JP2020068500A - Underwater communication system and underwater communication method - Google Patents

Abstract

To provide an underwater communication system capable of appropriately acquiring information based on an information signal from a received signal even if a problem occurs in the received signal due to interference, etc.SOLUTION: An underwater communication system 1 includes: a transmitter for transmitting a packet signal including a synchronization signal and an information signal into water as an ultrasonic signal; a receiver for receiving the ultrasonic signal; a synchronization signal detection unit 24 for detecting a synchronization signal from the received signal; a gate generation unit 25 for generating a gate of the information signal on the basis of a detection timing of the synchronization signal; a frequency estimation unit 27 for calculating an estimated frequency of the information signal in the gate; and a frequency correction unit 28 for correcting the estimated frequency of the information signal on the basis of a first detection timing of the synchronization signal and a second detection timing which is a detection timing prior to the first detection timing of the synchronization signal.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an underwater communication system and an underwater communication method for performing underwater communication in the sea, for example, transmitting and receiving information such as the depth of a fish net between a transmitter installed on a fish net and a receiver installed on a fishing boat. It is suitable for use in this case.

  Conventionally, an underwater communication system for underwater communication of predetermined information has been used in purse seine fishing or the like. For example, the transmitter installed on the fishnet sends information such as the depth of the fishnet, water temperature, and the distance to the seabed to the receiver installed on the fishing boat at any time, and this information is displayed on the receiver's display. Is displayed. The operator of the fishing boat can proceed with the fishing efficiently by referring to these information.

  The following Patent Document 1 describes an underwater communication system in which a synchronization signal, a reference signal and an information signal are transmitted as ultrasonic waves from a transmitter to a receiver as packet signals. In this underwater communication system, the synchronization signal is modulated so as to be distinguishable from the reference signal and the information signal. The reference signal is set to a sine wave signal with a known frequency. Further, the information signal is modulated according to transmission information indicating the depth of the fishnet, the water temperature, and the like.

  On the receiver side, the Doppler shift of the reference signal is detected based on the frequency of the received reference signal and the known frequency. Then, the frequency of the information signal is corrected based on the detected Doppler shift, and the transmission information is acquired based on the corrected frequency. Thereby, the influence of the Doppler effect based on the relative movement between the fishing boat and the fishnet is suppressed, and the transmission information can be accurately acquired at the receiver side.

Japanese Patent No. 4386282

  However, in the underwater communication system as described above, a signal from a fish finder, a scanning sonar, or the like installed on another ship may interfere with the received signal, and the received signal may not be properly acquired. In this case, for example, if interference occurs in the reference signal, the Doppler shift based on the reference signal cannot be properly detected. As a result, the receiver may not be able to properly acquire the transmission information based on the information signal, and the depth or the like may not be displayed.

  In view of such a problem, it is an object of the present invention to provide an underwater communication system that can appropriately acquire information based on an information signal from a received signal even if a problem occurs in the received signal due to interference or the like.

  A first aspect of the invention relates to an underwater communication system. The underwater communication system according to this aspect includes a transmitter that transmits a packet signal including a synchronization signal and an information signal into the water as an ultrasonic signal, a wave receiver that receives the ultrasonic signal, and the received wave. A synchronization signal detection unit that detects the synchronization signal from a signal, a gate generation unit that generates a gate for referring to the information signal based on the detection timing of the synchronization signal, and an estimation of the information signal in the gate Estimation of the information signal based on a frequency estimation unit that calculates a frequency, a first detection timing of the synchronization signal, and a second detection timing that is a detection timing earlier than the first detection timing of the synchronization signal. A frequency correction unit that corrects the frequency.

  Here, the frequency correction unit may be configured to correct the estimated frequency of the information signal based on the Doppler shift value calculated based on the first detection timing and the second detection timing, for example. The Doppler shift value can be acquired based on the difference between the predicted timing of the synchronization signal set based on the second detection timing and the transmission cycle of the packet signal and the first detection timing.

  A second aspect of the present invention relates to an underwater communication method. In the underwater communication method according to this aspect, a packet signal including a synchronization signal and an information signal is transmitted in water as an ultrasonic signal, the ultrasonic signal is received, and the synchronization signal is detected from the received signal. Then, based on the detection timing of the synchronization signal, to generate a gate for referring to the information signal, based on the information signal in the gate, to calculate the estimated frequency of the information signal, The estimated frequency of the information signal is corrected based on the first detection timing and the second detection timing which is the detection timing before the first detection timing of the synchronization signal.

  A third aspect of the invention relates to a receiver. A receiver according to this aspect includes a synchronization signal detection unit that detects the synchronization signal from a packet signal including a synchronization signal and an information signal received as an ultrasonic signal via a wave receiver, and the detection of the synchronization signal. A gate generation unit that generates a gate for referring to the information signal based on the timing, a frequency estimation unit that calculates an estimated frequency of the information signal in the gate, and a first detection timing of the synchronization signal, A frequency correction unit that corrects the estimated frequency of the information signal based on a second detection timing that is a detection timing earlier than the first detection timing of the synchronization signal.

  According to the above aspect, the estimated frequency of the information signal calculated by the frequency estimation unit is corrected based on the first detection timing and the second detection timing of the synchronization signal. Therefore, even if a defect occurs in the reference signal due to interference or the like, the information based on the information signal can be properly acquired.

  A fourth aspect of the invention relates to an underwater communication system. The underwater communication system according to this aspect transmits a packet signal, which includes a synchronization signal subjected to predetermined modulation, a reference signal of a known frequency, and an information signal modulated according to transmission information, as an ultrasonic signal in water. A transmitter, a synchronization signal detector that detects the synchronization signal from the packet signal received by the receiver, and based on the detection timing of the synchronization signal, for referring to the reference signal and the information signal A gate generation unit that generates a gate, a frequency estimation unit that calculates an estimated frequency of the reference signal and the information signal in each gate, and the information based on the estimated frequency of the reference signal and the known frequency. A frequency correction unit that corrects the estimated frequency of the signal. Here, the gate generation unit, when the synchronization signal is not detected, based on a past Doppler shift value calculated based on the estimated frequency of the past reference signal and the known frequency, the synchronization signal of the synchronization signal. Set the detection timing.

  According to this aspect, when the synchronization signal detection unit does not detect the synchronization signal from the packet signal, the synchronization signal detection timing is set based on the estimated frequency of the past reference signal and the known frequency. Therefore, even if a problem occurs in the synchronization signal due to interference or the like, the information based on the information signal can be properly acquired.

  As described above, according to the present invention, it is possible to provide an underwater communication system that can appropriately acquire information based on an information signal from a received signal even if a problem occurs in the received signal due to interference or the like.

  The effects and significance of the present invention will be more apparent from the description of the embodiments below. However, the embodiment described below is merely an example for embodying the present invention, and the present invention is not limited to what is described in the embodiment below.

