Re: [Discuss-gnuradio] Reconnecting OFDM rx

[Martin Braun]

Hey Julius,

the OFDM codes work over the air, so I don't think statefulness is the
issue. Maybe you just have super-full buffers or something like that.

The packet detection is the most stable part -- can you see if that
works? Just use the Schmidl&Cox block from the rx and see if it prints tags?

M

On 14.07.2015 08:26, Julius Durst wrote:
> Hi list,
> 
> I want to reconfigure an OFDM system. For this, I am so far simply
> trying to reconnect the tx and rx in the loopback example from the
> gr-digital ofdm examples. I made only very small modifications to it
> with two selector blocks, so now the flowgraph looks like this:
> http://i.imgur.com/Otr0VUt.png
> grc file: http://pastebin.com/pTDFhgvq
> 
> As soon as the OFDM rx is not connected from the beginning of execution
> or is reconnected after being disconnected, it is not able to receive
> the data.
> 
> When being disconnected and reconnected again, one of the following
> scenarios occurs:
> 
> 1. Nothing happens, just nothing more is received:
> 
> ----------------------------------------------------------------------
> Tag Debug: Rx Packets
> Input Stream: 00
> Offset: 24150 Source: n/a Key: packet_num Value: 483
> Offset: 24150 Source: n/a Key: ofdm_sync_carr_offset Value: 0
> Offset: 24150 Source: n/a Key: rx_len Value: 50
> ----------------------------------------------------------------------
> 
>>>> Done
> 
> 
> 2. Sometimes I get output like this: (Is there a list with return codes?
> What is -9? Is it normal when killing flowgraph with the button in grc?)
> 
> ----------------------------------------------------------------------
> Tag Debug: Rx Packets
> Input Stream: 00
>    Offset: 33700  Source: n/a     Key: packet_num   Value: 674
>    Offset: 33700  Source: n/a     Key: ofdm_sync_carr_offset   Value: 0
>    Offset: 33700  Source: n/a     Key: rx_len   Value: 50
> ----------------------------------------------------------------------
> INFO: Detected an invalid packet at item 32400
> INFO: Parser returned #f
> 
>  >>> Done (return code -9)
> 
> 
> 3. The return code seems to not necessarily having to do with the INFO,
> because also got this:
> 
> ----------------------------------------------------------------------
> Tag Debug: Rx Packets
> Input Stream: 00
>    Offset: 26100  Source: n/a     Key: packet_num   Value: 522
>    Offset: 26100  Source: n/a     Key: ofdm_sync_carr_offset   Value: 0
>    Offset: 26100  Source: n/a     Key: rx_len   Value: 50
> ----------------------------------------------------------------------
> INFO: Detected an invalid packet at item 25104
> INFO: Parser returned #f
> 
>  >>> Done
> 
> 
> 4. When first connecting the null sink and then connecting rx to the
> already running tx:
> 
> Using Volk machine: avx_64_mmx_orc
> INFO: Detected an invalid packet at item 0
> INFO: Parser returned #f
> INFO: Detected an invalid packet at item 48
> INFO: Parser returned #f
> INFO: Detected an invalid packet at item 96
> INFO: Parser returned #f
> INFO: Detected an invalid packet at item 144
> INFO: Parser returned #f
> INFO: Detected an invalid packet at item 192
> INFO: Parser returned #f
> INFO: Detected an invalid packet at item 240
> INFO: Parser returned #f
>   ... and so on
> 
> 
> Note that the ">>> Done" is from manually killing the flowgraph, it did
> not stop by itself, just added it because of the exit code.
> 
> So my question is: Why is this not working? In the cases where I just
> did not get any new packets (1., 2. and 3.), it seems like the Schmidl &
> Cox block does not even detect a new packet, so maybe something is wrong
> with that block? I also checked the "detected" output of the Schmidl &
> Cox block, it only had zeros.
> 
> Thanks in advance for your help and ideas
> 
> Julius
> 
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