JP2007189549A - Modem for power line carrier communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a MODEM for power line carrier communication capable of implementing excellent communication by reducing the effect of noises or a disturbing signal or the like on a power line for hindering the power line carrier communication. <P>SOLUTION: The modem M for the power line carrier communication includes: a transmission section 5 for transmitting a LC signal in multicarrier on a power line L; a reception filter section 2 comprising a broadband filter BPF0 for passing the PLC signal with a whole communication frequency band ΔBW0 and narrow band filters BP1 to BPn for dividing the whole communication frequency band into a plurality of frequency bands and passing the PLC signals corresponding to frequency bands ΔBW1 to ΔBWn; a reception section 3 for processing the PLC signals extracted from the power line L and passing through the broadband filter BPF 0 and the narrow band filters BP1 to BPn; and a modem section 4 for capturing received data from the reception section 3 and transmitting the data onto the power line L through the transmission section 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power line carrier communication modem using a power line as a transmission line.

In a power line carrier communication system, there is a risk of being affected by noise transmitted from an electric device connected to the power line. For this reason, a power line communication device (modem for power line carrier communication) provided with a reception filter unit that passes a predetermined frequency band and a reception unit that acquires data from a signal that has passed through the reception filter unit has been provided (patent). Reference 1).
Japanese Patent Laying-Open No. 2005-236815 (paragraph numbers 0019 to 0022 FIG. 1)

  By the way, the power line that is a communication line is not a shielded line, and the end of the line is often open, so depending on the frequency (wavelength) of the radio wave propagating in the air, it is very efficient. There is a problem that radio waves get into the antenna.

  And when the frequency of the electric wave which got on the track | line is in the frequency band used for power line carrier communication, the following bad influence is given to power line carrier communication.

  For example, in the configuration of a general power line carrier communication modem, a signal amplifier for amplifying a power line carrier communication signal having a low level is provided in the reception input stage. When a radio wave gets in, this signal is also amplified, and the power line carrier communication signal level is low.If the radio wave coming from the air gets on the power line that is the communication line, the signal level is high. Amplifies a signal with a large level further and distorts an originally unnecessary signal.

  This distorted boarding signal is added to the originally desired power line carrier communication signal and is transmitted to the signal processing circuit at the subsequent stage. This causes a problem of affecting signal identification, and causes the communication performance of the power line carrier communication modem to deteriorate. It was.

  In addition, in a power line carrier communication modem equipped with a signal processing function (channel estimation function) suitable for the transmission environment, in order to grasp the environment of the communication line (power line) in advance, the signal level on the communication line is checked for each frequency, A suitable modulation method is selected for each frequency band (channel) used to maintain communication capability. However, in the case of this type of power line carrier communication modem, there has been a problem that the control of the signal processing function does not work due to the influence of the signal generated when radio waves enter the communication line from the air as described above.

  In addition, when a power line is used as a communication line, another power line carrier communication modem that is unknown to the other party may also be present on the line, which has been an obstacle to constructing a communication system.

  That is, in the case of power line carrier communication, it has been a problem to suppress the influence of an external signal (interference signal) other than the original power line carrier communication signal.

  The present invention has been made in view of the above-described points, and the object of the present invention is to reduce the influence of noise on the power line, interference signals, etc. that hinder the power line carrier communication, and to perform good communication. It is to provide a power line carrier communication modem.

  In order to achieve the above-described object, the invention of claim 1 includes a transmission unit that transmits a power line carrier communication signal on a power line using a multicarrier, and a power line carrier communication signal corresponding to the entire communication frequency band of the multicarrier. A wideband filter that passes and a narrowband filter that is provided for each frequency band that is set by dividing the entire communication frequency band into a plurality of parts, and that passes through the power line of each frequency band, and is extracted from the power line And receiving the power line carrier communication signal passing through the narrowband filter, demodulating data from the power line carrier communication signal received and processed by the receiver, and transmitting the power through the transmitter. And a modem unit that modulates data to be transmitted by a power line carrier communication signal on the line.

  According to a second aspect of the invention, there is provided the means of the first aspect, wherein the wideband filter and the narrowband filter of each frequency band are switched to select a filter that allows the power line carrier communication signal to pass during data communication. It is characterized by.

