Sonar device, communication method, and program

Abstract

To allow Doppler correction to be performed during demodulation processing, in a system that communicates using a modulation method that expresses a digital signal of one symbol, for example, by switching the center frequency and / or sweep direction of an LFM waveform.SOLUTION: A sonar device includes receiving means for receiving a transmitted signal or a signal reflected from the transmitted signal, which is transmitted by switching at least one of the center frequency and sweep direction of LFM (Linear Frequency Modulation) in accordance with the bit code of a digital signal to be transmitted, and Doppler velocity estimation means for generating a plurality of symbol waveforms that are Doppler modulated at a plurality of different Doppler velocities, performing cross-correlation processing between the received signal received by the receiving means and the plurality of symbol waveforms, and estimating the Doppler velocity based on results of the cross-correlation processing.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a sonar device, a communication method, and a program. [Background technology]

[0002] Sonar (also known as sound navigation and ranging, or sonar) systems use the propagation of sound to locate underwater objects and can be broadly divided into two types: passive sonar and active sonar. Passive sonar locates objects by receiving the sounds produced by underwater objects. Active sonar transmits sound from the sonar and locates the object's location from the reflected waves. Transmitting and receiving sound uses a transducer array that combines multiple transducer elements that convert electrical signals into acoustic signals. Active sonar generally transmits sound and receives reflected waves using the same transducer array. This type of sonar is called a monostatic active sonar.

[0003] Multistatic active sonar, which uses separate arrays for transmission and reception, is also used. With multistatic active sonar, time synchronization is required between the transmitter and receiver to determine the location of an object from the received reflected sound. While wireless communication is generally used for time synchronization, there are cases where wireless communication is not possible, such as when synchronizing with an underwater vehicle.

[0004] Underwater communications is known as a method for searching for objects using multistatic active sonar (called "multistatic search") in such situations. Underwater communications transmits information by modulating a digital signal, transmitting it as a sound wave, and then demodulating the received sound wave back into a digital signal. Modulation methods include PSK (phase shift keying), FSK (frequency shift keying), and OFDM (Orthogonal Frequency Division Multiplexing), but when used for time synchronization in multistatic searches, a modulation method with the following characteristics is suitable:

[0005] In multistatic searches, the transmitting and receiving points may be several thousand meters apart. Sound waves propagate while repeatedly reflecting off the sea surface and seabed. For this reason, the signal must be noise-resistant, allowing communication even when the signal level is attenuated by long-distance propagation, and must be resistant to phase shifts caused by reflections.

[0006] Patent Document 1 discloses an underwater communication device that performs modulation processing to express a digital signal for one symbol by switching the center frequency and sweep direction of an LFM (linear frequency modulation) or LPM (Linear Period Modulation) waveform, and demodulation processing to determine the center frequency and sweep direction of the LFM waveform by performing cross-correlation processing between the received signal and the symbol waveform. Patent Document 1 is expected to have high noise resistance due to the signal gain of the cross-correlation processing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2023-141678 Summary of the Invention [Problem to be solved by the invention]

[0008] When a sonar is mounted on a vehicle moving on or through water, the sound waves transmitted from the sonar are Doppler modulated by the movement of the vehicle, which can, for example, reduce signal gain and increase the probability of error during demodulation.

[0009] The present disclosure aims to provide a sonar device, a communication method, and a program that enable Doppler correction during demodulation processing in a system that communicates using a modulation method that expresses one symbol's worth of digital signal by switching the center frequency and / or sweep direction of an LFM waveform, for example. [Means for solving the problem]

[0010] According to one aspect of the present disclosure, a sonar device includes a receiving means for receiving a transmitted signal or a signal reflected from the transmitted signal, which is transmitted by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) in accordance with the bit code of the digital signal to be transmitted, and a Doppler velocity estimation means for generating a plurality of symbol waveforms that are Doppler modulated at a plurality of different Doppler velocities, performing cross-correlation processing between the received signal received by the receiving means and the plurality of symbol waveforms, and estimating the Doppler velocity based on the results of the cross-correlation processing.

[0011] According to one aspect of the present disclosure, a transmission signal or a signal reflected from the transmission signal is received by switching at least one of a center frequency and a sweep direction of LFM (linear frequency modulation) in accordance with a bit code of the digital signal to be transmitted, A plurality of symbol waveforms are generated that are Doppler modulated with a plurality of different Doppler velocities, and a cross-correlation process is performed between the received signal received by the receiving means and the plurality of symbol waveforms, and the Doppler velocity is estimated based on the results of the cross-correlation process.

[0012] According to one aspect of the present disclosure, a program causes a computer constituting a sonar device having a receiving means for receiving a transmitted signal or a signal reflected from the transmitted signal by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) in accordance with the bit code of the digital signal to be transmitted to perform the following processes: generating a plurality of symbol waveforms each Doppler-modulated at a plurality of different Doppler velocities; and performing cross-correlation processing between the received signal received by the receiving means and the plurality of symbol waveforms, and estimating the Doppler velocity based on the result of the cross-correlation processing. [Effects of the Invention]

[0013] According to the present disclosure, for example, in a system that communicates using a modulation method that expresses one symbol's worth of digital signal by switching the center frequency and / or sweep direction of an LFM waveform, Doppler correction is possible during demodulation processing. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating an example of the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating an example of a waveform according to the present disclosure. [Figure 3] FIG. 10 is a diagram illustrating an example of processing performed by the top-layer estimation device of the present disclosure. [Figure 4] FIG. 1 is a diagram illustrating an example of the present disclosure. [Figure 5] 10A and 10B are diagrams illustrating an example of processing by the demodulation processing device of the present disclosure. [Figure 6] FIG. 1 is a diagram illustrating an example (implementation example by a computer) of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present disclosure will be described. As described above, when a sonar is mounted on a vehicle moving on or underwater, sound waves transmitted from the sonar are modulated (Doppler modulated) at a Doppler frequency corresponding to the Doppler velocity (relative velocity) due to the movement of the vehicle. When a received signal is Doppler modulated, the signal gain decreases and the probability of errors during demodulation increases. In particular, in LFM, in which the frequency changes linearly with time, the cross-correlation between the transmitted waveform (replica) and the received waveform decreases due to changes in the frequency modulation rate caused by the Doppler effect. Furthermore, a shift in the demodulation clock may occur due to changes in wavelength caused by the Doppler effect, but it is required that demodulation be possible even when the transmitted waveform is received Doppler modulated.

[0016] Although the above problem is merely one example, according to the present disclosure, it is possible to perform Doppler correction during demodulation processing in a system that communicates using a modulation method in which a digital signal for one symbol is expressed by switching the center frequency and sweep direction of an LFM waveform. That is, according to the present disclosure, a signal (or its reflected signal) transmitted by switching at least one of the center frequency and sweep direction of the LFM in accordance with the bit code of the digital signal to be transmitted is received, and the Doppler velocity is estimated by performing cross-correlation processing between the received signal and a plurality of symbol waveforms that have been Doppler-modulated at different Doppler velocities.

[0017] According to the present disclosure, for example, in an underwater communication device (sonar device) equipped with a modulation processing function that expresses a digital signal for one symbol by switching the center frequency and sweep direction of an LFM waveform, a function that transmits the output signal of the modulation processing function as a sound wave, a function that converts the received sound wave into an electrical signal, and a demodulation processing function that determines the center frequency and sweep direction of an LFM waveform by performing cross-correlation processing between the received signal and the symbol waveform, the device is equipped with a Doppler speed estimation means that performs cross-correlation processing between the received signal and the Doppler-modulated symbol waveform for a plurality of predetermined, mutually different Doppler velocities, and estimates the Doppler speed based on the results of this cross-correlation processing, and performs demodulation processing using the estimated Doppler speed.

[0018] According to the present disclosure, the Doppler velocity estimation means may be configured to include a set of a plurality of symbol generation means that generate, for each combination of bit codes that constitute a symbol, a symbol waveform Doppler-modulated with the Doppler velocity for each of a plurality of Doppler velocities obtained by dividing a range of upper and lower limits of a preset Doppler velocity, and a plurality of cross-correlation calculation means that calculate the cross-correlation between the symbol waveforms generated by the plurality of symbol generation means and the received signal (received waveform).

[0019] According to the present disclosure, the Doppler velocity estimation means may be configured to include a set of first to fourth symbol generation means for generating, for each of a plurality of Doppler velocities obtained by dividing a preset upper and lower limit range of Doppler velocity into a plurality of equal intervals, for example, for each of 2-bit data "00", "01", "10", and "11", a symbol waveform Doppler-modulated with the Doppler velocity, and a set of first to fourth cross-correlation calculation means for calculating the cross-correlation between the symbol waveform generated by the first to fourth symbol generation means, respectively, and the received signal. The 2-bit data "00", "01", "10", and "11" have, for example, two center frequencies, but according to the present disclosure, the LFM waveform may be set to three or more center frequencies so as to increase the amount of information per symbol.

[0020] According to the present disclosure, the sweep direction of the LFM waveform may be fixed for each center frequency, for example, to reduce the error probability during demodulation.

[0021] According to the present disclosure, a process for detecting a peak for each symbol may be performed by obtaining the maximum value from the cross-correlation process result between the symbol waveform and the received signal.

[0022] According to the present disclosure, the average level of the peak of the cross-correlation between the symbol waveform and the received signal may be calculated for each Doppler velocity obtained by dividing the upper and lower limit ranges of the Doppler velocity into multiple sections, and the Doppler velocity of the received sound wave may be calculated by comparing these.

[0023] FIG. 1 is a diagram illustrating a schematic example of an example of the present disclosure. In FIG. 1, a modulation processing device 101 modulates digital information such as transmission information into a transmittable digital signal and outputs the modulated signal. A transmission unit 102 converts an input digital waveform into an analog waveform, power amplifies the analog waveform, and outputs the analog waveform. A transmitter 103 includes an array of ultrasonic transducers (not shown) and converts an electrical signal output from the transmitter 102 into an acoustic signal and transmits the acoustic signal underwater. A receiver 104 includes an array of ultrasonic transducers (not shown) and receives and converts underwater acoustic signals into an electrical signal. A receiver 105 converts the electrical signal waveform (analog waveform) output from the receiver 104 into a digital waveform and outputs the digital waveform. A Doppler estimation device 106 estimates the Doppler velocity (speed) by estimating the amount of frequency change due to Doppler in the received waveform (digital waveform) output from the receiver 105. A demodulation processing device 107 acquires digital information from the received waveform (digital waveform) based on the Doppler velocity estimated by the Doppler estimation device 106. The display device 108 displays the output of the demodulation processor 107 on its screen.

[0024] FIG. 2 is a diagram schematically illustrating an example of a waveform (frequency sweep pattern) output by modulation processing device 101. FIG. 2 shows a waveform in which multiple LFM waveforms (digital signal waveforms) with different center frequencies and sweep directions are connected in the time axis direction. Each LFM waveform corresponds to one symbol's worth of digital information. Although not particularly limited, in FIG. 2, each LFM waveform corresponds to 2-bit code data. In other words, a 2-bit code value is assigned to one frequency sweep time, and the value of the 2-bit code does not change during the frequency sweep time. In the case of the waveform shown in FIG. 2, there are two patterns of center frequencies and two patterns of sweep directions, UP and DOWN. Therefore, as will be explained below, one symbol contains 2 bits of digital information.

[0025] The transmission waveform of LFM can be expressed, for example, by the following equation (1).

[0026] TIFF2025147946000002.tif13153…(1)

[0027] In equation (1), A is the amplitude, fo is the sweep start frequency, and ξ is the frequency change rate (chirp rate). For convenience, equation (1) uses a complex notation, and j 2 = -1. Here, the length of the transmission signal (pulse length) is T (sweep time).

