RU2331981C2 - Method and device for searching wideband signal affected by narrowband interference - Google Patents

Abstract

FIELD: .

SUBSTANCE: invention may be used in communication systems with wideband signals. Method of search provides for splitting samples of input signal with interference into those overlapping in time having duration defined by reaction time of pulse interference effect or narrowband interference change. The said samples are multiplied by "window" with preset spectral properties. Fast Fourier transform of multiplication results is performed. Narrow-band interferences are rejected. Samples of each frequency with rejections are accumulated at each time interval equal to wideband signal. Accumulated reports from each frequency are then subject to Fast Fourier transform. Transformation results are multiplied by corresponding samples of complex-conjugate copy of signal. After that, multiplication results are subject to Fourier inversion. Then, cross correlation function modules are calculated and signal is sought. Search unit contains memory unit (1), weight processing unit (2), Fast Fourier transform units (3, 5₁-5_N), Fourier inversion unit (8), sample module calculator (9), narrow-band interference rejection unit (4), complex-conjugate signal copy generator (7), N•N₁ of multiplication units (6).

EFFECT: improvement of fast unit response.

2 cl, 2 dwg

Description

The invention relates to the field of radio engineering and can be used to search for a noise-like signal in the case of exposure to narrow-band interference, white noise and impulse noise, including in systems with CDMA and GPS.

At present, analog and digital methods for processing a noise-like signal (SHPS) are known.

In the article by O.F. Bokka “Signal Detection Against the Background of Colored Noise”, Part 3, Communication Technology (TSS) Series Radio Communication Technology (TRS), issue 7, 1989, p.87-95 and RF patent № 2206179 “Broadband signal receiving device” describes in detail a method for searching for broadband signaling under the influence of narrow-band interference. In these works, the analog processing of SHPS is considered. The advantages of this type of signal processing are well known, but with large signal bases the number of correlators increases significantly. Difficulties in implementing a large number of correlators lead to the creation of search devices based on the Wald procedure, and this leads to a decrease in performance.

In the article by V. D. Tabatsky “Weighted processing of a noise-like signal under the influence of narrow-band interference”, TSS series TRS, issue 3, 1987, p.143-148, a digital method for processing SHPS using a fast Fourier transform is considered. But this method, with an abrupt change in the interference, reacts to it only after a time equal to the signal duration time, while the speed of the notch block rejection unit is determined by the signal duration.

Closest to the proposed is the method described in the article by V. D. Tabatsky "Analysis of the algorithm and block diagram of a digital matched filter of noise-like signals", TCC series TRS, issue 7, 1990, p.100, adopted as a prototype.

The prototype method includes fast Fourier transform of samples, analysis of the spectrum of the input signal with noise, rejection of narrow-band interference, multiplication by a copy of the signal, the inverse Fourier transform, search for the signal at the output of the matched filter.

The disadvantage of the prototype method is the low and fixed speed of this algorithm on the impact of pulsed interference, as well as a step-like change in narrow-band interference.

The proposed method is free from the lack of a prototype.

This is achieved by the fact that in the method of searching for a broadband signal under the influence of narrow-band interference, which consists in dividing into segments in the time domain of the samples of the input signal, analyzing the spectrum of the segments of the input signal with interference, weighting (rejection of concentrated interference), multiplying by a copy of the signal, in calculating the correlation function and detecting the presence of a signal, according to the invention, the segments of the input signal are selected overlapping, the duration of the segments is determined by the response time to the action of pulsed noise or change lumped interference spectrum calculated sample sequence frequency corresponding to a time interval equal to the duration of the signal, and subsequent crosslinking of the calculation results of the spectrum.

The essence of the proposed method is as follows.

The spectrum of the input signal with interference is analyzed. The duration of the analysis is determined based on the speed of devices with a given frequency selectivity. The rejection of narrow-band interference is carried out by one of the known methods similar to analogue protection units. At each frequency at which the notch was performed, samples are accumulated over a time interval equal to the signal duration. After that, a more subtle spectrum analysis is performed - it corresponds to the analysis, which in the absence of interference is carried out over the entire duration of the signal. Then each sample is multiplied by a copy, and the correlation function is calculated from the multiplication results and the input signal is detected.

Using the proposed method allows to obtain a gain in speed, and the gain increases with increasing signal base.

The closest in technical essence to the proposed one is the device described in the article by V. D. Tabatsky “Analysis of the algorithm and block diagram of the digital matched filter of noise-like signals”, TCC series TRS, issue 7, 1990, p.104, adopted as a prototype .

The scheme of the prototype device is presented in figure 1, where it is indicated:

1.1, 1.2 - input random access memory (RAM);

3 - block fast Fourier transform (FFT);

6 - block multiplication;

8 - block inverse Fourier transform (OBPF);

9 - unit calculation modules of the received samples;

11.1, 11.2 - blocks of weight processing;

12 - control unit;

13 - block analysis of the spectrum;

14 - block forming the transfer function of the filter (FPF).

