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5.2. ANALYSIS OF SOME LINEAR-ELECTRICAL FILTERS IN OPTO-ELECTRIC OF THE TELECOMMUNICATION NETWORKS
Juraev Nurmuhammad Mamatovich head of department of telecommunication engineering. Ferghana branch of the Tashkent University of information technologies. E-mail: juraev-n@umail.uz
Abstract: Some of the filters, used in opto-electrical networks, are analyzed in this article. They are compared, conclusions are considered about the advantages and disadvantages of each type of filters.
Index terms: electrical filter, filter of Bessel, filter of Chebyshev, filter of Butterworth, jitter, intersymbol interference, eye diagram, histogram, simulation, OptSim.
1. INTRODUCTION. ELECTRICAL FILTERS AND THEIR APPLIANCE
Although it is the direction of development of telecommunications in the direction of optical transmission and optical networks, the electrical part of the telecommunications network cannot be ignored - at least in the present moment, when not all of the telecommunications networks are optical. One of the important element of the electrical part of optical telecommunications networks are electrical filters.
Filters used for the smooth (low attenuation) passing currents at some frequencies and delay (or bandwidth with high attenuation) other frequency currents. In short, the filters allow or delay some bandwidth. These bands are respectively called bandwidth (passband) and the band detention (stopband).
Typically, electric filters are manufactured in a two-port, installed between the power supply and the load electric filters can be applied in any telecommunications wired- or wireless networks, the transmitting or receiving channel.
Filters can be classified according to several criteria: according to the method of signal processing; for transmission / retention strip; by the transfer function.
According to a method of signal processing filters can be analog and digital (in this article we shall discuss about electric filters).
As bandwidth / detention filters can be low-pass filters (LPF), a high-pass filter (HPF) and a band-pass filter (PF).
According to the transfer function of the filters are divided into: Butterworth filters; Chebyshev filters; Bessel filters; elliptic filters.
2. SOME FILTERS AND THEIR TRANSFER FUNCTION
The transfer function is one of the main ways to describe some of the dynamic system. It expresses the relationship between input and output of the system, i.e., knowing the transfer function of the input signal and can anticipate on the output signal. In short, the transfer function gives a complete description of the filter in both time and frequency domain. The transfer function is a differential operator.
2. 1. BUTTERWORTH FILTER
This filter is one species of electronic filters. It's named by the name of a British engineer Stephen Butterworth who
first described this filter. This filter is the simplest to implement and specification [1]. The transfer function has the form
H(s)=-
(1)
nt=(s-sk/Mc)
wheres = +ja>; n - The order of the filter;
- Cut-off frequency (the frequency at which the amplitude is equal to -3dB);
^o - The gain on the constant component (gain at zero frequency);
2. 2 "cHEBYSHEV FILTER It's named after the famous Russian mathematician Chebyshev Pafnuty because this type of filter characteristics based on Chebyshev polynomials. It has two varieties. Chebyshev I and type II, which differ from one another coolness recession amplitude characteristic. We kind of Chebyshev II filter characteristic is less steep. Sometimes this type of filter is called inverse Chebyshev filter and it is used less frequently than the Chebyshev Type I filter. This article is about Che-byshev's filter type I [2].
This type of filter is best used where needed with a small order of the filter to provide the required amplitude-frequency characteristic (AFC), for example, good suppression of the suppression band of frequencies, and wherein the smoothness of the frequency response at frequencies and suppress transmission bands is not so important.
H(s) = n
(2)
(s spm)
where s~m - Only those poles which have a negative real part.
In general spm is defined as
spm = +sh(1arsh(1))sm(8m) + jch ^arsh^cos^) where m = 1,2,3,..., n. Value 6m is defined as i
n 2m-l 2 n
2. 3. BESSEL FILTER
This filter is one of the most common linear filters which has a smooth maximum group delay. This means that this filter has a linear phase response. This type of filter commonly used in audio crossovers [3].
Bessel filter transfer function is defined by the following formula:
where 0(s) - reverse Bessel polynomial, which is why the filter and its name; wo - Cut-off frequency.
3. A LITTLE ABOUT JITTER, EYE DIAGRAM, ABOUT ITS HISTOGRAMS AND THE BIT ERROR RATE
Jitter is called a deviation indicative signal portions of their desired position in time, i.e., as sooner or later the signal changes state with respect to the correct moment of transition jitter is due to the amplitude and phase noise, both internal and external origin. Jitter signal may have different characteristics depending on its causes and sources jitter D can be divided into the following main categories: random (random jitter - RJ) and regular (deterministic jitter - DJ).
Random jitter occurs due to noise processes occurring in all semiconductors and components.
Regular jitter arises from the processes acting on the signal occurring in the system equipment IAOD, and may occur under certain ways of presenting the data transmitted.
Jitter can detect eye diagrams and histograms.
