JP2007020113A - Power line communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power line communication apparatus for transmitting/receiving a signal for modulating a plurality of carriers whose frequencies differ from each other via a power line. <P>SOLUTION: A power calculation section 30 calculates power of the modulated signal on the basis of the amplitude of the carriers by each frequency corresponding to a reflection signal received from a Fourier transform section 24 and outputs the calculated power to a comparison section 31. The comparison section 31 compares the power of the signal by each frequency with a threshold value, outputs a difference signal denoting a difference between the signal power and the threshold value by each frequency to a control section 32 when the signal power is greater than the threshold value, or outputs a difference signal denoting zero by each frequency to the control section 32 when the signal power is smaller than the threshold value. The control section 32 generates a control signal by each frequency depending on the magnitude of the difference signal, and a quadrature amplitude modulation section 13 increases/decreases the amplitude of the carriers on the basis of the control signal and increases/decreases the transmission power of the modulation signal by each frequency of the carriers in response to a reflection loss. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power line communication apparatus that transmits and receives signals obtained by modulating a plurality of carrier waves having different frequencies via a power line.

  In recent years, optical fibers have been laid near urban distribution transformers in urban areas, and high-speed power line communication between this optical fiber and tens to hundreds of meters from the distribution transformer to each customer ( By realizing PLC (Power Line Communication), high-speed data communication can be expected without newly laying a communication line.

  For power line communication, modulation schemes such as Orthogonal Frequency Domain Multiplex (OFDM) and Spread Spectrum (SS) are adopted, and communication on power lines with inferior communication characteristics is realized.

  However, many power devices or electronic devices are connected to the power line, and various levels of noise are generated in the power line according to changes in the type, number of connections, and load status of these devices. Because of this change, there may be a time zone in which data communication cannot be performed.

Therefore, in order to prevent the occurrence of data transmission errors due to noise generated in the power line and the problem of communication quality degradation or communication inability to occur, the signal-to-noise ratio is estimated for each carrier, and the estimated signal-to-noise ratio There has been proposed a power line communication device that optimizes the amount of data allocated to carrier modulation according to the height and improves the quality of communication and wastes transmission power by not using a carrier that cannot be used for communication. (See Patent Document 1).
JP 2002-319919 A

  However, in the example of Patent Document 1, although the influence of communication quality due to noise generated in the power line is reduced, even when no noise is generated in the power line, the line impedance (characteristic impedance) of the power line depends on the line condition. Since it is unstable, it has been a cause of deterioration of communication quality in power line communication.

  For example, power lines are branched and laid at many locations to distribute power to each consumer, and the types of power cables used vary widely, so the frequency characteristics of the line impedance of the power lines depend on the laying situation. Different. In power line communication, signals in a wide frequency band are used for high-speed communication, so it is difficult to achieve impedance matching between the output impedance of the power line communication device and the line impedance of the power line over the entire use frequency band. In some frequency bands, reflection loss due to impedance mismatching becomes significant, and a signal of a required level cannot be superimposed on the power line.

  The present invention has been made in view of such circumstances, and detects the power of a reflected signal of a transmitted signal for each frequency of a plurality of carrier waves, and determines the transmission power of a signal to be transmitted based on the detected power as the frequency. By separately controlling, regardless of the frequency characteristics of the line impedance of the power line in the used frequency band, signals can be superimposed according to the line condition of the power line to obtain high quality communication quality using the entire used frequency band. An object of the present invention is to provide a power line communication device that can be used.

  Another object of the present invention is to provide a comparison means for comparing each of the reflected signal power of the transmitted signal with a threshold value, and by controlling the magnitude of the transmission power for each frequency based on the magnitude of the comparison result. It is an object of the present invention to provide a power line communication apparatus that can prevent the transmission power of a signal from becoming unnecessarily large and reduce the leakage electric field through the power line.

  Another object of the present invention is to provide a transmission means for transmitting a signal having substantially the same transmission power for each frequency, thereby compensating for the reflection loss according to the reflection loss due to impedance mismatch for each frequency. It is in providing the power line communication apparatus which can transmit.

