JPS6297434A - Reception system - Google Patents

Abstract

PURPOSE:To prevent data mis-demodulation by obtaining a reception signal and a reference signal and changing a threshold value suited to the data modulation when a level of a signal representing the obtained correlation reaches a prescribed level or over. CONSTITUTION:When an output of a matching filter 3 exceeds the 1st level (VSH1 at a time t1, a decision output signal from a correlation decision section 6 drives a phase synchronizing circuit 5 to synchronize the phase of the succeeding reception signal an a reference PN code, and a demodulation section 4 demodulates data according to the relation between an output of the filter 3 and threshold values (VSH1, -VSH1). When the output of the matching filter 3 exceeds the 2nd level (VSH2) at a time t2 the decision section 6 triggers the timer counter circuit 7 to start counting and the threshold value of the demodulation section 4 is set alternately to the 2nd level (VSH2, -VSH2) and the 3rd level (VSH3, -VSH3) based on the said time counting operation.

Description

DETAILED DESCRIPTION OF THE INVENTION B) Field of Industrial Application The present invention relates to a reception system for phase synchronized demodulation type communication, for example, spread spectrum communication (-).

(b) Conventional technology Conventionally, for example, a binary pseudo-noise code (Pseudo No. 1
So-called spread spectrum communication is known, in which a carrier modulated with a PN code (hereinafter referred to as a PN code) is transmitted, and the receiving side selectively receives only signals modulated with the same PN code used on the transmitting side. (For example, electronic Japanese studies 19
(See November 1978 issue).

Recently, a PN code polarity modulation method has been proposed, which modulates the polarity of the PN code according to the data in the process of converting the original data into a PN code, and then transmits the data, as a method that can easily extract data capture timing etc. has been done.

A reception method in conventional spread spectrum communication will be explained with reference to FIGS. 3 and 4. Note that the PN code corresponding to data "1°" is PNC, and the data "0゛'
The PN code corresponding to is written as PNC.

In the figure, 1) is the communication line, (2> is the coupling part between the communication line (1) and the receiver, and (3) is the received signal (PN code) applied via the coupling part (2) and the reception A matched filter (4) is a transversal filter that correlates with a reference PN code preset on the machine side.
(5) is a demodulation unit that demodulates baseband data based on a signal indicating the degree of correlation with the code;
This is a phase synchronization circuit for synchronizing the phase with the code.

Next, the operation will be explained.

A received signal (for example, a signal obtained by AM demodulating a carrier with a PN code) applied to the coupling unit (2) via the communication line (1) is subjected to AM detection in the coupling unit (2), and is then combined with the received PN code. After being applied to the matched filter (3), the reference PN
Correlation with the code is required.

By the way, when calculating the correlation between codes that decline, it is necessary to synchronize the received PN code and the base l11iPN code.
Usually, the receiving side is equipped with a code generator that generates the same series of codes as the spreading code (PN code) generator used on the transmitting side, and the correlation between the output code of a specific stage of this code generator and the received signal is Code synchronization is achieved by finding the point where is maximum.

When the correlation between codes synchronized in this manner is determined by the matched filter (3), the correlation output becomes a bipolar pulse train at equal time intervals as shown in FIG. 4(b).

Such a correlation output is applied to the demodulator (4), as shown in FIG. 2(c).
As shown in (d), when the preset threshold V51-1 is exceeded, the data is demodulated as "1", and when -Vs+i is exceeded, the data is demodulated as "0".

(c) Problems to be Solved by the Invention According to the above technology, it is possible to demodulate baseband data based on the PN code, but when a domestic power line is used as a communication line, The output of the matched filter (3) is disturbed as shown in Figure 2(e) due to noise and impedance fluctuations caused by household electrical equipment etc. connected to the line, and the demodulated data from the demodulator (4) is 2
As shown in FIGS. (f') and (g), the data becomes completely different from the original data, and normal communication cannot be performed.

Therefore, it is an object of the present invention to provide a receiving method that can accurately and reliably demodulate data even when a power line is used as a communication line.

(d) Means for Solving the Problems The features of the present invention for solving the above problems are a first step of determining the correlation between the received signal and the reference signal, and a degree of correlation obtained by this first step. a second step of demodulating the data based on the relationship between the level of the signal indicating the degree of correlation and a preset threshold, and the level of the signal indicating the degree of correlation obtained in the first step is at least a certain level a third process of determining whether or not
The receiving method includes a fourth step of changing the threshold value according to the determination result in the step.

Also, a first process of determining the correlation between the received signal and the reference signal, and a relationship between the level of the signal indicating the degree of correlation obtained by this first process and a preset threshold (first level). a second step of demodulating the data, a third step of determining whether the level of the signal indicating the degree of correlation obtained in the first step is equal to or higher than a predetermined level; a fourth step of setting the threshold to a second level according to the determination result; a fifth step of starting a timekeeping operation according to the determination result of the third step; and a fifth step of starting a timekeeping operation based on the timekeeping operation according to the fifth step. The reception method includes a sixth step of setting the threshold value to a first level or a third level at regular intervals.

According to the present invention, when the level of the signal indicating the correlation between the received signal and the reference signal -6= exceeds a predetermined level,
Change the threshold value in the process of demodulating data.

Furthermore, when the level of the signal indicating the degree of correlation becomes equal to or higher than a predetermined level, the threshold value is changed to a second value and a timing operation is started. Change to a level other than level 2.

(f) Example FIG. 1 is a diagram showing an embodiment of the present invention.

Incidentally, the same parts as in the prior art are given the same drawing numbers and their explanations are omitted.

