what is the unit of rssi?

[tobewinner]

what is the unit of rssi in esp-idf?
and what is the range of rssi?
I got rssi from

Code: Select all

esp_wifi_sta_get_ap_info

[kolban]

According to Wikipeida:

https://en.wikipedia.org/wiki/Received_ ... indication

There is no standardized relationship of any particular physical parameter to the RSSI reading. The 802.11 standard does not define any relationship between RSSI value and power level in milliwatts or decibels referenced to one milliwatt. Vendors and chipset makers provide their own accuracy, granularity, and range for the actual power (measured as milliwatts or decibels) and their range of RSSI values (from 0 to RSSI maximum).

If I read that correctly, the RSSI isn't an absolute but a relative. Two access points can this be compared to determine which of the two has a "better" signal strength and hence is a better candidate for connection.

[carlgonz]

Hello!

I agree with the given definition, in fact, RSSI units are arbitrary.
However, in some parts of the documentation they mention RSSI as dBm, see for example:

- https://docs.espressif.com/projects/esp ... figuration
- https://docs.espressif.com/projects/esp ... e-antennas

Kind regards,

[bbulkow]

While the wikipedia article is painfully correct, https://en.wikipedia.org/wiki/Received_ ... indication

All wifi chips support RSSI, and it's in Dbm, because ( as stated ) it's power and the most common unit of power is Dbm.

Be very cautious about reading too much into RSSI, but not overly cautious. Some of the tricks that will get you: one often reads RSSI on beacon packets, but those are running at a very low bit rate; I've seen strong RSSI from several miles away, but just for a few seconds, as reflectivity changes; antennas count, so which antenna and how it is bent obviously changes what the radio sees, so RSSI couldn't be compared even on similar hardware. That all being said, everyone uses RSSI for the "signal strength" of wifi despite its shortcomings, and chip vendors and implementations work moderately hard to have the same value even across different boards / chips.

[mbratch]

After taking several readings of the `rssi` value returned from `esp_wifi_sta_get_ap_info` it seems that it is in the range -127 to 0 and corresponds to power level, not what I would call RSSI. RSSI has no specific units and can have a different range depending upon the choice of the manufacturer who is providing the information through their API. In this case, RSSI is perhaps a bit misleading but, I suppose, is "acceptable" since, given RSSI units are relative/arbitrary, then the actual power reading is as good a value as any. :p

I set up a test that reads the "rssi" every second. I noticed that in some locations my my house the value fluctuates quite widely from -80 to -60 while I'm standing still.