Broadcast digital subscriber lines

The adoption of asymmetrical digital subscriber lines (ADSL) technology in conjunction with the broadcast digital subscriber lines (BDSL) proposed in this paper could provide a cost effective solution for the introduction of digital video services in the near term. BDSL provides the same digital broadcast video programs to all subscribers through existing twisted pair telephone loops. In this paper, the basics of telephone loop-based digital subscriber lines are first discussed. Then the potential of BDSL is explored in the twisted pair loop plant near end crosstalk (NEXT), far end crosstalk (FEXT), and white noise environment. The capability of BDSL is examined with different serving areas and transmit power levels. The possibility of using orthogonal quadrature amplitude modulation (QAM) to implement a zero guard-band BDSL system is studied. Computer BDSL performance simulations are then presented. The combination of high-bit-rate digital subscriber lines (HDSL), ADSL, and BDSL can provide telephone subscribers many digital broadband services     

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。     

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     

Digital optical CATV system using hubbed distribution architecture

A hubbed distribution architecture based on a bus-star configuration, three-level single single-mode fiber transmission using M-TPC line code, and high-speed IC technology is proposed. The architecture is cost-effective and compact. It is well suited to metropolitan area CATV systems and would allow a gradual transition to a broadband ISDN (integrated-services digital network) subscriber loop in the future. The proposed architecture is applied to a digital optical CATV system prototype. The equipment making up this system consists of a transmitter, hubs including video selectors, and subscriber unit. Two video channels are selected for each subscriber from eight video channels at hub stations. The transmission speed is 900 Mb/s, three-level for the trunk line and 200 Mb/s, three-level for each subscriber loop. Very compact and low-cost equipment is realized by using recently developed high-speed ICs. Experimental results show that the system satisfies requirements and that its commercial application is feasible     

An evolutionary transport structure for local loop distributionusing RF subcarriers

An evolutionary transport structure for local loop distribution based on RF subcarrier multiplexing and wavelength-division multiplexing is discussed. Issues relating to technology and cost are discussed. The transport structure provides private, high-bit-rate, premium services to business sites, and broadcast, low-bit-rate, low-cost services to residential users. The structure is transparent to various protocols or modulation schemes and can be configured to suit different needs. Up to 60 analog FM broadcast video channels downstream and 4 analog FM video channels upstream (or a single 155-Mb/s broadband ISDN channel) per subscriber can be provided for 16 subscribers per fiber feeder. It is possible that the transport structure could be deployed affordably in the near future. Future upgrades and expansions are possible because the transport structure is compatible with most promising future technologies. Various tradeoffs are also discussed     

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.     

Performance evaluation study of signal design and equalization options for high-bit-rate digital subscriber line transceivers

This paper analyses different equalization, coding and signal constellation alternatives for the proposed high-bit-rate (800 kb/s) digital subscriber loop transmission interface. The simulation results presented in the paper demonstrate that bit rates above 1000 kb/s at acceptably low bit-error rates (≤ 10^?7) are feasible, if baseband transceivers with appropriate equalization and simple trellis coding are used. It is also shown that baseband transmission and Tomlinson precoding provide a significant performance advantage over bandpass transmission and decision-feedback equalization, respectively.     

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     

Time-Shared Two-Wire Digital Subscriber Transmission System and Its Application to the Digital Telephone Set

Adopting digital techniques in the local network area will enhance the possibility of extending digital operation capability to the subscriber's equipment. The problem is to convey digital signals at a bit rate of at least 64 kbits/s in both directions over existing two-wire subscriber loops. This paper describes a time-shared two-wire digital subscriber transmission system in which the directional separation of two signals (GO and RETURN) is accomplished by the time division bidirectional transmission method in burst-mode, and also reports results of investigations on the feasibility of an all digital telephone subscriber loop system.     

