JP3693166B2 - Distribution line transport method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a distribution line conveyance method that avoids transmission errors caused by a phenomenon that a conveyance signal is periodically attenuated (periodic attenuation), for example, in distribution line conveyance used for distribution automation and the like. is there.
[0002]
[Prior art]
In recent years, automation of power distribution has been promoted for the purpose of remote monitoring and control of load devices connected to the power distribution system, measurement, power distribution management, automatic meter reading, etc., and information signal transmission methods such as monitoring, control, measurement, etc. 2. Description of the Related Art A distribution line carrying method for superimposing a carrier signal (modulated signal) obtained by modulating a carrier wave with an information signal (modulated signal) on the distribution line is well known.
[0003]
Here, FIG. 7 is a schematic configuration diagram of the distribution system, where FD indicates a distribution line to which, for example, a commercial power supply voltage of 100 V is supplied, and LD indicates various loads connected to the distribution line FD.
In many cases, the load LD uses a DC voltage. In this case, as shown in FIG. 8, the AC voltage is rectified and smoothed by a rectifier circuit REC and a capacitor C, and converted into a DC voltage. It is common to supply to. For this reason, the capacitor C repeats the charging operation from the rectifier circuit REC and the discharging operation for the load device.
[0004]
FIG. 9 is a waveform diagram schematically showing the AC input voltage (1), the output voltage (full-wave rectified voltage) (2), the voltage (3) of the capacitor C and the charging current in FIG. is there.
[0005]
As shown in voltage (3) of capacitor C, charging current is charged to capacitor C during a period when output voltage (2) of rectifier circuit REC is higher than the voltage of capacitor C, that is, near the peak of output voltage (2) of rectifier circuit REC. In the meantime, the voltage of the capacitor C rises, and then the voltage drops due to discharge until the vicinity of the next peak arrives. That is, the voltage of the capacitor C repeatedly rises and falls within a certain range.
In other words, the capacitor C becomes low impedance near the peak value every half cycle of the AC input voltage and is turned on, and the charging current flows during that period.
[0006]
If the carrier signal is superimposed on the power supply voltage (AC input voltage (1) in FIG. 9) as shown in FIG. 10, the capacitor C on the load LD side is near the positive and negative peak values of the power supply voltage as described above. Since the carrier signal is absorbed by the capacitor C, the carrier signal is known to be attenuated. This phenomenon is called “periodic decay”.
[0007]
[Problems to be solved by the invention]
For this reason, when the signal conveyed by the distribution line is received and demodulated, the original information signal is not accurately reproduced and an error may occur.
Conventionally, a frequency modulation method (FSK: Frequency Shift Keying) and a phase modulation method (PSK: Phase Shift Keying) are known as digital modulation methods, and in the distribution line carrier using these, the period attenuation of the carrier signal mentioned above is known. Measures are taken such that the portion is not handled as data.
[0008]
On the other hand, an orthogonal frequency division multiplexing (OFDM) method is known as a digital modulation / demodulation method considering a countermeasure against delay waves.
In this OFDM, a low bit rate signal is assigned to each carrier using a number of carriers that are orthogonal to each other with a frequency interval of (1 / effective symbol time interval) and that do not have intersymbol interference, It is a kind of multi-carrier transmission system that can obtain a desired bit rate as a whole,
1) The length of the effective symbol (data that can be sent by one change of the modulation signal) can be increased.
2) By providing a guard interval (a period in which a part of the signal is repeatedly transmitted), the influence (ghost) of the delayed wave can be reduced.
3) High frequency utilization efficiency,
There are advantages such as.
[0009]
Recently, OFDM has been applied to the digital modulation / demodulation method in distribution line conveyance, but the above-described measures for period attenuation have not been sufficiently taken.
[0010]
Therefore, the present invention intends to provide a distribution line conveyance method capable of reducing the influence of period attenuation when OFDM is applied to distribution line conveyance.
In addition, in OFDM, in consideration of the fact that the synchronization accuracy such as the carrier frequency, sampling frequency, and symbol position on the receiving side greatly affects the demodulation result, in the present invention, the distribution line carrier with improved synchronization detection accuracy on the receiving side. Is to provide a method.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention described in claim 1 is a distribution line carrying method for carrying an information signal to be transmitted superimposed on a distribution line, wherein OFDM (orthogonal frequency) is used as a digital modulation / demodulation method of the information signal. In the distribution line transport method using the division multiplexing method , a signal is not placed in a period corresponding to the guard interval of the OFDM signal having an effective symbol in which the information signal is stored , and this period is set to be positive or negative of the power supply voltage of the distribution line. It is provided near the peak.
