[gallager] 数字通信原理 principles of digital communication (英).pdf

6.450: Principles of Digital Communication Chapters 1-3 Robert G. Gallager, M.I.T. September 7, 2004 ii Preface: Introduction and Objectives The digital communication industry is an enormous and rapidly growing industry, roughly com- parable in size to the computer industry. The objective of this course is to study those aspects of digital communication systems that are unique to these systems. That is, rather than focus- ing on hardware and software for these systems, which is much like hardware and software for many other kinds of systems, we focus on the fundamental system aspects of modern digital communication. This is the first subject in the two-term sequence, 6.450 and 6.451. Our intention is that 6.450 may be taken on a stand-alone basis and be accessible to well-prepared undergraduates. It is also a prerequisite for 6.441 (Transmission of Information), 6.442 (Optical networks), and an alternate prerequisite for 6.432 (Stochastic processes, detection, and estimation). It should be taken by any student seriously interested in the digital communication field. Digital communication is a field in which theoretical ideas have had an unusually powerful impact on actual system design. The basis of the theory was developed 55 years ago by Claude Shannon, and is called information theory. For the first 25 years or so of its existence, information theory served as a rich source of academic research problems and as a tantalizing suggestion that communication systems could be made more efficient and more reliable by using these approaches. By the mid 1970’s, mainstream systems using information theoretic ideas began to be widely implemented. The first reason for this was the increasing number of engineers who understood both information theory and communication system development. The second reason was that the low cost and increasing proc