JP2008118425A - Device and network system for electric power line communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform signal level control rather not by units of carrier waves, but by units of subbands and reduce the control load. <P>SOLUTION: An electric power line communication device uses electric power lines as signal transmission lines and has a transmission means 20 for transmitting signals using a plurality of carrier waves in a specified frequency band and a control means 40 for controlling the signal levels of transmission signals. The control means divides the frequency band that is used for signal transmission into a plurality of subbands and manges them, and controls the signal levels of transmission signals by subband units. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power line communication device and a power line communication network system.

  Power line communication (PLC) is a technique for performing communication using a power line as a signal transmission path, and is described in Patent Document 1, for example.

FIG. 1 shows an example of a power line communication network system. The optical fiber 7 connected to the external Internet is connected to the photoelectric conversion device 6. A signal line S1 is connected to the photoelectric conversion device 6, and for example, broadband routers 50, 50 provided in each of the homes A, B, C of the apartment house as an ADSL line on the WAN side. , ... are connected.
The broadband router 50 is connected to parent modems (power line communication devices serving as parent devices) a1, b1, and c1 through a signal line S2 on the LAN side.

The transformer 5 is configured to connect a medium voltage distribution line that distributes a medium voltage of a three-layer AC (for example, 6 kV) to the primary side, and connect a power line 9 to the secondary side to reduce the medium voltage. It converts into voltage (for example, 200V). The power line 9 is connected to in-home power lines 9a, 9b, 9c in the homes A, B, C via a distribution board (not shown).
In each home, power outlets 10, 10,... Are appropriately provided on the home power lines 9 a, 9 b, 9 c, and the power outlet 10 is connected to a child modem (children connected to the parent modems a 1, b 1, c 1, and the personal computer 4. Power line communication device) a2, a3, b2, b3, c2, c3 are connected.

The power line communication networks (LANs) in the homes A, B, and C are operated as separate network groups. However, the in-home power lines 9a, 9b, 9c used as signal transmission paths in the power line communication network groups in the homes A, B, C are connected to the common power line 9.
JP-A-10-145265

In the power line communication apparatus, communication is performed by a modulation method using a plurality of carriers such as orthogonal frequency multiplexing (OFDM).
The number of carriers in OFDM is 1536, for example, and a very large number of carriers are used.
In this way, when trying to adjust the level of a transmission signal in units of a very large number of carriers, the control becomes complicated, and the load on the control unit that adjusts the level of the transmission signal increases.

Here, there are the following cases where the level adjustment of the transmission signal is necessary. For example, as shown in FIG. 1, when a plurality of in-house power lines 9a, 9b, 9c are connected to the secondary power line 9 of a transformer such as each dwelling unit of a housing complex or a single-family neighboring house, they are independent of each other. Even if power line communication is attempted in the home, signals may interfere with each other through a common power line (distribution line) 9.
That is, when two or more power line communication network groups are constructed via the common power line 9, the communication signal in the power line communication network group (LAN) in one home is sent to the other via the common power line 9. It reaches the power line network group (LAN) in the customer's home and becomes noise. Conversely, a communication signal in the power line communication network group (LAN) in the other house also becomes noise for the power line network group (LAN) in one house.

  Therefore, when two or more power line communication network groups are constructed through a common power line, the signal-to-noise ratio of signals used for the original power line communication in each network group is lowered, and the communication quality is deteriorated. .

Therefore, as a measure for preventing quality deterioration due to signals from adjacent power line communication network groups, it is conceivable to reduce the output level (output power) of the signals.
That is, by reducing the output level of the signal of the modem (power line communication device) to such an extent that it does not reach the adjacent network group after attenuation, the output signal from the modem (power line communication device) of one network group It is possible to prevent the S / N ratio of the original received signal level of the modems (power line communication apparatuses) of the network groups from being affected.

