2009/10/9 Mike Kershaw <dragorn (at) kismetwireless (dot) net [email concealed]>:
> On Fri, Oct 09, 2009 at 04:36:51PM +0100, Robin Wood wrote:
>> Hi
>> A friend has just demoed WiFiFoFum on his iPhone and we were trying to
>> work out how the radar feature worked. An AP we were watching appeared
>> to always stay in the correct position on the radar when we rotated
>> the phone.
>>
>> Anyone know how this works?
>
> With an omni? It doesn't.
>
> It's making up a position and keeping it consistent. There is no way
> to derive directionality from an omni, such as that in an iphone.
>
> You can do some really ghetto range guessing from signal level, if you
> ignore the fact that you have no clue what the tx antenna is, power is,
> if you're near a crappy linksys, a 200mW attacker, or in between two
> points of a directional PTP link.
>
> The *ONLY* way I can think that this would give any sort of REAL
> positional data is if it's also tying into Skyhook or one of the other
> wifi positional services, and has a mechanism by which it can request
> the location of a known BSSID. I don't know if any of the wifi
> positional services offers this API.
>
> The second option is it does what kismet does - tracks where it's seen a
> network, and as you're walking around, figures out where the strongest
> signal was and averages it out. I imagine you could jerry-rig this even
> further and assume that no network is near you, and combine ghetto-range
> detection from signal level with some sort of directionality derived
> from user movement (signal was strongest in quadrant X, draw a line from
> user to strongest point and extend N feet based on signal level), but
> would require a) user movement and b) gps lock.
>
> My money is on "magic BS" or skyhook-like remote calls.
>
My theory was along the lines of your second but I was stuck on how if
you turned it on in a location it knew where to place them for the
first position. We didn't test that so it may just randomly distribute
them round the map and work it out once you start moving. As it has a
compass built in it knows which way you are walking and if it is
getting weaker the signal will probably be behind you.
> On Fri, Oct 09, 2009 at 04:36:51PM +0100, Robin Wood wrote:
>> Hi
>> A friend has just demoed WiFiFoFum on his iPhone and we were trying to
>> work out how the radar feature worked. An AP we were watching appeared
>> to always stay in the correct position on the radar when we rotated
>> the phone.
>>
>> Anyone know how this works?
>
> With an omni? It doesn't.
>
> It's making up a position and keeping it consistent. There is no way
> to derive directionality from an omni, such as that in an iphone.
>
> You can do some really ghetto range guessing from signal level, if you
> ignore the fact that you have no clue what the tx antenna is, power is,
> if you're near a crappy linksys, a 200mW attacker, or in between two
> points of a directional PTP link.
>
> The *ONLY* way I can think that this would give any sort of REAL
> positional data is if it's also tying into Skyhook or one of the other
> wifi positional services, and has a mechanism by which it can request
> the location of a known BSSID. I don't know if any of the wifi
> positional services offers this API.
>
> The second option is it does what kismet does - tracks where it's seen a
> network, and as you're walking around, figures out where the strongest
> signal was and averages it out. I imagine you could jerry-rig this even
> further and assume that no network is near you, and combine ghetto-range
> detection from signal level with some sort of directionality derived
> from user movement (signal was strongest in quadrant X, draw a line from
> user to strongest point and extend N feet based on signal level), but
> would require a) user movement and b) gps lock.
>
> My money is on "magic BS" or skyhook-like remote calls.
>
My theory was along the lines of your second but I was stuck on how if
you turned it on in a location it knew where to place them for the
first position. We didn't test that so it may just randomly distribute
them round the map and work it out once you start moving. As it has a
compass built in it knows which way you are walking and if it is
getting weaker the signal will probably be behind you.
Robin
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