SU1755388A1 - Device for main frequency restoration - Google Patents

Abstract

Usage: radio engineering, coherent receivers of signals of binary phase shift manipulation. SUMMARY OF THE INVENTION The device contains two phase detectors, two comparators, two keys, an AND element, an OR-NOT element, a phase shifter per l: / 2, an adder, a narrow-band tracking filter made in the form of a PAPI ring, and a phase splitter. An increase in noise immunity under the influence of fluctuating noise is achieved by gating the input mixture with keys, and therefore only those parts of the input mixture on which the signal accumulates more efficiently than noise are passed. 1 Cpfla, 10 Il.

Description

TE., -,

The invention relates to radio engineering and can be used in coherent receivers of binary phase-manipulated (QPSK) signals.

Carrier frequency restoration devices are known that use a phase locked loop (PLL) with a quad, as well as a Costas circuit and Travin circuit.

The effectiveness of such devices drops sharply with decreasing signal-to-noise ratio.

The closest in technical essence to the present invention is a carrier frequency recovery device with a removal of manipulation (remodeling). This device contains the first phase detector (FD), whose input is connected to the multiplier input and is the device input, the output of the first PD is connected to another input of the multiplier, whose output is connected to the PLL circuit, is the output of the device and, in addition, is connected to the reference input of the first device FD.

The PLL circuit contains a second PD connected in series, a loop filter (OP), an adder, a tunable oscillator (PG), a phase shifter (PV), the PD input being the input, and the PV output the output of the PLL, the PG output, and additionally . It is the same to the reference input of the FD, and to the second input of the adder, the supply поиска of the signal search voltage.

As the signal-to-noise ratio decreases at the input, the phase error increases, measured by the rms deviation of the vector of the reference oscillation q (t, &) from the vector of the oscillating signal.

Xi

heard

00

With the greatest error, the areas of the input mixture with the phases near the sign are taken. + / 2.

The presence of noise in the input mixture leads to the appearance of a discrete component of noise in the output signal of the modulator of a discrete component. The phase of this component is equal to the phase of the reference oscillation, and the amplitude is determined by the noise level at the input of the device. The total discrete component at the input of the narrowband tracking filter (UPSF) is equal to the vector sum of the discrete component of the signal (DSS) and the DSB. Both terms have the same frequency and therefore the narrowing of the noise band of the UPSF DSSH circuit cannot be weakened. As the signal-to-noise ratio decreases, the LSS increases and UPSF starts tracking the evenly distributed phase of the noise, which determines the noise immunity limit of the carrier-frequency restoration devices based on the input signal remodeling.

The purpose of the invention is to improve the noise immunity of a carrier recovery device under the influence of fluctuating noise.

The goal is achieved by the fact that a device containing a serially connected PD and a comparator, the signal input of the PD is the input of the device, UPSF, the output of which is the output of the device, the second PD and the second comparator are introduced, the phase shifter ( Ф В) on nil and a phase splitter of a signal (FRS) on + / 4 and - l / 4, two keys and an adder. The signal input of the second PD is connected to the input of the first PD, the outputs of both PD through the corresponding comparators are simultaneously connected with the corresponding inputs of logic elements 2I and 2I-NOT, the outputs of which are connected to the control inputs of the corresponding keys. The outputs of both keys are connected via an adder and connected to the UPSF input. The signal inputs of the keys are connected to the input of the device, and the input of the second key is through a phase shifter per l II. The reference inputs of both PDs are connected to the corresponding FRS outputs: the first PD is connected to the output / 4, the second PD is connected to the output - / 4, the fed input is connected to the UPSF output.

Improving the noise immunity of the proposed device is achieved by gating the input mixture x (t) according to the phase attribute, which allows the synchronism of the recovered carrier to be maintained with the carrier frequency of the received QPSK signal at lower signal-to-interference ratios.

Fig, 1 shows the functional diagram of the proposed device, where indicated: 1.1 and 1.2 - FD, 2.1 and 2.2 - comparators, 3.1.1 - logical element 21/1, 3 2.1 - logical element 2OR-NOT, 3 1.2 and 3.2.2 - keys, 3.2.3 - FS on / 2, 4 - UPSF, 5 - adder, b - FRS on + / 4 and - / 4.

