Underwater wireless communication apparatus and method

Abstract

To provide an underwater wireless communication device and method capable of suppressing degradation of communication quality due to multipath waves.SOLUTION: An underwater wireless communication device 10 provided in a mobile body 2 capable of moving on or in water and performing underwater wireless communication using acoustic signals includes a wave transmission unit 30 that transmits an acoustic signal to the other party's underwater wireless communication device, a wave receiving unit 40 that receives an acoustic signal from the other party's underwater wireless communication device, and an acoustic communication control unit 20 that controls the wave transmission unit and the wave receiving unit, and the acoustic communication control unit includes a transmission timing control unit 21 that controls a transmission time and a transmission interval of signals transmitted from the wave transmission unit. The transmission timing control unit controls the transmission time and the transmission interval such that the influence of the deterioration of communication quality due to multipath waves in the wave receiving unit of the other party's underwater wireless communication device is less than or equal to a predetermined value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an underwater wireless communication device and method.

Background Art

[0002] In recent years, for the purpose of improving the efficiency of marine resource surveys, the development of technology for operating multiple AUVs (Autonomous Underwater Vehicles) has been actively carried out, and the underwater wireless communication technology used between a mother ship and an AUV has attracted attention. As underwater wireless communication technologies, methods using acoustic technology and optical technology have been proposed.

[0003] Acoustic wireless communication is suitable for long-distance communication underwater because the propagation loss is small. However, in underwater wireless communication, since the speed of sound is as slow as 1500 meters per second, the arrival time of multipath waves is slower compared to a communication system using radio waves. Therefore, there is a possibility that multipath waves interfere during the reception of direct waves, and when interference occurs, the communication quality deteriorates over a long period of time. For this reason, the technology disclosed in Patent Document 1 has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Multipath waves in underwater wireless communication have the following additional characteristics: Firstly, the received level of multipath waves is affected by the reflectivity of the sea surface, seabed, structures, etc., and differences in propagation paths. Therefore, the received level is not necessarily strongest in the order in which the multipath waves arrive, and the strength of the received levels may not be in order of arrival. Secondly, underwater, various reflected waves are received from multiple directions with different arrival delay times. Thirdly, when conducting underwater wireless communication in an outdoor field, the communication environment is not uniform due to the influence of wave changes due to weather, and the topography and geology below the surface, resulting in a deterioration of communication quality. Fourthly, because the relative position of the mother ship and the AUV fluctuates, the communication environment changes dynamically as the transmitting and receiving points move, resulting in a deterioration of communication quality. Fifthly, decision feedback equivalents, known as multipath wave rejection techniques, have difficulty dealing with multipaths with large delay times. This is because rejecting multipath waves with large delay times using decision feedback equivalents requires a large hardware circuit and high power consumption. Sixth, it is known that multipath waves can be removed by spatial separation techniques using beamforming (Patent Document 1), but in this case, it is difficult to remove multipath waves that arrive at the receiving section from the same direction as the direct wave.

[0006] The present invention has been made in view of the above problems, and aims to provide an underwater wireless communication device and method that can suppress the deterioration of communication quality due to multipath waves. [Means for solving the problem]

[0007] To solve the above problems, an underwater wireless communication device according to one aspect of the present invention is provided on a mobile body that can move on or underwater, and performs underwater wireless communication using acoustic signals, comprising: a transmitter that transmits acoustic signals to another underwater wireless communication device; a receiver that receives acoustic signals from the other underwater wireless communication device; and an acoustic communication control unit that controls the transmitter and receiver, wherein the acoustic communication control unit includes a transmission timing control unit that controls the transmission time and transmission interval of the signal transmitted from the transmitter, and the transmission timing control unit controls the transmission time and transmission interval so that the effect of multipath waves on the degradation of communication quality in the receiver of the other underwater wireless communication device is less than or equal to a predetermined value. [Effects of the Invention]

[0008] According to the present invention, the transmission time and transmission interval can be controlled so that the effect of multipath waves on the receiving section of the other party's underwater wireless communication device on the deterioration of communication quality is below a predetermined value, thereby suppressing deterioration of the quality of underwater wireless communication. [Brief explanation of the drawing]

[0009] [Figure 1] An overall schematic diagram of an underwater wireless communication system that uses acoustic signals to conduct underwater wireless communication between multiple moving objects. [Figure 2] Block diagram of an underwater wireless communication device. [Figure 3] An explanatory diagram showing how underwater wireless communication is performed between multiple acoustic communication control units. [Figure 4] An explanatory diagram showing examples of direct waves and multipath waves. [Figure 5] An explanatory diagram showing how multipath waves are removed by spatial separation using beamforming. [Figure 6] An example of a table for managing the transmission interval and data volume requested by the user. [Figure 7] An example of a table for managing the conditions for determining the transmission timing. [Figure 8] An example of a table for managing settings when actively measuring the effects of multipath waves (active type). [Figure 9] Example of a table for managing parameters for generating an acoustic signal. [Figure 10] Example of a table for managing the required input SNR (signal-noise ratio). [Figure 11] Example of a table for managing parameters used for estimating multipath waves. [Figure 12] Example of a table for managing the timing of transmitting an acoustic signal. [Figure 13] Example of a table for managing parameters used for frequency division when transmitting an acoustic signal by frequency division. [Figure 14] Example of a table for managing conditions for updating transmission timing. [Figure 15] Example of a table for managing measurement results of multipath waves by an active type. [Figure 16] Explanatory diagram showing the transmission time and transmission interval of a packet of an acoustic signal (also referred to as an acoustic packet). [Figure 17] Explanatory diagram when adding a multipath measurement signal to an acoustic packet. [Figure 18] Explanatory diagram when transmitting an acoustic packet by frequency division. [Figure 19] Flowchart of a process for controlling transmission timing. [Figure 20] Flowchart of a process for determining transmission timing in a passive type. [Figure 21] Explanatory diagram for determining the delay of a multipath wave that degrades communication quality from the level difference between a direct wave and a multipath wave, and determining the maximum transmission time and transmission waiting time (transmission interval). [Figure 22] Another explanatory diagram showing how to determine the transmission waiting time. [Figure 23] Flowchart of a process for determining transmission timing. [Figure 24] Flowchart following Figure 23. [Figure 25] Flowchart of a process for determining transmission timing in an active type. [Figure 26]A flowchart illustrating the process for determining when to update each parameter used to determine the transmission timing. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings. The underwater wireless communication device 10 according to this embodiment ensures the communication quality (SNR: Signal to Noise Ratio) necessary for communication between multiple underwater wireless communication devices by controlling the transmission timing so that the influence of the multipath wave 101 on the direct wave 100 at the receiving side is less than or equal to a predetermined value.

