment by adopting the transmission method of the OFDM underwater acoustic communication system in the embodiment. Compared with the prior art, the beneficial effects of the transmission device of the orthogonal frequency division multiplexing underwater acoustic communication system provided by the application are the same as those of the transmission method of the orthogonal frequency division multiplexing underwater acoustic communication system provided by the embodiment, and other technical features in the transmission device of the orthogonal frequency division multiplexing underwater acoustic communication system are the same as those disclosed by the method of the embodiment, so that the description is omitted.
The application provides an orthogonal frequency division multiplexing underwater sound communication system transmission device, which comprises at least one processor and a memory in communication connection with 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 underwater sound communication system transmission method in the first embodiment.
Referring now to fig. 13, a schematic diagram of a transmission device for an orthogonal frequency division multiplexing underwater acoustic communication system suitable for implementing an embodiment of the present application is shown. The transmission device of the orthogonal frequency division multiplexing underwater acoustic communication system in the embodiment of the present application may include, but is not limited to, mobile terminals such as mobile phones, notebook computers, digital broadcast receivers, PDAs (Personal DIGITAL ASSISTANT: personal digital assistants), PADs (Portable Application Description: tablet computers), PMPs (Portable MEDIA PLAYER: portable multimedia players), vehicle-mounted terminals (e.g., vehicle-mounted navigation terminals), and the like, and fixed terminals such as digital TVs, desktop computers, and the like. The transmission apparatus of the orthogonal frequency division multiplexing underwater acoustic communication system shown in fig. 13 is merely an example, and should not impose any limitation on the functions and the scope of use of the embodiment of the present application.
As shown in fig. 13, the orthogonal frequency division multiplexing underwater sound communication system transmission apparatus may include a processing device 1001 (e.g., a central processor, a graphic processor, etc.) which may perform various appropriate actions and processes according to a program stored in a Read Only Memory (ROM) 1002 or a program loaded from a storage device 1003 into a random access Memory (RAM: random Access Memory) 1004. In the RAM1004, various programs and data required for the operation of the transmission apparatus of the orthogonal frequency division multiplexing underwater acoustic communication system are also stored. The processing device 1001, the ROM1002, and the RAM1004 are connected to each other by a bus 1005. An input/output (I/O) interface 1006 is also connected to the bus. In general, a system including an input device 1007 such as a touch screen, a touch pad, a keyboard, a mouse, an image sensor, a microphone, an accelerometer, a gyroscope, etc., an output device 1008 including a Liquid crystal display (LCD: liquid CRYSTAL DISPLAY), a speaker, a vibrator, etc., a storage device 1003 including a magnetic tape, a hard disk, etc., and a communication device 1009 may be connected to the I/O interface 1006. The communication means 1009 may allow the orthogonal frequency division multiplexing underwater acoustic communication system transmission device to perform wireless or wired communication with other devices to exchange data. While fig. 13 illustrates an orthogonal frequency division multiplexing underwater acoustic communication system transmission device having various systems, it should be understood that not all illustrated systems are required to be implemented or provided. More or fewer systems may alternatively be implemented or provided.
In particular, according to embodiments of the present disclosure, the processes described above with reference to flowcharts may be implemented as computer software programs. For example, embodiments of the present disclosure include a computer program product comprising a computer program embodied on a computer readable medium, the computer program comprising program code for performing the method shown in the flow chart. In such an embodiment, the computer program may be downloaded and installed from a network through a communication device, or installed from the storage device 1003, or installed from the ROM 1002. The above-described functions defined in the method of the disclosed embodiment of the application are performed when the computer program is executed by the processing device 1001.
The transmission equipment of the OFDM underwater acoustic communication system provided by the application can solve the technical problem of unstable high data rate transmission in the underwater acoustic channel environment by adopting the transmission method of the OFDM underwater acoustic communication system in the embodiment. Compared with the prior art, the beneficial effects of the transmission device of the orthogonal frequency division multiplexing underwater acoustic communication system provided by the application are the same as those of the transmission method of the orthogonal frequency division multiplexing underwater acoustic communication system provided by the embodiment, and other technical features of the transmission device of the orthogonal frequency division multiplexing underwater acoustic communication system are the same as those disclosed in the method of the previous embodiment, and are not repeated herein.
It is to be understood that portions of the present disclosure may be implemented in hardware, software, firmware, or a combination thereof. In the description of the above embodiments, particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing is merely illustrative of the present application, and the present application is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
The present application provides a computer-readable storage medium having computer-readable program instructions (i.e., a computer program) stored thereon for performing the method of transmitting an orthogonal frequency division multiplexing underwater acoustic communication system in the above-described embodiments.
The computer readable storage medium provided by the present application may be, for example, a U disk, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, or device, or a combination of any of the foregoing. More specific examples of a computer-readable storage medium may include, but are not limited to, an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access Memory (RAM: random Access Memory), a Read-Only Memory (ROM), an erasable programmable Read-Only Memory (EPROM: erasable Programmable Read Only Memory or flash Memory), an optical fiber, a portable compact disc Read-Only Memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In this embodiment, a computer-readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, or device. Program code embodied on a computer readable storage medium may be transmitted using any appropriate medium, including but not limited to electrical wiring, fiber optic cable, RF (Radio Frequency) and the like, or any suitable combination of the foregoing.
The computer readable storage medium may be included in the transmission apparatus of the ofdm underwater sound communication system or may exist alone without being incorporated in the transmission apparatus of the ofdm underwater sound communication system.
