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.