From 246tnt at gmail.com Thu Jul 1 08:14:47 2021 From: 246tnt at gmail.com (Sylvain Munaut) Date: Thu, 1 Jul 2021 10:14:47 +0200 Subject: RACH scan In-Reply-To: References: Message-ID: 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 From johann.tzt at gmail.com Fri Jul 2 07:47:40 2021 From: johann.tzt at gmail.com (Johann T.) Date: Fri, 2 Jul 2021 09:47:40 +0200 Subject: RACH scan In-Reply-To: References: Message-ID: 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 > -------------- next part -------------- An HTML attachment was scrubbed... URL: From 246tnt at gmail.com Fri Jul 2 07:54:37 2021 From: 246tnt at gmail.com (Sylvain Munaut) Date: Fri, 2 Jul 2021 09:54:37 +0200 Subject: RACH scan In-Reply-To: References: Message-ID: Hi, What SDR are you using btw ? I know several of the mimo sdr (limesdr / b210 / ...) can RX on multiple channels but tuned to the same frequency. And I had the idea of using an external mixer to shift the uplink with an external mixer to make it match the downlink frequency. Never tried it in practice though. Cheers, Sylvain From johann.tzt at gmail.com Fri Jul 2 15:55:16 2021 From: johann.tzt at gmail.com (Johann T.) Date: Fri, 2 Jul 2021 17:55:16 +0200 Subject: RACH scan In-Reply-To: References: Message-ID: Hi Sylvain, I am using both the USRP B210 and B205-mini. So far I haven't attempted to receive on multiple channels. It might be an idea. Best regards, Johann On Fri, Jul 2, 2021 at 9:54 AM Sylvain Munaut <246tnt at gmail.com> wrote: > Hi, > > What SDR are you using btw ? > > I know several of the mimo sdr (limesdr / b210 / ...) can RX on > multiple channels but tuned to the same frequency. And I had the idea > of using an external mixer to shift the uplink with an external mixer > to make it match the downlink frequency. Never tried it in practice > though. > > Cheers, > > Sylvain > -------------- next part -------------- An HTML attachment was scrubbed... URL: