JPS6139634A - Higher harmonic noise removing method - Google Patents

Abstract

PURPOSE:To remove the higher harmonic wave of AC wave that becomes noises and to enable transmission of high-speed data in a system that uses a power line as a signal transmission line by subtracting a received signal of one period before of AC wave from the received signal. CONSTITUTION:Received signals inputted from an input terminal 1 are inputted to a sampling circuit 3 through a filter 2. The sampling circuit 3 makes sampling based on sampling pluse from a pulse generating circuit 5 and the result is inputted to a storing circuit 6 and an arithmetic circuit 7. The storing circuit 6 stores the input and outputs the result of sampling of one period before of AC wave based on inputted sampling pulse to an arithmetic discriminating circuit 7. The arithmetic discriminating circuit 7 subtracts the inputted signal from the storing circuit 6 from the inputted signals from the sampling circuit 3 and outputs to an output terminal 8.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a method for removing harmonic noise that is a problem when receiving power line carrier signals.

(Background of the Invention) In power line transmission, in which a power line to which alternating current waves are applied is used as a signal transmission path, and data is transmitted by superimposing signals on the alternating current waves, there are Harmonic noise of alternating current waves exists and becomes a major obstacle during signal reception and demodulation. Conventionally, as a method for removing harmonic noise, a method has generally been used in which a filter is provided on the receiver side and noise having a frequency other than the frequency of the transmitted signal is cut by the filter. However, on the other hand,
The data transmission rate is proportional to the signal transmission band. That is, in order to increase the data transmission speed, it is necessary to set the bandwidth of the filter on the receiver side to be wide. therefore,
Increase data transmission speed and remove harmonic noise
In order to make the /N ratio more than the allowable value, it is necessary for the filter to have extremely steep characteristics, but manufacturing a filter that satisfies such characteristics requires a small number of elements, shape, and price. , which is difficult to realize from the point of view of coordination. This means that the data transmission rate of current power line carrier signals is 1 to 10
This is one of the major reasons why it is kept at a low level (bit/sec).

(Objective of the Invention) An object of the present invention is to provide a harmonic noise removal method that solves the above-mentioned problems and enables data transmission at a higher speed than conventional methods.

(Characteristics of line cutting) In order to achieve the above object, the present invention uses a power line to which an alternating current wave is applied as a signal transmission path, and when receiving a signal superimposed on the alternating current wave and transmitted, the received signal from,
The received signal of one cycle of the alternating current wave is subtracted, and by taking advantage of the fact that the harmonics of the alternating current wave, which become noise, are synchronized with the fundamental wave, only the harmonics are removed. It is characterized by what it did.

(Example of the invention) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 2(a) shows the waveform of the AC wave applied to the power line, and FIG. 2(b) shows the waveform of harmonic noise mixed into the AC wave. Harmonic noise is a phase of harmonic waves of several different orders and has a complex waveform, but as shown in the figure, it is phase-synchronized with the alternating current wave that is the fundamental wave. Therefore, by subtracting the received signal of one cycle of the AC wave before the received signal, harmonic noise can be removed.

This can be expressed as follows.

8 (t) is the transmitted signal and N(tl is the harmonic noise), then the received signal 'E(tl) on the receiver side is expressed as follows.

E(tl = 5(t)+N(t)
(1) Signal E+(t
If the period of the alternating current wave is T, then &(t)-E(tl E(tT)=5(tl+N(t)-(S(t-T)+N(t-T))(
2) Here, since the harmonic noise N (t) is synchronized with the AC wave, N(t) = N (t-T)
(3) Therefore, from equation (2)1 equation (3).

El(t)=S(t)-8(t-'r)
(4), and the harmonic noise N(t) is removed. The above explanation and FIG. 2 are based on the harmonic noise N
(Although the case where tl is in a steady state is shown, in reality, the harmonic noise Nft1 may fluctuate due to a change in the connection state of the load on the power line that causes the harmonic noise Nft). However, this variation is small compared to the entire harmonic noise N(t), and what remains in the subtracted signal is only the variation from one cycle before the AC wave.
This is not a major problem, and a sufficient S/N value can be obtained.

Next, we will consider the conditions for the data to be correctly transmitted by the signal 5 (tl) to be transmitted by the signal E+(t) expressed by equation (4).

The first condition is that the signal 5(t) to be transmitted is not synchronized with the alternating current wave. This is because if they were synchronized, the signal S (t) would also be removed by subtraction processing, as in the case of harmonic noise, and the value of EITt) in equation (4) would become 0.

Then, the code value of the data according to the signal E+ft).

