JP2021108432A - Underwater communication system - Google Patents

Abstract

To provide an underwater communication system that is also suitable for POC and can accurately calculate correlation.SOLUTION: An underwater acoustic communication system 10 according to the present invention includes: a reference signal generator 11 that generates a reference signal; a data transmission unit 12 that digitally modulates the reference signal generated by the reference signal generator 11 into an ultrasonic signal containing data and transmits the ultrasonic signal underwater; a data reception unit 13 that receives the ultrasonic signal transmitted by the data transmission unit 12; an equalizer unit 14 that corrects the reference signal; and a correlation calculator 15 that calculates correlation between the ultrasonic signal received by the data reception unit 13 and the reference signal corrected by the equalizer unit 14.SELECTED DRAWING: Figure 1

Description

In the present invention, the data receiving unit receives a physical signal including data transmitted underwater by the data transmitting unit based on the reference signal, and the underwater communication for calculating the correlation between the physical signal received by the data receiving unit and the reference signal is calculated. Regarding the system.

As an underwater communication system in which a data receiving unit receives a physical signal including data transmitted underwater by the data transmitting unit based on a reference signal and calculates the correlation between the received physical signal and the reference signal for the physical signal received by the data receiving unit, for example. The underwater communication system described in Patent Document 1 is known.

As shown in FIG. 5, in such a conventional underwater communication system 1, the data transmission unit 3 performs PSK (Phase Shift Keying: phase) in the modulation unit 4 with respect to the reference signal which is the electric signal generated by the reference signal generator 2. In addition to performing digital modulation such as (phase shift keying), the converter (transductor) 5 converts it into a physical signal such as an ultrasonic signal or an optical signal containing data, and transmits it into water. Then, when the physical signal is returned due to reflection or the like on the object to be measured, the data receiving unit 6 receives the physical signal, performs bandpass filtering and amplification, and outputs the physical signal to the correlation calculator 7. A reference signal (synchronous signal in Patent Document 1) digitally modulated by the data transmitting unit 3 is input to the correlation calculator 7 together with the physical signal received by the data receiving unit 6, and the correlation computer 7 shows the figure. As shown in 6 (a), after those signals are Fourier transformed, the amplitude and phase are combined and inverse Fourier transformed, so that the physical signal received by the data receiving unit 6 is correlated with the reference signal. It is calculated.

Japanese Unexamined Patent Publication No. 2006-217267

By the way, in the conventional underwater communication system, the correlation result is dispersed due to the distortion of the transmission system due to the delay wave or the Doppler effect, and the correlation cannot be calculated accurately in many cases. Therefore, in order to make it easier to detect the peak of the correlation without dispersing the correlation result, it is conceivable to use a POC (Phase Only Correlation) algorithm. As described above, the amplitude and phase are usually used for the calculation of the correlation, but in POC, as shown in FIG. 6 (b), the peak of the correlation is likely to occur by calculating the correlation using only the phase. Become.

However, in POC, the accuracy of the reference signal and physical signal used in the correlation calculation must be high, and even if the accuracy is not a problem in the conventional underwater communication system, the error increases during the calculation by POC. There is a problem that it is not practical. For example, in the conventional calculation, the waveform shown in FIG. 7A (horizontal axis is phase or time, vertical axis is amplitude or correlation value) becomes the waveform shown in FIG. 7B in the calculation by POC. Even if it should be, in reality, it often happens that the waveform is similar to that shown in FIG.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an underwater communication system that is suitable for POC and can calculate correlations with high accuracy.

In order to solve the above problems, the underwater communication system according to the present invention digitally modulates a reference signal generating unit that generates a reference signal and a reference signal generated by the reference signal generating unit into a physical signal including data. A data transmission unit that transmits data in water, a data reception unit that receives a physical signal transmitted by the data transmission unit, an equalizer unit that corrects a reference signal or a physical signal received by the data reception unit, and the data. Correlation calculation unit that calculates the correlation between the physical signal received by the receiving unit and the reference signal corrected by the equalizer unit, or the correlation between the physical signal received by the data receiving unit and corrected by the equalizer unit and the reference signal. It is characterized by having and.

The equalizer unit may correct the reference signal or the physical signal received by the data receiving unit based on the transmission characteristics of the data transmitting unit and the data receiving unit, and the correlation calculation unit correlates by POC. You may calculate.

