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Ing. Pavel Lafata, Ph.D.

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Hybrid education in the field of digital technologies

  • Authors: Ing. Tomáš Zeman, Ph.D., Ing. Pavel Lafata, Ph.D.,
  • Publication: Proceedings of the 2022 31st Annual Conference of the European Association for Education in Electrical and Information Engineering (EAEEIE). Piscataway: IEEE, 2022. ISSN 2472-7687. ISBN 978-1-6654-8442-8.
  • Year: 2022
  • DOI: 10.1109/EAEEIE54893.2022.9820382
  • Link: https://doi.org/10.1109/EAEEIE54893.2022.9820382
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article is focused on the subject Digital technique, which is lectured at the Faculty of Electrical Engineering of the CTU in Prague. The subject is intended for the students of the 2nd grade of their basic study and each year approx. 70 students participate in this subject. Our aim is to continually increase the quality of laboratory measurements by including up-to-date and modern resources (FPGA development boards and kits) as well as interesting and important achievements in this area in order to make the subject as much interesting and motivating for the students as possible. Unfortunately, the last academic year teaching was negatively influenced by COVID pandemic and by various restrictions it caused, especially unpredictable opening and closures of the university for students, which caused the teaching was mostly performed in the online mode. Due to that, we decided to essentially update and transform the content of the subject towards modern resources and with respect to the abovementioned principles. The paper contains the description of these updates and upgrades we performed, especially focusing on the updates of laboratory tasks and experiments. The article describes the necessary prerequisites, restrictions and will focus deeper on laboratory tasks.

Experimental verification of a simulation model for extra-fast communication on twisted pair lines

  • DOI: 10.1109/ME49197.2020.9286697
  • Link: https://doi.org/10.1109/ME49197.2020.9286697
  • Department: Department of Telecommunications Engineering
  • Annotation:
    G.fast subscriber technology belongs to the most advanced access network technologies used in practice and it should be used for massive FTTx development. However, only the narrow band of G.fast subscriber lines is ready for practical deployment. Due to this fact, simulations and modeling of G.fast lines based on different transmission parameters and environment are important in order to estimate future access networks development. For that reason, it is important to relevant modeling and simulations of real access networks and various types of G.fast transmission lines. This paper deals with modeling and simulations of G.fast lines in typical twisted pairs in industry environment. The article provides calculations and simulations of G.fast lines for various types of metallic cables and under different conditions, including specific profiles of crosstalk spectral densities. Next, these theoretical simulations are compared with real measurements, which increases the accuracy of the modeling. These presented models can be used to accurately estimate the performance of local networks under different conditions in practice.

MODIFICATION OF HIERARCHICAL AGGLOMERATIVE CLUSTERING WITH COMPLETE LINKAGE FOR OPTIMAL USAGE WITH PASSIVE OPTICAL NETWORKS

  • DOI: 10.14311/AP.2018.58.0388
  • Link: https://doi.org/10.14311/AP.2018.58.0388
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Today, passive optical networks (PONs) represent a modern solution for high-speed FTTx subscriber lines and networks. Due to the fact that optical fibres and cables are deployed in last-mile network segments. Unfortunately, the costs of trenching and installation of optical cables in cities are still very high today. However, the application of mathematical methods and algorithms for designing optimum network solutions and topologies might significantly decrease the overall capital expenditures (CAPEX) of the whole process. This article introduces an efficient method based on agglomerative clustering for an optimization of deployment of PONs in practice. The paper describes its application and proposes the necessary modifications of the clustering method for the environment of PONs. The proposed algorithm uses the technique to cluster and connect the adjacent optical terminals and splitters of PONs and to calculate the optimum locations of these units in order to achieve the most optimum network solution and to minimize the summary capital expenditures.

Accurate low complexity modeling of twisted pairs suitable for G.fast frequencies

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: International Journal of Communication Systems. 2017, 30(6), 1-16. ISSN 1074-5351.
  • Year: 2017
  • DOI: 10.1002/dac.3093
  • Link: https://doi.org/10.1002/dac.3093
  • Department: Department of Telecommunications Engineering
  • Annotation:
    As the higher and higher frequency bands of existing metallic cables in access networks are being continuously exploited by modern transmission technologies, such as the G.fast, the necessity of providing accurate and suitable modeling of their transmission characteristics is evident. Therefore, this paper is focused on modeling of a propagation constant of twisted pairs and metallic cables at high frequencies up to 250 MHz, and an innovative arsinh model is proposed and described. This new model is based on an idea of adopting inverse hyperbolic sine function for modeling of both secondary line coefficients, attenuation constant and phase constant, and its main motivation is to provide their accurate estimations for G.fast frequencies up to 250MHz for various types of metallic cables while maintaining a low computational complexity. The proposed model was compared with numerous characteristics measured for various real metallic cables as well as with several existing models in order to illustrate its potential. The results, which are presented within this paper, clearly illustrate that the proposed arsinh model generally outperforms existing standard models based on the equal number of required parameters.

Optimizing of Passive Optical Network Deployment Using Algorithm with Metrics

  • Authors: Pehnelt, T., Ing. Pavel Lafata, Ph.D.,
  • Publication: Advances in Electrical and Electronic Engineering. 2017, 15(5), 866-876. ISSN 1336-1376.
  • Year: 2017
  • DOI: 10.15598/aeee.v15i5.2285
  • Link: https://doi.org/10.15598/aeee.v15i5.2285
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Various approaches and methods are used for designing of optimum deployment of Passive Optical Networks (PON) according to selected optimization criteria, such as optimal trenching distance, endpoint attenuation and overall installed fibre length. This article describes the ideas and possibilities for an algorithm with the application of graph algorithms for finding the shortest path from Optical Line Termination to Optical Network Terminal unit. This algorithm uses a combination of different methods for generating of an optimal metric, thus creating the optimized tree topology mainly focused on summary trenching distance. Furthermore, it deals with algorithms for finding an optimal placement of optical splitter with the help of K-Means clustering method and hierarchical clustering technique. The results of the proposed algorithm are compared with existing methods.

Bit channel with reused compressed bit sequences in downstream point-to-multipoint networks

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Int. Journal of Computers & Electrical Engineering. 2016, 56 1-14. ISSN 0045-7906.
  • Year: 2016
  • DOI: 10.1016/j.compeleceng.2016.09.038
  • Link: https://doi.org/10.1016/j.compeleceng.2016.09.038
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper brings an idea of establishing a downstream bit channel based on reusing of bit sequences and bit compression technique in point-to-multipoint passive optical networks for increasing their summary throughput. The downstream communication of these networks is based on broadcasting of multi-frames towards all active end-point nodes, therefore these frames cold be potentially reused multiple times to carry additional data in a form of segmented bit sequences spread within the entire bitstream. In order to achieve maximum effectiveness of a proposed method, bit addressing technique using relative sequence positions is proposed. Moreover, the presented bit compression technique might further increase the resulting summary throughput, while the application of existing bit compression algorithms cannot result in better performance. The illustrate the potential of a proposed algorithm together with the bit compression technique, the simulations and evaluations were performed and are presented within this paper as well.

Investigation of Phantom Circuit Benefits for Next Generation xDSL Systems

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: International Journal of Communication Systems. 2016, 29(1), 5-15. ISSN 1074-5351.
  • Year: 2016
  • DOI: 10.1002/dac.2786
  • Link: https://doi.org/10.1002/dac.2786
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper is focused on measurements and analysis of phantom mode benefits in G.fast and next generation xDSL systems. The investigation is based on real measurements performed for a multi-quad metallic cable together with theoretical evaluations of phantom circuit potentials. Because the presence of phantom circuits leads into increasing the summary crosstalk level in a metallic cable, the application of a phantom mode is questionable in practice. That is why the investigation was performed, and conclusions provided in this paper can be helpful to decide potential benefits of this method for future applications. The elimination of a crosstalk can be performed by using advanced modulation techniques such as vectored discrete multi-tone modulation (VDMT); however, its application in practice is limited because of its complexity and computational demands. That is why several scenarios are currently being discussed with either no VDMT application or with only partial crosstalk compensation. Because of that, this paper is focused on comparing the results for a first scenario without using any far-end crosstalk (FEXT) elimination technique, whereas a second scenario is based on partial FEXT suppression by VDMT application, to decide the effectiveness of using phantom modes in practice.

