Telecom Basics, Second Edition
This guide presents the groundwork of telecom technolgies, network, systems, and call processing.
TABLE OF CONTENTS Telecom Basics, Second Edition
Chapter 2: Signal Fundamentals
Telecommunication technology involves the transfer of information signals through wires, fiber, or through the air by the means of electrical or optical signals. Communication signals are usually characterized by their intensity (voltage and current) and frequency (cycles per second). To allow information to be transferred using communication signals, an information source (audio, data or video) is either represented by the signal itself (called the baseband signal) or the information slightly changes the wave shape of the communication signal (called the broadband signal). The information is imposed on the carrying signal (called the carrier) by varying the signal level or time changes (frequency shift).
Signal Types
There are two basic types of signals: analog and digital. Many communication systems receive analog signals (e.g., audio signals), convert them to a digital format, transport the digital signals through a network, and reconvert the digital signals back to their analog form when they reach their destination.
Analog
An analog signal can vary continuously between a maximum and minimum value and it can assume an infinite number of values between the two extremes. Analog information can be represented by a continuous and smoothly varying amplitude or frequency over a certain range such as voice or music. Analog communication lines allow the representation of information to closely resemble the original information.
Figure 2.1 shows a sample analog signal created by sound pressure waves. In this example, as the sound pressure from a person s voice is detected by a microphone, it is converted to its equivalent electrical...
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