[HN Gopher] GPS vs. Glonass vs. Galileo
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GPS vs. Glonass vs. Galileo
Author : cokernel_hacker
Score : 69 points
Date : 2022-11-27 17:51 UTC (5 hours ago)
(HTM) web link (www.gpsrchive.com)
(TXT) w3m dump (www.gpsrchive.com)
| rzimmerman wrote:
| Interestingly despite becoming "fully operational" in 1995, GPS
| was in use in the 1980s and played a huge part in the Gulf War in
| 1990/1991. "Fully operational" probably means 12 satellites in
| view at all times for any point on the earth between
| 55degN/55degS, but it's still very useful even at lower levels of
| service.
|
| It's pretty amazing that a system like that could be envisioned
| in the 1970s and be fundamentally life-changing by the 1990s.
| Truly a modern marvel of engineering that we rely upon for
| precise timing, power grid synchronization, navigation, and a lot
| more.
| smartmic wrote:
| Unfortunately, as it is with many European projects, Galileo is
| over-promised but yet under-delivered. Currently only 22
| satellites are usable: https://www.gsc-europa.eu/system-service-
| status/constellatio...
| wewxjfq wrote:
| Care to enlighten us how the satellite failures of Galileo are
| worse than the satellite failures of the other systems?
| mrtksn wrote:
| Here is an article explaining the 2019 outage and the issues
| with the satellites:
| https://berthub.eu/articles/posts/galileo-accident/
|
| The article argues that the Galileo project has a bit too
| many participants in the development. Europe does have some
| hugely successful multi-participant international projects
| like Airbus or CERN but it is indeed more challenging to run
| projects funded by 30 countries each having different
| culture, language and interests.
|
| It's really a re-occurring theme with no easy fix. The
| European countries are too small to do such large projects by
| themselves and our multi millennial history is about fighting
| each other, so it's not always a smooth sail.
| throw0101c wrote:
| If anyone wants to get into the nitty-gritty details of GPS /
| GNSS, there's a good series of lectures (course) available from
| Standford University; playlist:
|
| * https://www.youtube.com/watch?v=o1Fyn_h6LKU&list=PLGvhNIiu1u...
|
| Topics include navigation message structure, signal encoding,
| error budgets, Keplerian parameters, path loss/antenna gain/link
| budget, plus orbital details of GLONASS/QZSS/BeiDou/Galileo.
| rzimmerman wrote:
| The Position Calculation and Satellite Selection sections are a
| little over-simplified. It's not true that one satellite is used
| for time synchronization and three are used for trilateration. In
| a four-satellite case, all four are used to solve the four
| dimensional problem of "where am I in time and space?" In
| reality, upwards of 12 satellites are used to find a solution to
| this problem and adding more data improves accuracy.
|
| It's true that satellites overhead provide better more vertical
| position information and that satellites at low elevation are
| more impacted by the atmosphere. But the math isn't that simple -
| satellites aren't used for specific purposes. They all contribute
| to a position solution and useful parameters like vertical and
| horizontal uncertainty.
| dataflow wrote:
| How did L5 get enabled and still leave us with an accuracy worse
| than 3.5m? Wasn't it supposed to give us 30cm? What happened to
| that? https://en.wikipedia.org/wiki/Global_Positioning_System
| killingtime74 wrote:
| Don't quote me but I believe you have to use both bands to get
| that accuracy. Some devices support it.
| https://support.garmin.com/en-NZ/?faq=9NWiPDU4gM0JWMfdWFol7A.
|
| Real life test https://www.dcrainmaker.com/2022/04/garmin-
| vertix-accuracy.h...
| dataflow wrote:
| Thanks. I've tried a phone with support for both L1 and L5
| (and other systems) and I don't notice any improvements over
| my old phone. In fact it seems to take longer to get a fix. I
| would love to hear if anyone has found a phone that actually
| gets significantly better performance with L5.
| pifm_guy wrote:
| Time to get a fix is mostly what clever techniques the
| receiver uses. There are various papers demonstrating
| getting a fix that is probably correct with just a few
| milliseconds of signal and then lots of processing.
|
| You also have to cut corners to get a (probably correct)
| fix fast. Things like assuming the almanac hasn't changed
| since last time, the user hasn't moved more than a few
| hundred miles, the system clock hasn't drifted by more than
| a second or so, and no satellites have become unhealthy.
| chrisfosterelli wrote:
| I've always noticed my Garmin watch gets a fix extremely
| fast except for the first time I use it after traveling
| somewhere new. That first one always takes several
| minutes.
| trollerator23 wrote:
| Not all of the satellites have L5 either. As of today only
| 16.
| JCM9 wrote:
| GPS can be much more accurate than what the article says. For
| example, over the continental US the extra WAAS satellites
| provide accuracy down to more like 3-4 feet for GPS based
| aircraft navigation. These satellites broadcast correction
| signals to allow receivers to adjust for small fluctuations in
| the standard GPS signal. Using that system aircraft can navigate
| in 3D down to about 200 ft off the ground for a landing approach
| without the need for any ground-based equipment or transmitters
| at the airport.
| jonathankoren wrote:
| According to this paper, if you hook in all four sat nav systems,
| you can achieve 10 cm accuracy in minutes, 5cm in 30 minutes, and
| millimeter accuracy in a few hours.
|
| https://www.nature.com/articles/srep08328
| tdeck wrote:
| If you're interested in this, you might be interested in the
| terrestrial radio navigation systems that predated GPS:
|
| https://en.wikipedia.org/wiki/Omega_%28navigation_system%29
|
| https://en.wikipedia.org/wiki/LORAN
|
| https://en.wikipedia.org/wiki/Loran-C#e_LORAN
|
| https://en.wikipedia.org/wiki/Hyperbolic_navigation
| dale_glass wrote:
| Those maps are interesting.
|
| So GPS doesn't work well in Greenland or a good chunk of Russia?
| ck2 wrote:
| Also interesting is the American extension to GPS called WAAS
| which is used for aircraft precision.
|
| https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System
| ummonk wrote:
| Kind of weird not to describe BeiDou as well...
| danieldk wrote:
| GPSrChive is very much focused on Garmin GPSr and I don't think
| there are any Garmin devices that support BeiDou.
| z2 wrote:
| From Garmin, though without a breakdown of proportion of
| devices:
|
| In addition to GPS, Garmin products utilize other global
| navigation satellite systems (GNSS) including the Russian
| Global Navigation Satellite System (GLONASS), the European
| Union Galileo system (Galileo), and the Chinese BeiDou
| Navigation Satellite System (BDS), and satellite based
| augmentation systems (SBAS) including the U.S. Wide Area
| Augmentation System (WAAS), the Japanese MTSAT-based
| Satellite Augmentation System (MSAS) and Quasi-Zenith
| Satellite System (QZSS), and the European Geostationary
| Navigation Overlay Service (EGNOS) aviation Safety of Life
| (SoL) service.
|
| Though to the extent this is a US-centric site, the other
| reason for not caring much about Beidou is that the FCC still
| has a geofence block for Beidou, so that no signals may be
| used in US territory: https://www.gps.gov/spectrum/foreign/.
| It's as if Beidou doesn't exist in the US, and even a
| receiver that supports it will only start using the signal
| once it first confirms through other GNSS's that it's not
| located in US. (Example: most phones made in the last 3-5
| years)
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(page generated 2022-11-27 23:00 UTC)