On Sat, May 27, 2006, Johannes Stezenbach wrote: > 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...) There is one detail in EN 302 307 annex F that I haven't paid attention to, because I didn't understand it's significance: "The PLHEADER sequence shall comprise 90 bits to indicate the LP code rate being transmitted, as follow, shown octal encoded, MSB (leftmost bit) transmitted first:" I.e. the usual SOF, MODCOD, TYPE fields of PLHEADER are replaced with a special sequence. ------------------------------- The following applies to general DVB-S2, not just to BC mode: Well, EN 302 307 does not explain how it is possible for the receiver to decode the PLHEADER without knowing the modulation first. However, TR 102 376 annex B.1 does: "Independent from the modulation scheme of the LDPC coded block that follows, these fields are modulated by pi/2-BPSK modulation...". So if the frame sync and PL configuration (MODCODE etc.) is transmitted with a different, but fixed modulation scheme, it is clear that the receiver can indeed figure it out by itself, and if modcod changes on a by-frame basis the receiver can still track these changes and receive all frames. ------------------------------------------ Back to BC mode: EN 302 307 annex F show the PLHEADER is inserted before passing the DVB-S2 signal to the hierarchical mapper. TR 102 376 section 4.4.1 basically says the same. So, it seems that for hierarchical BC mode PLHEADER does not use pi/2-BPSK. Now, I don't know if and how the receiver could figure out that hierarchical modulation is used, however, once it knows that, it can get the other transmission parameters from the PLHEADER. While STB0899 does not seem to have a register for enabling hieararchical BC mode, it still has a (read-only) "low priority stream detection" bit in register TSULSTKM.) Maybe this is a hint that it can detect hieararchical BC mode by itself. Johannes _______________________________________________ linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
