Chapter 2. Radio Frequency Fundamentals

IN THIS CHAPTER, YOU WILL LEARN ABOUT THE FOLLOWING:

• Definition of radio frequency signal

• Radio frequency characteristics

  • Wavelength

  • Frequency

  • Amplitude

  • Phase

• Radio frequency behaviors

  • Wave propagation

  • Absorption

  • Reflection

  • Scattering

  • Refraction

  • Diffraction

  • Loss (attenuation)

  • Free space path loss

  • Multipath

  • Gain (amplification)

In addition to understanding the OSI model and basic networking concepts, you must broaden your understanding of many other networking technologies in order to properly design, deploy, and administer an 802.11 wireless network. For instance, when administering an Ethernet network, you typically need a comprehension of TCP/IP, bridging, switching, and routing. The skills to manage an Ethernet network will also aid you as a WLAN administer because most 802.11 wireless networks act as "portals" into wired networks. The IEEE defines the 802.11 communications at the Physical layer and the MAC sublayer of the Data-Link layer.

To fully understand the 802.11 technology, you need to have a clear concept of how wireless works at the first layer of the OSI model, and at the heart of the Physical layer is radio frequency (RF) communications.

In a wired LAN, the signal is confined neatly inside the wire, and the resulting behaviors are anticipated. However, just the opposite is true for a wireless LAN. Although the laws of physics apply, RF signals move through the air in a sometimes unpredictable manner. Because RF signals are not saddled inside an Ethernet wire, you should always try to envision a wireless LAN as an "ever changing" network.

Does this mean that you must be an RF engineer from Georgia Tech to perform a WLAN site survey or monitor a Wi-Fi network? Of course not, but if you have a good grasp of the RF characteristics and behaviors defined in this chapter, your skills as a wireless network administrator will be ahead of the curve. Why does a wireless network perform differently in an auditorium full of people than it does inside an empty auditorium? Why does the performance of a wireless LAN seem to degrade in a storage area with metal racks? Why does the range of a 5 GHz radio transmitter seem shorter than the range of a 2.4 GHz radio card? These are the types of questions that can be answered with some basic knowledge of how RF signals work and perform.

In this chapter, we first define what an RF signal does. Then we will discuss both the properties and the behaviors of RF.