Japan's Plan for Centimeter-Resolution GPS
spectrum.ieee.org
spectrum.ieee.org
The geosynchronous part is so that they only need a few sats to cover their region, unlike GPS which is global and requires some 32 sats.
It's not an equatorial geostationary orbit so that receivers at higher latitudes (in Japan) will see a sat overhead instead of always over the equator. This is to deal with the "canyon" effect. Guaranteeing a bird overhead, rather than GPS's catch-as-catch-can, should definitely help signal reliability.
These will be further away than GPS, which are medium Earth orbit.
Some other info (including an animation) here:
http://global.jaxa.jp/countdown/f18/overview/orbit_e.html
It should also be useful in Australia and parts between. They will also park spare sats in geostationary equatorial orbits.
It's a bit inspired, I think, by the Molniya orbit, another technique to get long-duration high-latitude overflight:
As far as "should be useful" goes do you know if Japan has ground stations in Australia?
http://www.insidegnss.com/auto/popupimage/QZSS%20ground%20se...
Dunno if those will help with the "centimeter resolution" bit, but it'll certainly augment GPS.
The dwell over Australia and other non-Japan areas for the non-stationary sats will be shorter, but still will be useful while they are visible. And outside of "canyon" areas that will be quite often. The geostationary sats will be useful over quite a lot of the west Pacific and east Indian oceans.
Isn't it closer to the Tundra (Тундра [in rus]) orbit?
https://en.wikipedia.org/wiki/Tundra_orbit
Found a video showing the difference in ground tracks between the two:
Molniya is cheaper, certainly, and has the interesting property of dwelling over both the United States and Russia. Tundra orbit is aggressively regional, and thus has no plausible deniability about being for local use. If you're not a Cold Warrior, however, that doesn't matter much, so we'll probably see more Tundra type systems in the future. Europe would benefit from this exact system, as would the US. China perhaps, too.
To continue with mixed standards -- a tennis court measures 23.78 by 10.97 meters (78 by 36 feet, I'm surprised it hasn't been metrified). The Japanese system should be about 3 orders of magnitude more precise than tennis-court-rated GPS.
area of an NFL football field in square meters: 5351m^2
area of a circle of radius 45 meters: 6361.73m^2
area of a tennis singles court in square meters: 196.7m^2
area of a circle of radius 6.5 meters: 133m^2
(A volleyball court would be closer at 162m^2.)
> To put it simply, with QZSS it is like the number of GPS satellites has been increased. Because QZSS has interoperability with GPS, the number of satellites that can transmit satellite signals at the same time is increased, which makes stable positioning possible. This also decreases the positioning errors as described. [1]
With L1 and L5 carriers on GPS now, you can definitely get down to cm-level positioning already. I think they are just launching more satellites in Japan-specific orbits so they have better, faster GPS coverage above Japan, and especially in dense cities where you need a high angle of elevation for positioning satellites.
The farming systems are more real-time kinematic GPS, which broadcast local corrections from a dedicated reference statiion. [2]
One of our big concerns back then, though, was that US Military would degrade the SA (Selective Availability) signal - it had happened in the Gulf War, and our tracks, which were normally accurate to within 3-4 meters, went wacky and were almost 50 meters off at times.
The solution was to mount a radio antenna, have it calculate it's "True" location by averaging a couple days worth of GPS signals, and then, continually transmit the difference between a current GPS signal and it's known location. This Differential GPS let us calculate paths to within 1m of accuracy.
When I asked what prevented a military opponent from doing the same thing, I was told that the first thing in the battlefield that gets hit as a command center would be anything transmitting RF, particularly if it was believed to be for D-GPS. Also, D-GPS isn't that effective for missile tracking, as you need to get differential signals in areas outside of your zone of control.
[1] http://en.wikipedia.org/wiki/Indian_Regional_Navigational_Sa... [2] http://en.wikipedia.org/wiki/GAGAN
[1]http://gpsworld.com/gagan-certified-for-aviation-in-india/
[2]http://www.isro.org/pressrelease/scripts/pressreleasein.aspx...
[3]http://en.wikipedia.org/wiki/Indian_Regional_Navigational_Sa...
If I would be in Japan, with a regular, GPS-tuned/understanding device, would I get better service? Or would I need a special device, that'd be able to understand GPS+"JPS"?
