JPH07135481A - Reference signal synchronization form spread spectrum communication system - Google Patents

Abstract

PURPOSE:To surely secure synchronization by providing a synchronizing signal generating means, a sender side code generating means, a delay code generating means and a reception side code generating means so as to demodulate data while multiplying a data use PN code and a demodulation use PN code. CONSTITUTION:A PN code generator 12 is synchronous, with a zero cross point of a synchronizing signal from a synchronization generating section 11 to provide from output of spread spectral signals pn1, pn2 of modulated PN codes from a data output section 10. A zero cross detection circuit 15 detects the zero cross point of the synchronizing signal and provides an output to delay time hold circuits 16A, 16B. The circuits 16A, 16B receives the detection signal and provide an output to code generators 17A, 17B synchronous with the sent PN codes pn1, pn2 sent based on the holding synchronization delay time. Multipliers 18A, 18B multiply the modulated PN codes with the PN codes outputted from the generators 17A, 17B and a DC component is outputted to a comparator circuit 20 via LPFs 19A, 19B. Data are reproduced by giving the signals to the circuit 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference signal synchronous spread spectrum communication system for transmitting information using a ground return circuit of a low voltage distribution line, and in particular, it is reliable even if a synchronous signal in a frequency band with a large transmission delay time is used. The present invention relates to a reference signal synchronization type spread spectrum communication system in which high reliability is ensured by ensuring high synchronization.

[0002]

2. Description of the Related Art In recent years, a communication system using a low voltage distribution line ground return circuit has been used for applications such as automatic meter reading of electric power meters of consumers and control of loads, and further monitoring of failures of consumers and distribution facilities. Practical application is being actively promoted.

In the above communication system, since the power intensity per band is limited by the Radio Law and the transmission characteristic of the low-voltage distribution line has a time-varying characteristic, it is considered as a highly reliable communication system under these conditions. A spread spectrum communication system in which a signal spectrum is distributed over a wide band is applied to a transmission line.

At present, there are two types of spread spectrum communication systems, a direct spread system and a reference signal synchronous spread system. In the former case, spread spectrum and FSK (Frepuency) are used.
Shift Keying) PN code modulated by transmission data is transmitted with a frequency bandwidth of 450 kHz or less allowed by the Radio Law, and synchronization is performed by a synchronization circuit using a delay lock loop or the like on the receiving side, and a few hundred to a few thousand. Information is transmitted at a transmission rate of bps.

On the other hand, in the latter case, 50 or 60 Hz
Of the commercial frequency and the pn code which has been spectrum-spread and modulated by the transmission data are transmitted, and the pn code is synchronized with the point where the voltage value of the reference signal becomes 0V, that is, the zero-cross point. , Tens of bp
Information is transmitted at a transmission speed of s.

As shown in FIG. 8, the transmission characteristic of the earth return circuit of the distribution line has large attenuation in the high frequency region. Therefore, when the delay lock loop is used as in the former case, the synchronization holding ability is lowered and noise is reduced. It becomes vulnerable to such fluctuations, and the transmission performance deteriorates depending on the conditions. Therefore, in the spread spectrum communication system using the earth return circuit of the distribution line, it is effective to apply the reference signal synchronization type spread system.

[0007]

However, according to the conventional reference signal synchronization type spread spectrum communication system, the regulation of the Radio Law is loose and the transmission characteristic is stable, for example, 10 k.
When a low-frequency signal of Hz or less is used as the synchronization signal,
As shown in FIG. 3, since the transmission rate of the synchronization signal is slower than that of the spread spectrum signal of the pn code, there is an inconvenience that the reliable synchronization cannot be secured due to the difference in the transmission rate of the pn code and the synchronization signal. .

Therefore, an object of the present invention is to spread a reference signal by using a reference signal synchronization type spread spectrum system which can ensure reliable synchronization even if a synchronization signal in a frequency band having a large transmission delay time is used. Is to provide.

[0009]

In view of the above problems, the present invention ensures reliable synchronization even when a synchronization signal in a frequency band with a large transmission delay time is used, thereby improving reliability against noise on a transmission line. In order to increase, a sine wave signal of 10 kHz or less is generated as a synchronizing signal and is transmitted through a low voltage distribution line, and a synchronization signal generating means is modulated by the data transmitted through the low voltage distribution line, and is spread spectrum to a predetermined bandwidth. At the same time, a transmitting side code generating means for generating a data pn code synchronized with the zero-cross point of the synchronizing signal and transmitting it through the low voltage distribution line, and a data p for transmitting the low voltage distribution line.
Delay time holding means for holding the delay time of the synchronizing signal with respect to the n code, and a receiving side for generating a demodulating pn code for demodulating data synchronized with the data pn code based on the zero cross point and the delay time of the synchronizing signal. The present invention provides a reference signal synchronization type spread spectrum system equipped with a code generating means and a data reproducing means for demodulating data by multiplying a pn code for data and a pn code for demodulation.

The transmitting side code generating means is adapted to generate the first and second data pn codes corresponding to the binary data, and the data reproducing means is adapted to generate the first data pn code. A first multiplier for multiplying a demodulation pn code equal to one data pn code, a second multiplier for multiplying a second data pn code by a demodulation pn code equal to the second data pn code, and a first multiplier , And the output of the first and second low-pass filters that pass the low-pass component of the output of the second multiplier, and the outputs of the first and second low-pass filters are compared to reproduce binary data. It is configured to include a comparison means for performing.

The delay time holding means generates the synchronizing signal from the synchronizing signal generating means before performing data communication, and is not modulated by the data synchronized with the zero cross point of the synchronizing signal from the transmitting side code generating means. A pn code is output, a pn code equal to the non-modulation pn code is generated from the receiving side code generating means while changing its generation timing, and the time at which the received power of the data reproducing means becomes maximum is held as the delay time. ing.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reference signal synchronization type spread spectrum communication system of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows the configuration of a communication system according to an embodiment of the present invention. This communication system was connected to a low voltage distribution line 5 consisting of distribution lines 5A, 5B and 5C (5A is a neutral line), a common ground line 6 to which the neutral line 5A is connected, and a neutral line 5A. It is composed of a transmitter station 1 and a plurality of customers 7 connected to the low-voltage distribution line 5.

The plurality of consumers 7 have a load 4 connected to the low-voltage distribution line 5 via the electric energy meter 3 and a receiving station 2 connected to the neutral line 5A via the electric energy meter 3. ing.

The transmitting station 1 inputs various commands and information from a centralized control center such as an electric power company business office via a high-speed transmission line, and transmits them to a plurality of receiving stations via a neutral line 5A of a low voltage distribution line 5. 2 to transmit.

FIG. 2 shows a simplified configuration of the communication system described above. As can be seen from this figure, a transmitting station 1 and a receiving station 2 each having a grounding resistance 9 connected between the ground are connected via a transmission line (low voltage distribution line) 5, and information is obtained by using a low voltage distribution line earth return circuit. Transmission is to take place.

FIG. 3 shows circuit configurations of the transmitting station 1 and the receiving station 2. The transmitting station 1 includes a data output unit 10 that outputs binary data such as commands and information to be transmitted, and 9.6.
A synchronization signal generator 11 for outputting a sine wave signal of kHz as a synchronization signal, and a code generator 12 for generating two pn codes corresponding to binary values of data in synchronization with the zero-cross point of the synchronization signal are provided. It is configured to transmit the sinusoidal synchronizing signal and the two modulated pn codes via 5.

On the other hand, the receiving station 2 has a center frequency of 9.6 kHz.
a sync signal separation circuit 14 having a z band pass filter or the like for separating the sync signal transmitted through the transmission path 5 from the transmission data, a zero cross detection circuit 15 for detecting a zero cross point of the separated sync signal, and a transmission path Pn that has transmitted 5
P for data based on the delay time of the synchronization signal with respect to the code
A delay time holding circuit 16A, 1 holding a synchronization delay time for generating a demodulation pn code synchronized with the n code
6B, zero-cross point of synchronization signal and delay time holding circuit 1
A code generator 17 for generating a demodulated pn code which is synchronized based on the synchronization delay time held in 6A and 16B.
A and 17B, multipliers 18A and 18B for multiplying the demodulation pn code by the data pn code separated from the synchronization signal in the synchronization signal separation circuit 14, and a low-pass filter that passes low-frequency components of the outputs of the multipliers 18A and 18B. 19A, 19B
And a comparison circuit 20 for reproducing the binary data by comparing the outputs of the low-pass filters 19A and 19B.

The synchronization delay time of the delay time holding circuits 16A and 16B will be described with reference to FIG. The delay time holding circuits 16A and 16B are the code generator 17
It may be a single circuit common to A and 17B. The delay time for synchronization is changed according to the characteristics of the transmission line 5, and its optimum value is searched for before communication. First, a point (time) at which the received power becomes maximum in the state where noise is not added is searched for. That is, as shown in FIG. 4, a synchronization signal and a non-modulated pn code synchronized with the zero-cross point of the synchronization signal are transmitted from the transmission side, and after the synchronization signal separation circuit 14 separates the synchronization signal, The delay time is changed to change the generation timing of the pn code from the code generators 17A and 17B, and the correlation output value from the low-pass filters 19A and 19B, that is, the synchronization delay time that maximizes the received power is searched. Then, the searched delay time for synchronization is held in the delay time holding circuits 16A and 16B.

