KR20170029899A - Apparatus and method for estimating lfm signal parameter of active sonar system - Google Patents

Apparatus and method for estimating lfm signal parameter of active sonar system Download PDF

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KR20170029899A
KR20170029899A KR1020150127056A KR20150127056A KR20170029899A KR 20170029899 A KR20170029899 A KR 20170029899A KR 1020150127056 A KR1020150127056 A KR 1020150127056A KR 20150127056 A KR20150127056 A KR 20150127056A KR 20170029899 A KR20170029899 A KR 20170029899A
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Prior art keywords
lfm
frequency
parameter
signal
time
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KR1020150127056A
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Korean (ko)
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백종대
배건성
박명호
석종원
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국방과학연구소
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
    • G01S7/52023—Details of receivers
    • G01S7/52025—Details of receivers for pulse systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/08—Systems for measuring distance only
    • G01S15/10—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G01S15/102—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves using transmission of pulses having some particular characteristics
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52001—Auxiliary means for detecting or identifying sonar signals or the like, e.g. sonar jamming signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/523—Details of pulse systems
    • G01S7/526—Receivers

Abstract

The present invention an apparatus and method for estimating a linear frequency modulation (LFM) signal parameter of an active sonar system that estimates a parameter of an LFM signal. The apparatus for estimating an LFM signal parameter of an active sonar system comprises: an LFM input part inputting an LFM signal spread from a target through a sensor; a partial Fourier transform part performing a partial Fourier transform on the input LFM signal by using an optimal change order; a time-frequency analysis part extracting a time-frequency parameter in the partial Fourier transformed spectral area; and an LFM parameter estimation part estimating a parameter of the LFM signal by using the extracted time-frequency parameter.

Description

[0001] APPARATUS AND METHOD FOR ESTIMATING LFM SIGNAL PARAMETER OF ACTIVE SONAR SYSTEM [0002]

The present invention relates to an apparatus and method for estimating an LFM signal parameter of an active sonar system for estimating a parameter of a linear frequency modulation (LFM) signal.

Active sonar is a technique that generates a transmission signal and processes the signal reflected on the target to detect the spread. In general, active sonar has higher detection performance than passive sonar and is known to be superior in terms of parameter estimation. Therefore, active sonar research is relatively active.

In active sonar, various types of active pulses can be used depending on the purpose. The most widely used pulses are continuous wave (CW) pulses and frequency modulation (FM) series pulses.

The linear frequency modulation (LFM) pulses are the most widely used active pulses of the FM series. However, as the frequency band used is wider, not only the frequency shift due to the Doppler effect but also the slope mismatch phenomenon occurs. There is a disadvantage in that detection performance deteriorates due to occurrence of correlation loss. So far, a method of parameter estimation of LFM signal using various time - frequency conversion techniques has been actively studied. Radon-Ambiguity transform, Wigner-Hough transform, Hough transform through short-time Fourier analysis, and Hilbert-Huang Hough transform have been studied.

However, since various detection techniques using actual sonar and radar are affected by various factors such as the environment and target attitude angle, there are many differences and distortions in the acoustic signals received from the same target. Especially, the technique related to LFM parameter estimation in underwater environment shows complicated characteristics reflecting underwater multi - path environment in which the underwater acoustic signal changes in time and spatially characteristics, which makes it difficult to estimate the actual parameters.

It is therefore an object of the present invention to provide an apparatus and method for estimating an LFM signal parameter of an active sonar system capable of estimating a parameter of a linear frequency modulation (LFM) signal used as a transmission signal for target detection in active sonar.

According to an aspect of the present invention, there is provided an apparatus for estimating an LFM signal parameter of an active sonar system, including: an LFM input unit for inputting an LFM signal spread from a target through a sensor; A partial Fourier transform unit for performing partial Fourier transform on the input LFM signal using an optimal change order; A time-frequency analysis unit for extracting a time-frequency parameter in the partial Fourier transformed spectral region; And an LFM parameter estimator for estimating a parameter of the LFM signal using the extracted time-frequency parameter.

According to another aspect of the present invention, there is provided a method of estimating an LFM signal parameter of an active sonar system, comprising: inputting an LFM signal generated from a target through a sensor; Performing partial Fourier transform on the input LFM signal using an optimal change order; Extracting a time-frequency parameter in the partial Fourier transformed spectral region; And estimating a parameter of the LFM signal using the extracted time-frequency parameter.

The present invention extracts a time-frequency parameter in a partial Fourier transform domain using a partial Fourier transform, which has a great advantage in analyzing a signal whose frequency changes with time, such as an LFM signal, and uses it to calculate a center frequency, a bandwidth , The pulse width, the start time, and the start frequency of the LFM signal.

