RU69689U1 - SIGNAL RECEIVING DEVICE EXACTLY FOR SMALL SIGNAL / NOISE RELATIONS - Google Patents

Abstract

The technical solution to the field of radio reception, namely the detection of a radio pulse known precisely against the background of the noise of the receiving device. The technical task to be solved, in a known radio pulse detection device, is precisely to increase the reliability of detection in the field of small signal-to-noise ratios by using additional information features contained in the structure of the additive mixture of signal and narrowband noise, as compared with the prototype. The essence of the utility model is that non-linear signal processing at the output of the optimal filter is performed, which allows you to get a control signal to turn off the deciding device if there is no signal known exactly at the input of the receiver, thereby reducing the likelihood of a false alarm when a low-power signal is received. The technical problem to be solved in the signal receiving device known exactly for small signal-to-noise ratios, containing the optimal linear filter connected to the solving device via an electronic key, the input of the optimal linear filter being the input of the device, and the output of the solving device being the output of the device, achieved by the linear filter is connected to the control input of the electronic key through a series-connected amplitude-phase converter, a narrow-band linear filter, det anector and a comparator, the second input of which is an input for supplying a reference voltage. 1 s.p. f-ly. 7 ill.

Description

The technical solution relates to the field of radio reception, namely to the detection of a radio pulse known precisely against the background of the noise of the receiving device.

It is known that a signal receiving device against a background of “white” noise (V. Kotelnikov. Theory of potential noise immunity. - M. Gosenergoizdat, 1956 [1]). The device consists of an optimal linear filter matched with the signal parameters of a well-known and threshold device.

When a signal is detected that is known precisely against the background of “white” noises, the decider makes a decision on the presence of a signal when the signal level at the output of the optimal linear filter exceeds a certain threshold level, which is selected according to one of the optimality criteria, depending on the type and purpose of the receiving device . (Chistyakov N.I., Sidorov M.V., Melnikov B.C. Radio receivers. - M.: State Publishing House of Literature on Communication and Radio. 1959. - 895 p. [2]).

There are also known ways to reduce the likelihood of a false alarm, which are based on turning off the decisive device at a time when the presence of a signal is unlikely. These methods are widely used in radar, since the arrival time of the reflected pulse is known.

However, in many other cases, when receiving a known signal, it is definitely difficult to decide that the appearance of a useful signal in a given time interval is possible or unlikely.

The closest technical solution adopted as a prototype is (Michatl Harlan G. Detected noise actuated, age noisequieting action dependent, and total noise level adaptive rf receiver squelch system. No. US 3188571, 1965-06-08).

The noise reduction device comprises a radio frequency amplifier, the input of which is the device’s input, a frequency converter in series, an intermediate frequency amplifier, a signal detector, an electronic key, an audio frequency amplifier and a speaker, which is the device’s output, and a local oscillator, the output of which is connected to the second the input of the frequency converter, as well as an automatic gain control system, the input of which is connected to the output of the signal detector, the output of which is connected to the control yuschim inputs radio frequency amplifier and intermediate frequency amplifier, and a serially coupled filter having an input connected to the output signal of the detector, the noise power, the noise detector and the comparator output is connected to the control input of the electronic key.

The main disadvantage of this device, taken as a prototype, is that the decision on the presence or absence of a signal is made by the amplitude of the noise voltage. If at the detector output the signal amplitude is below a certain level, then the information consumer is turned off. Thus, the device prevents the passage of noise to the consumer of information. However, in the case where the signal-to-noise ratio is small 0 <S / N <3, this device will prevent signal detection.

The technical problem of the proposed signal reception device known exactly at small signal-to-noise ratios is

reducing the probability of false alarm when receiving a useful signal known exactly at small signal-to-noise ratios (0 <S / N <3).

The technical problem to be solved in the signal receiving device known exactly for small signal-to-noise ratios, containing the optimal linear filter connected to the solving device via an electronic key, the input of the optimal linear filter being the input of the device, and the output of the solving device being the output of the device, achieved by the linear filter is connected to the control input of the electronic key through a series-connected amplitude-phase converter, a narrow-band linear filter, det anector and a comparator, the second input of which is an input for supplying a reference voltage.

For heterodyne reception, the signal after the converter is fed to an intermediate frequency amplifier, which is usually narrowband. The amplitude-frequency characteristic of the intermediate frequency amplifier when receiving a radio pulse is close to rectangular. This circumstance will be further taken into account when considering the signal spectra.

