
GPS Tracking Down to the Centimeter - lolptdr
http://ucrtoday.ucr.edu/34932
======
mojoB
I think this is a little misleading. The IEEE paper is about a reducing the
computational effort for a filtering technique (Contemplative Real-Time)
developed by one of the authors, which seems to be published here [1].

The original paper in compares the CRT approach to a more traditional Extended
Kalman Filter (EKF) approach. The EKF is very efficient but it does trade of
some accuracy, because it requires a linear approximation of the system to be
used. Both the CRT and EKF are used to blend or fuse inertial measurement data
with GPS.

To achieve the claimed centimeter-level accuracy requires a local (within ~20
miles) base station and a data connection to the base station to achieve the
levels of accuracy being discussed. Depending on the quality of the GPS
receiver there will be a few seconds up to 10s of minutes convergence period
for the GPS filters to initialise.

The results presented in [1] show that using a moderately expensive (dual
frequency, code tracking) GPS can approach (not exceed) the accuracy of a
high-end GPS (dual frequency, code and carrier phase).

In summary, this is a interesting incremental improvement, not a huge
breakthrough that's going to bring centimeter accuracy to cell-phone GPS
tracking.

[1]
[https://scholar.google.com/citations?view_op=view_citation&h...](https://scholar.google.com/citations?view_op=view_citation&hl=en&user=VPWEu7YAAAAJ&citation_for_view=VPWEu7YAAAAJ:4TOpqqG69KYC)

~~~
madaxe_again
In addition:

"Farrell said these requirements can be achieved by combining GPS measurements
with data from an inertial measurement unit (IMU) through an internal
navigation system (INS). In the combined system, the GPS provides data to
achieve high accuracy, while the IMU provides data to achieve high sample
rates and high bandwidth continuously."

I'd call that centimeter accurate _positioning_ , but still metre resolution
GPS.

Either way, it's a potentially useful advance.

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airesQ
Skimming through the article this looks like better signal processing coupled
with the usual sensor fusion (from accelerometers and other sensors).

My knowledge of location systems only extends so far, but from what I know 3G,
4G and WiFi have not introduced anything particularly remarkable here. Wifi
APs and various BSs are used as beacons (a la Skyhook), but their role doesn't
extend much beyond that.

Anyway, there is still hope that 5G or some IEEE standard will make a
difference here. They could perhaps provide something akin to a ground
satellites, maybe at a very low frequency (to get past obstacles), or/and
perhaps using UWB (helps with multipath, TOA determination). And then maybe we
would have zeroish-time-to-fix, indoor-location on cheap, low-power devices.

~~~
mojoB
Do you have any references for the ground-satellite abilities for 5G? I
couldn't turn up anything on Google.

Locata [1] has been in the high-end space for a while. I had heard of a lower-
end approach too, though the name escapes me, and they were only getting
~50cm.

Edit: The other one I was thinking of was decaWave [2], they claim 20cm in 2
dimensions.

[1] [http://www.locata.com/technology/locata-tech-
explained/](http://www.locata.com/technology/locata-tech-explained/)

[2] [http://www.decawave.com/technology](http://www.decawave.com/technology)

~~~
airesQ
I would like to see some location improvements in 5G, but I've no idea on
whether or not they will be there. (The little I've heard on 5G has been from
non-technical types, always as a buzzword).

From my limited knowledge it would nice if they provided a signal somewhat
similar to GPS. Perhaps at a low frequency, as to avoid reflections and
attenuation (or just a UWB signal). The main advantage of having this together
with 5G would be deployment, we would piggyback a location system on top of
5G.

Back to your comment, I did know about DecaWave, but not Locata.

Locata looks interesting, it really does seem like GPS brought to earth. One
good thing about GPS type systems is how well they scale. The satellites just
provide the signal, they don't even have to know how many receivers are out
there. (Also good from a privacy standpoint.)

DecaWave system is loosely based on IEEE 802.15.4a, which uses UWB. I think it
does two-way ranging (basically a very precise ping). And since they use UWB,
their system seems to be quite resilient to multipath.

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Havoc
Some pretty clued up comments on the reddit page as well...along with the
usual noise.

[https://www.reddit.com/r/technology/comments/45jd4r/scientis...](https://www.reddit.com/r/technology/comments/45jd4r/scientists_find_a_new_technique_makes_gps/)

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yousifa
See: [http://swiftnav.com](http://swiftnav.com)

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deutronium
They note 'In this paper, all GPS measurements are assumed to be processed
differentially',

I assume you couldn't get centimeter accuracy without DGPS?

~~~
eps
You can get a _millimeter_ accuracy without DGPS, but you need several hours
worth of signal for a single spot.

This is not a new tech (or a math rather), it's been around since the early
90s if not longer, and it has interesting practical applications like
measuring dam movements.

~~~
mojoB
Dam monitoring systems use DGPS, one receiver on the wall, the other nearby.

Without a local reference station, atmospheric and ionospheric disturbances
would totally overwhelm the effect they are trying to measure.

This [1] covers it quite well.

[1]
[http://pasadena.wr.usgs.gov/office/hudnut/SRL/](http://pasadena.wr.usgs.gov/office/hudnut/SRL/)

~~~
eps
Sure thing, that's the simple way :)

It was in mid 90s, but I can guarantee you that I sat next to a math PhD guy
who worked exactly on what I described, including the dam deployment. Single
receiver, 3mm precison from 3-4 hours of data, no DGPS. This wasn't in the US
though.

~~~
xemoka
And before selective availability[0] was turned off? So did he have military
GPS equipment and not consumer grade?

[0]
[http://www.gps.gov/systems/gps/modernization/sa/](http://www.gps.gov/systems/gps/modernization/sa/)

~~~
jevinskie
Very interesting data. It was cool to notice some graphs had much higher
variability and then notice that they were all sites that are far from the
equator. Then the article helpfully explained precisely why they had more
variance!

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jevinskie
Please, can somebody explain these integers that are being resolved? The paper
is behind a paywall and the article, of course, offers no clarification. I am
almost sure the author of the article has not read the paper for themselves.

~~~
deutronium
You can grab the paper here -
[https://www.researchgate.net/publication/286498140_Computati...](https://www.researchgate.net/publication/286498140_Computationally_Efficient_Carrier_Integer_Ambiguity_Resolution_in_Multiepoch_GPSINS_A_Common-
Position-Shift_Approach)

~~~
jevinskie
Very cool, thank you very much! ResearchGate seems very interesting. I
requested an account and am awaiting verification.

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dang
Url changed from [http://gizmodo.com/a-new-technique-makes-gps-accurate-to-
an-...](http://gizmodo.com/a-new-technique-makes-gps-accurate-to-an-
inch-1758457807), which points to the phys.org copy of this university press
release.

~~~
Gibbon1
I skimmed that paper... math is hard.

I kinda wonder if the path created by the inertial system is being used to
correct the sequence of GPS derived points. Reason being the inertial systems
error is tiny, but cumulative over time. Where the GPS error is large per
measurement but tiny when averaged over a set of geographically spaced points.

You have two errors, plain noise that causes the position at a particular
location to vary. And a location/time[1] specific error that is an offset. If
you know the shape of your path precisely then you can rectify both.

[1] Location due to interference of things like trees, buildings, etc. Time
because the positions of the satellites changes over time.

