RU2204885C2 - Noise-like signal retriever - Google Patents

Abstract

FIELD: radio navigation, radar, and digital data transfer systems. SUBSTANCE: device that may be used, for example, in digital data transfer systems using noise-like signals basing on pseudorandom phase (O, π) modulated sequences and may be found useful for reducing signal retrieval time in the course of putting in synchronism provides for reducing look-up time of desired area to retrieve frequency and time parameters of signal. It has signal delay meter incorporating detector, two multipliers, two reset integrators, harmonic- wave oscillator, divider, and computing device implementing y=atn(x) function. Signal delay meter functions to measure incoming signal delay to eliminate signal delay retrieval area from total area of frequency and time parameters which makes it possible to reduce look-up time of entire retrieval area by M_r times (by base times). EFFECT: reduced retrieval time. 1 cl, 2 dwg

Description

 The invention relates to the field of radio navigation, radar and discrete information transmission systems using noise-like signals based on pseudorandom sequences with phase (0, π) modulation, and can be used to reduce the search time of a signal during synchronization.

 The closest in technical features to this device is a receiver [1, p.12], which contains a servo synchronization system 1, a signal copy generator 2, a search system 3, a capture indicator 4 and a control device 5, shown in figure 1.

где А - амплитуда принимаемого сигнала;
ω_н, φ_0н - несущая частота и ее начальная фаза;
ω_τ, φ_0T - тактовая частота и ее начальная фаза;
Т - длительность сигнала;
τ_з - запаздывание сигнала;
N - количество элементов ПСП на периоде сигнала;
k(n) - код ПСП;
n₀ - начальное состояние ПСП (регистров сдвига генератора ПСП).The disadvantage of the prototype is that a necessary condition for normal operation is a strict coordination of the time-frequency parameters and modulation laws of local reference and received signals. Such coordination is provided by the tracking synchronization system. It includes a tracking system for frequency parameters (PLL - phase-locked loop) and time parameters (CVD - tracking scheme for signal delay). However, the transition to the tracking mode occurs under the condition that the time-frequency parameters of the signal fall into the capture region of the tracking systems. Noise-like signals based on pseudo-random sequences (PSP) with phase modulation (0, π) can be written as

where A is the amplitude of the received signal;
ω _n , φ _0n - carrier frequency and its initial phase;
ω _τ , φ _0T is the clock frequency and its initial phase;
T is the signal duration;
τ _s - the delay of the signal;
N is the number of memory bandwidth elements in the signal period;
k (n) is the SRP code;
n ₀ is the initial state of the SRP (shift registers of the SRP generator).

В корреляционном приемнике разрешающая способность по оцениваемым параметрам определяется интервалом корреляции по этим же параметрам. Тогда с учетом дискретизации область поиска может быть представлена в виде

,
где Δω - диапазон возможных значений несущей частоты;
r_ω - интервал корреляции сигнала по частоте.For unknown reasons, the unknown parameters at the receiving point are the carrier frequency ω _n and the signal delay τ _s , which are set by the ranges of admissible values Δω and Δτ to organize their search. The search signal is as follows. By command from the control system 5 in the reference signal generator 2, signal copies are generated by successive discrete shifts of the next signal copies by a value proportional to the resolution of the tracking system according to the estimated parameters

In the correlation receiver, the resolution of the estimated parameters is determined by the correlation interval for the same parameters. Then, taking into account discretization, the search area can be represented as

,
where Δω is the range of possible values of the carrier frequency;
r _ω is the frequency correlation interval of the signal.

The correlation receiver described in the prototype performs a search by spending time T _a , usually equal to T _s , of the signal duration, for the analysis time of each search point. The viewing time of the entire search area will be equal to T _n = M • T _a .

 The search system 3, on command from the control system 5, organizes the search path or the order of presentation of copies of the signal in the tracking synchronization system 1. The search order is determined by a priori information about the distribution of the values of the desired parameters in the search area. With a uniform distribution of parameters, the search device performs a cyclic search.

In the tracking synchronization system 1, correlation processing of the mixture of the received signal and noise is performed, at which the output voltage of the system is compared with a threshold. If the threshold is not exceeded, the adjustment unit changes the parameters of the reference signal every T _a seconds. If the threshold is exceeded by the output signal of the tracking synchronization system 1 at a certain frequency position of the search region and the delay number of the signal that determines the initial state of the generator shift register of the used pseudo-random sequence, the capture indicator 4 gives a command to capture the signal to the control device 5. In turn, the control system 5 issues a command to the synchronization tracking system 1, to the signal generator 2 and the search device 3 to stop the search and switch to the signal tracking mode.