Consider the conditions for the code values of data based on signal 5(t) to match. As an example of signal 5(t), the FSK signal (f
Consider the case of 5hift keying). That is, this is the case where the signal S (tl is obtained) (ω & l: mark signal angular frequency, ω, space signal angular frequency, A: signal amplitude)
. The subtraction result El(tl) obtained by applying Equation (4) to this signal S (t) is classified into the following four types.

Prison signal S (If the sign of tl is a mark at time t, it is also a mark at time t-T, one cycle before.

El (j) = Asln% t-As1aωm(t
T) (6) When time t is a space and time t -T is also a space.

El (il = As1aωg t −As1nω5
(tT) (O mark at time t, space at time t-T.

El(jl=Asincht-As1nω5(tT)■
In the case of a space at time t and a mark at time t-T.

E+ (1= As1nω5t-As1aωc(t-'
r) ωg-ω1 ωMT = 2 As1a (-t +-) The signal E+(t) found from the subtraction result is uniquely determined to have an angular frequency of ωyo or ω8 in the case of @ and @, so from now on, It becomes possible to determine the sign of the signal S (tl). However, in the case of (0, 0, both the signal El (
The angular frequency of t) is not uniquely determined, and the waveform is obtained by amplitude modulating a signal having the center frequencies of the mark frequency and the space frequency, so the sign of the original signal S (t) cannot be determined. The width of this interval in which it is impossible to determine the sign is the maximum width T(
Since the signal Et (from tl,
As a condition for determining the sign of signal 5(tl), it can be seen that the code length of signal 5(tl is insufficient for one cycle of the AC wave, and requires at least two cycles. Also, timing examples of the signs of the signal S (t) and the signal g+(l are shown. fat is an AC wave, (bl is the signal S (t
), tc+ is the signal 5 (t-T
), (d) are the signs of the signal El(t) obtained by subtracting (bl from fc). Here, the signal S (t)
An example is shown in which the code length of is the third cycle of the alternating current wave.

Furthermore, consider the following conditions for accurately determining the sign of the signal S (t) using the signal El(tl. The signal ltl
The sign of the signal S (t) can be determined by (4), ■)
2 As1n-”Z-.To accurately determine the sign,
It is desirable that this amplitude be as large as possible. This amplitude is determined by where f is the alternating wave frequency, y is the mark signal frequency, f,
Letting be the space signal frequency, it can be rewritten as follows.

Therefore, to make the amplitude as large as possible, f
It is necessary to make the values of M/f and ra/r as close as possible to yc+% (rL: integer).

The above conditions can be summarized as follows.

(1) The transmitted signal S (tl) is not synchronized with the AC wave.

(2) The code length of the signal S (t) shall be the minimum of three cycles of the AC wave.

(3) Mark signal frequency fu, space signal frequency fm
The value of is the ratio fw/f to the alternating current wave frequency f, f+
The values of /f shall be determined so that both values are as close as possible to 10% (where 1 is an integer).

Under the above conditions, from the received signal E(t).

It is obtained by subtracting the signal E(t-T) of one cycle of the alternating current wave. Signal E with harmonic noise removed.

+11, it is possible to accurately determine the sign of the transmitted signal S (t). The data transmission speed due to this is based on condition (2) [, and the period of the AC wave is 50 (Hz).
), the maximum is 25 Cbit/sec),
This is a significant increase compared to the conventional 1 to 10 Cbit/sec.

In addition, when deriving the conditions (1) to (3) mentioned above, the signal S
(As an example, we explained the case of FSX signal, but 1
The signal S (t) of the present invention is not limited to the FSK signal, but can be similarly applied to other signals. Below, the ASK signal (amp l 1-tude
5hift keying), PSK signal (
A case in which phase shiftkeying is used will be briefly explained.

Consider a case where an ASK signal expressed by a linear equation is used as the signal 5(t).

(ωC: signal angular frequency, A: signal amplitude) Subtraction result El (
tl is as follows.

If there is a mark at time t and a mark at time t-T, then E+ (t) = As1IIωc t −As1aω
c(tT)(B) Space at time t, time t-
If T is also a space, then El (t) = 0 0 = OQ4) 0 If time is a mark, if time is t - T, if it is a space, '& (it = As1nωc t -0 = As1
nωc t Q5)■ In the case of a space at time t and a mark at time t-T, El(Le-OAs1aωa(t-'r)"= As1
aωc(t-'r) (amplitude 2 in case of Ife prisoners As1a (ωCT/2)) is determined so that there are two people, and the slice level is set to A. As in the case of the FSX signal, The prisoner is determined to be a mark, (6) is determined to be a space, and (Q, ■ cannot be determined).

Also, consider a case where the signal S (tl is a PSK signal expressed by the following equation).

