Receiver and receiving method

Abstract

A receiver comprising: a plurality of acoustic receivers that receive signals coming from a predetermined direction; a plurality of detection units that are connected to at least some of the plurality of acoustic receivers and detect the arrival times of the signals received by the acoustic receivers to which the detection units are connected; and a plurality of adjustment units that adjust the deviation in arrival time between the plurality of acoustic receivers on the basis of the arrival times of the plurality of detected signals or the incoming directions thereof.　

Description

[Technical field]

[0001] The present invention relates to a receiver and a receiving method. [Background technology]

[0002] As has been known for a long time, radio waves are absorbed and attenuated extremely underwater. This makes it difficult to perform wireless communication using radio waves in the same way as on land. Therefore, for wireless communication underwater, sound waves of 1 MHz or less, which have relatively small absorption attenuation, are used. As a receiver configuration for underwater communication, there is a method in which multiple receivers are arranged in an array, FIR (Finite Impulse Response) filter processing is performed on the received signals received by each receiver, and the signals received by each receiver are combined to improve the received signal-to-noise ratio (SNR) (see, for example, Non-Patent Document 1), and a method in which long delay waves are suppressed (see, for example, Non-Patent Document 2).

[0003] FIG. 10 is a diagram showing the configuration of a conventional receiver 100. As shown in FIG. 10, the receiver 100 includes a plurality of receivers 110-1 to 110-n, a plurality of FIR filters 120-1 to 120-n, and a synthesis unit 130. Here, n is an integer equal to or greater than 2. The receivers 110-1 to 110-n receive sound waves arriving from the outside. The receivers 110-1 to 110-n convert the received sound waves into electrical signals and output the electrical signals to the FIR filters 120-1 to 120-n. The FIR filters 120-1 to 120-n perform FIR filtering on the electrical signals of the sound waves received by the receivers 110-1 to 110-n. The synthesis unit 130 synthesizes the electrical signals after the FIR filtering. This can improve the SNR and remove unwanted waves.

[0004] The propagation speed of sound in water is about 1,500 m / s, which is about 200,000 times slower than the propagation speed of radio waves. Therefore, in the configuration shown in Fig. 10, the arrival time difference caused by the path difference between receivers 110-1 to 110-n is 200,000 times larger than the arrival time difference caused by radio waves. Fig. 11 is a diagram showing the relationship between a sound wave arriving from one arrival direction and the impulse response observed at each receiver 110-1 to 110-n. As shown in Fig. 11, a path difference occurs between receivers 110-1 to 110-n unless the sound wave arrives from the front.

[0005] If the symbol rate of the signal is Fs, the path difference between the receivers 110-1 and 110-2 is Δx, and the propagation speed is c, the signal received by the receiver 110-2 is delayed by FsΔx / c symbols from the signal received by the receiver 110-1. For example, if the symbol rate Fs is 100 kHz and the path difference Δx is 0.1 m, the propagation speed of the radio wave is 3.3×10 -5 In contrast to a delay of one symbol (i.e. less than one symbol), underwater acoustics results in a delay of 6.7 symbols. Thus, with radio waves, when the symbol rate is on the order of GHz or less, the delay between receivers (antennas) is less than one symbol. Therefore, signal processing such as directional separation can be achieved using only phase shifters. In contrast, in underwater acoustic communications, when the symbol rate is on the order of several tens of kHz, a delay of one symbol or more occurs. Therefore, when applying signal processing at the symbol rate, it is necessary to take into consideration the delay time difference. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Robert SH Istepanian and Milica Stojanovic, “Underwater Acoustic Digital Signal Processing and Communication Systems,” Springer Science + Business Media, LLC. [Non-Patent Document 2] Hiroyuki Fukumoto, Yosuke Fujino, Marina Nakano, Toshimitsu Tsubaki, and Kazumitsu Sakamoto, "Study on Spatio-Temporal Equalization for High-Speed ​​Underwater Acoustic Communications," IEICE Technical Report, vol. 119, no. 296, RCS2019-233, pp. 169-174, November 2019. Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, when trying to synthesize sound waves arriving from a certain direction in a configuration with multiple receivers, it is necessary to take into account the delay time between the receivers, so it is necessary to set the tap length of the FIR filter longer than the arrival time difference between the receivers and absorb the delay difference in the calculation process of the FIR filter, as shown in Figure 11. If the difference in delay time between receivers is taken into account, the number of taps in the FIR filter becomes large, which creates a problem of a large amount of calculation.

