JP6888780B2 - Underwater receiver - Google Patents

Description

The present invention relates to a technique for performing acoustic communication underwater.

When performing acoustic communication between an underwater transmitter that transmits data and an underwater receiver that receives data, Doppler shifts to the transmitted data according to the relative speed between the underwater transmitter and the underwater receiver. Occurs.
As a countermeasure against Doppler shift, when transmitting and receiving frequency division multiplexed OFDM (Orthogonal Frequency Division Multiplexing) data, the underwater receiver performs A / D conversion of the received signal and then the amount of Doppler shift according to the relative speed. A method of performing resampling processing that changes the data sequence based on the above is known.

Patent Document 1 describes an acoustic communication technology for performing acoustic communication underwater. In the acoustic communication technique described in Patent Document 1, the underwater transmitter transmits a reference signal, which is a sinusoidal signal having a known frequency, in a frequency band different from that of the transmission data. The underwater receiver obtains the Doppler shift amount from the frequency of the received reference signal and the known frequency of the reference signal. Then, the underwater receiver removes the influence of the Doppler shift from the transmitted data based on the obtained Doppler shift amount. As a result, high-quality communication is realized.

Japanese Unexamined Patent Publication No. 2006-217267

The Doppler shift amount changes in a short period of time due to the influence of the water flow and the shaking of the underwater transmitter and the underwater receiver. Therefore, high-quality communication cannot be realized unless the influence of the Doppler shift is removed in consideration of the change in the Doppler shift amount in a short time.

Since the Doppler shift amount changes in a short period of time, in the acoustic communication technique described in Patent Document 1, the Doppler shift amount for the reference signal and the Doppler shift amount for the transmission data are different. Therefore, the influence of Doppler shift cannot be properly removed from the transmitted data.

An object of the present invention is to enable high quality underwater acoustic communication.

The underwater receiver according to the present invention is
An underwater receiver that receives data underwater
A receiver that receives transmission data transmitted from the underwater transmitter,
For each of the plurality of speeds, the speed is set as the relative speed between the underwater transmitting device and the underwater receiving device, and the transmission data received by the receiving unit is demolished based on the Doppler shift amount caused by the relative speed. , Received data generator that generates multiple received data,
It includes a reception data selection unit that selects high-quality reception data from a plurality of reception data generated by the reception data generation unit.

In the present invention, the transmission data is demodulated based on the Doppler shift amount caused by the relative speed, with each of the plurality of speeds as the relative speed between the underwater transmission device and the underwater reception device, and a plurality of reception data are generated. Then, the received data having good quality is selected from the plurality of received data. As a result, the influence of the Doppler shift can be appropriately removed, and high-quality underwater acoustic communication can be performed.

The block diagram of the underwater communication system 1 which concerns on Embodiment 1. FIG. The flowchart of the operation of the underwater communication system 1 which concerns on Embodiment 1. FIG. The figure which shows the condition of the simulation which concerns on the modification 1. The figure which shows the result of the simulation which concerns on the modification 1. The block diagram of the underwater communication system 1 which concerns on Embodiment 2. FIG. The flowchart of the operation of the underwater communication system 1 which concerns on Embodiment 2.

Embodiment 1.
*** Explanation of configuration ***
The configuration of the underwater communication system 1 according to the first embodiment will be described with reference to FIG.
The underwater communication system 1 includes an underwater transmitting device 10 and an underwater receiving device 20. The underwater transmission device 10 is a device that transmits transmission data, and the underwater reception device 20 is a device that receives transmission data. It should be noted that one device may have the functions of both the underwater transmitting device 10 and the underwater receiving device 20.

The underwater transmission device 10 includes a transmission data generation unit 11 and a transmission unit 12. The transmission data generation unit 11 includes an OFDM modulation unit 111 and a data addition switching unit 112. The transmission unit 12 includes a D / A conversion unit 121 (Digital to Analog conversion unit), a transmission amplifier 122, and a transmitter 123.
The OFDM modulation unit 111, the data addition switching unit 112, the D / A conversion unit 121, the transmission amplifier 122, and the transmitter 123 are realized by hardware such as a circuit or a device, or software.