Modelling of Propagation Constant of Twisted Pairs and Its Temperature Dependence at G.fast Frequencies

  • DOI: 10.5755/j01.eie.22.2.12448
  • Link: https://doi.org/10.5755/j01.eie.22.2.12448
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Today, accurate and low complexity modelling of secondary parameters of twisted copper pairs at high frequencies is necessary, especially for modern transmission systems. The newly presented G.fast subscriber technology can occupy frequencies up to 212 MHz. For the purpose of its performance evaluations as well as for quick and accurate estimations of its transmission channel, the possibilities for accurate twisted pair's parameters approximation should be investigated. Basically, the motivation presented within this paper is to propose a completely new model for estimations of a propagation constant and its temperature dependence of twisted pairs and metallic cables suitable for G.fast frequencies. The main idea of a presented model is the innovative adoption of an inverse hyperbolic sine function in order to provide more accurate approximation of a propagation constant. (f) and its temperature character. The accuracy of a proposed model was verified for various metallic cables with different constructional arrangement and parameters. Based on the comparison of our proposed model with other typical existing models, the presented model outperforms the accuracy of all existing models using equal number of necessary parameters.

Increasing the transmission capacity of digital subscriber lines with phantom circuit and crosstalk cancelation

  • DOI: 10.1007/s11235-014-9903-6
  • Link: https://doi.org/10.1007/s11235-014-9903-6
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The technique of realizing phantom circuits in multi-pair and multi-quad metallic cables enables creating additional transmission circuits over standard pairs and quads in metallic cables. Theoretically, these phantom circuits can be subsequently used for additional digital subscriber lines and thanks to that the overall transmission capacity of metallic cables can be possibly increased. However, the transmission rates of present digital subscriber lines are limited mainly by physical parameters of used cables, such as attenuation and impedance, and also by the disturbances caused mainly by a crosstalk. One of the most promising solutions for full cancelation of far-end crosstalk is vector discrete multi-tone modulation (VDMT). First, this article contains brief introduction about the current situation in access networks, digital subscriber lines and metallic cables. Next, the practical experiment with metallic cable and necessary equipment was performed, the phantom circuit was created over one star-quad of a cable and its parameters and characteristics were measured and they are presented in the next section of this article. Based on these results, the next part is focused on the simulation of a modern digital subscriber line (VDSL2) using phantom circuit together with and without crosstalk elimination technique using VDMT modulation. The results and calculations of possible transmission capacity of phantom circuit are compared with measured results for two most frequently used VDSL2 profiles.

Innovative Bit Channel in Downstream Passive Optical Network Frames Based on Reusing of Bit Sequences

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Microwave and Optical Technology Letters. 2015, 57(10), 2346-2351. ISSN 0895-2477.
  • Year: 2015
  • DOI: 10.1002/mop.29323
  • Link: https://doi.org/10.1002/mop.29323
  • Department: Department of Telecommunications Engineering
  • Annotation:
    In this paper, a novel idea of a hidden bit channel established in the downstream passive optical network (PON) frames is proposed. Since the downstream frames in time-division multiplexed (TDM) PONs are broadcasted and delivered to all active end-point optical network units (ONUs), this bitstream could be potentially used for creating an additional hidden bit channel containing bits for all ONUs. Therefore, the downstream frames could simply transmit standard information fields and ONU contributions according to the standard PON principles, however, these bits could be also reused multiple times to carry additional data for each ONU in a form of segmented bit sequences spread within the entire bitstream. In order to establish effective bit channel with positive bit gain, an effective algorithm for addressing its bits is necessary. The most promising bit addressing algorithm is proposed within this paper together with the results obtained by its simulations and performance evaluations.

Modelling of Metallic Cables at G.fast Frequencies

  • Authors: Ing. Pavel Lafata, Ph.D., Ing. Marek Nevosad,
  • Publication: 20th International Conference on Applied Electronics 2015. Pilsen: University of West Bohemia, 2015. pp. 145-148. ISSN 1803-7232. ISBN 978-80-261-0385-1.
  • Year: 2015
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Metallic cables are still frequently used in access telecommunications networks, especially in the last-mile network segments, together with digital subscriber line (DSL) technologies. Recently, the G.fast system for reaching gigabit transmission speed over short metallic lines has been introduced. In order to achieve such performance, the frequency band of G.fast was extended up to 106 MHz or 212 MHz and several innovative transmission concepts were adopted as well. However, these innovations require accurate approximations of a G.fast transmission channel. Due to that it is necessary to provide accurate approximation of metallic cable transmission characteristics, the attenuation constant α(f) as well as the phase constant β(f). Therefore, an innovative LN model was proposed and is presented in this paper. Its main motivation is to outperform the existing models with equal number of necessary parameters. The accuracy of a proposed LN model was tested for various metallic cables and compared with two typical existing models.

Novel Protection Strategies for Passive Optical Networks Based on Ring and Bus Topologies

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Transactions on Emerging Telecommunications Technologies. 2015, 26(9), 1131-1153. ISSN 2161-3915.
  • Year: 2015
  • DOI: 10.1002/ett.2846
  • Link: https://doi.org/10.1002/ett.2846
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper is focused on passive optical networks (PONs), especially on increasing their network resilience. Since the most critical components in PONs are usually the optical line termination unit (OLT) and optical fibers connecting all network nodes, the main motivation presented within this paper is to improve the resistance of PON against critical failures of OLT and optical fibers between them. Both presented solutions are based on using dual OLT units and the application of asymmetric splitters in order to balance the attenuation and optical signal levels throughout the entire network, while the main innovation consists in the application of ring and bus topologies. Both bus and ring topologies can be formed easily using only passive splitters with optimum splitting ratios, therefore no active components are necessary. The next advantage is the opportunity of placing both OLT units in physically diverse location, thus increasing the overall network resilience. Moreover, the presented idea with a bus topology offers an additional resistance against the failures of optical fibers connecting the splitters as well. Since the application of asymmetric passive splitters in both solutions is necessary in order to optimize the optical signal levels in the entire network, the mathematical models for calculating of their optimum splitting ratios are included. To verify the functionality of both topologies and their protection mechanisms, complex simulations were performed and are presented in this article as well.

Simple Attenauation Models of Metallic Cables Suitable for G.fast Frequencies

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Advances in Electrical and Electronic Engineering. 2015, 13(2), 147-155. ISSN 1336-1376.
  • Year: 2015
  • DOI: 10.15598/aeee.v13i2.1338
  • Link: https://doi.org/10.15598/aeee.v13i2.1338
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Recently, a new xDSL successor called G.fast, which can occupy frequencies up to 106 or 212~MHz, has been introduced in ITU-T G.9700 series of recommendations. Moreover, a new model of transmission characteristics suitable for various types of metallic cables has been designed and described as well. The model is based on 9 parameters specified for each type of metallic cable and can provide accurate estimations. However, its complexity together with the number of required parameters makes its practical application questionable, since the most important metallic cable characteristic, the attenuation, can be estimated using much simpler models. Therefore, two innovative attenuation models suitable for frequencies up to 250 MHz were designed and they will be introduced in this paper. The main motivation was to achieve an accurate approximation of attenuation character for various types of metallic cables, while maintaining low mathematical complexity and a number of necessary parameters. Both models were compared with attenuation characteristics measured for variety types of real metallic cables and also with other standard attenuation models. The results are included in this article as well.

A novel protection mechanism for local passive optical networks with bus topology and its verification

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Microwave and Optical Technology Letters. 2014, 9(56), 2005-2010. ISSN 0895-2477.
  • Year: 2014
  • DOI: 10.1002/mop.28510
  • Link: https://doi.org/10.1002/mop.28510
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The most critical components of passive optical networks (PONs) are usually the central optical line termination unit (OLT) and optical fibers. That is why this article contains the description of a novel protection mechanism for designing of a local PON with a bus topology and enhanced network resilience. The idea is based on using dual OLT units together with contra-directionally arranged passive splitters to form a bus topology. Thanks to that the resistance of presented PON solution against the potential malfunctions of OLT units as well as optical fibers is significantly increased. Since the application of asymmetric passive splitters is necessary to balance the attenuation and optical signal levels in the entire network, the mathematical model for calculating their optimum splitting ratios is presented as well. Moreover, the functionality of designed bus topology was verified by using real PON equipment and by performing complex measurements.

