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throw0101b

Given the orbit used:

* https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System

* https://en.wikipedia.org/wiki/Tundra_orbit

Australia, Indonesia, and Papa New Guinea will also benefit.

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My phone regularly picks up QZSS here in southern California for what it's worth. At least at certain times of the day with a good western view of the sky.

How do you know this???

Is there an app for displaying the exact signals your phone's GNSS receiver is getting? I've played with cgps and am familiar with it on the desktop side but never on mobile.

On Android you can read the raw NMEA sentences. Or just use an app that parses it out and tells you which constellations/augmentation sources are being used

There's SatStat[1] and GPSTest[2] on F-Droid. Simple little apps that show information about the satellites your phone is currently receiving signals from.

[1]https://f-droid.org/packages/com.vonglasow.michael.satstat/

[2]https://f-droid.org/en/packages/com.android.gpstest.osmdroid...

I've used this app [1] for years. It has some paid features you probably don't need or want, but the free version will show you all kinds of constellation info.

[1] https://play.google.com/store/apps/details?id=com.chartcross...

Here's an Android app from Google called GnssLogger [0]

[0] https://play.google.com/store/apps/details?id=com.google.and...

It's not likely to benefit unless it's near directly overhead afaik. It's hard to use GNSS satellites at those angles, and if you have a wide open view then most likely you've got better angles to something closer in.

Looking at the picture of the orbit, its a lot wider around Australia, is that a benefit given the shape of the country or happenstance

It's a consequence of the orbit's eccentricity - the perigee (low point) in the orbit is to the south. The satellite is moving faster around the perigee, and slower near the apogee (high point) over Japan.

More info here: https://gssc.esa.int/navipedia/index.php/QZSS

Per that Navipedia article, the Centimeter Level Augmentation Service (CLAS) of QZSS also allows for ionospheric correction data for the Indian and Pacific Oceans, which could be helpful for other GNSS systems:

* https://gssc.esa.int/navipedia/index.php/QZSS#Centimeter_Lev...

It's a version of the tundra orbit ( https://en.wikipedia.org/wiki/Tundra_orbit )

In https://en.wikipedia.org/wiki/Tundra_orbit#/media/File:Anima... its the green orbit.

The figure 8 shape can be seen in https://commons.wikimedia.org/wiki/File:Qzss-01-120s2.gif though it isn't quite as extreme in its eccentricity as orbits that are trying to service further north.

The shape is based on what is known as "apogee dwell" - that from the ground perspective a satellite at apogee (the furthest distance from earth) will be moving the slowest compared to the ground view. When the satellite is closer to Earth that same velocity will be covering more ground distance (there will also be some actual change in velocity based on how far down Earth's gravity well it goes in and out of, though I haven't done enough orbital mechanics to say with certainty). Judging by https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System it changes by about 10% as it gets closer to earth.

The main issue (and you'll see this if you use GPS in a city) is that GPS can have difficulty in canyons - either urban or natural.

https://www.traffictechnologytoday.com/news/connected-vehicl...

You need line of site to GPS in order to get an accurate fix. If there's mountain or building in the way, it can have difficulty. Japan's cities are susceptible to this.

The QZSS system is designed to have a satellite directly overhead of Japan so that when you are in a city there is a satellite visible.

> The primary purpose of QZSS is to increase the availability of GPS in Japan's numerous urban canyons, where only satellites at very high elevation can be seen. A secondary function is performance enhancement, increasing the accuracy and reliability of GPS derived navigation solutions. The Quasi-Zenith Satellites transmit signals compatible with the GPS L1C/A signal, as well as the modernized GPS L1C, L2C signal and L5 signals.

It's the narrow bit over Japan that is intended, but as it happens the orbit tracks closest to the most populated parts of Australia, on the coast. The central parts (tan on the map) are more or less unpopulated.

comment retracted

Dunno who down-voted you - but what environment are you operating in? One of the claims for the Japanese system (you can see it in its orbital design) is that it specifically provides more opportunities for overhead signal coverage, increasing reliability/accuracy in mountainous and heavily urbanized (ie, skyscraper canyons) terrain.

That all being said, I'm also of the opinion that this is more of a defense play. QZSS has the nice property have using geosync/geostationary orbits - I'd imagine that makes ASAT work a bit harder.

> In peacetime, at least

That's a huge proviso given recent geo-politics (and the possible change of that premise may be why Japan is hedging).

* https://news.antiwar.com/2023/04/16/defense-official-confirm...

* https://gpsjam.org

GPS is shit in Japanese cities because of the angle. Read the article on QZSS.

In a place like Ginza or Shinjuku it can be really frustrating to navigate using GPS when you exit a station and your location is off by 20m and your compass is also wrong by 90 degrees (I guess because of all the steel buildings). I haven't read up on it in a while but I think local augmentation for GPS, including indoors in malls, etc will eventually arrive once we figure out how to provide it as a public service instead of a bunch of companies competing to make a proprietary services that serve location-based ads.

GPS doesn't work in dense cities without specific corrections because it reflects off the buildings, which means you don't know how long a signal took to get to you.

QZSS helps but the receiver still has to be designed for this specific situation.

Isn't that essentially what we landed on with Wigle and the various wifi location engines?

The majority of the population in japan just lived with bad GPS for the last 2 decades?

As have we, and much longer than that. It is only fairly recently that GPS broadcasts an accurate signal on non-military bands.

The military eventually gave up the idea of having people pay for satellites they can't actually use. Mainly because capitalism decided to give up, call the taxpayer investment wasted and stolen from the people, and just build a location network on the ground that's more accurate than GPS. The military now uses $450 hammers and toilet seats to steal from the people.

https://en.wikipedia.org/wiki/Assisted_GNSS

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