FIG. 1A is a diagram showing a configuration of an underwater communication system according to the first embodiment. FIG. 1B is a diagram showing a format of a packet signal transmitted from the transmitter according to the first embodiment. FIG. 2 is a block diagram showing the configuration of the receiver according to the first embodiment. FIG. 3 is a timing chart schematically showing an example of a method of setting a gate and a detection range by a synchronization signal according to the first embodiment. FIG. 4A and FIG. 4B are flowcharts showing the basic flow of communication processing performed in the underwater communication system according to the first embodiment. FIG. 5A is a flowchart showing the processing flow of the gate generation processing according to the first embodiment. FIG. 5B is a flowchart showing a processing flow of frequency correction processing according to the first embodiment. FIG. 6A is a flowchart illustrating a process of determining whether the estimated frequency of the reference signal is appropriate, performed by the frequency estimation unit according to the first embodiment. FIG. 6B is a flowchart illustrating a process of determining whether the estimated frequency of the reference signal is appropriate, which is performed by the frequency correction unit according to the first embodiment. FIG. 7 is a timing chart schematically showing a deviation between the synchronization prediction timing and the synchronization detection timing caused by the Doppler shift according to the first embodiment. FIG. 8 is a diagram conceptually showing the format of the packet signal transmitted from the transmitter and the flow of noise component removal according to the second embodiment. 9 (a), 9 (b), 9 (c), and 9 (d) verify the state of the frequency spectrum when the noise removal processing in the frequency estimation unit according to the second embodiment is applied. It is the verification result. FIG. 10 is a flowchart showing a process of acquiring an estimated frequency from a frequency spectrum from which a noise component is removed according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiment shows an example in which the present invention is applied to an underwater communication system used for purse seine fishing or the like. However, the following embodiment is one embodiment of the present invention, and the present invention is not limited to the following embodiment.

<Embodiment 1>
FIG. 1A is a diagram showing the configuration of the underwater communication system 1.

  As shown in FIG. 1A, the underwater communication system 1 includes a transmitter 2, a wave receiver 3, and a receiver 4. The wave receiver 3 and the receiver 4 constitute a receiving device 5. The transmitter 2 is installed in a fish net, and the wave receiver 3 and the receiver 4 are installed in a fishing boat. The wave receiver 3 is installed, for example, at the bottom of the fishing boat, and the receiver 4 is installed inside the fishing boat. A plurality of transmitters 2 can be installed in one fish net. In this case, the wave receiver 3 is installed for each transmitter 2. The wave receiver 3 receives the ultrasonic signal transmitted from the transmitter 2, converts the received ultrasonic signal into an electric signal (hereinafter referred to as “received signal”), and supplies the electric signal to the receiver 4. The receiver 4 processes the received signal and displays information such as the depth of the fishnet on the display unit.

  The transmitter 2 includes a control unit 11, a water temperature gauge 12, a water pressure gauge 13, a wave transmitter / receiver 14, a wave transmitter 15, a voltage detection circuit 16, and a battery 17. The control unit 11 includes an arithmetic processing circuit such as a CPU (Central Processing Unit) and a memory, and controls each unit according to a program stored in the memory. The water thermometer 12 measures the temperature in the sea at the installation position of the transmitter 2. The water pressure gauge 13 measures the pressure in the sea at the installation position of the transmitter 2.

  The transmitter / receiver 14 transmits ultrasonic waves toward the seabed and receives echoes reflected on the seabed. By measuring the time from the transmission of ultrasonic waves to the reception of echoes, the distance from the fishnet to the seabed can be obtained. The wave transmitter 15 transmits information including the water temperature, the water pressure, the distance to the seabed, the voltage of the battery 17, and the like to the wave receiver 3 as an ultrasonic signal. The voltage detection circuit 16 detects the voltage of the battery 17. The battery 17 supplies power to each unit of the transmitter 2.

  FIG. 1B is a diagram showing a format of a packet signal transmitted from the transmitter 2.

  The packet signal having the format shown in FIG. 1B is generated by the control unit 11. The generated packet signal is transmitted underwater from the wave transmitter 15 as an ultrasonic signal. The packet signal includes a synchronization signal that is modulated in a predetermined manner, a reference signal of a known frequency, and an information signal that is modulated according to transmission information.

  In FIG. 1B, an example in which two information signals are included in one packet signal is shown for convenience, but the number of information signals included in one packet signal is not limited to this. . For example, one packet signal may include three or more information signals. The arrangement order of each signal in the packet signal is not limited to the example of FIG. For example, the information signal may be placed before the reference signal.

  The synchronization signal is a signal for synchronizing communication between the transmitter 2 and the receiver 4. The synchronization signal is, for example, a linear FM signal whose instantaneous frequency continuously changes. The modulation method of the synchronization signal is not limited to the linear FM, and can be appropriately changed as long as it can be distinguished from the reference signal and the information signal.

  The reference signal is a sine wave signal having a predetermined frequency. The information signal is a sine wave signal having a frequency corresponding to the value of the information such as water temperature and water pressure (hereinafter, referred to as “transmission information”). That is, the information signal is a signal that is frequency-modulated with the transmission information. The frequency of the information signal is fixed to the frequency corresponding to the value of the transmission information. The packet signal is transmitted underwater from the wave transmitter 15 at a constant cycle.

  FIG. 2 is a block diagram showing the configuration of the receiver 4.

  Note that FIG. 2 shows the configuration of the circuit system of the receiver 4 as functional blocks. These functional blocks can be realized by a signal processing circuit (processor) that executes processing according to a program. For example, in the configuration shown in FIG. 2, the functions of the respective units other than the frequency conversion unit 21 and the display unit 30 can be realized by the processing of the signal processing circuit (processor) 100. The signal processing circuit 100 does not necessarily have to be one piece of hardware, and may be composed of a plurality of pieces of hardware.

  The frequency converter 21 converts the center frequency of the reception signal input from the wave receiver 3 into a predetermined intermediate frequency. The frequency converter 21 also removes noise components superimposed on the received signal and amplifies the received signal. As described above, when a plurality of sets of transmitters 2 and receivers 3 are used and the center frequencies of the ultrasonic signals are different from each other, in order to standardize the signal processing in the receiver 4, Frequency conversion is performed in the frequency conversion unit 21. Therefore, if it is not necessary to consider this point, the received signal itself may be sampled without performing frequency conversion. In this case, the frequency converter 21 is omitted.

  The A / D converter 22 samples the received signal input from the frequency conversion unit 21 at a constant sampling rate and converts it into a digital signal.

  The quadrature detection unit 23 generates a complex envelope sequence of the received signal from the digital signal output from the A / D converter 22, and sets a sampling rate (data rate) of the generated complex envelope sequence at a predetermined rate (decimation). Ratio) and output. Here, the real part of the output complex envelope sequence is represented by I [n], and the imaginary part is represented by Q [n].

  The quadrature detection unit 23 includes a real part code conversion unit 231, an imaginary part code conversion unit 232, and thinning filters 233 and 234. The real part code conversion unit 231 generates the real part of the complex envelope sequence, and the imaginary part code conversion unit 232 generates the imaginary part of the complex envelope sequence. The decimation filters 233 and 234 perform the operations of the low-pass filter and the re-sampling (decimation) on the output sequences of the real part code conversion unit 231 and the imaginary part code conversion unit 232. This reduces the sampling rate of each output sequence. Since the sampling rate is reduced in this way, the load of subsequent signal processing is reduced.

  Note that the more detailed processing of the quadrature detection unit 23 is the same as the processing described in Patent Document 1, for example, and thus the description thereof is omitted here. As a detailed description of the quadrature detection unit 23, the description of Patent Document 1 can be incorporated by reference.

  The synchronization signal detector 24 detects a synchronization signal from the complex envelope series I [n], Q [n] input from the quadrature detector 23. The synchronization signal detecting section 24 includes a matched filter section 241, a buffer memory 242, and a maximum value detecting section 243.