  According to a third aspect of the invention, there is provided the detection means according to the second aspect of the invention, wherein the specific information included in the power line carrier communication signal passing through the wideband filter and the narrowband filter is detected, and the specific information detected by the detection means is provided. A narrowband filter other than the frequency band through which the power line carrier communication signal including information is passed is selected during data communication.

  According to a fourth aspect of the present invention, in the third aspect of the invention, the specific information is a specific frequency.

  According to a fifth aspect of the invention, in the third aspect of the invention, the specific information is a signal on the power line synchronized with a cycle of a commercial power supply frequency.

  According to a sixth aspect of the present invention, in the third aspect of the invention, the specific information includes a level value and a time occupation characteristic for each frequency of a power line carrier communication signal of another power line carrier communication system other than the power line carrier communication system to which the own station belongs. It is at least any one of these.

  The present invention can reduce the influence of noise on the power line, interference signals, etc. that hinder the power line carrier communication, and perform good communication even for a power line whose communication line environment cannot be specified depending on the place of use or use time zone. There is an effect.

Embodiments of the present invention will be described below.
(Embodiment 1)
FIG. 1A shows a circuit block of this embodiment. A power line carrier communication modem M of this embodiment includes a coupling circuit 1, a reception filter unit 2, a reception unit 3, and a modem as shown in the figure. A unit 4 and a transmission unit 5 are provided.

  The coupling circuit 1 includes capacitors C1 and C2 (the same capacitance value of C1) for cutting the commercial frequency, and a coupling transformer T connected to the power line L via the capacitors C1 and C2, and has a predetermined frequency band. Signals are allowed to pass in both directions, and the secondary side of the coupling transformer T is connected to the reception filter unit 2 and the transmission unit 5.

  The reception filter unit 2 is provided in the preceding stage of the reception unit 3 and is used for communication in all communication frequency bands (fL to fH <see FIG. 1B)> ΔBW power line carrier communication signal <hereinafter PLC (Power Line Communication) signal A wideband filter BPF0 that is a bandpass filter that is band-limited so as to pass through, and a bandpass filter that divides the entire communication frequency band ΔBW into a plurality of parts to correspond to the respective divided frequency bands ΔBW1 to ΔBWn. A plurality of narrowband filters ΔBPF1 to BPFn are provided.

  The reception unit 3 includes reception signal processing units 30 to 3n respectively corresponding to the filters BPF0 to BPFn, and performs A / D conversion processing on the PLC signals of the respective frequency bands that have passed through the filters BPF0 to BPFn, The signal after the A / D conversion is output to the modem unit 4.

  The modem unit 4 demodulates the PLC signal that has passed through the reception filter unit 2, converts it to a signal of an appropriate signal format and outputs it to the outside, and inputs a predetermined format signal from the outside to perform a predetermined modulation And a signal processing function for information exchange required in a power line carrier communication system (hereinafter referred to as a PLC communication system) to be described later.

  The transmission unit 5 includes a transmission signal processing unit 50 that performs D / A conversion on information that is modulated and output from the modem unit 4, and a multi-carrier PLC that supports all communication frequency bands (fL to fH) used in the communication system. A band-pass filter 51 that passes the signal and a transmission amplifier 52 that amplifies the PLC signal are configured to transmit the multi-carrier PLC signal to be transmitted on the power line L via the coupling circuit 1.

  The power line carrier communication modem M of this embodiment configured as described above constitutes a modem that supports all channels of multicarrier (number of channels N).

  FIG. 2A shows the use of the power line carrier communication modem M of the present embodiment for the master unit M0, the slave units M1,..., And the master unit M0 based on the control information transmitted by the PLC signal from the master unit through the power line L. The PLC system which communicates between the subunit | mobile_unit M1 ... is shown. In the illustrated example, the number of slave units is three, but the number is not particularly limited.

  The operation of this PLC system will be described with reference to the sequence diagram of FIG.

  First, in this PLC system, the base unit M0 transmits the control information CS at a constant cycle Tc by a multi-carrier PLC signal as shown in FIG. 2 (b) under the control of the modem unit 4. At this time, control information CS having the same content is transmitted to all channels of the multicarrier.

  Here, each of the slave units M1... Receives a PLC signal including the control information CS transmitted from the master unit M0, and the modem unit 4 performs a process of determining a reception channel with good signal quality.

