RSSI Calculation

[SKo]

Hi all,

I need to know the RSSI Value (distance) between my nRF 51 DK and my connected device (iOS Device). I made these code changes:

switch (p_ble_evt->header.evt_id)
{
    case BLE_GAP_EVT_CONNECTED:
        err_code = bsp_indication_set(BSP_INDICATE_CONNECTED);
        APP_ERROR_CHECK(err_code);
					sd_ble_gap_rssi_start(m_conn_handle,1,0);
        m_conn_handle = p_ble_evt->evt.gap_evt.conn_handle;
        break;

    case BLE_GAP_EVT_RSSI_CHANGED:
        rssi = p_ble_evt->evt.gap_evt.params.rssi_changed.rssi;
        break;
}

Everything works properly. The rssi variable is showing the RSSI Value. Now I need to know how the Nordic SW or HW is able to calculate this value? I can imagine that a RSSI Value is sent from iPhone to Nordic HW. The Nordic SW has to calculate the rssi Value from the value from the iPhone and the signal strenght of the message arriving at the DK. How is this made?

Thanks for your help.

[awneil]

"RSSI Value (distance)"

Note that RSSI Value is only loosely linked to distance - there is no direct relation.

This thread explains the RSSI value: devzone.nordicsemi.com/.../

[SKo]

The RSSI value is needed for an approximation not for receiving an exact distance. Are you able to say something to my question?

[awneil]

OK; when you said, "RSSI Value (distance)" that seemed to imply a simple, direct relation - it was not clear that you understood that RSSI can only give an approximation.

Does the cited thread not answer your question about how RSSI is calculated?

[Petter Myhre]

I'm not following. The RSSI is received signal strength indication. iOS is not sending an RSSI value, the nRF51 radio measures the strength of the received radio signal from the radio on the iOS device.