1 is a block diagram of an apparatus for estimating an LFM signal parameter of an active sonar system according to an embodiment of the present invention.
2 is a graph of the relationship between the chirp rate and the partial Fourier transform order.
3 is a graph showing the relationship between the partial Fourier transform domain and the time-frequency domain in the negative frequency domain.
4 is a graph showing the relationship between the LFM signal and the partial Fourier transform domain in the positive frequency domain.
5 is a graph of the starting point estimation of an LFM signal.
6 is a graph for starting frequency estimation of an LFM signal;

Acoustic signals emitted into the water in an active sonar transmitter are echoed by some target to the receiver, where detection of the echoed target signal component from the received signal is the primary target of target detection. In order to detect such a target signal component it is necessary to detect the parameters of the received linear frequency modulation (LFM) signal.

The present invention analyzes a LFM signal used as a transmission pulse in an active sonar using a partial Fourier transform, and proposes a parameter estimation method of an LFM signal based on the analysis.

1 is a block diagram of an apparatus for estimating LFM signal parameters of an active sonar system according to an embodiment of the present invention.

1, an LFM signal parameter estimating apparatus of an active sonar system includes an LFM input unit (not shown) for receiving and inputting an LFM signal emitted from a target located underwater, 100, a partial Fourier transform unit 200 for performing partial Fourier transform on the input LFM signal using an optimal change order, a time-frequency analysis unit 300 for extracting time-frequency parameters in the partial Fourier transformed region, And an LFM parameter estimator 400 for estimating a parameter of the LFM signal using the extracted time-frequency parameter.

The parameter of the LFM signal includes a center frequency, a bandwidth, a pulse duration, a start time, and a start frequency of the LFM signal.

Hereinafter, a method of estimating a parameter of an LFM signal using a partial Fourier transform according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In general, the LFM call is expressed by the following equation (1).

[Equation 1]

Figure pat00001

At this time,

Figure pat00002
(T) is the instantaneous frequency of s (t)
Figure pat00003
[Hz] can be obtained. In other words,
Figure pat00004
Is the start frequency of the LFM signal, and 2a is the chirp rate (ringing rate). These LFM signals have characteristics in which the instantaneous frequency varies linearly with time, and are used as transmission pulses for detection of targets in radar and active sonar systems.

First, the partial Fourier transform unit 200 performs a partial Fourier transform on the input LFM signal using an optimal change order.

2 is a graph of the relationship between the chirp rate and the partial Fourier transform order.

In Fig. 2, the LFM signal with the chirp rate of 2a is

Figure pat00005
Point on axis
Figure pat00006
In order to have the maximum value in the direction perpendicular to the chirp rate
Figure pat00007
largesse
Figure pat00008
You have to find the value,
Figure pat00009
The optimal transform order
Figure pat00010
. The optimal conversion order of the LFM signal having the chirp rate of 2 &
Figure pat00011
) Has a sampling frequency of
Figure pat00012
, And the total length of the analysis frame is N discrete regions, as shown in Equation (2).

&Quot; (2) "

Figure pat00013

(2)

Figure pat00014
- Partial Fourier transform spectral characteristics of order
Figure pat00015
The peak spectrum, that is, the maximum value, by the LFM component of the positive frequency band
Figure pat00016
from
Figure pat00017
Lt; RTI ID = 0.0 > bandwidth. ≪ / RTI > here
Figure pat00018
It can be a significant advantage over the conventional Fourier transform method in detecting the target signal of the active sonar in the presence of noise.

Next, the time-frequency analysis unit 300 extracts time-frequency parameters in the partial Fourier transformed region.

3 is a graph showing the relationship between the partial Fourier transform domain and the time-frequency domain in the negative frequency domain.

As shown in FIG. 3, the LFM signal starting at t = 0

Figure pat00019
Assume that there is an LFM signal with a time delay as long as. In this case, since both LFM signals have the same chirp rate,
Figure pat00020
(Peak spectrum) at the maximum value,
Figure pat00021
The maximum value is obtained at different positions in the partial Fourier transform domain due to the time delay of the time domain,
Figure pat00022
The instantaneous frequency at
Figure pat00023
As shown in FIG.

The position where the peak spectrum appears by each LFM signal component in the partial Fourier transform domain is

Figure pat00024
, The distance between the positions where the peak spectrum appears is
Figure pat00025
. Therefore, the distance from the two peak spectra in the partial Fourier transform domain
Figure pat00026
) Is the time delay (
Figure pat00027
), Instantaneous frequency difference (
Figure pat00028
) And the following equations (3) and (4), respectively.

