JPS6348461B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a device for receiving an arbitrary acoustic signal from among a plurality of narrowband acoustic signals having center frequencies close to each other.

Signal transmission using underwater acoustic signals is widely used in fields such as sonar, acoustic positioning, and acoustic tracking, and the transmission distances covered by these fields tend to increase, and in recent years have reached several kilometers or more. Trying to. However, in the transmission of acoustic signals underwater, the higher the frequency, the more rapidly the absorption loss increases as the propagation distance increases, so the upper limit of the frequency that can be practically used for signal transmission over several kilometers is 10 KHz. Considering the transmission efficiency of the sound source, the practically usable frequency bandwidth is only a few KHz. On the other hand, as the amount of information transmission required for acoustic positioning and acoustic tracking tends to increase, multiple narrowband acoustic signals having center frequencies close to each other are being transmitted within the narrow usable band. , the receiving device must have the ability to receive only the desired signal from among multiple acoustic signals, and if there is a large level difference between each acoustic signal, countermeasures are required to prevent interference between the signals. It was said that

Figure 1 shows a conventional narrowband acoustic signal receiving device, which uses a pulse wave with a known center frequency and envelope as the narrowband acoustic signal, calculates the envelope signal from the output of a quadrature demodulator, and calculates the level of the envelope signal. The presence or absence of a signal is determined by comparing it with a threshold value. In FIG. 1, 1 is an input terminal for a received signal;
2 is an amplifier, 3 is a wide band pass filter (WBPF), 4 is a quadrature demodulator, 5 is a quadrature demodulator 4
6 is a first integrator (or low-pass filter) having an integration time sufficiently longer than the time length of the pulse wave; 7 is an integrator A threshold generator 8 generates a threshold value based on the level information of the envelope signal generated by the threshold generator 7; 9 is an output terminal, and 10 is an output terminal that outputs the received signal to another circuit (not shown) when extracting a pulse wave of another center frequency. . The orthogonal demodulator 4 also includes a local oscillator 401 that generates two sine wave signals having the same frequency as the center frequency of the pulse wave to be received and a phase difference of 90 degrees, and a local oscillator 401 that generates two sine wave signals with a wide band Two multipliers 402 that multiply the received signal sent out from the pass filter 3
-1 and 402-2, and two low-pass filters (LPF) 403-1 and 403-2 that pass the baseband signal of the pulse wave to be received.

In the above configuration, a received signal (including noise components) inputted to the input terminal 1 from a receiver (not shown) is amplified to an appropriate level by the amplifier 2, and unnecessary frequency components are removed by the broadband pass filter 3. After being removed, the quadrature demodulator 4 and the output terminal 10
The orthogonal demodulator 4 outputs a signal having the same center frequency as the pulse wave to be received from the input received signal to the baseband using multipliers 402-1 and 402-2, and passes the signal to the baseband through low-pass filters 403-1 and 403. −
2, the envelope in-phase and quadrature components of the signal are extracted and output. A first envelope calculator 5 calculates an envelope signal (including noise components) from the in-phase and quadrature components, and the calculated envelope signal is sent to an integrator 6 and a comparator 8. The level information of the envelope signal integrated by the integrator 6 is sent to the threshold generator 7, which generates an appropriate threshold based on the level information and supplies it to the comparator 8. The comparator 8 sends to the output terminal 9 only a signal having a level higher than the threshold value, that is, a pulse wave to be received. The output of the output terminal 9 is sent to a device (not shown) for acoustic positioning, acoustic tracking, etc., and is processed as appropriate.

The threshold generator 7 operates to increase the threshold when the level of the output of the integrator 6 increases and to decrease the threshold when the level decreases, but the output level of the integrator 6 is Of the envelope signals output from the envelope calculator 5,
Since it corresponds to the level of the noise component that changes slowly compared to the time length of the pulse wave signal, the threshold value cannot respond to a noise component of the same degree as the time length of the pulse wave signal, and is classified as type 2. Errors (that is, erroneously determining that other noise is a pulse wave) are more likely to occur. By the way, when another pulse wave with a similar center frequency (hereinafter referred to as an interference pulse wave) exists, the low-pass filter 40 of the orthogonal demodulator 4
The spread component of the power spectrum of the interference pulse wave passes through the passbands 3-1 and 403-2, and its time width is almost the same as the time width of the pulse wave to be received.