Positioning the Subscriber Loop Network for Digital Services

The need to enhance the digital transmission capability of the local loop network to provide for new services is widely recognized in the telecommunications industry. Companies around the world [1]-[3] have been working towards this goal and plan to use digital loop carrier (DLC) to meet this demand. Although this approach is generally accepted, there has been little information presented on how to plan for the evolution of the local plant. To address these pressing issues, the Bell System is introducing a concept called fundamental subscriber carrier planning (FSCP). This paper discusses the impact that digital services will have on the subscriber loop network, including loop plant design requirements necessary to position the network for up to 64 kbit/s digital services. Existing cable plant has the capability to support most digital services, but there are specific design requirements that are quite different from those required for the "typical" analog voiceband service. This paper reviews the need to position the loop for digital services, and substantiates the major conclusion that digital loop carrier technology offers a significant advantage when provisioning for digital services.     

An overview of broad-band access technologies

The provision of broad-band services based on either the Internet or the asynchronous transfer mode (ATM) technique requires a new generation of access networks. In the short term, solutions such as x-digital subscriber line (DSL) and hybrid fiber coaxial (HFC), allowing the reuse of existing infrastructures look very promising. For the longer term, new infrastructures based either on radio or on optical access links seem preferable. Three x-DSL techniques aiming at high-bit-rate transmission over twisted pairs are presented: high-bit-rate DSL, asymmetrical DSL, and very-high-bit-rate DSL. An extension of existing cable television networks known as HFC is also described. Two other prospective approaches, wireless in the loop (WITL) and fiber in the loop (FITL), are then presented. Several techniques are considered for WITL: digital enhanced cordless telecommunication local multipoint distribution service, wireless ATM, and low Earth orbit satellite constellations. The various architectural alternatives for the FITL approach are discussed, a special interest being dedicated to the synchronous digital hierarchy self-healing loop and the ATM over a passive optical network. We mention the main experiments and the standardization activities inherent to the domain     

Equalization for DMT based broadband modems

Faced with fierce competition from cable operators, telephone companies are now aggressively investing in digital subscriber line technology with the objective of providing an economic broadband access alternative. However, high-bit-rate transmissions over the metallic access network is far from trivial. The subscriber loop predominantly consists of interconnection of twisted pair copper sections. This causes severe attenuation of the high-frequency components of the transmitted signal. Equalization refers to the signal processing in the transceiver to combat the effects of the dispersive channel on the transmitted signal. This article overviews equalization methods for discrete multitone modulation (DMT). The interference structure created by a non-ideally equalized channel is analyzed. Time modulation as well as frequency domain equalization methods are addressed     

High bit rate digital subscriber line: a copper bridge to thenetwork of the future

It is argued that the high bit rate digital subscriber line (HDSL), permitting low-cost 1.5 Mb/s copper access, will ease the transition to fiber access by accelerating the use of higher speed services. Copper will dominate over fiber customer access for at least the next ten years. During this period, the success of high-speed switched services will depend on the connectivity provided by both fiber and copper access. HDSL will initially be used to serve private-line DS 1, ISDN primary rate access, and digital loop carrier feeders. Later, the HDSL will be applied to switched services such as metropolitan area networks (MANs) and circuit switched DS1s     

High-speed copper access: a tutorial overview

Telecommunication companies (telcos) are beginning to exploit further their existing access networks by using new technologies capable of delivering data at up to 30 Mbit/s over unshielded twisted copper wire pairs. This tutorial paper provides a high-level overview of the key issues related to these digital subscriber line (DSL) technologies, including the environment in which they must operate, line codes, standards, and the current state of the market     

Simulation and experimental studies on the concept of arate-adaptive digital subscriber loop (RA-DSL)

The authors report simulation results and prototype control protocols for a digital subscriber loop transmission system, which will find and operate at the highest common bidirectional transmission rate that is viable on a given loop while preserving a specified noise margin. A prototype implements the rate-adaptation and transmission protocols over a captive multigauge cable facility. Simulation results predict the accompanying symbol rate versus reach characteristics for a transceiver with the same structure as basic rate access (BRA) systems under RA-DSL control. Results show that 1.5 Mb/s could be delivered to loops of up to 2 km while subscribers out to 10 km could receive 80 kb/s. For a number of specialized or short-notice situations, RA-DSL could be the basis for a fast and flexible response vehicle. If RA-DSL cannot serve an individual combination of distance and capacity, existing methods remain. However, a statistical assessment with metro population data shows the potential for RA-DSL to satisfy 4-6 times more n×DS-0 access requests than BRA on existing copper, without carrier serving area constraints     