The underwater reception device 20 includes a reception unit 21, a reception data generation unit 22, a reception data selection unit 23, a speed measurement unit 24, and a speed recording unit 25. The receiving unit 21 includes a receiver 211, a receiving amplifier 212, and an A / D conversion unit 213 (Analog to Digital conversion unit). The reception data generation unit 22 includes a plurality of generation processing units 221. Each generation processing unit 221 includes a resampling unit 222, a demodulation unit 223, and a quality measurement unit 224.
In the first embodiment, the reception data generation unit 22 is a plurality of generation processing units 221 such as a generation processing unit 221X corresponding to the speed X knot and a generation processing unit corresponding to the speed X-An knot to the speed X-A1 knot. It includes 2n + 1 generation processing units 221 of 221X-An to generation processing unit 221X-A1 and generation processing unit 221X + An to generation processing unit 221X + A1 corresponding to speed X + An knot to speed X + A1 knot. n is an integer of 1 or more. In the following description, the velocity X knot is referred to as the center velocity. Further, the speed A knot, which is the speed interval corresponding to each generation processing unit 221, is referred to as a reference interval.
The receiver 211, the receiving amplifier 212, the A / D conversion unit 213, the resampling unit 222, the demodulation unit 223, the quality measurement unit 224, the reception data selection unit 23, the speed measurement unit 24, and the speed. The recording unit 25 is realized by hardware such as a circuit or a device, or software.

*** Explanation of operation ***
The operation of the underwater communication system 1 according to the first embodiment will be described with reference to FIG.
The operation of the underwater transmission device 10 according to the first embodiment corresponds to the underwater transmission method according to the first embodiment. Further, the operation of the underwater transmission device 10 according to the first embodiment corresponds to the processing of the underwater transmission program according to the first embodiment.
The operation of the underwater receiving device 20 according to the first embodiment corresponds to the underwater receiving method according to the first embodiment. Further, the operation of the underwater receiving device 20 according to the first embodiment corresponds to the processing of the underwater receiving program according to the first embodiment.

(Step S1: Reference signal transmission process)
The transmission data generation unit 11 generates the sine wave data 31 having a frequency determined in advance between the underwater transmission device 10 and the underwater reception device 20, which is a reference signal, as the transmission data 34 as it is.
Then, the transmission unit 12 transmits the transmission data 34 as an acoustic signal into the water. Specifically, the D / A conversion unit 121 converts the transmission data 34 generated by the transmission data generation unit 11 from digital data to analog data. The transmission amplifier 122 amplifies the analog data converted by the D / A conversion unit 121, and the transmitter 123 transmits the transmission data 34, which is the analog data amplified by the transmission amplifier 122, into the water.

(Step S2: Reference signal reception process)
The receiving unit 21 receives the transmission data 34, which is the reference signal transmitted underwater in step S1. Specifically, the receiver 211 receives the transmission data 34 transmitted underwater, and the reception amplifier 212 amplifies the transmission data 34 received by the receiver 211. The A / D conversion unit 213 converts the transmission data 34 amplified by the reception amplifier 212 from analog data to digital data.

(Step S3: Speed measurement process)
The speed measurement unit 24 measures the Doppler shift amount and the change width of the Doppler shift amount from the frequency of the transmission data 34 converted in step S2 and the frequency determined in advance. As a result, the speed measuring unit 24 measures the relative speed between the underwater transmitting device 10 and the underwater receiving device 20 and the range of change in the relative speed.

(Step S4: Data transmission process)
The transmission data generation unit 11 generates transmission data 34 from the data 32 to be transmitted. Specifically, the OFDM modulation unit 111 modulates the data 32 by frequency division multiplexing to generate the OFDM data 33. The data addition switching unit 112 generates the transmission data 34 by adding the OFDM data 33 generated by the OFDM modulation unit 111 and the sine wave data 31.
Then, the transmission unit 12 transmits the transmission data 34 as an acoustic signal into the water. The specific method in which the transmission unit 12 transmits the transmission data 34 is the same as in step S1.

(Step S5: Data reception process)
The receiving unit 21 receives the transmission data 34 transmitted underwater in step S4. The specific method for the receiving unit 21 to receive the transmission data 34 is the same as in step S2.

(Step S6: Received data generation process)
The reception data generation unit 22 receives the speeds of each of the plurality of speeds by the reception unit 21 in step S5 based on the Doppler shift amount caused by the relative speeds as the relative speeds of the underwater transmission device 10 and the underwater reception device 20. By demolishing the transmitted data 34, a plurality of received data 35 are generated.
Specifically, the reception data generation unit 22 sets the reference speed range on the assumption that the relative speed measured in step S3 is used as the center speed and the change width of the relative speed calculated in step S3 changes before and after the center speed. Determine. Then, the reception data generation unit 22 demotes the transmission data 34 with each speed obtained by shifting the speed from the center speed (speed X knot) by the reference interval (speed A knot) within the reference speed range as the relative speed. To do.