  A power line communication device according to a first aspect of the present invention is a power line communication device for transmitting and receiving a signal obtained by modulating a plurality of carrier waves having different frequencies via a power line, and detecting means for detecting the power of a reflected signal of the transmitted signal for each frequency. Control means for controlling the transmission power of the signal to be transmitted for each frequency, and the control means controls the transmission power for each frequency based on the power of the reflected signal detected by the detection means. It is characterized by being.

  A power line communication apparatus according to a second aspect of the present invention includes a comparison unit that compares each power of the reflected signal detected by the detection unit with a threshold value in the first invention, and the control unit compares the comparison by the comparison unit. Based on the magnitude of the result, the magnitude of the transmission power is controlled for each frequency.

  A power line communication apparatus according to a third aspect of the present invention is the first or second aspect of the invention, further comprising transmission means for transmitting a signal having substantially the same transmission power for each frequency, and the detection means uses the power of the reflected signal of the signal. Detection is performed for each frequency.

  In the first invention, a signal obtained by modulating a plurality of carriers having different frequencies is transmitted by being superimposed on the power line. In the frequency band used as a carrier wave, the signal of the frequency that is impedance mismatch between the line impedance of the power line and the output impedance of the power line communication device is reflected by the power line, and the signal of the frequency that the impedance is matched is , Not reflected by the power line. The detection means detects the power of the reflected signal of the transmitted signal for each frequency of the carrier wave. When the power of the reflected signal is detected by the detecting means, the transmission power of the signal transmitted at the frequency causes a reflection loss according to the power of the reflected signal, and the transmitted signal is not sufficiently superimposed on the power line. . The control means controls the transmission power for each frequency based on the detected power of the reflected signal. Thereby, the transmission power of the signal to be transmitted is increased with respect to the frequency at which the reflection loss due to the impedance mismatch occurs.

  In the second invention, the comparison means compares the power of each of the reflected signals detected by the detection means for each frequency of the carrier with a threshold value. The said control means controls the magnitude of transmission power according to the said frequency based on the magnitude of a comparison result. For example, when the difference between the reflected signal power and the threshold is large, the increase rate of the transmission power of the frequency corresponding to the reflected signal is increased and the difference between the reflected signal power and the threshold is small, assuming that the reflection loss is large. In this case, assuming that the reflection loss is small, the increase rate of the transmission power of the frequency corresponding to the reflected signal is reduced. When the power of the reflected signal is smaller than the threshold value, the transmission power of the frequency corresponding to the reflected signal is not changed. Thereby, the magnitude of the transmission power for each frequency is controlled according to the magnitude of the threshold.

  In the third aspect of the invention, signals having substantially the same transmission power for each carrier frequency (for example, the amplitude of the carrier wave for each frequency are substantially equal) are transmitted. By transmitting signals having substantially the same transmission power, the power of the reflected signal for each frequency detected by the detecting means becomes a value corresponding to the magnitude of reflection loss due to impedance mismatch at the frequency.

  In the first invention, the power of the reflected signal of the transmitted signal is detected for each frequency of the plurality of carriers, and the transmission power of the signal to be transmitted is controlled for each frequency based on the detected power. Regardless of the frequency characteristics of the line impedance of the power line in the use frequency band, a signal having a sufficient level can be superimposed on the power line by compensating for the reflection loss over the entire use frequency band, and high communication quality can be obtained.

  In the second invention, there is provided comparison means for comparing each of the reflected signal power of the transmitted signal and a threshold value, and by controlling the magnitude of the transmission power for each frequency based on the magnitude of the comparison result, a specific band is obtained. In order to prevent the signal transmission power from becoming unnecessarily large and to reduce the leakage electric field through the power line by further increasing the transmission power of the signal that has already maintained sufficient transmission power without reflection loss. Can do.

