[time-nuts] Handy iPhone app

Oz-in-DFW lists at ozindfw.net
Fri Jul 16 11:52:38 UTC 2010



On 7/16/2010 1:57 AM, Hal Murray wrote:
> lists at ozindfw.net said:
>   
>> Most newer operational standards can't tolerate this and "accurate" time
>> (better than a ms) is important.  WiMAX requires TDD base stations to base
>> station alignment to be better than 1 microsecond.  Most telecom operators
>> want to avoid GPS at every site. It's a logistical PITA. 
>>     
> Does that mean that the time has to match UTC or that all the clocks in the 
> system have to be screwed up by close to the same amount?
>   
The spec is only relative, that is base station to base station not
absolute.  The only practical way to accomplish this is GPS, so as a
practical matter it's GPS time. 

There are a lot of problems with GPS in this application.  Urban
canyons, interference, logistics, indoor use, and politics are all
issues. Oddly enough Iran, China, and even many European countries don't
want critical infrastructure referenced to a US controlled system. 
Telecom systems are increasing moving indoors and this includes
cellular.  It would seem that bolting an antenna outside is no big deal,
but often that is the dominant cost in a low cost application like femto
base stations (those access point sized things that Verizon, AT&T, and
others are selling.)

-- 
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Oz
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