Overview

Wireless communication involves the transfer of information signals through the air by the means of electromagnetic waves. To create electromagnetic waves, an electrical signal, that continuously varies in power level and polarity, is applied to an antenna. As the level varies, the energy contained in the electrical signal is converted to electromagnetic waves that propagate away from the antenna. The electromagnetic waves are characterized by their energy (RF power) and frequency (cycles per second or Hz named after the German physicists Heinrich Rudoph Hertz). Commercial uses for these electromagnetic waves repeat their cycle in a frequency range of approximately 150,000 Hertz (150 kHz) to 300 billion (giga) Hertz (300 GHz).

To allow information to be transferred using electromagnetic waves, an information signal (typically audio) slightly changes the wave shape of the electromagnetic signal. This is called a radio signal.

Radio signals can co-exist with each other without interference if they are operating at different frequencies. Because an information signal slightly changes the electromagnetic signal, this produces small changes in frequency. This results in a single radio signal that occupies a frequency range, depending on the type and amount of information that is changing the electromagnetic wave. The maximum amount of frequency change is commonly called the channel bandwidth. Hence, a radio signal should not ordinarily operate in areas that other radio signals may occupy.

Dividing the Radio Frequency (RF) Spectrum

The radio frequency spectrum is divided into frequency bands that are authorized for use in specific geographic regions. In...