LDSL发展的第一步READSL

LDSL是ITU的一个研究课题,其目标是延长DSL传输距离。READSL是LDSL课题发展的第一步,它能使基于G.992.1／G.992.3的ADSL传输距离延长至18kft(约5.5km)。文中分析了延长ADSL传输距离的技术难点以及可行的解决方案,最后介绍了频谱分配技术在READSL中的应用。     

Residential broadband architecture over ADSL and G.Lite (C.992.2):PPP over ATM

The objective of this article is to present the end-to-end broadband service and protocol architecture over DSL that has been adopted for both ADSL and G.Lite (PPP over ATM). G.Lite is a new form of DSL, and its characteristics are discussed. The article then presents a vision for the evolution of an analog modem-based service to G.Lite and ADSL services. The article explains the standardized architecture of PPP over ATM for DSL, and explores how the unique characteristics of G.Lite affect higher-layer protocols (PPP over ATM). Finally, it discusses a vision of how DSL will be deployed together with home networking to provide broadband services to multiple devices in a user-friendly fashion     

ADSL网络体系结构

ADSL是DSL的一种非对称版本，是目前一种重要的宽带接入方式，ADSL能够向终端用户提供8Mbit/s的下行传输速率和1Mbit/s的上行传输速率，比传统的28．8kbit/s模拟调制解调器快将近200倍。文中讨论了一组能够支持基于PPP／ATM／ADSL接入网体系结构的核心网体系结构，分析了几种不同组网方式的特征与协议栈模型。     

Novel efficient bit-loading algorithms for peak-energy-limitedADSL-type multicarrier systems

We develop solutions for the loading of digital subscriber loop (DSL) multicarrier (MC) systems that present constraints both on overall available energy and maximum energy per carrier. In the emerging G.DMT-based systems planned for high-throughput multimedia applications, the constraint on the peak-energy arises from spectral compatibility issues. However, until today, optimal solutions for loading peak-energy constrained MC systems do not seem explicitly developed in the literature. Hence, starting from suitable applications of the Kuhn-Tucker conditions, we present the analytical relationships characterizing the optimal solution of the peak-energy-limited loading for the general case of concave "rate-functions", and then, we apply them in the context of the so-called "gap analysis". Thus, a low-complexity iterative algorithm implementing this solution is also developed, and its performance is numerically tested on several ANSI-standard asymmetric DSL (ADSL)-type loops impaired by crosstalk. Furthermore, a version of the presented loading algorithm that guarantees integer bit rates with low computational effort is also presented, and its performance is tested. The carried-out performance comparisons allow us to evaluate the throughput loss induced by peak-energy constraints in emerging ADSL-like services     

Dynamic spectrum management for next-generation DSL systems

The performance of DSL systems is severely constrained by crosstalk due to the electromagnetic coupling among the multiple twisted pairs making up a phone cable. In order to reduce performance loss arising from crosstalk, DSL systems are currently designed under the assumption of worst-case crosstalk scenarios leading to overly conservative DSL deployments. This article presents a new paradigm for DSL system design, which takes into account the multi-user aspects of the DSL transmission environment. Dynamic spectrum management (DSM) departs from the current design philosophy by enabling transceivers to autonomously and dynamically optimize their communication settings with respect to both the channel and the transmissions of neighboring systems. Along with this distributed optimization, when an additional degree of coordination becomes available for future DSL deployment, DSM will allow even greater improvement in DSL performance. Implementations are readily applicable without causing any performance degradation to the existing DSLs under static spectrum management. After providing an overview of the DSM concept, this article reviews two practical DSM methods: iterative water-filling, an autonomous distributed power control method enabling great improvement in performance, which can be implemented through software options in some existing ADSL and VDSL systems; and vectored-DMT, a coordinated transmission/reception technique achieving crosstalk-free communication for DSL systems, which brings within reach the dream of providing universal Internet access at speeds close to 100 Mb/s to 500 m on 1-2 lines and beyond 1 km on 2-4 lines. DSM-capable DSL thus enables the broadband age.     

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。     

Near-end crosstalk mitigation in ADSL systems

Near-end crosstalk (NEXT) is one of the major impairments to the current asymmetric digital subscriber line (ADSL) downstream transmission. This paper presents two methods for an ADSL receiver to cancel one (dominant) NEXT signal from other types of services (such as HDSL (high-bit-rate DSL), SDSL (single-pair, symmetric DSL), T1, etc.). The methods exploit the fact that the crosstalk signal has a large excess bandwidth and its spectra in the main lobe and in the excess band are strongly correlated. The principal idea is then to estimate the crosstalk in some frequency bands (e.g., excess band) and cancel it in other frequency bands (e.g., main lobe). The frequency-domain analysis in this paper provides an intuitive explanation of the crosstalk estimation and cancellation, as well as a guidance to select the right frequency bands to observe the crosstalk signal. Moreover, a fast algorithm is proposed for practical implementation. This algorithm avoids matrix inversion and large matrix multiplication in every transmission block. Simulation results show that one of the proposed methods, minimum mean-squares error estimation and cancellation, is very effective to cancel one (dominant) NEXT and the improvement is significant in terms of the data rate and the line reach for the ADSL service. For example, using a real measured NEXT transfer function, the proposed method can increase the ADSL downstream data rate by 200% for some loops. The methods are extended to estimate and cancel two or more crosstalkers. The amount of improvement depends on the crosstalkers' characteristics and it is generally less than that of a single crosstalker case     

