You have to set the Code rate in the Demod Reference Signals block and
the Viterbi decoder block. The Reed-Solomon block is already setup for
188/204, so no changes required there.
It looks like Hungary uses 1/4 guard interval, so you need to set the
Cyclic Prefix Length in the OFDM Symbol Acquisition block to 8192/4 =
2048 and the Guard Interval in the Demod Reference Signals block to 1/4.
Ron
On 2/10/22 04:08, Herman Tibor wrote:
Dear Ron,
I have one more question that I hope you can help me with.
Here in Hungary the DVB-T broadcast uses Reed-Solomon coding with
188/204 rate. The convolutional coder rate is 3/4. How do I set up the
Viterbi decoder, the Convolutional Deinterleaver and the R-S decoder
to match these values?
When I try to decode the signal received from the nearby station, I
see the nice constellation of 64QAM, but the video is not decoded
successfully, I cannot play it.
Tibor
Herman Tibor <tid...@gmail.com> ezt írta (időpont: 2022. febr. 10.,
Cs, 12:31):
Hi Ron,
Thank you for the advice, it's working now! I'll start to
construct the loopback version.
Cheers,
Tibor
Herman Tibor
Ron Economos <w...@comcast.net> ezt írta (időpont: 2022. febr.
10., Cs, 12:27):
You just have to match the parameters between the transmit and
receive flow graphs. The only difference is that the
transmitter is using 64QAM and the receiver is using 16QAM.
So you can either change the transmitter to 16QAM or change
the receiver to 64QAM.
You should add a throttle block to the transmitter (right
before the file sink will work).
Since you're not transmitting over the air, the sample rate
doesn't matter if you're just creating a baseband file and
playing it later.
However, if you want to play the output stream in real-time,
the sample rate and bitrate of the Transport Stream do matter.
Also, the performance of the computer running the receiver
flow graph has to be sufficient for real-time. That's why the
receive flow graph is configured for 16QAM as most 4 core CPUs
can support that bitrate.
Ron
On 2/10/22 02:59, Herman Tibor wrote:
Hi everyone,
I'd like to teach students about OFDM modulation and I'd like
to use Gnuradio for the purpose. I'm trying to create a
baseband signal with the dvbt_tx_8k.grc project and decode it
with the dvbt_rx_8k.grc project. The problem is that the rx
project cannot decode the baseband signal created with the tx
project. Has anyone tried this before? What am I missing? Do
I need to set something differently in the RX project
compared to the default?
Is it possible to do it without actually transmitting the
baseband signal? I would think so. But then what is the
sample rate? The variable is only used in the UHD: USRP sink
block, which I'd like to skip.
I know I can download a sample baseband file, which works and
I can see it is generated, because the SNR is basically
infinite. But I'd like to go further and demonstrate with a
longer video and possibly loop back the tx to rx to modify
the signal on the fly and finally play the stream in vlc.
Thanks,
Tibor
Herman Tibor
