CCNA® Wireless Study Guide

Chapter 3. Spread Spectrum Technologies and Modulations

THE CCNA WIRELESS TOPICS COVERED IN THIS CHAPTER ARE:

• Describe WLAN fundamentals

  • Describe basics of spread spectrum technology (modulation, DSSS, OFDM, MIMO, Channels reuse and overlap, Rate-shifting, CSMA/CA)

A great place to begin is by exploring two general categories of transmission methods commonly used today.

Note

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Transmission Methods: An Overview

As you've probably guessed, you can create RF transmissions a number of different ways. Even though WLANs don't use narrowband transmission, it's still a good thing to go over because it's great to understand for the sake of comparison.

Two important ways that narrowband transmission and transmission methods used by WLANs differ are:

• The amount of power used to transmit

• The way interference is dealt with

In narrowband transmission, the signal is sent on a single frequency; a good example of this transmission type is a radio station. In narrowband, very little bandwidth is used. Check out Figure 3.1.

In order to get around that interference issue, the signal is broadcasted at a much higher power level than a spread spectrum transmission would be. The amount of power is regulated by the FCC and has to be licensed so that the frequencies and controls used by each frequency in a given area won't interfere with one another. See ...