RU2383914C1 - Method of synchronising watches and device for realising said method - Google Patents

Abstract

FIELD: physics; communication.

SUBSTANCE: invention relates to communication engineering and radar and can be used for collating time scales spaced far apart. The result is achieved due to that, the device which realises the method of synchronising watches has a time and frequency standard, first and second heterodynes, a unit of heterodynes, a pseudonoise generator, a switch, power amplifiers, a duplexer 8, a transceiving antenna 9, first and second clippers, first and second memory elements, a correlator, an adjustable delay unit, a multiplier, a low-pass filter, an optimising peak-holding controller and a microprocessor.

EFFECT: more accurate measurement of differential time offset between probing and relayed noise-like signals through automatic tracking of movement of the extremum of the correlation function of the said signals along the abscissa axis.

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Description

The proposed method and device relate to communication and radar techniques and can be used to compare time scales spaced over long distances.

There is a known method and device for clock synchronization (autosw. USSR No. 970300, 118083, 1244632, 1278800; RF patents No. 2001423, 2003157, 2040035, 2177167, 2301437; BC Gubanov, AM Finkelshtein, P. A. Fridman. Introduction to radio astronomy. - M., 1983; and others).

Of the known methods and devices closest to the proposed are the "Method of clock synchronization" (RF patent No. 2003157, G04C 11/02, 1991) and the "Clock synchronization device" (RF patent No. 2001423, G04C 11/02, 1992), which selected as prototypes.

The aforementioned method and device provide a comparison of time scales spaced over a long distance, and are based on the use of the duplex communication method through a geostationary satellite repeater and correlation processing of noise-like signals.

The main advantage of the duplex communication method is that it eliminates the length of the signal path. Therefore, its accuracy mainly depends on the parameters of the onboard transponder, the type of signal used, and the technique for measuring time intervals.

To measure time intervals, correlation processing of noise-like signals is used, which have several advantages, one of which is a good property of the correlation function R (τ) of these signals: it has a relatively high level of the central lobe and a low level of side lobes.

It should be noted that the satellite repeater placed in a geostationary orbit, under the influence of various destabilizing factors, makes certain movements relative to the assumed stable position. Therefore, the correlation processing of noise-like signals should be carried out using the correlation extremal system.

In the indicated system for calculating the correlation function R (τ) between the probing and relayed noise-like signals, the movement of its extremum along the abscissa is monitored. The tracking process is carried out using a searchless system of extreme regulation. The extremum position of the correlation function R (τ) on the abscissa axis can be determined with high accuracy.

An object of the invention is to increase the accuracy of measuring the relative time shift between the probing and relayed noise-like signals by automatically tracking the movement of the extremum of the correlation function of these signals along the abscissa.

The problem is solved in that the clock synchronization method, based, according to the closest analogue, on the simultaneous reception of noise-like microwave signals from an artificial Earth satellite by spaced ground points, coherently converting them to a video frequency, digitally recording the received signals and determining the time delay of one of the same signal to synchronization points by the method of correlation processing of registered signals, the magnitude of which compares time scales, while at initial time t ₁ to the clock of the first item using the code sequences form a noise-like microwave signal is recorded it at the same point, the conditioned signal is converted to a frequency f _1, increase its power emit the amplified signal toward the artificial satellite - repeater in the same time point t _1, the clock of the second item with the same code sequence form the same noise-like microwave signal, it is recorded in the second paragraph, taking onboard equipment retro-hIS slyatora signal at frequency f _1, re-emit it at first and second points at the frequency f ₂ while preserving phase relationships, at an arbitrary time t ₃ by the clock of the second paragraph similarly formed and recorded noise-like microwave signal generated signal is converted to a frequency f ₁ strengthen in terms of power, an amplified signal is emitted in the direction of the same satellite repeater, at the same time t _3, according to the clock of the first point, using the same code sequence they generate the same noise-like microwave signal, register it on the first In the first paragraph, the signal at the frequency f _{1 is} received by the onboard equipment of the satellite repeater and re-emitted to the first and second points at the frequency f ₂ while maintaining the phase relations, differs from the closest analogue in that the registered probe signal is passed through an adjustable delay unit, multiplied by a registered relay signal, a low-frequency voltage is isolated, thereby forming a correlation function R (τ), where τ is the current time delay, by varying the delay τ, the correlation function R (τ) at the maximum level, fix the time delay τ _i (i = 1, 2, 3, 4) between two pairs of registered probing and relay signals, the value of which is used to compare time scales.

