Sonar systems, methods, programs

Abstract

To make it possible to avoid a decline in object searching ability in a sonar system that performs both object searching and communication.SOLUTION: A sonar system comprises a transmitting unit that includes: modulation means for generating a transmission waveform by switching at least one of the center frequency and sweep direction of LFM (Linear Frequency Modulation) or LPM (Linear Period Modulation) sweep in association with a bit code of a digital signal to be transmitted; and means for transmitting the transmission waveform as a sound wave.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sonar system, method, and program.

Background Art

[0002] A sonar (sound navigation and ranging: also called sonar) system that locates an object in water by utilizing the propagation of sound is roughly classified into two types: passive sonar and active sonar. A passive sonar identifies the position of an object by receiving the sound generated by the object in water. An active sonar transmits sound from the sonar and identifies the position of the object from the reflected wave. For sound transmission and reception, a transmitting and receiving array that combines a plurality of transmitting and receiving elements that convert electrical signals and acoustic signals is used. Generally, an active sonar performs sound transmission and reception of the reflected wave using the same transmitting and receiving array. Such a sonar is called a monostatic active sonar.

[0003] On the other hand, a multistatic active sonar that performs transmission and reception using separate arrays is also used. In a multistatic active sonar, when identifying the position of an object from the received reflected sound, time synchronization is required between the transmitting side and the receiving side. Generally, wireless communication is used for time synchronization, but there are cases where wireless communication cannot be used, such as when synchronizing time with an underwater vehicle.

[0004] Even in such a situation, a method that utilizes underwater communication is known as a technique for searching for an object using a multistatic active sonar (hereinafter referred to as "multistatic search"). However, in order to perform object search and underwater communication simultaneously, it is necessary to devise the transmission method, waveform selection, and the like.

[0005] Patent Document 1 discloses an underwater communication system in which a data transmission unit digitally modulates a reference signal to convert it into a physical signal containing data, transmits the physical signal containing data into the water, and a data receiving unit receives the physical signal containing the data, and the data receiving unit calculates the correlation between the received physical signal and the reference signal.

[0006] Generally, object search using active sonar involves cross-correlation between transmitted and received waveforms, and identifying the object's location from the reception time when the output level is highest. Transmitted waveforms typically include LFM (linear frequency modulation) and LPM (linear period modulation) waveforms, which have a high gain due to cross-correlation processing ("correlation processing gain"). Underwater communication using sound transmits information by modulating a digital signal as a sound wave and demodulating the received sound wave back into a digital signal. The sound waveforms used are typically PSK (phase shift keying) or FSK (frequency shift keying) waveforms, which are waveforms obtained by modulating digital signals ("digitally modulated waveforms").

[0007] One simple method for combining object search and underwater communication is for the transmitting side to send waveforms for object search and underwater communication at different times.

[0008] However, in object detection using active sonar, increasing the transmission time increases the reverberation level, making it more difficult to locate objects.

[0009] Furthermore, in multistatic search, the blind zone (the region where the direct wave from the transmitter and the reflected wave from the object are received at the same time, and the reflected wave is buried) becomes larger.

[0010] Another example of a method that combines object search and underwater communication is to use digitally modulated waveforms for object search. This means using digitally modulated waveforms to locate objects using cross-correlation processing. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2021-108432 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] When using digitally modulated waveforms for object detection, common digital modulated waveforms such as PSK and FSK have low correlation processing gain. Therefore, their object detection capabilities are reduced.

[0013] The present invention was conceived in view of the above problems, and aims to provide a sonar system, sonar method, and program that can avoid a decrease in object search capability in a sonar system that can perform object search and communication simultaneously. [Means for solving the problem]

[0014] According to one embodiment of the present invention, a sonar system is provided that includes a transmitting unit comprising: a modulation means for generating a transmission waveform by switching at least one of the center frequency and sweep direction of an LFM (linear frequency modulation) or LPM (linear period modulation) sweep in accordance with the bit code of a digital signal to be transmitted; and a means for transmitting the transmission waveform as a sound wave.

[0015] According to one embodiment of the present invention, a sonar method is provided in which the transmitting side of a sonar system generates a transmission waveform by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) or LPM (linear period modulation) sweep in accordance with the digital signal to be transmitted, and transmits the transmission waveform as a sound wave.

