Revolution Wi-Fi comments:

Have you ever wondered just “how” OFDM subcarriers are able to be spaced so tightly together without any guard band in-between? Most Wi-Fi textbooks will simply state that the spacing of the subcarriers allows the harmonics to overlap, thus canceling out any interference.

OFDM subcarrier spacing creates “nulls” canceling out inter-carrier interference (ICI) without the need for guard bands or expensive bandpass filters

Andrew does a great job of explaining a complicated topic in simple terms. If you really want to understand WiFi, you need to read this.

Read more at: PHY Basics: How OFDM Subcarriers Work