Hello, I am doing research where we are trying to implement TCP through gnuradio and USRP B210s. We want to use OFDM, so I have modified the ofdm_rx and ofdm_tx examples into one large graph with a TUN/TAP interface and USRP source/sink. Currently, I have the graph running on two separate Ubuntu 16.10 machines with gnuradio 3.7.10 and UHD 3.11, talking through the TUN/TAP interface. The graph seems to function normally except for the fact that the other node fails to decode or even hear any OFDM frames. The strange things is that when I disable the USRP source or sink on one of the machines (one machine is TX and the other RX) then graph works perfectly and packets decode without a hitch. But if on the transmitting machine, I simply enable a USRP source and pipe it into a null sink, the other machine will fail to decode packets. If I disable the USRP source and null sink, then the other machine decodes packets. Essentially, I can't have each machine function as a transceiver, only as a transmitter or a receiver. I have tried all sorts of things including changing the gains for TX/RX on both machines, the multiplication constant, and changing the TX/RX ports on the USRPs. Occasionally, I noticed that setting the transmit constant and gain very high would result in the other machine printing that it failed to parse the packet header, but that's all I could get working with one USRP per machine. The only way I have gotten the machines to transmit and receive at the same time successfully is by using two USRP B210s, one as the transmitter and the other as the receiver. For obvious reasons, this is not an optimal solution for us, so I was hoping that someone here may be able to shed some light on our issue. Thank you.
here is a link: http://fomitchev.net/upload/BFOFDM_TRX.grc to the .grc file we are using for reference. The graph is huge at the moment and should be broken up eventually, but for now it should still work.
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