Digital Communication Systems

CHAPTER

7

Signaling over AWGN Channels

7.1    Introduction

Chapter 6 on the conversion of analog waveforms into coded pulses represents the transition from analog communications to digital communications. This transition has been empowered by several factors:

1.  Ever-increasing advancement of digital silicon chips, digital signal processing, and computers, which, in turn, has prompted further enhancement in digital silicon chips, thereby repeating the cycle of improvement.

2.  Improved reliability, which is afforded by digital communications to a much greater extent than is possible with analog communications.

3.  Broadened range of multiplexing of users, which is enabled by the use of digital modulation techniques.

4.  Communication networks, for which, in one form or another, the use of digital communications is the preferred choice.

In light of these compelling factors, we may justifiably say that we live in a “digital communications world.” For an illustrative example, consider the remote connection of two digital computers, with one computer acting as the information source by calculating digital outputs based on observations and inputs fed into it; the other computer acts as the recipient of the information. The source output consists of a sequence of 1s and 0s, with each binary symbol being emitted every T_b seconds. The transmitting part of the digital communication system takes the 1s and 0s emitted by the source computer and encodes them into distinct signals denoted ...