  The matched filter unit 241 includes a real part sequence generation unit 241a, an imaginary part sequence generation unit 241b, and an absolute value calculation unit 241c. The real part sequence generation unit 241a and the imaginary part sequence generation unit 241b form a complex matched filter. The real part sequence generation unit 241a generates the real part sequence Imf [n] of the output of the complex matched filter, and the imaginary part sequence generation unit 241b generates the imaginary part sequence Qmf [n] of the output of the complex matched filter. The absolute value calculation unit 241c generates an absolute value series D [n] from the real part series Imf [n] and the imaginary part series Qmf [n].

  Specifically, the matched filter unit 241 performs the complex matched filter processing corresponding to the above-mentioned synchronization signal on the complex envelope series I [n] and Q [n] input from the quadrature detection unit 23, The absolute value series D [n] is output as the processing result. The filter length of the matched filter is determined so as to be equal to the data number of the complex envelope series I [n] and Q [n] related to the synchronization signal. The matched filter unit 241 uses the filter coefficients for the real part and the imaginary part supplied from the filter coefficient calculation unit 26, which will be described later, to perform correlation processing between the waveform of the received signal and the expected waveform of the synchronization signal, and An absolute value series D [n] indicating the correlation degree of the waveform is output. These filter coefficients are set so that the value of the absolute value series D [n] becomes maximum when all the complex envelope series I [n] and Q [n] related to the synchronization signal are aligned in the matched filter. It is set.

  The more detailed processing of the matched filter unit 241 is the same as the processing described in Patent Document 1, for example, and thus the description thereof is omitted here. As a detailed description of the matched filter unit 241, the description of Patent Document 1 can be incorporated by reference.

  The buffer memory 242 temporarily stores a part of the absolute value series D [n]. Specifically, the buffer memory 242 temporarily stores the absolute value series D [n] for a range of a predetermined time width (hereinafter, referred to as “detection range”) that may include the synchronization signal. The detection range is set by the gate generation unit 25 based on the detection timing of the synchronization signal detected in the packet signal one cycle before, as described later.

  The maximum value detection unit 243 extracts the maximum value of the absolute value series D [n] within the detection range stored in the buffer memory 242, and corresponds to this maximum value when the extracted maximum value is a predetermined value or more. The timing (hereinafter, referred to as “synchronization signal detection timing”) is output to the gate generation unit 25. The sync signal detection timing is a timing corresponding to the boundary between the sync signal and the reference signal due to the characteristics of the matched filter unit 241 described above. The synchronization signal detection timing is held in the memory in the gate generation unit 25 and further output to the frequency correction unit 28. When the absolute value series D [n] satisfying the above conditions does not exist, the maximum value detection unit 243 outputs a signal to that effect to the gate generation unit 25 instead of the synchronization signal detection timing.

  The gate generation unit 25 calculates the start timing and the end timing of the gate of the reference signal and the gate of the information signal with reference to the synchronization signal detection timing, and outputs each calculated timing to the frequency estimation unit 27. The gate generation unit 25 also calculates a timing (hereinafter, referred to as “synchronization signal prediction timing”) in which the packet period is added to the synchronization signal detection timing, and outputs the calculated synchronization signal prediction timing to the frequency correction unit 28. Further, the gate generation unit 25 sets the same time width in each of the time returning direction and the time advancing direction around the calculated synchronization signal prediction timing, calculates the above-described detection range, and calculates the calculated detection range. Output to the buffer memory 242.

  FIG. 3 is a diagram schematically showing an example of a method of setting a gate and a detection range by a synchronization signal.

  In the example of FIG. 3, the timing when the time T1 has elapsed from the synchronization signal detection timing td1 is set to the gate start timing ts1 set in the reference signal, and the timing when the time ΔT1 has elapsed from the start timing ts1 is It is set at the end timing te1 of the gate. Further, the timing when the time T2 has elapsed from the start timing ts1 is set to the start timing ts2 of the gate set in the first information signal, and the timing when the time ΔT1 has elapsed from the start timing ts2 is the timing of this gate. The end timing te2 is set. Further, the timing when the time T3 has elapsed from the start timing ts2 is set to the gate start timing ts3 set in the second information signal, and the timing when the time ΔT1 has elapsed from the start timing ts3 is the timing of this gate. The end timing te3 is set.

  Thus, the gate of the reference signal is set to the latter half of the reference signal, and the gate of the information signal is set to the latter half of the information signal. By setting the gate of the reference signal in this manner, it is possible to prevent the synchronization signal that has arrived after being reflected on the sea floor or the sea surface from being mixed in the gate of the reference signal. Similarly, by setting the gate of the information signal as described above, it is possible to prevent the reference signal arriving after being reflected on the sea floor or the sea surface from being mixed in the gate of the first information signal. The same applies to the second information signal.

  The timing at which the transmission period Tp of the packet signal has elapsed from the synchronization signal detection timing td1 is set as the synchronization signal prediction timing tp1 in the next packet signal. Then, the timings at which the same time width ΔT11 is set in the time return and time advance directions centering on the synchronization signal prediction timing tp1 are set as the detection range start timing ts11 and end timing te11. The time width ΔT11 is set to a time width in which the synchronization signal can be detected even if the possible Doppler shift occurs.

  Returning to FIG. 2, the frequency estimation unit 27 performs a DFT (discrete Fourier transform) on the complex envelope series I [n] and Q [n] in the gate of the reference signal and the information signal input from the gate generation unit 25. ) And spectrum interpolation (complementary processing), the estimated frequencies of the reference signal and the information signal are calculated. The estimated frequency calculated here is the frequency at which the Doppler shift has occurred, that is, the reception frequency. The frequency estimation unit 27 outputs the estimated values of the frequencies of the reference signal and the information signal to the frequency correction unit 28. Further, the frequency estimation unit 27 outputs the estimated value of the frequency of the reference signal to the gate generation unit 25.

  Note that the more detailed processing of the frequency estimation unit 27 is the same as the processing described in Patent Document 1, for example, and thus the description thereof is omitted here. As a detailed description of the frequency estimation unit 27, the description of Patent Document 1 can be incorporated by reference.

  The frequency correction unit 28 estimates the information signal calculated by the frequency estimation unit 27, based on the known frequency of the reference signal and the estimated frequency of the reference signal (frequency estimation value) calculated by the frequency estimation unit 27. Correct the frequency (estimated value of frequency). Here, the estimated frequency after correction of the information signal is fic, the known frequency of the reference signal is fp, the estimated frequency of the reference signal calculated by the frequency estimation unit 27 is fpe, and the estimated frequency of the information signal calculated by the frequency estimation unit 27 is Assuming that the estimated frequency is fie, the corrected estimated frequency fic is calculated by the following equation.

    fic = pie · fp / fpe (1)

  The estimated frequency fic calculated by the equation (1) is the frequency of the information signal from which the Doppler shift has been removed, and ideally becomes equal to the frequency when the information signal is transmitted.

  Here, the corrected estimated frequency fic is obtained directly from the frequencies fp, fpe, and fie, but the known frequency fp of the reference signal and the estimated frequency fpe of the reference signal calculated by the frequency estimation unit 27 are used. The estimated frequency Fie of the information signal may be corrected based on the Doppler shift value of the estimated frequency of the reference signal, and the estimated Doppler shift value of the information signal based on the obtained Doppler shift value.

  The numerical conversion unit 29 converts the corrected estimated frequency of the information signal into a value of transmission information. The converted value is output to the display unit 30. The display unit 30 displays the value of the received transmission information (water pressure, water temperature, etc.). For example, the fishnet depth converted from the water pressure is displayed on the display unit 30.

