Data transmission system and method

Abstract

This disclosure aims to provide a technology that enables the demodulation of received data regardless of the influence of the external environment. [Solution] The data transmission system 100 of this disclosure comprises a transmitting device 2 comprising an amplitude modulator 23 for amplitude modulating transmission data and a vibration generator 21 for applying vibration to the optical transmission path 14 in the optical fiber cable 13 with the amplitude modulated modulation signal, and a receiving device 1 comprising a vibration sensor 10 for detecting vibrations in the optical transmission path 14 and a demodulator 16 for demodulating the amplitude modulated transmission data from the vibrations in the optical transmission path 14.

Description

[Technical Field]

[0001] This invention relates to a sensor network technology for easily collecting information from sensor devices installed in remote locations. [Background technology]

[0002] A method for transmitting information to a remote location by applying vibration to an optical fiber cable has been known for some time (see, for example, Non-Patent Document 1). In Non-Patent Document 1, data from various electrical sensors is phase-modulated, and vibration is applied from the outer sheath of the optical fiber cable using a vibration speaker. The phase-modulated vibration is received by a photodetector as interference light from a Mach-Zehnder interferometer. By demodulating the output signal of the photodetector, it becomes possible to transmit sensor data from various electrical sensors. To date, 2-channel, 3bps information transmission has been achieved using an experimental system employing a Mach-Zehnder interferometer and a spread spectrum method.

[0003] However, as described in Non-Patent Document 1, the modulation amount of phase-modulated vibrations changes due to the influence of external temperature and other factors. For this reason, demodulation using a frequency corresponding to the applied phase modulation may not be able to demodulate the received data. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Tetsuya Manabe, Ryoga Hashimoto, Hiroki Fujita, Atsushi Nakamura, and Yusuke Koshikiya, “Low-speed Data Transmission using a Modulated Vibration Signal on an Optical Cable's Outer Sheath”, Proceedings of the 27th International Conference on Optical Fiber Sensors, W4.3, (2022) [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, this disclosure aims to provide a technology that enables the demodulation of received data regardless of the influence of the external environment. [Means for solving the problem]

[0006] To achieve the above objectives, the data transmission system and method disclosed herein employ a technique of amplitude modulation of the transmitted data.

[0007] Specifically, the data transmission system disclosed herein is: A transmitting device comprising: an amplitude modulator for amplitude-modulating the transmitted data; and a vibration generator that applies vibration to the optical transmission path in the optical fiber cable with the amplitude-modulated signal. A receiving device comprising: an optical fiber vibration sensor for detecting vibrations in the optical transmission path; and a demodulator for demodulating transmission data amplitude-modulated from vibrations in the optical transmission path. It is equipped with.

[0008] Furthermore, the transmitting device includes a serial-to-parallel converter that converts the transmitted data from serial to parallel. The amplitude modulator adds a different frequency to each signal that has been converted from serial to parallel depending on the presence or absence of vibration. The demodulation device may include a demodulation circuit that demodulates vibrations in the optical transmission path for each frequency, and a parallel-to-serial converter that converts the demodulated signal into a parallel-to-serial format to restore the transmission data.

[0009] Furthermore, the frequencies assigned to each signal parallelized by the serial-to-parallel converter may satisfy equation (24) described later.

[0010] Furthermore, the demodulation device may demodulate the vibrations frequency by frequency using an orthogonal demodulation method for the same frequency and twice the frequency of the vibrations applied by the vibration generator to the optical transmission path.

[0011] Also, compare two demodulated signals demodulated at the same frequency and the double frequency, if there is a difference between the two demodulated signals, the one with the larger absolute value may be used as the received data.

[0012] Specifically, the data transmission method of the present disclosure includes a procedure for amplitude-modulating transmission data, a procedure for applying vibration to an optical transmission path in an optical fiber cable with the amplitude-modulated modulation signal, a procedure for detecting the vibration of the optical transmission path, and a procedure for demodulating the transmission data amplitude-modulated from the vibration to the optical transmission path. It is provided with.

[0013] The device (transmission device, reception device, demodulation device, etc.) of the present disclosure can also be realized by a computer and a program, and it is also possible to record the program on a recording medium or provide it through a network. The program of the present disclosure is a program for causing a computer to realize each function provided in the device according to the present disclosure, and is a program for causing a computer to execute each procedure provided in the method executed by the device according to the present disclosure.

[0014] Note that the above disclosures can be combined as much as possible.