The problem is solved in that the clock synchronization device, containing, in accordance with the closest analogue, an AES repeater, first and second ground stations, each of which contains a time and frequency standard connected in series, a first local oscillator, a first mixer, the second input of which is through a switch connected to the first output of the pseudo-random signal generator, the first intermediate frequency amplifier, the first power amplifier, duplexer, the input-output of which is connected to the transmit-receive antenna, the second amplifier power, a second mixer, the second input of which is connected through the second local oscillator to the first output of the time and frequency standard, the second intermediate frequency amplifier, the second clipper, the second input of which is connected to the third output of the time and frequency standard, the second memory unit and the correlator, while the first output of the pseudo-random signal generator is connected in series with the first clipper, the second input of which is connected to the second output of the time and frequency standard, and the first memory block, the output of which is connected to the second input of the correl Ora, differs from the closest analogue in that the correlator is made in series with the output of the first memory block of the adjustable delay unit, a multiplier, the second input of which is connected to the output of the second memory block, a low-pass filter and an extreme controller, the output of which is connected to the second input of the adjustable block delays, to the second output of which a microprocessor is connected.

The geometric arrangement of ground points A and B and the satellite A relay S is shown in figure 1, where the following notation is introduced: O is the center of mass of the Earth; d is the base of the interferometer; r is the radius vector of the satellite.

The timing diagram of the duplex clock comparison method is shown in FIG. 2, where the following notation is introduced: S, A, B — time scales of the satellite repeater and points A and B, respectively.

Clock synchronization by the proposed method is as follows:

по часам первого пункта A с помощью кодовой последовательности формируют шумовой СВЧ-сигнал (сигнал α₁);at time

by the clock of the first point A using a code sequence form a noise microwave signal (signal α ₁ );

register it at the same point;

the generated signal is converted at a frequency f ₁ ;

reinforce it in power;

emit an amplified signal in the direction of the satellite repeater;

по часам второго пункта B с помощью той же кодовой последовательности формируют такой же шумовой СВЧ-сигнал (сигнал β₁);at the same time

by the clock of the second point B using the same code sequence form the same noise microwave signal (signal β ₁ );

register it at the second point B (signal β ₁ , which, however, is not sent for relay);

receive on-board equipment of the satellite repeater signal at a frequency f ₁ (signal α ₁ );

re-emit it at points A and B at a frequency f ₂ while maintaining phase relationships in the interval t _c ;

receive a relay signal at both points;

convert it to a video frequency;

и

соответственно (сигналы α₂, β₂);register it at time points

and

respectively (signals α ₂ , β ₂ );

по часам второго пункта аналогично формируют и регистрируют шумовой СВЧ-сигнал (сигнал β₃);at any time

according to the clock of the second point, a noise microwave signal (signal β ₃ ) is formed and recorded in a similar manner;

the generated signal is converted at a frequency f ₁ ;

reinforce it in power;

emit an amplified signal in the direction of the same satellite repeater;

по часам первого пункта A с помощью той же кодовой последовательности формируют такой же шумовой СВЧ-сигнал (сигнал α₃);at the same time

by the clock of the first paragraph A using the same code sequence form the same noise microwave signal (signal α ₃ );

register it at the first paragraph A (signal α ₃ , which, however, do not register);

receive on-board equipment of the satellite repeater signal at a frequency f ₁ (signal α ₃ );

and the corresponding interference frequencies F _i (i = l, 2,3,4), which determine the derivatives of these delays:

Where

a _j, b _l (j = 1,2,3) - the propagation time of the signal between the satellite and points A and B, respectively (figure 1);

- задержки сигналов в излучающей аппаратуре обоих пунктов;

- signal delays in the radiating equipment of both points;

- задержки сигналов в приемо-регистрирующей аппаратуре;

- signal delays in the receiving and recording equipment;

Δs - signal delay in the aircraft satellite repeater;

Δt = t _B -t _A is the desired difference in the clock readings in the same

physical moment.

,

, получаем:Assuming a _j and b _j linear functions with derivatives

,

we get:

Where

re-emit it to points A and B at a frequency f ₂ while maintaining phase relationships in the interval t _c ;

receive a relay signal at both points;

convert it to a video frequency;

и

соответственно (сигналы α₄, β₄);register it at time points

and

respectively (signals α ₄ , β ₄ );

Δ _AB ', Δ _AB ”- signal delay in the atmosphere at frequencies f ₁ and f ₂

respectively;

ν - relativistic correction (Sagnac effect);

c is the speed of light;

D - the area of the quadrangle OA'SB ', formed in the equatorial plane by the center of mass of the Earth, the projections of points A and B and the satellite repeater.

