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[Discuss-gnuradio] Simultaneous transmission HELP!

From: David Scaperoth
Subject: [Discuss-gnuradio] Simultaneous transmission HELP!
Date: Tue, 20 Mar 2007 09:43:05 -0400


I am trying to use both transceivers to transmit and receive data, which is fine with the current GNU Radio blocks.  On one of the transceivers I am currently using an independent piece of software to do a rough TDMA type waveform.  Basically, the GNU Radio flow graph for one side looks like:

usrp_source_c       => deinterleave => multiply_const_cc => file_descriptor_sink
usrp_sink_c           <=  interleave    <=  multiply_const_cc <= file_descriptor_source

(same source /deinterleave as above) => FM demod
(same sink / inteleave as above)         <=  FM mod

When I am running the TDMA code (connected through TCP sockets), the USRP underruns (uU) when no data is sent.  That's no big deal when I have one transceiver, but when I am running with two transceivers this REALLY messes with things because of the interleaving.  What I have tried to do is patch the file_descriptor_source by checking the socket for data (with a select() call with a timeout of 0) and then sending noutput_items complex zeros to the USRP to allow the data to be interleaved.  I still seem to be having problems with underruns.  I know that mblocks will solve my problems in this area, but I need a solution in a couple of weeks.  Should I throw my hands up and wait?  or do I need to make my own scheduler?  gr_buffer?  HELP!

Thanks for any guidance,


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