RU2390101C1 - Demodulator of phase-manipulated signals - Google Patents

Abstract

FIELD: radio engineering. ^ SUBSTANCE: demodulator of phase-manipulated signals comprises phase detector (1), multiplier (2) of phase by two, narrowband filter (3), divider (4) of phase into two, band pass (5), multiplier (6) of phase by four, frequency detector (7), trigger (8) and balance switch (9). ^ EFFECT: expansion of device functional capabilities. ^ 3 dwg

Description

The proposed demodulator relates to radio engineering and can be used in receiving devices for demodulating phase-shift keyed (PSK) signals.

Demodulators of FMN signals are known (ed. Certificate of the USSR No. 786571, 1322498, 1483666, 1536506; RF patents No. 2030750, 2326502; EP patent No. 0521525; patent WO No. 9826545; Sendersky V. A. On noise immunity of quasicoherent detection of signals from phase manipulation Radio engineering, 1973, No. 1; Radio receivers / Edited by A.G. Zyuko, Svyaz Publishing House, 1975, p. 354, Fig. 14.19, and others).

Of the known devices, the closest to the proposed one is a demodulator of phase-shift keyed signals (Radio receivers. Edited by A.G. Zyuko, Svyaz Publishing House, p. 354, Fig. 14.19, a), which was chosen as a prototype.

The reference voltage necessary for demodulating the phase-shifted signals is extracted in the known demodulator directly from the received PSK signal.

However, the phenomenon of “reverse operation” is inherent in the indicated demodulator, which reduces the reliability of isolating the modulating code (function) from the received FMN signal

In addition, the known demodulator provides demodulation of only signals with binary phase shift keying [FMN-2, φ _k (t) = {0, π}].

Among broadband signals with multiple phase shift keying, signals with four-phase shift keying (FMn-4s) are widely used. This is due to the fact that with this type of manipulation it is possible to avoid a phase shift of 180 °, which takes place with binary phase manipulation

_. and four phase phase manipulation

_.

These phase changes modulate the envelope of the signal as it passes through the selective elements. Envelope changes are undesirable, since additional amplification of the signal by nonlinear devices can increase the energy of the sidebands, increase interference in adjacent channels and cause distortion due to the influence of the conversion. AM / FMn.

With four-phase phase manipulation

no change in signal phase by 180 °.

An object of the invention is to expand the functionality of the device by demodulating signals with four-phase phase shift keying and eliminating the phenomenon of "reverse operation."

The problem is solved in that the demodulator of the phase-shifted signals, containing, in accordance with the closest analogue, a phase detector, a phase multiplier for two and a series-connected narrow-band filter and a phase divider for two, differs from the nearest analogue in that it is equipped with a band-pass filter, a phase multiplier four, with a frequency detector, a trigger and a balanced switch, and the output of the phase multiplier by two through a band-pass filter is connected to the first input of the phase detector, the output of which is the output m of the demodulator, the output of the narrow-band filter is connected to the output of the phase multiplier by four, and to the output of the phase divider by two, a frequency detector, a trigger and a balance switch are connected in series, the second input of which is connected to the output of the phase divider by two, and the output is connected to the second input of the phase detector , the inputs of the phase multiplier by two and the phase multiplier by four are combined and are the input of the demodulator.

The structural diagram of the demodulator phase-shifted signals (prototype) is presented in figure 1. The structural diagram of the proposed demodulator phase-shifted signals shown in figure 2. Timing diagrams explaining the principle of operation of the demodulator phase-shifted signals are shown in figure 3.

The phase-shifted signal demodulator (prototype) contains a phase 2 multiplier into two, a narrow-band filter 3, a phase divider 4 into two and a phase detector 1, the output of which is the output of the demodulator, while the second input of the phase detector 1 and the input of the phase 2 multiplier are combined and are the input of the demodulator.

The proposed demodulator phase-shifted signals contains a series-connected multiplier 2 phases into two, a bandpass filter 5 and a phase detector 1, the output of which is the output of the demodulator, series-connected multiplier 6 phases into four, a narrow-band filter 3, a divider 4 phases into two, frequency detector 7, trigger 8 and a balanced switch 9, the second input of which is connected to the output of the phase divider 4 into two, and the output is connected to the second input of the phase detector 1, the inputs of the phase multiplier 2 by two and the phase 6 multiplier by four We are unified and the input of the demodulator PSK signals.

The demodulator phase-shift signals works as follows. The received signal with four-phase phase shift keying (FMN-4s) (Fig.3, b)

U _c (t) = U _c cos [ω _c t + φ _k (t) + φ _c ], 0≤t≤T _c ,

where U _c , ω _c , φ _c , T _c - amplitude, carrier frequency, initial phase and signal duration;

- манипулируемая составляющая фазы, отображающая закон фазовой манипуляции в соответствии с манипулирующим кодом M(t) (фиг.3,а), причем

- the manipulated component of the phase, displaying the law of phase manipulation in accordance with the manipulating code M (t) (figure 3, a), and

φ _k (t) = const for kτ _e <t <(k + 1) τ _e and can change stepwise at t = kτ _e , i.e. at the borders between elementary premises (k = 1,2, ..., N-1);

τ _e , N - the duration and number of chips that make up the signal duration

T _c (T _c = Nτ _e ),

At the same time it enters the inputs of a multiplier of 2 phases into two and a multiplier of 6 phases into four.