  The filter coefficient calculation unit 26 calculates the filter coefficient of the real part and the imaginary part of the above-described matched filter based on the known frequency of the reference signal and the estimated frequency of the reference signal calculated by the frequency estimation unit 27. The filter coefficient calculation unit 26 holds the calculated filter count in the memory and supplies it to the matched filter unit 241.

  Note that the more detailed processing of the filter coefficient calculation unit 26 is the same as the processing described in Patent Document 1, for example, and thus the description thereof is omitted here. As a detailed description of the filter coefficient calculation unit 26, the description of Patent Document 1 can be incorporated by reference.

  4A and 4B are flowcharts showing a basic flow of communication processing performed in the underwater communication system 1. The process of FIG. 4A is performed in the transmitter 2, and the process of FIG. 4B is performed in the receiver 3 and the receiver 4.

  First, referring to FIG. 4A, the control unit 11 of the transmitter 2 controls the water temperature gauge 12, the water pressure gauge 13, and the wave transmitter / receiver 14 to detect the water temperature, the water pressure, and the distance to the seabed ( S1A). The control unit 11 generates transmission information based on the detection result (S2A), and transmits a packet signal including an information signal corresponding to the generated transmission information into the water as an ultrasonic signal (S3A). As described above, the packet signal includes the sync signal and the reference signal. The control unit 11 repeatedly executes the processing of S1A to S3A at a constant cycle (transmission cycle Tp).

  With reference to FIG. 4B, the receiver 4 receives the ultrasonic signal transmitted from the transmitter 2 via the receiver 3 (S1B). In response to this, the synchronization signal detector 24 of the receiver 4 detects the synchronization signal from the reception signal as described above (S2B). Further, the gate generation unit 25 of the receiver 4 generates the gates of the reference signal and the information signal based on the detection result of the synchronization signal (synchronization signal detection timing) as described above, and further predicts the next synchronization signal. The timing (synchronization signal prediction timing) and the detection range are set (S3B).

  Then, the frequency estimation unit 27 of the receiver 4 estimates the frequencies of the reference signal and the information signal in the gate (S4B), and the frequency correction unit 28 further estimates the information signal based on the estimated frequency of the reference signal. The frequency is corrected (S5B). Subsequently, the numerical conversion unit 29 of the receiver 4 converts the estimated frequency of the information signal into a numerical value, and displays the converted numerical value on the display unit 30 (S6B). The receiver 4 repeatedly executes the processes of S1B to S6B according to the reception of the received signal.

  By the way, in the underwater communication system 1, a signal from a fish finder, a scanning sonar, or the like installed on another ship may interfere with a received signal. As a result, the synchronization signal or the reference signal may not be properly acquired. In this case, the Doppler shift detection based on the reference signal cannot be properly performed, or the gate setting based on the synchronization signal cannot be properly performed. As a result, the transmission information based on the information signal cannot be properly acquired on the receiver 4 side, and erroneous display of the depth and the like, missing of the display, and the like may occur.

  Therefore, in the present embodiment, a configuration is provided for appropriately acquiring the transmission information of the information signal even when a problem occurs in the synchronization signal or the reference signal due to interference or the like. The configuration will be described below.

  First, a configuration for complementing the detection timing of the synchronization signal (synchronization signal detection timing) when a failure occurs in the synchronization signal in the received signal will be described. This structure is provided in the gate generation unit 25.

  FIG. 5A is a flowchart showing the processing flow of the gate generation processing performed in step S3B of FIG. 4B.

  When the gate generation unit 25 acquires the detection result of the synchronization signal from the synchronization signal detection unit 24 (maximum value detection unit 243) (S11), it determines whether or not the synchronization detection is properly performed based on the synchronization detection result. (S12).

  As described above, the maximum value detection unit 243 extracts the maximum value of the absolute value series D [n] within the detection range stored in the buffer memory 242, and when the extracted maximum value is equal to or larger than the predetermined value, the maximum value is detected. The synchronization signal detection timing, which is the timing corresponding to the value, is output to the gate generation unit 25 as the synchronization detection result, and if this condition is not satisfied, a signal indicating that is output as the synchronization detection result to the gate generation unit 25. Output to.

  When the synchronization signal detection timing is acquired as the synchronization detection result (S12: YES), the gate generation unit 25 sets the synchronization signal detection timing acquired as the synchronization detection result as the synchronization signal detection timing as it is (S13). On the other hand, when the synchronization signal detection timing is not acquired as the synchronization detection result (S12: NO), the gate generation unit 25 complements the synchronization detection timing from the past Doppler shift value (S14).

  As described above, the gate generation unit 25 constantly acquires the estimated frequency of the reference signal from the frequency estimation unit 27. Each time the gate generation unit 25 acquires the estimated frequency of the reference signal, the gate generation unit 25 calculates the Doppler shift value of the reference signal based on the estimated frequency and the known frequency of the reference signal, and holds the calculated Doppler shift value in the memory. To do.

  In step S14, the gate generation unit 25 calculates the synchronization prediction timing obtained by adding the cycle Tp of the packet signal to the previously set synchronization detection timing, that is, the synchronization prediction timing for this synchronization signal for the previous reference signal. The synchronization detection timing is corrected by the Doppler shift value, and the obtained synchronization detection timing is set as the synchronization detection timing for the current synchronization signal.

  Here, a method of calculating the synchronization detection timing based on the synchronization prediction timing and the Doppler shift value will be described.

  For example, the transmission frequency of the transmitter 2 is f (Hz), the reception frequency of the receiver 3 is f '(Hz), the moving speed of the transmitter 2 is vs (m / s), and the moving speed of the receiver 3 is Let v0 (m / s) and the speed of sound in water be V (m / s), the following relational expression holds.

  Here, if the moving speed vs of the transmitter 2 is zero and the moving speed v0 of the wave receiver 3 is treated as the relative speed v of the transmitter 2 and the wave receiver 3, the Doppler shift value Δf (Hz) is as follows. It is calculated by the formula.

  Further, assuming that the transmission cycle of the packet signal is Tp, the sampling cycle of the reception signal is ts, and the deviation of the synchronization detection timing from the synchronization signal prediction timing is n, the above equation (3) is transformed into the following equation.

  Here, the sampling period ts is the sampling period of the received signal after being thinned out by the thinning filters 233 and 234 shown in FIG. The deviation n defines the deviation of the synchronization detection timing from the synchronization signal prediction timing according to the number of sample timings in this sampling cycle.

  In the above formula (4), the frequency f is known as the transmission frequency of the reference signal, and the sampling period ts and the transmission period Tp of the packet signal are also known as the operating conditions of the device. Therefore, if the Doppler shift value Δf (difference between the estimated frequency fic after correction and the estimated frequency fie before correction) is obtained using the above equation (1) based on the estimated frequency of the reference signal, this is given by equation (4) The deviation n can be calculated by substituting into

  In step S14 of FIG. 5A, the gate generation unit 25 applies the Doppler shift value one packet before to the equation (4) to obtain the deviation n, and the obtained deviation n is the synchronization signal prediction of the current synchronization signal. The synchronization signal detection timing of the current synchronization signal is acquired by adding to the timing. In this way, the synchronization signal detection timing is complemented.

