WIFI RSSI values

How to configure Meshlium or use the Manager System
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dridge
Posts: 2
Joined: Thu Nov 06, 2014 10:53 am

WIFI RSSI values

Post by dridge » Wed Nov 12, 2014 11:52 pm

Hi, the WIFI RSSI values we are getting back from the Meshlium device are quite different from the bluetooth values. They range from -1 to 71, while the bluetooth values follow what is expected as per the technical documentation. From further research the Meshlium device uses the Atheros AR5213A - IEEE 802.11b/g for the WIFI scanner and I understand these RSSI values are proprietary:

“The end-user will likely observe a RSSI value when measuring the signal strength of a wireless network through the use of a wireless network monitoring tool like Wireshark, Kismet or Inssider. As an example, Cisco Systems cards have a RSSI_Max value of 100 and will report 101 different power levels, where the RSSI value is 0 to 100. Another popular Wi-Fi chipset is made by Atheros. An Atheros based card will return an RSSI value of 0 to 127 (0x7f) with 128 (0x80) indicating an invalid value.”
http://en.wikipedia.org/wiki/Received_s ... indication

The only conversion I have found to dbm values is this:
Conversion For Atheros
Unlike the other vendors described, Atheros uses a formula to derive dBm.
RSSI_Max = 60
Convert % to RSSI
Subtract 95 from RSSI to derive dBm
Notice that this gives a dBm range of –35dBm at 100% and –95dBm at 0%

http://www.n-cg.net/ncgpdf/WiFi_SignalValues.pdf

Please let me know if there is a conversion that should be used so we can estimate distances more reliably?

libelium-dev
Posts: 27967
Joined: Mon Sep 28, 2009 1:06 pm

Re: WIFI RSSI values

Post by libelium-dev » Thu Nov 13, 2014 11:48 am

Hi dridge,

We haven't any documentation about this exact conversion right now. Despite this, in many documentation about this is described that the exact calculation of dBm is based upon noise floor and this is only aproximated by the Atheros interface. So the RSSI is useful for relative positioning and not for absolute distance metering.

This thread talks aboit this:
http://lists.freebsd.org/pipermail/free ... 12007.html

Best regards,

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