Mimo 2x1 based on benchmark_ofdm_mimo.py

Hi all,

I continue working on trying a 2x1 mimo system based on the
benchmark_ofdm_mimo from Tom R.'s repository. I have done several
trials and I am losing my mind trying to see why it doesn’t work. I am
using two USRP2 in the transmitter side and another one in the recevier
side with XCVR2450 daughterboards, GNU C++ version 4.4.1 [gcc-4_4-branch
revision 150839]; Boost_103900; UHD_003.004.000-122b947. In the receiver
side all I see is a lot of messages with just an x, and every 10 x (more
or
less) I get a message: got preamble. I’ve been looking into the code and
this messages are generated in the alamouti frame acquisition block. I
guess the problem is in this very same block, when the synchronization
has
to be accomplished. I think this can be caused by a poor snr, but I
don’t
know how to improve this in order to get this mimo configuration to
work. I
would like to share also the way I’ve configured the uhd_usrp2 sinks to
see
if maybe there is any error there. At this point, I would really
appreciate
any help! Thanks in advance:

This is how I configured the usrp2:

    # UHD USRP2 sinks
    self.uhd_usrp_slave = uhd.usrp_sink(
        device_addr="addr=192.168.20.3",
        io_type=uhd.io_type.COMPLEX_FLOAT32,
        num_channels=1,
    )
    _config = uhd.clock_config()
    _config.ref_source = uhd.clock_config.REF_MIMO
    _config.pps_source = uhd.clock_config.PPS_MIMO
    self.uhd_usrp_slave.set_clock_config(_config, 0)
    self.uhd_usrp_slave.set_samp_rate(self.samp_rate)
    self.uhd_usrp_slave.set_center_freq(self.center_frequency, 0)
    self.uhd_usrp_slave.set_gain(self.tx_gain, 0)

    self.uhd_usrp_master = uhd.usrp_sink(
        device_addr="addr=192.168.10.4",
        io_type=uhd.io_type.COMPLEX_FLOAT32,
        num_channels=1,
    )
    self.uhd_usrp_master.set_clock_config(uhd.clock_config.internal(),0)
    self.uhd_usrp_master.set_samp_rate(self.samp_rate)
    self.uhd_usrp_master.set_center_freq(self.center_frequency, 0)
    self.uhd_usrp_master.set_gain(self.tx_gain, 0)

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