Since for most radio systems the condition

where ΔF is the passband of the intermediate band amplifier, F _pr is the intermediate frequency of the receiving device. That according to the work (V.I. Tikhonov. Statistical radio engineering. "Soviet Radio". M. 1966 [3]), the noise of the receiving device can be represented in the form

where A (t) and φ (t) are slowly varying functions in comparison with cosω ₀ t, which represent the envelope and random phase of narrow-band fluctuations. We represent the envelope A (t) in the form of expansion in a Fourier series:

since A (t) is a normal random process with zero mean value, there is no zero term in the expansion. With this in mind, the narrow-band process can be represented as

From formula (4) it follows that narrow-band noise in its structure is a beating signal.

Consider the structure of the output process for heterodyne reception, which is a mixture of the useful signal and the receiver's own noise. For definiteness, we assume that the useful signal is a harmonic signal with a constant amplitude U _c and an angular frequency equal to ω ₀ .

The specified output process, taking into account expression (3), can be represented as follows

From the expression it follows (5) that the structure of the additive mixture of signal and noise depends on the level of the harmonic signal. For large values of the amplitude of the harmonic signal S / N> 3, the structure of the mixture of signal and noise is similar to the structure of the amplitude-modulated signal, and for small levels of the harmonic signal 0 <S / N <3, the structure of the mixture

close to the structure of amplitude-modulated oscillations with a partially suppressed carrier.

Thus, the structure of narrow-band noise and a mixture of signal and noise are significantly different, and information on the presence and absence of a signal is available not only in the amplitude spectrum, but also in the structure of the narrow-band process.

Differences in the structures of processes lead to a change in the envelope spectrum as the latter passes through nonlinear circuits.

To solve the question of the possibility of using the found structural differences to increase the noise immunity of the receiving devices, we considered the differences between the signal with the structure of the beat signal (Figure 1) and the amplitude-modulated signal with 100% modulation (Figure 2) with the same envelope.

Figure 1 and Figure 2 presents the timing diagrams of the signals with the structure of the beats (Figure 1) and the structure of the amplitude-modulated signal (Figure 2) with the same envelope.

Figure 3 shows the spectrum of narrow-band noise at the output of a linear filter with a U-shaped amplitude-frequency characteristic.

Figure 4 shows the spectrum of narrow-band noise at the output of the amplitude-phase Converter.

Figure 5 shows a structural diagram of a device for receiving a signal known exactly at small signal-to-noise ratios.

Figure 6 shows the spectrum of narrow-band noise at the output of the narrow-band linear filter 6.

Figure 7 shows the spectrum of narrow-band noise at the output of the amplitude-phase Converter in the presence of a useful signal known exactly.

Figure 1-2 presents time diagrams of signals with the structure of the beats (Figure 1) and the structure of the amplitude-modulated signal (Figure 2) with the same envelope. As can be seen from (Figure 1) the beat signal is different

from the signal with the structure of the AM oscillation (Figure 2) only in that in the beat signal when the envelope reaches the zero level, the phase of the high-frequency component changes by π.

If the phase of the high-frequency component is changed by π in the beat signal when the envelope reaches the zero level, the converted signal will have the structure of an AM oscillation with a carrier. With the same envelope, the spectrum of AM-oscillations is two times wider than the spectrum of the beat signal since it has two symmetrical side bands (Figure 4).

Therefore, the difference in the structure of the signals leads to differences in the width of the envelope spectrum at the output of the nonlinear converter.

Differences in the shape of the spectra at the output of the amplitude-frequency converter in the presence or absence of a useful signal can be used to control the operation of an electronic key that allows you to turn off the solver if the structure of the input mixture corresponds to the beat signal, i.e. the probability of a signal is small.

The block diagram of the device shown in Fig.5. The device consists of an optimal linear filter 1, an electronic key 2, a solver 3 and an electronic key 4 operation control device consisting of an amplitude-phase converter 5, a narrow-band linear filter 6, a detector 7, and a comparator 8. The above blocks are provided with power supply.

The device operates as follows. If there is no useful signal at the input of the receiver, the output of the optimal linear filter 1 contains only narrow-band noises, which, as shown above, have the structure of a beating signal. The amplitude-phase Converter 5 at each achievement of the envelope of narrowband noise

zero level switches the phase of the high-frequency component to π, thereby changing the structure of narrow-band noise.

In this case, the shape of the spectrum at the output of the amplitude-phase converter has a triangular shape with a spectrum width that is twice the passband of the optimal linear filter (Figure 4).

