
Japan's Plan for Centimeter-Resolution GPS - JamilD
http://spectrum.ieee.org/aerospace/satellites/japans-plan-for-centimeterresolution-gps
======
jccooper
If anyone's wondering about the orbit, it's a geosynchronous but not
geostationary orbit.

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](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:

[http://en.wikipedia.org/wiki/Molniya_orbit](http://en.wikipedia.org/wiki/Molniya_orbit)

~~~
rdtsc
> It's a bit inspired, I think, by the Molniya orbit, another technique to get
> long-duration high-latitude overflight:

Isn't it closer to the Tundra (Тундра [in rus]) orbit?

[https://en.wikipedia.org/wiki/Tundra_orbit](https://en.wikipedia.org/wiki/Tundra_orbit)

Found a video showing the difference in ground tracks between the two:

[https://www.youtube.com/watch?v=Yo9rFmfX42Q](https://www.youtube.com/watch?v=Yo9rFmfX42Q)

~~~
jccooper
It _is_ a Tundra orbit. Both are pretty clever, but the Molniya is more famous
--being older and more used.

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.

------
dalek2point3
Very interesting. Actually, something similar happened in the US back in 2000,
when Clinton turned off something called "Selective Availability" in the US.
This program deliberately degraded civilian GPS signals. After SA was turned
off, we went from a GPS system that was accurate to a football field-type area
to one that is accurate to a tennis-court ish area.

Read more:
[http://www.gps.gov/systems/gps/modernization/sa/](http://www.gps.gov/systems/gps/modernization/sa/)

~~~
mkempe
I don't understand these units of measurement. Football-field GPS was 4 times
less accurate than tennis-field GPS? your reference indicates that uncertainty
was 45 meters and became 6.5 meters, one order of magnitude improvement.

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.

~~~
jws
Wolfram Alpha says:

    
    
      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
    

It's pretty close.

(A volleyball court would be closer at 162m^2.)

------
gorloth
This seems to be similar to the usage of WAAS in the US
([http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System](http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System)),
just on a smaller geographic scale. One of the bigger sources of error in GPS
today is due to various atmospheric effects that bend the signal and increase
the signals propagation delay. A ground stations in a known position can
generate correction for the errors but the farther it's from the ground
station the less useful the correction is. I've seen GPS systems used in
farming applications that use a local tower that can provide corrections to
give a very accurate position for the local area.

~~~
ghshephard
Back in 1995 I wrote the mapping software for a "Tundra Tracker", this was the
navigation software for a supply vehicle that could navigate in the arctic in
whiteout conditions. The idea was to have someone drive a path while
conditions were good, and we would then lock in all the waypoints. Rather than
store all the waypoints for the path, we were able to eliminate about 99% of
them with various splining algorithms.

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.

------
dfc
GPS is a misnomer, it should be JPS, Japan Positioning System, nothing global
to see here folks. It is unfortunate that the article does not stress that
this system is only useful in Japan; especially with the conclusion that many
nations will be watching the results given the "range of promised applications
_[range of use, certainly not geographic range]_ and relatively low cost."
That being said I am interested to see how the experiment with atomic
clockless birds goes. One of the most overlooked features of GPS is time
transfer.

~~~
MrUnderhill
Well, only sort of: GPS is the initialism for a specific system (and QZSS
provides corrections for that particular system's satellites, among other
things), not a generic term for global navigation satellite systems. Had it
said "Japan’s Plan for Centimeter-Resolution GNSS", it would have been
different. Europe has EGNOS, which is similar (and was recently granted €1.3
billion for upgrades), the US has WAAS, and India has something similar too
[1][2].

[1]
[http://en.wikipedia.org/wiki/Indian_Regional_Navigational_Sa...](http://en.wikipedia.org/wiki/Indian_Regional_Navigational_Satellite_System)
[2] [http://en.wikipedia.org/wiki/GAGAN](http://en.wikipedia.org/wiki/GAGAN)

~~~
dfc
"Well only sort of" what? Yes, "GPS is the initialism for a specific system"
and G is the initial for _Global_. The G in GNSS is also _global_ so I am not
sure how that is any different. The article is titled "Japan's Plan for
Centimeter-Resolution GPS" and then goes on to describe a system that is
anything but _global_.

~~~
swatkat
GNSS is a generic term for globally available satellite navigation system. GPS
is a GNSS implemented and maintained by the USA. Japan is planning to launch
thier own satellites as part of QZSS program, to augment this GPS coverage
over Japan. GPS receivers in Japan can make use of these "local" sats along
with American sats for more accurate positioning.

~~~
dfc
This system is _not globally available._

------
ersii
I'm having trouble understanding the practical consequences of this project.

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.

~~~
dfc

      > GPS doesn't need a constant feeding of data from ground stations 
    

This is not the case. USNO steers the clocks(4x) on the satellites. I think
they do this via the AF but I have always been a little uncertain of the exact
method:

    
    
      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]
    

One of the reasons for JPS's need for direct contact with ground stations is
that the newer satellites do not contain the any rubidium frequency standards
and use an experimental time synching system.

[^1]:
[http://tycho.usno.navy.mil/gpstt.html](http://tycho.usno.navy.mil/gpstt.html)

~~~
rasz_pl
W T F??? Why wouldnt they include rubidion clock on sats? Its at most $10K
expense on something costing tens of millions to launch.

Does this mean GPS will stop working when Zombies/Pandemic/whatever strikes
and wipes out US military?

~~~
dfc
The majority of GPS satellites do not have one rubidium clock on board, they
have four. For a discussion of the experimental time sync system planned for
QZSS see:
[http://web.archive.org/web/20130411122243/http://unsworks.un...](http://web.archive.org/web/20130411122243/http://unsworks.unsw.edu.au/fapi/datastream/unsworks:4274/SOURCE02)

I am curious before reading my comment did you think that GPS would continue
to work without navy.mil and af.mil?

~~~
rasz_pl
Hell yes I did. Whole point of Rubidium clocks is you dont have to correct
them.

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 :)

~~~
sliverstorm
Or you could learn to use a map and compass. I know, I know, antique and all
that, but reliable.

~~~
dfc
That is going to take the party out of Tactical Air Control Party.

------
vdm
[http://en.wikipedia.org/wiki/GNSS_augmentation](http://en.wikipedia.org/wiki/GNSS_augmentation)

------
pixelcort
Having moved to Tokyo last year, I'm really hopeful for more accurate altitude
data. Much of Tokyo is under and above ground level, and I wish the altitude
data were accurate enough to determine which floor I'm on.

Perhaps Bluetooth LE and beacons will eventually allow more accurate elevation
info.

------
Rusky
Wow, I didn't know GPS technology was even capable of that accuracy. It would
be interesting to see it used in augmented reality as well as the examples
from the article. You could actually have shared virtual objects positioned
out in the world.

------
coldcode
If you combined cm accuracy in cell phone tracking and a armed quadcopter, and
hacked the phone company, you could build a handy remote killing device.

------
bitL
I hope they are going to improve precision of elevation as well, not just
longitude and latitude.

~~~
GregorStocks
The article says it has 2.9 centimeter vertical resolution.

------
joushx
What a wonderful example for the "standards" xkcd:
[https://xkcd.com/927/](https://xkcd.com/927/)

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.

~~~
dfc
This has nothing to do with that XKCD comic. Did you read the article? This
system is not "independent of the US," it _augments_ the GPS system.

~~~
joushx
Yes. Did you read my comment? "[...], or in this example a extension for it"

