Shortened Guard Interval

The purpose of the guard interval is to introduce immunity to propagation delays, echoes and reflections of symbols in orthogonal frequency division multiplexing (OFDM) — a method by which information is transmitted via a radio signal in APs.

In OFDM, the beginning of each symbol is preceded by a guard interval. As long as the echoes fall within this interval, they do not affect the safe decoding of the actual data, as data is interpreted only outside the guard interval. Longer guard periods reduce the channel efficiency. 802.11n-compliant APs provide reduced guard periods, thereby increasing the throughput.