RACH scan

Johann T. johann.tzt at gmail.com
Fri Jul 2 07:47:40 UTC 2021


Hi Sylvain,

Thank you for getting back to me.
I suspected it would not be easy to decode the uplink speech and you
confirmed that. I will probably not spend more effort on it.

Your code and suggestions have helped me a lot. I have decoded my own
downlink speech and now the RACH.
Thanks again for your help.

Best regards,
Johann



On Thu, Jul 1, 2021 at 10:14 AM Sylvain Munaut <246tnt at gmail.com> wrote:

> Hi,
>
> > Thanks to your suggestions, I managed to decode the RACH from the
> captures on L-band. I just had to tweak a few parameters in the graphs. I
> have decoded the Paging Response and Location Update messages.
>
> TBH I'm impressed you managed to decode those from uplink without the
> sync from the downlink channels.
>
> > Do you have some suggestions on decoding the uplink speech? On the
> downlink, the code follows the Immediate Assignment and decodes the traffic
> channel. Due to the limitation of the SDR, I am not able to capture both
> the downlink and uplink channels simultaneously.
>
> Not really, they are already tricky to get from downlink because they
> are very small, use crappy sync patterns and have very little error
> correction applied, so on uplink that's going to make it even harder.
>
> Cheers,
>
>    Sylvain
>
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