0The proposed device contains PD

1.1 and 1.2, the inputs of which are combined and are the input of the entire device, and the outputs through comparators 2.1 and 2.2 are connected to the corresponding inputs of logic element 2 and 3.1.1 and logic element 2 OR-3.2.1, whose outputs are connected to control inputs of keys 3.1 2 and 3.2.2 respectively. The outputs of the keys 3 1.2 and 3.2.2 are connected via an adder 5 and under0 are connected to the input of UPSF 4, the output of which is the output of the device. The signal input of the key 3.1.2 is connected to the input of the phase shifter on / 2 3.2 3 and is connected to the input of the device and the inputs of FD 1.1 and 1.2. Output

5 phasers per / 2 3.2.3 connected to the key signal input 3.2.2. The reference inputs FD 1.1 and 1.2 are connected to the corresponding 6 FDS, the input of which is connected to the output UPSF 4

0 The proposed device operates as follows.

The mixture of the FMK signal and the interference x (t) S (t) -f + n (t) is fed to the signal inputs of PD 1.1 and 1.2 and the key 3.1 2. To the input of the key 32.2

5, the input mixture enters after inversion by the phase shifter 3.2.3. The control input FD 1.1 receives the reference oscillation qi (t, $) (t, F + / 4), obtained by delaying in the FRS by / 4 wheels of the bath p (t, F) produced by UPSF 4. Similarly, from the second output The fed 6 receives a reference oscillation g2 (t, f) q (t, 6 - / 4) to the control input of the FD 1.2. At the outputs of PD 1.1 and 1.2 voltages fi (t) and ft (t)

five

are positive or negative depending on the value of the angle DF of the deviation of the vector x (t) (Fig.2). Comparators 2.1 and 2.2 quantize the voltages Јi (t) and Ј2 (1), respectively, by two levels (O or 1) and feed ® to logic elements 3.1.1 and 32.1. Under the influence of signals (t) and 1fd2 (t) from the outputs of comparators 2.1 and 2.2, elements 3.1.1 and 3.2.1 produce logical signals Vi (t) and V2 (t). The key 3.1.2 under the influence of the signal V1 - 1 passes the input mixture x (t) to the UPSF only at - / 4 F. + / 4. The key 3.2.2 under the influence of the signal V2 G passes the inverted input mixture y (t) x (t) only at 3/4 l.

five

five . With l: / 4 L F 3 l / 4.3 l: / 4 A F 7 l: / 4 the voltage Vi (t) V2 (t) 0, the keys 3.1.2 and 3.22 open and the signal to the UPSF is stopped, the signal at the output of the adder 5, W (t) contains the DSS 5 UPSF 4, tracks the phase of this component and provides the reference oscillation q (t. &), which is an estimate of the carrier oscillation of the input QPSK signal S (t).

Interference n (t) in the absence of a signal has 10 uniform phase distribution (FIG. 3)

Psh (y) .Vector p (p)

takes in the range - l p l arbitrary positions with equal probability 15 (Fig. 4), therefore the input non-strobing (pure) noise does not contain a discrete component (each value n (corresponds to the same value n (de + l) - n (kn) and the total 20 value of the projections on the axis of the reference oscillation N (p) is zero.

The principle of operation of the proposed device (as well as the prototype device) is based on the formation of a 25 input discrete component mixture by the modulator, which the UPSF monitor monitors. The modulator converts the interval + n phase values of the input mixture x (t) to a value less than +, which leads k on the basis of the total discrete component of the signal and noise in its output signal W (t).

Figure 5 shows a vector diagram explaining the formation of the NSS (N) 35 DSSH when isolating components from the noise with phases limited by the interval (j) (p 1 /). where I ty I p.

In the proposed device, gates of the input mixture are passed (skipped) where the signal accumulates more efficiently than the noise and the remaining sections are blocked (erased).

The reduction in the likelihood of synchronization failure in a phase gated modulator is due to the prevention of a jump in the control voltage in the UPSF with large emissions of the quadrature noise component. Due to a sufficiently large constant time (narrow bandwidth), synchronism is preserved even when blanking a significant part of the mixture.

