Spectrum management of ADSL

The requirement for an automated test system has immensely increased due to the realization that manual testing is associated with additional resources and staffing constraints. In order to achieve a competitive edge, reduced development cost, timely product delivery, and product quality are mandatory in today's organization. Manual testing requires skilled operators that increase cost, time, and product delivery. The low cost computer based automated system helps to get an edge by fulfilling these organizational demands. In this paper, an automated testing system has been developed to support functional testing of Nortel Network's modem system (1-Meg SUT). The modem is an inherently complex asymmetric digital subscriber line (ADSL) product and its testing is far more complex than just verification of process faults. The complexity of ADSL system renders automated test system an important and imperative part of ADSL testing. The subject paper demonstrates the indispensable need of automated test system for ADSL testing and its advantages in providing a competitive edge for the organization.

In this paper the general ADSL (asymmetric digital subscriber line) noise environment is reviewed in the context of the telephone loop plant. Special attention is given to the unique unidirectional transmission nature of ADSL. A set of noise environments is presented for related computer simulation studies and hardware tests. A set of mid-CSA test loops is also proposed for performance evaluation under conditions of T1 NEXT interference. To simplify calibration procedures, noise and loop models are revealed in FIR (finite impulse response) filter form and can be measured in dB loss or dBm/Hz power density terms. A subchannel signal to noise ratio (SNR) based computer simulation method is then used to estimate potential ADSL performance under different noise environments for different serving areas. >

Revisiting Mackay Online

This paper presents the design and implementation of novel decimation filter structure for high speed asymmetric digital subscriber line (ADSL). Existing ADSL circuits use comb-FIR-FIR decimation filter structures, which have low throughput, more hardware and high power consumption. Unlike existing ADSL circuits, we design a novel high speed filter architecture and implement it using the minimal signed digit (MSD) representation. The MSD representation is suitable for common subexpression elimination, and it significantly reduces the number of adders required for the filter synthesis. Each digital-filter structure is simulated using Matlab, and its complete architecture is captured using DSP Blockset and Simulink. The resulting filter architecture has higher throughput, less hardware and consumes less power than the comb-FIR-FIR and comb-IIR-FIR architectures. The filter has been implemented on Xilinx FPGA using Virtex-2 technology. Compared to the comb-FIR-FIR and the comb-IIR-FIR architectures, the designed decimation filter architecture contributes to a hardware saving of 82% and 74%, respectively; in addition, it reduces the power dissipation by 91% and 79%, respectively.

The design and optimization of the high-speed digital subscriber line (HDSL) need powerful computational strategies. Traditional techniques of distributing poles and zeros on Smith charts generally do not work. In the past, such approaches have lead to suboptimal designs for applications where the data capacity sought is considerably less than the Shannon capacity of the lines. Typical subscriber loops are less than perfect and for the current demands on the HDSL at T1/T2 and El rates every possible venue for the HDSL design needs to be investigated, if not exploited. In this Chapter, flexible computational techniques are presented that explore and optimize system components in view of the operating environment of the HDSL and/or the asymmetric digital subscriber line (ADSL) and inherent limitations of system components. The optimization occurs automatically by forcing the computer to track the effects of incremental changes of the subsystem performance (e.g., echo cancelers or equalizers), or the component values (Rs and Cs in the matching circuits) in context to the functional constraints of the (HDSL, ADSL, duplex, dual-duplex, triplex, etc.) line in conjunction with various subscriber loop environments (CSA loops, loops <18 kft., American, Australian, European, ANSI, ETSI, etc.)

Multidimensional TCM schemes can be used to improve the performance of the asymmetrical digital subscriber line (ADSL). The operating principle of how M-D (multidimensional) TCM works in an ADSL channel is analysed and criteria for evaluating and choosing effective multidimensional TCM schemes are described. The results of a simulation for evaluating the performance is presented.

ADSL (Asymmetric Digital Subscriber Line) adopts modulation scheme called DMT (Discrete multi tone), a multi carrier system. The process of allocating bits into various sub-channels is called bit-loading. In this paper, a new bit-loading algorithm that reduces the power required to transmit data is proposed. Comparison on power cut back with other algorithms is presented. Also the implementation of the algorithm in the transmitter is discussed. A Matlab simulation model has been developed to simulate ADSL transmitter (with bit-loading), channel and receiver. The ADSL system with bit-loading algorithm is also implemented in hardware using TT's DSK6713 kit and comparison of software and hardware results are tabulated.