[0012]
The invention described in claim 2 is the distribution line conveying method according to claim 1,
When demodulating the OFDM signal, the received signal is divided into a plurality of blocks, and the correlation value for each block obtained by calculating the received signal of each block with the reference signal is the threshold value for each block. When a predetermined condition is satisfied, synchronization between transmitted and received signals is detected.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. 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 number of effective symbols obtained by modulating an information signal to be transmitted by a large number of carrier waves in time series, and between these effective symbols, A guard interval is provided.
[0014]
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 in the effective symbol period is repeatedly added. When demodulating this OFDM signal on the receiving side, if the period of Fourier transform is made 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. Thus, the influence of the delayed wave is reduced.
[0015]
In the present invention, no signal is put on the above-described 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 cause the ambient attenuation shown in FIG. 10, so that the attenuation of the information signal can be avoided, and the transmission characteristics can be reduced. Can be improved.
[0016]
Here, functional blocks of a digital signal processor (DSP) that transmits and receives an OFDM signal will be described with reference to FIG.
In FIG. 2, the modulation block 10 processes transmission data as follows and sends it to the D / A converter DAC as a transmission signal.
[0017]
In other words, transmission data sent from an FPGA (Field Programmable Gate Allay) is a convolutional code for correcting transmission data errors that occur during transmission, shift registers, and additions. It is encoded by a device or the like.
Further, in the next stage, differential encoding is performed in which the next signal is encoded using a phase difference based on the phase of the signal one symbol before. As a differential encoding method, DQPSK (Differential Quadrature Phase Shift Keying) or the like is used.
[0018]
Next, the error sequence of the error correction code is randomly changed along the frequency axis direction to perform interleaving processing to disperse signal degradation.
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 modulated by a carrier wave having a predetermined frequency through a low-pass filter LPF, sent to a D / A converter DAC as a transmission signal, and then superimposed on a distribution line and transmitted.
[0019]
On the other hand, the demodulation block 20 demodulates the received signal output from the A / D converter ADC, and converts the signal from the frequency domain to the time domain by fast Fourier transform (FFT) through the low-pass filter LPF.
At this time, in order to improve the synchronization accuracy such as the carrier frequency, the sampling frequency, and the symbol position, the following synchronization detection is executed in the present embodiment.
[0020]
That is, in the conventional, PN signal (reference _signal) a _1, a 2 a predetermined as shown in FIG. 3, ..., and receive _{a z} signal _{b 1,} b 2, ..., the sum of products of _{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 that the transmitted and received signals are synchronized when c> d.
However, according to this method, even when large spike noise or the like is mixed in the received signal, it is erroneously determined to be synchronized, and erroneous detection is likely to occur.
[0021]
Therefore, in this embodiment, the received signal _{b 11,} b ₁₂ as shown in FIG. _{4, ......, b 1z, b} 21, b 22, ......, b 2z, b 41, b 42, ......, b 4z and PN signal _{a 11, a 12, ......,} a 1z, a 21, a 22, ......, a 2z, a 41, a 42, ......, and each divided into a plurality of blocks of _{a 4z,} PN signal of each block And the correlation value c ₁ , c ₂ , c ₃ , c ₄ ,... For each block by the product sum of the received signal and the received signal, and these correlation values and threshold values d ₁ , d ₂ , By comparing d ₃ , d ₄ ,..., the relationship of correlation value> threshold value (c ₁ > d ₁ , c ₂ > d ₂ , c ₃ > d ₃ ,...) holds for all blocks. It was determined that synchronization was established.
In FIG. 4, both the PN signal and the received signal are divided into four blocks, but any number may be used.
[0022]
By adopting the method as shown in FIG. 4, for example, when spike noise is mixed in some blocks, even if the relationship of correlation value> threshold value is established only for the block, Since the relationship is not established and there is no possibility of erroneously detecting the synchronization, the synchronization detection accuracy can be improved as compared with the related art.
[0023]
FIG. 5 is a functional block diagram of the synchronization detection means for realizing the synchronization detection of FIG. 4, in which the comparators COMP _{1 to} COMP ₄ compare the correlation value and the threshold value relationship of each block, _{When 1} > d ₁ , c ₂ > d ₂ , c ₃ > d ₃ , c ₄ > d ₄ is established, a synchronization detection signal is output from the AND circuit AND.
[0024]
In the demodulating block 20 of FIG. 2, the signal that has passed through the low-pass filter LPF is converted into the time domain by Fast Fourier Transform (FFT). Synchronization 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 the received signal and the current received signal.
[0025]
Thereafter, error correction decoding is executed by an algorithm such as Viterbi decoding, and received data is extracted. The received data is sent to an external FPGA, and various processes are performed according to the received information signal.
[0026]
Next, FIG. 6 is a schematic block configuration diagram of a transmission / reception apparatus for carrying a distribution line, focusing on a DSP that performs the above-described modulation / demodulation processing of the OFDM signal.
In FIG. 6, 91 is an external I / F (interface) connected to an FPGA or the like, and 92 is an external I / F connected to the distribution line side.
[0027]
Reference numeral 30 denotes a DSP peripheral portion centering on the DSP 31 described above, and includes a ROM 32 in which a program is built, a DAC 33 and an ADC 34 for performing conversion between analog and digital.
A data I / F 80 is provided between the DSP peripheral part 30 and the external I / F 91. In this data I / F 80, the guard interval period provided in the OFDM signal is set near the positive and negative peaks of the power supply voltage. Synchronize with. For this reason, a timing near 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 detected signal is taken into the data I / F 80.
[0028]
Although the configuration and operation of the transmission unit 40, the coupling unit 50, and the reception unit 60 are well known and will not be described in detail, the transmission unit 40 includes a BPF (band pass filter) 41 and a transmission amplifier 42. The receiving unit 60 includes a BPF 61 and a receiving amplifier 62, and the coupling unit 50 includes a transmission coupler 51, a transmission / reception switching unit 52, and a reception coupler 53 to which a local oscillation frequency is applied.
[0029]
According to this 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 without repeating the original signal in the guide interval.
For this reason, 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 high-accuracy transmission without error can be performed.
[0030]
The principle of the present invention is also effective when the influence of noise or the like synchronized with the power supply voltage is great in addition to the influence of period attenuation.
[0031]
【The invention's effect】
As described in detail above, according to the first aspect of the present invention, an information signal to be transmitted in distribution line conveyance can be transmitted and received accurately and accurately without being attenuated.
Further, according to the invention described in claim 2, it is possible to improve the accuracy of synchronization detection on the demodulation side in OFDM.
Therefore, according to this invention, it is possible to implement | achieve the distribution line conveyance method with higher reliability than before.
[Brief description of the 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 distribution line conveyance to which an embodiment of the present invention is applied.
FIG. 7 is a schematic configuration diagram of a power distribution system.
8 is a configuration diagram on the input side of the load in FIG. 7;
9 is a diagram showing a voltage waveform of each part and a charging current waveform of a capacitor in FIG. 8. FIG.
FIG. 10 is an explanatory diagram of period attenuation.
[Explanation of symbols]
10 Modulation block 20 Demodulation block 30 DSP peripheral part 31 DSP
32 ROM
33 DAC
34 ADC
40 Transmitter 41, 61 BPF
42 transmission amplifier 50 coupling unit 51 transmission coupler 52 transmission / reception switching unit 53 reception coupler 60 reception unit 62 reception amplifier 70 power synchronization detector 80 data I / F
91, 92 External I / F
DSP digital signal processor COMP _{1 to} COMP ₄ comparator AND circuit

Claims (2)

In a distribution line carrying method for carrying an information signal to be transmitted superimposed on a distribution line, the distribution line carrying method using OFDM (Orthogonal Frequency Division Multiplexing) as a digital modulation / demodulation method of the information signal,
Distribution line carrier characterized in that the signal is not placed in a period corresponding to a guard interval of an OFDM signal having an effective symbol in which the information signal is stored , and this period is provided near the positive and negative peaks of the power supply voltage of the distribution line Method. In the distribution line conveyance method according to claim 1,
When demodulating the OFDM signal, the received signal is divided into a plurality of blocks, and the correlation value for each block obtained by calculating the received signal of each block with the reference signal is the threshold value for each block. A distribution line conveying method, wherein synchronization between transmission and reception signals is detected when a predetermined condition is satisfied.

Images