RU2353064C1 - Search method of noise-like signals with minimum frequency-shift modulation - Google Patents

Abstract

FIELD: radio-engineering.

SUBSTANCE: invention refers to radio-engineering, and can be used in radio navigation systems and radio communication systems for receiving noise-like signals with minimum frequency-shift modulation. For that purpose in each search cycle there performed is division of input noise-like signal into quadrature components, discretisation, digitalisation and integration of quadrature components at clock intervals that are m times shorter than durability of code sequence element. Integration results are stored for the period equal to durability of code sequence element, during which they are multiplied by readings of the appropriate reference noise-like signals generated with frequency that is M times bigger than clock frequency of input signal code sequence. At that during the period equal to one repetition period of code sequence, there formed is M of values of cross-correlation function modulus, which then are stored at the interval equal to a fixed number of repetition periods of code sequence. Decision on the value of delay time of input signal is taken by choosing maximum value of M of values of stored cross-correlation function moduli, by storing maximum value, its address and cycle number, and by repeating search procedure for a fixed number of times with a shift for M of elements of sequence when changing over to each next search cycle.

EFFECT: reducing signal search time at high interference resistance of reception and at low equipment costs.

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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.

There is a method of parallel search for noise-like signals by the delay time, which consists in multiplying the received signal with M pairs of reference noise-like signals, which are quadrature copies of the received signal for M discrete values of the delay time, integrating the multiplication results in 2M quadrature channels on an interval equal to the duration of the noise-like signal, highlighting M values of the module of the mutual correlation function (VKF) and the choice of the delay time of the reference delay as the estimate of the delay channel signal with the maximum value CCF [1].

The search method provides a potentially achievable noise immunity, the minimum possible search time, however, it is difficult to implement with the number of channels M >> 1.

There is a method of searching for pseudo-random signals, which consists in multiplying the input signal with N reference signals, calculating the cross-correlation function using the N-channel correlator, choosing the maximum value of the CCF using the maximum signal selector, and controlling the delay of the reference signals using the search control unit [2] .

However, the known method is difficult to implement with the number of channels N >> 1 and, moreover, is based on the use of synchronous detection of the received signal, which limits its application.

A known method for the cyclical search for noise-like signals, 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 a phase angle π / 2, forming in each quadrature channel on each search cycle the cross-correlation function adopted and reference noise-like signals, highlighting the cross-correlation function module on each cycle, comparing the value of the cross-correlation function module with pores gom detection and decision of the completion or continuation of the search at excess or of not exceeding the threshold, respectively [3].

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 is intended to solve the problem of reducing the search time 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, forming in each quadrature channel on each search cycle of the cross-correlation function of the input and reference noise-like signals, the allocation of the cross-correlation function module, according to the invention on each search cycle, discretization, digitization and integration of quadrature components of the input signal at clock intervals, m times shorter than the duration of the element T of the code sequence, storing for the duration of the element T the results of integration of the quadrature components of the input signal, the formation of M elements of the reference code sequence with a clock frequency , M times the clock frequency of the code sequence of the input signal, and on each elementary interval T to Each cycle, the reference code sequence is shifted by one element in the lead, the formation of 2M samples of the reference signals cosΘ (t) and sinΘ (t), which are quadrature copies of the complex envelope of the noise-like signal, multiplying the results of integration of the quadrature components of the input signal with samples of the corresponding reference quadrature signals, pairwise combination of the results of the multiplication of integrally accumulated quadrature components of the input signal with samples of the corresponding reference quadrature x signals, the formation of 2M values of quadrature components of the cross-correlation function by integrating at the intervals equal to the repetition period of the noise-like signal, the combined results of multiplication, the formation of M values of the module of the cross-correlation function, the interperiod accumulation of M values of the module of the cross-correlation function in an interval equal to a fixed number of repetition periods noise-like signal, selection of the maximum of the M values of the accumulated modules of the cross-correlation function, storing the maxim value, its address and cycle number, and when switching to each subsequent search cycle, the reference code sequence is shifted by M elements in the lead, while remembering the maximum value of the cross-correlation function module, its address and cycle number obtained for all search cycles, the number of which is fixed.

Figure 1 shows a diagram of a device for implementing the inventive method of searching for noise-like signals with minimal frequency manipulation, and figure 2 is a timing diagram explaining the operation of the specified device.