[0011] As will be described in detail later, in the underwater wireless communication device 10 according to this embodiment, the reception level and arrival time of the multipath wave at the receiving end are estimated from the coordinates of the transmitting underwater wireless communication device, the coordinates of the receiving underwater wireless communication device, and information of the communication field (water depth and bottom type).

[0012] To accurately transmit data from a transmitting underwater wireless communication device to a receiving underwater wireless communication device (the other party's underwater wireless communication device), a communication quality above a predetermined level is required. Therefore, if the transmitting underwater wireless communication device estimates the presence of multipath waves that degrade communication quality, it acquires the delay time and reception level of the multipath waves that are causing the degradation of communication quality.

[0013] The transmitting underwater radio communication device determines the transmission timing by determining the arrival time of the first multipath and the duration of the impact on communication quality caused by subsequent multipaths, which affect communication quality. The determined transmission timing includes several parameters, such as transmission time and transmission waiting time. The transmitting underwater radio communication device transmits data according to the determined transmission timing. This reduces the impact on communication quality caused by multipath waves.

[0014] Simply transmitting data according to a predetermined transmission timing may not always satisfy the user's requirements. For example, transmitting data at a predetermined timing may not meet the user's required transmission interval and the amount of data to be transmitted within that interval. In this case, the transmitting underwater wireless communication device divides the frequency bandwidth of the transmitted signal and sequentially switches between the frequency bandwidths of the transmitted signal to determine a transmission timing that satisfies the user's requirements (transmission interval and data amount).

[0015] Furthermore, in the underwater wireless communication device of this embodiment, the effects of estimated multipath waves are actively corrected by transmitting a multipath wave measurement signal. The multipath wave measurement signal is an acoustic signal transmitted from the transmitting underwater wireless communication device to the receiving underwater wireless communication device in order to measure the effects of multipath waves at the receiving end. The multipath wave measurement signal is transmitted from the transmitting underwater wireless communication device to the receiving underwater wireless communication device, and the receiving underwater wireless communication device measures the reception level and arrival time of multiple multipath waves. The receiving underwater wireless communication device transmits the measurement results (multipath wave information) to the transmitting underwater wireless communication device. This improves the accuracy of the transmission timing determined by the transmitting underwater wireless communication device and optimizes the transmission timing.

[0016] Furthermore, by using a decision feedback type equivalent in the receiving underwater wireless communication device, the influence of multipath waves with short delay times can be reduced. Therefore, by using the appropriate transmission timing determination method according to this embodiment in combination with a decision feedback type equivalent, both multipath waves with long delay times and multipath waves with short delay times can be reduced, thereby improving the quality of underwater wireless communication.

[0017] Thus, the underwater wireless communication device according to this embodiment can suppress SNR degradation due to multipath waves and maintain communication quality with a compact and low-power hardware configuration, without being limited by the delay time of multipath waves relative to the direct wave.

[0018] Furthermore, in the underwater wireless communication device of this embodiment, even when direct waves and multipath waves arrive at the receiving unit from the same direction, the influence of multipath waves can be suppressed and communication quality can be maintained. [Examples]

[0019] A first embodiment will be described using Figures 1 to 26. Figure 1 shows the overall configuration of the underwater wireless communication system 1. The underwater wireless communication system 1 includes an underwater wireless communication device 10M mounted on the first mobile body 2M and an underwater wireless communication device 10S mounted on the second mobile body 2S.

[0020] The first mobile body 2M and the second mobile body 2S are examples of "mobile bodies that can move on or underwater." The first mobile body 2M is, for example, a manned or unmanned vessel. The first mobile body 2M may also be an ASV (small unmanned vehicle) or a buoy. The second mobile body 2S is, for example, an unmanned or manned submersible. Hereinafter, mobile bodies 2 and 3 may be referred to as "underwater equipment." In this case, "underwater equipment" does not mean equipment that is always in the water, but rather equipment in which at least a part of its main body is located underwater.

[0021] This embodiment primarily describes the case in which an acoustic signal is transmitted from an underwater radio communication device 10M mounted on a mother ship 2M, which is the first mobile unit, to an underwater radio communication device 10S mounted on an AUV 2S, which is the second mobile unit. The underwater radio communication device 10M mounted on the mother ship 2M is the transmitting underwater radio communication device. The underwater radio communication device 10S mounted on the AUV 2S is the receiving underwater radio communication device (the other party's underwater radio communication device).

[0022] The underwater wireless communication device 10M comprises, for example, an acoustic communication control unit 20M, a transmitter 30M, and a receiver 40M, and is electrically connected to the sensor 50M and the higher-level system 60M. Details of the acoustic communication control unit 20M will be described later in Figure 2. The higher-level system 60M is a system that utilizes underwater wireless communication using acoustic signals, and is, for example, an ocean survey system, a seabed exploration system, or a remote control system. Various observation instruments may be used instead of the higher-level system 60M.

[0023] The acoustic communication control unit 20M determines the timing for transmitting an acoustic signal to the other party's underwater wireless communication device 10S to meet the user's requirements and controls the acoustic communication. The acoustic communication control unit 20M includes a transmission timing control unit 21M. Although not shown in Figure 1, the acoustic communication control unit 20S of AUV2A also includes a transmission timing control unit 21 (see Figure 2).

[0024] The transmitter 30M transmits acoustic signal packets (also called acoustic packets) toward the receiver 40S of the other underwater wireless communication device 10S. The receiver 40M receives the acoustic signals transmitted from the transmitter 30S of the other underwater wireless communication device 10S.

