HangX-Ma/Atheros-CSI

AR9380 Atheros CSI Tool deployment

Atheros CSI Tool

• Atheros-CSI-Tool(v2)
• Atheros-CSI-Tool-UserSpace-APP(v2)
• Guidance

Usage (UserSpace-APP)

• sendData. You needs to set your PC as AP mode and another PC as client mode(This means that another PC needs to connect to SSID "Atheros_csi_tool").

  sudo ./send_Data wlan0 TARGET_MAC_ADDRESS 20 50 1000 # 20 packets, 50ms interval, 1000 payload length

• recvData.

  sudo ./recv_Data xxx.dat

Tool Setting

If you successfully install the Atheros CSI Tool, hostapd can be started in Atheros-CSI-Tool-UserSpace-App/hostapd-2.5/hostapd. Type iwconfig you will see the wlan0 status will change to this.

wlan0   IEEE 802.11abgn  Mode:Master  Tx-Power=15 dBm
        Retry short limit:7  RTS thr:off  Fragment thr:off
        Power Management:off

Rate Configuration

The issue[payload len: 1924 #22] on github shows that high bitrate will cause errors. Therefore, we need to change the rate lower manually.

The following commands can be used to display information about the radios and set the mcs bitrates.

• This will return supported MCS rate indexes.

  iw phy <phyname> info | grep "MCS rate indexes"

• The command below will set mcs-bit rate index. These indexes are given in Appendix 1 of the this document.

  iw dev <devname> set bitrates [mcs-<2.4|5> <MCS index>]

This link will guide you how to configure 802.11n Wi-Fi Tx bitrate. The following picture is the reference setting correspond to Atheros rate indexes.

Example AR9380

You will find a folder whose name is your wlan0 mac address at following path. cat your_mac_address/current_tx_rate can check your rate setting.

cd /sys/kernel/debug/ieee80211/phy0/netdev:wlan0/stations

• Now we check the MCS rate indexes. You will find the total index number is equal to what 6 APPENDIX Ⅰ shows.

  iw phy phy0 info | grep "MCS rate indexes"
      HT TX/RX MCS rate indexes supported: 0-23

• We can change the bitrate now. According to the description of the issue, we set bitrate to 0x90. You will find the current_tx_rate will be changed to 19.5 MBit/s, which corresponds to the HT20(800ns GI) value. This setting also set the Stream to 3.

  iw dev wlan0 set bitrates mcs-2.4 16

I have test the rate 0x80 to 0x84, 0x8E to 0x91. I found the most suitable rate should be 0x90.

Some tests failed, in which the rates contains 0x83, 0x84, 0x8E, 0x8F, 0x91. My previous test has shown that 0x93 and 0x80 are also perform well.

From my perspective, the rate higher that 26 MBit/s will lead to unstable state of CSI data. The most obvious feature is the block length is greater than the file length. This is abnormal!