Further, the reference signal generation unit may be able to select the generated reference signal from a plurality of reference signals based on the calculation result of the correlation calculation unit, and the data reception unit may be the data transmission unit. The operation may be stopped when the physical signal is transmitted by.

According to the underwater communication system according to the present invention, it is also suitable for POC and the correlation can be calculated with high accuracy.

It is explanatory drawing which shows the underwater acoustic communication system which concerns on embodiment for carrying out an invention. It is explanatory drawing which shows the underwater acoustic communication system which concerns on another embodiment for carrying out an invention. It is explanatory drawing which shows the underwater acoustic communication system which concerns on still another form for carrying out an invention. (A) is an explanatory diagram showing the case where the reflected wave is delayed with respect to the fundamental wave of 8 waves of 1 symbol, and (b) shows the case where the delay of (a) is 4 waves and the S / N is 0 dB. An explanatory diagram, (c) is an explanatory diagram showing a case where the symbol length is doubled when the delay is four waves. It is explanatory drawing which shows the conventional underwater acoustic communication system. (A) is an explanatory diagram showing a conventional correlation calculation method, and (b) is an explanatory diagram showing a correlation calculation method by POC. (A) is an explanatory diagram showing an example of appearance of a peak by a conventional correlation calculation method, (b) is an explanatory diagram showing an example of an ideal appearance of a peak by a calculation method of correlation by POC, and (c) is an explanatory diagram showing an example of appearance of an ideal peak by a correlation calculation method by POC. It is explanatory drawing which shows the appearance example of the actual peak by the calculation method of.

A mode for carrying out the present invention will be described with reference to the drawings.

As shown in FIG. 1, the underwater acoustic communication system 10 according to the present embodiment includes a reference signal generator 11, a data transmission unit 12, a data reception unit 13, an equalizer unit 14, and a correlation calculator 15. Be prepared.

The reference signal generator 11 generates a reference signal such as an M sequence which is a digital signal and outputs the reference signal to the data transmission unit 12.

The data transmission unit 12 has a modulation unit 16 and a converter (transductor) 17, and when a reference signal generated by the reference signal generator 11 is input, the reference signal is digitally modulated by the modulation unit 16 and converted. After being converted into an analog signal by the device 17, it is transmitted underwater as an ultrasonic signal containing data.

When the ultrasonic signal transmitted by the data transmitting unit 12 returns due to reflection or the like on the object to be measured, the data receiving unit 13 receives the ultrasonic signal, performs bandpass filtering and amplification, and outputs the ultrasonic signal to the correlation calculator 15. do.

A reference signal digitally modulated by the modulation unit 16 is input to the equalizer unit 14, and the equalizer unit 14 corrects the reference signal based on the transmission characteristics of the data transmission unit 12 and the data reception unit 13. Then, the corrected reference signal is output to the correlation calculator 15. That is, since the data transmitting unit 12 and the data receiving unit 13 limit the band for the purpose of improving the S / N and the interference characteristics, the ultrasonic signal output by the data receiving unit 13 to the correlation calculator 15 is distorted. However, the equalizer unit 14 reproduces the inverse transmission function of the data transmission unit 12 and the data reception unit 13, and corrects the reference signal that correlates with the ultrasonic signal to distort the reference signal in the same manner as the ultrasonic signal.

When the ultrasonic signal received by the data receiving unit 13 and the reference signal corrected by the equalizer unit 14 are input, the correlation calculator 15 Fourier transforms both signals and then synthesizes the phases to perform inverse Fourier transform (FIG. 6). (See (b)), the correlation between both signals is calculated by POC. Based on this calculation result, in the underwater acoustic communication system 10 or an external computing device, the timing and transmission time of data demodulation (transmission from transmission to reception of ultrasonic signal) of the ultrasonic signal received by the data reception unit 13 Time) is required.

In the underwater acoustic communication system 10, as shown in FIG. 2, the equalizer unit 14 is not provided between the data transmission unit 12 and the correlation calculator 15, but between the data reception unit 13 and the correlation calculator 15. It may be provided. In this case, the equalizer unit 14 reproduces the transmission functions of the data transmission unit 12 and the data reception unit 13 and cancels the transmission system distortion by the data transmission unit 12 and the data reception unit 13 for the ultrasonic signal received by the data reception unit 13. The corrected ultrasonic signal is output to the correlation calculator 15. When the reference signal digitally modulated by the modulation unit 16 is input to the correlation calculator 15 from the data transmission unit 12, and the ultrasonic signal corrected by the equalizer unit 14 is input to the correlation calculator 15 together with the reference signal. After Fourier transforming both signals, the phases are synthesized and inverse Fourier transform is performed, and the correlation between both signals is calculated by POC.

