At first, I saw that wifi rate was talked about everywhere. Of course, I was surprised. I thought that PHY could be directly configured to a certain rate, but it was not.
The rate of wifi is a result. It is a result of combining MCS (modulation & coding Scheme), bandwidth (number of sub-carriers or tones), Spatial Stream (NSS) (NxN MIMO), and symbol interval (data interval & guard insertion).
The calculation formula is Rate = Nsc*Coding * NSS/( 3.2us + 0.8us)
For example, 11a/g, 40MHz channel, Nsc = 48, Coding max 3/4, Nss = 1, rate = 9 Mbps.
How to choose the right MCS(rate)?
Although the bandwidth is too wide, it has the potential to increase throughput, but the interference is also greater (depending on the SNR level), so if your SNR is low, you can use a larger bandwidth.
TX Power can also improve SNR. Higher SNR is conducive to using more complex MCS, such as 1024 QAM, but this should also match the TX power of RECV, because the other party can receive it, but we can’t receive it. Effective.
MCS (coding) is adapted based on the SNR level.
Nss should be as large as possible when power consumption is allowed.
The GI is as small as possible.
What if the RSSI is small?
The above requirement is only a smooth PHY speed curve, which improves the overall throughput rate over a period of time.