Analysis of Transmission Parameters of Metallic Cables Based on External Conditions

  • DOI: 10.1109/MECHATRONIKA.2014.7018333
  • Link: https://doi.org/10.1109/MECHATRONIKA.2014.7018333
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Today, the metallic cables in access networks in cities are usually installed underground at shallow depths, nevertheless aerial installations are still very common especially in suburban and rural areas. Moreover, power-line communication systems over outdoor aerial high-voltage transmission lines are often used for broadband transmission as well. Since the transmission parameters of metallic lines are influenced by external environmental conditions, such as the temperature, humidity, etc., the resulting transmission performance of digital systems using these cables are influenced as well. Today, the large buildings, data centers and houses are usually covered by structured metallic cables and installations in order to connect network nodes, computers, etc. Thanks to that the frequency characteristics of attenuation monitored at these cables might potentially serve for the localization of inhomogeneity caused by fire or any external heat. This effect of external conditions is mostly noticeable at higher frequencies that is why it is necessary to perform accurate measurements using calibrated equipment and defined conditions. In this paper, we focused on performing necessary measurements of transmission characteristics of metallic cables containing symmetrical pairs under defined temperatures and their locations inside the oven to analyze the influence of space and heat conditions.

Estimations of G.fast Transmission Performance over Phantom Modes

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: 37th International Conference on Telecommunications and Signal Processing. Brno: VUT v Brně, Fakulta elektrotechniky a komunikačních technologií, 2014. pp. 38-42. ISSN 1805-5435. ISBN 978-80-214-4983-1.
  • Year: 2014
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with newly developed G.fast transmission system and its application together with phantom mode transmissions. The main motivation is to estimate the performance of G.fast over phantom circuits for various real scenarios, which are based on measurements performed for a multi-quad metallic cable. Since the performance of G.fast is mostly limited by the crosstalk and especially by far-end crosstalk (FEXT), the estimations are focused mainly on comparisons for FEXT dominating scenario and the situation with completely eliminated FEXT contributions in a metallic cable binder as well as potential impedance mismatches. However, the full coordination of transmitted DMT symbols by vectored discrete multitone modulation (VDMT) for all subscriber lines in large cable binders is computationally very demanding in practice. The conclusions presented within this paper can be helpful to decide potential benefits of phantom mode transmission method in practice.

Optical Access Networks FTTx

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Communication over optical fibers are inherently backbone solutions for telecommunications networks, which gradually penetrates into access networks. It uses so-called. Passive optical network, where speeds of units to tens of Gbit / s, suitable for connecting to the Internet with extremely high data rates as well as other applications. The publication provides a comprehensive overview of optical access networks, their evolution and parameters, planning, construction and measurement and prospective directions of further development.

Advanced Algorithm for Optimizing the Deployment Cost of Passive Optical Networks

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Advances in Electrical and Electronic Engineering. 2013, 11(1), 36-45. ISSN 1336-1376.
  • Year: 2013
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article describes the method leading to evaluate an algorithm for designing suboptimal economic solutions and topologies for PONs by focusing on optimization of constructional length of distribution networks. While the typical PON topologies are star topologies or tree-star topologies, the rst part of this article introduces new sub algorithm for estimating the minimum star topology. The next section brings the evaluation of two sub algorithms for solving minimum constructional length problems. Finally, all these parts will be merged into a complex algorithm by using clusterization technique to solve optimum topologies.

Application of Fiber Ring for Protection of Passive Optical Infrastructure

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Today, passive optical networks (PONs) are mostly used as modern high-speed access networks for various applications. However, there are also several specific applications, such as in business, office, army or science sector, which require a complex protection and backup system against failures and malfunctions. Typically, tree or star topologies are used for passive optical networks PONs. These topologies are vulnerable mainly against the failures of central optical line termination (OLT) unit. This paper presents an innovative method for protecting PONs by using ring topologies, especially the OLT unit. The method is described in the article, and an elementary mathematical model for calculations of asymmetric passive optical splitters together with an example is included as well.

Designing and Testing of Passive Optical Network with Ring Topology

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The passive optical networks are usually based on star or tree topologies in practice. However, the application of a ring topology can bring several benefits, especially the possibility of creating a backup of central optical line termination unit (OLT). This paper is focused on designing of PON with ring topology and several measurements were performed as well.

Examination of Multiplexing VDSL2 over ADSL2+ Line

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Elektronika ir Elektrotechnika. 2013, 19(8), 123-127. ISSN 1392-1215.
  • Year: 2013
  • DOI: 10.5755/j01.eee.19.8.3116
  • Link: https://doi.org/10.5755/j01.eee.19.8.3116
  • Department: Department of Telecommunications Engineering
  • Annotation:
    A new idea about multiplexing VDSL2 line over ADSL2+ was examined and described in this article. Both of these lines using one single symmetrical pair in a cable must be separated by frequency multiplexing method, when ADSL2+ line occupies frequency band up to 2.2 MHz, while the VDSL2 line would operate from 2.2 MHz to higher frequencies. The method could possibly increase the number of xDSL lines in one cable and could connect more subscribers using existing metallic lines. This article describes the initial idea together with the process of designing possible VDSL2 over ADSL2+ splitter, which was subsequently used for performing real measurements. Thanks to these measurements, simulations of several possible scenarios were performed and are presented in this article as well.

Experimental Verification of Passive Optical Network With Ring Topology

  • DOI: 10.1002/mop.27783
  • Link: https://doi.org/10.1002/mop.27783
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Recently, an innovative idea about forming a simple ring topology by using asymmetric passive splitters together with secondary OLT unit has been presented and an elementary mathematical model for calculations of optimum splitting ratios of all splitters in a ring infrastructure has been described. The major advantage of presented ring topology is that both primary and secondary OLT units can be placed on the opposite sides of the ring, which could greatly increase the overall resistance of the whole network against critical failures, malfunctions, or sophisticated attacks. Next, this ring topology was successfully realized in practice by using real OLT and optical network units and the whole idea verified. The results of real measurements as well as theoretical calculations are presented in this article.

Impact of environmental temperature fluctuations on G.fast performance

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The transmission parameters of metallic cables are influenced by the temperature of the surrounding environment. Given that the newly developed G.fast system will occupy a wide frequency band, its transmission performance could be measurably affected by temperature fluctuations in real applications. Temperature oscillations are noticeable especially in mild climate regions, where the air and soil temperatures at shallow depths may vary significantly, mainly between winter and summer. The results of simulating G.fast performance in a temperature fluctuating environment, described in this article, could be helpful in identifying the potential challenges to G.fast deployment in practice.

Implementation of Modern Techniques for Designing and Realization of Digital Circuits into Education

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: 15th International Conference on Research in Telecommunication Technologies. Bratislava: Slovak University of Technology in Bratislava, 2013. pp. 7-9. ISBN 978-80-227-4026-5.
  • Year: 2013
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Today, the FPGA (Field Programmable Gate Array) together with VHDL language (VHSIC Hardware Description Language) are often used for designing and realization of modern digital circuits in many applications. That is why it is necessary to implement these new techniques into the education process of technically oriented high schools and universities as well. This paper contains the description of a FRVŠ project and it presents the solution of implementation of modern FPGA and VHDL language into the education of subject Digital Technique, which is being taught at the Department of Telecommunication Engineering of the Czech Technical University in Prague. The presented solution can be also used as an inspiration for similar projects at other universities and schools or for individual users, who are interested in modern techniques for designing and realization of digital circuits.

Influence of Bridged Taps on Transmission Performance of VDSL2 Lines

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: International Journal of Emerging Technologies in Computational and Applied Sciences. 2013, 3(1), 5-10. ISSN 2279-0047.
  • Year: 2013
  • Department: Department of Telecommunications Engineering
  • Annotation:
    One of the frequent elements in metallic access networks, which can negatively influence the transmission performance of modern digital systems, is bridged taps. This paper presents an analysis of the influence of bridged taps on transmission capacity of VDSL2 lines by using ABCD matrices. Thanks to that, the simulations can be performed for various scenarios and amounts of bridged taps and their parameters by simply cascading necessary matrices.

Investigation of VDSL2 Digital Lines Performance with Bridged Taps

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Advances in Electrical and Electronic Engineering. 2013, 11(3), 193-203. ISSN 1336-1376.
  • Year: 2013
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The presence of bridged taps can complexly affect resulting attenuation, impedance and also crosstalk characteristics of transmission lines, moreover while this influence may differ for various types of metallic cables. That is why a comparison for several typical cables used in last-mile segments was performed and is presented here. The simulations and calculations presented in this paper are based on ABCD matrices, and thanks to that the simulations can be performed for various scenarios and situations.