Eye diagram is called a total view of all the bit periods of the measured signal, superimposed on each other. In other words, the image signal from the beginning of the period 2 to the beginning of the period 3 is superimposed on the image signal from the beginning of the period 1 to the beginning of period 2, and so on for all bit periods. Eye diagram can identify the waveform, but only with a periodic signal structure.
The study eye diagrams allows a detailed analysis of the digital signal in the parameters directly related to the shape of the pulse fronts: setting inter-symbol interference (IS I), the data jitter and synchronization jitter.
The histogram is a distribution of the set of values provided by the measured parameter (generally, time or quantity, which are marked on the X axis), depending on their frequency of occurrence (Y axis).
Histogram and provides the information that the eye diagram is not available. When searching for a fault signal characteristics, such as the rise and fall time, period and duty cycle can be displayed on the histogram. These histograms illustrate distribution of productivity for different operating modes, which can be related to the functioning of the circuit conditions, for example, kind of transmitted sequence.
Coefficient bit error (BER - Bit Error Ratio) is the ratio of incorrectly received bits to the total number of them.
The lower the BER, the better the signal quality.
4. DESCRIPTION SOFTWARE MODELING OPT SIM
OptSim System is a suite of simulation of modern optical communication system and is intended for the pro-
Juraev N. M.
fessional design and cutting-edge research in fields of WDM, DWDM, TDM, cable TV, optical network, optical parallel bus, and other developing optical telecommunication systems, data transmission and other applications. On and it can be used as well for the development of optical communication systems, and their simulation to determine their effectiveness in view of the various components of the parameters. OptSim can be used with very high accuracy and ease of Windows platforms, LINUX and UNIX. It includes the most advanced component models and simulation algorithms, which ensures the highest possible accuracy and real results.
OptSim is an optical communication system with interconnected set of blocks, each block represents a component or sub-system in a communication system. Each block is simulated independently, using the parameters specified by the user for the data unit and the signal transmitted to it from the other blocks. This is known as a block-oriented methodology I was modeling. These blocks are represented graphically in the form of icons OptSim. Internally, they are presented in the form of complex data structures and numerical algorithms.
OptSim includes an extensive library of component models of the most commonly used components in mechanical engineering for the opto-electronic systems. This component library is constantly expanding due to ongoing research and cooperation with world-renowned experts in the modeling of large optical technology centers around the world.
OptSim includes models and algorithms developed in collaboration with the Polytechnic University of Turin, University of California at Santa Barbara and the University of Illinois at Urbana-Champaign. It includes the possibility iFROST (illinois FibeR-optic Link Demonstrator - The demonstrator fiber-optic line IL) of the University of Illinois at Urbana-Champaign, who received a license RSoft Design Group, FOLD (Fiber Optic Link demonstration) from the University of California at Santa Barbara, who received a license RSoft, LinkSIM™, which was developed RSoft Design Group, and OptSim™ version 3.5, which was n riobretena at ARTIS for RSoft.GUI. Some aspects of the product are derived from the simulation of software projects Ptolemy II and Ptolemy Classic University of California at Berkeley. OptSim also includes a large selection of pre-defined parameter sets component, representing a wide range of commercially available components. They can be easily selected in the edit box component of the model parameters.
In addition to an extensive library of components, OptSim 4.0 includes a new first, but easy to use graphical user interface (GUI). The user interface provides a hierarchical object-oriented environment for the development of CAD and schematic design of the system. The main window OptSim system shown in Figure 1.
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Fig.1. The main simulation system (product) window Opt Sim.
Each simulation scheme (document) in the Opt Sim The project is called, or connections between components and these documents are stored with the file extension .moml or. opm.
Simulation strategy in both the aforementioned documents Opt Sim are of two types: Strategy Selective Mode and Strategy block mode.
Selective Strategy Simulation Mode executes simulation in which the signal data transmitted between the components is one step at a time or time sampling Sampling mode provides two types modeled by IAOD:. Technique Spectral Distribution (Spectral Propagation Technique - SPT), which performs fast simulation of the optical spectrum, including The tea amplified spontaneous emission noise, optical amplification and optical filtering; and Variable Bandwidth simulation (VBS), which performs signal modeling full timedomain options to turn on all of the effects of noise or no noise, in a linear or non-linear modeling.
Strategy simulation block mode performs a simulation in which the signal data transmitted between the components is the whole simulation time in one data block. The advantage of this approach is that the constituent model and algorithms can easily work with a signal, converting it back and forth between the time and frequency domain for data in the most convenient algorithm for modeling. This modeling approach has been used in such products as LinkSIM and iFROST [4].
5. SIMULATION ANALYSIS OF ELECTRIC CIRCUITS FOR FILTERS
To determine the jitter electrical filters selected strategies and Simulates Selective Mode Simulation with m Variable Bandwidth (VBS).
