RU2781271C1 - Amplitude shift keying demodulator - Google Patents

Abstract

FIELD: radio communications.

SUBSTANCE: invention relates to radio communications and can be used in the demodulation of amplitude shift keying (ASK) signals. The effect is achieved due to a set of essential features in the claimed device, due to which an adaptive change in the decision threshold values ​​occurs based on the results of summing the amplitude values ​​of the signal packages processed on the current and previous cycles, which makes it possible to receive and demodulate ASK signals in channels with fading. Wherein the value of the adaptive decision threshold for the duration of each signal message is determined as a quarter of the result of summing the amplitude of the current and previous pulses of the sequence formed at the reception.

EFFECT: providing the possibility of receiving and demodulating ASK signals in channels with fading.

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Description

The invention relates to radio communications and can be used in the demodulation of amplitude shift keying (AM) signals in fading channels.

Known "Demodulator of AM and CT signals (Patent RU No. 2287217, H03D 5/00, publ. 10.11.2006, Bull. No. 31).

In the well-known demodulator of AM and FT signals, containing eight signal multipliers, two low-frequency filters (LPF), two amplifiers with a gain of Ku = 2, two generators of sinusoidal oscillations, a frequency multiplier by 2, two phase shifters (PV) that shift the initial phases of the signals arriving at their input by 90°, an integrator, a threshold device and three signal adders, the first input of the first signal adder being connected to the output of the first signal multiplier, the first input of which is connected to the first inputs of the second and third signal multipliers and is the input of the device, and the second input is connected to the output of the first generator of sinusoidal oscillations, the first input of the fourth signal multiplier and the input of the first PV, the output of which is connected to the first input of the fifth signal multiplier, the second input of which is connected to the output of the second PV, and the output - to the second input of the third signal multiplier, the output of which is connected to the input of the integrator, the output of which is connected to the input of n the threshold device, the output of which is the output of the information evaluation of the FT signal, the output of the first signal adder is connected to the input of the first low-pass filter, the output of which is connected to the second input of the sixth signal multiplier and the input of the first amplifier with a gain of Ku=2, the output of which is the output of the device, to in which there is an estimate of the amplitude of the AM signal, the first input of the sixth signal multiplier is connected to the output of the second generator of sinusoidal oscillations, to the input of the second FV, the input of the frequency multiplier by 2, the output of which is connected to the first input of the seventh signal multiplier, the second input of which is connected to the output of the second LPF and the input of the second amplifier with a gain of Ku=2, in addition, the first input of the sixth signal multiplier is connected to the first input of the eighth signal multiplier, the second input of which is connected to the output of the second amplifier with a gain of Ku=2, and the output is connected to the second input of the first signal adder, in addition, the first input sixth o of the signal multiplier is connected to the second input of the fourth signal multiplier, the output of which is connected to the second input of the second signal multiplier, the output of which is connected to the first input of the second signal adder, the second input of which is connected to the output of the sixth signal multiplier, and the output is connected to the first input of the third signal adder , the second input of which is connected to the output of the seventh signal multiplier, and the output is connected to the input of the second LPF.

A disadvantage of the known demodulator is the limited scope of its application, since it does not provide an adaptive change in the decision threshold when fading occurs in channels with fading.

Known coherent receiver of binary signals, see signal demodulator with relative phase modulation, see (Ivlev D.N. Digital transmission channels. Teaching aid. / D.N. Ivlev. - Nizhny Novgorod: Nizhny Novgorod State University, 2013. - 53 With, rice. 36, pp. 27-28).

In a well-known coherent receiver of binary signals, the input signal is filtered by a bandpass filter of the receiver in order to suppress part of the noise and interference, the spectrum of which lies outside the reception band. Next, the signal is demodulated through a frequency converter (multiplier) and a low-pass filter that replaces the integrator, and discrimination occurs in a decision circuit, which is a threshold comparison circuit. In this case, the carrier recovery circuit restores the carrier wave, eliminating its modulation by the information signal and thus making it possible to obtain a reference signal with the same frequency and initial phase as that of the received signal (coherent reception). And the clock recovery circuit performs clock (symbol) synchronization, i.e. selects those moments of time at which it is necessary to take samples in the signal at the output of the low-pass filter for submission to the threshold device.

The disadvantage of the known demodulator is the limited scope, since it is not designed to work in channels with fading. In addition, it does not provide for changing the level of the decision threshold.

The closest in its technical essence to the claimed device is the “Relative Phase Modulation Signal Demodulator” (Patent RU No. 2460224, H04L 27/22, publ. 27.08.2012, Bull. No. 24).

