[time-nuts] Timing Distribution in Mountainous Terrain

jimlux jimlux at earthlink.net
Fri Sep 10 05:04:25 UTC 2010

Ralph Smith wrote:
> O
> We are not syncing time slots for communications. The timing requirement
> is for determining aircraft position by multilateration. Timing errors
> translate into position uncertainty.
>> What's your carrier freq?  In mountainous regions you'll probably have
>> better luck at the lower end.  Please tell me you're not trying this at
>> GHz freqs at higher, rocky elevations. 
> Signal emitted by the aircraft is 1090 MHz, pulse-position modulated
> transponder squitter (Mode C/Mode S). Radio stations receive signal,
> determine time of reception, and forward the timestamped transmission via
> landline to a central facility for correlation and position determination.

and presumably, you have only one interrogation transmitter, and many 
listeners? (otherwise you could pulse each one in turn and essentially 
get a set of 2 way ranges to solve with)

I realize you're trying to do multilateration.. BUT, if you measure 
angle of arrival too, then you can throw that into the solution, and you 
can tolerate a greater uncertainty in the range measurement.

There's also the whole "using physics constraints"... combine multiple 
measurements, and model the vehicle dynamics.

You've basically got a "make a bunch of measurements and combine them, 
hoping to get a root(N) improvement" problem.  As you've noted, to get 
from 1000 ft to 30 ft requires a 30 fold improvement, implying a 1000 
measurements.. Yow..

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