JP7653685B2 - Information transmission system, information transmission method, and information transmission device - Google Patents

Description

This disclosure relates to technology related to a sensor network that allows for easy collection of information from sensor devices.

One of the conventional sensor information transmission technologies is a wireless sensor equipped with wireless functionality. By using wireless sensors, it is possible to install the necessary sensors in any location and transmit information. There are several communication standards for wireless transmission methods, such as WiFi and 5G. Among them, LPWA (Low Power Wide Area) is often used for IoT devices. LPWA is a communication standard that allows long-distance transmission at the expense of low speed. (Non-Patent Document 1) The second is a sensor information transmission technology using optical fiber communication. For example, there is a method of transmitting sensor information to a remote location using a media converter. (Non-Patent Document 2)

Madhumitha M. , Nikhil, Bhupendra Pratap Singh, “A survey on LPWAN technologies in content to IoT applications, ldeas and innovations in technology”, International journal of advance research, 2019 Dyden Corporation, "Environmentally Friendly 100BASE-TX/FX Media Converter", https://www.dyden.jp/network/download/specifications/DN2800E-2C-SIYO.pdf, (Accessed Online 2021.6.10)

However, the device put to practical use in Non-Patent Document 1 has the problem that, due to the nature of wireless technology, stable communication is not possible in spaces with obstacles, such as mountainous regions or underground spaces. In particular, when transmitting sensor information underwater, there is a problem that it is impossible to transmit information over practical distances due to radio wave absorption by seawater.

When using an optical fiber network as a sensor information transmission line as in Non-Patent Document 2, a lot of work is required to tear off the optical cable sheath at the location where the sensor device is to be installed, expose the optical fiber, and then connect it to the sensor device. In addition, there is a problem that the reliability of the optical fiber at the connection part may decrease, especially when used underwater.

The purpose of this disclosure is to enable the transmission of sensor information acquired by a sensor device installed in a remote location through simple construction using unused optical fiber in an existing optical fiber cable.

The present disclosure provides an information transmission system that transmits sensor information acquired by a sensor device via an optical fiber cable, the system comprising an information transmitting device that imparts vibrations to the optical fiber cable with a modulated signal modulated with the sensor information input from the sensor device, and an information receiving device that detects vibrations of the optical fiber in the optical fiber cable and demodulates the sensor information from the detected signal. In this manner, the present disclosure transmits the sensor information by imparting sensor information from the sensor device as vibrations from the outer sheath of the optical fiber cable and receiving the vibrations with an optical fiber vibration sensor in the optical fiber cable. As a result, the present disclosure makes it possible to enable transmission with simple construction using unused optical fibers in an existing optical fiber cable.

The information transmission system disclosed herein is an information transmission system in which an information transmitting device and an information receiving device are connected by an optical fiber cable.
The information transmitting device includes:
a modulation device that modulates sensor information acquired by the sensor device;
and a vibration generator that applies vibration to the optical transmission path in the optical fiber cable with the modulated signal.
The information receiving device includes:
an optical fiber vibration sensor that detects vibration of an optical transmission path in the optical fiber cable;
and a demodulation device that demodulates the sensor information modulated from the vibration to the optical transmission path.

The information transmission method of the present disclosure includes:
An information transmission method implemented by an information transmission system in which an information transmitting device and an information receiving device are connected by an optical fiber cable, comprising:
The information transmitting device includes:
The sensor information acquired by the sensor device is modulated,
Amplifying the modulated signal;
applying vibration to an optical transmission path in the optical fiber cable;
The information receiving device includes:
Detecting vibrations to an optical transmission path in the optical fiber cable;
The sensor information modulated from the vibration to the optical transmission line is demodulated.

According to the present disclosure, it is possible to transmit sensor information acquired by a sensor device installed in a remote location through simple construction using unused optical fiber in an existing optical fiber cable.