Modeling of Telecommunication Cables for Gigabit DSL Application

  • DOI: 10.15598/aeee.v11i5.874
  • Link: https://doi.org/10.15598/aeee.v11i5.874
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The first part of our paper brings the description and analysis of method used for modeling of metallic cable’s parameters according to the modified KPN model. Moreover we were able to perform measurements and estimations for real metallic cable’s with various transmission characteristics and constructional arrangement, for which we derived the necessary parameters of a new modeling method. Following part contains the comparison of measured characteristics with their models according to the modified KPN model. Finally, we discussed obtained results.

Protection of Passive Optical Networks by Using Ring Topology and Tunable Splitters

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: International Journal of Advances in Telecommunications, Electrotechnics, Signals and Systems. 2013, 2(1), 28-33. ISSN 1805-5443.
  • Year: 2013
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article proposes an innovative method for protecting of passive optical networks (PONs), especially the central optical unit – optical line termination (OLT). The method described in this paper is focused on forming PON network with ring topology using passive optical splitters. The main idea is based on the possibility of placing both OLT units (primary and secondary) on the opposite sides of the ring, which can potentially increase the resistance of network.

Realistic Modeling of Far-End Crosstalk in Metallic Cables

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: IEEE Communications Letters. 2013, 17(3), 435-438. ISSN 1089-7798.
  • Year: 2013
  • DOI: 10.1109/LCOMM.2013.012213.121955
  • Link: https://doi.org/10.1109/LCOMM.2013.012213.121955
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The standard FEXT model and ITU-T model gives only average results based on the sum of crosstalk in the entire cable, which is usually sufficient in case of summarizing FEXT contributions. However, the implementation of VDMT modulation would require individual modeling of FEXT crosstalk between all subscriber lines in a cable. That is why a new method for modeling of FEXT was developed and is presented here. The results of the model are also compared with measured characteristics for a typical UTP cable and several other cables. The proposed advanced FEXT model with minor modifications is applicable for any metallic cable to provide realistic FEXT characteristics.

Simulation of Ring-based Passive Optical Network and Its Experimental Verification

  • DOI: 10.5755/j01.eee.19.5.1683
  • Link: https://doi.org/10.5755/j01.eee.19.5.1683
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Passive Optical Networks (PONs) are mostly based mainly on tree or hybrid tree-star topologies in practice. However, these topologies are significantly vulnerable, especially in case of sophisticated attacks or global malfunctions of central optical line termination (OLT) units. Due to that, an innovative idea of forming PON with a simple ring topology by using standard passive splitters was proposed and is presented within this paper. The article contains the description of this idea and also necessary simulations were performed. To verify these theoretical assumptions, experimental PON network with a ring topology was created and its characteristics were measured and compared with simulations and models. Moreover, the functionality of the protection mechanism was confirmed as well as the functionality of the entire ring PON network.

Transmission Delay Modeling of Packet Communication over Digital Subscriber Line

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Certain multimedia and voice services, such as VoIP, IPTV, etc., are significantly delay sensitive and their performance is influenced by the overall transmission delay and its variance. One of the most common solutions used in access networks are xDSL lines, especially ADSL2+ or VDSL2. Although these subscriber lines also use packet communication, there are several differences and mechanisms, which influence their resulting delay. Their delay characteristics are also dependent on the individual settings of each xDSL provider, therefore we decided to investigate this area for typical commercially available lines in Czech Republic. Based on the measured values and experiments with real ADSL2+ lines we also developed a potential modeling method, which is presented in this article as well. The parameters for packet jitter based on the generalized Pareto distribution were modeled.

Transmission Parameters of Metallic Cables under Extreme Temperatures

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper deals with the measurement and modeling of transmission parameters of metallic cables under extreme temperatures. Several measurements and experiments with a fire retardant metallic cable in special laboratory with certification for fire tests were performed and are presented within this article. These results were subsequently used to estimate models and simulations of typical fire events and their influence on transmission characteristics of metallic cables.

Asymmetric passive splitters - 1st part

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Sdělovací technika. 2012, 11/2012(11), 5-7. ISSN 0036-9942.
  • Year: 2012
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article is focused on the problem of asymmetric passive splitters and designing their optimal splitting ratios. The application of passive splitters with asymmetric splitting ratio offers the opportunity to correct the total attenuation of specific branches of the optical distribution network, or to propose specific topologies.

Asymmetric passive splitters - 2nd part

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Sdělovací technika. 2012, 12/2012(12), 12-14. ISSN 0036-9942.
  • Year: 2012
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article is focused on the problem of asymmetric passive splitters and designing their optimal splitting ratios. The application of passive splitters with asymmetric splitting ratio offers the opportunity to correct the total attenuation of specific branches of the optical distribution network, or to propose specific topologies.

Designing and Realization of Free-Space Optical Link and Its Diagnostic

  • Authors: Ing. Pavel Lafata, Ph.D., Bakala, B.
  • Publication: Proceedings of 15th Mechatronika 2012. Praha: Czech Technical University in Prague, 2012. pp. 182-186. ISBN 978-80-01-04987-7.
  • Year: 2012
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Our project of designing and realization of low-cost FSO system is based on modified RONJA project. The goal was to design low-cost FSO system with several specific features and modifications for remote monitoring and diagnostic of the whole FSO system and its parameters. The mechanical improvements concern mainly constructional parameters, mechanical fixing system for aiming and focusing the optical beam, internal heating of lenses, external powering and data connection etc. The firmware for controlling the whole system can be uploaded remotely, therefore it is possible to upgrade the system further in the future. The paper also describes practical remarks and experiences concerning installation and operation of the whole system together with photos and documentation. The graphical interface of the diagnostic and control system was designed to be clear and simple and to contain only the most important functions. The diagnostic and remote functions are still under the development; however, several measured results and practical experience were already obtained and will be presented in this article.

Increasing the Transmission Capacity of Digital Subscriber Lines

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article first introduces the basic parameters of broadband measurements of phantom circuit created from pairs within one star-quad, together with the description of method for far-end crosstalk modeling. Based on these results, a practical experiment was performed using real metallic cable. The next part is focused on the simulation of digital subscriber line using phantom circuit together with and without crosstalk elimination technique using vector multi-tone modulation. The results and calculations of possible transmission capacity of phantom circuit are compared with measured results.

Investigation of Accurate Far-End Crosstalk Modeling in Metallic Cables

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Crosstalk and especially far-end crosstalk (FEXT) represents the most serious source of disturbance in today's digital transmission systems. It mostly limits the information capacity of current xDSL digital subscriber lines and also of local data networks with unshielded and or shielded twisted pairs (UTP/STP). The elimination of FEXT will require the implementation of advanced methods for its modeling to obtain required predictions of crosstalk behavior in a cable. The standard simple FEXT model and ITU-T FEXT model are not very accurate and do not provide realistic results. That is why a new method for modeling of FEXT was developed and is presented in this paper. The results of the model are also compared with measured characteristics for a typical UTP cable and several other cables. The proposed advanced FEXT model with minor modifications is applicable for any metallic cable to provide accurate and realistic FEXT characteristics.

Modeling of Metallic Cables' Attenuation for Extreme Temperatures

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with the influence of extreme temperatures (burning) on transmission parameters of metallic cables, especially on its attenuation. This paper contains the description of performed experimental measurement for specific metallic cable and it also presents derived mathematical models and simulations.

Modelling and measuring the SHDSL transmission for industrial applications

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Industrial networks are now largely based on Ethernet. It is possible to use modems, VDSL or SHDSL if optical fiber is not possible to use or network range is greater than 100 m. The article shows the results of modeling and measurement on industrial SHDSL nodes.

Optimization of Asymmetric Passive Optical Splitters

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: 2012 International Conference on Applied Electronics. Pilsen: University of West Bohemia, 2012. pp. 167-170. ISSN 1803-7232. ISBN 978-80-261-0038-6.
  • Year: 2012
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The asymmetric passive splitters offer several interesting advantages, because their splitting ratio could be possibly calculated and optimized for given specific scenario. Thanks to this optimization, the overall value of attenuation of all their branches could be balanced according to the whole optical infrastructure, which would enable reaching the optimal situation in the entire PON network. This article deals with the method of calculation the optimized splitting ratio of asymmetric splitters and it presents the application in Matlab environment, which serves for quick calculations and for designing the asymmetric splitters with desired parameters.

Parameters of Twisted Pairs Assessment for Frequency Band up to 1 GHz

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The paper describes the measuring and modeling of attenuation and near-end crosstalk for a specific metallic cable in a frequency band up to 1 GHz. The paper also includes primary transmission parameters of this cable, which consists of four twisted pairs and is designed for telecommunication infrastructures in buildings. The aim of this paper is to compare measurements and simulations obtained from appropriate models and to determine the parameters of analytic models for modelling the transmission performance of advanced transmisssion systems.