The device contains a constant generator that determines the threshold voltage level, a filter, the input of which is the input of the demodulator, and the output is connected to the first signal input of the correlator, the output of the reference signal generator is connected to the second signal input of which, the output of the correlator is connected to the signal input of the gating unit, the clock input of which connected to the second output of the clock pulse generator, the first output of which is connected to the setting input of the correlator, the output of the gating unit is connected to the input of the delay unit for duration T and to the second input of the subtractor, the first input of which is connected to the output of the delay unit for duration T, the output of the subtraction unit connected to the input of the module calculation unit, the output of which is connected to the first signal input of the decision block, the output of which is the output of the demodulator, and the clock input of the decision block is connected to the second output of the clock generator, and the correlator consists of a voltage multiplier the first and second inputs of which are, respectively, the first and second inputs of the correlator, and the integrator, the output and setting input of which are, respectively, the output and setting input of the correlator, and the output of the voltage multiplier is connected to the signal input of the integrator, the decision block consists of a voltage comparator, the first signal the input of which is, respectively, the first signal input of the decision block, the output of the voltage comparator is connected to the first input of the D-flip-flop, the clock input and output of which are respectively the clock input and output of the decision block, a register of L memory elements is additionally introduced into the device, the output of which is connected to the input a counter of single elements in the cells of the register, the output of which is connected to the input of the block for calculating the deviation of the correlation function, the output of which is connected to the second input of the block for correcting the threshold voltage level, to the first input of which the output of the constant generator is connected, the output of the block and correction of the threshold voltage level is connected to the second signal input of the decision block, which is the second signal input of its voltage comparator, and the register input of L memory elements is connected to the output of the decision block.

The disadvantage of the device is the limited scope, since it is only designed to receive digital signals with relative phase modulation. And it does not provide the possibility of receiving and demodulating AM signals in fading channels.

The objective of the invention is to create a method that makes it possible to adaptively change the value of the decision threshold based on the results of summing the amplitude values of the signal packages processed on the current and previous cycles.

EFFECT: reduced demodulation errors of AM signals in fading channels.

The claimed technical result is achieved by the fact that the amplitude signal demodulator manipulations containing a filter connected in series, a voltage multiplier and an integrator, as well as a delay unit for duration T, a voltage comparator and a reference signal generator, the output of which is connected to the second input of the voltage multiplier, and the filter input is the input of the device. by four, the output of the integrator is connected respectively to the first inputs of the voltage comparator, the adder and the delay unit for a duration of 5, the output of which is connected to the second input of the adder, the output of the voltage divider by four is connected to the second input of the voltage comparator, the output of which is the output of the device.

Thanks to a new set of essential features in the claimed device, an adaptive change in the value of the decision threshold occurs based on the results of summing the amplitude values of the signal packages processed on the current and previous cycles, which makes it possible to receive and demodulate AM signals in channels with fading.

The claimed invention is illustrated by drawings, where

in fig. 1 is a block diagram of an AM signal demodulator:

in fig. 2 - a fragment of the demodulated sequence of the AM signal that passed through the channel with fading, and the applied values of the decision thresholds G0 and G1, where G0 is the decision threshold, which has a constant value equal to E / 2 (E is the average value of the amplitude of the pulses corresponding to the information value " 1" in the channel without fading, obtained on the basis of the results of the demodulator during previous sessions); G1 - decision threshold, the value of which is calculated from the results of summing the amplitude values of the signal packages processed on the current and previous cycles.

And the following notation has been introduced:

1 - filter;

2 - voltage multiplier;

3 - integrator;

4 - reference signal generator;

5 - delay block for duration T, where T is the duration of the signal message;

6 - adder;

7 - voltage comparator;

8 - voltage divider by four.

The claimed device consists of a filter 1 connected in series, a voltage multiplier 2 and an integrator 3, as well as a reference signal generator 4, the output of which is connected to the second input of the voltage multiplier 2, the output of the integrator 3 is connected respectively to the input of the delay block for a duration T 5, the first input of the adder 6 and to the first input of the voltage comparator 7, the output of which is the output of the device, the output of the delay block for duration T 5 is connected to the second input of the adder 6, the output of which is connected to the input of a voltage divider by four 8, the output of which is connected to the second input of the voltage comparator 7.

The blocks included in the general scheme of the device have the following purpose.

Filter 1 is designed to filter the received AM signal.

A similar filter can be used as filter 1, see (Patent RU No. 2460225, H04L 27/22, publ. 27.08.2012 Bull. No. 24).

The voltage multiplier 2 is designed to calculate the correlation function by multiplying the received AM signal and the reference signal.

As a voltage multiplier 2, you can use a similar multiplier, see (Patent RU No. 2549360, H03D 3/00, publ. 27.04.2015 Bull. No. 12).

The integrator 3 is designed to form a pulse sequence of signal messages from the calculated correlation function.

As integrator 3, you can use a similar integrator (see Patent RU No. 2549360, H03D 3/00, publ. No. 17).

The reference signal generator 4 is designed to generate a reference harmonic signal corresponding to the structure of the harmonic signal used in the transmitter to generate the AM signal.

As the reference signal generator 4, you can use a similar master oscillator (see Patent RU No. 2439819, H04L 7/02, publ. 10.01.2012 Bull. No. 1).

The delay block for the duration T 5 is designed to delay the signal for the duration of the signal package equal to the time T.

As a delay block for duration T 5, you can use a similar block (see Patent RU No. 2460224, H04L 27/22, publ. 27.08.2012 Bull. No. 24).

The adder 6 is intended for summing the amplitude values of the current signal package, which comes from the output of the integrator 4, and the previous signal package, which comes from the delay block for duration T.

