Re: [Discuss-gnuradio] DVBT project receiver probelm

[Federico Larroca]

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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