[0008] Furthermore, when trying to control the FIR filter with adaptive algorithms such as the RLS (Recursive Least Square) method or the LMS (Least Mean Square) method, the total number of taps of the filter determines the convergence speed, so the more the number of taps increases, the slower the convergence speed becomes, causing a deterioration in compensation performance. However, if the length of the FIR filter is made shorter than the arrival time difference between receivers in order to improve the convergence speed and reduce the amount of calculation, there will be arrival directions that cannot be combined, which causes a problem of poor BER (Bit Error Rate) characteristics for sound waves from arrival directions that cannot be combined.

[0009] In view of the above circumstances, an object of the present invention is to provide a technique capable of synthesizing signals received by receivers while suppressing the number of taps of an FIR filter. [Means for solving the problem]

[0010] One aspect of the present invention is a receiver comprising a plurality of receivers that receive signals arriving from a predetermined direction, a plurality of detection units connected to at least some of the plurality of receivers and detecting the arrival times of signals received by the connected receivers, and a plurality of adjustment units that adjust the difference in arrival times between the plurality of receivers based on the arrival times or arrival directions of the detected plurality of signals.

[0011] One aspect of the present invention is a receiving method that receives signals arriving from a predetermined direction, detects the arrival times of at least some of the received signals, and adjusts the difference in arrival times between the multiple receivers based on the arrival times or directions of arrival of the detected signals. Effect of the Invention

[0012] According to the present invention, it is possible to combine signals received by receivers while suppressing the number of taps of an FIR filter. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram for explaining an overview of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of a receiver according to the first embodiment. [Diagram 3] FIG. 4 is a diagram showing an example of a data frame received by a receiver in the first embodiment. [Figure 4] 5 is a flowchart showing a flow of processing in a receiver in the first embodiment. [Diagram 5] FIG. 13 is a diagram showing the arrangement of transmitters and receivers during simulation. [Figure 6] FIG. 4 is a diagram illustrating a simulation result in the first embodiment. [Figure 7] FIG. 13 is a diagram illustrating a configuration of a receiver according to a modified example of the first embodiment. [Figure 8] 13 is a diagram for explaining an overview of a method for calculating a time difference from a reference time in the second embodiment. FIG. [Figure 9] FIG. 11 is a diagram illustrating a configuration of a receiver according to a second embodiment. [Figure 10] FIG. 1 is a diagram showing the configuration of a conventional receiver. [Figure 11] FIG. 1 is a diagram showing the relationship between a sound wave arriving from one direction of arrival and the impulse responses observed by each of receivers 110-1 to 110-n. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (overview) FIG. 1 is a diagram for explaining an overview of the present invention. In the present invention, the difference in arrival time between receivers 11-1 to 11-n is estimated in advance based on a signal arriving from a specific direction at the stage before the FIR filter, and the difference in the received signal is adjusted based on the estimation result. By performing such timing adjustment, the difference in arrival time caused by the path difference immediately before the FIR filter is compensated. This makes it possible to seemingly eliminate the difference in arrival time between receivers 11-1 to 11-n, and makes it possible to synthesize sound waves from any arrival direction even if the tap length of the FIR filter is shorter than the difference in arrival time between receivers 11-1 to 11-n. The configuration for achieving the above effects will be described below.

