Centimeter-Resolution GPS For Smartphones, VR, Drones

agent elevator writes: UT Austin engineers have come up with a software fix that corrects for the errors GPS has when using the tiny antennas on smartphones. They demoed it using a VR setup and got 2-cm accuracy. For now it runs on a separate processor from the smartphone, but they say they'll fix that. The demo appears to have been done on a rooftop. VR. Outside. On a roof. Doesn't seem like a good idea, does it?

Comments

Corrects multipath problem.

[140Mandak262Jamuna]

The cell phone GPS antennae are tiny they catch the signal from the satellite and also many reflections. These reflections confuse the processor trying to fix the distance between itself and the satellite. They seem to have developed some signal processing algorithm that would remove these reflections. The article is skimpy on details.

Re:Corrects multipath problem.

[Gen-GNU]

The link in the article, to here, gives a much better description of the SP algorithm. In fact, it's a much more informative article, but it doesn't have a picture of a guy with a cell phone strapped to his face.

Re:Corrects multipath problem.

[Anonymous Coward]

The key thing is that cm level positioning is only possible using differential techniques. You need a receiver at a fixed position and you then correlate the carrier phase measured by your mobile receiver to your fixed receiver. This is a technique known as carrier-phase differential positioning.

The problem is that carrier phase techniques are extremely sensitive to signal degradation - particularly multi-path signals (reflections from the ground/buildings/etc.) The conventional "code phase" technique is, in contrast, reasonably resistant to such signal degradation.

The problem then with carrier-phase techniques is that you need a good antenna. Traditionally, this technique has been restricted to survey grade equipment, in order to be able to track the phases accurately and resolve any ambiguities in the phase measurements (which can be huge in a multipath situation). This becomes much harder with lower quality patch antennas, and essentially impossible with a smartphone grade antenna (10 minute ambiguity resolution times using conventional techinques).

The paper described a combination of 2 techniques: 1. attempting to resolve phase ambiguities for each individual pair of carriers (satellite signals), something previously reported and 2. adding small random wavelength scale motion to the antenna, which can then be correlated to the carrier phase residuals in order to speed ambiguity resolution. The authors present data showing that by using these techniques, the phase differential ambiguity can be resolved, even with a smartphone antenna, within 20 seconds.

Re:Propagation delay

[heypete]

Nope, SA is turned off even in war zones, in fact the newest birds don't even have the SA feature.

True, Selective Availability is disabled or otherwise not available on the new satellites, but the government still retains the ability to deny GPS on a regional basis.

See :

"Why are you turning [SA] off?
A. The decision to end the degradation of civil accuracy on a global level was made by the President based on a Secretary of Defense recommendation coordinated with all applicable departments and agencies. This decision is based on the U.S. military commitment to develop and employ technologies to deny the civil services of GPS on a regional basis. Under this approach, it will be possible to deny GPS to potential adversaries in areas of operations while preserving the peaceful use of GPS services outside those areas"

That said, civilian GPS receivers are often quite a bit better, more handy, and more advanced than military ones and a lot of soldiers use them in combat areas. Sure, the military ones are more rugged and get the encrypted military-only channel with better accuracy, but sub-meter accuracy is only really needed for smart bombs and the like. It's less useful for driving a Humvee down the street somewhere or finding out how to get back to base. Handheld civil GPS receivers are typically accurate down to the 3-5 meter range, which is only slightly worse than the military ones.

Denying civil GPS signals in certain regions would almost certainly make things worse for US soldiers, so it's extremely unlikely that the military would ever do regional denial of civil GPS except in the most extreme situations. Even then it'd have limited effect because GLONASS (Russian), Compass (Chinese), and Galileo (EU) are or will soon be perfectly viable alternatives that bad guys could use for guidance.

Nice...

[Anonymous Coward]

if you are on a rooftop.

I have made my diploma in geodesy and if it would be so easy to get 2 cm with smartphone everywhere then it would be rolled out already. What they are showing is known and realized for like 6 years already, so nothing new. The positions problems will still persist on street level where like 99% of all peoples move and cars drive? The problem is not the antenna its the signal interruptions and multi-path reflections you have on the streets that you cannot simply fix with software as the amount of unique signals is limited.

It will actually be fixed by more satellites integrated into one software equalization equation and different signal modulation.
The first is taken care of by the GPS race between all superpowers entangled in it. By 2018 we will have around ~100 GP(S) Satellites in stationary or modular orbits. The only limiting factor here is the software of vendors which has to align and process the public signals GLONASS (RU), GALILEO (EU), GPS (US), BEIDU (CHINA), Indian and Japan signals. Which no one does atm, it is done at university level (for instance german TU Dresden).

The second one could improve position but just if all countries involved in GPS development and evolution would work together but actually they are not. Instead they compete for the frequencies ...very retarded game but that's another story.

What people need to understand is that most position software out there barely manage to get a better position out of GPS + GLONASS. There is nearly non that handles the four major systems because even these systems have, based on different earth models, different results for the same position.

The actual paper

[Anonymous Coward]

https://radionavlab.ae.utexas.edu/images/stories/files/papers/ion2014Pesyna.pdf