Underwater acoustic communication system, clock calibration method, wave transmission / reception unit, and program

Abstract

[Problem] To provide an underwater acoustic communication system capable of realizing clock calibration by wireless means. [Solution] This underwater acoustic communication system comprises: a first wave transmission / reception unit which comprises a clock part and is configured so as to transmit a first ultrasound message at a first clock time measured in the clock part; and a second wave transmission / reception unit which is configured so as to receive the first ultrasound message, acquire a second clock time at which the first ultrasound message was received, calculate one-way propagation time between the first clock time and the second clock time, and transmit a second ultrasound message including the one-way propagation time. The first wave transmission / reception unit is further configured so as to: receive the second ultrasound message; extract the one-way propagation time from the second ultrasound message; acquire a third clock time at which the second ultrasound message was received and which is measured in the clock part; calculate a round propagation time between the first clock time and the third clock time; and adjust the clock time of the clock part on the basis of the one-way propagation time and the round propagation time.

Description

Underwater acoustic communication system, clock calibration method, wave transmitting / receiving unit, and program

[0001] The present invention relates to an underwater acoustic communication system, a clock calibration method, a wave transmitting / receiving unit, and a program.

[0002] One method of distance measurement in underwater acoustic positioning is the pinger method, which involves transmitting an ultrasonic message from an underwater unit submerged in water, receiving the ultrasonic message with a measuring unit installed on a ship, and calculating the distance between the units from the time difference between the time of reception and the time of transmission.

[0003] In the pinger method, the clocks in the underwater unit and the measurement unit must be synchronized to avoid errors.

[0004] Patent document 1 discloses a technology for adjusting the reference time of a synchronization clock inside a synchronization pinger housing by supplying a synchronization signal to a connection cable that is hung from a ship and connected to an underwater synchronization pinger housing.

[0005] Japanese Patent Application Publication No. 7-151843

[0006] However, the above-described wired clock calibration is not practical because it limits the distance over which calibration is possible and there is also the risk of the cable becoming tangled.

[0007] The present invention has been made in consideration of the above-mentioned problems, and its main object is to provide an underwater acoustic communication system, a clock calibration method, a transmit-receive unit, and a program that are capable of achieving wireless clock calibration.

[0008] In order to solve the above problem, one aspect of the present invention provides an underwater acoustic communication system comprising: a first wave transceiver unit including a clock unit, the first wave transceiver unit configured to transmit a first ultrasonic message at a first time measured by the clock unit; and a second wave transceiver unit configured to receive the first ultrasonic message, obtain a second time at which the first ultrasonic message was received, calculate a one-way propagation time from the first time to the second time, and transmit a second ultrasonic message including the one-way propagation time, wherein the first wave transceiver unit is further configured to receive the second ultrasonic message, extract the one-way propagation time from the second ultrasonic message, obtain a third time at which the second ultrasonic message was received, measured by the clock unit, calculate a round-trip propagation time from the first time to the third time, and adjust the time on the clock unit based on the one-way propagation time and the round-trip propagation time. This makes it possible to achieve wireless clock calibration.

[0009] In the above aspect, the first wave transmitting / receiving unit may be configured to adjust the time of the clock unit based on the difference between the one-way propagation time and half the round-trip propagation time, thereby making it possible to correct a time discrepancy.

[0010] In the above aspect, the first wave transmitting / receiving unit may be configured to delay the time of the clock unit when the one-way propagation time is shorter than half of the round-trip propagation time, thereby making it possible to correct the advance of the time.

[0011] In the above aspect, the first wave transmitting / receiving unit may be configured to advance the time of the clock unit when the one-way propagation time is longer than half of the round-trip propagation time, thereby making it possible to correct a delay in the time.

[0012] In the above aspect, the first wave transmitting / receiving unit may be configured to adjust the time of the clock unit so that the one-way propagation time is equal to half of the round-trip propagation time, thereby making it possible to accurately correct a time discrepancy.

[0013] In the above aspect, the first ultrasonic message may include a timestamp representing the first time, and the second wave transmitting / receiving unit may be further configured to extract the first time from the first ultrasonic message, thereby enabling calculation of a one-way propagation time using the first time included in the first ultrasonic message.

[0014] In the above aspect, the second wave transmitting and receiving unit may further include a clock unit and be configured to acquire the second time measured by the clock unit, thereby enabling the clock unit of the first wave transmitting and receiving unit to be synchronized with the clock unit of the second wave transmitting and receiving unit.

[0015] In the above aspect, the first ultrasonic message may include a calibration request, and the second transceiver unit may be configured to transmit the second ultrasonic message when the first ultrasonic message includes the calibration request, thereby enabling clock calibration to be performed when the first ultrasonic message includes the calibration request.

[0016] In the above aspect, the first wave transmitting / receiving unit may be further configured to stop adjusting the time of the clock unit if the second ultrasonic message is not received within a predetermined time after transmitting the first ultrasonic message, thereby realizing a timeout when the second ultrasonic message cannot be received.

[0017] In the above aspect, the second wave transmitting and receiving unit may be further configured to calculate the distance between the first wave transmitting and receiving unit and the second wave transmitting and receiving unit based on the one-way propagation time, thereby making it possible to calculate the distance between the first wave transmitting and receiving unit and the second wave transmitting and receiving unit.

