CN112822135B - Single-carrier high-speed underwater acoustic communication method - Google Patents

Single-carrier high-speed underwater acoustic communication method Download PDF

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CN112822135B
CN112822135B CN202011403181.4A CN202011403181A CN112822135B CN 112822135 B CN112822135 B CN 112822135B CN 202011403181 A CN202011403181 A CN 202011403181A CN 112822135 B CN112822135 B CN 112822135B
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underwater acoustic
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frequency domain
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equalization processing
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CN112822135A (en
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杜鹏宇
任一石
王超
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715th Research Institute of CSIC
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/01—Equalisers
    • 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
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03159—Arrangements for removing intersymbol interference operating in the frequency domain

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Abstract

The invention discloses a single carrier high-speed underwater acoustic communication method, which comprises the following steps: (1) carrying out single carrier signal coding modulation, carrying out serial-parallel conversion on an original information sequence and mapping the original information sequence to a QPSK phase set by a transmitting terminal, adding a training sequence in the phase sequence after the mapping, and then carrying out carrier modulation to send out the information sequence; (2) estimating a channel, namely estimating the channel by using a locally known training sequence after a receiving end finishes signal detection and synchronization; (3) the frequency domain zero-forcing equalization processing is carried out, a weight matrix is constructed in the frequency domain by utilizing the channel obtained by estimation, and the weight matrix is multiplied by the received signal, so that the equalization processing of the channel is realized; (4) and performing decision feedback equalization processing, performing inverse Fourier transform on the signal subjected to the frequency domain zero forcing equalization processing back to a time domain, and performing final decoding processing by using a decision feedback equalizer embedded with a phase-locked loop. The invention has the beneficial effects that: the method has higher environmental adaptability, and can effectively solve the problem of parameter selection of the decision feedback equalizer, thereby obviously improving the performance of the single-carrier high-speed underwater acoustic communication system.

