[Olsr-users] Meraki's distance display - very nice

[Henning Rogge]

Am Montag 29 September 2008 02:19:44 schrieb Derek C:
> Hi Henning,
>
> I thought that perhaps with dynamic ACK (like in the Ubiquity HAL for
> madwifi) it might be possible to estimate the distance based on the
> automatic timings.
I'm at least a little bit sceptic about this. To measure the distance between 
two nodes you have to consider the speed of microwaves in the air, which is a 
good approximation to the speed of light. At a distance of 300 meters you 
have a transmission delay of just 1 mikrosecond, so ANYTHING in your hardware 
and software must have a measurable or known delay measured in nanoseconds.

WLAN cards don't have timers with nanosecond resolution and the most modern 
cards are a softmac design, which do a lot of stuff in software... which will 
add a random delay too.

> Still though - Meraki have it working now (down to metres) and its nice to
> look at - it seems quite accurate although I haven't actually taken to
> pacing out the distances between known nodes.

Most likely they are using more than the timing to measure the distance. See 
if you get higher distance if you put a thick wall between the radios.

Henning


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