  In the third aspect of the invention, by providing a transmission means for transmitting a signal having substantially the same transmission power for each frequency, the transmission power is compensated for the reflection loss according to the reflection loss due to impedance mismatch for each frequency. Can be controlled.

  Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof. FIG. 1 is an explanatory diagram showing an outline of power line conveyance. In the figure, reference numeral 1 denotes an intermediate voltage distribution line laid through a utility pole. The medium voltage distribution line 1 distributes a medium voltage (for example, 6 kV) of a three-phase alternating current. The intermediate voltage distribution line 1 is connected with a transformer 5 attached to a power pole, and the transformer 5 converts the medium voltage supplied by the medium voltage distribution line 1 into a low voltage (for example, 200v). The power line 2 is connected to the transformer 5, and the power line 2 supplies a low voltage to each consumer.

  The optical fiber 6 is connected to a communication network 8 such as the Internet, and the optical fiber 6 is connected to a photoelectric conversion device 7 attached to a utility pole. The photoelectric conversion device 7 converts an optical signal transmitted through the optical fiber 6 into a digital electrical signal. A modem 3 (power line communication device) is connected to the photoelectric conversion device 7, and the modem 3 performs predetermined processing on the digital signal input from the photoelectric conversion device 7, via the power line 2. The processed signal is transmitted to the modems 4, 4,... (Power line communication device) of each consumer. The personal computers 9a, 9a,... Are connected to the modems 4, 4,..., A predetermined process is performed on the signal received via the power line 2, and the processed data is stored in the personal computers 9a, 9a. Output to ... Moreover, the electric equipment 9b, 9b, ... of each consumer is connected to the power line 2.

  On the other hand, the personal computers 9a, 9a,... Output data for transmission to a server (not shown) of the communication network 8 to the modems 4, 4,. The modems 4, 4,... Perform predetermined processing on the data input from the personal computers 9 a, 9 a, and so on, and transmit the processed signals to the modem 3 through the power line 2. The modem 3 performs predetermined processing on the signals received from the modems 4, 4,..., And outputs the processed digital signal to the photoelectric conversion device 7. The photoelectric conversion device 7 converts the digital electrical signal input from the modem 3 into an optical signal, and transmits the converted optical signal to the communication network 8 through the optical fiber 6.

  FIG. 2 is a block diagram showing the configuration of the modem 3. In the figure, 10 is an error correction code part. The error correction coding unit 10 encodes data by adding an error correction code to the data bits composed of the bit string input from the transmission side (the photoelectric conversion device 7), and outputs the coded data to the buffer 11. .

  The buffer 11 temporarily stores the data input from the error correction encoding unit 10 and outputs the stored data to the serial / parallel conversion unit 12.

  The serial / parallel converter 12 converts the serial data input from the buffer 11 into parallel data, and outputs the converted parallel data to the quadrature amplitude modulator 13.

  The quadrature amplitude modulation unit 13 distributes the data input from the serial / parallel conversion unit 12 to a plurality of orthogonal carriers (for example, several hundreds), assigns the distributed data to each carrier, and assigns the allocated data ( Based on the symbol), quadrature amplitude modulation (QAM) for modulating the amplitude and phase of the carrier wave is performed, and the modulated signal is output to the inverse Fourier transform unit 14. Further, the quadrature amplitude modulation unit 13 stores a control signal for each frequency of each carrier wave input from the control unit 32 described later, and increases or decreases the amplitude of the carrier wave by a built-in amplifier circuit based on the control signal. As a result, the power of the modulation signal can be increased or decreased.

  The inverse Fourier transform unit 14 converts the modulation signal for each carrier wave input from the quadrature amplitude modulation unit 13 into a modulation signal in the time domain, and outputs the converted modulation signal to the parallel / serial conversion unit 15.

  The parallel / serial conversion unit 15 converts the modulation signal input from the inverse Fourier transform unit 14 into serial data and outputs the serial data to the guard interval unit 16.

