Estimation and detection of transmission line characteristics in the copper access network

The copper access-network operators face the challenge of developing and maintaining cost-effective digital subscriber line (DSL) services that are competitive to other broadband access technologies. The way forward is dictated by the demand of ever increasing data rates on the twisted-pair copper lines. To meet this demand, a relocation of the DSL transceivers in cabinets closer to the customers are often necessary combined with a joint expansion of the accompanying optical-fiber backhaul network. The equipment of the next generation copper network are therefore becoming more scattered and geographically distributed, which increases the requirements of automated line qualification with fault detection and localization. This scenario is addressed in the first five papers of this dissertation where the focus is on estimation and detection of transmission line characteristics in the copper access network. The developed methods apply model-based optimization with an emphasis on using low-order modeling and a priori information of the given problem. More specifically, in Paper I a low-order and causal cable model is derived based on the Hilbert transform. This model is successfully applied in three contributions of this dissertation. In Paper II, a class of low-complexity unbiased estimators for the frequency-dependent characteristic impedance is presented that uses one-port measurements only. The so obtained characteristic impedance paves the way for enhanced time domain reflectometry (a.k.a. TDR) on twisted-pair lines. In Paper III, the problem of estimating a nonhomogeneous and dispersive transmission line is investigated and a space-frequency optimization approach is developed for the DSL application. The accompanying analysis shows which parameters are of interest to estimate and further suggests the introduction of the concept capacitive length that overcomes the necessity of a priori knowledge of the physical line length. In Paper IV, two methods are developed for detection and localization of load coils present in so-called loaded lines. In Paper V, line topology identification is addressed with varying degree of a priori information. In doing so, a model-based optimization approach is employed that utilizes multi-objective evolutionary computation based on one/two-port measurements. A complement to transceiver relocation that potentially enhances the total data throughput in the copper access network is dynamic spectrum management (DSM). This promising multi-user transmission technique aims at maximizing the transmission rates, and/or minimizing the power consumption, by mitigating or cancelling the dominating crosstalk interference between twisted-pair lines in the same cable binder. Hence the spectral utilization is improved by optimizing the transmit signals in order to minimize the crosstalk interference. However, such techniques rely on accurate information of the (usually) unknown crosstalk channels. This issue is the main focus of Paper VI and VII of this dissertation in which Paper VI deals with estimation of the crosstalk channels between twisted-pair lines. More specifically, an unbiased estimator for the square-magnitude of the crosstalk channels is derived from which a practical procedure is developed that can be implemented with standardized DSL modems already installed in the copper access network. In Paper VII the impact such a non-ideal estimator has on the performance of DSM is analyzed and simulated. Finally, in Paper VIII a novel echo cancellation algorithm for DMT-based DSL modems is presented