1 shows an embodiment of the sensor information transmission system in which the optical fiber vibration sensor is a Mach-Zehnder interferometer. This embodiment shows a modulation device in which the modulation method for sensor information is binary phase shift keying (BPSK) and the multiplexing method is code division multiplexing. 1 shows an example of the relationship between a modulated wave and a received signal observed by a photoreceiver when the optical fiber vibration sensor is a Mach-Zehnder interferometer. This embodiment shows a demodulation device in which the demodulation method for sensor information is binary phase shift keying (BPSK) and the multiplexing method is code division multiplexing.

The following describes in detail the embodiments of the present disclosure with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are mutually identical.

In the information transmission system disclosed herein, an information transmitting device and an information receiving device are connected by an optical fiber cable.
The information transmitting device
A modulation device that modulates sensor information acquired by a sensor device installed at a remote location;
a vibration generator driver amplifier for amplifying the modulated signal;
an information transmission node including a vibration generator for applying vibration to an optical transmission path in the optical fiber cable by a modulated signal;
Equipped with.
The information receiving device
an optical fiber vibration sensor that detects vibrations in an optical transmission path in an optical fiber cable;
a demodulation device that demodulates the sensor information modulated from the vibration to the optical transmission line;
Equipped with.

As a result, this disclosure enables the transmission of sensor information to a remote information receiving device by measuring sensor information provided as vibrations from the outer sheath of the optical fiber cable by an information transmitting device using an optical fiber vibration sensor.

Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.
1 shows an embodiment of a sensor information transmission device in which the optical fiber vibration sensor of the present disclosure is a Mach-Zehnder interferometer. Sensor information such as temperature, humidity, illuminance, and tilt measured by a sensor device 3 is sent to an information transmission device 2. In the information transmission device 2, a modulation signal is created in a modulation device 230 from the sensor information. The modulation signal is amplified by a vibration generator drive amplifier 220 and drives a vibration generator 210. The vibration generator 210 applies vibration to the outer sheath of the optical fiber cable 120.

The optical fiber vibration sensor 110 in the example of FIG. 1 includes a light source 111, two optical couplers 113, three optical transmission paths 114 in an optical fiber cable 120, and an optical receiver 112. The optical signal emitted from the light source 111 is branched and transmitted to two optical transmission paths 114 by the optical coupler 113, and the interference waveform generated by the optical coupler 113 on the opposite side is measured by the optical receiver 112. When vibration corresponding to the modulated signal is applied from the vibration generator 210 of the information transmission device 2, the interference waveform changes in response to this vibration, and a received signal can be obtained by the optical receiver 112. The received signal is demodulated by the demodulator 130, and the sensor information from the sensor device 3 is output from the demodulator 130.

2 shows a signal processing function in a modulation device 230 when the modulation method of the sensor information is binary phase shift keying (BPSK) using phases 0 and π/2, and the multiplexing method is code division multiplexing. Sensor information s(t) from the sensor device 3 is converted to B(t) by a level converter 231. However,
B(t)=2s(t)-1 (1)
It is.

The spreading code sc(t) is multiplied by the ±1 level-converted B(t) by the multiplier 232 to obtain the code sequence S(t) of -1 and 1 after spreading. As the spreading code sc(t), a pseudorandom noise pattern with low autocorrelation such as an M-sequence or a Gold sequence can be used.

The phase of the carrier wave c(t) is shifted by 0 or π/2 by the phase modulator 234 according to the obtained S(t) to obtain the modulated wave _u (t).
Here, _ωc is the angular frequency of the carrier wave. Since the modulating wave u(t) uses phases 0 and π/2,
u(t)=A sin(ω _c t+π/4(S(t)+1)) (3)
The vibration generator 210 is driven by this modulated wave u(t).

Figure 3 illustrates the relationship between the modulated wave u(t) and the received signal y(t) observed by the optical receiver 112 when the optical fiber vibration sensor 110 is a Mach-Zehnder interferometer.

