[time-nuts] CM level GPS accuracy in a smartphone

[Attila Kinali]

On Tue, 5 May 2015 22:01:29 +0000
Mark Sims <holrum at hotmail.com> wrote:

> Should be fun when it becomes available...  they claim they can get
> accurate carrier phase info using a cheap antenna in the phone...
>  and in real time.   It should also be able to get accurate time.
> http://www.eurekalert.org/pub_releases/2015-05/uota-ncg050415.php 

>From what I know about carrier phase measurement, I am not so sure
they can actually deliver this accuracy in urban environments.

Yes, carrier phase measurement can give you cm level accuracy
(after you solve the integer ambiguity), but the biggest contributor
to dilution of precision is multipath and refraction (in urban
environments). These can easily make up several meters. I have
experienced my cell phone to be off by ~300m for several minutes
in an environment where I "only" had a large tree and some smallish
houses in a residential area. Yes, this was most likely just a fluke
of the gps receiver, but still, the biggest problem in the environment,
where most people would use gps for this kind of thing, is not the
limit of precision due to code-only tracking.

But anyways. Let's see what they will deliver.

			Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson