Wireless - can u tell direction and/or distance to other laptops?

[Ivan Krstić]

John Marshall wrote:
> Sorry if this has been asked already.  Will it be possible to tell
> distance and/or direction from one laptop to another?  If so, any idea
> how accurate such figures might be?

The hardware doesn't have any special support to do this, so you get
only what you can implement in software. That means you can forget
direction, and will have a very hard time doing precise distance, given
multipathing effects and general signal variability factors.

It'd be interesting, from a research point of view, to see how things
would work if you distributed the problem, and had a number of laptops
working together to calculate relative distances and such. It'd take
some work, though.

> What I'd ideally like to know is which of distance, direction and
> location may be achievable on the laptop and to what accuracy.  At this
> time, however, I'm only looking for an rough indication of if it's
> impossible, difficult, easy or simply unknown.

Some combination of impossible and difficult. There has been talk of
throwing a GPS chip into the machines, but not for generation 1. In
medium-noise environments where you've done previous data collection
legwork, you can usually do wi-fi positioning within about 50m. Without
previous data collection, you're pretty much out of luck.

I actually researched wi-fi positioning in a previous life. The
conclusion, from a paper which I never found time to get published:

"[...] we investigated the use of 802.11 access point
beacons to determine location and group devices by location.
Our experimental findings indicate that the high degree of
precision demonstrated by Bahl and Padmanabhan [1] probably
cannot be attained in heterogeneous, real-world systems. Our
findings, although not conclusive, suggest that a median error of
a few tens of meters, similar to that achieved by LaMarca et al [2].
in Place Lab, is the highest level of accuracy achievable outside
the laboratory. We do find, however, that beacons can be used
effectively to match groups of users within several tens of
meters of each other, which should be sufficient for most social
networking applications."

[1] Bahl, Paramvir and Venkata N. Padmanabhan, “RADAR:
    An In-Building RF-based User Location and Tracking
    System,” Proceedings of IEEE INFOCOM, 2000, pp 775-
    784.

[2] LaMarca, Anthony et al., “Place Lab: Device Positioning
    Using Radio Beacons in the Wild,” Intel Research, 2004.

-- 
Ivan Krstić <krstic at solarsail.hcs.harvard.edu> | GPG: 0x147C722D