Assume that light is incident from a light source 111 at the position Pin, passes through two paths, is combined, and a change in light intensity I is observed at Pout by a photodetector 112. If the amplitudes of the electric fields of the light in the two paths are _E1 and _E2 , the complex amplitude of the electric field E at Pout is expressed as follows:
E=E ₁ exp(i(ωt+Φ ₁ (t)))+E ₂ exp(i(ωt+Φ ₂ (t))) (4)
Here, Φ ₁ (t) and Φ ₂ (t) are the phases at time t at point Pout.

Here, since the light intensity I at a point Pout of the optical receiver 112 is proportional to the square of the amplitude,
I=|E| ² =E ₁ ² +E ₂ ² +2E ₁ E ₂ cos(Φ ₁ (t) - Φ ₂ (t)) (5)
It becomes.

The lengths of the two optical transmission paths 114 from the light source 111 at the point Pin to Pout are _L1 and _L2 , and the wavelength of the light is λ. When vibration u(t) is applied from the outside, a time difference occurs between the vibration arriving at the two optical transmission paths 114 according to the physical distance. When this time difference is 2Δt and the optical transmission path 114 expands or contracts due to the applied vibration,
L ₁ =L+ΔL・u(t−Δt) (6)
L ₂ =L+ΔL・u(t+Δt) (7)
Here, L is the length of the original optical transmission line 114, and ΔL is the maximum change due to the vibration u(t).

Therefore, the phase difference in equation (5) is
Φ ₁ (t) - Φ ₂ (t) = 2πL ₁ /λ - 2πL ₂ /λ
=2πΔL/λ(u(t-Δt)-u(t+Δt))

となる。ただし、ｎ（ｔ）は雑音である。 Here, from equation (3), Φ ₁ (t) - Φ ₂ (t)
=A'sin(ω _c Δt)・cos(ω _c t+π/4(S(t)+1)) (8)
However,
A'=-4πΔL/λ (9)
The received signal y(t) measured by the photoreceiver 112 at Pout is given by

where n(t) is noise.

4 shows the signal processing function in demodulator 130 when the demodulation method of the received signal is synchronous detection of a BPSK modulated wave using phases 0 and π, and the multiplexing method is code division multiplexing. However, since the recovered carrier wave has an angular frequency of _2ωc , which is twice that of the received signal, as shown below, the phase shift is also twice that of the received signal, 0 and π.

となる。ただし、Ｊ_ｎはベッセル関数である。 The received signal y(t) measured by the optical fiber vibration sensor 110 shown in equation (10) can be transformed as follows using a Bessel function:

Here, J _n is a Bessel function.

を得る。ただし、α＝４Ｅ_１Ｅ₂Ｊ_２（２Ａ’ｓｉｎ（ω_ｃΔｔ））である。また、ｎ′（ｔ）は帯域通過フィルタ１３１通過後の雑音である。 If the signal obtained by removing the DC component and components higher than the angular frequency _4ωc from the received signal y(t) by the band-pass filter 131 is denoted as z(t), then

Here, α=4E ₁ E ₂ J ₂ (2A′ sin(ω _c Δt)), and n′(t) is the noise after passing through the band-pass filter 131.

Next, a carrier regenerator 132 regenerates a carrier c'(t) from the received signal z(t) after passing through the band-pass filter 131, as follows: c'(t)=cos(2ω _c t) (13)
get.

The received signal z(t) and the recovered carrier wave c'(t) are multiplied by a multiplier 232 to obtain the following p(t).

Since the second and third terms of equation (14) can be removed from p(t) by the low-pass filter 133,
S'(t)=α/2cos(π/2(S(t)+1)) (15)
get.

The obtained S'(t) is despread by a multiplier 232 using a spreading code sc(t) to obtain B'(t) having a positive or negative value according to the sensor information. The discriminator 134 determines s'(t) depending on whether B'(t) is positive or negative as follows:
When B'(t)>0, s'(t)=1 (16)
If B'(t) < 0, then s'(t) = 0 (17)
This makes it possible to obtain an estimate s'(t) of the sensor information.

