Digital detector of complicated signals

FIELD: radio engineering.

SUBSTANCE: device implements algorithms of discontinuous Fourier transformation and fast folding of received and bearing signals, to provide search-less detection of complicated signals with sizeable bases. Digital synchronized filter processes at video-frequency with use of standard digital assemblies and elements. Device has multipliers 3,4,14,15, phase changer 2 for π/2, circuit for delay for length of signal element 1, low frequency filters 5,6, analog-digital converters 7,8,12, microprocessor systems of discontinuous Fourier transformation 9,10, microprocessor systems of reversed discontinuous Fourier transformation 16,17, generator of bearing pseudo-random series 11, microprocessor systems of discontinuous Fourier transformation of bearing pseudo-random series 13, square-ware generators 18,19, adder 20, arithmetic device for taking square root 21, threshold device 22, discontinuous process pulse generator 23, device for splitting frequency in two 24, clock generator 25, interconnected by appropriate functional connections.

EFFECT: broader functional capabilities, higher efficiency.

2 dwg

 

The invention relates to the field of radio communications, transmission systems discrete data using complex wideband signals based on a pseudo-random sequences of maximal period and signals Golda with binary phase shift keying (0, π) and is designed to build digital detectors of complex signals.

The closest to the technical characteristics of this device is the optimal detector complex signals with unknown amplitude and random initial phase [1, s]. This device has a maximum noise immunity in the normal noises with known parameters of the received signal, in addition to the amplitude and initial phase of high-frequency oscillations. The detector prototype contains two multiplier, the oscillator carrier frequency, the phase shifter on π/2, two identical concerted filter, two Quad and the adder. The generator of the harmonic of the reference oscillation futuremouse circuit generates two quadrature harmonic oscillations Cos(ω0t) and Sin(ω0t), where ω0- carrier frequency of the received signal. The use of quadrature channels allows to eliminate the influence of the random initial phase of the carrier wave. The outputs of multiplier products of the input signal is translated in videocasting region which are elements of a complex signal, which are processed by two identical agreed filters.

The disadvantage of the prototype is that for normal operation of the detector requires a priori information about the frequency of the received signal to convert the signal at videobest and complexity of manufacturing the agreed filters, especially for large databases of signals used.

To eliminate the mentioned disadvantages of the analog detector prototype is proposed to use a digital detector of complex signals. Due to the fact that the carrier frequency of the received signal due to various reasons not known with the required accuracy serves to highlight modulating the function of a mixture of signal and noise is to use the autocorrelation method of signal processing, as the optimal method of reception of signals of unknown form. The autocorrelation method applied to the problem of allocation of elements of a complex signal is the multiplication of the received signal and delayed by the duration element in a complex signal.

Photomanipulating pseudorandom sequence of the received radio signal can be represented in the form

s1(t)=Adi[rect(t-iτ)]Cos(ω0t+ϕ0), 0≤t≤Tc, i=0,1 ... N-1

where a is the signal amplitude;

ω0that ϕ0- carrier frequency and initial the phase of the harmonic oscillations;

Tc- duration signal;

τ - duration element signal;

di=(1, -1) - elements pseudo-random sequence;

In the interval duration element signal the result of the multiplication will be

y1(t)=s1(t)s1(t-τ)=AdiCos(ω0t+ϕ0)Adi-1Cos(ω0(t-τ)+ϕ0)=

=1/2A2didi-1[Cos(ω0τ)+Cos(2ω0t-ω0τ+2ϕ0)].

After adfilternone high-frequency component by using a lowpass filter will get

Z1(t)=1/2A2didi-1Cos(ω0τ).

As can be seen, that when the autocorrelation processing eliminates the dependence on the initial phase ϕ0harmonic oscillations, but there is a factor of Cos(ω0τ)that depends on the value of the carrier frequency and duration of the element signal. To eliminate this dependency, you must enter the quadrature channel. Accept. the signal is passed through fazovrashchatelei chain π/2 and we obtain

S2(t)=Adi[rect(t-iτ)]Cos(ω0t+ϕ0-π/2)=

=Adi[rect(t-iτ)]Sin(ω0t+ϕ0), 0≤t≤Tc, i=0,1 ... N-1.