Consider the issue of the proposed device entering into tracking mode .55

Let, at the initial moment, the phase of the reference oscillation is outside the interval Ј- / 4, π / 4 and for definiteness it is equal to π / 2. Then gates are gated.

the input mixture in the intervals / 4.3 l / 4, 5 l / 4, 7 l / 4 and DSS is zero. Therefore, UPSF starts tracking DSSH, the phase of which varies randomly. Under the action of noise fluctuations, the vector of the reference oscillation p (1, Φ) begins to shift from the position of / 2. The construction regions are also shifted, the DSS increases, the UPSF begins to track the sum of the DSS and DSSH, until the vector q (t, c $) moves to area 0 (or tc during the reverse operation), where the DSS is the maximum.

The recovery of the carrier frequency in a circuit with phase-re-modulated gating is based on the phase estimates of the single elements of the QPSK signal. Correct recognition of single elements increases the output signal-to-noise ratio, reduces phase dispersion and the probability of its jumps. Erroneous decisions lead to a decrease in the signal-to-noise ratio due to the mutual compensation of correctly and incorrectly received signal elements. Since the region of values of the phases l / A, 3 l / 4 and 5 l / 4. 7/4 correspond to solutions with an increased probability of error, they are blocked (Fig. 2).

Systems utilizing input mixture blanking to improve noise immunity are known. Thus, for example, in the phase tracking circuit of a discontinuous signal, if the signal disappears, the useful voltage at the discriminator output due to signal conversion disappears, but the fluctuation voltage remains. In order to eliminate its influence on the formation of the phase evaluation, the following system is opened. Since the compensation of the signal elements in the proposed device is equivalent to its disappearance, the blanking of the corresponding sections of the input mixture also has a positive effect.

Evidence of the achievement of the supplied circuit can be an evaluation of the effectiveness of the proposed device in comparison with the prototype, carried out for the case of a small deviation of the input mixture phase from the phase of the reference oscillation. To do this, we obtain the expression for the phase distribution function of the mixture of the binary QPSK signal and the narrowband Gaussian noise Pc (p) at low signal-to-noise ratios:

Pcm (p) (1P) + P1 (0n-).

where Pi () is the phase distribution function of a mixture of a sinusoidal signal with zero initial phase and Gaussian noise;

The P (# HI) is the phase distribution function of the mixture of a sinusoidal signal with an initial phase and Gaussian noise.

The function of the phase distribution of the mixture of a sinusoidal signal with an initial phase (i) 0 and Gaussian noise at signal-to-noise ratios "1" is determined by the expression:

Rem (C) 1+ cos (-fo) +

o2

cos 2 (f - po);

Rem (P) "5 + cozy),

4l- o2 - in l,

Figures 6 and 7 show a graph of the function Pcm (p) in Cartesian coordinates and in polar, respectively.

The proposed device gates the input mixture x (t) in phase within - / 4/4 and 3/4 5/4, while the prototype device - within - l / 2 p l / 2 and / 2 p 3/2 (Fig 2) We will show that the proposed device is more efficient than the prototype device and that the choice of gating intervals is / 4, / 4 J and

{3/4, 5/4 is optimal

To do this, suppose that the gating is performed in an arbitrary interval of 2 - ij) p ip and (- chr) p (l + C) In the proposed device, for this, it is necessary to set a delay in the FRS by # and - V (2 -). from the part of the mixture, the phase of which is enclosed in the interval - ty.ij) (Fig.7) A (ip), is proportional to

V value / P cm (p) cos (f d p

-V

Indeed, the amplitude of the discrete component is equal to the average value of the total projection of the mixture vector in a given phase interval on the axis of the reference oscillation. The angular distribution density of the average values of the modulus of the vector W (t) is determined by the phase distribution function

402 - l p l where a is the amplitude of the sinusoid;

o2 is the noise dispersion. Thus, for a mixture of a binary QFN signal and Gaussian noise with signal-to-noise ratios 1, the phase distribution function is defined by the expression 1. but

F I U) input mixture: / 0cr (p) p% P (p). Where / 9 ° Cp does not depend on p.

Consequently, the average projection A () of the vector W (t) on the q (t, cb) axis is equal to

ten

VФ

A lvhj pcpMcoscpdcj p ° J P (q).