  After setting the synchronization detection timing in any of steps S13 and S14, the gate generation unit 25 calculates the synchronization prediction timing of the next synchronization signal based on the set synchronization detection timing, and further detects the next synchronization signal. Set the range. The synchronization prediction timing of the next synchronization signal is obtained by adding the transmission cycle Tp of the packet signal to the synchronization detection timing. The detection range is obtained by adding and subtracting the time width ΔT11 to the synchronization prediction timing, as shown in FIG. The gate generation unit 25 holds the obtained synchronization prediction timing and detection range in the memory. Further, the gate generation unit 25 and the synchronization prediction timing are output to the frequency estimation unit 27, and the detection range is output to the buffer memory 242.

  Further, the gate generation unit 25 sets the gate of the reference signal and the gate of the information signal based on the synchronization detection timing set in any of steps S13 and S14 (S16). In this way, the processing according to the synchronization detection result ends. The gate generation unit 25 repeatedly executes the same processing each time the synchronization detection result is acquired in step S11.

  In the process of FIG. 5A, the calculation of the Doppler shift value based on the equation (4) is performed by the gate generation unit 25, but the calculation of the Doppler shift value may be performed by the frequency correction unit 28. In this case, the frequency correction unit 28 outputs the calculated Doppler shift value to the gate generation unit 25 at any time, and the gate generation unit 25 holds the input Doppler shift value in the memory. The gate generation unit 25 calculates and complements the synchronization detection timing by using the Doppler shift value one packet before stored in the memory and performing the same process as in step S14.

  Next, a configuration for complementing the Doppler shift value of the received signal when a defect occurs in the reference signal in the received signal will be described. This configuration is provided in the frequency correction unit 28.

  FIG. 5B is a flowchart showing the processing flow of the frequency correction processing performed in step S5B of FIG. 4B.

  When the frequency correction unit 28 acquires the estimation result of the frequency of the reference signal from the frequency estimation unit 27 (S21), the frequency correction unit 28 determines the appropriateness of the estimation based on the estimation result (S22). In the present embodiment, the frequency estimation unit 27 determines whether or not the frequency of the reference signal has been properly estimated. When the frequency of the reference signal can be properly estimated, the frequency estimation unit 27 outputs the estimated frequency of the reference signal to the frequency correction unit 28 as the estimation result. On the other hand, when the frequency of the reference signal cannot be properly estimated, the frequency estimation unit 27 outputs a signal indicating that to the frequency correction unit 28 as an estimation result.

  FIG. 6A is a flowchart showing the processing performed by the frequency estimation unit 27 to determine the suitability of the estimated frequency of the reference signal.

  The frequency estimation unit 27 determines that the estimated frequency of the reference signal is within the normal range (S31), that the amount of change of the estimated frequency of this time with respect to the estimated frequency of the previous time is less than the threshold value (S32), and that the S / On the condition that N is less than the threshold value (S33), it is determined whether or not the estimated frequency of the reference signal is appropriate. When all the steps S31 to S33 are YES, the frequency estimation unit 27 determines that the frequency estimation is appropriate and outputs the estimated frequency of the reference signal to the frequency correction unit 28 (S34). On the other hand, if at least one of steps S31 to S33 is NO, the frequency estimation unit 27 determines that the frequency estimation is improper and outputs a signal to that effect to the frequency correction unit 28 (S35).

  Returning to FIG. 5B, when the estimated frequency of the reference signal is acquired as the estimation result of the reference signal (S22: YES), the frequency correction unit 28 compares the acquired estimation result of the reference signal with the known frequency of the reference signal. Based on the above, the Doppler shift value of the reference signal is calculated using the above equation (1) (S23). On the other hand, when the estimated frequency of the reference signal is not acquired as the estimation result of the reference signal (S22: NO), the frequency correction unit 28 complements the Doppler shift value based on the synchronization detection timing (S24).

  Specifically, in step S24, the frequency correction unit 28 obtains the deviation n between the synchronization signal prediction timing and the synchronization signal detection timing acquired from the gate generation unit 25, and applies the obtained deviation n to the above equation (4). Then, the Doppler shift value Δf of the reference signal is calculated.

  The upper part of FIG. 7 shows the state of the received signal when there is no influence of the Doppler shift, and the middle and lower parts of FIG. 7 show the state of the received signal when there is the influence of the Doppler shift. For the sake of convenience, the synchronization signal detection timing td1 'one packet before is aligned in the upper stage, the middle stage, and the lower stage.

  In the example in the middle part of FIG. 7, since the received signal is contracted in the time axis direction due to the influence of Doppler shift, the synchronization signal detection timing td1 is advanced with respect to the synchronization signal prediction timing tp1. In this case, the deviation n has a negative value. On the other hand, in the example in the lower part of FIG. 7, since the received signal extends in the time axis direction due to the influence of Doppler shift, the synchronization signal detection timing td1 is delayed with respect to the synchronization signal prediction timing tp1. In this case, the deviation n has a positive value. The frequency correction unit 28 applies the deviation n thus obtained to the above equation (4) to calculate the Doppler shift value Δf of the reference signal.

  After setting the Doppler shift value in any of steps S23 and S24, the frequency correction unit 28 corrects the estimated frequency of the information signal based on the set Doppler shift value. This suppresses the influence of Doppler shift on the estimated frequency of the information signal. Thus, the process of correcting the estimated frequency of the information signal ends. The frequency correction unit 28 repeatedly executes the same processing each time the estimation result of the frequency of the reference signal is acquired in step S21.

  In the processing of FIG. 5B, the Doppler shift value is calculated by the frequency correction unit 28 based on the equation (4), but the Doppler shift value may be calculated by the gate generation unit 25. In this case, the gate generation unit 25 outputs the calculated Doppler shift value to the frequency correction unit 28 at any time, and the frequency correction unit 28 uses the input Doppler shift value to complement the Doppler shift value in step S24. To do.

  Further, in the determination of step S22 of FIG. 5B, the determination process of FIG. 6B may be added. The determination process of FIG. 6B is performed when the frequency estimation unit 27 outputs the estimated value of the frequency of the reference signal to the frequency correction unit 28, that is, the frequency estimation unit 27 properly estimates the frequency of the reference signal. If it is determined, it is additionally performed.

  In FIG. 6B, the frequency correction unit 28 acquires the Doppler shift value DS1 of the reference signal based on the estimated frequency of the reference signal input from the frequency estimation unit 27 and the known frequency (S41). This process is similar to step S23 in FIG. 5 (b). Next, the frequency correction unit 28 acquires the Doppler shift value DS2 based on the synchronization signal detection timing and the synchronization signal prediction timing input from the gate generation unit 25 (S42). This process is the same as step S24 in FIG. The order of steps S41 and S42 may be reversed.

  Then, the frequency correction unit 28 determines whether the absolute value of the difference between the Doppler shift values DS1 and DS2 exceeds the threshold value (S43). When the absolute value of the difference exceeds the threshold value (S43: YES), the frequency correction unit 28 determines that the estimated frequency of the reference signal is incorrect (S44). In this case, the determination in step S22 of FIG. 5B is NO. On the other hand, when the absolute value of the difference does not exceed the threshold value (S43: NO), the frequency correction unit 28 determines that the estimated frequency of the reference signal is appropriate. In this case, the determination in step S22 of FIG. 5B is YES.

  By performing the determination of FIG. 6B, for example, even when the estimated frequency of the reference signal is within the normal range in the process of FIG. 6A, the deviation between the Doppler shift values DS1 and DS2 is obtained. Is large, it is determined that the estimated frequency of the reference signal is not appropriate, and the frequency of the information signal is corrected using the Doppler shift value based on the synchronization detection timing. As a result, the transmission information corresponding to the information signal can be acquired more accurately.