  The guard interval unit 16 takes into account the delay time of each carrier in order to prevent intersymbol interference due to multipath transmission using a plurality of carriers with respect to the serial data input from the parallel-serial converter 15. A process of inserting a guard interval for increasing the symbol length by the guard interval is performed, and the processed signal is output to the D / A converter 17.

  The D / A conversion unit 17 converts the digital modulation signal input from the guard interval unit 16 into an analog modulation signal and outputs the analog modulation signal to the filter 18.

  The filter 18 removes the harmonic component of the modulation signal input from the D / A converter 17 and sends the processed modulation signal to the power line 2.

  On the other hand, the filter 20 removes harmonic components from the modulated signal received via the power line 2 and outputs the processed signal to the A / D converter 21.

  The A / D conversion unit 21 converts the analog modulation signal input from the filter 20 into a digital signal, and outputs the converted signal to the guard interval unit 22.

  The guard interval unit 22 performs a process of removing the guard interval from the signal input from the A / D conversion unit 21, and outputs the processed signal to the serial / parallel conversion unit 23.

  The serial / parallel converter 23 converts the signal input from the guard interval unit 22 into a set of parallel data equal to the number of subcarriers, and outputs the converted parallel data to the Fourier transform unit 24.

  The Fourier transform unit 24 converts the signal input from the serial / parallel conversion unit 23 into a frequency domain signal for each carrier wave, and outputs the converted signal to the quadrature amplitude demodulation unit 25 and the power calculation unit 30.

  The quadrature amplitude demodulation unit 25 performs demodulation processing for reproducing the transmitted data based on the serial data input from the Fourier transform unit 24, and outputs the processed data to the parallel / serial conversion unit 26. .

  The parallel / serial conversion unit 26 converts the demodulated data for each carrier wave into serial data, and outputs the converted data to the buffer 27.

  The buffer 27 temporarily stores the data input from the parallel / serial conversion unit 26 until the error correction decoding unit 28 reads the data.

  The error correction decoding unit 28 reads the data stored in the buffer 27, performs error correction when the read data has an error, outputs the corrected data to the reception side (photoelectric conversion device 7), and reads the data. If there is no error in the received data, the data is output to the receiving side.

  Under the control of the control unit 32, the power calculation unit 30 modulates a signal modulated based on the frequency components of a plurality of orthogonal carriers input from the Fourier transform unit 24, that is, the amplitude of the carrier for each frequency of the carrier. And the power calculated for each frequency is output to the comparison unit 31.

  The comparison unit 31 has selected a required threshold value from a plurality of threshold values stored in advance. The comparison unit 31 compares the signal power for each frequency input from the power calculation unit 30 and the threshold value. If the signal power is greater than the threshold value, the difference between the signal power and the threshold value for each frequency. Is output to the control unit 32. Further, when the power of the signal is smaller than the threshold value, the comparison unit 31 outputs a difference signal indicating zero to the control unit 32 for each frequency.

  The control unit 32 generates a control signal for each frequency according to the magnitude of the difference signal input from the comparison unit 31, and outputs the generated control signal to the quadrature amplitude modulation unit 13. Thereby, the magnitude of the transmission power of the modulation signal is controlled according to the magnitude of the difference signal.

  In addition, the control unit 32 controls mode conversion between a normal operation mode for transmitting or receiving a modulated signal and a test operation mode for adjusting the transmission power of the modulated signal.

  In the test operation mode, the control unit 32 outputs a test start signal to the power calculation unit 30 to place the power calculation unit 30 in an operating state. The control unit 32 outputs predetermined data to the error correction coding unit 10 and outputs a control signal of the same level for each frequency of the carrier wave to the quadrature amplitude modulation unit 12 to start a test operation mode.

  Since the modem 4 has the same configuration as the modem 3, the description thereof is omitted.

  Next, the operation of the modem 3 in the test operation mode will be described. The controller 32 outputs a test start signal to the power calculator 30, outputs predetermined data to the error correction encoder 10, and outputs a control signal of the same level for each frequency of the carrier wave to the quadrature amplitude modulator 12. Accordingly, the quadrature amplitude modulation unit 12 modulates a carrier wave having substantially the same amplitude for each frequency.