Simulation scheme for determining the jitter of the above filters is shown in Fig.2. The circuit consists of a set of elements of the transmission, reception and linear-amplifying sections of the optical network. The test filters are on the receiving side and connected in parallel to the output of the opto-electric converter (receiver).
Each element is connected to another one of the three lines: blue (electrical interface), red (optical interface) and dashed (measurement interface).
The transmitter section consists of Digital Data Source (DataSource); converter line signal NRZ (Non Returnto Zero - no return to zero); laser diode CW Lorentzian (Continuous wave Lorentzian laser or Continuous Laser Radiation Lo-rentz); modulator (applied sinusoidal modulator of Mach-Zehnder) and EDFA amplifiers (Erbium Doped Fiber Amplifier -fiber optical amplifier in an optical fiber doped with erbium ions). The latter has a coefficient of 6 dB gain, and noise introduced them equal to 5 dB.
As used single-mode line optical fiber with a mixed dispersion. An optical line length of 150 km, 50 km after each EDFA amplifiers are used with the same coefficient, as in the transmitter portion. The same power exists at the input of the receiving part. Test filters connected in parallel to the output of the opto-electric converter, and thus they have the same conditions for the studies.
The receiving part consists of an input amplifier, opto-electrical converter (photo detector); Bessel Filter, Cheby-shev and Butterworth; electric analyzer; estimator Q - factor and BER.
Fig.2. The simulation scheme for determining the jitter of the Bessel filter, Butterworth and Chebyshev.
6. RESULTS OF MEASUREMENTS AND DATA ANALYSIS
Figure 3 (a, b, c) shows respective ocellar Bessel filter diagrams, Chebyshev and Butterworth.
Juraev N. M.
options are ideal, ie, higher the Q, the BER lower, wider eye diagram, etc.
a)
-~ slm_SH1 Evs OianrflfnatM4, £COBa2, Run 1
; ; < j ;
......
i / V / \ /
mf
b)
Figure 3. E eyelets s Bessel filters diagram (a), Chebyshev (b) and Butterworth (c).
The signals of all three filters are duplex with a period Ts = 0.1 ns. By analyzing the signals can be determined that the track two-level signals in the eye diagram at time points corresponding to the reference point passes exactly through the normalized values « 2.5e-006 and =2.75e-005, therefore, the ISI on all signals available.
It is possible to distinguish that the Chebyshev filter (Figure 3, b) has a steeper slope, ie, a steeper fronts in this filter.
Butterworth and Bessel filters (Figure 3, a, c) have a pronounced two separate lines around the lower boundary edges of bandwidth, which means that these filters are deterministic jitter is closer to the lower limit bandwidth.
The width of the intersection of the rise and fall of the signal points is called the peak jitter or data jitter. As you can see, this option is a little more in the Chebyshev filter.
Figure 4 (a, b, c) shows the corresponding values for the average BER threshold values of the Bessel filter (a) Chebyshev (b) and Butterworth (c). The optimal thresholds all
iV-SH
-r......r......r......r......r......r......r......r......r-
-L______L______L______L_____i______L______L______L______L-
■-Y......t......t......f-......h-
-f-r-t-t
Figure 4. With lightened BER values for the average of the threshold values of the Bessel filter (a) Chebyshev (b) and Butterworth (c).
The graphs show that the Butterworth and Chebyshev filter coefficient lower BER (approximately equal) than the Bessel filter.
7. CONCLUSION
OptSim SYSTEM is a very effective tool for simulating and modeling optical networks, monitor the entire network and its individual elements.
Due to the fact that the simulation circuit used in a single-mode mode inter symbol interference (ISI) is not considered at all filters. From this we can conclude that if
these filters are applied in single-mode operation, the inter-symbol interference in these filters will not.
The ability to filter deteriorates (observed nonlinearity), closer to the borders of bandwidth, especially the lower boundary. This property is clearly seen especially in Bessel and Butterworth filters.
Although this option is not so pronounced in these filters, but the Chebyshev filter is more prone to data jitter.
Analysis of BER It indicates that immunity to the Bessel filter error less.
References:
1. V.S. Sitnikov, Degterev A.V. «Modelling and identification of the Butterworth filter when it is used as a digital integrating filter». X semenar «Modeling in applied research», 2004
2. Al-Noman A.A., Sergeev V.V. «Comparative analysis of the stability of l e stnichnyh jet filters Chebyshev and Kauer.» Magazine «Automation and Telem e mechanics», 1998, Issue 10, pp. 185-189.
3. Titov A.A. «Problems in the basics of radio.» Educational handbook for practical training for students and Radiotekhn cal specialties. - Tomsk: Tomsk State University iversitet s management systems and electronics 2007.
4. Optsim - User Guide RSoft Design Group, Inc.
