[linux-dvb] How to gather "Signal Quality" information from DVB drivers

Morgan Tørvolt morgan.torvolt at gmail.com
Mon Jul 30 12:04:51 CEST 2007


Hi.

Tecnically signal quality should be possible to get from eighter ber,
unc or snr. Signal level is not really important, because a low noise
floor with a weak signal could give you just as good a reception as a
strong signal with a strong noise floor. What you as an end user wants
is a bit-error free signal to your decoder. What the signal level is
like is not interesting.

In theory, snr, ber and unc are directly linked. You can use a formula
to calculate ber and unc from snr or any other way (ber->snr,
unc->snr, unc->ber and so on) if you have the modulation type, symbol
rate and other information. Since ber and unc can be zero (unc when
reception is ok, ber will be zero if the reception is perfect ie. no
need for fec or reed-solomon), the ber could be a good indicator.
ber=0 (in a given timeframe, say 10sec), should be an indicator that
the signal is very good. You will need to use snr to be able to give a
correct result for very good signal levels (better signal quality than
what is needed to receive the stream perfectly)

your real problem is not the quality part of this equation really. It
is the fact that all drivers implement this differently. A level of
0x2a35 on snr could mean perfect signal on one driver, and no
reception at all on a second driver. Some cards dont even give you
snr, maybe even a hardware constraint. Actually this will be different
from card to card as well (with the same frontend), given that there
is a different sensitivity on the tuner. Getting this right is really
a very difficult task right now, unless I am totally off here.

-Morgan-


On 30/07/07, Chun Chung LO <cclo at astri.org> wrote:
> Hi all,
>
> I wonder how I can gather the DVB-T signal quality information from the
> status value reported by driver (such as BER, Signal strength, S/N, UNC,
> etc).
>
> As I know I cannot simply use S/N as "signal quality" as it is only a
> ratio. But how to define "signal quality" of the DVB-T signal ? High
> signal strength ? Low BER? Low UNC? Or something else ?
>
> As I need to develop a simple callback to let GUI/application to get a
> value of signal quality in percentage. All I know is I have some driver
> status reading, but I do not know how to construct a percentage based
> DVB-T signal quality.
>
> (My hardware is TD1316 + TDA10046 + SAA7134)
>
> Please help.
>
> Best regards,
> Lo Chun Chung (Chung)
> ECE-DHT at ASTRI HK.
>
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