[time-nuts] Fundamental limits on performance

Marco IK1ODO ik1odo at spin-it.com
Sun Sep 13 12:28:45 UTC 2009


At 06.51 13/09/2009, you wrote:


>In the deep space exploration biz, we've been talking about time and 
>frequency transfer between spacecraft. It's pretty easy to figure 
>out what the "Shannon limit" for the link between the spacecraft is 
>(given power transmitted, antenna gain, etc... And with coding, we 
>get within tenths, if not hundredths of a dB of the limit)...
>
>So, if I have a clock of some performance on Spacecraft A, is there 
>a "simple" way to say how well I can do transfering that to Spacecraft B?

Jim,

I think you have to translate your arbitrary time resolution in a 
certain number of bits. I don't have the mathematical background to 
develop it further, but it should be feasible. Those that developed 
the GPS in the sixties should had it very clear :-) - here too you 
have great limitations in throughput (50 b/s if I remember it well), 
and the time sync is obtained by code despreading.

Marco IK1ODO




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