Perspective Application of Passive Optical Network with Optimized Bus Topology

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper presents selected aspects of passive optical networks and splitters with asymmetric splitting ratio. The essential part is focused on the practical demonstration of their use to optimize the passive optical network with bus topology, which acts as a local backbone network for structured cabling systems, and for local data networks in large buildings.

Protection of Passive Optical Network by Using Ring Topology

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: 35th International Conference Telecommunications and Signal Processing. Brno: VUT v Brně, Fakulta elektrotechniky a komunikačních technologií, 2012. pp. 105-110. ISBN 978-1-4673-1118-2.
  • Year: 2012

Simulation and Modeling of Transmission Parameters of Metallic Cables under Extreme Temperatures

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The transmission parameters of metallic cables and lines, such as attenuation, crosstalk, etc., are significantly influenced by external parameters and conditions, e.g. temperature, external deformations, bending of metallic cable, moisture, glaze ice on the cable, etc. This paper contains the description of performed experimental measurement for specific metallic cable and it also presents derived mathematical models and simulations.

Simulations and Measurements of Packet Network Synchronization by Precision Time Protocol

  • Authors: Pravda, M., doc. Ing. Jiří Vodrážka, Ph.D., Ing. Pavel Lafata, Ph.D.,
  • Publication: 35th International Conference Telecommunications and Signal Processing. Brno: VUT v Brně, Fakulta elektrotechniky a komunikačních technologií, 2012. pp. 116-120. ISBN 978-1-4673-1118-2.
  • Year: 2012
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The first part of this paper is focused on several measurements for real wireless network components and topologies. The following part presents the simulations and modeling of PTP protocol functionality based on the typical parameters and transmission characteristics of packet networks.

Time Division Multiplex over Packet Oriented Digital Subscriber Line

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article introduces the basic parameters of ADSL2+/VDSL2 data link at higher layers (packet delay, packet loss). Based on gained results, a practical experiment was performed using real xDSL network and TDM over IP gateway. Measurements covered transmission loss, transmission delay, bit error rate.

Using Advanced Far-end Crosstalk Modeling Method for Simulations of Very High Speed Digital Lines

  • DOI: 10.5755/j01.eee.121.5.1650
  • Link: https://doi.org/10.5755/j01.eee.121.5.1650
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The article describes methods for accurate modeling of the far end crosstalk, which is dominant for digital subscriber line. The second part of the article describes the crosstalk model used for calculating transmission performance of digital subscriber transmission line that uses vectored discrete multitone modulation to transfer user information. There are given specific values of the theoretical efficiency of transmission, depending on various conditions of transmission.

10 Gbps Passive Optical Networks

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Both IEEE (10GEPON) and ITU (XG-PON) presented new specifications for passive optical networks with transmission speed of 10 Gbps. This article brings their comparison and it also compares these new versions with their previous generation (EPON, GPON).

Advanced Realistic Far-End Crosstalk Modeling

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Crosstalk and especially far-end crosstalk (FEXT) represent the most serious source of disturbing in modern digital transmission systems using metallic lines and cables. The elimination of FEXT can be performed by Vectored DMT modulation. However, it will be necessary to simulate and model the character of FEXT crosstalk in given metallic cable for its proper implementation.

Analysis of Simulation Methods for Far-end Crosstalk Cancellation

  • Department: Department of Telecommunications Engineering
  • Annotation:
    FEXT is the dominant source of disturbance in current digital subscriber lines (xDSL). One of the most promising solutions for far-end crosstalk cancellation is Vectored Discrete Multi-tone modulation (VDMT). New method for modeling of far-end crosstalk was developed and is presented in this paper. This advanced model is based on the capacitive and inductive unbalances between pairs in a cable and it also respects the cable's internal structure. The results of the model are subsequently used for the simulation of VDMT modulation and its impact on the FEXT cancellation.

Analyzing and Modeling of Far-End Crosstalk in Twisted Multi-Pair Metallic Cables

  • Authors: Ing. Pavel Lafata, Ph.D., Pravda, M.
  • Publication: 2011 International Conference on Applied Electronics. Plzeň: Západočeská univerzita v Plzni, 2011. pp. 223-226. ISSN 1803-7232. ISBN 978-80-7043-987-6.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The main idea of the model is based on the assumptions concerning the propagation of electromagnetic waves through the cable and its simulation by proper harmonic functions. The results of the model are also compared with measured characteristics for a typical UTP a PEPKFH cable. On the other hand, proposed advanced FEXT model with minor modifications is applicable for any metallic cable to provide accurate and realistic FEXT characteristics.

Application of Passive Optical Network with Optimized Bus Topology for Local Backbone Data Network

  • DOI: 10.1002/mop.26291
  • Link: https://doi.org/10.1002/mop.26291
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article proposes an innovative application of passive optical networks with optimized bus topology for local backbone data networks. We present mathematical apparatus for calculating of the maximum number of splits and the number of bridge taps in the passive optical network with the bus topology and an example of obtained results.

Configuration and Testing of Triple Play Services in a Passive Optical Network

  • Authors: Ing. Pavel Lafata, Ph.D., Rohlík, M.
  • Publication: Elektrorevue. 2011, 14(3), 3-1-3-9. ISSN 1213-1539.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Passive optical access networks represent a promising solution in the access networks to provide modern multimedia services, Internet, and telephone service via VoIP (Voice over IP). This article presents a workplace of passive optical networks EPON (Ethernet PON), built in the laboratory of the Department of Telecommunication Engineering, Czech Technical University in Prague. In the next part, a sample network design and configuration of optical access network for triple play services (data, phone, video), and finally several tests are performed.

Diagnostic and Remote Monitoring of FSO Link

  • Authors: Ing. Pavel Lafata, Ph.D., Bakala, B.
  • Publication: Access server. 2011, 9(2012010001), 1-6. ISSN 1214-9675.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Previous article [1] described the realization of free space optical link (FSO) implemented on the basis of the modified project RONJA, its basic blocks and their function and it also presented a process of subsequent installation and practical operation. One of these modifications was a diagnostic module for remote monitoring and measurements. This article brings detailed description of the module and also several results from the measurements.

Experiments with Free Space Optics and Visible Light Communication

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper deals with the design and realization of two experimental communication links based on the modified project Ronja: point-to-point free space optical link (FSO) with red optical source and indoor visible light communication (VLC) with white optical source. We also implemented a diagnostic and monitoring module, which enables remote monitoring and measuring of several parameters, such as the level of optical received signal. This paper illustrates practical operation and discusses the results of prototypes constructed at our Department.

Exploitation of Local Symmetrical Pairs with Paper Insulation for High Frequency Transmissions

  • Authors: doc. Ing. Jiří Vodrážka, Ph.D., Ing. Pavel Lafata, Ph.D.,
  • Publication: 13th International Conference on Research in Telecommunication Technologies 2011. Brno: VUT v Brně, Fakulta elektrotechniky a komunikačních technologií, 2011. pp. 28-32. ISBN 978-80-214-4283-2.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    We performed several measurements and calculations of its primary and secondary transmission parameters and we compared these parameters with metallic cables with plastic (polymer) insulation. The last part of this article also brings the conclusion about using this cable for perspective VDSL2 digital subscriber systems.

Far-end Crosstalk Modeling Based on Capacitive and Inductive Unbalances Between Pairs in a Cable

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Advances in Electrical and Electronic Engineering. 2011, 9(1), 14-20. ISSN 1336-1376.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with new ways of far-end crosstalk (FEXT) modeling in multi-pair and multi-quad metallic cables. Current standard modeling methods provide only rough estimations of FEXT characteristics based on average values of crosstalk for the whole cable. However, for practical implementation of vector discrete multi-tone modulation (VDMT) is necessary to predict and simulate FEXT characteristics with sufficient accuracy and simulate FEXT transfer functions individually for each combination of symmetrical pairs in a cable. This article contains a theoretical analysis and description of the problem and suggests a new method for modeling of FEXT crosstalk using capacitive and inductive unbalances between pairs in a cable. This proposed model offers more accurate and realistic results of crosstalk. Theoretical simulations and results are also compared with the measured characteristics for specific metallic cable.

Implementation of Passive Optical Network with Optimized Bus Topology

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Passive optical networks represent a perspective solution pro modern access telecommunication networks. The optimization could be performed by using passive optical splitters with nonuniform splitting ratio. The passive optical network with optimized topology offers several advantages and can be used as a local data network.

