RACH scan

Johann T. johann.tzt at gmail.com
Wed Jun 2 08:06:43 UTC 2021

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

Best regards,

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
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