DSL技术及其在宽带设备中的应用

数字用户线(DSL)技术是国内宽带接入的主流技术,DSLAM(DSL接入复用器)是目前广泛使用的局端宽带接入设备。文中从传输速率、传输距离等方面介绍了ADSL(非对称用户线)、SHD-SL(单线对高速数字用户线)、VDSL(甚高速数字用户线)等多种DSL技术特性,讨论了DSLAM与DSL的复合技术,提出基于SHDSL技术的高速对称数据传输方案将成为IP-DSLAM系统的发展方向。还对基于SHDSL技术的IP-DSLAM网络结构、工作原理进行了阐述。     

VDSL技术及烽火新一代DMT-VDSL产品

VDSL是英文Very High Data Rate Digital Subscribe Line的缩写．即“甚高速数字用户线”。理论上．VDSL提供的速率最高可达100Mb／s以上．它包括对称传输和非对称传输以及多种不同的传输速率。由于VDSL的传输速率高．其对应的传输距离也较短(为300m到1．5km)．所以VDSL技术较适合于应用在用户居住相对密集的地区。目前在东亚、东     

第十八讲先进的数字用户线(DSL)技术

1 DSL--一种先进的调制接入技术 众所周知,常用的公用电话网(PSTN)在交换机内采用了全数字化的交换技术,但最终到达用户端的信号仍是模拟信号.按照这种方式将用户线接入全数字化的因特网,用户方必须先用调制解调器将计算机的数字信号转换为模拟信号,交换机方又必须将模拟信号转变为数字信号.经过数/模和模/数两次转换,传输速率就会受到很大限制.数字用户线技术是在现有用户电话线两侧同时接入专用的DSL调制解调设备,在用户线上利用数字信号高频段带宽的特性,直接采用数字信号传输,省去中间的模/数转换,突破了模拟信号传输极限速率为56 kb/s的限制.     

DSL技术的应用和发展趋势

与之竞争的宽带接入技术 DSL(Digital Subscriber Line,数字用户线)是指利用电话铜线上未用的频率,传输数据业务且速率可达数Mb/s的技术。这种技术允许话音和数据同时在同一线路上传输。DSL技术从80年代发展至今,常见的有SDSL、HDSL、SHDSL、ADSL、VDSL等数种,见表1描述。表中的距离是最高速率时的最远距离。 国外采用CABLE方式实现宽带接入不但起步早,而且发展迅速。在2002     

什么是xDSL

<正> DSL(“数字用户线”的英文首字母缩写)是一种先进的调制接入技术。众所周知,常用的公用电话网(PSTN)在交换机内采用了全数字化的交换技术,但最终到达用户端的信号仍是模拟信号。按照这种方式将用户线接入全数字化的因特网,用户侧必须先用调制解调器将计算机的数字信号变换为模拟信号,交换机侧又必须将模拟信号转变为数字信号。经过数/模和模/数两次转后,传输速率就会受到很大限制。数字用户线技术是在现有用户电话线两侧同时接入专用的DSL调制解调设备,在用户线上利用数字信号高频带     

VDSL技术发展和标准状况

VDSL(Very—higk—speed Digital Subscriber Line)即甚高速数字用户线，利用频分复用的方法，在同一对电话双绞线内同时传送低频话带和数据两个部分。该技术支持对称速率或非对称速率方式传输。主要讨论VDSL技术近期的发展情况及国内外标准的状况。     

一种基于VDSL的宽带接入解决方案

宽带接入网的接入技术有很多种,如HFC、ADSL、VDSL、LAN和FTTx等,其中VDSL接入技术因能满足快速接入和宽带多媒体业务的需求,越来越受到人们的青睐。 1.VDSL VDSL称为甚高比特率数字用户线,传送模式是基于IP和:Ethernet方式,通常采用DMT调制方式,在一对铜双绞线上实现数字传输。传输距离在1km之内,其速率理论值下行可达10-52Mbit/s,上行可达1.5-     

