A Digital Hybrid Transmission System for 280 Mbits/s and 560 Mbits/s

This paper presents the development of repeaters and line equipment for an experimental digital long-haul transmission system using coaxial cable. A comparison, of different types of digital transmission systems indicates that the digital repeater hybrid system with binary transmission code is the most desirable. This development has resulted in digital pulse reshaping repeaters with very small dimensions, low cost, and good reliability. Both digital repeaters that are without timing and regenerators that include timing have been developed. Their circuitry and the corresponding signal shapes are described. The dc power-feeding system and the fault-location system are also discussed. An experimental field trial with the Deutsche Bundespost was performed over 10-repeater sections of the International Telephone and Telegraph Consultative Committee (CCITT) normal coaxial tube with a section length of 1/2 mi, The experiments confirmed that a long-haul digital transmission system of 560 Mbits/s, and later of 1100 Mbits/s using the described system concept and technology, can be established with relatively low cost and good reliability.     

Speckle Noise Reduction in Fiber Optic Analog Video Transmission Using Semiconductor Laser Diodes

This paper investigates the effects of speckle noise on analog video transmission systems using semiconductor laser diodes. The system linearity degradation due to speckle noise is examined using different fiber types. Then this paper proposes a new modulation technique employing a superimposed pulse scheme to reduce speckle noise. It is experimentally confirmed that the proposed modulation method is effective in reducing speckle noise. Based on the above investigations, analog video transmission experiments are performed using single-mode fibers, step-index multimode fibers, and graded-index multimode fibers in the 0.8 and 1.3 μm wavelength regions. The results of the transmission tests have confirmed the feasibility of analog video transmission using semiconductor laser diodes.     

数据传输系统中的定时抖动

本文介绍了通过数字锁相环减弱定时抖动的分析计算方法。导出了不经过积螺，经过不同方法积螺进行相位调整时的抖动改善量计算公式，并给出抖动改善量与有关参数的关系曲线，可作为数据传输系统设计定量环路的参考。     

The effect of timing jitter on the performance of a discretemultitone system

The transmission of high-speed data over severely band-limited channels may be accomplished through the use of discrete multitone (DMT) modulation, a modulation technique that has been proposed for a number of new applications. While the performance of a DMT system has been analyzed by a number of authors, these analyses ignore the effect of timing jitter on system performance. Timing jitter becomes an increasingly important concern as higher data rates are supported and larger constellations are allowed on the DMT subchannels. Hence, in this paper, we assume that synchronization is maintained by using a digital phase-locked loop to track a pilot carrier, Given this model, we derive error rate expressions for an uncoded DMT system operating in the presence of timing jitter, and we derive an expression for the interchannel distortion that results from a varying timing offset across the DMT symbol. In addition, we investigate the performance of trellis-coded DMT modulation in the presence of timing jitter. Practical examples from the asymmetric digital subscriber line (ADSL) service are used to illustrate various results     

A comparison of QAM and VSB for hybrid fiber/coax: digitaltransmission

There are two competing transmission systems for downstream digital transmission on hybrid fiber/coax cable networks: quadrature amplitude modulation (QAM), and vestigial sideband modulation (VSB). Both QAM and VSB are bandwidth efficient, and have the same bandwidth efficiency. Detailed calculations and simulations of QAM and VSB transmission on hybrid fiber/coax are reported here. It is shown that, since VSB has a higher symbol rate, it has at most 1/2 dB less received SNR than QAM at low frequencies because of dispersion and symbol timing jitter. This difference is negligible. Vendors proposing VSB recover the carrier with a pilot tone and a PLL, and vendors proposing QAM use all-digital data-directed carrier recovery. Simulations reported here show that QAM and VSB have very similar carrier recovery performance. It is concluded that for hybrid fiber/coax, VSB and QAM have practically the same overall performance, and the choice between these transmission systems should be based on considerations other than performance     

Timing Recovery in Digital Subscriber Loops Using Baud-Rate Sampling

Sampled-data techniques are the most practical means of obtaining the necessary signal processing functions for timing recovery in the VLSI implementation of a digital subscriber loop transceiver. The sampled-data timing recovery techniques described in this paper are applicable to both echo cancellation and time-compression multiplexing systems. Timing recovery using baud-rate sampling in conjunction with a special pulse-shaping and timing function fulfills all the objectives for timing recovery in this application. It recovers a timing phase that has minimum precursor intersymbol interference, and makes possible the combination of decision feedback equalizer and echo canceler, reducing the convergence time and increasing the step size. The pulse-shaping function can be performed either in the transmitter by means of digital coding, or in the receiver by means of analog filtering. In the latter case, the transmitted pulse is compatible with more conventional approaches. The proposed partial-response line coding, a special form of AMI coding, is less susceptible to line impairments if detected as a two-level signal. Performance by analysis, simulation, and experimental measurements is reported on a variety of cable configurations, some including bridged taps. Analysis of jitter performance leads to design techniques for reducing the jitter magnitude.     