[0025] Sensor 50M measures the underwater environment and outputs a signal. Sensor 50M actually includes multiple types of sensors. Sensor 50M may include, for example, a position sensor, a water temperature sensor, a salinity sensor, a sound velocity sensor, etc. Some or all of the sensors attached to the engine or electric motor (not shown) of the mother ship 2M may be used as Sensor 50M.

[0026] In the following, unless otherwise specified, the underwater wireless devices 10M and 10S will be referred to as the underwater wireless communication device 10. Similarly, unless otherwise specified, the acoustic communication control units 20M and 20S will be referred to as the acoustic communication control unit 20. Unless otherwise specified, the transmitter units 30M and 30S, receiver units 40M and 40S, sensors 50M and 50S, and higher-level systems 60M and 60S will be referred to as the transmitter unit 30, receiver unit 40, sensor 50, and higher-level system 60, respectively.

[0027] When transmitting an acoustic signal from the transmitter 30M to the receiver 40S, a direct wave 100M and multiple multipath waves 101M are generated. Figure 1 shows only one multipath wave. If the multipath wave 101M is received while the direct wave 100M is being received, the SNR decreases. Similarly, when transmitting an acoustic signal from the transmitter 30S to the receiver 40M, a direct wave 100S and multiple multipath waves 101S are generated, affecting the communication quality.

[0028] Figure 2 is a block diagram showing the functional configuration of the acoustic communication control unit 20. The acoustic communication control unit 20 includes circuits such as a transmission timing control unit 21, a transmission data modulation unit 22, a signal coupling unit 23, a multipath measurement signal generation unit 24, and a receiving unit 25.

[0029] The transmission timing control unit 21 determines the transmission parameters when transmitting a signal containing at least one acoustic packet. These transmission parameters include, for example, the transmission time and the transmission interval. The transmission timing control unit 21 calculates the multipath waves generated in the receiving underwater wireless communication device using two methods, a passive type and an active type, and determines the transmission time and transmission interval such that the necessary communication can be performed as much as possible.

[0030] In the passive method of estimating multipath waves, the transmission timing control unit 21 estimates the multipath waves generated in the receiving underwater wireless communication device based on various measurement signals from the sensor 50 (passive type). When the transmission timing control unit 21 actively measures the multipath waves in the receiving underwater wireless communication device, it adds a multipath measurement signal to the transmission signal and transmits it from the transmitter unit 30, and obtains information on the multipath waves measured by that multipath measurement signal from the receiving underwater wireless communication device (active type).

[0031] The transmission data modulation unit 22 modulates the transmission data received from the higher-level system 60 to generate a transmission signal. Except when actively measuring multipath waves, the generated transmission signal is transmitted as is from the transmitter unit 30 to the other party's underwater wireless communication device.

[0032] In the signal coupling unit 23, the transmission signal generated by the transmission data modulation unit 22 is combined with the multipath measurement signal generated by the multipath measurement signal generation unit 24. In the passive type, the multipath measurement signal is not added to the transmission signal. Details on how to actively investigate the effect of multipath waves on the receiving side of an acoustic signal from the transmitting side will be explained further in Figure 3 and subsequent figures.

[0033] The receiving unit 40 receives the transmission signal (response signal) from the other party's underwater wireless communication device (the underwater wireless communication device that has received the transmission signal from the transmitting unit 30). The receiving unit 40 receives not only the direct wave 100 that arrives directly from the other party's underwater wireless communication device, but also multipath waves 101 that arrive after being reflected in various ways near the sea surface and on the seabed. If the other party's underwater wireless communication device transmits the acoustic signal at an appropriate transmission timing, the deterioration of communication quality due to multipath waves at the receiving unit 40 can be suppressed.

[0034] The receiving unit 25 demodulates the acoustic signal received by the wave receiving unit 40 using the demodulation unit 251. The receiving unit 25 removes multipath waves with a small arrival time difference from the direct wave 100 using a decision feedback type equivalent 252. The receiving unit 25 sends the demodulated data with improved communication quality to the higher-level system 60.

[0035] The following information is used when estimating the path through which acoustic signals propagate from the transmitting underwater wireless communication device to the receiving underwater wireless communication device.

[0036] The frequency range is determined from the "carrier frequency" and "signal bandwidth," and this frequency range is used to estimate the propagation path. When the frequency is divided, the "carrier frequency" and "signal bandwidth" for each division are input to the acoustic communication control unit 20.

[0037] The coordinate information of the transmitting device (the transmitting underwater radio communication device) and the coordinate information of the receiving device (the receiving underwater radio communication device) can be used to estimate multipath paths on the sea surface and seabed. The coordinate information is in the form of three axes (X, Y, Z). The coordinate information may also be expressed as latitude, longitude, depth of the transmitting unit, and depth of the receiving unit. The coordinate information may be absolute coordinates or relative coordinates between two points. When measuring with an active type, if position information can be obtained from the receiving device, the coordinate information provided by the receiving device to the transmitting device is used.

[0038] "Sea area depth information" refers to depth information from the sea surface to the seabed in the area where underwater wireless communication is conducted (communication area), and is used to estimate the multipath path to the seabed. When measuring using the active type, if there are results from adjusting the parameters of the propagation path model, those adjusted values ​​will be used.

[0039] The "seabed sediment (reflection coefficient)" is used to estimate the sound pressure level reflected by multipath waves off the seabed. When measuring with an active type, if there are results from adjusting the parameters of the propagation path model, those adjusted values ​​are used.

[0040] "Speed ​​of sound or sea surface temperature, salinity" are sound wave propagation parameters used for estimating multipath propagation paths. When measuring with an active type, if there are results from adjusting the parameters of the propagation path model, those adjusted values ​​are used.

[0041] "Transmitter directivity" is a parameter used in estimating multipath propagation paths, indicating the deviation of the transmitted level due to the transmitter directivity for each propagation path. "Receiver directivity" is a parameter used in estimating multipath propagation paths, indicating the deviation of the received level due to the receiver directivity for each propagation path.