  Data input to the error correction code unit 10 is converted into a modulated signal obtained by modulating a carrier wave having substantially the same amplitude for each frequency by a quadrature amplitude modulation unit 13 through a buffer 11 and a serial / parallel conversion unit 12, and an inverse Fourier transform unit. 14, the parallel / serial conversion unit 15, the guard interval unit 16, the D / A conversion unit 17, and the filter 18 are subjected to predetermined processing and superimposed on the power line 2.

  The modulation signal superimposed on the power line 2 is reflected by the power line 2 according to the degree of impedance mismatch in the frequency band of each carrier wave, and the reflected signal reflected by the filter 20, the A / D conversion unit 21, the guard interval. After being processed in each of the unit 22, serial / parallel conversion unit 23, and Fourier transform unit 24, it is output to the power calculation unit 30.

  The power calculation unit 30 calculates the power of the modulated signal based on the amplitude of the carrier wave for each frequency corresponding to the reflected signal input from the Fourier transform unit 24, and supplies the power calculated for each frequency to the comparison unit 31. Output.

  The comparison unit 31 compares the signal power for each frequency input from the power calculation unit 30 and the threshold value. If the signal power is greater than the threshold value, the comparison unit 31 calculates the difference between the signal power and the threshold value for each frequency. The difference signal shown is output to the control unit 32. Further, when the power of the signal is smaller than the threshold value, the comparison unit 31 outputs a difference signal indicating zero to the control unit 32 for each frequency.

  The control unit 32 generates a control signal for each frequency according to the magnitude of the difference signal input from the comparison unit 31, and outputs the generated control signal to the quadrature amplitude modulation unit 13. The quadrature amplitude modulation unit 13 increases or decreases the amplitude of the carrier wave based on the input control signal, and increases or decreases the transmission power of the modulation signal according to the reflection loss for each frequency of the carrier wave.

FIG. 3 is an explanatory diagram showing the carrier spectrum of the test signal. As shown in the figure, the amplitude of each carrier in the communication bandwidth (for example, 10 MHz) of the modem 3 (the frequency interval of each carrier is, for example, 4.8 kHz), that is, the level (power) of the test signal is the frequency. Are equivalent. In the figure, for the sake of simplicity, eleven frequencies f _k-5 , f _k-4, f _k-3, f _k-2, f _k−1 , f _k , f _{k + 1} , f _{k + are shown. 2,} f _{k + 3,} f _{k + 4, and} f _{k + 5} are shown, but the number of carriers is not limited to this.

FIG. 4 is an explanatory diagram showing an example of the carrier wave spectrum of the reflected signal. When the line impedance value of the power line is different (for example, several tens of ohms to several hundreds of ohms) in a wide frequency band using each carrier wave, a frequency band that causes impedance mismatch with the output impedance (for example, 50 ohms) of the modem 3 Then, the reflection loss increases depending on the degree of impedance mismatch. For example, as shown in FIG. 4, the frequencies f _k-5 , f _k-4, f _k-3, f _k-2, f _k−1 , f _k , f _{k + 1} , f _{k + 2,} f The level (power) of the reflected signal is detected according to the magnitude of the reflection loss at _{k + 3, fk + 4, and fk + 5} . At these frequencies, a reflection loss occurs in proportion to the level of the reflected signal, and it can be said that transmission power corresponding to the reflection loss is lost.

By setting the threshold value shown in the figure to a value that allows the reflection loss, the frequencies f _k-5 , f _k−1 , f _k , f _{k + 1} , f at which the level of the reflected signal exceeds the threshold value are set. _{In k + 4} , the transmission power can be increased to supplement the lost transmission power. In addition, the transmission power is increased or decreased at frequencies f _k-4, f _k-3, f _k-2, f _{k + 2,} f _{k + 3, and} f _{k + 5} at which the level of the reflected signal does not exceed the threshold value. By not further increasing the transmission power of the modulation signal already superimposed with sufficient transmission power, the transmission power of the signal can be prevented from becoming unnecessarily large, and the leakage electric field through the power line can be reduced. Can do.