The purpose of the paper is to describe a model that has been developed to predict the undesired coupled voltage at the network interface of the customer premises, caused by an ambient electric field incident on the drop wire. The model considered the effects of ground reflection, angle of incidence of the incoming wave on the plane of the drop wire, and the coupling caused by common-mode induced voltage due to network unbalance. The model has been simulated and verified in experiments at Bellcore's Chester facilities. The predicted results have also been compared with the measurements taken during surveys in different parts of the country that measured the coupled voltages at the network interface caused by high-power transmitters (that is, LORAN-C). The measured results show good agreement with those predicted by the model. The model is used to study electromagnetic interference at the asymmetric digital subscriber line (ADSL) transceiver caused by coupled voltage at the customer premises. >

Echo cancellation technique enables full duplex transmission using the same transmission band and thereby increases the aggregate data throughput of a channel. This tutorial paper introduces high speed echo cancellation for Full Rate (ITU-T Recommendation G.992.1) and Splitterless (ITU-T Recommendation G.992.2, aliased G.Lite) ADSL Transceivers. Symmetric and multirate Asymmetric echo cancellation Transceiver structures based completely on time domain or frequency domain as well as both time and frequency domain echo cancellation have been analyzed using different algorithms for performance and computational complexity. Combined Time and Frequency Domain Echo Cancellation (TAFDEC) structure with the so called DMT algorithm appears to be most suitable to achieve lower complexity with better performance as compared to echo cancellation in either time or frequency domain using LMS algorithm.

The discrete multitone (DMT) modulation/demodulation scheme is the standard transmission technique in the application of asymmetric digital subscriber lines (ADSL) and very-high-speed digital subsc...

The steadily growing deployment of resilience-critical Internet services is leading to an increasing number of Multi-Homed network sites. Asymmetric Digital Subscriber Lines (ADSL) are an inexpensive way to add a secondary Internet access connection. With the development of Multi-Path Transport Layer protocols - like Multipath TCP (MPTCP) and the Stream Control Transmission Protocol (SCTP) furnished by a Concurrent Multipath Transfer (CMT-SCTP) extension - there is also a strong interest in utilising all access connections simultaneously to improve the data throughput of the applications. However, combining network paths over ADSL with paths over other access technologies like fibre optic links implies highly dissimilar paths with significantly different bandwidths, delays and queuing behaviours. Efficient Multi-Path transport over such dissimilar paths is a challenging task for the new Transport Layer protocols under development. In this paper, we show the difficulties of Multi-Path transport in a real-world dissimilar path setup which consists of a high-speed fibre optic link and an ADSL connection. After that, we present an optimised buffer handling technique which solves the transport efficiency issues in this setup. Our optimisation is first analysed by simulations. Finally, we also show the usefulness of our approach by experimental evaluation in a real Multi-Homed Internet setup.

Energy-saving by low-power modes in ADSL2

At Prairie View A and M University (PVAMU), we developed a new Broadband (High-Speed) Access Technologies Research Laboratory (BATRL) over the last few years. This laboratory is used in helping our premier telecommunication companies in the area of interoperability and reliability studies. It is also used for the training of our students in this emerging area of technology and for research, especially, the Digital Subscriber Line (DSL) modem technology. DSL is a new technology for providing higher data rates over the twisted telephone copper wire. The Asymmetric Digital Subscriber Line (ADSL) is one of the first derivatives of this DSL technology. The DSL Forum has defined an ADSL interoperability test specification, known as TR-048, which is supported by all key Service Providers, access IC manufacturers and Independent Test Labs. This research project follows the test plan TR-048 to produce a complete automated testing suit, which can be used in the industry. The goal of the research project is to develop effective scripts, which can be used at PVAMU Center of Excellence for Communication Systems Technology Research (CECSTR) BATRL for ADSL Interoperability and Reliability tests for Sprint High Speed (Broadband) Communication Networks. The automation saves time, manpower and produces unbiased reports for the interoperability and the reliability tests. As part of our goal in the Electrical Engineering Department, our students are exposed to hands-on training. The students are given the opportunity to conduct the tests in the BATRL using the developed automation algorithms for interoperability and reliability tests. The results of these automated tests have been found to conform to industry standards. The lessons learned and recommendations will be discussed in this paper.

This paper presents a study of the effects of bridged taps on very high-speed digital subscriber line (VDSL) transmission systems. It is shown that the short bridged taps; which affect VDSL signals, are much more damaging than the longer bridged taps, which affect other xDSL signals, such as high-rate digital subscriber line (HDSL) and asymmetric digital subscriber line (ADSL). Specifically, short bridged taps introduce a lot of linear distortion in the loop&amp;apos;s transfer function. In addition, they also tend to introduce more overall propagation loss than longer bridged taps. The peak-power-to-average-power ratio (PAR) of the signal increases for the loop with short bridged taps, and thus more AID bits are needed in the implementation of a digital VDSL transceiver as compared to the loop with long bridged taps. The performance of various equalizer structures is discussed in the presence of a severe channel distortion caused by the bridged tap.

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation used in a variety of broadband systems, such as asymmetric digital subscriber lines, very-high-speed digital subscriber lines, digital video and audio broadcasting, and wide local area network standards. OFDM is a promising solution achieving high data rates in a mobile environment. In wireless communication systems, signal distortion and attenuation in transmission caused by multipath effects makes it necessary to obtain knowledge related to the channel impulse response using channel estimation to provide compensation. This study combined a back propagation neural network for the estimation of channel and compensation signals with a genetic algorithm to improve performance and the convergence rate. We compared bit error rates and the mean square error of the proposed neural network with that of the conventional neural network, the least square (LS) algorithm, and the minimum mean square error (MMSE) algorithm in existing OFDM channel environments. Our results demonstrate that the proposed algorithm outperforms the LS algorithm and is on par with the MMSE algorithm.