[0018] In the above aspect, the first wave transmitting and receiving unit may be further configured to correct the amount of adjustment of the time of the clock unit based on the amount of Doppler shift of the ultrasonic waves when the first or second ultrasonic message is received, thereby making it possible to achieve clock calibration even when the first or second wave transmitting and receiving unit is moving.

[0019] In the above aspect, the first wave transmitting and receiving unit may be installed on an underwater object, and the second wave transmitting and receiving unit may be further configured to calculate the position of the underwater object based on the one-way propagation time, thereby making it possible to calculate the position of the underwater object.

[0020] In the above aspect, the underwater object may be an unmanned underwater vehicle or a fishing net, which makes it possible to calculate the position of the unmanned underwater vehicle or the fishing net.

[0021] Another aspect of the present invention provides a clock calibration method for an underwater acoustic communication system including a first wave transceiver unit having a clock unit, and a second wave transceiver unit, the method comprising the steps of: transmitting a first ultrasonic message by the first wave transceiver unit at a first time measured by the clock unit; receiving the first ultrasonic message by the second wave transceiver unit; obtaining a second time at which the first ultrasonic message is received; calculating a one-way propagation time from the first time to the second time; transmitting a second ultrasonic message by the second wave transceiver unit; receiving the second ultrasonic message by the first wave transceiver unit; obtaining a third time at which the second ultrasonic message is received, which is measured by the clock unit; calculating a round-trip propagation time from the first time to the third time; and adjusting the time on the clock unit based on the one-way propagation time and the round-trip propagation time. This method makes it possible to achieve wireless clock calibration.

[0022] Another aspect of the present invention provides a wave transceiver unit that is included in an underwater acoustic communication system and includes a clock unit, and is configured to transmit a first ultrasonic message at a first time measured by the clock unit, receive a second ultrasonic message transmitted from a counterpart wave transceiver unit that has received the first ultrasonic message and that includes a one-way propagation time from the first time to a second time when the first ultrasonic message is received, extract the one-way propagation time from the second ultrasonic message, obtain a third time when the second ultrasonic message is received that is measured by the clock unit, calculate a round-trip propagation time from the first time to the third time, and adjust the time on the clock unit based on the one-way propagation time and the round-trip propagation time. This makes it possible to achieve wireless clock calibration.

[0023] Another aspect of the present invention provides a wave transceiver unit included in an underwater acoustic communication system, which is configured to receive a first ultrasonic message transmitted from a counterpart wave transceiver unit having a clock unit at a first time measured by the clock unit, obtain a second time at which the first ultrasonic message was received, calculate a one-way propagation time from the first time to the second time, and transmit a second ultrasonic message including the one-way propagation time. This makes it possible to achieve wireless clock calibration.

[0024] According to another aspect of the present invention, there is provided a program for causing a computer included in a wave transceiver unit having a clock unit included in an underwater acoustic communication system to execute the following operations: transmit a first ultrasonic message at a first time measured by the clock unit; receive a second ultrasonic message transmitted from a partner wave transceiver unit that has received the first ultrasonic message, the second ultrasonic message including a one-way propagation time from the first time to a second time when the first ultrasonic message is received; extract the one-way propagation time from the second ultrasonic message; obtain a third time measured by the clock unit when the second ultrasonic message is received, and calculate a round-trip propagation time from the first time to the third time; and adjust the time on the clock unit based on the one-way propagation time and the round-trip propagation time. This makes it possible to achieve wireless clock calibration.

[0025] According to another aspect of the present invention, there is provided a program for causing a computer included in a wave transmitting / receiving unit included in an underwater acoustic communication system to receive a first ultrasonic message from a counterpart wave transmitting / receiving unit having a clock unit, the first ultrasonic message being transmitted at a first time measured by the clock unit, obtain a second time at which the first ultrasonic message was received, calculate a one-way propagation time from the first time to the second time, and transmit a second ultrasonic message including the one-way propagation time. This makes it possible to perform wireless clock calibration.

[0026] According to the present invention, it is possible to realize wireless clock calibration.

[0027] Fig. 4 is a diagram showing an application example of an underwater acoustic communication system. Fig. 5 is a diagram showing a configuration example of an underwater acoustic communication system. Fig. 6 is a diagram showing an operation example of an underwater unit. Fig. 7 is a diagram continuing from Fig. 3. Fig. 8 is a diagram showing an operation example of a mother ship unit. Fig. 9 is a diagram for explaining clock calibration. Fig. 10 is a diagram for explaining clock calibration. Fig. 11 is a diagram showing a configuration example of an ultrasonic message.

[0028] The functions provided by the components described herein may be implemented in circuits or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a CPU (a Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to provide the described functions. A processor includes transistors and other circuitry and is considered a circuit or processing circuit. A processor may be a programmable processor that executes a program stored in a memory.

[0029] In this specification, circuits, units, and means are hardware that is programmed to realize the described functions or that performs this function, which may be any hardware disclosed herein or any hardware that is programmed to realize the described functions or that is known to perform this function.

[0030] If the hardware is a processor considered to be a type of circuit, the circuit, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0031] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification and the drawings, elements similar to those described above with reference to the previous drawings will be designated by the same reference numerals, and detailed descriptions thereof may be omitted as appropriate.