The correction γ for the mobility of the satellite repeater in time of a single measurement is most easily reduced to zero by the corresponding choice of the free parameter θ:

which should be calculated at the beginning of measurements by approximate ephemeris data, and then clarified by the results of current measurements. As for the correction δ for hardware delays, it can be found by calibration using the “zero base” method.

The atmospheric correction ε is also taken into account.

Estimation of the error in the measurement of time delays τ _i (i = 1,2,3,4).

The radio interferometric signal-to-noise ratio is

(3)

(3)

And the errors in measuring the time delay τ and interference frequency F have the form

where Δf is the band of received and recorded frequencies of the pseudo-noise signal;

R _c , R _W - signal power and noise at the input of the receiver;

t _c is the coherence interval of the signal when it is relayed.

Then, to obtain the error σ _τ = 0.1 ns, it is necessary that QΔf≥5 · 10 ⁹ . For example, at Δf = 10 MHz we get Q≥500, which is quite achievable even with the use of small-diameter terrestrial transmit-receive antennas.

согласно (4) оказывается достаточным и For Q = 500, Δf = 10 MHz and

according to (4) it turns out to be sufficient and

t _c = 5 · 10 ^-6 s. It is easy to show that such a coherence time is ensured even with the instability of the local oscillator local oscillator σ _f = 2 · 10 ^-6 .

, поэтому для вычисления γ с ошибкой 0,1 нс необходимо F знать с ошибкой σ_F= 3Гц. Тогда, используя формулы (4) и (5), получаем t_C=0,4·10^-3, что требует более высокой стабильности бортового гетеродина 3σ_f≈3·10^-8.As for the error in measuring the interference frequency F, when using an artificial satellite geostationary as a repeater, the following restrictions are usually fulfilled: [Θ] <τ ≈0.3c, [ν] = s [τ] <100

therefore, to calculate γ with an error of 0.1 ns, it is necessary to know F with an error σ _F = 3 Hz. Then, using formulas (4) and (5), we obtain t _C = 0.4 · 10 ^-3 , which requires higher stability of the onboard local oscillator 3σ _f ≈3 · 10 ^-8 .

The structural diagram of the equipment of one of the items (A) that implements the proposed method for clock synchronization is shown in Fig. 3, where the following notation is introduced: 1 - frequency and time standard, 2 - local oscillator unit - first 2.1 and second 2.2 local oscillators, 4 - switch, 5, 13 - mixers, 6, 14 - intermediate frequency amplifiers, 7, 12 - power amplifiers, 8 - duplexer, 9 - transceiver antenna, 10, 15 - clippers, 11, 16 - buffer storage devices, 17 - delay meter and their derivatives, the delay meter 17 comprises an adjustable delay unit 18 nozhitel 19, filter 20 is a lowpass extreme regulator 21 and microprocessor 22.

The principle of operation of the equipment is as follows. In the first step of single measurements, the pseudo-noise signal α ₁ (Fig. 2), created by the generator 3 using the frequency and time standard 1, is converted by the mixer 5 and the intermediate frequency amplifier 6 to the frequency f ₁ , amplified in the power amplifier 7 and radiated through a duplexer 8 and antenna 9 in the direction of the satellite repeater. At the same time, the same signal is clipped in the clock clipper 10 of the same frequency standard 1 and recorded in the buffer memory 11. The registration is synchronized by the frequency standard 1.

,

.The relay signal α ₂ at a frequency f _{2 is} received by the same antenna 9 and, after amplification in the power amplifier 12 and conversions to the video frequency in the mixer 13 and the intermediate frequency amplifier 14, is clipped in the clipper 15 and recorded in the buffer memory 16. The registration is synchronized by the frequency standard 1. In the second step (when transmitting the signal from point B), the switch 4 must be open, and the signal α ₃ from the generator 3 through the clipper 10 enters the same storage device 11. The relay signal α _{4 is} recorded as and α ₂ , to the storage device 16. Then, in the interval between the measurement acts, the pairs of signals α ₁ , α ₂ and α ₃ , α ₄ are subjected to correlation processing in the meter 17, and the delays τ ₂ , τ ₃ and their derivatives are calculated

,

.

The registered probe signal from the output of the memory unit 11 is supplied through the adjustable delay unit 18 to the first input of the multiplier 19, to the second input of which a registered relay signal from the output of the memory unit 16 is supplied. The voltage obtained at the output of the multiplier 19 is passed through a low-pass filter 20, at the output of which a correlation function R (τ) is formed. The extreme controller 21, designed to maintain the maximum value of the correlation function R (τ) and connected to the output of the low-pass filter 20, acts on the control input of the adjustable delay unit 18 and maintains the delay τ introduced by it equal to τ _i (i = 1,2,3, 4), which corresponds to the maximum value of the correlation function R (τ). Measurements of the values of τ _i enter the microprocessor 22, where their derivatives are determined.

