JP6906759B2 - Acoustic communication system, acoustic receiver, acoustic transmitter and acoustic transmission method - Google Patents

Description

The present invention relates to an acoustic communication system, an acoustic receiver, an acoustic transmitter and an acoustic transmission method.

Sound waves are often used for information communication in environments where it is difficult to propagate radio waves, such as underwater. For example, Patent Document 1 below states that "a digital information sequence is electrically modulated onto a carrier wave for underwater transmission (22), and the modulated carrier wave (23) is modulated with each other to provide an output signal (13) for acoustic transmission. The digital sequence is prefixed with at least two pulse signals (24) at known timings, which instruct the receiver to start transmitting and include Doppler information to resample the modulated signal prior to demodulation. When the information sequence is encoded into blocks of equal length, the relationships between successive blocks can be used for updating Doppler information and for later blocks. Channel information is also obtained from the pulse signal and / or the block and is the input signal. The next part of the can be raked. The pulsed signal preferably has good correlation characteristics and is a directly continuous and identical pair of linearly rising chapters. "(See abstract).
Further, Non-Patent Document 1 below describes the estimation of the Doppler effect on sound waves in water.

Special Table 2004-528773

Roee Diamant et.al, "Choosing the Right Signal: Doppler Shift Optimization for Underwater Acoustic Signals" 2012 ACM 978-1-4503-1773-3 / 12/11, [online], [Search December 6, 2016] , Internet <https://pdfs.semanticscholar.org/7eb3/55b9aa51e1a942fd72d397d080b6a763a979.pdf>

However, for example, when acoustic communication is performed between a ship on the water and a submersible underwater, the influence of reflection of sound waves on the water surface or the like becomes large. In such a case, the techniques described in Patent Document 1 and Non-Patent Document 1 cannot sufficiently compensate for the effects of the Doppler effect and multipath, and it is difficult to realize highly reliable acoustic communication.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an acoustic communication system, an acoustic receiver, an acoustic transmitter, and an acoustic transmission method capable of realizing highly reliable acoustic communication.

In order to solve the above problems, the acoustic communication system of the present invention receives an acoustic transmitter that outputs an output acoustic signal and an input acoustic signal that is the result of the output acoustic signal being propagated via a transmission path. The sound transmitter alternately outputs a reference signal having a predetermined bit string and a modulated signal modulated from the signal to be transmitted as the output sound signal. A first unit having a unit, the acoustic receiver performs a correlation calculation between the reference signal generation unit that generates the reference signal, the input acoustic signal, and the reference signal, and outputs the first calculation result. The correlation calculation unit, the calculation result storage unit that stores the first calculation result, the storage value stored in the past by the calculation result storage unit, and the first calculation result are subjected to the correlation calculation, and the second calculation result is performed. The input acoustic signal is obtained by obtaining the reception slot cycle based on the second correlation calculator that outputs the calculation result and the second calculation result, and dividing the reception slot cycle by the transmission slot cycle in the output acoustic signal. It is characterized by having a Doppler amount calculation unit for calculating the Doppler amount in the above.

According to the present invention, highly reliable acoustic communication can be realized.

It is a block diagram of the acoustic transmitter in the 1st Embodiment of this invention. It is a block diagram of the acoustic receiver in 1st Embodiment. It is a figure which shows the signal format of (a) output acoustic signal of an acoustic transmitter and (b) input acoustic signal of an acoustic receiver. It is a block diagram of the main part of the acoustic receiver in 1st Embodiment. It is a waveform diagram of the first correlation coefficient when (a) there is no signal deterioration and (b) signal deterioration occurs. It is a waveform diagram of the second correlation coefficient when (a) there is no signal deterioration and (b) signal deterioration occurs. It is a block diagram of the acoustic transmitter in the 2nd Embodiment. It is a figure which shows the signal format of the output acoustic signal of the acoustic transmitter in 2nd Embodiment. It is a block diagram of the main part of the acoustic receiver in 2nd Embodiment. It is a figure which shows (a) the signal format of the input acoustic signal of the acoustic receiver in 2nd Embodiment, (b) the waveform diagram of the 1st correlation coefficient, and (c) the waveform diagram of the 2nd correlation coefficient. ..

[First Embodiment]
Hereinafter, the acoustic communication system according to the first embodiment of the present invention will be described.
The acoustic communication system of the present embodiment can be applied to, for example, communication between a ship on water and a submersible, or communication between submersibles. The acoustic communication system of the present embodiment includes the acoustic transmitter TX1 shown in FIG. 1 and the acoustic receiver RX1 shown in FIG. Hereinafter, each configuration will be described.

