Radio based triangulation(Any electrical engineers about?)

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ladajo
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Post by ladajo »

Any links, I've really never seen any GPS get lower than 1 meter precision, and unless they switch to signal processing in place of clocks they simply physically can not with today's atomic clock tech.
I can not speak to this at any more detail in this forum. But in short. Yes and Yes. The clocks you see are exactly that, what you see. The processing you do not see is also exactly that, what you do not see.
The next Gen is not publically visible yet. Sorry, no links.

In your application, why do you need mm accuracy? Can you go with cm accuracy?

You could look at using multiple transmitters, out of phase, and thus simplify your receiver phase processing while improving accuracy.

How many objects are you trying to geolocate simultaneously in this 100m3 space? Set number or infinite?

bcglorf
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Post by bcglorf »

Aero wrote:I looked at the Cricket system - position locating receivers inside an instrumented building is something different to me. I don't have any experience with it.
It's a deceptively tricky problem when you want multiple devices with high accuracy and at a high polling frequency. The cricket gets a lot of that, but because it's using ultrasound it is accuracy drops quickly with distance and environment, and even with those perfect is still in the cm range. That might be able to get tightened down with improvements, but still only under ideal conditions and there are a lot of applications that need to fall outside 'ideal'.

The biggest thing I don't have a clue about myself is how precise and consistent a radio receiver can be. If you've got 3 receivers side by side listening to the same signal, what level of precision can you get from the receivers. Can the three signals be accurate within milliseconds of each other, nanoseconds or picoseconds? If picoseconds is feasible, I might be in business. If it's milliseconds, then ultrasound is the only game in down and I suck it up or build a better radio.

bcglorf
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Post by bcglorf »

In your application, why do you need mm accuracy? Can you go with cm accuracy?

Think MIT's efforts at augmented reality off GPS, only not just a gimmick but actually working as imagined. For real-time head and pointer tracking the difference between cm and mm gets big very fast.

How many objects are you trying to geolocate simultaneously in this 100m3 space? Set number or infinite?

More towards the infinite end. A couple hundred opens up a lot of opportunities, but I could easily envision making use of 10k plus.

Tom Ligon
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Post by Tom Ligon »

When I was a boy (cough, hack) I worked on an Omega Navigational System for Litton. How good was it? Well, when it was working well it could get you within sight of your destination airport over most places in the world. When not working so well, uh, the Boeing 747 airliner KAL007 was using one when it strayed in to Soviet airspace and was shot down.

Omega was originally intended for ships, and used analog phase relationships described in the original post. However, it worked in the audio frequency ranges, VLF. The lowest of the three frequencies was 10 kHz. Thus, the wavelength was so long as to make the errors out of reach for the intent of the original post.

But I think it shows the approach is not without merit, at considerably higher frequencies.

GPS can be used in conjunction with local reference transmitters to achieve sufficient accuracy for measuring movement of tectonic plates. However, even with DGPS technology, you need long-term averaging to get this precision. They routinely get results with accuracies of a few inches using dual-band equipment such as Novatel receivers.

http://en.wikipedia.org/wiki/Omega_(navigation_system)

bcglorf
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Post by bcglorf »

Maybe a simpler question as it relates to my problem.

Can you mirror the phase change trick used by laser range finders to measure the length of loop of wire with an electronic wave? Can you simply send a sine wave and modulate it at a frequency then compare the source signal to the return signal at the end of the loop by putting both into a multiplier and measuring the result? If you can, how precise can you get a result from that kind of setup?

ladajo
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Post by ladajo »

The accuracy depends on how many phases you intend to compare. But use of phase is an old trick with many applications.

Think of each phased "device" as a seperate ranging device. The more ranges from more angles, reduces your AOU with each one added.

With synch'd transmitters and a phase discriminating reciever, you should be able to dial down your uncertainty elipse. But the receiver will not be cheap.

Telecom has used phase for compression for a while. No reason you can't use it for ranging. At the end of the day it is all about the clock. Each wave cycle at a minimum gives you 4x freq. Up cycle, peak, down cycle, min. With better gear you can also get min, min-to-up, mid-up, up-to-peak, peak, peak-to-down, mid-down, down-to-min. That is freq x8. It can be carved up even more, but I think that will exceed your costing per rcvr.

Diogenes
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Post by Diogenes »

bcglorf wrote:Maybe a simpler question as it relates to my problem.

Can you mirror the phase change trick used by laser range finders to measure the length of loop of wire with an electronic wave? Can you simply send a sine wave and modulate it at a frequency then compare the source signal to the return signal at the end of the loop by putting both into a multiplier and measuring the result? If you can, how precise can you get a result from that kind of setup?
Time Domain reflectometer. Fluke makes them.
‘What all the wise men promised has not happened, and what all the damned fools said would happen has come to pass.’
— Lord Melbourne —

Diogenes
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Post by Diogenes »

ladajo wrote:The accuracy depends on how many phases you intend to compare. But use of phase is an old trick with many applications.

Think of each phased "device" as a seperate ranging device. The more ranges from more angles, reduces your AOU with each one added.

With synch'd transmitters and a phase discriminating reciever, you should be able to dial down your uncertainty elipse. But the receiver will not be cheap.