[0016] According to one embodiment of the present invention, a computer constituting a sonar system capable of performing object search and communication simultaneously performs a process to generate a transmission waveform by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) or LPM (linear period modulation) sweep in accordance with the digital signal to be transmitted, A program is provided that performs the following steps: detecting at least one of the center frequency and the sweep direction from the received waveform of the received sound wave; demodulating the digital signal based on at least one of the center frequency and the sweep direction; and measuring the distance of the reflection point of the transmitted waveform, which is the starting point of the received waveform, from the result of the cross-correlation between the received waveform and the reference waveform. Furthermore, according to the present invention, a computer-readable recording medium ((for example, a semiconductor storage such as RAM (Random Access Memory), ROM (Read Only Memory), or EEPROM (Electrically Erasable and Programmable ROM)), an HDD (Hard Disk Drive), a CD (Compact Disc), or a DVD (Digital Versatile Disc)) storing the above program is provided. [Effects of the Invention]

[0017] According to the present invention, in a sonar system capable of simultaneously performing object search and communication, it is possible to avoid a decrease in the object search capability. [Brief explanation of the drawing]

[0018] [Figure 1] This figure schematically illustrates the system configuration of an embodiment of the present invention. [Figure 2] This figure schematically illustrates a demodulation processing device in an embodiment of the present invention. [Figure 3] This figure schematically illustrates a signal processing device according to an embodiment of the present invention. [Figure 4]It is a diagram schematically showing an example of a transmission waveform in an embodiment of the present invention. [Figure 5] It is a diagram for explaining an embodiment of the present invention. [Figure 6] It is a diagram schematically showing an example of a transmission waveform in a modification of an embodiment of the present invention. [Figure 7] It is a diagram schematically showing the configuration of an embodiment of the present invention.

Mode for Carrying Out the Invention

[0019] Embodiments of the present invention will be described below. According to the embodiment, it is possible to simultaneously perform object search and underwater communication using a digital modulation waveform based on an LFM or LPM waveform excellent in correlation processing gain. As an example, a 2-bit (bit) code of a digital signal is represented by four combinations related to the center frequencies of two different sweep frequency bands, an up sweep in which the frequency increases with time, and a down sweep in which the frequency decreases with time. Digital information (2-bit code) is represented by a combination of the center frequency of the sweep and the switching of the sweep direction, and the bit sequence of the digital signal is composed of a waveform obtained by connecting LFM or LPM waveforms with different center frequencies and sweep directions.

[0020] FIG. 1 is a diagram for explaining the system configuration of an embodiment. FIG. 1 schematically shows a multi-static active sonar system that performs time synchronization using underwater communication. In FIG. 1, one transmitter 103 and one receiver 104 are shown as separately provided transmitting arrays and receiving arrays.

[0021] The modulation processing device 101 is a device that modulates and outputs information necessary for time synchronization into a digital waveform that can be transmitted.

[0022] The transmitter 102 converts the input digital signal waveform into an analog signal waveform using an AD converter (analog digital convertor) not shown, and power-amplifies it using a power amplifier not shown and outputs it.

[0023] The transmitter 103 of the transmission array converts the input electrical signal into an acoustic signal and transmits it underwater.

[0024] The receiver 104 of the receiving array receives acoustic signals from underwater and converts them into electrical signals.

[0025] The receiver 105 converts the input analog signal waveform into a digital signal waveform using a DA converter (digital-to-analog converter) (not shown) and outputs it.

[0026] The demodulation processing unit 106 demodulates the input digital signal waveform to obtain the information necessary for time synchronization.

[0027] The signal processing unit 107 performs signal processing on the received signal waveform sent from the receiver 105 and the time synchronization information sent from the demodulation processing unit 106.

[0028] The display device 108 displays the output of the demodulation processing device 106 and the output of the signal processing device 107 on the screen.

[0029] Figure 4 schematically shows an example of a transmission waveform (digital waveform) output by the modulation processing device 101. The transmission waveform is a waveform formed by concatenating LFM waveforms with different center frequencies and sweep directions, and each LFM waveform corresponds to data in a 2-bit code. That is, a 2-bit code value is assigned to each frequency sweep period, and the value of the 2-bit code does not change during the frequency sweep period.

[0030] The LFM transmission waveform (pulse compression waveform) can be represented, for example, by the following equation (1).

[0031] TIFF0007877750000001.tif13153… (1) The amplitude is 1, and the length of the transmitted signal (pulse length) is T (sweep period).

