JP2003188777A - Distribution line transport method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the attenuation of an information signal to be transmitted, to avoid a transmission error and to improve the accuracy of synchronizing detection on a demodulation side. <P>SOLUTION: In the distribution line carrying method for carrying the information signal to be transmitted by superimposing it on a distribution line and for using an OFDM as a digital modulation/demodulation system for the information signal, a guard interval to be provided in an OFDM signal together with an effective symbol to store the information signal is provided near the positive and negative peaks of a power supply voltage on the distribution line. Besides, a received signal is divided into a plurality of blocks and when a correlative value for each block obtained by operating the received signal of each of blocks with a reference signal fulfills a prescribed status with respect to a threshold for each block, synchronizing between transmitted and received signals is detected. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to avoid a transmission error caused by a phenomenon (periodic attenuation) in which a carrier signal is periodically attenuated in a distribution line carrier used for automation of distribution, for example. The present invention relates to a distribution line transportation method.

[0002]

2. Description of the Related Art In recent years, distribution automation has been promoted for the purpose of remote monitoring and control of load devices connected to a distribution system, measurement, distribution management, automatic meter reading, and the like. Information signal (modulation signal) for control, measurement, etc.
A distribution line conveying method for superimposing a carrier signal (modulated signal) obtained by modulating a carrier wave on a distribution line is well known.

Here, FIG. 7 is a schematic configuration diagram of a power distribution system, where FD indicates a distribution line to which a commercial power supply voltage of, for example, 100 V is supplied, and LD indicates various loads connected to the distribution line FD. Many devices use a DC voltage for the load LD. In that case, as shown in FIG. 8, the AC voltage is rectified and smoothed by a rectifying circuit REC and a capacitor C, and converted into a DC voltage to load the device. It is common to supply to. Therefore, the capacitor C repeats the charging operation from the rectifying circuit REC and the discharging operation for the load device.

FIG. 9 is a waveform diagram schematically showing the AC input voltage, the output voltage (full-wave rectified voltage) of the rectifier circuit REC, the voltage of the capacitor C and the charging current thereof in FIG.

As indicated by the voltage of the capacitor C, the charging current flows through the capacitor C during the period when the output voltage of the rectifier circuit REC is higher than the voltage of the capacitor C, that is, near the peak of the output voltage of the rectifier circuit REC. The voltage of the capacitor C increases, and then the voltage decreases due to discharge until the next peak comes. That is, the voltage of the capacitor C repeatedly rises and falls within a certain range. From a different point of view, the capacitor C becomes low impedance and turns on every half cycle of the AC input voltage near its peak value, and the charging current flows during that period.

Now, as shown in FIG.
When the carrier signal is superposed on the AC input voltage at, the capacitor C on the load LD side is turned on near the positive and negative peak values of the power supply voltage as described above, and the carrier signal is also absorbed by the capacitor C. As a result, it is known that the carrier signal is attenuated. This phenomenon is called "periodic decay"
Say.

[0007]

Therefore, when the signal carried on the distribution line is received and demodulated, the original information signal may not be accurately reproduced and an error may occur. Conventionally, a frequency modulation method (FS) has been used as a digital modulation method.
K: Frequency Shift Keying or phase modulation method (PS
K: Phase Shift Keying) is known, and in the distribution line transportation using these, a measure is taken such that the above-described periodic attenuation part of the transportation signal is not treated as data.

On the other hand, an orthogonal frequency division multiplexing system (OFDM) is used as a digital modulation / demodulation system in consideration of measures against delayed waves.
Orthogonal Frequency Division Multiplexing) is known. In this OFDM, a low bit rate signal is assigned to each carrier by using a large number of carriers that are orthogonal to each other with a frequency interval of (1 / time interval of effective symbols) and are free from intersymbol interference. It is a type of multi-carrier transmission system that achieves a desired bit rate as a whole. 1) The length of effective symbols (data that can be sent by a single change of the modulation signal) can be lengthened. 2) Guard interval (signal It is possible to reduce the influence (ghost) of the delayed wave by providing a period for repeatedly transmitting a part of (3), and (3) there are advantages such as high frequency utilization efficiency.

