Hi Taka,
> On more broader sense, was GPS originally designed to provide timing
service?
Yes, from the beginning GPS was a so-called PNT (Positioning, Navigation
and Timing) system.
> Or is it a byproduct of needing to measure location and speed, thus it
> needed a constant signal, and that using it to sync reference signal
> is just an ancillary and after-thought use cases?
Precise timing is not so much a by-product but the key feature that
makes GPS work.
Here's some reading, with an emphasis on the early history and design of
GPS:
"TIMATION - a GPS Predecessor Program"
https://directory.eoportal.org/web/eoportal/satellite-missions/t/timation
"Pre GPS History of Satellite Navigation", Francis M. Czopek
https://web.stanford.edu/group/scpnt/pnt/PNT08/Presentations/2_Czopek_PNT_2008.pdf
"True Origins and Major Original Challenges for GPS Success (1962 –
1978)", Brad Parkinson
https://web.stanford.edu/group/scpnt/pnt/PNT09/presentation_slides/13_Parkinson_Creating_GPS.pdf
"Launching the Brick Moon: GPS’ path from the Space Race to Smartphone",
Aaron Lovell
https://www.wilsonquarterly.com/quarterly/summer-2015-an-age-of-connectivity/launching-the-brick-moon-gps-path-from-the-space-race-to-smartphone/
"GPS Declassified: From Smart Bombs to Smartphones", Richard Easton
http://www.gpsdeclassified.com
"The Origins of GPS", Stephen T. Powers, Brad Parkinson
Article published in May & June 2010 issues of GPS World
https://www.u-blox.com/sites/default/files/the_origins_of_gps.pdf
"Initial Results of the NAVSTAR GPS NTS-2 Satellite", James A Buisson,
Roger L. Easton, Thomas B. McCaskill
"General Relativity in the Global Positioning System", Neil Ashby
http://www.leapsecond.com/history/Ashby-Relativity.htm
/tvb
On 8/9/2020 6:33 PM, Taka Kamiya via time-nuts wrote:
I've done some quick research. I do not see timing as one of the services
provided. I wonder if it can be achieved by just listening into what's already
transmitted (like GPS) and do some math on our side.
On more broader sense, was GPS originally designed to provide timing service?
Or is it a byproduct of needing to measure location and speed, thus it needed a
constant signal, and that using it to sync reference signal is just an
ancillary and after-thought use cases?
---------------------------------------
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
On Sunday, August 9, 2020, 9:21:23 PM EDT, Bob kb8tq<[email protected]> wrote:
Hi
On Aug 9, 2020, at 7:03 PM, Tom Van Baak<[email protected]> wrote:
Hi Stu,
There's no problem with a semi-commercial posting here. You've been a member
for a decade and frequent contributor plus the subject matter is exactly
on-topic. So thanks for posting.
I spent a while on your web site and didn't uncover a trove of white papers. If
you could post some URL's that would be appreciated. You don't have to worry
about being less accurate than GPS. I mean, there are often far more important
factors than nanosecond precision.
To that point ( as accurate as GPS ) ….. GPS is simply a convent comparison
system. Saying that
this or that is better or worse at this or that tau is *not* the same as saying
it has more or less value.
It’s simply a system that is out there to be compared to.
Bob
You didn't mention pricing; it's hard to imagine it's as free as GPS so that
seems like another disadvantage to me.
Your comment about fewer satellites is spot on. That will be taken care of if
you give SpaceX / Starlink a call and join that bandwagon. There are already
597 Starlink [1] satellites up there vs. 82 Iridium [2] satellites, yes?
If you have entry-level / hobbyist grade evaluation kits I'm sure a number of
us would be very interested to try it out.
Thanks,
/tvb
[1]https://en.wikipedia.org/wiki/Starlink
[2]https://en.wikipedia.org/wiki/Iridium_satellite_constellation
On 8/9/2020 2:53 PM, Stewart Cobb wrote:
Taka Kamiya and Forrest Christian both asked recently about the alternative
satellite PNT system using the Iridium satellites. That system was
developed by my company, Satelles. It has been commercially available for
more than a year now.
The biggest advantage is that our signal is at least 30 dB stronger than
GNSS signals (the exact numbers depend on whether you're talking to
engineering or marketing :). You can easily get a usable signal in deep
jungle, or a data center in the middle of a building's basement, or even
inside a locked shipping container. The stronger signal is correspondingly
more difficult to jam or spoof than GNSS, and our signal has anti-spoofing
features as well.
The biggest disadvantage is that it is not quite as accurate as GPS,
because there are fewer satellites in view at any given time.
I don't want to quote exact timing numbers here, because they depend a lot
on system integration details, but you can easily steer an OCXO within a
few hundred nanoseconds of USNO time. With a rubidium, you can do
considerably better.
If you want to know more, our website iswww.satellesinc.com.
(If this message has been too commercial, I apologize in advance. The
boundary between information and salesmanship is not always sharp.)
Cheers!
--Stu
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