Re: Recovering symbols from burst transmissions with unknown sample rate

Hi Adrian,
if you don't know the sample rate, then how can you get a detection by correlating with
the midamble? Is the midamble structured to be tolerant against sample frequency offset
(SFO)? In that case, therein probably lies an approach to getting your decoding to work.

But we'd really need to know more about the signal; I feel at least

- burst length compared to midamble length,
- pulse shaping if known,
- constellation type

would be necessary.

Furthermore, you say not all bursts have such a known midamble: but then, how do you
figure out such a burst started? Sounds like there's *also* some kind of preamble.

Best,
Marcus

On 18.10.24 08:19, Adrian Musceac wrote:
> Hello,
>
> As the title says, I'd like to know if it would be possible to recover symbols
> from a transmission containing regular bursts separated by noise (TDMA), using
> just blocks present in GNU Radio (or some custom algorithm that can be
> implemented as a block).
>
> I've tried using the correlation estimator together with the symbol
> synchronization block, but the problem I had was that the known
> synchronization sequence is placed in the middle of the data burst (as in most
> such real life transmissions). This meant that the "time_est" tag will not
> jump start the symbol synchronizer in time to recover all symbols of the
> burst.
>
> What is even worse is that not all data bursts have an embedded
> synchronization sequence, so there is no way to estimate the difference from
> expected to actual sample rate until the next sync sequence is transmitted
> (every 6 frames).
>
> Is there a way to overcome this apparent limitation of the corr_est + symbol
> sync combination?
>
> Thank you,
> Adrian
>
>
>