[0015] (First embodiment) 2 is a diagram showing the configuration of a receiver 10 in the first embodiment. The receiver 10 is a receiver used for underwater acoustic communication. The receiver 10 includes a plurality of receivers 11-1 to 11-n, a plurality of detection units 12-1 to 12-n, an offset value calculation unit 13, a plurality of timing adjustment units 14-1 to 14-n, a plurality of FIR filters 15-1 to 15-n, and a synthesis unit 16.

[0016] The receivers 11-1 to 11-n receive sound waves arriving from the outside. For example, the receivers 11-1 to 11-n receive sound waves arriving from a direction in which a path difference occurs. The direction in which a path difference occurs is, for example, a direction other than the front direction of the receivers 11-1 to 11-n. The receivers 11-1 to 11-n convert the received sound waves into electrical signals and output them as received signals to the detectors 12-1 to 12-n.

[0017] The detectors 12-1 to 12-n detect the reception signals output from the receivers 11-1 to 11-n.

[0018] The method of detecting the received signal may be, for example, that the transmitting device adds a known signal to a data frame as shown in Fig. 3 and transmits it, and the detectors 12-1 to 12-n detect the received signal by detecting peaks from the cross-correlation between the known signal and the received signal. The transmitting device may transmit a data frame containing a repeated known signal, and the detectors 12-1 to 12-n detect the received signal by detecting peaks from the autocorrelation of the received signal. The received signal detected by the detectors 12-1 to 12-n is the signal from the desired arrival direction.

[0019] The detectors 12-1 to 12-n detect the time when the sound wave reaches the receivers 11-1 to 11-n by detecting a known signal included in the received signal. The detectors 12-1 to 12-n output the detected time information to the offset value calculator 13.

[0020] Offset value calculation section 13 calculates a deviation from the reference time for each of the received signals detected by detection sections 12-1 to 12-n based on the difference between the reference time and the arrival time of the received signal detected by each of detection sections 12-1 to 12-n.

[0021] The reference time may be, for example, the time when a sound wave reaches any of receivers 11-1 to 11-n, or may be a time set in advance by the user of receiver 10, or may be the average time, median, latest time, or earliest time when a sound wave reaches receivers 11-1 to 11-n.

[0022] The timing adjustment units 14-1 to 14-n adjust the deviation (e.g., lead or delay) of the received signal from the reference time based on the deviation from the reference time of each received signal calculated by the offset value calculation unit 13. Here, adjusting the deviation (e.g., lead or delay) of the received signal from the reference time means adjusting to reduce the deviation. For example, adjusting the deviation (e.g., lead or delay) of the received signal from the reference time means adjusting to reduce the deviation to zero. The timing adjustment unit 14 is one aspect of an adjustment unit.

[0023] The FIR filters 15-1 to 15-n perform FIR filtering by receiving the received signals adjusted by the timing adjustment units 14-1 to 14-n. The FIR filters 15-1 to 15-n may be configured such that the filter coefficients are adaptively controlled by an adaptive algorithm such as the RLS method or the LMS method, or may be configured such that the filter coefficients are set based on the channel estimation results using a pilot signal. The FIR filters 15-1 to 15-n may be configured as decision feedback type feedback filters that receive as input a sequence obtained by symbol-detecting the summation results of the outputs of the FIR filters 15-1 to 15-n, and the output results of the feedback filters may be added to or subtracted from the summation results of the outputs of the FIR filters 15-1 to 15-n. The adaptive algorithm may simultaneously control the filter coefficients of the FIR filters 15-1 to 15-n and the filter coefficients of the feedback filters.

[0024] The combiner 16 adds the outputs of the FIR filters 15-1 to 15-n, and based on the result of the addition by the combiner 16, demodulation processing including symbol determination is performed.

[0025] Fig. 4 is a flowchart showing a process flow of the receiver 10 in the first embodiment. In Fig. 4, a method of correcting the timing of the received signals received by the receivers 11-1 to 11-n using the arrival time of the latest data frame among the N receivers 11 as a reference time, on the assumption that the data frame shown in Fig. 3 is received by the receiver 10, will be described.