Effect of the Invention

[0015] According to the present disclosure, received data can be demodulated without being affected by the external environment.

Brief Description of Drawings

[0016] [Figure 1] It is a diagram for explaining the outline of a data transmission system. [Figure 2] It is a diagram for explaining the outline of a transmission device. [Figure 3] It is a diagram for explaining the outline of a demodulation device. [Figure 4]This figure illustrates the configuration of a data transmission system according to an embodiment of the present disclosure. [Figure 5] This figure illustrates the basic configuration of a modulation device according to an embodiment of the present disclosure. [Figure 6] This figure illustrates the basic configuration of a demodulator according to an embodiment of the disclosure. [Figure 7] This diagram illustrates the generation of multiple modulated signals with different frequencies. [Figure 8] This diagram illustrates the process of converting demodulated signals for each frequency into parallel-to-serial signals. [Figure 9] This is a diagram illustrating the configuration of the related data transmission system. [Modes for carrying out the invention]

[0017] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components.

[0018] (Overview of the data transmission system) An overview of the data transmission system 100 according to the embodiment of this disclosure will be described with reference to Figures 1 to 3.

[0019] As shown in Figure 1, the data transmission system 100 comprises a receiving device 1 and a transmitting device 2. The receiving device 1 comprises a vibration sensor 10 and a demodulator 16.

[0020] The vibration sensor 10 comprises a light source 11, a photodetector 12, an optical cable 13, two transmission lines 14 made of optical fibers, and a Mach-Zehnder interferometer 15 made of the two transmission lines 14. Light from the light source 11 is received by the photodetector 12 via the two transmission lines 14. The optical cable 13 is configured to receive a predetermined vibration from an external transmitter 2. When the predetermined vibration is applied to the optical cable 13, the polarization state of the two transmission lines 14 changes in response to the vibration, causing the interference waveform of the Mach-Zehnder interferometer 15 to change. As a result, the photodetector 12 can acquire a received signal corresponding to the predetermined vibration. In other words, the vibration sensor 10 acquires vibration (vibration data) applied to the optical cable 13. The photodetector 12 sends the vibration data to the demodulator 16.

[0021] The transmitting device 2 comprises a vibration generator 21, a serial-to-parallel converter 22, and an amplitude modulator 23. The serial-to-parallel converter 22 converts the transmission signal from serial to parallel and sends it to the amplitude modulator 23. The amplitude modulator 23 amplitude modulates each of the multiple serial-to-parallel converted transmission signals and sends them to the vibration generator 21. Specifically, as shown in Figure 2, multiple amplitude modulators 23 are provided according to the frequency of the carrier wave generated by the carrier wave generator 24. Each of the multiple amplitude modulators 23 controls the modulation signal of the carrier wave generated by the carrier wave generator 24 depending on the presence or absence of vibration. The signal adder 25 adds the modulation signals from the multiple amplitude modulators 23. The vibration generator 21 excites the optical cable 13 based on the added signals.

[0022] The demodulator 16 comprises a demodulation circuit 17 and a parallel-to-serial converter 18. The demodulation circuit 17 demodulates the vibration data acquired from the photodetector 12. Specifically, as shown in Figure 3, multiple demodulation circuits 17 are provided according to the frequency of the vibration data. The parallel-to-serial converter 18 converts the demodulated signal to a parallel-to-serial format and restores the transmitted signal.

[0023] As described above, the data transmission system 100 according to this embodiment is A transmitting device 2 comprises an amplitude modulator 23 that amplitude modulates the transmitted data, and a vibration generator 21 that vibrates the optical transmission path 14 in the optical fiber cable 13 with the amplitude modulated signal. A receiving device 1 comprises a vibration sensor 10 for detecting vibrations in the optical transmission path 14, and a demodulator 16 for demodulating transmission data amplitude-modulated from vibrations in the optical transmission path 14. It is equipped with.

[0024] In particular, the data transmission system 100 is The transmitting device 2 includes a serial-to-parallel converter 22 that converts the transmitted data from serial to parallel. The amplitude modulator 23 adds a different frequency to each signal that has been converted from serial to parallel depending on the presence or absence of vibration. The demodulator 16 includes a demodulation circuit 17 that demodulates vibrations transmitted to the optical transmission line 14 for each frequency, and a parallel-to-serial converter 18 that converts the demodulated signal into a parallel-to-serial format to restore the transmitted data.

