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Thread: Available bandwith on a DVB-S mux?

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    Senior Member allstarnz's Avatar
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    Default Available bandwith on a DVB-S mux?

    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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    Junior Member frank_spencer's Avatar
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    Quote Originally Posted by allstarnz View Post
    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.
    depends on modulation scheme then FEC and symbol rate

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    Senior Member allstarnz's Avatar
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    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.

    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.
    so the transponder that has Winter Olympics has a total 12 channels on that transponder, leaving an average bandwidth 2.7 Mbits/s.

    Miserable sods.

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    Quote Originally Posted by allstarnz View Post
    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.
    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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