[0042] "Multipath delay" is the relative delay time of the multipath wave, with the arrival time of the direct wave as the reference time.

[0043] "Multipath reception level" is the relative reception level of the multipath wave, with the direct wave as the reference reception level.

[0044] As shown in Figure 3, the relationship between the transmitting underwater wireless communication device and the receiving underwater wireless communication device can also be reversed. Figure 3 is a simplified explanatory diagram showing the communication between underwater wireless communication devices.

[0045] The transmission timing control unit of the acoustic communication control unit 20M controls the transmission timing of the transmission signal to be sent to the acoustic communication control unit 20S.

[0046] As mentioned above, there are two types of algorithms for controlling the transmission timing: passive and active. In the passive type, the transmission timing control unit estimates the delay time and reception level of multipath caused by communication between the transmitting underwater wireless communication device and the receiving underwater wireless communication device, based on information input from the higher-level system 60M of the acoustic communication control unit 20M and various information input from the sensor 50. Once the transmission timing control unit estimates the delay time and reception level of the multipath wave, it determines the transmission timing and signal length (in other words, the transmission interval) in order to avoid multipath, which is a factor that degrades communication quality, in order to ensure the required communication quality (required SNR).

[0047] In the active type, the acoustic communication control unit 20M transmits a broadband signal (e.g., pulse compression) as the transmission signal. The transmission signal propagates through the propagation path MS and is received by the acoustic communication control unit 20S. The acoustic communication control unit 20S measures the multipath conditions of the propagation path MS from the received broadband signal. The acoustic communication control unit 20S includes the measured multipath conditions in the transmission signal as information indicating the communication environment and transmits it to the acoustic communication control unit 20M. By receiving the transmission signal from the acoustic communication control unit 20S, the acoustic communication control unit 20M can understand the multipath conditions of the propagation path MS and select an appropriate transmission timing.

[0048] The passive and active transmission timing control described above can be performed individually (bidirectionally) by the acoustic communication control units 20M and 20S, respectively. When focusing on the acoustic communication control unit 20S, the multipath situation of the propagation path SM becomes a concern.

[0049] The propagation paths MS and SM include the directional characteristics of the transmitter 30 and the receiver 40. Therefore, when both the acoustic communication control units 20M and 20S use the same product or a transmitter 30 and receiver 40 with similar directional characteristics, and communicate using the same frequency band, the propagation paths MS and SM can be considered as the same propagation path. In this case, it is sufficient to actively measure the multipath by transmitting a multipath measurement signal from either the acoustic communication control unit 20M or 20S. The measurement results can then be applied to the transmission timing control unit of the other acoustic communication control unit.

[0050] Figure 4 is an explanatory diagram showing an example of a direct wave 100 and a multipath wave 101. The acoustic signal transmitted from the transmitting unit 30 to the receiving unit 40 includes not only the direct wave 100 that reaches the receiving unit 40 directly from the transmitting unit 30, but also multipath waves 101 that reach the receiving unit 40 after being reflected in various ways by the sea surface or seabed, or by sediment, obstacles, floating objects (not shown). The difference between the time when the multipath wave 101 is received by the receiving unit 40 and the time when the direct wave 100 is received by the receiving unit 40, i.e., the delay time, varies in length. If the multipath waves 101 arrive at the receiving unit 40 one after another while the receiving unit 40 is receiving the direct wave 100, the communication quality deteriorates. Therefore, in this embodiment, the transmission timing and transmission interval when transmitting an acoustic signal from the transmitting underwater wireless communication device to the receiving underwater wireless communication device are appropriately determined so as to minimize the deterioration of communication quality due to multipath waves.

[0051] Figure 5 schematically illustrates how multipath waves are removed by spatial separation using beamforming. The acoustic communication control unit 20 receives only acoustic signals arriving from the three beam patterns BP. Multipath waves 101A reaching the receiving unit 40 from sources other than the beam patterns BP are not received.

[0052] Since the beam pattern BP is set to match the direction of arrival of the direct wave 100, the acoustic communication control unit 20 can receive the direct wave 100. However, multipath waves 101 arriving from a direction close to the direction of arrival of the direct wave 100 are also received by the receiving unit 40. Since it is not possible to remove multipath waves 101 arriving from a direction that matches the beam pattern BP, it is difficult to eliminate the effects of multipath waves using only the beam pattern BP. Therefore, in this embodiment, as described above, the acoustic communication control unit 20 appropriately determines the transmission timing (transmission time and transmission interval) and transmits to the other party's underwater wireless communication device.

[0053] Figures 6 to 15 illustrate examples of tables used in the acoustic communication control unit 20. Figure 6 shows table T1 for managing user request values. The user request value management table T1 includes items and the corresponding request values. User request values ​​are the performance requirements requested by the user for underwater wireless communication. Examples of user request values ​​include the requested transmission interval and the amount of data to be transmitted.

[0054] Figure 7 shows table T2, which manages the conditions for determining the transmission timing. The transmission timing determination condition management table T2 manages, for example, the maximum transmittable frequency range, ambient noise (sound pressure equivalent value), transmission level, near-range multipath reflection rejection range, and near-range multipath rejection residual correction. The values ​​of these conditions are input to the acoustic communication control unit 20 from the user or the higher-level system 60.

[0055] The following describes the information used to determine the transmission timing. The "Maximum Usable Frequency Range" is the maximum frequency range information available for the transmitted signal. When transmitting by dividing the frequency, the frequency is divided within the maximum frequency range.

[0056] "Required Input SNR" indicates the ratio of the direct wave reception level to the interference level required for reception processing.

[0057] The "User Request Transmission Interval" is the transmission interval and the amount of data transmitted per transmission interval, determined by the user according to the application being used (e.g., video, telemetry).

[0058] "Multipath delay" and "multipath reception level" are pieces of information used to calculate the input SNR. The multipath delay and multipath reception level are calculated using either the propagation path estimation result (passive type) or the multipath measurement result (active type).