<Configuration of sound transmitter TX1>
FIG. 1 is a block diagram of the acoustic transmitter TX1.
In FIG. 1, the acoustic transmitter TX1 has a modulation signal generation unit 101 and a reference signal generation unit 102. The modulation signal generation unit 101 outputs the modulation signal MS. Here, the modulated signal MS is a digital signal in which the baseband signal to be transmitted to the acoustic receiver RX1 is encoded and modulated. Further, the reference signal generation unit 102 repeatedly outputs the reference signal RS having a predetermined bit string.

The switch 103 alternately selects the modulation signal MS and the reference signal RS. The total period of the period in which the switch 103 selects the modulation signal MS once and the period in which the reference signal RS is selected once is referred to as a transmission slot period Tslot. Here, the signal length of the modulated signal MS may be determined, for example, in consideration of the signal length required for the characteristics of error correction and the fluctuation period of the propagation environment. Further, the signal length of the reference signal RS may be determined in consideration of, for example, the resistance to noise and the Doppler effect.

The D / A converter 104 converts the digital signal output from the switch 103 into an analog signal. Further, the antialiasing filter 105 outputs the analog signal after attenuating unnecessary signal components. Further, the power amplifier 106 amplifies the output signal of the antialiasing filter 105 to a desired signal level. The signal converter 107 converts the analog signal output from the power amplifier 106 into an output acoustic signal Sout and outputs it. The output acoustic signal Sout deteriorates while being affected by the Doppler effect, multipath, fading, etc. in the underwater propagation path, and reaches the acoustic receiver RX1 as the input acoustic signal Sin as shown in FIG.

<Configuration of sound receiver RX1>
FIG. 2 is a block diagram of the acoustic receiver RX1.
The acoustic receiver RX1 outputs from a signal converter 202 (receiver) that converts the received input acoustic signal Sin into an electric signal, a low noise amplifier 203 that amplifies the electric signal to a desired level, and a low noise amplifier 203. It has an A / D converter 204 that converts an electric signal, that is, an analog signal, into a digital signal Sind.

3A and 3B are diagrams showing signal formats of the output acoustic signal Sout and the input acoustic signal Sin, respectively.
As shown in FIG. 3A, the reference signal RS and the modulated signal MS appear alternately in the output acoustic signal Sout for each transmission slot period Tslot. Further, in the illustrated example, the transmission slot period Tslot is constant.

Further, in the input acoustic signal Sin shown in FIG. 3B, the output acoustic signal Sout is deteriorated due to the influence of the Doppler effect, multipath, fading, and the like. Therefore, the slot period of the input acoustic signal Sin is not always constant. Therefore, the slot period in the input acoustic signal Sin is called a "reception slot period" and is expressed in the form of "TslotRX (k)". Here, k is a slot number, which is an integer of 0 or more. Then, in the input acoustic signal Sin, the reception reference signal RSR, which is the result of the deterioration of the reference signal RS described above, and the reception modulation signal MSR, which is the result of the deterioration of the modulation signal MS, appear alternately.

Returning to FIG. 2, the synchronization detector 205 detects the reception reference signal RSR from the digital signal Sind output by the A / D converter 204. Then, the synchronous detector 205 turns off the switch 209 during the period when the reception reference signal RSR is detected, and turns on the switch 209 during the other period. As a result, the reception modulation signal MSR included in the digital signal Sind is output via the switch 209. The counter 206 (Doppler amount calculation unit) measures the time interval at which the synchronization detector 205 detects the reception reference signal RSR.

This time interval becomes equal to the reception slot period TslotRX (k) shown in FIG. 3 (b) unless a false detection or the like described later occurs. The arithmetic unit 207 (Doppler amount calculation unit) outputs the Doppler ratio DR (Doppler amount) of the input acoustic signal Sin by dividing the detected reception slot period TslotRX (k) by the slot period Tslot. The corrector 208 corrects the signal deterioration occurring in the reception modulation signal MSR based on the Doppler ratio DR.

FIG. 4 is a detailed block diagram of a main part of FIG. 2, and in particular, shows a detailed configuration of the synchroscope 205 and the corrector 208.
In FIG. 4, the synchronous detector 205 includes a correlator 301 (first correlation calculator), a reference signal generation unit 302 that outputs a reference signal RS, a detector 303, and a storage unit 304 (calculation result storage unit). , And a correlator 305 (second correlation calculator). The correlator 301 calculates the first correlation coefficient CC1 (first calculation result) between the digital signal Sind and the reference signal RS output by the reference signal generation unit 302. The detector 303 monitors the peak level of the first correlation coefficient CC1 and detects the start timing of the reception slot period TslotRX (k) based on whether or not the peak level is equal to or higher than a predetermined threshold value.

