

GPS satellites get a serious upgrade  - cwan
http://www.physorg.com/news/2011-04-gps-satellites.html

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makmanalp
> "Well, currently GPS can estimate your location to an area of about 20
> feet."

With DGPS we get about +-10cm for our non-military robotics project. So this
isn't really true. We use a paid subscription but the free WAAS signal brings
the accuracy to about +- 1m which is already pretty friggin good.

I wonder what justified this (probably expensive) upgrade?

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jws
The existing satellites have been in service too long. It is a "replace it or
lose it" question.

It took me a while to find out why they are more accurate, I eventually found
this quote: _Greater accuracy is a product of advanced atomic clocks in the
new satellites, Torok said._ I think it's safe to safe that tiny atomic clock
technology advanced in the decade between the existing satellites and this
round.

They added a new military signal, presumably jam resistant. (It has a
"spotlight" antenna that can provide a 100 times more power to a fighting
theater. _I'll see your alibab.com gps jammer and raise you 20dB…_ )

They also added another civilian signal (L5 - safety of life) which presumably
has a purpose, but darned if I can find it. Probably related to different
frequency, more power, different coding, something about the ionosphere… my
guess is that it won't crap out at the same time the other one does from
interference.

~~~
superdude
The L5 moniker "safety of life" is an accurate name. It will assist GPS
aircraft navigation, especially during the safety-critical landing approaches.
Aircraft rely heavily on both GPS and WAAS satellites for corrections.
Actually, L5 has been broadcasting on the two WAAS satellites for several
years, but most end-users would not have used it. AFAIK, L5 decreases the
error from multipathing and the ionsphere, among other improvements.

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zmmmmm
Will it get a lock any quicker?

It would be nice if accuracy could be traded off for time, so that instead of
getting a more accurate lock, we're getting a the old accuracy but quicker.

For me the biggest limitation of GPS is that it can take > 1 min to get a lock
on a regular basis. I know this is hardware and software dependent ... but
it's still common for it to be at least 20 seconds even on the best hardware,
I think. Apart from making apps that rely on GPS awkward ("please wait an
indeterminate amount of time while we find your location") it also means much
greater power use because the GPS has to be active for longer (GPS seems to be
something that noticeably uses a lot of power in my Nexus One).

~~~
guygurari
I used to have this problem on older devices, but the GPS on my iPhone 4
consistently gets a lock almost instantaneously. I guess YMMV.

~~~
enf
A lot of the delay in getting an initial GPS fix is downloading the almanac
for the satellites at the very slow GPS bit rate. The iPhone 4 probably
periodically retrieves the almanac over GSM instead, allowing much faster
location fixes. (Several models of Android phones do this.)

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aw3c2

      This enhancement means that the next generation of GPS technology may be able to work with augmented reality technology indoors.
    

Rubbish. GPS needs an open sky above. The signal is really weak.

~~~
beej71
My GPSmap62st sometimes figures out where it is on my desk indoors 3 m away
from the nearest window. Accuracy is horrible (it often thinks it is outside),
but it averages to the right place eventually.

And there's another floor above mine, as well, complicating things. I'm quite
impressed it is able to receive anything, but it just goes to show that with
the right antenna and DSP, amazing things are possible.

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guygurari
Will existing devices benefit from the improved accuracy?

~~~
nikcub
Yes, but the receiver clock plays a large part in accuracy (as does software).
With the satellites travelling at 14,000km/h, even being accurate to 10^-6
seconds means you can be off by 280-300m.

This new series of GPS satellites will have more accurate atomic clocks, and
some other changes (such as being upgradable remotely). So I doubt older
devices would be a lot more accurate since they still have clocks that are
orders of magnitude less accurate than the clocks on the satellites.

With these fine measurements, even the smallest delay or inaccurate
measurement in software or hardware can make a big difference.

There is a better technical description of the new series here:

[http://www.dailytech.com/First+Block+2F+GPS+Satellite+Launch...](http://www.dailytech.com/First+Block+2F+GPS+Satellite+Launched+Needed+to+Prevent+System+Failure/article18483.htm)

and description and more details about the project straight from Boeing:

<http://www.boeing.com/defense-space/space/gps/index.html>