Fiber Optic Analog--Digital Hybrid Signal Transmission Employing Frequency Modulation

Investigations are carried out on the SNR performance in fiber optic FM transmission systems which use multimode fibers and 1.3 μm laser diodes. Both laser diode noise and modal noise are quantitatively evaluated in systems with and without employing a superimposed pulse modulation scheme. Based on these investigations, parameters for analog-digital hybrid signal transmission systems employing FM are determined. The hybrid signal consists of audio, video, and 2 Mbit/s digital data. The results obtained in transmission experiments satisfied the design objectives and confirmed the technical feasibility of an analog-digital hybrid transmission employing FM. The obtained results make the fiber optic FM transmission system with a 1.3mumLD an attractive alternative in subscriber systems, and video transmission systems for microwave IF links and CATV trunks.     

Characteristics of an Experimental Guided Millimeter-Wave Transmission System

An experimental guided millimeter-wave transmission system is constructed employing two 806-Mbit/s digital repeaters, an 8.4-km waveguide line loop, and channel coupling networks. This paper presents its characteristics, such as waveforms, amplitude and delay, error rate, and timing jitter in some detail.     

普通单模光纤中光孤子传输问题的研究

在使用普通单模光纤的光孤子传输系统中,放大器自发辐射（ASE）噪声和色散波逸出是限制光孤子传输的两个主要因素,它们将引起孤子能量科动和定时抖动,从而导致系统误码。本文分别研究了带限光滤波器对ASE噪声的抑制和非线性增益对色散波的抑制以及对孤子传输系统的稳定作用,并设计了使用普通单模光纤的光孤子传输系统。     

一种定时脉冲低抖动传输方案设计

针对时统系统中脉冲传输问题,提出了一种定时脉冲低抖动传输方案。介绍了定时脉冲低抖动传输系统的方案设计,对数字内插、锁相环、调制解调方案和相位模糊检测等关键技术进行了阐述,最后给出了定时脉冲低抖动传输系统设计实现方案及性能测试结果分析,利用示波器观察时统系统中脉冲传输抖动控制在4 ns以内,通过实际工程证明了其有效性。     

400 Mbit/s Digital Repeater Circuitry Provided by a New Design Method and Beam Lead GHz Transistors

A stable, compact, and high-performance regenerative repeater circuitry, suitable for digital transmission systems up to several hundred Mbit/s, has been provided through utilization of new devices, such as 7 GHz beam lead shielded junction transistors, and through a new computer-aided design method, and has been successfully applied to the 400 Mbit/s experimental coaxial cable PCM system. Major features of this repeater circuitry are: (1) an equalizing amplifier with low noise figure (7.6 dB), small intersymbol interference (12%), and automatic line equalization of 21 dB tracking range at 200 MHz; (2) a regenerative output circuit with bipolar pulses of 2.4 Vop amplitude and 700 ps rise time; and (3) total performance with sufficient noise margin (10 dB for error rate 10^-11over a line of 56 dB loss at 200 MHz), small static pattern jitter (20°pp), smaller size (270 times 160 times 52mm), and lower power (5.8 W). These have been achieved by use of: (1) new devices such as beam lead transistors with fTof 7 GHz,Leof 0.2 nH andCobof 0.4 pF and tantalum thin film hybrid integrated circuits; and (2) a new CAD system including block simulation, network design/ simulation, layout design subsystems which use transmission quality (error rate and jitter) as a design criterion, and which can also be directly connected to the manufacture automation systems, e.g., for mask preparation, and transistor mounting by bonding.     

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     

用声表面波滤波器实现高速光纤传输系统的定时恢复

在高速光纤数字传输系统中,尤其在长中继链路系统中,定时恢复的质量直接影响到传输系统的性能。本文分析了100Mbit/s以上光纤数字传输系统用声表面波滤波器(SAW—F)定时提取电路。首先给出SAW—F的基本原理;然后讨论了SAW—F定时提取实现方案并分析了其抖动积累特性,得出SAW—F定时提取电路的设计依据;最后,根据理论分析的结果,我们设计了一个可用于155.520Mbit/s光纤数字传输系统的SAW—F定时提取电路。分析和实验表明,SAW-F适合用作100Mbit/s以上数字传输系统的定时提取。     

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.     

Timing jitter in dispersion-managed soliton systems with distributed, lumped, and hybrid amplification

We analyze the role of distributed amplification in controlling timing jitter in dispersion-managed soliton systems and discuss, using analytical and numerical techniques, how timing jitter is reduced by up to a factor of two when lumped amplification is replaced by complete or partial distributed amplification. We derive an analytical expression for the timing jitter at any position within the fiber link in the case of ideal distributed amplification for which losses are exactly compensated by gain at every point. We show that the timing jitter is well approximated by this formula in the case of erbium-based amplification. We derive a similar expression for the timing jitter for lumped amplifiers and compare it with the case of distributed amplification. We find that with erbium-based distributed amplification, timing jitter depends on the density of dopants and is smaller for lower densities. In the case of hybrid Raman amplification, the transmission distance of a 40-Gb/s system can be increased by up to 30% depending on the amount of Raman gain. Finally, we show that timing jitter decreases for stronger maps at a given bit rate (constant minimum pulsewidth).     

