Device Scanner RSSI Values
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The 802.11 specification does not provide a relationship between the RSSI value and the actual power value. Here are the definitions from the specification.
- RSSI in FHSS PHY: The RSSI is an optional parameter that has a value of 0 through RSSI Max. This parameter is a measure by the PHY of the energy observed at the antenna used to receive the current PPDU. RSSI shall be measured between the beginning of the SFD and the end of the PLCP HEC. RSSI is intended to be used in a relative manner. Absolute accuracy of the RSSI reading is not specified.
- RSSI in DSSS PHY: The RSSI shall be a measure of the RF energy received by the DSSS PHY. RSSI indications of up to 8 bits (256 levels) are supported.
- RSSI in OFDM PHY: The allowed values for the RSSI parameter are in the range from 0 through RSSI maximum. This parameter is a measure by the PHY of the energy observed at the antenna used to receive the current PPDU. RSSI shall be measured during the reception of the PLCP preamble. RSSI is intended to be used in a relative manner, and it shall be a monotonically increasing function of the received power.
Different vendors implement these value in their own way. The ComProbe 802.11 uses an Atheros chipset which provides RSSI values in the range of 0 to 128. The radio hardware in the ComProbe 802.11 has two receive chains (one for each antenna). Each received packet has RSSI values for both antennas as well as the combined value.
The hardware provides the following five values:
- rssi_ant00: Receive signal strength indicator of control channel chain 0.
- rssi_ant01: Receive signal strength indicator of control channel chain 1.
- rssi_ant10: Receive signal strength indicator of extension channel chain 0.
- rssi_ant11: Receive signal strength indicator of extension channel chain 1
- rssi_combined: Receive signal strenth indicator of combination of all active chains on the control and extension channels.
All five of these values are shown in the PHY layer decoder for every packet. The Wi-Fi scanner shows the combined value.