At the output of the multiplier 2 phases into two, a signal is generated with binary phase shift keying (Fig. 3, c)

U ₁ (t) = U ₁ cos [ω ₁ t + φ _k1 (t) + φ ₁ ], 0≤t≤T _c

;Where

;

ω ₁ = 2ωc;

φ _k1 (t) = 2φ _k (t) = {0, π, 3π};

φ ₁ = 2φ _c ,

which is allocated by a band-pass filter 5 and fed to the first (information) input of the phase detector 1.

At the output of the multiplier of phase 6 into four, a harmonic voltage is generated (Fig. 3, g)

U ₂ (t) = U ₂ cos [ω ₂ t + φ ₂ ], 0≤t≤T _c ,

;Where

;

ω ₂ = 4ωc;

φ ₂ = 4φ _c ,

which is allocated by a narrow-band filter 3 and fed to the input of the divider 4 phases into two.

Since 4φ _k (t) = {0.2π, 6π}, phase manipulation is already absent in the indicated voltage.

At the output of the divider 4 phases into two, a voltage is formed (Fig. 3, d)

U ₀ (t) = U ₀ · cos [ω ₁ t + φ ₁ ], 0≤t≤T _c ,

wherein ω ₁ = ω _2/2 = 2ω _c;

φ ₁ = φ _2/2 = 2φ _c.

which is used as the reference voltage and through the balance switch 9 is fed to the second (reference) input of the phase detector 1. At the output of the phase detector, a low-frequency voltage is allocated in the direct code (Fig. 3, e)

U _n1 (t) = U _n cosφ _to (t), 0≤t≤T _c ,

or inverse (reverse) code (figure 3, h)

U _n2 (t) = U _n sinφ _k (t), 0≤t≤T _c ,

Where

However, the well-known demodulator phase-shifted signals (figure 1) is inherent in the phenomenon of "reverse operation", which can be of two types.

The first type of "reverse operation" is due to the uncertainty of the initial phase of the reference voltage U ₀ (t), which is extracted directly from the received PSK signal U ₁ (t). With the equally probable value of the variable component of the signal phase, φ ₁ = 0 and φ ¹ ₁ = π, there is no sign that would allow the phase to be “linked”

φ ₁ , the reference voltage U ₀ (t) to one of the phases of the signal. Therefore, the phase of the reference voltage always has two stable states: φ ₁ , (Fig. 3, e) and φ ₂ = φ ₁ + π (Fig. 3, g). This is easy to show analytically.

If you make a division similar to the previous one, but after adding the angle 2π to the argument, which does not change the initial voltage, then after dividing the phase by two, you get the voltage that is phase shifted by π (Fig. 3, g)

.

.

Consequently, the ambiguity of the phase of the obtained reference voltage follows from the fission process itself. The physically indicated two-valued phase is due to the unstable operation of the divider 4 phases into two.

Thus, even having a reference voltage at the receiving point with a constant phase and frequency equal to the frequency of the PSK signal, an analogue of either the original modulating function U _н1 (t) (Fig. 3, e) or the inverse (inverse) modulating function U _H2 (t) (Fig. 3, h) depending on how the PSK signal U ₁ (t) (Fig. 3, c) and the reference voltage (Fig. 3, d, g) are phased.

However, analyzing the analog of the modulating function M (t) (Fig. 3, a) extracted from the received QPSK signal U ₁ (t) (Fig. 3, c) in direct U _н1 (t) (Fig. 3, f) or reverse U _n2 (t) ( _Fig.3 , h) code, it is possible to reliably determine its parameters (the law of phase manipulation, duration τ and the number N of chips).

In this case, it is not important, in the forward or reverse stroke, the analogues of the modulating function are analyzed. It is necessary that the phase of the reference voltage, and therefore the analog of the modulating function, be maintained constant throughout the entire time of reception, demodulation and analysis.

This is precisely the situation that arises in those real reception conditions when there is no a priori information about the parameters of the received FMN-4c signal. Therefore, in the process of coherent reception and synchronous detection of PSK 4c signals, there is no need to disclose the uncertainty of the phase of the reference voltage, which is an internal property of these signals.

Therefore, the first type of “reverse operation” does not reduce the noise immunity of the reception and demodulation of FMN-4c signals and does not affect the reliability of determining their parameters.

The second type of “reverse operation” is due to spasmodic transitions of the phase of the reference voltage from one state φ ₁ to another φ ₁ + π under the influence of noise, short termination of reception, and other factors. These transitions during the reception of the signal occur at random times, for example t1, t2 (figure 3, and). At the same time, at the output of the phase detector 1, a distorted analog of the modulating function U _n3 (t) is _highlighted ( _Fig.3 , k).