Recently, OFDM has been applied to a digital modulation / demodulation system even in distribution line transportation, but the above-mentioned measures against periodic attenuation are not sufficiently taken.

Therefore, the present invention is intended to provide a distribution line conveying method capable of reducing the influence of periodic attenuation when OFDM is applied to the distribution line conveyance. Further, in OFDM, in consideration of the fact that the synchronization accuracy of the carrier frequency, sampling frequency, symbol position, etc. on the receiving side greatly affects the demodulation result, the present invention provides a distribution line carrier with improved synchronization detection accuracy on the receiving side. It is intended to provide a method.

[0011]

In order to achieve the above object, the invention described in claim 1 is a distribution line conveying method for superimposing an information signal to be transmitted on a distribution line to convey the signal.
OFDM as a digital modulation / demodulation system for the information signal
In the distribution line carrying method using the (orthogonal frequency division multiplexing method), a guard interval provided in the OFDM signal together with the effective symbol in which the information signal is stored is provided near the positive and negative peaks of the power supply voltage of the distribution line.

According to the invention described in claim 2, in the distribution line carrying method according to claim 1, when demodulating an OFDM signal, the received signal is divided into a plurality of blocks, and the received signal of each block is used as a reference signal. When the correlation value for each block obtained by the above calculation satisfies a predetermined condition for the threshold value for each block, the synchronization between the transmitted and received signals is detected.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a diagram showing the principle of the present invention. In FIG. 1, an OFDM signal (transmission symbol) carried on a distribution line has a large number of effective symbols obtained by modulating an information signal to be transmitted with a large number of carriers in time series, and between these effective symbols. , Guard intervals are provided.

As is well known, the guard interval is a period provided to reduce the influence of the delayed wave, and usually a part of the signal waveform of the effective symbol period is repeatedly added. When demodulating this OFDM signal on the receiving side,
If the period of performing the Fourier transform is equal to the effective symbol period, if the signal delay time is shorter than the guard interval, the delayed wave of the adjacent effective symbol does not enter the Fourier transform period, and the influence of the delayed wave is reduced. Become.

In the present invention, a signal is not placed on the above-mentioned guard interval, and the period of the guard interval is synchronized with the vicinity of the positive and negative peaks of the distribution line power supply voltage. As a result, each effective symbol of the OFDM signal is not located near the positive and negative peaks of the power supply voltage that causes the ambient attenuation shown in FIG. 10, so that the attenuation of the information signal can be avoided and the transmission characteristic can be improved. Can be improved.

Here, a functional block of a digital signal processor (DSP) for transmitting / receiving an OFDM signal will be described with reference to FIG. In FIG. 2, the modulation block 10 processes the transmission data as follows and sends it as a transmission signal to the D / A converter DAC.

That is, FPGA (Field Programmable)
Gate Allay: Transmission data sent from a field-rewritable large-scale integrated circuit) is encoded by a shift register, adder, etc., using a convolutional code for correcting transmission data errors that occur during transmission. It Further, in the next stage, differential encoding is performed in which the next signal is encoded using the phase difference based on the phase of the signal one symbol before. As a differential encoding method, DQPSK (Differential Q
uadrature Phase Shift Keying) is used.

Next, the error sequence of the error correction code is randomly changed along the frequency axis direction and interleave processing is performed to disperse the deterioration of the signal. The interleaved signal is arithmetically processed by inverse fast Fourier transform (IFFT), and orthogonal processing for transforming from the time domain to the frequency domain is performed. The orthogonally transformed signal is a low-pass filter L
After passing through the PF, it is modulated by a carrier wave of a predetermined frequency, sent to the D / A converter DAC as a transmission signal, and then superimposed on the distribution line and transmitted.

On the other hand, the demodulation block 20 demodulates the received signal output from the A / D converter ADC and transforms it from the frequency domain to the time domain by fast Fourier transform (FFT) through the low pass filter LPF. At that time, in order to improve the synchronization accuracy of the carrier frequency, the sampling frequency, the symbol position, etc., the following synchronization detection is performed in this embodiment.