&Quot; (3) "

Figure pat00029

&Quot; (4) "

Figure pat00030

Hence, using Equations (3) and (4), the difference between the frequency axis and the time axis through the distance between each peak spectrum in the partial Fourier transform domain

Figure pat00031
,
Figure pat00032
), Which can be easily obtained by interpreting the time delay and the instantaneous frequency difference of the superimposed LFM signal components in the partial Fourier transform domain.

4 is a graph showing the relationship between the LFM signal and the partial Fourier transform domain in the positive frequency domain.

Referring to FIG. 4, the bandwidth and pulse width of the LFM signal are

Figure pat00033
when,
Figure pat00034
- a partial Fourier transform domain of order
Figure pat00035
On axis
Figure pat00036
from
Figure pat00037
Lt; RTI ID = 0.0 > bandwidth. ≪ / RTI >
Figure pat00038
and
Figure pat00039
To the equations (3) and (4) using the distance
Figure pat00040
and
Figure pat00041
, The relationship between the instantaneous frequency difference and the time delay of the two straight lines extending along the direction perpendicular to the r axis is obtained. In other words,
Figure pat00042
,
Figure pat00043
The length of the inter-
Figure pat00044
, And on the time axis
Figure pat00045
Respectively. It is easy to see that this is equivalent to twice the actual bandwidth and pulse width, respectively, by the theorem of isosceles triangles.

As a result, the LEM parameter estimation unit 400

Figure pat00046
- the starting point of the spectrum of bandwidth appearing in the partial Fourier transform spectrum of the order
Figure pat00047
And endpoint
Figure pat00048
The pulse width of the LFM signal
Figure pat00049
And bandwidth
Figure pat00050
, Which can be summarized in Equations 5 and 6.

&Quot; (5) "

Figure pat00051

&Quot; (6) "

Figure pat00052

5 is a graph for estimating the starting point of the LFM signal.

Figures 4 and 5 consider the rotation origin N / 2 in the analysis frame of length N. [ In the analysis frame, the starting point (time) of the LFM signal is

Figure pat00053
And the instantaneous (start) frequency at that time is
Figure pat00054
When you say,
Figure pat00055
- Partial Fourier transform spectra of order
Figure pat00056
In the peak spectrum,
Figure pat00057
From
Figure pat00058
A spectrum of bandwidth type appears.

first

Figure pat00059
To estimate
Figure pat00060
Wow
Figure pat00061
Centered
Figure pat00062
Looking for,
Figure pat00063
And the rotation origin (N / 2) are substituted into the equation (3)
Figure pat00064
And the rotation origin
Figure pat00065
, And finally, through Equation (7)
Figure pat00066
Can be estimated.

&Quot; (7) "

Figure pat00067

Likewise

Figure pat00068
Wow
Figure pat00069
(Time) of the LFM signal through the distance of
Figure pat00070
) Can be estimated.

6 is a graph of the start frequency estimation of the LFM signal.

6

Figure pat00071
This time, to estimate
Figure pat00072
Wow
Figure pat00073
Is substituted into the equation (4)
Figure pat00074
Twice the size of
Figure pat00075
And can be obtained by the following expression (8)
Figure pat00076
Can be estimated. The end frequency of the LFM signal (
Figure pat00077
) Also
Figure pat00078
Wow
Figure pat00079
Can be obtained by using the distance of

&Quot; (8) "

Figure pat00080

Therefore, the LFM parameter estimator 400 estimates the extracted bandwidth, the start frequency, The center frequency is detected using the frequency.

As described above, the present invention extracts time-frequency parameters in a partial Fourier transform domain using a partial Fourier transform, which has a great advantage in analyzing a signal whose frequency varies with time, such as an LFM signal, Such as the center frequency, bandwidth, pulse width, start time, and start frequency of the LFM signal.

It will be appreciated that the configurations and methods of the embodiments described above are not to be limited and that the embodiments may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, it should be understood that the above-described embodiments are to be considered in all respects as illustrative and not restrictive.

100: LEM input unit 200: Partial Fourier transform unit
300: time-frequency analysis unit 400: LFM parameter estimation unit

Claims (10)

An LFM input unit for inputting a linear frequency modulation (LFM) signal spread from a target through a sensor;
A partial Fourier transform unit for performing partial Fourier transform on the input LFM signal using an optimal change order;
A time-frequency analysis unit for extracting a time-frequency parameter in the partial Fourier transformed spectral region; And
And an LFM parameter estimator estimating a parameter of the LFM signal using the extracted time-frequency parameter. The method of claim 1, wherein the parameter of the LFM signal is
A center frequency of the LFM signal, a bandwidth, a pulse width, a start time, and a start frequency of the LFM signal. The apparatus of claim 1, wherein the time-frequency analyzer
In the partial Fourier transform spectrum,
Figure pat00081
Point on axis
Figure pat00082
The peak spectrum is extracted by the LFM component
Figure pat00083
from
Figure pat00084
And extracting a spectrum having a bandwidth up to a maximum value of the LFM signal parameter of the active sonar system. The apparatus of claim 1, wherein the time-frequency analyzer
Wherein a time delay and an instantaneous frequency difference are detected using the following equation when a plurality of LFM signals are present.
Figure pat00085
,
Figure pat00086