The prototype device contains RAM 1.1 and 1.2, the outputs of which are connected to the first inputs of the respective weight processing units 11.1 and 11.2, the outputs of which are connected to the corresponding inputs of the FFT 3, the output of which is connected to the first input of the transfer function forming unit of the filter 14 and the input of the spectrum analysis unit 13, the first output of which is connected to the second input of the FPF block 14, the second output of the spectrum analysis block 13 and the output of the FPF block 14 are connected to the first and second inputs of the multiplication block 6, respectively, whose output is connected to the first Odom IFFT unit 8, the output of which is connected to the calculation unit modules obtained results 9. The third output 13 of the spectrum analysis unit is connected to the third input of the weighting processing unit 11.2. The first output of the control unit 12 is connected to the second inputs of the weighing blocks 11.1 and 11.2, the second output of the block 6 is connected to the second inputs of the RAM blocks 1.1 and 1.2, the third output of the block 12 is connected to the third input of the FPF block 14, the fourth output of the block 12 is connected to the second input OBPF block 8.

The prototype device works as follows.

The input signal enters the RAM blocks 1.1 and 1.2, where a sample is taken in the time domain with a duration equal to the signal base and is read into the weight processing block 11.1. Both RAM 11.1 and 11.2 are made in parallel, which allows you to simultaneously write and read input samples. The first readout of samples from RAM is carried out without multiplication by the weight function. The spectrum analysis unit 13 detects narrowband interference and determines the number of spectral components of narrowband interference. If their number is greater than N / 2, then, in accordance with the above algorithm, the recorded input samples are read from the RAM again and multiplied by the weight function in the weight processing block 11.2. The spectrum of the weighted input sample array is recalculated. When analyzing the spectrum, block 13 supplies the block 14 with the coordinates of the spectral components in which concentrated interference is detected. In block 14, a transfer characteristic is formed from the point of view of matching and from the point of view of whitening “non-white noise”. In the multiplication block 6, the complex conjugate signal is multiplied by a copy of the signal, the output is a signal with “cut out” noise and with a linear phase characteristic. After multiplying the input mixture and the transfer function in block 6, the spectral components of the interference will be equal to zero. The resulting product of two sequences in the block OBPF 8 is converted into the time domain. At the output of OBPF 8 we obtain the correlation function of the signal. And then, in the block of calculation of module 9, the modules of the obtained samples are calculated. The control unit 12 provides synchronous operation of blocks 1.1, 1.2, 11.1, 11.2, 8 and 14.

The disadvantage of the prototype device is the low and fixed speed when exposed to pulsed interference and abrupt change in narrow-band interference.

The proposed device is free from the lack of prototype.

This is achieved by the fact that in a broadband signal search device under the influence of narrow-band interference, comprising a memory device, a weight processing unit, a first Fourier transform unit, a first multiplication unit, an inverse Fourier transform unit, a calculation module of the obtained samples, in accordance with the invention the first block of fast Fourier transform is designed for the interval determined by the reaction time to the action of pulsed noise or change focused interference, the outputs of which are connected to the corresponding inputs of the rejection unit of narrow-band interference, the outputs of which are connected to the inputs of the N corresponding blocks of the fast Fourier transform, designed for the signal duration, the outputs of which are connected to the first inputs of the corresponding multiplication blocks, the second inputs of which are connected to the outputs of the generator conjugate signal instances, the outputs (N · N ₁ -1) multiplication units connected to respective inverse Fourier transform unit inputs, the output of calculating unit m modulus obtained samples connected to the input detecting unit.

A diagram of the proposed search device is shown in figure 2, where indicated:

1 - RAM;

2 - block weighing and multiplying by copy;

3 - the first block of the fast Fourier transform (FFT);

4 - block rejection of narrowband interference;

5 ₁ -5 _N - blocks of the fast Fourier transform (FFT);

- блоки умножения;

- multiplication blocks;

7 - generator complex conjugate copies of the signal;

8 - block inverse Fourier transform (OBPF);

9 - unit calculation modules of the received samples;

10 is a detection device.

There are a lot of examples of execution of a detection device in the literature, for example, Fig. 7.12, p. 285 V.I. Borisov, V.M. Zinchuk, A.E. Limarev, N.P. Mukhin, G.S. Nakhmanson "Interference immunity of radio communication systems with the expansion of the spectrum of signals by modulation of the carrier pseudorandom sequence ”edited by V.I. Borisov. M., “Radio and Communication” 2003, fig. 2.5.1 p. 70 “Noise-like signals in information transmission systems” edited by VB Pestryakov. M., "Owls. radio ", 1973

