Wi-Fi Test Tips 12: What is the difference and impact between long GI and short GI

1. The role of GI
Short GI (Guard Interval) is an improvement made by 802.11n for 802.11a/g. When the RF chip uses OFDM modulation to send data, the entire frame is divided into different data blocks for transmission. For the reliability of data transmission, there will be GI between the data blocks to ensure that the receiving side can correctly parse out Each data block. Wireless signal transmission in space will cause a delay on the receiving side due to factors such as multipath. If the subsequent data block is sent too fast, it will interfere with the previous data block, and GI is used to avoid this interference.

2. The difference between long GI and short GI
The long GI generally has a duration of 800ns, while the short GI duration is 400ns.

3. The impact of long GI and short GI
The main impact is the interference with other data. The following figure shows the effects of long GI and short GI respectively during data transmission. When the GI duration is appropriate, the last data will not interfere with the next set of front signals, and when the GI duration is too short, it will interfere.