Filtering, accurate synchronous timing, and a variety of error correcting
approaches can help distinguish the true signal from reflections, interference, and other
noise.
Low output power limits 802.11 WLAN transmissions to fairly short effective ranges,
measured in hundreds of feet indoors. Signal quality, and hence network throughput,
diminishes with distance and interference. The higher data rates rely on more complex
encoding methods. These in turn require an ability to distinguish very subtle modulations in
the RF signals.
The WLAN standards for physical media (802.11a, b, and g) define the full set of
channels for each type of network. Each channel is defined as a range of frequencies within
a narrow band around a center frequency. When a WLAN radio uses a channel, it actually
transmits or receives on multiple frequencies around that center frequency. The particular
pattern of frequency use is determined by the encoding method, which also determines the
nominal data rate.
RF spectrum is a limited resource which must be shared by competing users. While
the standards define the range of possible channels, the actual channels used and the power
outputs permitted on them are set by each regulatory agency for all 802.
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