ADSL帧结构分析

非对称数字用户线（ＡＤＳＬ）是利用现有电话网的铜双绞线为用户提供宽带业务的一种新技术，本文首先介绍了ＡＤＳＬ的基本概念，原理，然后着重对ＡＤＳＬ原帧结构进行了分析。     

Performance evaluation of a multichannel transceiver system forADSL and VHDSL services

The authors study the performance of a multichannel modulation method for asymmetric digital subscriber lines (ADSLs) and very high-speed digital subscriber lines (VHDSLs). In the ADSL case, over all unloaded North American subscriber lines in the test set, a unidirectional 1.536 Mb/s data rate service from the end office to the customer premises is possible on a single twisted pair at an error rate of 10^-7 with at least a 6 dB margin used coded multichannel modulation with sufficient transmit power. In the VHDSL case, data rates in excess of 100 Mb/s can be transmitted reliably, at an error rate of 10^-7, using uncoded multichannel modulation on a single twisted pair over a distance ⩽150 ft with a sufficiently high sampling rate (≈24 MHz) and transmit power. It is shown that a cost-effective multichannel transceiver design suggested for high-speed digital subscriber line (HDSL) service will also work well for ADSL and VHDSL services with only minimal modifications     

Broadband access using subcarrier multiplexing and asymmetric digital subscriber lines

A broadband access system using subcarrier multiplexing on optical fibre and asymmetric digital subscriber lines (ADSL) or very high‐speed digital subscriber lines (VDSL) on unshielded twisted‐pair is proposed to provide broadband access. In this hybrid‐fibre/twisted‐pair (HFTP) system, the digital multiplexing/demultiplexing process is moved back to the central office by using subcarrier multiplexing for fibre transmission. Instead of installing in remote node, ADSL/VDSL transceivers are installed at the central office to greatly reduce the remote node complexity. The local node simply down‐converts the subcarrier multiplexed ADSL/VDSL signal to the baseband, suitable to send directly into the twisted‐pair. The reduction of complexity could result in a lower initial installation cost, especially for a low service penetration rate. Copyright © 2000 John Wiley & Sons, Ltd.     

Performance study of high-speed asymmetric digital subscriber linestechnology

Computer simulation results are presented for the loop range coverage of an asymmetric digital subscriber lines (ADSL) system that uses the quadrature amplitude modulation (QAM) signaling scheme, ADSL performance is evaluated in the presence of background additive white Gaussian noise (AWGN), and crosstalk noise from existing services in the local telephone loop plant. It is shown that coverage of the extreme carrier serving area (CSA) is possible at transmission rates that are well above the existing T1 rate     

High-bit-rate digital subscriber lines

High-bit-rate digital subscriber line (HDSL) technology provides a simple, cost-effective solution for the rapid provision of a new digital telecommunication services direct to a customer's premises over existing twisted copper pair telephone lines. It makes full use of the existing network infrastructure and hence removes the need for the costly replacement of copper twisted pairs by alternative transmission media     

ADSL技术基本原理和展望

非对称数字用户线（ＡＤＳＬ）是利用现有电话网的铜双铰线为用户提供宽带业务的一种新技术。本文介绍了ＡＤＳＬ的基本概念、原理、并对ＡＤＳＬ市场的当前善作了简单分析。     

ADSL: a new twisted-pair access to the information highway

The asymmetric digital subscriber line (ADSL) takes advantage of the existing twisted-pair copper loop that currently provides customer access to the telephone network. An ADSL modem is placed at each end of the loop to create a high speed access link above the existing telephone service. Since ADSL makes use of the existing copper telephone line, its application in the telephone network can conceivably be nearly as ubiquitous as the public telephone network itself. With ADSL, it is possible to connect small numbers of customers to broadband services in areas where full upgrade to hybrid fiber coaxial or fiber facilities is not economical in the near term. ADSL systems offer a means to introduce broadband services using the embedded base of metallic loops in areas where optic fiber-based, hybrid fiber-coaxial radio systems or other broadband transport systems may not be scheduled for deployment in time to meet business needs and customer demand. The article concentrates on ADSL systems capable of at least a nominal 6 Mb/s payload transport toward the customer, in addition to associated upstream channels and symmetrical “telephony” services via nonloaded loops that comply with carrier serving area design guidelines     

