[time-nuts] iGPS?

[Attila Kinali]

On Sun, 17 May 2015 16:07:05 -0700
Chris Albertson <albertson.chris at gmail.com> wrote:

> Anyone know anything about "iGPS"?  Apparently the Iridium low orbit
> communications sats are now modified via software update to send
> signals that when combined with GPS allow for a receiver that is MUCH
> more precise and harder to jam and can work in urban areas better.
> Apple just bought a company that is building iGPS receivers. 

I think the main business idea is to supply people with indoor
navigation, which is impossible in most cases with GPS.
This is mostly due to the higher receive power of the Iridium satellites
(deeper penetration) and their fast movement (shadowing happens
only for a short time). On the other hand, the fast movement is
a problem for acquiring a fix (satellites are only visible for a
couple of minutes), but I guess they solved that issue for their
phone system already.

IIRC (been some time since i looked at it) the system is based
on triangulation based on doppler shift instead of the time-delay
GPS uses. Which allows the system to work with less than 4 satellites
visible.

More informations can be found here:

[1] "Boing Talks on Indoor Navigation at ION 2011"
http://www.youtube.com/watch?v=cHsGp7ykbv0

[2] "Iridium/GPS Carrier Phase Positioning and Fault Detection Over
Wide Areas", by Joerger, Neale, Pervan, 2009

[3] "iGPS: Integrated Nav & Com Augmentation of GPS",
presentation by David Whelan, 2010
http://scpnt.stanford.edu/pnt/PNT10/presentation_slides/10-PNT_Symposium_Whelan.pdf


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