From johann.tzt at gmail.com Wed Jun 2 08:06:43 2021 From: johann.tzt at gmail.com (Johann T.) Date: Wed, 2 Jun 2021 10:06:43 +0200 Subject: RACH scan In-Reply-To: References: Message-ID: Hi Sylvain, Thank you for getting back on this. I will look further into the block as you suggested. It is also possible that the uplink signal of my initial capture was too strong and somehow saturated the receiver. I plan to perform more tests in the coming weeks as the weather is getting better. Best regards, Johann On Tue, May 25, 2021 at 7:26 PM Sylvain Munaut <246tnt at gmail.com> wrote: > Hi, > > > I have made some captures on the L-band uplink channels and tried to > decode the RACH messages. All four consecutive TCH channels (according to > the spot beam) were recorded and a call was made during the recording. > > > > I am using the GRC block gmr_rach_scan.grc. I have removed the IQ swap > from the graph, as suggested in the mailing list. The sampling rate and > samples-per-symbol values have been set to 93.6k and 4, respectively. > > Oops, looks like I complete missed this ... sorry. > > That graph was made to scan large bandwidth capture for RACH ... It's > very probable that a bunch of constants and thresholds value are just > not appropriate for a narrow band capture. > It kind of always required tweaking depending on the case. Basically > manually finding a RACH (in frequency and time), then look at all the > intermediate steps of the graphs (and possibly inside the block) to > see if it detects that particular one and tweak it until it does. And > then you can run it to find the other ones. > > I don't have any setup any more to capture C-band uplink so I have not > run that graph in years .... but that's all I remember about it. > > Cheers, > > Sylvain > -------------- next part -------------- An HTML attachment was scrubbed... URL: From johann.tzt at gmail.com Thu Jun 24 11:03:48 2021 From: johann.tzt at gmail.com (Johann T.) Date: Thu, 24 Jun 2021 13:03:48 +0200 Subject: Fwd: RACH scan In-Reply-To: References: Message-ID: Hi Sylvain, 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. 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. Thank you again. Best regards, Johann On Tue, May 25, 2021 at 7:26 PM Sylvain Munaut <246tnt at gmail.com> wrote: > Hi, > > > I have made some captures on the L-band uplink channels and tried to > decode the RACH messages. All four consecutive TCH channels (according to > the spot beam) were recorded and a call was made during the recording. > > > > I am using the GRC block gmr_rach_scan.grc. I have removed the IQ swap > from the graph, as suggested in the mailing list. The sampling rate and > samples-per-symbol values have been set to 93.6k and 4, respectively. > > Oops, looks like I complete missed this ... sorry. > > That graph was made to scan large bandwidth capture for RACH ... It's > very probable that a bunch of constants and thresholds value are just > not appropriate for a narrow band capture. > It kind of always required tweaking depending on the case. Basically > manually finding a RACH (in frequency and time), then look at all the > intermediate steps of the graphs (and possibly inside the block) to > see if it detects that particular one and tweak it until it does. And > then you can run it to find the other ones. > > I don't have any setup any more to capture C-band uplink so I have not > run that graph in years .... but that's all I remember about it. > > Cheers, > > Sylvain > -------------- next part -------------- An HTML attachment was scrubbed... URL: