CN110851781A - Channel impulse response window estimation method based on frequency domain energy and group delay screening - Google Patents
Channel impulse response window estimation method based on frequency domain energy and group delay screening Download PDFInfo
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Abstract
The invention discloses a channel impulse response window estimation method based on frequency domain energy and group delay screening, which comprises the following steps: (1) initializing parameters; (2) calculating the group delay of the frequency response of the underwater acoustic channel and forming a matrix M; (3) arranging M in ascending order according to group delay and forming a matrix T; (4) searching a row number p corresponding to the minimum propagation delay value and a row number w corresponding to the group delay median value in the matrix T; (5) setting a frequency range by taking w as a center, constructing a frequency interval, and counting frequency domain energy E in the constructed frequency interval; (6) if the ratio of the E to the total energy P of the frequency domain is smaller than the threshold, returning to the step 5; otherwise, outputting the starting time and the ending time of the underwater sound channel impulse response window. The method and the device aim at the problem that the frequency response group delay of the underwater acoustic channel is distorted due to the loss of the normal wave group velocity and the multipath propagation, and realize the estimation of the starting time and the ending time of the impulse response window of the underwater acoustic channel.
Description
Technical Field
The invention relates to the technical field of underwater acoustic signal processing, in particular to a channel impulse response window estimation method based on frequency domain energy and group delay screening.
Background
The underwater acoustic modeling and simulation are one of the important means of the underwater acoustic scientific research and are also the main ways for predicting and analyzing the performance of the complex underwater acoustic system in the actual marine environment. The signal level simulation of the complex underwater acoustic system can realize the whole process simulation of underwater acoustic information generation, transmission, processing and perception, and is the key for completing the simulation, analysis and evaluation of the underwater acoustic system. The real-time simulation of multi-sensor and multi-target broadband signals is a difficult point of underwater acoustic signal level simulation, and an underwater acoustic channel propagation characteristic calculation model with good marine environment adaptability, accuracy and instantaneity needs to be established.
The Fourier synthesis (Fourier synthesis) method is one of the most widely used wideband modeling methods for underwater acoustic channels, and the method calls a propagation model code for multiple times with a certain frequency domain resolution and calculates to obtain the channel frequency response in a specified frequency band range. The Fourier synthesis method is simple in principle and high in calculation accuracy, and is suitable for most existing propagation model codes. However, when the frequency response obtained by the fourier synthesis method is converted into an impulse response function, the frequency response needs to have a high resolution in order to ensure that aliasing does not occur in the time domain. The propagation model code is more in calling times and large in calculation amount, and application of the Fourier synthesis method in an underwater acoustic signal level real-time simulation system is restricted. When the traditional Fourier synthesis method is used for estimating the starting point of the time window of the impulse response function, a conservative estimation method is adopted, the minimum group velocity of the normal wave is utilized for estimating the end point of the time window, when a parabolic equation model is used for calculating the frequency response, the group velocity of the normal wave cannot be given, and the frequency response group delay is distorted due to the multi-path propagation of a channel, so that the end point of the time window of the impulse response function is very difficult to determine. Aiming at the problems, the invention provides a channel impulse response window starting time and ending time estimation method based on frequency domain energy-group delay combined screening.
Disclosure of Invention
In order to solve the existing problems, the invention provides a channel impulse response window estimation method based on frequency domain energy and group delay screening, aiming at the estimation problems of the starting time and the ending time of an underwater acoustic channel impulse response window under the condition that the underwater acoustic channel frequency response group delay is distorted due to the loss of normal wave group velocity and multipath propagation, and aiming at achieving the purpose, the invention provides the channel impulse response window estimation method based on the frequency domain energy and the group delay screening, which is characterized by comprising the following steps:
1) initializing parameters;
2) calculating the group delay of the frequency response of the underwater acoustic channel and forming a matrix M;
3) arranging M in ascending order according to group delay and forming a matrix T;
4) searching a row number p corresponding to the minimum propagation delay value and a row number w corresponding to the group delay median value in the matrix T;
5) setting a frequency range by taking w as a center, constructing a frequency interval, and counting frequency domain energy E in the constructed frequency interval;
6) if the ratio of the E to the total energy P of the frequency domain is smaller than the threshold, returning to the step 5; otherwise, outputting the starting time and the ending time of the underwater sound channel impulse response window.
As a further improvement of the invention, step 1 comprises the following steps:
setting maximum value c of underwater sound velocitymaxDistance r of the source from the receiver, minimum propagation delay value tmin=r/cmaxCalculating the frequency range [ fl,fh]Sampling frequency fsFrequency resolution Δ f, channel frequency response sequence length N +1, threshold value η, and variable j equal to 1.
As a further improvement of the invention, the step 2 comprises the following steps:
according to a frequency sequence fiAmplitude-frequency response sequence AiPhase frequency response sequencei is 0,1, …, N, and the group delay sequence of the frequency response is calculated using equation (1):
will f isk、τk、AkForm a matrix M, as shown in formula (2):
wherein k is 1, …, N-1.
As a further improvement of the invention, the step 3 comprises the following steps:
arranging the matrix M in ascending order according to the value of the 2 nd column to obtain a matrix T, wherein the matrix T is shown as a formula (3):
wherein, tau'1≤τ’2≤…≤τ’k≤…≤τ’N-1。
As a further improvement of the invention, the step 4 comprises the following steps:
(5.1) search for the first larger than T in column 2 of the matrix TminGroup delay value of τ'pP is the corresponding matrix row number;
(5.2) searching a row number corresponding to a value in the group delay sequence in the 2 nd column of the matrix T, wherein the row number is specifically shown as the formula (4):
as a further improvement of the present invention, the step 5 comprises the following steps:
(6.1) values of a and b are determined by expressions (5) and (6), respectively, to construct a frequency segment [ f'a,f’b]:
(6.2) calculating the segment [ f 'from formula (7)'a,f’b]Inner frequency domain energy E:
(6.3) calculating the frequency domain total energy P by using the formula (8):
(6.4) calculating the energy ratio Q using the equation (9):
as a further improvement of the invention, the step 6 comprises the following steps:
(7.1) if Q < η, making j equal to j +1, and returning to step 5;
(7.2) if Q is more than or equal to η, let the group delay value tau 'of the 2 nd column and the a th row in the matrix T'aThe group delay value tau 'of the 2 nd column and the b th row in the matrix T is used as the starting time of a channel impulse response window'bIs the end time of the channel impulse response window.
The invention discloses a channel impulse response window estimation method based on frequency domain energy and group delay screening, which can be used for estimating an underwater acoustic channel impulse response window. The method of the invention can realize accurate estimation of the initial time and the final time of the underwater acoustic channel impulse response window under the condition that the normal wave group velocity is lost and the underwater acoustic channel frequency response group delay is distorted due to multi-path propagation. Compared with the traditional Fourier synthesis method, the method does not need the information of the group velocity of the normal waves, and has wider application range.
Drawings
FIG. 1 is a flow chart of an embodiment of the method of the present invention;
FIG. 2 is an amplitude-frequency response sequence of a distance dependent underwater acoustic channel in an embodiment;
FIG. 3 is a sequence of phase-frequency responses of the range-dependent underwater acoustic channel in an embodiment;
FIG. 4 is a frequency response group delay sequence of a range dependent underwater acoustic channel in an embodiment;
fig. 5 is an amplitude-frequency response sequence of the sequenced underwater acoustic channels in the embodiment.
Detailed Description
The invention is described in further detail below with reference to the following detailed description and accompanying drawings:
the invention provides a channel impulse response window estimation method based on frequency domain energy and group delay screening, which aims at the estimation problem of the initial time and the ending time of an underwater acoustic channel impulse response window under the condition that the underwater acoustic channel frequency response group delay is distorted due to the loss of normal wave group velocity and multi-path propagation.
Example 1: the invention is further elucidated with reference to the drawings and the detailed description.
A channel impulse response window estimation method based on frequency domain energy and group delay screening, as shown in fig. 1, includes the following steps:
setting maximum value c of underwater sound velocitymax1534.74m/s, the distance r between sound source and receiver is 10000m, and the minimum propagation delay t ismin=r/cmax6.5158s, calculating the frequency range fl=100Hz,fh500Hz, sampling frequency fs10000Hz, 0.1Hz, 801 channel frequency response sequence length N +1, 800, 0.926 threshold η, and 1 variable j.
Step 2, calculating the group delay of the underwater acoustic channel frequency response and forming a matrix M, and the concrete steps are as follows:
the amplitude-frequency response sequence and the phase-frequency response sequence of the channel are shown in fig. 2 and 3, respectively, according to the frequency sequence fiAmplitude-frequency response sequence AiPhase frequency response sequencei is 0,1, …, N, and the group delay of the frequency response is calculated by equation (1)Time series, calculated group delay as shown in FIG. 4, equation (2) for fk、τk、AkA matrix M is formed, where k is 1, …, N-1.
And 3, arranging the matrix M in an ascending order according to the group delay to form a matrix T, and specifically comprising the following steps:
the matrix M is arranged in ascending order according to the value of the 2 nd column to obtain a matrix T shown as a formula (3), wherein tau'1≤τ’2≤…≤τ’k≤…≤τ’N-1The ordered amplitude-frequency response sequence is shown in fig. 5.
Step 4, searching the row number p corresponding to the minimum propagation delay value and the row number w corresponding to the group delay median value in the matrix T, comprising the following steps:
(4.1) find the first greater than T in column 2 of the matrix TminGroup delay value τ 'of 6.5158 s'p6.5166s to give τ'pThe corresponding matrix row number p in the matrix T is 127.
(4.2) searching the column 2 of the matrix T for the row number corresponding to the median in the group delay sequence, where N is an even number, and taking w as N/2 as 400 according to equation (4), the row number w of the median in the group delay sequence in the second column of the matrix T is obtained as 400.
Step 5, setting a frequency range by taking w as a center, constructing a frequency interval, counting frequency domain energy E in the constructed frequency interval, intercepting the frequency interval by taking a frequency corresponding to a median of the group delay sequence as a center, and continuously increasing the interval range, wherein the specific steps are as follows:
(5.1) determining values of a and b by using expressions (5) and (6), wherein w is 400, p is 127, N is 800, initializing j is 1, according to a first row of the matrix T, an initial value of a is 399, an initial value of b is 401, and a frequency interval [ f'a,f’b];
(5.2) calculating the segment [ f 'from formula (7)'a,f’b]Inner frequency domain energy E-2.855 × 10-4;
(5.3) calculating the frequency domain total energy P by the equation (8) of 3.193 × 10-4;
(5.4) the energy ratio Q ═ E/P is calculated by the formula (9).
Step 6, if Q is smaller than the threshold, return to step 5; otherwise, outputting the starting time and the ending time of the underwater acoustic channel impulse response window, and specifically comprising the following steps:
(6.1) if Q < η, making j equal to j +1, and returning to step 5;
(6.2) when Q is not less than η, j is 306, E is 2.957 × 10-4Q0.9261, a 127, b 706, let the group delay τ 'in the 2 nd column and row a of the matrix T'a6.5166s is the starting time of the channel impulse response window, let the group delay value tau 'of the 2 nd column and b th row in the matrix T'b6.8509s is the end time of the channel impulse response window.
The embodiment shows that in the process of estimating the impulse response function window, the information of the group velocity of the normal wave is not needed, the problem of the group delay distortion of the frequency response caused by multi-path propagation is effectively solved, the starting time and the ending time of the window are determined, and the accurate estimation of the channel impulse response window is realized.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, but any modifications or equivalent variations made according to the technical spirit of the present invention are within the scope of the present invention as claimed.
Claims (7)
1. The channel impulse response window estimation method based on frequency domain energy and group delay screening is characterized by comprising the following steps of:
1) initializing parameters;
2) calculating the group delay of the frequency response of the underwater acoustic channel and forming a matrix M;
3) arranging M in ascending order according to group delay and forming a matrix T;
4) searching a row number p corresponding to the minimum propagation delay value and a row number w corresponding to the group delay median value in the matrix T;
5) setting a frequency range by taking w as a center, constructing a frequency interval, and counting frequency domain energy E in the constructed frequency interval;
6) if the ratio of the E to the total energy P of the frequency domain is smaller than the threshold, returning to the step 5; otherwise, outputting the starting time and the ending time of the underwater sound channel impulse response window.
2. The channel impulse response window estimation method based on frequency domain energy and group delay screening as claimed in claim 1, wherein: the step 1 comprises the following steps:
setting maximum value c of underwater sound velocitymaxDistance r of the source from the receiver, minimum propagation delay value tmin=r/cmaxCalculating the frequency range [ fl,fh]Sampling frequency fsFrequency resolution Δ f, channel frequency response sequence length N +1, threshold value η, and variable j equal to 1.
3. The channel impulse response window estimation method based on frequency domain energy and group delay screening as claimed in claim 1, wherein: the step 2 comprises the following steps:
according to a frequency sequence fiAmplitude-frequency response sequence AiPhase frequency response sequenceCalculating a group delay sequence of the frequency response using equation (1):
will f isk、τk、AkForm a matrix M, as shown in formula (2):
wherein k is 1, …, N-1.
4. The channel impulse response window estimation method based on frequency domain energy and group delay screening as claimed in claim 1, wherein: the step 3 comprises the following steps:
arranging the matrix M in ascending order according to the value of the 2 nd column to obtain a matrix T, wherein the matrix T is shown as a formula (3):
wherein, tau'1≤τ’2≤…≤τ’k≤…≤τ’N-1。
5. The channel impulse response window estimation method based on frequency domain energy and group delay screening as claimed in claim 1, wherein: step 4 comprises the following steps:
(5.1) search for the first larger than T in column 2 of the matrix TminGroup delay value of τ'pP is the corresponding matrix row number;
(5.2) searching a row number corresponding to a value in the group delay sequence in the 2 nd column of the matrix T, wherein the row number is specifically shown as the formula (4):
6. the channel impulse response window estimation method based on frequency domain energy and group delay screening as claimed in claim 1, wherein: the step 5 comprises the following steps:
(6.1) values of a and b are determined by expressions (5) and (6), respectively, to construct a frequency segment [ f'a,f’b]:
(6.2) calculating the segment [ f 'from formula (7)'a,f’b]Inner frequency domain energy E:
(6.3) calculating the frequency domain total energy P by using the formula (8):
(6.4) calculating the energy ratio Q using the equation (9):
7. the channel impulse response window estimation method based on frequency domain energy and group delay screening as claimed in claim 1, wherein: step 6 comprises the following steps:
(7.1) if Q < η, making j equal to j +1, and returning to step 5;
(7.2) if Q is more than or equal to η, let the group delay value tau 'of the 2 nd column and the a th row in the matrix T'aThe group delay value tau 'of the 2 nd column and the b th row in the matrix T is used as the starting time of a channel impulse response window'bIs the end time of the channel impulse response window.
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