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  • Author: G. Ivanovs x
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Comparison of Different Modulation Formats and their Compatibility with WDM Transmission System

In the work, the intensity and phase modulation methods are compared for different versions of the wavelength division multiplexing (WDM) system. Binary and multilevel code formats are evaluated numerically, with OptSim simulation software at the bit rate of 10 and 40 Gbit/s, using long-fiber spans and dispersion compensation technique. The problems to be overcome at exploitation of multiterabit WDM systems based on 40 Gbit/s optical transmissions are: chromatic dispersion (CD), polarization-mode dispersion (PMD), dispersion slope, and nonlinear effects of the transmission line. We have investigated the potentialities of modulation formats for 40 Gbit/s WDM networks where most of the listed problems are avoided. It is shown that Duobinary and differential phase shift keying (DPSK) modulation formats are perfectly suitable for ultra-high spectral efficient WDM systems and possess high resistance to dispersion and nonlinear optical effects (NOE).


On the basis of an improved method of determining the combustibility of tobacco comprehensive investigations were carried out of factors which influence combustibility. On the strength of statistical studies of the correlations, the following conclusions were drawn:

1. The most precise unit of measurement of the combustion of tobacco leaf is the product of “duration of combustion” and “amount of substances burnt” (secs. × mg).

2. The mineral components influence combustibility variously, K2O positively, Cl-, Na2O, Fe2O3 and P2O5 negatively, whilst SO4- -, SiO2, CaO and MgO have no influence.

3. The coefficients of combustibility suggested up till now, which are based solely on the composition of the mineral components, demonstrate only a very weak correlation.

4. Isolated groups of organic substances demonstrate no incisive correlation to combustibility.

5. The concentration of all organic substances in the volume unit, the “substance density”, shows a high, negative correlation to combustibility; the “porosity” of the leaf is also clearly correlated to combustibility.

6. Combustibility is influenced by the combined action of part of the inorganic components, the concentration of organic substances in the volume unit and the porosity of the leaf. The combustibility index (C.I.), which was ascertained on the strength of these combined actions, seems to be the most suitable indicator of combustibility.

DWDM Transmission Based on the Thin-Film Filter Technology

A dense wavelength division multiplexing (DWDM) transmission scheme with two thin-film filters (FWHM bandwidth 100 GHz and 200 GHz) has been realized to evaluate the minimum channel interval needed for a satisfactory bit error ratio. For this purpose, detailed research was conducted into the impact of the filters on the optical signal's de-multiplexing in a DWDM system, in which the measurements of eye diagrams and the optical power spectral densities of a received signal were made. From the results of measurements the minimum channel interval has been found for the optical filters that ensures reliable data transmission and higher spectral efficiency of the whole system. It was found that for a DWDM system with a 100 GHz filter a sufficient channel interval is 75 GHz at 10 Gbit/s data transmission speed, which means that its spectral efficiency is increased from 0.1 bit/s/Hz to 0.1333 bit/s/Hz.

Investigation into the Potentialities of Quasi-Rectangular Optical Filters in HDWDM Systems

Currently, many research topics in the field of optical transmission systems (mostly grounded on novel modulation techniques) are focused on increasing the total data transmission speed of an individual optical fiber. An alternative - but equally valid - approach to increasing the data transmission is to decrease the WDM channel spacing to high-dense dimensions while keeping the existing data transmission speed for an exact channel. We have developed an experimental HDWDM transmission system based on the quasi-rectangular optical filter technique. The results indicate that for 2.5 Gbit/s HDWDM transmission the suitable channel interval should be greater than 25 GHz, and for the 10 Gbit/s HDWDM solution - not less than 37.5 GHz between adjacent channels.