Figure 2 shows the situation at this time. In the figure, 20 is the power spectrum of the pulse wave to be received which has been dropped to the baseband by the multipliers 402-1 and 402-2, and 21 is the center frequency of the pulse wave to be received. and the power spectrum of the interference pulse wave with a center frequency different by △f ₁ , 22 is the low-pass filter 403
-1,403-2 frequency response characteristics. That is, the diffused components shown by diagonal lines of the power spectrum 21 of the interference pulse wave pass through the passbands of the low-pass filters 403-1 and 403-2, and as a result, the outputs of the low-pass filters 403-1 and 403-2 In this case, a pulsed interference wave whose length is approximately the same as the time length of the pulsed wave to be received is output. Therefore, when only a specific pulse wave is received from a large number of pulse waves having center frequencies that are similar to each other, the second
Mistakes in species are more likely to occur. Furthermore, the dynamic range of the acoustic signal may be about 80 dB, and when a large level difference exists between pulse waves, there is a drawback that the type 2 error rate further increases.

In order to eliminate the above-mentioned conventional drawbacks, the present invention eliminates interference by passing the received signal dropped to the baseband by the multiplier of the orthogonal demodulator through a low-frequency rejection filter that blocks the pulse waves to be received. The output obtained by receiving the main lobe of the power spectrum of the pulse wave, further calculating its envelope, and passing it through a second integrator (or low-pass filter) whose integration time is sufficiently short compared to the time length of the pulse wave to be received. and the first integrator (or low pass filter)
the output of the comparator, or the gain of a separately provided gain-controllable amplifier of the received signal,
It is designed to control one or both of them, and its purpose is to reduce the error rate in determining the presence or absence of a pulse wave. below,
The drawings will be explained in detail.

FIG. 3 shows a first embodiment of the present invention,
In the figure, the same components as in FIG. 1 are denoted by the same reference numerals. That is, 1 is the input terminal, 2 is the amplifier,
3 is a wide band pass filter, 4 is a quadrature demodulator, 5 is a first envelope calculator, 6 is a first integrator,
8 is a comparator, 9 is an output terminal, 10 is an output terminal to other circuits, 11-1 and 11-2 are low terminals connected to the outputs of multipliers 402-1 and 402-2 in orthogonal demodulator 4, respectively. Area rejection filter (LSF), 12
13 is a second envelope calculator that calculates an envelope signal from the outputs of the low-pass filters 11-1 and 11-2, and 13 is a second envelope calculator that has a sufficiently short integration time compared to the time length of the pulse wave to be received. 14 is a threshold generator that determines and generates a threshold value based on the output level of the first integrator 6 and the output level of the second integrator 13. .

The low-pass rejection filters 11-1 and 11-2 block the passage of the main lobe of the power spectrum of the pulse wave to be received and pass the main lobe of the power spectrum of the adjacent interference pulse wave, as shown at 23 in Fig. 4. It has a frequency response characteristic, particularly in the passband, and has a negative slope, so that the amount of passage decreases as the difference between the center frequency of the pulse wave to be received and the center frequency of the interference pulse wave increases.
That is, when a plurality of interference pulse waves exist, more of the power spectrum of the interference pulse wave with a center frequency close to the center frequency of the pulse wave to be received (which has a large influence on the determination of the presence or absence of a pulse wave) is passed through,
Interference pulse wave with far center frequency (small influence)
It is designed to reduce the amount of water passing through.

The second envelope calculator 12 has the same configuration as the first envelope calculator, and has a low-frequency rejection filter 1.
The envelope signal of the interference pulse wave that has passed through 1-1 and 11-2 is calculated and sent to the second integrator 13. FIG. 5 shows the first envelope calculator 5 (or the second envelope calculator 1).
2) shows an example of a specific configuration. In FIG. 5, 501 and 502 are input terminals, and 503 and 5 are input terminals.
04 is a square value calculator (SQ) that calculates the square value of the input signal; 505 is an adder; 506 is a square root calculator (√) that calculates the square root of the input signal; 507 is an output terminal; The in-phase and quadrature components of the envelope of the pulse wave to be received (or interference pulse wave) input from 502 are squared by square value calculators 503 and 504, respectively, added by adder 505, and then squared by square root calculator 506.
The square root is obtained and sent as an envelope signal from the output terminal 507 to the first integrator 6 and comparator
(or the second integrator 13).

FIG. 6 shows an example of a specific configuration of the threshold generator 14. In FIG. 6, 141 and 142 are input terminals, 143 and 144 are level setting amplifiers, 145 is an adder, and 146 is an adder. The level information of the first integrator 6 and the second integrator 13, which are output terminals and inputted to input terminals 141 and 142, respectively, is appropriately amplified by amplifiers 143 and 144, respectively, and added by an adder 145. It becomes a threshold value and is outputted to the comparator 8 from the output terminal 146.