The error performance of digital subscriber lines in the presenceof impulse noise

This paper describes the error performance of the ISDN basic access digital subscriber line (DSL), the high bit rate digital subscriber line (HDSL), and the asymmetric digital subscriber line (ADSL) in the presence of impulse noise. Results are found by using data from the 1986 NYNEX impulse noise survey in simulations. It is shown that a simple uncoded ADSL would have an order of magnitude more errored seconds than DSL and HDSL     

DSL技术的发展趋势

详细介绍了当前三种主要的DSL技术--ADSL、VDSL、SHDSL的发展过程及趋势,并结合DSL的应用情况分析了DSLAM技术的发展趋势.     

金属线缆用户接入网技术

说明了充分利用现有金属线缆用户线的必要性，介绍了数字用户线ＤＳＬ技术的概念，对各种ＤＳＬ技术类型的传输速率、传输距离做了比较，对其中的ＨＤＳＬ和ＡＤＳＬ技术类型的思路、原理等做了详细的说明。     

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     

Programmable implementations of xDSL transceiver systems

After a background on digital subscriber line (DSL) technology, this article evaluates the trade-offs between programmable and custom implementations of communications products with an emphasis on xDSL modems. These trade-offs include time to market, risk, flexibility, power consumption, and cost. A key issue is the processing power required to implement the modem. The article takes a detailed look at the processing power required to implement an ADSL or VDSL modem on a programmable platform. It is demonstrated that today's digital signal processors meet the processing power requirements for an ADSL modem, and it is estimated that the processing requirements of a VDSL modem will be met in the near future     

2001年全球DSL发展回顾

DSL作为一种大众化的宽带接入技术,已在所有发达国家和大多数发展中国家得到推广应用。到2001年第二季度,亚太的用户数首次超过北美,成为世界上最大的市场。一般来说,住宅用户的比例高于商业用户;在DSL发展较快的地区,住宅用户比例更高些;而在DSL发展较慢的地区,商业用户较多。目前各国普遍采用的推广措施主要包括:建立专门的宽带门户网站、与ISP捆绑接入、为一定服务期限的用户打折、为现有的电话用户打折、免费提供支持DSL的计算机,以及提供家用网络业务等。     

Optimal multiuser spectrum balancing for digital subscriber lines

Crosstalk is a major issue in modern digital subscriber line (DSL) systems such as ADSL and VDSL. Static spectrum management, which is the traditional way of ensuring spectral compatibility, employs spectral masks that can be overly conservative and lead to poor performance. This paper presents a centralized algorithm for optimal spectrum balancing in DSL. The algorithm uses the dual decomposition method to optimize spectra in an efficient and computationally tractable way. The algorithm shows significant performance gains over existing dynamics spectrum management (DSM) techniques, e.g., in one of the cases studied, the proposed centralized algorithm leads to a factor-of-four increase in data rate over the distributed DSM algorithm iterative waterfilling.     

SHDSL接入技术研究进展与网络应用

2江苏联合通信有限公司,江苏南京210029)【摘要】随着ADSL技术与商业应用的成功,SHDSL技术借助DSP技术以及线路编码技术发展而有所突破。论文先叙述SHDSL系列的分类、编码调制、发展优势,讨论了SHDSL的综合接入应用范围,最后对DLSAM技术中的IPoverATMoverDSL协议结构进行了探讨。     

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     

A line terminating LSI using echo cancelling method for ISDNsubscriber loop transition

A 144-kb/s digital subscriber loop (DSL) transmission system based on hybrid transmission with an echo cancelling method is described. It incorporates advanced LSI technology to obtain compactness, low cost, and high reliability. An echo canceller (EC) LSI has been developed using CMOS technology. Combined with the multiplexing processor (MXP) LSI, the EC LSI provides basic DSL equipment functions. A specially arranged frame format with a newly developed digital phase-locked loop (DPLL) circuit for stable timing extraction, an automatic balancing network, and a two-stage echo canceller characterize the system. Using this line termination circuit, the DSL equipment showed a reach of over 6 km when used with 0.5 mm diameter cable for 160-kb/s bidirectional digital transmission     

宽带接入服务器

文章在给出宽带接入服务器概念的基础上,以ADSL系统为例,详细论述了从ATU-R经DSLAM到BAS的3种DSL接入方式的工作原理,最后介绍了中兴通讯宽带接入服务器的系统特点.     

基于ADSL和G.Lite的PPP 0ver ATM

主要讨论了基于ADSL和G.Lite技术的PPP over ATM的应用。ADSL和G.Lite作为新型的宽带接入技术,将给目前基于模拟Modem的网络接入服务带来意义深远的变革。因此在介绍ADSL和G.Lite的基本原理、功能及对高层协议（PPP over ATM)影响的基础上,讨论了ADSL系统在应用中的有关PPP起点和业务会聚的问题。