[0032] In this specification, "time" refers to a period from one point to another in the flow of time, and "time instant" refers to a point in time.

[0033] 1 is a schematic diagram showing an application example of an underwater acoustic communication system 100. The underwater acoustic communication system 100 includes an underwater unit 1 and a mother ship unit 2.

[0034] The underwater unit 1 and the mother ship unit 2 realize underwater acoustic communication using ultrasonic waves and can transmit and receive ultrasonic messages to and from each other. The underwater unit 1 is an example of a first wave-transmitting and receiving unit. The mother ship unit 2 is an example of a second wave-transmitting and receiving unit.

[0035] The underwater unit 1 is installed on an underwater object ST. The underwater object ST is, for example, an unmanned underwater vehicle or a fishing net. The mother ship unit 2 is installed on a ship SH on the water. The transmitting and receiving part of the mother ship unit 2 protrudes downward from the bottom of the ship SH. The mother ship unit 2 is not limited to being installed on the ship SH, and may also be installed on a structure on the water, such as a buoy or a pier.

[0036] FIG. 2 is a block diagram showing an example of the configuration of the underwater unit 1 and the mother ship unit 2 included in the underwater acoustic communication system 100.

[0037] The underwater unit 1 is a computer including a processing unit 10, and further includes a wave transmitting unit 11, a wave receiving unit 12, and a clock unit 13. Similarly, the mother ship unit 2 is a computer including a processing unit 20, and further includes a wave transmitting unit 21, a wave receiving unit 22, and a clock unit 23.

[0038] The processing units 10 and 20 are, for example, a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array).

[0039] The wave transmitting units 11 and 21 convert the transmission signal into an ultrasonic message and emit the ultrasonic message into the water. The wave receiving units 12 and 22 receive the ultrasonic message propagating through the water and convert the ultrasonic message into a received signal.

[0040] An ultrasound message consists of a synchronization pulse and a data pulse (see FIG. 8), and the data pulse contains various information.

[0041] The clock units 13 and 23 are, for example, real time clocks (RTCs), or may be the clock function of a CPU.

[0042] The clock unit 23 of the mother ship unit 2 is not required, and the processing unit 20 may obtain the time from another computer installed on the ship SH, or may obtain the time by accessing an NTP (Network Time Protocol) server.

[0043] The underwater acoustic communication system 100 is capable of performing underwater acoustic positioning using the pinger method. That is, the mother ship unit 2 measures the propagation time of an ultrasonic message M1 (hereinafter also referred to as "pinger M1") propagating from the underwater unit 1 to the mother ship unit 2, and calculates the position of the underwater unit 1 based on that propagation time.

[0044] In underwater acoustic positioning using this pinger method, to prevent a decrease in distance measurement accuracy, it is necessary to periodically synchronize the clock unit 13 of the underwater unit 1 with the clock unit 23 of the mother ship unit 2. Therefore, in this embodiment, the clock unit 13 of the underwater unit 1 is calibrated using the method described below.

[0045] 3 to 5 are flow charts showing an example of the procedure of a clock calibration method implemented in the underwater acoustic communication system 100. Figures 6 and 7 are diagrams showing an example of clock calibration.

[0046] 3 and 4 are flow charts showing an example of operation of the underwater unit 1. The processing unit 10 of the underwater unit 1 executes the information processing shown in the figures in accordance with a program. Fig. 5 is a flow chart showing an example of operation of the mother ship unit 2. The processing unit 20 of the mother ship unit 2 executes the information processing shown in the figures in accordance with a program.

[0047] The underwater unit 1 operates in a normal mode and a calibration mode. The calibration mode is executed at predetermined intervals (for example, every few minutes to every few hundred minutes).

[0048] 4, in normal mode, the underwater unit 1 transmits a pinger M1 (S22) each time a predetermined pinger transmission time arrives (S21: YES). The pinger M1 transmitted in normal mode does not include a calibration request. The pinger M1 may include detection data such as water pressure detected by a sensor (not shown).

[0049] Then, when the next calibration timing arrives (S23: YES), the underwater unit 1 transitions from the normal mode to the calibration mode.

[0050] 3, in the calibration mode, when a predetermined pinger transmission time T1 arrives (S11: YES), the underwater unit 1 transmits a pinger M1 (S12). The pinger M1 transmitted in the calibration mode includes a calibration request.

[0051] The pinger M1 includes a timestamp indicating the pinger transmission time T1 measured by the clock unit 13. Note that if the mother ship unit 2 stores the pinger transmission time T1 in advance, the pinger M1 does not need to include a timestamp indicating the pinger transmission time T1.

[0052] As shown in FIG. 5, when the mother ship unit 2 receives a pinger M1 transmitted from the underwater unit 1 (S31: YES), it acquires the pinger reception time T2 at which the pinger M1 was received (S32).

[0053] In this embodiment, the pinger reception time T2 measured by the clock unit 23 of the mother ship unit 2 is obtained, but this is not limited to this, and the pinger reception time T2 may also be obtained from outside the mother ship unit 2.

[0054] Pinger M1 is composed of a synchronization pulse and a data pulse (see Figure 8), and normally the reception start time of the data pulse is detected. Therefore, if the reception time of the synchronization pulse is not negligible, it is preferable to set the pinger reception time T2 to the time obtained by subtracting a value equivalent to the reception time of the synchronization pulse from the reception start time of the data pulse.