Low Cost Free-Space Optical System and Its Application

  • Authors: Ing. Pavel Lafata, Ph.D., Bakala, B.
  • Publication: 23rd Conference and Exhibition on Optical Communications 2011 - Scientific Section Proceedings. Praha: Agentura Action M, 2011. pp. 48-51. ISBN 978-80-86742-32-8.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper deals with the design and realization of free space optical link (FSO) implemented on the basis of the modified project RONJA. The main goal was to design free space optical system with the lowest cost possible and to implement several improvements and upgrades. The first part of this article describes the basic blocks and their function, while the second one presents a process of subsequent installation and practical operation of a sample constructed at the Department of Telecommunication Engineering, FEE, CTU in Prague.

Modelling of Attenuation and Crosstalk of Cascaded Transmission Lines

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Advances in Electrical and Electronic Engineering. 2011, 9(3), 127-135. ISSN 1336-1376.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper deals with the measurements and modelling of attenuation and near-end (NEXT) and far-end (FEXT) crosstalk for cascaded metallic transmission lines. The article brings the description of complex measurements performed for the combination of three different metallic cables and based on these measurements, several conclusions about the possibilities of modelling the attenuation and NEXT and FEXT crosstalk for cascaded transmission lines are presented.

Passive Optical Network with Optimized Bus Topology

  • Authors: Ing. Pavel Lafata, Ph.D., doc. Ing. Jiří Vodrážka, Ph.D.,
  • Publication: Proceedings of the 2011 International Conference on Telecommunication Systems Management. Dallas, TX: American Telecommunications Systems Management Association Inc., 2011. pp. 112-120. ISBN 978-0-9820958-4-3.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Passive optical networks represent a promising solution for access networks to meet the increasing demand on transmission rate. The optimization process depends on the type of topology, primarily on the balance of attenuation and several other features. Considering the possibility of optimization, passive optical network with a bus topology provides several interesting opportunities for specific applications. Its potential application is for example, the network infrastructure in large buildings and industrial centers and base stations of mobile networks connections in the bus topology along the highway or railway networks.

Possibilities of Upstream Data Eavesdropping in Passive Optical Networks

  • Authors: Ing. Petr Jareš, Ph.D., Ing. Pavel Lafata, Ph.D.,
  • Publication: 23rd Conference and Exhibition on Optical Communications 2011 - Scientific Section Proceedings. Praha: Agentura Action M, 2011. pp. 27-29. ISBN 978-80-86742-32-8.
  • Year: 2011
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Due to the reflections on various interfaces (connectors, splices, splitters) and in several specific situations can the upstream traffic be passively eavesdropped and it could be possible to obtain transmitted upstream data of neighbor users. In this article, we investigated the possibilities of upstream traffic eavesdropping under certain specific conditions and we performed several measurements by using real passive optical network.

Precise Time Protocol in Ethernet over SDH Network

Reach Extended GPON Networks

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The original specification of GPON passive optical network according to ITU-T recommendation G.984 was limited by the maximum range up to 20 km (physical range) and the maximum splitting ratio was set up to 1:64. However, the requirements to increase its maximum range or splitting ratio often appeared in practical applications of GPON networks. Therefore, additional modifications have been implemented together with new attenuation classes added as well as the possibility of using active optical amplifiers and regenerators. Such passive optical networks are usually called Reach Extended (or Long Reach) GPON.

Simulations of Far-end Crosstalk Based on Modified Matrices of Transmission Line

  • DOI: 10.5755/j01.eee.116.10.876
  • Link: https://doi.org/10.5755/j01.eee.116.10.876
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The standard simple FEXT model is not very accurate and does not provide realistic results. That's why a new advanced method for modeling of FEXT was developed and is presented here. This advanced FEXT model is based on the modified transmission matrices together with calculation of capacitive and inductive unbalances between pairs in a cable and it also respects cable's internal structure. This paper includes mathematical derivation of the advanced FEXT model as well as examples of obtained results, which are also compared with standard FEXT model and with measured characteristics.

Advanced Far-end Crosstalk Modelling

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Workshop 2010. Praha: České vysoké učení technické v Praze, 2010. pp. 130-131. CTU Reports. ISBN 978-80-01-04513-8.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with the problems of far-end crosstalk (FEXT) between symmetrical pairs in metallic cable in xDSL digital systems. The reduction of crosstalk by VDMT modulation is not possible in present systems due to its overall complexity and demands on computational units in DSLAMs. Therefore, the possibility of using space selection of disturbing sources is proposed, which would allow the use of vectored DMT modulation only for a limited number of the most disturbing systems. A new method was proposed and designed for simulating and modeling of FEXT transmission functions in xDSL digital lines. The model is based on detailed analyses of the transmission environment and its parameters, statistical evaluation of measured results, generation of pseudorandom characteristics and the processing of their filtering.

An Easy and Fast Calculation of Attenuation Budget of PON Network

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The computional tool was developed for calculating the attenuation budget of passive optical networks PON with different topologies and configurations for the purposes of teaching and practical applications.

Current and Future Possibilities and Solutions of Access Network for IPTV

  • Authors: Krejčí, J., Ing. Pavel Lafata, Ph.D.,
  • Publication: Elektrorevue. 2010, 13(64), 64-1-64-8. ISSN 1213-1539.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The paper deals with current and future possibilities of IPTV transmission in access network. It is described to typically requirements for transfer rate and other parameters of access networks, which are necessary for reliable income of IPTV. Report also contains analysis of most frequently occurring disturbances and adverse effects on the image quality. The considering progressive development of optical access networks, in the paper it is mentioned possible alternative - passive optical access network adapted to distribute television broadcasting and IPTV.

Dependence of Far-end Crosstalk on Capacitive and Inductive Unbalances between Pairs in Cable

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Knowledge in Telecommunication Technologies and Optics - KTTO 2010. Ostrava: VŠB - TUO, FEI, Katedra elektroniky a telekomunikační techniky, 2010. pp. 77-82. ISBN 978-80-248-2330-0.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper presents initial mathematical formulas of far-end crosstalk dependence on capacitive and inductive unbalances between two parallel pairs in a cable and a method of their derivation. These formulas will be subsequently implemented into new method for far-end crosstalk simulation and modeling.

Expansion of FTTx Lines

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper describes the koncept of FTTx optical lines, the analysis of their current expansion and the estimation for the incoming years. The triple play services are often mentioned together with the FTTx lines. The fully functional workplace of passive optical network was built at the Department of Telecommunication Engineering, FEE, CTU in Pratur. This article also contains the description of this workplace and an example of its possible configuration.

Free Space Optics

  • Authors: Ing. Pavel Lafata, Ph.D., Bakala, B.
  • Publication: Telekomunikace. 2010, 47(5/2010), 8-10. ISSN 0040-2591.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article describes the essential principles of free space optic links, FSO. This description is focused od basic features, principles and parameters of FSO technology.

Generator of Crosstalk Transmission Functions for Modeling of Multi-quad and Multi-pair Metallic Cables

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The new far-end crosstalk model, called Advanced FEXT model, which is based on cable's internal structure and parameters, is proposed here. The presented generator of crosstalk transmission functions is based on advanced FEXT model and provides accurate and realistic simulations and calculations of crosstalk characteristics.

Improving the Functionality of Free-Space Optical Link

  • Authors: Bakala, B., Ing. Pavel Lafata, Ph.D.,
  • Publication: Access server. 2010, 8(201012), 0004. ISSN 1214-9675.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper deals with the realization of free space optical link (FSO) implemented on the basis of the modified project RONJA, describes the basic blocks and their function and it also presents a process of subsequent installation and practical operation of a sample constructed at the Department of Telecommunication Engineering, FEE, CTU in Prague.

Improving the Methods of Transmission Line Primary Parameters Modeling

  • Authors: Hampl, M., Ing. Pavel Lafata, Ph.D.,
  • Publication: Access server. 2010, 8.(201007), 0003. ISSN 1214-9675.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with the modeling of primary parameters of telecommunication lines. The introduction presents a method of measuring and calculating the primary parameter for a specific metallic cable and the calculation of parameters British Telecom model. Subsequently, this model is complemented by pseudo-randomly generated frequency components, whose parameters are derived from the measured characteristics.

