JPH06347539A - Adaptive noise canceller - Google Patents

Abstract

PURPOSE:To provide an adaptive noise canceller of a small in lowering a noise reducing effect, even if a desired signal is included in a reference signal. CONSTITUTION:A subtracter 21 to which a main signal and false signal are inputted and an adaptive filter 22 for forming a false noise from a reference signal inputted by renewing a tap coefficient on the basis of an output signal of the subtracter are provided. Further, an echo detector 23 for detecting a desired signal from the output signal of the subtracter 21 and a switch 24 for preventing the output signal of the subtracter 21 from being inputted to the adaptive filter 22, while the desired signal is detected by the echo detector 23, are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive noise canceller, and more particularly to an adaptive noise canceller for active sonar.

[0002]

2. Description of the Related Art Some active sonars employ an ANC (adaptive noise canceller) method to reduce noise components (eg, running noise) in a sonar reception signal and improve the S / N ratio. There is something.

In this method, a main signal (Primary signal) obtained by forming a reception beam having a main axis directed in a predetermined direction
And a reference signal (reference signal) obtained by forming a reception beam in which the sensitivity in the predetermined direction becomes insensitive (null). More specifically, the main signal obtained by the reception beam having the main axis directed in the predetermined direction contains the desired signal and noise. Further, the reference signal obtained by the reception beam in which the sensitivity in the predetermined direction is insensitive does not include a desired signal, but includes only a signal highly correlated with noise included in the main signal. Therefore, if pseudo noise is generated from the reference signal and pseudo noise is subtracted from the main signal, a desired signal should be obtained.

[0004]

An active sonar is usually mounted on a ship for use. Therefore, when the ship is swayed by the waves, the receive beam of the active sonar also sways. Therefore, the desired signal may be included in the reference signal that originally does not include the desired signal. in this case,
The conventional ANC also reduces the desired signal, and there is no effect of noise reduction, or the signal itself disappears.

It is an object of the present invention to provide an adaptive noise canceller in which the noise reduction effect is less deteriorated even when a reference signal includes a desired signal.

[0006]

According to the present invention, a subtracter for subtracting a pseudo noise signal from a main signal including a desired signal and a noise signal, and a tap coefficient updated on the basis of the output of the subtractor are used. In an adaptive noise canceller having an adaptive filter that generates the pseudo signal from a reference signal having a high correlation with a noise signal, a detector that detects the desired signal from the output of the subtractor, and the adaptive filter according to the output of the detector. An adaptive noise canceller having a tap coefficient update interruption means for interrupting the update of the tap coefficient is obtained.

[0007]

The present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a sounding machine to which an embodiment of the present invention is applied. This sounding machine is a signal generator 11 that generates a transmission signal, a power amplifier 12 that amplifies the transmission signal, transmits the transmission signal as an acoustic signal, receives the reflected acoustic signal (echo), and outputs the reception signal. Two transmitter / receiver elements 13 and 14, preamplifiers 15 and 16 for amplifying received signals, and transmitter / receiver element 13 for transmitting signals from the power amplifier
Of the pre-amplifiers 15 and 16, and a phase shifter 18 for adding the outputs of the pre-amplifiers 15 and 16 to the reception signals from the transducer elements 13 and 14 to the pre-amplifiers 15 and 16, respectively. It has a phase adjuster 19 for obtaining a difference between outputs, and an adaptive noise canceller (ANC) 20. The ANC 20 is a subtractor 2
1, an adaptive (transversal) filter 22,
It has an echo detector 23 and a switch 24.

Next, the operation of this sounding machine will be described. In the following description, it is assumed that the sounding machine is installed on a ship to measure the depth of the seabed.

The transmission signal generated by the signal generator 11 is amplified by the power amplifier 12 and transmitted to the transmitter / receiver elements 13 and 14 via the transmission / reception switching device 17. Transducer element 1
3 and 14 are fixed to the hull in the same direction (gravitational direction) with a fixed distance from each other. Then, these transducer elements 13 and 14 convert the transmission signal into an acoustic signal and send it out directly under the ship (in the direction of gravity).

