GPS vs. TDOA (was Re: release date)

[Andrew Becherer]

On 5/19/07, admin at mmri.us <admin at mmri.us> wrote:

> I think you guys need to get this out asap.
> The only reason I do not buy the iphone right now is because it does not
> have GPS.

In the United States the iPhone, no doubt, makes use of radiolocation
instead of GPS. Cingular uses Time difference of arrival (TDOA). This
system uses multilateration, much like GPS.

It is my understanding that civilian GPS is generally accurate within
15 meters. The FCC requires American cellular providers to be able to
determine the position of a phone within 100 meters 67% of the time
and 300 meters 95% of the time. It is my understanding that TDOA can
currently achieve accuracy within 30 meters.

Many modern phones support the Location API for J2ME (JSR 179). On a
Cingular or T-Mobile network this location is provided by TDOA (unless
your phone has GPS which it usually does not). I've used J2ME location
based applications on Cingular's network to good effect. I have not
been able to compare TDOA to GPS because I haven't had access to a GPS
enabled phone.

I think my question is why is everybody freaking out about the iPhone
not having GPS? It will report location as close as 30 meters, usually
within 100 meters and almost always within 300 meters. This accuracy
is good enough for most applications. Even better cellular TDOA is
accurate inside building as well as outside buildings (which in my
experience GPS is not).  Are location detection services like
TruePosition's U-TDOA (used by Cingular and T-Mobile in the USA) not
available internationally?

So why is GPS the killer functionality the Neo has over the iPhone?

(note: I understand why the OpenMoko development platform is better
than the iPhone. I'm just talking about GPS vs. carrier provided
location detection.)

-- 
Andrew Becherer
Undergraduate, Computing and Software Systems
University of Washington, Tacoma