  When the slave unit, for example, M1, needs to make a request for the individual control information to the master unit M0, the slave unit M1 controls the communication request information RQ with the multi-carrier PLC signal under the control of the modem unit 4. At this time, the slave unit M1 transmits the channel information as communication environment information based on the determination of the channel having the good signal quality described above.

  The modem unit 4 of the parent device M0 acquires channel information from the received communication environment information, sets a transmission channel for the acquired channel, and transmits the individual control information S to the child device M1 as a communication environment response in the transmission channel. Send.

  The modem unit 4 of the parent device M0 receives the communication environment information transmitted from the child device M1 by multi-carrier, thereby determining a reception channel with good signal quality for the parent device M0, and sends the channel information to the child device M1. It is included in the individual control information S and sent.

  The modem unit 4 of the slave unit M1 sets a transmission channel based on channel information from the master unit M0, and transmits an ACK signal as a communication environment confirmation response to the master unit M0 using the transmission channel as a PLC signal.

  Thereafter, data communication between the parent device M0 and the child device M1 is performed using only a channel (frequency band) with good signal quality. However, the entire communication frequency band ΔBW0 is used when receiving the control information CS periodically transmitted from the base unit M0.

  Similarly, data communication using a channel with good signal quality is performed between the slave unit M2 and the master unit M0 and between the slave unit M3 and the slave unit M0 through the above-described procedure.

2B, the signal D1 indicates a data communication signal with the slave unit M1, D2 indicates a data communication signal with the slave unit M2, and D3 indicates a data communication signal with the slave unit M3.
(Embodiment 2)
In the receiving unit 3 of the above-described first embodiment, the reception signal processing units 30 to 3n corresponding to the respective filters BPF0 to BPFn of the reception filter unit 2 are provided. However, in the present embodiment, as shown in FIG. It comprises a received signal processing unit 3a and a changeover switch unit 3b as a switching means for selecting and connecting any one of the filters BPF0 to BPFn of the receiving filter unit 2 to the received signal processing unit 3a. The circuit scale is reduced by sharing the reception signal processing unit 3a.

  The changeover switch portion 3b is changed over manually, and may be a mechanical switch such as a slide switch or a push button switch, or an electronic switch constituted by a semiconductor switch element.

  Thus, when the PLC system as shown in FIG. 2A is constructed by using the power line carrier communication modem M of the present embodiment, the specification of the usage environment of the PLC system can be estimated in advance (there is always an interference signal). Narrow band corresponding to a frequency band other than the frequency band of the known interference signal among the narrow band filters BPF1 to BPFn in the master unit M0 and the slave units M1. The filter is switched and selected by the selector switch unit 3b and connected to the received signal processing unit 3a.

Information on the communication band thus selected (channel information) is sent from the slave unit M1 to the master unit M0 by including the communication request information RQ in the same procedure as in the first embodiment, and from the master unit M0 to the slave unit M1. Are included in the individual control information S to establish an optimal communication path and perform data communication.
(Embodiment 3)
In the second embodiment, the reception filter unit 2 includes a wideband filter BPF0 composed of a bandpass filter corresponding to the entire communication frequency band, and a bandpass filter corresponding to each divided frequency band by dividing the multicarrier into a plurality of parts. The narrowband filters BPF1 to BPFn are respectively provided and manually selected for switching. In this embodiment, the entire communication frequency band ΔBW0 is obtained by switching the frequency band to be passed as shown in FIG. And a bandpass filter BPFx with a frequency band switching function capable of forming a narrowband filter corresponding to each frequency band ΔBW0 to ΔBWn set by dividing the entire communication frequency band ΔBW0 into a plurality of parts The filter unit 2 has a frequency band of the bandpass filter BPFx. It has a switching of the performed by the switching control signal K from the switching controller 40 of the modem unit 4.

  The switching control by the switching control unit 40 is based on detection by a specific frequency detection circuit (detection means) 6 that detects an interference signal of a specific frequency (specific information) included in a PLC signal passing through the bandpass filter BPFx. .

  The specific frequency detection circuit 6 uses a heterodyne method generally used in wireless communication, amplifies the interference signal frequency f1 that has passed through the bandpass filter BPFx by the amplifier 60, and then generates a local frequency generated by the PLL synthesizer 61. The signal is mixed in the mixer 62 by the fosc and converted into the intermediate frequency band Δf, and after this frequency conversion, the bandpass filter 63 having the center frequency fd (= f1−fosc) and having Δf as the passband is passed. When there is an interference signal having a specific frequency f1, a signal having a Δf component pulse waveform is output from the limiter 64 to the switching control unit 40 of the modem unit 4.