After multiplication in the quadrature channel get

y2(t)=s2(t)s1(t-4 )=AdiSin(ω0t+ϕ0)Adi-1Cos(ω0(t-τ)+ϕ0)=

=1/2A2didi-1[Sin(ω0τ)+Sin(2ω0t-ω0τ+2ϕ0)].

At the output of the lowpass filter of the second channel will receive

z2(t)=1/2A2didi-1Sin(ω0τ).

Note that the product of the elements of the sequence didi-1of the elements (1, -1) is equivalent to addition modulo two elements of didi-1composed of (1, 0). One of the properties of linear recurrence sequences is that, if the sequence is folded modulo two with the same sequence but shifted some unequal period of the signal the number of elements [2, p.58], we get the same sequence, but with a different shift. The same is true for sequences Golda, because they are obtained by summing modulo two two different recurrent sequences of maximal period. Thus, the sequence

dk=didi-1, k=0, 1 ... N-1

will the same sequence as received, but with a different delay.

Hence, the outputs of low-pass filters in both channels is allocated modulating the function of the dkwith some unknown constant coefficients Cos(ω0< ) and Sin(ω0τ). Later in both channels is identical to the digital processing of the selected modulation function of the received signal.

Analog signals from outputs of low-pass filters in both channels is quantized. The sampling frequency associated with the maximum frequency spectrum of the modulating function. Typically, the emitted signal on the transmission side is limited by the range of the main lobe of the spectrum of the modulating function. The width of the main lobe is determined by the duration of elementary symbol and is equal to the clock frequency fτ=1/τ, which must be taken for the maximum frequency of the spectrum discretizing signal, that is, fmax=fτ. Then, according to the Nyquist theorem, the sampling frequency is chosen equal to

fd≥2fmax=2fτ.

To define the signal we will use the discrete convolution of two time functions - signal output from the quadrature channel and the reference signal generated in the generator copy of the signal of the detector. The calculation of the discrete convolution should be produced by the algorithm is not temporary, and in the spectral region, which requires fewer operations, especially when using the "fast Fourier transform".

Because the digital detector should produce the output signal coincident in shape with mutually-correlation function of the received and reference signals, the signal processing can be implemented by algorithm "high-speed convolution. After analog-to-digital conversion sequence is encoded in the number of times

x1(k)=z1(kTd), k=0, 1 ... Nd-1,

where Tdthe sampling interval equal to Td=1/fd;

Nd=EC[Tc/Td] is the number of samples per signal duration;

EC[x] is the integer part of the number x,

served on micropocessor system, performing a discrete Fourier transform (DFT). Its output is a sequence of spectral coefficients

S1(n)=DFT[x1(k)], n=0, 1 ... Nd-1

multiplied by the sequence of spectral coefficients

S0(n)=DFT[x0(k)], n=0, 1 ... Nd-1,

obtained from the reference sequence generator of the copied signal. Thus obtained sequence

S10(n)=S1(n)S0(n), n=0, 1... Nd-1

exposed in microprocessore system inverse discrete Fourier transform (DPF)

H1(k)=DPF[S10(n)], k=0,1 ... Nd-1.

The output of the second quadrature channel similarly get

S2(n)=DFT[x2(k)], S20(n)=S2(n)S0(n) and H2(k)=DPF[S20(n)].

In modern practice, DFT and ODPF is carried out in the same device. To eliminate the effect of the coefficients of Cos(ω0τ) Sin(ω0τ) the outputs of both channels vonvodat is to be squared and added. Finally the output signal of the digital detector has the form

H(k)=[H12(k)+H22(k)]l/2.

The claimed device with digital processing complex photomanipulating (0, π) signal is shown in figure 1. It contains:

1 - the delay circuit for the duration of the element signal τ;

2 - Phaser π/2;

3, 4, the first and second multiplier products;

5, 6, the first and second low pass filters;

7, 8, the first and second analog-to-digital converters;

9, 10, the first and second microprocessore system DFT;

11 - reference generator pseudo-random sequence;

12 - the third analog-to-digital Converter;

13 - microprocessor system DFT reference sequence;

14, 15 - the third and fourth multiplier products;

16, 17, the first and second micropocessor system ODPP;

18, 19, the first and second Quad;

20 - adder;

21 - arithmetic unit cure the square root of the number;

22 - threshold device;

23 - the pulse generator sampling;

24 is a frequency divider by two;

25 is a generator of clock pulses;