here,
Figure pat00087
Is the peak-to-peak distance of the two LFM signals in the partial Fourier transform domain, Time delay,
Figure pat00089
Represents the instantaneous frequency difference. 2. The apparatus of claim 1, wherein the LFM parameter estimator
The starting point of the bandwidth spectrum in the partial Fourier transform spectrum (
Figure pat00090
) And endpoints
Figure pat00091
), The pulse width of the LFM signal (
Figure pat00092
) And bandwidth (
Figure pat00093
Of the LFM signal parameters of the active sonar system.
Figure pat00094
,
Figure pat00095
 2. The apparatus of claim 1, wherein the LFM parameter estimator
In the partial Fourier transform spectrum
Figure pat00096
Point on axis (
Figure pat00097
) And the starting point of the bandwidth spectrum
Figure pat00098
(
Figure pat00099
),
Figure pat00100
And the rotation origin (N / 2)
Figure pat00101
) To determine the start time of the LEM signal (
Figure pat00102
), And in the same way
Figure pat00103
Wow
Figure pat00104
The end time of the LFM signal through the distance of
Figure pat00105
And estimating an LFM signal parameter of the active sonar system.
Figure pat00106
 2. The apparatus of claim 1, wherein the LFM parameter estimator
In the partial Fourier transform spectrum
Figure pat00107
Point on axis (
Figure pat00108
) And the starting point of the bandwidth spectrum
Figure pat00109
) And the distance
Figure pat00110
And the starting point of the spectrum
Figure pat00111
) Is divided by a sine value to estimate a starting frequency and an ending frequency, respectively, and estimating the LFM signal parameter of the active sonar system. 2. The apparatus of claim 1, wherein the LFM parameter estimator
Extracted bandwidth, start frequency and ?? And the center frequency is detected by using the frequency. Inputting a linear frequency modulation (LFM) signal spread from a target through a sensor;
Performing partial Fourier transform on the input LFM signal using an optimal change order;
Extracting a time-frequency parameter in the partial Fourier transformed spectral region; And
Estimating a parameter of the LFM signal using the extracted time-frequency parameter; and estimating a parameter of the LFM signal using the extracted time-frequency parameter. 10. The method of claim 9, wherein the parameter of the LFM signal is
A center frequency of the LFM signal, a bandwidth, a pulse width, a start time, and a start frequency of the LFM signal.
KR1020150127056A 2015-09-08 2015-09-08 Apparatus and method for estimating lfm signal parameter of active sonar system KR20170029899A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107526064A (en) * 2017-07-10 2017-12-29 上海电机学院 Adaptive LFM modulated parameter estimating methods based on two dimensional character
CN107800659A (en) * 2017-10-12 2018-03-13 西安电子科技大学 LFM signal modulation method for parameter estimation under Alpha Stable distritation noises
CN109031260A (en) * 2018-06-28 2018-12-18 东南大学 A kind of LFM signal time delay measurement method based on the analysis of fractional Fourier modulation rate
KR102011962B1 (en) * 2019-02-21 2019-08-19 엘아이지넥스원 주식회사 Apparatus and method for detection performance analysis
KR20190135826A (en) * 2018-05-29 2019-12-09 국방과학연구소 Method for estimating a chirp rate of a linear frequency modulation signal and apparatus therefor

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107526064A (en) * 2017-07-10 2017-12-29 上海电机学院 Adaptive LFM modulated parameter estimating methods based on two dimensional character
CN107800659A (en) * 2017-10-12 2018-03-13 西安电子科技大学 LFM signal modulation method for parameter estimation under Alpha Stable distritation noises
CN107800659B (en) * 2017-10-12 2020-09-08 西安电子科技大学 LFM signal modulation parameter estimation method under Alpha stable distribution noise
KR20190135826A (en) * 2018-05-29 2019-12-09 국방과학연구소 Method for estimating a chirp rate of a linear frequency modulation signal and apparatus therefor
CN109031260A (en) * 2018-06-28 2018-12-18 东南大学 A kind of LFM signal time delay measurement method based on the analysis of fractional Fourier modulation rate
CN109031260B (en) * 2018-06-28 2022-04-26 东南大学 LFM signal time delay measurement method based on fractional Fourier modulation rate analysis
KR102011962B1 (en) * 2019-02-21 2019-08-19 엘아이지넥스원 주식회사 Apparatus and method for detection performance analysis

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