  The switching control unit 40 counts the signal from the limiter 64 and determines that there is an interference signal when the count value reaches a predetermined value.

  Instead of the limiter 64, an element that outputs only amplitude information, such as a diode, may be used. In this case, the presence / absence of an interfering signal is indicated by the amplitude of the output signal, and can be handled digitally as a “High” / “Low” signal. Further, the local frequency fosc is generated by the PLL synthesizer 61. However, the local frequency fosc may be fixed to a frequency assumed in advance. In this case, an oscillator that oscillates a fixed frequency may be used instead of the PLL synthesizer 61.

  Thus, when the PLC system as shown in FIG. 2A is constructed using the power line carrier communication modem M of the present embodiment, the following processing is performed at the start of operation.

  That is, the switching control unit 40 of the modem unit 4 of the parent device M0 and the child device M1... Sequentially switches the frequency band of the bandpass filter BPFx of the reception filter unit 2 from the entire communication frequency band ΔBW0 to ΔBW1, ΔBW2,. The switching control signal K to be set is output, and in each frequency band BW0 to ΔBWn, the detection signal from the specific frequency detection circuit 6 is counted to determine the presence or absence of an interference signal. A frequency band in which communication can be performed is determined, and control is performed to set the frequency band of the bandpass filter BPFx corresponding to this frequency band.

  FIG. 5B shows each frequency band ΔBW0... And the interference signal of the specific frequency fx that is detected, and the switching control unit 40 of the modem unit 4 does not include the interference signal of the specific frequency fx in the frequency band. As described above, the frequency band of the bandpass filter BPFx is switched and controlled.

  The frequency band information set by the bandpass filter BPFx, that is, channel information, is sent from the slave unit M1 to the master unit M0 in the communication request information RQ in the same procedure as in the first embodiment, and from the master unit M0, the slave unit M0 By including them in the individual control information S and sending them to the machines M1..., Data communication can be performed through an optimum communication path in which no interference signal exists.

According to this embodiment, even if signals in a specific frequency band (amateur radio, medium wave broadcast, various radio waves, etc.) exist in the system construction environment, those signals can be avoided without bothering humans. The frequency band (channel) in which good communication can be performed can be automatically set, can coexist with the PLC system using those specific frequency bands, and the use filter of the reception filter unit 2 is a block filter with a switching function. The circuit scale can be further reduced by using only BPFx.
(Embodiment 4)
In the third embodiment, an interference signal having a specific frequency is detected by a specific frequency detection circuit 6 provided in the reception unit 3, and the frequency band of the bandpass filter BPFx of the reception filter unit 2 is switched in accordance with the detection of the interference signal. However, the present embodiment is characterized in that the influence of noise synchronized with the commercial power supply frequency generated by the electric equipment existing on the power line L used in the PLC system is eliminated.

  That is, in the present embodiment, as shown in FIG. 6, a commercial power supply synchronization detection circuit (detection means) 7 for detecting a zero cross of a commercial power supply and generating a detection signal having a predetermined time width based on the zero cross detection is provided, and a modem is provided. In the unit 4, a switching control unit 40 that outputs a switching control signal K for switching control of the frequency band of the bandpass filter BPFx of the reception filter unit 2, and a signal monitoring unit that monitors the level of the signal passing through the bandpass filter BPFx 41.

Here, the commercial power supply synchronization detection circuit 7 connects the input end of the photocoupler 70 to the power line connection side of the coupling circuit 1 to insulate it from the commercial power supply, and then outputs the output of the photocoupler 70 to the low-pass filter 71 and the limiter. By passing 72, a pulse-shaped detection signal having a width corresponding to the positive half cycle of the commercial power supply is output as shown in FIG. 7B, as shown in FIG. 7A. That is, a detection signal synchronized with the commercial power cycle Ts is generated. Therefore, when the power line carrier communication modem M of this embodiment starts operation, the switching control unit 40 of the modem unit 4 starts from the commercial power synchronization detection circuit 7. First, as shown in FIG. 7C, the switching of the frequency band of the bandpass filter BPFx and the setting of the setting period Tm of the frequency band (a fixed period equal to or longer than the commercial power cycle Ts) are controlled. First, the frequency band of the bandpass filter BPFx is set to the entire communication frequency band ΔBW0.