FIG. 5 is an explanatory diagram illustrating an example of a carrier spectrum of an increased transmission signal. As shown in FIG. 5, the level (power) of the increased transmission signal is the frequencies f _k−5 , f _k−1 , f _k , f _{k + 1} , f _k at which the level of the reflected signal exceeds the threshold. It is equal to the difference between the level of the reflected signal at ₊₄ and the threshold value. As a result, the same power as the transmission power lost due to the reflection loss is added to the transmission power to supplement the loss.

  As described above, in the present invention, the reflected signal power of the transmitted signal is detected for each frequency of a plurality of carrier waves, the detected reflected signal power is compared with a threshold value, and the magnitude of the comparison result is large. By controlling the magnitude of the transmission power according to frequency based on the frequency, the signal loss with a sufficient level is compensated for the reflection loss over the entire frequency band of use regardless of the frequency characteristics of the line impedance of the power line in the frequency band of use of the carrier wave. It can be superimposed on the power line, and high communication quality can be obtained. Furthermore, in a specific band, the transmission power of a signal that does not have a reflection loss and has already maintained a sufficient transmission power is further increased to prevent the signal transmission power from becoming unnecessarily large, and leakage through the power line In addition to being able to reduce the electric field, it is possible to reduce the level (power) difference for each carrier wave within the used frequency band, and to improve the utilization efficiency of the in-band frequency.

  In the above-described embodiment, the configuration uses quadrature amplitude modulation, but the present invention is not limited to this. For example, a configuration using phase modulation (PSK: Phase Shift Keying), amplitude modulation (ASK: Amplitude Shift Keying), or the like may be used.

  In the above-described embodiment, the test signal is used. However, the present invention is not limited to this. When actually transmitting data to another modem 4, the transmission signal is used as the test signal. The configuration may be such that the power of the reflected signal is detected.

  In the above-described embodiment, the threshold value to be compared with the signal power can be set to a desired value according to the output power of the power line communication device, the line impedance of the power line, and the like. For example, the threshold can be set to zero and power corresponding to the reflection loss can be added to the signal to be transmitted.

It is explanatory drawing which shows the outline | summary of electric power line conveyance. It is a block diagram which shows the structure of a modem. It is explanatory drawing which shows the spectrum of the carrier wave of a test signal. It is explanatory drawing which shows the example of the spectrum of the carrier wave of a reflected signal. It is explanatory drawing which shows the example of the spectrum of the carrier wave of the increase transmission signal.

Explanation of symbols

2 Power line 3, 4 Modem
DESCRIPTION OF SYMBOLS 12, 23 Serial / parallel conversion part 13 Quadrature amplitude modulation part 14 Inverse Fourier transform part 15, 26 Parallel / serial conversion part 24 Fourier transform part 25 Quadrature amplitude demodulation part 30 Power calculation part 31 Comparison part 32 Control part

Claims (3)

In a power line communication device that transmits and receives a signal obtained by modulating a plurality of carrier waves having different frequencies via a power line,
Detecting means for detecting the power of the reflected signal of the transmitted signal for each frequency;
Control means for controlling the transmission power of a signal to be transmitted for each frequency, and
The control means includes
The power line communication apparatus, wherein transmission power is controlled for each frequency based on the power of the reflected signal detected by the detection means. Comparing means for comparing each power of the reflected signal detected by the detecting means with a threshold value,
The control means includes
2. The power line communication apparatus according to claim 1, wherein the magnitude of transmission power is controlled for each frequency based on a comparison result compared by the comparison unit. Transmission means for transmitting signals having substantially the same transmission power for each frequency,
The detection means includes
The power line communication apparatus according to claim 1 or 2, wherein the power of the reflected signal of the signal is detected for each frequency.

Images