Video on phone lines: technology and applications

This paper reviews the telephone loop plant characteristics, current DSL (digital subscriber line) technologies, recent efforts in video coding standards, and the interrelationship between DSL technologies and visual communications over subscriber lines. In overview of the loop plant characteristics we examine its physical makeup and transmission properties, where for the latter we discuss frequency and time responses of wire-pair lines and the impairments of echo, crosstalk, impulse noise, and radio frequency interference. We trace the historical development of various DSL technologies and comment on possible future evolution. Transmission technologies used in the ISDN basic-access DSL, the high bit-rate DSL, and the asymmetric DSL are portrayed. And the issue of spectrum compatibility among different transmission systems is explained. Several important video coding standards are briefly described, including ITU-T's H.261 and ISO's JPEG and MPEG series, which are either completed or emerging. The synergistic relationship between these standards and the DSL technologies is elucidated. As a result, DSL technologies provide the potential of delivering certain broadband services well in advance of direct fiber access for telephone subscribers     

Systems considerations for the use of xDSL technology for dataaccess

A variety of signal processing techniques have been developed over the past 10 years to increase the bit rate of digital transmission through telephone loop twisted pairs. The ISDN basic rate access 2B1Q digital subscriber line (DSL) was the first technology of this type to be deployed commercially at 160 kb/s full-duplex transmission on a single twisted pair. Other transmitter/receiver circuits have been developed over the years that support symmetric and asymmetric data transmission from several hundreds of kilobits per second to several megabits per second using the 2B1Q line code in the case of HDSL and various modulation techniques (QAM, CAP, and DMT) in the case of ADSL. These more recent forms of xDSL circuitry have begun to be used to provide commercial Internet access. This article analyzes the system level considerations for using these technologies in the increasing complex loop network of telephone companies. A “next generation” of xDSL access system is proposed, and the requirements for such a system are discussed     

Alternative technologies and delivery systems for broadband ISDNaccess

Switched on-demand video is expected to become a major consumer of bandwidth. Two-way video offers televisting, tele-education, and telecommuting services, which together could represent a further substantial bandwidth demand. High-speed data services to provide the fiber distributed data interface (FDDI) between locations, or even operate a computer-aided design (CAD) terminal remotely from its local area network (LAN), are likely new applications for broadband integrated services digital networks (B-ISDN). The video quality evolution and digital modulation techniques that are making broadband digital delivery of TV signals possible are reviewed. Cable TV B-ISDN delivery, short twisted pair B-ISDN delivery, and TV broadcast digital delivery are discussed     

Binder MIMO Channels

This paper introduces a multiple-input multiple-output channel model for the characterization of a binder of telephone lines. This model is based on multiconductor transmission line theory, and uses parameters that can be obtained from electromagnetic theory or measured data. The model generates frequency-dependent channel/binder transfer function matrices as a function of cable type, geometric line-spacing and twist-length parameters, and source--load configurations. The model allows the extraction of the magnitude and the phase of individual near end crosstalk, far end crosstalk, split-pair, and phantom transfer functions from the transfer function matrix of the binder. These individual crosstalk transfer functions are often found to be very sensitive to small imperfections in the binder. Examples of category 3 twisted pair American telephone lines and ldquoquadrdquo telephone cables are also presented.     

Video communications and services in the copper loop

There are several technologies available for providing access using the embedded copper loop plant. However, none of these technologies can provide a high-bit-rate digital transport capability (1.544 Mb/s) over the existing loop plant. The authors describe continuing advances in both VLSI implementation and signal processing algorithms that are making it possible to provide the high-bit-rate digital subscriber line (HDSL) for a repeaterless T1 capability within carrier serving areas (CSAs); asymmetric digital subscriber lines (ADSL) for a 1.5-Mb/s transport capability over the nonloaded copper loop plant; and the next-generation ADSL-II for a 3 to 4 Mb/s transmission rate over CSA ranges. It is argued that, coupled with advances in video compression techniques and recent standards activities in CCITT, these bit rates will allow local exchange carriers (LECs) to provide video communication and services using highly compressed digital video by allowing the LECs to use their existing embedded loop plant to enter the video market and establish a base of customers     