[0026] The receivers 11-1 to 11-n receive a data frame (sound wave) arriving from the outside (step S101). The receivers 11-1 to 11-n convert the received data frame (sound wave) into an electrical signal and output it to the detectors 12-1 to 12-n as a received signal. The detectors 12-1 to 12-n detect the time at which the data frame reaches the receivers 11-1 to 11-n by detecting a known signal added to the beginning of the received signal output from the receivers 11-1 to 11-n (step S102). The detectors 12-1 to 12-n output the detected time information to the offset value calculator 13.

[0027] The offset value calculation unit 13 uses the time information output from the detection units 12-1 to 12-n to compare the arrival times of the data frames between the receivers 11-1 to 11-n. The offset value calculation unit 13 sets the latest arrival time as the reference time (step S103). The offset value calculation unit 13 calculates the deviation of the received signal from each receiver 11-i (i is 1, ..., n) from the reference time using the following formula (1) based on the set reference time and the arrival times at the receivers 11-1 to 11-n (step S104).

[0028] Deviation from the reference time = (reference time) - (arrival time of the receiver 11-i) Equation (1)

[0029] The offset value calculation unit 13 outputs information on the calculated deviation from the reference time to the timing adjustment unit 14-i corresponding to the receiver 11-i. For example, the offset value calculation unit 13 outputs information on the deviation from the reference time to the arrival time of the data frame at the receiver 11-1 to the timing adjustment unit 14-1. For example, the offset value calculation unit 13 outputs information on the deviation from the reference time to the arrival time of the data frame at the receiver 11-n to the timing adjustment unit 14-n.

[0030] The timing adjustment unit 14-i pads zeros to the beginning of the data frame based on the deviation information output from the offset value calculation unit 13 (step S105). Specifically, the timing adjustment unit 14-i pads zeros to the beginning of the data frame so that the deviation indicated by the deviation information output from the offset value calculation unit 13 becomes zero. This aligns the beginning positions of the data frames received by all receivers 11-i to the reference time. The timing adjustment unit 14-i outputs the adjusted data frame to the FIR filter 15-i.

[0031] The FIR filter 15-i performs filtering using the output from the timing adjustment unit 14-i as an input signal (step S106). The signal filtered by the FIR filter 15-i is combined by the combiner 16 (step S107).

[0032] (Simulation evaluation) Next, a comparison will be made between the BER characteristics with respect to the number of taps of the FIR filter when correction based on the arrival time between the receivers 11 is performed as in the first embodiment and when correction is not performed. The simulation was performed under the following conditions. Modulation method: QPSK (Quadrature Phase Shift Keying) Bandwidth: 200kHz Center frequency: 300kHz Transmitting antennas: 2 Receiving antennas: 2 ·Eb / No(Electric Bit to Noise):13dB Transmission method: Single carrier

[0033] Fig. 5 is a diagram showing the arrangement of the wave transmitters 21-1 to 21-2 and the wave receivers 11-1 to 11-2 during the simulation. As shown in Fig. 5, this simulation is performed assuming a 2x2 MIMO (Multiple Input Multiple Output) and the BER characteristics of the wave transmitter 21-1 are compared. The FIR filter 15 is trained by the RLS method with the error between the known signal and the filter output as the cost.

[0034] Fig. 6 is a diagram showing the simulation results in the first embodiment. In Fig. 6, the horizontal axis represents the number of taps of the FIR filter, and the vertical axis represents the BER. As shown in Fig. 6, when correction is performed based on the arrival time between the receivers 11 as in the first embodiment, the BER is constant regardless of the number of taps of the FIR filter. On the other hand, in the conventional method, the BER characteristic is deteriorated when the number of taps of the FIR filter is less than 85. As described above, it can be seen that the BER characteristic at the receiver end does not deteriorate even if the tap length of the FIR filter 15 is set short by applying the present invention.

