CN109547377B - Method for reducing peak-to-average power ratio of multi-carrier underwater acoustic communication system by improving companding conversion receiving end - Google Patents

Method for reducing peak-to-average power ratio of multi-carrier underwater acoustic communication system by improving companding conversion receiving end Download PDF

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CN109547377B
CN109547377B CN201811125597.7A CN201811125597A CN109547377B CN 109547377 B CN109547377 B CN 109547377B CN 201811125597 A CN201811125597 A CN 201811125597A CN 109547377 B CN109547377 B CN 109547377B
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communication system
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吴金秋
刘浩源
孙立晶
田丙奇
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Tangshan Zhaolan Marine Technology Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2614—Peak power aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B11/00—Transmission systems employing sonic, ultrasonic or infrasonic waves
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00
    • H04B13/02—Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only

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Abstract

The invention relates to a method for reducing the peak-to-average power ratio (PAPR) of a multi-carrier underwater acoustic communication system by improving a companding conversion receiving end, which belongs to the field of underwater acoustic communication and relates to a companding conversion method for reducing the PAPR of an Orthogonal Frequency Division Multiplexing (OFDM) underwater acoustic communication system, in order to avoid the problem that the orthogonality among sub-carriers of the OFDM system is influenced by the clipping distortion generated when an underwater acoustic power amplifier works in a nonlinear area due to the overhigh signal peak power, and further influence the error rate of the whole communication system. The invention improves the companding conversion method at the transmitting end and the receiving end respectively, reduces the influence of the companding conversion method on the error code performance of the system, and the simulation result aiming at the underwater environment shows that when the signal to noise ratio is 20dB, the error rate of the underwater sound system adopting the improved companding conversion method is 10 lower than that of the underwater sound system adopting the traditional companding conversion method‑1And the improved method is proved to be more suitable for the underwater sound field of the complex channel environment.