[0055] Next, the mother ship unit 2 extracts the pinger transmission time T1 from the pinger M1 (S33). That is, the mother ship unit 2 demodulates the data pulse of the pinger M1 to obtain the pinger transmission time T1 contained in the timestamp. Note that the order of S32 and S33 may be reversed.

[0056] In this embodiment, the pinger transmission time T1 is extracted from the pinger M1, but this is not limiting, and if the pinger transmission time T1 is stored in advance, it may be used.

[0057] Next, the mother ship unit 2 calculates the one-way propagation time P1 (= T2 - T1) from the pinger transmission time T1 to the pinger reception time T2 (S34). The one-way propagation time P1 is the time required for the pinger M1 to propagate from the underwater unit 1 to the mother ship unit 2.

[0058] Next, the mother ship unit 2 calculates the inter-unit distance between the underwater unit 1 and the mother ship unit 2 based on the calculated one-way propagation time P1 (S35). Specifically, the mother ship unit 2 calculates the inter-unit distance by multiplying the one-way propagation time P1 by the propagation speed of ultrasonic waves in water.

[0059] Furthermore, if the mother ship unit 2 is equipped with multiple receiving units 22, it is also possible to calculate the orientation of the underwater unit 1 relative to the mother ship unit 2 based on the difference in time at which multiple receiving units 22 arranged horizontally apart from each other receive the pinger M1.

[0060] In addition, calculation of the distance between the units (S35) may be performed only when the pinger M1 does not include a calibration request (S36: NO), i.e., only when the pinger M1 transmitted in normal mode is received.

[0061] The series of processes from transmitting the pinger M1 to calculating the inter-unit distance described above are processes based on the pinger method. In this embodiment, to calibrate the clock section 13 of the underwater unit 1, a process based on the transponder method described below is further executed.

[0062] If the pinger M1 includes a calibration request (S36: YES), i.e., if the mother ship unit 2 receives the pinger M1 transmitted in calibration mode, it transmits an ultrasonic message M2 (hereinafter also referred to as "response M2") including the one-way propagation time P1 (S37).

[0063] In this embodiment, the one-way propagation time P1 is included in the response M2, but this is not limiting, and the inter-unit distance may also be included in the response M2. As described above, the inter-unit distance is based on the one-way propagation time P1, so in this case too, it can be said that the response M2 includes the one-way propagation time P1.

[0064] 3, when the underwater unit 1 receives the response M2 transmitted from the mother ship unit 2 (S14: YES), it extracts the one-way propagation time P1 from the response M2 (S15). That is, the underwater unit 1 demodulates the data pulse of the response M2 to obtain the one-way propagation time P1.

[0065] Next, the underwater unit 1 acquires the response reception time T3 at which the response M2 is received, which is measured by the clock section 13 (S16).

[0066] For response M2, if the reception time of the synchronization pulse is not negligible, it is preferable to determine the response reception time T3 by subtracting a value equivalent to the reception time of the synchronization pulse from the reception start time of the data pulse.

[0067] Furthermore, in the case of response M2, the reception time of pinger M1 (reception time of synchronization pulse + reception time of data pulse) must also be taken into consideration, so it is preferable to determine the response reception time T3 by further subtracting a value equivalent to the reception time of pinger M1.

[0068] In addition, the processing time from when the mother ship unit 2 receives the pinger M1 to when it sends the response M2 is usually small enough not to affect clock calibration, but if the processing time is not negligible, it is preferable to determine the response reception time T3 by subtracting a value equivalent to the processing time.

[0069] Next, the underwater unit 1 calculates the round trip propagation time P2 (=T3-T1) from the pinger transmission time T1 to the response reception time T3 (S17). Note that S15 and S16-17 may be performed in reverse order.

[0070] The round-trip propagation time P2 is the time required for the pinger M1 to propagate from the underwater unit 1 to the mother ship unit 2 and for the response M2 to propagate from the mother ship unit 2 to the underwater unit 1, i.e., the time required for the ultrasonic message to travel round trip between the underwater unit 1 and the mother ship unit 2.

[0071] Therefore, half of the round-trip propagation time P2 (= (T3 - T1) / 2) corresponds to the time required for the ultrasonic message to propagate one way between the underwater unit 1 and the mother ship unit 2. Such round-trip propagation time P2 is a measurement value used in the transponder method, which does not require clock calibration.

[0072] Next, the underwater unit 1 calculates the error between the one-way propagation time P1 (=T2-T1) and half the round-trip propagation time P2 (=(T3-T1) / 2) (S18).

[0073] Next, the underwater unit 1 adjusts the time of the clock unit 13 based on the calculated error (S19). Specifically, the underwater unit 1 adjusts the time of the clock unit 13 so that the one-way propagation time P1 is equal to half the round-trip propagation time P2, that is, so that the error becomes zero.

[0074] For example, as shown in Figure 6, if the one-way propagation time P1 is less than half the round-trip propagation time P2, the time on the clock unit 13 is ahead of the clock unit 23 of the mother ship unit 2, so the underwater unit 1 delays the time on the clock unit 13.

