[Discuss-gnuradio] Reconnecting OFDM rx

[Julius Durst]

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