Chapter 4. API Guides
channelsecondary
chan-
nel
none below above
packet
information
signal
mode
non
HT
HT non
HT
HT non
HT
HT
channel
band-
width
20
MHz
20 MHz 20
MHz
20 MHz 40 MHz 20
MHz
20 MHz 40 MHz
STBC non
STBC
non
STBC
STBC non
STBC
non
STBC
STBC non
STBC
STBC non
STBC
non
STBC
STBC non
STBC
STBC
sub-
carrier
index
LLTF 0~31,
-
32~-
1
0~31,
-
32~-
1
0~31,
-
32~-
1
0~63 0~63 0~63 0~63 0~63 -
64~-
1
-
64~-
1
-
64~-
1
-
64~-
1
-
64~-
1
HT-
LTF
•
0~31,
-
32~-
1
0~31,
-
32~-
1
•
0~63 0~62 0~63,
-
64~-
1
0~60,
-
60~-
1
•
-
64~-
1
-
62~-
1
0~63,
-
64~-
1
0~60,
-
60~-
1
STBC-
HT-
LTF
• •
0~31,
-
32~-
1
• •
0~62
•
0~60,
-
60~-
1
• •
-
62~-
1
•
0~60,
-
60~-
1
total bytes 128 256 384 128 256 380 384 612 128 256 376 384 612
All of the information in the table can be found in the structure wifi_csi_info_t.
• Secondary channel refers to secondary_channel field of rx_ctrl field.
• Signal mode of packet refers to sig_mode field of rx_ctrl field.
• Channel bandwidth refers to cwb field of rx_ctrl field.
• STBC refers to stbc field of rx_ctrl field.
• Total bytes refers to len field.
• The CSI data corresponding to each Long Training Field(LTF) type is stored in a buffer starting from the buf
field. Each item is stored as two bytes: imaginary part followed by real part. The order of each item is the
same as the sub-carrier in the table. The order of LTF is: LLTF, HT-LTF, STBC-HT-LTF. However all 3
LTFs may not be present, depending on the channel and packet information (see above).
• If first_word_invalid field of wifi_csi_info_t is true, it means that the first four bytes of CSI data is invalid due
to a hardware limitation in ESP32-S2.
• More information like RSSI, noise floor of RF, receiving time and antenna is in the rx_ctrl field.
Note:
• For STBC packet, CSI is provided for every space-time stream without CSD (cyclic shift delay). As each
cyclic shift on the additional chains shall be -200 ns, only the CSD angle of first space-time stream is recorded
in sub-carrier 0 of HT-LTF and STBC-HT-LTF for there is no channel frequency response in sub-carrier 0.
CSD[10:0] is 11 bits, ranging from -pi to pi.
• If LLTF, HT-LTF or STBC-HT-LTF is not enabled by calling API esp_wifi_set_csi_config(), the
total bytes of CSI data will be fewer than that in the table. For example, if LLTF and HT-LTF is not enabled
and STBC-HT-LTF is enabled, when a packet is received with the condition above/HT/40MHz/STBC, the
total bytes of CSI data is 244 ((61 + 60) * 2 + 2 = 244, the result is aligned to four bytes and the last two bytes
is invalid).
4.33.25 Wi-Fi Channel State Information Configure
To use Wi-Fi CSI, the following steps need to be done.
Espressif Systems 1545
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