FIG. 5 shows cutoff frequencies of 40, 70, 100 when the transmission line is approximated by a low-pass filter.
The change in received power when the frequency is changed to kHz is shown. Here, the horizontal axis represents the synchronization delay time in units of pn code chips, and the vertical axis represents the root mean square value of the received voltage of the receiving station 2. As can be seen from this figure, the optimum reception state changes depending on the conditions of the transmission path. Moreover, since the transmission characteristics of the earth return circuit are considered to be constant over a relatively long period of time, once the optimum value of the delay time for synchronization is obtained, the ideal synchronization point is maintained while the transmission characteristics are constant. It

Further, the search for the synchronization point when noise is applied can be similarly performed. FIG. 6 shows the low-pass filters 19A and 1A when noise (narrow band / white noise) is present.
The output value of 9B is shown. As can be seen, the optimum sync point is obtained even in the presence of noise.

The operation of the reference signal synchronization type spread spectrum communication system of the present invention will be described below with reference to the timing chart of FIG. First, as described above, the synchronization signal generator 11 of the transmitting station 1 outputs the synchronization signal before communication, and the pn code generator 12 synchronizes the synchronization signal with the unmodulated pn code spread spectrum signal. And output
Both signals are received by the receiving station 2 via the transmission path 5. On the other hand, in the receiving station 2, the delay times for synchronization of the delay time holding circuits 16A and 16B are changed to change the code generators 17A and 17B.
The synchronization point of the pn code generated from the pn code of the received spread spectrum signal is searched for. That is, the received spread spectrum signal and pn from the code generators 17A and 17B.
The correlation output value of the signal obtained by multiplying the code by each of the multipliers 18A and 18B and passing through the low-pass filters 19A and 19B, that is, the delay time for synchronization that maximizes the received power is searched for and the delay time is calculated. It is held in the holding circuits 16A and 16B.

Then, the data is transmitted from the transmitting station 1 to the receiving station 2. That is, the data output unit 10 outputs binary data and the synchronization signal generation unit 11 outputs 9.6 kHz.
The sine wave synchronization signal S of z is output. Further, the pn code generator 12 synchronizes with the zero-cross point of the synchronizing signal and is modulated according to the binary data from the data output unit 10.
The code spread spectrum signals pn1 and pn2 are output.
Then, the output synchronization signal S and the pn codes pn1 and pn
The spread spectrum signal No. 2 ((a) in FIG. 7) is transmitted to the receiving station 2 via the transmission line 5.

The synchronization signals S and pn transmitted through the transmission line 5
The spread spectrum signals of codes pn1 and pn2 are transmitted through the transmission line 5
Due to the difference in the transmission speed of the above, the synchronization signal is received by the receiver 2 with a delay of time t with respect to the pn codes pn1 and pn2 ((b) of FIG. 7). In the receiver 2, the synchronization signal separation circuit 14
And the pn code pn1 and pn2 received at
Of the spread spectrum signal, the sync signal S to the zero-cross detection circuit 15, and the pn codes pn1 and p.
n2 is output to the multipliers 18A and 18B, respectively.

When the zero-cross detection circuit 15 detects the zero-cross point of the synchronization signal, it outputs the detection signal to the delay time holding circuit 1.
Output to 6A and 16B. Delay time holding circuit 16A, 1
6B is a pn code pn1, pn2 transmitted based on the synchronization delay time held after the detection signal is input.
In synchronization with the above, the pn codes pn1 and pn2 are output from the code generators 17A and 17B to the multipliers 18A and 18B, respectively ((c) in FIG. 7).

The spread spectrum signal of the pn code thus modulated by the multipliers 18A and 18B and the code generator 1
When the pn code generated at a predetermined timing is input from 7A and 17B, the modulated pn code and the code generator 17 are input.
The pn code output from A and 17B is multiplied.

That is, the code generator 17A has a configuration shown in FIG.
When the pn code pn1 as shown in (c) is output and this is multiplied by the data pn codes pn1 and pn2 in the multiplier 18A, as shown in (d) of FIG. However, the high frequency component H is obtained by pn2 × pn1. When the DC component L and the high frequency component H are input to the low pass filter 19, the high frequency component H is removed and only the DC component L is output. On the other hand, the code generator 17B outputs the pn code pn2,
The multiplication of pn1 × pn2 and pn2 × pn2 is the multiplier 18B.
Done in. Therefore, the output of the low-pass filter 19B is not output when the DC component D of the low-pass filter 19A is output, and is not output when the high-frequency component H is cut.
2 × pn2) is output. Low-pass filter 19A,
By inputting this output of 19B to the comparison circuit 20, “1” (= pn1 × pn1), “0” (= pn2 × pn)
The data of 2) is reproduced.

