Low-power digital radio as a ubiquitous subscriber loop

The recent growth in the use of digital radio is reviewed. The technology used to implement low-power digital radio in the local exchange loop plant is discussed. The integration of digital radio subscriber loops withnetwork intelligence is explored. The relationship between low-power digital radio loops and broadband fiber loops is briefly examined, and standards and frequency allocation activities are summarized     

A CMOS line equalizer for a digital subscriber loop

An adaptive line equalizer for a 200-kb/s digital subscriber loop is developed in the form of a monolithic LSI and implemented using 2.5-/spl mu/m CMOS technology. Most analog portions consist of switched-capacitor circuits successfully designed to minimize power consumption, the amount of hardware, and off-chip components. The main features of the LSI equalizer are an /spl radic/f step equalizer, a five-tap decision-feedback equalizer using /spl Delta/M D/A conversion, a newly developed wave difference method (WDM), tankless timing extraction PLL, and a line driver. Consequently, the LSI can equalize a 52-dB line loss with four bridge taps; it dissipates only 67 mW, and the chip area is 5.7/spl times/5.9 mm/SUP 2/.     

A long reach digital subscriber loop transceiver

An echo-cancelling duplex transmission system is described for the digital subscriber loop which uses a 4-level zero redundancy line code (2B1Q) to give very long reach in the presence of crosstalk. Novel digital signal processing algorithms are used to simplify the analogue line interface circuitry. All the digital signal processing, along with sophisticated maintenance and interfacing circuitry, can be contained on a single LSI circuit. Measured performance results are presented.     

New line code for digital subscriber loop

A new line code is presented which may find applications in the future digital subscriber loop. The line code is well balanced and has a narrow frequency spectrum.     

A digital chip timing recovery loop for band-limiteddirect-sequence spread-spectrum signals

Migration towards a full-digital implementation of modems is currently one of the main trends in transmission systems design. The authors describe a noncoherent all-digital delay lock loop (DDLL) suited for chip timing synchronization in band-limited direct sequence spread spectrum (DS/SS) systems, and they thoroughly analyze its performance. The key features of this novel scheme are represented by its low-complexity processing section together with its good tracking capability. Analytical expressions for the DDLL S-curve and steady-state timing jitter are derived and confirmed by a time-domain computer simulation. Furthermore, the Mean Time to Lose Lock (MTLL) of the loop is evaluated and some numerical results are reported. The proposed chip timing synchronization scheme reveals also an improved tracking performance when compared to the traditional analog DLL for rectangular chip DS/SS signals     

甚高速数字用户环路概述

首先介绍了甚高速数字用户环路（VDSL）的一些基本规范,然后就VDSL的关键技术如QAM和DMT调制技术,频分复用以及用户区网关等作为描述,最后,展望了VDSL的发展前景。     

Fiberguide systems in the subscriber loop

This paper presents an overview of the application of fiber optics in the subscriber loop plant. A review of the limitations of existing loop plant networks is given and the characteristics that fiber optics offer to overcome these limitations are examined. Possible network topologies for fiber optic loop systems are discussed and current designs, particularly those based on a centrally switched star configuration, are described. The component availability, system cost and other considerations are discussed. Finally, features of major current fiber optic loop system field trials and experiments are highlighted.     

Passive components in the subscriber loop

The status of passive optical components for optical fiber subscriber loop systems is reviewed in the context of the most often discussed architectures. These architectures and the passive component types and functions are described. It is shown how the components are meeting the key functional requirements of interconnection, furcation, and filtration. A logic flow to the evolution of the architecture which is based on the expected development of the passive components is indicated     

Near optimum timing recovery for digitally implemented datareceivers

A timing recovery scheme based on the maximization of the spectrum of the sampled received signal at the frequency of f-=1/2T is proposed. The quadrature amplitude modulated data signals are considered. Algorithms for both initial adjustment of the timing phase and its tracking during transmission of actual data bits are developed. The algorithms are tested by computer simulations for a typical telephone line channel. It is shown that the proposed scheme is quite robust with respect to channel impairments such as noise and phase jitter and also with respect to the correlation to the transmitted data symbols     

Laser power sharing in the subscriber loop

An experimental system that demonstrates the sharing of laser power among 64 and 128 subscribers is reported. In this system only two laser transmitters are employed at the `remote electronics? site while 600 Mbit/s signals are transmitted up and downstream between subscribers and the remote electronics sites using Ti:LiNbO3 external modulators.     

