26 Aug
2019
26 Aug
'19
3:05 p.m.
Hi Ingo,
On Mon, 2019-08-26 at 14:35 +0200, Ingo.Wolf(a)gmx.de wrote:
But if you bypass demodulator, don't you have to
demodulate in software then?
Indeed. That's why you don't bypass the DVB-T demodulator if you want
to use your TV dongle as TV dongle.
How can you just say "NO" isn't that
nonsense?
Because it's not nonsense.
Can the RTL2832U capture the 10MHz Bandwidth?
No.
Wasn't it something like 3MB/s max on the RTL,
does that mean 3MHz with 8 Bit Samples?
That's what it can transport in raw IQ sample across USB.
That has nothing to do with what the integrated DVB receiver /
demodulator can deal with. The contained MPEG data stream is much less
in bits per second than the raw samples.
Wether CPU can handle is another topic, but GHz Multicore + GPU don't look like
completely impossible.
It's not completely impossible, just very hard. I'm not aware of any
DVB-T2 software decoder that would work on laptop-grade hardware. You
seem to be fond of stating a few unfounded assumptions here:
I'd recommend looking into gr-dtv, which is software decoders for DVB-
** standards, and look how far in rate you can push them with purely
recorded or simulated signals. I think you don't realize how complex
the problem of concatenated LDPC and BCH decoders is. The LDPC block
for DVB-T2 is 64800 bits long, and that means that channel decoding
means you have to find solutions x to
xH=y
where H is a 64800×(64800/2, /3, /4, /8) matrix, and y is the received
softbits vector of length 64800, multiple hundred times a second. Good
luck doing that in software without spending a lot of time optimizing
the architecture of your solver (that solver is called a LDPC decoder).
Suddenly, your fast CPU isn't fast enough for real-time decoding – by
orders of magnitude, not by a factor of 2 or 5 or so.
Best regards,
Marcus
-----Ursprüngliche Nachricht-----
Von: "Müller, Marcus (CEL)" <mueller(a)kit.edu>
Gesendet: Montag, 26. August 2019 14:11
An: "Ingo.Wolf(a)gmx.de" <ingo.wolf(a)gmx.de>
Cc: "osmocom-sdr(a)lists.osmocom.org" <osmocom-sdr(a)lists.osmocom.org>
Betreff: Re: AW: Re: DVB-T2
</osmocom-sdr@lists.osmocom.org></ingo.wolf@gmx.de>
No.
The fact that you can use your RTL dongle as SDR device is because one
can *bypass* most of the digital logic (demodulator, decoder, stream
extractor…) and just get a raw IQ stream.
Decoding DVB-T in software is a really CPU-intense problem, due to
high-rate (in both senses of the word) channel coding, complex
synchronization, and high-order constellations used.
Best regards,
Marcus
On Sun, 2019-08-25 at 05:02 +0200, Ingo.Wolf(a)gmx.de wrote:
> But isn't SDR demodulation in software?
>
> -----Ursprüngliche Nachricht-----
> Von: "Steve Markgraf" <steve(a)steve-m.de>
> Gesendet: Samstag, 24. August 2019 18:19
> An: osmocom-sdr(a)lists.osmocom.org; Ingo.Wolf(a)gmx.de
> Betreff: Re: DVB-T2
> Hi,
>
> On 24.08.19 12:14, Ingo.Wolf(a)gmx.de wrote:
> > can somebody confirm RTL-chip is not DVB-T2 capable not having 10MHz
> > bandwidth needed?
>
> The RTL2832U does not support DVB-T2 as it lacks the required
> demodulater hardware. On the RTL2832P, an external demodulator can be
> attached via a parallel MPEG TS interface. This is used by dongles
> manufactured by Astrometa, which attach a Panasonic MN88472 DVB-T2
> demodulator, see [1].
>
> Regards,
> Steve
>
> [1] https://steve-m.de/pictures/rtl-sdr/rtl2832p_dvbt2/
>