[Discuss-gnuradio] mimo 2x1 based on benchmark_ofdm_mimo.py

[Jorge Hernandez]

Hi all,

I continue working on trying a 2x1 mimo system based on the benchmark_ofdm_mimo from Tom Rondeau'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)