[time-nuts] Fw: Cell timing error

Joseph Orsak jorsak at nc.rr.com
Sun Dec 16 02:11:52 UTC 2012


GSM sites do indeed have GPS antennas. But Dennis is correct; all of them 
use GPS for E911 compliance, the GSM standard wasn't up to that task so 
sites have an outboard box (LMU -  Location Messaging Unit) which provides 
E911 Location independent of the actual cell site base station.
By the way - that's where most of the surplus Thunderbolts came from - a 
particular LMU manufacturer ran up against some patent issues and had to 
take a bunch of product off the market.

That said, yes, some, but a very few, GSM BTS's that I'm familiar with use 
GPS as a radio timing source.

Unless your 3G UMTS smartphone has an AGPS chip built in and turned on when 
you dial 911 the system hands down your call to GSM for the LMU to do it's 
thing. Same for 4G LTE, well at this point in the USA anyway, when you make 
any voice call from an LTE device it drops the call down onto the 3G or GSM 
network. I think Korea has LTE VOIP working maybe?

-Joe

----- Original Message ----- 
From: "Dennis Ferguson" <dennis.c.ferguson at gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Saturday, December 15, 2012 8:04 PM
Subject: Re: [time-nuts] Cell timing error


> GSM cell sites in the US have GPS because it is required to
> support E911 positioning.  I'm not sure if it is used for anything
> other than this, but it doesn't have to be.
>
> In some other parts of the world it has been considered bad taste
> to let the operation of telecommunications infrastructure become
> dependent on a facility owned by the US military, so the standards
> that are popular there often try to avoid that.
>
> Dennis Ferguson
>
> On 15 Dec, 2012, at 18:59 , lists at lazygranch.com wrote:
>> I can assure you the GSM shacks have GPS timing in them. I can dig up the 
>> photos if you want.
>>
>> -----Original Message-----
>> From: "Joseph Orsak" <jorsak at nc.rr.com>
>> Sender: time-nuts-bounces at febo.com
>> Date: Sat, 15 Dec 2012 18:24:20
>> To: Discussion of precise time and frequency 
>> measurement<time-nuts at febo.com>
>> Reply-To: Discussion of precise time and frequency measurement
>> <time-nuts at febo.com>
>> Subject: Re: [time-nuts] Cell timing error
>>
>> AT&T uses UMTS in most areas which is a "self-synchronizing" modulation
>> scheme. Supposedly one of the selling points is "no dependence on GPS". 
>> All
>> the extra sync channels and sync messaging is a capacity hog, not a very
>> spectrally efficient standard in my opinion.
>>
>> About 85 maximum simultaneous voice calls in a 5Mhz UL / 5 Mhz DL
>> sector/carrier before it starts to fall apart. A big step backwards from
>> good old CDMA2000 (also just my opinion).
>>
>> But hey, you can surf the web while you talk on the same device.
>>
>>
>>
>> -Joe W4WN
>>
>>
>> ----- Original Message ----- 
>> From: "Jim Lux" <jimlux at earthlink.net>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at febo.com>
>> Sent: Saturday, December 15, 2012 5:43 PM
>> Subject: Re: [time-nuts] Cell timing error
>>
>>
>>> On 12/15/12 2:16 PM, Scott McGrath wrote:
>>>> In a prior life we had a CDMA timing receiver for NTP which used VZ for
>>>> its source
>>>>
>>>> On Dec 15, 2012, at 12:18 PM, Graham / KE9H <timenut at austin.rr.com>
>>>> wrote:
>>>>
>>>>> You should switch to Verizon.
>>>>> They are inherently accurate to milliseconds.
>>>>> Sub micro-seconds inside the base stations.
>>>>>
>>>>>
>>>>> On 12/15/2012 12:51 PM, Greg Troxel wrote:
>>>>>> In central mass, AT&T and tracfone (? carrier) are showing phone 
>>>>>> times
>>>>>> very close to 1 min slow.  Virgin/sprint is ok.   I've never seen 
>>>>>> this
>>>>>> before - usually it's a few s slow.
>>>>>>
>>>
>>>
>>> The time *displayed* on the phone might not reflect the time from the
>>> network.
>>>
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>>
>>
>>
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>
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