Propagation delays often occurs in data transmission process and influence the capability of the wireless network. It can result from multiple factors, such as multipath effect. GI (Guard Interval) is intended to solve the problem based on delays, and Short GI is used to improve the throughput of the wireless network based on the GI in the environment with small delays.

Data frames will be divided into several symbols when being transmitted. If there are severe propagation delays during the transmission, the latter symbol will interfere with the earlier symbol. To avoid this kind of interference, GI is added at the beginning of every symbol. GI is usually set as 800ns. It can be cut down properly to shorten the interval between two frames when the delays are small. When Short GI is enabled, the guard interval will be set as 400ns and this function will boost the performance about 11%.

When deploying a wireless network in an environment with many obstacles, there will be diffraction, scattering and reflection. The situation above can result in serious multipath time delay. Short GI function will reduce the throughput instead of improving it. Therefore, it is recommended to not use Short GI in a situation where the multipath effect is significant.