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113 lines
5.7 KiB
Markdown
113 lines
5.7 KiB
Markdown
We extend the **CSI** (Channel State Information) to **CSI** (Chip State Information)!
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## Quick start
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- Power on the SDR board.
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- Connect a computer to the SDR board via Ethernet cable. The computer should have static IP 192.168.10.1. Open a terminal on the computer, and then in the terminal:
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```
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ssh root@192.168.10.122
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(password: openwifi)
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cd openwifi
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./wgd.sh
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(Wait for the script completed)
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./monitor_ch.sh sdr0 11
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(Monitor on channel 11. You can change 11 to other channel that is busy)
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insmod side_ch.ko
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./side_ch_ctl g
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```
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You should see on board outputs like:
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```
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loop 64 side info count 61
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loop 128 side info count 99
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...
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```
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If the second number (61, 99, ...) is not zero and keeps increasing, that means the CSI (Chip State Information) is going to the computer smoothly.
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- Open another terminal on the computer, and run:
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```
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cd openwifi/user_space/side_ch_ctl_src
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python3 side_info_display.py
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```
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The python script needs "matplotlib.pyplot" and "numpy" packages installed. Now you should see 3 figures showing run-time **frequency offset**, **channel state/response** and **constellation form equalizer**. Meanwhile the python script prints the **timestamp**.
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While running, all informations are also stored into a file **side_info.txt**. A matlab script **test_side_info_file_display.m** is offered to help you do analysis on the Chip State Information offline.
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## Understand CSI feature
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The CSI information is extracted via the openwifi **side channel** infrastructure. This figure explains the related modules (also related source code file name) and how the information goes from the SDR board to the computer.
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The CSI information format is shown in this figure.
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For each element, the actual size is 64bit.
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- timestamp: 64bit TSF timer value, which is the same timestamp value shown by other sniffer software, like tcpdump, wireshark or openwifi printing in dmesg.
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- freq_offset: Only the 1st 16bit is used.
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- csi (channel state/response) and equalizer: Only the first two 16bit are used for I/Q of channel response and equalizer output. The remaining two 16bit are reserved for future multi-antenna cases.
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The python and Matlab scripts are recommended for you to understand the CSI packet format precisely.
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## Config the capture condition and interval
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The quick start guide will monitor all CSI informations of all packets decoded by the WiFi ofdm receiver. To monitor only specific packets that match the specific conditions: FC (Frame Control), addr1 (target MAC address), addr2 (source MAC address), configuration command should be issued before executing "**side_ch_ctl g**". The configuration command is realized by feeding a different parameter to "**side_ch_ctl**".
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A quick example: Capture only CSI of those packets from the device with MAC address 56:5b:01:ec:e2:8f
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```
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./side_ch_ctl wh1h4001
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./side_ch_ctl wh7h01ece28f
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./side_ch_ctl g
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```
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The parameter string format is explained in detail:
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```
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whXhY
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```
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The X is the register index, and the Y is the value in hex format. The remaining "w", "h" and "h" should be kept untouched.
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- To turn on conditional capture, X should be 1. For Y: bit11~bit0 should be 001(hex), bit12: on/off of FC match, bit13: on/off of addr1 match, bit14 : on/off of addr2 match. Examples:
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```
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Turn on FC only match:
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./side_ch_ctl wh1h1001
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Turn on addr2 (source address) only match:
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./side_ch_ctl wh1h4001
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Turn on both FC and addr1 (target address) match:
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./side_ch_ctl wh1h3001
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Turn off conditional capture (all packets will be captured):
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./side_ch_ctl wh1h0001
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```
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- To specify the condition matching target (when that type of match is turned on by above command):
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```
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Specify the FC matching target:
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./side_ch_ctl wh5hY
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Specify the addr1 (target address) matching target:
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./side_ch_ctl wh6hY
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Specify the addr2 (source address) matching target:
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./side_ch_ctl wh7hY
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```
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The command "**side_ch_ctl g**" will perform CSI capture every 100ms until you press ctrl+C. To use a different capture interval:
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```
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side_ch_ctl gN
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```
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The interval will become N*100ms
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## Config the num_eq
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The num_eq (number of equalizer output) is configurable in case you don't need so many equalizer informations. The valid value is 0~8. You should align the num_eq value at the side_ch.ko, side_info_display.py and test_side_info_file_display.m.
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- When insert the kernel module, use:
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```
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insmod side_ch.ko num_eq_init=3
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```
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You can replace 3 by number 0~8. (8 is the default value. You don't need to specify it like in the Quick start section)
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- When launch the python script, use:
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```
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side_info_display.py 3
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```
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- When use the Matlab script, please change the num_eq variable in the script to 3 (3 is just an example).
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## Run CSI together with mode other than monitor
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The openwifi CSI feature could run with not only monitor mode but also other modes, such as AP-Client or ad-hoc mode. After the communication functionality is fully up in those modes, you can start CSI feature from "**insmod side_ch.ko**" and "**./side_ch_ctl g**" on board as described in the previous sections to extract CSI to your computer.
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## Map the CSI information to the WiFi packet
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If you want to relate the CSI information to the WiFi packet, you need to capture WiFi packets (tcpdump/wireshark/etc) while capturing CSI. Then you can match the timestamp (TSF timer value) between WiFi packet and CSI information, because this is the unique same identity of a Wifi packet and related CSI information.
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Please learn the python and Matlab script to extract CSI information per packet according to your requirement.
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