[time-nuts] sub-minute time-precision in court-case

Gabs Ricalde gsricalde at gmail.com
Wed Sep 4 09:53:16 EDT 2013


I noticed that my old Nokia phones kept time better than computers, then
I learned that the oscillator in the phone is adjusted to match the BTS
carrier [1].

To verify this I ran ntpd in an Android phone synced to a stratum 1
server via USB tethering. (USB has a lower latency and jitter than
WLAN.) The frequency offset was between 25 ppb and 50 ppb (loopstats
graph attached). When the phone is put in airplane mode, the frequency
offset jumped to 11 ppm.

Unfortunately Android's timekeeping gets messed up when the phone
suspends since the time is restored from a possibly low resolution RTC
when waking up [2, sec. 3]. The phone is prevented from suspending when
connected to a USB port, another reason for using USB tethering during
the test.


[1] http://gnuradio.org/redmine/projects/gnuradio/wiki/OpenBTSClocks
[2] https://lwn.net/images/pdf/suspend_blockers.pdf


On Wed, Sep 4, 2013 at 7:58 AM, Bill Hawkins <bill at iaxs.net> wrote:
> Who among you has volunteered to do the research for this?
>
> I don't have a camera in my cell phone, and I avoid market research
> masquerading as insecure social networks.
>
> Bill Hawkins
>
>
> -----Original Message-----
> Tom Van Baak said,
>
> "For extra credit, further photos can be sent each hour for hours or
> days to determine the cell phone frequency drift and stability
> parameters."
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
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