[0025] (Effects of the data transmission system) Next, the effects of the data transmission system 100 will be explained in comparison with the related data transmission system 100A shown in Figure 9. In Figure 9, configurations corresponding to the configuration of the data transmission system 100 are indicated by adding the letter A to the reference numeral in the data transmission system 100.

[0026] In the related data transmission system 100A, the transmitting device 2A is equipped with a phase modulator 26A. The phase modulator 26A phase-modulates the transmission signal and sends it to the vibration generator 21. However, in this method of phase modulation, the amount of modulation changes due to the influence of external temperature and other factors. Therefore, in some cases, the received data cannot be demodulated by demodulation using the frequency corresponding to the applied phase modulation.

[0027] In contrast, in this embodiment, modulation to amplitude is performed using an amplitude modulator 23. This allows the received data to be demodulated regardless of the influence of the external environment.

[0028] Furthermore, in conventional configurations, the transmission speed during 2-channel multiplex transmission is limited to 3 bps (see Non-Patent Document 1). Improving the information transmission speed is essential for applications with high practicality, such as image transmission. To improve the information transmission speed, increasing the carrier frequency of the applied modulation vibration is effective. However, vibrations applied to the outer sheath of the optical fiber cable are attenuated significantly at higher frequencies due to the mechanical structure of the optical fiber cable before they are transmitted to the internal optical fiber, making high-speed data transmission difficult.

[0029] In contrast, this embodiment employs a parallel transmission method using multiple modulated vibrations within a limited bandwidth, rather than increasing the frequency of the modulated vibration. This enables faster information transmission.

[0030] (First example) The first embodiment will be described with reference to Figures 4 to 6. Figure 4 shows an embodiment in which the interference waveform of a Mach-Zehnder interferometer 115 is received as the received signal by the photodetector 112 in the data transmission system 100.

[0031] The transmission data acquired remotely by various sensors is sent to the transmission device 2. Based on the transmission data, the transmission device 2 generates vibrations to be applied to the optical fiber cable 120. The modulation device 230 generates an amplitude-modulated signal based on the transmission data. The amplitude-modulated signal is amplified by the vibration generator drive amplifier 220 and drives the vibration generator 210. The vibration generator 210 applies vibrations to the outer sheath of the optical fiber cable 120.

[0032] When the vibration generator 210 of the transmitting device 2 applies vibrations corresponding to the amplitude modulation signal to the optical fiber cable 120, the polarization state of the optical fiber 114 changes in response to these vibrations. The interference waveform of the Mach-Zehnder interferometer 115 changes in response to this change in polarization state, and a received signal can be obtained by the photodetector 112. The received signal is demodulated as received data in the demodulator 140.

[0033] Assuming that the light incident from the light source 111 into the optical fiber 114 of the optical fiber vibration sensor 110 is linearly polarized, the electric field E(t) is expressed by the following equation.

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[0034] If this electric field E(t) rotates by β(t) due to external vibrations while propagating through the optical fiber 114, then the electric field E incident on the Mach-Zehnder interferometer 115 in (t) is expressed by the following equation.

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[0035] Furthermore, if Δt is the difference in propagation time due to the difference in the lengths of the two propagation paths of the Mach-Zehnder interferometer 115, then the output light E of the Mach-Zehnder interferometer 115 out (t) is expressed by the following equation.

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[0036] The change in light intensity I(t) of the interference waveform of the Mach-Zehnder interferometer 115, measured by the photodetector 112, is expressed by the following equation.

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[0037] Here, we assume that the change in the rotation angle β(t) due to vibration applied to the optical fiber cable is given by the following equation.

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[0038] From equations (4) and (6), the received signal I(t) received by the photodetector 112 is expressed by the following equation.

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[0039] Figure 5 shows the modulation method when the modulation scheme for the transmitted data in the modulation device 230 is the ASK (Amplitude Shift Keying) method, which transmits 0s and 1s depending on the presence or absence of vibration. The amplitude modulator 233 controls the modulation signal u(t) of the carrier wave generated by the carrier wave generator 232 based on the 1s and 0s of the data to be transmitted.

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[0040] Figure 6 shows the demodulation method when the demodulation method of the received data in the demodulator 140 is quadrature demodulation for the same frequency and twice the frequency of the vibration applied to the optical fiber cable 120 by the transmitter 2. In other words, the demodulator 140 demodulates the vibrations frequency by frequency using quadrature demodulation for the same frequency and twice the frequency of the vibrations applied to the optical transmission line 114 by the vibration generator 210. The demodulator 140 includes a demodulation circuit 160 consisting of a multiplier 141, a low-pass filter 142, a squarer 143, a square root generator 144, an adder 145, a discriminator 146, an equal cosine wave generator 147, an equal sine wave generator 148, a double cosine wave generator 149, and a double sine wave generator 150.