The average search time T _cp depends on the a priori distribution of the signal parameters in the search areas, the search path and the signal-to-noise ratio at the receiver input. Therefore, T _cp can be shorter than the time of viewing the search area T _n , and much exceed it. So, with a uniform a priori distribution and a S / N ratio> 1 in the absence of signal gaps and false alarms, the average time T _cp = 0.5T _n is half the time it takes to view the entire search area. At lower signal-to-noise ratios, i.e. in the presence of gaps in the signal and false alarms, the average search time T _c >> T _n , i.e. significantly exceeds the viewing time of the entire search area.

 To eliminate the noted drawbacks, a correlation search receiver of the prototype, including a synchronization tracking system 1, a signal copy generator 2, a search system 3, a capture indicator 4 and a control device 5, additionally introduces a signal delay meter.

 Additionally, the introduced device consists of a detector 6, two multipliers 7 and 8, a harmonic oscillation generator 9, a phase shifter π / 2 10, two integrators with a reset 11 and 12, a divider 13, and a computing device 14.

 The proposed technical solution is illustrated in figure 1, which presents a General structural diagram of a device for searching for a noise-like signal.

 The device operates as follows.

An analysis of the amplitude and phase characteristics of the spectra of the used pseudo-random sequences shows that the spectrum includes N harmonic components that are multiples of Ω = 2π / T. The calculations show that the initial phase of the 1st harmonic (n = 1) is linearly related to the initial state of the shift register of the SRP generator and, therefore, to the signal delay. The graph (Fig. 2) shows the dependence of the initial phase of the 1st harmonic φ ₀ on the initial state of the SRP generator, consisting of n ₀ symbols, which are formed by shifting n ₀ symbols of the periodic SRP by one clock cycle.

где с_1g и φ_1g - амплитуда и начальная фаза первой гармоники.In the received signal, the spectrum of the video sequence is transferred to the high-frequency region at the carrier frequency ω _n . To calculate the initial phase of the first harmonic of the received signal, its spectrum must be transferred to the low-frequency region, for example, using a linear or quadratic detector. The first harmonic phase for a quadratic detector is calculated using the Fourier transform according to the algorithm

where with _1g and φ _1g is the amplitude and initial phase of the first harmonic.

 Since the function atn (*) on the interval [0, 2π] is ambiguous, to eliminate the ambiguity, it is necessary to take into account the signs of the quadrature components.

Then, on the interval [0, 2π], the initial phase can be written
Ф _1g = φ _1g for a _1g > 0, b _1g >0;
Ф _1g = π + φ _1g for a _1g > 0, b _1g <0;
Ф _1g = π + φ _1g for a _1g <0, b _1g <0;
Ф _1g = 2π-φ _1g for a _1g <0, b _1g > 0.

Фаза первой гармоники с каждым тактом запаздывания изменяется на величину Δφ = 2π/N. Поэтому первоначально измеряется значение начальной фазы при нулевой задержке сигнала. Тогда текущий искомый номер задержки относительно известного начального состояния регистра сдвига, формирующего ПСП, на передающей стороне будет равен

который показывает на сколько текущих позиций необходимо сдвинуть копию местного генератора псевдослучайной последовательности для вхождения в синхронизм. Поскольку оценки задержки сигнала независимы, то за N испытаний вероятность захвата сигнала будет равна
P_N=1-(1-p₁)^N,
где р₁ - вероятность захвата сигнала при одном испытании.The received signal from the input of the receiver through the detector 6 is fed to the inputs of the multipliers 7 and 8, the other inputs of which are supplied with voltage from the harmonic oscillation generator 9, moreover, it is supplied directly to one input, and to π / 2 through the phase shifter (10). The frequency of the harmonic oscillation generator is chosen equal to Ω = 2π / T - the frequency of the first harmonic of the PSP video spectrum. From the outputs of the multipliers, the signal goes to the inputs of the integrators with a reset 11 and 12, the outputs of which are connected to the first and second inputs of the divider 13. From the output of the divider, the signal goes to the computing device 14, which performs the function y = atn (x). In the proposed device, the lower limit of the integrator with a reset with each clock pulse is shifted by the value of the period of the clock frequency. The upper limit is shifted from the lower one by the value of the signal duration T. Since the correlation interval for the delay in the received signal is equal to the clock frequency, the obtained estimates of the initial phase of the first harmonic of the signal spectrum will be independent, and therefore the associated signal delay estimate

The phase of the first harmonic with each delay cycle changes by Δφ = 2π / N. Therefore, the initial phase value is initially measured at zero signal delay. Then the current sought delay number relative to the known initial state of the shift register forming the SRP at the transmitting side will be equal to

which shows how many current positions it is necessary to shift a copy of the local pseudo-random sequence generator to enter synchronism. Since estimates of the signal delay are independent, for N tests the probability of signal capture will be equal to
P _N = 1- (1-p ₁ ) ^N ,
where p ₁ is the probability of signal capture in one test.

The proposed technical solution is illustrated by the drawings:
Figure 1 presents a structural diagram of a device for searching for a signal.

 In FIG. Figure 2 shows the dependence of the current phase of the first harmonic of the signal spectrum on the delay.

The correlation receiver described as a prototype searches for a signal by a carrier frequency in the region M _ω and a delay in the region M _τ . The input signal is fed to the tracking synchronization system 1 and the search system 3. The search system organizes the order of viewing the specified areas M _ω , M _τ and discretely changes the frequency and time parameters of the reference signal generator 2. If at any moment the values of the frequency parameter region of M _ω and the time parameter from the region M _τ simultaneously enter the capture area of the synchronization system 1 and the capture indicator 4 issues a command to the capture signal, the control apparatus 5 issues a command to terminate Finding and carried tracking signal.

Thus, the viewing time of the entire search area of the frequency M _ω and temporary M _τ parameters is
T _n = M _ω • M _τ • T _a ,
where T _a is the analysis time of one point in the search area.

Usually T _{a is} taken equal to T - signal duration.

Таким образом, в следящую систему синхронизации на каждой тактовой позиции по команде устройства управления на каждой частотной позиции области поиска M_ω подается оценка текущего значения задержки сигнала

Следовательно, в данном случае время просмотра всей заданной области поиска определяется временем просмотра только частотной области поиска и T_n=M_ω•Т_а. Поэтому в предложенном техническом решении время просмотра области поиска уменьшается в M_τ раз. Поскольку M_τ - есть число элементов используемых псевдослучайных последовательностей сложного сигнала, т.е. его база, то M_τ>>1.At the same time, the input signal is supplied to the device for measuring the time parameter - signal delay τ _s . The signal through the detector 6 is fed to the multipliers 7 and 8, the other inputs of which are connected to the harmonic oscillation generator 9 directly and through the phase shifter 10. The results of multiplying the input signal are fed to two integrators with a reset 11 and 12, the outputs of which are connected to the divider 13. The division result is supplied to a computing device that implements the function y = atn (x), the output of which yields an estimate of the signal delay

Thus, in the tracking synchronization system at each clock position, at the command of the control device at each frequency position of the search area M _ω , an estimate of the current value of the signal delay

Therefore, in this case, the viewing time of the entire specified search area is determined by the viewing time of only the frequency search area and T _n = M _ω • T _a . Therefore, in the proposed technical solution, the viewing time of the search area is reduced by M _τ times. Since M _τ is the number of elements of the used pseudo-random sequences of a complex signal, i.e. its base, then M _τ >> 1.

. Это позволяет исключить этап поиска сигнала по запаздыванию, а следовательно, в M_τ раз уменьшить общее время поиска сигнала.A comparative analysis of the proposed technical solution with the prototype showed that the claimed device differs from the prototype by the introduction of a delay meter for received complex signals, which allows to receive a current estimate of the phase of the first harmonic in each clock interval of the signal, and therefore the associated delay estimate

. This makes it possible to exclude the stage of searching for a signal by delay, and therefore, reduce the total signal search time by M _τ times.

Thus, the totality of the introduced devices and their connections allows us to obtain an estimate of the current signal delay, which eliminates the need to search for the signal by delay, and reduce the total search time by M _τ times (where M _τ = N is the number of elements of the signal bandwidth), which was impossible with using a prototype. Therefore, the technical solution meets the criterion of "novelty." In addition, since the required technical result is achieved by the entire set of essential features introduced, which is not found in the well-known patent and scientific literature at the filing date of the application, the invention meets the criterion of "inventive" level.

Sources of information
1. Zhuravlev V.I. Search and synchronization in broadband systems. - M .: Radio and communications, 1986. - 240 p.

 2. AC 330563 (USSR). Synchronization device. Published in BI 8, 1972.

 3. AC 311415 (USSR). A device for the cyclical search for broadband noise-like signals by delay. Publ. in BI 24, 1971.

Claims (1)

 A complex signal search device, consisting of a synchronization tracking system, a signal copy generator, a search system, a capture indicator and a control device, characterized in that the device additionally includes a detector, first and second multipliers, harmonic oscillation generator, π / 2 phase shifter, first and a second integrators with reset, a divider and a computing device that implements the function y = atn (x), and the input of the detector is connected to the input of the device, the output of the detector is connected to the first inputs of the first and second multipliers, the output of harmonic generator of oscillations connected to the second input of the first multiplier and via a phase shifter to π / 2 to the second input of the second multiplier; the output of the first multiplier is connected to the input of the first integrator with a reset, the output of the second multiplier is connected to the input of the second integrator with a reset; the output of the first integrator with a reset is connected to the first input of the divider, the output of the second integrator with a reset is connected to the second input of the divider, the output of the divider is connected to the input of a computing device that implements the function y = atn (x), the output of the computing device is connected to the second input of the control device.

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