I remember OCX
from my Visual Basic days. Ah, happy memories when things like security were non-existent !!!
US defence technology firm Raytheon’s advanced GPS project has encountered yet more cost-inflating delays, according to reports. Raytheon’s Operational Control Network is being built to take advantage of the latest technology updates in GPS III satellites. Amongst other things, the company is “integrating robust cyber …
"Broadly speaking, in Raytheon’s words, the ground system which collates signals from the satellites to deduce the user’s location is the 'brain of the entire GPS system'."
Raytheon didn't say anything like that (okay, the actual words in the quotation marks are correct, but that paraphrasing before that isn't.) The OCX system does not "collate signals from the satellites to deduce the user's location." An individual user's GPS receiver does that. This is kind of GPS 101 here...
The link to Raytheon does a pretty good job explaining what the OCX system is for; you might want to read it again, and pay attention this time. And Wikipedia can tell you all about GPS in general...
Indeed, I also have to constantly correct a very prevalant myth that somehow GPS receivers "transmit your location" to the satellites involved.
Er... no. It's a passive system. Though there is some emergency transmission systems piggybacked on it, you won't use that unless you're piloting a large cruise ship. Your TomTom doesn't go telling the GPS sats "WHERE AM I?". The sats are saying "It's this time here at Sat 1, it's this time here at Sat 2, it's this time here at Sat 3" and your little box listens and then does some clever sums to work out - depending on the time differences of those satellites - where it must be on the planet (it's called triangulation, people...)
"where it must be on the planet (it's called triangulation, people...)"
Perfect explanation of how GPS operates! But my inner pedant won't let "triangulation" pass. "Trilateration" is the three-dimensional geometric equivalent to two-dimensional geometry's triangulation.
As a mathematician, I would have to correct and say that trilateration is done by the measurement of distances, triangulation by the measurement of angles (there's a clue in each word!).
Though you are correct that GPS is therefore trilateration, it has nothing to do with how many dimensions you use.
Sorry Lee, had to down vote you.
You forget to mention that all of the clocks in the satellite are synced.
So at time T, each sat broadcasts the time and based on your distance from the geo stationary sats, the signals will arrive at different times. So that you can triangulate your position by knowing the fixed positions of the sats and the deltas in the clock signals. (All signals travel at the same speed, c. )
Its not the time differences, but the deltas for the same time signal to arrive at your location.
A small nit, but a big difference.
The OCX "ground system" is just the command and control system for the GPS constellation. Whereas the previous systems were located in just a few places worldwide, this new system seems to be intended for deployment to dozens (hundreds) of locations at various capability levels. You don't want *everyone* to have the capability to turn the sats on and off and alter their orbits.
I do.
The ground stations help to make sure that the satellites are in correct orbit and position. Which is important so that your phone's GPS can give you a reasonable approximation.
(Its not just the number of sats you can 'see' but also the clock in your phone.) The more sats and the more accurate your clock... the more accurate your position... within a certain degree due to atmospheric conditions..
If the sats move, then your calculations are off.
There are two things you can do.
Either move the sats back in to their fixed positions or adjust the coordinates and publish them for a more accurate fix. (Assume that the sats 'wobble' what then? )
Naval navigation can combine land based radio stations with GPS to get a good fix. Aircraft can do the same too.
"GPSIII - mmm, does that mean your device gives you three possible locations for where you might be at any given time ? (just asking)"
Strange you should mention that, as that's pretty much how the receivers correct their clock rate.
With four satellites in view they can calculate three possible positions, each position based on data from three satellites - since you can obviously only be in one place at a time, adjusting the clock rate to minimize the difference between the three calculated positions ensures the clock is running at the correct rate. This allows the receivers to provide accurate positioning with a cheap and simple clock chip, as opposed to needing an atomic clock.
Presumably the more satellites a receiver is tracking the more accurate this clock rate correction process is and hence the more accurate the final position calculated..
All is not going well, however. Bloomberg News reports that the system, which was meant to have gone live in October 2016, will instead go live in 2022 at a cost of at least $6bn.
Not going well for whom? I'm pretty sure that Raytheon and Lockheed Martin along with the congress people they own are fine with the situation.