[0075] On the other hand, as shown in Figure 7, when the one-way propagation time P1 is greater than half the round-trip propagation time P2, the time on the clock unit 13 is delayed relative to the clock unit 23 of the mother ship unit 2, so the underwater unit 1 advances the time on the clock unit 13.

[0076] In other words, the underwater unit 1 adjusts the time of the clock unit 13 so that the pinger reception time T2 measured by the clock unit 23 of the mother ship unit 2 is located in the middle between the pinger transmission time T1 and the response reception time T3.

[0077] This completes the calibration mode by the underwater unit 1. The underwater unit 1 then returns to the normal mode.

[0078] In the calibration mode, if a pinger M1 including a calibration request is sent (S12) and a response M2 is not received within a predetermined time (S14: NO), the underwater unit 1 will stop clock calibration, i.e., perform a so-called timeout (S13: YES).

[0079] According to the embodiment described above, wireless clock calibration can be achieved by adjusting the time of the clock unit 13 based on the one-way propagation time P1 and the round-trip propagation time P2.

[0080] That is, since the one-way propagation time P1 and the round-trip propagation time P2 are times measured using ultrasonic messages that propagate at approximately the same time, along the same route, and at the same speed, the one-way propagation time P1 and half the round-trip propagation time P2 should match, and if there is an error between them, this means that the two clock units 13, 23 are not synchronized. Therefore, by adjusting the time of the clock unit 13 so that this error is zero, it is possible to synchronize the two clock units 13, 23.

[0081] Furthermore, because the clock is calibrated wirelessly using ultrasonic messages, it is possible to calibrate the clock over ultrasonic propagation distances (e.g., hundreds to thousands of meters) during operation. Also, troublesome tasks such as cable connections are unnecessary. Furthermore, because ultrasonic messages propagating along the same path are used, calibration accuracy is not affected by changes in the speed of sound with depth (including acoustic ray refraction).

[0082] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made by those skilled in the art.

[0083] For example, the underwater unit 1 may correct the time adjustment amount of the clock unit 13 based on the amount of Doppler shift of the ultrasonic waves when receiving the pinger M1 or the response M2. This makes it possible to maintain calibration accuracy even when the underwater unit 1 or the mother ship unit 2 is moving.

[0084] In other words, when the underwater unit 1 or the mother ship unit 2 moves, a difference occurs between the outbound propagation distance and the return propagation distance of the ultrasonic message, so both units measure the Doppler amount when receiving the ultrasonic message and correct the time adjustment amount taking into account the fluctuation in propagation distance. The Doppler amount measured by the mother ship unit 2 is included in response M2 and provided to the underwater unit 1.

[0085] In addition, some of the processing of the underwater unit 1 or the mother ship unit 2 may be executed by the other unit or another computer. For example, the response M2 sent from the mother ship unit 2 may include the pinger reception time T2, and the underwater unit 1 may calculate the one-way propagation time P1.

[0086] Representative embodiments of the present invention will be listed below.

[0087] (1) An underwater acoustic communication system comprising: a first wave transceiver unit having a clock unit, the first wave transceiver unit configured to transmit a first ultrasonic message at a first time measured by the clock unit; and a second wave transceiver unit configured to receive the first ultrasonic message, obtain a second time at which the first ultrasonic message was received, calculate a one-way propagation time from the first time to the second time, and transmit a second ultrasonic message including the one-way propagation time, wherein the first wave transceiver unit is further configured to: receive the second ultrasonic message, extract the one-way propagation time from the second ultrasonic message, obtain a third time at which the second ultrasonic message was received, which is measured by the clock unit, calculate a round-trip propagation time from the first time to the third time, and adjust the time on the clock unit based on the one-way propagation time and the round-trip propagation time.

[0088] (2) The underwater acoustic communication system according to (1), wherein the first wave transmitting / receiving unit is configured to adjust the time of the clock unit based on the difference between the one-way propagation time and half the round-trip propagation time.

[0089] (3) The underwater acoustic communication system according to (1) or (2), wherein the first wave transmitting / receiving unit is configured to delay the time of the clock unit when the one-way propagation time is shorter than half of the round-trip propagation time.

[0090] (4) The underwater acoustic communication system according to any one of (1) to (3), wherein the first wave transmitting / receiving unit is configured to advance the time of the clock unit when the one-way propagation time is longer than half of the round-trip propagation time.

[0091] (5) The underwater acoustic communication system according to any one of (1) to (4), wherein the first wave transmitting / receiving unit is configured to adjust the time of the clock unit so that the one-way propagation time is equal to half of the round-trip propagation time.

[0092] (6) The underwater acoustic communication system according to any one of (1) to (5), wherein the first ultrasonic message includes a timestamp representing the first time, and the second wave transmitting / receiving unit is further configured to extract the first time from the first ultrasonic message.

[0093] (7) The underwater acoustic communication system according to any one of (1) to (6), wherein the second wave transmitting / receiving unit further includes a clock unit and is configured to acquire the second time measured by the clock unit.

[0094] (8) The underwater acoustic communication system according to any one of (1) to (7), wherein the first ultrasonic message includes a calibration request, and the second transceiver unit is configured to transmit the second ultrasonic message when the first ultrasonic message includes the calibration request.

[0095] (9) The underwater acoustic communication system according to any one of (1) to (8), wherein the first wave transmitting / receiving unit is further configured to stop adjusting the time of the clock unit when the second ultrasonic message is not received within a predetermined time after transmitting the first ultrasonic message.