[0028] In equation (1), the phase TIFF2025147946000003.tif13153…(2) By differentiating with respect to time, the instantaneous frequency f(t) is given by

[0029] TIFF2025147946000004.tif13153…(3)

[0030] In equation (3), when the frequency change rate (chirp rate) ξ is positive (negative), the instantaneous frequency f(t) increases (decreases) linearly from the sweep start frequency f0 at time t = 0 to the frequency sweep time T (the sweep end frequency at frequency sweep time T is f0 + ξT). Note that the phase φ(0) (initial phase) at time t = 0 is set to 0.

[0031] For the time interval: nT≦t≦(n+1)T (n=0, 1, 2, …), <2 bits:"00">: Sweep start frequency fs=f0 Sweep end frequency fe=f0+ξT Center frequency: fc1=f0+ξT / 2 Sweep frequency band: 1 Sweep direction: Up sweep Instantaneous frequency: f(t)=f0+ξ(t-nT) …(4)

[0032] <2 bits:"01"> Sweep start frequency fs=f0+ξT Sweep end 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) …(5)

[0033] <2 bits:"10"> Sweep start frequency fs=f0+ξT Sweep end frequency fe=f0+2ξT Center frequency: fc2=f0+(3 / 2)ξT Swept frequency bands: 2 Sweep direction: Up sweep Instantaneous frequency f(t)=f0+ξT+ξ(t-nT) =f0+ξ(t-(n-1)T) …(6)

[0034] <2 bits:"11"> Sweep start frequency fs=f0+2ξT Sweep end frequency fe=f0+ξT Center frequency: fc2=f0+(3 / 2)ξT Swept frequency bands: 2 Sweep direction: Down sweep Instantaneous frequency f(t)=f1+2ξT-ξ(t-nT) =f0+ξ((n+2)Tt) …(7)

[0035] 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, and specifying (identifying) the center frequencies is equivalent to specifying (identifying) the sweep frequency band number. Therefore, a combination of center frequency and sweep direction is also a combination of a sweep frequency band and a sweep direction in that sweep frequency band. Of course, the number of center frequencies is not limited to two, and three or more may be used. In this case, one symbol corresponds to code data of three or more bits.

[0036] 3 is a diagram schematically illustrating an example of the processing of the Doppler estimation device 106 of FIG. 1. In FIG. 3, symbol waveform generation processing 202 generates a waveform (a received waveform expected for a transmitted waveform) by Doppler modulating the symbol waveform of equation (1). Symbol waveform generation processing 202 includes symbol waveform generation processing (00) that generates a symbol waveform by Doppler modulating the symbol waveform of 2-bit data "00" (equation (4), see symbol 00 in FIG. 2), symbol waveform generation processing (01) that generates a symbol waveform by Doppler modulating the symbol waveform of 2-bit data "01" (equation (5), see symbol 01 in FIG. 2), symbol waveform generation processing (10) that generates a symbol waveform by Doppler modulating the symbol waveform of 2-bit data "10" (equation (6), see symbol 10 in FIG. 2), and symbol waveform generation processing (11) that generates a symbol waveform by Doppler modulating the symbol waveform of 2-bit data "11" (equation (7), see symbol 11 in FIG. 2). In each set of symbol waveform generation processes (00) to (11), a waveform is generated by expanding or contracting each symbol waveform in the time direction according to the assumed (pre-set) Doppler shift (Doppler speed).

[0037] For example, if a reflected signal (reflected echo) from a target at a distance r ahead is received at time t, the received waveform will be the same as the transmitted signal sent at time t-2r / c (c is the speed of sound in water). u(t-2r / c) …(8) It is an echo of

[0038] In this case, the received waveform is generally TIFF2025147946000005.tif11153 …(9) TIFF2025147946000006.tif11153 …(10) It is expressed as: In equation (9), the coefficient k represents the attenuation of the transmitted signal as it propagates through the water and is reflected by the target. η is the Doppler scaling factor, which represents the expansion and contraction along the time axis due to the Doppler effect.

[0039] The reflected echo e(t) is the time shift τ of u(t). o and the time axis expansion coefficient η as parameters. In equation (9), the component u(0) at the time origin of the transmitted waveform and the reflection from the target are exactly τ o In this case, the round-trip propagation delay time from when the transmitted waveform u(0) is transmitted, reflected by the target, to when it is observed again is τ0.

[0040] When the receiver 104 in FIG. 1 communicates underwater with the transmitter 103, if the distance between the transmitter 103 and the receiver 104 is r, then equation (8) is u(tr / c) …(8') In the received waveform of equation (9), τ o teeth, TIFF2025147946000007.tif11153…(10') This becomes:

[0041] Here, the reflection time τ o If the distance to the target at / 2 is r and the relative velocity to the target is v, η is given by the following equation (11): TIFF2025147946000008.tif14150…(11)

[0042] When the receiver 104 in FIG. 1 communicates underwater with the transmitter 103, if the relative velocity between the receiver 104 and the transmitter 103 is v, then η is given by the following equation (11′). TIFF2025147946000009.tif12150…(11')

[0043] The following is applicable to both underwater communication between the transmitter 103 and receiver 104 in Figure 1, and to the case where the receiver 104 receives a signal that is the transmission signal transmitted from the transmitter 103 and reflected by an object (when object search and communication are performed together).

[0044] Transmit symbol waveform S s(t) (complex representation) (replica) is the LFM of the following equation (12). TIFF2025147946000010.tif13153 TIFF2025147946000011.tif14153 …(12) Here, T0 may be the frequency sweep time T described above.

[0045] Depending on whether the 2-bit data is "00" to "11", the sweep start frequency f0 and the instantaneous waveform frequency f(t) in equation (12) are given by equations (4) to (7), respectively.

[0046] Received waveform S at time t r If k=B / A, (t) can be expressed by the following equation (13). TIFF2025147946000012.tif11153 TIFF2025147946000013.tif13150 TIFF2025147946000014.tif12153…(13)

[0047] In equation (13), the values ​​of the distance r (and therefore τ0), relative velocity (Doppler velocity) v, and scaling factor η are unknown. Here, the Doppler velocity v is the object of estimation.