As is apparent from the above embodiments, the synchronization delay time of the delay time holding circuits 16A and 16B is searched and held from the delay time of the synchronization signal with respect to the spread spectrum signal of the pn code before the data communication. Since the synchronization point of the pre-modulated pn code and the pn code for demodulation is secured, reliable synchronization can be obtained even if a synchronization signal with a large transmission delay time of 10 kHz or less is used, and transmission reliability is improved. You can Further, even if the sine wave signal for synchronization can be detected even under the condition where the signal is attenuated, the synchronization can be secured.

[0029]

As described above, according to the reference signal synchronizing type spread spectrum communication system of the present invention, the synchronizing signal generating means for generating the sine wave signal of 10 kHz or less as the synchronizing signal and transmitting it through the low voltage distribution line. And the data transmitted through the low-voltage distribution line are modulated by the data transmitted through the low-voltage distribution line, spectrum-spread to a predetermined bandwidth, and a data pn code synchronized with the zero-cross point of the synchronization signal is generated and transmitted through the low-voltage distribution line. Side code generating means, delay time holding means for holding the delay time of the synchronization signal with respect to the data pn code transmitted through the low voltage distribution line, and data synchronized with the data pn code based on the zero-cross point and the delay time of the synchronization signal. Receiving side code generating means for generating a demodulating pn code for demodulating the data, and the data is demodulated by multiplying the data pn code by the demodulating pn code. Due to the provision of a data reproducing unit,
Even if a synchronization signal in a frequency band with a large transmission delay time is used, reliable synchronization can be ensured and transmission reliability can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a circuit configuration of the communication system of FIG.

FIG. 3 is a block diagram showing a circuit configuration of a transmitting station and a receiving station according to an embodiment.

FIG. 4 is an explanatory diagram showing an operation flow when searching and holding a synchronous delay time of the delay time holding circuit according to the embodiment.

FIG. 5 is a graph showing changes in reception conditions due to a transmission line in which noise does not exist.

FIG. 6 is a graph showing changes in reception conditions due to a transmission line in the presence of noise.

FIG. 7 is a timing chart showing each signal according to one embodiment.

FIG. 8 is a graph showing transmission characteristics of a low voltage distribution line.

FIG. 9 is a graph showing transmission characteristics of a low voltage distribution line.

[Explanation of symbols]

1 transmitting station 2
Receiving station 3 Electricity meter 4
Load 5 Low-voltage distribution line (transmission line) 5A
Common ground line 5B, 5C Distribution line 6
Aerial ground wire 7 Customer 10
Data output unit 11 Synchronous signal generation unit 12
Code generator 13 Spreading modulation circuit 14
Sync signal separation circuit 15 Zero cross detection circuit 16A, 16B Delay time holding circuit 17A,
17B Code Generator 18A, 18B Multiplier 19A, 19B Low-pass Filter 20
Comparison circuit

Claims (3)

[Claims] 1. A spread spectrum communication system using a ground return circuit of a low-voltage distribution line, a synchronization signal generating means for generating a sine wave signal of 10 kHz or less as a synchronization signal and transmitting it through the low-voltage distribution line, Modulated by the data transmitted on the low voltage distribution line,
Transmitting side code generating means for generating a data pn code synchronized with the zero-cross point of the synchronization signal and transmitting it through the low-voltage distribution line, and spectrum-spreading to a predetermined bandwidth, and transmitting the low-voltage distribution line A delay time holding means for holding a delay time of the synchronization signal with respect to the data pn code, and for demodulating the data synchronized with the data pn code based on the zero cross point of the synchronization signal and the delay time. A reference signal synchronizing type, comprising: a receiving side code generating means for generating a demodulating pn code; and a data reproducing means for multiplying the data pn code by the demodulating pn code to demodulate the data. Spread spectrum communication system. 2. The transmission side code generating means generates first and second data pn codes corresponding to binary data, and the data reproducing means converts the first data pn code into the first data pn code. A first multiplier that multiplies a demodulating pn code equal to the data pn code; a second multiplier that multiplies the second data pn code by a demodulating pn code equal to the second data pn code; The outputs of the first and second low-pass filters are compared with those of the first and second low-pass filters, which pass low-frequency components of the outputs of the first and second multipliers. The reference signal synchronous type spread spectrum communication system according to claim 1, further comprising a comparing means for reproducing the value data. 3. The delay time holding means generates the synchronization signal from the synchronization signal generating means before performing data communication, and uses the data synchronized with the zero-cross point of the synchronization signal from the transmission side code generating means. A non-modulated pn code that is not modulated is output, and a pn code equal to the non-modulating pn code is generated from the reception side code generation means while changing its generation timing, and the received power of the data reproduction means becomes maximum. The reference signal synchronization type spread spectrum communication system according to claim 1, wherein the delay time is held as follows.