[0096] (10) The underwater acoustic communication system according to any one of (1) to (9), wherein the second wave transmitting and receiving unit is further configured to calculate a distance between the first wave transmitting and receiving unit and the second wave transmitting and receiving unit based on the one-way propagation time.

[0097] (11) The underwater acoustic communication system according to any one of (1) to (10), wherein the first wave transmitting / receiving unit is further configured to correct an adjustment amount of the time of the clock unit based on an amount of Doppler shift of the ultrasonic waves when the first or second ultrasonic message is received.

[0098] (12) The underwater acoustic communication system according to any one of (1) to (11), wherein the first wave transmitting and receiving unit is installed on an underwater object, and the second wave transmitting and receiving unit is further configured to calculate a position of the underwater object based on the one-way propagation time.

[0099] (13) The underwater acoustic communication system according to (12), wherein the underwater object is an unmanned underwater vehicle or a fishing net.

[0100] (14) A clock calibration method for an underwater acoustic communication system comprising a first wave transmitting and receiving unit having a clock unit, and a second wave transmitting and receiving unit, the method comprising: transmitting a first ultrasonic message by the first wave transmitting and receiving unit at a first time measured by the clock unit; receiving the first ultrasonic message by the second wave transmitting and receiving unit; obtaining a second time at which the first ultrasonic message is received; calculating a one-way propagation time from the first time to the second time; transmitting a second ultrasonic message by the second wave transmitting and receiving unit; receiving the second ultrasonic message by the first wave transmitting and receiving unit; obtaining a third time at which the second ultrasonic message is received, which is measured by the clock unit; calculating a round-trip propagation time from the first time to the third time; and adjusting the time on the clock unit based on the one-way propagation time and the round-trip propagation time.

[0101] (15) A wave transmitting and receiving unit included in an underwater acoustic communication system and having a clock unit, configured to: transmit a first ultrasonic message at a first time measured by the clock unit; receive a second ultrasonic message transmitted from a counterpart wave transmitting and receiving unit that has received the first ultrasonic message, the second ultrasonic message including a one-way propagation time from the first time to a second time at which the first ultrasonic message is received; extract the one-way propagation time from the second ultrasonic message; obtain a third time at which the second ultrasonic message is received, measured by the clock unit; calculate a round-trip propagation time from the first time to the third time; and adjust the time on the clock unit based on the one-way propagation time and the round-trip propagation time.

[0102] (16) A wave transmitting and receiving unit included in an underwater acoustic communication system, the wave transmitting and receiving unit being configured to: receive a first ultrasonic message transmitted at a first time measured by a clock unit from a counterpart wave transmitting and receiving unit; acquire a second time at which the first ultrasonic message was received; calculate a one-way propagation time from the first time to the second time; and transmit a second ultrasonic message including the one-way propagation time.

[0103] (17) A program that causes a computer included in a wave transmitting and receiving unit having a clock unit, included in an underwater acoustic communication system, to execute the following: transmitting a first ultrasonic message at a first time measured by the clock unit; receiving a second ultrasonic message transmitted from a partner wave transmitting and receiving unit that has received the first ultrasonic message, the second ultrasonic message including a one-way propagation time from the first time to a second time when the first ultrasonic message is received; extracting the one-way propagation time from the second ultrasonic message; obtaining a third time when the second ultrasonic message is received, measured by the clock unit; calculating a round-trip propagation time from the first time to the third time; and adjusting the time on the clock unit based on the one-way propagation time and the round-trip propagation time.

[0104] (18) A program that causes a computer included in a wave transmitting / receiving unit included in an underwater acoustic communication system to execute the following: receive a first ultrasonic message transmitted from a counterpart wave transmitting / receiving unit having a clock unit at a first time measured by the clock unit; acquire a second time at which the first ultrasonic message is received; calculate a one-way propagation time from the first time to the second time; and transmit a second ultrasonic message including the one-way propagation time. term

[0105] Not necessarily all objects or advantages may be achieved in accordance with any particular embodiment described herein. Thus, for example, one skilled in the art will appreciate that a particular embodiment may be configured to operate to achieve or optimize one or more advantages as taught herein without necessarily achieving other objects or advantages as taught or suggested herein.

[0106] All processes described herein may be embodied and fully automated by software code modules executed by a computing system including one or more computers or processors. The code modules may be stored on any type of non-transitory computer-readable medium or other computer storage device. Some or all of the methods may be embodied in dedicated computer hardware.

[0107] Many other variations beyond those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain operations, events, or functions of any of the algorithms described herein may be performed in a different sequence, added, merged, or omitted entirely (e.g., not all described acts or events are necessary to execute an algorithm). Furthermore, in certain embodiments, operations or events may be performed in parallel rather than sequentially, e.g., via multithreading, interrupt processing, or multiple processors or processor cores, or on other parallel architectures. Furthermore, different tasks or processes may be performed by different machines and / or computing systems that may function together.