  On the other hand, the signal monitoring unit 41 sets a period during which the level of the signal passing through the bandpass filter BPFx is sampled for a certain period of time centering on the zero cross of the commercial power supply as shown in FIG. The width is set, the signal level is monitored for each period, and the signal level is stored.

  Thereafter, the switching control unit 40 of the modem unit 4 performs control to sequentially switch the frequency band of the bandpass filter BPFx from ΔBW1 to the last ΔBWn every time the set period Tm elapses (FIGS. 7 (d) to (f)), and the signal monitoring unit As shown in FIG. 7G, 41 sets a sampling period corresponding to the zero cross of the commercial power supply corresponding to each setting period Tm, and monitors the signal level in the frequency band. When the signal level monitoring in the last frequency band ΔBWn is completed, the switching control unit 40 determines the frequency band corresponding to the lowest level among the signal levels stored in the signal monitoring unit 41 as the channel used for data communication. Then, a switching control signal for switching control to the frequency band is sent to the bandpass filter BPFx, and the frequency band of the bandpass filter BPFx is set. As a result, data communication is possible through a communication path using an S / N level channel that provides desired communication performance.

Here, when the PLC system shown in FIG. 2A is constructed using the power line carrier communication modem M of the present embodiment, the communication request information RQ is transmitted from the slave units M1 to the master unit M0 as in the first embodiment. In this case, the above-mentioned set frequency band information (channel information) is included and sent. In addition, when the individual control information S is sent from the parent device M0 to the child devices M1,... Including the set frequency band (channel information), an optimum communication path that is not affected by noise generated by the electric device. Thus, data communication can be performed.
(Embodiment 5)
As shown in FIG. 8, the power line carrier communication modem M according to the present embodiment includes the specific frequency detection circuit 6 according to the third embodiment in the reception unit 3 and a commercial power source that detects the synchronization signal of the commercial power cycle according to the fourth embodiment. It is provided with the synchronization detection circuit 7, and by combining the configurations of the third and fourth embodiments, it is possible to suppress the influence of a specific frequency (interference signal) and the influence of noise of electric equipment. There are features.

  In FIG. 8, the same components as those of the third and fourth embodiments are denoted by the same reference numerals, and the description of the configurations is omitted.

  Next, the operation of the power line carrier communication modem M of this embodiment will be described.

  First, before starting the data communication, the switching control unit 40 in the modem unit 4 uses the bandpass filter BPFx to check for the presence of a specific frequency interference signal using the specific frequency detection circuit 6 as in the third embodiment. This is performed for each frequency band ΔBW0 to BWn of each channel to be set.

  Next, the switching control unit 40 in the modem unit 4 is based on the detection signal from the commercial power supply synchronization detection circuit 7 shown in FIG. 9B synchronized with the commercial power supply cycle Ts shown in FIG. Similarly to FIG. 9C, control is performed to sequentially switch the frequency band of the bandpass filter BPFx of the reception filter unit 2 from ΔBW0 to ΔBWn as shown in FIGS. In the signal monitor unit 41, in each setting period Tm (a constant period equal to or greater than the commercial power supply period Ts), a sampling period for capturing a signal passing through the bandpass filter BPFx is set at a constant period as shown in FIG. . During the sampling period set here, the period synchronized with the zero cross of the commercial power supply (the period indicated by the oblique lines) is a period for checking the noise component generated by the electric equipment on the power line L, and is a period other than the zero cross (The period shown in white) is a period for checking the level value and the time occupation characteristic of each PLC signal used in the PLC system other than its own station. And the signal monitor part 41 memorize | stores the signal level in each period. Then, after the monitoring in the last frequency band ΔBW is completed, the switching control unit 40 has the lowest signal level among the signal levels stored in the signal monitoring unit 41 in the frequency band (channel) in which no interference signal of the specific frequency exists. The corresponding frequency band is determined as the frequency band of the bandpass filter BPFx, and the frequency band of the bandpass filter BPFx is set to the frequency band by the switching control signal K.

  Here, when the PLC system shown in FIG. 2A is constructed using the power line carrier communication modem M of the present embodiment, the communication request information RQ is transmitted from the slave units M1 to the master unit M0 as in the first embodiment. In this case, the above-mentioned set frequency band information (channel information) is included and sent. Further, when the individual control information S is transmitted from the parent device M0 to the child devices M1,... Including the set frequency band (channel information) as described above, there is no interference signal and the noise component of the electric device is reduced. Data communication can be performed through a communication path using a good frequency band (channel) that does not exist and is not affected by other PLC systems.

