JPH0736569B2 - Demodulation method of amplitude shift keying signal - Google Patents

Description

The present invention relates to demodulation for demodulating binary data of mark (1) and space (0) transmitted and received by amplitude shift keying (ASK) at high speed and without distortion. Regarding the scheme.

(Prior Art) Signal transmission by amplitude shift keying is widely used because it is easy to modulate and demodulate data during transmission and reception. For example, in a supervisory control system of a distribution system that uses a high-voltage distribution line as a signal transmission line, an amplitude shift keying signal of a carrier frequency is superimposed on a commercial frequency AC voltage or current for power transmission, and the signal is transmitted along the distribution line. The condition of switches distributed over the entire area is monitored, switching is controlled, and information such as load voltage and current is collected.

The method conventionally used to receive and demodulate such amplitude shift keying signals is to detect the signal with a filter tuned to the carrier frequency and rectify it, or by some other method, the original mark. (1), space (0) signal is restored.

The problems of the conventional method will be described below by using an example of a ripple control system which is widely used at present as one of the systems using the amplitude shift demodulation method.

In the information transmission using the distribution line as described above, when extracting the signal from the distribution line, avoid the influence of the harmonics of the commercial frequency and the non-stationary noise components existing in a wide band,
Due to the necessity of increasing the signal-to-noise ratio, a filter having an extremely narrow band has been used as the bandpass filter for detecting the signal. However, when passing through a narrow band filter, the rise time of the signal becomes long and the waveform is distorted.
The signal transmission speed was very slow, about several bits / second.

(Problems to be Solved by the Invention) It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a demodulation method that dramatically increases the signal transmission rate by amplitude shift keying modulation. is there.

(Means for Solving the Problem) The present invention, as shown in FIG. 1, includes a signal generating means 1 for generating a signal representing a waveform of a sine wave and a cosine wave having a frequency equal to that of a carrier of an amplitude shift keying signal. A sequential correlation calculating means 2 for obtaining a correlation value between a signal representing a waveform of a sine wave and a cosine wave generated by the signal generating means 1 and an amplitude shift keying received signal successively one bit period over time. From the output of the successive correlation calculating means 2, the original mark (1),
The information code reproducing means 3 for reproducing the information code of the space (0) signal is provided.

According to one aspect of the present invention, the signal generating means 1 generates a set of coefficient values obtained by sampling a sine wave at a constant synchronization and a set of coefficient values obtained by sampling a cosine wave at a constant period. And a signal generator that operates. Then, the successive correlation calculating means 2 combines each signal in the 1-bit period of the signal obtained by sampling the amplitude shift keying received signal at the same period as the constant period and the coefficient value obtained by sampling the sine wave at the constant period. Of the amplitude shift keying received signal sampled at the same cycle as the constant cycle, and each signal in a 1-bit period, and the cosine wave at the constant cycle A second multiplication unit 6 that multiplies each coefficient value of a set of coefficient values obtained by the above, and a first addition unit 7 that obtains the sum of the multiplication results corresponding to each sampling of the first multiplication unit 5.
A second adder 8 that obtains the sum of the multiplication results corresponding to each sampling of the second multiplier 6, and a first square calculator 9 that squares the output of the first adder 7. Second adder 8
A second squaring unit 10 for squaring the output of the above, a third adding unit 11 for adding the output of the first squaring unit 9 and the output of the second squaring unit 10, and And a square root calculator 12 that calculates the square root of the output of the adder 11 (second
See figure).

According to one aspect of the present invention, the information code reproducing means 3 compares the output of the successive correlation calculating means 2 with a predetermined threshold value and determines whether the original mark is larger or smaller than the threshold value. (1), a space (0) signal is reproduced by a threshold value comparator 15 (see FIG. 3).