  Note that the determination process of FIG. 6B may be performed instead of the determination process of FIG. 6A, and the determination process of any one of steps S31 to S33 of FIG. The determination processing of) may be combined.

<Effect of Embodiment>
According to this embodiment, the following effects can be achieved.

  As described with reference to FIG. 5B, the estimated frequency of the information signal calculated by the frequency estimation unit 27 is corrected based on the synchronization signal detection timing and the past synchronization signal detection timing. Specifically, as shown in steps S24 and S25 of FIG. 5B, the sync signal detection timing detected by the sync signal detection unit 24 and the past (in this embodiment, one packet before) sync signal detection. The estimated frequency of the information signal calculated by the frequency estimation unit 27 is corrected based on the Doppler shift value calculated based on the timing. Here, the Doppler shift value is the synchronization signal prediction timing set based on the past synchronization signal detection timing (one packet before) and the packet signal transmission cycle Tp, and the synchronization signal detected by the synchronization signal detection unit 24. It is obtained by the above equation (4) based on the difference from the signal detection timing. Therefore, even if a defect occurs in the reference signal due to interference or the like, it is possible to properly acquire the transmission information based on the information signal.

  As illustrated in FIG. 5B, when the frequency correction unit 28 cannot correct the estimated frequency of the information signal based on the estimated frequency of the reference signal calculated by the frequency estimation unit 27 and the known frequency (S22). : NO), the estimated frequency of the information signal is corrected based on the Doppler shift value (S24) complemented by the synchronization signal detection timing (S24). This makes it possible to correct the estimated frequency of the information signal using the Doppler shift value complemented by the synchronization signal detection timing while effectively utilizing the correction process of the estimated frequency of the information signal based on the estimated frequency of the reference signal. it can.

  In this embodiment, since the estimated frequency of the information signal can be corrected by the synchronization signal detection timing, the reference signal is not always necessary from the viewpoint of correcting the estimated frequency of the information signal. Therefore, from this viewpoint, the reference signal may be omitted from the packet signal. However, in the present embodiment, as shown in FIG. 5A, when the sync signal cannot be detected from the received signal, the sync signal detection timing is set by the Doppler shift value based on the reference signal. Therefore, from this viewpoint, it is necessary that the packet signal includes the reference signal. In the present embodiment, the reference signal and the synchronization signal work in a complementary manner to each other, so that the transmission information according to the information signal can be accurately acquired even if a problem occurs in one of them due to interference or the like. To be done.

  As shown in FIG. 6B, the frequency correction unit 28 acquires the Doppler shift value DS1 based on the estimated frequency of the reference signal calculated by the frequency estimation unit 27 and the known frequency (S41), Based on the difference between the Doppler shift value DS1 and the Doppler shift value DS2 (S42) acquired at the synchronization signal detection timing, the propriety of the estimated frequency of the reference signal is determined (S43, S44). Then, when the estimated frequency of the reference signal is not appropriate, the frequency correction unit 28 estimates the information signal based on the Doppler shift value complemented from the synchronization signal detection timing in steps S24 and S25 of FIG. 5B. Correct the frequency. This prevents the estimated frequency of the information signal from being corrected based on the incorrect estimated frequency of the reference signal. Therefore, the transmission information according to the information signal can be acquired more accurately.

  As shown in FIG. 5A, when the synchronization signal detection unit 24 does not detect the synchronization signal (S12: NO), the gate generation unit 25 estimates the past reference signal calculated by the frequency estimation unit 27. The synchronization signal detection timing is set based on the past Doppler shift value calculated based on the frequency and the known frequency (S14). Specifically, the gate generation unit 25 sets the sync signal detection timing by applying a time shift based on the past Doppler shift value to the sync signal prediction timing set based on the transmission cycle of the packet signal. . As a result, the gates of the reference signal and the information signal can be set even when the synchronization signal is not detected due to interference with other signals (S16). Therefore, the communication information corresponding to the information signal can be properly displayed without interruption.

  Here, when the synchronization signal is not detected by the synchronization signal detection unit 24, the gate generation unit 25 synchronizes the synchronization signal detection range with respect to the reception signal based on the synchronization signal detection timing set from the past Doppler shift value. The signal detection unit 24 (buffer memory 242) is set (S15). As a result, the next sync signal can be smoothly detected, and the gate setting process based on the sync signal detection timing can be smoothly advanced. Therefore, the communication information corresponding to the information signal can be properly displayed without interruption.

  The Doppler shift value of the reference signal can also be predicted from the change tendency of the estimated frequency of the reference signal in the past and the change tendency of the past Doppler shift value based on these estimated frequencies. Therefore, the frequency correction unit 28 may further execute the process of acquiring the current Doppler shift value based on the past reference signal estimated frequency or the past Doppler shift value based on the past reference signal estimated frequency. Then, even if the Doppler shift value cannot be acquired by this processing, the frequency correction unit 28 is configured to correct the estimated frequency of the information signal based on the Doppler shift value acquired at the synchronization signal detection timing. Good.

  For example, immediately after the processing based on the received signal is started, the estimated frequency of the past reference signal and the past Doppler shift value do not exist, so the current Doppler shift value cannot be acquired based on these. Therefore, in the period from when the process based on the received signal is started until the Doppler shift value can be acquired by the process based on the past reference signal, based on the Doppler shift value calculated by the synchronization signal detection timing, the information signal The frequency correction unit 28 may be configured to correct the frequency of.

<Example of change>
In the equation (4) of the Doppler shift value shown in the above embodiment, the change (acceleration) in the relative velocity between the transmitter 2 and the wave receiver 3 is not taken into consideration. Further, the Doppler shift value may be calculated in consideration of this acceleration.

  In this case, assuming that the Doppler shift value is Δfa and the acceleration is a, the equation (4) is modified as follows.

  Here, the acceleration a can be obtained from, for example, the relative velocity obtained from the Doppler shift value obtained from the frequency of the reference signal, and the change tendency of the obtained relative velocity.

  By using equation (5), a more accurate Doppler shift value can be obtained. In this case, the threshold value in step S43 of FIG. 6A may be modified to a value according to equation (5).

  Further, in the above embodiment, the Doppler shift value is calculated by the frequency correction unit 28 in steps S23 and S24 of FIG. 5B, but the Doppler shift value is not necessarily calculated in the correction of the estimated frequency of the information signal. You don't have to. For example, the correction value for correcting the estimated frequency of the information signal may be directly calculated based on the synchronization signal detection timing and the synchronization signal prediction timing, or the synchronization signal detection timing and the synchronization signal prediction timing may be calculated. Based on this, the estimated frequency of the corrected information signal may be directly calculated. In this case, the calculation process of the Doppler shift value is merged with these calculation formulas.

<Embodiment 2>
In the second embodiment, the frequency estimation unit 27 further removes noise components superimposed on the reference signal and the information signal due to interference of other signals.

  FIG. 8 is a diagram conceptually showing the configuration of the packet signal according to the second embodiment and the flow of noise component removal.

  As shown in FIG. 8, in the second embodiment, the packet signal includes a pause section RT in which there is no signal. The gate generator 25 further sets a gate for the rest period RT. The frequency estimation unit 27 acquires the frequency spectrum of the gate set in the rest period RT. Since there is no signal in the pause section RT, the frequency spectrum obtained from the pause section RT is a frequency spectrum of noise due to an interference wave or the like (hereinafter referred to as “noise spectrum”). The noise spectrum is a frequency spectrum before the interpolation processing is performed by the frequency estimation unit 27.

