LTE-Tracker

James Peroulas james at peroulas.com
Sun Nov 18 16:09:37 UTC 2012


On Sun, Nov 18, 2012 at 3:05 AM, Dimitri Stolnikov <horiz0n at gmx.net> wrote:

> I had to apply the attached patch for it to compile on my machine.
>

Thanks for the patch! cmake is something very new to me :)


> Unfortunately i wasn't able to test the tools, as both of them segfaulted
> in xc_peak_freq? Backtrace fragment attached.
>

Fixed (and pushed)! That was an easy bug to find and was related to the
fact that LTE cells in your area were at such a high frequency (1.8GHz).
The one's I've worked on were in the 700MHz band.


> Also, i noticed that you calculate the expected tuning frequency for e4k
> tuners in order to make your calculations more exact. Can you tell us which
> tuning errors you get from the e4k driver usually and how this affects your
> application?
>

Well, it's like this. Since the LO and sampling clock are derived from the
same reference, if I can figure out the frequency error of the LO, I will
know the frequency error of the ADC and I can use the frequency error of
the ADC to predict where I should be sampling the data. That way, in
LTE-Tracker, when the dongle's chrystal output stabilizes, the time offset
of the tracked basestations should not change (as long as the dongle itself
is not moving). I needed to calculate the actual LO and sampling
frequencies used by the dongle in order to remove the small time offset
drift I was observing.

As a new feature request, it would be nice for the library to return the
actual frequency that was programmed into the dongle in floating point
(fractions of a Hz sometimes matter). So, if I request 739,000,000Hz, the
library would be able to tell me that the actual programmed frequency was
739000025.5123... Hz. Similarly for the sampling rate.


>  http://www.evrytania.com/lte-**tools/lte-tracker<http://www.evrytania.com/lte-tools/lte-tracker>
>>
>
> Nice documentation & videos! Linked the page on the rtl-sdr wiki.
>

Thanks for the comments and the link!

James

-- 
*Integrity is a binary state - either you have it or you don’t.* - John
Doerr
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