Further, according to another aspect of the present invention, the information code reproducing means 3 differentiates the output of the successive correlation calculating means 2 to obtain +
It is also possible to leave the mark (1) for +1 and the space (0), 0 for -1 of the output of the differential operation unit 13 as the differential operation unit 13 for converting into a ternary signal of 1, -1,0. Code conversion unit 14 for reproducing mark (1) and space (0) signals
It consists of

(Operation) In the successive correlation calculating means 2, the correlation value between the signal representing the waveform of the sine wave and the cosine wave generated by the signal generating means 1 and the amplitude shift keying received signal is sequentially 1 bit time as time passes. Then, the correlation values of the triangular wave or the trapezoidal wave as shown in FIGS. 4 (a) and (b) or FIGS. 5 (a) and (b) are obtained. The information code reproducing means 3 reproduces the original mark (1) and space (0) signals from the output of the successive correlation calculating means 2.

In the present invention, instead of the narrow-band filter, which has been the largest factor limiting the signal transmission rate in the prior art, the successive correlation calculating means 2 based on the principle of Fourier series calculation is provided, and distortion-free with a fast rise is provided. Of the original code (1) and the space (0) is restored by converting the demodulated waveform, so that the signal transmission rate by amplitude shift keying modulation is dramatically increased. be able to.

(Examples) Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 2 shows an embodiment of the present invention in which the successive correlation calculating means 2 and the information code reproducing means 3 are constituted by a digital signal processor.

As shown in the figure, the sine wave and cosine wave coefficients of the carrier frequency are generated and stored in the memory of the signal processor for one bit length. It should be noted that both the sine wave and the cosine wave of the carrier frequency are prepared so that a special circuit for synchronizing with the received signal is not required. First, the ASK received signal of the filter number is converted into a parallel digital signal sequence by 1-bit length for each sampling period T by the serial-parallel converter 4 with respect to the signal received from the distribution line by the wideband bandpass filter. The 1-bit length parallel digital signal and the 1-bit length coefficient of the sine wave and the cosine wave are multiplied in the multiplication units 5 and 6, respectively, and added to the addition units 7 and 8.
In, the multiplication results are added. The outputs of the adders 7 and 8 are squared in the square calculators 9 and 10, respectively, and the results of these calculations are added by the adder 11. The square root calculation unit 12 calculates the square root of the addition result. The above calculation is sequentially calculated while shifting the received data by one for each sampling period T, and an output signal representing the temporal transition of the correlation value between the ASK received signal and the carrier frequency signal is obtained.

The amplitude shift keying waveform is considered to have been modulated into an ASK signal by multiplying the carrier frequency by a rectangular wave corresponding to the information code 1,0. The DC component contained in the information code is converted from a rectangular wave to a triangular wave or a trapezoidal wave as shown in FIG. Further, the noise frequency components other than the carrier wave are removed by performing the 1-bit length correlation calculation. Therefore, in principle, the system of the present invention does not cause waveform delay or distortion unlike the conventional narrow-band filter, and thus has high-speed and high-resolution filter characteristics.

Next, the information code reproducing means 3 is composed of a differential calculating section 13 and a code converting section 14, and is a section for reproducing the triangular wave or the trapezoidal wave demodulated in the preceding stage into the original 1,0 rectangular wave.

The differential operation section 13 has a positive slope of +1 according to the slope of the triangular wave or the trapezoidal wave shown in FIGS. 4 (a) and 4 (b),
It outputs three values, -1 for negative slope and 0 for flat part. The differential operation section 13 in FIG. 2 is an example in which the differential function is configured by the digital signal processor as described above, but as shown in the figure, the difference in waveform between several sampling points separated from each other. Can be obtained for each sampling period T to obtain the above waveforms of 1, -1,0.

The code conversion unit 14 performs conversion by leaving +1 of the output of the differential operation unit 13 as information code 1, −1 as information code 0,0 as information code previously determined as it is, and leaving it as it is. The information code of mark (1) and space (0) is reproduced.

FIG. 3 shows another embodiment of the information code reproducing means 3, which comprises a threshold value comparing section 15 for comparing the output of the successive correlation calculating section 2 with a predetermined threshold value. By setting the threshold value to approximately one half of the amplitude of the triangular wave or trapezoidal wave in FIG. 5, the reproduction information code in FIG. 5 can be obtained.