[0032] phase TIFF0007877750000002.tif13153… (2) By differentiating with respect to time, the instantaneous frequency f(t) is given by the following:

[0033] TIFF0007877750000003.tif13153… (3)

[0034] The instantaneous frequency f(t) increases (decreases) linearly from the sweep start frequency f0 at time t=0 to the sweep period T, when the frequency change rate (chirp rate) ξ is positive (negative) (the sweep end frequency at sweep period T is f0 + ξT). Note that the phase φ(0) (initial phase) at time t=0 is set to 0.

[0035] For the time interval nT<=t<=(n+T) (n=0,1,2,…), <2 bits: "00">: Sweep start frequency fs=f0 Sweep completion frequency fe = f0 + ξT Center frequency: fc1 = f0 + ξT / 2 Sweep frequency band: 1 Sweep direction: Upward sweep Instantaneous frequency: f(t)=f0+ξ(t-nT)

[0036] <2 bits: "01"> Sweep start frequency fs=f0+ξT Sweep completion frequency fe = f0 Center frequency: fc1 = f0 + ξT / 2 Sweep frequency band: 1 Sweep direction: Down sweep Instantaneous frequency: f(t)=f0+ξT-ξ(t-nT)=f0+ξ((n+1)Tt)

[0037] <2 bits: "10"> Sweep start frequency fs=f0+ξT Sweep completion frequency fe = f0 + 2ξT Center frequency: fc2 = f0 + (3 / 2)ξT Sweep frequency band: 2 Sweep direction: Upward sweep Instantaneous frequency f(t)=f0+ξT+ξ(t-nT)=f0+ξ(t-(n-1)T)

[0038] <2 bits: "11"> Sweep start frequency fs=f0+2ξT Sweep completion frequency fe = f0 + ξT Center frequency: fc2 = f0 + (3 / 2)ξT Sweep frequency band: 2 Sweep direction: Down sweep Instantaneous frequency f(t)=f1+2ξT-ξ(t-nT)=f0+ξ((n+2)Tt)

[0039] The two center frequencies fc1 and fc2 correspond to sweep frequency band 1 ([f0, f0 + ξT]) and sweep frequency band 2 ([f0 + ξT, f0 + 2ξT]), respectively. Identifying the center frequencies is equivalent to identifying the sweep frequency band numbers. Therefore, the combination of center frequency and sweep direction is also the combination of sweep frequency band and the sweep direction within that sweep frequency band.

[0040] In Figure 4, the sweep center frequency is represented by the first bit of the 2-bit code (fc1: 0, fc2: 1), and the sweep direction by the second bit (up sweep: 0, down sweep: 1). This combination is switched each time an LFM sweep is performed (every sweep period T). (Of course, the same center frequency and sweep direction as the previous sweep period may be continued in the next sweep period.) Note that Figure 4 shows an example of assigning the center frequency and sweep direction combination to a 2-bit code, and the assignment of the center frequency and sweep direction combination to a 2-bit code is not limited to Figure 4.

[0041] Figure 2 is a diagram illustrating the functional configuration of the demodulation processing device 106 of the embodiment.

[0042] Cross-correlation processing 202 for data 11, cross-correlation processing 203 for data 10, cross-correlation processing 204 for data 01, and cross-correlation processing 205 for data 00 calculate the cross-correlation between the LFM waveform (reference waveform) and the received waveform 201 corresponding to each data (2-bit code: 11, 10, 01, 00).

[0043] The synchronization detection cross-correlation process 206 calculates the cross-correlation between the synchronization detection waveform (reference waveform) and the received waveform 201.

[0044] The maximum value acquisition processes 207 for data 11, 208 for data 10, 209 for data 01, and 210 for data 00 take input the cross-correlation processing results of each data (2-bit code: "11", "10", "01", "00") output from the cross-correlation process 202 for data 11, 203 for data 10, 204 for data 01, and 205 for data 00, respectively, and the information (time information) output from the cross-correlation process 206 for synchronization detection, and acquire the maximum value of the cross-correlation processing results of each data (2-bit code: "11", "10", "01", "00") at regular intervals (time interval T).

[0045] The center frequency determination process 211 receives the maximum value of the cross-correlation processing result for each data (2-bit code: "11", "10", "01", "00") output from the data 11 maximum value acquisition process 207, data 10 maximum value acquisition process 208, data 01 maximum value acquisition process 209, and data 00 maximum value acquisition process 210 at regular intervals (time interval T), and determines the center frequency by comparing the maximum values ​​of the cross-correlation processing results for each data.