  By the way, by using a device-embedded network technology called EMIT (Embedded Micro Internetworking Technology) (a network technology having a function of easily incorporating middleware into a device and connecting to the network, hereinafter referred to as EMIT technology). Various equipment (illumination equipment, air conditioning equipment, power equipment, sensors) from external terminals (not shown) such as mobile phones, PCs (Personal Computers), PDAs (Personal Digital Assistants), PHSs (Personal Handy phone Systems) An electric lock, a web camera, and the like are hereinafter referred to as an EMIT terminal.) There is a system that can access <not shown> to remotely monitor and control the EMIT terminal.

  Note that the EMIT terminal is a built-in device equipped with a microcomputer, and is a device-embedded middleware for connecting to the network and is equipped with EMIT software that realizes the EMIT technology.

  As a system to which the above-mentioned EMIT technology is applied (hereinafter referred to as an EMIT system), an external terminal remotely monitors and controls an EMIT terminal via a center server (not shown) provided on the Internet. For example, a configuration in which an EMIT terminal is directly accessed from an external terminal equipped with EMIT software to remotely monitor and control the EMIT terminal without using a center server.

  Therefore, when constructing a PLC system using the power line carrier communication modem of the present invention, the EMIT software is installed by configuring the power line carrier communication modem serving as the master unit or the slave unit of the above-mentioned EMIT terminal. You may make it accessible from an external terminal.

(A) is a circuit block diagram of Embodiment 1, (b) is an explanatory diagram of the communication frequency band of the multicarrier used. (A) is a block diagram of a PLC system using the first embodiment, (b) is a timing chart for explaining the operation of the PLC system. It is a sequence diagram for explaining the operation of the PLC system using the first embodiment. FIG. 6 is a circuit block diagram of a second embodiment. (A) is a circuit block diagram of Embodiment 3, and (b) is an explanatory diagram of interference signals existing in the multicarrier communication frequency band. FIG. 6 is a circuit block diagram of a fourth embodiment. 10 is a timing chart for explaining the operation of the fourth embodiment. FIG. 9 is a circuit block diagram of a fifth embodiment. 10 is a timing chart for explaining the operation of the fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coupling circuit 2 Reception filter part 3 Reception part 30-3n Reception signal processing part 4 Modem part 5 Transmission part 50 Transmission signal processing part 51 Band pass filter 52 Transmission amplifier M Power line carrier communication modem L Power lines C1, C2 Capacitor T Coupling transformer BPF0 Wideband filter BPF1 to BPFn Narrowband filter

Claims (6)

A transmission unit that transmits a power line carrier communication signal on a power line by a multicarrier, a wideband filter that passes a power line carrier communication signal corresponding to the entire communication frequency band of the multicarrier, and the whole communication frequency band is divided into a plurality of parts. Power line carrier communication that is provided for each frequency band that is set in the above, and that passes through the power line of each frequency band, and that is extracted from the power line and passes through the wideband filter and the narrowband filter. A receiving unit that receives and processes a signal, and a modem unit that demodulates data from the power line carrier communication signal received and processed by the receiving unit and modulates data to be transmitted by the power line carrier communication signal on the power line through the transmitter And a power line carrier communication modem. The power line carrier communication modem according to claim 1, further comprising means for switching between the wideband filter and the narrowband filter of each frequency band to select a filter to be used during data communication. A detection means for detecting specific information included in the power line carrier communication signal passing through the wideband filter and the narrow band filter, and a frequency band other than the frequency band through which the power line carrier communication signal including the specific information detected by the detection means is passed 3. The power line communication modem according to claim 2, wherein the narrowband filter is selected during data communication. The power line carrier communication modem according to claim 3, wherein the specific information is a specific frequency. 4. The modem for power line carrier communication according to claim 3, wherein the specific information is a signal on the power line synchronized with a cycle of a commercial power supply frequency. The specific information is at least one of a level value and a time occupation characteristic for each frequency of a power line carrier communication signal of another power line carrier communication system other than the power line carrier communication system to which the own station belongs. 4. The power line carrier communication modem according to 3.

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