However, when the output of the modem is lowered, the signal level received by the original communication partner (the modem in the own network group) is also lowered, the SN ratio is lowered, and the communication quality is lowered.
Therefore, from the viewpoint of improving communication quality, it is desirable to keep the output signal level large by minimizing the degree of decrease in the output signal level of the modem as much as possible.
Thus, for frequency bands that may cause interference to other network groups, it is conceivable to avoid the interference while partially reducing the signal level of the transmission signal and maintaining the signal level as a whole high.

  However, if the level of the transmission signal is adjusted in units of carriers for frequency bands that may cause interference to other network groups, if there are many carriers, the control becomes complicated and the load on the control unit increases. End up.

Therefore, an object of the present invention is to provide a new technique for reducing the control load.
Another object of the present invention is to avoid interference with other network groups.

[Power line communication equipment]
The present invention is a power line communication apparatus that uses a power line as a signal transmission path, a transmission unit that transmits a signal using a plurality of carriers in a predetermined frequency band, a control unit that controls a signal level of a transmission signal, The control means divides and manages the frequency band used for signal transmission into a plurality of subbands, and controls the signal level of the transmission signal in units of the subbands.

  According to the present invention, since the signal level of the transmission signal is controlled in units of subbands, the frequency of signal level control can be reduced compared to the case where the signal level is controlled in units of carrier waves. Therefore, the control load is small.

  Another aspect of the present invention obtains information necessary for controlling the signal level of a transmission signal in subband units from the outside of the power line communication apparatus, and based on the obtained information, the signal level of the transmission signal in subband units. It is a power line communication apparatus provided with the control means which controls.

  By acquiring information necessary for controlling the signal level of the transmission signal from the outside of the apparatus, the level of the transmission signal can be adjusted depending on factors outside the apparatus. Moreover, since the level is adjusted in units of subbands, the control load is small.

  The control means, in order to reduce the signal level of the interference frequency causing interference to other power line communication network group connected to the power line common to the power line used by the power line communication network group to which the own power line communication device belongs, It is preferable to reduce the signal level of the transmission signal of the entire subband to which the carrier having the interference frequency belongs.

  By reducing the signal level of the interference frequency that causes interference with other network groups, interference with other network groups can be prevented. In addition, the signal level is not lowered in units of subcarriers of the interference frequency, but the signal level is lowered in units of subbands, so that the control is simplified and the control load is small.

  The control means obtains information indicating an interference frequency causing interference with the other power line communication network group or information indicating a subband to which a carrier of the interference frequency belongs from the other power line communication network group, Based on the acquired information indicating the interference frequency or the information indicating the subband, the signal level of the transmission signal of the entire subband to which the carrier having the interference frequency belongs is preferably reduced.

  In this case, since the information indicating the interference frequency or the information indicating the subband to which the carrier wave of the interference frequency belongs can be obtained from another network group, the signal level can be easily adjusted.

  The control means preferably controls the signal level of the transmission signal in units of subbands so that the signal level of the transmission signal of each subband does not exceed a predetermined threshold value.

The control means preferably controls the signal level of the transmission signal of the subband based on a comparison result between the subband level that is a signal level representing the subband and a predetermined threshold value.
The subband level may be the maximum signal level of each transmission signal in the subband, and in this case, interference between network groups can be reliably prevented.
The subband level may be an average signal level of each transmission signal in the subband or a median value of signal levels of each transmission signal in the subband. In these cases, the maximum signal level is set to the subband level. Compared with the case, the output level can be kept relatively high.

  The threshold value is preferably set for each subband. In this case, different control is possible for each subband.

[Power line communication network system]
From another viewpoint, the present invention provides a power line communication network system in which at least a first power line communication network group and a second power line communication network group are connected to a common power line, and a signal level of a transmission signal in the first power line communication network group. The control means divides and manages a frequency band used for signal transmission into a plurality of subbands, and from the first power line communication network group to the second power line communication network group. In order to reduce the signal level of the interference frequency that causes the interference, the signal level of the transmission signal in the first power line communication network group is decreased in units of subbands to which the signal of the interference frequency belongs.