Further, in FIG. 4, the corrector 208 includes a frequency converter 306 (frequency correction unit), a carrier frequency designation unit 307, a multiplier 308, a multiplier 311 (variable downsample unit), and a downsample unit 309 (variable). It has a downsampling unit) and a downsampling ratio designating unit 310.

The carrier frequency designation unit 307 outputs the carrier frequency fc. This carrier frequency fc is equal to the carrier frequency of the output acoustic signal Sout (see FIG. 1) output by the acoustic transmitter TX1. The multiplier 308 multiplies the carrier frequency fc and the Doppler rate DR, and outputs the multiplication result DR · fc. The frequency converter 306 corrects the reception modulation signal MSR so that the carrier frequency of the reception modulation signal MSR becomes equal to the carrier frequency fc based on the multiplication result DR · fc, and outputs the correction result as the correction modulation signal MSC. In other words, the frequency converter 306 corrects the frequency shift that has occurred in the received modulation signal MSR due to the Doppler effect, and outputs it as the corrected modulation signal MSC.

Further, the downsampling ratio designation unit 310 specifies the downsampling ratio DSR when demodulating the correction modulation signal MSC. The multiplier 311 multiplies the downsampling ratio DSR by the Doppler ratio DR, and outputs the multiplication result DR / DSR. The downsampling unit 309 demodulates the modified modulation signal MSC by downsampling the modified modulation signal MSC with the multiplication result DR / DSR as the downsample ratio.

5 (a) and 5 (b) are examples of waveform diagrams of the first correlation coefficient CC1 output from the correlator 301. Assuming that the signal length of the reference signal RS is sufficiently long and the orthogonality between the codes can be ensured, the waveform of the first correlation coefficient CC1 is shown in FIG. 5A under ideal conditions without signal deterioration. Will be shown in. That is, the correlation waveform CW10 appears with a width of one symbol of the digital signal Sind. When the correlation processing is performed within the pass band of the digital signal Sind, the first correlation coefficient CC1 vibrates in the cycle of the carrier frequency as shown in the figure. Then, at the timing when the symbol timing and the timing of the carrier frequency match, that is, at time t1, the peak of the maximum value occurs in the first correlation coefficient CC1.

Here, it is assumed that one of the acoustic transmitter TX1 (see FIG. 1) and the acoustic receiver RX1 (see FIG. 2) is provided near the water surface. In such a case, a multipath is generated by a direct wave propagating from the sound transmitter TX1 to the sound receiver RX1 and a reflected wave reflected from the sound transmitter TX1 to the water surface and propagating to the sound receiver RX1.

Since the reflectance of sound waves on the water surface is relatively high, the level of the reflected wave is also relatively high, and the level of the correlation waveform with respect to the reflected wave is also high. An example thereof is shown in FIG. 5 (b). In the illustrated example, the correlation waveform CW11 is due to a direct wave and the correlation waveform CW12 is due to a reflected wave. Then, depending on the multipath situation, the peak level at time t13 due to the reflected wave may exceed the peak level at time t11 and t12 due to the direct wave.

Further, due to the influence of the group delay characteristics in the signal converter 107 (see FIG. 1), the signal converter 202 (see FIG. 2), and the underwater propagation path, in the example shown in FIG. Also, the symbol width is widened, and almost equal peak levels appear at time t11 and t12. Under these circumstances, if the start timing of the reception slot period TslotRX (k) is simply detected based on the determination result of the peak level in the first correlation coefficient CC1, there is a possibility that this start timing will be erroneously detected. There is. If the start timing is erroneously detected, the Doppler rate DR calculated by the arithmetic unit 207 becomes an erroneous value, and it becomes difficult to properly demodulate the received modulation signal MSR.

Therefore, in the present embodiment, as shown in FIG. 4, the above-mentioned problem is solved by providing the storage unit 304 and the correlator 305 in the synchronous detector 205. First, the storage unit 304 has a storage medium such as a register, and is the first of a predetermined time width before and after the time when the detector 303 detects the peak level of the first correlation coefficient CC1. The value of the correlation coefficient CC1 is stored. The stored value of the first correlation coefficient CC1 is shown in FIGS. 5 (a) and 5 (b), for example. The storage unit 304 delays the stored value of the first correlation coefficient CC1 and outputs the result as the delay correlation coefficient CCD1 (stored value). The correlator 305 calculates the correlation coefficient between the first correlation coefficient CC1 and the delay correlation coefficient CCD1, and outputs the result as the second correlation coefficient CC2 (second calculation result).

