Re: [Discuss-gnuradio] question about the qa_ofdm_sync_sc_cfb.py

[Martin Braun]

Hi,

Is your fft length really 10? The gist of it is, the detection of the
sync burst will be delayed, and hence you also need to delay the signal.
The delay is caused by the averaging filters in the sync block.

As for an example, rx_ofdm.grc should show you how it is connected.
You'll notice that the detection signal goes to one input of the
Header/Payload Demux and that triggers a capture.

Cheers,
Martin

On 08.11.2015 00:16, w xd wrote:
> Hi all,
> 
>          Thank you in advance.I‘'m so confused about the block Schmidl &
> Cox synch,
>        
>          1.I'm check the qa_ofdm_sync_sc_cfb.py to try to understand the
> block.
>            
>           The original sequence: 5 zeros+4 cp_len+10 fft_len+14 data
>           Just like this:[0, 0, 0, 0, 0, 1, -1, -1, -1, 1, 1, -1, -1,
> -1, 1, 1, -1, -1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, 1, 1, 1, 1]
>           The result of detect:
>            (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0,
> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)   1 is in the position of 17
> 
>           And in the example
> gnruadio/gr-digital/examples/ofdm/rx_ofdm.grc.You have add a delay
> block,and it delay cp_len+fft_len.
> 
>          According to this,after the delay,our original sequence will be:
>          14 zeros+[0, 0, 0, 0, 0, 1, -1, -1, -1, 1, 1, -1, -1, -1, 1, 1,
> -1, -1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, 1, 1, 1, 1]
> 
>          Now we use the detect result to find the start point of the
> original sequence.we will find the start point:
>          14 zeros+ 0  +0  +0(the position of 17).......And I think the
> result may be wrong.
> 
>          Can someone explain it? Clear it.
> 
>          2.How the above block cooperate with the block(head/payload
> Demux) to find the start point of the sequence？
> 
>         Can someone use the above example to explain it?
> 
> 
> Thank you so much.I'm so confused about the design of the receiver.
> 
> 
> Best regards,
> xd
> 
> 
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