[0048] In the symbol waveform generation process 202, a Doppler modulated symbol waveform S g For example, a replica S of the transmitted symbol waveform is generated. s Symbol waveform S g Generate (t). TIFF2025147946000015.tif14153 TIFF2025147946000016.tif14153 …(14)

[0049] Since the scaling factor η in equation (14) is given by equation (11) or (11'), the value of η cannot be determined unless the Doppler velocity v is determined. As an example, if the upper limit of the preset Doppler velocity v is V and the lower limit is -V, and the interval between them is divided into (N-1) equal parts, for example, with each step width being Δ, then the i-th Doppler velocity can be given by the following equation (15).

[0050] TIFF2025147946000017.tif11153 …(15)

[0051] In the symbol waveform generation process 202, the symbol waveform generation process 202 calculates the respective scaling coefficients η[i] according to each of the N Doppler velocities v[i] (i=1, ..., N). When the receiver 104 receives the transmitted waveform from the transmitter 103 as a reflected echo from an object, TIFF2025147946000018.tif15153 …(16) When the transmitter 103 and receiver 104 in FIG. 1 communicate underwater (in the case of direct waves), TIFF2025147946000019.tif15153 …(16')

[0052] In the symbol waveform generation process 202, the symbol waveform: TIFF2025147946000020.tif14153 TIFF2025147946000021.tif14153 …(17) is generated and stored in a storage unit (not shown).

[0053] The symbol waveforms generated by the symbol waveform generation process (00) to the symbol waveform generation process (11) corresponding to the 2-bit data "00" to "11" are S g00 , S g01 , S g10 , S g11 Let's say.

[0054] The symbol waveform S in equation (17) g The right side of (t) is the received waveform S r In (t) TIFF2025147946000022.tif6150…(18) (τ0 is unknown when estimating the Doppler velocity.) This τ0 is essentially estimated by calculating the correlation between the received waveform and the symbol waveform in the demodulation process described later.

[0055] The cross-correlation processing 203 includes a cross-correlation processing (00) for 2-bit data "00", a cross-correlation processing (01) for 2-bit data "01", a cross-correlation processing (10) for 2-bit data "10", and a cross-correlation processing (11) for 2-bit data "11".

[0056] In the cross-correlation processing (00) to (11) for 2-bit data "00" to "11", the received waveform S received by the receiving unit 105 is r (τ) (t in equation (17) is expressed as τ) and each symbol waveform S g00 (t), S g01 (t), S g10 (t), S g11 The cross-correlation R is calculated by multiplying the time t of (t) (the symbol waveform of 2-bit data "00", "01", "10", "11" generated and stored in the symbol waveform generation processes (00) to (11)) by the value shifted by t-τ, and integrating the result (convolution integral) while shifting the time τ within the time interval [-To / 2, To / 2] as shown in the following equations (19a) to (19d). 00 , R 01 , R 10 , R 11 The "*" on the shoulder of Sr represents the complex conjugate.

[0057] TIFF2025147946000023.tif12150…(19a) TIFF2025147946000024.tif12150…(19b) TIFF2025147946000025.tif12150…(19c) TIFF2025147946000026.tif12150…(19d)

[0058] The following equations (19'a) to (19'd) are calculations (discrete time calculations) that use the sum Σ instead of integration (m and n correspond to τ and t in the following equations (19a) to (19d), respectively). TIFF2025147946000027.tif9150…(19'a) TIFF2025147946000028.tif9150…(19'b) TIFF2025147946000029.tif9150…(19'c) TIFF2025147946000030.tif9150…(19'd)

[0059] The maximum value acquisition process 204 is a process for obtaining the cross-correlation value R calculated in the cross-correlation processes (00), (01), (10), and (11). 00 , R 01 , R 10 , R 11 The value that maximizes the cross-correlation processing result between the received waveform 201 and each Doppler-modulated symbol waveform is obtained.

[0060] The peak detection process 205 detects peaks at predetermined intervals for the maximum value output from the maximum value acquisition process 204. In the peak detection process 205, the predetermined interval is implementation-specific and arbitrary. There are no particular restrictions, but it may be, for example, an integer multiple of the frequency sweep time T (corresponding to multiple symbols).

[0061] The average value calculation process 206 calculates the average value of the signal levels of the peaks detected by the peak detection process 205 (values ​​obtained by smoothing the peaks). In the average value calculation process 206, the number of peaks to be averaged (or the period over which the average is calculated) is implementation-specific and arbitrary. Although not particularly limited, for example, the average of each peak may be calculated over a period of 4 or an integral multiple of the frequency sweep time T in correspondence with the four symbol waveform generation processes (00), (01), (10), and (11).

[0062] The processing unit (module) 210 for the symbol waveform generation process 202, cross-correlation process 203, maximum value acquisition process 204, peak detection process 205, and average value calculation process 206 is provided with N processing modules 210-1 to 210-N corresponding to N Doppler velocities v[i] obtained by equally dividing the upper limit V and lower limit -V of the assumed Doppler velocity.

[0063] The Doppler estimation process 207 compares the outputs of the average value calculation process 206 in the N processing modules 210-1 to 210-N. If the value in the average value calculation process 206 of the kth (1≦k≦N) processing module 210-k among the N processing modules 210-1 to 210-N is the highest, the kth v[k] among the N Doppler velocities v[1] to v[N] is set as the estimated value v of the Doppler velocity. v = v[k] …(20)

[0064] Figure 4 shows an image of the output results of cross-correlation processing 203 and maximum value acquisition processing 204. The four graphs from the top are the results of cross-correlation processing between the received waveform and the Doppler-modulated symbol waveform, and the bottom graph is the result of acquiring the maximum value from them. In Figure 4, T is the frequency sweep time, and the length of the cross-correlation is, for example, the number of sampling points corresponding to the frequency sweep time T. Also, T0 in equations (13), (14), etc. can be made to correspond to T in Figure 4.

