Wi-Fi Vendor Features

[中文]

ESP-WIFI-MESH

For details, see the ESP-WIFI-MESH.

Wi-Fi 80211 Packet Send

The esp_wifi_80211_tx() API can be used to:

  • Send the beacon, probe request, probe response, and action frame.

  • Send the non-QoS data frame.

It cannot be used for sending encrypted or QoS frames.

Preconditions of Using esp_wifi_80211_tx()

  • The Wi-Fi mode is station, or AP, or station/AP.

  • Either esp_wifi_set_promiscuous(true), or esp_wifi_start(), or both of these APIs return ESP_OK. This is because Wi-Fi hardware must be initialized before esp_wifi_80211_tx() is called. In ESP32-C5, both esp_wifi_set_promiscuous(true) and esp_wifi_start() can trigger the initialization of Wi-Fi hardware.

  • The parameters of esp_wifi_80211_tx() are hereby correctly provided.

Data Rate

Side-Effects to Avoid in Different Scenarios

Theoretically, if the side-effects the API imposes on the Wi-Fi driver or other stations/APs are not considered, a raw 802.11 packet can be sent over the air with any destination MAC, any source MAC, any BSSID, or any other types of packet. However, robust or useful applications should avoid such side-effects. The table below provides some tips and recommendations on how to avoid the side-effects of esp_wifi_80211_tx() in different scenarios.

Scenario

Description

No Wi-Fi connection

In this scenario, no Wi-Fi connection is set up, so there are no side-effects on the Wi-Fi driver. If en_sys_seq==true, the Wi-Fi driver is responsible for the sequence control. If en_sys_seq==false, the application needs to ensure that the buffer has the correct sequence.

Theoretically, the MAC address can be any address. However, this may impact other stations/APs with the same MAC/BSSID.

Side-effect example#1 The application calls esp_wifi_80211_tx() to send a beacon with BSSID == mac_x in AP mode, but the mac_x is not the MAC of the AP interface. Moreover, there is another AP, e.g., “other-AP”, whose BSSID is mac_x. If this happens, an “unexpected behavior” may occur, because the stations which connect to the “other-AP” cannot figure out whether the beacon is from the “other-AP” or the esp_wifi_80211_tx().

To avoid the above-mentioned side-effects, it is recommended that:

  • If esp_wifi_80211_tx() is called in station mode, the first MAC should be a multicast MAC or the exact target-device’s MAC, while the second MAC should be that of the station interface.

  • If esp_wifi_80211_tx() is called in AP mode, the first MAC should be a multicast MAC or the exact target-device’s MAC, while the second MAC should be that of the AP interface.

The recommendations above are only for avoiding side-effects and can be ignored when there are good reasons.

Have Wi-Fi connection

When the Wi-Fi connection is already set up, and the sequence is controlled by the application, the latter may impact the sequence control of the Wi-Fi connection as a whole. So, the en_sys_seq need to be true, otherwise ESP_ERR_INVALID_ARG is returned.

The MAC-address recommendations in the “No Wi-Fi connection” scenario also apply to this scenario.

If the Wi-Fi mode is station mode, the MAC address1 is the MAC of AP to which the station is connected, and the MAC address2 is the MAC of station interface, it is said that the packet is sent from the station to AP. Otherwise, if the Wi-Fi is in AP mode, the MAC address1 is the MAC of the station that connects to this AP, and the MAC address2 is the MAC of AP interface, it is said that the packet is sent from the AP to station. To avoid conflicting with Wi-Fi connections, the following checks are applied:

  • If the packet type is data and is sent from the station to AP, the ToDS bit in IEEE 80211 frame control should be 1 and the FromDS bit should be 0. Otherwise, the packet will be discarded by Wi-Fi driver.

  • If the packet type is data and is sent from the AP to station, the ToDS bit in IEEE 80211 frame control should be 0 and the FromDS bit should be 1. Otherwise, the packet will be discarded by Wi-Fi driver.

  • If the packet is sent from station to AP or from AP to station, the Power Management, More Data, and Re-Transmission bits should be 0. Otherwise, the packet will be discarded by Wi-Fi driver.

ESP_ERR_INVALID_ARG is returned if any check fails.

Wi-Fi Vendor IE Configuration

By default, all Wi-Fi management frames are processed by the Wi-Fi driver, and the application can ignore them. However, some applications may have to handle the beacon, probe request, probe response, and other management frames. For example, if you insert some vendor-specific IE into the management frames, it is only the management frames which contain this vendor-specific IE that will be processed. In ESP32-C5, esp_wifi_set_vendor_ie() and esp_wifi_set_vendor_ie_cb() are responsible for this kind of tasks.

Wi-Fi Channel State Information

Channel state information (CSI) refers to the channel information of a Wi-Fi connection. In ESP32-C5, 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. Except for the IEEE 802.11g mode, all other modes have two LTF sequences (LLTF + HT/VHT/HE-LTF). ESP32-C5 can determine whether to include LLTF or HT/VHT/HE-LTF through acquire_csi_force_lltf field of wifi_csi_acquire_config_t. 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 are shown in the following table.

channel

secondary channel

none

below

above

packet

information

signal mode

non HT

HT

HE

non HT

HT

non HT

HT

channel bandwidth

20 MHz

20 MHz

20 MHz

20 MHz

20 MHz

40 MHz

20 MHz

20 MHz

40 MHz

STBC

non STBC

non STBC

STBC

non STBC

STBC

non STBC

non STBC

STBC

none STBC

STBC

non STBC

non STBC

STBC

non STBC

STBC

sub-carrier

index

LLTF

0~26, -26~-1

—

—

—

—

0~52

—

—

—

—

-53~-1

—

—

—

—

HT-LTF (HT-LTF1)

—

0~28, -28~-1

0~28, -28~-1

—

—

—

0~56

0~56

0~58, -58~-1

0~58, -58~-1

—

-57~-1

-57~-1

0~58, -58~-1

0~58, -58~-1

HT-LTF2

—

—

0~28, -28~-1

—

—

—

—

0~56

—

0~58, -58~-1

—

—

-57~-1

—

0~58, -58~-1

HE-LTF (HE-LTF1)

—

—

—

0~122, -122~1

Determined by

wifi_csi_config_t

—

—

—

—

—

—

—

—

—

—

HE-LTF2

—

—

—

—

—

—

—

—

—

—

—

—

—

—

total bytes

106

114

228

490

490

106

114

228

234

468

106

114

228

234

468

Note

  • In HT/VHT/HE modes, there are two LTF sequences: LLTF + HT/VHT/HE-LTF. If the acquire_csi_force_lltf field of wifi_csi_acquire_config_t is set to false, the CSI data will only contain HT/VHT/HE-LTF (as shown in the table above); otherwise, the CSI data will only contain LLTF. The sub-carrier index and total bytes for LLTF in HT/VHT/HE modes are the same as those for LLTF in non-HT modes.

  • In VHT mode, the sub-carrier index and total bytes are the same as those in HT mode.

All of the information in the table can be found in the structure wifi_csi_info_t.

  • Secondary channel refers to second field of rx_ctrl field.

  • signal mode of packet refers to cur_bb_format 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.

  • If first_word_invalid 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-C5.

  • If rx_channel_estimate_info_vld of rx_ctrl field is 1, indicates that the CSI data is valid; otherwise, the CSI data is invalid.

  • More information like RSSI, noise floor of RF, receiving time and antenna is in the rx_ctrl field.

For STBC packets, the subcarrier indices of HE-LTF1 and HE-LTF2 are determined by acquire_csi_he_stbc_mode field of wifi_csi_config_t. Please refer to the table below for details.

acquire_csi_he_stbc

HE-LTF1

HE-LTF2

0

-122~-1, 0~122

—

1

—

-122~-1, 0~122

2

Sample evenly among the HE-LTF1 and HE-LTF2

When imaginary part and real part data of sub-carrier are used, please refer to the table below.

PHY standard

Sub-carrier range

Invalid sub-carrier

Sub-carrier (total/data)

802.11a/g

-26 to +26

0

53 total, 52 usable

802.11n, 20 MHz

-28 to +28

0

57 total, 56 usable

802.11n, 40 MHz

-58 to +58

-1, 0, 1

117 total, 114 usable

802.11ac, 20 MHz

-28 to +28

0

57 total, 56 usable

802.11ax, 20 MHz (SU)

-122 to + 122

-1, 0, 1

245 total, 242 usable

Note

  • When the PHY is 802.11ax, please refer to the protocol for sub-carrier range and invalid sub-carrier for MU packets.

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-LTF1 (HE-LTF1) and HT-LTF2 (HE-LTF2) for there is no channel frequency response in sub-carrier 0. CSD[10:0] is 11 bits, ranging from -pi to pi.

Wi-Fi Channel State Information Configure

To use Wi-Fi CSI, the following steps need to be done.

The CSI receiving callback function runs from Wi-Fi task. So, do not do lengthy operations in the callback function. Instead, post necessary data to a queue and handle it from a lower priority task. Because station does not receive any packet when it is disconnected and only receives packets from AP when it is connected, it is suggested to enable sniffer mode to receive more CSI data by calling esp_wifi_set_promiscuous().

Wi-Fi Multiple Antennas

Please refer to the PHY.

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