Measurement And Modeling Of Short Copper Cables For Ultra-wideband Communication

High-speed communication using the copper network, originally installed for telephony, is one of the dominant Internet access techniques. Several variants of a technology referred to as digital subscriber line (DSL) have been developed, standardized and installed during the last two decades. Essentially, DSL achieves high rates by exploiting wide bands of the copper cable channel. The shorter the cable, the wider the band that can be used efficiently for communication. Current DSL standards foresee the use of bands up to 30MHz. Cable properties have been studied by means of measurements, characterization and modeling up to frequencies of 30MHz. Recent investigations have shown that it is feasible both from technical and from economical point of view to exploit very short cables (up to 200m) even further and use bands above 30MHz. A prerequisite for further evaluation and the design of such ultra-wideband copper (UWBC) systems is the extension of existing cable models to higher frequencies. This paper presents wideband measurement results of insertion loss and crosstalk coupling in a 10-pair cable of various length values for frequencies up to 200MHz. We compare the results with extrapolations of cable models that are established in the 30MHz-range.6390Chen, W.Y., (1998) DSL: Simulation Techniques and Standards Development for Digital Subscriber Line Systems, , Macmillan Technical Publishing, ISBN 1-57870-017-5G.selt: Updated issues list for G.selt (2004) ITU-T Temporary Document SS U09, , ITU-TAsymmetric digital subscriber line (ADSL) transceivers (1999) ITU Recommendation G.992.1, , ITU-T, JuneAsymmetric digital subscriber line (ADSL) transceivers (1999) ITU Recommendation G.992.2, , ITU-T, JuneAsymmetric digital subscriber line (ADSL) extended bandwidth (ADSL2+) (2005) ITU Recommendation G.992.5, , ITU-TStarr, T., Cioffi, J.M., Silverman, P., (1998) Understanding Digital Subscriber Line Technology, , Prentice Hall, Englewood CliffsDedieu, H., The copper channel - Loop charactersitics and models (2005) Fundamentals of DSL Technology, , ch. ISBN 0849319137, AUERBACHVan Der Brink, R.F.M., (1998) Cable Reference Models for Simulating Metallic Access Networks, , Permanent Document TM6(97), ETSI STC TM6, Luleå, Sweden, JunePaul, C.R., (1994) Analysis of Multiconductor Transmission Lines, , Wiley, ISBN 0-471-02080-XCook, J.W., (1996) Parametric Modelling of Twisted Pair Cables for VDSL, , Temporary Document TD22, ETSI STC TM6, Vienna, Austria, MarVan Der Brink, R.F.M., (1997) Measurements and Models on Dutch Cables, , Temporary Document TD15, ETSI STC TM6, Tel Aviv, Israel, MarPollakowski, M., (1996) DTAG Cables Transmission Characteristics, , Temporary Document TD40, ETSI STC TM6, Vienna, Austria, MarPythoud, F., (1998) Model of Swiss Access Network Cables, , Temporary Document TD48, ETSI STC TM6, Madrid, Spain, JanHeylen, L., Musson, J., (1999) Cable Models Predict Physically Impossible Behavior in Time Domain, , Temporary Document TD08, ETSI STC TM6, Amsterdam, Netherlands, NovMusson, J., (1998) Maximum Likelihood Estimation of the Primary Parameters of Twisted Pair Cables, , Temporary Document TD06, ETSI STC TM6, Madrid, Spain, SeptBoets, P., Zekri, M., Van Biesen, L., Bostoen, T., Pollet, T., On the identification of cables for metallic access networks (2001) 18th IEEE Instrumentation and Measurement Technology Conference IMTC2001, 2, pp. 1348-1353. , Budapest, Hungary, MayBostoen, T., Boets, P., Zekri, M., Van Biesen, L., Pollet, T., Rabijns, D., Estimation of the transfer function of the access network by means of one-port scattering parameter measurements at the central office (2002) IEEE Journal on Selected Areas in Communication, 20, pp. 936-948. , JuneVery-high-bit-rate Digital Subscriber Line (VDSL) metallic interface part 1: Functional requirement and common specification (2001) T1E1.4/2000-009R3, , ANSI T1E1.4, FebVan Der Brink, R.F.M., (2001) Laboratory Performance Tests for XDSL Systems, , Permanent Document TM6(98)10, ETSI STC TM6, Sophia Antipolis, France, FebValenti, C., NEXT and FEXT models for twisted-pair North American loop plant (2002) IEEE Journal on Selected Areas in Communication, 20, pp. 893-900. , JuneNedev, N.H., McLaughlin, S., Cook, J.W., Wideband UTP cable measurements and modelling for MIMO systems (2004) Proc. European Signal Processing Conf. EUSIPCO 2004, , (Vienna, Austria), SeptMagesacher, T., Henkel, W., Tauböck, G., Nordström, T., Cable measurements supporting xDSL technologies (2002) Journal E&i Elektrotechnik und Informationstechnik, 199, pp. 37-43. , FebMagesacher, T., Ödling, P., Börjesson, P.O., Henkel, W., Nordström, T., Zukunft, R., Haar, S., On the capacity of the copper cable channel using the common mode (2002) Proc. IEEE Global Telecommun. Conf. GLOBECOM 2002, , (Taipei, Taiwan), NovTomita, N., Ohmura, M., Low-frequency crosstalk loss characteristics of balanced cables (1989) Electron. Commun. Japan, Part 1, 72 (3), pp. 95-105Goedbloed, J.J., Aspects of EMC at the equipment level (1997) Proc. 12th Intl. Symp. Electromagn. 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Characterization of the Line Configuration in Wired Communication Networks

This thesis presents an algorithm to identify the full configuration of a wired transmission line from its frequency response. It is assumed that the line can have up to two bridged taps. Each bridged tap divides the main line to two segments, and with two bridged taps there will be at most three segments in the main line. Furthermore, each segment of the main line and the bridged taps can have three different gauges. The problem of characterizing the line configuration is concerned with identifying each segment (main line segments and bridged taps) in terms of its length and gauge. The problem is solved in two phases: initialization and optimization. The algorithm can be used as single ended line testing, which means the line can be characterized by performing a simple test from the central office. Simulations demonstrate the accuracy of the proposed method