That is, conventionally, as shown in FIG. 3, predetermined PN signals (reference signals) a ₁ , a ₂ , ..., A _z
, And received signals b ₁ , b ₂ , ..., B _z , a single correlation value c is calculated for the entire transmission symbol, and this correlation value c is compared with a threshold value d to determine c> d. Sometimes it was determined that the transmitted and received signals were in sync. However, according to this method, even if a large spike noise or the like is mixed in the received signal, it is erroneously determined as synchronization, and erroneous detection is likely to occur.

Therefore, in this embodiment, as shown in FIG.
Signal b₁₁, B₁₂, ……, b_{1 z}, B₂₁，
b₂₂, ……, b_2z, B₄₁, B₄₂, ……, b_4z
And PN signal a₁₁, A₁₂, ……, a_1z, A₂₁，
a₂₂, ……, a_2z, A₄₁, A ₄₂, ……, a_4z
Is divided into a plurality of blocks, and P for each block is divided.
Correlation for each block by sum of products of N signal and received signal
Value c₁, C_Two, C_Three, C_Four, ... and calculate
These correlation values and the threshold value d for each block₁, D_Two，
d_Three, D_Four, ... and compare all blocks
Correlation value> threshold value (c₁> D₁, C_Two> D_Two, C_Three
> D_Three, ...) is established, the synchronization is established.
I decided to judge. In addition, in FIG. 4, PN signal, reception
All signals are divided into 4 blocks, but
It only needs to be plural.

By adopting the method as shown in FIG. 4, for example, when spike noise is mixed in a part of blocks, even if the relationship of correlation value> threshold value is satisfied only in the block, other blocks are satisfied. With respect to the above, the above relationship is no longer established, and there is no possibility of erroneously detecting synchronization, so that the synchronization detection accuracy can be improved more than in the past.

FIG. 5 is a functional block diagram of the synchronization detecting means for realizing the synchronization detection of FIG.
_{1 to} COMP ₄ compare the correlation value of each block and the magnitude relation of the threshold value, and c ₁ > d ₁ , c ₂ > d ₂ , c ₃ > d
_{When 3} , c ₄ > d ₄ , the AND circuit AND outputs a synchronization detection signal.

In the demodulation block 20 shown in FIG. 2, the signal passed through the low-pass filter LPF is transformed into the time domain by the fast Fourier transform (FFT). At this time, the synchronization detection signal described above is used, and the signal is transmitted to the transmission signal. Synchronization of received signals is ensured. The signal after the fast Fourier transform is subjected to deinterleave processing and differential decoding (delay detection), and is decoded using the received signal one symbol before as a reference and the phase difference between this and the received signal this time.

After that, error correction decoding is executed by an algorithm such as Viterbi decoding and the received data is extracted. This received data is sent to an external FPGA, and various kinds of processing according to the received information signal is executed.

Next, FIG. 6 is a schematic block configuration diagram of a transmission / reception device for distributing line, which mainly shows a DSP for performing the modulation / demodulation processing of the above-mentioned OFDM signal. In FIG. 6, reference numeral 91 is an external I / F (interface) connected to the FPGA, and 92 is an external I / F connected to the distribution line side.
Is.

Reference numeral 30 designates a DSP peripheral portion centering on the above-mentioned DSP 31, and an RO containing a program.
M32 and D for converting between analog and digital
It is equipped with AC33 and ADC34. A data I / F 80 is provided between the DSP peripheral section 30 and the external I / F 91.
Is provided, and in this data I / F 80, O
The period of the guard interval provided in the FDM signal is synchronized with the positive and negative peaks of the power supply voltage. Therefore, the timing of the positive and negative peaks of the power supply voltage is detected from the external I / F 92 by the power supply synchronization detector 70, and the detection signal is captured in the data I / F 80.

The configurations and operations of the transmitting section 40, the coupling section 50 and the receiving section 60 are well known and will not be described in detail. However, the transmitting section 40 is a BPF (band pass filter).
41 and a transmission amplifier 42, the reception unit 60 is configured by a BPF 61 and a reception amplifier 62, and the coupling unit 50 is configured by a transmission coupler 51 to which a local oscillation frequency is added, a transmission / reception switching unit 52 and a reception coupler 53. There is.

