Re: [Discuss-gnuradio] DVBT project receiver probelm

[Federico Larroca]

Hi Ihab,

I've just realized that the flowgraph obtaining_the_parameters is not very clear, and I will modify it shortly.Thanks for the feedback. Could you please connect the output of Sym Align OFDM that reads "Likelihood" to a Time Sink? That is the one that should show a triangle. (BTW, you may also disable the OFDM Synchronization and TMCC decoder blocks, since they only work for ISDB-T only and are causing all that text in the terminal).

Regarding your constellation, I don't think you'll get a decent transport stream with it, it's too noisy. You should try to receive a better signal. Things I would try:

 1 - You are still getting several O's. Delete the noise source, which was there on the first place to simulate a channel. You already have one. In my experience, random generators are a costly thing.

 2 - Delete the multiplication at the input, which purpose I ignore. However, since it also multiplies noise, I don't think it will change much.

 3 - Record the signal at a better spot, where the signal is better.

Regarding the use of our ofdm_sym_acquisition, if I am not mistaken, gr-dvbt blocks downstream expect a certain tag which we changed. You should be careful with that too.

Best

Federico

2015-11-30 9:17 GMT-03:00 Ihab Zine <address@hidden>:

Hi Frederico,Marcus and Ron,

I have good news and bad news.

Frederico I used the flow graph  (obtaining parameters) you told me to use but i didn't get the triangle or spike, i have attached a screen shot please see ( obtaining_parameters.grc, Screenshot from ObtainingParameter & Screenshot_obtaining_parameters_Terminal).

Marcus I have tried the command "sysctl -w kernel.shmmax" to increase the available shared memory but i got (bash: sysctl: command not found).

The good news is that i'm finally able to get the DVBT signal synchronized and it was working earlier and i got some video and audio working from the source,  please see ( Screenshot_receiving  & Screenshot_after_ISDBT_ofdm_sym_acuistion) attached blow. i think the problem was because of  samples dropped, after i used stream to vector & vector to stream at the start of the flow graph i start seeing something working then i was adjusting SNR and then it was working. Now im not able to get a video don't know why at lease i'm getting the constellation  which is good. I'll keep going and trying to get the video and audio working again. I'll let you know guys when i have something new.

Big Thanks :)

Ihab    

 

On 27 November 2015 at 18:20, Ihab Zine <address@hidden> wrote:

---------- Forwarded message ----------
From: Federico Larroca <address@hidden>
Date: Friday, November 27, 2015
Subject: DVBT project receiver probelm
To: Ihab Zine <address@hidden>

Hi Ihab,

You only answered to me, maybe you should forward your mail to the list.

Regarding the grc, I would also remove the channel model (used for simulations), as in my experience it consumes much CPU.

best

Federico

2015-11-27 7:22 GMT-03:00 Ihab Zine <address@hidden>:

---

Hi Frederico,Marcus and Ron

I just got access to the system, ill try to follow what you have told me guys and ill let you know how it goes.

Thanks

Ihab

On 26 November 2015 at 17:22, Federico Larroca <address@hidden> wrote:

Hi Ihab,

Those "restart aquisition" are generated by the ofdm_sym_acquisition block when it does not find a peak on the correlation function he uses to detect the beginning of the OFDM symbol. You should verify there is indeed a DVB signal precisely at 570 MHz. To do this you may use our "Sym Align OFDM" block (not a very nice name) available with gr-isdbt (https://github.com/git-artes/gr-isdbt) and check that you see a "triangle" (please refer to the readme, the examples, and even the issues on our git). The symbol alignment is totally equivalent between DVB-T and ISDB-T.

Moreover, I see several "O"s, meaning that somewhere samples are being dropped. That does not help either. If you do not have a very fast machine, you may use at the beginning of the flowgraph a "Stream to Vector" followed by a "Vector to Stream" with a very big "Num Items" (some millions).

best

Federico

2015-11-26 12:59 GMT-03:00 Ihab Zine <address@hidden>:

Hi,

I’m trying to receive a live signal from an antenna on the roof through a cable connected to my SDR (hackrf one ).The bandwidth of the DVB-T in ireland is 8 Mhz , and the parametetrs Here in ireland as following:

Bandwidth: 8 MHz
Stream code rate (hi prio): FEC 2/3
Stream code rate (lo prio): FEC 2/3
Modulation: QAM 64
Transmission mode: 8k mode
Guard interval: 1/32
Hierarchy: none

net_data_rate = 24.128 Mbits/s

I used dvbt_rx_demo_8k_QAM64_rate78.grc flow graph with the following changes :

• frequency of hackrf Mhz, sampling rate = ((8*8e6)/7).

• Cyclic Prefix to (8192/32, is this right?)

• Code Rate HP : 2/3

• Code Rate LP : 2/3

• Guard Interval : 1/32

The problem i have is that no output data coming out after the demod_reference_signals BLOCK(no cancellation map), and got the following:

restart aquisition

OOrestart aquisition

d_freq_offset: -5

Od_freq_offset: -5

d_freq_offset: -5

d_freq_offset: -5

d_freq_offset: -5

d_freq_offset: -5

d_freq_offset: -5

d_freq_offset: -5

restart aquisition

OOd_freq_offset: -5

d_freq_offset: -5

so I had to add a signal source to shift the signal. After shfting the signal i got the following :

restart aquisition

restart aquisition

restart aquisition

restart aquisition

Orestart aquisition

I have read a lot about DVB , mapping ,ofdm and others, i have spent weeks on this but still the same problem, if it is synchronization problem what i should do?

So please i need a some help with this problem .

Thanks

Ihab

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