[0065] 5 is a diagram illustrating an example of processing by the demodulation processing device 107 of FIG. 1. The symbol waveform generation process 302 includes a symbol waveform generation process (00) that generates a symbol waveform of 2-bit data "00" (see symbol 00 in FIG. 2), a symbol waveform generation process (01) that generates a symbol waveform of 2-bit data "01" (see symbol 01 in FIG. 2), a symbol waveform generation process (10) that generates a symbol waveform of 2-bit data "10" (see symbol 10 in FIG. 2), and a symbol waveform generation process (11) that generates a symbol waveform of 2-bit data "11" (see symbol 11 in FIG. 2). When the Doppler velocity v estimated by the Doppler estimation device 106 is received, the four symbol waveform generation processes (00) to (11) each generate a symbol waveform that has been Doppler modulated in accordance with the received Doppler velocity v. As described above, in Doppler modulation, the symbol waveform is expanded or contracted in the time direction in accordance with the Doppler velocity. That is, in the symbol waveform generation process 302, the Doppler velocity v estimated by the Doppler estimation device 106 is used to generate the scaling factor η'. When the receiver 104 receives the transmitted waveform from the transmitter 103 as a reflected echo from an object, TIFF2025147946000031.tif15153 …(twenty one)

[0066] When the transmitter 103 and receiver 104 in FIG. 1 communicate directly underwater (in the case of direct waves), TIFF2025147946000032.tif14153 …(twenty one')

[0067] In the symbol waveform generation process 302, the symbol waveform S' is generated using this expansion / contraction coefficient η'. g Generate. TIFF2025147946000033.tif14153 TIFF2025147946000034.tif14153 …(twenty two)

[0068] The cross-correlation processing 303 performs a Doppler modulation on the received waveform 301 using the symbol waveform S' generated by the four symbol waveform generation processes (00) to (11) of the symbol waveform generation processing 302. g (t) of the received waveform 301. r (τ) (τ is t in equation (21)) and the symbol waveform S′ generated by the symbol waveform generation processes (00) to (11) of the symbol waveform generation process 302 g00 (t)~S' g11 The cross-correlation is calculated by multiplying the value of (t) by the value obtained by shifting the time t to t-τ, and integrating or summing the result while shifting the time τ within the time interval [-To / 2, To / 2]. g00 ~S g11 S' by equation (22) g00 ~S' g11 Just replace it with.

[0069] 5, received waveform 301 may be a received waveform input to demodulation processing device 107 at the time when Doppler velocity v is estimated by Doppler estimation device 106 in Fig. 1. Although it depends on the underwater communication protocol (e.g., serial transmission / block transmission, frame format, etc.) between the transmitter and receiver, as an example, received waveform 201 (digital signal waveform) received by receiver 105 is sequentially stored in a receiving buffer (FIFO (First In First Out) or dual port RAM (Random Access Memory) or the like) not shown, and at the stage when Doppler velocity v is estimated based on the received waveform 201 in Doppler estimation device 106, cross-correlation processing 303 of demodulation processing device 107 sequentially inputs received waveform 201 from the receiving buffer not shown as received waveform 301 and generates symbol waveform S' g00 ~S' g11In the Doppler estimation device 106, if it takes n cycles of frequency sweep time T from the time when the receiving unit 105 receives the received waveform 201 to the time when the Doppler velocity v is estimated in the Doppler estimation process 207 via the cross-correlation process 203, maximum value acquisition process 204, peak detection process 205, and average value calculation process 206, the received waveform 201 may be temporarily stored in a receiving buffer (not shown) for T×n time (n symbols). Alternatively, in the cross-correlation process 303 of the demodulation processing device 107, a symbol waveform S' generated using the received waveform 301 received, for example, T×n time after the receiving unit 105 receives the received waveform 201, and the Doppler velocity v estimated by the Doppler estimation device 106 may be temporarily stored in a receiving buffer (not shown). g00 ~S' g11 In this case, the frame format may correspond to a configuration in which a signal for Doppler velocity estimation (preamble signal) is added before the data portion.

[0070] Received waveform S r is the symbol waveform S' g The cross-correlation value between the received waveform and the symbol waveform is maximized at the time when the received waveform is most similar to the symbol waveform. r The symbol waveform S' that is most similar to g It can be said that finding (finding the maximum value of cross-correlation) is essentially equivalent to estimating, for example, the time delay parameter τ0 of equation (13). In maximum value acquisition processing 304, the maximum value is obtained for each fixed time period (for example, an integer multiple of the frequency sweep time T) for the cross-correlation processing results of each symbol waveform. Maximum value acquisition processing (11) for 2-bit data "11", maximum value acquisition processing (10) for 2-bit data "10", maximum value acquisition processing (01) for 2-bit data "01", and maximum value acquisition processing (00) for 2-bit data "00" input the cross-correlation calculation results output from cross-correlation processing (11), cross-correlation processing (10), cross-correlation processing (01), and cross-correlation processing (00), and obtain the maximum value for each fixed time period.

[0071] The center frequency discrimination process 305 discriminates the center frequency by comparing the maximum value of the calculation result of the cross-correlation between each symbol waveform of 2-bit data "00" to "11" and the received waveform. That is, the center frequency discrimination process 305 inputs the maximum value of the calculation result of the cross-correlation output at regular intervals from the maximum value acquisition process (11) for 2-bit data "11", the maximum value acquisition process (10) for 2-bit data "10", the maximum value acquisition process (01) for 2-bit data "01", and the maximum value acquisition process (00) for 2-bit data "00", and discriminates the center frequency by comparing the maximum value of the cross-correlation process result of each data.

[0072] The sweep direction determination process 306 determines the sweep direction by comparing the maximum value of the calculation result of the cross-correlation between each symbol waveform of 2-bit data "00" to "11" and the received waveform. That is, the sweep direction determination process 306 receives the maximum value of the cross-correlation outputted at regular intervals from the maximum value acquisition process (11), maximum value acquisition process (10), maximum value acquisition process (01), and maximum value acquisition process (00), and determines the sweep direction by comparing the maximum value of the cross-correlation at regular intervals.

[0073] The digital signal output 307 outputs 2-bit data (either "00", "10", "01", or "11") corresponding to the center frequency and sweep direction.

