Troubleshooting Osmocom Performance on Reception

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Troubleshooting Osmocom Performance on Reception

Post by gprob2017 » Mon Apr 16, 2018 1:43 pm

As a background: I am a masters student in electrical engineering currently attempting to quantize a bit error rate for different antennas using SDR. For this, I am using GNU Radio Companion to design the SDR for two bladeRF devices (one is x40 and one is x115) that will form the communication channel.

Attached are the flow graphs for transmission and reception. I am transmitting a known binary file using BPSK and I have analyzed this transmitted waveform separately in MATLAB so that I have all necessary information to compare the received signal. On receive, I have gone through many different approaches. At first, I tried to enact synchronization between the two FPGAs by using a polyphase clock synch, CMA Equalizer, and Costas Loop blocks to attempt to account for any timing mismatch between the two FPGAs and any transmission dependent phase mismatch. This was unsuccessful. I have previously attempted to do upconversion and downconversion for my transmitted waveform, but this appears to be an unnecessary step as, according to an oscilloscope, the osmocom block is capable of producing a sinusoid at the carrier frequency without any upconversion. This leads me to believe that this block encodes for a superheterodyne transciever that is able to accomplish the upconversion from and downconversion to baseband. Currently, I am simply trying to transmit the known waveform at the carrier frequency of the antenna, and simply receive the oversampled raw waveform for postprocessing. While I have tried an oversampling factor of 10 and greater, the MATLAB scripts I wrote previously are unable to determine the actual determination points of the raw signal in order to reconstruct the original signal. Additionally, my received IQ chart simply looks like a uniform circle.

Does anybody have a suggestion for how I can receive my raw signal in real time for post processing?

(Attached is a picture of my Transmission/Reception flow graph and my IQ graph from the received data)

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