Optical power distribution in multimode fibers with angular-dependent mode coupling

An expression for the power flow, in multimode optical fibers, is derived, which is mathematically simple and allows a clear physical interpretation of the effects of mode coupling. Coupling strength is assumed to decrease with increasing axial angle. The solution obtained under this assumption is supported by experimental observations. Following the analysis, an experimental procedure to determine the coupling constant is devised. The theoretical results enable the prediction of the loss due to the mode coupling and the transmission bandwidth of the angular multiplexed channels in step-index optical fibers.     

Presence of residual echo and impulsive noise

A general analysis is presented for the jitter performance of a common type of symbol timing recovery (STR) system employed in a digital subscriber loop (DSL) transceiver for high-speed digital data transmission over twisted copper pair cables in the presence of residual echo and impulsive noise (IN). Numerical results, obtained for an experimental study of a timing recovery system, show that the presence of these disturbing signals can substantially degrade the STR performance     

Timing Recovery in Digital Subscriber Loops

Tradeoffs in the design of the timing recovery functions in a subscriber loop receiver are analyzed. The techniques considered are applicable to both the echo cancellation (EC) and time compression multiplexing (TCM) methods of full duplex transmission. Emphasis is on those techniques that lend themselves to implementation in MOSLSI technology, where the objective requirement is that timing recovery be implemented on a sampled-data signal (with the minimum possible sampling rate where EC is used). The wave difference method (WDM) for timing recovery appears to be the best candidate. A detailed study of its performance is carried out analytically and by computer simulation for the case of binary and alternate mark-inversion (AMI) line coding. A closed form expression describing the binary jitter performance of the WDM and its continuous time counterpart, the spectral line technique, is used to compare the two techniques. Analytical and simulation results for recovered phase and jitter are presented for various cable pulse responses carefully chosen to represent worst-case or nearly worst-case conditions. Two methods for including frequency detection in the WDM, the quadricorrelator and the rotational detector, are also simulated.     

Characterization of All-Optical Regeneration Potentials of a Bistable Semiconductor Ring Laser

All-optical pulse reamplification, reshaping (2R), and retiming (3R) using a monolithic bistable semiconductor ring laser (SRL) is demonstrated for the first time. The regeneration performance of the SRL is characterized with an all-optical settable switching threshold, achieving significant increases in the extinction ratio (ER) of the output pulse for input ER as low as 1 dB. For retiming, a rectangular retiming window generated by a clean clock signal is used to eliminate the timing jitter in the input pulse. For input pulse with peak-to-peak timing jitter as high as $sim {hbox {12}}%$ of the bit period, the timing jitter in the retimed output pulse is reduced to $ ≪ 2%$ of the bit period. The pulsewidth of the final regenerated data can be controlled by changing the width of the retiming window. The SRL is, therefore, shown to have a “hard” digital performance in both amplitude and time domain suitable for all-optical 3R.      

PCM-FDM: System Capability and Performance Improvement on Waveform Equalization and Synchronization

To obtain wider waveform equalization range and higher synchronization accuracy, we have introduced: 1) a multilevel pilot-pulse equalization system and 2)an in-band in-phase pilot synchronization system into multilevel VSB-conversion PCM-FDM equipment. This equipment is used to transmit digital signals on existing analog lines. 1) Multilevel pilot pulses with a smaller number of levels than the information pulses are inserted into the information pulse train. Due to the larger eye opening of the received pilot pulse, the automatic equalizer can converge and equalize the distortion more quickly and easily. For example, let 2-level pilot pulses be inserted into every 32 16-level information pulses. As long as the eye pattern of the pilot pulse is open, it is possible to allow up to 15 times more distortion in the transmission line. Thus the transmission span can be greatly extended. There are various other advantages in using this pilot pulse, such as dc drift suppression, in-service error rate monitoring, etc. 2) A carrier pilot and a sample timing pilot for phase synchronization are superimposed on the carrier frequency and 1/2 Nyquist rate, respectively, within the transmission signal spectra. Thus no excess bandwidth for pilots is necessary, and the phase error between pilot and signal is smaller. In this case, the phase jitter of regenerated carrier and timing clock caused by the neighboring signal spectra can decrease if the pilots are coupled in the same phase with the neighboring signal. For example, phase jitter of less than 0.5° (which was experimentally 1/10 phase error of the quadrature coupling) could be realized easily, even if the signal-to-pilot ratio is about 20 dB.