[0046] The sweep direction determination process 212 takes the maximum value of the cross-correlation processing result for each data (2-bit code: "11", "10", "01", "00") output from the data 11 maximum value acquisition process 207, data 10 maximum value acquisition process 208, data 01 maximum value acquisition process 209, and data 00 maximum value acquisition process 210 as input at regular intervals (time interval T), and determines the sweep direction by comparing the maximum values ​​of the cross-correlation processing results for each data.

[0047] The digital signal output 213 outputs a corresponding 2-bit code sequence ("11", "10", "01", "00") based on the center frequency and sweep direction (up sweep / down sweep).

[0048] Figure 5 illustrates the maximum value acquisition processes 207 for data 11 to 210 for data 00. The results of the cross-correlation process 205 for data 00, the cross-correlation process 204 for data 01, the cross-correlation process 203 for data 10, and the cross-correlation process 202 for data 11 are divided in the time direction so that the peak of the cross-correlation process 206 for synchronization detection falls in the center of the time section. In Figure 5, the time is divided into time sections of length T so that the peak of the cross-correlation process 206 for synchronization detection falls in the center. In the cross-correlation process 206 for synchronization detection, the cross-correlation with the reference waveform for synchronization detection is calculated with respect to the received waveform 201 while shifting the time (the length of the correlation calculation is, for example, the number of sampling points corresponding to the sweep period T). Since the cross-correlation peaks at the time when the received waveform 201 is most similar, this peak is taken as the time when the echo for synchronization detection arrives, i.e., the synchronization detection time, and the period ±T / 2 before and after the synchronization detection time is defined as one section T. If there are temporal changes in the underwater sound propagation environment, for example, a shift in the sound wave reception time may occur at each sweep period (interval) T. However, by setting interval T so that the peak of the cross-correlation processing result for synchronization detection is at the center, robustness to reception time shifts of ±T / 2 is achieved.

[0049] The maximum value acquisition processes 207 for data 11 and 210 for data 00 output the maximum value (the value corresponding to the height of the shaded rectangle in Figure 5) at regular intervals (divided time intervals T). In Figure 5, for example, the time interval (shaded interval) of the cross-correlation processing result for data 00 is shown as two intervals: the second time interval in which a peak was detected and the previous first time interval (the interval in which a peak was detected in the cross-correlation processing result for synchronization detection). This is because, in the cross-correlation processing for data 00 205, the cross-correlation with the reference waveform for data 00 is calculated with respect to the received waveform 201 while shifting the time, and when the division by interval T set based on the synchronization detection point is applied to the calculation result, the start of the second time interval and the tail (rising edge) of the peak in the cross-correlation processing for data 00 overlap, resulting in the two intervals being shown. The same applies to the two consecutive shaded time intervals of the cross-correlation processing result for data 00. On the other hand, for the cross-correlation processing results for data 11 and data 10, the peaks and tails are contained within a single interval T set based on the synchronization detection time.

[0050] Figure 3 is a diagram illustrating the signal processing device 107. The conversion process 303 performs the same processing on the digital signal 301, which is the output of the demodulation processing device 106, as the modulation processing device 101, to generate a transmission waveform.

[0051] The cross-correlation process 304 calculates the cross-correlation between the received waveform 302 and the transmitted waveform (a replica of the transmitted waveform), which is the output of the conversion process 303, using the transmitted waveform as a reference waveform. The peak of the cross-correlation appears at the time when the waveforms of the reference waveform and the received waveform 302 coincide (corresponding to the time delay between the transmission of the transmitted waveform and the reflected wave).

[0052] The distance conversion process 305 determines the arrival time of the received waveform 302 from the cross-correlation between the reference waveform and the received waveform 302, and converts this arrival time into the distance to the reflection point (the starting point of the received waveform 302, which is the reflected wave of the transmitted waveform).

[0053] The direction calculation process 306 calculates the signal arrival direction (object direction) from the received waveform 302 by performing phase adjustment and other processes.

[0054] The luminance data output processor 307 outputs image data to the display device 108 in which the horizontal axis represents direction, the vertical axis represents distance, and the luminance is the value of the cross-correlation processing result.

