Demodulating short bursts of BPSK

GNU Radio
1

I have an application that needs to decode short bursts of DBPSK data
(which I am not generating myself). The problem I am having is that
the standard PSK Demod blocks don’t lock up in time to correctly
decode the first few flags in the packetised data, which means I
generally lose the first packet. Is there a solution to this - e.g.
once the demodulator has locked up, go back some time (samples) and
start again knowing the locked parameters?

Mike

2

Mike,

Let’s call short bursts of data packets (because that’s really what they
are). In packet transmissions, there are a few ways of ensuring that the
synchronizers have enough time to lock up. The easiest way for you to go
about this, is adding a packet header that carries no information, such
as
101010101, but can be used by the sync blocks to synchronize. The sync
blocks require transitions to make the magic happen. If you add this in
front of all your real data bursts, you will lose some of those SYNC
frame
bits each time, but you don’t care about that because it’s not real data
AND the synchronizers will be locked by the time the real data starts.

v/r,
Rich

3

If the packets have a preamble, there’s a block called
correlate_and_sync
which should do what you want, although it has some issues. See a thread
I
started a few days ago about that…