6 (a) and 6 (b) are examples of waveform diagrams of the second correlation coefficient CC2.
When the waveforms of the first correlation coefficient CC1 and the delay correlation coefficient CCD1 are both as shown in FIG. 5A, that is, under ideal conditions without signal deterioration, the second correlation coefficient CC2 The waveform of is shown in FIG. 6 (a). In the second correlation coefficient CC2 shown in FIG. 6A, a correlation waveform CW20 occurs before and after the time t21. The correlation waveform CW20 shows a slight spread on the time axis as compared with the correlation waveform CW10 in FIG. 5A, but both waveforms are similar. Further, the time t21 at which the maximum peak appears in the correlation waveform CW20 is also clear.

Further, when the waveforms of the first correlation coefficient CC1 and the delay correlation coefficient CCD1 are both waveforms as shown in FIG. 5B, that is, under the condition that multipath or group delay characteristics are deteriorated. The waveform of the second correlation coefficient CC2 is as shown in FIG. 6 (b). In the second correlation coefficient CC2 shown in FIG. 6B, correlation waveforms CW21, CW22, and CW23 are generated at three places. The correlation waveform CW21 appearing at the head of these corresponds to the correlation waveform between the correlation waveform CW11 due to the direct wave and the correlation waveform CW12 due to the reflected wave shown in FIG. 5 (b). When the reflecting surface is, for example, a water surface, the phase of the reflected wave is inverted at the reflecting surface, so that the correlation coefficient between the direct wave and the reflected wave becomes low.

Further, in the correlation waveform CW11 shown in FIG. 5B, substantially the same peak level appeared at times t11 and t12 due to the group delay characteristics, but in FIG. 6B, the peak of the correlation waveform CW22 is the time. It appears only once at t22. As described above, according to the present embodiment, since the synchronous detection is performed using the correlators 301 and 305, the synchronous detection can be executed at a stable timing as compared with the case where the synchronous detection is performed only by the correlator 301. can.

That is, in the counter 206 (see FIG. 4), the next peak appears from the timing when the peak appears in the second correlation coefficient CC2 (for example, time t21 in FIG. 6A or time t22 in FIG. 6B). Until, clock signals (not shown) having a predetermined cycle are counted, and the start timing of the reception slot cycle TslotRX (k) is detected based on the count result. As a result, the accurate reception slot period TslotRX (k) can be obtained, and the Doppler rate DR can be accurately estimated by the arithmetic unit 207.

Here, it is assumed that the downsampling unit 309 (see FIG. 4) performs downsampling by a simple thinning process. In such a case, since the downsampling ratio is an integer value, the fractions after the decimal point of the multiplication result DR / DSR output from the multiplier 311 are rounded to an integer, and the fractions after the decimal point by rounding down or rounding up are accumulated and added. You should go. In this process, the downsampling ratio shifts by ± 1 with time, but if the downsampling ratio DSR is relatively large, the effect is minor.

As described above, according to the present embodiment, it is based on the timing at which the peak appears in the second correlation coefficient CC2 by the synchronous detector 205 (for example, time t21 in FIG. 6A or time t22 in FIG. 6B). Since the start timing of the reception slot period TslotRX (k) is detected, even if the Doppler ratio DR changes every moment, the signal deterioration of the reception modulation signal MSR can be corrected while following the change. In particular, when the output acoustic signal Sout is reflected on the water surface and reaches the acoustic receiver RX1, the Doppler ratio DR changes every moment due to the waves on the water surface. In the present embodiment, even in such a case, the signal deterioration of the reception modulation signal MSR can be accurately corrected.

Further, when the modulated signal MS is encoded by an error correction code in the acoustic transmitter TX1 (see FIG. 1), it is preferable to generate the modulated signal MS in units of the code length of the error correction code. The reason will be explained. First, when the modulated signal MS is changed to the received modulated signal MSR and supplied to the corrector 208 (see FIG. 4), a delay time of one slot occurs when the corrector 208 corrects the signal deterioration. However, the delay time for one slot is the time required for the decoding process of the error correction code in the first place. Therefore, if the modulation signal MS is generated in units of the code length of the error correction code, even if a delay time occurs in the corrector 208, an additional communication delay does not occur in particular.