[0041] The same cosine wave generator 147 and the same sine wave generator 148 generate signals with the same frequency as the vibration applied to the optical fiber cable, while the double cosine wave generator 149 and the double sine wave generator 150 generate signals with twice the frequency. Then, each signal is multiplied by the received signal y(t) using the multiplier 141. This allows for the demodulation of both a signal with the same frequency as the applied vibration and a signal with twice the frequency of the applied vibration. A detailed explanation follows below.

[0042] The first and second terms of the AC component of the received signal when vibration is applied to the optical fiber cable 120 by amplitude modulation of equation (9) can be expressed from equation (8) as follows:

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[0043] For this received signal y(t), the angular frequency ω ν The sine and cosine waves are multiplied by the multiplier 141, and the signal Z is obtained after passing through the low-pass filter 142. I1 (t), Z Q1 (t) can be expressed as follows:

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[0044] Here, the signals obtained by Equation (11) and Equation (12) are squared by the squarer 143, added by the adder 145, and the square root is calculated by the square rooter 144 to obtain the following signal.

Equation

[0045] Similarly, for the received signal y(t), a sine wave and a cosine wave with an angular frequency of 2ω ν are multiplied by the multiplier 141, and the signals Z I2 (t), Z Q2 (t) can be expressed as follows.

Equation

Equation

[0046] Here, the signals obtained by Equation (14) and Equation (15) are squared by the squarer 1 A signal is obtained by adding by the adder 145 and calculating the square root by the square rooter 144.

Equation

[0047] By quadrature demodulation for the amplitude modulation given by Equation (9), the following two demodulated signals p1 and p2 are obtained from the transmitted data.

Equation

Equation

[0048] The magnitudes of the obtained demodulated signals p1 and p2 vary depending on the difference Δθ in rotation angle due to factors other than vibration, such as the refractive index and polarization of the optical fiber 114 of the optical fiber vibration sensor 110 and the Mach-Zehnder interferometer 115, so there may be discrepancies in the identification of the received data. Therefore, in this embodiment, the classifier 146 is used to distinguish between 0 and 1 of the received data based on the two demodulated signals p1 and p2 represented by equations (17) and (18), according to the following criteria.

[0049] First, determine the R1 and R2 results of the data discrimination from the demodulated signals p1 and p2.

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[0050] If there is no difference between the two judgment results R1 and R2, the received data d' is calculated using the following formula. k To decide.

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[0051] If there is a difference between the two judgment results R1 and R2, the judgment result R1 or R2 with the larger absolute value difference between the demodulated signals p1 and p2 and their respective thresholds Th1 and Th2 is used to process the received data d'. k The demodulator 140 determines the two demodulated signals, one at the same frequency and the other at twice the frequency. If there is a difference between the two demodulated signals, the one with the larger absolute value is used as the received data.

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[0052] The above modulation and demodulation method makes it possible to reliably demodulate received data even when Δθ fluctuates due to the effects of refractive index and polarization of the optical fiber 114 and Mach-Zehnder interferometer 115 of the optical fiber vibration sensor 110.

[0053] (Second example) Figure 7 shows an embodiment in which the modulation method for the transmitted data in the modulation device 230 is amplitude modulation using vibrations of multiple frequencies.

[0054] First, the serial transmission data is converted into parallel by the serial-to-parallel converter 234. The number of parallel connections is the same as the number of frequencies used. Here, we will explain the case of n parallel connections. The n-bit data, which has been parallelized by the serial-to-parallel converter 234, is amplitude-modulated by the amplitude modulator 33. Specifically, the amplitude modulator 33 uses an angular frequency of ω ν1 From ω νn By controlling n carrier generators 232 that generate carrier waves up to a certain point, amplitude modulation of n-bit data is performed. The modulated individual signals are added together by a signal adder 235 to form a modulated signal u(t). Specifically, u(t) is expressed by the following equation.

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[0055] When using the Mach-Zehnder interferometer 115, as shown in equation (9), not only the frequency of the vibration applied to the received signal but also harmonics are generated. Therefore, in parallel transmission using vibrations of multiple frequencies, the vibration frequencies used must satisfy the following conditions. Theoretically, harmonics of four times or higher are generated, but in practice, it is sufficient to consider frequencies up to three times the frequency.