[0035] The receiver 10 configured as above includes a plurality of receivers 11-1 to 11-n that receive data frames arriving from a predetermined direction, a plurality of detectors 12-1 to 12-n that are connected to the plurality of receivers 11-1 to 11-n and detect the arrival times of the data frames received by the connected receivers 11-1 to 11-n, a plurality of timing adjusters 14-1 to 14-n that adjust the difference in arrival times between the plurality of receivers 11-1 to 11-n based on the arrival times of the detected plurality of data frames, a plurality of FIR filters 15-1 to 15-n that perform filtering using the adjusted data frames as input signals, and a combiner 16 that combines the output results of the plurality of FIR filters 15-1 to 15-n. By adjusting the difference in arrival times in this way, the start positions of the data frames received by each of the plurality of receivers 11-1 to 11-n are aligned with the reference time. Therefore, even if the tap length of the FIR filter is shorter than the arrival time difference between the receivers 11-1 to 11-n, it is possible to synthesize sound waves from any direction of arrival. With this configuration, even if the tap length of the FIR filter is set short, the BER characteristics at the receiver end do not deteriorate. As a result, the required tap length of the FIR filter is shortened, and the amount of calculation can be reduced. When the FIR filter is controlled by an adaptive algorithm, the convergence speed of the adaptive algorithm is improved.

[0036] The receiver 10 further includes an offset value calculation unit 13 that calculates the difference between the arrival time of the data frame received by each receiver 11-i and a reference time. The timing adjustment units 14-i adjust each data frame received by each receiver 11-i so as to reduce the difference calculated by the offset value calculation unit 13. This makes it possible to reduce the difference (e.g., delay) in the arrival time caused by the path difference. Therefore, even if the tap length of the FIR filter is shorter than the arrival time difference between the receivers 11-1 to 11-n, it becomes possible to synthesize sound waves from all arrival directions.

[0037] The receiver 10 sets the time obtained based on the arrival times detected by the multiple detectors 12-i as the reference time. Here, the time obtained based on the arrival times is the time when the sound waves arrive, the time set in advance by the user of the receiver 10, or the average, median, latest, or earliest time when the sound waves arrive at the receivers 11-1 to 11-n. This makes it possible to set a reference time for adjusting the difference in arrival times caused by path differences. As a result, it is possible to adjust the difference in arrival times caused by path differences. Therefore, even if the tap length of the FIR filter is shorter than the difference in arrival times between the receivers 11-1 to 11-n, it becomes possible to synthesize sound waves from all directions of arrival.

[0038] (Modification of the first embodiment) The receiver 10 shown in Fig. 2 may be configured to include leading counter value setting units 17-1 to 17-n shown in Fig. 7 instead of the offset value calculation unit 13 and the timing adjustment units 14-1 to 14-n. With this configuration, it becomes possible to compensate for the difference in arrival time between the receivers 11-1 to 11-n without correcting the received signals on the time axis.

[0039] 7 is a diagram showing the configuration of a receiver 10a in a modified example of the first embodiment. The receiver 10a includes a plurality of receivers 11-1 to 11-n, a plurality of detection units 12-1 to 12-n, a plurality of leading counter value setting units 17-1 to 17-n, a plurality of FIR filters 15-1 to 15-n, and a synthesis unit 16. The receiver 10a is different in configuration from the receiver 10 in that the receiver 10a includes leading counter value setting units 17-1 to 17-n instead of the offset value calculation unit 13 and the timing adjustment units 14-1 to 14-n. The other configurations of the receiver 10a are the same as those of the receiver 10. Therefore, only the differences will be described.

[0040] The head counter value setting unit 17-i holds the sample number of the received signal at the head position of the data frame detected by the detection unit 12-i. For example, the received signal sequence of the receiver 11-i is i (m) (m is the time index), m=M iThe head counter value setting unit 17-i is M i When the leading counter value setting unit 17-i calculates the output at time k, the parameter M i The input signal to the FIR filter 15-i is set based on the following equation (2) using the above formula: The leading counter value setting unit 17-i is one aspect of the adjustment unit.