A Hybrid TDM/WDM-Pon System with FWM-Generated Source of Multiwavelength Optical Signals

A new approach to FTTx solutions is proposed, in the framework of which a hybrid TDM/WDM system using cascaded FWM-generated optical signals is evaluated by calculating the BER parameter and the optical power budget. Computer simulation is employed as the main method of calculations, with the results presented both in numerical and graphical forms. The results show that the use of a forward error correction allows the power margin of 4 dB to be achieved for the system to work reliably. The system can provide the total number of users up to 128 (8γx16 TDM users) with a bandwidth of multiple hundreds of Mbit/s p.u. by means of the existing passive optical networking infrastructure, with only minor improvements needed.

Efficient Wavelength Filters for DWDM Systems

The authors investigate the best parameters of optical filters for dense wavelength division multiplexing (DWDM) systems. The investigation is based on the OptSim 5.0 simulation software using the method for solving a complex set of differential equations taking into account the optical and electrical noise as well as linear and nonlinear effects. It is shown that the bandwidth of optical filter extends as the data transmission speed increases, and that the most efficient are Supergaussian and Raised Cosine optical band-pass filters. It is also revealed that an ASK-RZ 40 Gbit/s data transmission system is impossible to realize with a channel interval less than 50 GHz because of wide spectral density and lower chromatic dispersion tolerance of this modulation format.


The 694-790 MHz (700 MHz) band was allocated by the 2012 World Radiocommunication Conference (WRC-12) in ITU Region 1 (Europe included), to the mobile service on a co-primary basis with other services to which this band was allocated on the primary basis and identified for the International Mobile Telecommunications (IMT). At the same time, the countries of Region 1 will be able also to continue using these frequencies for their broadcasting services if necessary. This allocation will be effective immediately after 2015 World Radiocommunication Conference (WRC-15). In order to make the best possible use of this frequency band for mobile service, a worldwide harmonized frequency arrangement is to be prepared to allow for large economies of scale and international roaming as well as utilizing the available spectrum in the best possible way, minimizing possible interference between services, facilitating deployment and cross-border coordination. The authors analyze different possible frequency arrangements and conclude on the frequency arrangement most suitable for Europe.

The increased demand of mobile broadband consumers on services in the mobile environment with high data rate and technologically developed mobile broadband communication systems will require more spectrum to be available in the future. The new technologies as well as the existing services require frequencies for their development. The authors investigate the available and potential future mobile terrestrial frequency bands - worldwide and in Europe. An insight into the spectrum management is provided, with radio access technologies, methods for more efficient use of mobile frequency bands and frequency cross-border coordination also addressed. It is stressed that the radio frequency spectrum is a limited national resource that will become increasingly precious in the future.

Research of Traffic Management in Fttx Optical Communication Systems

The paper presents an overview of widely accepted passive optical networks (PONs), and provides the results of comparative OPTSIM simulation for PON technological facilities involving optical layers, with the aim to reveal fiber-to-the-x (FTTx) technologic solutions. Traffic load is simulated over a PON optical layer using the OPNET Modeler to determine potential advantages and drawbacks of the proposed FTTx solution with PON elements in the access networks. The authors show that the optimal transmission speed for PON FTTx would lie in the range 1.25-5.0 Gbit/s with a standard PON architecture, which could be raised to 10 Gbit/s, however in this case we have to change the end user's equipment. In standards that specify the PON's functionality two distances: 10 km and 20 km are indicated. Our simulation shows that, after upgrading the receiver electrical filter, 10 Gbit/s transmissions over 40 km could be reached.

Schemes for Compensation of Chromatic Dispersion in Combined HDWDM Systems

The authors seek best ways to realize chromatic dispersion (CD) compen-sation schemes for differently modulated optical signals in high-speed mixed data rate HDWDM systems. The research is based on OptSim 5.1. simulation software, which numerically solves nonlinear Schrödinger equation using the split-step Fourier method. It is shown that the CD compensation scheme is crucial for the performance evaluation in combined HDWM transmission channels. Therefore, a scheme of the type is proposed that is suited best for a very complicated combined fiber optical transmission system. It is also found that asymmetrical CD compensation schemes in pre- and post-compensation modules are the most efficient, allowing the best BER in a channel to be achieved.