  The frequency estimation unit 27 compares the noise spectra of one to three cycles before for each spectrum element, acquires the maximum value in each spectrum element, combines the acquired maximum values for each spectrum element, and combines the frequency spectrum of the noise component. (Hereinafter referred to as “removed spectrum”). Then, the frequency estimation unit 27 subtracts the level of the removal spectrum for each spectrum element from the frequency spectrum of the reference signal and the information signal acquired from the current packet signal (frequency spectrum before interpolation processing). As a result, noise components are removed from the frequency spectra of the reference signal and the information signal. After that, the frequency estimation unit 27 acquires the estimated frequencies of the reference signal and the information signal based on the frequency spectra of the reference signal and the information signal after noise removal.

  9A to 9D are verification results for verifying the state of the frequency spectrum when the noise removal processing in the frequency estimation unit 27 is applied. In FIGS. 9A to 9D, the horizontal axis represents the spectrum element and the vertical axis represents the level of each spectrum element. The horizontal axis is standardized to 256 gradations.

  Here, the interference signal of the frequency spectrum shown in FIG. 9B is superimposed on the waveform of the original signal of the frequency spectrum shown in FIG. 9A to generate a superimposed signal. By applying DFT to this superimposed signal, the frequency spectrum of FIG. 9C was obtained. Further, the frequency spectrum of FIG. 9B is used as a removal spectrum, and the subtraction process is performed on the frequency spectrum of the superimposed signal of FIG. 9C for each spectrum element. As a result, the frequency spectrum of FIG. 9D was obtained.

  In the frequency spectrum of FIG. 9C, the frequency spectrum of the interference wave is mixed in addition to the spectrum element of the original signal, and the level of the spectrum element other than the spectrum element of the original signal is maximum. Therefore, the frequency of the original signal cannot be properly detected from this frequency spectrum. On the other hand, in the frequency spectrum after subtraction of the removal spectrum, the frequency spectrum of the interference wave disappears and a peak appears in the same spectrum element as the frequency spectrum of the original signal, as shown in FIG. 9D. Therefore, the frequency of the original signal can be accurately detected by performing the subtraction process using the removal spectrum. That is, it was confirmed that the estimated frequencies of the reference signal and the information signal can be accurately acquired by performing the subtraction process using the removal spectrum.

  FIG. 10 is a flowchart showing the process of acquiring the estimated frequency from the frequency spectrum from which the noise component has been removed. This process is performed in step S4B of FIG.

  When the frequency estimation unit 27 acquires the frequency spectrum (frequency spectrum before interpolation processing) from the reference signal or the information signal (S51), it acquires from the memory the noise spectrum acquired from the pause section RT one to three packets before (S52). ). Next, the frequency estimation unit 27 detects the maximum value for each spectrum element from the acquired three noise spectra, and sets the removal spectrum by combining the detected maximum values (S53).

  Further, the frequency estimation unit 27 subtracts the removal spectrum for each spectrum element from the frequency spectrum from the reference signal or the information signal acquired in step S11 (S54). Then, the frequency estimation unit 27 performs complement processing on the frequency spectrum after the subtraction to obtain the estimated frequency of the reference signal or the information signal (S55).

  In step S55, first, the spectral element having the maximum level is detected in the frequency spectrum after the removal spectrum is subtracted. Next, in the frequency band in the vicinity of the detected spectral element, the complementing process is performed using the frequency spectrum before the subtraction spectrum is subtracted. Then, the frequency having the maximum level is searched from the frequency spectrum after the interpolation processing, and the searched frequency is acquired as the estimated frequency of the reference signal or the information signal. The interpolation process described in Patent Document 1 may be used for the interpolation process.

  Note that in step S53 of FIG. 10, the removal spectrum is configured by combining the maximum values acquired for each spectrum element from the three noise spectra, but the removal spectrum may not necessarily be the maximum value, and, for example, an average value or a median value, Alternatively, the removal spectrum may be configured by combining values calculated by multiplying each level by a coefficient. According to the inventor's verification, the method using the maximum value is most effective in removing the noise component.

  Further, in step S54 of FIG. 10, the removal spectrum is directly subtracted from the frequency spectrum of the reference signal or the information signal, but the subtraction spectrum may not necessarily be subtraction, and for example, division or multiplication of each level of the removal spectrum by a predetermined coefficient may be performed. A method of subtracting different levels may be used. According to the verification by the inventor, the subtraction method of the removal spectrum as it is was most effective in removing the noise component.

  Further, in step S54 of FIG. 10, the subtraction process is uniformly applied to all the spectrum elements, but the absolute value of the level difference between the frequency spectrum of the reference signal or the information signal (original signal) and the removal spectrum is predetermined. For spectral elements above the threshold of, the process may be modified so that the level of the removed spectrum is not subtracted from the frequency spectrum of the original signal. That is, if subtraction is performed on such a spectral element, the level of the spectral element that should originally correspond to the estimated frequency becomes too small, and the spectral element corresponding to the estimated frequency may not be properly extracted. . In order to avoid this, the process of step S54 may be modified so that the subtraction process is not applied to the spectrum element whose absolute value of the level difference exceeds the threshold value as described above. Note that this modification may be applied only when the level difference between the frequency spectrum of the original signal and the removal spectrum is a positive value, that is, only when the level of the frequency spectrum of the original signal is higher.

  Further, in the process of FIG. 10, as in the process shown in FIG. 8, the noise spectrum is acquired from the pause period RT of one to three packets before, but the number of the pause periods RT from which the noise spectrum is obtained is limited to this. However, the noise spectrum may be acquired from, for example, a pause section RT of four or more packet signals. However, as the number of the rest sections RT increases, a deviation easily occurs between the removal spectrum and the current noise spectrum. Therefore, it is preferable to limit the number of pause sections RT for generating the removal spectrum to about three as described above.

  It should be noted that the noise spectrum acquired from the pause period RT of the immediately preceding packet signal may be used as it is as the removal spectrum to perform the subtraction process on the frequency spectrum of the reference signal or the information signal. However, in this case, the influence of the interference wave superimposed on the reference signal or the information signal cannot be suppressed when the reception of the interference wave is temporarily blocked in the immediately preceding rest period due to factors such as blisters. There are cases. From this point of view, it is preferable to set the number of pause sections RT for generating the removal spectrum to about 3 as described above.

  According to the second embodiment, as described above, the noise component that is superimposed on the reference signal or the information signal due to interference by other signals or the like is suppressed by the processing using the removal spectrum, and thus the estimated frequency of the reference signal or the information signal Can get more accurately. Therefore, the communication information according to the information signal can be displayed more accurately.

  The configuration of the second embodiment is also effective when the synchronization signal complementing process (S14) and the Doppler shift value complementing process (S24) shown in the first embodiment are omitted. That is, the process of FIG. 10 alone can effectively suppress the influence of the detection signal due to interference or the like.

<Other changes>
In the first embodiment, the matched filter processing is used to detect the synchronization signal, but another method may be used as long as it performs correlation processing between the waveform of the received signal and the expected waveform of the synchronization signal. You may be asked.

  In the first embodiment, the maximum value detection unit 243 extracts the maximum value of the absolute value series D [n], and when the extracted maximum value is equal to or larger than the predetermined value, the timing corresponding to this maximum value. Is acquired as the synchronization detection timing, but the maximum value of S / N is extracted instead of the maximum value of the level of the absolute value series D [n], and the maximum value of S / N is equal to or greater than a predetermined value. Alternatively, the synchronization detection timing may be acquired. Alternatively, after the maximum value of the level of the absolute value series D [n] is extracted, the synchronization detection timing may be acquired depending on whether the S / N at the extraction point is a predetermined value or more.