[0041] Ri(k) = (r i (M i +k),…,r1(M i +kN t ))...Equation (2)

[0042] In formula (2), N t represents the number of taps of the FIR filter 15-i. By configuring in this way, it is possible to realize the same process as in the first embodiment, in which correction between the receivers 11-i is performed on the time axis.

[0043] Second Embodiment In the first embodiment, a configuration was shown in which data frames received by all of the receivers 11-i were detected. In the second embodiment, a portion of the data frames of the receivers 11-i are detected, and the arrival times of all of the receivers 11-i are estimated based on the arrival times of the detected data frames. This is different from the first embodiment.

[0044] First, a method of calculating the time difference from the reference time in the second embodiment will be described. Fig. 8 is a diagram for explaining an outline of a method of calculating the time difference from the reference time in the second embodiment. Fig. 8 shows a linear array in which receivers 11-1 to 11-4 are arranged in a line at equal intervals. As shown in Fig. 8, it is assumed that sound waves arrive from a direction of arrival in a four-element linear array. In this case, the arrival time difference between receivers 11-2 to 11-4 relative to receiver 11-1 changes linearly.

[0045] Therefore, if the arrival time of the data frame received at the receiver 11-1 is used as a reference and the arrival time of one or more data frames at the receivers 11-2 to 11-4 and the positional relationship of the receiver 11-i are known, the gradient of the arrival timing (a parameter defined as T in FIG. 8) can be estimated. With this configuration, it is possible to estimate the time at which the data frame arrives at all receivers 11-i without detecting the data frames received at all receivers 11-i. As a result, it is possible to calculate the deviation from the reference time without detecting the data frames received at all receivers 11-i.

[0046] 9 is a diagram showing the configuration of a receiver 10b in the second embodiment. The receiver 10b is a receiver used for underwater acoustic communication. The receiver 10b includes a plurality of receivers 11-1 to 11-4, a plurality of detectors 12-1 to 12-2, an offset value calculator 13, a plurality of timing adjusters 14-1 to 14-4, a plurality of FIR filters 15-1 to 15-4, a combiner 16, and an arrival time estimator 18.

[0047] 9 shows an example of a configuration in which four receivers 11, four timing adjustment units 14 and four FIR filters 15, and two detectors 12 are provided, but the number of receivers 11, the timing adjustment units 14 and the FIR filters 15 may be three or more (n=3), and the same number of detectors 12 may be provided. Furthermore, the number of detectors 12 may be at least two (n-1), and the number of detectors 12 may be less than the number of receivers 11, the timing adjustment units 14 and the FIR filters 15.

[0048] In Fig. 9, the detector 12-1 is connected to the receiver 11-3, and the detector 12-2 is connected to the receiver 11-4. In this manner, the detector 12 is provided in some of the N (4 in Fig. 9) receivers 11. The detectors 12-1 and 12-2 detect the received signals output from the receivers 11 (for example, the receivers 11-3 and 11-4) to which they are connected. Furthermore, the detectors 12-1 and 12-2 detect the arrival times of the data frames.

[0049] The arrival time estimation unit 18 estimates the arrival times of all the receivers 11-i based on the arrival times obtained by the detection units 12-1 and 12-2. Any algorithm may be used to estimate the arrival times. For example, due to linear independence, if the array is arranged linearly, the arrival times of all the receivers 11-i can be theoretically estimated based on information on the arrival time difference of the data frames between two or more receivers 11-i. Alternatively, if the array is arranged in a plane, the arrival times of all the receivers 11-i can theoretically be estimated based on information on the arrival time difference of the data frames between three or more receivers 11-i (for example, the arrival time difference of the receiver 11-2 and the arrival time difference of the receiver 11-3 with the receiver 11-1 as the reference).

[0050] The offset value calculation unit 13 calculates the deviation from the reference time for each of the wave receivers 11-i based on the difference between the reference time and the arrival times at all of the wave receivers 11-i obtained by the arrival time estimation unit 18.