According to the present embodiment, the period of the guard interval provided in the OFDM signal is synchronized with the vicinity of the positive and negative peaks of the power supply voltage, and the signal is not carried in the guide interval without repeating the original signal. . Therefore, as shown in FIGS. 9 and 10, the attenuation of the information signal due to the periodic attenuation is avoided in the vicinity of the positive and negative peaks of the power supply voltage, and error-free and highly accurate transmission can be performed.

The principle of the present invention is also effective when the influence of noise synchronized with the power supply voltage is large in addition to the influence of the periodic attenuation.

[0031]

As described in detail above, according to the invention described in claim 1, the information signal to be transmitted in the distribution line can be transmitted and received accurately and highly accurately without being attenuated. According to the invention described in claim 2,
It is possible to improve synchronization detection accuracy on the demodulation side in OFDM. Therefore, according to the present invention, it is possible to realize a distribution line transportation method having higher reliability than conventional methods.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a functional block diagram of a DSP that performs OFDM modulation / demodulation in the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional synchronization detection method.

FIG. 4 is an explanatory diagram of a synchronization detection method according to the embodiment of the present invention.

FIG. 5 is a functional block diagram of synchronization detection means in the embodiment of the present invention.

FIG. 6 is a schematic block configuration diagram of a transmission / reception device for distributing line to which the embodiment of the present invention is applied.

FIG. 7 is a schematic configuration diagram of a power distribution system.

8 is a configuration diagram of the input side of the load in FIG.

9 is a diagram showing a voltage waveform of each part and a charging current waveform of a capacitor in FIG.

FIG. 10 is an explanatory diagram of periodic attenuation.

[Explanation of symbols]

10 Modulation Block 20 Demodulation Block 30 DSP Peripheral Section 31 DSP 32 ROM 33 DAC 34 ADC 40 Transmitter 41, 61 BPF 42 Transmitter Amplifier 50 Combiner 51 Transmitter Combiner 52 Transmit / Receive Switcher 53 Receive Combiner 60 Receiver 62 Receive Amplifier 70 Power supply synchronization detector 80 Data I / F 91, 92 External I / F DSP Digital signal processor COMP _{1 to} COMP ₄ Comparator AND AND circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshinori Matsuzawa             1-7-1, Yurakucho, Chiyoda-ku, Tokyo East             Within Kodenki Co., Ltd. (72) Inventor Motoki Maruyama             1-7-1, Yurakucho, Chiyoda-ku, Tokyo East             Within Kodenki Co., Ltd. (72) Inventor Haruhiko Ishida             1-3-1, Uchisaiwaicho, Chiyoda-ku, Tokyo East             Inside Kyoden Electric Co., Ltd. (72) Inventor Shin Maruyama             1-3-1, Uchisaiwaicho, Chiyoda-ku, Tokyo East             Inside Kyoden Electric Co., Ltd. (72) Inventor Masaaki Sugimori             1-3-1, Uchisaiwaicho, Chiyoda-ku, Tokyo East             Inside Kyoden Electric Co., Ltd. (72) Inventor Yoshifumi Nishiyama             1-3-1, Uchisaiwaicho, Chiyoda-ku, Tokyo East             Inside Kyoden Electric Co., Ltd. F term (reference) 5K046 AA03 BA05 BB06 PS01 PS36                       PS42 PS49 PS53

Claims (2)

[Claims] 1. A distribution line carrying method for carrying an information signal to be transmitted by superimposing it on a distribution line, which uses OFDM (Orthogonal Frequency Division Multiplexing System) as a digital modulation / demodulation system of the information signal. , OFDM with valid symbols in which the information signal is stored
A distribution line conveying method, characterized in that a guard interval provided for a signal is provided near the positive and negative peaks of the power supply voltage of the distribution line. 2. The distribution line carrier method according to claim 1, wherein when demodulating an OFDM signal, the received signal is divided into a plurality of blocks, and the received signal of each block is obtained by calculation with a reference signal. A distribution line conveying method, wherein synchronization between transmitted and received signals is detected when a correlation value for each block satisfies a predetermined condition for a threshold value for each block.