Signals
Viewing signals in frequency

The study of how signals vary with time is called time domain analysis. Another way to learn about signals is to analyze the frequencies that they use. Engineers refer to this process as frequency-domain analysis. An electronic device known as a spectrum analyzer creates power versus frequency graphs, such as the one shown in Figure .

To understand frequency-domain analysis as it relates to WLANs, it is helpful to first examine a more familiar radio system, namely commercial broadcast FM radio. In this case, the term radio refers to a receiver device, which might be located in a home or a car.

When an FM radio is tuned, it changes the settings of the radio, so that the radio responds to the frequency that is selected. The different stations each have a different center or carrier frequency. This is so that they do not interfere with each other, by transmitting on the same frequencies. Also, depending on factors such as the transmitted power and location of a station, as well as any potential obstacles, the strength of the signal at the FM radio receiver may be weak or strong.

These same factors exist in a WLAN. For example, to gain the most benefit from multiple APs in the same location, it is important that they do not overlap in frequency. Otherwise, the APs will interfere with one another instead of multiplying the amount of useable bandwidth by the number of APs.