[0055] According to the sonar system of the embodiment described above, it becomes possible to perform object search and communication using acoustic signals simultaneously.

[0056] This enables multi-static searches using underwater vehicles. Because object search and underwater communication are performed with a single pulse, the transmission time can be shortened compared to when separate pulses are used. In addition, because cross-correlation processing is used in demodulation, underwater communication is possible even in situations with high levels of noise.

[0057] In some embodiments, a configuration using another waveform such as LPM may be used instead of the LFM waveform. The LPM signal is represented, for example, by equation (4), and is a signal whose period changes linearly with time.

[0058] TIFF0007877750000004.tif11153… (4) a(t) is the envelope function, and b is a parameter related to the modulation rate.

[0059] By taking the phase as the time component, we obtain the instantaneous frequency f(t). TIFF0007877750000005.tif9150… (5)

[0060] In this embodiment, either the center frequency or the sweep direction (up or down) may be used alone. In this case, for example, one bit of 0 or 1 may be represented by the center frequency of the first frequency band and the center frequency of the second frequency band of the two sweep frequency bands, fc1 and fc2, respectively. Alternatively, one bit of 0 or 1 may be represented by the sweep direction, either up or down.

[0061] Figure 6 illustrates a modified example of the embodiment. In the example of Figure 4 described above, the two sweep frequency bands corresponding to the 2-bit code are fixed to [f0, f0+ξT] and [f0+ξT, f0+2ξT], but the combination of the two sweep frequency bands corresponding to the 2-bit code may be changed in steps over time. In the example of Figure 6, the combination of the two sweep frequency bands corresponding to the 2-bit code is changed in four steps (frequency bands fB1 to fB4) over time. Each of the frequency bands fB1 to fB4 consists of two sweep frequency bands, a higher and a lower one. In the example of Figure 6, the selection of frequency bands fB1 to fB4 is performed sequentially from the lower frequency band fB1 to the higher frequency band fB4, but the order of selection is arbitrary. This modified example is applicable to continuous wave transmission. When using a continuous wave as the transmission signal for object detection, the transmitted wave and the reflected wave from the object are received simultaneously. However, if the frequency bands of the transmitted wave and the reflected wave overlap, the reflected wave with lower sound pressure will be masked. Therefore, in the modified example, the frequency band of the transmitted signal that is frequency-swept is changed in stages, making it possible to separate the transmitted wave and the reflected wave that have different propagation distances.

[0062] Although the above embodiment described its use with underwater sound waves, it can be similarly applied to sound waves propagating through the air.

[0063] Figure 7 is a diagram illustrating an embodiment, showing the configuration when the direction estimation device is implemented in a computer device 400. Referring to Figure 7, the computer device 400 includes a processor 401, a memory 402 such as a semiconductor memory (or an HDD (Hard Disk Drive)) such as RAM (Random Access Memory), ROM (Read Only Memory), or EEPROM (Electrically Erasable Programmable Read-Only Memory), a display device 403 (corresponding to the display device 108 in Figure 1), and an interface 404 (bus interface) connected to the transmitter 102 and receiver 105 in Figure 1. The processor 401 may also be a DSP (Digital Signal Processor). By executing a program stored in the memory 402, the processor 401 performs the processing of, for example, the modulation processing device 101, demodulation processing device 106, and signal processing device 107 in Figure 1.

[0064] Furthermore, the disclosure of Patent Document 1 mentioned above is incorporated herein by reference. Within the framework of the full disclosure of the present invention (including the claims), further modifications and adjustments to the embodiments or examples are possible based on the fundamental technical concept. Also, within the framework of the claims of the present invention, various combinations or selections of various disclosed elements (including each element of each claim, each element of each embodiment, each element of each drawing, etc.) are possible. In other words, the present invention naturally includes the full disclosure, including the claims, and various modifications and alterations that a person skilled in the art could make in accordance with the technical concept. [Explanation of symbols]

