JPH0354796B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for transmitting acoustic information underwater.

(Background technology) Conventionally, a method in which a receiver is installed on the seabed and information from an underwater vehicle is expressed by the interval between two ultrasonic burst signals transmitted from the underwater vehicle uses signals of the same frequency. It was on. That is, first a burst signal of a certain frequency (this is called a first pulse) is transmitted, and after t seconds, a burst signal of the same frequency as the first pulse (this is called a second pulse) is transmitted. By changing the interval between the first pulse and the second pulse, various information can be transmitted.

However, when the first pulse is transmitted, the sound propagates from the underwater vehicle to the receiver installed on the seabed via various paths. That is, directly
In addition to those that propagate, there are propagation paths that reflect from the sea surface and the ocean floor and reach a receiver.

Therefore, when the receiver receives the first pulse, it first receives the directly propagated signal, and then receives the signal reflected from the sea surface or the seabed. Therefore, when attempting to detect the second pulse after receiving the first pulse, the reflected wave of the first pulse may be mistakenly received as the second pulse, and the pulse interval may also be incorrectly measured. .

FIG. 1 shows a conventional signal format, in which (a) is a signal waveform in the time domain, and (b) is a signal spectrum in the frequency domain.

11 is the waveform of the first pulse, 12 is the waveform of the second pulse, and 13 is the spectrum of the first pulse and the second pulse.

FIG. 2 is a block diagram of a conventional pulse interval detector. 21 is an amplifier, 22 is a filter, 23 is a pulse detection section, 24 is a counter control section, 25 is a counter, 26 is a start terminal of the counter, and 27 is a stop terminal of the counter.

The first pulse, the second pulse, and their reflected waves are amplified by an amplifier 21, and after passing through a filter 22, they are verified to be the first pulse or the second pulse by a pulse detector 23. Ru. The counter control section 24 regards the pulse that is first verified as a pulse as the first pulse, and the start terminal 26 of the counter 25 outputs a count start signal to start measuring the pulse interval. Next, the second pulse that is verified to be a pulse is regarded as the second pulse, and a count stop signal is output to the stop terminal 27 of the counter 25 to stop counting. In this way, the measurement of the pulse interval is completed. Therefore, if the reflected wave of the first pulse is received before the second pulse is received, the first pulse and the second pulse
There is a drawback that the interval between the first pulse and its reflected wave is received without measuring the interval between the pulses.

(Problem of the Invention) An object of the present invention is to improve the above-mentioned drawbacks of the prior art, and its characteristics include: an acoustic wave transmitting information according to the time interval of two temporally separated acoustic burst signals underwater; In the information transmission method, there is an acoustic information transmission method in which the frequencies of two burst signals are different from each other.

(Structure and operation of the invention) FIG. 3 shows the format of the signal in the present invention, (a)
is the signal waveform in the time domain, and (b) is the signal spectrum in the frequency domain. 31 is the waveform of the first pulse, 32 is the waveform of the second pulse, 33 is the spectrum of the first pulse, and 34 is the spectrum of the second pulse.

FIG. 4 is a block diagram of the pulse interval detector. 41 is an amplification unit, 42 is a filter that allows only the first pulse to pass through, 43 and 45 are pulse detection units, 4
4 is a filter that allows only the second pulse to pass; 46
47 is a counter, 48 is a start terminal of the counter, and 49 is a stop terminal of the counter.

First, the first pulse received by the receiver is 41
is amplified by the amplifying section, passes through a filter 42, and then is verified to be the first pulse by a pulse detecting section 43. Then, a count start signal is output from the counter control section 46 to the start terminal 48 of the counter 47, and measurement of the pulse interval is started. Once the counter 47 starts, the reflected wave of the first pulse is received, and even if the pulse detection unit 43 verifies that it is the first pulse, the counter control unit 46 does not send the counter start signal to the counter 47. Not issued.

Next, when the second pulse is received, it is amplified by an amplification section 41, passes through a filter 44, and then is verified as a second pulse by a pulse detection section 45.
Then, a count stop signal is output from the counter control section 46 to the stop terminal 49 of the counter 47, and the measurement of the pulse interval is completed. The contents of the counter 47 after the measurement is completed are the first pulse and the second pulse.
This is a numerical value that represents the interval between pulses.

(Effects of the Invention) As explained above, in this invention, the frequencies of the first pulse and the second pulse are set to different frequencies.
When transmitting information by acoustic means under the sea, especially in shallow seas, it has the advantage of preventing erroneous reception due to reflections from the sea surface and the seabed.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a conventional signal format, Fig. 2 is a block diagram of a conventional receiving section, Fig. 3 is a diagram showing a signal format of the present invention, and Fig. 4 is a block diagram of a receiving section of the present invention. be. Explanation of symbols; Fig. 4, 41; Amplifier, 42, 4
4; Filter, 43, 45; Pulse detection section, 4
6: Counter control unit, 47: Counter, 48: Start terminal, 49: Stop terminal.

Claims (1)

[Claims] 1. On the transmitting side, the two acoustic burst signals are set in accordance with the information to be transmitted, by setting a combination of the length and shortness of the time interval between the two acoustic burst signals, and transmitting the first and second acoustic burst signals, which are different from each other. A receiving side at a different point from the transmitting side receives an acoustic burst signal from underwater, and calculates the time interval between the detection of a burst of the first frequency and the detection of a burst of the second frequency. An acoustic information transmission method characterized in that information to be transmitted is identified according to a combination of length and shortness.