Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"Rastislav RÓKA"

Bandwidth Scheduling Methods for the Upstream Traffic in Passive Optical Networks DOI:10.15199/48.2018.04.03

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During the last couple of years, passive optical networks PON has been identified as one of the most important mile technologies. As a consequence of the solution of passive optical networks, a huge amount of users can benefit from the use of broadband services worldwide. Particular subscribers have an increased demand with regards to the allocated bandwidth in passive optical networks as well. The main reason for that we can see is that there are various services introduced year by year like IPTV, HQ Video Services, etc. In a common structure of a passive optical network, the source traffic is initiated from a unit called as optical line termination OLT. That unit is located mainly in the central office CO and passing thru the data into the optical fiber for a distance of decades in kilometers. The next unit handling this incoming traffic is an optical splitter which is distributing the signal into several optical fibers. The traffic from here is handled towards by a network unit ONT, which is usually deployed next to the customer premises. [1] The optical signal is terminated here before it will pass over to the users and subscribers. Certainly there are different subscribers with different nature of requirements, therefore the requested time slots as well as the transmission delays within the network topologies are various. To satisfy these needs, the developers have to constantly find new solutions on how to allocate bandwidth. So far, one of the most effective option seems to be to assign the time containers T-CONTs in many various ways. If this is accomplished, the architecture FTTX can still remain attractive to the subscribers. To make this solution competitive with regards to the other available network solutions, the initial cost of this system also has to be kept as low as possible. Passive optical networks PON are now available for many years. There are several standards out there for passive optical networks a[...]

Analysis and simulation of dynamic properties for the DFB laser DOI:10.15199/48.2018.07.04

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Constantly increasing end-user requirements lead to increased demands for the data transmission speed and thus to the need to develop new technologies used in optical transmission networks. Recently, the focus has been paid to the transmission systems with capacity in excess of 100 Gb.s-1 per one channel [1]. This amount of capacity can be only reached using high order modulation formats, multiplexing techniques, such as the wavelength division multiplexing (WDM), the spatial division multiplexing (SDM), and high-quality optical sources with a very narrow spectral linewidth [1-4]. Laser noises [5-7] are one of the most limiting factors of the optical transmission system. Therefore, is necessary to create a model of the DFB laser that can represent behavior of the light source including its limitations. The DFB laser model must be based on measured parameters in order to predict its corresponding system performance. In general, the intent of creating an optical transmission system model is important for testing optical modulation and/or coding techniques, noise thresholds, etc. [8-9]. In this paper, the complete numerical approach used in a simulation model for the DFB laser is presented, as improvement in existing optical transmission system developed before [10-11]. Laser output characteristics as the electron number, the photon number, the optical phase, the optical power and laser noises caused by fluctuations of these characteristics are obtained as results from the laser rate equation model based on parameters extracted by I. Fatadin and his team in [12]. We propose a mathematical methodology that can be used to model the DFB laser’s behavior under different operating conditions. In the Section I., the laser rate equation model including noise fluctuations is introduced. In the Section II., results of numerical simulations are presented and, finally, a conclusion of our work is situated. I. The Laser Rate Equati[...]

Simulation Platform for Analyzing Environmental Effects in Multi-Wavelength Transmission Systems in Matlab Simulink DOI:10.15199/48.2019.06.03

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One of methods that can increase a transmission capacity of the optical fiber is the Wavelength Division Multiplexing (WDM). Various forms of wavelength multiplexing techniques are considered for utilization in future metro-access networks with a combination of different network topologies [1]-[5]. Moreover, advanced modulation formats are investigated for utilization in nextgeneration passive optical networks with the WDM implementation [6]. This work aims to investigate environmental effects in multi-wavelength transmission systems and their specific influences on transmitted information signals [7]-[11]. With regard of the utilized frequency spectrum, two WDM forms can be under consideration [12]-[13]. One of advantages for Coarse WDM systems [14] is a cheaper implementation, since there is a larger channel spacing that allows using of simpler components like lasers and optical filters. Their main disadvantages are a smaller maximum count of transmitted channels and a complicated amplification, since a wider spectral transmission band is used and optical amplifiers are usually designed for a narrower spectrum. One of main advantages for Dense WDM systems [15] is a larger count of transmitted channels (up to hundreds) and a simpler possibility of optical amplification e.g. using EDFA amplifiers. For our investigation, it is crucial to prepare and create a reliable simulation platform that can be used for analyzing environmental effects at multi-wavelength signal transmission in optical systems. Therefore, the main part of this paper is intended for detailed description of particular block functionalities in the specific simulation platform for WDM systems and, subsequently, for analysis of environmental effects in CWDM and DWDM transmission systems. Principles of WDM Systems and Their Available Frequency Spectrum WDM systems allow transmitting of multiple user data channels through the one optical transmission path. T[...]

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