  Further, in the first embodiment, the synchronization signal is detected and the frequency is estimated using the complex envelope sequence output from the quadrature detection unit 23, but the received signal may be processed as the real part sequence. Good. Further, the configuration may be such that one wave receiver 3 receives signals from a plurality of transmitters 2. In this case, the receiver 4 may be installed for each transmitter 2, and the signal received by one wave receiver 3 may be distributed to the corresponding receiver 4 by the distributor.

  Furthermore, although the case where the underwater communication system 1 is used for purse seine fishing has been described in the first embodiment, the present invention can be applied to other underwater communication systems.

  In the second embodiment, the pause section RT is arranged after the second information signal, but the arrangement position of the pause section RT is not limited to this. For example, the reference signal and the first information are arranged. A pause section RT may be arranged between the signal and the signal.

  Besides, the embodiment of the present invention can be variously modified as appropriate within the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Underwater communication system 2 Transmitter 3 Receiver 4 Receiver 5 Receiver 24 Synchronous signal detector 25 Gate generator 27 Frequency estimator 28 Frequency corrector RT Pause interval

Claims (17)

A transmitter that transmits a packet signal including a synchronization signal and an information signal underwater as an ultrasonic signal,
A receiver for receiving the ultrasonic signal,
A synchronization signal detection unit for detecting the synchronization signal from the received signal,
A gate generator that generates a gate for referring to the information signal based on the detection timing of the synchronization signal;
A frequency estimator for calculating an estimated frequency of the information signal in the gate,
A frequency correction unit that corrects the estimated frequency of the information signal based on a first detection timing of the synchronization signal and a second detection timing that is a detection timing earlier than the first detection timing of the synchronization signal, With
An underwater communication system characterized in that The underwater communication system according to claim 1,
The frequency correction unit corrects the estimated frequency of the information signal based on a Doppler shift value calculated based on the first detection timing and the second detection timing,
An underwater communication system characterized in that The underwater communication system according to claim 2,
The Doppler shift value is acquired based on a difference between the predicted timing of the synchronization signal set based on the second detection timing and the transmission cycle of the packet signal and the first detection timing.
An underwater communication system characterized in that The underwater communication system according to claim 2 or 3,
The information signal is modulated according to the transmission information,

The packet signal further includes a reference signal of known frequency,
The gate generator further generates another gate for referring to the reference signal based on the first detection timing,
The frequency estimation unit further calculates an estimated frequency of the reference signal in the other gate,
The frequency correction unit corrects the estimated frequency of the information signal based on the Doppler shift value when the estimated frequency of the information signal cannot be corrected based on the estimated frequency of the reference signal and the known frequency. To do
An underwater communication system characterized in that The underwater communication system according to claim 4,
The frequency correction unit, based on the estimated frequency of the reference signal and the known frequency, calculates another Doppler shift value, based on the difference between the other Doppler shift value and the Doppler shift value, Determine the suitability of the estimated frequency of the reference signal, if the estimated frequency of the reference signal is not correct, based on the Doppler shift value, correct the estimated frequency of the information signal,
An underwater communication system characterized in that The underwater communication system according to claim 5,
The frequency corrector compares the difference between the other Doppler shift value and the Doppler shift value with a predetermined threshold value to determine whether or not the estimated frequency of the reference signal is appropriate.
An underwater communication system characterized in that The underwater communication system according to any one of claims 4 to 6,
When the synchronization signal is not detected, the gate generation unit sets the detection timing of the synchronization signal based on a past Doppler shift value calculated based on a past estimated frequency of the reference signal and the known frequency. To do
An underwater communication system characterized in that The underwater communication system according to claim 7,
The gate generation unit sets a detection timing of the synchronization signal by applying a time shift based on the past Doppler shift value to a prediction timing of the synchronization signal set based on a transmission cycle of the packet signal. To do
An underwater communication system characterized in that A transmitter that transmits a packet signal containing a synchronization signal having a predetermined modulation, a reference signal of a known frequency, and an information signal modulated according to transmission information as an ultrasonic signal in water,
A synchronization signal detection unit that detects the synchronization signal from the packet signal received by the wave receiver,
A gate generator that generates a gate for referring to the reference signal and the information signal based on the detection timing of the synchronization signal;
A frequency estimator that calculates an estimated frequency of the reference signal and the information signal in each gate,
A frequency correction unit that corrects the estimated frequency of the information signal based on the estimated frequency of the reference signal and the known frequency,
The gate generation unit, when the synchronization signal is not detected, based on the past Doppler shift value calculated based on the estimated frequency of the reference signal in the past and the known frequency, the detection timing of the synchronization signal, Set,
An underwater communication system characterized in that The underwater communication system according to claim 9,
The gate generation unit sets a detection timing of the synchronization signal by applying a time shift based on the past Doppler shift value to a prediction timing of the synchronization signal set based on a transmission cycle of the packet signal. To do
An underwater communication system characterized in that The underwater communication system according to claim 9,
The gate generation unit, when the synchronization signal is not detected, based on the detection timing of the synchronization signal set from the past Doppler shift value, the detection range of the next synchronization signal, to the synchronization signal detection unit Set for
An underwater communication system characterized in that The underwater communication system according to any one of claims 1 to 11,
The packet signal includes a signalless pause period,
The frequency estimating unit suppresses a noise component of the information signal based on the signal in the idle period, and calculates an estimated frequency of the information signal based on the information signal after the noise component suppression,
An underwater communication system characterized in that The underwater communication system according to claim 12,
The frequency estimating unit acquires a frequency spectrum of the noise component from the signal of the pause interval, performs a process of removing the frequency spectrum of the acquired noise component from the frequency spectrum of the information signal, the information after processing Calculating an estimated frequency of the information signal based on a frequency spectrum of the signal,
An underwater communication system characterized in that The underwater communication system according to claim 13,
The frequency estimating unit acquires the frequency spectrum of the noise component from the signals of the pause section of a plurality of past times,
An underwater communication system characterized in that The underwater communication system according to claim 14,
The frequency estimating unit acquires a maximum value for each spectrum element with respect to a frequency spectrum of a signal in the pause section of a plurality of past times, and combines the maximum values for each of the acquired spectrum elements to obtain a frequency spectrum of the noise component. To get the
An underwater communication system characterized in that A synchronization signal detection unit that detects the synchronization signal from a packet signal including a synchronization signal and an information signal received as an ultrasonic signal through a wave receiver,
A gate generator that generates a gate for referring to the information signal based on the detection timing of the synchronization signal;
A frequency estimator for calculating an estimated frequency of the information signal in the gate,
A frequency correction unit that corrects the estimated frequency of the information signal based on a first detection timing of the synchronization signal and a second detection timing that is a detection timing earlier than the first detection timing of the synchronization signal, With
A receiver characterized in that. A packet signal including a synchronization signal and an information signal is transmitted underwater as an ultrasonic signal,
Receiving the ultrasonic signal,
Detecting the synchronization signal from the received signal,
Generating a gate for referring to the information signal based on the detection timing of the synchronization signal,
Calculating an estimated frequency of the information signal based on the information signal in the gate,
Based on a first detection timing of the synchronization signal and a second detection timing that is a detection timing before the first detection timing of the synchronization signal,
An underwater communication method for correcting an estimated frequency of the information signal.

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