Issue with USRP signal reception when stream is produced by a Vector Sou

Hello to everyone on the list,

To begin with, my overall goal is to build an adaptive modulation scheme using GnuRadio and USRPs. Concept-wise, this will be implemented by calculating the BER at the receiver, feeding this data to the transmitter, and switching between two different modulation schemes based on threshold BER values.

I am currently working on an 8DPSK modulation format. After succesfully building and testing the flowchart in simulation, I split the transmit and receive chain in order to actually test the setup using two B210 USRPs.

After a little bit of experimentation, transmission is great when using a random source at the transmitter. The FFT plot and the Constellation appear as expected. However, when using a vector source, which is mighty helpful for my purpose since I have a known bit sequence to compare at the receiver, my ouputs are unexpected (screenshots attached). This is baffling because the only thing that changed is the bit sequence and nothing in the actual signal processing chain (to be frank a packed to unpacked, and upacked to packed block were used after the vector source, but I'm getting pretty much the same results without them). I have experimented with different parameters but to no avail. It is important to note, that the simulations were working fine, regardless of the source that was used.

Any thoughts on why this is happening? I have also attached screenshots of the flowcharts.

Thank you very much for all the effort you are putting into the project.

Best regards,

George

From:	Γιώργος Γιώργος
Subject:	Issue with USRP signal reception when stream is produced by a Vector Source
Date:	Tue, 8 Jun 2021 14:32:55 +0000