In case anyone was wondering I am currently debugging the
DVB-S2 module in the Express software. So far I have
managed to get my SatLink box to lock to the signal and
report that it is DVB-S2 and the FEC rate, modulation and
roll off. Unfortunately there is something not quite right.
It only works if I invert the 26 bit sync sequence in the
physical header. The physical header is transmitted using
BPSK with a 90 deg offset to prevent the usual 180 degree shift
with BPSK. The information is sent using a bi-orthogonally
coded (64,7) Reed Muller based code. The 7 bits being the
code rate, modulation, frame type and presence of pilots
information. The physical header is 90 symbols in duration.
I spent most of this morning making sure the CRC8 code which is
used to check the baseband header and the transport packets
was correct. I also checked the LDPC (Low Density Parity Check)
lookup tables were correct. I still have the BCH encoders to
check. Unfortunately there is little help in the ETSI EN 302 307
spec with any test vectors so I just have to double check everything
and keep my fingers crossed. As I now have a couple of ways to
receive DVB-S2 I will know when it is all working.
The QPSK FEC=1/4 mode looks interesting as that will operate
at below the noise level. So MPEG4, 70 cms, 1 MS/s and DVB-S2
look like a pretty powerful combination.
I am sure I will return to this later in my blog.
Hi Charles - this all sounds really. While I really don't understand too much of the software behind this it sounds like you are on to a winner.
ReplyDeleteMy gut feeling is the MPEG4 DVB S2 encoding is the way forward for ATV (rather than MPEG 2) - could be especially interesting if proposals to widen 2m ever come to fruition.
Keep up the good work - always intersted to read your blog.
Look forward to seeing your demo snd your project at the BATC convention.
73 Ian
Hi Ian, thanks for the feedback. Hopefully this blog will get people not traditionally interested in TV or Amateur Radio curious. With 1MS/s we could almost use 10m or 6M. With HVEC (H.265) which uses half the data rate of H.264 coming along things are getting quite exciting. I managed to transmit/receive DVB-S2 pictures this morning but there still appears to be a problem as I am getting very high error rates even with the antennas 10 cm apart. Back to the code!
ReplyDelete