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

[Tim Shoppa]

A 300M error is not "just a GPS determination" but is likely the phone
using a few extrapolated stale GPS readings maybe combined with some kind
(probably wrong kind) of dead reckoning.

Automotive dead reckoning applied to pedestrian movement can produce really
interesting results! As I walk around my house or yard, my phone keeps on
jumping my location to the middle of a 12-lane superhighway a few hundred
feet away. Most GPS code is based on automotive dead reckoning algorithms
but the cellphone manufacturers also are working on "pedestrian dead
reckoning" modes, activated when the inertial sensors indicate walking.

Tim N3QE



On Thu, May 7, 2015 at 9:32 AM, Attila Kinali <attila at kinali.ch> wrote:

> 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
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>