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Posted by:eldanielo
Subject:Signal strength inconsistent
Date:22:39:14 29/12/2012

Hello,

at the moment, I am trying to measure the signal strength (RSSI) of APs in the vicinity with a OpenWRT device to implement a positioning algorithm.

The setup: TL-WA901NDv2 with r34812 in monitoring mode in the 2.4 GHz network with kismet-drone opkg package installed.
The hardware is based on the ar71xx architecture and uses the Atheros AR5416 (onboard)wireless adaptor and uses the ath9k driver.

I discovered that there are basically two different methods to measure the received signal strength which yield inconsistent results:

1. Active Scanning
e.g. using "iwinfo wlan0 scan"

2. Passive with RSSI per captured packet
e.g. using a Kismet drone


However, it is very strange that method 1. and 2. yield totally different results:
Using iwinfo the RSSI value for the closest AP is between -20dBm and -25 dBm but the values displayed using Kismet are between -50dBm and -60dBm.

How comes there is such a discrepancy?

Thanks for any advice!


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