CN111447157A - Ocean underwater acoustic communication blind channel equalization method - Google Patents

Ocean underwater acoustic communication blind channel equalization method Download PDF

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Publication number
CN111447157A
CN111447157A CN202010192869.6A CN202010192869A CN111447157A CN 111447157 A CN111447157 A CN 111447157A CN 202010192869 A CN202010192869 A CN 202010192869A CN 111447157 A CN111447157 A CN 111447157A
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underwater acoustic
acoustic communication
blind channel
channel equalization
equalization method
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张祥光
汪嘉宁
王凡
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Qingdao National Laboratory for Marine Science and Technology Development Center
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Qingdao National Laboratory for Marine Science and Technology Development Center
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    • 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
    • H04L25/0202—Channel estimation
    • H04L25/0238—Channel estimation using blind estimation
    • 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

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  • Computer Networks & Wireless Communication (AREA)
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Abstract

The invention discloses a blind channel equalization method for marine underwater acoustic communication, which comprises the following steps: (1) sampling the received signal to construct an observation vector x (i); (2) calculating the correlation function R of the observation vector x (i)xObtaining RxTime-averaged estimation of the time delay at 0 respectively
Figure DDA0002416551530000011
Time-averaged estimate of sum delay of 1
Figure DDA0002416551530000012
(3) According to
Figure DDA0002416551530000013
Estimating the noise variance σ2And the dimension d of the signal subspace; (4) calculating RxF; (5) according to
Figure DDA0002416551530000014
And
Figure DDA0002416551530000015
carrying out time average estimation on the transmission function of the ocean underwater acoustic communication blind channel to obtain
Figure DDA0002416551530000016
(6) Estimating the information source signal to obtain
Figure DDA0002416551530000017
The ocean underwater acoustic communication blind channel equalization method adopts the blind channel identification technology to control the parameters of the time-varying and space-varying channels in time and update the parameters of the equalizer in time, so that a receiving end can correctly receive the signal sent by the information source under the condition of not knowing the channel parameters, and the stable and efficient transmission of the signal under the complex ocean environment is ensured.

Description

Ocean underwater acoustic communication blind channel equalization method
Technical Field
The invention belongs to the technical field of communication, and relates to a blind channel equalization method for marine underwater acoustic communication.
Background
In the marine environment, the field observation data of the deep sea subsurface buoy is transmitted to the water surface through a marine underwater sound channel, the time, space and multi-path effects of the underwater sound channel exist, the transmission function of the underwater sound channel is unknown, after the discrete underwater sound digital signals are transmitted through the channel, the inter-symbol interference is inevitably generated due to the multi-path effect of the channel and the influence of various noises, the signal distortion is serious, so that a receiving end cannot correctly receive the signals sent by the information source, and the reliability and the accuracy of data transmission are influenced. Therefore, the blind equalization processing of the channel is very important, and the blind equalization of the channel is to recover the signal of the transmitting end at the receiving end of the signal through the compensation of the channel.
Therefore, how to provide an ocean underwater sound communication blind channel equalization method for equalizing an underwater sound blind channel and improving the reliability and accuracy of data transmission is a technical problem mainly solved by the invention.
Disclosure of Invention
The invention provides an ocean underwater acoustic communication blind channel equalization method aiming at the technical problem that the reliability and accuracy of ocean underwater acoustic communication blind channel data transmission in the prior art are poor, and the problem can be solved.
In order to realize the purpose of the invention, the invention is realized by adopting the following technical scheme:
a marine underwater acoustic communication blind channel equalization method comprises the following steps:
(1) sampling the received signal to construct an observation vector x (i):
x(i)＝[x(t0+Δ+iT),...,x(t0+mΔ+iT)]T,i＝0,1,...；
wherein T is an inter-symbol space, and T ═ TsΔ，TsThe sampling length L satisfies L ═ m delta, and m is a positive integer;
(2) calculating the correlation function R of the observation vector x (i)xObtaining RxTime-averaged estimation of the time delay at 0 respectively
Figure BDA0002416551510000011
Time-averaged estimate of sum delay of 1
Figure BDA0002416551510000012
(3) According to
Figure BDA0002416551510000021
Estimating the noise variance σ2And the dimension d of the signal subspace;
(4) calculating RxF;
(5) according to
Figure BDA0002416551510000022
And
Figure BDA0002416551510000023
carrying out time average estimation on the transmission function of the ocean underwater acoustic communication blind channel to obtain
Figure BDA0002416551510000024
(6) Estimating the information source signal to obtain
Figure BDA0002416551510000025
Further, in the step (2),
Figure BDA0002416551510000026
Figure BDA0002416551510000027
n is the number of samples of observation vector x (i).
Further, step (3) comprises:
(31) to, for
Figure BDA0002416551510000028
Correcting the correlation matrix to a noise-free correlation matrix Rx(0)；
(32) R is then reacted withx(0) The diagonal decomposition of (a) yields the noise variance σ2And the dimension d of the signal subspace.
Further, step (31) is on
Figure BDA0002416551510000029
The correction method comprises the following steps:
Figure BDA00024165515100000210
wherein I is a unit diagonal matrix.
Further, in step (32), R is addedx(0) The diagonal decomposition method comprises the following steps:
UHRx(0)U＝diag(λ1+σ2,...,λd+σ2,σ2,...σ2)Σ＝diag(σ1,…,σd)；
wherein U is RxThe eigenvalue decomposition matrix of (a), the noise variance σ being obtained from the above equation2And the dimension d of the signal subspace.
Further, in the step (4), R is calculatedxThe method for diagonal decomposition of F comprises:
Figure BDA00024165515100000211
wherein Σ is represented by Rx(0) Is a diagonal matrix of principal singular values, Us＝[u1,...,ud]，udRepresents the d-th column of U.
Further, the method for performing time-averaged estimation on the transfer function of the marine underwater acoustic communication blind channel in step (5) comprises:
defining the intermediate variable R:
R＝FRx(1)FH；
and decomposing the characteristic value of R to obtain:
Figure BDA0002416551510000031
wherein, ydColumn d of F; z is a radical ofdIs FHThe d-th column of (1);
Figure BDA0002416551510000032
is a characteristic value of R;
Figure BDA0002416551510000033
phi is a real phase;
wherein Q ═ yd,Ryd,...,R(d-1)yd]。
Further, in step (6), the source signal
Figure BDA0002416551510000034
The extraction method comprises the following steps:
Figure BDA0002416551510000035
further, in the above-mentioned case,
Figure BDA0002416551510000036
is a column full rank complex matrix;
Figure BDA0002416551510000037
a stationary process with zero mean value, the correlation matrix having the followingForm (a):
Figure BDA0002416551510000038
j is a shift matrix of d × d.
Further, in the above-mentioned case,
Figure BDA0002416551510000039
compared with the prior art, the invention has the advantages and positive effects that: the ocean underwater acoustic communication blind channel equalization method adopts the blind channel identification technology to control the parameters of the time-varying and space-varying channels in time and update the parameters of the equalizer in time, so that a receiving end can correctly receive the signal sent by the information source under the condition of not knowing the channel parameters, and the stable and efficient transmission of the signal under the complex ocean environment is ensured.
Other features and advantages of the present invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a block diagram of an abstract representation of a blind channel identification and equalization method according to the present invention;
FIG. 2 is a diagram of a finite impulse response channel of a blind channel identification and equalization method according to an embodiment;
FIG. 3 is an observation interval I in FIG. 20＝(t0,t0+ L);
fig. 4 is a QPSK source symbol constellation diagram in the second embodiment;
FIG. 5 is a received signal constellation that has not been equalized by the method of the first embodiment;
fig. 6 is the estimated channel at SNR of 20 dB;
fig. 7 is a received signal constellation diagram equalized by the method of the first embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and examples.
Example one
The blind channel identification and equalization described in this disclosure can be abstracted to a model as shown in fig. 1.
As shown in fig. 1, for a time-varying (and space-varying) channel, the received complex baseband signal x (-) can be represented as
Figure BDA0002416551510000041
Here, skRepresenting a sequence of characters transmitted by a digital communication system; t represents an inter-code interval; h (-) represents a discrete equivalent channel, mainly comprising a pulse forming filter, a channel, a receiving filter and the like; n (-) represents additive noise.
The goal of blind channel identification is to estimate h (-) from the received signal x (t), and once channel estimation is complete, the source skRecovery can be performed by a simple method. To achieve channel estimation, we make the following assumptions:
(1) t is known and is a multiple of the sampling interval, T being the inter-code interval.
(2) The impulse response of the channel is a finite impulse response.
(3) Source character sequence skIs zero mean, and
Figure BDA0002416551510000051
(4) noise n (-) is zero mean, and skStatistics are irrelevant, and:
Figure BDA0002416551510000052
in the above assumptions, (1), (2), and (3) are assumed to match the actual situation. For assumption (4), since the additive noise is random additive noise, the assumption can also be considered approximately true.
The invention discloses a marine underwater acoustic communication blind channel equalization method, which comprises the following steps:
s1, sampling the received signal, and constructing an observation vector x (i):
x(i)＝[x(t0+Δ+iT),...,x(t0+mΔ+iT)]T,i＝0,1,...；
wherein T is an inter-symbol space, and T ═ TsΔ，TsFor the oversampling period, Δ is the sampling interval, and the sampling length L satisfies L ═ m Δ, where m is a positive integer.
Sampling the received signal x (t) to discretize it into x (i), whether x (i) is stationary or cyclostationary, depending on the sampling rate, x (i) being stationary if sampled with the baud rate of the transmitting source; if the sampling rate is higher than the baud rate of the source, x (i) is cyclostationary. Let T besThe sampling period is several times higher than the source baud rate, and the sampling interval is delta-T/TsThen T issIs an integer greater than 1, and therefore has
Figure BDA0002416551510000053
Figure BDA0002416551510000054
Under the condition of assumption (1), the observation signal subspace defined in an arbitrary observation interval I is a time-shifted linear space including a series of h (·). Namely: r(s,h)(I) Abbreviated as r (i) and defined as:
Figure BDA0002416551510000055
for the finite impulse response channel h (t), if its response time length is LhFor observation interval I0＝(t0,t0+ L), signal space R (I)0) Will be h (t-K)0T),...,h(t-(K0+ (d-1)) T) as shown in FIGS. 2 and 3.
S2, calculating the correlation function R of the observation vector x (i)xObtaining RxTime-averaged estimation of the time delay at 0 respectively
Figure BDA0002416551510000061
Time-averaged estimate of sum delay of 1
Figure BDA0002416551510000062
S3, according to
Figure BDA0002416551510000063
Estimating the noise variance σ2And the dimension d of the signal subspace;
s4, calculating RxF;
s5, according to
Figure BDA0002416551510000064
And
Figure BDA0002416551510000065
carrying out time average estimation on the transmission function of the ocean underwater acoustic communication blind channel to obtain
Figure BDA0002416551510000066
S6, estimating the source signal to obtain
Figure BDA0002416551510000067
The scalar expression for the oversampled observed signal is equation (2), and the vector expression for the oversampled observed signal x (i) is:
x(iT)＝Hs(iT)+n(iT),i＝0,1,... (15)
scalar expressions represent a cyclostationary process, while vector expressions represent a stationary process.
In this embodiment, a vector process x (i) is used, where i is 0,1, …, and its model is (15), and the following constraint conditions are satisfied:
1) h is a column full rank complex matrix of m × d;
2) s (i) is a zero-mean stationary process whose correlation matrix has the following form:
Figure BDA0002416551510000068
where J is a "shift" matrix of d × d
Figure BDA0002416551510000069
In the absence of noise, H is represented by R if H and s (i) satisfy the constraint in assumption (1)x(0) And Rx(1) And (4) unique identification.
In this example, assume that
Figure BDA0002416551510000071
Is a column full rank complex matrix;
Figure BDA0002416551510000072
a stationary process with zero mean, whose correlation function matrix has the following form:
Figure BDA0002416551510000073
therefore, in the scheme, R is obtainedx(0) And Rx(1) Carrying out time average estimation on the transmission function of the marine underwater acoustic communication blind channel to obtain
Figure BDA0002416551510000074
In the step S2 of the present embodiment,
Figure BDA0002416551510000075
Figure BDA0002416551510000076
n is the number of samples of observation vector x (i).
Step S3 is based on
Figure BDA0002416551510000077
Estimating the noise variance σ2And the dimension d of the signal subspace includes:
s31, pair
Figure BDA0002416551510000078
Correcting the correlation matrix to a noise-free correlation matrix Rx(0)；
S32, adding Rx(0) The diagonal decomposition of (a) yields the noise variance σ2And the dimension d of the signal subspace.
Pair in step S31
Figure BDA0002416551510000079
The correction method comprises the following steps:
Figure BDA00024165515100000710
wherein I is a unit diagonal matrix.
This step estimates the time average when the delay is 0
Figure BDA00024165515100000711
Modified to noiseless correlation matrix Rx(0) And using it to calculate the noise variance σ2And the dimension d of the signal subspace.
When there is noise, the observed signal x (i) is
x(i)＝Hs(i)+n(i) (50)
The correlation matrix is
Rx(k)＝HRs(k)HH+Rn(k) (51)
If the noise is white noise, the correlation matrix of the noise is
Figure BDA00024165515100000712
In the formula, σ2,TsRespectively the variance of the noise and the oversampling rate.
Due to the variance σ of the noise2The sum signal subspace dimension d is unknown, so a correlation matrix R from the observed signals is requiredx(0) And (6) obtaining.
In step S32, R is addedx(0) The diagonal decomposition method comprises the following steps:
UHRx(0)U＝diag(λ1+σ2,...,λd+σ2,σ2,...σ2)Σ＝diag(σ1,…,σd)；
wherein U is RxThe eigenvalue decomposition matrix of (a), the noise variance σ being obtained from the above equation2And the dimension d of the signal subspace.
In step S4, R is calculatedxThe method for diagonal decomposition of F comprises:
Figure BDA0002416551510000081
Σ＝diag(σ1,…,σd)
Us＝[u1,...,ud]，udd column representing U
Wherein Σ is represented by Rx(0) Is a diagonal matrix of principal singular values, UsIs with Rx(0) And (4) a matrix formed by eigenvectors corresponding to the main eigenvalues of (1).
Calculating and estimating:
Figure BDA0002416551510000082
the method for performing time-averaged estimation on the transmission function of the marine underwater acoustic communication blind channel in step S5 includes:
defining the intermediate variable R:
R＝FRx(1)FH；
and decomposing the characteristic value of R to obtain:
Figure BDA0002416551510000083
wherein, ydColumn d of F; z is a radical ofdIs FHThe d-th column of (1);
Figure BDA0002416551510000084
is a characteristic value of R;
Figure BDA0002416551510000085
phi is the real phase.
Wherein Q ═ yd,Ryd,...,R(d-1)yd]。
In step S6, a source signal
Figure BDA0002416551510000086
The extraction method comprises the following steps:
Figure BDA0002416551510000087
example two
In order to verify the blind channel equalization method for marine underwater acoustic communication in the first embodiment, simulation is performed in the first embodiment. A QPSK uniformly distributed hydroacoustic source, the hydroacoustic channel is a 3-path multi-path channel with the property of roll-off coefficient of 0.13L cosine, that is
h(t)＝0.6c(t,0.13)+0.4c(t-2.5,0.13)+0.2c(t-5,0.13)
The period of the source symbol is T (4 delta), the oversampling rate of the receiving end is delta, the finite impulse response length of the channel is 6T, and the length of the observation window of the receiving end is 5T. Thus d is 10 and m is 20. The results of the simulation are as follows.
Fig. 4 is a QPSK source symbol constellation; FIG. 5 is a constellation diagram of a received signal without equalization; fig. 6-7 show the results of estimating the channel and equalized QPSK symbols when the SNR is 20 dB. The estimated channel has little error with the original channel, and the equalization effect is good by comparing the equalized signal with the original signal.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions.

Claims (10)

1. A marine underwater acoustic communication blind channel equalization method is characterized by comprising the following steps:
(1) sampling the received signal to construct an observation vector x (i):
x(i)＝[x(t0+Δ+iT),...,x(t0+mΔ+iT)]T,i＝0,1,...；
wherein T is an inter-symbol space, and T ═ TsΔ，TsThe sampling length L satisfies L ═ m delta, and m is a positive integer;
(2) calculating the correlation function R of the observation vector x (i)xObtaining RxTime-averaged estimation of the time delay at 0 respectively
Figure FDA0002416551500000011
Time-averaged estimate of sum delay of 1
Figure FDA0002416551500000012
(3) According to
Figure FDA0002416551500000013
Estimating the noise variance σ2And the dimension d of the signal subspace;
(4) calculating RxF;
(5) according to
Figure FDA0002416551500000014
And
Figure FDA0002416551500000015
carrying out time average estimation on the transmission function of the ocean underwater acoustic communication blind channel to obtain
Figure FDA0002416551500000016
(6) Estimating the information source signal to obtain
Figure FDA0002416551500000017
2. The ocean underwater acoustic communication blind channel equalization method according to claim 1,
in the step (2),
Figure FDA0002416551500000018
Figure FDA0002416551500000019
n is the number of samples of observation vector x (i).
3. The ocean underwater acoustic communication blind channel equalization method according to claim 1,
the step (3) comprises the following steps:
(31) to, for
Figure FDA00024165515000000110
Correcting the correlation matrix to a noise-free correlation matrix Rx(0)；
(32) R is then reacted withx(0) The diagonal decomposition of (a) yields the noise variance σ2And the dimension d of the signal subspace.
4. The ocean underwater acoustic communication blind channel equalization method according to claim 3,
in step (31) to
Figure FDA00024165515000000111
The correction method comprises the following steps:
Figure FDA00024165515000000112
wherein I is a unit diagonal matrix.
5. The ocean underwater acoustic communication blind channel equalization method according to claim 4,
in step (32), R isx(0) The diagonal decomposition method comprises the following steps:
UHRx(0)U＝diag(λ1+σ2,...,λd+σ2,σ2,...σ2)Σ＝diag(σ1,…,σd)；
wherein U is RxThe eigenvalue decomposition matrix of (a), the noise variance σ being obtained from the above equation2And the dimension d of the signal subspace.
6. The ocean underwater acoustic communication blind channel equalization method according to claim 5,
in the step (4), R is calculatedxThe method for diagonal decomposition of F comprises:
Figure FDA0002416551500000021
wherein Σ is represented by Rx(0) Is a diagonal matrix of principal singular values, Us＝[u1,...,ud]，udRepresents the d-th column of U.
7. The blind channel equalization method for marine underwater acoustic communication according to claim 6,
the method for carrying out time average estimation on the transmission function of the marine underwater acoustic communication blind channel in the step (5) comprises the following steps:
defining the intermediate variable R:
R＝FRx(1)FH；
and decomposing the characteristic value of R to obtain:
Figure FDA0002416551500000022
wherein, ydColumn d of F; z is a radical ofdIs FHThe d-th column of (1);
Figure FDA0002416551500000023
is a characteristic value of R;
Figure FDA0002416551500000024
phi is a real phase;
wherein Q ═ yd,Ryd,...,R(d-1)yd]。
8. The blind channel equalization method for marine underwater acoustic communication according to claim 7,
in step (6), the source signal
Figure FDA0002416551500000025
The extraction method comprises the following steps:
Figure FDA0002416551500000026
9. the ocean underwater acoustic communication blind channel equalization method according to claim 1,
Figure FDA0002416551500000027
is a column full rank complex matrix;
Figure FDA0002416551500000028
a stationary process with zero mean, whose correlation function matrix has the following form:
Figure FDA0002416551500000031
j is a shift matrix of d × d.
10. The blind channel equalization method for marine underwater acoustic communication according to claim 9,
Figure FDA0002416551500000032
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Application publication date: 20200724