That is, the generation processing unit 221X demodulates the transmission data 34 and generates the reception data 35X, assuming that the center speed is the relative speed. Further, the generation processing unit 221X-An demodulates the transmission data 34 and generates the reception data 35X-An, assuming that the relative speed is a speed A × n slower than the center speed. Similarly, in the generation processing unit 221X-A (n-1) to the generation processing unit 221X-A1, the relative speed is a speed A × (n-1) to a speed A × 1 slower than the center speed, respectively. As the transmission data 34 is demodulated, the reception data 35X-A (n-1) to the reception data 35X-A1 are generated. Further, the generation processing unit 221X + A1 demodulates the transmission data 34 and generates the reception data 35X + A1, assuming that the relative speed is a speed A × 1 faster than the center speed. Similarly, the generation processing unit 221X + A2 and the generation processing unit 221X + An demodulate the transmission data 34, assuming that the relative speed is a speed A × 2 to a speed A × n faster than the center speed, respectively, and receive data 35X + A2. ~ Generates received data 35X + An.
At this time, the resampling unit 222 of each generation processing unit 221 performs the resampling processing based on the Doppler shift amount caused by the relative speed corresponding to the generation processing unit 221. The demodulation unit 223 demodulates the transmission data 34 resampled by the resampling unit 222 by frequency division multiplexing to generate the reception data 35. The demodulation unit 223 measures the quality of the generated received data 35. For example, the demodulation unit 223 calculates a BER (Bit Error Rate).

(Step S7: Received data selection process)
The reception data selection unit 23 selects and outputs the reception data 35 having the highest quality from the plurality of reception data 35 generated in step S6.
The reception data selection unit 23 stores the relative speed according to the Doppler shift amount used when demodulating the selected reception data 35 in the speed recording unit 25 as the previous speed.

When the data 32 to be transmitted remains, the process of step S4 is executed again on the underwater transmission device 10 side, and the processes of steps S5 to S7 are executed again on the underwater receiver 20 side. At this time, in step S6, the reception data generation unit 22 treats the previous speed stored in the speed recording unit 25 in the latest step S7 as the central speed.

*** Effect of Embodiment 1 ***
As described above, the underwater communication system 1 according to the first embodiment sets transmission data based on the Doppler shift amount caused by the relative speed, with each of the plurality of speeds as the relative speed between the underwater transmitting device 10 and the underwater receiving device 20. It demotes and generates a plurality of received data 35. Then, the received data 35 having good quality is selected from the plurality of received data 35. As a result, even if the Doppler shift amount changes in a short time due to the influence of the water flow and the shaking of the underwater transmitter and the underwater receiver, the influence of the Doppler shift can be appropriately removed. It is possible to perform high quality acoustic communication underwater.

*** Other configurations ***
<Modification example 1>
The reception data generation unit 22 may determine the reference interval, that is, the value of the speed A knot, according to the communication modulation method. The communication modulation method includes 64QAM (Quadrature Amplitude Modulation), 16QAM, QPSK (Quadrature Phase Shift Keying) and the like.
As a result of performing the simulation under the conditions shown in FIG. 3, the result shown in FIG. 4 was obtained. As shown in FIG. 4, in the case of a maximum frequency of 60 kHz, 64QAM requires a relative velocity resolution of 0.15 knots or less. 16QAM requires a relative velocity resolution of 0.3 knots or less. QPSK requires a relative velocity resolution of 0.65 or less.
Therefore, when the upper limit of the transmission frequency is changed, the relative speed resolution = the relative speed resolution when the maximum transmission frequency is 60 kHz / {(maximum transmission frequency) / (60 kHz)}.

<Modification 2>
The underwater transmission device 10 may include a noise measurement unit that measures the communication quality of the transmission data 34. The noise measuring unit measures the quality of the transmission data 34 received in step S2. Specifically, the noise measuring unit measures the C / N ratio of the transmission data 34 received in step S2.
When the quality of the measured transmission data 34 is worse than the first reference quality, the noise measurement unit requests the underwater transmission device 10 to re-execute the reference signal transmission process of step 1. The first standard quality is, for example, a C / N ratio of 6 dB. This makes it possible to accurately measure the relative velocity in step S3.
Further, when the quality of the measured transmission data 34 is worse than the first reference quality, the noise measurement unit instructs the underwater transmission device 10 to simultaneously transmit the transmission data 34 at a plurality of different frequencies. May be good. Even if the communication quality at one of the frequencies is poor, the communication quality at the other frequency may be good. Therefore, high quality communication can be realized.