количество которых N·N1, вторые входы блоков умножения

соединены с соответствующими выходами генератора 7, выходы блоков умножения

соединены с соответствующими входами блока ОБПФ 8, выход которого соединен с входом блока вычисления модулей 9, выход которого соединен с входом устройства обнаружения 10.The proposed search device contains a series-connected RAM 1, a weighing and multiplying by copy 2 block, a first FFT block 3, N outputs of which are connected to the corresponding inputs of the narrow-band interference rejection block 4, N outputs of which are connected to the inputs of the corresponding FFT blocks 5 ₁ -5 _N , N ₁ outputs of each FFT block 5 ₁ -5 _{N are} connected to the first inputs of the corresponding multiplication blocks

the number of which is N · N1, the second inputs of the blocks of multiplication

connected to the corresponding outputs of the generator 7, the outputs of the multiplication blocks

connected to the corresponding inputs of the OBPF block 8, the output of which is connected to the input of the module calculation unit 9, the output of which is connected to the input of the detection device 10.

The proposed search device operates as follows.

In block 1, it is partitioned into overlapping arrays so that after multiplying by the “window” during addition, the original sequence is obtained. Moreover, depending on the type of window used and the overlap coefficient, the sequence may have spurious amplitude modulation (PAM), which leads to some deterioration in the sensitivity of the device. When constructing the device by selecting the overlap coefficient, the PAM level of the permissible value of the device sensitivity reduction is controlled. In block 2, multiplication by a “window” is performed, i.e. The required selectivity of the protection unit is ensured. When designing, a “window” is selected with the appropriate spectral properties that provide the necessary dynamic range for protection against concentrated interference (“Using Windows in Harmonic Analysis by the Discrete Fourier Transform”. F.J. Harris, TIIER, Vol. 66, No. 1, January 1978 g.). In block 3, the FFT is calculated for the arrays weighted with the “window”. Each sample at the output of the FFT 3 unit corresponds to its frequency of the notch block rejection unit 4. Block 4 performs the notch rejection of narrow-band interference by traditional algorithms. In each FFT block 5 ₁ -5 _N , a sequence is calculated from each output of the narrowband interference rejection block 4 on the signal interval. From the N1 outputs of each FFT block, the signal is supplied to the inputs of the multipliers 6, the number of which is N · N1, the second inputs of which from the block 7 receive the samples of the complex conjugate copy. In blocks 6, multiplication by a complex conjugate copy is performed. The resulting product in the block OBPF 8 is converted into the time domain. In block 9, the modules of the inter-correlation function are calculated. From the calculation unit of module 9, the signal enters the detection device 10, where the signal is searched according to the traditional algorithm.

The technical and economic efficiency of the application of the data of the method and device in comparison with the prototype is shown by the example of using the fast Fourier transform (FFT), so that the conditions are the same with the prototype.

, т.е. полоса, занимаемая сигналом, в 1,6 раза больше тактовой частоты.Suppose, for example, the signal base is B = 2047, the bandwidth limit coefficient

, i.e. the band occupied by the signal is 1.6 times the clock frequency.

For the prototype method, the number of samples for the FFT is:

N = B · 2 · K = 6550 points,

for the proposed method:

N1 = nK

where n is the number of channels through which the notch is performed.

The maximum number of channels used in analog receivers is n≈40.

. Причем при увеличении базы сигнала (В) выигрыш будет еще больше.Thus, N1 = 60 points. The gain in comparison with the prototype is

. Moreover, with an increase in the signal base (B), the gain will be even greater.

Claims (2)

1. A method of searching for a broadband signal under the influence of interference, which consists in dividing the samples of the input signal with interference into time-overlapping segments, the duration of which is determined by the response time to the effect of pulsed noise or to a change in narrow-band interference, multiply these segments by a “window” with the given spectral properties, perform fast Fourier transform (FFT) of the multiplication results, perform the rejection of narrow-band interference, on a time interval equal to the duration of the broadband signal In this case, they accumulate samples of each frequency at which the notch was performed, perform FFT of accumulated reports of each frequency, multiply the conversion results by the corresponding samples of the complex conjugate copy of the signal, perform the inverse Fourier transform (IFFT) of the multiplication results, calculate the modules of the correlation function and search for the signal. 2. A device for searching for a broadband signal under the influence of interference, comprising a series-connected memory device, a weight processing unit and a first FFT unit, a series-connected IFFT unit and a calculation unit for the module of received samples, characterized in that N outputs of the first FFT are connected to the corresponding inputs of the narrowband rejection unit interference, N outputs of which are connected to the inputs of N corresponding FFT blocks, N1 outputs of each of the N FFT blocks are connected to the first inputs of the corresponding multiplication blocks, orye inputs are connected to outputs of the generator complex conjugate signal copies outputs N • N ₁ units of multiplication are connected to corresponding IFFT unit inputs, the output obtained samples module calculating block is connected to the input of the detection device, wherein the conversion of the first block FFT determined response time of the effect pulsed interference or narrowband interference variation, the conversion time of each of the N FFT blocks is determined by the duration of the broadband signal.

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