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Workshop: Managing Wi-Fi Networks

ABCs of RF Communication

Like dial-up and cable modems, Wi-Fi networks use a technique called modulation to convert digital signals from your computer into analog RF signals. The speed at which data can be transmitted over a modulated carrier depends on a number of factors, including available bandwidth and the specific type of modulation used. Complex modulation schemes, such as 64-Quadrature Ampliture Modulation on 54-Mbps 802.11 WLANs, carry more bits per unit of time than simpler schemes, like the Differential Binary Phase Shift Keying used on 1-Mbps WLANs. If a complex modulation scheme isn't supported by high-quality RF signals, errors will occur.

Because signal quality decreases over the RF medium, there's always a trade-off between speed and distance. Radio waves that travel through the air attenuate faster than RF signals carried by cable modems running over a hybrid fiber-coax cabling system.

Wi-Fi networks use radio spectrum designated by the FCC and other regulatory bodies for unlicensed operators. This "buy, install and run" approach is one thing that makes Wi-Fi so appealing. Although you don't need a license to operate a Wi-Fi system, vendors' products must be certified to ensure they adhere to FCC rules.

FCC regulations govern the use of 83.5 MHz of spectrum between 2.4 and 2.4835 GHz, known as the 2.4 GHz ISM (Industrial, Scientific and Medical) band, as well as the 300 MHz of spectrum in the 5 GHz UNII (Unlicensed National Information Infrastructure) bands. The 5 GHz UNII bands include 200 MHz between 5.15 and 5.35 GHz and 100 MHz between 5.725 and 5.825 GHz.

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