Next, the operation will be explained. The process until the received signal inputted from the input terminal 1 reaches the orthogonal demodulator 4 is the same as the conventional one. Multiplier 402 in quadrature demodulator 4
-1,402-2, the received signal dropped to the baseband is passed through a low pass filter 403-1,403-
2 and low-pass rejection filters 11-1 and 11-2. Low pass filter 403-1, 403
-2, the in-phase and quadrature components of the envelope including the main lobe of the pulse wave to be received are input to the first envelope calculator 5, the envelope signal is calculated, and the first integrator 6 and comparator 8 sent to. On the other hand, the low frequency rejection filter 1
The in-phase and quadrature components of the envelope including the main lobe of the interference pulse wave that passed through 1-1 and 11-2 are input to the second envelope calculator, and the envelope signal is calculated and input to the second integrator 13. be done. The level information of the envelope signal integrated by the second integrator 13 in a shorter integration time than the pulse wave to be received is transferred to the first integrator 6.
It is sent to the threshold generator 14 together with the level information of , and the threshold value is determined. The threshold value is applied to a comparator 8, and the comparator 8 outputs a signal equal to or higher than the threshold value to an output terminal 9 as a pulse wave from the envelope outputted by the first envelope calculator 5.
Send to.

According to the above embodiment, the low frequency rejection filter 11-
1, 11-2 to extract signal components other than the desired pulse wave in the received signal, integrate the envelope signal over a short time length in a second integrator, and input it to the threshold generator 14. , because the threshold value is controlled, even if there is an interfering pulse wave with a center frequency close to the center frequency of the pulse wave to be received, the main lobe of the power spectrum of the interfering pulse wave is
1-1 and 11-2, the second integrator 13 increases its output level in response to the envelope signal, and the threshold generated by the threshold generator 14 can be increased; An appropriate threshold can be set in comparator 8. Therefore, a specific pulse wave can be received from among a large number of pulse waves having center frequencies close to each other with a substantially constant type 2 error rate, regardless of the number of pulse waves or the level difference.

Additionally, as a result, it is possible to significantly increase the amount of information transmitted over the acoustic link within a limited band, which is required to increase transmission distance, and realize high-performance, long-range acoustic positioning and acoustic tracking. becomes possible.

FIG. 7 shows a second embodiment of the present invention,
A gain-controllable received signal amplifier is provided, and the gain of the amplifier is controlled based on the output levels of the first integrator (or low-pass filter) and the second integrator (or low-pass filter). This is what I did. That is, in the figure, 15 is a gain controllable amplifier provided immediately before the orthogonal demodulator 4, and 16 is a first
17 is a comparator 8;
The gain control signal generator 16 is realized by the same configuration as the threshold generator 14 in the first embodiment, and the gain control signal generator 16 is an input terminal with a constant threshold value input to the amplifier 15. decreases when the gain control signal increases, and increases when the gain control signal decreases. Because of this configuration, if there is an interference pulse wave, the second
The output level of the integrator 13 increases, the gain of the amplifier 15 decreases correspondingly, and the overall level of the received signal decreases, so the presence or absence of the pulse wave to be received can be appropriately determined as in the first embodiment. be able to. Note that the other configurations and functions are the same as those of the first embodiment.

FIG. 8 shows a third embodiment, in which the second
The threshold generator 14 in the first embodiment is provided in the configuration of the embodiment, and the first integrator (or low-pass filter) 6 and the second integrator (or low-pass filter) 13 are The output is applied to the threshold generator 14 and the generated threshold is provided to the comparator 8. Therefore, both the gain of the amplifier 15 and the threshold of the comparator 8 are determined by the first and second integrators 6 and 1.
Control is performed based on the output level of No. 3, and is particularly effective when the level difference between pulse waves is large. For other configurations and operations, see Part 1.
and the same as in the second embodiment.

As explained above, according to the present invention, the received signal dropped to the baseband by the multiplier of the orthogonal demodulator is passed through a low-frequency rejection filter that blocks only the pulse waves that are desired to be received, thereby eliminating interference. An output obtained by receiving the main lobe of the power spectrum of the pulse wave, further calculating its envelope, and passing it through a second integrator or low-pass filter whose integration time is sufficiently short compared to the time length of the pulse wave to be received; Based on the output of the first integrator, the threshold value of the comparator, the gain of a separately provided amplifier for the received signal whose gain can be controlled, or both are controlled. It has the advantage of being able to receive a specific pulse wave without increasing the type 2 error rate even when there are many interfering pulses with center frequencies close to the center frequency. It is effective for use in acoustic positioning and acoustic tracking, which require a significant increase in the amount of information transmitted over acoustic links.

[Brief explanation of the drawing]

The drawings serve to explain the present invention. Fig. 1 is a block diagram showing an example of a conventional narrowband acoustic signal receiving device, and Fig. 2 shows a power spectrum 20 of a baseband signal of a pulse wave to be received and an interference pulse wave. FIG. 3 is an explanatory diagram showing the relationship on the frequency axis between the power spectrum 21 of the baseband signal and the frequency response characteristics 22 of the low-pass filters 402-1 and 402-2. FIG. 4 is a block diagram showing the first embodiment of the present invention, and FIG. 4 shows the power spectrum 20 of the baseband signal of the pulse wave to be received, the power spectrum 21 of the baseband signal of the interference pulse wave, and the low-pass filter 402-
Frequency response characteristic 22 of 1,402-2 and frequency response characteristic 2 of low-pass rejection filter 11-1, 11-2
5 is an explanatory diagram showing an example of a specific configuration of the envelope calculator 5 (or 12), and FIG. 6 is an explanatory diagram showing a specific configuration of the threshold generator 14. FIG. 7 is a block diagram showing a second embodiment of the invention, and FIG. 8 is a block diagram showing a third embodiment of the invention. 4... Quadrature demodulator, 401... Local oscillator, 4
02-1, 402-2... Multiplier, 403-1,
403-2...Low pass filter, 5...First envelope calculator, 6...First integrator or low pass filter, 8...Comparator, 11-1,1
1-2...Low pass rejection filter, 12...Second envelope calculator, 13...Second integrator or low pass filter, 14...Threshold generator, 1
5... gain controllable amplifier, 16... gain control signal generator.

Claims (1)

[Claims] 1. Orthogonal demodulation comprising a multiplier that multiplies a received signal by a signal with a frequency equal to the center frequency of the pulse wave to be received, and a low-pass filter that passes the baseband signal of the number of pulses. The vessel and
Narrowband acoustic signal reception comprising a first envelope calculator that calculates an envelope signal from the output of the orthogonal demodulator, and a comparator that compares the envelope signal with a threshold and outputs a signal that is equal to or higher than the threshold. In the apparatus, a first integrator or low-pass filter having an integration time sufficiently longer than the time length of the pulse wave connected to the first envelope calculator and the output of the multiplier of the quadrature demodulator. a second envelope calculator that calculates an envelope signal from the output of the low-pass rejection filter; and a pulse wave connected to the second envelope calculator. a second integrator or low-pass filter having an integration time sufficiently shorter than the time length of , and determining the threshold value based on the output signals of the first and second integrators or low-pass filters. What is claimed is: 1. A narrowband acoustic signal receiving device comprising: a threshold generator; 2. An orthogonal demodulator comprising a multiplier that multiplies the received signal by a signal with a frequency equal to the center frequency of the pulse wave to be received, and a low-pass filter that passes the baseband signal of the number of pulses;
Narrowband acoustic signal reception comprising a first envelope calculator that calculates an envelope signal from the output of the orthogonal demodulator, and a comparator that compares the envelope signal with a threshold and outputs a signal that is equal to or higher than the threshold. In the apparatus, a first integrator or low-pass filter having an integration time sufficiently longer than the time length of the pulse wave connected to the first envelope calculator and the output of the multiplier of the quadrature demodulator. a second envelope calculator that calculates an envelope signal from the output of the low-pass rejection filter; and a pulse wave connected to the second envelope calculator. a second integrator or low-pass filter having an integration time sufficiently shorter than the time length of , a gain-controllable amplifier for the received signal, and outputs of the first and second integrators or low-pass filters. A narrowband acoustic signal receiving device comprising: a gain control signal generator that generates a gain control signal for the amplifier based on the signal. 3. An orthogonal demodulator comprising a multiplier that multiplies the received signal by a signal with a frequency equal to the center frequency of the pulse wave to be received, and a low-pass filter that passes the baseband signal of the pulse wave;
Narrowband acoustic signal reception comprising a first envelope calculator that calculates an envelope signal from the output of the orthogonal demodulator, and a comparator that compares the envelope signal with a threshold and outputs a signal that is equal to or higher than the threshold. In the apparatus, a first integrator or low-pass filter having an integration time sufficiently longer than the time length of the pulse wave connected to the first envelope calculator and the output of the multiplier of the quadrature demodulator. a second envelope calculator that calculates an envelope signal from the output of the low-pass rejection filter; and a pulse wave connected to the second envelope calculator. a second integrator or low-pass filter having an integration time sufficiently shorter than the time length of , and determining the threshold value based on the output signals of the first and second integrators or low-pass filters. a gain control signal for generating a gain control signal for the amplifier based on output signals of the first and second integrators or low-pass filters; A narrowband acoustic signal receiving device comprising: a generator;