In point B, the equipment works in the same way, only the order of steps there is the opposite. To calculate the difference in the clock readings Δt according to formula (2), it is now sufficient to exchange between points obtained by digital data, which can be done using ordinary telephone or telegraph communication channels.

The described operations allow you to:

- achieve extreme measurement accuracy (about ± 0.1 ns) using PCDB technique and relay technique, which is already widely used in practice;

- generate the necessary microwave signals for measurements at ground stations, which makes it possible to gradually increase the accuracy of measurements by optimizing the signal structure and improving the ground-based recording technique without interfering with the onboard satellite equipment;

- increase the efficiency of measurements, i.e. bring the time interval from the beginning of measurements to obtain results up to several tens of seconds (almost to the time of correlation signal processing);

- to avoid the installation of highly stable time keepers and time interval meters onboard the satellite, to limit the on-board equipment only to the system of phase-stable registration of microwave signals.

Thus, the proposed method and device in comparison with the prototypes provide an increase in the accuracy of measuring the relative time shift between the probing and relayed noise-like signals. This is achieved by automatically tracking the movement of the extremum of the correlation function of these signals along the abscissa.

From the point of view of measurement technology, the proposed correlation extreme system is a compensation measuring system, i.e. in it, the measured value (time interval) is compared with some reference value (time delay). The compensation method allows measurement with very high accuracy. The proposed correlation measuring system provides a methodological measurement error equal to fractions of a percent.

Claims (2)

1. A clock synchronization method based on the simultaneous reception of noise-like microwave signals from an artificial Earth satellite by spaced ground stations, their coherent conversion to a video frequency, digital recording of received signals and determining the time delay of the arrival of the same signal to synchronization points by correlation processing of recorded signal, the magnitude of which is made comparison of time scales, with the initial time t ₁ to the first clock item using the code n sequence form a noise-like microwave signal is recorded it at the same point, the conditioned signal is converted to a frequency f ₁ increase its power emit the amplified signal in the direction of the artificial satellite of the Earth - a repeater in the same time point t _1, the clock of the second paragraph with using the same code sequence, the same noise-like microwave signal is generated, recorded at the second point, received on-board equipment of an artificial Earth satellite relay signal at a frequency f ₁ , re-emitted to the first and second points at a frequency f ₂ while maintaining the phase relationships, at an arbitrary time t ₃ according to the clock of the second point, a noise-like microwave signal is generated and recorded in a similar way, the generated signal is converted to frequency f ₁ , amplified by power, emitted amplified signal direction of the same artificial satellite repeater Earth at the same time point t _3, the clock of the first item by using the same code sequence form the same noise-like microwave signal, it is recorded in the first paragraph, the received dissolved onboard equipment artificial satellite repeater signal at frequency f ₁ and re-emit it at first and second points on the f ₂ frequency while preserving phase relationships, characterized in that the registered probe signal passed through the unit adjustable delay, multiply it with a registered repeated signals, isolate the low-frequency voltage, thereby forming a correlation function R (τ), where τ is the current time delay, by varying the delay τ, the correlation function R (τ) is maintained on m ksimalnom level, fixed time delay τ _{i (i} = 1, 2, 3, 4) between two pairs for the probing and registred signals, the magnitude of which is made comparison of time scales. 2. A clock synchronization device comprising an IS3 repeater, first and second ground stations, each of which contains a time and frequency standard connected in series, a first local oscillator, a first mixer, the second input of which is connected via a switch to the first output of the pseudo noise signal generator, and the first intermediate amplifier frequency, the first power amplifier, a duplexer, the input-output of which is connected to the transceiver antenna, the second power amplifier, the second mixer, the second input of which is connected through the second get a oscillator with the first output of the time and frequency standard, a second intermediate frequency amplifier, a second clipper, the second input of which is connected to the third output of the time and frequency standard, a second memory unit and a correlator, while the first clipper, the second input are connected to the second output of the pseudo-noise signal generator which is connected to the second output of the standard time and frequency and the first memory unit, the output of which is connected to the second input of the correlator, characterized in that the correlator is made in the form of series-connected x adjustable block to the output of the first memory block delay, multiplier, a second input coupled to an output of the second memory unit, a lowpass filter and extreme regulator whose output is connected to the second input of the adjustable delay unit, to the second output of which is connected a microprocessor.

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