Physical Layer Techniques for High Frequency Wireline Broadband Systems

This thesis collects contributions to wireline and wireless communication systems with an emphasis on multiuser and multicarrier physical layer technology. To deliver increased capacity, modern wireline access systems such as G.fast extend the signal bandwidth up from tens to hundreds of MHz. This ambitious development revealed a number of unforeseen hurdles such as the impact of impedance changes in various forms. Impedance changes have a strong effect on the performance of multi-user crosstalk mitigation techniques such as vectoring. The first part of the thesis presents papers covering the identification of one of these problems, a model describing why it occurs and a method to mitigate its effects, improving line stability for G.fast systems.A second part of the thesis deals with the effects of temperature changes on wireline channels. When a vectored (MIMO) wireline system is initialized, channel estimates need to be obtained. This thesis presents contributions on the feasibility of re-using channel coefficients to speed up the vectoring startup procedures, even after the correct coefficients have changed, e.g., due to temperature changes. We also present extensive measurement results showing the effects of temperature changes on copper channels using a temperature chamber and British cables. The last part of the thesis presents three papers on the convergence of physical layer technologies, more specifically the deployment of OFDM-based radio systems using twisted pairs in different ways. In one proposed scenario, the idea of using the access copper lines to deploy small cells inside users' homes is explored. The feasibility of the concept, the design of radio-heads and a practical scheme for crosstalk mitigation are presented in three contributions

Modeling and simulation of branched wiring network

Journal ArticleThe impact of antenna polarization on channel capacity is explored in multiple-input, multiple-output (MIMO) systems. An idealized polarization model involving branch power rations (BPR's) and channel cross-coupling is incorporated into channel-specific capacity calculations. Results are compared for several measured channels including line-of-sight (LOS) and non-line-of-sight (NLOS) both indoors and outdoors yielding valuable sensitivity analyses for channel capacity. Virtually all channels achieve perchannel peak capacities of 50% above that of single-input, single-output (SISO) channels and are well suited to opportunistic scheduling. However, systems exclusively dependent on polarization diversity will often exhibit outage capacities of just 10% above SISO capacity and will perform worse than those dependent on additional degrees of freedom

Transmission lines, quantum graphs and fluctuations on complex networks

High-frequency devices are commonplace and at their foundations often lie cable networks forming fundamental sub-systems with the primary role of transferring energy and information. With increasing demand for ”more electric” systems, the emerging trends in Internet of Things (IoT), as well as the surge in global mobile data traffic, the complexities of the underlying networks become more challenging to model deterministically. In such scenarios, statistical approaches are best suited because it becomes daunting to accurately model details of such networks. In this thesis, I present a quantum graph (QG) approach of modelling the transfer of energy and information through complex networks. In its own right, the graph model is used to predict the scattering spectrum in wired communications, as well as statistical predictions in wireless communication systems. I derive a more generalised vertex scattering matrix that takes into account cables of different characteristics connected at a common node. This is significant in real applications where different kinds of cables are connected. For example, in digital subscriber line (DSL) networks, the final loop drop may consist of cables with different characteristics. The proposed graph model is successfully validated both with a Transmission Line (TL) approach, and with laboratory experiments. The model agrees well with the universal predictions of Random Matrix Theory (RMT). In particular, the statistics of resonance is compared with the predictions of Weyl's law, while the level-spacing distribution is compared with the Wigner's surmise, which is a telltale signature of chaotic mixing of the underlying waves. In addition, I propose an analogue of the so-called random coupling model (RCM), which is important in the study of electromagnetic waves propagating in chaotic cavities. To achieve this, I present a procedure for symmetrising the transfer operator, which we use to modify the QG model in order for it to be comparable to RCM. Unlike the RCM which depends on Gaussian random variables, the graph model works for both Gaussian and non-Gaussian statistics. We use the analogue model to investigate the impact of different boundary conditions on the distribution of energy in networks with different topologies and connectivities. I further present a novel technique of using quantum graphs to predict the statistics of multi-antenna wireless communication systems. In this context, I present three different ways of calculating the probability density function of Shannon channel capacity. The analytical calculations compare favourably with numerical simulations of networks of varying complexities. In the area of wired communications, the graph model is used to model the distribution of data in G.fast networks (the fourth-generation Digital Subscriber Line (DSL) networks), using realistic cable parameters from the so-called TNO-Ericsson model. In particular, we show that quantum graph formalism can be used to simulate the in-premises distribution network at G.fast frequencies. The parameters of CAD$55$ (or B$05$a) cables and the in-house distribution network reported in the International Telecommunication Union documentation were used in the simulations

Analysis of MIMO Communications Systems Based on Experimentally Observed Channels

