Multilevel sequences and line codes

M.Ing. (Electrical Engineering)As the demand for high-speed data communications over conventional channels such as coaxial cables and twisted pairs grows, it becomes neccesary to optimize every aspect of the communication system at reasonable cost to meet this demand effectively. The choice of a line code is one of the most important aspects in the design of a communications system, as the line code determines the complexity, and thus also the cost, of several circuits in the system. It has become known in recent years that a multilevel line code is preferable to a binary code in cases where high-speed communications are desired. Apart from ternary codes, not many multilevel codes are available. Some of the existing line codes also suffer from serious drawbacks regarding a lack of complying to input restrictions, small values of efficiency, and great code complexity. In this study, Markov models and values of channel capacity are presented for several classes of restricted multilevel sequences which are thought to be of practical importance in view of the channel input restrictions that these codes satisfy. Different coding methods are used to construct low-complexity encoders and decoders for generating and decoding these sequences with high values of efficiency, good error behaviour and favourable power spectral densitie

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

Switched-capacitor filters and their application in data communications

There have been considerable developments in the field of switched-capacitor filter design over the past decade. Those developments which allow the operating frequency range of switched-capacitor filters to be extended are considered. The solution to the approximation and synthesis problems for l.d.i.-based switched-capacitor ladder filters discovered by Scanlan is explained. Computer software which implements his technique for low-pass filters is presented. A number of techniques for synthesising the network are investigated. It is shown that numerical difficulties limit the order of filter which can be synthesised. The sensitivity properties of switched-capacitor ladder filters are explored. A technique, which has been implemented in software, for evaluating the amplitude sensitivity of such filters is described. This program is used to demonstrate that the frequency variable terminations in the equivalent circuit of the switched-capacitor ladder filter adversely affect its sensitivity properties. Grcuit topologies which result in improved high frequency performance are considered, and a fully differential filter structure for high frequency operation is proposed. Circuits are presented for a digitally programmable switched-capacitor line equaliser and optimisation techniques for its design are investigated. The extension of the design to incorporate adaptive operation is discussed, and circuits based on the above designs which have been fabricated at the National Micro-electronics Research Centre (N.M.R.C.) in Cork are described

Reports to the President

A compilation of annual reports for the 1988-1989 academic year, including a report from the President of the Massachusetts Institute of Technology, as well as reports from the academic and administrative units of the Institute. The reports outline the year's goals, accomplishments, honors and awards, and future plans

Federal Register

Daily publication of the U.S. Office of the Federal Register contains rules and regulations, proposed legislation and rule changes, and other notices, including "Presidential proclamations and Executive Orders, Federal agency documents having general applicability and legal effect, documents required to be published by act of Congress, and other Federal agency documents of public interest" (p. ii). Table of Contents starts on page iii