[0059] "Environmental noise" refers to noise levels other than multipath noise at the receiving point, such as mechanical and electrical noises emitted by various devices mounted on the mobile device.

[0060] The "near-range multipath reflection rejection range" is calculated from the number of filter taps and the signal bandwidth to determine the minimum value of the multipath delay to be detected using the method described in this embodiment.

[0061] "Near-range multipath removal residual correction" is the residual level after removal by the near-range multipath removal function, and is used as a correction when calculating the input SNR.

[0062] "Transmission interval" is the transmission interval for each carrier frequency. "Transmission time" is the transmission time within each carrier frequency transmission interval. "Number of frequency divisions" is the number of divisions used to divide the maximum usable frequency range, which determines the carrier frequency and signal bandwidth.

[0063] Figure 8 shows an example of Table T3 for managing settings when actively measuring the effects of multipath waves (active type). This Table T3 manages items and their corresponding input values ​​(settings). For example, Table T3 manages the type of multipath measurement signal and the time interval from the multipath measurement signal to the acoustic packet. The types of multipath measurement signals will be described later in Figure 17.

[0064] Figure 9 shows table T4, which manages the parameters for generating acoustic signals. The acoustic signal generation parameter management table T4 manages items and their input values. Items include, for example, the coding rate of user data, the number of bits per symbol, the number of bits for error detection information, and the total number of symbols for overhead information. Overhead information includes, for example, synchronization signals, training signals, and control signals.

[0065] Here, the control signal is the information transmitted from the transmitting underwater wireless communication device to the receiving underwater wireless communication device in order to reconstruct the received data. The control signal includes the coding rate of the user data and the number of bits per symbol as described above.

[0066] The acoustic signal generated based on Table T4 in Figure 9 is transmitted to the receiving underwater wireless communication device as multiple acoustic packets. The acoustic packets, described later in Figures 16 and 17, consist of a synchronization signal, a training signal, a control signal, and user data. Of these, the information other than the user data, namely the synchronization signal, training signal, and control signal, is overhead information.

[0067] Figure 10 shows table T5, which manages the required input SNR. The required input SNR value increases with the number of bits per symbol. The input SNR value may be fixed as an initial value or may be changeable by the user.

[0068] Figure 11 shows table T6, which manages the parameters for estimating multipath. The multipath estimation parameter management table T6 manages the items and their input values. Items include, for example, the propagation path model, the coordinates of the transmitter (latitude, longitude, depth), the coordinates of the receiver (latitude, longitude, depth), seafloor depth, transmitter directivity data (azimuth, deviation), receiver directivity data (azimuth, deviation), seafloor reflection coefficient (less than or equal to 1), and sound velocity data for the sea area.

[0069] Figure 12 shows table T7, which manages the transmission timing. The underwater radio communication device 20 transmits acoustic packets to the other underwater radio communication device (receiving underwater radio communication device) according to the parameters recorded in the transmission timing management table T7. Table T7 manages parameters such as transmission time, transmission interval, number of frequency divisions, and modulation signal bandwidth as parameters that control the transmission timing.

[0070] Figure 13 shows table T8, which manages the parameters used for frequency division when transmitting an acoustic signal. The frequency division parameter management table T8 manages, for example, the guard band and its value (input value).

[0071] Figure 14 shows table T9, which manages the conditions for updating the transmission timing. The transmission timing update determination condition management table T9 manages the conditions for determining the update timing for both passive and active types.

[0072] In the passive type, that is, the timing for passively estimating the impact of multipath waves on communication quality, is determined, for example, by the updated timer value, the slant range deviation, and the deviation between the coordinates of the transmitting device and the receiving device. The updated timer value is the time period for updating the passive type estimate. The slant range deviation is the change in the perpendicular distance between the transmitting device and the receiving device.

[0073] In the case of the active type, the timing for actively measuring the impact of multipath waves on communication quality at the receiving underwater radio communication device is also determined by the updated timer value, the slant range deviation, and the deviation between the coordinates of the transmitting underwater radio communication device and the receiving underwater radio communication device.

[0074] Here, in order to make the update frequency of the active type less frequent than that of the passive type, the above-mentioned judgment values ​​(timer value, slant range deviation, and deviation between the coordinates of the transmitting device and the receiving device) are all set to be larger for the active type than for the passive type. This is because it takes more time to measure the effect of multipath waves with the active type than to estimate the effect of multipath waves with the passive type. It is preferable to implement the active type only when absolutely necessary. However, the expression "preferred" in this specification merely states that it is effective from one perspective and does not limit the scope of this disclosure in any way.

[0075] Figure 15 shows table T10, which manages the measurement results of multipath waves using the active type. The measurement result management table T10 manages items and their input values. Items include, for example, receiver location information, multipath delay time, direct wave reception level, multipath reception level, and received input SNR.

[0076] "Receiver position information" refers to information (latitude, longitude, receiver depth, and altitude from the seabed) from the INU (Inertial Navigation Unit) installed in the receiver. The depth (distance) from the sea surface to the seabed can be calculated from the receiver depth and altitude from the seabed.

[0077] "Multipath delay time" is information calculated from multipath measurement results and is the relative delay time of the multipath wave, with the direct wave as the reference time.

[0078] "Direct wave reception level" is the reception level of the direct wave, and its unit is [dB] (0dB = 1V / μPa). "Multipath reception level" is information obtained from the multipath measurement results and is the relative reception level of the multipath wave with respect to the direct wave reception level. "Received input SNR" indicates the ratio of the noise level (N) to the signal level (S) of the synchronization signal immediately before receiving the acoustic packet.

[0079] Figure 16 shows the transmission time and transmission interval of acoustic signal packets (acoustic packets). The duration of a single acoustic packet is the transmission time PT1. The time interval between adjacent acoustic packets is the transmission interval PT2.

[0080] Figure 17 is an explanatory diagram illustrating the case where a multipath measurement signal is added to an acoustic packet. First, the multipath measurement signal is transmitted, followed by one or more acoustic packets. The time interval PT3 between the multipath measurement signal and the first acoustic packet is set to more than twice the user-requested transmission interval PT2.