The acoustic signals transmitted from the transducer elements 13 and 14 are reflected on the seabed, and are received by the transducer elements 13 and 14 as echoes. The transducer elements 13 and 14 convert the received echo into an electric signal (reception signal) and output it to the preamplifiers 15 and 16 via the transmission / reception switcher 17.

Here, the transmitter / receiver elements 13 and 14 output not only echoes but also noises as reception signals. However, since the transmitter / receiver elements 13 and 14 are attached with a certain distance therebetween, the noise contained in the received signals of both does not have the same waveform. Therefore, if the sum and difference of these two received signals are obtained, a main signal with an enhanced echo component and a reference signal with the echo component removed should be obtained. That is, if the sum of the two received signals is obtained, it is possible to form the reception beam 25 having the main axis extending in the predetermined direction, and to form the reception beam 26 in which the sensitivity in the predetermined direction is insensitive (null). .

The preamplifier 15 amplifies the received signal from the transducer element 13, and the preamplifier 16 amplifies the received signal from the transducer element 14. Then, the preamplifiers 15 and 16 output the amplified received signals to both the phase shifters 18 and 19, respectively.

The phase adjuster 18 adds the two received signals that have been input. Further, the phase adjuster 19 obtains the difference between the two input signals. As a result, the reception beam 25 having the main axis extending in the predetermined direction and the reception beam 26 having the insensitivity in the predetermined direction are formed.
That is, the phase shifter 18 outputs a main signal including a desired signal and a noise signal based on the two received signals, and the phase shifter 19
Outputs a reference signal that does not include a desired signal but includes a signal highly correlated with a noise signal. These main signal and reference signal are
It is input to the adaptive noise canceller (ANC) 20.

The main signal input to the ANC 20 is input to the subtractor 21. In addition, the reference signal input to the ANC 20 is input to the adaptive filter 22. The adaptive filter 22 updates the tap coefficient on the basis of the output of the subtractor 21, generates a pseudo noise signal from the input reference signal, and outputs the pseudo noise signal to the subtractor 21. The subtractor 20 subtracts the pseudo noise signal from the main signal, and outputs the noise-reduced main signal. Ideally, only the desired signal (echo) is included in the main signal with reduced noise.

The echo detector 23 detects an echo from the signal output from the subtractor 21. Then, while the echo is being detected, a control signal for turning off the switch 24 is output. The switch 24 is turned off when an echo is detected according to the control signal from the echo detector,
Turns on when no echo is detected.

As a result, the adaptive filter 22
When there is no echo, adaptive processing is performed as usual, but when there is echo, updating of tap coefficients is stopped and processing is performed. Therefore, even if the echo signal is included on the reference signal side, the level of the pseudo noise signal is not increased, and the signal level of the echo on the main signal side is not reduced more than necessary.

[0017]

According to the present invention, in the adaptive noise canceller for reducing the noise contained in the main signal by using the reference signal, the updating of the tap coefficient of the adaptive filter is suspended while the echo is detected. As a result, the noise reduction performance does not deteriorate even when the reference signal includes an echo.

[Brief description of drawings]

FIG. 1 is a block diagram of an active sonar to which an embodiment of the present invention is applied.

[Explanation of symbols]

11 signal generator 12 power amplifier 13,14 transducer element 15,16 preamplifier 17 duplexer 18 phaser 19 phaser 20 adaptive noise canceller (ANC) 21 subtractor 22 adaptive (transversal) filter 23 echo detector 24 switch 25 reception beam having a main axis directed in a predetermined direction 26 reception beam in which sensitivity in a predetermined direction becomes insensitive (null)

Claims (2)

[Claims] 1. A subtracter for subtracting a pseudo noise signal from a main signal including a desired signal and a noise signal, and a tap coefficient is updated based on an output of the subtractor, and a reference signal having a high correlation with the noise signal In an adaptive noise canceller having an adaptive filter that generates a pseudo signal,
An adaptive noise canceller, comprising: a detector that detects the desired signal from the output of the subtractor; and a tap coefficient update interrupting unit that interrupts the update of the tap coefficient of the adaptive filter according to the output of the detector. 2. The adaptive noise canceller, wherein the tap coefficient update interrupting means is a switch provided on a connection line connecting the output side of the subtractor and the adaptive filter.