[0108] The various illustrative logical blocks and modules described in connection with the embodiments disclosed herein may be implemented or executed by a machine such as a processor. The processor may be a microprocessor, but alternatively, the processor may be a controller, microcontroller, or state machine, or a combination thereof. The processor may include electrical circuitry configured to process computer-executable instructions. In another embodiment, the processor includes an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable device that performs logical operations without processing computer-executable instructions. A processor may also be implemented as a combination of computing devices, such as a combination of a digital signal processor (DSP) and a microprocessor, multiple microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration. Although described herein primarily with reference to digital technology, a processor may also include primarily analog elements. For example, some or all of the signal processing algorithms described herein may be implemented by analog circuitry or mixed analog and digital circuitry. The computing environment can include any type of computer system, including, but not limited to, a microprocessor, mainframe computer, digital signal processor, portable computing device, device controller, or computer system based on a computational engine within an appliance.

[0109] Unless otherwise specified, conditional language such as "can," "could," "would," or "potential" is understood within the context in which it is generally used to convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not. Thus, such conditional language does not generally imply that features, elements, and / or steps are required in any manner in one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps are included in or performed in any particular embodiment.

[0110] Disjunctive language such as "at least one of X, Y, Z," unless specifically stated otherwise, is understood in its general context to indicate that an item, term, etc. can be either X, Y, Z, or any combination thereof (e.g., X, Y, Z). Thus, such disjunctive language does not generally imply that a particular embodiment requires at least one of X, at least one of Y, or at least one of Z, respectively, to be present.

[0111] Any process descriptions, elements, or blocks in the flow diagrams described herein and / or illustrated in the accompanying drawings should be understood as potentially representing modules, segments, or portions of code, comprising one or more executable instructions for implementing a particular logical function or element in the process. Alternative embodiments are included within the scope of the embodiments described herein, in which elements or functions may be performed out of order, substantially simultaneously, or in reverse order from that shown or described, depending on the functionality involved, as will be understood by those skilled in the art.

[0112] Unless otherwise expressly stated, numeral terms such as "one" should generally be construed to include one or more described items. Thus, phrases such as "one device configured to" are intended to include one or more listed devices. Such one or more listed devices may also be collectively configured to perform the recited reference. For example, "a processor configured to perform the following A, B, and C" may include a first processor configured to perform A and a second processor configured to perform B and C. Additionally, even if a specific number of enumerations of the introduced embodiments are explicitly recited, those skilled in the art should construe such enumerations to typically mean at least the recited number (e.g., the mere enumeration of "two enumerations" without other modifiers typically means at least two enumerations, or two or more enumerations).

[0113] In general, it will be appreciated by those skilled in the art that the terms used herein generally intend "non-limiting" terms (e.g., the term "including" should be interpreted as "including but not limited to at least," the term "having" should be interpreted as "having at least," the term "including" should be interpreted as "including, but not limited to," etc.).

[0114] For purposes of description, the term "horizontal" as used herein is defined as a plane parallel to the plane or surface of the floor of the area in which the described system is used or the plane in which the described method is performed, regardless of its orientation. The term "floor" can be interchanged with the terms "ground" or "water surface." The term "vertical / plumb" refers to a direction perpendicular / vertical to a defined horizontal line. Terms such as "upper," "lower," "below," "top," "side," "higher," "lower," "above," "over," "below," etc. are defined relative to the horizontal plane.

[0115] As used herein, the terms "attach," "connect," "mate," and other related terms, unless otherwise noted, should be interpreted to include detachable, movable, fixed, adjustable, and / or removable connections or couplings. Connections / couplings include direct connections and / or connections with intermediate structures between the two components described.

[0116] Unless otherwise expressly stated, as used herein, numbers preceded by terms such as "approximately," "about," and "substantially" are inclusive of the recited number and also refer to an amount close to the recited amount that performs the desired function or achieves the desired result. For example, "approximately," "about," and "substantially" refer to values ​​less than 10% of the recited numerical value, unless otherwise expressly stated. As used herein, features of the disclosed embodiments preceded by terms such as "approximately," "about," and "substantially" refer to features that have some variability that also perform the desired function or achieve the desired result for that feature.

[0117] Many variations and modifications may be made to the above-described embodiments, and these elements should be understood to be among other acceptable examples. All such modifications and variations are intended to be included within the scope of this disclosure and are protected by the following claims.

[0118] REFERENCE SIGNS LIST 1 Underwater unit (example of first wave transmitting / receiving unit), 2 Mother ship unit (example of second wave transmitting / receiving unit), 10 Processing unit, 11 Wave transmitting unit, 12 Wave receiving unit, 13 Clock unit, 20 Processing unit, 21 Wave transmitting unit, 22 Wave receiving unit, 23 Clock unit, 100 Underwater acoustic communication system, SH Ship, ST Underwater object

Claims

1. An underwater acoustic communication system comprising: a first wave transceiver unit having a clock unit, the first wave transceiver unit configured to transmit a first ultrasonic message at a first time measured by the clock unit; and a second wave transceiver unit configured to receive the first ultrasonic message, obtain a second time at which the first ultrasonic message was received, calculate a one-way propagation time from the first time to the second time, and transmit a second ultrasonic message including the one-way propagation time, wherein the first wave transceiver unit is further configured to: receive the second ultrasonic message, extract the one-way propagation time from the second ultrasonic message, obtain a third time at which the second ultrasonic message was received, measured by the clock unit, calculate a round-trip propagation time from the first time to the third time, and adjust the time on the clock unit based on the one-way propagation time and the round-trip propagation time.

