Long guard intervals and Reduced Inter frame space

The basic concept is that 802.11n uses OFDM, where bits of information are send access mini-channels called tones or sub-carriers within the 20 MHz signal. Each chunk of information is followed by a small silence (the guard interval). This silence is in fact a time during which the subcarrier does not send any useful information. The reason is that we want to let the reflections and other multipach echoes occur before sending the next chunk of information, to avoid collision. The default silence time is 800 nanoseconds. It can be reduced to 400 nanoseconds, offering overall 11% more throughput, but also more collision risk

CLI from WLC:

config 802.11a 11nSupport guard_interval long

802.11n also introduces RIFS(Reduced Inter Frame Spaces), where a station can send blasts of data, separated by 2 microsecond inter frame spaces. RIFS improves the efficiency of the 802.11n network,
but my disturb networks where a lot of non-802.11n stations are present.

CLI from WLC:

config 802.11a 11nSupport rifs rx enable