This type of "reverse operation" is very harmful in the technique of coherent reception and synchronous detection of FMN-4c signals and makes it impossible to reliably determine the above parameters.

Currently, there are several methods to eliminate the "reverse work" of the second type.

You can apply, for example, special test parcels to confirm the correct installation of the initial phase in the receiver [Petrovich NT, Razmakhnin MK Communication systems with noise-like signals. M .: Sov. radio, 1980 - 440 p.]; you can also use special codes that detect and correct errors caused by "reverse work" of the second type [Khomenyuk Yu.V. On elimination of "reverse work" in a coherent receiver of phase-manipulated signals. Radio Electronics, 1966, No. 6]. However, these methods are associated with the introduction of a certain redundancy into the signal, which reduces the efficiency of using phase manipulation.

The “reverse work” was eliminated in a radical way, when instead of the usual phase manipulation (PSK), N. Petrovich relative phase manipulation (OFMn) was proposed [N. Petrovich Transfer of discrete information in communication channels with phase shift keying. M .: Sov. radio, 1965]. The essence of this method lies in the fact that the reference voltage for each elementary premise is the previous premise. The practical implementation of phase manipulation in OFMn systems complicates the equipment while reducing the noise immunity of the system. The transition from PSK to PSK is associated with an equivalent double increase in channel noise. In addition, the OFMn system for its implementation requires a priori knowledge of the duration τ _e , elementary premises and has a tendency to group errors together, i.e. the appearance of one error entails the appearance of the second.

Consequently, the overall probability of errors increases significantly.

Therefore, the development of methods and devices that ensure the elimination of the phenomenon of "reverse work" of the second type in phase manipulation systems has always been and remains relevant.

The proposed demodulator of phase-shifted signals uses the method of stabilizing the phase of the reference voltage, which is implemented by the frequency detector 7, trigger 8 and the balance switch 9. In this case, the frequency detector 7 provides detection of the moment of occurrence of "reverse operation" of the second type, and trigger 8 and the balance switch 9 eliminate it .

With an abrupt change in the phase of the reference voltage by + 180 ° at time t1 (Fig. 3, i), a short positive pulse appears at the output of the frequency detector 7, and when the phase jumps by -180 ° at time t2 (the phase of the reference voltage signal returns to initial state) - a short negative impulse. Alternating pulses from the output of the frequency detector 7 control the operation of the trigger 8, the output voltage of which, in turn, controls the operation of the balance switch 9.

In a stable state, when the phase of the reference voltage coincides, for example, with the zero phase of the received PSK signal, a negative voltage is generated at the output of trigger 8 and the balance switch 9 is in its initial position, at which the reference voltage from the output of the 4 phase divider into two flows through balanced switch 9 to the reference input of the phase detector 1 without change.

When the phase of the reference voltage jumps by 180 °, due, for example, to the unstable operation of the phase divider 4 into two under the influence of interference, trigger 8 is transferred by a short positive pulse from the output of the frequency detector 7 to another stable state. In this case, the output voltage of trigger 8 at time t1 becomes and remains positive until the next phase jump at time t2, which returns the phase of the reference voltage to its original state.

The positive output voltage of trigger 8 (Fig. 3, m) transfers the balance switch 9 to another stable state, in which the reference voltage from the output of the phase divider 4 to two is applied to the reference input of the phase detector 1 with a phase change of -180 °. This eliminates the instability of the phase of the reference voltage caused by its abrupt change under the influence of interference, and the associated "reverse work" of the second type.

Thus, the proposed demodulator of phase-shift signals in comparison with the prototype and other technical solutions of a similar purpose provides demodulation of signals with four-phase phase shift keying (FMN-4s) and eliminates the phenomenon of "reverse work" of the second type. This is achieved by preliminary transforming the signal with four-phase phase shift keying (Fmn-4s) into a signal with binary phase shift keying (Fmn-2) by multiplying its phase by two and using the method of stabilizing the phase of the reference voltage. Moreover, to implement this method, a frequency detector, a trigger and a balance switch are used. The frequency detector provides detection of the moment of occurrence of the "reverse work" of the second type, and the trigger and the balance switch eliminate it.

Thus, the functionality of the phase-shifted demodulator. signals are expanded.

Claims (1)

A phase-shift signal demodulator comprising a phase detector, a phase multiplier for two and a sequentially connected narrow-band filter and a phase divider for two, characterized in that it is equipped with a band-pass filter, a phase multiplier by four, a frequency detector, a trigger and a balanced switch, and the output of the phase multiplier by two through a band-pass filter is connected to the first input of the phase detector, the output of which is the output of the demodulator, the input of the narrow-band filter is connected to the output of the phase multiplier by four, and to the outputs The frequency detector, trigger and balance switch are connected in series to the phase divider into two, the second input of which is connected to the output of the phase divider by two, and the output is connected to the second input of the phase detector, the inputs of the phase multiplier by two and the phase multiplier by four are combined and are the input of the demodulator .

Images