[Communication method]
From the viewpoint of the communication method, the present invention is a communication method using a power line communication apparatus provided with a transmission means for transmitting a signal using a plurality of carriers in the predetermined frequency band, and is used for signal transmission. The frequency band is divided into a plurality of subbands and managed, and the signal level of the transmission signal is controlled in units of the subbands.

[Power line communication equipment]
Another aspect of the present invention is a power line communication apparatus that uses a power line as a signal transmission path, a means for transmitting or receiving a signal using a plurality of carriers in a predetermined frequency band, and transmission or reception of a signal. Control means for controlling, and the control means divides and manages the frequency band used for signal transmission or reception into a plurality of subbands, and is used by the power line communication network group to which the own power line communication device belongs. The power line communication to which the power line communication device belongs is connected to a subband including an interference frequency that causes interference from another power line communication network group connected to the power line common to the power line to the power line communication network group to which the power line communication device belongs. Send or receive signals without using them to send or receive signals in a network group. The one in which the features.

  According to the present invention, even when a plurality of power line communication network groups are connected to a common power line, the frequency that receives interference from other network groups is not used for communication within the own network group. Interference can be avoided. In addition, since the entire subband including the interference frequency that causes interference with the network group is not used for communication, the control is simplified and the control load is small.

  According to the present invention, since the signal is controlled in units of subbands, the control load is small.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First embodiment]
As described above, FIG. 1 shows a power line communication network system in which a plurality of power line communication network groups are connected to a common power line 9. Note that the above description regarding FIG. 1 also applies to this embodiment.

  Hereinafter, the power line communication network group (PLC-LAN) constructed in the home A in FIG. 1 is referred to as a network group A, and the power line communication network group (PLC-LAN) constructed in the home B in FIG. The power line communication network group (PLC-LAN) constructed in the home C in FIG.

Each of the network groups A, B, and C is configured to perform power line communication using the power lines 9a, 9b, and 9c in the house as signal transmission paths. Each of the residential power lines 9a, 9b, 9c is branched from the common power line 9.
The original power line communication is performed separately in each of the network groups A, B, and C. However, communication signals in a certain network group may reach other network groups via the common power line 9. it can.

Each network group A, B, C is provided with one or a plurality of modems (power line communication devices) a1, a2, a3, b1, b2, b3, c1, c2, c3.
Within each network group, any one of the modems a1, b1, and c1 functions as a parent modem (master) that performs overall control of communication within the own network, and the other modems a2, a3, b2, b3, c2, and c3. Functions as a child modem (slave).

  In addition, in order to realize communication between different network groups A, B, and C, one modem among the parent modems (masters) of the plurality of network groups A, B, and C is connected to the plurality of network groups A, B, and C. It functions as an inter-group parent modem (master master; management modem) that controls the overall communication.

  Normally, the parent modem of the network group that tends to improve the communication quality with respect to other network groups is selected as the inter-group parent modem. For example, in the case of FIG. 1, since the network group B is close to the network group A and the network group C, it is preferable to cause the parent modem b1 of the network group B to function as an inter-group parent modem.

  In order to distinguish each of the network groups A, B, and C, an SSID (Service Set Identifier) is assigned to each group as a group name for identifying the group. Further, the MAC address assigned to each modem is used to identify each modem.

The SSID and the MAC address are added to the communication data (packet) between the modems for transmission / reception. Therefore, when the modem receives the signal, it recognizes the SSID included in the received data, and determines whether the signal is from the modem of its own network group or from another network group. be able to.
Further, when receiving a signal, the modem can identify the transmission source by recognizing the transmission source MAC address included in the received data.

  The parent and child modems communicate by a frequency multiplexing method using a plurality of carriers (carrier waves) in a predetermined frequency band for power line communication (for example, 2M to 30 MHz). Specifically, the modem performs modulation using a modulation method called orthogonal frequency domain multiplexing (OFDM).

  In addition, since all the modems of each network group communicate using the same frequency band (for example, 2M to 30 MHz) or overlapping frequency bands, when a communication signal in the own group reaches another group, the other The modems in this group receive the signal, resulting in noise that interferes with the original communication signal of the other group.

