>-- Original-Nachricht -- >Date: Mon, 29 May 2006 12:45:46 +0200 >From: Johannes Stezenbach <js@xxxxxxxxxxx> >To: christophpfister@xxxxxxxxxxx >Cc: linux-dvb@xxxxxxxxxxx, Manu Abraham <abraham.manu@xxxxxxxxx> >Subject: Re: [PATCH] Re: [PATCH] Multi protocol support (stage >#1) > > >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. No. Try to encode the relevant SOF, MODCOD and TYPE fields by hand. Then you get the values mentioned there... > > >------------------------------- >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. Correct. > > >------------------------------------------ >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. Where do you know that the transmitter doesn't use pi/2-BPSK for 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 No need for a special BC mode... Christoph _______________________________________________ linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