The computer readable storage medium carries one or more programs, when the one or more programs are executed by the transmission device of the orthogonal frequency division multiplexing underwater acoustic communication system, the transmission device of the orthogonal frequency division multiplexing underwater acoustic communication system carries out phase modulation and linear conversion on the transmitted information bits at a transmitting end to obtain a real number sequence, the real number sequence has sparse characteristics, carries out inverse discrete Hartley transformation modulation on the real number sequence to obtain modulated information, transmits the modulated information to a receiving end through an underwater acoustic channel, carries out signal transformation and demodulation on the modulated information at the receiving end, and recovers original information bits.
Computer program code for carrying out operations of the present application may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, smalltalk, C ++ and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the case of remote computers, the remote computer may be connected to the user's computer through any kind of network, including a local area network (LAN: local Area Network) or a wide area network (WAN: wide Area Network), or may be connected to an external computer (for example, through the Internet using an Internet service provider).
The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present application. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
The modules involved in the embodiments of the present application may be implemented in software or in hardware. Wherein the name of the module does not constitute a limitation of the unit itself in some cases.
The readable storage medium provided by the application is a computer readable storage medium, and the computer readable storage medium stores computer readable program instructions (namely computer program) for executing the transmission method of the orthogonal frequency division multiplexing underwater acoustic communication system, so that the technical problem of unstable high data rate transmission in an underwater acoustic channel environment can be solved. Compared with the prior art, the beneficial effects of the computer readable storage medium provided by the application are the same as those of the transmission method of the orthogonal frequency division multiplexing underwater acoustic communication system provided by the embodiment, and the detailed description is omitted herein.
The application also provides a computer program product comprising a computer program which when executed by a processor implements the steps of the method for transmitting an orthogonal frequency division multiplexing underwater acoustic communication system as described above.
The computer program product provided by the application can solve the technical problem of unstable high data rate transmission in the underwater acoustic channel environment. Compared with the prior art, the beneficial effects of the computer program product provided by the application are the same as those of the transmission method of the orthogonal frequency division multiplexing underwater acoustic communication system provided by the embodiment, and are not described in detail herein.
The foregoing description is only a partial embodiment of the present application, and is not intended to limit the scope of the present application, and all the equivalent structural changes made by the description and the accompanying drawings under the technical concept of the present application, or the direct/indirect application in other related technical fields are included in the scope of the present application.
Claims (10)
1. A method for transmitting an orthogonal frequency division multiplexing underwater acoustic communication system, the method comprising:
Carrying out phase modulation and linear conversion on the transmitted information bits at a transmitting end to obtain a real number sequence, wherein the real number sequence has sparse characteristics;
performing inverse discrete hartley transformation modulation on the real number sequence to obtain modulated information;
transmitting the modulated information to a receiving end through an underwater sound channel;
And carrying out signal conversion and demodulation on the modulated information at a receiving end, and recovering original information bits.
2. The method of claim 1, wherein the step of performing phase modulation and linear conversion on the transmission information bits at the transmitting end to obtain the real number sequence comprises:
Performing high-order phase modulation on the transmitted information bits at a transmitting end to obtain a complex signal;
And performing sequence conversion on the complex signal through a real-complex conversion algorithm to obtain a real sequence.
3. The method of claim 2, wherein the step of performing inverse discrete hartley transform modulation on the real sequence to obtain modulated information comprises:
performing inverse discrete Hartley transformation modulation on the real number sequence to obtain a baseband signal;
up-sampling the baseband signal, and adding a cyclic prefix to obtain a preprocessed signal;
And carrying out carrier modulation on the preprocessed signals to obtain modulated information.
4. A method according to any one of claims 1 to 3, wherein the step of signal transforming and demodulating the modulated information at the receiving end to recover the original information bits comprises:
the modulated information is processed through demodulation and signal transformation, and a real number sequence is recovered;
the real sequence is converted into a complex signal and the original information bits are recovered by phase demodulation.
5. The method of claim 4, wherein the step of recovering the real sequence by demodulating and signal converting the modulated information comprises:
Carrying out carrier demodulation on the modulated information, removing the cyclic prefix and carrying out downsampling to obtain a downsampled signal;
carrying out equalization processing on the down-sampled signal by combining with channel estimation, and outputting an equalized time domain signal;
And performing discrete Hartley transform demodulation on the equalized time domain signal, and outputting a real number sequence.
6. The method of claim 5, wherein the step of converting the real sequence into a complex signal and recovering the original information bits by phase demodulation comprises:
performing real-to-complex conversion on the real sequence and outputting a frequency domain complex signal;
and performing high-order phase demodulation on the frequency domain complex signal to obtain original information bits.
7. An apparatus for transmitting an orthogonal frequency division multiplexing underwater acoustic communication system, the apparatus comprising:
the modulation conversion module is used for carrying out 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 sparse characteristics;
The inverse transformation modulation module is used for carrying out inverse discrete Hartley transformation modulation on the real number sequence to obtain modulated information;
The underwater sound channel transmission module is used for transmitting the modulated information to a receiving end through an underwater sound channel;
And the demodulation recovery module is used for carrying out signal conversion and demodulation on the modulated information at the receiving end and recovering original information bits.
8. An orthogonal frequency division multiplexing underwater acoustic communication system transmission apparatus, characterized in that the apparatus comprises 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 underwater acoustic communication system transmission method as claimed in any one of claims 1 to 6.
9. A storage medium, characterized in that the storage medium is a computer-readable storage medium, on which a computer program is stored, which computer program, when being executed by a processor, realizes the steps of the transmission method of an orthogonal frequency division multiplexing underwater acoustic communication system as claimed in any of claims 1 to 6.
10. A computer program product, characterized in that the computer program product comprises a computer program which, when being executed by a processor, implements the steps of the method for transmitting an orthogonal frequency division multiplexing underwater sound communication system according to any of the claims 1 to 6.
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