  FIG. 2 shows functional blocks of a parent and a child modem (power line communication device). The modem includes a transmission unit 20 for transmitting a signal to a power line, a reception unit 30 for receiving a signal from the power line, and a control unit 40 for controlling transmission / reception of the modem.

  The error correction code unit 21 of the transmission unit 20 receives an input of a bit string as a transmission content from a terminal device such as the personal computer 4 connected to the modem or the photoelectric conversion device 6, and adds an error correction code to the bit string. The data is encoded, and the encoded data is output to the buffer 22.

The buffer 22 temporarily stores the data input from the error correction encoder 21 and outputs the stored data to the serial / parallel converter 23.
The serial / parallel converter 23 converts the serial data input from the buffer 11 into parallel data, and outputs the converted parallel data to the quadrature amplitude modulator 24.

  The quadrature amplitude modulation unit 24 distributes the data input from the serial / parallel conversion unit 23 to each of a plurality of (for example, 1536) orthogonal carriers (carriers) and assigns the distributed data to each carrier. Further, the quadrature amplitude modulation unit 24 performs quadrature amplitude modulation (QAM) for modulating the amplitude and phase of the carrier wave based on the assigned data (symbol), and outputs the modulated signal to the inverse Fourier transform unit 25. To do.

The quadrature amplitude modulation unit 24 increases or decreases the amplitude of the carrier wave based on the control signal from the control unit 40. As shown in FIG. 3, the control unit 40 manages all the carrier waves (1536) as a plurality of subbands. One subband includes a plurality (16) of continuous carriers, and the entire carrier is divided into 96 subbands in total. The control unit 40 can increase or decrease the signal level of the transmission signal output from the transmission unit in units of subbands.
Here, the number of all carriers, the number of subbands, and the number of carriers belonging to the subbands are not particularly limited. The number of subbands only needs to be smaller than the number of all carriers.

The inverse Fourier transform unit 25 converts the modulation signal for each carrier wave input from the quadrature amplitude modulation unit 24 into a time domain modulation signal, and outputs the converted modulation signal to the parallel / serial conversion unit 26.
The parallel / serial conversion unit 26 converts the modulation signal input from the inverse Fourier transform unit into serial data and outputs the serial data to the guard interval unit 27.

  The guard interval unit 27 considers the delay time of each carrier in order to prevent inter-code interference due to multipath transmission using a plurality of carriers with respect to the serial data input from the parallel / serial converter 26. A process is performed to insert a guard interval that increases the symbol length of the transmission signal block by the guard interval, and the processed signal is output to the D / A converter 28.

The D / A conversion unit 28 converts the digital modulation signal input from the guard interval unit 27 into an analog modulation signal and outputs the analog modulation signal to the filter 29.
The filter 29 removes the harmonic component of the modulation signal input from the D / A conversion unit 28 and sends the processed modulation signal to the power line.

  The filter 31 of the receiving unit 30 removes harmonic components from the modulated signal received via the power line. Subsequently, the A / D conversion unit 32 converts the analog modulation signal into a digital signal, and the guard interval unit 33 performs processing for removing the guard interval.

Further, the serial / parallel converter 34 converts the signal into a set of parallel data equal to the number of subcarriers, and the Fourier transformer 35 converts the signal into a frequency domain signal for each carrier wave.
The output of the Fourier transform unit 35 is also output to the control unit 40 in addition to being output to the subsequent quadrature amplitude demodulation unit 36 for normal reception processing.

The quadrature amplitude demodulation unit 36 performs a demodulation process for reproducing the transmitted data based on the data input from the Fourier transform unit 35, and outputs the processed data to the parallel / serial conversion unit 37.
The parallel / serial conversion unit 37 converts the demodulated data for each carrier wave into serial data, and outputs the converted data to the buffer 38. The buffer 38 temporarily stores the data input from the parallel / serial conversion unit 37 until the error correction decoding unit 39 reads the data.