To transmit sensor information from multiple information transmission devices 2 using code division multiplexing, multiplexing is possible by using a different spreading code sc(t) for each information transmission device 2.

In this embodiment, the optical fiber vibration sensor 110 is a Mach-Zehnder interferometer, the modulation method of the modulator 230 is BPSK (Binary Phase Shift Keying), the demodulation method of the demodulator 130 is synchronous detection of BPSK modulated waves, and the multiplexing method is spread spectrum. It goes without saying that other optical fiber vibration sensors 110, modulation/demodulation methods, and multiplexing methods can also be realized by applying a modulated signal corresponding to the sensor information as vibration from the outer sheath of the optical fiber cable 120. Also, in this embodiment, the case where there is one information transmission device 2 has been described, but it goes without saying that multiple information transmission devices 2 can be used by using a multiplexing method.

(Effects of the present disclosure)
As described above, according to the present disclosure, by utilizing unused optical fibers in the optical fiber cables laid nationwide to realize FTTH, it is possible to install any existing sensor device for temperature, humidity, illuminance, tilt, etc., with easier construction than before, regardless of whether it is above ground, underground, or underwater, and monitor various types of infrastructure.

This disclosure can be applied to the information and communications industry.

1. Information receiving device 2. Information transmitting device 3. Sensor device 110. Optical fiber vibration sensor 111. Light source 112. Light receiver 113. Optical multiplexer/splitter coupler 114. Optical transmission path 120. Optical fiber cable 130. Demodulator 131. Band-pass filter 132. Carrier regenerator 133. Low-pass filter 134. Discriminator 210. Vibration generator 220. Vibration generator driver amplifier 230. Modulator 231. Level converter 232. Multiplier 233. Carrier generator 234. Phase modulator

Claims (5)

An information transmission system in which an information transmitting device and an information receiving device are connected by an optical fiber cable,
The information transmitting device includes:
a modulation device that modulates sensor information acquired by the sensor device;
a vibration generator that applies vibration to an optical transmission path in the optical fiber cable by a modulated signal;
The information receiving device includes:
an optical fiber vibration sensor that detects vibration of an optical transmission path in the optical fiber cable;
a demodulation device that demodulates the sensor information modulated from the vibration to the optical transmission path ,
An information transmission system , wherein the modulation and demodulation method in said modulator and demodulator is phase modulation and demodulation . The optical fiber vibration sensor includes:
a light source that inputs an optical signal into an optical transmission path in the optical fiber cable;
a Mach-Zehnder interferometer that causes the optical signal to interfere in the optical transmission line after the optical signal has been subjected to vibration by the vibration generator;
an optical receiver that receives the optical signal interfered by the Mach-Zehnder interferometer;
2. An information transmission system according to claim 1, comprising: 3. An information transmission system according to claim 1, wherein a multiplexing method in said modulation device and said demodulation device is code division multiplexing. An information transmission method implemented by an information transmission system in which an information transmitting device and an information receiving device are connected by an optical fiber cable, comprising:
The information transmitting device includes:
The sensor information acquired by the sensor device is modulated,
The modulated signal is used to vibrate the optical transmission path in the optical fiber cable;
The information receiving device includes:
Detecting vibrations to an optical transmission path in the optical fiber cable;
demodulating sensor information modulated from the vibration to the optical transmission path;
An information transmission method , wherein the modulation and demodulation are carried out using a phase modulation/demodulation method. An information transmitting device connected to an information receiving device by an optical fiber cable,
a modulation device that modulates sensor information acquired by the sensor device;
a vibration generator that applies vibration to an optical transmission path in the optical fiber cable by a modulated signal;
Equipped with
An information transmitting apparatus , wherein the modulation method in said modulation device is phase modulation .

Images