JP2790909B2 - Passive sonar broadband signal reception method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a passive sonar that searches for a target, measures a position of the target, and categorizes the target using a sound wave radiated by a target moving in a three-dimensional space (underwater). Alternatively, the present invention relates to a method for receiving a wideband signal of a passive sonar among active sonars which irradiate a sound wave toward a target and search for the target using a reflected wave (echo). More specifically,
According to the present invention, a continuous wideband signal having a high degree of stationery, such as a running sound of a ship or the like, is received by a sensor, and detection of the wideband signal is performed using intensity information (hereinafter, referred to as “power”) of the sensor output. The present invention relates to a passive sonar broadband signal receiving method.

(Prior Art) Conventionally, techniques in such a field include: PROCEEDINGS OF T
HE IEEE), 69 [11] (1981-11) (US) WCKNIGHT ea
tl "Digital Signal Processing Fore
Sonar (Digital Signal Processing for Sonar) "P.1
There were those described in 451-1506. Hereinafter, the configuration will be described with reference to the drawings.

FIG. 2 is a functional block diagram showing an example of a configuration of a receiving apparatus using the conventional passive sonar broadband signal receiving method described in the above document.

This broadband signal receiving method is a square-law detection receiving method, for example, a sensor 1, an amplifier 2, a band limiting filter 3,
Sampler 4, square calculator 5, integrator 6, and output terminal 7
Is processed as follows.

The wideband signal Sin from the target is received by the sensor 1,
The sensor output is amplified by the amplifier 2 to an appropriate level. After unnecessary frequency components of the amplified received signal are removed by the band control filter 3, the signal is converted into a digital signal by the sampler 4 and sent to the square calculator 5.

The square calculator 5 calculates a square value of the digital reception signal output from the sampler 4 to obtain a wideband signal.
Strength at time t _k of Sin (hereinafter referred to as "instantaneous power") sent to the integrator 6 in search of P (k). The integrator 6 integrates the instantaneous power P (t) to form a broadband signal Si.
n long-term integrated power (hereinafter referred to as "power")
(K) is obtained and output from the output terminal 7 as power information. Then, using the time series data of the power output from the output terminal 7, detection of the wideband signal Sin and the like are performed.

Here, the integrator 6 can be composed of, for example, a finite impulse response filter (hereinafter, referred to as “FIR filter”) or an infinite impulse response filter (hereinafter, referred to as “IIR filter”). When a wideband signal Sin is received, using an FIR filter complicates signal processing and increases processing time. Therefore, the integrator 6 is usually configured using an IIR filter so as to simplify the signal processing and increase the processing speed.

(Problems to be solved by the invention) However, the conventional receiving method has the following problems.

In the conventional receiving method, a high-level pulse signal ps also called a search sound transmitted from an active sonar,
When an IIR filter is used for the integrator 6 when the broadband signal Sin exists in the target frequency band, there is a problem that the power of the broadband signal Sin is masked for a long time by the power of the pulse signal ps.

FIG. 3 is a more detailed illustration of such a problem. In the figure, P ₁ (t) indicates the instantaneous power of only the wideband signal Sin at time t, P ₂ (t) indicates the instantaneous power of only the pulse signal ps at time t, and (t) indicates the wideband signal Sin and the pulse. This shows the power of the signal added to the signal ps. In addition, in order to simplify description, it is all shown in a continuous system.

As shown in FIG. 3, the pulse signal ps pulse duration T _p which continues from time t1 to t2 is when present in the target frequency band of the wideband signal Sin, (t) is the integrator 6 using an IIR filter Affected, after time t2, approximately at time t3
During the time T _i leading to.