[0051] The receiver 10b configured as described above eliminates the need to detect data frames received by all receivers 11-i, making it possible to significantly reduce the amount of calculation required for frame detection when a large number of receivers 11-i are used.

[0052] The timing adjustment unit 14 may adjust the difference in arrival time between the multiple receivers 11 based on the arrival directions of the multiple detected signals.

[0053] Some of the functional units of the receivers 10, 10a, and 10b in the above-described embodiments may be realized by a computer. In this case, a program for realizing the functions may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed. Note that the term "computer system" here includes hardware such as an OS and peripheral devices.

[0054] In addition, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. Furthermore, the term "computer-readable recording medium" may also include those that dynamically hold a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, and those that hold a program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or client in such a case. Furthermore, the above program may be one that realizes part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in the computer system, or may be one that is realized using a programmable logic device such as an FPGA.

[0055] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Industrial Applicability]

[0056] The present invention is applicable to underwater acoustic communication technology. [Explanation of symbols]

[0057] 10, 10a, 10b... receiver, 11-1 to 11-n... receiver, 12-1 to 12-n... detector, 13... offset value calculator, 14-1 to 14-n... timing adjuster, 15-1 to 15-n... FIR filter, 16... synthesis unit, 17-1 to 17-n... head counter value setting unit, 18... arrival time estimator

Claims

1. A plurality of receivers for receiving signals arriving from a predetermined direction; A plurality of detectors connected to at least some of the plurality of receivers to detect arrival times of signals received by the connected receivers; a plurality of adjustment units that adjust the difference in arrival time between the plurality of receivers based on the arrival times or directions of arrival of the plurality of detected signals; an offset value calculation unit that calculates the difference between the arrival time of a signal received by each receiver and a reference time; Equipped with The plurality of adjustment units adjust each signal received by each of the plurality of receivers so as to reduce the deviation calculated by the offset value calculation unit, A known signal is added to the signal, The plurality of detection units are connected to some of the plurality of receivers, and detect the arrival time of the signal by peak detection based on cross-correlation between the known signal added to the signal received by some of the plurality of receivers and a received signal of the portion of the signal, or autocorrelation of a received signal that is repeatedly received; an arrival time estimation unit that estimates an arrival time of a signal received at each of the wave receivers based on an arrival time of the signal received at each of the wave receivers to which the plurality of detection units are connected; Further equipped with The offset value calculation unit calculates the difference between the arrival time of the signal received at each receiver, estimated by the arrival time estimation unit, and a reference time.

2. A plurality of FIR (Finite Impulse Response) filters that perform filtering using the adjusted signal as an input signal; A synthesis unit that synthesizes output results of the plurality of FIR filters; Further comprising:

2. The receiver of claim 1.

3. the offset value calculation unit sets the reference time to a time obtained based on the arrival times detected by the plurality of detection units or to a time set in advance.

2. The receiver of claim 1.

4. the plurality of adjustment units align the start positions of the signals by padding zeros to the start positions of the signals based on the deviations calculated by the offset value calculation unit; Receiver according to any one of claims 1 to 3.

5. Detecting arrival times of signals received by at least some of a plurality of receivers receiving signals arriving from a predetermined direction; adjusting the difference in arrival time between the plurality of receivers based on the arrival times or directions of arrival of the plurality of detected signals; Calculate the time of arrival of the signal received by each receiver and the deviation from the reference time. adjusting each signal received by each of the plurality of receivers so as to reduce the calculated deviation; A known signal is added to the signal, Detecting the arrival time of the signal by peak detection based on cross-correlation between the known signal added to the signal received by a receiver connected to a plurality of detectors connected to some of the plurality of receivers and a received signal of a portion of the signal, or auto-correlation of a received signal that is repeatedly received; estimating the arrival time of the signal received by each receiver based on the detected arrival time of the signal; Calculating the deviation between the estimated arrival time of the signal received at each receiver and a reference time; Receiving method.

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