Digital Signal Processing in Telecommunications

This book is intended to be of use to two broad groups of readers. The first group comprises those who have good familiarity with Digital Signal Processing (DSP) and/or Telecommunications. The second group consists of those who need at least a casual or, perhaps, detailed, knowledge of the applications of DSP in telecommunications. A typical member of the second group is someone who is involved in a design project utilizing DSP but whose area of expertise is a different branch of electrical engineering, such as software, hardware, systems engineering, or application-specific integrated circuit (ASIC) design. Included in the second group are students who wish to get a feel for how DSP is applied. The book is comprised of nine chapters. The intent of Chapter 1 is to provide the spectrum of readership a preamble that puts the material in the subsequent chapters in perspective. Chapters 2 and 3 are targeted toward the second group and cover the fundamental concepts of communication theory and digital signal processing. Readers in the first group could skip directly to Chapter 4 or skim Chapters 2 and 3 to get a feel for the notation used. Chapters 4 through 9 are reasonably self contained and draw on material from the first three chapters. Those well versed in telecommunications would find the material useful in understanding the concepts of DSP; experts in DSP would find a description of some telecommunications concepts in a familiar jargon. Except for Chapters 1 and 5, one section of each chapter consists of selected exercises. For Chapters 2 and 3 these exercises are chosen to enhance the understanding of the material in a mathematical sense. Applying pencil and paper remains the best way to develop a proficiency in dealing with the mathematical, and sometimes abstract, notions introduced. The exercises in the later chapters assume the availability of some form of computing power, either a PC or ad workstation, or some other form of desktop computing. These exercises are better described as suggestions for computer programs to simulate the structures and execute the algorithms described in the text. Chapter 1 discusses some of the unique characteristics and thought processes associated with the telephone channel. In particular, the implications of the access portion of a telephone channel, the coding requirements for conversion between analog and digital formats, and the need for echo control in circuits that have substantial transmission delay. From the viewpoint of transmission, the subscriber's signal is affected first by the cable plant that is used to physically connect the station set to the network. This connection, called the subscriber loop, materially impacts the signal, especially when the subscriber is geographically distant from the central office, a distance that could be in excess of three miles. At the central office the signal experiences bandlimiting; the telephone network principally supports channels that have a (nominal) cutoff frequency of about 4 kHz. Furthermore, the signal is converted from analog to digital format using a nonlinear encoding proces s. The subscriber loop is full duplex, or "two-wire," with the cable pair supporting signals in both directions. The Network is "four-wire," assigning separate (possibly logically separate) paths for signals in the two directions. This split is achieved by a hybrid and the non ideal nature of the hybrid gives rise to the phenomenon of echo. The focus of Chapter 1 is an explanation of the principal characteristics and impairments of the subscriber loop, signal processing in the "line circuit, " signal processing in the trunking network, and the need for echo control. Since telecommunications has its own jargon with several acronyms, which often times have lost their origin, an appendix is provided where several commonly used acronyms are expanded and a short description provided in some cShenoi, Kishan is the author of 'Digital Signal Processing in Telecommunications' with ISBN 9780130967510 and ISBN 0130967513.