(ωC: Signal angular frequency, A: Signal amplitude) Subtraction result El
(tl is as follows.

If there is a mark at time t and a mark at time t-T, then El (t) ”= As1nωc t-A, si6ω
c(tT) ■) If there is a space at time t and a space at time t-T, then El (t) = AsinωcT (As1IIωc(
tT))0 Mark at time t, space at time t-T El (tl = As1aωct(As1nωc(t
T)) 0, space at time t, mark at time t-T El (i) = As1nωc t −As1aω
If the phase of the signal El (tl in the case of a(t-'r) (4) is a mark, then (B) is determined to be a space,
(0 and 0 cannot be distinguished, and this case is similar to the case of the FSX signal.

Here, a signal sampling method in the subtraction process of the present invention will be explained. In the present invention, it is necessary to store the received signal, make the received signal at time t correspond to the received signal at time t-T, which is one cycle before the alternating current wave, and perform subtraction processing.

The problem here is that the period T of the AC wave is not constant. In general, the period of the AC wave that supplies power is when the source is not a constant frequency power supply.

A fluctuation of several percent must be expected. therefore.

In the present invention, the period T of the alternating current wave is stored as a constant,
If the received signals at time t and time t-T are continuously subtracted, the received signal at time t-T will deviate from the received signal one period before time t, and harmonic noise will not be removed. It may not be possible to do it accurately.

In consideration of the above points, the present invention defines the sampling timing of the received signal as follows.

When the received signal is sampled at a constant period τ, as shown in Figure 3, the alternating current wave has a constant phase (in Figure 3, the alternating current wave changes polarity from negative to positive at the zero point). ), sampling is started anew.

That is, sampling is started every - period at points D and B in Fig. 3(b), and sampling is performed at point A, which is time t and is n times the sampling period τ8 from point B. The received signal is made to correspond to a received signal sampled at a point 0, which is a multiple of the sampling link period τ, from point D, and a subtraction process is performed. By determining the sampling timing in this way, even if the period T of the AC wave changes, correspondence with the received signal one period before the AC wave can be made with a considerable degree of accuracy, and by the subtraction process.

Effective removal of harmonic noise becomes possible.

FIG. 4 is a block diagram of an example of a harmonic noise removal circuit implementing the present invention. The received signal input from the input terminal 1 is converted into an alternating current wave and a high frequency random signal through a simple low-order filter 2 provided to improve resolution when converting sampling values into digital values and reliability during demodulation. Noise is removed and the signal is input to the sampling circuit 3. The received signal is also input to the AC wave phase detection circuit 4, and when a predetermined constant phase of the AC wave is detected here, the information is sent to the sampling pulse generation circuit 5, where the information is sent. A new sampling starts each time. The sampling pulse outputted from the sampling pulse generation circuit 5 is input to the sampling circuit 3 and the memory circuit 6. In the sampling circuit 3, sampling is performed based on the sampling pulse 2, and the result is used for the memory circuit 6 and calculation discrimination. Input to circuit 7. The memory circuit 6 stores this input, and outputs the sampling result of one cycle of the AC wave before to the calculation/determination circuit 7 based on the input sampling pulse.

The arithmetic determination circuit 7 subtracts the input signal from the storage circuit 6 from the input signal from the sampling circuit 3, determines the sign thereof, and outputs it to the output terminal 8.

Note that the method of the present invention can be applied regardless of whether voltage or current is used as the signal.

(Effects of the Invention) As explained above, according to the present invention, a power line to which an alternating current wave is applied is used as a signal transmission path, and when receiving a signal transmitted superimposed on an alternating current wave, it is possible to ,
The received signal of one cycle of the alternating current wave is subtracted, and by taking advantage of the fact that the harmonics of the alternating current wave, which become noise, are synchronized with the fundamental wave, only the harmonics are removed. Therefore, there is no need to pass through a filter that limits data transmission speed, and high-speed data transmission can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the method for removing harmonic noise from an FSK signal according to the present invention, Fig. 2 is a waveform diagram showing the relationship between AC waves and harmonic noise, and Fig. 3 is an example of the sampling timing in the present invention. FIG. 4 is a block diagram showing an example of a harmonic noise removal circuit implementing the present invention. 1...Input terminal, 3...Sampling circuit, 6...
- Memory circuit, 7... Calculation discrimination circuit, 8... Output terminal, τ,... Sampling period.

Claims (1)

[Claims] 1. A power line to which an alternating current wave is applied is used as a signal transmission path, and when receiving a signal superimposed on an alternating current wave and transmitted, the received signal of one cycle of the alternating current wave is subtracted from the received signal. This is a harmonic noise removal method.