  The error correction decoding unit 39 reads the data stored in the buffer 38, performs error correction when the read data has an error, and outputs the corrected data to the terminal device or the photoelectric conversion device 6.

  In the power line communication network system as shown in FIG. 1, the power lines (distribution line paths) 9, 9a, 9b, 9c, which are signal transmission paths, have complicated attenuation characteristics. For example, the attenuation amount of the power lines 9a, 9, 9b from the modem a1 of the network group A to the modem b1 of the other network group B is greatly different for each frequency as shown in FIG.

  When the lines 9a, 9 and 9b have such attenuation, the signal Ds shown in FIG. 5 (frequency band 5 to 25 MHz, signal level of each carrier wave is equal) is transmitted from one group A to the own group A. Then, the modem b1 of the other group B receives the attenuated interference signal Dr as shown in FIG. This interference signal Dr becomes noise for the modem b1, and reduces the SN ratio of the original received signal (signals from other modems b2 and b3 in the same group B).

  However, the interference signal Dr from group A does not significantly reduce the SN ratio of the original received signal of the modem b1 in the entire frequency band. That is, the interference signal Dr is a frequency band in which the signal level is higher than a predetermined level (threshold value) L without significantly deteriorating the SN ratio of the original received signal of the modem b1 in a frequency band where the signal level is sufficiently low. In fi, the S / N ratio of the original received signal of the modem b1 is greatly reduced. In the frequency band fi of FIG. 5, the maximum value of the amount L1 exceeding the threshold value L is about 10 dB.

  In the first embodiment, in order to prevent interference from group A to group B (decrease in S / N ratio), the signal Ds1 transmitted from the modem a1 of group A may cause interference in group B. In fi, the signal level is lowered according to the amount L1 exceeding the threshold L (see FIGS. 6A and 6B). On the other hand, among the frequency bands used for communication, the signal level is maintained relatively high in frequency bands other than the frequency band fi.

  By setting the transmission signal Ds1 of the modem a1 as described above, the level of the signal received by the modem b1 of the group B becomes equal to or less than the threshold value L even in the frequency band fi and is used for communication within the group B. In all the frequency bands that are generated, it is possible to prevent a decrease in SNR (interference) due to a signal from group A.

  Moreover, in order to avoid interference from the group A to the group B, the signal level of the signal Ds1 is generally higher than that of the signal Ds2 in which the level of the output signal Ds1 of the modem a1 is simply lowered by 10 dB as a whole. . Therefore, the modem a1 of the group A can effectively use the level difference between the two signals Ds1 and Ds2 for the original communication in the group A, and the communication quality is improved as compared with the case where the signal level is lowered as a whole. The degree of performance degradation from the communication quality (communication quality of group A alone) is also minimized.

Hereinafter, the above processing will be described in more detail with reference to FIG.
Here, a case will be described as an example where the network groups B and C of FIG. 1 are already operating and the output signal levels of the modems a1, a2, and a3 are determined so that the network group A starts communication.

  As described above, the communication beyond the network group is controlled by the parent modem selected as the inter-group parent modem (for example, the parent modem b1 of group B). In the following processing, for example, the intra-group communication and the inter-group communication are performed in a time division manner so that the intra-group communication and the inter-group communication do not interfere with each other.

  First, the control unit 40 of the group A modem a1 performs a negotiation process for establishing communication with other group B and C modems. If only a part of the frequency bands used for power line communication can be used, communication is established using the frequency band (carrier) (inter-group communication establishment function of the control unit).

  When communication between both modems is established, the modem a1 is notified of the SSID as data specifying the transmission source group A and the MAC address as data specifying the transmission source modem a1. With these data, the modem b1 can recognize the transmission source group A and the transmission source modem a1 of the test signal.

  When communication between both modems a1 and b1 is established, the control unit 40 of the modem b1 checks the SSID notified from the modem a1 and recognizes that the signal is transmitted from another network group A instead of the own group. (Other group signal recognition function of the control unit).

