The standard also introduces new guard interval options. In Wi-Fi 6, longer guard intervals are designed to provide improved performance in environments with multi-path and delay spread. These longer guard intervals help to prevent inter-symbol interference in outdoor environments and therefore improve coverage and performance. 802.11ac had two Guard Interval (GI) options – long GI (0.8µs) and short GI (0.4µs). 802.11ax has three types of GI – the normal GI (0.8 µs), double (1.6 µs) GI and quadruple (3.2 µs) GI. Overall efficiency is preserved since in 802.11ax the symbol duration is four times longer than in 802.11ac, therefore the overhead generated by even the longest guard interval is the same percentage of the symbol time as in the previous generation, but with the added benefits of longer guard interval.