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xieyaxiongfly
N-Tx Changing in CSI matrix
I have my NIC card attached computer as an AP. I ping it from another device which has 2X2 MIMO. However, the csi matrix is not consistently 2X3X30. Rather it varies between 1X3X30 and 2X3X30. That means the number of TX antenna is changing over the time. Why does this phenomenon occur?
You need to understand that CSI matrix is not an Nrx by Ntx matrix, rather an Nrx by Nss matrix where Nss us number spatial streams.
When Wi-Fi transmit packets, it will select the configuration (e.g., the data rate, the antenna number, whether to use MIMO or not, and so on) for that transmission.
The configuration may change across packets unless you explicitly tell the system to fix the configuration.
An easy way to fix the antenna number is to fix the data rate. Some data rate has to use MIMO with 2 tx antennas.
To fix the data rate, use " echo 0 >> /sys/kernel/debug/ieee80211/phy#/rc/fixed_rate_idx"
The index 0 means the data rate is 0x80. You can change it to 1 and the rate becomes 0x81. Rate 0x88 use 2 antennas.
On Tue, Jun 12, 2018 at 12:02 AM, Tamzeed [email protected] wrote:
I have my NIC card attached computer as an AP. I ping it from another device which has 2X2 MIMO. However, the csi matrix is not consistently 2X3X30. Rather it varies between 1X3X30 and 2X3X30. That means the number of TX antenna is changing over the time. Why does this phenomenon occur?
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*-- Yaxiong Xie / *谢亚雄
School of Computer Engineering
Nanyang Technological University, Singapore
@xieyaxiongfly Could you please tell me which datarate should I fix so I get 3x3x114 ? I setup the system at 5 GHz and 40 Mhz Bandwidth, and all I get is either 3x2x114 or 3x3x56.
Thank you!