FIG. 6 shows an experimental result of demodulating the received signal of the ASK signal actually transmitted through the distribution line by using the apparatus of the embodiment of FIG. The carrier frequency is 450 Hz and the signal transmission rate is 60 bits / second. As shown in the figure, the noise component is well removed from the waveform of the signal A received from the distribution line, which is obtained by passing the ASK received signal after being filtered by the wideband bandpass filter through the successive correlation calculating unit 2. The data is completely reproduced. The conventional method is several bits /
It can be seen that, while it is as slow as about a second, a dramatic speedup of 60 bits / second is realized in this embodiment.

(Effects of the Invention) As described in detail above, according to the present invention, the principle of Fourier series calculation is used instead of the narrow-band filter that has been the largest factor limiting the signal transmission rate in the prior art. By providing the successive correlation calculating means 2 based on this to realize distortion-free demodulation with a fast rise, and further by converting this demodulated waveform, the information code signal of the original mark (1) and space (0) is restored. It is possible to dramatically increase the signal transmission rate by amplitude shift keying.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention. FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 3 is a diagram showing another embodiment of the information code reproducing means. FIGS. 4 (a) and 4 (b) are diagrams showing waveforms of respective parts for explaining the operation of the embodiment shown in FIG. FIGS. 5 (a) and 5 (b) are diagrams showing the waveform of each part for explaining the operation of the embodiment shown in FIG. FIG. 6 shows the experimental results of demodulating the received signal of the ASK signal actually transmitted via the distribution line using the apparatus of the embodiment of FIG. 1 ... Signal generation means, 2 ... sequential correlation calculation means, 3 ...
Information code reproducing means, 4 ... serial / parallel conversion, 5,6 ... multiplier, 7,8,11 ... adder, 9,10 ... square calculator, 12 ... square root calculator, 13 ... Differentiator, 14 ... Code converter,
15 …… Threshold comparison section.

Claims (4)

[Claims] 1. A signal generating means for generating a signal showing a waveform of a sine wave and a cosine wave having a frequency equal to that of a carrier of an amplitude shift keying signal, and a waveform of a sine wave and a cosine wave generated by the signal generating means. A successive correlation calculating means for sequentially obtaining a correlation value between the signal and the amplitude shift keying received signal for each one bit period with the passage of time; and an original mark (1) from the output of the successive correlation calculating means,
An information code reproducing means for reproducing an information code of a space (0), and a demodulation method of an amplitude shift keying signal. 2. The signal generating means comprises a signal generating section for generating a set of coefficient values obtained by sampling a sine wave at a constant period and a set of coefficient values obtained by sampling a cosine wave at a constant period. The successive correlation calculation means is configured to combine each signal of a 1-bit period of a signal obtained by sampling the amplitude shift keying received signal at the same period as the constant period and a coefficient value obtained by sampling a sine wave at a constant period. A first multiplication unit that respectively multiplies each coefficient value, each signal in a 1-bit period of a signal obtained by sampling the amplitude shift keying received signal at the same period as the constant period, and sampling a cosine wave at a constant synchronization. A second multiplication unit that multiplies each coefficient value of the obtained set of coefficient values with each other; a first addition unit that calculates a sum of multiplication results corresponding to each sampling of the first multiplication unit; A second adder that obtains the sum of the multiplication results corresponding to each sampling of the multiplier, a first square calculator that squares the output of the first adder, and an output of the second adder. A second square calculation unit that squares, an addition unit that adds the output of the first square calculation unit and the output of the second square calculation unit, and a square root that calculates the square root of the output of the addition unit A demodulation system for an amplitude shift keying signal according to claim 1, characterized in that the demodulation system comprises an arithmetic unit. 3. The information code reproducing means compares the output of the successive correlation calculating means with a predetermined threshold value, and reproduces the original information code depending on whether it is larger or smaller than the threshold value. A demodulation system for an amplitude shift keying signal according to claim 1, further comprising a value comparison section. 4. The information code reproducing means differentiates the output of the successive correlation calculating means into a ternary signal of +1, −1, 0, and +1 of the output of the differential calculating portion. And a code conversion unit for reproducing the information code of the original mark (1) and space (0) by leaving the mark (1) and -1 as space (0) and 0 as they are. The demodulation method of the amplitude shift keying signal according to claim 1.