Wireless LAN (WLAN)
Ben Piper · 2020
This chapter describes how to analyze design principles of a WLAN deployment. It also explains the components of network security design. When it comes to radio, visualizing the physical medium and direction of signals becomes more difficult because it's invisible energy traveling through empty space. Because of this significant difference, you need to take a moment to understand the mysterious properties of radio waves. Photons are what actually carry all forms of electromagnetic energy, from microwaves to visible light to X-rays. Radio waves use electromagnetic energy, but a radio wave is fundamentally different than a wave on the ocean or a light wave. A radio wave has two components: frequency or wavelength and amplitude. Frequency is measured in Hertz (Hz), what used to be called cycles-per-second (cps). To simplify things, visualize a radio wave as a burst of a cloud of photons emanating from an antenna and moving outward at roughly the speed of light (the exact direction depends on the design of the antenna). Photons are carriers of electromagnetic energy, so you may also think of photons as simply energy if you prefer. The amplitude of a signal measures the power of a radio wave at a given point in space. The strength of a radio signal is proportional to the photon density. As the waves move farther from the transmitter, the amplitude decreases. A receiver standing right next to the transmitter will get hit with a lot more photons-and hence a lot more energy-than a receiver 10 miles away. The farther away you are, the fewer photons you can receive, and the weaker the signal will be. Signal strength decreases with distance.