US-12627382-B2 - Receiving apparatus and receiving method

Abstract

A receiver including a plurality of wave receivers that receive signals arriving from a predetermined direction, a plurality of detection units that is connected to at least some of the plurality of wave receivers and detect arrival times of signals received by a connected wave receivers, and a plurality of adjustment units that adjust a deviation between arrival times of the plurality of wave receivers based on arrival times or arrival directions of the plurality of detected signals.

Inventors

• Hiroyuki Fukumoto
• Yosuke Fujino
• Toshimitsu Tsubaki
• Miharu OIWA
• Yuya Ito
• Marina NAKANO

Assignees

• NTT, INC.

Dates

Publication Date

20260512

Application Date

20210519

Claims (6)

1. 1 . A receiver comprising: a plurality of wave receivers configured to receive sound waves arriving from a predetermined direction; a plurality of detectors that is connected to at least some of the plurality of wave receivers and detect arrival times of sound waves received by a connected wave receiver; and a plurality of adjusters configured to adjust a deviation of the arrival times of sound waves of between the plurality of wave receivers based on arrival times a plurality of detected sound waves wherein the receiver further comprised: an offset value calculator is configured to calculate a deviation between the arrival time of sound waves received by each wave receiver and a reference time, wherein the plurality of adjusters is configured to adjust each sound wave received by each of the plurality of wave receivers so as to reduce the deviation calculated by the offset value calculator.
2. 2 . The receiver according to claim 1 , further comprising: a plurality of finite impulse response (FIR) filters configured to perform filtering processing using an adjusted sound waves as an input sound waves; and a synthesizer configured to synthesize the output results of the plurality of FIR filters.
3. 3 . The receiver according to claim 1 , wherein the offset value calculator sets a time obtained based on arrival times detected by the plurality of detectors or a preset time as the reference time.
4. 4 . The receiver according to claim 1 , further comprising: an arrival time estimator configured to estimate an arrival time of a sound waves received by each wave receiver based on an arrival time of a sound waves received by the wave receiver to which the plurality of detectors are connected, wherein the plurality of detectors is connected to a part of the plurality of wave receivers, and the offset value calculator calculates a deviation between an arrival time of a sound waves received by each wave receiver estimated by the arrival time estimator and the reference time.
5. 5 . The receiver according to claim 1 , wherein the plurality of adjusters align a header of the each sound waves by padding the heads of the sound waves with zeros based on the deviation calculated by the offset value calculator.
6. 6 . A receiving method comprising: detecting an arrival time of sound waves received by at least two or more wave receivers among a plurality of wave receivers that receive the sound waves arriving from a predetermined direction; and adjusting a deviation of the arrival times of sounds waves of between the plurality of wave receivers based on arrival times of a plurality of detected sound waves received by at least two or more wave receivers, wherein the receiving method further comprised: calculating a deviation between the arrival time of sound waves received by each wave receiver and a reference time, wherein the adjusting each sound wave received by each of the plurality of wave receivers so as to reduce the deviation calculated.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a 371 U.S. National Phase of International Application No. PCT/JP2021/018901, filed on May 19, 2021. The entire disclosure of the above application is incorporated herein by reference. TECHNICAL FIELD The present invention relates to a receiver and a receiving method. BACKGROUND ART As conventionally known, absorption and attenuation of radio waves in water are extremely large, Therefore, it is difficult to perform wireless communication using radio waves in the same way as on the land. Therefore, a sound wave of 1 MHz or less having relatively small absorption attenuation is used for wireless communication in water. As a form of a receiver for underwater communication, there are a method of improving a reception signal-to-noise ratio (SNR) by arranging a plurality of wave receivers in an array, performing finite impulse response (FIR) filtering processing on reception signals received by the respective wave receivers, and combining the signals received by the respective wave receivers (for example, refer to, Non Patent Literature 1), and a method of suppressing a long delay wave (for example, refer to Non Patent Literature 2). FIG. 10 is a diagram illustrating a configuration of a conventional receiver 100. As illustrated in FIG. 10, the receiver 100 includes a plurality of wave receivers 110-1 to 110-n, a plurality of FIR filters 120-1 to 120-n, and a synthesis unit 130, Here, n indicates an integer of 2 or more. The wave receivers 110-1 to 110-n receive sound waves coming from the outside. The wave receivers 110-1 to 110-n convert the received sound waves into electric signals and output the electric signals to the FIR filters 120-1 to 120-n. The FIR filters 120-1 to 120-n perform FIR filtering processing on the electric signals of the sound waves received by the wave receivers 110-1 to 110-n. The synthesis unit 130 synthesizes the electric signals subjected to the FIR filtering processing. As a result, the SNR can be improved and unnecessary waves can be removed. 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 illustrated in FIG. 10, the arrival time difference caused by the path difference between the wave receivers 110-1 to 110-n is 200,000 times larger than the arrival time difference caused by the radio wave. FIG. 11 is a diagram illustrating a relationship between a sound wave arriving from one arrival direction and an impulse response observed by each of the wave receivers 110-1 to 110-n. As illustrated in FIG. 11, a path difference occurs between the wave receivers 110-1 to 110-n unless a sound wave arrives from the front. When the symbol rate of the signal is Fs, the path difference between the wave receiver 110-1 and the wave receiver 110-2 is Δx, and the propagation speed is c, the reception signal of the wave receiver 110-2 is delayed by FsΔx/c symbol with respect to the reception signal of the wave receiver 110-1. For example, in a case where the symbol rate Fs is 100 kHz and the path difference Δx is 0.1 m, the delay of radio wave is delayed by 3.3×10−5 symbols (that is, less than 1 symbol), whereas the underwater sound is delayed by 6.7 symbols. As described above, in the radio wave, in a case where the symbol rate is on the order of GHz or less, the delay between the wave receivers (antennas) is less than one symbol. Therefore, signal processing such as direction separation can be realized only by the phase shifter. On the other hand, in underwater acoustic communication, a delay of 1 symbol or more occurs at a symbol rate of an order of several tens of kHz. Therefore, when signal processing is applied at a symbol rate, it is necessary to consider a delay time difference. CITATION LIST Non Patent Literature Non Patent Literature 1: Robert S. H. Istepanian and Milica Stojanovic, “Underwater Acoustic Digital Signal Processing, and Communication Systems,” Springer Science+Business Media, LLC.Non Patent Literature 2: Hiroyuki Fukumoto, Youske Fujino, Marina Nakano, Toshimitsu Tsubaki, Ikko Sakamoto. “Study on spatiotemporal equalization for speeding up subsea acoustic communication,” IEICE Technical Report vol. 119, no. 296, RCS2019-233, pp. 169-174, November 2019. SUMMARY OF INVENTION Technical Problem As described above, in a configuration having a plurality of wave receivers, in order to synthesize sound waves arriving from a certain direction, it is necessary to consider a delay time between the wave receivers. Therefore, as illustrated in FIG. 11, it is necessary to set the tap length of the FIR filter to be larger than the arrival time difference between the wave receivers, and to absorb the delay difference by calculation processing of the FIR filter. When the difference in delay time between the wave receivers is taken into consideration, there is a problem that the number of taps of the FIR filter become