[time-nuts] Fundamental limits on performance
Lux, Jim (337C)
james.p.lux at jpl.nasa.gov
Sat Sep 19 14:35:32 UTC 2009
On 9/13/09 3:54 PM, "Magnus Danielson" <magnus at rubidium.dyndns.org> wrote:
> Magnus Danielson wrote:
> One aspect of why synchronous data and carrier may be worth pointing
> out. If the carrier and modulation is asynchronous, then the carrier
> tracking and data reception needs to recover their respective clocks
> independently. However, by transmitting them in a synchronous fashion
> and making use of this fact at the receiver, then the carrier tracking
> can aid the code tracking in which case the code tracking only need to
> retain the phase, which leaves more margin to propperly decoding the
> message. Thus, a better BER is achieved for the same S/N or for that
> matter, a worse S/N can be tolerated for the same achived BER compared
> to the asynchronous modulation technique.
As in GPS, for instance, where chip rate is related to carrier frequency.
> Anyway, the questions you are asking have been covered before. It should
> come as no suprise that Dr. Simon was (is?) with JPL.
Marv Simon is still at JPL..
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