Further, as shown in FIG. 3, a plurality of underwater acoustic communication systems 10 may be combined, and in the figure, two underwater acoustic communication systems 10 are combined to distinguish each underwater acoustic communication system 10. A and B are added to the end of the code. For example, the underwater acoustic communication system 10A can be installed on the sea (on board), and the underwater acoustic communication system 10B can be installed on the seabed.

The ultrasonic signal transmitted from the data transmission unit 12A of the underwater acoustic communication system 10A is received by the data reception unit 13B of the underwater acoustic communication system 10B and then input to the correlation calculator 15B. A reference signal generated by the reference signal generator 11B, digitally modulated by the modulation section 16B of the data transmission section 12B, and further corrected by the equalizer section 14B is also input to the correlation calculator 15B. The correlation with the ultrasonic signal received by the data receiving unit 13B is calculated.

On the other hand, when the underwater acoustic communication system 10B receives the ultrasonic signal from the underwater acoustic communication system 10A, the data transmission unit 12B transmits the ultrasonic signal to the underwater acoustic communication system 10A. The ultrasonic signal transmitted from the data transmission unit 12B is received by the data reception unit 13A of the underwater acoustic communication system 10A and then input to the correlation calculator 15A. A reference signal generated by the reference signal generator 11A, digitally modulated by the modulation section 16A of the data transmission section 12A, and further corrected by the equalizer section 14A is also input to the correlation calculator 15A. The correlation with the ultrasonic signal received by the data receiving unit 13A is calculated.

In the present embodiment, the reference signal generator 11 can select a reference signal generated based on the calculation result of the correlation calculator 15 from a plurality of reference signals, and selects a reference signal suitable for distortion of the transmission system. It can also be generated.

For example, to explain a transmission system in which the delay wave is longer than the assumed delay, as shown in FIG. 4A, the modulation unit 16 modulates the reference signal by changing the phase for each symbol with the PSK (FIG. 4 shows 6). An example is shown in which a reference signal is composed of symbols (6 bits) and 8 sine waves are included in one symbol section.) When the reflected wave _{arrives with a delay of time t I with} respect to the fundamental wave, the fundamental wave Of these, _{the part corresponding to t I} is interfered with, and the S / N of the symbol becomes _{t S} / t _{I (the part corresponding to t I} + the part corresponding to t _S = 1 symbol).

Therefore, as shown in FIG. 6B, if _{the portion corresponding to t I} and the portion corresponding to t _S are both four waves, the S / N becomes 0 dB and cannot be used as a reference signal, but the reference signal. As shown in FIG. 3C, the generator 11 can select and generate a reference signal that doubles the symbol length, whereby the S / N becomes 10 dB and can be used as the reference signal. become.

The underwater acoustic communication system 10 according to the present embodiment digitally modulates the reference signal generator 11 that generates a reference signal and the reference signal generated by the reference signal generator 11 into an ultrasonic signal including data. A data transmission unit 12 that transmits underwater, a data reception unit 13 that receives an ultrasonic signal transmitted by the data transmission unit 12, an equalizer unit 14 that corrects a reference signal or an ultrasonic signal received by the data reception unit 13, and an equalizer unit 14. Calculates the correlation between the ultrasonic signal received by the data receiving unit 13 and the reference signal corrected by the equalizer unit 14, or the correlation between the ultrasonic signal received by the data receiving unit 13 and corrected by the equalizer unit 14 and the reference signal. Since the correlation calculator 15 is provided, the reference signal and the ultrasonic signal used for the correlation calculation are corrected by the equalizer unit 14, and the inside of the transmitter / receiver other than the underwater transmission system at the time of the correlation calculation (data transmission unit 12 and data reception unit 13). By removing the influence of transmission system distortion (internal), the correlation can be calculated with high accuracy.