Description

Method for reducing peak-to-average power ratio of multi-carrier underwater acoustic communication system by improving companding conversion receiving end
Technical Field
The invention relates to a method for reducing the peak-to-average power ratio (PAPR) of a multi-carrier underwater acoustic communication system by improving a companding transform receiving end, belonging to the field of underwater acoustic communication and relating to a companding transform method for reducing the PAPR of an Orthogonal Frequency Division Multiplexing (OFDM) underwater acoustic communication system, wherein the traditional companding transform method is improved at the receiving end, a synchronized signal is divided into two paths, information is combined after the two paths are respectively processed, the influence of quantization noise caused by companding transform on the system error code performance is reduced, and a simulation result aiming at an underwater environment shows that when the signal-to-noise ratio is 20dB, the error code ratio of the underwater acoustic system adopting the improved companding transform method is 10 dB lower than that of the traditional companding transform method-1In order to prove that the improved method is more suitableThe method is used in the underwater acoustic field of complex channel environment.
Background
The realization of the high-speed underwater acoustic communication system depends on the development of a multi-carrier modulation technology, however, the increase of the number of carriers can lead to higher peak-to-average power ratio (PAPR), and a related algorithm is adopted to reduce the PAPR, so that the probability of error codes of the system can be reduced, and the improvement of the energy efficiency utilization rate of the system can be realized to a greater extent. The method comprises the steps of compressing a transmission time domain signal by adopting a companding function at a transmitting end of a multi-carrier underwater acoustic communication system, and correspondingly expanding the transmission time domain signal at a receiving end, wherein the compression and the expansion are both nonlinear processes, so that quantization noise can be generated, and the system performance is influenced. Therefore, before the expansion operation of the receiving end, the influence of the channel on the received signal needs to be eliminated, otherwise, the despreading will generate a large amount of despreading noise, so for the companding transform, time domain equalization needs to be performed, and the influence of the channel is eliminated before the companding. However, for the multi-carrier underwater acoustic communication system, the advantages are that the frequency domain equalization is simple and accurate and is easy to implement, if the time domain equalization is adopted, the accuracy of the system for estimating the channel is influenced, the system performance is influenced, the complexity of the system is increased, the advantage of orthogonal multi-carrier is lost, the system is not similar to a single carrier communication system, the simple time domain equalization can be implemented, and the system has the advantage of low PAPR. In the previous research, partial companding algorithm is improved at the receiving end, so that despreading is not needed at the receiving end, and despreading is avoided to eliminate time domain equalization processing, however, the improved method and the amplitude limiting method have the same defects and generate nonlinear noise, the influence of the noise on the performance of a communication system cannot be fundamentally solved, the generated nonlinear noise is increased along with the increase of companding parameters, and the nonlinear noise generated by the companding conversion method is larger than the amplitude limiting method under the condition that the effect of reducing the peak-to-average ratio of partial algorithm is the same, so that the error rate performance of the system is poorer. Although the decompression technology of the receiving end can reduce the nonlinear distortion introduced by the compression and expansion, the channel additive noise can be amplified simultaneously, so the invention provides a corresponding improved method for the receiving end of the compression and expansion transformation.
Disclosure of Invention
The invention aims to provide a method for reducing the peak-to-average power ratio of a multi-carrier underwater sound communication system, which improves a companding conversion receiving end, in order to avoid the problem that the correlation among sub-carriers of the multi-carrier underwater sound communication system is influenced by the clipping distortion generated when an underwater sound power amplifier works in a nonlinear area due to an overhigh PAPR (peak-to-average power ratio), and further influence the error rate of the whole communication system.
The purpose of the invention is realized as follows: the method comprises the following steps:
the method comprises the following steps: at a transmitting end, a transmitting signal is subjected to series-parallel transformation and then is subjected to an inverse fast Fourier transform module, and a frequency domain signal is converted into a time domain signal;
step two: at a transmitting end, carrying out companding conversion processing on the time domain signal by using the average amplitude as a companding parameter;
step three: at a transmitting end, adding a cyclic prefix to the companded signal and transmitting the signal to an underwater sound channel;
step four: at a receiving end, carrying out synchronous operation on a received signal;
step five: at a receiving end, performing cyclic prefix removing operation on the synchronized signal;
step six: at a receiving end, dividing the signal without the cyclic prefix into two paths, simultaneously processing, performing fast Fourier transform on one path, extracting a pilot signal, performing channel estimation, and performing fast Fourier transform on the other path after decompression and expansion transform;
step seven: at a receiving end, combining the two paths of signals in the step six of the receiving end, and respectively estimating a transmitting signal by using a channel estimation result and a decompression signal in the combined signals;
the invention also includes such features:
1. in the sixth step, the receiving end divides the signal without the cyclic prefix into two paths for processing, wherein one path is not subjected to the operation of decompression and expansion transformation, and directly extracts the pilot signal after the fast Fourier transformation for channel estimation, so that the pilot signal Y received by the receiving endpCan be expressed as:
Yp＝C(Xp)·HP
wherein s isnFor signals before companding, scnFor companded signals, V mean(s)n) Representing the mean of the signal.
2. In the sixth step, the receiving end divides the signal without the cyclic prefix into two paths for processing, wherein the other path of signal is subjected to fast Fourier transform after decompression and expansion transformation.
3. In the seventh step, the two paths of signals in the sixth step are combined, the transmitted signal is estimated by utilizing the channel estimation result obtained without decompression and expansion and the decompressed signal, and the channel transmission function at the pilot frequency position is interpolated to obtain the channel transmission functions at all carriers, namely the channel transmission functions at all carriers
H＝lnterp(HP)
Where lnterp () represents the interpolation and H represents the entire channel transfer function, the resulting transmitted signal is estimated
Figure BDA0001812344320000021
Can be expressed as:
Figure BDA0001812344320000022
compared with the prior art, the invention has the beneficial effects that: the structure of a receiving end of companding transform is improved, a received signal is divided into two paths to be processed respectively, wherein one path extracts pilot frequency information before the companding transform, channel estimation is realized by using a corresponding channel estimation algorithm, the other path of signal is subjected to the companding transform integrally, and after the fast Fourier transform, the signal is estimated jointly with the other path of signal to be transmitted. The method extracts the pilot frequency information before despreading, avoids despreading noise, has better channel estimation capability than the traditional companding transformation method, can reduce the influence of the companding transformation on the system performance, and has the advantages that the comparison can be expressed in detail as follows:
in the conventional companding transform method, the pilot signal obtained at the receiving end can be represented as:
Yp＝C-1[C(Xp)·H]
wherein C (-) represents the companding transformation of the transmitting end, C-1(. cndot.) represents the de-spread transform at the receiving end (the inverse of the transmit-end de-spread transform). The pilot signal of the receiving end is obtained by carrying out companding transformation on the pilot signal of the transmitting end, then carrying out companding transformation on the pilot signal through an underwater acoustic channel, estimating the obtained channel by using the pilot signal, and converting YpSubstitution can obtain:
Figure BDA0001812344320000031
assuming noise generated by companding and companding on pilot
Figure BDA0001812344320000032
And
Figure BDA0001812344320000033
expressed separately, the above equation can be simplified to:
Figure BDA0001812344320000034
the above equation shows that the error between the estimated channel and the true underwater acoustic channel is
Figure BDA0001812344320000035
I.e., companding and despreading noise at the pilot. The pilot frequency obtained by the receiving end of the improved algorithm extracts the pilot signal before the expansion, so YpCan be expressed as:
Yp＝C(Xp)·H
the channel obtained by using pilot frequency estimation is as follows:
Figure BDA0001812344320000036
it can be seen that, in the channel estimation results obtained from the two results, the method for reducing the peak-to-average power ratio of the multi-carrier underwater acoustic communication system, which is provided by the invention, of the improved companding transform receiving end can obtain a more accurate channel estimation result, thereby effectively improving the error rate performance of the system.
Drawings
Fig. 1 is a flow diagram of an improved companding transform method for reducing peak-to-average ratio in a multi-carrier underwater acoustic communication system;
FIG. 2 is a graph comparing complementary cumulative distribution functions;
FIG. 3 is a graph comparing the bit error rate performance under the underwater acoustic channel;
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
The invention comprises the following steps:
the method comprises the following steps: at a transmitting end, a transmitting signal is subjected to series-parallel transformation and then is subjected to an inverse fast Fourier transform module, and a frequency domain signal is converted into a time domain signal;
step two: at a transmitting end, carrying out companding conversion processing on the time domain signal by using the average amplitude as a companding parameter;
step three: at a transmitting end, adding a cyclic prefix to the companded signal and transmitting the signal to an underwater sound channel;
step four: at a receiving end, carrying out synchronous operation on a received signal;
step five: at a receiving end, performing cyclic prefix removing operation on the synchronized signal;
step six: at a receiving end, dividing the signal without the cyclic prefix into two paths, simultaneously processing, performing fast Fourier transform on one path, extracting a pilot signal, performing channel estimation, and performing fast Fourier transform on the other path after decompression and expansion transform;
step seven: at a receiving end, combining the two paths of signals in the step six of the receiving end, and respectively estimating a transmitting signal by using a channel estimation result and a decompression signal in the combined signals;
the invention relates to a method for reducing the peak-to-average ratio of a multi-carrier underwater acoustic communication system by improving a companding conversion receiving end, which is described in more detail as follows:
the receiving end divides the signal without the cyclic prefix into two paths for processing, wherein one path is not subjected to the operation of decompression and expansion transformation, and directly extracts the pilot signal after the fast Fourier transformation for channel estimation, so that the pilot signal Y received by the receiving endpCan be expressed as:
Yp＝C(Xp)·HP
wherein s isnFor signals before companding, scnFor companded signals, V mean(s)n) Representing the mean of the signal.
The channel obtained by using pilot frequency estimation is as follows:
Figure BDA0001812344320000041
wherein the content of the first and second substances,
Figure BDA0001812344320000042
noise generated for companding transform.
The other path of signal is decompressed and expanded, then is processed by fast Fourier transform, and two paths of signals are combined, and the channel estimation result obtained without decompressing and expanding and the decompressed signal are used to jointly estimate the transmitting signal, and the channel transmission function at the pilot frequency position is interpolated to obtain the channel transmission functions at all carriers, namely the channel transmission functions at all carriers
H＝lnterp(HP)
Where lnterp () represents the interpolation and H represents the entire channel transfer function, the resulting transmitted signal is estimated
Figure BDA0001812344320000043
Can be expressed as:
Figure BDA0001812344320000051
now, the beneficial contribution of the companding transform method to the receiving end on the aspect of the system error code performance is analyzed:
y for pilot signal received at receiving endpRepresentative, transmitted pilot signals by XpIt is shown that the underwater acoustic channel transfer function is denoted by H.
The conventional companding transform method does not extract the pilot signal before despreading at the receiving end, so the pilot signal obtained by the receiving end can be expressed as:
Yp＝C-1[C(Xp)·H]
wherein C (-) represents the compression transformation of the transmitting end, C-1(. cndot.) represents the expansion transform at the receiving end (the inverse of the compression transform at the transmitting end). The pilot signal of the receiving end is obtained by compressing and converting the pilot signal of the transmitting end, then performing inverse pressure-expanding conversion on the compressed and converted pilot signal through an underwater acoustic channel, estimating the obtained channel by using the pilot signal, and converting YpSubstitution can obtain:
Figure BDA0001812344320000052
assuming errors due to compression and expansion transformations on pilots
Figure BDA0001812344320000053
And
Figure BDA0001812344320000054
expressed separately, the above equation can be simplified to:
Figure BDA0001812344320000055
the above equation shows that the error between the estimated channel and the true underwater acoustic channel is
Figure BDA0001812344320000056
I.e., compressing and expanding noise at the pilot. The pilot frequency obtained by the receiving end of the improved algorithm extracts the pilot signal before the expansion, so YpCan be expressed as:
Yp＝C(Xp)·H
the channel obtained by using pilot frequency estimation is as follows:
Figure BDA0001812344320000057
as can be seen from the above formula, after the structure of the receiving end is improved, the obtained channel is estimated
Figure BDA0001812344320000058
Compared with the result that
Figure BDA0001812344320000059
Compared with H, the method has the error generated when only one companding transformation is carried out, and the channel obtained by estimation in the traditional method
Figure BDA00018123443200000510
Is composed of
Figure BDA00018123443200000511
Noise is the accumulation of noise produced by both companding and companding. The improved companding transform method extracts pilot frequency information before despreading, avoids despreading noise, has better channel estimation capability than the traditional companding transform method, and can reduce the influence of companding transform on the system performance.
The above embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention in any way, and all simple modifications and equivalent variations of the above embodiments according to the technical spirit of the present invention are within the scope of the present invention.

