Renato Dogliotti

Error probability in optical fiber transmission systems

A method for evaluating the average error probability in digital fiber optic transmission systems is described. It takes into account the statistical properties of the main impairments that affect the information signal, i.e., shot noise (dark current included), thermal noise, and intersymbol interference. Unlike other methods, the analysis of shot-noise statistics does not entail the second-moment characterization alone, but uses a number of moments sufficient to evaluate the error probability with a high degree of accuracy. For this purpose it is shown how the cumulants of shot noise and intersymbol interference of any order can be computed. The baseband pulse response and the statistical distribution of the avalanche-photodetector gain are assumed to be available. Moreover, techniques for exploiting the cumulants are given; knowledge of the cumulants allows one to compute the probability of error by means of Gaussian numerical integration rules. Finally, some results and comparisons are reported.

Baseband equalization in fibre optic digital transmission

The problem of baseband equalization in optical p.c.m. fibre systems is considered. Zero-forcing, minimum-mean-square error, and Kaiman equalizers are briefly reviewed and their relative merits discussed. The performance of the overall communication system is the average probability of error, which can be computed by means of the proposed method with high accuracy. A final section presents some diagrams that may be useful in designing the equalizer and in evaluating the degradation affecting the error probability with respect to ideal conditions. A presentation ofadaptive equalization results concludes the paper.

Signal processing in digital fiber communications

Transmission ofpcmsignals over optical fibers is limited in transmission rate by the inherent imperfections of the carrier medium. The paper discusses the model for an optical telecommunications system (signal and noise models), simulation in base-band (stressing the rational approximation made for the fiber’s transfer function) pulse equalization, encoding and synchronization. Equalizers, whether linear or not, recursive or not, adjustable or not, reduce intersymbol interference, by compensation of distortion in compliance with certain criteria with a view to improving the error rate. The encoding used is a trade-off between bandwidth, tolerance to intersymbol interference and acquisition and tracking of the signal.AnalyseLa transmission de signauxmicsur fibres optiques est limitée en débit par les caractéristiques imparfaites de la voie. L’article discute la modélisation d’un système de télécommunication optique (modèles de signal et de bruit), la simulation en bande de base (en insistant sur l’approximation rationnelle de la fonction de transfert de la fibre), l’égalisation des impulsions, le codage et la synchronisation. Des égaliseurs linéaires ou non, récursifs ou non, réglables ou non, réduisent le brouillage mutuel des symboles, en compensant la distorsion selon certains critères de façon à améliorer le taux d’erreurs. Le codage réalise un compromis entre la largeur de bande, la tolérance au brouillage entre symboles, et l’acquisition et la poursuite du signal.

Timing error tolerant waveforms in optical fibre systems

The problem of pulse shaping and sensitivity to timing errors in optical fibre data communication is considered. The performance of the overall transmission system is the average probability of error, which is computed for intersymbol interference, thermal noise, and shot noise in avalanche photodiodes. An analysis of the immunity to small sampling errors of various Nyquist pulses indicates useful design criteria.

Evolving system architecture towards B‐ISDN

The paper aims at describing a possible evolution strategy of a telecommunication network architecture which should provide users with a wide range of broadband services in a relatively short term. The discussion reflects the work carried out within the Italian «Progetto Finalizzato Telecomunicazioni» and it assumes, as starting points, the deployment of a digital network structure, together with the first introduction of the new Synchronous Digital Hierarchy (SDH) equipment. On the basis of the mentioned hypotheses, the exploitation in the network of the SDH capabilities, the role of Metropolitan Area Networks (MANs) and the issues related to the deployment of optical fibres in the distribution network are discussed with the target to provide a «grace-ful» evolution path towards the future ATM-based Broadband ISDN (B-ISDN).