Wireless Computing
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Introduction to Wireless

Wireless Technologies

Interference

Network Security

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Frequency

An Introduction to Wireless - Frequency - Wireless Standards

The concept of frequency underlies all modern radio, including wireless networking. A signal's frequency is the number of times it oscillates (completes an up-down cycle) per unit of time. The standard measurement of frequency is the hertz (Hz), the number of cycles per second. There is a huge range of known frequencies, but only a limited number of which are practical for sending radio signals. In radio, one refers to the allowable range of frequencies as the bandwidth. For example, the 2.4 Ghz to 2.5 Ghz spectrum would have a 100 Mhz bandwidth.

Example radio waveform
An example radio waveform

Unfortunately, available bandwidth for radio is sharply limited. In order to avoid interference, most governments have agencies (the Federal Communication Comission [FCC] in the US) responsible for allocating particular bandwidths to particular uses. Large parts of the useful frequency spectrum are reserved for military use; others are auctioned away to companies for cellular, radio, and television. Conflicts between the licensing schemes of various countries further reduce the frequencies available on a consistent worldwide scale. This leaves only a few specific unlicensed bands for many competing technologies, including wireless networking. The two frequency bands most commonly used for networking are 2.4 Ghz and 5 Ghz, both of which are relatively unregulated worldwide.

Digital data is transmitted over radio by mapping the signal to a sequence of bits, either 0 or 1. Many different modulation technologies exist which pack the signal to get as much information in each cycle as possible.

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