ESP32 Forum

Posted: **Sun May 23, 2021 4:16 pm**

Hello together,

I try figure out if wifi devices are in the same room as an ESP32. So started my Idea by writing a proof of concept on my laptop in python. I used Scapy as library and saw that the DOT11 Radiotap header supported something called "dBm_AntSignal". After switching my network card into monitor mode I was able to see the relative signal strength to them and to which AP they are connected to.
https://scapy.readthedocs.io/en/latest/ ... 1.RadioTap

Important to mention here is the fact that it was the relative signal strength between my laptop and the sending device.
So with this in mind I tried to reproduce this in Arduino C++ with an ESP32.
So by using:

Code: Select all


void wifi_sniffer_init()
{

  nvs_flash_init();
  tcpip_adapter_init();
  ESP_ERROR_CHECK(esp_event_loop_init(event_handler, NULL));
  wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
  ESP_ERROR_CHECK(esp_wifi_init(&cfg));
  ESP_ERROR_CHECK(esp_wifi_set_country(&wifi_country)); /* set country for channel range [1, 13] */
  ESP_ERROR_CHECK(esp_wifi_set_storage(WIFI_STORAGE_RAM));
  ESP_ERROR_CHECK(esp_wifi_set_mode(WIFI_MODE_NULL));
  ESP_ERROR_CHECK(esp_wifi_start());

  esp_wifi_set_promiscuous_filter(&wifi_filter); // set frame filter
  //esp_wifi_set_ps(WIFI_PS_MIN_MODEM);              //WORKAROUND FOR BT
  esp_wifi_set_promiscuous(true);
  esp_wifi_set_promiscuous_rx_cb(&wifi_sniffer_packet_handler);
}

Code: Select all

void wifi_sniffer_packet_handler(void *buff, wifi_promiscuous_pkt_type_t type)
{
/*  if (type != WIFI_PKT_MGMT)
    return;
*/
  const wifi_promiscuous_pkt_t *ppkt = (wifi_promiscuous_pkt_t *)buff;
  const wifi_ieee80211_packet_t *ipkt = (wifi_ieee80211_packet_t *)ppkt->payload;
  const wifi_ieee80211_mac_hdr_t *hdr = &ipkt->hdr;
  const wifi_header_frame_control_t *frame_ctrl = (wifi_header_frame_control_t *)&hdr->frame_ctrl;
}

ppkt->rx_ctl.rssi contains the signal strength between Router and Device. But in my usecase I'm only able to look at packets with a monitor mode or passive method.
But this is only the signal strength between device and router and not between the sending device and my esp.

I've read about 802.11mc ToF measurement via rtt but I think its not very compatible and available on my ESP-WROOM-32D.

Is it possible to get the raw signal strength that arrived at esp32 antenna ?

Thank you :>

Posted: **Sun Feb 05, 2023 3:28 pm**

rssi is the "Received Signal Strength Indicator(RSSI) of packet. unit: dBm".
It's just this absolute value, reported by the osi layer 2 radio driver of esp32, regardless from where or to where a packet is originated / designated.

Perhaps i don't understand you question, what else are you looking for?

ESP32 Forum

ESP32 promiscuous mode RSSI relative to sender

ESP32 promiscuous mode RSSI relative to sender

Re: ESP32 promiscuous mode RSSI relative to sender