[time-nuts] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement

Magnus Danielson magnus at rubidium.dyndns.org
Wed Sep 29 18:27:04 UTC 2010

On 09/29/2010 07:17 PM, Jeffrey Okamitsu wrote:
> More importantly, does this impose an upper limit on data transport speed over
> networks, in particular wireless networks?

No, not really.

> If and when one produces the network
> technology that would demand the accuracy and precision of these new
> standards, if one object is moving relative to the other, there could be loss of
> data as the moving clock goes out of sync with the stationary one.  We know this
> was possible just from special relativity, but motion at "normal" speeds does
> not contribute appreciably at the currently achievable accuracies and
> precisions.  However, with the next generation, driving in a car or certainly
> flying in a plane will limit bandwidth.  And, of course there's the gravitation
> effect to contend with in the future as well, which could also limit bandwidth.

The imprecision of oscillators being used is so huge that gravitational 
effects is swamped in normal everyday life. You need significant 
elevation such as that of GPS satellites, but much of that effect can be 
treated using frequency offset and the remaining effect involves movement.

> As I am thinking about this, does this impose a limit on GPS accuracy and
> precision based on the next gen technology?

No, gravitational effects is first degree compensated and only a minor 
second degree effect needs compensation for some case. These effects is 
very predictable.

You can always find cases where a particular effect forms a limit, but 
relative theory doesn't form a practical limit for most of the day to 
day life and use of technology.

For the case of telecommunication networks, the receiver will recover 
the symbol rate of the signal in order to sample the symbols and later 
those symbols is converted into bits. That the transmitter and receiver 
has different gravitational potential causes a small offset in 
frequency, but since the receiver PLL tracks the frequency then 
frequency errors due to oscillator offsets, temperature changes, doppler 
effects as one moves around etc.

Doppler effects is much more important, and it's effects is being 
treated regularly, such as when talking in the GSM phone while driving 
the car...


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