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[0056] Figure 8 shows the demodulation method of the received data in the demodulator 140 when the transmitting device 2 applies multiple frequency vibrations to the optical fiber cable 120 that satisfy the conditions of equation (24) and are generated by equation (23), and the demodulation method is quadrature demodulation for the same frequency and twice the frequency of each vibration. Specifically, the demodulator 140 is equipped with demodulation circuits 160 corresponding to the number of multiple frequencies.

[0057] The received signal y(t) has an angular frequency of ω ν1 From ω νn The signal is demodulated by the n demodulators shown in equations (10) to (22) that operate on the carrier wave up to d'. k The data (k=1, 2, ..., n) is obtained. This is converted into serial data by the parallel-to-serial converter 235 and output sequentially, thereby obtaining the original transmission data.

[0058] As described above, by using vibrations at multiple frequencies, it became possible to increase the transmission speed while keeping the symbol rate the same.

[0059] The apparatus in the above embodiment (receiving device 1, transmitting device 2, demodulator 16, etc.) can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. The program of this disclosure is a program that causes a computer to realize each function of the apparatus relating to this disclosure, and a program that causes a computer to execute each procedure of the method executed by the apparatus relating to this disclosure. [Industrial applicability]

[0060] The data transmission system disclosed herein can be applied to the information and communication industry. [Explanation of symbols]

[0061] 100: Data transmission system 1: Receiving device 2: Transmitter 10 vibration sensors 11:Light source 12:Receiver 13: Fiber optic cable 14: Fiber optic 16: Demodulator 17: Demodulation Circuit 18: Parallel-to-Serial Converter 21: Vibration generator 22: Serial-to-Parallel Converter 23: Amplitude modulator 24: Carrier wave generator 25: Signal Adder 110: Vibration sensor 111: Light source 112:Receiver 114: Optical fiber 115: Mach-Zehnder interferometer 120: Fiber optic cable 140: Demodulator 141: Multiplier 142: Low-pass filter 143: Squarer 144: Square root tool 145: Adder 146: Discriminator 147: Cosine wave generator 148: Sine wave generator 149: 2x cosine wave generator 150:2x sine wave generator 160: Demodulation Circuit 162: Parallel-to-Serial Converter 210: Vibration generator 220: Vibration Generator Drive Amplifier 230: Modulator 232: Carrier wave generator 233: Amplitude modulator 234: Serial-to-Parallel Converter 235: Signal Adder

Claims

1. A transmitting device comprising: an amplitude modulator for amplitude-modulating the transmitted data; and a vibration generator that applies vibration to the optical transmission path in the optical fiber cable with the amplitude-modulated signal. A receiving device comprising: an optical fiber vibration sensor for detecting vibrations in the optical transmission path; and a demodulator for demodulating transmission data amplitude-modulated from vibrations in the optical transmission path. Equipped with, Data transmission system.

2. The transmitting device includes a serial-parallel converter that converts the transmitted data from serial to parallel, The amplitude modulator adds a different frequency to each signal that has been converted from serial to parallel depending on the presence or absence of vibration. The demodulation device comprises a demodulation circuit that demodulates vibrations in the optical transmission path for each frequency, and a parallel-serial converter that converts the demodulated signal into a parallel-serial format to restore the transmission data. The data transmission system according to claim 1.

3. The frequencies assigned to each signal parallelized by the serial-to-parallel converter satisfy the following relationship: The data transmission system according to claim 2. [Math C1] However, ω νｋ This is the frequency of the vibration assigned to the k-th parallel signal.

4. The demodulation device demodulates the vibrations frequency by frequency using an orthogonal demodulation method for the same frequency and twice the frequency of the vibrations applied by the vibration generator to the optical transmission path. The data transmission system according to claim 2.

5. The two demodulated signals, one demodulated at the same frequency and the other at twice the frequency, are compared. If there is a difference between the two demodulated signals, the one with the larger absolute value is used as the received data. The data transmission system according to claim 4.

6. The procedure for amplitude modulating the transmitted data, A procedure for applying vibration to the optical transmission path in an optical fiber cable using an amplitude-modulated signal, A procedure for detecting vibrations in the optical transmission path, A procedure for demodulating transmission data amplitude-modulated from vibrations in the optical transmission path, Equipped with, Data transmission method.

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