Description

Single-carrier high-speed underwater acoustic communication method
Technical Field
The invention belongs to the technical field of underwater acoustic communication, and mainly relates to a single carrier high-speed underwater acoustic communication method.
Background
The underwater acoustic technology, one of the leading technologies in the ocean development in the 21 st century, will have a very wide development space, and an important research field in the underwater acoustic technology is underwater acoustic communication. The underwater acoustic communication plays a vital role in the aspects of underwater positioning, navigation, detection and the like, and is a main means for underwater comprehensive information perception and information interaction at present. Since the transition from incoherent to coherent modulation techniques was completed by underwater acoustic communication modulation techniques in the late 90 s of the 20 th century, the development of underwater acoustic communication techniques has been relatively rapid. In coherent underwater acoustic communications, it is of milestone significance that m.stojanovic successfully applies a Phase Locked Loop (PLL) in a Decision Feedback Equalizer (DFE). Before this, the coherent underwater acoustic communication signals can not be effectively processed by a decision feedback equalizer, and the main reason is that the phase of the received signals jumps due to the influence of marine environment. The decision feedback equalizer embedded with the phase-locked loop well deals with the influence of phase and intersymbol interference on received signals, so that the performance of a coherent underwater acoustic communication system is obviously improved. Nowadays, a decision feedback equalizer embedded with a phase-locked loop is still applied to single-carrier underwater acoustic communication and is widely developed as a basic technology of single-carrier underwater acoustic communication. However, the single carrier underwater acoustic communication still faces many problems in practical application, and it is first of all that the decision feedback equalizer works extremely unstably due to the difference of multipath spread interference of channels under different hydrological environments. The method for improving the decoding performance of the single carrier receiving end by adopting a plurality of array elements for receiving and acquiring the space diversity gain is a commonly used method at present, but the method needs the underwater acoustic channels corresponding to the plurality of array elements to have larger difference, and if the receiving aperture of the plurality of array elements is smaller and cannot acquire enough space difference, the decoding performance of the single carrier is obviously reduced. The invention provides a frequency domain zero forcing equalization method, which can still realize single carrier steady decoding under the condition that a receiving end cannot obtain enough space difference, thereby obviously improving the reliability and the environment adaptability of single carrier high-speed underwater acoustic communication.
Disclosure of Invention
The invention provides a single carrier underwater acoustic communication method based on frequency domain zero forcing equalization, aiming at the problem of intersymbol interference in high-speed single carrier underwater acoustic communication, which comprises the following steps: the suppression of intersymbol interference is realized by constructing a weighting matrix in a frequency domain and multiplying the weighting matrix by a received signal, and final decoding is completed in a time domain by combining a decision feedback equalizer. The method can obviously improve the reliability of the single-carrier underwater acoustic communication system.
The purpose of the invention is achieved by the following technical scheme. A single carrier high-speed underwater acoustic communication method comprises the following steps:
(1) carrying out single carrier signal coding modulation, carrying out serial-to-parallel conversion on an original information sequence by a transmitting terminal, mapping the original information sequence to a QPSK phase set, adding a training sequence in front of the mapped phase sequence, and then carrying out carrier modulation to send out the original information sequence;
(2) estimating a channel, namely estimating the channel by using a locally known training sequence after a receiving end finishes signal detection and synchronization;
(3) the frequency domain zero-forcing equalization processing is carried out, a weight matrix is constructed in the frequency domain by utilizing the channel obtained by estimation, and the weight matrix is multiplied by the received signal, so that the equalization processing of the channel is realized; the multipath expansion interference of the underwater acoustic channel can be obviously inhibited after the frequency domain zero-forcing equalization processing is utilized, so that the reliability of feedback equalization decoding is judged.
(4) And performing decision feedback equalization processing, namely performing inverse Fourier transform on the signal subjected to the frequency domain zero forcing equalization processing back to a time domain, and performing final decoding processing by using a decision feedback equalizer embedded with a phase-locked loop. The received signal is firstly converted into a frequency domain, the signal is converted into a time domain after zero forcing equalization processing, final decoding processing is carried out on the time domain by using a decision feedback equalizer embedded with a phase-locked loop, the filter coefficient of the decision feedback equalizer can be kept unchanged in most underwater acoustic environments, manual dynamic adjustment is not needed, and the environmental adaptability of the system is remarkably improved.
The beneficial effects of the invention are as follows: according to the single-carrier high-speed underwater acoustic communication method, the frequency domain weight matrix is constructed according to the actual underwater acoustic environment, the influence of intersymbol interference brought by channel multipath expansion can be effectively inhibited after the frequency domain weight matrix is multiplied by the received signal, and stable and reliable decoding processing can be completed in the time domain by combining a decision feedback equalizer. The method has higher environmental adaptability, and can effectively solve the problem of parameter selection of the decision feedback equalizer, thereby obviously improving the performance of the single-carrier high-speed underwater acoustic communication system.
Drawings
Fig. 1 is a flow chart of a transmitting end communication encoding;
FIG. 2 is a flow chart of receiver information processing;
fig. 3 shows the channel estimation result under the actual sea trial data;
FIG. 4 is a result of correlation peak-to-contrast for training sequence matching before and after frequency domain zero-forcing equalization;
