UDC: 621.391.837:621.397.13

Artyukhin V.V. – PhD, associate professor KUPS, Almaty

Shabelnicov E.A. - PhD, associate professor KUPS, Almaty

Safin R.T. - senior lecturer, master student of KazATC, Almaty

Robust nonlinear filtration of signals with a variable spectrum

Abstract

The results of experiments on increase of a noise stability video systems of means of the nonlinear filter with the changing cut frequency are given in a work.

Keywords: robastny filtration, processing of signals, increase of a noise stability, signal spectrum.

Get a widespread system, which changes the signal spectrum, which complicates the decision of its noise immunity. The main objective of this work is to determine the possibility of improvement the quality of the video signal with variable width of the spectrum and pulse interference.

One of the simplest decisions of improvement the quality of signal is the use of linear filtration. Linear filtration exclude out-of-band interference, but to exclude or reduce the in-band interference can not. That is, linear filtration averages without considering all possible values of interference.[1]

One of the prospective methods is the use of robust nonlinear filtration The main difference and the main advantage nonlinear filtration from the linear filtration is the use in practical implementations, when unknown characteristics of the signals and interference. The main ones are temporary stationarity, i.e. unchanged in time the main statistical and spectral-correlation characteristics of signals and interference, and often a Gaussian distribution law of the noise, that need to be put down. Therefore, noise immunity of robust system more than the matched filtration (МF) approximately 3 dB, and the quasi-optimal linear filtration (QLF) - 5 dB. [2]

Figure 1 presents functional scheme of robust nonlinear filter.[3]

Figure 1– Functional scheme of robust nonlinear filter

In perspective of the use of this non-linear filtration advisable its possible use in video surveillance systems. The work presents experimental research possibilities of this method. The principal difference of the new filter is modification of the clock frequency switching of nonlinear capacitance as a function of the width of the spectrum of the input signal. On the basis of this scheme has been designed model on the PCB; her scheme is shown in Figure 2.

Figure 2– Tracing PCB of model robust nonlinear filter

Block scheme of the experiment included: robust nonlinear filter on the chip K500LM102 with TTL logic field-effect n-channel MOS transistors with insulated gate BSS 138; the oscilloscope С1-220; generator G4-151 with a maximum frequency of 150 MHz; a video camera with different resolution, and therefore, with different width of the output signal (NVC-825DN) and a pulse generator (interference) UTS-2010.

Figure 3 presents a block scheme of the experimental equipment.

Figure 3 – Block scheme of the experiment

The program of the experiment included:

- getting the test image from a video camera connected to a video monitor, without the presence of any interference;

- check the filter with the presence (connection) in-band pulse interference of different frequencies from the pulse generator GCP UTS-2010 with a change frequency of the clock pulses from generator G4-151.

The spectrum of the input signal changed by switching the TV lines 380 to 580 TVL. Pulse interference connected at frequencies equal 3,33 MHz, 4,0 MHz, 5,0 MHz, 6,67 MHz. Table 1 shows the values obtained in the experiment, and the waveform (Figure 4) shows, that when connecting the robust nonlinear filter high frequency pulse interferences disappear, but it decreases the signal level at 25% in contrast to the original.

Figure 4– Image of waveform when checking the filter

T a b l e 1 – Signal levels for 420 TVL, at U_mout = 1,0 V, U_pulse.interf = 2,0 V

fclock, MHz	50	60	70	80	82,1	90	100	110	120	123,33	130	140
Umout, video, V	0,9	0,9	0,9	0,9	0,9	0,9	0,9	0,85	0,75	0,7	0,5	0,2
Umout, puls. interf. 1 (3,33 MHz),V	1,9	1,9	1,85	0,8	0,5	-	-	-	-	-	-	-
Umout, puls. interf. 2 (4,0 MHz), V	1,9	1,9	1,9	1,9	1,9	1,85	0,45	-	-	-	-	-
Umout, puls. interf. 3 (5,0 MHz), V	1,9	1,9	1,9	1,9	1,9	1,9	1,9	1,85	1,78	0,45	-	-
Umout, puls. interf. 4 (6,67 MHz), V	-	-	-	-	-	-	-	-	-	-	-	-

Figure 5 shows the dependence of the output signal from the clock frequency for the different frequency of pulse interference.

Figure 5 - The dependence of voltage U_{m out} from the clock frequency for the different frequency of pulse interference

It can be seen, that at the value of the clock frequency of about 123.33 MHz occurs blockage characteristics to a value not exceeding 0.7 the maximum, and all the signals of pulse interference are practically absent, that confirming the theoretical positions, that the clock frequency of switching of filter must correspond to 25-times the width spectrum of the input signal. Similar values were obtained for the input signals with other width spectrum. The values of the clock frequency conformed to the theoretical.

Conclusion:

Thus, the experiment confirmed that a robust nonlinear filter is capable of operating in a changing of input signal spectrum, also requires a matched frequency of clock generator. Simulation and experimental results of robust systems indicate that increasing the noise immunity compared with known structures can be up to (10 - 20) dB and they may be used in systems with a changing of input signal spectrum.

List of used literature:

1. Марчук В.И., Воронин В.В. Методы и алгоритмы восстановления изображений в условиях неполной априорной информации. Монография. – М.: ГОУ ВПО «ЮРГУЭС», 2010.

2. Huber J. Robustness in statistics: translation from English [Text] / J. Huber. - M .: Nauka, 1984 - 304 p.

3. Makhlin A.A. Filters on switched-capacitor / AA Makhlin // Magazine "Components and technologies." - 2008. - T.10, №6. - P. 10-12.