Telecom has used phase for compression for a while. No reason you can't use it for ranging. At the end of the day it is all about the clock. Each wave cycle at a minimum gives you 4x freq. Up cycle, peak, down cycle, min. With better gear you can also get min, min-to-up, mid-up, up-to-peak, peak, peak-to-down, mid-down, down-to-min. That is freq x8. It can be carved up even more, but I think that will exceed your costing per rcvr.
Not to intrude, but Trimble makes equipment which comes the closest to doing what he was asking for. I daresay they are the foremost leaders in this sort of technology. I have personally seen (and worked on) a trimble system which uses a gps portable base with additional transcievers that are used to increase the accuracy of surveying operations down into the inch range or so.

Over the Horizon millimeter accuracy is not something that I think is feasable with radio technology. Over the Horizon requires wavelengths longer than a meter, and millimeter accuracy requires wavelengths shorter than a millimeter: Two mutually exclusive requirements. (Short wavelengths will not "bend" over the horizon. They propogate in straight lines the way light does. )


http://www.trimble.com/
‘What all the wise men promised has not happened, and what all the damned fools said would happen has come to pass.’
— Lord Melbourne —

Mikemcc01
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Post by Mikemcc01 »

bcglorf wrote:
ladajo wrote:GPS is all about the clocks. The atomic synch clocking is how the trangulation is determined. This is some other stuff that goes into it to account for atmospherics, frame drag, and what not, but the core idea is that you know when the signal is sent (encoded in the signal), and you know the timing offset of when you recieve it. Thus the Delta gives you the distance. Three distance arcs give you a position. The other magic of the system is in that the satellite positions are kept in an almanac, and courtesy of Kepler, we know the bird positions, the atomic clocking gives the distances, cut the arc intersects, and viola, you know where you are in 4D. Simple, and silli-accurate. The accuracy is a primary function of the clocks.

In you system, it would be possible to do something similar. It is a multi-static radar application. If you encode the transmission timing into your emitted signal, developed a way to seperate tranmitted pulse from reflected (timing estimates), and then used your multiple recievers (also clocked), you could certainly easily track object position in your monitored space volume.

When you say you are line of sight limited, what do you mean?
Also, there is another means to develop tracking information from "reverb" reflections in a volume, but that is math and horsepower heavy. It can, and has been done though.
The clocks are the trouble. Even the absolute fastest clocks you can get still allow light travel nearly a meter between ticks. Laser range finders, the millimeter accurate ones, don't use clocks or oscillators to measure time, they modulate the laser at a high frequency, and use THAT to measure time over shorter bursts than any clock in existence.

I am basically looking at GPS, but without the clocks. I want mm accuracy, and clocks don't cut it then.
What I'm really wanting is a GPS like device to track location in real-time with mm accuracy, ideally one that isn't hindered by environmental obstacles. MIT has basically what I want, but it uses ultrasound making it's accuracy very dependent on environment, and inherently less accurate than I really want too.

I am thinking of transmitting a radio signal with a modulating signal ala laser range finders. Then the trick is how can a remote device see that signal, and figure out TOF. If 3 receivers each see the signal, I can compare each signal and pick out how much longer the signal traveled to each receiver, but not the total flight time. I'm just wondering if i can work that backwards to get the original signal(I think that's doable, and pretty straightforward at that). I'm more wondering if there's any problems in receiving a radio signal with precision and accuracy I'm going to need.

Finally, in the event that it should all work, why can't I find anyone that's already using it? GPS could easily be running with 100-1000X the accuracy it is now.
If there is an easy way to improve on even the mil-spec GPS receivers I'm pretty damned sure the US DoD would be using it. That they don't speaks volumes on affordability of the techniques to improve accuracy of the mil GPS work too.

For most civ survey work (such as done by the UK Ordnance Survey (worlds greatest maps by a LONG way!) is done using differential GPS (http://en.wikipedia.org/wiki/Differential_GPS).

If anyone knew how to seriously improve on GPS then they would probably keep schtumm because of the usefulness for such information in weapons tech. Even if they didn't attact attention from the folk wanting such tech, they probably would gain the attention of folk trying to prevent the dissemination of such tech.

Mikemcc01
Posts: 19
Joined: Tue May 03, 2011 10:23 am

Post by Mikemcc01 »

Diogenes wrote:
ladajo wrote:The accuracy depends on how many phases you intend to compare. But use of phase is an old trick with many applications.

Think of each phased "device" as a seperate ranging device. The more ranges from more angles, reduces your AOU with each one added.

With synch'd transmitters and a phase discriminating reciever, you should be able to dial down your uncertainty elipse. But the receiver will not be cheap.

Telecom has used phase for compression for a while. No reason you can't use it for ranging. At the end of the day it is all about the clock. Each wave cycle at a minimum gives you 4x freq. Up cycle, peak, down cycle, min. With better gear you can also get min, min-to-up, mid-up, up-to-peak, peak, peak-to-down, mid-down, down-to-min. That is freq x8. It can be carved up even more, but I think that will exceed your costing per rcvr.
Not to intrude, but Trimble makes equipment which comes the closest to doing what he was asking for. I daresay they are the foremost leaders in this sort of technology. I have personally seen (and worked on) a trimble system which uses a gps portable base with additional transcievers that are used to increase the accuracy of surveying operations down into the inch range or so.

Over the Horizon millimeter accuracy is not something that I think is feasable with radio technology. Over the Horizon requires wavelengths longer than a meter, and millimeter accuracy requires wavelengths shorter than a millimeter: Two mutually exclusive requirements. (Short wavelengths will not "bend" over the horizon. They propogate in straight lines the way light does. )


http://www.trimble.com/
For OTH, think closer to a resolution of kilometers+. OTH works by surface transmission or ionispheric reflection. Neither or which work at sensible wavelengths.

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