A narrow-band linear filter 6 selects the components of the spectrum lying outside the bandwidth of the optimal linear filter 1 (Fig.6). The extracted components are detected by an amplitude detector 7 and fed to a comparator 8 which compares the received voltage with the reference U _on . In the case when the voltage level from the out-of-band components exceeds the reference voltage, the comparator 8 generates a control signal and by means of an electronic key 2 disconnects the deciding device 3 from the optimal linear filter 1, because the appearance of a useful signal is unlikely. This eliminates the error of making a false decision about the presence of a useful signal.

If there is a useful signal at the input of the receiving device with the structure of AM-oscillation, an additive mixture of the useful signal and narrow-band noise will be present at the output of the optimal filter. In this case, the structure of the mixture of the useful signal and narrowband noise has the structure of an AM oscillation with a partially suppressed carrier (At 0 <S / N <3) or an AM signal with a carrier (At S / N> 3). In this case, the envelope of the mixture does not reach the zero level and phase switching to π does not occur. Thus, the narrow-band process with the output of the optimal linear filter 1 passes through the amplitude-frequency converter 5 without changing the spectrum and energy of the useful signal Fig.7.

The level of out-of-band spectrum components at the output of the narrow-band linear filter 6 is close to zero. In this case, the comparator 8 by means of an electronic key 2 connects the output of the optimal linear filter 1 to the resolver 3.

Since the signal is not detected at those time intervals when the structure of the spectrum at the output of the optimal linear filter allows us to conclude that there is no useful signal, it can be concluded that the proposed receiver with will have higher noise immunity than the linear optimal receiver.

As an optimal linear filter 1, a high-frequency path of the receiving device consistent with the parameters of the received signal can be used.

The block diagram and algorithm of the amplitude-phase converter are given in the appendix to the application.

Thus, the applied method can significantly improve the sensitivity of the receiving device and reduce the likelihood of a false alarm at minimum cost and slight modification of the radio receiver.

The amplitude-phase converter converts the structure of narrow-band noise from the structure of the beat signal to the structure of the amplitude-modulated signal by changing the phase of the high-frequency component by π each time the envelope of narrow-band noise reaches zero.

The block diagram of the amplitude-phase converter in Fig. 1.

The amplitude-phase converter consists of a paraphase cascade, which generates at its outputs antiphase voltages of the same amplitude that are supplied to the output through the first and second electronic switches. Electronic keys work in antiphase. Those. when the second electronic key is on, the first electronic key is off. In this case, the voltage at the converter output is in phase with the input voltage. If the state of the electronic switches changes, then the phase difference between the input and output voltage of the amplitude-phase converter will be 180 °.

To control the operation of electronic keys, a control circuit is used, which includes an amplitude detector, a comparator and a trigger.

The amplitude detector selects the envelope of narrow-band noise and supplies the resulting voltage to one of the inputs of the comparator. The comparator compares the voltage from the output of the amplitude detector with the reference voltage applied to the second input. The voltage supplied to the second input is set near the zero level, and the value is selected so that a positive impulse appears at the output of the comparator every time the envelope of narrowband noise of the zero level is reached.

A positive voltage drop at the output of the comparator is used to control the operation of the trigger, the outputs of which are connected to electronic keys.

Thus, each time the envelope of narrow-band noise of the zero level is reached, a control signal is generated in the control circuit, which changes the state of the trigger and thereby changes the phase of the high-frequency component of the output process by π.

If a mixture of a useful signal and noise is supplied to the input of the amplitude-phase converter, then the structure of the input process will correspond to the structure of the amplitude-modulated signal with a carrier, with a modulation coefficient of less than 100%. In this case, the envelope of the narrow-band process does not reach the zero level and phase switching does not occur. In this case, the amplitude-phase converter operates as a linear element and the spectrum width does not change.

The paraphase cascade can be performed according to any of suitable circuits using a field effect, bipolar transistor, or an operational amplifier. (For example: Scheme 1.29, Lank J. Electronic circuits: A practical guide. Transl. From English. - M.: Mir, 1985. - 343 p., Ill.). The amplitude detector is made according to the scheme of the diode detector (For example: Circuit 2.15, Lank J. Electronic circuits: A practical guide. Translated from English. - M.: Mir, 1985. - 343 p., Ill.). The comparator, trigger and electronic keys are performed on standard microchips for domestic use (For example; K521CA3, K561KP1, K561TM2).

Claims (1)

A signal receiving device known precisely for small signal-to-noise ratios, comprising an optimal linear filter connected to the resolver via an electronic key, the input of the optimal linear filter being the input of the device, and the output of the resolving device being the output of the device, characterized in that the optimal linear filter is connected to the control input of the electronic key through a series-connected amplitude-phase converter, a narrow-band linear filter, a detector and a comparator, the second input d which is the input for supplying the reference voltage.