This book is a result of the recent rapid advances in two related technologies: com-
munications and computers. Over the past few decades, communication systems
have increased in complexity to the point where system design and performance
analysis can no longer be conducted without a significant level of computer sup-
port. Many of the communication systems of fifty years ago were either power or
noise limited. A significant degrading effect in many of these systems was thermal
noise, which was modeled using the additive Gaussian noise channel.