<Effect of the first embodiment>
As described above, according to the present embodiment, the acoustic transmitter (TX1) modulates the reference signal (RS) having a predetermined bit string and the signal to be transmitted as the output acoustic signal (Sout). It has a transmitter (107) that alternately outputs the modulated signal (MS), and the acoustic receiver (RX1) has a reference signal generator (302) that generates a reference signal (RS) and an input. The first correlation calculator (301) that performs the correlation calculation between the acoustic signal (Sin) and the reference signal (RS) and outputs the first calculation result (CC1), and the first calculation result (CC1). A correlation calculation is performed between the calculation result storage unit (304) to be stored, the storage value (CCD1) stored in the past by the calculation result storage unit (304), and the first calculation result (CC1), and the second calculation result is performed. A second correlation calculator (305) that outputs (CC2) and a Doppler amount calculation unit (206,) that calculates the Doppler amount (DR) in the input acoustic signal (Sin) based on the second calculation result (CC2). 207) and.
As a result, the timing corresponding to the reference signal (RS) is likely to appear in the second calculation result (CC2), and highly reliable acoustic communication can be realized.

Further, the acoustic receiver (RX1) corrects and corrects the frequency of the reception modulation signal (MSR) included in the input acoustic signal (Sin) corresponding to the modulation signal (MS) based on the Doppler amount (DR). A frequency correction unit (306) that outputs the result as a correction modulation signal (MSC), and a variable downsample unit (309,) that downsamples the correction modulation signal (MSC) while adjusting the thinning interval based on the Doppler amount (DR). 311) and further.
As a result, the influence of signal deterioration on the modified modulation signal (MSC) can be reduced, and more reliable acoustic communication can be realized.

[Second Embodiment]
Next, the second embodiment of the present invention will be described. In the following description, the parts corresponding to the respective parts of FIGS. 1 to 6 may be designated by the same reference numerals, and the description thereof may be omitted.
The acoustic communication system of the present embodiment includes the acoustic transmitter TX2 shown in FIG. 7 and the acoustic receiver RX2 shown in FIG. Hereinafter, each configuration will be described.

<Configuration of sound transmitter TX2>
FIG. 7 is a block diagram of the acoustic transmitter TX2.
In FIG. 7, the modulation signal generation unit 101 and the reference signal generation unit 102 (reference signal group generation unit) are the same as those of the first embodiment (see FIG. 1). The acoustic transmitter TX2 in the present embodiment is further provided with other reference signal generation units 601, 602 (reference signal group generation unit). The reference signal generation unit 601 outputs the front reference signal RS + at a timing before the reference signal RS, and the reference signal generation unit 602 outputs the rear reference signal RS− at a timing after the reference signal RS. The bit strings of the front reference signal RS + and the rear reference signal RS- are the same as those of the reference signal RS.

Further, the switch 103 in the present embodiment selects and outputs any one of the modulated signal MS, the reference signal RS, the pre-reference signal RS +, and the post-reference signal RS-. The acoustic transmitter TX2 of the present embodiment further includes a D / A converter 104, an antialiasing filter 105, a power amplifier 106, and a signal converter 107. These configurations are the same as those of the acoustic transmitter TX1 of the first embodiment (see FIG. 1), and the output acoustic signal Sout is output from the signal converter 107.

FIG. 8 is a diagram showing a signal format of the output acoustic signal Sout in the present embodiment. The above-mentioned pre-reference signal RS +, reference signal RS, and post-reference signal RS- are collectively referred to as "reference signal group RSG". As shown in the figure, the reference signal group RSG and the modulated signal MS appear alternately in the output acoustic signal Sout for each transmission slot period Tslot. Further, in the illustrated example, the transmission slot period Tslot is constant.

<Configuration of sound receiver RX2>
FIG. 9 is a block diagram of a main part of the acoustic receiver RX2.
The overall configuration of the sound receiver RX2 is the same as that of the sound receiver RX1 of the first embodiment (see FIGS. 2 and 4). However, in the present embodiment, the synchronous detector 215 and the counter 216 shown in FIG. 9 are applied instead of the synchronous detector 205 and the counter 206 of the first embodiment.

The synchronous detector 215 has the same components 301 to 305 as the synchronous detector 205 (see FIG. 4) of the first embodiment, and further has an amplitude value storage unit 322. The amplitude value storage unit 322 stores the amplitude level (or envelope level) of the first correlation coefficient CC1 for a predetermined period of time. Further, the counter 216 detects the start timing of the reception slot period TslotRX (k) based on the time interval in which the peak appears in the second correlation coefficient CC2 and the storage content of the amplitude value storage unit 322. The details will be described later.