Here, even if the equalizer unit 14 corrects the reference signal or the ultrasonic signal received by the data receiving unit 13 based on the transmission characteristics of the data transmitting unit 12 and the data receiving unit 13, the correlation can be calculated by POC. Since the waveform shown in 7 (b) is obtained, the correlation calculator 15 calculates the correlation by POC, and the peak of the correlation is accurately detected.

Further, since the reference signal generator 11 can select the generated reference signal from a plurality of reference signals based on the calculation result of the correlation calculator 15, it seems difficult to calculate the correlation with one reference signal. In some cases, the correlation can be calculated (see FIGS. 4 (b) and 4 (c)), and various analyzes using the correlation can be performed.

Although the embodiments for carrying out the present invention have been illustrated above, the embodiments of the present invention are not limited to those described above, and may be appropriately modified without departing from the spirit of the invention.

For example, the physical signal transmitted and received by the underwater communication system is not limited to an ultrasonic signal, but may be an optical signal or the like. (In FIG. 4C, the symbol length is doubled, but the number of symbols may remain 6 and one symbol may have 16 waves).

Further, the data receiving unit may be configured to stop the operation when the data transmitting unit transmits the physical signal so as not to receive the physical signal, whereby the data receiving unit receives the physical signal not transmitted by the data transmitting unit. It is possible to prevent a situation in which the unit receives the data erroneously and adversely affects the correlation calculation.

10 Underwater acoustic communication system (underwater communication system)
11 Reference signal generator (reference signal generator)
12 Data transmission unit 13 Data reception unit 14 Equalizer unit 15 Correlation calculator (correlation calculation unit)

A reference signal digitally modulated by the modulation unit 16 is input to the equalizer unit 14, and the equalizer unit 14 corrects the reference signal based on the transmission characteristics of the data transmission unit 12 and the data reception unit 13. Then, the corrected reference signal is output to the correlation calculator 15. That is, since the data transmitting unit 12 and the data receiving unit 13 limit the band for the purpose of improving the S / N and the interference characteristics, the ultrasonic signal output by the data receiving unit 13 to the correlation calculator 15 is distorted. However, the equalizer unit 14 reproduces the transmission functions of the data transmission unit 12 and the data reception unit 13 and makes corrections that distort the reference signal that correlates with the ultrasonic signal in the same manner as the ultrasonic signal.

In the underwater acoustic communication system 10, as shown in FIG. 2, the equalizer unit 14 is not provided between the data transmission unit 12 and the correlation calculator 15, but between the data reception unit 13 and the correlation calculator 15. It may be provided. In this case, the equalizer unit 14 reproduces the inverse transmission function of the data transmission unit 12 and the data reception unit 13, and transmits the ultrasonic signal received by the data reception unit 13 to the transmission system distortion by the data transmission unit 12 and the data reception unit 13. It is corrected so as to be canceled, and the corrected ultrasonic signal is output to the correlation calculator 15. When the reference signal digitally modulated by the modulation unit 16 is input to the correlation calculator 15 from the data transmission unit 12, and the ultrasonic signal corrected by the equalizer unit 14 is input to the correlation calculator 15 together with the reference signal. After Fourier transforming both signals, the phases are synthesized and inverse Fourier transform is performed, and the correlation between both signals is calculated by POC.

Claims (5)

A reference signal generator that generates a reference signal,
A data transmission unit that digitally modulates the reference signal generated by the reference signal generation unit, converts it into a physical signal containing data, and transmits it underwater.
A data receiving unit that receives a physical signal transmitted by the data transmitting unit, and
An equalizer unit that corrects the reference signal or the physical signal received by the data receiving unit, and
Correlation between the physical signal received by the data receiving unit and the reference signal corrected by the equalizer unit, or the correlation of calculating the correlation between the physical signal received by the data receiving unit and corrected by the equalizer unit and the reference signal. An underwater communication system including a calculation unit. The underwater communication system according to claim 1, wherein the equalizer unit corrects the reference signal or the physical signal received by the data receiving unit based on the transmission characteristics of the data transmitting unit and the data receiving unit. .. The underwater communication system according to claim 1 or 2, wherein the correlation calculation unit calculates the correlation by POC. Any one of claims 1 to 3, wherein the reference signal generation unit can select the generated reference signal from a plurality of reference signals based on the calculation result of the correlation calculation unit. The underwater communication system described in the section. The underwater communication system according to any one of claims 1 to 4, wherein the data receiving unit stops its operation when the data transmitting unit transmits a physical signal.

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