Re: [PATCH RFCv3] dvb: Add DVBv5 properties for quality parameters

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em Wed, 2 Jan 2013 00:38:50 +0530
Manu Abraham <abraham.manu@gmail.com> escreveu:

> On Tue, Jan 1, 2013 at 10:59 PM, Mauro Carvalho Chehab
> <mchehab@redhat.com> wrote:
> > Em Tue, 1 Jan 2013 22:18:49 +0530
> > Manu Abraham <abraham.manu@gmail.com> escreveu:
> >
> >> On Tue, Jan 1, 2013 at 8:30 PM, Mauro Carvalho Chehab
> >> <mchehab@redhat.com> wrote:
> >>
> >> > [RFCv4] dvb: Add DVBv5 properties for quality parameters
> >> >
> >> > The DVBv3 quality parameters are limited on several ways:
> >> >         - Doesn't provide any way to indicate the used measure;
> >> >         - Userspace need to guess how to calculate the measure;
> >> >         - Only a limited set of stats are supported;
> >> >         - Doesn't provide QoS measure for the OFDM TPS/TMCC
> >> >           carriers, used to detect the network parameters for
> >> >           DVB-T/ISDB-T;
> >> >         - Can't be called in a way to require them to be filled
> >> >           all at once (atomic reads from the hardware), with may
> >> >           cause troubles on interpreting them on userspace;
> >> >         - On some OFDM delivery systems, the carriers can be
> >> >           independently modulated, having different properties.
> >> >           Currently, there's no way to report per-layer stats;
> >>
> >> per layer stats is a mythical bird, nothing of that sort does exist.
> >
> > Had you ever read or tried to get stats from an ISDB-T demod? If you
> > had, you would see that it only provides per-layer stats. Btw, this is
> > a requirement to follow the ARIB and ABNT ISDB specs.
> 
> I understand you keep writing junk for ages, but nevertheless:
> 
> Do you have any idea what's a BBHEADER (DVB-S2) or
> PLHEADER (DVB-T2) ? The headers do indicate what MODCOD
> (aka Modulation/Coding Standard follows, whatever mode ACM,
> VCM or CCM) follows. These MODCOD foolows a TDM approach
> with a hierarchial modulation principle. This is exactly what ISDB
> does too.

No, I didn't check DVB-S2/T2 specs deeply enough to understand
if they're doing the same thing as ISDB.

Yet, ISDB-T doesn't use a TDM approach for hierarchical modulation.
It uses a FDM (OFDM is a type of Frequency Division Multiplexing).

So, if you're saying that DVB-S2 uses TDM, it is very different than
ISDB-T. As DVB-T2 uses an FDM type of modulation (OFDM), it would
be possible to segment the carriers there, just like ISDB, or to
use TDM hierarchical modulation techniques.

> 
> And for your info:
> 
> " The TMCC control information is
> common to all TMCC carriers and
> error correction is performed by using
> difference-set cyclic code."

Yes, TMCC carriers are equal and they are always modulated using DBPSK.
That is done to make it possible to receive the TMCC carriers even under
worse SNR conditions, where it may not be possible to decode the segment
groups.

It seems that you completely missed the point though. On ISDB-T, the 
carriers that belong to each group of segments (except for the control
carriers - carriers 1 to 107) uses a completely independent modulation.
Also, as they're spaced in frequency, the interference of each segment
is different. So, error indications are different on each segment.

Btw, in any case, the datasheets of ISDB-T demods clearly shows that
the BER measures are per segment group (layer).

For example, for the BER measures before Viterbi, those are the register
names for a certain demod:

	VBERSNUMA Bit count of BER measurement before Viterbi in A layer
	VBERSNUMB Bit count of BER measurement before Viterbi in B layer
	VBERSNUMC Bit count of BER measurement before Viterbi in C layer

It has another set of registers for BER after Viterbi, and for PER after
Viterbi and RS, for bit count errors, etc.

There's no way to get any type of "global" BER measure, simply because
ISDB-T demods don't provide.

Regards,
Mauro