2. The underwater acoustic communication system according to claim 1, wherein the first wave transmitting / receiving unit is configured to adjust the time of the clock unit based on the difference between the one-way propagation time and half the round-trip propagation time.

3. The underwater acoustic communication system according to claim 1, wherein the first wave transmitting / receiving unit is configured to delay the time of the clock unit when the one-way propagation time is shorter than half the round-trip propagation time.

4. The underwater acoustic communication system according to claim 1, wherein the first wave transmitting / receiving unit is configured to advance the time of the clock unit when the one-way propagation time is greater than half the round-trip propagation time.

5. An underwater acoustic communication system according to claim 1, wherein the first wave transmitting / receiving unit is configured to adjust the time of the clock unit so that the one-way propagation time is equal to half of the round-trip propagation time.

6. The underwater acoustic communication system of claim 1, wherein the first ultrasonic message includes a timestamp representing the first time, and the second transceiver unit is further configured to extract the first time from the first ultrasonic message.

7. The underwater acoustic communication system according to claim 1, wherein the second wave transmitting / receiving unit further comprises a clock unit and is configured to acquire the second time measured by the clock unit.

8. The underwater acoustic communication system of claim 1, wherein the first ultrasonic message includes a calibration request, and the second transceiver unit is configured to transmit the second ultrasonic message when the first ultrasonic message includes the calibration request.

9. The underwater acoustic communication system according to claim 1, wherein the first transmitting / receiving unit is further configured to stop adjusting the time of the clock unit if the second ultrasonic message is not received within a predetermined time after transmitting the first ultrasonic message.

10. The underwater acoustic communication system according to claim 1, wherein the second wave transmitting / receiving unit is further configured to calculate the distance between the first wave transmitting / receiving unit and the second wave transmitting / receiving unit based on the one-way propagation time.

11. The underwater acoustic communication system according to claim 1, wherein the first wave transmitting / receiving unit is further configured to correct the amount of adjustment of the time of the clock unit based on the amount of Doppler shift of the ultrasonic waves when the first or second ultrasonic message is received.

12. The underwater acoustic communication system of claim 1, wherein the first wave transmitting / receiving unit is installed on an underwater object, and the second wave transmitting / receiving unit is further configured to calculate the position of the underwater object based on the one-way propagation time.

13. The underwater acoustic communication system according to claim 12, wherein the underwater object is an unmanned underwater vehicle or a fishing net.

14. A clock calibration method for an underwater acoustic communication system comprising a first wave transceiver unit having a clock unit, and a second wave transceiver unit, comprising: transmitting a first ultrasonic message by the first wave transceiver unit at a first time measured by the clock unit; receiving the first ultrasonic message by the second wave transceiver unit; obtaining a second time at which the first ultrasonic message is received; calculating a one-way propagation time from the first time to the second time; transmitting a second ultrasonic message by the second wave transceiver unit; receiving the second ultrasonic message by the first wave transceiver unit; obtaining a third time at which the second ultrasonic message is received, which is measured by the clock unit; calculating a round-trip propagation time from the first time to the third time; and adjusting the time on the clock unit based on the one-way propagation time and the round-trip propagation time.

15. A wave transmitting and receiving unit included in an underwater acoustic communication system and equipped with a clock unit, configured to: transmit a first ultrasonic message at a first time measured by the clock unit; receive a second ultrasonic message transmitted from a partner wave transmitting and receiving unit that has received the first ultrasonic message, the second ultrasonic message including a one-way propagation time from the first time to a second time at which the first ultrasonic message is received; extract the one-way propagation time from the second ultrasonic message; obtain a third time at which the second ultrasonic message is received, measured by the clock unit; calculate a round-trip propagation time from the first time to the third time; and adjust the time on the clock unit based on the one-way propagation time and the round-trip propagation time.

16. A wave transmitting and receiving unit included in an underwater acoustic communication system, configured to: receive a first ultrasonic message transmitted from a counterpart wave transmitting and receiving unit having a clock unit at a first time measured by the clock unit; obtain a second time at which the first ultrasonic message was received; calculate a one-way propagation time from the first time to the second time; and transmit a second ultrasonic message including the one-way propagation time.

17. A program that causes a computer included in a wave transmitting and receiving unit equipped with a clock unit, included in an underwater acoustic communication system, to execute the following operations: transmitting a first ultrasonic message at a first time measured by the clock unit; receiving a second ultrasonic message, which is transmitted from a partner wave transmitting and receiving unit that has received the first ultrasonic message and which includes a one-way propagation time from the first time to a second time when the first ultrasonic message is received; extracting the one-way propagation time from the second ultrasonic message; obtaining a third time when the second ultrasonic message is received, which is measured by the clock unit; calculating the round-trip propagation time from the first time to the third time; and adjusting the time on the clock unit based on the one-way propagation time and the round-trip propagation time.

18. A program that causes a computer included in a transmitter / receiver unit included in an underwater acoustic communication system to perform the following operations: receive a first ultrasonic message transmitted from a counterpart transmitter / receiver unit having a clock unit at a first time measured by the clock unit; obtain a second time at which the first ultrasonic message was received; calculate a one-way propagation time from the first time to the second time; and transmit a second ultrasonic message including the one-way propagation time.

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