[0074] As described above, according to the present disclosure, Doppler correction is possible during demodulation processing for a modulation method that expresses one symbol's worth of digital signal by switching the center frequency and sweep direction of an LFM waveform. This disclosure is not limited to LFM waveforms, but is also applicable to LPM (Linear Period Modulation), in which the signal period changes linearly over time. It is also applicable to DFM (Deep Frequency Modulation) and HFM (Hyperbolic Frequency Modulation), which is resistant to Doppler shift. The LPM transmission waveform is expressed by the following equation: St(t)=a(t)exp{jblog(t)} …(23) (a(t) is the envelope function, and b is a parameter related to the modulation rate). In DFM, f DFM (t)=Δ f 2cos(2πf m t+φ m ) …(twenty four) (However, Δ f is the modulation depth, f m is the modulation frequency, φ m is the modulation phase) is applied to the signal source. h (t) is 0≦t≦T h in S h (t)=exp{-jφ0ln((t'-t) / t')} …(25) otherwise 0 (where t'=T h ×f h1 / (f h1 -f h0 ), φ0=2πf h0 t') f h1 >f h0 When this happens, it is called positive HFM (HFM + (Written as follows). f h0 >f h1 In this case, it is called inverse HFM (HFM - (Written as follows).

[0075] In the present disclosure, the sweep direction (up or down) may be fixed for each center frequency. For example, of two sweep frequency bands, the sweep direction of the center frequency fc1 of the first frequency band may be fixed as up, and the sweep direction of the center frequency fc2 of the second frequency band may be fixed as down.

[0076] FIG. 6 is a diagram illustrating an embodiment, illustrating a configuration in which a receiving device is implemented as a computer device 400. Referring to FIG. 6, the computer device 400 includes at least one processor 401, a memory 402 such as a semiconductor memory (e.g., a random access memory (RAM), a read-only memory (ROM), or an electrically erasable programmable read-only memory (EEPROM)) (or a hard disk drive (HDD)), a display device 403 (corresponding to the display device 108 in FIG. 1), and an interface 404 (bus interface) connected to the receiving unit 105 in FIG. 1. The processor 401 may be a digital signal processor (DSP). By executing a program stored in the memory 402, the processor 401 performs, for example, any of the processing of the Doppler estimation device 106, the processing of the demodulation processing device 107, and display control of the display device 108 in FIG. 1, or performs any combination of these or all of the processing.

[0077] The sonar system of the above-described embodiment makes it possible to simultaneously perform object search and communication using acoustic signals. This enables multistatic search using underwater vehicles, for example. Because object search and underwater communication are performed using a single pulse, transmission time can be shortened compared to when separate pulses are used. Furthermore, because cross-correlation processing is used for demodulation, underwater communication is possible even in situations where the influence of noise is significant.

[0078] Although the present disclosure has described use with underwater acoustic waves, it can also be similarly applied to acoustic waves propagating through air. Note that in the cross-correlation processing 202, 302 of the Doppler estimation device 106 and the demodulation processing device 107, instead of performing a convolution operation in the time domain between the received waveform and the symbol waveform, the time-domain received waveform and the symbol waveform may be converted into the frequency domain using an FFT (Fast Fourier Transform) or a DFT (Discrete Fourier Transform) or the like, and the cross-correlation may be calculated by a multiplication operation in the frequency domain.

[0079] The above-described embodiment is subject to the following additional notes (but is not limited to the following):

[0080] (Supplementary Note 1) The sonar device comprises a receiving means for receiving a transmitted signal or a signal reflected from the transmitted signal, which is transmitted by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) in accordance with the bit code of the digital signal to be transmitted, and a Doppler velocity estimation means for generating a plurality of symbol waveforms that are Doppler modulated at a plurality of different Doppler velocities, performing cross-correlation processing between the received signal received by the receiving means and the plurality of symbol waveforms, and estimating the Doppler velocity based on the result of the cross-correlation processing.

[0081] (Supplementary Note 2) In the sonar device of Supplementary Note 1, the Doppler velocity estimation means includes a set of a plurality of symbol generation means for generating symbol waveforms Doppler-modulated with the Doppler velocity, corresponding to each combination of bit codes constituting a symbol, for each Doppler velocity obtained by dividing a range of upper and lower limits of a preset Doppler velocity into a plurality of sections, and a plurality of cross-correlation calculation means for calculating the cross-correlation between the received signal and the plurality of symbol waveforms generated by the plurality of symbol generation means, for each Doppler velocity obtained by dividing a range of upper and lower limits of the preset Doppler velocity into a plurality of sections.

[0082] (Supplementary Note 3) In the sonar device of Supplementary Note 1 or 2, the Doppler speed estimation means For each Doppler speed obtained by dividing the range of upper and lower limits of the preset Doppler speed into a plurality of ranges, first to fourth symbol generating means for generating symbol waveforms Doppler modulated at the respective Doppler velocities for each of the two-bit data "00", "01", "10", and "11"; first to fourth cross-correlation calculation means for calculating the cross-correlation between the symbol waveforms generated by the first to fourth symbol generation means, respectively, and the received signal; It is equipped with a set of:

[0083] (Supplementary Note 4) In the sonar device of Supplementary Note 3, the Doppler speed estimation means For each Doppler speed obtained by dividing the range of upper and lower limits of the preset Doppler speed into a plurality of ranges, a maximum value detection means for detecting a maximum value of the cross-correlation calculated by each of the first to fourth cross-correlation calculation means at predetermined time intervals; a peak detection means for detecting a peak of the maximum value of the cross-correlation; an average value calculation means for calculating an average value of the peaks of the cross-correlation maxima; A set of The apparatus further comprises means for estimating the Doppler velocity from the average value of the peaks of the maximum values ​​of the cross-correlation for a plurality of Doppler velocities obtained by dividing a preset range of upper and lower limits of the Doppler velocity into a plurality of ranges.