Passive Optical Network 10GEPON

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The final version of the new recommendations IEEE 802.3av was released in September 2009. The recommendation defines a new version of passive optical network 10GEPON, which represents the next evolution step of the previous version EPON. The new type of passive optical network offers the transmission speed of 10 Gbps and improves the transmission characteristics of the previous version EPON in many ways. Together with these improvements, it was possible to mantain the backward compatibility with EPON, which allows the simultaneous operation of both types within a single optical network.

Passive Optical Network with Transmission Speed of 10 Gbit/s

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Passive optical access networks are built either on the basis of ITU-T (GPON) or Ethernet (EPON). The new optical network 10GEPON (10 Gigabit EPON) according to IEEE 802.3av is based on the previous version EPON defined in IEEE 802.3ah.

Passive Optical Networks with Optimized Splitting Ratios

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The proces of design and construction of passive network infrastructure for passive optical access networks requires performing the calculations and simulations of attenuation balance especially because of the use of purely passive elements. I tis necessary to take into account certain specific characteristics of the passive type of optical networks. One of the perspective solutions are also the optical splitters with adjustable attenuation rattio at their output branches.

Plastic Optical Fibers - Solution for Next Generation Access Networks?

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Sdělovací technika. 2010, 58.(12/2010), 5-8. ISSN 0036-9942.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    The article presents the research knowledge during the development of transmission, mechanical and other characteristics of plastic optical fiber and an overview of their current and prospective applications.

Precision Clock Synchronization Protocol and Its Implementation into Laboratory Ethernet Network

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with the synchronization in packet-based data networks, especially in the Ethernet. Generally, there are several protocols and standards, which could be used for this purpose, but one the most promising is IEEE 1588 Precision Clock Synchronization Protocol (PTP), which will be described in this paper. The main section of this article is focused on the practical implementation of IEEE 1588 protocol into the fully operational Ethernet network. The network consists of several network devices, some of them support IEEE 1588 PTP protocol and others, like standard Ethernet switch and hub, do not support this synchronization protocol. We also performed several measurements and comparisons of the accuracy of precision time distribution for different network topologies and under various network conditions. These results, in the form of graphs, are also commented here and several conclusions about the influence of network devices are given in this article.

Pseudorandom Generator of Crosstalk Transmission Functions for Modeling of Multi-quad Metallic Cables

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Crosstalk, and mainly far-end crosstalk (FEXT), is one the most serious source of disturbance in present xDSL lines (Digital Subscriber Line). It mostly limits the maximum achievable transmission speeds. This paper presents the possibility of using space selection of disturbing sources among the metallic cable, which would allow the use of VDMT modulation only for a limited number of the most disturbing pairs. The new far-end crosstalk model, called advanced FEXT model, which is based on cable internal structure and parameters, is proposed here. The presented generator of crosstalk transmission functions is based on the advanced FEXT model.

Security Threats in the Current Generation of Passive Optical Access Networks

  • Authors: Rohlík, M., Ing. Pavel Lafata, Ph.D.,
  • Publication: Elektrorevue. 2010, 13(37), 37-1-37-6. ISSN 1213-1539.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Thanks to the progressive development and deployment of passive optical access network, a wide number of households and the end users will be soon covered with powerful access solution, which will allow to access advanced multimedia and interactive services. However, it appears to be necessary to adequately secure transmitted data and also the optical networks itself against various types of security risks. This paper describes the most serious security threats in the current generation of passive optical networks and it offers several possibilities for their elimination.

Security Threats in the Current Generation of PON

  • Authors: Rohlík, M., Ing. Pavel Lafata, Ph.D.,
  • Publication: Sdělovací technika. 2010, 58(10/2010), 5-8. ISSN 0036-9942.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article discusses the current security risks of passive optical access networks and presents the possibilities of their removal. For the demands of future applications it will be necessary to adequately secure the transmitted data and their own optical networks against various types of security risks.

The Applications for the Calculation and Optimization of Passive Optical Networks Attenuation Characteristics

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The program for the purposes of rapid calculation of the passive optical network attenuation was designed. It supports various network topologies and it enables to enter initial parameters of optical network. The outputs in the tabular form also include the assessment of the suitability of proposed optical network for the different variants of passive optical networks.

The Possibilities of Measuring the Parameters of Passive Optical Networks

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper is focused on description and measurement techniques of parameters of optical access networks. It also contains examples of measured results and their analysis.

Time Synchronization in Packet Networks and Influence of Network Devices on Synchronization Accuracy

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with a relatively new synchronization protocol - the IEEE 1588 Precision Clock Synchronization Protocol (PTP). This protocol reaches the typical accuracy better than 100 nanoseconds and uses hierarchical synchronization network infrastructure, which enables to synchronize all devices connected into this network. The first part of the article describes the Precise Time Protocol, while the second part deals with synchronization accuracy measurements for various network topologies with different network devices. This paper contains the presentation of a laboratory synchronization network as well as it includes practical results and comments concerning its functionality and performance.

Use of Crosstalk Advanced Model for Modeling of VDMT Modulation Benefits

  • Authors: Ing. Pavel Lafata, Ph.D., Ing. Petr Jareš, Ph.D.,
  • Publication: TSP 2010 - 33rd International Conference on Telecommunications and Signal Processing. Budapest: Asszisztencia Szervező Kft., 2010. pp. 386-390. ISBN 978-963-88981-0-4.
  • Year: 2010
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper presents new method for realistic simulations of far-end crosstalk, which is able to generate pseudo-random characteristics of far-end crosstalk. This advanced crosstalk model could be used to generate realistic far-end characteristics and to simulate vectored discrete multi-tone modulation's impact on the reduction of crosstalk level. This paper also presents future development of new methods for digital subscriber line high-speed data transmission and above all proposes new simulation method of modeling benefits for the vectored discrete multi-tone modulation, which can be used for creating the high-speed transmission environment with the use of current algorithms and analytics models.

Advanced Far-end Crosstalk Modeling Based on Cable's Constructional Arrangement

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: 13th International Student Conference on Electrical Engineering. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2009. p. C2.
  • Year: 2009
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Far-end crosstalk represents serious source of disturbance for nowadays digital xDSL subscriber lines. Implementation of new modulation techniques, such as Vectored DMT modulation, is going to be probably one of the best possibilities for reducing FEXT influence, but these operations are still too much complex and demanding for today's computing units. This paper describes a method of cable separation according to its manufacturing parameters into groups and subgroups of pairs. This would allow preparing transmission models with determining of contributions of each constructional category and performing Vectored DMT modulation for only limited number of pairs or even sub-channels. Together with new method for modeling, which is based on statistical evaluations of measured characteristics and supplemented by a pseudorandom component of filtered frequency response, could make the whole operation and calculation significantly easier.

Advanced Far-end Crosstalk Modeling for Modern Metallic Networks

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Elektrorevue. 2009, 11.(2009/34), 34-1-34-6. ISSN 1213-1539.
  • Year: 2009
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper deals with modeling and simulations of far-end crosstalk for multipair metallic cables. It results from using space selection of disturbing systems and analysis of f contributions of each constructional category. This paper describes a method of cable separation according to its manufacturing parameters into groups and subgroups of pairs. This would allow preparing transmission models with determining o and performing Vectored DMT modulation for only limited number of pairs or even sub-channels. Together with new method for modeling, which is based on statistical evaluations of measured characteristics and supplemented by a pseudorandom component of filtered frequency response, could make the whole operation and calculation significantly easier. The paper also brings an example of measured results.

Advanced Modeling of Far-end Crosstalk Transfer Functions in Metallic Cables

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Transmission speed of current digital subscriber lines is limited mainly by interferences occurring in metallic cables as a result of crosstalk between metallic pairs in a cable. Presented method for the elimination of far-end crosstalk's influence by performing Vectored DMT modulation is not possible to use for real application in large cable systems due to its high demands on transmission processors, caused by its overall complexity. One of the possibilities, how to simplify the whole process, would be performing Vectored DMT modulation only for limited number of pairs, or even only for several xDSL systems' sub-channels, by performing space selection of most disturbing sources in a cable.

Calculation of Attenuation Characteristics of Passive Optical Networks

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper is focused on detailed analysis and study of attenuation characteristics of passive optical networks. Paper presents parameters of typical components of passive optical networks. A calculation of total attenuation budget is presented and the results are interpreted.

Implementation of Innovative Tools into the Education of Digital Technology Courses

  • Authors: Ing. Pavel Lafata, Ph.D., Podgorný, R.
  • Publication: International Workshop wRTT 2009. Praha: České vysoké učení technické v Praze, 2009. pp. 0057_0011. ISBN 978-80-01-04411-7.
  • Year: 2009
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper describes the possibilities of using modern resources and technologies in the education process of digital circuits, microprocessors and digital gates. The article describes the solution and results of FRVŠ Project: Innovation of the laboratory tasks in the education course of Fundamentals of digital technology, which was solved at the Department of Telecommunication Engineering.

