Pavel Lafata

Increasing the transmission capacity of digital subscriber lines

The digital subscriber lines with very high speed data rates combined together with passive optical networks are considered as a promising high-speed solution for modern metallic and hybrid access networks. To increase the transmission capacity in such case, it would be possible to implement an idea of using multiple pairs of local cables and group them together using an inverse multiplexing technique. 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.

Simulations and measurements of packet network synchronization by precision time protocol

Today, local data networks, many last-mile access networks and even some backbone networks are based on packet transmission protocols, especially the Ethernet. Generally, there are several protocols and standards, which could be used for the purpose of clock distribution (synchronization) over packet networks. One of the most accurate protocols is Precision Clock Synchronization Protocol (PTP, IEEE 1588), which will be described in paper. However, the packet data networks usually suffer specific disadvantages. The dependence on the network elements load and packet delay dispersion has a major impact on the synchronization accuracy. 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.

Modeling of metallic cables' attenuation for extreme temperatures

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. There are already several models to describe some of these phenomena, but these models are usually valid only for a limited range. 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.

Precise time protocol in Ethernet over SDH network

This article deals with transmission of Precision Time Protocol (PTP) over SDH (Synchronous Digital Hierarchy) network. Precision Time Protocol described in standard IEEE 1588 — Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems — is a protocol for synchronization in packet networks. This article discusses the transmission of Ethernet synchronization messages over existing SDH networks. The introduction in this paper provides possibilities of synchronization in telecommunication networks and packet networks. Synchronous Ethernet and Precision Time Protocol are methods for synchronization in packet network. The second part of this article describes several measurements and comparisons of the accuracy of precision time distribution for different conditions in Ethernet over SDH network. These results are also commented here and several conclusions about the influence of transmission capacity are given in this article.

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

Summary 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 250 MHz 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. Copyright

Investigation of phantom circuit benefits for next generation xDSL systems

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. Copyright

Analysis of transmission parameters of metallic cables based on external conditions

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.

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

Optimum segmentation step strongly affects the resulting bit gain of a proposed bit addressing technique.Existing bit masking compression techniques are inefficient for random bitstreams contained in downstream network frames.Proposed bit masking technique with pre-defined codeword dictionary can achieve compression ratio less than 1.The complexity of a proposed bit masking technique is generally equal to the complexity of existing methods.Application of both proposed algorithms for bit addressing and bit compression for downstream point-to-multipoint networks can increase their summary throughput. 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. Display Omitted

Estimations of G.fast transmission performance over phantom modes

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.

Investigation of VDSL2 Digital Lines with Bridged Taps and Various Parameters

Modern Very-High Speed Digital Subscriber Lines (VDSL2) can potentially increase the transmission rates in access networks up to tens of Mbps in both directions. However, the real transmission performance of VDSL2 technology is heavily influenced by real conditions of symmetrical pairs and quads in local metallic cables. This paper is primarily focused on the bridged taps and their influence on transmission performance of VDSL2 lines. 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.