Just out of interest, what's the total available bandwidth on a DVB-S mux?
In particular I'm trying to work out what is available to Sky and Freeview NZ on Optus D1 if that makes any diff.
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allstarnz (26-01-10)
SR 22500
FEC 3/4
QPSK modulation
to perhaps answer my own question, a post from someone who I know does have a very good understanding of this stuff.
so the transponder that has Winter Olympics has a total 12 channels on that transponder, leaving an average bandwidth 2.7 Mbits/s.Classically DVB-S as currently used uses QPSK, which is a four point modulation system, thus currently each of SkyNZ's transponders run at 22.5MSym/sec, this giving a raw data rate of 45Mbit/s, after error correction (FEC) this reduces to around 33Mbit/s.
Miserable sods.
Actually, it's even less than that.
Foxtel has a symbol rate of 27.8 MS/s also with FEC of 3/4.
Now using QPSK means you have 2 bits per Symbol so transmitted bitrate is 27.8 x 2 = 55.6Mbps, then only 3/4 is usable (1/4 used for error correction) so a raw rate of 41.7 Mbps is streamed - BUT there are overheads in DVB-S that need to be subtracted.
For anyone familiar with Foxtel knows that the usable DVB-S payload total mux rate is actually 38.4 Mbps. So approx 7.9% is lost in overheads.
So assuming the same overheads are subtracted from the SkyNZ/Freeview transmission should leave a total of:
22.5 MS/s x 2 x 3/4 x 0.921 = 31.1 Mbps per DVB-S mux.
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