The time Ti affected by the power of the pulse signal ps is P
_It is determined by the relative level of ₁ (t) and P ₂ (t), the pulse width T _p , and the equivalent integration time τ of the integrator 6. When, for example, an exponential function is selected as a response function of the IIR filter constituting the integrator 6, In this case, the time Ti is on the order of about 60 to 80 seconds. When the power of the wideband signal Sin is masked for a long time as described above, the power of the wideband signal Sin cannot be continuously detected, the receiving accuracy is reduced, and it is difficult to solve the problem. there were.

The present invention has a problem that the prior art has a problem that when a relatively high-level pulse signal is included in a reception target frequency band of a wideband signal, the pulse signal remains for a long time after the end of the duration of the pulse signal. It is another object of the present invention to provide a passive sonar broadband signal receiving method which solves the problem that the power of the wideband signal is masked and the receiving accuracy is reduced.

(Means for Solving the Problems) In order to solve the above problems, the present invention is to receive a wideband signal from a target by a sensor and obtain a power which is an intensity of the wideband signal based on the sensor output. In the passive sonar broadband signal receiving method, the following measures are taken.

That is, the wideband signal of the sensor output is divided into narrowband components and subjected to frequency analysis, and the instantaneous power density, which is short-time integrated power, is obtained for each of the divided frequencies using the frequency analysis result. Pulse detection of a pulse-like signal component is performed for each of the divided frequencies using the time series data of the density. Then, an integration constant is set for the frequency at which the pulse is detected, and the instantaneous power density is integrated in the time domain using the integration constant to obtain a long-term integrated power for each frequency. The power is added in the frequency domain to calculate the power of the wideband signal.

(Operation) According to the present invention, since the wideband signal receiving method is configured as described above, the received wideband signal is divided into narrowband components, and the instantaneous power density is calculated for each of the divided frequencies. Is done. Further, a pulse-like signal component is detected for each frequency using the time series data of the instantaneous power density, and an integration constant for calculating the long-term integrated power is set for each frequency at which the pulse is detected. Then, using the set integration constant, integration for the instantaneous power density is performed for each of the divided frequencies, and then added in the frequency domain to output the power of the wideband signal. Thereby, the influence of the pulse signal is removed and the power of the wideband signal is continuously obtained. Therefore, the above problem can be solved.

(Embodiment) FIG. 1 shows an embodiment of the present invention and is a functional block diagram of a receiving apparatus using a passive sonar broadband signal receiving method, which is common to the elements in FIG. Elements are assigned common symbols.

The difference between this receiving apparatus and the conventional one shown in FIG. 2 is that a frequency analyzer 11, an instantaneous power density calculator 12, a pulse detector 13, and an integration unit are used instead of the square calculator 5 and the integrator 6 shown in FIG. That is, a constant setting device 14, an integrator 15, and a power calculator 16 are provided.

The frequency analyzer 11 performs M narrow band components by digital Fourier transform such as fast Fourier transform (hereinafter, referred to as FFT). (K; m) (where, m = 1,..., M), and this is supplied to the instantaneous power density calculator 12. The instantaneous power density calculator 12 outputs the frequency analyzer output. It has a function of calculating each instantaneous power density P (k; m) from (k; m) and giving the calculation result to the pulse detector 13 and the integrator 15.

The pulse detector 14 has a function of detecting a pulse component from the output of the instantaneous power density advancer and providing the detection result to the integration constant setting unit 14. The integration constant setting unit 14 uses the pulse detector output to calculate the integration constant α (k; m) for each frequency,
It has a function of generating β (k; m) and giving it to the integrator 15.

The integrator 15 uses the integration constants α (k; m) and β (k; m)
This is a circuit that integrates the output of the instantaneous power density calculator and gives the integration result to the power calculator 16. The power calculator 16 is
Long-term integration power by adding the integrator output in the frequency domain
_a (k) is obtained and output to the output terminal 7.

FIG. 4 is a functional block diagram showing one configuration example of the pulse detector 13 in FIG.