  When communication between the modem a1 of the group A and the modem b1 of the other group B is established, the control unit 40 of the modem a1 has the same signal level in the signal Ds (all frequency bands used for communication) as shown in FIG. ) Is transmitted as a test signal from the transmission unit 20 to the power line 9a (test signal transmission function of the control unit).

  The test signal Ds reaches the modem b1 of the group B via the power lines 9a, 9, 9b. However, the test signal Ds reaches the modem b1 as an attenuated signal Dr as shown in FIG. The signal Dr has a frequency band fi having a level that exceeds a threshold L that is a level receivable by the modem b1. In addition, the carrier of this frequency band fi is used for communication establishment between both modems a1 and b1.

  Here, when the level of the signal Dr reaching the modem b1 is lower than the threshold value, the communication between the two modems a1 and b1 cannot be established. Since no interference occurs, the following processing is not necessary.

Subsequently, the control unit 40 of the modem b1 detects whether or not there is a subband having a level exceeding the threshold L in the interference signal Dr (interference subband detection function of the control unit).
Specifically, the control unit 40 of the modem b1 obtains a subband level of each subband, and determines whether each subband level exceeds a threshold value.

  The subband level of each subband is obtained as follows. First, the control unit 40 of the modem b1 checks the signal level for each of a plurality of carriers (carriers) given from the Fourier transform unit 35 of the modem receiving unit 30. FIG. 8 shows an example of the signal level of each carrier in one subband. As shown in FIG. 8, the highest value among the signal levels of the carriers in the subband is determined as a subband level that is a signal level representing the subband.

  Note that the subband level is not limited to the maximum value of each carrier signal level, and may be an average value or a median value of each carrier signal level. It is not limited. Note that it is preferable to employ the maximum value as the subband level as in this embodiment because the output signal can be sufficiently lowered.

  When the subband level of each subband is obtained, the control unit 40 of the modem b1 compares the subband level with the threshold value L. FIG. 9 shows the relationship between subbands and threshold values for 10 subbands among all subbands. As shown in FIG. 9, the threshold value L is set for each subband. Specifically, the threshold value L of the subbands S6 to S7 is higher than the threshold value L of the subbands S1 to S5. Is set larger. By setting the threshold value L for each subband, flexible control according to the frequency is possible.

  For example, in communication within the local network group B, the bit allocation for data transmission is reduced in a frequency band with a lot of noise and a low S / N ratio, so there are few problems even if some interference is received from another network group A. Therefore, the threshold value L can be increased for the subband corresponding to the frequency band originally affected by noise. Note that the threshold value L may be the same in all frequency bands.

When the control unit 40 of the modem b1 compares the subband level and the threshold value L for each subband, a subband (interference subband) exceeding the threshold value L is obtained (interference subband detection function of the control unit). ). In FIG. 9, only the subband S7 is a subband exceeding the threshold value L, but actually, a plurality of subbands exceed the threshold value L.
Further, the control unit 40 of the modem b1 detects an amount L1 exceeding the threshold L in a subband larger than the threshold L (interference amount detection function of the control unit).

  The control unit 40 of the modem b1 sends the transmission unit of the modem b1 to notify the modem a1 of the group A of the interference subbands and the amount L1 exceeding the threshold value L in those subbands as the detection result of the interference signal. 20, the detection result is transmitted to the modem a1 (detection result notification function of the control unit). L1 is reported for each subband.

  When detecting the interference signal, it may be detected whether the threshold value is exceeded for each carrier wave, not for each subband, and the subband in which interference occurs based on the detection result for each carrier wave. In addition, the amount of interference for each subband may be obtained. Further, the control unit 40 of the modem b1 notifies the modem a1 of the group A not of the interference subband but the frequency itself causing the interference, and determines the subband to which the interference frequency belongs on the modem a1 side, You may make it control a subband.

  The above processing is performed not only between the modem a1 and the modem b1, but also between the modem a1 and the other modems b2 and b3 of the group B and the modems c1, c2 and c3 of the group C.