FIG. 5 is a schematic diagram of a decision feedback equalizer with an embedded phase locked loop;
fig. 6 is an underwater acoustic communication decoding result.
Detailed Description
The invention will be described in detail below with reference to the following drawings:
the technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
In the single-carrier high-speed underwater acoustic communication method provided by the embodiment of the invention, the implementation flow of a transmitting terminal is shown in fig. 1, an original information sequence of the transmitting terminal is mapped to a QPSK phase set through serial-parallel conversion, and then a training sequence is added at the front end of the phase information sequence and then the phase information sequence is transmitted through carrier modulation. As shown in fig. 2, after the received signals are synchronized, the received signals are first subjected to channel estimation by using a training sequence, then a weight matrix is constructed in a frequency domain by using the estimated channel and multiplied by the received signals, and finally the final decoding process is completed in a time domain by using a decision feedback equalizer embedded with a phase-locked loop. The method specifically comprises the following steps:
And carrying out single carrier signal coding modulation, carrying out serial-parallel conversion on the original information sequence by a transmitting terminal, mapping the original information sequence to a QPSK phase set, adding a training sequence in the phase sequence after mapping, and then carrying out carrier modulation to send out the information.
In this embodiment, let the original transmission sequence be an(an∈[-1,1]). Firstly, a is carried outnSerial-to-parallel conversion to obtain bn：
Figure BDA0002817624070000031
B is to benMapping to the QPSK phase set ([1+ i,1-i, -1+ i, -1-i)]) To obtain
Figure BDA0002817624070000032
Figure BDA0002817624070000033
In the formula,' indicates matrix multiplication. In that
Figure BDA0002817624070000034
The information sequence is added before and then can be sent out through carrier modulation:
Figure BDA0002817624070000035
in the formula (f)cAt carrier center frequency, TrnIs a training sequence.
And channel estimation, namely after the receiving end finishes signal detection and synchronization, estimating a channel by using a locally known training sequence.
In this embodiment, the receiving end adopts multiple array elements for reception (without limitation to the array type), and the signal received by the ith array element is treated by demodulation and down-sampling
Figure BDA0002817624070000036
Where Ld is the length of the training sequence, the received signal may be given in matrix form:
ri＝Shi+ni (4)
in the formula (I), the compound is shown in the specification,
Figure BDA0002817624070000037
an underwater acoustic channel corresponding to the ith receiving array element;
Figure BDA0002817624070000038
is noise interference;
Figure BDA0002817624070000039
then the least square method is used to obtain the estimated channel
Figure BDA00028176240700000310
Figure BDA00028176240700000311
Fig. 3 shows the channel estimation result based on actual data.
And (4) carrying out frequency domain zero-forcing equalization processing, namely constructing a weight matrix in a frequency domain by using the channel obtained by estimation, and multiplying the weight matrix by the received signal to realize equalization processing of the channel.
In this embodiment, the frequency domain form of the underwater acoustic channel corresponding to the ith array element obtained by estimation is set as HiThen, the weight matrix constructed in the frequency domain is:
Figure BDA00028176240700000312
in the formula (I), the compound is shown in the specification,
Figure BDA00028176240700000313
the result of the received signal after the frequency domain zero-forcing equalization processing is:
Figure BDA00028176240700000314
in the formula (I), the compound is shown in the specification,
Figure BDA0002817624070000041
fig. 4 shows the training sequence matching output results before and after equalization, and it can be seen that multipath spreading interference of the equalized channel is significantly suppressed.
And (4) decision feedback equalization processing, namely performing inverse Fourier transform on the signal subjected to the frequency domain zero forcing equalization processing back to a time domain, and performing final decoding processing by using a decision feedback equalizer embedded with a phase-locked loop.
In this embodiment, first, the signal after the frequency domain equalization is converted into a time domain signal y through inverse fourier transform, and then the time domain signal y is sent to a decision feedback equalizer embedded with a phase locked loop to perform final equalization decoding processing. Because multipath expansion interference of the underwater sound channel is obviously inhibited after the frequency domain zero forcing equalization, coefficients of a feedforward filter and a feedback filter of the decision feedback equalizer can be relatively fixed, and dynamic adjustment according to the multipath expansion size of the actual underwater sound channel is not needed. In this embodiment, the decision feedback equalizer has a feedback coefficient of 20 and the feedforward coefficient of 24. The RLS algorithm is adopted, and the forgetting factor is 0.998. Fig. 5 shows a schematic diagram of a decision feedback equalizer embedded with a phase-locked loop, wherein a received signal y is first multiplied by the output phase of the phase-locked loop to suppress the influence of random fluctuation phase on symbol decision, and then passes through a feedforward filter. The decided symbol of the decision feedback equalizer passes through a feedback filter, and outputs the result together with a feedforward filter, and the error e is calculated by taking the result as input. And the symbol decision device, the second-order phase-locked loop and the RLS algorithm respectively decide and adjust the current symbol, the correction phase and the feedforward and feedback filter coefficients according to the calculated error e. Fig. 6 shows the decoding result of the single carrier communication of the actual sea test data, the communication rate is 6kbps, and the communication distance is 12 km.
According to the single-carrier high-speed underwater acoustic communication method, the weight matrix is constructed in the frequency domain according to the actual channel condition and multiplied by the received signal, so that the multipath expansion interference of the underwater acoustic channel can be effectively inhibited. The intersymbol interference of the frequency domain equalization output signal is greatly reduced, so that the stable work of the decision feedback equalizer is ensured, and the single carrier high-speed underwater acoustic communication performance and the environmental adaptability are obviously improved.
The particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the present invention should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (4)