[0084] (Supplementary Note 5) In the sonar device of any one of Supplementary Notes 1 to 4, a demodulation processing means is provided that receives the estimation result of the Doppler velocity estimated by the Doppler velocity estimation means, and the demodulation processing means first to fourth symbol generating means for generating Doppler-modulated symbol waveforms for each of the two-bit data using the estimated Doppler velocities; first to fourth cross-correlation calculation means for respectively calculating cross-correlations between the received signal and the symbol waveforms generated by the first to fourth symbol generation means, respectively, based on the estimated Doppler velocity; the first to fourth maximum value detecting means for detecting the maximum value of the cross-correlation calculated by the first to fourth cross-correlation calculating means for each predetermined time; a detection means for detecting at least one of the center frequency and the sweep direction by comparing the maximum values ​​detected by the first to fourth maximum value detection means; The apparatus further includes a demodulation means for demodulating a digital signal based on the detection by the detection means.

[0085] (Appendix 6) The sonar communication method is receiving a transmission signal or a signal reflected from the transmission signal, the transmission signal being transmitted by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) in accordance with the bit code of the digital signal to be transmitted; A plurality of symbol waveforms are generated that are Doppler modulated with a plurality of different Doppler velocities, and a cross-correlation process is performed between the received signal received by the receiving means and the plurality of symbol waveforms, and the Doppler velocity is estimated based on the results of the cross-correlation process.

[0086] (Supplementary Note 7) In the communication method of Supplementary Note 6, a plurality of symbol generation processes are performed in parallel for each Doppler velocity, the plurality of processes being for generating symbol waveforms Doppler-modulated by the Doppler velocity in correspondence with each combination of bit codes constituting a symbol, for each Doppler velocity obtained by dividing a range of upper and lower limits of a preset Doppler velocity; A plurality of cross-correlation processes for calculating cross-correlations between the received signal and the plurality of symbol waveforms generated by the plurality of symbol generating means respectively are performed in parallel for each of the Doppler velocities.

[0087] (Appendix 8) In the communication method of appendix 6 or 7, For each Doppler speed obtained by dividing the range of upper and lower limits of the preset Doppler speed into a plurality of ranges, first to fourth symbol generation processes for generating symbol waveforms Doppler modulated at the respective Doppler velocities for each of the two-bit data "00", "01", "10", and "11"; first to fourth cross-correlation calculation processes for calculating cross-correlations between the symbol waveforms generated in the first to fourth symbol generation processes, respectively, and the received signal; a process of detecting a maximum value of the cross-correlations calculated in each of the first to fourth cross-correlation calculation processes for each predetermined time period; detecting a peak of the maximum value of the cross-correlation; calculating an average value of the peaks of the cross-correlation maxima; a set of the above steps is executed for each Doppler speed obtained by dividing the range of upper and lower limits of the preset Doppler speed into a plurality of ranges, The Doppler velocity is estimated from the average value of the peaks of the maximum values ​​of the cross-correlation for each of the Doppler velocities obtained by dividing the predetermined range of upper and lower limits of the Doppler velocity into a plurality of ranges.

[0088] (Appendix 9) In any of the communication methods in Appendices 6 to 8, Based on the Doppler speed estimation result, first to fourth symbol generation processes for generating Doppler-modulated symbol waveforms for each of the two-bit data "00", "01", "10", and "11" based on the estimated Doppler velocity; first to fourth cross-correlation calculation processes for calculating cross-correlations between the symbol waveforms generated by the first to fourth symbol generation processes, respectively, based on the estimated Doppler velocity and the received signal; the first to fourth maximum value detection processes for detecting maximum values ​​of the cross-correlations calculated in the first to fourth cross-correlation calculation processes, respectively, for each predetermined time period; a detection process for detecting at least one of the center frequency and the sweep direction by comparing the maximum values ​​in the first to fourth maximum value detection processes; Based on the detection in the detection process, a demodulation process is executed to demodulate the digital signal.

[0089] (Appendix 10) A computer constituting a sonar device having a receiving means for receiving a transmitted signal or a signal reflected from the transmitted signal by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) in accordance with the bit code of the digital signal to be transmitted, generating a plurality of symbol waveforms each Doppler modulated at a plurality of different Doppler velocities; a process of performing a cross-correlation process between the received signal received by the receiving means and the plurality of symbol waveforms, and estimating a Doppler velocity based on the result of the cross-correlation process; A program that executes the following.

[0090] The disclosure of Patent Document 1 is incorporated herein by reference. Modifications and adjustments of the embodiments and examples are possible within the scope of the entire disclosure of the present invention (including the scope of the claims), and further based on the basic technical concept thereof. Furthermore, various combinations and selections of the various disclosed elements (including each element of each claim, each element of each example, each element of each drawing, etc.) are possible within the scope of the claims of the present invention. In other words, the present invention naturally includes various modifications and alterations that would be possible for a person skilled in the art based on the entire disclosure, including the scope of the claims, and the technical concept thereof. [Explanation of symbols]

[0091] 101 Modulation processing device 102 Transmitter 103 Transmitter 104 Receiver 105 Receiving unit 106 Doppler Estimator 107 Demodulation Processing Device 108 Display device 201, 301 received waveform 202, 302 Symbol waveform generation processing 203, 303 Cross-correlation processing 204, 304 Maximum value acquisition process 205 Peak detection processing 206 Average Value Calculation Processing 207 Doppler estimation processing 210-1~210-N Processing Module 305 Center frequency discrimination processing 306 Sweep direction discrimination processing 307 Digital signal output 400 Computer equipment 401 processor 402 memory 403 Display device 404 Interface

Claims

1. a receiving means for receiving a transmitted signal or a signal reflected from the transmitted signal by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) in accordance with the bit code of the digital signal to be transmitted; a Doppler velocity estimation means for generating a plurality of symbol waveforms each Doppler modulated with a plurality of different Doppler velocities, performing cross-correlation processing between the received signal received by the receiving means and the plurality of symbol waveforms, and estimating the Doppler velocity based on the result of the cross-correlation processing; A sonar device equipped with

2. The Doppler velocity estimation means a plurality of symbol generating means for generating symbol waveforms Doppler-modulated by a predetermined upper and lower limit range of Doppler velocities corresponding to each combination of bit codes constituting a symbol, the symbol waveforms being Doppler-modulated by the Doppler velocities; a plurality of cross-correlation calculation means for calculating cross-correlations between the received signal and the plurality of symbol waveforms generated by the plurality of symbol generation means, respectively; 2. The sonar device according to claim 1, wherein a set of the above is provided for each of a plurality of Doppler velocities obtained by dividing the range of upper and lower limits of the preset Doppler velocity.