The pulse detector 13 has a plurality of input terminals 31 _{1 to} 31 _M for inputting the output of the instantaneous power density calculator 12, which includes an integrator 32 _{1 to} 32 _M and a threshold setting unit 33 _{1 to} 33 _M. , Comparators 34 _{1 to} 34 _M , and output terminals 35 _{1 to} 3 to the integration constant setting unit 14
5 _M each are connected.

Next, a method of receiving a wideband signal using the above-described receiving apparatus will be described.

In FIG. 1, a broadband signal Sin from a target is received by a sensor 1 and the sensor output is amplified by an amplifier 2 to an appropriate level. Unnecessary frequency components of the amplified received signal are removed by the band control filter 3, then converted into digital signals by the sampler 4,
Sent to

The frequency analyzer 11 converts the sample outputs η (k) of the wideband signal output from the sampler 4 into M narrowband components, respectively. (K; m) (where m = 1,..., M). Split narrowband component (K; m) is input to the instantaneous power density calculator 12 for each of M pieces, and the instantaneous power density is calculated for each of them. However, m = 1,..., M is calculated. The instantaneous power density P (k; m) is input to the integrator 15 and the pulse detector 13 for each M pieces.

In the pulse detector 13, time series data of the instantaneous power density..., P (k−2; m), P (k−1; m), P (k; m) (where m = 1,..., M) , Only the pulse components included in P (k; m) are detected for each frequency.

That is, in the pulse detector 13 of FIG. 4, the integrator 32 ₁
~ 32 _M is an integrator having an equivalent integration time sufficiently longer than the maximum time width of the pulse signal to be detected, based on the instantaneous power density calculator output from the input terminals 31 _{1 to} 31 _M ,
To determine the-threshold for detecting a pulse, to estimate the level of the signal components other than the pulse and sends the estimation result-threshold setter 33 _to 333 to the _M.

The threshold setters 33 _{1 to} 33 _M are connected to the respective integrators 32 _{1 to} 3
By adding a predetermined constant value to the level output from _{2M, the} threshold value TH at time k is obtained.
(K; 1), TH ( k; 2), ..., TH; outputs (k M) to a comparator 34 ₁ to 34C _M a. Here, the value to be added is set by the minimum level to be subjected to pulse component removal determined by the false alarm probability in pulse detection.

Comparators 34 _{1 to} 34 _M are threshold setting units 33 _{1 to} 33 _M
And the input terminals 31 _{1 to} 3
The instantaneous power density at time k input from 1 _M is compared for each frequency, and P (k; m) TH (k; m) where m = 1,. outputs to the output terminals 35 ₁ to 35 _M gives to the integral constant setter 14 of FIG. 1.

The integration constant setting unit 14 uses the pulse detection signal input from the pulse detector 13 to set an integration constant α (k;
m) and β (k; m) are generated and output to the integrator 15. For example, when the response function of the integrator 15 is given by the following equation, (k; m) = α (k; m) · P (k; m) + β (k; m) · (k−1; m) In the integration constant setting unit 14, the integration constants α (k; m) and β (k;
m) is set as follows.

Here, α ₀ ; an integration constant corresponding to an integration time for obtaining a long-term integration power. The integrator 15 calculates the integration constants α (k; m) and β (k; m) generated by the integration constant setting unit 14. Then, a response function is calculated and output to the power calculator 16.

For example, in the integration constant setting method, γ ₁ = 0, γ ₂ =
If a pulse is detected, the instantaneous power density P (k; m) at that frequency is removed, and the integrated output (k-1; m) at time k-1 is changed to the integrated output (k-1; m) at time k. k; m). The power calculator 16 calculates the M from the integrator 15
By adding the integral outputs (k; m) (m = 1, 2,..., M) in the frequency domain, a long-term integral power _a (k) is obtained and output to the output terminal 7.