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     

A 160-kb/s digital subscriber loop transceiver with memory compensation echo canceller

A full-duplex transceiver chip incorporating an adaptive echo canceling modem and a 2.048-Mb/s serial interface is described. The device provides a full-duplex communication link at 160 or 80 kb/s on up to 4 or 5 km, respectively, of 0.5-mm twisted-pair cable. Full integration is achieved through the use of RAM-based sign-algorithm echo-cancellation, biphase line code, a fixed switched-capacitor equalizer, and a digital phase locked loop. The authors emphasize system design considerations and a chip architecture minimizing power dissipation, silicon area, and off-chip components. A double poly 3-/spl mu/m CMOS technology is used to implement the 5-V 22-pin device which dissipates less than 50 mW and occupies 27.7 mm/SUP 2/.     

Gardner定时同步环路参数设计及性能分析

以数字锁相环理论为依据,对Gardner定时误差检测器反馈定时环路参数的设计进行了深入研究,基于MATLAB对一阶、二阶环路性能进行了仿真,重点分析了环路阶数和等效噪声带宽对系统性能的影响,得到了等效噪声带宽与定时同步环路性能的关系,为定时同步环路的设计提供了理论依据。     

Optical network for broadband services in the subscriber loop

During the course of the last ten years optical transmission systems have more and more taken over the functions of their copper counterparts in the trunk network. However, replacement of copper-based transmission by optical-fibre-based transmission is only the first step in the utilisation of the large transmission capabilities of optical fibre. Deployment of optical fibres will penetrate further to the local loop to bring broadband and narrowband services directly to the customer. In the RACE 2024 project research is being undertaken towards a cost-effective broadband access facility (BAF) for the small business and residential customer and based on the asynchronous transfer mode (ATM). The authors highlight the characteristics of a suitable passive optical network to be used in the BAF system. Following an overview of the complete BAF system layout, attention is focused on the optical network, topology and realisation aspects     

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.     

Fiber-optic subscriber loop systems for integrated services--The strategy for introducing fibers into the subscriber network

Two approaches to fiber-optic subscriber loop system development in Japan are described. In the first. Approach I, NTT aims at introducing inexpensive fiber-optic subscriber loop systems using conventional LED's, multimode fiber, and analog transmission techniques in the near future. In the second, Approach II, fiber-optic subscriber loop systems will be made highly functional by evolving from analog to digital transmission. This paper presents system fabrication examples for each approach and the results obtained in the tests.     

Business and residential services for the evolving subscriber loop

The role of new loop technologies in providing new and valuable services from increasingly dynamic and intelligent networks is examined. Important market trends in business services are discussed, and the needs of large business customers are considered. Evolutionary service opportunities for the low-end market are identified. It is shown that meeting the total communications needs of large corporate enterprises necessarily involves providing much improved communications capabilities to the low end of the market. The role of the advanced intelligent network is considered     

CMOS implementation of nonlinear spectral-line timing recovery in digital data-communication systems

In many of the digital communication systems where a form of passband modulation scheme is used, carrierless amplitude and phase modulation (CAP) or quadrature and amplitude modulation for example, the signal waveform does not contain a baud-rate spectral line. This paper describes analog and all-digital implementations of timing recovery using the nonlinear spectral-line method. The analog implementation of the timing-recovery integrated circuit was fabricated in 0.9-/spl mu/m CMOS process and verified to meet all the requirements for a system utilizing the CAP modulation scheme, and initial results of the all-digital implementation confirm an even better performance that is process independent. The 51.84-MHz recovered clock allows the receiver to achieve better than a 10/sup -10/ bit-error rate (BER).     

Error correction performance in digital subscriber looptransmission systems

The author describes an error correction system for digital subscriber loop transmission systems which use time compression multiplexing (TCM). An interleaved block code is used to correct the burst errors due to impulse noise from analog telephone circuits. This interleaving method requires no extra hardware and contributes no additional delay. To evaluate the transmission performance of this error correction system, the bit error rate after decoding is derived on the basis of a burst error model for 200 kb/s digital subscriber transmission using the alternate mark inversion (AMI) line code. The experimental results for a 200 kb/s TCM system show that burst errors are substantially reduced     

Profile detection in multiuser digital subscriber line systems

Multiuser transmission methods for digital subscriber line (DSL) systems have become of interest with the potential for increased data rate and loop reach. These methods often assume that the set of crosstalk interferers, called the crosstalk profile, and their associated channel responses are known. For DSL systems, the interferers are often uncoordinated, so that in a dynamic environment where DSL transmitters can energize and deenergize, the crosstalk profile cannot be transmitted to the user of interest. While the crosstalk channel estimation problem in a dynamic environment can be intractable for general transmission systems, channel and crosstalk analysis can make use of the specific DSL environment. Namely, the physical channels in a DSL system do not change rapidly, and hence estimates of the crosstalk channel can be saved for future reference. For this reason, we introduce the concept of a channel profile. We develop several algorithms to detect the crosstalk profile and investigate the asymptotic behavior of the new algorithms. Simulations show that for typical crosstalk interference scenarios, the observation time to determine the correct crosstalk profile at probability of error less than 10^-3 can be less than 2 ms