what is the unit of rssi?

tobewinner
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Joined: Thu Dec 10, 2015 5:27 am

what is the unit of rssi?

Postby tobewinner » Tue Aug 01, 2017 8:52 am

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

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kolban
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Re: what is the unit of rssi?

Postby kolban » Tue Aug 01, 2017 1:48 pm

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.
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carlgonz
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Joined: Mon Sep 14, 2020 5:25 am

Re: what is the unit of rssi?

Postby carlgonz » Mon Sep 14, 2020 5:31 am

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
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Re: what is the unit of rssi?

Postby bbulkow » Tue Sep 15, 2020 6:21 pm

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.

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