JP5580245B2 - Electric field communication system and electric field communication method - Google Patents

Description

  The present invention relates to an electric field communication system and an electric field communication method in which an electric field is induced in an electric field transmission medium such as a human body, and the induced electric field is detected to perform communication, and more specifically, an electric field communication system using a common mode choke coil And an electric field communication method.

  In recent years, research on human body communication in which an electric field is propagated through a human body has been performed as an alternative to wireless communication that propagates radio waves in the air (see Patent Document 1).

  FIG. 7 is a configuration diagram of a conventional electric field communication system. In general, power is supplied to the installed receiver 3 via an AC power source. In this case, an electrical coupling 4 occurs between the circuit ground G1 of the receiver 3 and the ground G2 of the outlet into which the AC power supply is inserted. In the vicinity of the installed electrodes P3 and P4, there is generally a conductive member (building ground G3) constituting the building. In general, a noise voltage (noise source) 20 is generated between the building ground G3 and the outlet ground G2, and a noise current I2 flows along the path R4. On the other hand, the signal current I1 flows along the path R1, the signal current I2 flows along the path R2, and the signal current I3 flows along the path R3. In FIG. 7, the total signal current I1 + I2 + I3 is described as “It”. The receiver 3 detects the voltage applied to the load resistance R. When the noise current I2 is large, the signal-to-noise ratio (SNR) of the received signal is lowered and the communication quality is lowered.

  Such noise is known as common mode noise, and a common mode choke coil (CMC) 5 is known as a device for reducing the common mode current (see Non-Patent Document 1). A conventional example of an electric field communication system using the CMC 5 is shown in FIG. When the CMC 5 is used as shown in FIG. 8, the current flowing from the circuit ground G1 to the outlet ground G2 decreases. Therefore, the noise current I2 (path R4) decreases.

JP 2007-174570 A

F.-Y. Shih et al., IEEE Trans. Power Electron., Vol. 11, no. 1, pp. 170-181, 1996.

  However, when the CMC 5 is used, the noise current I4 decreases, and at the same time, the signal current I1 also decreases. Therefore, if the signal current I2 + I3 is not sufficiently large, there is a problem that when the CMC 5 is inserted, both the signal and noise are reduced, and the SNR is not improved.

  The present invention has been made to solve the above-mentioned problems, and its object is to minimize the decrease in signal current and dramatically reduce only the noise current when CMC is used. An electric field communication system and an electric field communication method are provided.

In order to solve the above-described problem, an electric field communication system according to an embodiment of the present invention is an electric field communication system using a common mode choke coil, and an impedance of a predetermined path among communication paths is set in the electric field communication system. An impedance adjustment unit that dynamically adjusts in a manner according to the situation, and a transmission unit that transmits a data signal using a path whose impedance is adjusted by the impedance adjustment unit only when the user touches a predetermined electrode And a receiver for receiving the data signal transmitted by the transmitter, the transmitter being a transmitter carried by the user, and applying a voltage between the electrode P1 and the electrode P2 mounted on the transmitter. The data signal is transmitted by applying the signal, and the receiving unit applies to the electrode P3 and the electrode P4 via the common mode choke coil. The data signal is received by detecting a potential difference generated between the electrode P3 and the electrode P4 only while the user touches the electrode P3, and the impedance adjustment unit By increasing the capacitance between P4 and the electrode P2 or the capacitance between the electrode P4 and the ground, the impedance of the predetermined path is reduced .

  Further, the electrode P4 may be connected to a building ground constituting the building.

  Further, the area of the electrode P4 may be larger than the area of the electrode P3.

  Moreover, you may further provide the electrode P5 connected to the said electrode P4.

  The electrode P4 may be arranged so as not to be directly below the electrode P3.

In order to solve the above problems, the electric field communication method in the embodiment of the present invention, there is provided a field communication method in an electric field communication system using the common mode choke coil, the field impedance of the predetermined path in the communication path An impedance adjustment step that dynamically adjusts in a manner according to the installation status of the communication system, and a data signal using a path in which the impedance is adjusted in the impedance adjustment step only when the user is touching a predetermined electrode A transmitting step for transmitting, and a receiving step for receiving the data signal transmitted in the transmitting step. In the transmitting step, a voltage is applied between the electrode P1 and the electrode P2 mounted on the transmitter carried by the user. Transmitting the data signal by applying, in the receiving step, the common mode The data signal is received by detecting a potential difference generated between the electrode P3 and the electrode P4 only while the user touches the electrode P3, and is connected to the electrode P3 and the electrode P4 via a choke coil. In the impedance adjustment step, the impedance of the predetermined path is reduced by increasing the capacitance between the electrode P4 and the electrode P2 or the capacitance between the electrode P4 and the ground .

  According to the present invention, since the impedance of a predetermined path among the communication paths is adjusted, when the CMC is used, the decrease in the signal current is minimized and only the noise current is dramatically decreased. It is possible to provide an electric field communication system and an electric field communication method that can be used.

It is a figure which shows the equivalent circuit model of the electric field communication system in 1st Embodiment. It is a block diagram of the electric field communication system in 1st Embodiment. It is a flowchart which shows operation | movement of the electric field communication system in 1st Embodiment. It is a block diagram of the electric field communication system in 2nd Embodiment. It is a block diagram of the electric field communication system in 3rd Embodiment. It is a block diagram of the electric field communication system in 4th Embodiment. It is a block diagram of the conventional electric field communication system. It is a block diagram of the electric field communication system using the conventional CMC.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First embodiment]
The electric field communication system according to the first embodiment is a system that performs communication by inducing an electric field in an electric field transmission medium such as a human body and detecting the induced electric field. Again, as in the prior art, a common mode choke coil (CMC) is used to reduce the common mode current.

  An equivalent circuit model of this electric field communication system is shown in FIG. The parameters in the figure represent the following physical quantities.

C ₀ : Capacitance between electrode P3 and electrode P4 C ₁ : Capacitance between building ground G3 and electrode P2 C ₂ : Capacitance between electrode P4 and electrode P2 C ₃ : Electrode P1 and human body capacitance C 4 between _the: electrode P3 and the capacitance between the human body C _5: electrode P4 and the capacitance between the building ground G3 C _6: capacitance between the human body and the building ground G3 omega: Angular frequency L: CMC common mode inductance R: Receiver input resistance (load resistance R)
X (ω): Fourier transform of transmitted signal voltage Y (ω): Fourier transform of received signal voltage N (ω): Fourier transform of noise voltage When the received signal Y (ω) is calculated using the model of FIG. become that way.

Since the denominator of equation (1) is a complex equation, it is summarized as function F without showing a specific function form. When a signal-to-noise ratio (SNR) is calculated using equation (1), equation (4) is obtained. The first term on the right side of the equation (4) represents the SNR when CMC5 is not used. The second term represents the SNR increment by CMC5.

First, conditions for improving the SNR without using the CMC 5 will be considered. For this purpose, it is necessary to reduce A in the equation (3). In this case, the only parameter that can be controlled is C ₂ , and it can be seen that increasing C ₂ is effective. However, (3) for the expression of the first term on the right side, there is a limit to reduce the A simply by increasing the C _2. Therefore, when the CMC 5 is not used, it is generally difficult to sufficiently improve the SNR.

Next, conditions for improving the SNR using the CMC 5 will be considered. From equation (4), it can be seen that if 1 << ω ² LC _eff , the SNR is greatly improved by the insertion of CMC5. ω is a parameter that depends on the communication system, and generally has no design freedom. L should be selected as large as possible. Similarly, it is important to increase C _eff . It is C ₂ and C ₅ that can be controlled by parameters affecting C _eff , and at least one of them needs to be increased. Conversely, when the _{C 2} and _{C 5} are both small, it can be seen that the SNR be inserted CMC5 is not sufficiently improved. Also, from the equations (2) to (4), it can be seen that the SNR does not depend on C ₀ and C ₄ when the modeling of FIG. 1 is performed.

Therefore, in the present invention, the impedance adjustment unit 10 that adjusts the impedance of a predetermined path among the communication paths is provided. The impedance adjusting portion 10, by increasing the like C ₂ and C _5, and so as to reduce the impedance of such path R3 and route R2.

  Specifically, when the electric field communication system is installed on a floor or the like, the electric field communication system is built in an appropriate embodiment according to the installation location. In other words, the impedance adjustment unit 10 dynamically adjusts the impedance in a manner according to the installation status of the electric field communication system. This point will be described in detail later.

  FIG. 2 is a configuration diagram of the electric field communication system according to the first embodiment. The same reference numerals are used for the same parts as those in the conventional configuration diagram. As indicated by reference numeral 10 in the figure, since the electrode P4 is short-circuited to a large metal (building ground G3) constituting a building or the like, the impedance of the path R2 is small, and therefore the signal current I2 flowing through the path R2 is large. Therefore, even when the signal current I1 flowing through the path R1 is interrupted by the CMC5, the signal current It flowing through the load resistor R is sufficiently secured, so that the SNR of the received signal is improved by introducing the CMC5.

Thus, in 1st Embodiment, the electrode P4 and building ground G3 are short-circuited, and the impedance between these is made small. Reducing the impedance is equivalent to increasing the C _5, C _eff as a result, the SNR is improved because increases.