This thesis presents an analysis of multiple-input/multiple-output (MIMO) communications systems where the objective is to provide a unified solution to the problems of (i) crosstalk coupling in transmission line channels (ii) multi-path fading in the time variant high frequency wireless channel. In the case of transmission line channels, a comparative analysis is presented of the performance of MIMO communications systems based on balanced CAT 5 twisted-pair transmission lines, balanced twisted-pair telephone transmission lines scheme as well as unbalanced flat-pair transmission lines. The unbalanced flat-pair transmission lines are viewed as a model for digital subscriber lines (DSLs) which may be deemed out-of-range for high speed internet connections because of the circumstances of poor balance, high insertion losses and high degrees of crosstalk. This comparative analysis is then extended to examine effect of imperfect knowledge of the transmission line channels on MIMO communications system performance. In the case of wireless channels, an analysis is presented which investigates the effect of both the Rayleigh and Ricean channels on MIMO communications system performance. Again the analysis of the wireless channels is extended to examine the effect of imperfect knowledge of the channel on MIMO communications systems performance. All of the analyses in this work are based on experimentally observed channels. In the case of the transmission line channels, it is concluded that MIMO communications systems do offer the possibility of high speed internet connectivity on transmission lines that, hereto, would have been considered out-of-range for such services. Considering the CAT 5 transmission line channels, it is concluded that the MIMO communications system provide enhancement at frequencies above 50 MHz and therefore the possibly of extending length and coverage above the standard 100 metres is proposed. On the other hand, the improved performance of the twisted-pair telephone transmission lines is consistent over the range from 300 kHz to 100 MHz when the MIMO system is applied. For all the transmission line channels that are examined, the extent of imperfect knowledge of the channel that can be allowed while maintaining a reasonable MIMO communications system performance is indicated. In the case of the wireless channels, it is concluded that MIMO communications system performance is better in the case of Rayleigh channel than in the case of Ricean channel provided that the degree of correlation of the multi-path channel impulse response components is equivalent. Also, as the number of transmitters and receivers, N T, increases the effect of a given degree of imperfect knowledge of the wireless channel becomes more detrimental on MIMO communication system performance. This work thus indicates the extent of imperfect knowledge of the wireless channel that can be allowed while maintaining a reasonable MIMO communications system performance. The trade-off between increased capacity gain and decreased accuracy of knowledge of the channel as the dimension, N T, was increased is highlighted

Semiconductor Optical Amplifiers and mm-Wave Wireless Links for Converged Access Networks

Future access networks are converged optical-wireless networks, where fixed-line and wireless services share the same infrastructure. In this book, semiconductor optical amplifiers (SOA) and mm-wave wireless links are investigated, and their use in converged access networks is explored: SOAs compensate losses in the network, and thereby extend the network reach. Millimeter-wave wireless links substitute fiber links when cabling is not economical

Dynamically reconfigurable optical access network

This dissertation presents the research results on a fiber-optic high-bitrate access network which enables dynamic bandwidth allocation as a response to varying subscribers' demands and bandwidth needs of emerging services. The motivation of the research is given in Chapter 1 "Introduction" together with a brief comparative discussion on currently available and future access networks. The idea of wavelength reconfigurability in the last-mile networks is described as a solution for more efficient bandwidth utilization and a subject of the Broadband Photonics project. Chapter 2 "Wavelength-flexible WDM/TDM access network - architecture" provides a comprehensive description of the proposed solution with each network element being analyzed in terms of its functionalities. This includes a colorless optical network unit and a reconfigurable optical add/drop multiplexer. An estimation of power budget is followed by the choice of wavelength set and network control and management layer overview. In Chapter 3 "Reflective transceiver module for ONU" after discussing different communication schemes and modulation formats three approaches to a colorless high-bitrate transmitter are analyzed in detail. This includes experiment and simulation results on a reflective semiconductor optical amplifier, reflective electro-absorption modulator and a Michelson-interferometer modulator. The Chapter is concluded with a comparative discussion. Chapter 4 "Reconfigurable optical add/drop multiplexer" discusses another key element in the proposed network architecture which is an integrated structure of micro-ring resonators providing wavelength reconfigurability. The measured characteristics assess the applicability of the device able to support unicast and multicast transmission. A range of possible sources of signal degradation in the access links are analyzed in Chapter 5 "Transmission and network impairments in the access network". An estimation of potential power penalties resulting from such impairments in the proposed system follow afterwards. Special attention is paid to optical in-band crosstalk penalties and improvement methods in Chapter 6 "Interferometric crosstalk in the access network with an RSOA". This subject is treated extensively with the support of mathematical considerations and experimental results. Proof-of-concept experiments of the proposed network architecture are presented in Chapter 7 "Reconfigurable WDM/TDM access network - experiments". The results of bidirectional transmission of high-bitrate WDM signals in different wavelength allocation schemes are discussed in detail. From there, by means of simulations the behavior of a full-scale network is assessed. In Chapter 8 "Migration towards WDM/TDM access network" the migration scenario from currently deployed fiber-optic access networks towards the novel solution is proposed. Afterwards, a short dispute on the economics of last-mile fiber technologies is included. Finally, the work is concluded and potential future research ideas based on this thesis are given in Chapter 9 "Conclusions and further work"