  The modem a1 receives detection results from the modem b1 and other modems in the other groups B and C (a detection result (information indicating interference subband) acquisition function of the control unit). The modem a1 stores the detection result. When the modem a1 performs the original communication in its own network group A, the transmission signal Ds1 shown in FIG. 6 is used to transmit each transmission signal in the subband that causes interference to the modems of other groups. The signal level is lowered according to L1 (transmission signal control function of the control unit).

  Such adjustment of the output signal level is performed in units of subbands S-A to S-I as shown in FIG. 6A and FIG. 6B which is a partially enlarged view thereof. That is, the control unit 40 of the modem a1 gives a control signal for signal level adjustment to the quadrature amplitude modulation unit of the transmission unit 20, and the amplitudes of all carriers belonging to the interference subbands are subbands SA Decrease in accordance with the amount of interference L1 for SI.

  In FIG. 6A and FIG. 6B, for comparison, the signal level when the signal level is adjusted for each carrier is indicated by a dotted line. Compared to the case where the signal level is adjusted in units of carrier waves, when the adjustment is performed in units of subbands, the signal level becomes stepwise, but the number of subbands is smaller than the total number of carriers, The frequency of signal level adjustment is low and control is easy.

  Note that the level reduction degree may be the same as the interference amount L1, or the reduction degree may be larger than the interference amount L1. Further, the output level of a carrier that causes interference may be 0, that is, a carrier that causes interference may not be used.

  With the above processing, the adjustment processing of the output signal level of the modem a1 is completed. Subsequently, in parallel with the processing of the modem a1, the adjustment processing of the output signal level is similarly performed for the other modems a2 and a3 of the group A. When the adjustment of the output signal level is completed for all the modems a1, a2, and a3 in the group A, even if communication is performed in the group A, it does not interfere with communication in the other groups B and C.

  Further, the output signal level of each of the modems b1, b2, b3, c1, c2, and c3 of the groups B and C is set by the same process as described above so as not to interfere with the modems a1, a2, and a3 of the group A. Adjusted.

  As described above, even when a plurality of independent power line communication network groups A, B, and C exist on the common power line 9, interference with other groups is suppressed while minimizing communication quality degradation within the own group. Can be prevented.

[Second Embodiment]
FIG. 10 shows a second embodiment of the present invention. The points not particularly described in the second embodiment are the same as those in the first embodiment.
When the process according to the second embodiment shown in FIG. 10 is compared with the process of FIG. 7 which is the first embodiment, the process up to the detection of the interference subband is the same. In the first embodiment, when the modem b1 detects the interference subband, the modem a1 on the group A side copes with the interference (signal level reduction process) based on the detection result. In the second embodiment, The modem b1 on the group B side handles the interference.

  That is, when the control unit 40 of the modem b1 detects a subband exceeding the threshold value L, in the communication within the own network group B, the subband carrier is not used for communication. The same applies to the other modems b2 and b3 in the group B. That is, in each of the modems b1, b2, and b3 in group B, the subband to which the frequency that receives interference from other groups A and C belongs is not used in communication within group B.

  However, even in the case of an interference subband, a frequency band that originally has a lot of noise may be used for intra-group B communication because there is little influence from other groups. That is, only some of the plurality of interference subbands may not be used for intra-group communication.

Specifically, at the time of signal transmission, the quadrature amplitude modulation unit 24 of the modem transmission unit 20 does not use the interference subband carrier in the frequency band used in power line communication for modulation, and communicates with the remaining subband carriers. I do. Further, at the time of signal reception, the quadrature amplitude demodulation unit 37 of the modem reception unit 30 demodulates by ignoring the interference subband signal.
As a result, in group B, communication is originally performed in a frequency band other than the frequency band that receives interference from other groups A and C among the communication frequency bands used in group B. Therefore, it is possible to suppress a decrease in communication quality within the own group while avoiding interference from other groups.

  The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the spirit of the present invention. For example, signal level adjustment in units of subbands may be performed not for avoiding interference from other network groups but for other purposes. For example, at the time of communication within the own network group, it is possible to increase the signal level of a frequency with a large attenuation in units of subbands to which the frequency belongs. In this case, the information acquired by the control unit to control the signal level of the transmission signal in units of subbands can be a reflected signal of the signal transmitted by the own power line communication device. And if a control part acquires a reflected signal, the signal level of the subband in which the reflective loss has arisen can be enlarged.

