In a Wifi 802.11n context, I'm looking to find the sampling rate to perform some processing on the signal and I've something I cannot understand : in the book Next Generation Wireless LAN's: 802.11n and 802.11ac, I would like to know the meaning of this sentence :
In 802.11a, the fundamental sampling rate is 20 MHz, with a 64-point FFT/IFFT. The Fourier transform symbol period, T, is 3.2 μs in duration and F is 312.5 kHz.
Why is the sampling rate « 20 MHz » ? The bandwitch of the Wifi 802.11 is 20 MHz so my first idea would be to double this value to validate the Nyquist-Shannon criterion. In addition, the guard interval is not included ?