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Wireless & Mobility · Intermediate

Guard Interval (GI)

A period between OFDM symbols that absorbs multipath echoes to prevent inter-symbol interference.

Definition

Legacy and 802.11n/ac use an 800 ns GI or an optional 400 ns short GI. 802.11ax and 802.11be support 0.8, 1.6, and 3.2 microsecond GIs for indoor and outdoor environments. Shorter GIs increase data rate but risk ISI in high delay-spread environments.

Example

Enabling short GI on 802.11n raises data rate by about 11 percent.

Exam tip

Short GI (400 ns) is an 802.11n/ac option; 802.11ax does not use 400 ns.

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