- /, ./.I

-v

-v

From where

h

.r JP (cflcosCfJcf

Wed:

h

or

A (V) - / P () costf dtf

V

Similarly, the discrete component in the interval -C). + VI is equal to + V

A (V) / pcm (cp) costf d (/

-

Wherein

AZD -A (V) Figures 8 and 9 show vector diagrams explaining the formation of discrete components A () and A () at the output of the modulator by gating the input mixture x (t} in the interval + (relative to O and, respectively) and component Ax .V) of the output mixture W (t). obtained by adding A (j)) and inverted A (),

The total discrete component for both phase gating intervals, taking into account the inversion of the input mixture in the phase shifter 3.2.3, is equal to

V4

45 AM (cos2 (p) costf

ei "

(|) + (co5 (, 5iW (p),

j

The term N (ip) - sin if) does not depend on

signal is the jyou. The term S ($

o2

 (Cos -sfn 2 V + sin V-) is

S cr

DSS. A study on the extremum of expression for S (V) shows that the BCS has a maximum at ch / 4 (Fig. 10);

max S (VO S (n / 4). t / Evil2

DSSH at - mc / A is equal to

M (/ 4) 4Dl device prototype pp / 1 DSS and DSSH, respectively, are:

8 (/ 2) -

Evil: o2

1ST

(/ 2) Ј- Thus, for the proposed device as compared with the prototype, the gain in the signal-to-noise ratio is V2 due to the increase in the DSS and / 2 - due to the decrease in the JSS (which cannot be attenuated by narrowing the noise band UPSF 4, so how the frequencies of DSS and DSSH are the same),

Claims (2)

1. A carrier frequency restoration device containing a series-connected narrowband tracking filter, a signal phase splitter of + / 4 and - p / 4, a first phase detector and a first comparator, connected in series a second phase detector and a second comparator, connected in series, the first Dual-channel remodeling l o0 with st0o & //) ozza / pa in phase-shifting lriziak 0 five 0 five 0 multiplier and adder, as well as a phase shifter connected in series by / 2 and a second multiplier, the second input of the adder connected to the output of the second multiplier, and the output of the adder to the input of the narrowband tracking filter, the second input of the second phase detector connected to the second output of the splitter by + p / 4 and - / 4, and the input of the first multiplier, the phase shifter by w / 2 and the first inputs of the first and second phase detectors are the input of the device, in order to increase the noise immunity of and the influence of fluctuating noise, the element AND and the element OR NONE are entered into it, and the first and second multipliers are made in the form of keys, the output of the element AND connected to the control input of the first key, the output of the element OR NOT with the control input of the second key the first inputs of the AND and OR-NOT elements are connected to the output of the first comparator, and their second inputs to the output of the second comparator, 2. Pop-up device 1, characterized in that the narrow-band servo filter is made in the form of a phase locked loop consisting of ring-connected phase detector, loop filter and adjustable oscillator, the second input of the phase detector being the device input and the output of the adjustable generator is its output. ulf ( -t- ti (t) 0. (t) .tr, W) t himYu.o, hlyu 0; Ukk) I The input of x (t) is inverted and enters nl UPSF 1, 2 - areas of values phases corresponding to increased likelihood mistakes % AFЈ P Јj (t) 0, xtti (t) j; n ft} ъ t2 (t) Q, Xd2 (t) 0: (t) Oa The input x (t) does not go to the NSF Jf l / l 5 $ -, 4 $ n (t) .tr, W) t0 0; UCK) I cx x (t) the inver comes in t 4 L t, tt) 7a, & tj (t) ity r Јg№70 xpug, Entry mixture K (t) no steps # a UDSF -4 SL SL 00 00 00 l Ohno % 2 (f) 2 (f ъ l, (t) 0, $ dl (Us v M Q tz (t) r0, Xrt (t) G, V2 (t) 0 Input mixture x (t) fie goes to UPSF FIG. 2 - well P (i + i) FIG. four / X V 5 / cm 112 W about Fig.Z tf tp (%) H (V) 0 $ () N (V) 0 q. (T, 0) W & I h W ///// WJ  f - I J Q four Sh $$ Ш ..  : .-: ..-.% . ; -J was eating 01 CJ 00 00  C W //////// fa $ (t, 0 + ff / 2) (t, $)  Mt and Fig.8 , Ф + V / 2 7 (tt Ф) V A W A fftj) 2jak / t (9), L J (w 7 (t, f) y- v FIG. 9