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esp32: correct a mistake about secondary channel of CSI in wifi.rst

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XiaXiaotian 2018-09-29 15:32:09 +08:00
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docs/en/api-guides/wifi.rst
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@ -1450,7 +1450,7 @@ Wi-Fi Channel State Information
Channel state information (CSI) refers to the channel information of a Wi-Fi connection. In ESP32, this information consists of channel frequency responses of sub-carriers and is estimated when packets are received from the transmitter. Each channel frequency response of sub-carrier is recorded by two bytes of signed characters. The first one is imaginary part and the second one is real part. There are up to three fields of channel frequency responses according to the type of received packet. They are legacy long training field (LLTF), high throughput LTF (HT-LTF) and space time block code HT-LTF (STBC-HT-LTF). For different types of packets which are received on channels with different state, the sub-carrier index and total bytes of signed characters of CSI is shown in the following table. Channel state information (CSI) refers to the channel information of a Wi-Fi connection. In ESP32, this information consists of channel frequency responses of sub-carriers and is estimated when packets are received from the transmitter. Each channel frequency response of sub-carrier is recorded by two bytes of signed characters. The first one is imaginary part and the second one is real part. There are up to three fields of channel frequency responses according to the type of received packet. They are legacy long training field (LLTF), high throughput LTF (HT-LTF) and space time block code HT-LTF (STBC-HT-LTF). For different types of packets which are received on channels with different state, the sub-carrier index and total bytes of signed characters of CSI is shown in the following table.
+-------------+--------------------+-----------------------------------------+--------------------------------------------------------+----------------------------------------------------------+ +-------------+--------------------+-----------------------------------------+--------------------------------------------------------+----------------------------------------------------------+
| channel | secondary channel | none | above | below | | channel | secondary channel | none | below | above |
+-------------+--------------------+-------------+---------------------------+----------+---------------------------------------------+----------+-----------------------------------------------+ +-------------+--------------------+-------------+---------------------------+----------+---------------------------------------------+----------+-----------------------------------------------+
| packet | signal mode | non HT | HT | non HT | HT | non HT | HT | | packet | signal mode | non HT | HT | non HT | HT | non HT | HT |
+ +--------------------+-------------+---------------------------+----------+-----------------+---------------------------+----------+-------------------+---------------------------+ + +--------------------+-------------+---------------------------+----------+-----------------+---------------------------+----------+-------------------+---------------------------+