As described above, in the present embodiment, the frequency analyzer 11 replaces the processing of the conventional square calculator 5 with the sample output η.
(K) is the narrow band component (K; m), and the instantaneous power calculator 12 calculates the instantaneous power density, which is the short-time integrated power for each of the divided frequencies. Is calculated. Then, the pulse detector 13 uses the time series data of the instantaneous power density,..., P (k−2; m), P (k−1; m), P (k; m) k; m) is detected, and the integration constant setting unit 14 controls the integration constant for calculating the long-term integration power for each frequency at which the pulse is detected. Then, the integrator 15 integrates for each of the divided frequencies using the set integration constant, and the power calculator 16 adds the value in the frequency domain.
_a (k) is output as the power of the wideband signal. Therefore, even in the case of having a long-time integration function using an IIR filter, the interference of the pulse signal is reduced over a long period of time, and except for the frequency band in which the strong power of the pulse signal exists, the pulse signal is Since it can be used continuously without being affected, loss of power information of a wideband signal can be reduced.

In the present embodiment, the amount of memory used is larger than in the case where the IIR filter is used for the conventional long-time integrated power calculation function. However, when the integration time is longer than the time corresponding to the size of the FFT of the frequency analyzer 11, it is possible to reduce the memory amount as compared with the case where the conventional long-time integrated power calculation function is configured by the FIR filter. Becomes effective.

Note that the present invention is not limited to the above embodiment, and various modifications are possible. For example, there are the following modifications.

(I) In the integration constant setting unit 14 of FIG. ₁ , the value of γ1 of α (k; m) when a pulse is detected is switched according to the amplitude value of the pulse. That is, When γ ₂ = 1−α ₀ is set, even if a pulse having a different amplitude value is incident, it is treated as a constant amplitude value, and masking is performed for a long time by setting the value of P ₀ near the threshold TH. Without being performed, and the pulse can be detected.

(Ii) Each block in FIG. 1 may be processed by a digital signal processor (DSP), a microprocessor or the like to receive a wideband signal.

(Effects of the Invention) As described above in detail, according to the present invention, a wideband signal output from a sensor is divided into narrowband components, and an instantaneous power density is obtained for each of the divided frequencies. Then, a pulse signal is detected for each frequency using the time series data of the instantaneous power density, and the integration constant in the long-time integrated power calculation function is controlled based on the pulse detection information. Therefore, even in the case of having the long-time integration function using the IIR filter, while receiving less interference of the pulse signal for a long time, except for the frequency band where the strong power of the pulse signal exists,
Since it can be used continuously without being affected by the pulse signal, loss of power information of the wideband signal can be reduced.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a receiving apparatus using a passive sonar broadband signal receiving method according to an embodiment of the present invention.
FIG. 1 is a functional block diagram of a receiving apparatus using a conventional passive sonar broadband signal receiving method. FIG. 3 is an explanatory view of a problem of the conventional receiving method. FIG. 4 is a function of a pulse detector in FIG. It is a block diagram. 1 ... Sensor, 4 ... Sampler, 11 ... Frequency analyzer,
12: Instantaneous power density calculator, 13: Pulse detector, 14
…… Integration constant setting device, 15 …… Integrator, 16 …… Power calculator.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01S 3/802-3/809

Claims (1)

(57) [Claims] 1. A wideband signal from a target is received by a sensor.
In the passive sonar broadband signal receiving method for obtaining the power that is the strength of the wideband signal based on the sensor output, the wideband signal of the sensor output is divided into narrowband components for frequency analysis, and the frequency analysis result is used by using the frequency analysis result. Determining an instantaneous power density that is a short-time integrated power for each of the divided frequencies; performing pulse detection of a pulse-like signal component for each of the divided frequencies using time-series data of the instantaneous power density; Setting the integration constant for the set frequency, integrating the instantaneous power density in the time domain using the integration constant to obtain a long-term integrated power for each frequency, and calculating the long-term integrated power in the frequency domain. A method for receiving a wideband signal by a passive sonar, comprising: calculating a power of a wideband signal by adding the signals.