RU2420005C1 - Method to search for noise-like signals with minimum frequency manipulation - Google Patents

Abstract

FIELD: information technologies. ^ SUBSTANCE: at each cycle of searching, counts of quadrature components of an input noise-like signal are accumulated at clock intervals, memorised, 4N counts of quadrature components of the input noise-like signal Z1k and z2k are generated. The sign double-stage approximation of the quadrature reference video signals Ik and Qk shape is carried out, results of quadrature components z1k and Z2k multiplication are combined in pairs with counts of approximated quadrature reference video signals Ik and Qk, 2N counts of quadrature components of mutual correlation function are calculated. N values of this function module are separated, the value of the code sequence element delay is identified to set synchronism of a code generator with the received signal. ^ EFFECT: reduction of time required to search for noise-like signals at high noise-immunity of reception. ^ 2 dwg

Description

The invention relates to the field of radio engineering and can be used in radio navigation and radio communication systems for code synchronization of receivers of noise-like signals with minimal frequency manipulation.

A known method for the parallel search for noise-like signals by the delay time [Radio systems / Yu.P. Grishin, V.P. Ipatov, Yu.M. Kazarinov and others; under the editorship of Yu.M. Kazarinova. - M .: higher. шк., 1990, p.64 (Fig.3.16), p.99 (Fig.4.6)], which consists in multiplying the received signal with N pairs of reference noise-like signals, which are quadrature copies of the received signal for N discrete values of the delay time, integrating the results multiplying in 2N quadrature channels on an interval equal to the duration of a noise-like signal, extracting N values of the cross-correlation function (VCF) module and choosing the delay signal for the reference signal in the channel with the maximum VCF value as an estimate of the delay time.

The search method provides a potentially achievable noise immunity, the shortest possible search time, but it is difficult to implement when the number of channels is N >> 1.

A known method for the rapid search for noise-like signal (SHPS) [patent RU No. 2206180, MKI H04L 7/10, publ. 06/10/2003], which consists in sequentially evaluating the characters of a pseudorandom sequence (PSP), which allows one to synthesize a signal with the required delay in any receiving unit of a PSP with a length of m characters. M estimates of the received binary symbols of the pseudo-random sequence are recorded in the register of the reference generator of the NPS of the correlation storage and then the affiliation of this m-valued combination of symbols with the desired noise-like signal is checked. If the received m-digit combination of characters does not belong to a noise-like signal (false alarm), then the register is reset and filled again with the next character estimates of the pseudorandom sequence of the desired noise-like signal for subsequent verification using a correlation accumulator.

The quick search method provides a reduction in the time of searching for BSS, but only with a sufficiently large signal-to-noise ratio for the BSC element.

A known method of the cyclical search for noise-like signals [E.P. Petrov, D.E. Prozorov, I.E. Petrov, A.V. Smirnov. A quick search for noise-like signals / Advances in Modern Electronics, 2008, No. 8, pp. 47-48], which consists in dividing the input signal into quadrature components by multiplying the input signal with reference harmonic carrier signals shifted relative to each other by the phase angle π / 2 . Form in each quadrature channel on each search cycle, the functions of mutual correlation of the received and reference noise-like signals. On each cycle, the cross-correlation function module is isolated and the cross-correlation function module value is compared with the detection threshold. Based on the results of the comparison, a decision is made about the presence or absence of a noise-like signal.

The disadvantage of this method is the significant search time with a large base noise-like signal (pseudo-random sequence length N >> 1), due to the need for repeated repetition of the search procedure.

The closest technical solution to the claimed invention is a method of searching for noise-like signals with minimal frequency manipulation [patent RU No. 2353064, MKI H04L 27/14, publ. 04/20/2009], which consists in the fact that at each search cycle, the input noise-like signal is divided into quadrature components, sampling, digitizing and integrating the quadrature components at clock intervals m times shorter than the length of the code sequence element. Separation of the input noise-like signal is carried out by multiplying it with reference harmonic signals of the carrier frequency, shifted relative to each other by the phase angle π / 2. The integration results are stored for a time equal to the duration of the code sequence element, during which they are multiplied with samples of the corresponding reference noise-like signals generated with a frequency M times the clock frequency of the input signal code sequence. Moreover, for a time equal to the repetition period of the code sequence, M values of the cross-correlation function module are generated, which are then accumulated over an interval equal to a fixed number of repetition periods of the code sequence. The decision on the value of the delay time of the input signal is made by choosing the maximum of the M values of the accumulated modules of the cross-correlation function, remembering the maximum value, its address and cycle number and repeating the search procedure a fixed number of times with a shift by M elements of the sequence during the transition to each subsequent search cycle.

The disadvantage of this method is the significant search time with a large base noise-like signal (pseudo-random sequence length N >> 1), due to the need for repeated repetition of the search procedure.

The present invention solves the problem of reducing the time to search for a noise-like signal with minimal frequency manipulation with high noise immunity and low hardware costs.

The problem is solved in that in a method for searching for noise-like signals with minimal frequency manipulation, which consists in dividing the input signal into quadrature components by multiplying the input signal with reference harmonic signals of the carrier frequency, shifted relative to each other by the phase angle π / 2, the formation in each quadrature channel on each search cycle of the value of the cross-correlation function of the input and reference noise-like signals, the allocation of the module of the mutual function According to the invention, in each search cycle, samples of the quadrature components of the input noise-like signal are accumulated at clock intervals equal to half the duration of the code sequence element, they are stored for a time equal to n repetition periods of the input noise-like signal, the results of the accumulation of quadrature components of the input noise-like signal, form 4N samples quadrature components of the input spread-spectrum signal z _1k and z _2k, form a 4N samples of quadrature reference videosig als I _k = cosΘ (t _k) and Q _k = sinΘ (t _k) for a fixed time delay element code t _k sequences produce symbolic two-stage approximation of the shape of the quadrature reference video signals I _k and Q _k, where samples of quadrature reference video signal with the sign two- the approximations are equal to I _k = (± a ₁ , ± a ₂ ) and Q _k = (± a ₂ , ± a ₁ ), where a ₁ and a ₂ are weight coefficients, on each search cycle in each quadrature channel multiply quadrature readings a noise-like signal component of the input z _1k and z _2k samples are approximated with en quadrature reference video I _k = (± a _1, ± a ₂₎ and Q _k = (± a _2, ± a ₁₎ pairwise combined results of multiplying the quadrature component z _1k and z _2k with samples approximated quadrature reference video I _k = (± a ₁ , ± a ₂ ) and Q _k = (± a ₂ , ± a ₁ ), 2N samples of quadrature components of the cross-correlation function are calculated by integrating the combined multiplication results for a fixed delay of the code sequence element t _k , N values of the function module are extracted cross-correlation, determine the value of the delay element code sequence corresponding to the maximum value of the mutual correlation functions of the module, the value found using delay code sequence for setting a condition code generator synchronism with the received spread spectrum signal with minimum shift keying.

Figure 1 shows a variant of the circuit of a device that implements the inventive method of searching for noise-like signals with minimal frequency manipulation, and figure 2 is a diagram of a decoding unit for this device.

A device for implementing a method for searching for noise-like signals with minimal frequency manipulation comprises a bitwise processing unit 1 connected to a decoding unit 6. The element-wise processing unit 1 includes input multipliers 2 ₁ and 2 ₂ , the signal inputs of which are combined, and the reference inputs are connected to the corresponding output of the reference generator 5. The outputs of the first and second multipliers 2 ₁ and 2 _{2 are} connected to the signal inputs of the first and second accumulating adders 3 ₁ and 3 ₂ , the outputs of which are connected to the information inputs of the first and second random access memory devices 4 ₁ and 4 _2, respectively. The clock inputs of random access memory devices 4 ₁ and 4 _{2 are} connected to the corresponding outputs of the clock generator 12 (not shown in FIG. 1). The outputs of the storage devices 4 ₁ and 4 _{2 are} connected respectively to the signal inputs of the third and fourth accumulating adders 3 ₃ and 3 ₄ , the reference inputs of which are connected to the corresponding information outputs of the data storage unit 16.

Block 6 decoding (see figure 2) consists of the seventh and eighth, ninth and tenth multipliers 2 ₇ and 2 ₈ , 2 ₉ and 2 ₁₀ , the outputs of which are pairwise combined through the first and second subtractors 17 ₁ and 17 ₂ respectively, and from the eleventh and twelfth, thirteenth and fourteenth multipliers 2 ₁₁ and 2 ₁₂ , 2 ₁₃ and 2 ₁₄ , the outputs of which are paired through the third and fourth adders 7 ₃ and 7 _4, respectively. The combined signal inputs of the multipliers 2 ₇ , 2 ₉ , 2 ₁₁ , 2 ₁₃ and 2 ₈ , 2 ₁₀ , 2 ₁₂ , 2 _{14 are} connected to the output of the third and fourth accumulating adders 3 ₃ and 3 _4, respectively. The reference inputs of the multipliers 2 ₇ and 2 ₁₂ , 2 ₉ and 2 ₁₄ , 2 ₈ and 2 ₁₁ , 2 ₁₀ and 2 ₁₃ are paired and connected to the corresponding outputs of block 15 of the formation of codes. The outputs of the first and second subtractors 17 ₁ and 17 _{2 are} connected respectively to the inputs of the fifth and sixth accumulating adders 3 ₅ and 3 ₆ , and the outputs of the third and fourth adders 7 ₃ and 7 _{4 are} connected to the inputs of the seventh and eighth accumulating adders 3 ₇ and 3 ₈ .

The outputs of the fifth, sixth, seventh and eighth accumulating adders 3 ₅ , 3 ₆ , 3 ₇ and 3 _{8 are} connected to the signal inputs of the third, fourth, fifth and sixth multipliers 2 ₃ , 2 ₄ , 2 ₅ and 2 _6, respectively. The outputs of the third and fourth, fifth and sixth multipliers 2 ₃ and 2 ₄ , 2 ₅ and 2 _{6 are} combined, respectively, through the first and second adders 7 ₁ and 7 ₂ , to the outputs of which are connected the corresponding inputs of the transmitter 8 of the module. To the output of the calculator 8 of the module are connected in series connected decision block 9 and the control unit 10, the output of which is connected to the signal input of the element 11 of the controlled delay. The clocked input of the controlled delay element 11 is connected to the corresponding output of the clock generator 12, and the output of the controlled delay element 11 is connected to the input of the code generator 13. The output of the code generator 13, which is the output of the search device (see Fig. 1), is connected to the input of the synthesizer 14 samples, the first and second outputs of which are connected to the corresponding signal inputs of the code generation unit 15. The paired combined reference inputs of the third and fifth, fourth and sixth multipliers 2 ₃ and 2 ₅ , 2 ₄ and 2 ₆ connected to the corresponding signal inputs of the code generation unit 15 are connected to the corresponding information outputs of the data storage unit 16. The reference input of the data storage unit 16 connected to the corresponding output of the clock generator 12 (figure 1. not shown).

The method of searching for noise-like signals is as follows.

The input of the search device (Fig. 1) receives with a sampling step T _{d the} samples of the received periodic noise-like signal (SHPS) with minimal frequency manipulation (index k is not specified):

где ω₀ - средняя частота;

where ω ₀ is the average frequency;

φ is the initial phase (the amplitude is assumed to be unity);

Θ (t) is the function that determines the law of angular modulation;

d (t) is a binary signal corresponding to a code pseudo-random sequence (PSP) d ₀ , d ₁ , ..., d _N-1 ;

rect (t) - rectangular function (pulse of unit amplitude and duration T);

N - the length of the SRP, which determines the period T _p = NT repetition of SHPS

M - the number of samples in the period.

Input multipliers Feb. ₁ and Feb. ₂ carried multiplication of signal samples (1) from the counts of reference carrier frequency signal cosω ₀ t _ij and sinω ₀ t _ij, are generated by reference generator 5. The outputs of the multipliers ₂ January and ₂ February formed samples of the input signal components respectively videochastotnyh :

as well as double frequency components 2ω ₀ , which are filtered out by the subsequent processing path.

The samples of the video-frequency components (2) of the input signal x _jk and y _jk are respectively received at the signal inputs of the accumulating adders 3 ₁ and 3 ₂ , at the outputs of which values are formed, respectively:

Summation over i in (3) is carried out at integration intervals equal to half the duration of the SRP element. Moreover, the number of samples on each kth integration interval is m = T / (2T _d ). The accumulated values are supplied to storage devices (memory) 4 ₁ and 4 ₂ , where they are stored for the observation time equal to n period T _p . According to the control signal, the storage devices 4 ₁ and 4 ₂ respectively send samples X _jk and Y _jk to the signal inputs of the third and fourth accumulative adders 3 ₃ and 3 ₄ , to the reference inputs of which the values u _1j and u _2j respectively.

In the accumulating adders 3 ₃ and 3 ₄ , coherent interperiodic accumulation of the corresponding quadrature components (3) is carried out according to the following algorithm:

The accumulation results (4), obtained for n periods of repetition of SHPS, are used to sequentially calculate N discrete values of the module of mutual correlation function (VKF) in the post-processing mode on a time interval equal to:

nT _n <t <nT _n + T _add ,

where T _add - additional time spent on post-processing.

где k=1, 2, …, 2N. Отсчеты квадратурных опорных видеочастотных сигналов I_k=cosΘ(t_k) и Q_k=sinΘ(t_k) поступают на соответствующие сигнальные входы блока 15 формирования кодов, на соответствующие опорные входы которого поступают значения весовых коэффициентов a₁=cos(π/8) и a₂=sin(π/8), хранящиеся в блоке хранения данных 16. В результате знаковой двухступенчатой аппроксимации формы квадратурных опорных видеочастотных сигналов I_k=cosΘ(t_k) и Q_k=sinΘ(t_k), осуществляемой в блоке 15 формирования кодов, отсчеты квадратурных опорных видеочастотных сигналов принимают следующие значения: I_k=(±a₁, ±a₂) и Q_k=(±a₂, ±а₁). На каждом интервале поиска на основе полученных в результате аппроксимации отсчетов квадратурных опорных видеочастотных сигналов I_k=(±а₁, ±a₂) и Q_k(±a₂, ±a₁) в блоке 15 формирования кодов получают элементы кодов b_1k и b_2k, c_1k и c_2k в соответствии со следующим алгоритмом:At each search interval, in the synthesizer of 14 samples, samples of quadrature reference video-frequency signals I _k = cosΘ (t _k ) and Q _k = sinΘ (t _k ) are formed at a fixed value of the SRP delay equal to

where k = 1, 2, ..., 2N. Samples of the quadrature reference video-frequency signals I _k = cosΘ (t _k ) and Q _k = sinΘ (t _k ) are supplied to the corresponding signal inputs of the code generation unit 15, the corresponding reference inputs of which receive the values of the weight coefficients a ₁ = cos (π / 8) and a ₂ = sin (π / 8) stored in the data storage unit 16. As a result of the sign two-step approximation of the shape of the quadrature reference video signals I _k = cosΘ (t _k ) and Q _k = sinΘ (t _k ), carried out in block 15 formation of codes, samples of quadrature reference video-frequency signals take the following values Variations: I _k = (± a ₁ , ± a ₂ ) and Q _k = (± a ₂ , ± a ₁ ). On each search interval, based on the approximation of the samples of the quadrature reference video frequency signals I _k = (± a ₁ , ± a ₂ ) and Q _k (± a ₂ , ± a ₁ ) in the code generation unit 15, code elements b _1k and b _2k , c _1k and c _2k in accordance with the following algorithm:

where sign (x) is the sign function.

In accordance with the above algorithm (5), the code elements b _1k , b _2k , c _1k , c _2k take the values 0, 1, or -1.

The quadrature components of the input signal z _1k and z _2k are respectively supplied (see FIG. 2) to the combined signal inputs of the multipliers 2 ₇ , 2 ₉ , 2 ₁₁ , 2 ₁₃ and 2 ₈ , 2 ₁₀ , 2 ₁₂ , 2 ₁₄ of the decoding unit 6. The pairwise combined reference inputs of the multipliers 2 ₇ and 2 ₁₂ , 2 ₈ and 2 ₁₁ , 2 ₉ and 2 ₁₄ , 2 ₁₀ and 2 ₁₃ are respectively supplied with the code elements b _1k , c _1k , b _2k , c _2k generated by the code generation unit 15 . The signals from the outputs of the multipliers 2 ₇ and 2 ₈ , 2 ₉ and 2 ₁₀ , 2 ₁₁ and 2 ₁₂ , 2 ₁₃ and 2 ₁₄ are combined in pairs in the subtractors 17 ₁ and 17 ₂ and in the adders 7 ₃ and 7 ₄ , respectively, forming the corresponding quadrature components z ' _1k , z'' _1k , z' _2k , z '' _2k .

From the outputs of the subtractors 17 ₁ , 17 ₂ and adders 7 ₃ , 7 ₄ of the decoding unit 6, the quadrature components z ' _1k , z'' _1k , z' _2k , z '' _2k are respectively supplied to the fifth, sixth, seventh and eighth accumulating adders 3 ₅ , 3 ₆ , 3 ₇ , 3 ₈ , forming values:

The accumulation results (6) are fed to the signal inputs of the respective multipliers 2 ₃ , 2 ₄ , 2 ₅ , 2 ₆ . The reference inputs of the respective multipliers 2 ₃ and 2 ₅ , 2 ₄ and 2 ₆ respectively are weighted coefficients a ₁ and a ₂ stored in the data storage unit 16. "Weighted" multiplication results are combined in the adders 7 ₁ and 7 ₂ respectively, forming the corresponding quadrature components of the VKF input and reference signals:

The combination of expressions (6) and (7) is equivalent to the calculation of the quadrature components of the VKF of the input and reference signals with a sign two-stage approximation of the quadrature reference video signals:

where I _k = (± a ₁ , ± a ₂ ) and Q _k = (± a ₂ , ± a ₁ ) are the samples of the quadrature reference video signals with a sign two-stage approximation of the shape of the quadrature reference video signals;

z _1k and z _2k are samples of quadrature components of the input noise-like signal.

On each search interval with a fixed delay of the SRP τ _l = lT, where l = 0, 1, ..., (N-1) is the number of the quadrature channel, the calculator 8 of the module generates the value of the VKF module of the input and reference signals:

The decision block 9 determines the maximum value of the module VKF input and reference signals:

which is used in the control unit 10, when generating the delay code of the reference SRP

where µ is the address of the channel with Z _µ = max.

The delay code of the reference memory bandwidth is supplied to the control input of the controlled delay element 11, the reference input of which is supplied with a frequency f _{t of} clock pulses generated by the clock generator 12. This code determines the delay estimate of the received BSS and is used to set the code generator 13 in synchronism with the received BSC with accuracy no worse than ± T / 2 (provided that there are no abnormal errors).

Qualitative parameters described search method characterized PNS probability P _err anomalous errors greater than a value T / 2 (absolute value) and the search t _search time. When the code SRP length N >> 1, the problem of searching for NPS by the delay time can be reduced to the problem of recognizing N orthogonal signals, in relation to which the error probability can be estimated as [5]:

where Ф (х) is the probability integral, q is the signal-to-noise ratio at the output of the "synchronous" channel (with a relative delay of the received and reference signals τ = 0).

The loss in the signal-to-noise ratio due to the "equilibrium" element-wise processing is about 0.2 dB compared to the optimal correlation processing [V.N. Bondarenko / Optimal algorithm for searching for a noise-like signal with minimal frequency manipulation. - M., "Radio Engineering and Electronics", 2008, vol. 53, No. 2. S.222-229], i.e. the proposed search method provides noise immunity close to potentially achievable.

While searching for the proposed method, when the processor clock frequency f _m = 1 GTZ, including accumulation periods n = 25, the duration T _p PNS = 40 ms observation time exceeds the amount of extra time T ² T ≈N _{additional complexity} spent in post-processing results. When searching in real time using a single-channel device that implements a cyclic search method, the search time for the same conditions is t _search = nT _p N≈4.5 min .

Thus, the proposed method for searching for broadband radios with minimal frequency manipulation can significantly reduce the search time compared to the prototype (more than 270 times) with negligible loss in noise immunity (less than 0.2 dB). This is the technical and economic effect in comparison with the known methods for searching for noise-like signals.

Claims (1)

A method for searching for noise-like signals with minimal frequency manipulation, namely, that the input noise-like signal is divided into quadrature components by multiplying it with reference harmonic signals of the carrier frequency shifted relative to each other by the phase angle π / 2, calculated in each quadrature channel on each the search cycle, the cross-correlation function of the input and reference signals, allocate the cross-correlation function module, characterized in that on each search cycle carry out the accumulation of samples of the quadrature components of the input noise-like signal at clock intervals equal to half the duration of the code sequence element, is stored for a time equal to n repetition periods of the input noise-like signal, the results of the accumulation of quadrature components of the input noise-like signal, form 4N samples of the quadrature components of the input noise-like signal z _1k and z _2k , form 4N samples of quadrature reference video signals I _k = cosΘ (t _k ) and Q _k = sinΘ (t _k ) for a fixed delay time element and the code sequence t _k , a sign two-step approximation of the shape of the quadrature reference video signals I _k and Q _{k is} performed, and the samples of the quadrature reference video signals with a sign two-stage approximation are I _k = (± a ₁ , ± a ₂ ) and Q _k = (± a ₂ , ± a ₁ ), where a ₁ and a ₂ are weight coefficients, on each search cycle in each quadrature channel, the samples of the quadrature components of the input noise-like signal z _1k and z _2k are multiplied with the samples of the approximated quadrature reference video signals I _k = (± a ₁ , ± a ₂ ) and Q _k = (± a ₂ , ± a ₁ ), n pairwise combine the results of multiplying the quadrature components z _1k and z _2k with samples of approximated quadrature reference video signals I _k = (± a ₁ , ± a ₂ ) and Q _k (± a ₂ , ± a ₁ ), calculate 2N samples of quadrature components of the cross-correlation function by integrating the combined multiplication results with a fixed delay of the code sequence element t _k , N values of the cross-correlation function module are extracted, the delay value of the code sequence element corresponding to the maximum mode value is determined For the cross-correlation functions, use the found code sequence delay value to set the code generator in a state of synchronism with the received noise-like signal with minimal frequency manipulation.

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