[kismac] Re: Signal strength

  • From: "John Warren" <xaive1@xxxxxxxxx>
  • To: kismac@xxxxxxxxxxxxx
  • Date: Wed, 1 Mar 2006 14:49:41 -0800

I like it.  It makes sense to me.  Each computer learns it's range and
scales it to a "uniform"  range.  The users will know whether or not
they scaled their own readings.  It is left up to them to decide what
they want and act accordingly.

On 3/1/06, Robin L Darroch <robin@xxxxxxxxxxxxx> wrote:
> >       Whatever numbers are produced, regardless of all
> >proscriptions against such behaviour, people are going to use them
> >for comparison purposes, and then they are going to get mightily
> >confused.  In FreeBSD parlance, this would be a serious violation of
> >POLA (Principle of Least Astonishment).
> Hi Brad,
> I think your principles are correct, but your conclusion is actually
> counter to those principles.  As you say, people are going to use
> numbers to compare no matter what we tell them.  Now lets look at two
> scenarios for such a comparison:
> - warwalker Alice has a 12" iBook with Airport Extreme passive mode.
> When she's parked right next to a router, she gets a raw strength of
> 110.  When a network is on the threshold of reception, she gets 60.
> - warwalker Brian has a 17" PowerBook, also with Airport Extreme
> passive mode.  Sitting next to a router, he gets raw strength 150.
> At the threshold of reception, he gets 70.
> 1) No scaling - existing raw numbers only:
> * Alice walks past the north side of a house, and gets a signal of 80.
> * Brian walks past the south side of the same house, and gets a signal of 100.
> * Alice and Brian compare notes.  Since they both have computers
> using Airport Extreme passive mode, they quite reasonably assume that
> the numbers are comparable, and thus conclude that the router is
> closer to the south side of the house than the north side.  Imagine
> their astonishment when they visit the occupants and find the router
> sitting in one of the northern rooms!
> 2) Auto-scaling using the algorithm posted:
> * Alice walks past the north side of the house, and gets a scaled
> strength of 41.
> * Brian walks past the south side of the same house, and gets a
> scaled strength of 38.
> * Alice and Brian compare notes (although we told them not to) and
> conclude that the router is closer to the north side of the house.
> When they make the same visit, they admire how clever they were to
> ignore our warnings.
> In this case, the POLA is actually to provide auto-scaling, not the
> raw values KisMAC currently shows.
> However, I'm not sure you've understood my proposal as I intended it
> (and I probably didn't explain it that well).  The auto-scaling
> should NOT happen the way the graphs are currently auto-scaled.  The
> graphs are (quite appropriately) scaled based on "what signal
> strengths have I seen lately".  By contrast, the scaling values for
> signal strength will have to be auto-learned from the time when that
> driver was first added to the list in KisMAC (i.e. "what signal
> strengths have I seen *ever*").  This means that they increase in
> accuracy in a logarithmic curve, very rapidly improving at first
> (i.e. the first several networks scanned since installing the driver
> will have rough and inaccurate scaled strengths, although still
> relatively correct with respect to each other), then reaching the
> point where the weakest and strongest signals ever seen probably
> won't change much at all (because they'll have encountered - at least
> once - the "right next to the router" and the "threshold of hearing"
> situations).  Essentially, KisMAC would always be learning, but after
> the initial period of inaccuracy, it would be pretty close to the
> mark.
> In some cases (e.g. the apartment where I live), the training would
> be almost instantaneous: I have a network of my own, and there's
> another network which the Airport can only just pick up from time to
> time.  If I ran KisMAC here, then later took it wardriving, my
> auto-scaled strengths would be pretty close to the mark right away,
> and would be far more comparable to anyone else's (reasonably
> trained) auto-scaled strengths than any existing raw figures.
> Yes, it should be optional to turn it on, but I don't think the fact
> that it might be used to make an inappropriate comparison is a reason
> to exclude it from the program altogether: we already present data
> that will give wildly inaccurate comparisons, and don't even warn
> people that they shouldn't compare.  The case I've given above goes
> much more in favour of learned auto-scaling if Alice has a DWL-122
> instead of Airport Extreme (e.g. signals ranging from 5 to 50).  In
> that case, she'd have got a raw strength of 23 compared to Brian's
> 100, and they would have figured that the router must be outside the
> south wall of the house, or even across the street to the south,
> which is a completely incorrect conclusion.  If using auto-scaled
> values, Alice would still have got 41.
> As for what to save in KisMAC's data files, that's another matter.
> Perhaps with each network saved, save the raw signal strength, and
> include an index number for what adapter picked it up, and then at
> the end of the file list the adapter(s) installed when the file was
> created (with some uniquely identifying number for each... MAC
> address?  BSSID?) and their current minimum and maximum signal
> values.  That way, the strengths can be displayed according to the
> user's preference (i.e. raw or auto-scaled) on either the same
> computer or another computer, while still allowing the scaling to
> improve in accuracy with later learning on the original computer that
> did the scan.
> Hmm... this is getting a bit big... but the more I think about it,
> the more convinced I am that it would be a considerable improvement
> to the current numbers we show - we just need to be sure to get it
> right.
> This doesn't exclude the possibility of using dBm if/when we can
> gather data on translating raw signals to dBm for all supported
> adapters: just let the user choose - raw, dBm, or auto-scaled.
> --
> -------------------------------------------------------------------------
>   Robin L. Darroch - PO Box 2715, South Hedland WA 6722 - +61 421 503 966
>        robin@xxxxxxxxxxxxx - robin@xxxxxxxxxxx - robin@xxxxxxxxxxxxx

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