https://docs.espressif.com/projects/esp ... nformation
Recently, I'm doing something about CSI in ESP32 and come up against difficulties.
I can't understand the sub-carrier index shown in that table.
Because when channel bandwidth is 20 MHz,the signal is divided into 64 sub-carriers,which is posted in the website below。
I' m confused how the sub-carrier index can be valued from -64 to 63 ???
From https://www.electronics-notes.com/artic ... 02-11n.php
The signal formats are changed according to the mode in which the system is operating:
Legacy Mode: This may occur as either a 20 MHz signal or a 40 MHz signal:
20 MHz: In this mode the 802.11n signal is divided into 64 sub-carriers. 4 pilot signals are inserted in sub-carriers -21, -7, 7 and 21. In the legacy mode, signal is transmitted on sub-carriers -26 to -1 and 1 to 26, with 0 being the centre carrier. In the HT modes signal is transmitted on sub-carriers -28 to -1 and 1 to 28.
40 MHz: For this transmission two adjacent 20MHz channels are used and in this instance the channel is divided into 128 sub-carriers. 6 pilot signals are inserted in sub-carriers -53, -25, -11, 11, 25, 53. Signal is transmitted on sub-carriers -58 to -2 and 2 to 58.
In terms of the frames that are transmitted conform to the legacy 802.11a/g OFDM format.
Mixed Mode: In this 802.11n mode, packets are transmitted with a preamble compatible with the legacy 802.11a/g. The rest of the packet has a new MIMO training sequence format.
Greenfield Mode: In the Greenfield mode, high throughput packets are transmitted without a legacy compatible part. As this form of packet does not have any legacy elements, the maximum data throughput is much higher.
I'd like to known the exact meaning of the sub-carrier index, because I need to calculate the frequency of each sub-carrier.
I have not found the method yet.