Modeling of Far-end Crosstalk in Multi-quad Cables Based on Capacitive and Inductive Unbalances Between Pairs

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: TSP - 32nd International Conference on Telecommunications and Signal Processing. Budapest: Asszisztencia Szervező Kft., 2009. p. 84-88. ISBN 978-963-06-7716-5.
  • Year: 2009
  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper deals with the modeling of far-end crosstalk between symmetrical pairs in multi-quad metallic cables. The article follows author's previous publications about far-end crosstalk modeling based on cable constructional arrangement and brings new methods and ideas of simulations and calculations. New model will come from the mathematical and geometrical description of capacitive and inductive couplings between pairs, quads and subgroups of pairs in a cable. For the purpose of this description, new detailed and complex geometrical model should be provided and it will be also necessary to consider many effects and conditions for real situations in multi-quad metallic cable. On the other hand, resulting model will be very universal and will allow derivation and calculation of far-end crosstalk characteristics for various types of metallic cables and situations by using only few constructional parameters of selected cable.

Modeling of Transmission Functions and Crosstalk in Metallic Cables for Implementation of MIMO Concept

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The new promising wireless networks based on multi-carrier modulations (MCM) and multiple-input multiple-output concept (MIMO) will soon offer high-speed digital connections. Their access points are mostly connected by fixed metallic lines to core data and telecommunication networks. That is why it will also be necessary to increase the transmission speed and overall performance of these fixed access networks adequately in order to meet the expected requirements of wireless connections. It would be possible to use VDSL2 digital subscriber lines and implement MIMO concept into the existing metallic networks for this purpose, but before that it will be necessary to solve several problems first. The transmission capacity of present VDSL2 digital lines is limited mainly by crosstalk occurring in metallic cables.

Modern Solution for Access Networks - Passive Optical Network and Its Demonstration in Education

  • Authors: Ing. Pavel Lafata, Ph.D.,
  • Publication: Workshop 09 CTU REPORTS. Praha: České vysoké učení technické v Praze, 2009. pp. 120-121. ISBN 978-80-01-04286-1.
  • Year: 2009
  • Department: Department of Telecommunications Engineering
  • Annotation:
    Passive Optical Network (PONs) will offer the end users necessary transmission capacity for fast access to the Internet, services such as VoD (Video on Demand), IP TV in High Definition (HD) and others. However the development of optical access networks in Czech Republic is still very slow, the main barrier appears to be the cost of necessary optical lines and components of optical networks. That's why we decided to build the demonstrational laboratory workplace of passive optical network for our students to introduce them this new optical solution for access network.

Passive Optical Access Networks

  • Department: Department of Telecommunications Engineering
  • Annotation:
    Together with the evolution of access networks are currently being discussed more and more optical or combined optical-metallical subscriber lines called FTTx (Fiber to the x), whose optical part will be based on some variant of passive optical networks (Passive Optical Network, PON), often on a variant GPON (Gigabit Passive Optical Network) or EPON (Ethernet Passive Optical Network).

Passive Optical Network - EPON

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper provides a description and characteristics of passive optical access network type EPON (IEEE 802.3ah) and its incoming generation 10GEPON (IEEE 802.3av). Article also complements the previous description of passive optical access networks and is focused on variants based on transmission using Ethernet frames.

Passive Optical Network - GPON

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper is focused on detailed analysis of features and functions of Passive Optical Networks, especially on GPON type. It also contains compact description of important characteristics and some specific problems and their solutions in the field of passive access optical networks - GPON.

Present and Future Potentialities of Passive Optical Networks

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article is focused on detailed analysis of features and functions of Passive Optical Networks. It contains compact description of important characteristics and some specific problems and their solutions in the field of passive access optical networks. The paper also deals with the future possibilities in the field of passive optical access networks, especially with usage of wavelength multiplexing techniques, or its combination with time-dividing mechanism.

WDM Passive Optical Networks - WDM-PON

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The paper deals with the future possibilities in the field of passive optical access networks, especially with usage of wavelength multiplexing techniques (WDM), or its combination with time-dividing mechanism (TDMA). These networks, often called as WDM-TDMA PON or hybrid networks, are going to be a promising evolution of optical access networks.

Advanced Crosstalk Modelling - Generating of Characteristics

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The paper follows previous publication, gives new insights in FEXT simulation based on metallic cable constructional arrangement using statistical evaluation of measured parameters. This statistical model is subsequently modified by generated random waveform to simulate realistic results using statistical values of measured characteristic and its filtration.

Advanced Crosstalk Modelling - Measuring and Assumptions

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with the problems of simulations and statistical evaluations of far end crosstalk (FEXT) between symmetrical pairs in metallic cable. The paper presents new idea of crosstalk evaluations based on theoretical assumptions, which resulting of metallic cable constructional arrangement. To verify theoretical assumptions, several measurements were performed and proceedings of gained values of crosstalk are included in this article. This paper will also present an idea of the Generator of transmission functions between symmetrical pairs in metallic cable.

Introduction of New Approaches and Technologies to the Education of Telecommunications

  • Authors: Ing. Pavel Lafata, Ph.D., Prokop, T.
  • Publication: Pedagogický software 2008. České Budějovice: Scientific Pedagogical Publishing, 2008. pp. 83-85. ISBN 80-85645-59-9.
  • Year: 2008

Practical Application of FEXT Models for VDMT Modulation

  • Department: Department of Telecommunications Engineering
  • Annotation:
    The paper presents and idea of a generator of transmission functions between symmetric pairs in metalic cables, focusing especially on questions concerning far-end crosstalk, its simulations and statistical evaluation of measured values.

Programme for Evaluation of Metallic Cables Measurements

  • Department: Department of Telecommunications Engineering
  • Annotation:
    In the Matlab environment was created graphical interface for analyzing of measured characteristics of metallic cables with a variety of optional parameters for evaluation.

Projection and Realization of Laboratory Workplace of EPON Passive Optical Networks and Its Utilization for Education

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper will focus on passive optical access networks (PONs), especially EPON. The paper includes basic introduction into PONs, further describes the design and utilization of passive optical network workplace in the laboratory of the Department of Telecommunication Engineering, Faculty of Electrical Engineering, CTU in Prague. The paper also shows possibilities of using this workplace for education and for student's work on their diploma and bachelor thesis. Article also presents the possibilities of future directions of research projects in the field of passive optical networks.

Simulations and Statistical Evaluations of FEXT Crosstalk in xDSL Systems Using Metallic Cable Constructional Arrangement

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This article deals with the problems of simulations and statistical evaluations of far end crosstalk between symmetrical pairs in metallic cable. The paper follows previous publications, gives new insights into questions associated with crosstalk evaluations based on theoretical assumptions, which resulting of metallic cable constructional arrangement. Paper also presents an idea of application these results in Generator of transmission functions to analyze the overall impact of Vectored DMT modulation on digital subscriber line traffic. To verify theoretical assumptions, several measurements were performed and proceedings of gained values of crosstalk are included in this article.

Test Optical Access Network EPON and Its Use in Education

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper will focus on passive optical access networks (PONs), especially EPON. The paper includes basic introduction into PONs, further describes the design and utilization of passive optical network workplace in the laboratory of the Department of Telecommunication Engineering, Faculty of Electrical Engineering, CTU in Prague. The paper also shows possibilities of using this workplace for education and for student's work on their diploma and bachelor thesis as well as presents the possibilities of future directions of research projects in the field of passive optical networks.

Influence of xDSL Spatial Selection for DMT Modulation

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper will present problems regarding crosstalk on far end between symmetrical pair in metallic cable. Especially focusing on questions concerning crosstalk simulation and questions associated with traffic of digital subscriber line, which will be using vectored discrete multi-tone modulation to ensure increased transmission efficiency. To verify theoretical assumptions, which are result of metallic cable constructional arrangement, article includes also proceeded actual gained values of crosstalk on far end.

Transmission Environment Modeling for VDMT System Simulation

  • Department: Department of Telecommunications Engineering
  • Annotation:
    This paper describes the practical results from measurements done at the Department of Telecommunications Engineering, Faculty of Electrical Engineering, CTU in Prague and presents the concept of a transfer and crosstalk function generator for VDMT System Simulation.

Responsible person Ing. Mgr. Radovan Suk