<Modification example 3>
The reception data generation unit 22 has a relative speed according to the Doppler shift amount used when demodulating the reception data 35 selected by the reception data selection unit 23 in step S7, and a lower limit speed or an upper limit speed of the reference speed range. If the speed difference between the two is within the difference threshold, the reference speed range may be widened.
As a specific example, when the relative speed according to the Doppler shift amount used when demodulating the selected received data 35 is faster than "center speed + ((speed A x n) x 0.5)". And, when it is slower than "center speed-((speed A x n) x 0.5)", the reception data generation unit 22 may widen the reference speed range. That is, when the fluctuation of the optimum value of the relative speed obtained by the resampling process exceeds 50% of ± (A × n) knots, the reference speed range may be widened.
This makes it possible to realize high-quality communication, although the amount of calculation increases.

Further, when the speed difference between the relative speed according to the Doppler shift amount used when the selected received data 35 is demodulated and the center speed is within the difference threshold, the reception data generation unit 22 determines. The reference speed range may be narrowed. That is, the reception data generation unit 22 may narrow the reference speed range when the speed difference between the relative speed according to the used Doppler shift amount and the center speed is small.
This makes it possible to reduce the amount of calculation.

<Modification example 4>
If the quality of the received data 35 selected by the received data selection unit 23 in step S7 is worse than the first reference quality, the speed measuring unit 24 may remeasure the relative speed.
That is, the reception data generation unit 22 does not treat the previous speed stored in the speed recording unit 25 in the latest step S7 as the center speed, but treats the relative speed measured by the speed measurement unit 24 again as the center speed. May be good. In this case, the speed measuring unit 24 may request the underwater transmission device 10 to re-execute the reference signal transmission process of step 1, and the underwater transmission device 10 may retransmit the reference signal.
As a result, when the relative speed changes significantly and the communication quality deteriorates, it is possible to prevent the communication in a poor quality state from continuing.

<Modification 5>
In the first embodiment, the sine wave data 31 having a predetermined frequency is used as a reference signal. However, when the fluctuation of the relative velocity is small, the known preamble data which is a part of the data 32 may be used as the reference signal instead of the sine wave data 31.
This eliminates the need to communicate the sine wave data 31.

<Modification 6>
It is known that in an environment where strong multipath is generated, frequency selective fading that deteriorates a specific frequency characteristic occurs. When frequency selective fading occurs, the C / N ratio of the sinusoidal data 31 may decrease, and the measurement accuracy of the relative velocity may decrease. Therefore, instead of the sine wave data 31, a known OFDM-modulated pilot signal, which is a frequency-spread signal, may be used as a reference signal.
As a result, the measurement accuracy of the relative velocity can be maintained at a certain level even when the frequency selective fading occurs.

<Modification 7>
The underwater receiver 20 may further include a communication indicator that switches between the data length of the transmission data 34 and at least one of the modulation schemes.

When the quality of the received data 35 selected by the received data selection unit 23 in step S7 is worse than the first reference quality, the communication instruction unit sends the data of the transmission data to the underwater transmission device 10 next. It indicates at least one of shortening the length and making the modulation method a slower method.
To make the modulation method slower, for example, when the modulation method is 64QAM, the modulation method is 16QAM, and when the modulation method is 16QAM, the modulation method is QPSK.

Further, when the quality of the received data 35 selected by the received data selection unit 23 in step S7 is better than the second standard quality, which is the quality equal to or higher than the first standard quality, the communication instruction unit sends the underwater transmission device 10 to the underwater transmission device 10. On the other hand, at least one of increasing the data length of the transmission data to be transmitted next and making the modulation method a high-speed method is instructed.
To make the modulation method a high-speed method, for example, when the modulation method is QPSK, the modulation method is set to 16QAM, and when the modulation method is 64QAM, the modulation method is set to 16QAM.

Embodiment 2.
The second embodiment is different from the first embodiment in that the relative velocity is not measured in advance. In the second embodiment, these different points will be described, and the same points will be omitted.

In the first embodiment, the relative speed between the underwater transmission device 10 and the underwater receiving device 20 is first measured, and the transmission data 34 including the data 32 is demodulated with the measured relative speed as the central speed. However, it may be known that the distance between the underwater transmitter 10 and the underwater receiver 20 is fixed or the relative speed is low. In this case, the relative speed between the underwater transmitting device 10 and the underwater receiving device 20 can be treated as 0.

As described in the first modification, as shown in FIG. 4, in the case of a maximum frequency of 60 kHz, a relative velocity resolution of 0.15 knot or less is required at 64QAM. 16QAM requires a relative velocity resolution of 0.3 knots or less. QPSK requires a relative velocity resolution of 0.65 or less.
Assuming that the fluctuation is 4 to 10 times the relative speed resolution and the condition that the relative speed is low is 2 to 5 times the relative speed resolution, when the upper limit of the transmission frequency is changed, the relative speed resolution = the maximum transmission frequency. Is the relative velocity resolution at 60 kHz / {(maximum transmission frequency) / (60 kHz)}.