The device operates as follows. The received radio signal from the input of the detector is fed to the first input of the first multiplier (3) directly, and to the first input of the second multiplier (4) through a phase shifter on π/2 2). On the second inputs of the multiplier products (3) and (4) the signal passes through delay element (1) for the duration of the element signal τ. The plot of the signals at the outputs of various devices of the digital detector is shown in figure 2. The first chart shows a pseudo-random sequence (modulating function) u(t)you want to allocate for processing, and the reference pseudosuchia sequence uo(t), which is supplied from the generator copy of the signal. The reference sequence is a mirror reflection of the received sequence, i.e. uo(t)=u(Tc-t), where Twith- the duration of the signal. Here are recurrent sequences maximum period of 15 elements. The second graph shows the function s1(t) - harmonic signal modulated by the phase sequence of u(t) with some delay. In the drawings, which shows two dependencies, one of them rises (or falls) for clarity. The third graph shows the dependence of y1(t) and y2(t) at the outputs of the first and second multiplier products. The fourth graph shows the signals (x1kand x2kwith output filters low frequencies after sampling them in analog-to-digital converters. The signals x1kand x2krepresent a sequence of digital samples, the following intervals sampling rate Td . The last chart shows the inverse discrete Fourier transform for discrete convolutions signal of the first quadrature channel and the reference sequence N1kdiscrete convolution signal of the second channel and the reference sequence H2kand the resulting function Hk=(H1k2+H2k2)1/2

which is a function of cross-correlation of the received signal and the reference sequence generator of the copied signal. Signal Hkand is the output of the digital detector, which detects the signal. After selecting the maximum count of Hk maxand comparing it with a threshold, the decision about the signal, if it is exceeded.

Thus, the combination of the entered devices and their relationships allows to eliminate the influence of the a priori uncertainty about the carrier frequency and to carry out digital processing of the received signal for detection, which was absent in the prototype.

Therefore, the technical solution meets the criterion of "novelty". In addition, because the required technical result is achieved of all the newly introduced set of essential features, which are known in the patent and scientific literature is not detected on the day of filing, the invention meets the criterion of "from rettelse" level.

Sources of information

1. Varakin LA communication Systems with noise-like signals. - M.: Radio and communication, 1985. - 384 C., Il.

2. Dadonov N.G. and Senin A.I. Orthogonal and quasiorthogonal signals. Edited Amoresano. M: Communications, 1977. - 224 S., Il.

Digital detector complex signals containing the first and second multiplier products, Phaser π/2, characterized in that it further introduced the delay circuit for the duration of the element signal, the first and second low pass filters, first and second analog-to-digital converters, the first and second microprocessor systems the discrete Fourier transform, the generator of the reference pseudo-random sequence, the third analog-to-digital Converter, microprocessor system of the discrete Fourier transform of the reference pseudo-random sequence, third and fourth multiplier products, the first and second microprocessor systems inverse discrete Fourier transform, the first and second Quad, adder, arithmetic the device taking the square root of a number, a threshold device, the pulse generator sampling frequency divider by two, the clock, and the first input of the first multiplier connected to the input of the detector directly, the first input of the second multiplier connected to input about what augites through the Phaser on π /2, the second inputs of the first and second multiplier products connected to the input of the detector through a delay circuit for the duration of the element signal, the output of the first multiplier connected in series through the first low pass filter, the first analog-to-digital Converter, the first microprocessor system of the discrete Fourier transform, the third multiplier, the first microprocessor system inverse discrete Fourier transform and the first squarer connected to the first input of the adder, the output of the second multiplier connected in series through a second low pass filter, the second analog-to-digital Converter, the second microprocessor system of the discrete Fourier transform, the fourth multiplier, a second microprocessor system inverse discrete Fourier transform and the second the squarer connected to the second input of the adder, one output of the pulse generator sampling through serially connected frequency divider by two, the clock pulse generator of the reference pseudo-random sequence, the third analog-to-digital Converter and a microprocessor system of the discrete Fourier transform of the reference pseudo-random sequence is connected to the second inputs of the third and fourth multiplier products, another generator output pulse is s sample rate connected to the second inputs of the first, the second and third analog-to-digital converters, the output of the adder through the arithmetic unit taking the square root of a number is connected to the input of the threshold device, the output of the threshold device is a digital output detector complex signals.



 

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