3. The Doppler velocity estimation means For each Doppler speed obtained by dividing the range of upper and lower limits of the preset Doppler speed into a plurality of ranges, first to fourth symbol generating means for generating symbol waveforms Doppler modulated at the respective Doppler velocities for each of the two-bit data "00", "01", "10", and "11"; first to fourth cross-correlation calculation means for calculating the cross-correlation between the symbol waveforms generated by the first to fourth symbol generation means, respectively, and the received signal; 10. The sonar system of claim 1, further comprising:

4. The Doppler velocity estimation means For each Doppler speed obtained by dividing the range of upper and lower limits of the preset Doppler speed into a plurality of ranges, a maximum value detecting means for detecting a maximum value of the cross-correlation calculated by each of the first to fourth cross-correlation calculating means at predetermined time intervals; a peak detection means for detecting a peak of the maximum value of the cross-correlation; an average value calculation means for calculating an average value of the peaks of the cross-correlation maxima; A set of 4. The sonar device according to claim 3, further comprising means for estimating the Doppler velocity from the average value of the peaks of the maximum values ​​of the cross-correlation for a plurality of Doppler velocities obtained by dividing a predetermined range of upper and lower limits of the Doppler velocity into a plurality of ranges.

5. demodulation processing means for receiving the Doppler velocity estimation result estimated by the Doppler velocity estimation means; The demodulation processing means first to fourth symbol generating means for generating Doppler-modulated symbol waveforms for each of the two-bit data using the estimated Doppler velocities; first to fourth cross-correlation calculation means for respectively calculating cross-correlations between the received signal and the symbol waveforms generated by the first to fourth symbol generation means, respectively, based on the estimated Doppler velocity; the first to fourth maximum value detecting means for detecting the maximum value of the cross-correlation calculated by the first to fourth cross-correlation calculating means for each predetermined time; a detection means for detecting at least one of the center frequency and the sweep direction by comparing the maximum values ​​detected by the first to fourth maximum value detection means; 5. The sonar device according to claim 4, further comprising demodulation means for demodulating a digital signal based on detection by said detection means.

6. A sonar communication method, comprising: A transmission signal or a signal reflected from the transmission signal is received by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) in accordance with the bit code of the digital signal to be transmitted, A communication method comprising: generating a plurality of symbol waveforms each Doppler-modulated with a plurality of different Doppler velocities; performing cross-correlation processing between a received signal received by the receiving means and the plurality of symbol waveforms; and estimating the Doppler velocity based on the result of the cross-correlation processing.

7. a plurality of symbol generation processes are performed in parallel for each Doppler velocity, the plurality of processes being for generating symbol waveforms Doppler-modulated by the Doppler velocities corresponding to each combination of bit codes constituting a symbol, the plurality of Doppler velocities being obtained by dividing a range of upper and lower limits of a preset Doppler velocity; 7. The communication method according to claim 6, wherein a plurality of cross-correlation processes for calculating cross-correlations between the received signal and a plurality of the symbol waveforms generated by the plurality of symbol generating means, respectively, are performed in parallel for each of the Doppler velocities.

8. For each Doppler speed obtained by dividing the range of upper and lower limits of the preset Doppler speed into a plurality of ranges, first to fourth symbol generation processes for generating symbol waveforms Doppler modulated at the respective Doppler velocities for each of the two-bit data "00", "01", "10", and "11"; first to fourth cross-correlation calculation processes for calculating cross-correlations between the symbol waveforms generated in the first to fourth symbol generation processes, respectively, and the received signal; a process of detecting a maximum value of the cross-correlations calculated in each of the first to fourth cross-correlation calculation processes for each predetermined time period; detecting a peak of the maximum value of the cross-correlation; calculating an average value of the peaks of the cross-correlation maxima; a set of the above steps is executed for each Doppler speed obtained by dividing the range of upper and lower limits of the preset Doppler speed into a plurality of ranges, 8. The communication method according to claim 7, wherein the Doppler velocity is estimated from an average value of the peaks of the maximum values ​​of the cross-correlation for each of a plurality of Doppler velocities obtained by dividing the range of upper and lower limits of the preset Doppler velocity.

9. Based on the Doppler speed estimation result, first to fourth symbol generation processes for generating Doppler-modulated symbol waveforms for each of the two-bit data "00", "01", "10", and "11" based on the estimated Doppler velocity; first to fourth cross-correlation calculation processes for calculating cross-correlations between the symbol waveforms generated by the first to fourth symbol generation processes, respectively, based on the estimated Doppler velocity and the received signal; the first to fourth maximum value detection processes for detecting maximum values ​​of the cross-correlations calculated in the first to fourth cross-correlation calculation processes, respectively, for each predetermined time; a detection process for detecting at least one of the center frequency and the sweep direction by comparing the maximum values ​​in the first to fourth maximum value detection processes; The communication method according to claim 8 , further comprising the step of: executing a demodulation process for demodulating a digital signal based on the detection in the detection process.

10. A computer constituting a sonar device having a receiving means for receiving a transmitted signal or a signal reflected from the transmitted signal by switching at least one of the center frequency and sweep direction of LFM (linear frequency modulation) in accordance with the bit code of the digital signal to be transmitted, generating a plurality of symbol waveforms each Doppler modulated at a plurality of different Doppler velocities; a process of performing a cross-correlation process between the received signal received by the receiving means and the plurality of symbol waveforms, and estimating a Doppler velocity based on the result of the cross-correlation process; A program that executes the following.

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