A similar block can be used as adder 6 (see Patent RU No. 2486681, H04L 7/00, publ. 27.06.2013 Bull. No. 18).

As a voltage comparator 7 can be used a similar unit from the composition of the device described in the prototype method (see Patent RU No. 2460224, H04L 27/22, publ. 27.08.2012 Bull. No. 24). The operation of threshold devices is discussed in detail in (Patent RU No. 2382495, H04B 1/10, publ. 20.02.2010 Bull. No. 5).

The voltage comparator 7 is designed to set the required value of the threshold level under the action of the voltage from the block 7, and make a decision about the demodulated symbol.

The voltage divider by four 8 is designed to reduce the voltage value entering its input by four times.

A voltage divider by four 8 can be implemented either on a 174PS1 chip, see the Handbook of the developer and designer of REA. Element base. Book 1. - M., 1993. Comp. Maslennikov M.Yu., Sobolev E.A. and others, in accordance with (Patent RU No. 2549360, H03D 3/00, publ. 27.04.2015 Bull. No. 12), or see (Patent RU No. 2382495, H04B 1/10, publ. 20.02.2010, Bull. No. 5).

The claimed device works as follows.

The signal S1(t) incoming over the communication channel is fed to the input of filter 1, which is the input of the demodulator. Filter 1 attenuates frequency components that are outside the frequency band of the demodulated signal.

At the output of filter 1, a filtered signal Z(t) is obtained, which is fed to the first input of the voltage multiplier 2, to the second input of which a reference signal with a constant amplitude S0(t) is supplied from the reference signal generator 4, which is similar in structure to the signal used on the transmitting side to generate an AM signal. The difference between the signal S1(t) and S0(t) will be due to the influence of additive noise and fading in the communication channel.

At the output of the voltage multiplier 2, the resulting signal Y(t) is obtained, which is fed to the input of the integrator 3, at the output of which a low-frequency pulse sequence U(t) is formed.

In the presence of fading in the communication channel, the amplitude of the signal S1(t) at different times will be different. Moreover, the value of the amplitude will be determined by the nature of the fading. Consequently, the amplitude of the pulses of the sequence U(t) obtained after the integrator 4 will also be different.

As an example, in FIG. 2 shows the pulses of the sequence U(t) with different amplitudes.

From the output of the integrator 3, the pulses of the sequence U(t) are simultaneously fed to the first input of the voltage comparator 7, to the input of the adder 6 and to the input of the delay unit for duration T 5.

In the delay block for duration T 5, the pulse is delayed for a duration equal to the duration of the signal message, i.e. for the duration of the pulse. As a result, at the moment when the next pulse of the sequence U(t) arrives at the first input of the adder 6, the pulse of the previous signal message of the same sequence U(t) arrives at the second input of the adder 6.

Thus, at the output of the adder 6, a pulse sequence C(t) is formed, each pulse of which is equal to the sum of the current and previous pulse of the sequence U(t).

From the output of the adder 6, the pulse sequence C(t) is fed to the input of a voltage divider by four 8, at the output of which a pulse sequence X(t) is formed, the amplitude of the pulses of which is 4 times less than the amplitude of the pulses C(t).

And further, the pulse sequence X(t) is fed to the second input of the voltage comparator 7, where the threshold comparison of the pulses of the sequence U(t) arriving at the first input of the voltage comparator 7 takes place with the threshold values determined by the pulses of the sequence X(t). As an example, in FIG. 2, the designation "1" is introduced for pulses that exceeded the threshold value and "0" for pulses that did not exceed the threshold value.

According to the results of pairwise comparison, at the duration of each signal message at the third output of the voltage comparator 7, which is the output of the demodulator, a decision is made on the correspondence of the received pulse to the information value "1" or "0".

As an example, Fig. 2 shows a fragment of the pulses of the sequence U(t) with different amplitudes and the set values of the decision thresholds G0 and G1. Here, G0 is formed from the results of averaging the value of the amplitude of the pulses corresponding to the information value "1" in the channel without fading (see the description of Fig. 2). And G1 - is formed from the pulses of the X(t) sequence.

Pulses of the sequence U(t) exceeding the decision threshold correspond to the information value "1", and not exceeding - to the information value "0" (indicated in Fig. 2).

Compared with the prototype, it is obvious that the choice of a constant value of the decision threshold G0 does not provide the possibility of demodulating AM signals received in fading channels, since erroneous decisions are possible. And the application of the decision threshold G1 provides, which indicates the achievement of the claimed technical result.

Claims (1)

An amplitude manipulation signal demodulator containing a filter, a voltage multiplier and an integrator connected in series, as well as a delay unit for duration T, a voltage comparator and a reference signal generator, the output of which is connected to the second input of the voltage multiplier, and the filter input is the input of the device, characterized in that the device is additionally connected in series with an adder and a voltage divider by four, the output of the integrator is connected respectively to the first inputs of the voltage comparator, the adder and the duration delay unit, the output of which is connected to the second input of the adder, the output of the voltage divider by four is connected to the second input of the voltage comparator, whose output is the output of the device.

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