  By the way, such an electric field communication system is typically applied to an entrance / exit management system that manages the entry and exit of people. In this case, the user carries the portable terminal by dropping it from the neck or putting it in a pocket. Thus, the user carrying the terminal can perform authentication by electric field communication only by standing on the electrode (corresponding to P3) installed on the floor near the office door. Unlike the conventional IC card system, it is not necessary to hold the portable terminal over the reader.

  FIG. 3 is a flowchart showing the operation of the electric field communication system according to the first embodiment. Here, it is assumed that the impedances of the path R3 and the path R2 have already been adjusted in a manner according to the installation state of the electric field communication system.

  First, the installation terminal periodically sends a link signal to the installation electrode (steps S31 → S32). The installation terminals referred to here are terminals installed in the environment such as the receiver 3 and the electrodes P3 and P4. On the other hand, the portable terminal (corresponding to the transmitter 2) carried by the user is in a standby state, and when the user stands on the installation terminal, the link signal is received by electric field communication (step S21: Yes). The mobile terminal that has received the link signal transmits an ACK to the installation terminal and then transmits a data signal to be transmitted (steps S22 → S23). The installation terminal that has received the ACK stops transmission of the link signal for a certain period and receives the data signal from the mobile terminal (steps S33 → S34). Specifically, a data signal is received by detecting a potential difference generated between the electrodes P3 and P4. After receiving the data signal, the installation terminal periodically transmits the link signal again (steps S35 → S36).

As described above, in the electric field communication system in the first embodiment, since the electrode P4 is connected to the ground, C ₅ increases, the impedance of the path R2 is reduced. As a result, when the CMC is used, it is possible to minimize the decrease in the signal current and dramatically reduce only the noise current. That is, it is possible to increase the SNR of the received signal and ensure more stable communication.

[Second Embodiment]
In the second embodiment, by increasing the C ₂ and C _5, and so as to reduce the impedance of the path R3 and route R2. The second embodiment is the same as the first embodiment except that the impedance adjustment method is different. Hereinafter, only the points in which the present embodiment is different from the first embodiment will be described.

  FIG. 4 is a configuration diagram of an electric field communication system according to the second embodiment. In this case, since the area of the electrode P4 is larger than that in the case of FIG. 8, the capacity between the electrode P4 and the building ground G3 becomes larger than that in the case of FIG. Further, since the area of the electrode P4 is larger than the area of the electrode P3, the capacitance between the electrode P4 and the electrode P2 becomes larger than that in the case of FIG. Due to these effects, the impedances of the paths R2 and R3 are reduced, so that the signal currents I2 and I3 flowing through the paths R2 and R3 are increased. Therefore, even when the signal current I1 flowing through the path R1 is interrupted by the CMC5, the signal current It flowing through the load resistor R is sufficiently secured, so that the SNR of the received signal is improved by introducing the CMC5.

As described above, in the electric field communication system according to the second embodiment, since the direction of the area of the electrode P4 than the area of the electrode P3 is large, C ₂ and C ₅ is increased, the impedance of the path R3 and route R2 Get smaller. As a result, when the CMC is used, it is possible to minimize the decrease in the signal current and dramatically reduce only the noise current. That is, it is possible to increase the SNR of the received signal and ensure more stable communication.

[Third embodiment]
In the third embodiment, by increasing the C ₂ and C _5, and so as to reduce the impedance of the path R3 and route R2. The second embodiment is the same as the first embodiment except that the impedance adjustment method is different. Hereinafter, only the points in which the present embodiment is different from the first embodiment will be described.

FIG. 5 is a configuration diagram of an electric field communication system according to the third embodiment. Since the electrode P4 is connected to the new electrode P5, it can be considered that the electrodes P4 and P5 are integrated. Accordingly, the same effect as in FIG. 4 can be obtained, so that the SNR of the received signal is improved. As shown in the second embodiment, it suffices if the electrode P4 can be made sufficiently large. However, for example, when the installation place of the electrode P4 is narrow, the electrode P4 cannot always be made sufficiently large. However, if the third embodiment is used, even in an environment where the second embodiment cannot be applied by disposing the electrode P5 in a place where a sufficient space is secured away from the installation place, Sufficient SNR can be ensured. In addition, although there is no restriction | limiting in the place which installs the electrode P5, the one near the building ground G3 is desirable. Although the area of the electrode P5 is advantageously larger, generally if 100cm ² ~2000cm ² mm, often sufficient SNR is obtained. In addition, as the distance between the electrode P5 and the building ground G3 is shorter, a larger effect can be obtained with a smaller area.

As described above, in the electric field communication system according to the third embodiment, since further comprising an electrode P5 connected to the electrode P4, the greater the C ₂ and C _5, low impedance path R3 and route R2 Become. As a result, when the CMC is used, it is possible to minimize the decrease in the signal current and dramatically reduce only the noise current. That is, it is possible to increase the SNR of the received signal and ensure more stable communication.

[Fourth embodiment]
In the fourth embodiment, by increasing the C _2, and so as to reduce the impedance of the path R3. The second embodiment is the same as the first embodiment except that the impedance adjustment method is different. Hereinafter, only the points in which the present embodiment is different from the first embodiment will be described.

  FIG. 6 is a configuration diagram of an electric field communication system according to the fourth embodiment. For example, in the example shown in FIG. 8, since the electrode P4 is disposed immediately below the electrode P3, the capacitance between the electrode P4 and the electrode P2 is generally small. However, by arranging the electrode P4 so as not to be directly below the electrode P3 as shown in FIG. 6, the capacitance between the electrode P4 and the electrode P2 increases as compared with the case of FIG. Therefore, since the impedance of the path R2 is smaller than that in FIG. 8, the signal current I2 flowing along the path R2 is increased. Therefore, the signal current It flowing through the load resistor R increases, contributing to an improvement in the SNR of the received signal. Since such an effect is obtained unless the electrode P4 is directly under the electrode P3, the electrode P4 in FIG. 6 does not need to be disposed on the same plane as the electrode P4 in FIG.

As described above, in the electric field communication system according to the fourth embodiment, since the electrode P4 is arranged so as not to directly under the electrode P3, C ₂ is increased, the impedance of the path R3 decreases. As a result, when the CMC is used, it is possible to minimize the decrease in the signal current and dramatically reduce only the noise current. That is, it is possible to increase the SNR of the received signal and ensure more stable communication.

  In the embodiment described above, the electrodes P3 and P4 are placed on the floor, but their installation location is not limited to the floor and may be a wall or the like. Further, the human body touches the electrode P3 is not limited to the foot, and any part of the human body may be used.

  In the above-described embodiment, the entrance / exit management system is illustrated, but the present invention is not limited to this. In other words, the present invention can be applied to the electric field communication system using CMC in the same manner as described above. Of course, the electric field transmission medium is not limited to the human body. That is, other animals or dielectrics can be used as the electric field transmission medium.

2 ... Transmitter (transmitter)
3. Receiving part (receiver)
5. Common mode choke coil (CMC)
10: Impedance adjustment unit R1, R2, R3 ... Path P1, P2, P3, P4 ... Electrode

Claims (6)

An electric field communication system using a common mode choke coil,
An impedance adjustment unit that dynamically adjusts the impedance of a predetermined path among the communication paths in a manner according to the installation state of the electric field communication system ;
A transmission unit that transmits a data signal using a path whose impedance is adjusted by the impedance adjustment unit only when the user touches a predetermined electrode;
A receiver that receives the data signal transmitted by the transmitter;
Equipped with a,
The transmitter is a transmitter carried by the user, and transmits the data signal by applying a voltage between the electrodes P1 and P2 mounted on the transmitter,
The receiver is connected to the electrode P3 and the electrode P4 via the common mode choke coil, and a potential difference generated between the electrode P3 and the electrode P4 only while the user touches the electrode P3. Receiving the data signal by detecting,
The impedance adjusting unit reduces the impedance of the predetermined path by increasing a capacitance between the electrode P4 and the electrode P2 or a capacitance between the electrode P4 and the ground.
An electric field communication system. Electric field communication system according to claim 1, wherein said electrode P4 is connected to the building ground constituting the building. Electric field communication system according to claim 1, wherein it is larger area of the electrode P4 than the area of the electrode P3. Electric field communication system according to claim 1, further comprising an electrode P5 connected to the electrode P4. Electric field communication system according to claim 1, wherein said electrode P4 is arranged so as not to directly below the electrode P3. An electric field communication method in an electric field communication system using a common mode choke coil,
An impedance adjustment step for dynamically adjusting the impedance of a predetermined path in the communication path in a manner according to the installation state of the electric field communication system ;
A transmission step of transmitting a data signal using a path whose impedance is adjusted in the impedance adjustment step only when a user is touching a predetermined electrode;
A receiving step for receiving the data signal transmitted in the transmitting step;
Equipped with a,
In the transmitting step, the data signal is transmitted by applying a voltage between the electrodes P1 and P2 mounted on the transmitter carried by the user,
In the receiving step, the potential difference generated between the electrode P3 and the electrode P4 is connected to the electrode P3 and the electrode P4 through the common mode choke coil and only while the user touches the electrode P3. Receiving the data signal by detecting,
In the impedance adjustment step, the impedance of the predetermined path is reduced by increasing the capacitance between the electrode P4 and the electrode P2 or the capacitance between the electrode P4 and the ground.
An electric field communication method characterized by the above.

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