[0081] Examples of multipath measurement signals include chirp signals and PCW (Pulse Continuous Wave) frequency discontinuation signals. A chirp signal is a signal whose frequency increases continuously over time. A PCW frequency discontinuation signal is a signal whose frequency increases gradually over time. Other signals may also be used as multipath measurement signals.

[0082] Figure 18 shows an example of transmitting acoustic packets using frequency division. In Figure 18, two carrier frequencies, a first carrier frequency f1 and a second carrier frequency f2, are set within the maximum frequency range, and acoustic packets are transmitted on each. A guard band is provided between each carrier frequency f1 and f2 to prevent interference. If communication quality can be ensured without a guard band, then a guard band is not necessary.

[0083] The process of controlling the transmission timing will be explained using Figures 19 to 26. Figure 19 is a flowchart showing the overall process of transmission timing control. The acoustic communication control unit 20 executes a passive type transmission timing determination process (S10), an active type transmission timing determination process (S20), and an update determination process (S30).

[0084] Figure 20 is a flowchart of the process for determining the transmission timing using a passive method. The passive method for determining the transmission timing (S10) includes, for example, a process for estimating the propagation path (S11), a process for determining multipath delays that affect communication quality (S12), a process for determining the maximum transmission time (S13), and a process for determining the transmission timing (S14).

[0085] In the propagation path estimation process (S11), the delay time and received level of the direct wave and multipath wave between the transmitting and receiving devices are estimated based on a sound wave propagation model such as ray theory or normal mode theory.

[0086] In the propagation path estimation process (S11), the multipath reception level is determined by considering the changes in the signal reception level due to the transmission directivity of the transmitter and the reception directivity of the receiver, based on the sound wave incidence angles between the seabed and the sea surface for each propagation path.

[0087] In the propagation path estimation process (S11), the coordinates of the transmitting device, the coordinates of the receiving device, sea area test degree, salinity, temperature depth distribution, or sound velocity profile, transmission directivity, and reception directivity are input to the acoustic communication control unit 20 from the sensor 50, external system 60, or user interface device.

[0088] The propagation path estimation process (S11) outputs the estimated delay time of the multipath wave relative to the direct wave and the received level of the multipath wave relative to the direct wave as estimation results.

[0089] Figure 21 is an explanatory diagram of the process (S12) for determining multipath delays that affect communication quality and the process (S13) for determining the maximum transmission time and transmission waiting time. Hereafter, the process for determining the effects on communication quality (S12) will also be referred to as the multipath delay determination process (S12).

[0090] In the multipath delay determination process (S12), the area outside the multipath wave rejection range of the determination feedback type equivalent is targeted for multipath wave detection, and the input SNR is determined as the ratio of the interference level, which consists of the combined energy of the multipath waves, to the direct wave reception level. Then, in the multipath delay determination process (S12), the multipath delay time (τ) corresponding to the input SNR that satisfies the required input SNR (the minimum decodeable input SNR for various communication schemes) is determined.

[0091] Next, we will explain the process (S13) for determining the maximum transmission time and transmission waiting time. In the process (S13) for determining the maximum transmission time and transmission waiting time, the received input SNR is calculated based on (Equation 1) and (Equation 2) shown in Figure 21, and the maximum transmission time and transmission waiting time are determined.

[0092] The maximum transmission time (Tmax) is explained below. The transmission time (acoustic packet time) must be less than or equal to the multipath delay time that first affects reception performance. Therefore, the maximum transmission time is defined as the delay time of the first multipath (N) that satisfies the received input SNR > required input SNR.

[0093] This section explains the transmission pause. Multipath interference that affects reception performance may occur even after the multipath of the maximum transmission time. Therefore, the transmission pause is set to delay the signal until the last multipath that affects reception performance, and the signal is transmitted with a time interval from the end of the transmission signal. For multipath components after the multipath of the maximum transmission time (N), a multipath satisfying the condition that reception input SNR < required input SNR is searched.

[0094] In Figure 21, short-range multipaths exist near the direct wave (near on the time axis), but these can be removed by a decision feedback equivalent. Long-range multipaths arrive with delays DT1, DT2, and DT3 from the reception of the direct wave. When multipaths with delays DT1 and DT2 overlap, the communication quality deteriorates to below a predetermined value (input SNR < required input SNR). Therefore, the time to avoid the slowest delay DT2 that satisfies input SNR < required input SNR becomes the maximum transmission time.

[0095] Figure 22 is another explanatory diagram showing how the transmission waiting time is determined. Following Figure 21, the method for determining the transmission waiting time (Tpause) is explained. In Figure 21, the delayed wave (multipath) of DT2 prevented the received input SNR from meeting the required SNR. Here, the received input SNR is determined for the multipath after DT2, and its impact on the required SNR is assessed.

[0096] Figure 22 shows the results of calculating the received input SNR for multipath signals from DT3 onwards. The required SNR is no longer met at the DT4 multipath. Furthermore, when the received input SNR is calculated excluding DT4 and continuing from DT5 onwards, the required SNR is met. This result indicates that the reception characteristics are affected up to the DT4 multipath. Therefore, in the example in Figure 22, the transmission standby time is set to DT4 or higher.

[0097] Figure 23 is a flowchart of the process for determining the transmission timing. When the maximum transmission time (Tmax) is met, and the transmission interval (Tu) is determined from the user's requested transmission interval (Tcount) and the amount of data to be transmitted, the acoustic communication control unit 20 transmits the data based on the maximum available bandwidth.

[0098] The transmission time and transmission interval, which are determined by the transmission interval and amount of data to be transmitted as requested by the user, are calculated by (Equation 3) in Figure 23. The acoustic communication control unit 20 determines the following pre-set conditions 1, 2, and 3 (S141), and determines the transmission time and transmission interval according to the applicable conditions (S142) (S143~S145).

[0099] (Condition 1) If the requested transmission time (Tcount) is less than the maximum transmission time (Tmax) and the transmission interval (Tcont + Tpause) is less than the transmission interval Tu, then the transmission time is set to Tcont and the transmission interval to Tcont + Tpause (S143).

