On Fri, May 26, 2006, christophpfister@xxxxxxxxxxx wrote: > >On Thu, May 25, 2006, christophpfister@xxxxxxxxxxx wrote: > > > >your quoting is broken :-( It still is... > >Please explain why you think hierarchical BC mode uses > >MIS and stream_ids to select HP/LP. It contradicts > >my understanding of the standard. > > Let's try this way: > > 1. What SISMIS is used in the hierarchical modulation for the DVB-S2 stream? > -> if SISMIS == SIS then there is no problem > -> if SISMIS == MIS then there is a problem (see 2.) > I think this question isn't answered clearly by the standards. > As long as we don't know the correct answer we can't dicuss further on > that. > (Well Manu and I suppose that SISMIS == MIS) > > 2. How does the demod filter? Does it exact matching or intelligent matching? > -> intelligent matching means that if we use SIS we get the whole stream > -> exact matching means that we have to use MIS and the correct stream_id, > otherwise we don't receive anything > Both would be possible (because HP and LP are already distinguished by > different modcods), but again: We don't know. Well, since the LP stream is a DVB-S2 stream it could in theory be either a SIS or a MIS stream (except that figure F.1 only shows a single input to the DVB-S2 outer & inner coding block). However, I think that MIS/stream_id filter is not used to seperate the HP and LP stream. Look again at figures F.1 and F2: The LP (DVB-S) stream uses different framing that the HP (DVB-S2) stream. Although in theory you could build a hardware which could receive both streams at the same time, it doesn't make sense to do so, since you need to seperate them later anyway. The hierarchical modulator combines the HP and LP streams in the following way: It takes two bits from the HP stream to determine the quadrant in the constellation diagram for the current symbol. Then it takes one bit from the LP stream and modifies the phase a little. So, a (DVB-S) QPSK demodulator will see just the HP stream (with a lot of phase noise). The DVB-S2 demodulator in hierarchical BC mode (yes, the hw needs a dedicated mode) will however use a 8PSK demodulator, modified to deal with the non-uniform phase distribution, and will throw away the two bits per symbol from the quadrant, and just use the one bit offset-within-the-quadrant to extract the DVB-S2 stream. If it wouldn't do this, the output of the first demodulator stage would be a mix of a DVB-S and DVB-S2 stream (with totally different frame formats), which the next demodulator stages cannot make sense of. Summary: Hierarchical BC mode and MIS mode are two totally seperate concepts and have nothing to do with each other. To receive the HP stream one needs a DVB-S demod, for the LP stream one needs a DVB-S2 demod which supports a "hierarchical LP stream" mode. (I must admit, however, that I have difficulties to find the "hierarchical LP stream" mode in the STB0899 data sheet...) Johannes _______________________________________________ linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
