[time-nuts] GSM/GPRS module timing accuracy

Tom Harris celephicus at gmail.com
Tue Nov 11 19:12:40 EST 2014

I am in Australia and the accuracy of the NITZ service can be slow by up to
15 SECONDS. I have no idea why it is so bad. You can try this for yourself.
Just get a GSM modem connected to your laptop, set it up to accept NITZ
updates and print the results on the serial port, and take a drive around
your neighbourhood. As you go between towers you will get new NITZ updates,
and you can log the accuracy.

Try not to get arrested as a terrorist :)

There is a simplified NTP service that only receives a small packet, I
think I saw an example for Arduino.

Tom Harris <celephicus at gmail.com>

On 12 November 2014 09:34, Tony <tnuts at toneh.demon.co.uk> wrote:

> On 11/11/2014 21:52, Tom Harris wrote:
>> How are you getting time from the GSM network? If you are using the NITZ
>> (look it up) service then you can use an unactivated SIM for free, but the
>> accuracy is woeful, it can be seconds out.
> I'm not at the moment; mobile phones do set their clocks from the network
> but I've no idea how accurately it can be done - which is why I was asking.
>> Else you will have to have a live SIM and use NTP to a server. If you make
>> any progress please post to the list. I have not heard of being able to
>> access the clock in the tower over the network.
>> The beauty of phone network is that it works in buildings, where GPS does
>> not reach.
>> Tom Harris <celephicus at gmail.com>
> I would have a live SIM as the modem would be used periodically (but not
> necessarily frequently - perhaps every 24 hours or more) to send data. I
> would not want to use an NTP service as I would only have a
> micro-controller with limited memory.
> Tony H
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