Yes, rotated constellations are a new feature of DVB-T2. More reading here.
http://www.etsi.org/deliver/etsi_ts/102800_102899/102831/01.02.01_60/ts_102831v010201p.pdf
See section 9.2.3. In addition to the rotation, the I and Q components
of a QAM/QPSK symbol are cyclically delayed. Since there's a time and a
frequency interleaver after the modulator, the I and Q components of a
symbol get sent at a different time and a different frequency (OFDM
carrier). Almost all DVB-T2 broadcasters turn this feature on, even with
256QAM. All DVB-T2 receivers must support rotated constellations.
Be sure to change the "Constellation rotation" parameter in *both* the
Modulator block and the Frame Mapper block, or the receiver will get
confused.
BTW, both the DVB-T2 and DVB-S2 transmitters will be included in GNU
Radio in the next release (3.7.7) as part of gr-dtv.
If you place a Scope Sink after the modulator, you can see the "virtual"
constellation mentioned in the link above.
Virtual 16QAM
Ron
On 04/06/2015 10:14 PM, Ralph A. Schmid, dk5ras wrote:
It _is_ intended:
http://dcis2009.unizar.es/FILES/CR2/p41.pdf
So forget about my question :)
Ralph.
*From:*discuss-gnuradio-bounces+ralph=schmid....@gnu.org
[mailto:discuss-gnuradio-bounces+ralph=schmid....@gnu.org] *On Behalf
Of *Ralph A. Schmid, dk5ras
*Sent:* Tuesday, April 7, 2015 07:04
*To:* discuss-gnuradio@gnu.org
*Subject:* Re: [Discuss-gnuradio] DVB-T/T2
Hmm, now I see, there is an option "constellation rotation" in the
modulator block. Maybe this is not an accident, but wanted behavior?!
I will check this evening...
Ralph.
*From:*discuss-gnuradio-bounces+ralph=schmid....@gnu.org
<mailto:discuss-gnuradio-bounces+ralph=schmid....@gnu.org>
[mailto:discuss-gnuradio-bounces+ralph=schmid....@gnu.org] *On Behalf
Of *Ralph A. Schmid, dk5ras
*Sent:* Tuesday, April 7, 2015 06:39
*To:* discuss-gnuradio@gnu.org <mailto:discuss-gnuradio@gnu.org>
*Subject:* [Discuss-gnuradio] DVB-T/T2
Hi,
With Rons help I got the DVB-T/T2 flowgraphs up and running.
DVB-T works great, no issues at all, while DVB-T2 is somehow flaky in
reception.
When using a cheap DVB-x tester, the DVB-T2 constellation is phase
shifted. I have no real world T2 signals to compare, but at least the
tester shows normal constellation views when looking at S and T
signals off the air.
This is how things look:
http://dk5ras.dyndns.org/tmp/DVB/
The flowgraphs are almost original, just adopted to the USRP B210, and
I added channel slider...
Any ideas what I could tweak?
Ralph.
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