On 1/31/13 8:37 PM, Rick Harold wrote:
To time experts/EE's.
I would like to triangulate a position of a device which moves using 3
fixed positions devices of known location.
The idea is to have these operate on 915mhz or 434mhz or 2.4ghz or
appropriate frequency.
These two type of devices (fixed and mobile) are all under my control and
thus customized as needed.
The mobile device (not a phone, custom device) would be the least expensive
item. I'd like a range of 150 feet or better and accuracy of 3 feet or
better.
When manufactured these items they can be calibrated in order to adjust for
any variation in IC's, discrete components etc...
We can assume for now the temperature is constant 70 degree temperature.
Cost is the key design factor.
Don't do "pinging" and time of flight. Do phase measurements. At 900
MHz the wavelength is 33cm. Essentially rather than trying to ping,
you're measuring the positions of multiple zero crossings averaged over
some amount of time.
Can your "base stations" be interconnected so they can share a common
reference signal?
What position accuracy do you need? How big an area?
Can you initialize at a known position and then track, or do you need to
come up cold?
There's a lot of clever schemes that use multiple frequencies from a
common source to disambiguate phase: e.g. if I measure phase at 908 MHz
and phase at 928 MHz, I can effectively also measure phase as if I were
radiating at 20 MHz, so that gives me coarse position (out of 15m
wavelength) and fine position (out of 33cm wavelength)
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