[0065] 101 Modulation Processing Unit 102 Transmitter 103 Transmitter 104 Receiver 105 Receiver 106 Demodulation Processing Unit 107 Signal Processing Device 108 Display device 201 Received waveform 202 Cross-correlation processing for Data 11 203 Cross-correlation processing for Data 10 204 Cross-correlation processing for Data 01 205 Cross-correlation processing for data 00 206 Cross-correlation processing for synchronization detection 207 Maximum value acquisition process for data 11 208 Maximum value acquisition process for data 10 209 Maximum value acquisition process for data 01 210 Maximum value acquisition process for data 00 211 Center frequency discrimination process 212 Sweep direction determination process 213 Digital signal output 301 Digital Signal 302 Received waveform 303 Conversion process 304 Cross-correlation processing 305 Distance conversion process 306 Direction Calculation Process 307 Brightness data output processing 400 Computer devices 401 Processor 402 memory 403 Display device 404 Interface

Claims

1. A modulation means that generates a transmitted waveform by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) or LPM (linear period modulation) sweep, corresponding to the bit code of the digital signal to be transmitted, Means for transmitting the aforementioned transmission waveform as a sound wave, It includes a transmitting unit, The modulation means is a sonar system that represents the 2-bit code of the digital signal in four combinations relating to the center frequencies of two different sweep frequency bands and two types of sweep directions: upward sweep and downward sweep.

2. A demodulation means for detecting at least one of the center frequency and the sweep direction from the received waveform of a sound wave, and demodulating the digital signal based on at least one of the center frequency and the sweep direction, A means for measuring the distance of the reflection point of the transmitted waveform, which is the starting point of the received waveform, based on the result of the cross-correlation between the received waveform and the reference waveform, The sonar system according to claim 1, comprising a receiving unit including

3. A modulation means for generating a transmitted waveform by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) or LPM (linear period modulation) sweep in accordance with the bit code of the digital signal to be transmitted, Means for transmitting the aforementioned transmission waveform as a sound wave, It includes a transmitting unit, The modulation means represents a 2-bit code of the digital signal using a combination of the center frequencies of two sweep frequency bands from among a plurality of frequency bands and two types of sweep directions, upward and downward, and the combination of the two sweep frequency bands is changed over time in this sonar system.

4. In a sonar system in which sound wave transmission and reception are performed by separate acoustic arrays, The sonar system according to any one of claims 1 to 3, wherein the modulation means modulates information necessary for time synchronization between the transmitting and receiving sides into the transmission waveform of the digital signal.

5. On the transmitting side of the sonar system, The transmission waveform is generated by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) or LPM (linear period modulation) sweep, corresponding to the digital signal to be transmitted. The aforementioned transmission waveform is transmitted as a sound wave. A sonar method in which the two-bit code of the aforementioned digital signal is represented by four combinations of the center frequencies of two different sweep frequency bands and two types of sweep directions: upward sweep and downward sweep.

6. On the receiving end of the sonar system, From the received waveform of the sound wave, at least one of the center frequency and the sweep direction is detected, and based on at least one of the center frequency and the sweep direction, the digital signal is demodulated, and further, The sonar method according to claim 5, wherein the reflection point of the transmitted waveform, which is the starting point of the received waveform, is measured based on the result of the cross-correlation between the received waveform and the reference waveform.

7. The transmission and reception of sound waves are performed by separate acoustic element arrays. The sonar method according to claim 5 or 6, wherein information necessary for time synchronization between the transmitting and receiving sides is modulated into the transmission waveform of the digital signal and transmitted.

8. On the transmitting side of the sonar system, The transmission waveform is generated by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) or LPM (linear period modulation) sweep, corresponding to the digital signal to be transmitted. The aforementioned transmission waveform is transmitted as a sound wave. The two-bit code of the digital signal is represented by a combination of the center frequencies of two sweep frequency bands from among multiple frequency bands, and two types of sweep directions: upward and downward. A sonar method that changes the combination of the two sweep frequency bands over time.

9. A computer that constitutes a sonar system capable of simultaneously performing object search and communication, A process for generating a transmitted waveform by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) or LPM (linear period modulation) sweep, corresponding to the digital signal to be transmitted, The process of representing the 2-bit code of the aforementioned digital signal using four combinations of the center frequencies of two different sweep frequency bands and two types of sweep directions: upward sweep and downward sweep. A program that executes the command.

10. A computer comprising a sonar system capable of performing object search and communication simultaneously, A process for generating a transmitted waveform by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) or LPM (linear period modulation) sweep, corresponding to the digital signal to be transmitted, The two-bit code of the digital signal is represented by a combination of the center frequencies of two sweep frequency bands from among multiple frequency bands, and two types of sweep directions: upward and downward. A process that changes the combination of the two sweep frequency bands over time. A program that executes the command.

Images