Claims (3)

1. A method for reducing the peak-to-average ratio of a multi-carrier underwater acoustic communication system at the receiving end of improved companding transform is characterized in that: the method comprises the following steps:
the method comprises the following steps: at a transmitting end, a transmitting signal is subjected to series-parallel transformation and then is subjected to an inverse fast Fourier transform module, and a frequency domain signal is converted into a time domain signal;
step two: at a transmitting end, carrying out companding conversion processing on the time domain signal by using the average amplitude as a companding parameter;
step three: at a transmitting end, adding a cyclic prefix to the companded signal and transmitting the signal to an underwater sound channel;
step four: at a receiving end, carrying out synchronous operation on a received signal;
step five: at a receiving end, performing cyclic prefix removing operation on the synchronized signal;
step six: at a receiving end, dividing the signal without the cyclic prefix into two paths, simultaneously processing, performing fast Fourier transform on one path, extracting a pilot signal, performing channel estimation, and performing fast Fourier transform on the other path after decompression and expansion transform;
step seven: and at the receiving end, combining the two paths of signals in the step six of the receiving end, and respectively estimating a transmitting signal by using a channel estimation result and a decompression signal in the combined signals.
2. The method of claim 1, wherein the method for reducing the peak-to-average power ratio of the multi-carrier underwater acoustic communication system at the receiving end of the companding transform is further characterized in that: in the sixth step, the receiving end divides the signal without the cyclic prefix into two paths for processing, wherein one path is not subjected to the operation of decompression and expansion transformation, and directly extracts the pilot signal after the fast Fourier transformation for channel estimation, so that the pilot signal Y received by the receiving endpCan be expressed as:
Yp＝C(Xp)·HP
wherein, the pilot signal of the transmitting terminal uses XpExpressed as H for the transfer function of the underwater acoustic channel at the pilotPAnd C (-) represents the companding conversion process of the transmitting end.
3. The method of claim 1, wherein the method for reducing the peak-to-average power ratio of the multi-carrier underwater acoustic communication system at the receiving end of the companding transform is further characterized in that: in the seventh step, the two paths of signals in the sixth step are combined, the transmitted signal is estimated by utilizing the channel estimation result obtained without decompression and expansion and the decompressed signal, and the channel transmission function at the pilot frequency position is interpolated to obtain the channel transmission functions at all carriers, namely the channel transmission functions at all carriers
H＝lnterp(HP)
Where lnterp () represents the interpolation and H represents the entire channel transfer function, the resulting transmitted signal is estimated
Figure FDA0003214402060000011
Can be expressed as:
Figure FDA0003214402060000012
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