Question on Frequency of RSSI Update

Questions and configuration information about the NetStumbler software

Question on Frequency of RSSI Update

Postby chrisjmeagher » Sun May 06, 2007 2:31 pm

Hi Everyone,
This is my first post on this forum. I tried finding the answer to my question with several searches beforehand, but didn't find what I was looking for.

The question is: how often is signal strength (or RSSI) updated by a driver. This probably varies from chip to chip, but let's take the Orinoco Classic Gold card as an example. I've learned that receive signal strength is calculated for every packet, but the RSSI that the card returns is a time average of these per-packet values, right?

The reason I want to know is that I'm working on a simple tracking algorithm for a switched antenna system. If several directional (sector) antennas are tied to an RF switch, one could theoretically "track" a moving wifi user by sampling the RSSI on adjacent sectors to choose the one with the highest signal strength. However, timing becomes important here. If RSSI is averaged (and therefore "valid") at 1sec intervals, say, I'd have to wait 2sec after switching to a sector before sampling its RSSI.

Any help or links would be much appreciated!
- Chris
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Postby Thorn » Sun May 06, 2007 3:19 pm

It depends on what you select for the Scan Speed. It can be set from 1 to 4 times per second.

View > Options > General (tab) > Scan Speed
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Postby chrisjmeagher » Sun May 06, 2007 9:19 pm

I understand that is a Netstumbler option, but does that mean that the fastest a compatible Wifi card (like the Orinoco one) updates its averaged RSSI value is 250ms? Or is it 125ms?

Actually, I'm trying to implement this in C# using calls to WMI. I didn't put the question in the scripting section because the script isn't ready...yet.

Alternatively, if the above [querying RSSI every 250ms] can be done with NS or Ministumbler scripts, I can try that as well.

- Chris
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