FIG. 10A is a diagram showing a signal format of the input acoustic signal Sin propagating to the acoustic receiver RX2 in the present embodiment.
In the input acoustic signal Sin, the reception reference signal group RSGR and the reception modulation signal MSR appear alternately for each reception slot period TslotRX (k) (where k is the slot number). Here, in the reception reference signal group RSGR and the reception modulation signal MSR, the reference signal group RSG and the modulation signal MS shown in FIG. 8 are deteriorated via the transmission line, respectively.

Then, the reception reference signal group RSGR includes the pre-reception reference signal RSR +, the reception reference signal RSR, and the post-reception reference signal, which are the results of deterioration of the pre-reference signal RS +, the reference signal RS, and the post-reference signal RS- shown in FIG. Contains RSR-. Here, the boundary position between the front reception reference signal RSR + and the reception reference signal RSR is called BD + (first boundary position), and the boundary position between the reception reference signal RSR and the rear reception reference signal RSR- is BD- (second boundary position). Boundary position).

FIG. 10B is an example of a waveform diagram of the first correlation coefficient CC1 output by the correlator 301 in the present embodiment. Further, FIG. 10C is an example of a waveform diagram of the second correlation coefficient CC2 output by the correlator 305.
The first correlation coefficient CC1 shown in FIG. 10B is near the times t34, t36, and t38 corresponding to the start timings of the pre-reception reference signal RSR +, the reception reference signal RSR, and the post-reception reference signal RSR-. Correlated waveforms CW30, CW31, and CW32 are generated. Further, at the time t40 when the signal length of the reference signal RS has elapsed from the time t38, the first correlation coefficient CC1 is almost zero. The first correlation coefficient CC1 assumes that the reference signal generation unit 302 (see FIG. 9) outputs the reference signal RS during the period corresponding to the time t37 to t39.

That is, if the input acoustic signal Sin does not have a Doppler shift, the start timings of the reception reference signal RSR and the reference signal RS should match at time t37. However, since the immediately preceding receive slot period TslotRX (0) (see FIG. 10A) is shorter than the transmission slot period Tslot (see FIG. 8) due to the Doppler shift, the start timing t36 of the reception reference signal RSR is set as a reference. It is earlier than the start timing t37 of the signal RS.

Since the start timings t36 and t38 of the reception reference signal RSR and the post-reception reference signal RSR-are close to the start timing t37 of the reference signal RS, the peak levels of the correlation waveforms CW31 and CW32 are relatively high. On the other hand, since the start timing t34 of the pre-reception reference signal RSR + is considerably far from the time t37, the peak level of the correlation waveform CW30 is a relatively low value.

Further, in the illustrated example, the peak levels of the correlation waveforms CW31 and CW32 are substantially equal, and it is shown in FIG. 10B whether the start timing of the reception reference signal RSR is time t36 or t38. It is difficult to make a judgment based only on the correlation coefficient CC1 of 1. On the contrary, when the reception slot period TslotRX (0) becomes longer than the transmission slot period Tslot, the start timing of the reference signal RS becomes, for example, around time t35. In this case, the peak levels of the correlation waveforms CW30 and CW31 are relatively high, and the peak levels of the correlation waveforms CW32 are relatively low. In this case as well, it is difficult to determine whether the start timing of the reception reference signal RSR is at time t34 or t36 based only on the first correlation coefficient CC1.

Therefore, in the present embodiment, similarly to the first embodiment, the synchronous detector 215 (see FIG. 9) is provided with the storage unit 304 and the correlator 305, and the correlator 305 has the second correlation coefficient. Output CC2.
In FIG. 10C, the second correlation coefficient CC2 has correlation waveforms CW40, CW41, CW42, and CW43 near the times t50, t51, t52, and t53. The main dominant factor of the correlation waveform CW41 is the correlation of the correlation waveforms CW30 and CW31, and has a relatively low peak level. The main dominant factor of the correlation waveform CW42 is the correlation of the correlation waveforms CW31 and CW32, and has a relatively high peak level. In the correlation waveform CW42, the correlation level may be slightly lowered due to the time transition of the propagation path, but basically a high peak level appears.

The time t52 at which the peak level of the second correlation coefficient CC2 appears corresponds to the boundary position BD− in the examples of FIGS. 10A and 10C. On the other hand, when the reception slot period TslotRX (0) becomes longer than the transmission slot period Tslot, the peak level of the second correlation coefficient CC2 occurs at the time t51 corresponding to the boundary position BD +.

In other words, the pre-reference signal RS + (see FIG. 8) and the pre-reception reference signal RSR + are with reference signal RS when a positive Doppler shift occurs in which the receive slot period TslotRX (k) is longer than the transmission slot period Tslot. Since the correlation is high, it corresponds to a positive Doppler shift.