[0100] (Condition 2) If the requested transmission time (Tcount) is less than the maximum transmission time (Tmax) and the transmission interval (Tcont + Tpause) is greater than or equal to the transmission interval Tu, the transmission interval is adjusted by frequency division (S144).

[0101] (Condition 3) If the requested transmission time (Tcount) is greater than or equal to the maximum transmission time (Tmax), the transmission time will be Tmax and the transmission interval will be Tmax + Tpause (S145).

[0102] Figure 24 is a flowchart following Figure 23. Figure 24 shows the process when dividing the frequency band.

[0103] By dividing the maximum usable frequency band (Bw) into N sections, it becomes possible to transmit in a cyclical manner across different frequency bands, thereby negligibly reducing interference between frequency bands and shortening the transmission interval.

[0104] The acoustic communication control unit 20 performs frequency division transmission if the equation (Equation 4) shown in step S146 is satisfied. If it is not satisfied, it may transmit according to condition 3 or according to this result.

[0105] Then, for each frequency-divided carrier frequency, the multipath delay determination process (S12) that affects the communication quality as described above is performed (S147), and the maximum transmission time and transmission waiting time determination process (S13) is performed (S148). The minimum value is selected from the maximum transmission time for each carrier frequency (S149).

[0106] As shown in Figure 24, the process determines the maximum transmission time TmaxBwn and the transmission waiting time for each carrier frequency. Furthermore, the acoustic communication control unit 20 determines the required transmission time Tcont in the divided signal bandwidth. The transmission interval for the carrier frequencies after frequency division is given by Ts(n) = Tcont + Tpause(n). The acoustic communication control unit 20 sets the maximum value from the transmission intervals of each carrier frequency as the maximum transmission interval.

[0107] The average transmission interval is given by the maximum transmission interval / number of frequency divisions, as shown in (Equation 5).

[0108] TsAve = max(Ts(n)) / Div (Equation 5)

[0109] The acoustic communication control unit 20 determines whether the maximum transmission time for all carrier frequencies is equal to or greater than the requested transmission time (Tcont), and whether the average transmission interval (TsAve) is equal to or less than the requested transmission interval (S150). If "YES" is determined in step S150, the user's requirements can be met by transmitting data using frequency division (S151).

[0110] If the answer in step S150 is "NO", the acoustic communication control unit 20 asks the user whether or not to perform frequency division (S152). If the user selects to transmit data by frequency division (S152:YES), the process moves to step S151 and the data is transmitted by frequency division. If the user does not select to perform frequency division (S152:NO), the data transmission is performed according to condition 3 shown in step S145 of Figure 23 (S153).

[0111] The meanings of the variables used in equations 4 and 5 above are as follows: Tu: User request transmission interval 2Tmax: Twice the maximum transmission time Div: Wavenumber division number Bw: Maximum usable frequency bandwidth Bwn: Modulation signal bandwidth after frequency division GB: Guard band bandwidth for adjacent interference suppression Tcount: Transmission time (same as transmission interval) Ds: Number of symbols that can be sent within the transmission interval Du: Number of transmission symbols within the transmission interval of the user request Ts(n): Transmission interval for each carrier frequency n TsAve: Average transmission interval

[0112] Figure 26 is a flowchart of the process for determining the transmission timing using an active type. The acoustic communication control unit 20 of the transmitting device transmits a multipath measurement signal (S21). Before transmitting the data to be transmitted in an acoustic packet, the acoustic communication control unit 20 transmits a multipath measurement signal to allow the receiving device to measure the multipath propagation time and reception level. The multipath measurement signal uses pulse compression or multiple simple pulse waves of different frequencies to support frequency division transmission within the maximum usable frequency band.

[0113] When the acoustic communication control unit 20 of the receiving device receives a multipath measurement signal, it measures the multipath in the receiving device and returns the measurement result to the acoustic communication control unit 20 of the transmitting device (S22). The acoustic communication control unit 20 of the receiving device measures the propagation time and reception level of the multipath. The acoustic communication control unit 20 of the receiving device sends a response signal to the source of the multipath measurement signal, which includes the propagation delay amount of the multipath wave relative to the direct wave and the reception level of the multipath wave relative to the direct wave.

[0114] When the acoustic communication control unit 20, which transmitted the multipath measurement signal, receives a response signal (multipath measurement result) from the receiving device (S23), it estimates the propagation path in the same way as the processing in the passive type (S24).

[0115] The acoustic communication control unit 20 of the transmitting device adjusts the parameters used in the propagation path estimation model based on the difference between the propagation path estimation result calculated in step 24 and the multipath measurement result received in step S23 (S25).

[0116] The acoustic communication control unit 20 can perform underwater wireless communication that responds to environmental changes caused by the movement of the transmitting and receiving devices during the passive operation period by correcting the propagation path estimation error. In other words, by improving the tracking ability of multipath estimation due to environmental changes, the frequency of transmission of multipath measurement signals can be reduced, and the frequency of execution of active type processing using multipath measurement signals can be reduced, thereby reducing the resource consumption of acoustic communication.

[0117] Then, the acoustic communication control unit 20 of the transmitting device determines the multipath delay that affects communication quality (S26), determines the maximum transmission time and minimum transmission interval (S27), and determines the transmission timing (S28), as described in the processing for the passive type.

[0118] Figure 27 is a flowchart of the process (S30) for determining when to update each parameter for determining the transmission timing. If the conditions for a passive type transmission timing update trigger or an active type transmission timing update trigger are met, processing is resumed according to the processing flow for each type.

[0119] The acoustic communication control unit 20 determines whether it is time to update the passive type (S131). The triggers for updating the passive type are, for example, as follows: when a certain amount of time (Tpass) has elapsed since the last update; when the slant range (direct distance) between the transmitting device and the receiving device has changed by a certain value (SRpass) or more; or when the coordinates of the transmitting device or the receiving device have changed by a certain value (Xpass, Ypass, Zpass) or more in the depth, latitude, and longitude directions.