1. A single carrier high-speed underwater acoustic communication method is characterized in that: the method comprises the following steps:
(1) carrying out single carrier signal coding modulation, carrying out serial-parallel conversion on an original information sequence by a transmitting terminal, mapping the original information sequence to a QPSK phase set, adding a training sequence in front of the mapped phase sequence, and then carrying out carrier modulation to send out the training sequence;
(2) Estimating a channel, namely after finishing signal detection and synchronization by a receiving end, estimating the channel by using a locally known training sequence;
(3) performing frequency domain zero-forcing equalization processing, namely constructing a weight matrix in a frequency domain by using the channel obtained by estimation, and multiplying the weight matrix by a received signal to realize equalization processing of the channel;
(4) and performing decision feedback equalization processing, namely performing inverse Fourier transform on the signal subjected to the frequency domain zero forcing equalization processing back to a time domain, and performing final decoding processing by using a decision feedback equalizer embedded with a phase-locked loop.
2. Single carrier high speed underwater acoustic communication method according to claim 1, characterized in that: in the step (1), the raw material is processed,
let original send sequence be an(an∈[-1,1]) First, a isnSerial-to-parallel conversion to obtain bn：
Figure FDA0002817624060000011
B is tonMapping to the QPSK phase set ([1+ i,1-i, -1+ i, -1-i)]) To obtain
Figure FDA0002817624060000012
Figure FDA0002817624060000013
Wherein '. prime' denotes a matrix multiplication in
Figure FDA0002817624060000014
The information sequence is added before and then can be sent out through carrier modulation:
Figure FDA0002817624060000015
in the formula (f)cAt carrier center frequency, TrnIs a training sequence.
3. Single carrier high speed underwater acoustic communication method according to claim 1, characterized in that: in the step (2),
the receiving end adopts a plurality of array elements for receiving, and the signal of the ith array element after the signal received is demodulated and down-sampled is set as
Figure FDA0002817624060000016
Where Ld is the training sequence length, the received signal is given in matrix form:
ri＝Shi+ni (4)
in the formula (I), the compound is shown in the specification,
Figure FDA0002817624060000017
an underwater acoustic channel corresponding to the ith receiving array element;
Figure FDA0002817624060000018
is noise interference;
Figure FDA0002817624060000019
then the least square method is used to obtain the estimated channel
Figure FDA0002817624060000021
Figure FDA0002817624060000022
4. Single carrier high speed underwater acoustic communication method according to claim 1, characterized in that: in the step (3), the step (c),
setting the frequency domain form of the underwater acoustic channel corresponding to the ith array element obtained by estimation as HiThen, the weight matrix constructed in the frequency domain is:
Figure FDA0002817624060000023
in the formula (I), the compound is shown in the specification,
Figure FDA0002817624060000024
the result of the received signal after the frequency domain zero-forcing equalization processing is:
Figure FDA0002817624060000025
in the formula (I), the compound is shown in the specification,
Figure FDA0002817624060000026
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