电信辞库

甚高比特率数字用户线(VDSL)VDSL 是继高比特率数字用户线(HDSL)和不对称数字用户线(ADSL)之后出现的铜缆接入新技术,其特点是在更短的传输     

VDSL与ADSL技术的比较

文章介绍了非对称数字用户线(ADSL)与甚高速数字用户线(VDSL)的关键技术，并对这两种数字用户线技术从调制技术、拓扑结构和应用环境等方面做了全方位的比较．     

CATV光发射机原理及应用（3）——第三章 光发射机的射频激励功能电路

光发射机的任务是把从前端送来的高频电视信号变成光信号，使其能在光导纤维中传输。光发射机按照调制方式来划分有调频、调幅和数字调制等多种。目前用得最多的是多路调幅光发射机，在调幅光发射机中按照强度调制的方式不同又分为直接调制光发射机和外调制光发射机。直接调制光发射机是利用高频电视信号(将信号电流叠加到激光器的偏置电流上)来控制半导体激光器的偏流，     

Filter bank modulation techniques for very high speed digitalsubscriber lines

Multicarrier basis functions and related issues are overviewed in this article with an emphasis on filtered multitone (FMT) modulation for VDSL. The combination of filtering, small amounts of excess bandwidth, multicarrier channel partitioning, and some equalization are shown to allow a good match for spectrum management and performance challenges in VDSL transmission. The FMT basic functions are overviewed in the context of filter banks, with appropriate changes for nonzero excess bandwidth     

Low-jitter digital timing recovery techniques for CAP-based VDSL applications

In this paper, a digital timing recovery technique for carrierless amplitude and phase modulation (CAP)-based very-high-speed digital subscriber line (VDSL) applications is presented. A digital spectral line method is proposed for the timing tone extraction. It avoids the bandwidth expansion normally caused by the nonlinear property of the timing tone extraction block, and lowers the required sampling clock frequency. Also, an adaptive loop gain control scheme is proposed to reduce the timing jitter, simultaneously achieving both fast locking and low steady-state jitter. A prototype timing recovery circuit in a 0.35-/spl mu/m CMOS technology achieves 12.02-ps and 86-ps rms and peak-to-peak jitter, respectively, at 40-MHz operation. This is equivalent to about 0.1% of the symbol rate, and suitable for VDSL applications. The prototype IC consumes about 55 mW with a 3.0-V power supply.     

Single carrier modulation technology for very high-speed digitalsubscriber line

This article gives an overview of very high-speed digital subscriber lines, including the main issues of VDSL system design, such as its basic architecture, applications, and data rates, as well as the technological challenges of practical implementation due to different loop plant realities and spectral compatibility considerations. Some specific characteristics of the VDSL transceiver startup procedure and high-level architecture, as well as a summary of first laboratory tests and field trials, are also presented. The article concentrates on VDSL implementations using single-carrier modulation, which integrates the well-known carrierless amplitude/phase modulation and quadrature amplitude modulation technologies. Currently, SCM technology is considered one of the main candidates for the VDSL standard in the United States and Europe, and internationally     

Systems aspects of APON/VDSL deployment

The purpose of this article is to provide an overview of some system aspects allowing full service deployment over hybrid fiber-twisted pair access networks with a VDSL drop. Although VDSL and ADSL systems are similar from the point of view of transmission technology, there are differences in the architecture and implementation due to both the higher bandwidth and shorter copper loop length for VDSL. The VDSL drivers are given in the introduction. The next section describes the system architecture and the functionality of the various building blocks. Special attention is paid to optical feeder technology, for which APON is a well-suited technology. Concepts to reduce the cost of ownership are also discussed     

