On 01/03/2013 06:29 PM, Mauro Carvalho Chehab wrote:
Em Thu, 3 Jan 2013 14:14:29 -0200
Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> escreveu:
Em Thu, 03 Jan 2013 16:18:26 +0100
Klaus Schmidinger <Klaus.Schmidinger@xxxxxxx> escreveu:
On 03.01.2013 14:20, Mauro Carvalho Chehab wrote:
Em Wed, 2 Jan 2013 00:38:50 +0530
Manu Abraham <abraham.manu@xxxxxxxxx> escreveu:
On Tue, Jan 1, 2013 at 10:59 PM, Mauro Carvalho Chehab
<mchehab@xxxxxxxxxx> wrote:
Em Tue, 1 Jan 2013 22:18:49 +0530
Manu Abraham <abraham.manu@xxxxxxxxx> escreveu:
On Tue, Jan 1, 2013 at 8:30 PM, Mauro Carvalho Chehab
<mchehab@xxxxxxxxxx> 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.
Maybe we should put all this theoretical discussion aside for the moment and
think about what is *really* needed by real world applications. As with any
receiver, VDR simply wants to have some measure of the signal's "strength"
and "quality". These are just two values that should be delivered by each
frontend/demux, using the *same* defined and mandatory range. I don't care
what exactly that is, but it needs to be the same for all devices.
What values a particular driver uses internally to come up with these
is of no interest to VDR. The "signal strength" might just be what is
currently returned through FE_READ_SIGNAL_STRENGTH (however, normalized to
the same range in all drivers, which currently is not the case). The "signal
quality" might use flags like FE_HAS_SIGNAL, FE_HAS_CARRIER, FE_HAS_VITERBI,
FE_HAS_SYNC, as well as SNR, BER and UNC (if available) to form some
value where 0 means no quality at all, and 0xFFFF means excellent quality.
If a particular frontend/demux uses totally different concepts, it can
just use whatever it deems reasonable to form the "strength" and "quality"
values. The important thing here is just that all this needs to be hidden
inside the driver, and the only interface to an application are ioctl()
calls that return these two values.
So I suggest that you define this minimal interface and allow applications
to retrieve what they really need. Once this is done, feel free to implement
whatever theoretical bells and whistles you fell like doing - that's all
fine with me, as long as the really important stuff keeps working ;-)
Klaus,
On ISDB-T, it splits the TS into (up to) three independent physical channels
(called layers).
Each channel has its own statistics, as they're completely independent:
they use different inner FEC's, use different modulations, etc.
The ISDB demods don't provide a single value for the 3 layers. They
can't, as they're independent. So, signal-strengh and SNR measures are
also independent for each of those 3 layers.
A typical ISDB transmission uses 13 segments of carriers, each segment
using a 4.28 kHz bandwidth, grouped into 3 layers. While it is up to
the broadcaster to decide how to group the segments, it is typically
arranged like that:
layer A - 1 segment for LD programs - modulated using QPSK;
layer B - 3 segments for SD programs - modulated using 16QAM;
layer C - 9 segments for HD programs - modulated using 64QAM.
The TDM TS packets from the Transport Stream are broken into those 3
layers, each being an independent transmission channel.
So, all channel level QoS measure are per-layer (SNR, signal strength,
BER, MER, ...).
While the demods I have datasheets here don't provide it, it would be
possible to provide error counts for a given program ID, by summing
the error count that applies to each PID.
So, let's assume, for example, that the UCB count is:
layer A = 0
layer B = 12
layer C = 30
an 1-seg LD program will have 0 uncorrected blocks;
an SD program will have 12 uncorrected error blocks;
a HD program will have 42 uncorrected error blocks.
It shouldn't be that hard to take it into account on userspace, but
doing it at kernel level would be very painful, if possible, as
kernelspace would be required to know what PID's are being shown, in
order to estimate the error count measures for them. Also, it would
require a much more complex kernelspace-userspace interface.
Two additional notes:
1) If you want to get further information, it is available on ARIB
STD-B31 spec:
http://www.arib.or.jp/english/html/overview/doc/6-STD-B31v1_6-E2.pdf
There, table 3-2 shows the main characteristics of the modulation;
how the 3 independent channels are handled and fig. 3.4
shows a simplified diagram to give an idea on how the hierarchical TS
packets are broken into the 3 layers
2) There are in the market some narrow-band decoders. Those tunes only
1 segment (440kHz), and are meant to be used on mobile devices that can
receive only LD programs. Only for those devices, it is possible to
offer a single set of statistics (SNR, strength, BER, UCB, etc),
because it can decode just one layer. I have a few of them here,
and we have 2 drivers for those 1-seg devices (s921 and siano).
The full-seg drivers currently provide crappy information or don't
provide any QoS stats at all due to the lack of a proper API.
Regards,
Mauro
What I propose is quite near what Klaus wants. Just only new simple ways
to report current statistics with beforehand scale/values.
1) Signal Strength
* linear scale 0-0xffff
2) Quality SNR
* SNR in resolution 0.1dB
3) Quality BER
* ~like currently (no exact units)
* measured from inner coding
4) Quality UCB
* ~like currently (no exact units)
* measured from outer coding (naturally)
* counter is increased over lifetime
* tune resets counter?
* driver is responsible of polling statistic in background and report
from cache
I would not like to define exact units for BER and USB as those are
quite hard to implement and also non-sense. User would like just to see
if there is some (random) numbers and if those numbers are rising or
reducing when he changes antenna or adjusts gain. We are not making a
professional signal analyzers - numbers does not need to be 100% correctly.
ISDB-T statistics are forced also to that simple API. Calculating
average value for example. Statistic differences between layers are so
minor that users does not even care to know.
And as there is some persons who surely like to do QoS API like need of
$10k professional equipment, I propose to add more accurate reports as
alternative BUT that minimalist API should be offered even professional
API exits.
regards
Antti
--
http://palosaari.fi/
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