Further, the post-reference signal RS- (see FIG. 8) and the post-reception reference signal RSR- are reference signals when a negative Doppler shift occurs in which the reception slot period TslotRX (k) becomes shorter than the transmission slot period Tslot. Since the correlation with RS becomes high, it corresponds to a negative Doppler shift.

Similar to the counter 206 (see FIG. 4) of the first embodiment, the counter 216 has the next peak appearing from the timing when the peak appears in the second correlation coefficient CC2 (for example, the time t52 in FIG. 10C). Counts clock signals (not shown) with a predetermined cycle until. Further, the counter 216 determines whether the timing corresponds to the boundary position BD + or BD− based on the stored contents of the amplitude value storage unit 322 when the peak level occurs in the second correlation coefficient CC2. do. Then, the counter 216 appropriately adds or subtracts the signal length of the reference signal RS from the count result based on the determination result, and outputs the result as the reception slot period TslotRX (k).

For example, in FIGS. 10B and 10C, the time position of the first correlation coefficient CC1 corresponding to the peak position (time t52) of the second correlation coefficient CC2 is time t38. The counter 216 compares the amplitude level of the first correlation coefficient CC1 at the times t36 and t40 before and after the signal length of the reference signal RS with respect to this peak position (t38). In this case, the level at "the time position before the peak position (t38) by the signal length of the reference signal RS", that is, at time t36 is higher. As a result, the counter 216 determines that the peak position at time t52 corresponds to the boundary position BD−.

On the other hand, although not shown, when the peak position of the second correlation coefficient CC2 is the time t51, the time position of the corresponding first correlation coefficient CC1 is the time t36. The counter 216 compares the amplitude level of the first correlation coefficient CC1 at the times t34 and t38 before and after the signal length of the reference signal RS with respect to this peak position (t36). In this case, the “time position after the signal length of the reference signal RS from the peak position (t36)”, that is, the amplitude level at time t38 is higher than the amplitude level at time t34. As a result, the counter 216 determines that the peak position appearing in the second correlation coefficient CC2 corresponds to the boundary position BD +.

<Effect of the second embodiment>
As described above, the acoustic transmitter (TX2) of the present embodiment has a pre-reference signal (RS +) having a predetermined bit string and a pre-reference signal (RS +) having the same bit string as the pre-reference signal (RS +). A reference signal group (RSG) having a reference signal (RS) output later and a rear reference signal (RS-) having the same bit string as the front reference signal (RS +) and being output after the reference signal (RS). ), A reference signal group generation unit (601, 102, 602), and a modulation signal generation unit (101) that generates a modulation signal (MS) obtained by modulating the signal to be transmitted. , The reference signal group (RSG) and the modulated signal (MS) are alternately output as an output acoustic signal (Sout).

Further, in the acoustic receiver (RX2) of the present embodiment, the second calculation result (CC2) is the first boundary position (BD +) which is the boundary position between the front reference signal (RS +) and the reference signal (RS). Corresponds to the first timing corresponding to (time t51 in FIG. 10C) or the second boundary position (BD-) which is the boundary position between the reference signal (RS) and the post-reference signal (RS-). The peak level occurs at any of the second timings (time t52 in FIG. 10C), and the Doppler amount calculation unit (216, 207) determines that the timing at which the peak level occurs is the first timing ( Which of the time t51) and the second timing (time t52) is determined based on the first calculation result (CC1), and based on the judgment result and the second calculation result (CC2). It calculates the Doppler amount (DR).
As a result, the Doppler amount (DR) can be detected more accurately, and more reliable acoustic communication can be realized.

[Modification example]
The present invention is not limited to the above-described embodiment, and various modifications are possible. The above-described embodiments are exemplified for the purpose of explaining the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Further, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Further, it is possible to delete a part of the configuration of each embodiment, or add / replace another configuration. In addition, the control lines and information lines shown in the figure show what is considered necessary for explanation, and do not necessarily show all the control lines and information lines necessary for the product. In practice, it can be considered that almost all configurations are interconnected. Possible modifications to the above embodiment are, for example, as follows.

(1) Since the hardware of the acoustic transmitters TX1 and TX2 and the acoustic receivers RX1 and RX2 in each of the above embodiments can be realized by using a general computer, FIGS. 1, FIG. 2, FIG. 4, FIG. 7, and FIGS. A program or the like that realizes the algorithm shown in 9 may be stored in a storage medium or distributed via a transmission line. Further, a part or all of these algorithms may be replaced with hardware-like processing using an ASIC (Application Specific Integrated Circuit), an FPGA (field-programmable gate array), or the like.

(2) Further, the acoustic communication system of each of the above embodiments is not limited to one that performs underwater communication, and is not limited to communication between objects in the air, communication between objects in the ground, or is buried in a building. It may be applied to communication between objects.

(3) In the above embodiment, the amplitude level of the first correlation coefficient CC1 compared by the counter 216 is the timing corresponding to the peak position of the second correlation coefficient CC2 (for example, time t38 in FIG. 10B). The timing was before and after (for example, time t36, t40) by a predetermined length (signal length of the reference signal RS). However, this predetermined length may be a value other than the signal length of the reference signal RS. However, in order to obtain a significant detection result, it is preferable that this predetermined length is in the range of “signal length of reference signal RS” ± 20%.

101 Modulated signal generator 102 Reference signal generator (reference signal group generator)
107 Signal converter (transmitter)
202 signal converter (receiver)
206,216 counter (Doppler amount calculation unit)
207 Arithmetic unit (Doppler amount arithmetic unit)
301 Correlator (first correlation calculator)
302 Reference signal generation unit 304 Storage unit (Calculation result storage unit)
305 Correlator (second correlation calculator)
306 Frequency converter (frequency correction part)
309 Downsampling section (variable downsampling section)
311 Multiplier (variable downsample part)
601,602 Reference signal generation unit (reference signal group generation unit)
BD + boundary position (first boundary position)
BD-Boundary position (second boundary position)
CC1 first correlation coefficient (first calculation result)
CC2 Second correlation coefficient (second calculation result)
CCD1 Delay correlation coefficient (memory value)
DR Doppler rate (Doppler amount)
MS modulation signal RS reference signal RS + pre-reference signal RS-post-reference signal RSG reference signal group RX1, RX2 sound receiver Sin input sound signal Sout output sound signal TX1, TX2 sound transmitter

Claims (4)

It has an acoustic transmitter that outputs an output acoustic signal and an acoustic receiver that receives an input acoustic signal that is the result of the output acoustic signal being propagated via a transmission line.
The acoustic transmitter has a transmitter that alternately outputs a reference signal having a predetermined bit string and a modulated signal obtained by modulating the signal to be transmitted as the output acoustic signal.
The sound receiver is
A reference signal generator that generates the reference signal,
A first correlation calculator that performs a correlation calculation between the input acoustic signal and the reference signal and outputs the first calculation result.
An operation result storage unit that stores the first operation result, and
A second correlation calculator that performs a correlation calculation between the stored value stored in the past by the calculation result storage unit and the first calculation result and outputs the second calculation result.
A Doppler amount calculation unit that calculates the Doppler amount in the input acoustic signal by obtaining the reception slot period based on the second calculation result and dividing the reception slot period by the transmission slot period in the output acoustic signal. An acoustic communication system characterized by having. An output acoustic signal having a reference signal having a predetermined bit string and a modulated signal obtained by modulating the signal to be transmitted receives an input acoustic signal that is the result of being propagated via a transmission line. Receiver and
A reference signal generator that generates the reference signal,
A first correlation calculator that performs a correlation calculation between the input acoustic signal and the reference signal and outputs the first calculation result.
An operation result storage unit that stores the first operation result, and
A second correlation calculator that performs a correlation calculation between the stored value stored in the past by the calculation result storage unit and the first calculation result and outputs the second calculation result.
The calculated reception slot period on the basis of the second operation result, and a Doppler calculation unit for calculating a Doppler amount in the input audio signal by dividing the transmission slot period the receiving slot period in the output sound signal An acoustic receiver characterized by having. A frequency correction unit that corrects the frequency of the reception modulation signal included in the input acoustic signal corresponding to the modulation signal based on the Doppler amount and outputs the correction result as the correction modulation signal.
A variable downsampling unit that downsamples the modified modulation signal while adjusting the thinning interval based on the Doppler amount, and
2. The audio receiver according to claim 2. The input acoustic signal includes a pre-reference signal having the same bit string as the reference signal and occurring before the reference signal, and a post-reference signal having the same bit string as the reference signal and occurring after the reference signal. Have
The second calculation result is at the first timing corresponding to the first boundary position which is the boundary position between the front reference signal and the reference signal, or at the boundary position between the reference signal and the rear reference signal. A peak level occurs at any of the second timings corresponding to a second boundary position.
The Doppler amount calculation unit determines which of the first timing and the second timing is the timing at which the peak level occurs based on the first calculation result, and the determination result and the determination result The acoustic receiver according to claim 2, wherein the Doppler amount is calculated by obtaining the reception slot period based on the second calculation result.

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