A Bandwidth Efficient Turbo Coding Scheme for VDSL Systems

The current forward error correction (FEC) scheme for very high bit-rate digital subscriber line (VDSL) systems in the ANSI standard employs a 16-state four-dimensional (4D) Wei code as the inner code and the Reed-Solomon (RS) code as the outer code. The major drawback of this scheme is that further improvement cannot be achieved without a substantial increase in the complexity and power penalty. Also, a VDSL system employing the 4D Wei-RS scheme operates far below the channel capacity. In 1993, powerful turbo codes were introduced whose performance closely approaches the Shannon limit. In this paper, we propose a bandwidth and power efficient turbo coding scheme for VDSL modems in order to obtain high data rates, extended loop reach and increased transmission robustness. We also propose a pipelined decoding scheme to reduce the latency at the receiver end. The objective of the proposed scheme is to provide a higher coding gain than that given by the 4D Wei-RS scheme, resulting in an improved performance of the VDSL modems in terms of bit rate, loop length and transmitting power. The scheme is investigated for various values of transmitting power, signaling frequencies and numbers of crosstalkers for a targeted bit error rate of 10⁻⁵ and is implemented in a system with a quadrature amplitude modulation in which a mixed set partitioning mapping is employed to reduce the decoding complexity. The effects of code complexity, interleaver length, the number of decoding iterations and the level of modulation on the performance of VDSL modems are explored. Simulation results are presented and compared to those of the 4D Wei-RS scheme. The results show that the choice of turbo codes not only provides a significant coding gain over the standard FEC scheme but also efficiently maximizes the loop length and bit rate at a very low transmitting power in the presence of dominant far-end crosstalk and intersymbol interference. In order to compare the hardware complexity, we synthesize the proposed and 4D Wei-RS schemes using SYNOPSYS with the target technology of Xilinx 4020e-3. The Xilinx field programmable gate array statistics of the proposed scheme is compared with that of the 4D Wei-RS scheme.     

A short overview of the VDSL system requirements

This article gives an overview of VDSL and summarizes the main system requirements developed by ANSI-T1E1.4, ETSI-TM6, and ITU-T Study Group 15/Question 4 in a coordinated effort. For the time being, both single-carrier modulation and multicarrier modulation schemes have been proposed for standardization. VDSL is an enabling and cost-effective access solution for the last mile of the network over ordinary existing telephone lines. This new standard targets aggregated data rates up to 52 Mb/s on short loops. VDSL can be used to provision broadband services for both residential and business.     

Highly efficient xDSL line drivers in 0.35-/spl mu/m CMOS using a self-oscillating power amplifier

The design of two highly efficient line drivers in a digital 0.35-/spl mu/m, 3.3-V technology are presented. The self-oscillating power amplifier (SOPA) architecture has been developed in order to obtain a high efficiency for systems with a high crest factor like discrete multitone modulated xDSL modems. The SOPA architecture is an unclocked switching-type line driver. By using self-oscillation and noise-shaping, a high signal linearity can be obtained for low over-switching ratios. By coupling two SOPA line drivers with a signal transformer, the two limit cycle oscillations are pulled toward synchronization. This gives an important mean switching frequency suppression toward the line. The need for an extra filter dealing with the mean switching frequency is in that way heavily relaxed. A zeroth-order SOPA and a third-order SOPA are prototyped. The zeroth-order line driver meets ADSL-Lite specifications with a missing tone power ratio (MTPR) of 41 dB for an 800-kHz bandwidth. The maximum efficiency is 41%. The third-order version meets ADSL and VDSL specifications with an MTPR of 56 dB and an 8.6-MHz bandwidth. An efficiency of 47% was measured for an ADSL signal with a crest factor >5.     

VDSL数字用户环路的调制方法分析

首先介绍了超高速数字用户环路（VDSL）的基本构造和线路编码，然后分析了VDSL的主要两种调制方法，即时分复用（TDD）方式和频分复用（FDD）方式。     

基于VDSL的以太网接入技术

介绍了基于VDSL的以太网接入技术（EoVDSL)。它结合了VDSL技术和以太网技术的优点，还可以与EPON技术相结合，作为一种经济高效的宽带接入方案。     

Competing for throughput in the local loop

The voice-grade telephone channel is the communication medium most widely available throughout the world. Its limitations, a relatively narrow bandwidth and a moderate SNR figure, have challenged telecommunication researchers and engineers over several decades to develop technologies able to pass higher and higher data rates. The sophisticated combination of trellis coding and quadrature amplitude modulation increases the bandwidth utilization close to the Shannon limit of 10 b/s/Hz for the 3.1 kHz bandwidth voice channel. However, the resultant data rate of about 30 kb/s does not even begin to approach the throughput needed by multimedia applications. Fortunately, twisted pair bandwidth reaches up to several megahertz, so multilevel signaling implemented as in the xDSF family of modems enables data rates of several megabits per second to be reached. Standard ADSL modems are able to deliver 8 Mb/s to a subscriber in the best case. VDSL modems can deliver 52 Mb/s, but only up to 300 m, so their mass implementation will only become possible when fiber migrates into an access network closer to the user premises. Both broadband xDSL solutions approach the Shannon limit and the related spectral efficiency as well, so there is not much room left for a transmission improvement