A device for implementing a method for searching for noise-like signals with minimal frequency manipulation contains the first and second multipliers 1 and 2, the signal inputs of which are combined, the reference input of each is connected to the corresponding output of the reference generator 3, and the output of each multiplier is connected to the corresponding input of the analog-to-digital converter 4. The quadrature outputs of the latter are connected to the inputs of the first and second integrators 5 and 6, respectively, whose outputs are connected to the information inputs of the first and second op -cooperative memory devices 7 and 8 respectively. The outputs of the storage devices 7 and 8 are connected to pairwise combined signal inputs of the third and fifth, fourth and sixth multipliers 9 and 11, 10 and 12, respectively. The outputs of the third and sixth, fourth and fifth multipliers 9 and 12, 10 and 11 are combined, respectively, through a subtractor 13 and a first adder 14, to the outputs of which are connected the corresponding inputs of the module 15 for generating the modules of the mutual correlation function. This block 15 contains the third and fourth integrators 16 and 17, the first and second quadrants 18 and 19, as well as the second adder 20, the square root extraction element 21 and the fifth integrator 22 connected in series. The output of the fifth integrator 22 is connected to the input of the decision block 23, the output of which is connected in series to a control unit 24, a controlled delay element 25, a code pseudo-random sequence (PSP) generator 26, and a sample synthesizer 27. Moreover, the clock input of the controlled delay element 25 is connected to the first output of the time interval forming unit 28, the clock input of the sample synthesizer 27 is connected to the second output of the time interval forming unit 28, and the synchronizing inputs of the first and second integrators 5 and 6, the first and second random access memory 7 and 8 are interconnected and with the third output of the block 28 forming time intervals. Additional outputs of the block 28 forming time intervals are connected to the synchronizing inputs of the third and fourth integrators 16 and 17 and the control unit 24 and the fifth integrator 22, respectively. The reference inputs of the third and fourth, fifth and sixth multipliers 9 and 10, 11 and 12 are interconnected and with the corresponding outputs of the synthesizer 27 samples. The control input of the latter is connected to the output of the code-bandwidth generator 26, which is also the output of the device for searching for noise-like signals with minimal frequency manipulation.

The method of searching for noise-like signals (SHPS) is as follows. At the input of the search device (Fig. 1), a received signal is received, which is an additive mixture of NPS with minimal frequency shift keying (MFM) and broadband interference with a power spectral density uniform in the NPS band. The input noise-like MFM signal can be represented as

where τ is the delay time; f ₀ is the average frequency; φ is the initial phase (the amplitude is assumed to be unity); D (t) is the binary information signal; Θ (f) is the function that determines the law of angular modulation:

where 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.

Input multipliers 1 and 2 multiply the signal (1) with the reference harmonic signals cos (2πf ₀ t) and sin (2πf ₀ t) generated by the reference generator 3. At the outputs of the multipliers 1 and 2, video-frequency components are generated (Fig. d) respectively

where I (t) = cosΘ (t), Q (t) = sinΘ (t).

When recording (4), it was taken into account that the frequency components 2f _{0 are} filtered out by the subsequent processing path.

Timing diagrams (Fig. 2) are given for the case when the delay of the NPS corresponds to the beginning of the a priori interval [0, T _p ], i.e. τ = 0, the initial phase is φ = 0 (in the absence of interference, the components in (4) proportional to sin φ are equal to zero).

After sampling and digitizing the signals (4) in the analog-to-digital Converter 4, the quadrature components are fed to the inputs of the integrators 5 and 6, forming the values (Fig.2, e, f)

where x _i = x (t _i ) and y _i = y (t _i ) are the samples of quadrature components (4), arriving with a step T _d . The summation over i in (5) is carried out from the value i = (k-1) n + (j-1) N _p +1 to i = k _n + (j-1) N _p , where n = T / mT _d is the number samples on the integration interval equal to T / m; m and n are integers, k = 1, ..., mN; N _p = nmN is the number of samples in the interval equal to the period T _{p the} repetition of the SRP (3); j = 1, ..., K, K is the number of SRP periods in the observation interval equal to the duration T _{c of} one search cycle.

The gating of integrators 5, 6 is carried out by sync pulses generated by the block 28 forming the time intervals.

The results of integration (5) are stored for a time equal to the duration T of the SRP element in random access memory 7 and 8, after which the integrators 5, 6 are reset and the next NPS element is integrated with a duration of T / m. The results of integration into random access memory 7, 8 and the integration of integrators 5, 6 are recorded with a frequency mf _T , f _T = 1 / T is the clock frequency of the memory bandwidth (3).

In the multipliers 9, 10, 11, 12, the results (5) of the element-wise accumulation stored in the memory devices 7 and 8 are multiplied by the reference quadrature signals, which the synthesizer 27 samples form. The reference inputs of multipliers 9 and 10 receive samples I _{k + μ of the} reference signal I (t) = cosΘ (t), and the reference inputs of multipliers 11 and 12 receive samples Q _{k + μ of the} reference signal Q (t) = sinΘ (t) (Fig.2, c, d) - index j indicating the number of the period of the SHPS, omitted for the sake of simplicity.

In the first search cycle (Fig. 2, g, h) µ = m (ν-1), where ν = 1,2, ..., M are the values of the relative delay of the reference signals, expressed as the number of SRP elements, M is the integer (determines number of "parallel" channels). The sampling frequency of reference quadrature signals is M times the frequency of data from the outputs of random access memory 7 and 8 to the inputs of the multipliers 9, 11 and 10, 12, respectively (time diagrams in Fig. 2 correspond to the case m = 2 and M = 4 and the absence of interference).

The signals from the outputs of the multipliers 9 and 12, 10 and 11 are combined in pairs in the subtractor 13 and the adder 14, forming the corresponding quadrature components (figure 2, h). The latter are supplied to the inputs of the block 15 of the formation of modules of the mutual correlation function (VKF) of the received and reference SHPS, which contains integrators 16 and 17, including random access memory for storing M integration results, squares 18 and 19, as well as an adder 20, square extraction element 21 root (allocation of the module) and the fifth integrator 22 - inter-period storage with random access memory for storing M accumulation results. The integrators 16, 17 integrate at intervals equal to the period T _{p of the} repetition of the SHPS corresponding quadrature components arriving at their inputs, forming the values

(the index j indicating the number of the SHPS period is omitted for simplicity).

The integration results (6), which are the values of the quadrature components of the VKF for each of the M channels, are squared and combined in the adder 20. A module of the VKF corresponding to the relative delay of the received and reference SHPS fixed for each channel is formed at the output of the square root extraction element 21 .

The inter-period accumulator 22 accumulates M modules of VCF values generated at each repetition period of the NPS for a time T _c = LT _p , which determines the duration of the search cycle. After the time T _{c, the} decision block 23 selects the maximum value from M correlations generated by block 15:

where z _1νj and z _2νj are correlations (6) formed at the jth period of accumulation in the νth channel.

The value of Z _max , as well as its "address" ν _m and the number l of the search cycle are stored for the time T _c , after which the integrators 16, 17, 22 are reset by the clock pulses generated by the block 28 for the formation of time intervals (outputs T _p and T _c ), and the next search cycle begins (second). In this case, the control unit 24 generates a delay code of the reference reference bandwidth τ ₀ = MT, which differs from the value τ ₀ = 0 in the first search cycle by a shift of M elements in advance. The delay code is supplied to the control input of the controlled delay element 25, to the clock input of which clock pulses are generated with the frequency Mf _t generated by the time interval generating unit 28 (output "Mf _t "). The value d _{m of the} first element of the reference SRP generated by the code pseudo-random sequence generator 26 is determined by the code at the input of the control unit 24 (the delay code is M in the second cycle). PSP generator 26 generates a code sequence segment d _m , d _{m + 1} , ..., d _{N-1 + M} with a length of M elements. From the output of the PSP generator 26, the code sequence arrives at the control input of the synthesizer 27 samples of reference quadrature signals made according to the well-known scheme [6]: "accumulating adder - read-only memory (ROM) that implements a tabular method for generating cosΘ _i and sinΘ _i samples (Θ _i is the phase value generated by the accumulating adder at time t = t _i and determining the address of the kth cell of the ROM.) The value of the element d _{k of the} SRP fed to the control input of the synthesizer 27 samples determines the sign of the phase increment ΔΘ _k at the current those (Fig.2, a, b).

The search procedure, including operations (5) - (7), in the second search cycle is performed similarly to the first cycle, differing only in that the reference quadrature signal samples are shifted by mM positions in the lead (values μ = (l-1) mM + m (ν-1) in (6) on the 1st cycle). Moreover, the value of Z _max (7) obtained on the 2nd cycle, as well as its "address" ν _m and the number l = 2 of the cycle are stored for the time T _c , if Z _max ≥Z ' _max , Z' _max is the maximum value VKF obtained in the first search cycle. Otherwise, the results Z ' _max , ν' _m and l = 1 of the search procedure on the first cycle are remembered.

The described cyclic search procedure is repeated L times (taking into account the shift of the reference memory bandwidth by M positions with the transition to the next cycle). The number of cycles L = integ (N / M + 0.5), integ (x) is an integer from x. The search time is fixed and determined by the required one to ensure the given probability of the correct search completion by the accumulation time and the number of cycles: t _search = LT _c = LKT _p . At the end of the last cycle with number L, a delay code (τ / Т) = (l _m -1) M + ν _m corresponding to the number l _{m of the} cycle and the value ν _{m of the} relative delay of the reference memory bandwidth of that channel is supplied to the control unit 24 from the decision block 23 in which the absolute maximum value is observed (for all search cycles)

The specified code determines the estimate of the delay of the received SHPS relative to the time scale specified by block 28 of the formation of time intervals. This estimate is used to set the code PSP generator 26 in a state of synchronism with the received SHPS with an accuracy of no worse than ± T / 2 (provided that there are no anomalous errors).

Qualitative parameters described search method characterized PNS probability P _err anomalous errors greater than a value T / 2 (in absolute value), and _search the search time t. When the code SRP length is 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 [4]:

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). Formula (8) is written under the assumption that the number of accumulation periods is K >> 1 (this allows us to approximate the distribution of the output quantity by the normal distribution).

It can be shown that for m = 2 (a four-level step approximation of the quadrature reference signals), the loss in the signal-to-noise ratio of the "equilibrium" elementwise processing in comparison with the optimal correlation processing is about 0.2 dB, i.e. the proposed search method provides noise immunity close to potentially achievable [5].

The search time for the proposed method is M times less than the value of t _search = NKT _p in a cyclic (step-by-step) search method implemented using a single-channel device.

Thus, the proposed method for the search for SHPS with minimal frequency manipulation allows you to achieve noise immunity close to potentially achievable (loss of about 0.2 dB), and to reduce the search time in M times compared with the prototype with little additional cost for the implementation of the proposed method for finding ShPS minimum frequency manipulation. This is the technical and economic effect in comparison with the known methods for searching for noise-like signals.

Information sources

1. Radio engineering systems / Yu.P. Grishin, V. P. Ipatov, Yu. M. Kazarinov and others; Ed. Yu.M. Kazarinova. - M .: Higher. school, 1990, p. 64 (Fig. 3 .16), p. 99 (Fig. 4 .6).

2. Patent 2206180 (RF). A device for initial synchronization of a pseudo-random signal receiver. Publ. BIPM No. 16, 06/10/2003.

3. G.I. Tuzov. Statistical theory of the reception of complex signals. - M .: Owls. Radio, 1977, p. 326 (Fig. 7.2).

4. L.E. Varakin. Theory of signal systems. - M .: Owls. Radio, 1978, p. 60 (f-la (2.34)).

5. A.M. Aleshechkin, V.N. Bondarenko, V.I. Kokorin. Noise immunity of the correlation receiver of a noise-like signal with minimal frequency manipulation / Radio Engineering, 2006, No. 12, p.10.

6. Digital phase synchronization systems / M.I.Zhodzishsky, S.Yu.Sila-Novitsky, V.A. Prasolov and others; Under. Ed. M.I.Zhodzishsky. - M .: Owls. Radio, 1980 .-- P.55-57.

Claims (1)

A method for searching for noise-like signals with minimal frequency manipulation, which consists in dividing the input noise-like signal 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 noise-like signals, allocate the cross-correlation function module, characterized in that on each search cycle they carry out sampling, digitization and integration of the quadrature components of the input noise-like signal at clock intervals m times shorter than the length of the code sequence element, remember for a time equal to the duration of the code sequence element, the results of integration of the quadrature components of the input noise-like signal, form M code sequence elements with a clock frequency , M times the clock frequency of the code sequence of the input noise-like signal, p why at each interval equal to the duration of the element of the code sequence, in each cycle the code sequence is shifted by one element in the advance direction, 2M samples of reference noise-like signals cosΘ (t) and sinΘ (t) are formed, which coincide in shape with the quadrature components of the input noise-like signal, multiply the results of integration of quadrature components of the input noise-like signal with samples of the corresponding reference noise-like signals, pairwise combine the results of multiplication integrally by filmed quadrature components of the input noise-like signal with readings of the corresponding reference noise-like signals, calculate 2M values of quadrature components of the cross-correlation function by integrating the combined multiplication results at intervals equal to the repetition period of the code sequence, extract M values of the cross-correlation function module, accumulate M values of the cross-correlation function module on an interval equal to a fixed number of repetition periods of the code sequence and, choose the maximum of the M values of the accumulated modules of the cross-correlation function, remember the maximum value, its address and cycle number, and when switching to each subsequent search cycle, the code sequence is shifted by M elements in the advance direction, while the maximum value of the cross-correlation function module is stored , its address and cycle number obtained for all search cycles, the number of which is fixed.

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