Architecture for delivery of broadband services to the residence

This paper presents a technology and architecture perspective on the cost of evolving today's copper access network, optimized for POTS, to a fibre access network providing both narrowband and broadband services. Architectures are assessed using application studies based on cost models for actual routes in North America. This study identifies three architectures as serious candidates (i.e. close to copper in cost) for providing POTS service in 1992: the double star, the active pedestal and the star-bus. The active pedestal and the star-bus architectures were similar in first costs and were the least expensive, costing between 5 and 15 per cent more than the copper reference depending on the number of subscribers subtending a given optical fibre. The double star is 20 per cent more expensive than the copper reference. All three architectures are potentially attractive for broadband service upgrade depending on the bandwidth required per subscriber. The star-bus is most bandwidth sensitive. Moderate video bandwidths, nominally 150 Mb/s/subscriber, favour the active pedestal architecture. Conversely, service environments requiring much greater than 150 Mb/s/subscriber favour the double star architecture.     

Applicability of ADSL to support video dial tone in the copper loop

An ADSL-3 architecture providing a downstream payload above 6 Mb/s has been proposed for operation over carrier serving area (CSA) loops. To determine whether such a system can be reliably deployed in the telephone company copper loop plant, a detailed model for loops and noise is presented. Results show that a sophisticated system, including echo cancellation and trellis coding, can reliably achieve CSA coverage, if T1 is not present in the plant. In the presence of assumed T1 worst case conditions, either the downstream bit rate must be reduced, or the operating range needs to be decreased to a serving area smaller than the CSA. A smaller “mid-CSA” serving area is proposed, and it is demonstrated that a 6.3-Mb/s ADSL (asymmetric digital subscriber line) system can operate in the presence of T1 in adjacent binder groups over this smaller serving area, which is roughly defined by 6 kilofeet of 26 gauge and 8 kilofeet of 24 gauge. A statistical study utilizing actual T1 line data suggests that if CSA coverage is attempted in the presence of T1 in adjacent binder groups, a success rate of greater than 92 percent can be expected     

Electronic Systems and Equipment for Evolving Loop Plant

This paper discusses a French plan for enhanced subscriber service, and some of the systems and equipment that will meet these goals on existing loop plant. Since 1972, the French PTT has been installing digital central offices at the national, regional, and local levels. Coverage is expected to reach 10000000 lines by 1985, so that when integrated services can be offered, the nation will be ready to take advantage of them. A PTT-sponsored program, directed toward all-digital subscriber loops, has revealed four principal phases. The first of these is already in progress: both digital and analog pair-gain systems are now being installed on existing loop plant. Soon to come is the second Phase: residential subscribers will be able to obtain two-channel subscribercarrier installations, with the carrier channel supporting data services, independent of the voice service on the same loop plant. Integrated Services Digital Networks, the third phase, should stretch the French loop plant to maximum capacity. When the demand for broad-band services overrides the capabilities of the existing copper pair plant, fiber optics cable installation will be fully planned and implemented as the fourth phase.     

An Approach to Multi-Service Subscriber Loop System Using Packetized Voice/Data Terminals

A new subscriber communication system and its design philosophy are described. In addition to telephone communication, the system is simultaneously able to offer data communication, still picture communication, etc. The system is composed of a packetized voice/data terminal, a multi-service switching equipment and the digital subscriber loop connecting between them. The system utilizes the existing subscriber line efficiently and is entirely suitable for coming telephone and data public digital network. 64 kbit/s PCM coded voice conversation and 48 kbit/s data communication were achieved simultaneously over 96 kbit/s digital subscriber line which was spanned up to 2 km.