TRANSMISSION CAPABILITY OF DISCRETE MULTITONE MODULATION FOR TAIWAN’S SUBSCRIBER LOOPS

The transmission of 1.5 Mb/s and beyond data rate in the conventional twisted-pair local loops, called asymmetrical digital subscriber line (ADSL) technology, will be possible to create a new transport access capability to provide economic wideband voice/data/video integrated services directly to residential customers. The term ‘asymmetric’ in ADSL refers to the much higher data rate in the direction from central office (CO) to the customer and the lower rate of return (control) data from the customer to the CO. Discrete multitone (DMT) modulation has been selected as the modulation scheme in ADSL. Because the crosstalk of local loops in Taiwan is 10–15 dB worse than that in the US, the service capability of DMT ADSL for Taiwan’s local loops may be different from that in other countries, and thus needs to be evaluated. On the basis of the characteristics of Taiwan’s local loops, transmission capability is estimated to be 1.544 Mb/s and 6 Mb/s in Taiwan. Simulation results also show what percentage of users in Taiwan may have 1.544 Mb/s or 6 Mb/s of ADSL services. Far-end crosstalk (FEXT) and additive white Gaussian noise (AWGN) are considered to be the dominant noise sources in the work.     

Simulation of ADSL over ISDN on German subscriber lines

The shortcomings of the existing asymmetric digital subscriber line (ADSL) standard ANSI T1.413 for application with the integrated services digital network (ISDN) are explained. An ADSL system modified by increasing the high-pass cutoff frequency of the splitter to about 140 kHz and, therefore, moving also the pilots, has been simulated under noise conditions and the ISDN requirements of the German subscriber line network. The reach reduction due to ISDN compared with the “plain old telephone service” (POTS) application is shown to he between 10% and 15%. It is proposed to apply ISDN ADSL rather than POTS ADSL     

基于HFC的宽带接入网关键技术

随着通信的发展和“信息高速公路”概念的提出,网络运营商越来越倾向集视频、话音、数据于一体的宽带综合业务,如今世界各国相继开发了基于现有铜缆的接入网技术高比特率数字用户环路(HDSL)和不对称数字用户环路(ADSL)、基于光缆接入技术的光接入网(OAN)、混合光纤同轴电缆(HFC)网络以及无线接入技术等宽带用户接入网技术,文章详细分析了HFC宽带接入网的网络结构及其关键技术。     

A frequency-domain approach to crosstalk identification in xDSLsystems

Crosstalk between multiple services transmitting through the same telephone cable is the primary limitation to digital subscriber line services. From a spectrum management point of view, it is important to have an accurate map of all the services that generate crosstalk into a given pair. If crosstalk is measured via modem-based methods, i.e., while a digital subscriber line (DSL) system is running, what is measured is the crosstalk in the bandwidth of the considered DSL system. For this reason, DSL services running on adjacent pairs may not be detected if their bandwidth is not significantly overlapping with the bandwidth of the disturbed system. This is a major drawback of modem-based system identification techniques since, from a spectrum management point of view, it is important to be able to identify all crosstalkers. We address the important problem of crosstalk identification when the pair under test does not bear DSL services, i.e., via a non-modem-based approach. Crosstalk sources are identified in the frequency domain by finding the maximum correlation with a “basis set” of representative measured crosstalk couplings. The effectiveness of the proposed technique is also verified on the basis of real crosstalk measurements performed on actual cables. Finally, new techniques based on multiple regression and best basis selection are also discussed     

不对称数字用户线（ADSL）

本文对不对称数字用户线（ＡＤＳＬ）的基本概念，所能提供的宽带业务、技术性能、系统组成作了和说明，并指出利用ＡＤＳＬ，把宽带信息沿普通电话线（铜线）送到千家万户，是数十年时间内过渡到光纤到家（ＦＴＴＨ）的有效传输手段。     

ADSL技术发展及应用

ADSL技术是一种调制技术,在双绞铜线的两端分别接入ADSL调制解调器,即可利用其高频宽带特性高速传送数据.本文全面阐述了实现用户线路高速化的ADSL的技术以及应用.     

ADSLDSLAM局端设备的性能分析

ADSL是利用已接入千家万户的电话网的双绞线,实现用户高速上网的技术,已成为目前人们在接入网方面研究的重点.本文论述了ADSL局端的两种DSLAM接入方案,分析了它们对数据包传输的效率,比较了优缺点,重点论述了传输效率比较高的IP直接接入的DSLAM设备.并对实现中遇到的几个关键问题,进行了论述.