The part where they transmit correction data to the satellites also confuse me, if that's what they're doing; It's not the same as the United States Global Positioning Service if that'd be the case, right? For what I've understood, the GPS doesn't need a constant feeding of data from ground stations - it's ""simply"" a bunch of satellites sending out the current time from their on-board atomic clocks.
> GPS doesn't need a constant feeding of data from ground stations
GPS time is automatically steered to UTC(USNO) on a daily basis to keep
system time within one microsecond of UTC(USNO) modulo 1 second, but during
the last several years has been within a few hundred nanoseconds. The
rate of steer being applied is +/-1.0E-19 seconds per second squared.[^1]
In some senses, the technique is just an augmentation/expansion of WAAS [0] to Japan (WAAS is strictly North American).
[0] http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System
EDIT: And to the OP, you would need some sort of GPS+ device.
Does this mean GPS will stop working when Zombies/Pandemic/whatever strikes and wipes out US military?
Since those clocks need to be super precise, it's easier to have an accurate reference on the ground where everything's not getting shaken and baked to bits.
I am curious before reading my comment did you think that GPS would continue to work without navy.mil and af.mil?
I was hoping GPS would stay up for at least 5-10 years - I assumed all they needed was periodic orbit corrections.
Well, there goes my GPS to the rescue Zombie survival plan :/. Time to learn how to read stars, or better yet - find android app that does it automagically from a picture :)
http://www.losangeles.af.mil/library/factsheets/factsheet.as...
The next generation (III) will take away the Cs and only rely on (three) Rb:
http://www.losangeles.af.mil/library/factsheets/factsheet.as...
The current GPS constellation status can be seen here, Plane/Slot describes the position in orbit, SVN is the "Space Vehicle Number", "PRN" is typically the "Sattelite Number" as displayed on a GPS receiver, because it describes the "Pseudorandom number (sequence)" used to decode signals of this particular satellite. Clock is just for information what the satellite right now uses as a timebase. As of 2014-04-27
There's still plenty of other maintenance, like delta-v maneuvers that need to get done or the system will eventually fail. Likely within a year.
This system will probably be useful for quickly determining what moved in an earthquake.
This system add additional satellites that a normal GPS receiver can receive. By using different orbits they can improve reception. It also transmits on multiple frequencies that allow the effects of the atmosphere on the signal to be better calculated. It will also transmit augmentation information to improve accuracy further.
When you get a GPS fix the very first thing your handset does is download the ephemeris data. This is broadcast at regular intervals along with the location signals. This data tells you the orbital parameters of each satellite, without it you couldn't get a precise location fix because you wouldn't know where the satellites you were getting signals from were.
The GPS satellites are incapable of calculating their own ephemeris data, it needs to be uploaded from the ground. The system cannot simply reuse the same data forever because the orbits of the satellites change over time, and because the system is sensitive to very small changes a lot of higher order effects (such as radiation pressure, the non-sphericity of the Earth's geoid, and so on) come into play which are not easily calculable. Over short periods the future ephemeris are predictable within reasonable bounds of precision, so the USAF uploads 30 days worth of ephemeris data to the GPS satellites on a regular basis.
If it were no longer possible to upload that data the system would eventually become either non-functional (depending on how the satellites and individual handsets are designed) or increasingly inaccurate until no longer useful.
> If it were no longer possible to upload that data the system
> would eventually become either non-functional (depending on how
> the satellites and individual handsets are designed) or
> increasingly inaccurate until no longer useful.
It is, after all, now computed on the ground and uploaded to the GPS constellation, having it be provided by the satellites is just a convenience, not a necessity.
Perhaps Bluetooth LE and beacons will eventually allow more accurate elevation info.
Many countries in these days try to build their own alternative to GPS, or in this example a extension for it. This for sure makes the location mor accurate and the systems are independant from the united states.
On the other hand for instance mobile phones have to implement all these systems and this makes them much more expensive and complicated. From my point of view it would be better to build up a universal international system. Yes, and I know this is nearly undoable.
At some point, you need to break up the augmentation systems on a continent/country-wide basis so that you can optimize the satellite orbits to work for you, instead of against you.
Additionally, QZSS seems to be pretty similar to WAAS. I get the feeling it's probably the same sort of system (though I haven't taken a look), so it's likely easy to implement from a GPS chip perspective.