Radio based triangulation(Any electrical engineers about?)

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bcglorf
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Radio based triangulation(Any electrical engineers about?)

Postby bcglorf » Fri Jun 10, 2011 8:42 pm


D Tibbets
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Postby D Tibbets » Sat Jun 11, 2011 12:46 am

To error is human... and I'm very human.

bcglorf
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Postby bcglorf » Sat Jun 11, 2011 1:17 am

Do laser range finders use phase change to measure distance? I thought it was a simple time of flight there and back again.

Both. :)

Time of flight measurements would seem more straight forward. Either radar, returning a round trip pulse, or atomic clocks on the sender and receiver that are calibrated should serve.

The clocks are the trick. Light is of course stupidly fast, so if you want millimeter precision on a time of flight calculation for something like light, synched atomic locks just don't cut it. You need sub pico-second accuracy.

The way laser ranger finders get around this are two-fold. First, the light is sent and received from the same spot, so no need for synching. Secondly is the phasing. By modulating the laser signal at a very high frequency, you can compare the phase of the light coming back to the phase you are currently sending and thus measure smaller time slices than any oscillator can manage.

The trick is I have applications where line of sight is too limiting. So on to radio waves. The transmitter sends a signal that's oscillating at some frequency to be read at each receiver. The receivers then will each have three signals offset by the difference of time of flight to each of them. I'm wondering if you can compare those signals the way a laser range finder does and get out a useful distance measurement that can be used for accurate triangulation...

I'm sure the GPS guys will have considered this though, and my guess is something about the radio signal processing hoses the idea, but I really want to know what it is. The applications for it are just really tempting.

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Postby ladajo » Sun Jun 12, 2011 12:23 am


bcglorf
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Postby bcglorf » Sun Jun 12, 2011 1:03 am


D Tibbets
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Postby D Tibbets » Sun Jun 12, 2011 1:53 am

To error is human... and I'm very human.

bcglorf
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Postby bcglorf » Sun Jun 12, 2011 2:43 am


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Postby Aero » Sun Jun 12, 2011 3:06 am

Aero

bcglorf
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Postby bcglorf » Sun Jun 12, 2011 3:26 am


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Postby Aero » Sun Jun 12, 2011 5:05 am

Aero

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Postby bcglorf » Sun Jun 12, 2011 1:04 pm


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Postby ladajo » Sun Jun 12, 2011 2:50 pm


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Postby Aero » Sun Jun 12, 2011 8:47 pm

Aero

bcglorf
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Postby bcglorf » Sun Jun 12, 2011 10:44 pm

The timing issue as stated is handled by Atomic clocks. These colocks are silly accurate, and keep the entire system in synch.

Yep, the problem is my application needs better than silly accurate, I need an impossibly accurate clock. Not even the most expensive atomic clocks available right now go much past a billion ticks per second, I need 300 billion.

The next generation of GPS on the boards right now, (at MIT ironically for you) is even another leap in accuracy. I recently got a look at it in conjunction with a seminar by arguably the smartest guy in the world on GPS. It involves clock improvements again, as well as signal processing.

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.

How big is the monitored space?
100 cubic meters would work well enough.


How fast (often) do you need updates?

60 per second minimum(reliably), but the more the better.

What are your issues with Line of Sight?
It needs to work as a wearable device in a building with plenty of walls and moving objects.

It is accurate because the clock errors are eliminated by using the same clock for signal transmission and signal reception.

Hmmm, I thought it was like laser range finders where in essence the signal IS the clock. My idea is right out if you can't do something similar with radio or other em waves.


I am basically looking to eliminate the clock errors by letting the clocking in essence be in the signal. My first receiver only knows it's got a signal. The second further on uses that as a base signal, and compares it to what it see's itself to know how much further/closer it is relative to the first. Then repeat for as many receivers as needed to get out something accurate.

If I understand correctly, the distance between receivers is much, much less than the distance to your transmitter. If that is the case, go back up-thread and read the reference on GDOP to understand why that won't work with any reasonable tech.

My receivers would absolutely be much, much closer. That has been used though in other location systems, MIT's cricket does it and gets good results still. Are you seeing problems with accuracy errors being multiplied?

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Postby Aero » Sun Jun 12, 2011 11:37 pm

Aero


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