1 is an overall configuration diagram of a power line communication network system. It is a functional block diagram of a modem. It is explanatory drawing of a subband. It is a figure which shows the frequency-attenuation amount characteristic of a power line. It is a figure which shows the transmission signal Ds and the attenuated reception signal Dr. It is a figure which shows the output signal Ds1 which adjusted the level partially, and the output signal Ds2 which lowered the level entirely. It is a procedure figure of the interference coping process in 1st Embodiment. It is a related figure of each carrier of a subband and a subband level. FIG. 6 is a relationship diagram between each subband and a threshold value L. It is a procedure figure of the interference coping process in 2nd Embodiment.

Explanation of symbols

A Power line communication network group B Power line communication network group C Power line communication network group a1, a2, a3 Modem (power line communication device)
b1, b2, b3 modem (power line communication device)
c1, c2, c3 modem (power line communication device)
9 Power Line 20 Transmitter 30 Receiver 40 Control Unit fi Interference Frequency Band L Threshold L1 Amount Exceeding Threshold

Claims (8)

A power line communication device using a power line as a signal transmission path,
Transmitting means for transmitting a signal using a plurality of carriers in a predetermined frequency band;
Control means for controlling the signal level of the transmission signal,
The control means divides and manages the frequency band used for signal transmission into a plurality of subbands, and controls the signal level of the transmission signal in units of the subbands. The control means includes an acquisition means for acquiring information necessary for controlling the signal level of the transmission signal in units of subbands from outside the power line communication device,
The power line communication apparatus according to claim 1, wherein the control unit controls the signal level of the transmission signal in units of subbands based on the information acquired by the acquisition unit.   The control means, in order to reduce the signal level of the interference frequency causing interference to other power line communication network group connected to the power line common to the power line used by the power line communication network group to which the own power line communication device belongs, 3. The power line communication apparatus according to claim 1, wherein the signal level of the transmission signal of the entire subband to which the carrier wave of the interference frequency belongs is lowered. The control means obtains information indicating an interference frequency causing interference with the other power line communication network group or information indicating a subband to which a carrier of the interference frequency belongs from the other power line communication network group,
4. The power line communication according to claim 2, wherein the signal level of the transmission signal of the entire subband to which the carrier of the interference frequency belongs is reduced based on the acquired information indicating the interference frequency or the information indicating the subband. apparatus.   The control means is configured to control the signal level of the transmission signal of the subband based on a comparison result between the subband level that is a signal level representing the subband and a predetermined threshold value. The power line communication device according to claim 1, wherein the power line communication device is a power line communication device.   6. The power line communication apparatus according to claim 5, wherein the subband level is a maximum signal level of each transmission signal in the subband. In a power line communication network system in which at least a first power line communication network group and a second power line communication network group are connected to a common power line,
Control means for controlling a signal level of a transmission signal in the first power line communication network group;
The control means divides and manages a frequency band used for signal transmission into a plurality of subbands, and sets an interference frequency that causes interference from the first power line communication network group to the second power line communication network group. In order to lower a signal level, the signal level of a transmission signal in the first power line communication network group is reduced in units of subbands to which a signal of the interference frequency belongs, and the power line communication network system. A power line communication device using a power line as a signal transmission path,
Means for transmitting or receiving a signal using a plurality of carriers in a predetermined frequency band;
Control means for controlling transmission or reception of signals,
The control means divides and manages the frequency band used for signal transmission or reception into a plurality of subbands, and is connected to a power line common to a power line used by a power line communication network group to which the own power line communication device belongs. The transmission or reception of a signal from another power line communication network group including the interference frequency that causes interference to the power line communication network group to which the own power line communication device belongs to the power line communication network group to which the own power line communication device belongs. Send or receive signals without using
A power line communication apparatus.

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