[0120] If the acoustic communication control unit 20 determines that it is time to update the passive type (S131: YES), it updates the transmission timing using the passive type (S132).

[0121] The acoustic communication control unit 20 determines whether it is time for an active type update (S133) if it is not time for a passive type update (S131: NO). The triggers for an active type update are, for example, as follows: when a certain amount of time (Tact) has elapsed since the last update; when the slant range (direct distance) between the transmitting device and the receiving device has changed by a certain value (SRact) or more; or when the coordinates of the transmitting device or the receiving device have changed by a certain value (Xact, Yact, Zact) or more in the depth, latitude, and longitude directions. In order to make the frequency of updates for the transmission timing in the active type less frequent than that of the transmission timing in the passive type, the condition value for the trigger for an active type update is set to be larger than the condition value for the trigger for a passive type update. This reduces the opportunities for a series of processes such as transmitting a multipath measurement signal, measuring multipath, and returning the measurement result to be executed as much as possible, thereby preventing the consumption of computer resources, power resources, and communication resources. In particular, when the mother ship 2M and AUV2S are powered by batteries, reducing battery consumption allows for longer operating times. Furthermore, since normal data communication between the mother ship 2M and AUV2S is not possible while exchanging multipath measurement signals and their results, reducing the update frequency of the active type using multipath measurement signals ensures that the frequency and amount of normal data transmission can be maintained.

[0122] According to this embodiment, the transmission time and transmission interval can be controlled so that the impact of multipath waves on the other party's underwater wireless communication device on communication quality degradation is below a predetermined value, thereby suppressing quality degradation of underwater wireless communication.

[0123] According to this embodiment, it is possible to suppress SNR degradation due to multipath waves and maintain communication quality with a small and low-power hardware configuration, without being limited by the delay time of multipath waves relative to the direct wave.

[0124] Furthermore, according to this embodiment, even when direct waves and multipath waves arrive at the receiving section from the same direction, the influence of multipath waves can be suppressed and communication quality can be maintained.

[0125] It should be noted that the present invention is not limited to the embodiments described above. Those skilled in the art can make various additions and modifications within the scope of the present invention. The embodiments described above are not limited to the configuration examples shown in the accompanying drawings. The configuration and processing methods of the embodiments can be appropriately modified within the scope of achieving the objectives of the present invention.

[0126] Furthermore, each component of the present invention can be arbitrarily selected, and an invention comprising the selected components is also included in the present invention. Moreover, the components described in the claims can be combined in combinations other than those explicitly stated in the claims. [Explanation of symbols]

[0127] 1: Underwater wireless communication system, 2M: Mother ship, 2S: AUV, 10M, 10S: Underwater wireless communication device, 20M, 20S: Acoustic communication control unit, 30M, 30S: Transmitter, 40M, 40S: Receiver, 50M, 50S: Sensor

Claims

1. An underwater wireless communication device that is installed on a moving body that can move on or underwater and that communicates underwater wirelessly using acoustic signals, a transmitting unit for transmitting an acoustic signal to the other party's underwater wireless communication device; a receiving unit for receiving an acoustic signal from the other underwater wireless communication device; an acoustic communication control unit that controls the wave transmitting unit and the wave receiving unit; the acoustic communication control unit includes a transmission timing control unit that controls a transmission time and a transmission interval of a signal transmitted from the wave transmitting unit, The transmission timing control unit controls the transmission time and the transmission interval so that the influence of communication quality degradation due to multipath waves in the wave receiving unit of the partner underwater wireless communication device is equal to or less than a predetermined value. Underwater radio communication equipment.

2. The transmission timing control unit calculates predetermined parameters for estimating multipath waves at other wave receiving units of the other mobile unit having the other underwater wireless communication device from the position of the mobile unit and the position of the other mobile unit having the other underwater wireless communication device, and controls the transmission time and the transmission interval based on the multipath waves estimated from the calculated predetermined parameters.

2. The underwater wireless communication device according to claim 1.

3. The transmission timing control unit calculates a time until an acoustic signal, the reception level of which at the other wave receiving unit is below a predetermined threshold, reaches the other wave receiving unit based on the estimated multipath wave, determines a maximum transmission time and a transmission standby time from the calculated time, and determines the transmission time and the transmission interval from the determined maximum transmission time and transmission standby time, a transmission interval requested by a user, and an amount of transmission data requested by the user.

3. The underwater wireless communication device according to claim 2.

4. The transmission timing control unit transmits to the other underwater wireless communication device a multipath wave measurement signal for the other underwater wireless communication device to measure the multipath wave received by the other wave receiving unit, receives from the other underwater wireless communication device a measurement result of the multipath wave received by the other wave receiving unit, and corrects the predetermined parameter based on the measurement result of the received multipath wave.

3. The underwater wireless communication device according to claim 2.

5. The frequency of correcting the predetermined parameter is set to be less than the frequency of calculating the predetermined parameter from the position of the moving body and the position of the other moving body.

5. The underwater wireless communication device according to claim 4.

6. the acoustic communication control unit further includes a band dividing unit that divides a communication band; The transmission timing control unit determines the transmission time and the transmission interval based on a maximum transmission time for each of the plurality of communication bands divided by the band dividing unit.

3. The underwater wireless communication device according to claim 2.

7. The band dividing unit divides the communication band based on a transmission interval and a transmission data amount requested from the outside.

7. The underwater wireless communication device according to claim 6.

8. A method for underwater wireless communication using acoustic signals, which is provided on a mobile body that can move on or underwater, a wave transmitting unit that transmits an acoustic signal to a partner underwater wireless communication device, a wave receiving unit that receives an acoustic signal from the partner underwater wireless communication device, and an acoustic communication control unit that controls the wave transmitting unit and the wave receiving unit, the acoustic communication control unit includes a transmission timing control unit that controls a transmission time and a transmission interval of a signal transmitted from the wave transmitting unit, The transmission timing control unit controls the transmission time and the transmission interval so that the influence of communication quality degradation due to multipath waves in the wave receiving unit of the partner underwater wireless communication device is equal to or less than a predetermined value. Underwater wireless communication method.

Images