RACH scan

Sylvain Munaut 246tnt at gmail.com
Thu Jul 1 08:14:47 UTC 2021


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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