bluetooth proximity

Tilman Baumann tilman at
Mon Jun 16 19:04:49 CEST 2008

AVee wrote:
> On Monday 16 June 2008 14:40, David Kepplinger wrote:
>> Hi,
>> I don't think that's feasible. To measure (with 2 devices) you need
>> two very synchronous clocks and a very exact measurement. Because the
>> signal travels with approximately the speed of light (about 300.000
>> km/s), an error of 1µs is an error of 300m. There are a lot of reasons
>> why this is not feasible. Sorry.
> I tend to agree, however, things might change if you add gps. You'd might just 
> transmit your own speed and location, although you will probably hate the 
> precision of that without DGPS (which may never work on the Freerunner) and 
> if may not work al that well indoors. 
> But GPS could also solve the first problem you mentioned, it can provide the 
> same clock to the two device. That leaves only the 'exact measurement' to be 
> solved.
> It might work, but the precision will probably still be far to low to be 
> useable for anything.

I don't think so. What you get is effectively something like DGPS. Both 
receivers (while being near each other) receive the same skew/offset.
Both will have wrong readings for the absolute position. But the 
relative position should be extremely high. (As high as DGPS can get)

At least in theory.
DGPS works just this way with the difference that with DGPS one receiver 
is stationary and propagates a correction signal to all receivers nearby.

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