*** Explanation of configuration ***
The configuration of the underwater communication system 1 according to the second embodiment will be described with reference to FIG.
It differs from the underwater transmission device 10 shown in FIG. 1 in that the transmission data generation unit 11 of the underwater transmission device 10 does not include the data addition switching unit 112. Further, the underwater receiving device 20 is different from the underwater receiving device 20 shown in FIG. 1 in that the speed measuring unit 24 and the speed recording unit 25 are not provided.

*** Explanation of operation ***
The operation of the underwater communication system 1 according to the second embodiment will be described with reference to FIG.
The processing of steps S11 to S14 corresponds to the processing of steps S4 to S7 of FIG. However, in step S13, the center speed is set to 0 knots.

*** Effect of Embodiment 2 ***
As described above, in the second embodiment, when the distance between the underwater transmitting device 10 and the underwater receiving device 20 is fixed or it is known that the relative speed is low, the relative speed is measured in advance. It is possible to perform high-quality acoustic communication underwater without doing so.

1 Underwater communication system, 10 Underwater transmitter, 11 Transmission data generator, 111 OFDM modulator, 112 Data addition switching unit, 12 Transmitter, 121 D / A converter, 122 Transmitter amplifier, 123 Transmitter, 20 Underwater reception Equipment, 21 receiver, 211 receiver, 212 receiver amplifier, 213 A / D conversion unit, 22 reception data generation unit, 221 generation processing unit, 222 resampling unit, 223 demodulation unit, 224 quality measurement unit, 23 reception data Selection unit, 24 speed measurement unit, 25 speed recording unit, 31 sine wave data, 32 data, 33 OFDM data, 34 transmission data, 35 reception data.

Claims (11)

An underwater receiver that receives data underwater
A receiver that receives transmission data transmitted from the underwater transmitter,
For each of the plurality of speeds, the speed is set as the relative speed between the underwater transmitting device and the underwater receiving device, and the transmission data received by the receiving unit is demolished based on the Doppler shift amount caused by the relative speed. , Received data generator that generates multiple received data,
An underwater receiver including a reception data selection unit that selects high-quality reception data from a plurality of reception data generated by the reception data generation unit. The first aspect of claim 1, wherein the received data generation unit demodulates the transmitted data with each speed obtained by shifting the speed by a reference interval within a reference speed range having a certain speed as the center speed as the relative speed. Underwater receiver. The underwater receiver further
A speed measuring unit for measuring the relative speed between the underwater transmitting device and the underwater receiving device based on a reference signal is provided .
Before Symbol receiving data generation unit, the relative velocity measured by the speed measuring unit, underwater receiving device according to claim 2, the central speed. The receiving unit receives a plurality of transmission data from the underwater transmission device, and receives a plurality of transmission data.
The reception data generation unit sets a relative speed according to the Doppler shift amount used when demodulating the reception data selected by the reception data selection unit as the center speed when demodulating the next transmission data. The underwater receiver according to claim 2 or 3. The underwater receiving device according to claim 2, wherein the receiving data generation unit has the central speed as 0. The underwater receiving device according to any one of claims 2 to 5, wherein the receiving data generation unit determines the reference interval according to the communication modulation method. The received data generation unit has a speed difference between a relative speed according to the Doppler shift amount used when demodulating the received data selected by the received data selection unit and a lower limit speed or an upper limit speed of the reference speed range. However, when the difference is within the difference threshold, the underwater receiving device according to any one of claims 2 to 6 for widening the reference speed range. The underwater receiving device according to claim 3, wherein the speed measuring unit remeasures the relative speed when the quality of the received data selected by the received data selection unit is worse than the first reference quality. The underwater receiver according to claim 3, wherein the reference signal is a part of the transmission data. The underwater receiver according to claim 3, wherein the reference signal is a frequency-spread signal. The underwater receiver further
When the quality of the received data selected by the received data selection unit is worse than the first reference quality, the data length of the transmitted data to be transmitted next to the underwater transmission device is shortened, and a modulation method is used. If the quality of the received data selected by the received data selection unit is better than the second standard quality equal to or higher than the first standard quality, the above is indicated. Claims 1 to 10 include a communication instruction unit that instructs the underwater transmission device to at least one of increasing the data length of the transmission data to be transmitted next and changing the modulation method to a high-speed method. The underwater receiver according to any one of the items up to.

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