How strong/consistent is the coverage of various parts of Mongolia by the different satellite navigation systems like GPS/GLONASS?

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    If you want to use it for navigation, you need not only coverage (which you have), but also good maps (which you might not have). – gerrit Aug 8 '18 at 14:33

Same as anywhere else in the world, in terms of the space-based GPS system and receiving the signals from those satellites.

The main difference would be with A-GPS (assisted GPS) which can use wifi networks or cell towers to accelerate the location determination algorithm. The lack of these in the Mongolian desert would presumably slow you down a bit, however as long as you can pick up a few of the satellites' signals, you'll get it.

Source: I've been to Mongolia and used GPS on my old smartphone.

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    Clarification: It will only "slow you down a bit" with respect to the time it takes to get an initial fix. Once the GPS device knows where it is and is getting continuous data from satellites, further position updates and speed measurement will be just as fast as anywhere else on the planet. – Greg Hewgill Aug 8 '18 at 3:54
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    @GregHewgill, correct, I assumed the context would explain that, but worth specifiying. – Mark Mayo Aug 8 '18 at 4:24
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    Actually there’s no GPS SBAS (WAAS, EGNOS, etc) in Mongolia, so accuracy (and fault detection reliability, if you have such a receiver) will be lower than the continental US and Europe. There is Beidou SBAS coverage though. – user71659 Aug 8 '18 at 5:28
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    To clarify, that's augmentation, not GPS. But indeed. – Mark Mayo Aug 8 '18 at 7:53
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    @MarkMayo: "Same as anywhere else in the world" is not technically correct. Satellite navigation is very weak near the poles. But as far as Mongolia goes, it won't be a problem. – ales Aug 8 '18 at 9:42

GLONASS system provides a real-time map of integral availability for the current day. Availability is measured as the percentage of the time during the day when you could get a reasonably precise fix in an open area. It used to be important a few years ago when the coverage was less good. This is how it looks today:

enter image description here

As you can see, there's 100% coverage over Mongolia and 99.8% coverage globally. As a reference, this is how GLONASS coverage looked in 2010.

GPS currently provides 100% coverage everywhere, every day, so they don't publish coverage maps. Instead, they publish the DOP (Dilution of Precision) maps which help to estimate how precise a fix will be. Essentially, this is a factor by which you have to multiply the estimated error due to poor satellites location (error is bigger when satellites are concentrated in one region of the sky, and gets smaller when they are spread out evenly).

enter image description here

As you can see on the current map, the PDOP (position DOP) factor is 1 almost everywhere including Mongolia, so you can expect nominal GPS precision there. In a few places the PDOP factor is 2, so the position error can be twice as large there.

If your GPSS receiver combines GPS and GLONASS, then you're practically guaranteed to get 100% coverage with DOP factor less than 1 everywhere at any time, assuming you have unobstructed sky view (which should not be a problem in Mongolia).

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    Now for a laugh and a giggle let's see the GALILEO coverage map ;) – Lightness Races in Orbit Aug 8 '18 at 10:49
  • No, that relates to the visibility of the ground segment – Lightness Races in Orbit Aug 8 '18 at 11:01
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    @gmauch, it's the percentage of the past day for which the quality of the location fix obtainable is "good enough". (If I'm interpreting things correctly, "good enough" means the 95% confidence interval for position is less than 6 meters.) – Mark Aug 8 '18 at 23:24
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    @Mark It's the percentage of the time during which you have PDOP >= 6. In the worst case (PDOP=6 and only older satellites are in view) this means an error can be as large as 6*7=42 meters. – Dmitry Grigoryev Aug 9 '18 at 7:44
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    @Travelguy, it has to do with the orbits the GLONASS satellites are in. You need 24 satellites in six distinct orbits to get 100% coverage of the planet; if you prioritize the near-polar orbits over the near-equatorial orbits, you get full coverage of Russia (and Antarctica, and Greenland, and other northern and southern locations) before you get full coverage of places like India and Australia. The yellow patches on the map will move around from day to day, but will stay in two bands near the equator (and will vanish once Russia finishes filling out the low-inclination orbits). – Mark Aug 9 '18 at 20:26

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