In FIG. 1, (6) is a correlation degree determining unit that determines the level of a signal indicating the degree of correlation from the matched filter (3);
) is a timing circuit triggered by the determination output from the correlation degree determination section (6), and (8) is the determination output signal (81) from the correlation degree determination section (6) and the output signal from the sub-time circuit (7). (
s 2) (81) (s 2) (81) This is a threshold control unit that controls the threshold level based on s J.

Next, the operation will be explained.

The received signal (for example, a signal obtained by AM modulating a 125 kHz carrier with a PN code [see Fig. 2 (a)]) applied to the coupling unit (2) via the communication line (1) is applied to the coupling unit (2). After the AM signal is detected by the received PN code, it is applied to the matched filter (3) to find the correlation with the reference PN code.The correlation output of the matched filter (3) is shown in Fig. 2 (b).
).

In the initial state, the correlation degree determination unit (6) determines that the output of the matched filter (3) is at the first level (Vs
l+1, -Vs+++) or more,
Further, the threshold control section (8) is set to set the threshold of the demodulation section (4) to a first level (VsE++, -Vs+(+)).

In this state, as shown in FIG. 2, the output of the matched filter (3) reaches the first level (V SH+ +
-Vs+,), the phase synchronization circuit <5) is driven by the determination output signal (ss) from the correlation degree determination section (6), and the phase of the subsequent received signal and the reference PN code are synchronized.

In addition, in the demodulation section (4>, the output of the matched filter 3) -8
= Force and threshold (Vs+1, -V5+++) (7) Relationship When the output of the matched filter (3) exceeds V eHl, data is "1", and when it exceeds VSI-11, data is "O" and 1. , f demodulator-1 21st m(c)(d
)reference).

In such a state, for example, at time t2, the matched filter (
3) output is at the first level (Vs++++−Vs+(+
) greater second (7) 'v hell (V 5N 2
, V 5H2), the correlation degree determination unit (6)
outputs a judgment output signal (a,) (ss), and uses this judgment output signal (S6) to trigger the clock circuit (7) to start the timing operation, and also uses the judgment output signal (Iil) to trigger the threshold control section. (8) to set the threshold of the demodulator (4) to the second level (VSH2, -Vs++2>).

When the timekeeping operation of the timekeeping circuit (7) progresses and a predetermined time (for example, a time corresponding to the PN code-period) has elapsed, the second
A count-up signal is output as shown in Figure (e).

Based on the count-up signal (S2), the threshold value controller (
8) sets the threshold of the demodulator (4) to a third level (VSH3) that is smaller than the first level.

-VS143). After that, when the time corresponding to 1 bit of the PN code has elapsed, the clock circuit (7)
returns to the timekeeping operation state and outputs a signal (s-). Such a signal (SO) is applied to the threshold control section (8>),
The threshold of the demodulator (4) is set again to the second level (VsH2, -
V5H2>Ni constant.

That is, the output of the matched filter (3) is at the second level (Vs
+2. -Vs+-+2), the correlation value is determined through a predetermined time window, and the data is demodulated based on the result.

Further, if there is no demodulated output for a certain period of time (for example, a period corresponding to 3 data bits), the operation of the timer circuit (7) is stopped. When the clock circuit (7) stops, the output signal (S7) from the clock circuit (7) causes the phase synchronization circuit (
5) and resets the threshold value control section (8) using the output signal (S4) to set the threshold value of the demodulation section (4) to the first level (VSHI).

-Vs++1).

Although the present invention has been described above in the case where it is applied to spread spectrum communication, it goes without saying that it can also be applied to communication using other phase synchronization demodulation methods.

=10- (G) Effects of the Invention According to the present invention, the correlation between the received signal and the reference signal is determined,
Since the threshold applied to data demodulation is changed when the level of the calculated correlation signal reaches a predetermined level or higher by -14, erroneous demodulation of data can be prevented.

In addition, the correlation between the received signal and the reference signal is determined, and when the level of the signal indicating the determined degree of correlation becomes a predetermined 1 degree or more -F, the threshold applied to data demodulation is changed and the timing operation is performed. Since the RF power idle value is changed at regular intervals based on this timing operation, there is no erroneous demodulation or omission of data, and even in communication channels with extremely poor transmission characteristics (for example, electric power lines). Accurate communication can be achieved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of each part thereof, FIG. 3 is a diagram showing a conventional example, and FIG. 4 is a diagram of waveforms of each part thereof. (3)...Matched filter, (4)...Demodulator, (6
)...Correlation degree determination unit, (7)...J] time circuit, (8
)...Threshold value control section.

Claims (2)

[Claims] (1) A first process of determining the correlation between the received signal and the reference signal, and demodulating the data based on the relationship between the level of the signal indicating the degree of correlation obtained in this first process and a preset threshold value. a second step of determining whether the level of the signal indicating the degree of correlation obtained in the first step is equal to or higher than a predetermined level; and according to the determination result in this third step, A receiving method comprising a fourth step of changing the threshold value. (2) A first process of determining the correlation between the received signal and the reference signal, and a signal level indicating the degree of correlation obtained by this first process and a preset threshold (first level). a second step of demodulating data according to the relationship; a third step of determining whether the level of the signal indicating the degree of correlation obtained in the first step is equal to or higher than a predetermined level; a fourth step of setting the threshold to a second level according to the determination result in the third step; a fifth step of starting a timekeeping operation according to the determination result in the third step; and a timekeeping operation according to the fifth step. a sixth step of setting the threshold value to a first level or a third level at regular intervals based on the above.